PlayGround

<p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Introduction: <o:p></o:p>'<p class=MsoNormal style='margin-bottom:12.0pt'> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Gram-Negative Bacteria:<o:p></o:p>'<p class=MsoNormal>For survival, bacteria have a cell envelope surrounding the cytoplasm that gives the cell its shape, selectively allows the passage of molecules into and out of the cytoplasm, and protects the cell<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“iIaRvdN8”,“properties”:{“formattedCitation”:“\\super 1\\nosupersub{}”,“plainCitation”:“1”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>¹<!–[if supportFields]><![endif]–> (Silhavy, Kahne, & Walker, 2010). The bacteria fall into two groups, depending on their cell envelope: Gram-negative bacteria and Gram-positive bacteria. <i style='mso-bidi-font-style:normal'>E. coli is an example of a Gram-negative bacteria</span></span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“CJIH8jEe”,“properties”:{“formattedCitation”:“\\super 1\\nosupersub{}”,“plainCitation”:“1”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>1<!–[if supportFields]><![endif]–> (Silhavy, Kahne, & Walker, 2010).<o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><i style='mso-bidi-font-style:normal'>E. coli’s cell envelope, shown in figure X, consists of an inner membrane (IM), a peptidoglycan cell wall, and an outer membrane (OM) which is unique to Gram-negative bacteria<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“k70Th6wE”,“properties”:{“formattedCitation”:“\\super 1\\nosupersub{}”,“plainCitation”:“1”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>¹<!–[if supportFields]><![endif]–> (Silhavy, Kahne, & Walker, 2010). The IM is a phospholipid (PL) bilayer<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“B661XGj7”,“properties”:{“formattedCitation”:“\\super 2\\nosupersub{}”,“plainCitation”:“2”,“noteIndex”:0},“citationItems”:[{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>²<!–[if supportFields]><![endif]–> (Bishop, 2020). Proteins responsible for energy production, lipid biosynthesis, protein secretion, and transport are located in the IM due to a lack of intracellular organelles<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“mcVZ8LiH”,“properties”:{“formattedCitation”:“\\super 1,2\\nosupersub{}”,“plainCitation”:“1,2”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}},{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>^1,2<!–[if supportFields]><![endif]–> (Bishop, 2020; Silhavy, Kahne, & Walker, 2010). The peptidoglycan cell wall, found in the periplasmic space between the IM and OM, is made up of repeating units of the disaccharide N-acetyl glucosamine-N-acetyl muramic acid (NAG-NAM), cross-linked by pentapeptide side chains<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“jhF990s7”,“properties”:{“formattedCitation”:“\\super 1,3\\nosupersub{}”,“plainCitation”:“1,3”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}},{“id”:619,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/HWCQ9FUI”],“itemData”:{“id”:619,“type”:“article-journal”,“abstract”:“Gram-negative bacteria are surrounded by a complex cell envelope that includes two membranes. The outer membrane prevents many drugs from entering these cells and is thus a major determinant of their intrinsic antibiotic resistance. This barrier function is imparted by the asymmetric architecture of the membrane with lipopolysaccharide (LPS) in the outer leaflet and phospholipids in the inner leaflet. The LPS and phospholipid synthesis pathways share an intermediate. Proper membrane biogenesis therefore requires that the flux through each pathway be balanced. In Escherichia coli, a major control point in establishing this balance is the committed step of LPS synthesis mediated by LpxC. Levels of this enzyme are controlled through its degradation by the inner membrane protease FtsH and its presumed adapter protein LapB (YciM). How turnover of LpxC is controlled has remained unclear for many years. Here, we demonstrate that the essential protein of unknown function YejM (PbgA) participates in this regulatory pathway. Suppressors of YejM essentiality were identified in lpxC and lapB, and LpxC overproduction was shown to be sufficient to allow survival of ΔyejM mutants. Furthermore, the stability of LpxC was shown to be reduced in cells lacking YejM, and genetic and physical interactions between LapB and YejM were detected. Taken together, our results are consistent with a model in which YejM directly modulates LpxC turnover by FtsH-LapB to regulate LPS synthesis and maintain membrane homeostasis.\nIMPORTANCE The outer membrane is a major determinant of the intrinsic antibiotic resistance of Gram-negative bacteria. It is composed of both lipopolysaccharide (LPS) and phospholipid, and the synthesis of these lipid species must be balanced for the membrane to maintain its barrier function in blocking drug entry. In this study, we identified an essential protein of unknown function as a key new factor in modulating LPS synthesis in the model bacterium Escherichia coli. Our results provide novel insight into how this organism and most likely other Gram-negative bacteria maintain membrane homeostasis and their intrinsic resistance to antibiotics.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.00939-20”,“issue”:“3”,“note”:“publisher: American Society for Microbiology”,“page”:“e00939-20”,“source”:“journals.asm.org (Atypon)”,“title”:“An Essential Membrane Protein Modulates the Proteolysis of LpxC to Control Lipopolysaccharide Synthesis in Escherichia coli”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.00939-20”,“volume”:“11”,“author”:[{“family”:“Fivenson”,“given”:“Elayne M.”},{“family”:“Bernhardt”,“given”:“Thomas G.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",5,19}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>^1,3<!–[if supportFields]><![endif]–> (Fivenson, & Bernhardt, 2020; Silhavy, Kahne, & Walker, 2010). This rigid cell wall is responsible for the maintenance of <i style='mso-bidi-font-style:normal'>E. coli’s characteristic rod shape</span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“QysnGSot”,“properties”:{“formattedCitation”:“\\super 1\\nosupersub{}”,“plainCitation”:“1”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>1<!–[if supportFields]><![endif]–> (Silhavy, Kahne, & Walker, 2010). The peptidoglycan layer is connected to the OM through a lipoprotein, murein/Braun’s lipoprotein (Lpp)<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“ExJWWN7s”,“properties”:{“formattedCitation”:“\\super 1\\nosupersub{}”,“plainCitation”:“1”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>1<!–[if supportFields]><![endif]–> (Silhavy, Kahne, & Walker, 2010). The OM is an asymmetric lipid bilayer that is essential for <i style='mso-bidi-font-style:normal'>E.coli’s survival because it acts as the first line of defence against external threats</span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“G4EUP7vu”,“properties”:{“formattedCitation”:“\\super 1,2\\nosupersub{}”,“plainCitation”:“1,2”,“noteIndex”:0},“citationItems”:[{“id”:614,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/H9G2P5QM”],“itemData”:{“id”:614,“type”:“article-journal”,“abstract”:“The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. The cell envelopes of most bacteria fall into one of two major groups. Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives. Threading through these layers of peptidoglycan are long anionic polymers, called teichoic acids. The composition and organization of these envelope layers and recent insights into the mechanisms of cell envelope assembly are discussed.”,“container-title”:“Cold Spring Harbor Perspectives in Biology”,“DOI”:“10.1101/cshperspect.a000414”,“ISSN”:“, 1943-0264”,“issue”:“5”,“journalAbbreviation”:“Cold Spring Harb Perspect Biol”,“language”:“en”,“note”:“Company: Cold Spring Harbor Laboratory Press\nDistributor: Cold Spring Harbor Laboratory Press\nInstitution: Cold Spring Harbor Laboratory Press\nLabel: Cold Spring Harbor Laboratory Press\npublisher: Cold Spring Harbor Lab\nPMID: 20452953”,“page”:“a000414”,“source”:“cshperspectives.cshlp.org”,“title”:“The Bacterial Cell Envelope”,“URL”:“http://cshperspectives.cshlp.org/content/2/5/a000414”,“volume”:“2”,“author”:[{“family”:“Silhavy”,“given”:“Thomas J.”},{“family”:“Kahne”,“given”:“Daniel”},{“family”:“Walker”,“given”:“Suzanne”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",1,5}}},{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>1,2<!–[if supportFields]><![endif]–> (Bishop, 2020; Silhavy, Kahne, & Walker, 2010). It prevents the entry or exit of large, hydrophobic molecules and works together with the peptidoglycan cell wall to provide mechanical strength to the bacterial cell, protecting it from osmotic lysis<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“Pm7E79sY”,“properties”:{“formattedCitation”:“\\super 4\\nosupersub{}”,“plainCitation”:“4”,“noteIndex”:0},“citationItems”:[{“id”:621,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/D7M3VN8M”],“itemData”:{“id”:621,“type”:“article-journal”,“abstract”:“Lipopolysaccharide (LPS) is an essential glycolipid present in the outer membrane (OM) of many Gram-negative bacteria. Balanced biosynthesis of LPS is critical for cell viability; too little LPS weakens the OM, while too much LPS is lethal. In Escherichia coli, this balance is maintained by the YciM/FtsH protease complex, which adjusts LPS levels by degrading the LPS biosynthesis enzyme LpxC. Here, we provide evidence that activity of the YciM/FtsH protease complex is inhibited by the essential protein YejM. Using strains in which LpxC activity is reduced, we show that yciM is epistatic to yejM, demonstrating that YejM acts upstream of YciM to prevent toxic overproduction of LPS. Previous studies have shown that this toxicity can be suppressed by deleting lpp, which codes for a highly abundant OM lipoprotein. It was assumed that deletion of lpp restores lipid balance by increasing the number of acyl chains available for glycerophospholipid biosynthesis. We show that this is not the case. Rather, our data suggest that preventing attachment of lpp to the peptidoglycan sacculus allows excess LPS to be shed in vesicles. We propose that this loss of OM material allows continued transport of LPS to the OM, thus preventing lethal accumulation of LPS within the inner membrane. Overall, our data justify the commitment of three essential inner membrane proteins to avoid toxic over- or underproduction of LPS.\nIMPORTANCE Gram-negative bacteria are encapsulated by an outer membrane (OM) that is impermeable to large and hydrophobic molecules. As such, these bacteria are intrinsically resistant to several clinically relevant antibiotics. To better understand how the OM is established or maintained, we sought to clarify the function of the essential protein YejM in Escherichia coli. Here, we show that YejM inhibits activity of the YciM/FtsH protease complex, which regulates synthesis of the essential OM glycolipid lipopolysaccharide (LPS). Our data suggest that disrupting proper communication between LPS synthesis and transport to the OM leads to accumulation of LPS within the inner membrane (IM). The lethality associated with this event can be suppressed by increasing OM vesiculation. Our research has identified a completely novel signaling pathway that we propose coordinates LPS synthesis and transport.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.00598-20”,“issue”:“2”,“note”:“publisher: American Society for Microbiology”,“page”:“e00598-20”,“source”:“journals.asm.org (Atypon)”,“title”:“YejM Modulates Activity of the YciM/FtsH Protease Complex To Prevent Lethal Accumulation of Lipopolysaccharide”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.00598-20”,“volume”:“11”,“author”:[{“family”:“Guest”,“given”:“Randi L.”},{“family”:“Samé Guerra”,“given”:“Daniel”},{“family”:“Wissler”,“given”:“Maria”},{“family”:“Grimm”,“given”:“Jacqueline”},{“family”:“Silhavy”,“given”:“Thomas J.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",4,14}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>4<!–[if supportFields]><![endif]–> (Guest et al., 2020). The OM is made of PLs in the inner leaflet and lipopolysaccharide (LPS) glycolipid molecules in the outer leaflet<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“jGfiKmxu”,“properties”:{“formattedCitation”:“\\super 5\\nosupersub{}”,“plainCitation”:“5”,“noteIndex”:0},“citationItems”:[{“id”:623,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/HUNH4ZWD”],“itemData”:{“id”:623,“type”:“article-journal”,“abstract”:“The cell envelope is the first line of defense between a bacterium and the world-at-large. Often, the initial steps that determine the outcome of chemical warfare, bacteriophage infections, and battles with other bacteria or the immune system greatly depend on the structure and composition of the bacterial cell surface. One of the most studied bacterial surface molecules is the glycolipid known as lipopolysaccharide (LPS), which is produced by most Gram-negative bacteria. Much of the initial attention LPS received in the early 1900s was owed to its ability to stimulate the immune system, for which the glycolipid was commonly known as endotoxin. It was later discovered that LPS also creates a permeability barrier at the cell surface and is a main contributor to the innate resistance that Gram-negative bacteria display against many antimicrobials. Not surprisingly, these important properties of LPS have driven a vast and still prolific body of literature for more than a hundred years. LPS research has also led to pioneering studies in bacterial envelope biogenesis and physiology, mostly using Escherichia coli and Salmonella as model systems. In this review, we will focus on the fundamental knowledge we have gained from studies of the complex structure of the LPS molecule and the biochemical pathways for its synthesis, as well as the transport of LPS across the bacterial envelope and its assembly at the cell surface.”,“container-title”:“EcoSal Plus”,“DOI”:“10.1128/ecosalplus.ESP-0001-2018”,“issue”:“1”,“note”:“publisher: American Society for Microbiology”,“source”:“journals.asm.org (Atypon)”,“title”:“Function and Biogenesis of Lipopolysaccharides”,“URL”:“https://journals.asm.org/doi/10.1128/ecosalplus.ESP-0001-2018”,“volume”:“8”,“author”:[{“family”:“Bertani”,“given”:“Blake”},{“family”:“Ruiz”,“given”:“Natividad”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2018",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>5<!–[if supportFields]><![endif]–> (Bertani & Ruiz, 2018). The OM also consists of OM proteins (Omps), exopolysaccharides (EPS), flagella and type I fimbria<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“cseFSYyV”,“properties”:{“formattedCitation”:“\\super 6\\nosupersub{}”,“plainCitation”:“6”,“noteIndex”:0},“citationItems”:[{“id”:625,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/5RDB5DKM”],“itemData”:{“id”:625,“type”:“article-journal”,“abstract”:“Escherichia coli is generally used as model bacteria to define microbial cell factories for many products and to investigate regulation mechanisms. E. coli exhibits phospholipids, lipopolysaccharides, colanic acid, flagella and type I fimbriae on the outer membrane which is a self-protective barrier and closely related to cellular morphology, growth, phenotypes and stress adaptation. However, these outer membrane associated molecules could also lead to potential contamination and insecurity for fermentation products and consume lots of nutrients and energy sources. Therefore, understanding critical insights of these membrane associated molecules is necessary for building better microbial producers. Here the biosynthesis, function, influences, and current membrane engineering applications of these outer membrane associated molecules were reviewed from the perspective of synthetic biology, and the potential and effective engineering strategies on the outer membrane to improve fermentation features for microbial cell factories were suggested.”,“container-title”:“Microbial Cell Factories”,“DOI”:“10.1186/s12934-021-01565-8”,“ISSN”:“1475-2859”,“issue”:“1”,“journalAbbreviation”:“Microbial Cell Factories”,“page”:“73”,“source”:“BioMed Central”,“title”:“Insights into the structure of Escherichia coli outer membrane as the target for engineering microbial cell factories”,“URL”:“https://doi.org/10.1186/s12934-021-01565-8”,“volume”:“20”,“author”:[{“family”:“Wang”,“given”:“Jianli”},{“family”:“Ma”,“given”:“Wenjian”},{“family”:“Wang”,“given”:“Xiaoyuan”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2021",3,20}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>6<!–[if supportFields]><![endif]–> (Wang, Ma, & Wang, 2021). EPS, flagella, and fimbria are nonessential structures; therefore, they are not present in all <i style='mso-bidi-font-style: normal'>E. coli strains</span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“NU8TNhlB”,“properties”:{“formattedCitation”:“\\super 6\\nosupersub{}”,“plainCitation”:“6”,“noteIndex”:0},“citationItems”:[{“id”:625,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/5RDB5DKM”],“itemData”:{“id”:625,“type”:“article-journal”,“abstract”:“Escherichia coli is generally used as model bacteria to define microbial cell factories for many products and to investigate regulation mechanisms. E. coli exhibits phospholipids, lipopolysaccharides, colanic acid, flagella and type I fimbriae on the outer membrane which is a self-protective barrier and closely related to cellular morphology, growth, phenotypes and stress adaptation. However, these outer membrane associated molecules could also lead to potential contamination and insecurity for fermentation products and consume lots of nutrients and energy sources. Therefore, understanding critical insights of these membrane associated molecules is necessary for building better microbial producers. Here the biosynthesis, function, influences, and current membrane engineering applications of these outer membrane associated molecules were reviewed from the perspective of synthetic biology, and the potential and effective engineering strategies on the outer membrane to improve fermentation features for microbial cell factories were suggested.”,“container-title”:“Microbial Cell Factories”,“DOI”:“10.1186/s12934-021-01565-8”,“ISSN”:“1475-2859”,“issue”:“1”,“journalAbbreviation”:“Microbial Cell Factories”,“page”:“73”,“source”:“BioMed Central”,“title”:“Insights into the structure of Escherichia coli outer membrane as the target for engineering microbial cell factories”,“URL”:“https://doi.org/10.1186/s12934-021-01565-8”,“volume”:“20”,“author”:[{“family”:“Wang”,“given”:“Jianli”},{“family”:“Ma”,“given”:“Wenjian”},{“family”:“Wang”,“given”:“Xiaoyuan”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2021",3,20}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>6<!–[if supportFields]><![endif]–> (Wang, Ma, & Wang, 2021). There are three important Omps: OmpC, OmpF, and OmpA<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“6h9AoQlU”,“properties”:{“formattedCitation”:“\\super 6\\nosupersub{}”,“plainCitation”:“6”,“noteIndex”:0},“citationItems”:[{“id”:625,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/5RDB5DKM”],“itemData”:{“id”:625,“type”:“article-journal”,“abstract”:“Escherichia coli is generally used as model bacteria to define microbial cell factories for many products and to investigate regulation mechanisms. E. coli exhibits phospholipids, lipopolysaccharides, colanic acid, flagella and type I fimbriae on the outer membrane which is a self-protective barrier and closely related to cellular morphology, growth, phenotypes and stress adaptation. However, these outer membrane associated molecules could also lead to potential contamination and insecurity for fermentation products and consume lots of nutrients and energy sources. Therefore, understanding critical insights of these membrane associated molecules is necessary for building better microbial producers. Here the biosynthesis, function, influences, and current membrane engineering applications of these outer membrane associated molecules were reviewed from the perspective of synthetic biology, and the potential and effective engineering strategies on the outer membrane to improve fermentation features for microbial cell factories were suggested.”,“container-title”:“Microbial Cell Factories”,“DOI”:“10.1186/s12934-021-01565-8”,“ISSN”:“1475-2859”,“issue”:“1”,“journalAbbreviation”:“Microbial Cell Factories”,“page”:“73”,“source”:“BioMed Central”,“title”:“Insights into the structure of Escherichia coli outer membrane as the target for engineering microbial cell factories”,“URL”:“https://doi.org/10.1186/s12934-021-01565-8”,“volume”:“20”,“author”:[{“family”:“Wang”,“given”:“Jianli”},{“family”:“Ma”,“given”:“Wenjian”},{“family”:“Wang”,“given”:“Xiaoyuan”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2021",3,20}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>6<!–[if supportFields]><![endif]–> (Wang, Ma, & Wang, 2021). OmpC and OmpF regulate the entry of small molecule solutes into the cytoplasm while OmpA maintains <i style='mso-bidi-font-style: normal'>E. coli’s cell surface integrity</span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“84c6pWvo”,“properties”:{“formattedCitation”:“\\super 6\\nosupersub{}”,“plainCitation”:“6”,“noteIndex”:0},“citationItems”:[{“id”:625,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/5RDB5DKM”],“itemData”:{“id”:625,“type”:“article-journal”,“abstract”:“Escherichia coli is generally used as model bacteria to define microbial cell factories for many products and to investigate regulation mechanisms. E. coli exhibits phospholipids, lipopolysaccharides, colanic acid, flagella and type I fimbriae on the outer membrane which is a self-protective barrier and closely related to cellular morphology, growth, phenotypes and stress adaptation. However, these outer membrane associated molecules could also lead to potential contamination and insecurity for fermentation products and consume lots of nutrients and energy sources. Therefore, understanding critical insights of these membrane associated molecules is necessary for building better microbial producers. Here the biosynthesis, function, influences, and current membrane engineering applications of these outer membrane associated molecules were reviewed from the perspective of synthetic biology, and the potential and effective engineering strategies on the outer membrane to improve fermentation features for microbial cell factories were suggested.”,“container-title”:“Microbial Cell Factories”,“DOI”:“10.1186/s12934-021-01565-8”,“ISSN”:“1475-2859”,“issue”:“1”,“journalAbbreviation”:“Microbial Cell Factories”,“page”:“73”,“source”:“BioMed Central”,“title”:“Insights into the structure of Escherichia coli outer membrane as the target for engineering microbial cell factories”,“URL”:“https://doi.org/10.1186/s12934-021-01565-8”,“volume”:“20”,“author”:[{“family”:“Wang”,“given”:“Jianli”},{“family”:“Ma”,“given”:“Wenjian”},{“family”:“Wang”,“given”:“Xiaoyuan”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2021",3,20}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>6<!–[if supportFields]><![endif]–> (Wang, Ma, & Wang, 2021). <o:p></o:p><p class=MsoNormal><!–[if gte vml 1]><v:shapetype id=“_x0000_t75” coordsize=“21600,21600” o:spt=“75” o:preferrelative=“t” path=“m@4@5l@4@11@9@11@9@5xe” filled=“f” stroked=“f”><v:stroke joinstyle=“miter”/><v:formulas><v:f eqn=“if lineDrawn pixelLineWidth 0”/><v:f eqn=“sum @0 1 0”/><v:f eqn=“sum 0 0 @1”/><v:f eqn=“prod @2 1 2”/><v:f eqn=“prod @3 21600 pixelWidth”/><v:f eqn=“prod @3 21600 pixelHeight”/><v:f eqn=“sum @0 0 1”/><v:f eqn=“prod @6 1 2”/><v:f eqn=“prod @7 21600 pixelWidth”/><v:f eqn=“sum @8 21600 0”/><v:f eqn=“prod @7 21600 pixelHeight”/><v:f eqn=“sum @10 21600 0”/></v:formulas><v:path o:extrusionok=“f” gradientshapeok=“t” o:connecttype=“rect”/><o:lock v:ext=“edit” aspectratio=“t”/></v:shapetype><v:shape id=“image5.png” o:spid=“_x0000_i1034” type=“#_x0000_t75” style='width:4in;height:166.5pt;visibility:visible;mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image001.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img width=384 height=222 src=“Wiki%20Draft%20(1)_files/image002.gif” v:shapes=“image5.png”><![endif]><o:p></o:p><p class=MsoNormal>Figure X: The cell envelope of E. coli. The cell envelope is made of the inner membrane, peptidoglycan cell wall, and outer membrane. The inner membrane consists of a phospholipid (PL) bilayer. The peptidoglycan cell wall can be found in the periplasmic space between the IM and OM. It is made up of the NAG-NAM disaccharide, cross-linked by pentapeptide side chains. The peptidoglycan cell wall is connected to the OM via murein or Braun’s lipoprotein, Lpp (coloured dark blue). The OM consists of PLs in its inner leaflet, LPS molecules in its outer leaflet, and outer membrane proteins, Omps (coloured green). The outer membrane may also contain non essential structures such as exopolysaccharides (EPS), flagella and type I fimbria.<o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>LPS Structure<o:p></o:p>'<p class=MsoNormal><a href=“https://www.ocl-journal.org/articles/ocl/full_html/2020/01/ocl200025s/ocl200025s.html”>https://www.ocl-journal.org/articles/ocl/full_html/2020/01/ocl200025s/ocl200025s.html</a><u><o:p></o:p></u><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm'>LPS are glycolipids comprised of three primary regions. The first is the lipid A region, which is typically made up of a bis-phosphorylated glucosamine disaccharide that carries fatty acids in ester and amide linkages. This region is connected to the second core oligosaccharide region via 2-keto-3 deoxy-octulosonic acid (Kdo). The third region is the O-chain, consisting of repeating oligosaccharide units and differs from one bacterium to another.<o:p></o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm'>LPS Function<o:p></o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm;text-indent:36.0pt'>LPS provides a permeability barrier that prevents the entry of harmful molecules. High density of saturated fatty acids cause broadly and strong interaction with the acyl chain, and it synthesizes a low fluidity of the membrane bilayer. In addition, divalent cations between LPS molecules stabilize the high negativity of the membrane, which is caused by the presence of the phosphate group. Polyionic interaction within the outer membrane promotes LPS packing, and constructs LPS as a permeability barrier.<o:p></o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm;text-indent:36.0pt'>LPS also contributes to impacting the virulence of the bacteria cell. LPS is more stable  by comparing with bacterial exotoxins, and is the primary<o:p></o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm;text-indent:36.0pt'><a href=“https://www.ncbi.nlm.nih.gov/books/NBK554414/#:~:text=The%20primary%20function%20of%20LPS,inhabitation%20in%20the%20gastrointestinal%20tract”>https://www.ncbi.nlm.nih.gov/books/NBK554414/#:~:text=The%20primary%20function%20of%20LPS,inhabitation%20in%20the%20gastrointestinal%20tract</a>. <!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“zc9EP2pc”,“properties”:{“formattedCitation”:“\\super 7\\nosupersub{}”,“plainCitation”:“7”,“noteIndex”:0},“citationItems”:[{“id”:646,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/T75BDR5A”],“itemData”:{“id”:646,“type”:“chapter”,“abstract”:“Lipopolysaccharides (LPS) are important outer membrane components of gram-negative bacteria. They are large amphipathic glycoconjugates that typically consist of a lipid domain (hydrophobic) attached to a core oligosaccharide and a distal polysaccharide. These molecules are also known as lipogylcans due to the presence of lipid and sugar molecules. The lipopolysaccharides are composed of: 1. Lipid A: the hydrophobic domain, which is an endotoxin and the main virulence factor. 2. O-antigen, the repeating hydrophilic distal oligosaccharide. 3. The hydrophilic core polysaccharide. The lipid A component varies from one organism to another and is essential in imparting specific pathogenic attributes to the bacteria. Inherent to gram-negative bacteria, LPS provides integrity to the bacterial cell and a mechanism of interaction of the bacteria to other surfaces. Most bacterial LPS molecules are thermostable and generate a robust pro-inflammatory stimulus for the immune system in mammals. Since different types of LPS are present in different genera of gram-negative bacteria, LPS is used for serotyping gram-negative bacteria. More specifically, the O-antigen imparts serological distinction to the bacterial species. Also, the size and composition of LPS are highly dynamic among bacterial species. Due to its unique properties, LPS has gained considerable research focus to understand its complex structure, biogenesis, transport, and assembly. Besides, LPS is also a recognized biomarker due to its central role in host-pathogen interaction that facilitates the infection process.”,“call-number”:“NBK554414”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32119301”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Biochemistry, Lipopolysaccharide”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK554414/”,“author”:[{“family”:“Farhana”,“given”:“Aisha”},{“family”:“Khan”,“given”:“Yusuf S.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>7<!–[if supportFields]><![endif]–> (Farhana)<o:p></o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm;text-indent:36.0pt'><a href=“https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6091223/”>https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6091223/</a><u></u><!–[if supportFields]><u> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“NPayMhvD”,“properties”:{“formattedCitation”:“\\super 5\\nosupersub{}”,“plainCitation”:“5”,“noteIndex”:0},“citationItems”:[{“id”:623,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/HUNH4ZWD”],“itemData”:{“id”:623,“type”:“article-journal”,“abstract”:“The cell envelope is the first line of defense between a bacterium and the world-at-large. Often, the initial steps that determine the outcome of chemical warfare, bacteriophage infections, and battles with other bacteria or the immune system greatly depend on the structure and composition of the bacterial cell surface. One of the most studied bacterial surface molecules is the glycolipid known as lipopolysaccharide (LPS), which is produced by most Gram-negative bacteria. Much of the initial attention LPS received in the early 1900s was owed to its ability to stimulate the immune system, for which the glycolipid was commonly known as endotoxin. It was later discovered that LPS also creates a permeability barrier at the cell surface and is a main contributor to the innate resistance that Gram-negative bacteria display against many antimicrobials. Not surprisingly, these important properties of LPS have driven a vast and still prolific body of literature for more than a hundred years. LPS research has also led to pioneering studies in bacterial envelope biogenesis and physiology, mostly using Escherichia coli and Salmonella as model systems. In this review, we will focus on the fundamental knowledge we have gained from studies of the complex structure of the LPS molecule and the biochemical pathways for its synthesis, as well as the transport of LPS across the bacterial envelope and its assembly at the cell surface.”,“container-title”:“EcoSal Plus”,“DOI”:“10.1128/ecosalplus.ESP-0001-2018”,“issue”:“1”,“note”:“publisher: American Society for Microbiology”,“source”:“journals.asm.org (Atypon)”,“title”:“Function and Biogenesis of Lipopolysaccharides”,“URL”:“https://journals.asm.org/doi/10.1128/ecosalplus.ESP-0001-2018”,“volume”:“8”,“author”:[{“family”:“Bertani”,“given”:“Blake”},{“family”:“Ruiz”,“given”:“Natividad”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2018",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} </u><![endif]–>5<!–[if supportFields]><u></u><![endif]–><o:p></o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm;text-indent:36.0pt'><o:p> </o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm;text-indent:36.0pt'><o:p> </o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm'><o:p> </o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm'><o:p> </o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm'><o:p> </o:p><p class=MsoNormal style='margin-top:12.0pt;margin-right:0cm;margin-bottom: 12.0pt;margin-left:0cm'><o:p> </o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.0 LPS synthesis<o:p></o:p>'<p class=MsoNormal>The LPS biosynthesis pathway is crucial for the structural makeup of gram-negative bacteria’s outer membrane<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“duQKHHWi”,“properties”:{“formattedCitation”:“\\super 8\\nosupersub{}”,“plainCitation”:“8”,“noteIndex”:0},“citationItems”:[{“id”:638,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/ZRPN7M3N”],“itemData”:{“id”:638,“type”:“article-journal”,“abstract”:“Lipopolysaccharide that constitutes the outer leaflet of the outer membrane of most Gram-negative bacteria is referred to as an endotoxin. It is comprised of a hydrophilic polysaccharide and a hydrophobic component referred to as lipid A. Lipid A is responsible for the major bioactivity of endotoxin, and is recognized by immune cells as a pathogen-associated molecule. Most enzymes and genes coding for proteins responsible for the biosynthesis and export of lipopolysaccharide in Escherichia coli have been identified, and they are shared by most Gram-negative bacteria based on genetic information. The detailed structure of lipopolysaccharide differs from one bacterium to another, consistent with the recent discovery of additional enzymes and gene products that can modify the basic structure of lipopolysaccharide in some bacteria, especially pathogens. These modifications are not required for survival, but are tightly regulated in the cell and closely related to the virulence of bacteria. In this review we discuss recent studies of the biosynthesis and export of lipopolysaccharide, and the relationship between the structure of lipopolysaccharide and the virulence of bacteria.”,“container-title”:“Progress in Lipid Research”,“DOI”:“10.1016/j.plipres.2009.06.002”,“ISSN”:“0163-7827”,“issue”:“2”,“journalAbbreviation”:“Progress in Lipid Research”,“language”:“en”,“page”:“97-107”,“source”:“ScienceDirect”,“title”:“Lipopolysaccharide: Biosynthetic pathway and structure modification”,“title-short”:“Lipopolysaccharide”,“URL”:“https://www.sciencedirect.com/science/article/pii/S0163782709000526”,“volume”:“49”,“author”:[{“family”:“Wang”,“given”:“Xiaoyuan”},{“family”:“Quinn”,“given”:“Peter J.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",4,1}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>8<!–[if supportFields]><![endif]–> (Wang & Quinn, 2010). Reflected in the structure of LPS, its synthesis is dependent on the formation of its three regions: Lipid A, the core oligosaccharide, and the O-antigen. LPS synthesis occurs within the cytoplasm along the inner membrane surface.<o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.1 Lipid A synthesis<o:p></o:p>'<p class=MsoNormal>The LPS biosynthesis starts with the conserved pathway of lipid A synthesis as displayed in <b style='mso-bidi-font-weight:normal'>Figure X '</span><!–[if supportFields]><b style='mso-bidi-font-weight:normal'> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“2I1GZm5a”,“properties”:{“formattedCitation”:“\\super 9\\nosupersub{}”,“plainCitation”:“9”,“noteIndex”:0},“citationItems”:[{“id”:642,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/WA5WMMWJ”],“itemData”:{“id”:642,“type”:“article-journal”,“abstract”:“Lipopolysaccharide molecules represent a unique family of glycolipids based on a highly conserved lipid moiety known as lipid A. These molecules are produced by most gram-negative bacteria, in which they play important roles in the integrity of the outer-membrane permeability barrier and participate extensively in host?pathogen interplay. Few bacteria contain lipopolysaccharide molecules composed only of lipid A. In most forms, lipid A is glycosylated by addition of the core oligosaccharide that, in some bacteria, provides an attachment site for a long-chain O-antigenic polysaccharide. The complexity of lipopolysaccharide structures is reflected in the processes used for their biosynthesis and export. Rapid growth and cell division depend on the bacterial cell's capacity to synthesize and export lipopolysaccharide efficiently and in large amounts. We review recent advances in those processes, emphasizing the reactions that are essential for viability.”,“container-title”:“Annual Review of Biochemistry”,“DOI”:“10.1146/annurev-biochem-060713-035600”,“ISSN”:“0066-4154”,“issue”:“1”,“journalAbbreviation”:“Annu. Rev. Biochem.”,“note”:“publisher: Annual Reviews”,“page”:“99-128”,“title”:“Biosynthesis and Export of Bacterial Lipopolysaccharides”,“URL”:“https://doi.org/10.1146/annurev-biochem-060713-035600”,“volume”:“83”,“author”:[{“family”:“Whitfield”,“given”:“Chris”},{“family”:“Trent”,“given”:“M. Stephen”}],“accessed”:{“date-parts”:"2023",2,2},“issued”:{“date-parts”:"2014",6,2}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} '<![endif]–>9<!–[if supportFields]><b style='mso-bidi-font-weight:normal'>'<![endif]–> (Whitfield & Trent, 2014). This pathway begins with a UDP-N-acetylglucosamine (UDP-GlcNAc) molecule<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“TH4VaFYV”,“properties”:{“formattedCitation”:“\\super 8\\nosupersub{}”,“plainCitation”:“8”,“noteIndex”:0},“citationItems”:[{“id”:638,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/ZRPN7M3N”],“itemData”:{“id”:638,“type”:“article-journal”,“abstract”:“Lipopolysaccharide that constitutes the outer leaflet of the outer membrane of most Gram-negative bacteria is referred to as an endotoxin. It is comprised of a hydrophilic polysaccharide and a hydrophobic component referred to as lipid A. Lipid A is responsible for the major bioactivity of endotoxin, and is recognized by immune cells as a pathogen-associated molecule. Most enzymes and genes coding for proteins responsible for the biosynthesis and export of lipopolysaccharide in Escherichia coli have been identified, and they are shared by most Gram-negative bacteria based on genetic information. The detailed structure of lipopolysaccharide differs from one bacterium to another, consistent with the recent discovery of additional enzymes and gene products that can modify the basic structure of lipopolysaccharide in some bacteria, especially pathogens. These modifications are not required for survival, but are tightly regulated in the cell and closely related to the virulence of bacteria. In this review we discuss recent studies of the biosynthesis and export of lipopolysaccharide, and the relationship between the structure of lipopolysaccharide and the virulence of bacteria.”,“container-title”:“Progress in Lipid Research”,“DOI”:“10.1016/j.plipres.2009.06.002”,“ISSN”:“0163-7827”,“issue”:“2”,“journalAbbreviation”:“Progress in Lipid Research”,“language”:“en”,“page”:“97-107”,“source”:“ScienceDirect”,“title”:“Lipopolysaccharide: Biosynthetic pathway and structure modification”,“title-short”:“Lipopolysaccharide”,“URL”:“https://www.sciencedirect.com/science/article/pii/S0163782709000526”,“volume”:“49”,“author”:[{“family”:“Wang”,“given”:“Xiaoyuan”},{“family”:“Quinn”,“given”:“Peter J.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",4,1}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>8<!–[if supportFields]><![endif]–> (Wang & Quinn, 2010). Lipid A synthesis involves the addition of hydrophobic fatty acid chains to UDP-GlcNAc catalyzed by LpxA, LpxC and LpxD, forming UDP-diacyl-GlcN. Although the biosynthesis begins with the acylation of UDP-GlcNAc, catalyzed by LpxA, this reaction is thermodynamically unfavourable<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“8vx6d2Gc”,“properties”:{“formattedCitation”:“\\super 10\\nosupersub{}”,“plainCitation”:“10”,“noteIndex”:0},“citationItems”:[{“id”:632,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/W6EZIQHQ”],“itemData”:{“id”:632,“type”:“article-journal”,“abstract”:“Multi-drug resistant (MDR), pathogenic Gram-negative bacteria pose a serious health threat, and novel antibiotic targets must be identified to combat MDR infections. One promising target is the zinc-dependent metalloamidase UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC), which catalyzes the committed step of lipid A (endotoxin) biosynthesis. LpxC is an essential, single copy gene that is conserved in virtually all Gram-negative bacteria. LpxC structures, revealed by NMR and X-ray crystallography, demonstrate that LpxC adopts a novel ‘β-α-α-β sandwich’ fold and encapsulates the acyl chain of the substrate with a unique hydrophobic passage. Kinetic analysis revealed that LpxC functions by a general acid-base mechanism, with a glutamate serving as the general base.   Many potent LpxC inhibitors have been identified, and most contain a hydroxamate group targeting the catalytic zinc ion. Although early LpxC-inhibitors were either narrow-spectrum antibiotics or broad-spectrum in vitro LpxC inhibitors with limited antibiotic properties, the recently discovered compound CHIR-090 is a powerful antibiotic that controls the growth of Escherichia coli and Pseudomonas aeruginosa, with an efficacy rivaling that of the FDA-approved antibiotic ciprofloxacin. CHIR-090 inhibits a wide range of LpxC enzymes with sub-nanomolar affinity in vitro, and is a two-step, slow, tight-binding inhibitor of Aquifex aeolicus and E. coli LpxC. The success of CHIR-090 suggests that potent LpxCtargeting antibiotics may be developed to control a broad range of Gram-negative bacteria.”,“container-title”:“Current Pharmaceutical Biotechnology”,“issue”:“1”,“language”:“en”,“page”:“9-15”,“source”:“www.eurekaselect.com”,“title”:“Mechanism and Inhibition of LpxC: An Essential Zinc-Dependent Deacetylase of Bacterial Lipid A Synthesis”,“title-short”:“Mechanism and Inhibition of LpxC”,“URL”:“https://www.eurekaselect.com/article/11296”,“volume”:“9”,“author”:[{“family”:“Zhou”,“given”:“Pei”},{“family”:“Barb”,“given”:“Adam W.”}],“accessed”:{“date-parts”:"2023",2,1}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>10<!–[if supportFields]><![endif]–> (Barb & Zhou, 2008). Thus, the first committed step of lipid A biosynthesis is the deacetylation reaction catalyzed by LpxC. LpxC is a crucial enzyme as it catalyzes the non-reversible step in lipid A synthesis which is the deacetylation of UDP-3-O-(acyl)-GlcNAc. LpxC also has a unique sequence compared to other deacetylases and plays a regulatory role in lipid A biosynthesis, which makes it an attractive target for antibiotic development<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“8KyB55he”,“properties”:{“formattedCitation”:“\\super 8\\nosupersub{}”,“plainCitation”:“8”,“noteIndex”:0},“citationItems”:[{“id”:638,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/ZRPN7M3N”],“itemData”:{“id”:638,“type”:“article-journal”,“abstract”:“Lipopolysaccharide that constitutes the outer leaflet of the outer membrane of most Gram-negative bacteria is referred to as an endotoxin. It is comprised of a hydrophilic polysaccharide and a hydrophobic component referred to as lipid A. Lipid A is responsible for the major bioactivity of endotoxin, and is recognized by immune cells as a pathogen-associated molecule. Most enzymes and genes coding for proteins responsible for the biosynthesis and export of lipopolysaccharide in Escherichia coli have been identified, and they are shared by most Gram-negative bacteria based on genetic information. The detailed structure of lipopolysaccharide differs from one bacterium to another, consistent with the recent discovery of additional enzymes and gene products that can modify the basic structure of lipopolysaccharide in some bacteria, especially pathogens. These modifications are not required for survival, but are tightly regulated in the cell and closely related to the virulence of bacteria. In this review we discuss recent studies of the biosynthesis and export of lipopolysaccharide, and the relationship between the structure of lipopolysaccharide and the virulence of bacteria.”,“container-title”:“Progress in Lipid Research”,“DOI”:“10.1016/j.plipres.2009.06.002”,“ISSN”:“0163-7827”,“issue”:“2”,“journalAbbreviation”:“Progress in Lipid Research”,“language”:“en”,“page”:“97-107”,“source”:“ScienceDirect”,“title”:“Lipopolysaccharide: Biosynthetic pathway and structure modification”,“title-short”:“Lipopolysaccharide”,“URL”:“https://www.sciencedirect.com/science/article/pii/S0163782709000526”,“volume”:“49”,“author”:[{“family”:“Wang”,“given”:“Xiaoyuan”},{“family”:“Quinn”,“given”:“Peter J.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",4,1}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>8<!–[if supportFields]><![endif]–> (Wang & Quinn, 2010). Following LpxD action, UDP-diacyl-GlcN undergoes a series of reactions catalyzed by three other enzymes, LpxH, LpxB and LpxK, to compose lipid IVA.  Two Kdo molecules are added to Lipid IVA, catalyzed by the bifunctional KdtA. Kdo2-LipidIVA is further modified with acyltransferases, LpxL and LpxM, to form Kdo2-Lipid A.  Kdo2-Lipid A is the active form that is used for the addition of core oligosaccharides and overall assembly of LPS.<o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.2 Core Oligosaccharides synthesis/addition<o:p></o:p>'<p class=MsoNormal>The core oligosaccharides are added to lipid A on the cytoplasmic surface of the inner membrane through membrane-bound glycosyltransferases and nucleotide sugar donors<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“Hvjl9LDm”,“properties”:{“formattedCitation”:“\\super 8\\nosupersub{}”,“plainCitation”:“8”,“noteIndex”:0},“citationItems”:[{“id”:638,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/ZRPN7M3N”],“itemData”:{“id”:638,“type”:“article-journal”,“abstract”:“Lipopolysaccharide that constitutes the outer leaflet of the outer membrane of most Gram-negative bacteria is referred to as an endotoxin. It is comprised of a hydrophilic polysaccharide and a hydrophobic component referred to as lipid A. Lipid A is responsible for the major bioactivity of endotoxin, and is recognized by immune cells as a pathogen-associated molecule. Most enzymes and genes coding for proteins responsible for the biosynthesis and export of lipopolysaccharide in Escherichia coli have been identified, and they are shared by most Gram-negative bacteria based on genetic information. The detailed structure of lipopolysaccharide differs from one bacterium to another, consistent with the recent discovery of additional enzymes and gene products that can modify the basic structure of lipopolysaccharide in some bacteria, especially pathogens. These modifications are not required for survival, but are tightly regulated in the cell and closely related to the virulence of bacteria. In this review we discuss recent studies of the biosynthesis and export of lipopolysaccharide, and the relationship between the structure of lipopolysaccharide and the virulence of bacteria.”,“container-title”:“Progress in Lipid Research”,“DOI”:“10.1016/j.plipres.2009.06.002”,“ISSN”:“0163-7827”,“issue”:“2”,“journalAbbreviation”:“Progress in Lipid Research”,“language”:“en”,“page”:“97-107”,“source”:“ScienceDirect”,“title”:“Lipopolysaccharide: Biosynthetic pathway and structure modification”,“title-short”:“Lipopolysaccharide”,“URL”:“https://www.sciencedirect.com/science/article/pii/S0163782709000526”,“volume”:“49”,“author”:[{“family”:“Wang”,“given”:“Xiaoyuan”},{“family”:“Quinn”,“given”:“Peter J.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",4,1}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>8<!–[if supportFields]><![endif]–> (Wang & Quinn, 2010). The core oligosaccharides have two components: the inner core and the outer core. The inner core is the conserved region of the core oligosaccharides and includes Kdo molecules as well as the L-glycero-D-manno-heptose molecule (Hep)<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“9jd2Utu1”,“properties”:{“formattedCitation”:“\\super 9\\nosupersub{}”,“plainCitation”:“9”,“noteIndex”:0},“citationItems”:[{“id”:642,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/WA5WMMWJ”],“itemData”:{“id”:642,“type”:“article-journal”,“abstract”:“Lipopolysaccharide molecules represent a unique family of glycolipids based on a highly conserved lipid moiety known as lipid A. These molecules are produced by most gram-negative bacteria, in which they play important roles in the integrity of the outer-membrane permeability barrier and participate extensively in host?pathogen interplay. Few bacteria contain lipopolysaccharide molecules composed only of lipid A. In most forms, lipid A is glycosylated by addition of the core oligosaccharide that, in some bacteria, provides an attachment site for a long-chain O-antigenic polysaccharide. The complexity of lipopolysaccharide structures is reflected in the processes used for their biosynthesis and export. Rapid growth and cell division depend on the bacterial cell's capacity to synthesize and export lipopolysaccharide efficiently and in large amounts. We review recent advances in those processes, emphasizing the reactions that are essential for viability.”,“container-title”:“Annual Review of Biochemistry”,“DOI”:“10.1146/annurev-biochem-060713-035600”,“ISSN”:“0066-4154”,“issue”:“1”,“journalAbbreviation”:“Annu. Rev. Biochem.”,“note”:“publisher: Annual Reviews”,“page”:“99-128”,“title”:“Biosynthesis and Export of Bacterial Lipopolysaccharides”,“URL”:“https://doi.org/10.1146/annurev-biochem-060713-035600”,“volume”:“83”,“author”:[{“family”:“Whitfield”,“given”:“Chris”},{“family”:“Trent”,“given”:“M. Stephen”}],“accessed”:{“date-parts”:"2023",2,2},“issued”:{“date-parts”:"2014",6,2}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>9<!–[if supportFields]><![endif]–> (Whitfield & Trent, 2014). The formation and attachment of Hep are mediated by enzymes synthesized by the <i style='mso-bidi-font-style:normal'>gmhD</span><i style='mso-bidi-font-style:normal'>operon. On the other hand, the outer core region is less conserved. The outer core oligosaccharides are synthesized by gene products of the waaQ operons.<o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.3 O-antigen addition<o:p></o:p>'<p class=MsoNormal>The O-antigen polymers are added to the outer core oligosaccharides through glycosyltransferases and nucleotide sugar donors<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“TLflZagS”,“properties”:{“formattedCitation”:“\\super 8\\nosupersub{}”,“plainCitation”:“8”,“noteIndex”:0},“citationItems”:[{“id”:638,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/ZRPN7M3N”],“itemData”:{“id”:638,“type”:“article-journal”,“abstract”:“Lipopolysaccharide that constitutes the outer leaflet of the outer membrane of most Gram-negative bacteria is referred to as an endotoxin. It is comprised of a hydrophilic polysaccharide and a hydrophobic component referred to as lipid A. Lipid A is responsible for the major bioactivity of endotoxin, and is recognized by immune cells as a pathogen-associated molecule. Most enzymes and genes coding for proteins responsible for the biosynthesis and export of lipopolysaccharide in Escherichia coli have been identified, and they are shared by most Gram-negative bacteria based on genetic information. The detailed structure of lipopolysaccharide differs from one bacterium to another, consistent with the recent discovery of additional enzymes and gene products that can modify the basic structure of lipopolysaccharide in some bacteria, especially pathogens. These modifications are not required for survival, but are tightly regulated in the cell and closely related to the virulence of bacteria. In this review we discuss recent studies of the biosynthesis and export of lipopolysaccharide, and the relationship between the structure of lipopolysaccharide and the virulence of bacteria.”,“container-title”:“Progress in Lipid Research”,“DOI”:“10.1016/j.plipres.2009.06.002”,“ISSN”:“0163-7827”,“issue”:“2”,“journalAbbreviation”:“Progress in Lipid Research”,“language”:“en”,“page”:“97-107”,“source”:“ScienceDirect”,“title”:“Lipopolysaccharide: Biosynthetic pathway and structure modification”,“title-short”:“Lipopolysaccharide”,“URL”:“https://www.sciencedirect.com/science/article/pii/S0163782709000526”,“volume”:“49”,“author”:[{“family”:“Wang”,“given”:“Xiaoyuan”},{“family”:“Quinn”,“given”:“Peter J.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2010",4,1}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>8<!–[if supportFields]><![endif]–> (Wang & Quinn, 2010). The <i style='mso-bidi-font-style:normal'>rfb</span> gene cluster enzyme derivatives contribute to O-antigen diversity through the creation of enzymes for varying sugar-nucleotide precursors. The <i style='mso-bidi-font-style:normal'>rfb</span> operon also synthesizes glycosyltransferases, polymerases, and proteins needed for O-antigen transport through the inner membrane.<o:p></o:p></span><p class=MsoNormal style='margin-bottom:12.0pt'> <!–[if gte vml 1]><v:shape id=“image1.png” o:spid=“_x0000_i1033” type=“#_x0000_t75” style='width:468pt;height:328pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image003.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img border=0 width=624 height=437 src=“Wiki%20Draft%20(1)_files/image004.gif” v:shapes=“image1.png”><![endif]><o:p></o:p><p class=MsoNormal style='margin-bottom:12.0pt'><b style='mso-bidi-font-weight: normal'>Figure X': Kdo2-Lipid A synthesis, the first part of LPS synthesis. Kdo2-Lipid A synthesis involves the first committed step in LPS synthesis, catalyzed by LpxC, which is the deacetylation of UDP-3-O-(acyl)-GlcNAc (red box)<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“IUPlTF6N”,“properties”:{“formattedCitation”:“\\super 11\\nosupersub{}”,“plainCitation”:“11”,“noteIndex”:0},“citationItems”:[{“id”:636,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/KN5AUCNU”],“itemData”:{“id”:636,“type”:“article-journal”,“abstract”:“UDP-N-acetylglucosamine (UDP-GlcNAc) acyltransferase (LpxA) catalyzes the first step of lipid A biosynthesis, the reversible transfer of the R-3-hydroxyacyl chain from R-3-hydroxyacyl acyl carrier protein to the glucosamine 3-OH group of UDP-GlcNAc. Escherichia coli LpxA is highly selective for R-3-hydroxymyristate. The crystal structure of the E. coli LpxA homotrimer, determined previously in the absence of lipid substrates or products, revealed that LpxA contains an unusual, left-handed parallel β-helix fold. We have now solved the crystal structures of E. coli LpxA with the bound product UDP-3-O-(R-3-hydroxymyristoyl)-GlcNAc at a resolution of 1.74 Å and with bound UDP-3-O-(R-3-hydroxydecanoyl)-GlcNAc at 1.85 Å. The structures of these complexes are consistent with the catalytic mechanism deduced by mutagenesis and with a recent 3.0-Å structure of LpxA with bound UDP-GlcNAc. Our structures show how LpxA selects for 14-carbon R-3-hydroxyacyl chains and reveal two modes of UDP binding.”,“container-title”:“Proceedings of the National Academy of Sciences”,“DOI”:“10.1073/pnas.0705833104”,“issue”:“34”,“note”:“publisher: Proceedings of the National Academy of Sciences”,“page”:“13543-13550”,“source”:“pnas.org (Atypon)”,“title”:“Structural basis for the acyl chain selectivity and mechanism of UDP-N-acetylglucosamine acyltransferase”,“URL”:“https://www.pnas.org/doi/full/10.1073/pnas.0705833104”,“volume”:“104”,“author”:[{“family”:“Williams”,“given”:“Allison H.”},{“family”:“Raetz”,“given”:“Christian R. H.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2007",8,21}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>11<!–[if supportFields]><![endif]–> (Williams & Raetz, 2007). <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>LPS transport <o:p></o:p>'<p class=MsoNormal> <o:p></o:p><p class=MsoNormal>LPS transport begins with the movement of LPS from the inner membrane to the outer membrane and involves MsbA translocation (Sperandeo et al., 2017). MsbAflippase catalyzes the flipping of the Lipid A core moiety across the inner membrane. Following complete synthesis, the movement of the mature LPS molecule to the cell surface is assisted by the LPT molecular machine. Broadly, the transport of LPS from the inner membrane to the outer membrane can be divided into three key steps: LPS detachment from the inner membrane, LPS transport across the periplasm, and LPS insertion and assembly in the outer membrane at the cell surface (Sperandeo et al., 2017). <p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Regulation <o:p></o:p>'<p class=MsoNormal> <o:p></o:p><p class=MsoNormal>LPS assembly begins on the internal surface of the <i style='mso-bidi-font-style:normal'>E.coli</span> membrane. The rate of LPS assembly is controlled by LpxC. Prior to the completion of LPS biosynthesis, the lipid undergoes further modifications when it is flipped to the external surface of the inner membrane. Following synthesis completion, LPS is transported to the outer membrane’s external surface via a protein bridge that connects both the inner and outer membranes</span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“vnUtrtYB”,“properties”:{“formattedCitation”:“\\super 2\\nosupersub{}”,“plainCitation”:“2”,“noteIndex”:0},“citationItems”:[{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>2<!–[if supportFields]><![endif]–> (Bishop, 2020).  <o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal>Feedback inhibition is a key cellular control mechanism where the activity of a key enzyme within a pathway is inhibited by that same enzyme's end product(s). This control mechanism is essential in controlling and regulating LPS biosynthesis. It is currently unknown but it has been suspected that LPS or a precursor of LPS is the feedback signal responsible for LPS regulation<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“EPagjeP8”,“properties”:{“formattedCitation”:“\\super 2\\nosupersub{}”,“plainCitation”:“2”,“noteIndex”:0},“citationItems”:[{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>2<!–[if supportFields]><![endif]–> (Bishop, 2020).<o:p></o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image4.png” o:spid=“_x0000_i1032” type=“#_x0000_t75” style='width:467.5pt;height:200.5pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image005.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img border=0 width=623 height=267 src=“Wiki%20Draft%20(1)_files/image006.gif” v:shapes=“image4.png”><![endif]> <o:p></o:p><p class=MsoNormal> There are 3 scenarios involving LPS biosynthesis that will be discussed:  typical LPS biosynthesis, LPS excess, and LPS deficiency. <o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal>Beginning with normal LPS synthesis that takes place within the cell cytoplasm, the enzyme LpxC controls the biosynthesis of LPS while utilizing precursors located in the cytoplasm . Following biosynthesis, the immature LPS is flipped onto the external surface of the inner membrane and is then transported to the outer membrane. The FtsH enzyme, guided by interactions with LapB, degrades LpxC which disrupts LPS biosynthesis<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“OZBbxks7”,“properties”:{“formattedCitation”:“\\super 2\\nosupersub{}”,“plainCitation”:“2”,“noteIndex”:0},“citationItems”:[{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>2<!–[if supportFields]><![endif]–> (Bishop, 2020). However, Clairefeuille and colleagues show that a protein, PbgA, inhibits LapB-FtsH activity to promote LPS biosynthesis (2020). <o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image8.png” o:spid=“_x0000_i1031” type=“#_x0000_t75” style='width:465.5pt;height:326.5pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image007.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img border=0 width=621 height=435 src=“Wiki%20Draft%20(1)_files/image008.gif” v:shapes=“image8.png”><![endif]><o:p></o:p><p class=MsoNormal>Figure _. LPS synthesis and degradation of LpxC. The enzyme LpxC controls the biosynthesis of LPS, utilizing precursors located within the <i style='mso-bidi-font-style:normal'>E.coli</span><i style='mso-bidi-font-style:normal'>cell cytoplasm. After being flipped to the external surface of the inner membrane through an ABC transporter, the mature LPS is transported to the outer membrane using LPT machinery. The enzyme FtsH, aided by interactions with the protein LapB, degrades LpxC. <o:p></o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image10.png” o:spid=“_x0000_i1030” type=“#_x0000_t75” style='width:467.5pt;height:336pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image009.png” o:title=“” cropright=“494f”/></v:shape><![endif]–><![if !vml]><img border=0 width=623 height=448 src=“Wiki%20Draft%20(1)_files/image010.gif” v:shapes=“image10.png”><![endif]><o:p></o:p><p class=MsoNormal>Figure _. Inhibition of FtsH-LapB activity. PbgA is a protein that inhibits the actions of FtsH-LapB to promote LPS biosynthesis. <o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal>Next, when LPS is being synthesized in excessive amounts, it will accumulate on the external surface of the inner membrane and bind to PbgA<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“8hpU9wVs”,“properties”:{“formattedCitation”:“\\super 2\\nosupersub{}”,“plainCitation”:“2”,“noteIndex”:0},“citationItems”:[{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>2<!–[if supportFields]><![endif]–> (Bishop, 2020). Thereby, PbgA will lessen its control on the LapB-FtsH complex activity, allowing for the degradation of LpxC to restore normal LPS levels.<o:p></o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image9.png” o:spid=“_x0000_i1029” type=“#_x0000_t75” style='width:468pt;height:319.5pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image011.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img border=0 width=624 height=426 src=“Wiki%20Draft%20(1)_files/image012.gif” v:shapes=“image9.png”><![endif]><o:p></o:p><p class=MsoNormal>Figure _. LPS excess. When LPS is being synthesized in excess, it will begin to accumulate on the external surface of the inner membrane and bind to PbgA. Bound to LPS, the protein will relax its inhibitory control on FtsH-LapB to promote LpxC degradation and therefore, restores normal LPS levels. <o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal>There is a truncation mutation of PbgA that leads to the depletion of LPS. This is most likely because the mutant fails to strongly inhibit the LapB-FtsH interaction that degrades LpxC and thereby, promotes LpxC degradation<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“KLS9MM71”,“properties”:{“formattedCitation”:“\\super 2\\nosupersub{}”,“plainCitation”:“2”,“noteIndex”:0},“citationItems”:[{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>2<!–[if supportFields]><![endif]–> (Bishop, 2020). PLs then fill in the gaps that are left by the LPS in the outer membrane, enabling greasy antibiotics and detergents to penetrate local PL bilayers, and large soluble compounds to leak through transient boundary defects where LPS and the PL phases meet<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“xpZv7lIL”,“properties”:{“formattedCitation”:“\\super 2\\nosupersub{}”,“plainCitation”:“2”,“noteIndex”:0},“citationItems”:[{“id”:617,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/FDC6F69M”],“itemData”:{“id”:617,“type”:“article-journal”,“abstract”:“PbgA proteins controls lipopolysaccharide synthesis in Escherichia coli.”,“container-title”:“Nature”,“DOI”:“10.1038/d41586-020-02256-x”,“issue”:“7821”,“language”:“en”,“license”:“2021 Nature”,“note”:“Bandiera_abtest: a\nCg_type: News And Views\nnumber: 7821\npublisher: Nature Publishing Group\nSubject_term: Structural biology, Microbiology”,“page”:“348-349”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of a lipopolysaccharide regulator reveals a road to new antibiotics”,“URL”:“http://www.nature.com/articles/d41586-020-02256-x”,“volume”:“584”,“author”:[{“family”:“Bishop”,“given”:“Russell E.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>2<!–[if supportFields]><![endif]–> (Bishop, 2020).<o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image7.png” o:spid=“_x0000_i1028” type=“#_x0000_t75” style='width:455.5pt;height:319.5pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image013.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img border=0 width=607 height=426 src=“Wiki%20Draft%20(1)_files/image014.gif” v:shapes=“image7.png”><![endif]><o:p></o:p><p class=MsoNormal style='margin-bottom:12.0pt'> Figure_. PbgA truncation mutation leads to LPS depletion. A depletion of LPS occurs when there is a PbgA truncation mutation, most likely due to the mutant failing to inhibit FtsH-LapB strongly enough. Therefore, PLs will attempt to fill in the gaps left by the depletion of LPS in the outer membrane. This enables greasy antibiotics and detergents to penetrate as well as large soluble compounds to leak through. <o:p></o:p><p class=MsoNormal><a href=“https://journals.asm.org/doi/10.1128/ecosalplus.ESP-0001-2018”>https://journals.asm.org/doi/10.1128/ecosalplus.ESP-0001-2018</a><u><o:p></o:p></u><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X: PbgA<o:p></o:p>'<p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.1 PbgA Structure <o:p></o:p>'<p class=MsoNormal> <o:p></o:p><p class=MsoNormal>PbgA, also known as YejM, is an essential protein in <i style='mso-bidi-font-style:normal'>E. coli that is required for regulating LPS synthesis and maintaining membrane homeostasis</span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“UlToei0B”,“properties”:{“formattedCitation”:“\\super 12\\nosupersub{}”,“plainCitation”:“12”,“noteIndex”:0},“citationItems”:[{“id”:628,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/K232PHWH”],“itemData”:{“id”:628,“type”:“article-journal”,“abstract”:“Gram-negative bacteria produce an asymmetric outer membrane (OM) that is particularly impermeant to many antibiotics and characterized by lipopolysaccharide (LPS) exclusively at the cell surface. LPS biogenesis remains an ideal target for therapeutic intervention, as disruption could kill bacteria or increase sensitivity to existing antibiotics. While it has been known that LPS synthesis is regulated by proteolytic control of LpxC, the enzyme that catalyzes the first committed step of LPS synthesis, it remains unknown which signals direct this regulation. New details have been revealed during study of a cryptic essential inner membrane protein, YejM. Multiple functions have been proposed over the years for YejM, including a controversial hypothesis that it transports cardiolipin from the inner membrane to the OM. Strong evidence now indicates that YejM senses LPS in the periplasm and directs proteolytic regulation. Here, we discuss the standing literature of YejM and highlight exciting new insights into cell envelope maintenance.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.02624-20”,“issue”:“6”,“note”:“publisher: American Society for Microbiology”,“page”:“e02624-20”,“source”:“journals.asm.org (Atypon)”,“title”:“Restoring Balance to the Outer Membrane: YejM’s Role in LPS Regulation”,“title-short”:“Restoring Balance to the Outer Membrane”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.02624-20”,“volume”:“11”,“author”:[{“family”:“Simpson”,“given”:“Brent W.”},{“family”:“Douglass”,“given”:“Martin V.”},{“family”:“Trent”,“given”:“M. Stephen”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",12,15}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>12<!–[if supportFields]><![endif]–> (Simpson et al., 2020). <o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal>As shown in Figure X, PbgA is an inner membrane protein with a five-transmembrane-domain N terminus (residues 1-190) that is essential for growth and a nonessential C-terminal periplasmic domain (residues 191-586). Nonsense mutations that cause truncations in the periplasmic domain in PbgA cause phenotypes consistent with defects in outer membrane assembly, including reduced LPS/PL ratio, vancomycin sensitivity, temperature sensitivity, and leakage of periplasmic proteins<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“KISnKvoZ”,“properties”:{“formattedCitation”:“\\super 3\\nosupersub{}”,“plainCitation”:“3”,“noteIndex”:0},“citationItems”:[{“id”:619,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/HWCQ9FUI”],“itemData”:{“id”:619,“type”:“article-journal”,“abstract”:“Gram-negative bacteria are surrounded by a complex cell envelope that includes two membranes. The outer membrane prevents many drugs from entering these cells and is thus a major determinant of their intrinsic antibiotic resistance. This barrier function is imparted by the asymmetric architecture of the membrane with lipopolysaccharide (LPS) in the outer leaflet and phospholipids in the inner leaflet. The LPS and phospholipid synthesis pathways share an intermediate. Proper membrane biogenesis therefore requires that the flux through each pathway be balanced. In Escherichia coli, a major control point in establishing this balance is the committed step of LPS synthesis mediated by LpxC. Levels of this enzyme are controlled through its degradation by the inner membrane protease FtsH and its presumed adapter protein LapB (YciM). How turnover of LpxC is controlled has remained unclear for many years. Here, we demonstrate that the essential protein of unknown function YejM (PbgA) participates in this regulatory pathway. Suppressors of YejM essentiality were identified in lpxC and lapB, and LpxC overproduction was shown to be sufficient to allow survival of ΔyejM mutants. Furthermore, the stability of LpxC was shown to be reduced in cells lacking YejM, and genetic and physical interactions between LapB and YejM were detected. Taken together, our results are consistent with a model in which YejM directly modulates LpxC turnover by FtsH-LapB to regulate LPS synthesis and maintain membrane homeostasis.\nIMPORTANCE The outer membrane is a major determinant of the intrinsic antibiotic resistance of Gram-negative bacteria. It is composed of both lipopolysaccharide (LPS) and phospholipid, and the synthesis of these lipid species must be balanced for the membrane to maintain its barrier function in blocking drug entry. In this study, we identified an essential protein of unknown function as a key new factor in modulating LPS synthesis in the model bacterium Escherichia coli. Our results provide novel insight into how this organism and most likely other Gram-negative bacteria maintain membrane homeostasis and their intrinsic resistance to antibiotics.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.00939-20”,“issue”:“3”,“note”:“publisher: American Society for Microbiology”,“page”:“e00939-20”,“source”:“journals.asm.org (Atypon)”,“title”:“An Essential Membrane Protein Modulates the Proteolysis of LpxC to Control Lipopolysaccharide Synthesis in Escherichia coli”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.00939-20”,“volume”:“11”,“author”:[{“family”:“Fivenson”,“given”:“Elayne M.”},{“family”:“Bernhardt”,“given”:“Thomas G.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",5,19}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>3<!–[if supportFields]><![endif]–> (Fivenson & Bernhardt, 2020). <o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image6.png” o:spid=“_x0000_i1027” type=“#_x0000_t75” style='width:269pt;height:259pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image015.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img border=0 width=359 height=345 src=“Wiki%20Draft%20(1)_files/image016.gif” v:shapes=“image6.png”><![endif]><o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Figure X: Pymol structure of PbgA. <o:p></o:p>'<p class=MsoNormal>Crystal structure of PbgA, an essential inner transmembrane protein in <i style='mso-bidi-font-style:normal'>E. coli that is used for regulating LPS synthesis and outer membrane homeostasis. The C-terminal periplasmic domain is depicted in green. The N-terminal domain is a five-transmembrane domain depicted in red, yellow, orange, purple, and cyan. <o:p></o:p></span><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.2 PbgA protein similarity <o:p></o:p>'<p class=MsoNormal>PbgA is structurally related to LtaS, an enzyme found in many gram-positive bacteria that synthesizes lipoteichoic acids. PbgA, like LtaS, contains a hydrophobic binding pocket in its periplasmic domain that is required for protein activity. However, the crystal structure of the PbgA domain indicates that it lacks residues required for LtaS catalytic activity, so it is unlikely to have a homologous enzymatic function<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“Igh9S5xC”,“properties”:{“formattedCitation”:“\\super 3\\nosupersub{}”,“plainCitation”:“3”,“noteIndex”:0},“citationItems”:[{“id”:619,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/HWCQ9FUI”],“itemData”:{“id”:619,“type”:“article-journal”,“abstract”:“Gram-negative bacteria are surrounded by a complex cell envelope that includes two membranes. The outer membrane prevents many drugs from entering these cells and is thus a major determinant of their intrinsic antibiotic resistance. This barrier function is imparted by the asymmetric architecture of the membrane with lipopolysaccharide (LPS) in the outer leaflet and phospholipids in the inner leaflet. The LPS and phospholipid synthesis pathways share an intermediate. Proper membrane biogenesis therefore requires that the flux through each pathway be balanced. In Escherichia coli, a major control point in establishing this balance is the committed step of LPS synthesis mediated by LpxC. Levels of this enzyme are controlled through its degradation by the inner membrane protease FtsH and its presumed adapter protein LapB (YciM). How turnover of LpxC is controlled has remained unclear for many years. Here, we demonstrate that the essential protein of unknown function YejM (PbgA) participates in this regulatory pathway. Suppressors of YejM essentiality were identified in lpxC and lapB, and LpxC overproduction was shown to be sufficient to allow survival of ΔyejM mutants. Furthermore, the stability of LpxC was shown to be reduced in cells lacking YejM, and genetic and physical interactions between LapB and YejM were detected. Taken together, our results are consistent with a model in which YejM directly modulates LpxC turnover by FtsH-LapB to regulate LPS synthesis and maintain membrane homeostasis.\nIMPORTANCE The outer membrane is a major determinant of the intrinsic antibiotic resistance of Gram-negative bacteria. It is composed of both lipopolysaccharide (LPS) and phospholipid, and the synthesis of these lipid species must be balanced for the membrane to maintain its barrier function in blocking drug entry. In this study, we identified an essential protein of unknown function as a key new factor in modulating LPS synthesis in the model bacterium Escherichia coli. Our results provide novel insight into how this organism and most likely other Gram-negative bacteria maintain membrane homeostasis and their intrinsic resistance to antibiotics.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.00939-20”,“issue”:“3”,“note”:“publisher: American Society for Microbiology”,“page”:“e00939-20”,“source”:“journals.asm.org (Atypon)”,“title”:“An Essential Membrane Protein Modulates the Proteolysis of LpxC to Control Lipopolysaccharide Synthesis in Escherichia coli”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.00939-20”,“volume”:“11”,“author”:[{“family”:“Fivenson”,“given”:“Elayne M.”},{“family”:“Bernhardt”,“given”:“Thomas G.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",5,19}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>3<!–[if supportFields]><![endif]–> (Fivenson & Bernhardt, 2020).<o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.3 Initial Proposed Function of PbgA<o:p></o:p>'<p class=MsoNormal>In <i style='mso-bidi-font-style:normal'>S. Typhimurium, cells that use a two-component regulatory system, PhoPQ, require PbgA to coordinate this process. The PhoPQ system induces changes to the outer membrane to protect cells from infection by sensing changes in the environment. One of the changes that occurs is an increase in the content of the PL, cardiolipin (CL). PbgA was found to bind to CL in vitro and since the deletion of PbgA showed no increase in CL content, it led to the assumption that it acts as a transporter that brings CL from the inner membrane to the outer membrane</span><!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“uTPTGZpN”,“properties”:{“formattedCitation”:“\\super 12\\nosupersub{}”,“plainCitation”:“12”,“noteIndex”:0},“citationItems”:[{“id”:628,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/K232PHWH”],“itemData”:{“id”:628,“type”:“article-journal”,“abstract”:“Gram-negative bacteria produce an asymmetric outer membrane (OM) that is particularly impermeant to many antibiotics and characterized by lipopolysaccharide (LPS) exclusively at the cell surface. LPS biogenesis remains an ideal target for therapeutic intervention, as disruption could kill bacteria or increase sensitivity to existing antibiotics. While it has been known that LPS synthesis is regulated by proteolytic control of LpxC, the enzyme that catalyzes the first committed step of LPS synthesis, it remains unknown which signals direct this regulation. New details have been revealed during study of a cryptic essential inner membrane protein, YejM. Multiple functions have been proposed over the years for YejM, including a controversial hypothesis that it transports cardiolipin from the inner membrane to the OM. Strong evidence now indicates that YejM senses LPS in the periplasm and directs proteolytic regulation. Here, we discuss the standing literature of YejM and highlight exciting new insights into cell envelope maintenance.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.02624-20”,“issue”:“6”,“note”:“publisher: American Society for Microbiology”,“page”:“e02624-20”,“source”:“journals.asm.org (Atypon)”,“title”:“Restoring Balance to the Outer Membrane: YejM’s Role in LPS Regulation”,“title-short”:“Restoring Balance to the Outer Membrane”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.02624-20”,“volume”:“11”,“author”:[{“family”:“Simpson”,“given”:“Brent W.”},{“family”:“Douglass”,“given”:“Martin V.”},{“family”:“Trent”,“given”:“M. Stephen”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",12,15}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>12<!–[if supportFields]><![endif]–> (Simpson et al., 2020). <o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal>However, other studies have shown that PbgA may not act as a cardiolipin transporter as it lacks an outer membrane partner while other complexes that transport substrates from the inner membrane to the outer membrane have inner membrane, periplasmic, and outer membrane components. Additionally, if PbgA were essential for cardiolipin synthesis, then it would be expected that cardiolipin deficiency would lead to toxic levels of PbgA, but this does not occur. Finally, because PbgA is known to have an impact on outer membrane permeability, but truncations of PbgA periplasmic domain show outer membrane permeability defects, indicating that both the inner membrane and periplasmic domain of PbgA are involved in the same function. Therefore, it is unlikely that PbgA is involved in cardiolipin transport<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“FLnydd47”,“properties”:{“formattedCitation”:“\\super 12\\nosupersub{}”,“plainCitation”:“12”,“noteIndex”:0},“citationItems”:[{“id”:628,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/K232PHWH”],“itemData”:{“id”:628,“type”:“article-journal”,“abstract”:“Gram-negative bacteria produce an asymmetric outer membrane (OM) that is particularly impermeant to many antibiotics and characterized by lipopolysaccharide (LPS) exclusively at the cell surface. LPS biogenesis remains an ideal target for therapeutic intervention, as disruption could kill bacteria or increase sensitivity to existing antibiotics. While it has been known that LPS synthesis is regulated by proteolytic control of LpxC, the enzyme that catalyzes the first committed step of LPS synthesis, it remains unknown which signals direct this regulation. New details have been revealed during study of a cryptic essential inner membrane protein, YejM. Multiple functions have been proposed over the years for YejM, including a controversial hypothesis that it transports cardiolipin from the inner membrane to the OM. Strong evidence now indicates that YejM senses LPS in the periplasm and directs proteolytic regulation. Here, we discuss the standing literature of YejM and highlight exciting new insights into cell envelope maintenance.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.02624-20”,“issue”:“6”,“note”:“publisher: American Society for Microbiology”,“page”:“e02624-20”,“source”:“journals.asm.org (Atypon)”,“title”:“Restoring Balance to the Outer Membrane: YejM’s Role in LPS Regulation”,“title-short”:“Restoring Balance to the Outer Membrane”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.02624-20”,“volume”:“11”,“author”:[{“family”:“Simpson”,“given”:“Brent W.”},{“family”:“Douglass”,“given”:“Martin V.”},{“family”:“Trent”,“given”:“M. Stephen”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",12,15}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>12<!–[if supportFields]><![endif]–> (Simpson et al., 2020). <o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.4 Novel Discovery of PbgA Function<o:p></o:p>'<p class=MsoNormal>A recent study suggests that PbgA serves a larger but undefined role in envelope assembly, such as preventing excessive turnover of LpxC and promoting LpxC accumulation by shielding it from the FtsH-LapB proteolytic system. They also found that the N-terminal transmembrane of PbgA alone interacts with the LapB component of the FtsH-LapB proteolytic system to promote LpxC accumulation<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“OfDNMfny”,“properties”:{“formattedCitation”:“\\super 3\\nosupersub{}”,“plainCitation”:“3”,“noteIndex”:0},“citationItems”:[{“id”:619,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/HWCQ9FUI”],“itemData”:{“id”:619,“type”:“article-journal”,“abstract”:“Gram-negative bacteria are surrounded by a complex cell envelope that includes two membranes. The outer membrane prevents many drugs from entering these cells and is thus a major determinant of their intrinsic antibiotic resistance. This barrier function is imparted by the asymmetric architecture of the membrane with lipopolysaccharide (LPS) in the outer leaflet and phospholipids in the inner leaflet. The LPS and phospholipid synthesis pathways share an intermediate. Proper membrane biogenesis therefore requires that the flux through each pathway be balanced. In Escherichia coli, a major control point in establishing this balance is the committed step of LPS synthesis mediated by LpxC. Levels of this enzyme are controlled through its degradation by the inner membrane protease FtsH and its presumed adapter protein LapB (YciM). How turnover of LpxC is controlled has remained unclear for many years. Here, we demonstrate that the essential protein of unknown function YejM (PbgA) participates in this regulatory pathway. Suppressors of YejM essentiality were identified in lpxC and lapB, and LpxC overproduction was shown to be sufficient to allow survival of ΔyejM mutants. Furthermore, the stability of LpxC was shown to be reduced in cells lacking YejM, and genetic and physical interactions between LapB and YejM were detected. Taken together, our results are consistent with a model in which YejM directly modulates LpxC turnover by FtsH-LapB to regulate LPS synthesis and maintain membrane homeostasis.\nIMPORTANCE The outer membrane is a major determinant of the intrinsic antibiotic resistance of Gram-negative bacteria. It is composed of both lipopolysaccharide (LPS) and phospholipid, and the synthesis of these lipid species must be balanced for the membrane to maintain its barrier function in blocking drug entry. In this study, we identified an essential protein of unknown function as a key new factor in modulating LPS synthesis in the model bacterium Escherichia coli. Our results provide novel insight into how this organism and most likely other Gram-negative bacteria maintain membrane homeostasis and their intrinsic resistance to antibiotics.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.00939-20”,“issue”:“3”,“note”:“publisher: American Society for Microbiology”,“page”:“e00939-20”,“source”:“journals.asm.org (Atypon)”,“title”:“An Essential Membrane Protein Modulates the Proteolysis of LpxC to Control Lipopolysaccharide Synthesis in Escherichia coli”,“URL”:“https://journals.asm.org/doi/10.1128/mBio.00939-20”,“volume”:“11”,“author”:[{“family”:“Fivenson”,“given”:“Elayne M.”},{“family”:“Bernhardt”,“given”:“Thomas G.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",5,19}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>3<!–[if supportFields]><![endif]–> (Fivenson & Bernhardt, 2020).<o:p></o:p><p class=MsoNormal> <o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Polymyxin Antibiotics and Antibiotic Resistance:<o:p></o:p>'<p class=MsoNormal><o:p> </o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.1. Polymyxin Antibiotics<o:p></o:p>'<p class=MsoNormal>Polymyxins are an important class of antibiotics used in the treatment of systemic infections caused by multidrug-resistant gram-negative bacteria such as pseudomonas aeruginosa<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“wRfcvQq5”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). Currently, these antibiotics are used as a last line of treatment against such infections<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“n7wlnoFI”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). The main drugs in clinical use within this antibiotic class are Polymyxin B and Polymyxin E (also called colistin), which target infections of the urinary tract, meninges, and bloodstream<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“tYAD01ia”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). <o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.2. Mechanism of Action of Colistin<o:p></o:p>'<p class=MsoNormal>Polymyxins target the lipid A core of LPS<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“7ZVsLxVx”,“properties”:{“formattedCitation”:“\\super 14\\nosupersub{}”,“plainCitation”:“14”,“noteIndex”:0},“citationItems”:[{“id”:612,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/S5FNUZAL”],“itemData”:{“id”:612,“type”:“article-journal”,“abstract”:“Lipopolysaccharide (LPS) resides in the outer membrane of Gram-negative bacteria where it is responsible for barrier function1,2. LPS can cause death as a result of septic shock, and its lipid A core is the target of polymyxin antibiotics3,4. Despite the clinical importance of polymyxins and the emergence of multidrug resistant strains5, our understanding of the bacterial factors that regulate LPS biogenesis is incomplete. Here we characterize the inner membrane protein PbgA and report that its depletion attenuates the virulence of Escherichia coli by reducing levels of LPS and outer membrane integrity. In contrast to previous claims that PbgA functions as a cardiolipin transporter6–9, our structural analyses and physiological studies identify a lipid A-binding motif along the periplasmic leaflet of the inner membrane. Synthetic PbgA-derived peptides selectively bind to LPS in vitro and inhibit the growth of diverse Gram-negative bacteria, including polymyxin-resistant strains. Proteomic, genetic and pharmacological experiments uncover a model in which direct periplasmic sensing of LPS by PbgA coordinates the biosynthesis of lipid A by regulating the stability of LpxC, a key cytoplasmic biosynthetic enzyme10–12. In summary, we find that PbgA has an unexpected but essential role in the regulation of LPS biogenesis, presents a new structural basis for the selective recognition of lipids, and provides opportunities for future antibiotic discovery.”,“container-title”:“Nature”,“DOI”:“10.1038/s41586-020-2597-x”,“ISSN”:“1476-4687”,“issue”:“7821”,“language”:“en”,“license”:“2020 The Author(s), under exclusive licence to Springer Nature Limited”,“note”:“number: 7821\npublisher: Nature Publishing Group”,“page”:“479-483”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of the essential inner membrane lipopolysaccharide–PbgA complex”,“URL”:“http://www.nature.com/articles/s41586-020-2597-x”,“volume”:“584”,“author”:[{“family”:“Clairfeuille”,“given”:“Thomas”},{“family”:“Buchholz”,“given”:“Kerry R.”},{“family”:“Li”,“given”:“Qingling”},{“family”:“Verschueren”,“given”:“Erik”},{“family”:“Liu”,“given”:“Peter”},{“family”:“Sangaraju”,“given”:“Dewakar”},{“family”:“Park”,“given”:“Summer”},{“family”:“Noland”,“given”:“Cameron L.”},{“family”:“Storek”,“given”:“Kelly M.”},{“family”:“Nickerson”,“given”:“Nicholas N.”},{“family”:“Martin”,“given”:“Lynn”},{“family”:“Dela Vega”,“given”:“Trisha”},{“family”:“Miu”,“given”:“Anh”},{“family”:“Reeder”,“given”:“Janina”},{“family”:“Ruiz-Gonzalez”,“given”:“Maria”},{“family”:“Swem”,“given”:“Danielle”},{“family”:“Han”,“given”:“Guanghui”},{“family”:“DePonte”,“given”:“Daniel P.”},{“family”:“Hunter”,“given”:“Mark S.”},{“family”:“Gati”,“given”:“Cornelius”},{“family”:“Shahidi-Latham”,“given”:“Sheerin”},{“family”:“Xu”,“given”:“Min”},{“family”:“Skelton”,“given”:“Nicholas”},{“family”:“Sellers”,“given”:“Benjamin D.”},{“family”:“Skippington”,“given”:“Elizabeth”},{“family”:“Sandoval”,“given”:“Wendy”},{“family”:“Hanan”,“given”:“Emily J.”},{“family”:“Payandeh”,“given”:“Jian”},{“family”:“Rutherford”,“given”:“Steven T.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>14<!–[if supportFields]><![endif]–> (Clairfeuille et al., 2020). These antibiotics destabilize the PLs and LPS present in the outer membrane of gram-negative bacteria<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“c9oHqDO2”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). Since polymyxins are positively charged, they electrostatically interact with the phosphate groups on both of the negatively charged phosphorylated sugars that make up lipid A<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“Htyh6yVV”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). This causes the divalent cations (such as calcium and magnesium) from the phosphate groups within the membrane lipids to become displaced, creating increased permeability<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“dd4opF7M”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). This leads to the outer membrane becoming disrupted, allowing small molecules and other intracellular contents to leak out of the cell and cause bacterial cell death<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“KQVXUWc2”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). <o:p></o:p><p class=MsoNormal>In addition, polymyxins can neutralize the endotoxin effect of pathogens<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“jz6XGLzg”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). Since the endotoxic part of gram-negative bacteria corresponds to the lipid A core, polymyxins can bind to the LPS that was released as a result of cellular death<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“Clnnlrv8”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022). This results in the neutralization of the endotoxin, preventing its effects in circulation<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“PhtPbk2K”,“properties”:{“formattedCitation”:“\\super 13\\nosupersub{}”,“plainCitation”:“13”,“noteIndex”:0},“citationItems”:[{“id”:608,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/U2DBWKJG”],“itemData”:{“id”:608,“type”:“chapter”,“abstract”:“Polymyxins are a class of medications used in the management and treatment of systemic infections caused by susceptible strains of multidrug-resistant organisms such as Pseudomonas aeruginosa. It is in the antibiotic class of drugs. This activity reviews the indications, action, and contraindications for polymyxin as a valuable agent in the treatment of multidrug-resistant infections. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent for members of the interprofessional team in the treatment of patients with polymyxins who are infected by susceptible strains of gram-negative pathogens resistant most of the other antibiotic classes.”,“call-number”:“NBK557540”,“container-title”:“StatPearls”,“event-place”:“Treasure Island (FL)”,“language”:“eng”,“license”:“Copyright © 2022, StatPearls Publishing LLC.”,“note”:“PMID: 32491472”,“publisher”:“StatPearls Publishing”,“publisher-place”:“Treasure Island (FL)”,“source”:“PubMed”,“title”:“Polymyxin”,“URL”:“http://www.ncbi.nlm.nih.gov/books/NBK557540/”,“author”:[{“family”:“Shatri”,“given”:“Genti”},{“family”:“Tadi”,“given”:“Prasanna”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2022"}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>13<!–[if supportFields]><![endif]–> (Shatri & Tadi, 2022).<o:p></o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image3.png” o:spid=“_x0000_i1026” type=“#_x0000_t75” style='width:457pt;height:217.5pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image017.png” o:title=“” cropbottom=“1110f” cropleft=“630f” cropright=“528f”/></v:shape><![endif]–><![if !vml]><img border=0 width=609 height=290 src=“Wiki%20Draft%20(1)_files/image018.gif” v:shapes=“image3.png”><![endif]><o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Figure X:' Colistin electrostatically interacts with the lipid A core of LPS, creating a disruption of the membrane and allowing small molecules to leak out of the cell.<o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>X.3. Antibiotic Resistance<o:p></o:p>'<p class=MsoNormal>Polymyxins are an extremely important and clinically relevant class of drugs since they are the last line of defence against gram-negative bacteria that are resistant to all other antibiotics<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“1nRHZKva”,“properties”:{“formattedCitation”:“\\super 14\\nosupersub{}”,“plainCitation”:“14”,“noteIndex”:0},“citationItems”:[{“id”:612,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/S5FNUZAL”],“itemData”:{“id”:612,“type”:“article-journal”,“abstract”:“Lipopolysaccharide (LPS) resides in the outer membrane of Gram-negative bacteria where it is responsible for barrier function1,2. LPS can cause death as a result of septic shock, and its lipid A core is the target of polymyxin antibiotics3,4. Despite the clinical importance of polymyxins and the emergence of multidrug resistant strains5, our understanding of the bacterial factors that regulate LPS biogenesis is incomplete. Here we characterize the inner membrane protein PbgA and report that its depletion attenuates the virulence of Escherichia coli by reducing levels of LPS and outer membrane integrity. In contrast to previous claims that PbgA functions as a cardiolipin transporter6–9, our structural analyses and physiological studies identify a lipid A-binding motif along the periplasmic leaflet of the inner membrane. Synthetic PbgA-derived peptides selectively bind to LPS in vitro and inhibit the growth of diverse Gram-negative bacteria, including polymyxin-resistant strains. Proteomic, genetic and pharmacological experiments uncover a model in which direct periplasmic sensing of LPS by PbgA coordinates the biosynthesis of lipid A by regulating the stability of LpxC, a key cytoplasmic biosynthetic enzyme10–12. In summary, we find that PbgA has an unexpected but essential role in the regulation of LPS biogenesis, presents a new structural basis for the selective recognition of lipids, and provides opportunities for future antibiotic discovery.”,“container-title”:“Nature”,“DOI”:“10.1038/s41586-020-2597-x”,“ISSN”:“1476-4687”,“issue”:“7821”,“language”:“en”,“license”:“2020 The Author(s), under exclusive licence to Springer Nature Limited”,“note”:“number: 7821\npublisher: Nature Publishing Group”,“page”:“479-483”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of the essential inner membrane lipopolysaccharide–PbgA complex”,“URL”:“http://www.nature.com/articles/s41586-020-2597-x”,“volume”:“584”,“author”:[{“family”:“Clairfeuille”,“given”:“Thomas”},{“family”:“Buchholz”,“given”:“Kerry R.”},{“family”:“Li”,“given”:“Qingling”},{“family”:“Verschueren”,“given”:“Erik”},{“family”:“Liu”,“given”:“Peter”},{“family”:“Sangaraju”,“given”:“Dewakar”},{“family”:“Park”,“given”:“Summer”},{“family”:“Noland”,“given”:“Cameron L.”},{“family”:“Storek”,“given”:“Kelly M.”},{“family”:“Nickerson”,“given”:“Nicholas N.”},{“family”:“Martin”,“given”:“Lynn”},{“family”:“Dela Vega”,“given”:“Trisha”},{“family”:“Miu”,“given”:“Anh”},{“family”:“Reeder”,“given”:“Janina”},{“family”:“Ruiz-Gonzalez”,“given”:“Maria”},{“family”:“Swem”,“given”:“Danielle”},{“family”:“Han”,“given”:“Guanghui”},{“family”:“DePonte”,“given”:“Daniel P.”},{“family”:“Hunter”,“given”:“Mark S.”},{“family”:“Gati”,“given”:“Cornelius”},{“family”:“Shahidi-Latham”,“given”:“Sheerin”},{“family”:“Xu”,“given”:“Min”},{“family”:“Skelton”,“given”:“Nicholas”},{“family”:“Sellers”,“given”:“Benjamin D.”},{“family”:“Skippington”,“given”:“Elizabeth”},{“family”:“Sandoval”,“given”:“Wendy”},{“family”:“Hanan”,“given”:“Emily J.”},{“family”:“Payandeh”,“given”:“Jian”},{“family”:“Rutherford”,“given”:“Steven T.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>14<!–[if supportFields]><![endif]–> (Clairfeuille et al., 2020). Unfortunately, there is an emergence of bacteria that are also resistant to polymyxins<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“d0lBYWG3”,“properties”:{“formattedCitation”:“\\super 14\\nosupersub{}”,“plainCitation”:“14”,“noteIndex”:0},“citationItems”:[{“id”:612,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/S5FNUZAL”],“itemData”:{“id”:612,“type”:“article-journal”,“abstract”:“Lipopolysaccharide (LPS) resides in the outer membrane of Gram-negative bacteria where it is responsible for barrier function1,2. LPS can cause death as a result of septic shock, and its lipid A core is the target of polymyxin antibiotics3,4. Despite the clinical importance of polymyxins and the emergence of multidrug resistant strains5, our understanding of the bacterial factors that regulate LPS biogenesis is incomplete. Here we characterize the inner membrane protein PbgA and report that its depletion attenuates the virulence of Escherichia coli by reducing levels of LPS and outer membrane integrity. In contrast to previous claims that PbgA functions as a cardiolipin transporter6–9, our structural analyses and physiological studies identify a lipid A-binding motif along the periplasmic leaflet of the inner membrane. Synthetic PbgA-derived peptides selectively bind to LPS in vitro and inhibit the growth of diverse Gram-negative bacteria, including polymyxin-resistant strains. Proteomic, genetic and pharmacological experiments uncover a model in which direct periplasmic sensing of LPS by PbgA coordinates the biosynthesis of lipid A by regulating the stability of LpxC, a key cytoplasmic biosynthetic enzyme10–12. In summary, we find that PbgA has an unexpected but essential role in the regulation of LPS biogenesis, presents a new structural basis for the selective recognition of lipids, and provides opportunities for future antibiotic discovery.”,“container-title”:“Nature”,“DOI”:“10.1038/s41586-020-2597-x”,“ISSN”:“1476-4687”,“issue”:“7821”,“language”:“en”,“license”:“2020 The Author(s), under exclusive licence to Springer Nature Limited”,“note”:“number: 7821\npublisher: Nature Publishing Group”,“page”:“479-483”,“source”:“www-nature-com.libaccess.lib.mcmaster.ca”,“title”:“Structure of the essential inner membrane lipopolysaccharide–PbgA complex”,“URL”:“http://www.nature.com/articles/s41586-020-2597-x”,“volume”:“584”,“author”:[{“family”:“Clairfeuille”,“given”:“Thomas”},{“family”:“Buchholz”,“given”:“Kerry R.”},{“family”:“Li”,“given”:“Qingling”},{“family”:“Verschueren”,“given”:“Erik”},{“family”:“Liu”,“given”:“Peter”},{“family”:“Sangaraju”,“given”:“Dewakar”},{“family”:“Park”,“given”:“Summer”},{“family”:“Noland”,“given”:“Cameron L.”},{“family”:“Storek”,“given”:“Kelly M.”},{“family”:“Nickerson”,“given”:“Nicholas N.”},{“family”:“Martin”,“given”:“Lynn”},{“family”:“Dela Vega”,“given”:“Trisha”},{“family”:“Miu”,“given”:“Anh”},{“family”:“Reeder”,“given”:“Janina”},{“family”:“Ruiz-Gonzalez”,“given”:“Maria”},{“family”:“Swem”,“given”:“Danielle”},{“family”:“Han”,“given”:“Guanghui”},{“family”:“DePonte”,“given”:“Daniel P.”},{“family”:“Hunter”,“given”:“Mark S.”},{“family”:“Gati”,“given”:“Cornelius”},{“family”:“Shahidi-Latham”,“given”:“Sheerin”},{“family”:“Xu”,“given”:“Min”},{“family”:“Skelton”,“given”:“Nicholas”},{“family”:“Sellers”,“given”:“Benjamin D.”},{“family”:“Skippington”,“given”:“Elizabeth”},{“family”:“Sandoval”,“given”:“Wendy”},{“family”:“Hanan”,“given”:“Emily J.”},{“family”:“Payandeh”,“given”:“Jian”},{“family”:“Rutherford”,“given”:“Steven T.”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2020",8}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>14<!–[if supportFields]><![endif]–> (Clairfeuille et al., 2020). One bacterial resistance mechanism that has been discovered is due to the expression of EptA, a protein part of the same family as PbgA<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“ZB2uPOlP”,“properties”:{“formattedCitation”:“\\super 15\\nosupersub{}”,“plainCitation”:“15”,“noteIndex”:0},“citationItems”:[{“id”:610,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/4G5T5MW8”],“itemData”:{“id”:610,“type”:“article-journal”,“abstract”:“Polymyxins, a family of cationic antimicrobial cyclic peptides, act as a last line of defense against severe infections by Gram-negative pathogens with carbapenem resistance. In addition to the intrinsic resistance to polymyxin E (colistin) conferred by Neisseria eptA, the plasmid-borne mobilized colistin resistance gene mcr-1 has been disseminated globally since the first discovery in Southern China, in late 2015. However, the molecular mechanisms for both intrinsic and transferable resistance to colistin remain largely unknown. Here, we aim to address this gap in the knowledge of these proteins. Structural and functional analyses of EptA and MCR-1 and -2 have defined a conserved 12-residue cavity that is required for the entry of the lipid substrate, phosphatidylethanolamine (PE). The in vitro and in vivo data together have allowed us to visualize the similarities in catalytic activity shared by EptA and MCR-1 and -2. The expression of either EptA or MCR-1 or -2 is shown to remodel the surface of enteric bacteria (e.g., Escherichia coli, Salmonella enterica, Klebsiella pneumoniae, etc.), rendering them resistant to colistin. The parallels in the PE substrate-binding cavities among EptA, MCR-1, and MCR-2 provide a comprehensive understanding of both intrinsic and transferable colistin resistance. Domain swapping between EptA and MCR-1 and -2 reveals that the two domains (transmembrane [TM] region and phosphoethanolamine [PEA] transferase) are not functionally exchangeable. Taken together, the results represent a common mechanism for intrinsic and transferable PEA resistance to polymyxin, a last-resort antibiotic against multidrug-resistant pathogens.\nIMPORTANCE EptA and MCR-1 and -2 remodel the outer membrane, rendering bacteria resistant to colistin, a final resort against carbapenem-resistant pathogens. Structural and functional analyses of EptA and MCR-1 and -2 reveal parallel PE lipid substrate-recognizing cavities, which explains intrinsic and transferable colistin resistance in gut bacteria. A similar mechanism is proposed for the catalytic activities of EptA and MCR-1 and -2. Together, they constitute a common mechanism for intrinsic and transferable polymyxin resistance.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.02317-17”,“issue”:“2”,“note”:“publisher: American Society for Microbiology”,“page”:“e02317-17”,“source”:“journals.asm.org (Atypon)”,“title”:“An Evolutionarily Conserved Mechanism for Intrinsic and Transferable Polymyxin Resistance”,“URL”:“https://journals.asm.org/doi/full/10.1128/mBio.02317-17”,“volume”:“9”,“author”:[{“family”:“Xu”,“given”:“Yongchang”},{“family”:“Wei”,“given”:“Wenhui”},{“family”:“Lei”,“given”:“Sheng”},{“family”:“Lin”,“given”:“Jingxia”},{“family”:“Srinivas”,“given”:“Swaminath”},{“family”:“Feng”,“given”:“Youjun”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2018",4,10}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>15<!–[if supportFields]><![endif]–> (Xu et al., 2018). This protein has been shown to remodel the surface of the bacteria, making it resistant to colistin<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“W7GaEfgH”,“properties”:{“formattedCitation”:“\\super 15\\nosupersub{}”,“plainCitation”:“15”,“noteIndex”:0},“citationItems”:[{“id”:610,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/4G5T5MW8”],“itemData”:{“id”:610,“type”:“article-journal”,“abstract”:“Polymyxins, a family of cationic antimicrobial cyclic peptides, act as a last line of defense against severe infections by Gram-negative pathogens with carbapenem resistance. In addition to the intrinsic resistance to polymyxin E (colistin) conferred by Neisseria eptA, the plasmid-borne mobilized colistin resistance gene mcr-1 has been disseminated globally since the first discovery in Southern China, in late 2015. However, the molecular mechanisms for both intrinsic and transferable resistance to colistin remain largely unknown. Here, we aim to address this gap in the knowledge of these proteins. Structural and functional analyses of EptA and MCR-1 and -2 have defined a conserved 12-residue cavity that is required for the entry of the lipid substrate, phosphatidylethanolamine (PE). The in vitro and in vivo data together have allowed us to visualize the similarities in catalytic activity shared by EptA and MCR-1 and -2. The expression of either EptA or MCR-1 or -2 is shown to remodel the surface of enteric bacteria (e.g., Escherichia coli, Salmonella enterica, Klebsiella pneumoniae, etc.), rendering them resistant to colistin. The parallels in the PE substrate-binding cavities among EptA, MCR-1, and MCR-2 provide a comprehensive understanding of both intrinsic and transferable colistin resistance. Domain swapping between EptA and MCR-1 and -2 reveals that the two domains (transmembrane [TM] region and phosphoethanolamine [PEA] transferase) are not functionally exchangeable. Taken together, the results represent a common mechanism for intrinsic and transferable PEA resistance to polymyxin, a last-resort antibiotic against multidrug-resistant pathogens.\nIMPORTANCE EptA and MCR-1 and -2 remodel the outer membrane, rendering bacteria resistant to colistin, a final resort against carbapenem-resistant pathogens. Structural and functional analyses of EptA and MCR-1 and -2 reveal parallel PE lipid substrate-recognizing cavities, which explains intrinsic and transferable colistin resistance in gut bacteria. A similar mechanism is proposed for the catalytic activities of EptA and MCR-1 and -2. Together, they constitute a common mechanism for intrinsic and transferable polymyxin resistance.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.02317-17”,“issue”:“2”,“note”:“publisher: American Society for Microbiology”,“page”:“e02317-17”,“source”:“journals.asm.org (Atypon)”,“title”:“An Evolutionarily Conserved Mechanism for Intrinsic and Transferable Polymyxin Resistance”,“URL”:“https://journals.asm.org/doi/full/10.1128/mBio.02317-17”,“volume”:“9”,“author”:[{“family”:“Xu”,“given”:“Yongchang”},{“family”:“Wei”,“given”:“Wenhui”},{“family”:“Lei”,“given”:“Sheng”},{“family”:“Lin”,“given”:“Jingxia”},{“family”:“Srinivas”,“given”:“Swaminath”},{“family”:“Feng”,“given”:“Youjun”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2018",4,10}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>15<!–[if supportFields]><![endif]–> (Xu et al., 2018). EptA does this by modifying the phosphate groups on both of the phosphorylated sugars on lipid A; thereby, reducing its overall negative charge<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“wH3osBJS”,“properties”:{“formattedCitation”:“\\super 15\\nosupersub{}”,“plainCitation”:“15”,“noteIndex”:0},“citationItems”:[{“id”:610,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/4G5T5MW8”],“itemData”:{“id”:610,“type”:“article-journal”,“abstract”:“Polymyxins, a family of cationic antimicrobial cyclic peptides, act as a last line of defense against severe infections by Gram-negative pathogens with carbapenem resistance. In addition to the intrinsic resistance to polymyxin E (colistin) conferred by Neisseria eptA, the plasmid-borne mobilized colistin resistance gene mcr-1 has been disseminated globally since the first discovery in Southern China, in late 2015. However, the molecular mechanisms for both intrinsic and transferable resistance to colistin remain largely unknown. Here, we aim to address this gap in the knowledge of these proteins. Structural and functional analyses of EptA and MCR-1 and -2 have defined a conserved 12-residue cavity that is required for the entry of the lipid substrate, phosphatidylethanolamine (PE). The in vitro and in vivo data together have allowed us to visualize the similarities in catalytic activity shared by EptA and MCR-1 and -2. The expression of either EptA or MCR-1 or -2 is shown to remodel the surface of enteric bacteria (e.g., Escherichia coli, Salmonella enterica, Klebsiella pneumoniae, etc.), rendering them resistant to colistin. The parallels in the PE substrate-binding cavities among EptA, MCR-1, and MCR-2 provide a comprehensive understanding of both intrinsic and transferable colistin resistance. Domain swapping between EptA and MCR-1 and -2 reveals that the two domains (transmembrane [TM] region and phosphoethanolamine [PEA] transferase) are not functionally exchangeable. Taken together, the results represent a common mechanism for intrinsic and transferable PEA resistance to polymyxin, a last-resort antibiotic against multidrug-resistant pathogens.\nIMPORTANCE EptA and MCR-1 and -2 remodel the outer membrane, rendering bacteria resistant to colistin, a final resort against carbapenem-resistant pathogens. Structural and functional analyses of EptA and MCR-1 and -2 reveal parallel PE lipid substrate-recognizing cavities, which explains intrinsic and transferable colistin resistance in gut bacteria. A similar mechanism is proposed for the catalytic activities of EptA and MCR-1 and -2. Together, they constitute a common mechanism for intrinsic and transferable polymyxin resistance.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.02317-17”,“issue”:“2”,“note”:“publisher: American Society for Microbiology”,“page”:“e02317-17”,“source”:“journals.asm.org (Atypon)”,“title”:“An Evolutionarily Conserved Mechanism for Intrinsic and Transferable Polymyxin Resistance”,“URL”:“https://journals.asm.org/doi/full/10.1128/mBio.02317-17”,“volume”:“9”,“author”:[{“family”:“Xu”,“given”:“Yongchang”},{“family”:“Wei”,“given”:“Wenhui”},{“family”:“Lei”,“given”:“Sheng”},{“family”:“Lin”,“given”:“Jingxia”},{“family”:“Srinivas”,“given”:“Swaminath”},{“family”:“Feng”,“given”:“Youjun”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2018",4,10}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>15<!–[if supportFields]><![endif]–> (Xu et al., 2018). This makes the bacteria resistant to polymyxins because they can no longer have the previously mentioned electrostatic interactions and thus cannot bind to the modified lipid A core<!–[if supportFields]> ADDIN ZOTERO_ITEM CSL_CITATION {“citationID”:“Ev7M9sq2”,“properties”:{“formattedCitation”:“\\super 15\\nosupersub{}”,“plainCitation”:“15”,“noteIndex”:0},“citationItems”:[{“id”:610,“uris”:[“http://zotero.org/users/local/DWdd4k1w/items/4G5T5MW8”],“itemData”:{“id”:610,“type”:“article-journal”,“abstract”:“Polymyxins, a family of cationic antimicrobial cyclic peptides, act as a last line of defense against severe infections by Gram-negative pathogens with carbapenem resistance. In addition to the intrinsic resistance to polymyxin E (colistin) conferred by Neisseria eptA, the plasmid-borne mobilized colistin resistance gene mcr-1 has been disseminated globally since the first discovery in Southern China, in late 2015. However, the molecular mechanisms for both intrinsic and transferable resistance to colistin remain largely unknown. Here, we aim to address this gap in the knowledge of these proteins. Structural and functional analyses of EptA and MCR-1 and -2 have defined a conserved 12-residue cavity that is required for the entry of the lipid substrate, phosphatidylethanolamine (PE). The in vitro and in vivo data together have allowed us to visualize the similarities in catalytic activity shared by EptA and MCR-1 and -2. The expression of either EptA or MCR-1 or -2 is shown to remodel the surface of enteric bacteria (e.g., Escherichia coli, Salmonella enterica, Klebsiella pneumoniae, etc.), rendering them resistant to colistin. The parallels in the PE substrate-binding cavities among EptA, MCR-1, and MCR-2 provide a comprehensive understanding of both intrinsic and transferable colistin resistance. Domain swapping between EptA and MCR-1 and -2 reveals that the two domains (transmembrane [TM] region and phosphoethanolamine [PEA] transferase) are not functionally exchangeable. Taken together, the results represent a common mechanism for intrinsic and transferable PEA resistance to polymyxin, a last-resort antibiotic against multidrug-resistant pathogens.\nIMPORTANCE EptA and MCR-1 and -2 remodel the outer membrane, rendering bacteria resistant to colistin, a final resort against carbapenem-resistant pathogens. Structural and functional analyses of EptA and MCR-1 and -2 reveal parallel PE lipid substrate-recognizing cavities, which explains intrinsic and transferable colistin resistance in gut bacteria. A similar mechanism is proposed for the catalytic activities of EptA and MCR-1 and -2. Together, they constitute a common mechanism for intrinsic and transferable polymyxin resistance.”,“container-title”:“mBio”,“DOI”:“10.1128/mBio.02317-17”,“issue”:“2”,“note”:“publisher: American Society for Microbiology”,“page”:“e02317-17”,“source”:“journals.asm.org (Atypon)”,“title”:“An Evolutionarily Conserved Mechanism for Intrinsic and Transferable Polymyxin Resistance”,“URL”:“https://journals.asm.org/doi/full/10.1128/mBio.02317-17”,“volume”:“9”,“author”:[{“family”:“Xu”,“given”:“Yongchang”},{“family”:“Wei”,“given”:“Wenhui”},{“family”:“Lei”,“given”:“Sheng”},{“family”:“Lin”,“given”:“Jingxia”},{“family”:“Srinivas”,“given”:“Swaminath”},{“family”:“Feng”,“given”:“Youjun”}],“accessed”:{“date-parts”:"2023",2,1},“issued”:{“date-parts”:"2018",4,10}}}],“schema”:“https://github.com/citation-style-language/schema/raw/master/csl-citation.json”} <![endif]–>15<!–[if supportFields]><![endif]–> (Xu et al., 2018). With polymyxin resistance becoming a bigger problem, more research on PbgA will be beneficial for future antibiotic discovery.<o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal><!–[if gte vml 1]><v:shape id=“image2.png” o:spid=“_x0000_i1025” type=“#_x0000_t75” style='width:468pt;height:134pt;visibility:visible; mso-wrap-style:square'><v:imagedata src=“Wiki%20Draft%20(1)_files/image019.png” o:title=“”/></v:shape><![endif]–><![if !vml]><img border=0 width=624 height=179 src=“Wiki%20Draft%20(1)_files/image020.gif” v:shapes=“image2.png”><![endif]><o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Figure X: 'The enzyme EptA modifies LPS and reduces the negative charge of lipid A; therefore, prevents colistin from binding and makes bacteria resistant to the antibiotic.<o:p></o:p><p class=MsoNormal><b style='mso-bidi-font-weight:normal'><o:p> </o:p>'<p class=MsoNormal><b style='mso-bidi-font-weight:normal'>Conclusion:<o:p></o:p>'<p class=MsoNormal>Antibiotic resistance is a growing concern today and for our future. Gram-negative bacteria have been particularly associated with antibiotic resistance due to the presence of LPS in their cell wall, acting  as a protective barrier against drugs. The ability of these bacteria to rapidly evolve and develop resistance to antibiotics has made it an ongoing challenge for scientists to find new ways to combat these infections. Understanding the pathways in which LPS is synthesized and regulated demonstrates importance pertaining to antibiotic drug targeting. Clairfeullie et al. contribute to this research through characterizing PbgA and demonstrating how manipulation of this protein could possibly be utilized in the lowering of LPS levels and subsequently virulence by <i style='mso-bidi-font-style:normal'>E. coli''.<o:p></o:p><p class=MsoNormal><o:p> </o:p><p class=MsoNormal><o:p> </o:p></div></body></html>