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Shah M, Anwar A, Qasim A, Jaan S, Sarfraz A, Ullah R, Ali EA, Nishan U, Shehroz M, Zaman A, Ojha SC. Proteome level analysis of drug-resistant Prevotella melaninogenica for the identification of novel therapeutic candidates. Front Microbiol 2023; 14:1271798. [PMID: 37808310 PMCID: PMC10556700 DOI: 10.3389/fmicb.2023.1271798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 08/30/2023] [Indexed: 10/10/2023] Open
Abstract
The management of infectious diseases has become more critical due to the development of novel pathogenic strains with enhanced resistance. Prevotella melaninogenica, a gram-negative bacterium, was found to be involved in various infections of the respiratory tract, aerodigestive tract, and gastrointestinal tract. The need to explore novel drug and vaccine targets against this pathogen was triggered by the emergence of antimicrobial resistance against reported antibiotics to combat P. melaninogenica infections. The study involves core genes acquired from 14 complete P. melaninogenica strain genome sequences, where promiscuous drug and vaccine candidates were explored by state-of-the-art subtractive proteomics and reverse vaccinology approaches. A stringent bioinformatics analysis enlisted 18 targets as novel, essential, and non-homologous to humans and having druggability potential. Moreover, the extracellular and outer membrane proteins were subjected to antigenicity, allergenicity, and physicochemical analysis for the identification of the candidate proteins to design multi-epitope vaccines. Two candidate proteins (ADK95685.1 and ADK97014.1) were selected as the best target for the designing of a vaccine construct. Lead B- and T-cell overlapped epitopes were joined to generate potential chimeric vaccine constructs in combination with adjuvants and linkers. Finally, a prioritized vaccine construct was found to have stable interactions with the human immune cell receptors as confirmed by molecular docking and MD simulation studies. The vaccine construct was found to have cloning and expression ability in the bacterial cloning system. Immune simulation ensured the elicitation of significant immune responses against the designed vaccine. In conclusion, our study reported novel drug and vaccine targets and designed a multi-epitope vaccine against the P. melaninogenica infection. Further experimental validation will help open new avenues in the treatment of this multi-drug-resistant pathogen.
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Affiliation(s)
- Mohibullah Shah
- Department of Biochemistry, Bahauddin Zakariya University, Multan, Pakistan
| | - Amna Anwar
- Department of Biochemistry, Bahauddin Zakariya University, Multan, Pakistan
| | - Aqsa Qasim
- Department of Biochemistry, Bahauddin Zakariya University, Multan, Pakistan
| | - Samavia Jaan
- Department of Biochemistry, Bahauddin Zakariya University, Multan, Pakistan
| | - Asifa Sarfraz
- Department of Biochemistry, Bahauddin Zakariya University, Multan, Pakistan
| | - Riaz Ullah
- Medicinal Aromatic and Poisonous Plants Research Center, College of Pharmacy King Saud University, Riyadh, Saudi Arabia
| | - Essam A. Ali
- Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh, Saudi Arabia
| | - Umar Nishan
- Department of Chemistry, Kohat University of Science and Technology, Kohat, Pakistan
| | - Muhammad Shehroz
- Department of Bioinformatics, Kohsar University Murree, Murree, Pakistan
| | - Aqal Zaman
- Department of Microbiology and Molecular Genetics, Bahauddin Zakariya University, Multan, Pakistan
| | - Suvash Chandra Ojha
- Department of Infectious Diseases, The Affiliated Hospital of Southwest Medical University, Luzhou, China
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2
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Zhao J, Cochrane CS, Najeeb J, Gooden D, Sciandra C, Fan P, Lemaitre N, Newns K, Nicholas RA, Guan Z, Thaden JT, Fowler VG, Spasojevic I, Sebbane F, Toone EJ, Duncan C, Gammans R, Zhou P. Preclinical safety and efficacy characterization of an LpxC inhibitor against Gram-negative pathogens. Sci Transl Med 2023; 15:eadf5668. [PMID: 37556556 PMCID: PMC10785772 DOI: 10.1126/scitranslmed.adf5668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Accepted: 07/20/2023] [Indexed: 08/11/2023]
Abstract
The UDP-3-O-(R-3-hydroxyacyl)-N-acetylglucosamine deacetylase LpxC is an essential enzyme in the biosynthesis of lipid A, the outer membrane anchor of lipopolysaccharide and lipooligosaccharide in Gram-negative bacteria. The development of LpxC-targeting antibiotics toward clinical therapeutics has been hindered by the limited antibiotic profile of reported non-hydroxamate inhibitors and unexpected cardiovascular toxicity observed in certain hydroxamate and non-hydroxamate-based inhibitors. Here, we report the preclinical characterization of a slow, tight-binding LpxC inhibitor, LPC-233, with low picomolar affinity. The compound is a rapid bactericidal antibiotic, unaffected by established resistance mechanisms to commercial antibiotics, and displays outstanding activity against a wide range of Gram-negative clinical isolates in vitro. It is orally bioavailable and efficiently eliminates infections caused by susceptible and multidrug-resistant Gram-negative bacterial pathogens in murine soft tissue, sepsis, and urinary tract infection models. It displays exceptional in vitro and in vivo safety profiles, with no detectable adverse cardiovascular toxicity in dogs at 100 milligrams per kilogram. These results establish the feasibility of developing oral LpxC-targeting antibiotics for clinical applications.
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Affiliation(s)
- Jinshi Zhao
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
| | | | - Javaria Najeeb
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
- Current address: Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - David Gooden
- Department of Chemistry, Duke University, Durham, NC 27708, USA
- Small Molecule Synthesis Facility, Duke University, Durham, NC 27708, USA
| | - Carly Sciandra
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
| | - Ping Fan
- Pharmacokinetics/Pharmacodynamics (PK/PD) Core Laboratory, Duke Cancer Institute, Durham, NC 27710, USA
| | - Nadine Lemaitre
- Univ. Lille, CNRS, Inserm, CHU Lille, Institut Pasteur de Lille, U1019-UMR9017-CIIL-Centre d’Infection et d’Immunité de Lille, Lille, France
| | - Kate Newns
- Departments of Pharmacology and Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
- Current address: Envision Pharma Group, Philadelphia, PA 19109, USA
| | - Robert A. Nicholas
- Departments of Pharmacology and Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599
| | - Ziqiang Guan
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
| | - Joshua T. Thaden
- Department of Medicine, Duke University School of Medicine, Durham, NC 27710, USA
| | - Vance G. Fowler
- Department of Medicine, Duke University School of Medicine, Durham, NC 27710, USA
| | - Ivan Spasojevic
- Pharmacokinetics/Pharmacodynamics (PK/PD) Core Laboratory, Duke Cancer Institute, Durham, NC 27710, USA
- Department of Medicine, Duke University School of Medicine, Durham, NC 27710, USA
| | - Florent Sebbane
- Univ. Lille, CNRS, Inserm, CHU Lille, Institut Pasteur de Lille, U1019-UMR9017-CIIL-Centre d’Infection et d’Immunité de Lille, Lille, France
| | - Eric J. Toone
- Department of Chemistry, Duke University, Durham, NC 27708, USA
- Current address: Breakthrough Energy Ventures, 4110 Carillon Point Kirkland, WA 98033 USA
| | | | | | - Pei Zhou
- Department of Biochemistry, Duke University School of Medicine, Durham, NC 27710, USA
- Department of Chemistry, Duke University, Durham, NC 27708, USA
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3
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Liston SD, Ovchinnikova OG, Kimber MS, Whitfield C. A dedicated C-6 β-hydroxyacyltransferase required for biosynthesis of the glycolipid anchor for Vi antigen capsule in typhoidal Salmonella. J Biol Chem 2022; 298:102520. [PMID: 36152747 DOI: 10.1016/j.jbc.2022.102520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Revised: 09/15/2022] [Accepted: 09/16/2022] [Indexed: 11/17/2022] Open
Abstract
Vi antigen is an extracellular polysaccharide produced by Salmonella enterica Typhi, Citrobacter freundii, and some soil bacteria belonging to the Burkholderiales. In Salmonella Typhi, Vi-antigen capsule protects the bacterium against host defenses, and the glycan is used in a current glycoconjugate vaccine to protect against typhoid. Vi antigen is a glycolipid assembled in the cytoplasm and translocated to the cell surface by an export complex driven by an ABC transporter. In Salmonella Typhi, efficient export and cell-surface retention of the capsule layer depend on a reducing terminal acylated-HexNAc moiety. Although the precise structure and biosynthesis of the acylated terminus has not been resolved, it distinguishes Vi antigen from other known glycolipid substrates for bacterial ABC transporters. The genetic locus for Vi antigen-biosynthesis encodes a single acyltransferase candidate (VexE), which is implicated in the acylation process. Here, we determined the structure of the VexE in vitro reaction product by mass spectrometry and nuclear magnetic resonance spectroscopy, to reveal that VexE catalyzes β-hydroxyacyl-ACP dependent acylation of the activated sugar precursor, uridine-5'-diphospho-N-acetylglucosamine (UDP-GlcNAc), at C-6 to form UDP-6-O-[β-hydroxymyristoyl]-α-d-GlcNAc. VexE belongs to the lysophosphatidyl acyltransferase (LPLAT) family, and comparison of an Alphafold VexE model to solved LPLAT structures, together with modeling enzyme:substrate complexes, led us to predict an enzyme mechanism. This study provides new insight into Vi terminal structure, offers a new model substrate to investigate the mechanism of glycolipid ABC transporters, and adds biochemical understanding for a novel reaction used in synthesis of an important bacterial virulence factor.
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Affiliation(s)
- S D Liston
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - O G Ovchinnikova
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - M S Kimber
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada
| | - C Whitfield
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
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4
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Wang Z, Zheng Y, Ji M, Zhang X, Wang H, Chen Y, Wu Q, Chen GQ. Hyperproduction of PHA copolymers containing high fractions of 4-hydroxybutyrate (4HB) by outer membrane-defected Halomonas bluephagenesis grown in bioreactors. Microb Biotechnol 2022; 15:1586-1597. [PMID: 34978757 PMCID: PMC9049619 DOI: 10.1111/1751-7915.13999] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Revised: 12/16/2021] [Accepted: 12/17/2021] [Indexed: 01/07/2023] Open
Abstract
Bacterial outer membrane (OM) is a self‐protective and permeable barrier, while having many non‐negligible negative effects in industrial biotechnology. Our previous studies revealed enhanced properties of Halomonas bluephagenesis based on positive cellular properties by OM defects. This study further expands the OM defect on membrane compactness by completely deleting two secondary acyltransferases for lipid A modification in H. bluephagenesis, LpxL and LpxM, and found more significant advantages than that of the previous lpxL mutant. Deletions on LpxL and LpxM accelerated poly(3‐hydroxybutyrate) (PHB) production by H. bluephagenesis WZY229, leading to a 37% increase in PHB accumulation and 84‐folds reduced endotoxin production. Enhanced membrane permeability accelerates the diffusion of γ‐butyrolactone, allowing H. bluephagenesis WZY254 derived from H. bluephagenesis WZY229 to produce 82wt% poly(3‐hydroxybutyrate‐co‐23mol%4‐hydroxybutyrate) (P(3HB‐co‐23mol%4HB)) in shake flasks, showing increases of 102% and 307% in P(3HB‐co‐4HB) production and 4HB accumulation, respectively. The 4HB molar fraction in copolymer can be elevated to 32 mol% in the presence of more γ‐butyrolactone. In a 7‐l bioreactor fed‐batch fermentation, H. bluephagenesis WZY254 supported a 84 g l−1 dry cell mass with 81wt% P(3HB‐co‐26mol%4HB), increasing 136% in 4HB molar fraction. This study further demonstrated that OM defects generate a hyperproduction strain for high 4HB containing copolymers.
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Affiliation(s)
- Ziyu Wang
- School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Yifei Zheng
- School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Mengke Ji
- School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Xu Zhang
- School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Huan Wang
- School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Yuemeng Chen
- School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Qiong Wu
- School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Guo-Qiang Chen
- School of Life Sciences, Tsinghua University, Beijing, 100084, China.,Center for Synthetic and Systems Biology, Tsinghua University, Beijing, 100084, China.,Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing, 100084, China.,MOE Key Lab of Industrial Biocatalysis, Dept Chemical Engineering, Tsinghua University, Beijing, 100084, China
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5
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Bachert BA, Richardson JB, Mlynek KD, Klimko CP, Toothman RG, Fetterer DP, Luquette AE, Chase K, Storrs JL, Rogers AK, Cote CK, Rozak DA, Bozue JA. Development, Phenotypic Characterization and Genomic Analysis of a Francisella tularensis Panel for Tularemia Vaccine Testing. Front Microbiol 2021; 12:725776. [PMID: 34456897 PMCID: PMC8386241 DOI: 10.3389/fmicb.2021.725776] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 07/21/2021] [Indexed: 11/23/2022] Open
Abstract
Francisella tularensis is one of several biothreat agents for which a licensed vaccine is needed to protect against this pathogen. To aid in the development of a vaccine protective against pneumonic tularemia, we generated and characterized a panel of F. tularensis isolates that can be used as challenge strains to assess vaccine efficacy. Our panel consists of both historical and contemporary isolates derived from clinical and environmental sources, including human, tick, and rabbit isolates. Whole genome sequencing was performed to assess the genetic diversity in comparison to the reference genome F. tularensis Schu S4. Average nucleotide identity analysis showed >99% genomic similarity across the strains in our panel, and pan-genome analysis revealed a core genome of 1,707 genes, and an accessory genome of 233 genes. Three of the strains in our panel, FRAN254 (tick-derived), FRAN255 (a type B strain), and FRAN256 (a human isolate) exhibited variation from the other strains. Moreover, we identified several unique mutations within the Francisella Pathogenicity Island across multiple strains in our panel, revealing unexpected diversity in this region. Notably, FRAN031 (Scherm) completely lacked the second pathogenicity island but retained virulence in mice. In contrast, FRAN037 (Coll) was attenuated in a murine pneumonic tularemia model and had mutations in pdpB and iglA which likely led to attenuation. All of the strains, except FRAN037, retained full virulence, indicating their effectiveness as challenge strains for future vaccine testing. Overall, we provide a well-characterized panel of virulent F. tularensis strains that can be utilized in ongoing efforts to develop an effective vaccine against pneumonic tularemia to ensure protection is achieved across a range F. tularensis strains.
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Affiliation(s)
- Beth A Bachert
- Division of Bacteriology, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Joshua B Richardson
- Center for Genome Sciences, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Kevin D Mlynek
- Division of Bacteriology, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Christopher P Klimko
- Division of Bacteriology, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Ronald G Toothman
- Division of Bacteriology, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - David P Fetterer
- Division of Biostatistics, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Andrea E Luquette
- Biodefense Reference Material Repository, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Kitty Chase
- Biodefense Reference Material Repository, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Jessica L Storrs
- Biodefense Reference Material Repository, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Ashley K Rogers
- Biodefense Reference Material Repository, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Christopher K Cote
- Division of Bacteriology, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - David A Rozak
- Biodefense Reference Material Repository, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
| | - Joel A Bozue
- Division of Bacteriology, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States
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6
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Georgieva M, Heinonen T, Vitale A, Hargraves S, Causevic S, Pillonel T, Eberl L, Widmann C, Jacquier N. Bacterial surface properties influence the activity of the TAT-RasGAP 317-326 antimicrobial peptide. iScience 2021; 24:102923. [PMID: 34430812 PMCID: PMC8365389 DOI: 10.1016/j.isci.2021.102923] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 07/05/2021] [Accepted: 07/27/2021] [Indexed: 12/13/2022] Open
Abstract
Antibiotic resistance is an increasing threat for public health, underscoring the need for new antibacterial agents. Antimicrobial peptides (AMPs) represent an alternative to classical antibiotics. TAT-RasGAP317-326 is a recently described AMP effective against a broad range of bacteria, but little is known about the conditions that may influence its activity. Using RNA-sequencing and screening of mutant libraries, we show that Escherichia coli and Pseudomonas aeruginosa respond to TAT-RasGAP317-326 by regulating metabolic and stress response pathways, possibly implicating two-component systems. Our results also indicate that bacterial surface properties, in particular integrity of the lipopolysaccharide layer, influence peptide binding and entry. Finally, we found differences between bacterial species with respect to their rate of resistance emergence against this peptide. Our findings provide the basis for future investigation on the mode of action of TAT-RasGAP317-326, which may help developing antimicrobial treatments based on this peptide.
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Affiliation(s)
- Maria Georgieva
- Department of Biomedical Sciences, University of Lausanne, Lausanne 1005, Switzerland
| | - Tytti Heinonen
- Institute of Microbiology, Lausanne University Hospital and University of Lausanne, Lausanne 1011, Switzerland
| | - Alessandra Vitale
- Department of Plant and Microbial Biology, University of Zurich, Zurich 8008, Switzerland
| | - Simone Hargraves
- Institute of Microbiology, Lausanne University Hospital and University of Lausanne, Lausanne 1011, Switzerland
| | - Senka Causevic
- Institute of Microbiology, Lausanne University Hospital and University of Lausanne, Lausanne 1011, Switzerland
| | - Trestan Pillonel
- Institute of Microbiology, Lausanne University Hospital and University of Lausanne, Lausanne 1011, Switzerland
| | - Leo Eberl
- Department of Plant and Microbial Biology, University of Zurich, Zurich 8008, Switzerland
| | - Christian Widmann
- Department of Biomedical Sciences, University of Lausanne, Lausanne 1005, Switzerland
- Corresponding author
| | - Nicolas Jacquier
- Institute of Microbiology, Lausanne University Hospital and University of Lausanne, Lausanne 1011, Switzerland
- Corresponding author
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7
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Nilsson I, Lee SY, Sawyer WS, Baxter Rath CM, Lapointe G, Six DA. Metabolic phospholipid labeling of intact bacteria enables a fluorescence assay that detects compromised outer membranes. J Lipid Res 2020; 61:870-883. [PMID: 32156718 PMCID: PMC7269758 DOI: 10.1194/jlr.ra120000654] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2020] [Revised: 03/03/2020] [Indexed: 01/09/2023] Open
Abstract
Gram-negative bacteria possess an asymmetric outer membrane (OM) composed primarily of lipopolysaccharides (LPSs) on the outer leaflet and phospholipids (PLs) on the inner leaflet. The loss of this asymmetry due to mutations in the LPS biosynthesis or transport pathways causes the externalization of PLs to the outer leaflet of the OM and leads to OM permeability defects. Here, we used metabolic labeling to detect a compromised OM in intact bacteria. Phosphatidylcholine synthase expression in Escherichia coli allowed for the incorporation of exogenous propargylcholine into phosphatidyl(propargyl)choline and exogenous 1-azidoethyl-choline (AECho) into phosphatidyl(azidoethyl)choline (AEPC), as confirmed by LC/MS analyses. A fluorescent copper-free click reagent poorly labeled AEPC in intact wild-type cells but readily labeled AEPC from lysed cells. Fluorescence microscopy and flow cytometry analyses confirmed the absence of significant AEPC labeling from intact wild-type E. coli strains and revealed significant AEPC labeling in an E. coli LPS transport mutant (lptD4213) and an LPS biosynthesis mutant (E. coli lpxC101). Our results suggest that metabolic PL labeling with AECho is a promising tool for detecting a compromised bacterial OM, revealing aberrant PL externalization, and identifying or characterizing novel cell-active inhibitors of LPS biosynthesis or transport.
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Affiliation(s)
- Inga Nilsson
- Infectious Diseases Area Novartis Institutes for BioMedical Research, Emeryville, CA; Global Discovery Chemistry Novartis Institutes for BioMedical Research, Emeryville, CA
| | - Sheng Y Lee
- Infectious Diseases Area Novartis Institutes for BioMedical Research, Emeryville, CA
| | - William S Sawyer
- Infectious Diseases Area Novartis Institutes for BioMedical Research, Emeryville, CA
| | | | - Guillaume Lapointe
- Global Discovery Chemistry Novartis Institutes for BioMedical Research, Emeryville, CA
| | - David A Six
- Infectious Diseases Area Novartis Institutes for BioMedical Research, Emeryville, CA. mailto:
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8
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Rough-type and loss of the LPS due to lpx genes deletions are associated with colistin resistance in multidrug-resistant clinical Escherichia coli isolates not harbouring mcr genes. PLoS One 2020; 15:e0233518. [PMID: 32433662 PMCID: PMC7239443 DOI: 10.1371/journal.pone.0233518] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 05/06/2020] [Indexed: 12/21/2022] Open
Abstract
The emergence of multidrug-resistant Escherichia coli has become a great challenge in treating nosocomial infections. The polymyxin antibiotic colistin is used as a ‘last-line’ therapy for such strains, but resistance to colistin is increasingly emerging all over the world. In this study, we investigated lipopolysaccharides (LPS) of colistin-resistant isolates and examined mutations in lpx genes in strains not harbouring mcr genes. We examined 351 clinical E. coli isolates with 38 showing reduced susceptibility to colistin. These isolates were collected from different clinical specimens including blood, urine, and wounds, but no stool. After confirmation of the isolates via a BD Phoenix-100 system (Becton Dickinson, USA), we performed antimicrobial susceptibility tests to characterize the resistance pattern of these isolates to different classes of antibiotics, using the disk diffusion test. The Minimum Inhibitory Concentration (MIC) of colistin was determined using E-test strips. The presence of mobile colistin resistance (mcr-1 and mcr-2) genes was tested for all isolates. LPS (including lipid A) were extracted from all isolates and associated lpx genes analyzed by PCR and sequencing. Among the 38 clinical E. coli isolates with reduced susceptibility to colistin, 52% were resistant to colistin. The MICs of colistin ranged from 0.5 μg/ml to ˃256 μg/ml. Within the 20 colistin-resistant strains, six isolates carried the mcr-1 gene, but not mcr-2. Heterologous expression of the mcr-1 gene in susceptible E. coli DH5α increased the MIC of colistin by eight-fold. The remaining 14 isolates, were negative for both mcr genes. Six isolates were further negative for LPS production and five showed rough LPS phenotypes. Here we present evidence that loss of LPS or lipid A-deficiency can lead to colistin-resistance in clinical E. coli isolates not harbouring mcr genes.
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9
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Current Progress in the Structural and Biochemical Characterization of Proteins Involved in the Assembly of Lipopolysaccharide. Int J Microbiol 2018; 2018:5319146. [PMID: 30595696 PMCID: PMC6286764 DOI: 10.1155/2018/5319146] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 10/29/2018] [Indexed: 12/25/2022] Open
Abstract
The lipid component of the outer leaflet of the outer membrane of Gram-negative bacteria is primarily composed of the glycolipid lipopolysaccharide (LPS), which serves to form a protective barrier against hydrophobic toxins and many antibiotics. LPS is comprised of three regions: the lipid A membrane anchor, the nonrepeating core oligosaccharide, and the repeating O-antigen polysaccharide. The lipid A portion is also referred to as endotoxin as its overstimulation of the toll-like receptor 4 during systemic infection precipitates potentially fatal septic shock. Because of the importance of LPS for the viability and virulence of human pathogens, understanding how LPS is synthesized and transported to the outer leaflet of the outer membrane is important for developing novel antibiotics to combat resistant Gram-negative strains. The following review describes the current state of our understanding of the proteins responsible for the synthesis and transport of LPS with an emphasis on the contribution of protein structures to our understanding of their functions. Because the lipid A portion of LPS is relatively well conserved, a detailed description of the biosynthetic enzymes in the Raetz pathway of lipid A synthesis is provided. Conversely, less well-conserved biosynthetic enzymes later in LPS synthesis are described primarily to demonstrate conserved principles of LPS synthesis. Finally, the conserved LPS transport systems are described in detail.
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10
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Henderson JC, Herrera CM, Trent MS. AlmG, responsible for polymyxin resistance in pandemic Vibrio cholerae, is a glycyltransferase distantly related to lipid A late acyltransferases. J Biol Chem 2017; 292:21205-21215. [PMID: 29101229 DOI: 10.1074/jbc.ra117.000131] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2017] [Revised: 10/19/2017] [Indexed: 12/21/2022] Open
Abstract
Cationic antimicrobial peptides (CAMPs), such as polymyxins, are used as a last-line defense in treatment of many bacterial infections. However, some bacteria have developed resistance mechanisms to survive these compounds. Current pandemic O1 Vibrio cholerae biotype El Tor is resistant to polymyxins, whereas a previous pandemic strain of the biotype Classical is polymyxin-sensitive. The almEFG operon found in El Tor V. cholerae confers >100-fold resistance to antimicrobial peptides through aminoacylation of lipopolysaccharide (LPS), expected to decrease the negatively charged surface of the V. cholerae outer membrane. This Gram-negative system bears striking resemblance to a related Gram-positive cell-wall remodeling strategy that also promotes CAMP resistance. Mutants defective in AlmEF-dependent LPS modification exhibit reduced fitness in vivo Here, we present investigation of AlmG, the hitherto uncharacterized member of the AlmEFG pathway. Evidence for AlmG glycyl to lipid substrate transferase activity is demonstrated in vivo by heterologous expression of V. cholerae pathway enzymes in a specially engineered Escherichia coli strain. Development of a minimal keto-deoxyoctulosonate (Kdo)-lipid A domain in E. coli was necessary to facilitate chemical structure analysis and to produce a mimetic Kdo-lipid A domain AlmG substrate to that synthesized by V. cholerae. Our biochemical studies support a uniquely nuanced pathway of Gram-negative CAMPs resistance and provide a more detailed description of an enzyme of the pharmacologically relevant lysophosphospholipid acyltransferase (LPLAT) superfamily.
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Affiliation(s)
- Jeremy C Henderson
- From the Department of Infectious Diseases, Center for Vaccines and Immunology, College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602
| | - Carmen M Herrera
- From the Department of Infectious Diseases, Center for Vaccines and Immunology, College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602
| | - M Stephen Trent
- From the Department of Infectious Diseases, Center for Vaccines and Immunology, College of Veterinary Medicine, University of Georgia, Athens, Georgia 30602
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11
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Nilsson I, Grove K, Dovala D, Uehara T, Lapointe G, Six DA. Molecular characterization and verification of azido-3,8-dideoxy-d- manno-oct-2-ulosonic acid incorporation into bacterial lipopolysaccharide. J Biol Chem 2017; 292:19840-19848. [PMID: 29018092 DOI: 10.1074/jbc.m117.814962] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Revised: 10/05/2017] [Indexed: 11/06/2022] Open
Abstract
3-Deoxy-d-manno-oct-2-ulosonic acid (Kdo) is an essential component of LPS in the outer leaflet of the Gram-negative bacterial outer membrane. Although labeling of Escherichia coli with the chemical reporter 8-azido-3,8-dideoxy-d-manno-oct-2-ulosonic acid (Kdo-N3) has been reported, its incorporation into LPS has not been directly shown. We have now verified Kdo-N3 incorporation into E. coli LPS at the molecular level. Using microscopy and PAGE analysis, we show that Kdo-N3 is localized to the outer membrane and specifically incorporates into rough and deep-rough LPS. In an E. coli strain lacking endogenous Kdo biosynthesis, supplementation with exogenous Kdo restored full-length core-LPS, which suggests that the Kdo biosynthetic pathways might not be essential in vivo in the presence of sufficient exogenous Kdo. In contrast, exogenous Kdo-N3 only restored a small fraction of core LPS with the majority incorporated into truncated LPS. The truncated LPS were identified as Kdo-N3-lipid IVA and (Kdo-N3)2-lipid IVA by MS analysis. The low level of Kdo-N3 incorporation could be partly explained by a 6-fold reduction in the specificity constant of the CMP-Kdo synthetase KdsB with Kdo-N3 compared with Kdo. These results indicate that the azido moiety in Kdo-N3 interferes with its utilization and may limit its utility as a tracer of LPS biosynthesis and transport in E. coli We propose that our findings will be helpful for researchers using Kdo and its chemical derivatives for investigating LPS biosynthesis, transport, and assembly in Gram-negative bacteria.
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Affiliation(s)
| | - Kerri Grove
- Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California 94608
| | | | | | - Guillaume Lapointe
- Global Discovery Chemistry, Novartis Institutes for BioMedical Research, Emeryville, California 94608
| | - David A Six
- From the Departments of Infectious Diseases and
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12
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Zhu L, Li Y, Wang J, Wang X. Identification of two secondary acyltransferases of lipid A in Pseudomonas putida
KT2442. J Appl Microbiol 2017; 123:478-490. [DOI: 10.1111/jam.13499] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2017] [Revised: 05/16/2017] [Accepted: 05/16/2017] [Indexed: 12/18/2022]
Affiliation(s)
- L. Zhu
- School of Biotechnology; Jiangnan University; Wuxi China
| | - Y. Li
- State Key Laboratory of Food Science and Technology; Wuxi China
| | - J. Wang
- School of Biotechnology; Jiangnan University; Wuxi China
| | - X. Wang
- School of Biotechnology; Jiangnan University; Wuxi China
- State Key Laboratory of Food Science and Technology; Wuxi China
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13
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Kadlcik S, Kamenik Z, Vasek D, Nedved M, Janata J. Elucidation of salicylate attachment in celesticetin biosynthesis opens the door to create a library of more efficient hybrid lincosamide antibiotics. Chem Sci 2017; 8:3349-3355. [PMID: 28507704 PMCID: PMC5416915 DOI: 10.1039/c6sc04235j] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 02/27/2017] [Indexed: 11/21/2022] Open
Abstract
Combinatorial biosynthesis for more efficient antibiotics: 150 novel lincosamides prepared by combining lincomycin and celesticetin biosynthetic pathways.
Lincosamides, which are produced by streptomycetes, compose a small but clinically important class of antibiotics. The recent elucidation of the condensation and post-condensation biosynthetic steps of the lincosamides lincomycin and celesticetin revealed several unexpected reaction mechanisms. Here, we prepared recombinant proteins involved in the celesticetin biosynthetic pathway and used them for in vitro assays that were monitored by LC-MS. Our results elucidate the last biosynthetic step of celesticetin: the attachment of salicylic acid is catalyzed by the Ccb2 acyl-CoA ligase and the Ccb1 acyltransferase. Ccb1 belongs to the WS/DGAT protein family and, in contrast to the characterized members of the family, has unusual substrate specificity. To the best of our knowledge, Ccb1 is the first protein in this family that transfers a benzoyl derivative-CoA conjugate and is the first WS/DGAT protein involved in the biosynthesis of secondary metabolites. Furthermore, we exploited the relaxed substrate specificities of Ccb1 and Ccb2, as well as three additional upstream post-condensation biosynthetic proteins in the celesticetin pathway, and combined the lincomycin and the celesticetin biosynthetic pathways in vitro. In this way, we prepared a library of 150 novel hybrid lincosamides, including two unnatural chimeras of lincomycin and celesticetin, which were shown to have antibacterial properties more pronounced than clinically used lincomycin. These achievements may be considered a case study in applying knowledge about biosynthetic machinery to assemble a large number of compounds from originally a small group of natural products without the need for chemical synthesis.
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Affiliation(s)
- S Kadlcik
- Institute of Microbiology , Czech Academy of Sciences , BIOCEV , Prumyslova 595 , 252 50 Vestec , Czech Republic .
| | - Z Kamenik
- Institute of Microbiology , Czech Academy of Sciences , BIOCEV , Prumyslova 595 , 252 50 Vestec , Czech Republic .
| | - D Vasek
- Institute of Microbiology , Czech Academy of Sciences , BIOCEV , Prumyslova 595 , 252 50 Vestec , Czech Republic .
| | - M Nedved
- Institute of Microbiology , Czech Academy of Sciences , BIOCEV , Prumyslova 595 , 252 50 Vestec , Czech Republic .
| | - J Janata
- Institute of Microbiology , Czech Academy of Sciences , BIOCEV , Prumyslova 595 , 252 50 Vestec , Czech Republic .
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14
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Glycolipid substrates for ABC transporters required for the assembly of bacterial cell-envelope and cell-surface glycoconjugates. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:1394-1403. [PMID: 27793707 DOI: 10.1016/j.bbalip.2016.10.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Revised: 10/19/2016] [Accepted: 10/20/2016] [Indexed: 01/07/2023]
Abstract
Glycoconjugates, molecules that contain sugar components, are major components of the cell envelopes of bacteria and cover much of their exposed surfaces. These molecules are involved in interactions with the surrounding environment and, in pathogens, play critical roles in the interplay with the host immune system. Despite the remarkable diversity in glycoconjugate structures, most are assembled by glycosyltransferases that act on lipid acceptors at the cytosolic membrane. The resulting glycolipids are then transported to the cell surface in processes that frequently begin with ATP-binding cassette transporters. This review summarizes current understanding of the structure and biosynthesis of glycolipid substrates and the structure and functions of their transporters. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.
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15
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Garrett TA. Major roles for minor bacterial lipids identified by mass spectrometry. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:1319-1324. [PMID: 27760388 DOI: 10.1016/j.bbalip.2016.10.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Revised: 10/03/2016] [Accepted: 10/04/2016] [Indexed: 01/31/2023]
Abstract
Mass spectrometry of lipids, especially those isolated from bacteria, has ballooned over the past two decades, affirming in the process the complexity of the lipidome. With this has come the identification of new and interesting lipid structures. Here is an overview of several novel lipids, from both Gram-negative and Gram-positive bacteria with roles in health and disease, whose structural identification was facilitated using mass spectrometry. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.
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Affiliation(s)
- Teresa A Garrett
- Department of Chemistry, Vassar College, 124 Raymond Avenue, Poughkeepsie, NY 12604, United States.
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16
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Structure-guided enzymology of the lipid A acyltransferase LpxM reveals a dual activity mechanism. Proc Natl Acad Sci U S A 2016; 113:E6064-E6071. [PMID: 27681620 DOI: 10.1073/pnas.1610746113] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Gram-negative bacteria possess a characteristic outer membrane, of which the lipid A constituent elicits a strong host immune response through the Toll-like receptor 4 complex, and acts as a component of the permeability barrier to prevent uptake of bactericidal compounds. Lipid A species comprise the bulk of the outer leaflet of the outer membrane and are produced through a multistep biosynthetic pathway conserved in most Gram-negative bacteria. The final steps in this pathway involve the secondary acylation of lipid A precursors. These are catalyzed by members of a superfamily of enzymes known as lysophospholipid acyltransferases (LPLATs), which are present in all domains of life and play important roles in diverse biological processes. To date, characterization of this clinically important class of enzymes has been limited by a lack of structural information and the availability of only low-throughput biochemical assays. In this work, we present the structure of the bacterial LPLAT protein LpxM, and we describe a high-throughput, label-free mass spectrometric assay to characterize acyltransferase enzymatic activity. Using our structure and assay, we identify an LPLAT thioesterase activity, and we provide experimental evidence to support an ordered-binding and "reset" mechanistic model for LpxM function. This work enables the interrogation of other bacterial acyltransferases' structure-mechanism relationships, and the assay described herein provides a foundation for quantitatively characterizing the enzymology of any number of clinically relevant LPLAT proteins.
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17
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Identification of Two Genes Encoding for the Late Acyltransferases of Lipid A in Klebsiella pneumoniae. Curr Microbiol 2016; 73:732-738. [PMID: 27534404 DOI: 10.1007/s00284-016-1117-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 07/12/2016] [Indexed: 12/15/2022]
Abstract
Lipid A, the hydrophobic anchor of lipopolysaccharide, is an essential component in the outer membrane of most gram-negative bacteria. It is recognized by the TLR4/MD2 receptor of the innate immune system, which triggers an inflammatory response accompanied by massive overproduction of cytokines and leads to gram-negative septic shock. Human pathogen Klebsiella pneumoniae, which may synthesize two lipid A species, differs by the length of the secondary acyl chain. In this study, we identified two genes encoding the putative late acyltransferases of lipid A biosynthesis pathway in K. pneumoniae. Based on the sequence alignment, proteins YP_002239312.1 encoded by KPK3489 and YP_002239899.1 encoded by KPK4096 are homologous to E. coli LpxL, which were designated as LpxL1 and LpxL2, respectively. Functions of the two acyltransferases were confirmed by overexpressing the genes in E. coli, isolating lipid A and analyzing their structures using an ESI/MS. Like E. coli LpxL, K. pneumoniae LpxL1 transfers a C12:0 secondary acyl chain to the 2'-position of lipid A, while K. pneumoniae LpxL2 transfers a C14:0 secondary acyl chain to the 2'-position primary acyl chain of lipid A. These two acyltransferases might play important roles in the biosynthesis of lipid A and the innate immune system recognition in K. pneumoniae.
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18
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Unique lipid anchor attaches Vi antigen capsule to the surface of Salmonella enterica serovar Typhi. Proc Natl Acad Sci U S A 2016; 113:6719-24. [PMID: 27226298 DOI: 10.1073/pnas.1524665113] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Polysaccharide capsules are surface structures that are critical for the virulence of many Gram-negative pathogenic bacteria. Salmonella enterica serovar Typhi is the etiological agent of typhoid fever. It produces a capsular polysaccharide known as "Vi antigen," which is composed of nonstoichiometrically O-acetylated α-1,4-linked N-acetylgalactosaminuronic acid residues. This glycan is a component of currently available vaccines. The genetic locus for Vi antigen production is also present in soil bacteria belonging to the genus Achromobacter Vi antigen assembly follows a widespread general strategy with a characteristic glycan export step involving an ATP-binding cassette transporter. However, Vi antigen producers lack the enzymes that build the conserved terminal glycolipid characterizing other capsules using this method. Achromobacter species possess a Vi antigen-specific depolymerase enzyme missing in S enterica Typhi, and we exploited this enzyme to isolate acylated Vi antigen termini. Mass spectrometry analysis revealed a reducing terminal N-acetylhexosamine residue modified with two β-hydroxyl acyl chains. This terminal structure resembles one half of lipid A, the hydrophobic portion of bacterial lipopolysaccharides. The VexE protein encoded in the Vi antigen biosynthesis locus shares similarity with LpxL, an acyltransferase from lipid A biosynthesis. In the absence of VexE, Vi antigen is produced, but its physical properties are altered, its export is impaired, and a Vi capsule structure is not assembled on the cell surface. The structure of the lipidated terminus dictates a unique assembly mechanism and has potential implications in pathogenesis and vaccine production.
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19
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Emiola A, George J, Andrews SS. A Complete Pathway Model for Lipid A Biosynthesis in Escherichia coli. PLoS One 2015; 10:e0121216. [PMID: 25919634 PMCID: PMC4412817 DOI: 10.1371/journal.pone.0121216] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2014] [Accepted: 02/12/2015] [Indexed: 11/19/2022] Open
Abstract
Lipid A is a highly conserved component of lipopolysaccharide (LPS), itself a major component of the outer membrane of Gram-negative bacteria. Lipid A is essential to cells and elicits a strong immune response from humans and other animals. We developed a quantitative model of the nine enzyme-catalyzed steps of Escherichia coli lipid A biosynthesis, drawing parameters from the experimental literature. This model accounts for biosynthesis regulation, which occurs through regulated degradation of the LpxC and WaaA (also called KdtA) enzymes. The LpxC degradation signal appears to arise from the lipid A disaccharide concentration, which we deduced from prior results, model results, and new LpxK overexpression results. The model agrees reasonably well with many experimental findings, including the lipid A production rate, the behaviors of mutants with defective LpxA enzymes, correlations between LpxC half-lives and cell generation times, and the effects of LpxK overexpression on LpxC concentrations. Its predictions also differ from some experimental results, which suggest modifications to the current understanding of the lipid A pathway, such as the possibility that LpxD can replace LpxA and that there may be metabolic channeling between LpxH and LpxB. The model shows that WaaA regulation may serve to regulate the lipid A production rate when the 3-deoxy-D-manno-oct-2-ulosonic acid (KDO) concentration is low and/or to control the number of KDO residues that get attached to lipid A. Computation of flux control coefficients showed that LpxC is the rate-limiting enzyme if pathway regulation is ignored, but that LpxK is the rate-limiting enzyme if pathway regulation is present, as it is in real cells. Control also shifts to other enzymes if the pathway substrate concentrations are not in excess. Based on these results, we suggest that LpxK may be a much better drug target than LpxC, which has been pursued most often.
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Affiliation(s)
- Akintunde Emiola
- School of Health, Sports and Bioscience, University of East London, London, United Kingdom
- * E-mail:
| | - John George
- School of Health, Sports and Bioscience, University of East London, London, United Kingdom
| | - Steven S. Andrews
- Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
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20
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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.
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Affiliation(s)
- Chris Whitfield
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada;
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21
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Li Y, Wang Z, Chen J, Ernst RK, Wang X. Influence of lipid A acylation pattern on membrane permeability and innate immune stimulation. Mar Drugs 2013; 11:3197-208. [PMID: 24065161 PMCID: PMC3806461 DOI: 10.3390/md11093197] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2013] [Revised: 07/29/2013] [Accepted: 08/09/2013] [Indexed: 12/13/2022] Open
Abstract
Lipid A, the hydrophobic anchor of lipopolysaccharide (LPS), is an essential component in the outer membrane of Gram-negative bacteria. It can stimulate the innate immune system via Toll-like receptor 4/myeloid differentiation factor 2 (TLR4/MD2), leading to the release of inflammatory cytokines. In this study, six Escherichia coli strains which can produce lipid A with different acylation patterns were constructed; the influence of lipid A acylation pattern on the membrane permeability and innate immune stimulation has been systematically investigated. The lipid A species were isolated and identified by matrix assisted laser ionization desorption-time of flight/tandem mass spectrometry. N-Phenyl naphthylamine uptake assay and antibiotic susceptibility test showed that membrane permeability of these strains were different. The lower the number of acyl chains in lipid A, the stronger the membrane permeability. LPS purified from these strains were used to stimulate human or mouse macrophage cells, and different levels of cytokines were induced. Compared with wild type hexa-acylated LPS, penta-acylated, tetra-acylated and tri-acylated LPS induced lower levels of cytokines. These results suggest that the lipid A acylation pattern influences both the bacterial membrane permeability and innate immune stimulation. The results would be useful for redesigning the bacterial membrane structure and for developing lipid A vaccine adjuvant.
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Affiliation(s)
- Yanyan Li
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China; E-Mails: (Y.L.); (Z.W.); (J.C.)
| | - Zhou Wang
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China; E-Mails: (Y.L.); (Z.W.); (J.C.)
| | - Jiuzhou Chen
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China; E-Mails: (Y.L.); (Z.W.); (J.C.)
| | - Robert K. Ernst
- Department of Microbial Pathogenesis, University of Maryland Dental School, Baltimore, MD 21201, USA; E-Mail:
| | - Xiaoyuan Wang
- State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China; E-Mails: (Y.L.); (Z.W.); (J.C.)
- Author to whom correspondence should be addressed; E-Mail: ; Tel./Fax: +86-510-8532-9239
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22
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Abstract
Long-chain-length hydrophobic acyl residues play a vital role in a multitude of essential biological structures and processes. They build the inner hydrophobic layers of biological membranes, are converted to intracellular storage compounds, and are used to modify protein properties or function as membrane anchors, to name only a few functions. Acyl thioesters are transferred by acyltransferases or transacylases to a variety of different substrates or are polymerized to lipophilic storage compounds. Lipases represent another important enzyme class dealing with fatty acyl chains; however, they cannot be regarded as acyltransferases in the strict sense. This review provides a detailed survey of the wide spectrum of bacterial acyltransferases and compares different enzyme families in regard to their catalytic mechanisms. On the basis of their studied or assumed mechanisms, most of the acyl-transferring enzymes can be divided into two groups. The majority of enzymes discussed in this review employ a conserved acyltransferase motif with an invariant histidine residue, followed by an acidic amino acid residue, and their catalytic mechanism is characterized by a noncovalent transition state. In contrast to that, lipases rely on completely different mechanism which employs a catalytic triad and functions via the formation of covalent intermediates. This is, for example, similar to the mechanism which has been suggested for polyester synthases. Consequently, although the presented enzyme types neither share homology nor have a common three-dimensional structure, and although they deal with greatly varying molecule structures, this variety is not reflected in their mechanisms, all of which rely on a catalytically active histidine residue.
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Affiliation(s)
- Annika Röttig
- Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität, Münster, Germany
| | - Alexander Steinbüchel
- Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität, Münster, Germany
- Environmental Sciences Department, King Abdulaziz University, Jeddah, Saudi Arabia
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23
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Sohlenkamp C, Raetz CRH, Ingram BO. The calcium-stimulated lipid A 3-O deacylase from Rhizobium etli is not essential for plant nodulation. Biochim Biophys Acta Mol Cell Biol Lipids 2013; 1831:1250-9. [PMID: 23583844 DOI: 10.1016/j.bbalip.2013.04.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Revised: 03/28/2013] [Accepted: 04/05/2013] [Indexed: 01/01/2023]
Abstract
The lipid A component of lipopolysaccharide from the nitrogen-fixing plant endosymbiont, Rhizobium etli, is structurally very different from that found in most enteric bacteria. The lipid A from free-living R. etli is structurally heterogeneous and exists as a mixture of species which are either pentaacylated or tetraacylated. In contrast, the lipid A from R. etli bacteroids is reported to consist exclusively of tetraacylated lipid A species. The tetraacylated lipid A species in both cases lack a β-hydroxymyristoyl chain at the 3-position of lipid A. Here, we show that the lipid A modification enzyme responsible for 3-O deacylation in R. etli is a homolog of the PagL protein originally described in Salmonella enterica sv. typhimurium. In contrast to the PagL proteins described from other species, R. etli PagL displays a calcium dependency. To determine the importance of the lipid A modification catalyzed by PagL, we isolated and characterized a R. etli mutant deficient in the pagL gene. Mass spectrometric analysis confirmed that the mutant strain was exclusively tetraacylated and radiochemical analysis revealed that 3-O deacylase activity was absent in membranes prepared from the mutant. The R. etli mutant was not impaired in its ability to form nitrogen-fixing nodules on Phaseolus vulgaris but it displayed slower nodulation kinetics relative to the wild-type strain. The lipid A modification catalyzed by R. etli PagL, therefore, is not required for nodulation but may play other roles such as protecting bacterial endosymbionts from plant immune responses during infection.
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Affiliation(s)
- Christian Sohlenkamp
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Av. Universidad s/n, Apdo. Postal 565-A, Cuernavaca, Morelos, CP62210, Mexico.
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24
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Emptage RP, Pemble CW, York JD, Raetz CRH, Zhou P. Mechanistic characterization of the tetraacyldisaccharide-1-phosphate 4'-kinase LpxK involved in lipid A biosynthesis. Biochemistry 2013; 52:2280-90. [PMID: 23464738 DOI: 10.1021/bi400097z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The sixth step in the lipid A biosynthetic pathway involves phosphorylation of the tetraacyldisaccharide-1-phosphate (DSMP) intermediate by the cytosol-facing inner membrane kinase LpxK, a member of the P-loop-containing nucleoside triphosphate (NTP) hydrolase superfamily. We report the kinetic characterization of LpxK from Aquifex aeolicus and the crystal structures of LpxK in complex with ATP in a precatalytic binding state, the ATP analogue AMP-PCP in the closed catalytically competent conformation, and a chloride anion revealing an inhibitory conformation of the nucleotide-binding P-loop. We demonstrate that LpxK activity in vitro requires the presence of a detergent micelle and formation of a ternary LpxK-ATP/Mg(2+)-DSMP complex. Using steady-state kinetics, we have identified crucial active site residues, leading to the proposal that the interaction of D99 with H261 acts to increase the pKa of the imidazole moiety, which in turn serves as the catalytic base to deprotonate the 4'-hydroxyl of the DSMP substrate. The fact that an analogous mechanism has not yet been observed for other P-loop kinases highlights LpxK as a distinct member of the P-loop kinase family, a notion that is also reflected through its localization at the membrane, lipid substrate, and overall structure.
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Affiliation(s)
- Ryan P Emptage
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
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25
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Six DA, Lambert B, Raetz CRH, Doerrler WT. Density gradient enrichment of Escherichia coli lpxL mutants. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:989-93. [PMID: 22554681 DOI: 10.1016/j.bbalip.2012.04.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Revised: 03/30/2012] [Accepted: 04/04/2012] [Indexed: 10/28/2022]
Abstract
We previously described enrichment of conditional Escherichia coli msbA mutants defective in lipopolysaccharide export using Ludox density gradients (Doerrler WT (2007) Appl Environ Microbiol 73; 7992-7996). Here, we use this approach to isolate and characterize temperature-sensitive lpxL mutants. LpxL is a late acyltransferase of the pathway of lipid A biosynthesis (The Raetz Pathway). Sequencing the lpxL gene from the mutants revealed the presence of both missense and nonsense mutations. The missense mutations include several in close proximity to the enzyme's active site or conserved residues (E137K, H132Y, G168D). These data demonstrate that Ludox gradients can be used to efficiently isolate conditional E. coli mutants with defects in lipopolysaccharide biosynthesis and provide insight into the enzymatic mechanism of LpxL.
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Affiliation(s)
- David A Six
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
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26
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Lipopolysaccharide (LPS) inner-core phosphates are required for complete LPS synthesis and transport to the outer membrane in Pseudomonas aeruginosa PAO1. mBio 2011; 2:mBio.00142-11. [PMID: 21810964 PMCID: PMC3147165 DOI: 10.1128/mbio.00142-11] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Gram-negative outer membrane (OM) integrity is maintained in part by Mg2+ cross-links between phosphates on lipid A and on core sugars of adjacent lipopolysaccharide (LPS) molecules. In contrast to other Gram-negative bacteria, waaP, encoding an inner-core kinase, could not be inactivated in Pseudomonas aeruginosa. To examine this further, expression of the kinases WaaP or WapP/WapQ/PA5006 was placed under the control of the arabinose-regulated pBAD promoter. Growth of these strains was arabinose dependent, confirming that core phosphorylation is essential in P. aeruginosa. Transmission electron micrographs of kinase-depleted cells revealed marked invaginations of the inner membrane. SDS-PAGE of total LPS from WaaP-depleted cells showed accumulation of a fast-migrating band. Mass spectrometry (MS) analysis revealed that LPS from these cells exhibits a unique truncated core consisting of two 3-deoxy-d-manno-octulosonic acids (Kdo), two l-glycero-d-manno-heptoses (Hep), and one hexose but completely devoid of phosphates, indicating that phosphorylation by WaaP is necessary for subsequent core phosphorylations. MS analysis of lipid A from WaaP-depleted cells revealed extensive 4-amino-4-deoxy-l-arabinose modification. OM prepared from these cells by Sarkosyl extraction of total membranes or by sucrose density gradient centrifugation lacked truncated LPS. Instead, truncated LPS was detected in the inner membrane fractions, consistent with impaired transport/assembly of this species into the OM. Gram-negative bacteria have an outer membrane (OM) comprised of a phospholipid inner leaflet and a lipopolysaccharide (LPS) outer leaflet. The OM protects cells from toxic molecules and is important for survival during infection. The LPS core kinase gene waaP can be deleted in several Gram-negative bacteria but not in Pseudomonas aeruginosa. We used a controlled-expression system to deplete WaaP directly in P. aeruginosa cells, which halted growth. WaaP depletion also caused gross changes in cell morphology and led to the accumulation of an aberrant LPS lacking several core sugars and all core phosphates. The aberrant LPS failed to reach the OM, suggesting that WaaP is essential in P. aeruginosa because it is required to produce the full-length LPS that is recognized by the OM transport/assembly machinery in this organism. Therefore, WaaP may constitute a good target for the development of novel antipseudomonal agents.
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Sun W, Six D, Kuang X, Roland KL, Raetz CR, Curtiss R. A live attenuated strain of Yersinia pestis KIM as a vaccine against plague. Vaccine 2011; 29:2986-98. [PMID: 21320544 PMCID: PMC3073832 DOI: 10.1016/j.vaccine.2011.01.099] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2010] [Revised: 01/15/2011] [Accepted: 01/30/2011] [Indexed: 10/18/2022]
Abstract
Yersinia pestis, the causative agent of plague, is a potential weapon of bioterrorism. Y. pestis evades the innate immune system by synthesizing tetra-acylated lipid A with poor Toll-like receptor 4 (TLR4)-stimulating activity at 37°C, whereas hexa-acylated lipid A, a potent TLR4 agonist, is made at lower temperatures. Synthesis of Escherichia coli LpxL, which transfers the secondary laurate chain to the 2'-position of lipid A, in Y. pestis results in production of hexa-acylated lipid A at 37°C, leading to significant attenuation of virulence. Previously, we described a Y. pestis vaccine strain in which crp expression is under the control of the arabinose-regulated araC P(BAD) promoter, resulting in a 4-5 log reduction in virulence. To reduce the virulence of the crp promoter mutant further, we introduced E. coli lpxL into the Y. pestis chromosome. The χ10030(pCD1Ap) (ΔlpxP32::P(lpxL)lpxL ΔP(crp21)::TT araC P(BAD)crp) construct likewise produced hexa-acylated lipid A at 37°C and was significantly more attenuated than strains harboring each individual mutation. The LD(50) of the mutant in mice, when administered subcutaneously or intranasally was >10(7)-times and >10(4)-times greater than wild type, respectively. Mice immunized subcutaneously with a single dose of the mutant were completely protected against a subcutaneous challenge of 3.6×10(7) wild-type Y. pestis and significantly protected (80% survival) against a pulmonary challenge of 1.2×10(4) live cells. Intranasal immunization also provided significant protection against challenges by both routes. This mutant is an immunogenic, highly attenuated live Y. pestis construct that merits further development as a vaccine candidate.
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Affiliation(s)
- Wei Sun
- Center for Infectious Disease and Vaccinology, The Biodesign Institute, Arizona State University. Tempe, AZ, 85287, USA
| | - David Six
- Department of Biochemistry, Duke University Medical Center, Box 3711 DUMC, Durham, NC 27710, USA
| | - Xiaoying Kuang
- Center for Infectious Disease and Vaccinology, The Biodesign Institute, Arizona State University. Tempe, AZ, 85287, USA
| | - Kenneth L Roland
- Center for Infectious Disease and Vaccinology, The Biodesign Institute, Arizona State University. Tempe, AZ, 85287, USA
| | - Christian R.H. Raetz
- Department of Biochemistry, Duke University Medical Center, Box 3711 DUMC, Durham, NC 27710, USA
| | - Roy Curtiss
- Center for Infectious Disease and Vaccinology, The Biodesign Institute, Arizona State University. Tempe, AZ, 85287, USA
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28
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Evolution of the Kdo2-lipid A biosynthesis in bacteria. BMC Evol Biol 2010; 10:362. [PMID: 21106097 PMCID: PMC3087551 DOI: 10.1186/1471-2148-10-362] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2010] [Accepted: 11/24/2010] [Indexed: 11/21/2022] Open
Abstract
Background Lipid A is the highly immunoreactive endotoxic center of lipopolysaccharide (LPS). It anchors the LPS into the outer membrane of most Gram-negative bacteria. Lipid A can be recognized by animal cells, triggers defense-related responses, and causes Gram-negative sepsis. The biosynthesis of Kdo2-lipid A, the LPS substructure, involves with nine enzymatic steps. Results In order to elucidate the evolutionary pathway of Kdo2-lipid A biosynthesis, we examined the distribution of genes encoding the nine enzymes across bacteria. We found that not all Gram-negative bacteria have all nine enzymes. Some Gram-negative bacteria have no genes encoding these enzymes and others have genes only for the first four enzymes (LpxA, LpxC, LpxD, and LpxB). Among the nine enzymes, five appeared to have arisen from three independent gene duplication events. Two of such events happened within the Proteobacteria lineage, followed by functional specialization of the duplicated genes and pathway optimization in these bacteria. Conclusions The nine-enzyme pathway, which was established based on the studies mainly in Escherichia coli K12, appears to be the most derived and optimized form. It is found only in E. coli and related Proteobacteria. Simpler and probably less efficient pathways are found in other bacterial groups, with Kdo2-lipid A variants as the likely end products. The Kdo2-lipid A biosynthetic pathway exemplifies extremely plastic evolution of bacterial genomes, especially those of Proteobacteria, and how these mainly pathogenic bacteria have adapted to their environment.
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Ingram BO, Masoudi A, Raetz CRH. Escherichia coli mutants that synthesize dephosphorylated lipid A molecules. Biochemistry 2010; 49:8325-37. [PMID: 20795687 DOI: 10.1021/bi101253s] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The lipid A moiety of Escherichia coli lipopolysaccharide is a hexaacylated disaccharide of glucosamine that is phosphorylated at the 1 and 4' positions. Expression of the Francisella novicida lipid A 1-phosphatase FnLpxE in E. coli results in dephosphorylation of the lipid A proximal unit. Coexpression of FnLpxE and the Rhizobium leguminosarum lipid A oxidase RlLpxQ in E. coli converts much of the proximal glucosamine to 2-amino-2-deoxygluconate. Expression of the F. novicida lipid A 4'-phosphatase FnLpxF in wild-type E. coli has no effect because FnLpxF cannot dephosphorylate hexaacylated lipid A. However, expression of FnLpxF in E. coli lpxM mutants, which synthesize pentaacylated lipid A lacking the secondary 3'-myristate chain, causes extensive 4'-dephosphorylation. Coexpression of FnLpxE and FnLpxF in lpxM mutants results in massive accumulation of lipid A species lacking both phosphate groups, and introduction of RlLpxQ generates phosphate-free lipid A variants containing 2-amino-2-deoxygluconate. The proposed lipid A structures were confirmed by electrospray ionization mass spectrometry. Strains with 4'-dephosphorylated lipid A display increased polymyxin resistance. Heptose-deficient mutants of E. coli lacking both the 1- and 4'-phosphate moieties are viable on plates but sensitive to CaCl(2). Our methods for reengineering lipid A structure may be useful for generating novel vaccines and adjuvants.
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Affiliation(s)
- Brian O Ingram
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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30
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Chung HS, Raetz CRH. Interchangeable domains in the Kdo transferases of Escherichia coli and Haemophilus influenzae. Biochemistry 2010; 49:4126-37. [PMID: 20394418 DOI: 10.1021/bi100343e] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Kdo(2)-lipid A, a conserved substructure of lipopolysaccharide, plays critical roles in Gram-negative bacterial survival and interaction with host organisms. Inhibition of Kdo biosynthesis in Escherichia coli results in cell death and accumulation of the tetra-acylated precursor lipid IV(A). E. coli KdtA (EcKdtA) is a bifunctional enzyme that transfers two Kdo units from two CMP-Kdo molecules to lipid IV(A). In contrast, Haemophilus influenzae KdtA (HiKdtA) transfers only one Kdo unit. E. coli CMR300, which lacks Kdo transferase because of a deletion in kdtA, can be rescued to grow in broth at 37 degrees C if multiple copies of msbA are provided in trans. MsbA, the inner membrane transporter for nascent lipopolysaccharide, prefers hexa-acylated to tetra-acylated lipid A, but with the excess MsbA present in CMR300, lipid IV(A) is efficiently exported to the outer membrane. CMR300 is hypersensitive to hydrophobic antibiotics and bile salts and does not grow at 42 degrees C. Expressing HiKdtA in CMR300 results in the accumulation of Kdo-lipid IV(A) in place of lipid IV(A) without suppression of its growth phenotypes at 30 degrees C. EcKdtA restores intact lipopolysaccharide, together with normal antibiotic resistance, detergent resistance, and growth at 42 degrees C. To determine which residues are important for the mono- or bifunctional character of KdtA, protein chimeras were constructed using EcKdtA and HiKdtA. These chimeras, which are catalytically active, were characterized by in vitro assays and in vivo complementation. The N-terminal half of KdtA, especially the first 30 amino acid residues, specifies whether one or two Kdo units are transferred to lipid IV(A).
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Affiliation(s)
- Hak Suk Chung
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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31
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Jiang Y, Morgan-Kiss RM, Campbell JW, Chan CH, Cronan JE. Expression of Vibrio harveyi acyl-ACP synthetase allows efficient entry of exogenous fatty acids into the Escherichia coli fatty acid and lipid A synthetic pathways. Biochemistry 2010; 49:718-26. [PMID: 20028080 DOI: 10.1021/bi901890a] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Although the Escherichia coli fatty acid synthesis (FAS) pathway is the best studied type II fatty acid synthesis system, a major experimental limitation has been the inability to feed intermediates into the pathway in vivo because exogenously supplied free fatty acids are not efficiently converted to the acyl-acyl carrier protein (ACP) thioesters required by the pathway. We report that expression of Vibrio harveyi acyl-ACP synthetase (AasS), a soluble cytosolic enzyme that ligates free fatty acids to ACP to form acyl-ACPs, allows exogenous fatty acids to enter the E. coli fatty acid synthesis pathway. The free fatty acids are incorporated intact and can be elongated or directly incorporated into complex lipids by acyltransferases specific for acyl-ACPs. Moreover, expression of AasS strains and supplementation with the appropriate fatty acid restored growth to E. coli mutant strains that lack essential fatty acid synthesis enzymes. Thus, this strategy provides a new tool for circumventing the loss of enzymes essential for FAS function.
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Affiliation(s)
- Yanfang Jiang
- Department of Microbiology, University of Illinois, Urbana, Illinois 61801, USA
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32
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Ingram BO, Sohlenkamp C, Geiger O, Raetz CRH. Altered lipid A structures and polymyxin hypersensitivity of Rhizobium etli mutants lacking the LpxE and LpxF phosphatases. Biochim Biophys Acta Mol Cell Biol Lipids 2010; 1801:593-604. [PMID: 20153447 DOI: 10.1016/j.bbalip.2010.02.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2009] [Revised: 01/21/2010] [Accepted: 02/01/2010] [Indexed: 01/02/2023]
Abstract
The lipid A of Rhizobium etli, a nitrogen-fixing plant endosymbiont, displays significant structural differences when compared to that of Escherichia coli. An especially striking feature of R. etli lipid A is that it lacks both the 1- and 4'-phosphate groups. The 4'-phosphate moiety of the distal glucosamine unit is replaced with a galacturonic acid residue. The dephosphorylated proximal unit is present as a mixture of the glucosamine hemiacetal and an oxidized 2-aminogluconate derivative. Distinct lipid A phosphatases directed to the 1 or the 4'-positions have been identified previously in extracts of R. etli and Rhizobium leguminosarum. The corresponding structural genes, lpxE and lpxF, respectively, have also been identified. Here, we describe the isolation and characterization of R. etli deletion mutants in each of these phosphatase genes and the construction of a double phosphatase mutant. Mass spectrometry confirmed that the mutant strains completely lacked the wild-type lipid A species and accumulated the expected phosphate-containing derivatives. Moreover, radiochemical analysis revealed that phosphatase activity was absent in membranes prepared from the mutants. Our results indicate that LpxE and LpxF are solely responsible for selectively dephosphorylating the lipid A molecules of R. etli. All the mutant strains showed an increased sensitivity to polymyxin relative to the wild-type. However, despite the presence of altered lipid A species containing one or both phosphate groups, all the phosphatase mutants formed nitrogen-fixing nodules on Phaseolus vulgaris. Therefore, the dephosphorylation of lipid A molecules in R. etli is not required for nodulation but may instead play a role in protecting the bacteria from cationic antimicrobial peptides or other immune responses of plants.
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Affiliation(s)
- Brian O Ingram
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
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33
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Reynolds CM, Raetz CRH. Replacement of lipopolysaccharide with free lipid A molecules in Escherichia coli mutants lacking all core sugars. Biochemistry 2009; 48:9627-40. [PMID: 19754149 DOI: 10.1021/bi901391g] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Escherichia coli mutants deficient in 2-keto-3-deoxy-D-manno-octulosonic acid (Kdo) biosynthesis are conditionally lethal, but their phenotypes are bypassed by certain suppressor mutations or by overexpression of MsbA, the inner membrane flippase for core-lipid A. These strains grow on broth with the tetraacylated precursor lipid IV(A) replacing lipopolysaccharide [Meredith, T. C., et al. (2006) ACS Chem. Biol. 1, 33-42]. Deletion of kdtA, which encodes the Kdo transferase, is possible under these conditions. We now show that lipid IV(A) reaches the outer surface of the outer membrane in these strains, as judged by its accessibility to the lipase PagL. On the assumption that MsbA is optimized to transport penta- or hexaacylated lipid A, we overexpressed the lauroyl- or the myristoyltransferase of lipid A biosynthesis, encoded by lpxL and lpxM, respectively, and demonstrated that kdtA deletion mutants were also viable in this setting. Although E. coli LpxL is stimulated by the presence of the Kdo disaccharide in its acceptor substrate, LpxL does slowly acylate lipid IV(A). Overexpression of LpxL from a plasmid suppressed the lethality of kdtA deletions on nutrient broth at 30 or 37 degrees C without the need for MsbA overproduction. These strains accumulated penta- and hexaacylated free lipid A containing a secondary laurate chain or a laurate and a myristate chain, respectively. Deletion of kdtA in strains overexpressing LpxM accumulated pentaacylated lipid A with a secondary myristate moiety. None of the strains lacking kdtA grew in the presence of bile salts at any temperature or on nutrient broth at 42 degrees C. Our findings show that the main function of Kdo is to provide the right substrates for the acyltransferases LpxL and LpxM, resulting in the synthesis of penta- and hexaacylated lipid A, which is optimal for the MsbA flippase.
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Affiliation(s)
- C Michael Reynolds
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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34
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Söderberg MA, Cianciotto NP. Mediators of lipid A modification, RNA degradation, and central intermediary metabolism facilitate the growth of Legionella pneumophila at low temperatures. Curr Microbiol 2009; 60:59-65. [PMID: 19768502 DOI: 10.1007/s00284-009-9502-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 08/27/2009] [Accepted: 09/02/2009] [Indexed: 11/26/2022]
Abstract
Legionella pneumophila is an aquatic bacterium that is also the agent of Legionnaires' disease pneumonia. Since L. pneumophila is transmitted directly from the environment to the lung, it is important to understand how legionellae survive at low temperatures. To identify genes that are needed for L. pneumophila growth at low temperature, we screened a population of mutagenized legionellae for strains that are specifically impaired for growth at 17 degrees C. From the 7,400 mutants tested, 11 displayed defects ranging from ca. 10-fold to a complete inability to grow at the low temperature. PCR and sequence analysis were then utilized to identify the genes whose loss had compromised growth. The proteins thereby implicated in low-temperature growth included components of the type II secretion system (LspE, LspG, LspH), a lipid A biosynthetic enzyme (LpxP), a ribonuclease (RNAse R), an RNA helicase (CsdA/DeaD), TCA cycle enzymes (citrate synthase), enzymes linked to fatty acid (FadB) or amino acid (aspartate aminotransferase) catabolism, and two putative membrane proteins that were, based upon their sequences, unlike previously characterized proteins. Given the magnitude of their mutant's defect, the aspartate aminotransferase, RNA helicase, and one of the putative membrane proteins were the factors most critical for L. pneumophila low-temperature growth. Thus, L. pneumophila not only employs some of the same processes and factors as other bacteria do in order to survive at low temperatures (e.g., LpxP, CsdA), but it also appears to possess novel modes of cold adaptation.
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Affiliation(s)
- Maria A Söderberg
- Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, IL 60611, USA
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35
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Bartling CM, Raetz CRH. Crystal structure and acyl chain selectivity of Escherichia coli LpxD, the N-acyltransferase of lipid A biosynthesis. Biochemistry 2009; 48:8672-83. [PMID: 19655786 PMCID: PMC2748855 DOI: 10.1021/bi901025v] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
LpxD catalyzes the third step of lipid A biosynthesis, the R-3-hydroxyacyl-ACP-dependent N-acylation of UDP-3-O-(acyl)-alpha-D-glucosamine, and is a target for new antibiotic development. Here we report the 2.6 A crystal structure of the Escherichia coli LpxD homotrimer (EcLpxD). As is the case in Chlamydia trachomatis LpxD (CtLxpD), each EcLpxD chain consists of an N-terminal uridine-binding region, a left-handed parallel beta-helix (LbetaH), and a C-terminal alpha-helical domain. The backbones of the LbetaH domains of the two enzymes are similar, as are the positions of key active site residues. The N-terminal nucleotide binding domains are oriented differently relative to the LbetaH regions, but are similar when overlaid on each other. The orientation of the EcLpxD tripeptide (residues 303-305), connecting the distal end of the LbetaH and the proximal end of the C-terminal helical domains, differs from its counterpart in CtLpxD (residues 311-312); this results in a 120 degrees rotation of the C-terminal domain relative to the LbetaH region in EcLpxD versus CtLpxD. M290 of EcLpxD appears to cap the distal end of a hydrophobic cleft that binds the acyl chain of the R-3-hydroxyacyl-ACP donor substrate. Under standard assay conditions, wild-type EcLpxD prefers R,S-3-hydroxymyristoyl-ACP over R,S-3-hydroxypalmitoyl-ACP by a factor of 3, whereas the M290A mutant has the opposite selectivity. Both wild-type and M290A EcLpxD rescue the conditional lethality of E. coli RL25, a temperature-sensitive strain harboring point mutations in lpxD. Complementation with wild-type EcLpxD restores normal lipid A containing only N-linked hydroxymyristate to RL25 at 42 degrees C, as judged by mass spectrometry, whereas the M290A mutant generates multiple lipid A species containing one or two longer hydroxy fatty acids in place of the usual R-3-hydroxymyristate at positions 2 and 2'.
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Affiliation(s)
- Craig M. Bartling
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710
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36
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Hankins JV, Trent MS. Secondary acylation of Vibrio cholerae lipopolysaccharide requires phosphorylation of Kdo. J Biol Chem 2009; 284:25804-12. [PMID: 19617350 DOI: 10.1074/jbc.m109.022772] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The lipopolysaccharide of Vibrio cholerae has been reported to contain a single 3-deoxy-d-manno-octulosonic acid (Kdo) residue that is phosphorylated. The phosphorylated Kdo sugar further links the hexa-acylated V. cholerae lipid A domain to the core oliogosaccharide and O-antigen. In this report, we confirm that V. cholerae possesses the enzymatic machinery to synthesize a phosphorylated Kdo residue. Further, we have determined that the presence of the phosphate group on the Kdo residue is necessary for secondary acylation in V. cholerae. The requirement for a secondary substituent on the Kdo residue (either an additional Kdo sugar or a phosphate group) was also found to be critical for secondary acylation catalyzed by LpxL proteins from Bordetella pertussis, Escherichia coli, and Haemophilus influenzae. Although three putative late acyltransferase orthologs have been identified in the V. cholerae genome (Vc0212, Vc0213, and Vc1577), only Vc0213 appears to be functional. Vc0213 functions as a myristoyl transferase acylating lipid A at the 2'-position of the glucosamine disaccharide. Generally acyl-ACPs serve as fatty acyl donors for the acyltransferases required for lipopolysaccharide biosynthesis; however, in vitro assays indicate that Vc0213 preferentially utilizes myristoyl-CoA as an acyl donor. This is the first report to biochemically characterize enzymes involved in the biosynthesis of the V. cholerae Kdo-lipid A domain.
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Affiliation(s)
- Jessica V Hankins
- Department of Molecular Biochemistry and Biochemistry, Medical College of Georgia, Augusta, Georgia 30912, USA
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37
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Mamat U, Schmidt H, Munoz E, Lindner B, Fukase K, Hanuszkiewicz A, Wu J, Meredith TC, Woodard RW, Hilgenfeld R, Mesters JR, Holst O. WaaA of the hyperthermophilic bacterium Aquifex aeolicus is a monofunctional 3-deoxy-D-manno-oct-2-ulosonic acid transferase involved in lipopolysaccharide biosynthesis. J Biol Chem 2009; 284:22248-22262. [PMID: 19546212 DOI: 10.1074/jbc.m109.033308] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The hyperthermophile Aquifex aeolicus belongs to the deepest branch in the bacterial genealogy. Although it has long been recognized that this unique Gram-negative bacterium carries genes for different steps of lipopolysaccharide (LPS) formation, data on the LPS itself or detailed knowledge of the LPS pathway beyond the first committed steps of lipid A and 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) synthesis are still lacking. We now report the functional characterization of the thermostable Kdo transferase WaaA from A. aeolicus and provide evidence that the enzyme is monofunctional. Compositional analysis and mass spectrometry of purified A. aeolicus LPS, showing the incorporation of a single Kdo residue as an integral component of the LPS, implicated a monofunctional Kdo transferase in LPS biosynthesis of A. aeolicus. Further, heterologous expression of the A. aeolicus waaA gene in a newly constructed Escherichia coli DeltawaaA suppressor strain resulted in synthesis of lipid IVA precursors substituted with one Kdo sugar. When highly purified WaaA of A. aeolicus was subjected to in vitro assays using mass spectrometry for detection of the reaction products, the enzyme was found to catalyze the transfer of only a single Kdo residue from CMP-Kdo to differently modified lipid A acceptors. The Kdo transferase was capable of utilizing a broad spectrum of acceptor substrates, whereas surface plasmon resonance studies indicated a high selectivity for the donor substrate.
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Affiliation(s)
- Uwe Mamat
- Divisions of Structural Biochemistry, D-23845 Borstel, Germany
| | - Helgo Schmidt
- Divisions of Structural Biochemistry, D-23845 Borstel, Germany; Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, D-23538 Lübeck, Germany
| | - Eva Munoz
- the Institutes of Chemistry, D-23538 Lübeck, Germany
| | - Buko Lindner
- Immunochemistry, Research Center Borstel, Leibniz-Center for Medicine and Biosciences, D-23845 Borstel, Germany
| | - Koichi Fukase
- Department of Chemistry, Graduate School of Science, Osaka University, Osaka 560-0043, Japan
| | | | - Jing Wu
- Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - Timothy C Meredith
- Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - Ronald W Woodard
- Department of Medicinal Chemistry, University of Michigan, Ann Arbor, Michigan 48109
| | - Rolf Hilgenfeld
- Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, D-23538 Lübeck, Germany
| | - Jeroen R Mesters
- Biochemistry, Center for Structural and Cell Biology in Medicine, University of Lübeck, D-23538 Lübeck, Germany
| | - Otto Holst
- Divisions of Structural Biochemistry, D-23845 Borstel, Germany
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Hatzios SK, Schelle MW, Holsclaw CM, Behrens CR, Botyanszki Z, Lin FL, Carlson BL, Kumar P, Leary JA, Bertozzi CR. PapA3 is an acyltransferase required for polyacyltrehalose biosynthesis in Mycobacterium tuberculosis. J Biol Chem 2009; 284:12745-51. [PMID: 19276083 PMCID: PMC2676004 DOI: 10.1074/jbc.m809088200] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mycobacterium tuberculosis possesses an unusual cell wall that is
replete with virulence-enhancing lipids. One cell wall molecule unique to
pathogenic M. tuberculosis is polyacyltrehalose (PAT), a
pentaacylated, trehalose-based glycolipid. Little is known about the
biosynthesis of PAT, although its biosynthetic gene cluster has been
identified and found to resemble that of the better studied M.
tuberculosis cell wall component sulfolipid-1. In this study, we sought
to elucidate the function of papA3, a gene from the PAT locus
encoding a putative acyltransferase. To determine whether PapA3 participates
in PAT assembly, we expressed the protein heterologously and evaluated its
acyltransferase activity in vitro. The purified enzyme catalyzed the
sequential esterification of trehalose with two palmitoyl groups, generating a
diacylated product similar to the 2,3-diacyltrehalose glycolipids of M.
tuberculosis. Notably, PapA3 was selective for trehalose; no activity was
observed with other structurally related disaccharides. Disruption of the
papA3 gene from M. tuberculosis resulted in the loss of PAT
from bacterial lipid extracts. Complementation of the mutant strain restored
PAT production, demonstrating that PapA3 is essential for the biosynthesis of
this glycolipid in vivo. Furthermore, we determined that the PAT
biosynthetic machinery has no cross-talk with that for sulfolipid-1 despite
their related structures.
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Affiliation(s)
- Stavroula K Hatzios
- Department of Chemistry and Molecular and Cell Biology, Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA
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Raetz CRH, Guan Z, Ingram BO, Six DA, Song F, Wang X, Zhao J. Discovery of new biosynthetic pathways: the lipid A story. J Lipid Res 2008; 50 Suppl:S103-8. [PMID: 18974037 DOI: 10.1194/jlr.r800060-jlr200] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The outer monolayer of the outer membrane of Gram-negative bacteria consists of the lipid A component of lipopolysaccharide (LPS), a glucosamine-based saccharolipid that is assembled on the inner surface of the inner membrane. The first six enzymes of the lipid A pathway are required for bacterial growth and are excellent targets for the development of new antibiotics. Following assembly, the ABC transporter MsbA flips nascent LPS to the periplasmic side of the inner membrane, whereupon additional transport proteins direct it to the outer surface of the outer membrane. Depending on the bacterium, various covalent modifications of the lipid A moiety may occur during the transit of LPS to the outer membrane. These extra-cytoplasmic modification enzymes are therefore useful as reporters for monitoring LPS trafficking. Because of its conserved structure in diverse Gram-negative pathogens, lipid A is recognized as foreign by the TLR4/MD2 receptor of the mammalian innate immune system, resulting in rapid macrophage activation and robust cytokine production.
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Affiliation(s)
- Christian R H Raetz
- Department of Biochemistry, Duke University Medical Center, P.O. Box 3711, Durham, NC 27710, USA.
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