201
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The K1 capsular polysaccharide of Acinetobacter baumannii strain 307-0294 is a major virulence factor. Infect Immun 2010; 78:3993-4000. [PMID: 20643860 DOI: 10.1128/iai.00366-10] [Citation(s) in RCA: 229] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Acinetobacter baumannii is a pathogen of increasing medical importance with a propensity to be multidrug resistant, thereby making treatment challenging. Little is known of virulence traits in A. baumannii. To identify virulence factors and potential drug targets, random transposon (Tn) mutants derived from the A. baumannii strain AB307-0294 were screened to identify genes essential for growth in human ascites fluid in vitro, an inflammatory exudative fluid. These studies led to the identification of two genes that were predicted to be required for capsule polymerization and assembly. The first, ptk, encodes a putative protein tyrosine kinase (PTK), and the second, epsA, encodes a putative polysaccharide export outer membrane protein (EpsA). Monoclonal antibodies used in flow cytometric and Western analyses confirmed that these genes are required for a capsule-positive phenotype. A capsule-positive phenotype significantly optimized growth in human ascites fluid, survival in human serum, and survival in a rat soft tissue infection model. Importantly, the clearance of the capsule-minus mutants AB307.30 (ptk mutant, capsule minus) and AB307.45 (epsA mutant, capsule minus) was complete and durable. These data demonstrated that the K1 capsule from AB307-0294 was an important protectin. Further, these data suggested that conserved proteins, which contribute to the capsule-positive phenotype, are potential antivirulence drug targets. Therefore, the results from this study have important biologic and translational implications and, to the best of our knowledge, are the first to address the role of capsule in the pathogenesis of A. baumannii infection.
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202
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Kim TH, Sebastian S, Pinkham JT, Ross RA, Blalock LT, Kasper DL. Characterization of the O-antigen polymerase (Wzy) of Francisella tularensis. J Biol Chem 2010; 285:27839-49. [PMID: 20605777 DOI: 10.1074/jbc.m110.143859] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The O-antigen polymerase of gram-negative bacteria has been difficult to characterize. Herein we report the biochemical and functional characterization of the protein product (Wzy) of the gene annotated as the putative O-antigen polymerase, which is located in the O-antigen biosynthetic locus of Francisella tularensis. In silico analysis (homology searching, hydropathy plotting, and codon usage assessment) strongly suggested that Wzy is an O-antigen polymerase whose function is to catalyze the addition of newly synthesized O-antigen repeating units to a glycolipid consisting of lipid A, inner core polysaccharide, and one repeating unit of the O-polysaccharide (O-PS). To characterize the function of the Wzy protein, a non-polar deletion mutant of wzy was generated by allelic replacement, and the banding pattern of O-PS was observed by immunoblot analysis of whole-cell lysates obtained by SDS-PAGE and stained with an O-PS-specific monoclonal antibody. These immunoblot analyses showed that O-PS of the wzy mutant expresses only one repeating unit of O-antigen. Further biochemical characterization of the subcellular fractions of the wzy mutant demonstrated that (as is characteristic of O-antigen polymerase mutants) the low molecular weight O-antigen accumulates in the periplasm of the mutant. Site-directed mutagenesis based on protein homology and topology, which was carried out to locate a catalytic residue of the protein, showed that modification of specific residues (Gly(176), Asp(177), Gly(323), and Tyr(324)) leads to a loss of O-PS polymerization. Topology models indicate that these amino acids most likely lie in close proximity on the bacterial surface.
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Affiliation(s)
- Tae-Hyun Kim
- Department of Microbiology and Molecular Genetics, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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203
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Abstract
Leptospira is a genus of spirochaetes that includes organisms with a variety of lifestyles ranging from aquatic saprophytes to invasive pathogens. Adaptation to a wide variety of environmental conditions has required leptospires to acquire a large genome and a complex outer membrane with features that are unique among bacteria. The most abundant surface-exposed outer membrane proteins are lipoproteins that are integrated into the lipid bilayer by amino-terminal fatty acids. In contrast to many spirochaetes, the leptospiral outer membrane also includes lipopolysaccharide and many homologues of well-known beta-barrel transmembrane outer membrane proteins. Research on leptospiral transmembrane outer membrane proteins has lagged behind studies of lipoproteins because of their aberrant behaviour by Triton X-114 detergent fractionation. For this reason, transmembrane outer membrane proteins are best characterized by assessing membrane integration and surface exposure. Not surprisingly, some outer membrane proteins that mediate host-pathogen interactions are strongly regulated by conditions found in mammalian host tissues. For example, the leptospiral immunoglobulin-like (Lig) repeat proteins are dramatically induced by osmolarity and mediate interactions with host extracellular matrix proteins. Development of molecular genetic tools are making it possible to finally understand the roles of these and other outer membrane proteins in mechanisms of leptospiral pathogenesis.
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Affiliation(s)
- David A Haake
- Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.Departments of Medicine,Urology,Microbiology, Immunology & Molecular Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA
| | - James Matsunaga
- Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.Departments of Medicine,Urology,Microbiology, Immunology & Molecular Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA
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204
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Korkmaz-Ozkan F, Köster S, Kühlbrandt W, Mäntele W, Yildiz O. Correlation between the OmpG secondary structure and its pH-dependent alterations monitored by FTIR. J Mol Biol 2010; 401:56-67. [PMID: 20561532 DOI: 10.1016/j.jmb.2010.06.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2010] [Revised: 06/01/2010] [Accepted: 06/08/2010] [Indexed: 11/16/2022]
Abstract
The channel activity of the outer-membrane protein G (OmpG) from Escherichia coli is pH-dependent. To investigate the role of the histidine pair His231/His261 in triggering channel opening and closing, we mutated both histidines to alanines and cysteines. Fourier transform infrared spectra revealed that the OmpG mutants stay-independent of pH-in an open conformation. Temperature ramp experiments indicate that the mutants are as stable as the open state of wild-type OmpG. The X-ray structure of the alanine-substituted OmpG mutant obtained at pH 6.5 confirms the constitutively open conformation. Compared to previous structures of the wild-type protein in the open and closed conformation, the mutant structure shows a difference in the extracellular loop L6 connecting beta-strands S12 and S13. A deletion of amino acids 220-228, which are thought to block the channel at low pH in wild-type OmpG, indicates conformational changes, which might be triggered by His231/His261.
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Affiliation(s)
- Filiz Korkmaz-Ozkan
- Institute of Biophysics, Goethe-University, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main, Germany
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205
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Teriete P, Yao Y, Kolodzik A, Yu J, Song H, Niederweis M, Marassi FM. Mycobacterium tuberculosis Rv0899 adopts a mixed alpha/beta-structure and does not form a transmembrane beta-barrel. Biochemistry 2010; 49:2768-77. [PMID: 20199110 DOI: 10.1021/bi100158s] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The membrane protein Rv0899 (OmpATb) from Mycobacterium tuberculosis, has been proposed to act as an outer membrane porin and to contribute to the bacterium's adaptation to the acidic environment of the phagosome during infection. The gene is restricted to pathogenic mycobacteria and, thus, is an attractive candidate for the development of anti-tuberculosis chemotherapy. The 326-residue protein contains three domains: an N-terminal domain (residues 1-72) that includes a sequence of 20 hydrophobic amino acids required for membrane translocation, a central B domain (residues 73-200) with homology to the conserved putative lipid-binding BON (bacterial OsmY and nodulation) superfamily, and a C domain (residues 201-326) with homology to the OmpA-C-like superfamily of periplasmic peptidoglycan-binding sequences, found in several types of bacterial membrane proteins, including in the C-terminus of the Escherichia coli outer membrane protein OmpA. We have characterized the structure and dynamics of the B and C domains and have determined the three-dimensional structure of the B domain. Rv0899 does not form a transmembrane beta-barrel. Residues 73-326 form a mixed alpha/beta-globular structure, encompassing two independently folded modules corresponding to the B and C domains connected by a flexible linker. The B domain folds with three parallel/antiparallel alpha-helices packed against six parallel/antiparallel beta-strands that form a flat beta-sheet. The core is hydrophobic, while the exterior is polar and predominantly acidic. The structure of a BON homology domain is revealed here for the first time. In light of this unexpected structure, it is hard to reconcile an outer membrane porin activity with the central domain of the protein. The structure of the B domain and the overall architecture of the protein suggest alternative modes of membrane association.
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Affiliation(s)
- Peter Teriete
- Sanford Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
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206
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Abstract
Bacteria produce a remarkable range of surface and secreted polysaccharides. Two pathways have been defined for the biosynthesis and export of capsular polysaccharides and exopolysaccharides in Gram-negative bacteria. A structure of AlgK described in this issue provides structural insight into a third previously unrecognized pathway associated with important biopolymers (Keiski et al., 2010).
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207
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Bacterial Adaptor Membrane Fusion Proteins and the Structurally Dissimilar Outer Membrane Auxiliary Proteins Have Exchanged Central Domains in alpha-Proteobacteria. Int J Microbiol 2010; 2010:589391. [PMID: 20379386 PMCID: PMC2850547 DOI: 10.1155/2010/589391] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2009] [Accepted: 01/31/2010] [Indexed: 12/03/2022] Open
Abstract
Transport systems frequently include auxiliary proteins that perform subfunctions within the transporter protein complex. Two such proteins found in Gram-negative bacteria are the Membrane Fusion Proteins (MFPs) and the Outer Membrane Auxiliary (OMA) proteins. We here demonstrate that OMAs present in α-proteobacteria (but not in other bacterial types) contain a long α-helical region that is homologous to corresponding regions in the MFPs. The results suggest that during their evolution, OMAs, specifically from α-proteobacteria, exchanged their own α-helical domain for one derived from an MFP. The structural and functional implications of these findings are discussed.
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208
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209
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Abstract
In reviewing the structures of membrane proteins determined up to the end of 2009, we present in words and pictures the most informative examples from each family. We group the structures together according to their function and architecture to provide an overview of the major principles and variations on the most common themes. The first structures, determined 20 years ago, were those of naturally abundant proteins with limited conformational variability, and each membrane protein structure determined was a major landmark. With the advent of complete genome sequences and efficient expression systems, there has been an explosion in the rate of membrane protein structure determination, with many classes represented. New structures are published every month and more than 150 unique membrane protein structures have been determined. This review analyses the reasons for this success, discusses the challenges that still lie ahead, and presents a concise summary of the key achievements with illustrated examples selected from each class.
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210
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Remmert M, Biegert A, Linke D, Lupas AN, Söding J. Evolution of outer membrane beta-barrels from an ancestral beta beta hairpin. Mol Biol Evol 2010; 27:1348-58. [PMID: 20106904 DOI: 10.1093/molbev/msq017] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Outer membrane beta-barrels (OMBBs) are the major class of outer membrane proteins from Gram-negative bacteria, mitochondria, and plastids. Their transmembrane domains consist of 8-24 beta-strands forming a closed, barrel-shaped beta-sheet around a central pore. Despite their obvious structural regularity, evidence for an origin by duplication or for a common ancestry has not been found. We use three complementary approaches to show that all OMBBs from Gram-negative bacteria evolved from a single, ancestral beta beta hairpin. First, we link almost all families of known single-chain bacterial OMBBs with each other through transitive profile searches. Second, we identify a clear repeat signature in the sequences of many OMBBs in which the repeating sequence unit coincides with the structural beta beta hairpin repeat. Third, we show that the observed sequence similarity between OMBB hairpins cannot be explained by structural or membrane constraints on their sequences. The third approach addresses a longstanding problem in protein evolution: how to distinguish between a very remotely homologous relationship and the opposing scenario of "sequence convergence." The origin of a diverse group of proteins from a single hairpin module supports the hypothesis that, around the time of transition from the RNA to the protein world, proteins arose by amplification and recombination of short peptide modules that had previously evolved as cofactors of RNAs.
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Affiliation(s)
- M Remmert
- Department of Biochemistry, Gene Center Munich and Center for Integrated Protein Science (CIPSM), Ludwig-Maximilians-Universtät München, Munich, Germany
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211
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Repositioning of transmembrane alpha-helices during membrane protein folding. J Mol Biol 2010; 397:190-201. [PMID: 20109468 DOI: 10.1016/j.jmb.2010.01.042] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Revised: 01/19/2010] [Accepted: 01/19/2010] [Indexed: 11/30/2022]
Abstract
We have determined the optimal placement of individual transmembrane helices in the Pyrococcus horikoshii Glt(Ph) glutamate transporter homolog in the membrane. The results are in close agreement with theoretical predictions based on hydrophobicity, but do not, in general, match the known three-dimensional structure, suggesting that transmembrane helices can be repositioned relative to the membrane during folding and oligomerization. Theoretical analysis of a database of membrane protein structures provides additional support for this idea. These observations raise new challenges for the structure prediction of membrane proteins and suggest that the classical two-stage model often used to describe membrane protein folding needs to be modified.
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212
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Mycobacterial outer membranes: in search of proteins. Trends Microbiol 2010; 18:109-16. [PMID: 20060722 DOI: 10.1016/j.tim.2009.12.005] [Citation(s) in RCA: 156] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Revised: 12/01/2009] [Accepted: 12/09/2009] [Indexed: 01/29/2023]
Abstract
The cell wall is a major virulence factor of Mycobacterium tuberculosis and contributes to its intrinsic drug resistance. Recently, cryo-electron microscopy showed that mycobacterial cell wall lipids form an unusual outer membrane. Identification of the components of the uptake and secretion machinery across this membrane will be crucial for understanding the physiology and pathogenicity of M. tuberculosis and for the development of better anti-tuberculosis drugs. Although the genome of M. tuberculosis appears to encode over 100 putative outer membrane proteins, only a few have been identified and characterized. Here, we summarize the current knowledge on the structure of the mycobacterial outer membrane and its known proteins. Through comparison to transport processes in Gram-negative bacteria, we highlight several hypothetical outer membrane proteins of M. tuberculosis that await discovery.
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213
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Kowalska K, Soscia C, Combe H, Vasseur P, Voulhoux R, Filloux A. The C-terminal amphipathic α-helix of Pseudomonas aeruginosa PelC outer membrane protein is required for its function. Biochimie 2010; 92:33-40. [DOI: 10.1016/j.biochi.2009.10.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Accepted: 10/14/2009] [Indexed: 11/26/2022]
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214
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Hunt S, Green J, Artymiuk PJ. Hemolysin E (HlyE, ClyA, SheA) and Related Toxins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 677:116-26. [DOI: 10.1007/978-1-4419-6327-7_10] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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215
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Chandran V, Fronzes R, Duquerroy S, Cronin N, Navaza J, Waksman G. Structure of the outer membrane complex of a type IV secretion system. Nature 2009; 462:1011-5. [PMID: 19946264 PMCID: PMC2797999 DOI: 10.1038/nature08588] [Citation(s) in RCA: 248] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Accepted: 10/19/2009] [Indexed: 02/07/2023]
Abstract
Type IV secretion systems are secretion nanomachines spanning the two membranes of Gram-negative bacteria. Three proteins, VirB7, VirB9 and VirB10, assemble into a 1.05 megadalton (MDa) core spanning the inner and outer membranes. This core consists of 14 copies of each of the proteins and forms two layers, the I and O layers, inserting in the inner and outer membrane, respectively. Here we present the crystal structure of a approximately 0.6 MDa outer-membrane complex containing the entire O layer. This structure is the largest determined for an outer-membrane channel and is unprecedented in being composed of three proteins. Unexpectedly, this structure identifies VirB10 as the outer-membrane channel with a unique hydrophobic double-helical transmembrane region. This structure establishes VirB10 as the only known protein crossing both membranes of Gram-negative bacteria. Comparison of the cryo-electron microscopy (cryo-EM) and crystallographic structures points to conformational changes regulating channel opening and closing.
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Affiliation(s)
- Vidya Chandran
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, United Kingdom
| | - Rémi Fronzes
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, United Kingdom
| | - Stéphane Duquerroy
- Institut Pasteur, Unité de Virologie Structurale, Virology Department and CNRS URA 3015, Paris, France
| | - Nora Cronin
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, United Kingdom
| | - Jorge Navaza
- Laboratoire de Microscopie Electronique, Institut de Biologie Structurale J.P. Ebel, 41 rue Jules Horowitz, F-38027 Grenoble Cedex 1, France
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, Malet Street, London WC1E 7HX, United Kingdom
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216
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Punta M, Love J, Handelman S, Hunt JF, Shapiro L, Hendrickson WA, Rost B. Structural genomics target selection for the New York consortium on membrane protein structure. ACTA ACUST UNITED AC 2009; 10:255-68. [PMID: 19859826 PMCID: PMC2780672 DOI: 10.1007/s10969-009-9071-1] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Accepted: 09/30/2009] [Indexed: 01/02/2023]
Abstract
The New York Consortium on Membrane Protein Structure (NYCOMPS), a part of the Protein Structure Initiative (PSI) in the USA, has as its mission to establish a high-throughput pipeline for determination of novel integral membrane protein structures. Here we describe our current target selection protocol, which applies structural genomics approaches informed by the collective experience of our team of investigators. We first extract all annotated proteins from our reagent genomes, i.e. the 96 fully sequenced prokaryotic genomes from which we clone DNA. We filter this initial pool of sequences and obtain a list of valid targets. NYCOMPS defines valid targets as those that, among other features, have at least two predicted transmembrane helices, no predicted long disordered regions and, except for community nominated targets, no significant sequence similarity in the predicted transmembrane region to any known protein structure. Proteins that feed our experimental pipeline are selected by defining a protein seed and searching the set of all valid targets for proteins that are likely to have a transmembrane region structurally similar to that of the seed. We require sequence similarity aligning at least half of the predicted transmembrane region of seed and target. Seeds are selected according to their feasibility and/or biological interest, and they include both centrally selected targets and community nominated targets. As of December 2008, over 6,000 targets have been selected and are currently being processed by the experimental pipeline. We discuss how our target list may impact structural coverage of the membrane protein space.
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Affiliation(s)
- Marco Punta
- Department of Biochemistry and Molecular Biophysics, Columbia University, 630 West 168th Street, New York, NY, 10032, USA.
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217
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McLuskey K, Roszak AW, Zhu Y, Isaacs NW. Crystal structures of all-alpha type membrane proteins. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:723-55. [DOI: 10.1007/s00249-009-0546-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2009] [Revised: 08/19/2009] [Accepted: 08/26/2009] [Indexed: 01/05/2023]
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218
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Lu T, Tan H, Lee D, Chen G, Jia Z. New insights into the activation of Escherichia coli tyrosine kinase revealed by molecular dynamics simulation and biochemical analysis. Biochemistry 2009; 48:7986-95. [PMID: 19634880 DOI: 10.1021/bi900811p] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Escherichia coli tyrosine kinase (Etk) regulates the export of pathogenic capsular polysaccharide (CPS) by intermolecularly autophosphorylating its C-terminal tyrosine cluster. The kinase Etk, however, needs to be first activated by the intramolecular phosphorylation of a tyrosine residue, Y574, next to the active site. The recently determined structure of Etk shows that dephosphorylated Y574 blocks the active site and prevents substrate access. After phosphorylation, the negatively charged P-Y574 side chain was previously postulated to flip out to associate with a positively charged R614, unblocking the active site. This proposed activation is unique among protein kinases; however, there is no direct structural evidence in support of this hypothesis. In this paper, we carried out molecular dynamics simulation, mutagenesis, and biochemical analysis to study the activation mechanism of Etk. Our simulation results are in excellent agreement with the proposed molecular switch involving P-Y574 and R614 in the activation of Etk. Further, we show that a previously unidentified residue, R572, modulates the rotation of the P-Y574 side chain through electrostatic interaction, slowing down the opening of the active site. Our enzymatic assays demonstrate that the R572A mutant of Etk possesses significantly increased kinase activity, providing direct experimental support for the unique activation mechanism of Etk. In addition, the simulation of the Etk Y574F mutant predicted short periods of unblocked active site by Y574F, in good agreement with the low kinase activity of this mutant. The C-terminal substrate peptide and the nucleotide cofactor were also docked into the active site, and their implications are discussed.
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Affiliation(s)
- Tian Lu
- Department of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China
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219
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Shu HY, Fung CP, Liu YM, Wu KM, Chen YT, Li LH, Liu TT, Kirby R, Tsai SF. Genetic diversity of capsular polysaccharide biosynthesis in Klebsiella pneumoniae clinical isolates. MICROBIOLOGY-SGM 2009; 155:4170-4183. [PMID: 19744990 DOI: 10.1099/mic.0.029017-0] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Klebsiella pneumoniae is an enteric pathogen causing community-acquired and hospital-acquired infections in humans. Epidemiological studies have revealed significant diversity in capsular polysaccharide (CPS) type and clinical manifestation of K. pneumoniae infection in different geographical areas of the world. We have sequenced the capsular polysaccharide synthesis (cps) region of seven clinical isolates and compared the sequences with the publicly available cps sequence data of five strains: NTUH-K2044 (K1 serotype), Chedid (K2 serotype), MGH78578 (K52 serotype), A1142 (K57 serotype) and A1517. Among all strains, six genes at the 5' end of the cps clusters that encode proteins for CPS transportation and processing at the bacterial surface are highly similar to each other. The central region of the cps gene clusters, which encodes proteins for polymerization and assembly of the CPS subunits, is highly divergent. Based on the collected sequence, we found that either the wbaP gene or the wcaJ gene exists in a given K. pneumoniae strain, suggesting that there is a major difference in the CPS biosynthesis pathway and that the K. pneumoniae strains can be classified into at least two distinct groups. All isolates contain gnd, encoding gluconate-6-phosphate dehydrogenase, at the 3' end of the cps gene clusters. The rmlBADC genes were found in CPS K9-positive, K14-positive and K52-positive strains, while manC and manB were found in K1, K2, K5, K14, K62 and two undefined strains. Our data indicate that, while overall genomic organization is similar between different pathogenic K. pneumoniae strains, the genetic variation of the sugar moiety and polysaccharide linkage generate the diversity in CPS molecules that could help evade host immune attack.
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Affiliation(s)
- Hung-Yu Shu
- Genome Research Center, National Yang-Ming University, Taipei, Taiwan, ROC.,Department of Bioscience Technology, Chang Jung Christian University, Tainan County, Taiwan, ROC
| | - Chang-Phone Fung
- Institute of Tropical Medicine, School of Medicine, National Yang-Ming University, Taipei, Taiwan, ROC.,Division of Infectious Diseases, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan, ROC
| | - Yen-Ming Liu
- Division of Molecular and Genomic Medicine, National Health Research Institutes, Zhunan, Miaoli County, Taiwan, ROC
| | - Keh-Ming Wu
- Institute of Biomedical Informatics, National Yang-Ming University, Taipei, Taiwan, ROC.,Division of Molecular and Genomic Medicine, National Health Research Institutes, Zhunan, Miaoli County, Taiwan, ROC
| | - Ying-Tsong Chen
- Division of Molecular and Genomic Medicine, National Health Research Institutes, Zhunan, Miaoli County, Taiwan, ROC
| | - Ling-Hui Li
- Division of Molecular and Genomic Medicine, National Health Research Institutes, Zhunan, Miaoli County, Taiwan, ROC
| | - Tze-Tze Liu
- Genome Research Center, National Yang-Ming University, Taipei, Taiwan, ROC
| | - Ralph Kirby
- Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan, ROC
| | - Shih-Feng Tsai
- Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan, ROC.,Division of Molecular and Genomic Medicine, National Health Research Institutes, Zhunan, Miaoli County, Taiwan, ROC.,Genome Research Center, National Yang-Ming University, Taipei, Taiwan, ROC.,Institute of Biomedical Informatics, National Yang-Ming University, Taipei, Taiwan, ROC
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220
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Walther DM, Rapaport D, Tommassen J. Biogenesis of beta-barrel membrane proteins in bacteria and eukaryotes: evolutionary conservation and divergence. Cell Mol Life Sci 2009; 66:2789-804. [PMID: 19399587 PMCID: PMC2724633 DOI: 10.1007/s00018-009-0029-z] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 03/26/2009] [Accepted: 04/01/2009] [Indexed: 01/01/2023]
Abstract
Membrane-embedded beta-barrel proteins span the membrane via multiple amphipathic beta-strands arranged in a cylindrical shape. These proteins are found in the outer membranes of Gram-negative bacteria, mitochondria and chloroplasts. This situation is thought to reflect the evolutionary origin of mitochondria and chloroplasts from Gram-negative bacterial endosymbionts. beta-barrel proteins fulfil a variety of functions; among them are pore-forming proteins that allow the flux of metabolites across the membrane by passive diffusion, active transporters of siderophores, enzymes, structural proteins, and proteins that mediate protein translocation across or insertion into membranes. The biogenesis process of these proteins combines evolutionary conservation of the central elements with some noticeable differences in signals and machineries. This review summarizes our current knowledge of the functions and biogenesis of this special family of proteins.
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Affiliation(s)
- Dirk M. Walther
- Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany
- Department of Proteomics and Signal Transduction, Max-Planck-Institute of Biochemistry, 82152 Martinsried, Germany
| | - Doron Rapaport
- Interfaculty Institute for Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany
| | - Jan Tommassen
- Department of Molecular Microbiology, Institute of Biomembranes, Utrecht University, 3584 CH Utrecht, The Netherlands
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221
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Kaiser D. Are there lateral as well as polar engines for A-motile gliding in myxobacteria? J Bacteriol 2009; 191:5336-41. [PMID: 19581372 PMCID: PMC2725618 DOI: 10.1128/jb.00486-09] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Dale Kaiser
- Departments of Biochemistry and Developmental Biology, Stanford University School of Medicine, Stanford, California 94305-5329, USA.
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222
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Kohayagawa Y, Nakao K, Ushita M, Niino N, Koshizaki M, Yamamori Y, Tokuyasu Y, Fukushima H. Pyogenic liver abscess caused by Klebsiella pneumoniae genetic serotype K1 in Japan. J Infect Chemother 2009; 15:248-51. [PMID: 19688245 DOI: 10.1007/s10156-009-0695-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Accepted: 04/06/2009] [Indexed: 11/28/2022]
Abstract
Pyogenic liver abscess caused by Klebsiella pneumoniae is an emerging disease worldwide, and we know the serotype K1 strain to be the most virulent strain. We report a Japanese case of septic pyogenic liver abscess caused by K. pneumoniae genetic serotype K1. A 60-year old man presented at our hospital in a state of cardiopulmonary arrest. From the patient's chief complaint of chest pain, we suspected acute coronary syndrome, i.e., acute myocardial infarction. We used extracorporeal circulation and checked coronary angiography, but the 75% stenosis by itself could not adequately account for the patient's critical condition. The patient's laboratory data indicated multiple organ failure. The patient's condition did not improve while in intensive care and he died 20 h after the onset of the cardiopulmonary arrest. Pathological autopsy later showed colliquative necrosis in the deltoid and left greater pectoral muscles, as well as liver abscesses. The patient's blood, gastric juice, and stool cultures all grew a Gram-negative bacillus identified as Klebsiella pneumoniae. We also performed capsular polysaccharide synthesis (cps) genotyping by polymerase chain reaction for the detection of K serotype-specific alleles at the wzx and wzy loci. The result indicated that wzx_K1 and wzy_K1 were positive. This is the first reported Japanese case of septic pyogenic liver abscess caused by K. pneumoniae genetic serotype K1.
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Affiliation(s)
- Yoshitaka Kohayagawa
- Department of Critical Care and Emergency Medicine, Shimane Prefectural Central Hospital, 4-1-1 Himebara, Izumo, Shimane, 693-8555, Japan.
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223
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Abstract
The capsule is a cell surface structure composed of long-chain polysaccharides that envelops many isolates of Escherichia coli. It protects the cell against host defenses or physical environmental stresses, such as desiccation. The component capsular polysaccharides (CPSs) are major surface antigens in E. coli. They are named K antigens (after the German word Kapsel). Due to variations in CPS structures, more than 80 serologically unique K antigens exist in E. coli. Despite the hypervariability in CPS structures, only two capsule-assembly strategies exist in E. coli. These have led to the assignment of group 1 and group 2 capsules, and many of the key elements of the corresponding assembly pathways have been resolved. Structural features, as well as genetic and regulatory variations, give rise to additional groups 3 and 4. These employ the same biosynthesis processes described in groups 2 and 1, respectively. Each isolate possesses a distinctive set of cytosolic and inner-membrane enzymes, which generate a precise CPS structure, defining a given K serotype. Once synthesized, a multiprotein complex is needed to translocate the nascent CPS across the Gram-negative cell envelope to the outer surface of the outer membrane, where the capsule structure is assembled. While the translocation machineries for group 1 and group 2 CPSs are fundamentally different from one another, they possess no specificity for a given CPS structure. Each is conserved in all isolates producing capsules belonging to a particular group.
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224
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Hagelueken G, Huang H, Mainprize IL, Whitfield C, Naismith JH. Crystal structures of Wzb of Escherichia coli and CpsB of Streptococcus pneumoniae, representatives of two families of tyrosine phosphatases that regulate capsule assembly. J Mol Biol 2009; 392:678-88. [PMID: 19616007 PMCID: PMC2777267 DOI: 10.1016/j.jmb.2009.07.026] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Revised: 07/07/2009] [Accepted: 07/09/2009] [Indexed: 12/11/2022]
Abstract
Many Gram-positive and Gram-negative bacteria utilize polysaccharide surface layers called capsules to evade the immune system; consequently, the synthesis and export of the capsule are a potential therapeutic target. In Escherichia coli K-30, the integral membrane tyrosine autokinase Wzc and the cognate phosphatase Wzb have been shown to be key for both synthesis and assembly of capsular polysaccharides. In the Gram-positive bacterium Streptococcus pneumoniae, the CpsCD complex is analogous to Wzc and the phosphatase CpsB is the corresponding cognate phosphatase. The phosphatases are known to dephosphorylate their corresponding autokinases, yet despite their functional equivalence, they share no sequence homology. We present the structure of Wzb in complex with phosphate and high-resolution structures of apo-CpsB and a phosphate-complexed CpsB. We show that both proteins are active toward Wzc and thereby demonstrate that CpsB is not specific for CpsCD. CpsB is a novel enzyme and represents the first solved structure of a tyrosine phosphatase from a Gram-positive bacterium. Wzb and CpsB have completely different structures, suggesting that they must operate by very different mechanisms. Although the mechanism of Wzb can be inferred from previous studies, CpsB appears to have a tyrosine phosphatase mechanism not observed before. We propose a chemical mechanism for CpsB based on site-directed mutagenesis and structural data.
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Affiliation(s)
- Gregor Hagelueken
- Centre for Biomolecular Sciences, The University of St. Andrews, Fife KY16 9RH, UK
| | - Hexian Huang
- Centre for Biomolecular Sciences, The University of St. Andrews, Fife KY16 9RH, UK
| | - Iain L. Mainprize
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - Chris Whitfield
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
| | - James H. Naismith
- Centre for Biomolecular Sciences, The University of St. Andrews, Fife KY16 9RH, UK
- Corresponding author.
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225
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Role of periplasmic chaperones and BamA (YaeT/Omp85) in folding and secretion of intimin from enteropathogenic Escherichia coli strains. J Bacteriol 2009; 191:5169-79. [PMID: 19525348 DOI: 10.1128/jb.00458-09] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Intimin is a bacterial adhesin located on the surface of enteropathogenic Escherichia coli and other related bacteria that is believed to self-translocate across the outer membrane (OM), and therefore it has been regarded as a member of the type V secretion system (T5SS), which includes classical autotransporters (ATs). However, intimin has few structural similarities to classical ATs and an opposite topology with an OM-embedded N region and a secreted C region. Since the actual secretion mechanism of intimin is unknown, we investigated intimin biogenesis by analyzing its requirement of periplasmic chaperones (DsbA, SurA, Skp, and DegP) and of OM protein BamA (YaeT/Omp85) for folding, OM insertion, and translocation. Using full-length and truncated intimin polypeptides, we demonstrate that DsbA catalyzes the formation of a disulfide bond in the D3 lectin-like domain of intimin in the periplasm, indicating that this secreted C-terminal domain is at least partially folded prior to its translocation across the OM. We also show that SurA chaperone plays the major role for periplasmic transport and folding of the N region of intimin, whereas the parallel pathway made by Skp and DegP chaperones plays a secondary role in this process. Further, we demonstrate that BamA is essential for the insertion of the N region of intimin in the OM and that the protease activity of DegP participates in the degradation of misfolded intimin. The significance of these findings for a BamA-dependent secretion mechanism of intimin is discussed in the context of T5SSs.
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226
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227
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Tamang DG, Rabus R, Barabote RD, Saier MH. Comprehensive analyses of transport proteins encoded within the genome of "Aromatoleum aromaticum" strain EbN1. J Membr Biol 2009; 229:53-90. [PMID: 19506936 DOI: 10.1007/s00232-009-9168-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2008] [Accepted: 03/31/2009] [Indexed: 10/20/2022]
Abstract
The denitrifying bacterium "Aromatoleum aromaticum" strain EbN1 is specialized for the aerobic utilization of aromatic compounds including crude oil constituents. We here report whole-genome analyses for potential transport proteins in A. aromaticum strain EbN1. This organism encodes very few transporters for simple sugars and most other common carbon sources. However, up to 28% of its putative transporters may act on fairly hydrophobic aromatic and aliphatic compounds. We categorize the putative transporters encoded within the genome, assign them to recognized families, and propose their preferred substrates. The bioinformatic data are correlated with available metabolic information to obtain an integrated view of the metabolic network of A. aromaticum strain EbN1. The results thus indicate that this organism possesses a disproportionately large percentage of transporters for the uptake and efflux of hydrophobic and amphipathic aromatic and aliphatic compounds compared with previously analyzed organisms. We predict that these findings will have important implications for our ecophysiological understanding of bioremediation.
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Affiliation(s)
- Dorjee G Tamang
- Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093-0116, USA
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228
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Tastan O, Klein-Seetharaman J, Meirovitch H. The effect of loops on the structural organization of alpha-helical membrane proteins. Biophys J 2009; 96:2299-312. [PMID: 19289056 DOI: 10.1016/j.bpj.2008.12.3894] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2008] [Revised: 11/25/2008] [Accepted: 12/01/2008] [Indexed: 11/30/2022] Open
Abstract
Loops connecting the transmembrane (TM) alpha-helices in membrane proteins are expected to affect the structural organization of the thereby connected helices and the helical bundles as a whole. This effect, which has been largely ignored previously, is studied here by analyzing the x-ray structures of 41 alpha-helical membrane proteins. First we define the loop flexibility ratio, R, and find that 53% of the loops are stretched, where a stretched loop constrains the distance between the two connected helices. The significance of this constraining effect is supported by experiments carried out with bacteriorhodopsin and rhodopsin, in which cutting or eliminating their (predominately stretched) loops has led to a decrease in protein stability, and for rhodopsin, in most cases, also to the destruction of the structure. We show that for nonstretched loops in the extramembranous regions, the fraction of hydrophobic residues is comparable to that for soluble proteins; furthermore (as is also the case for soluble proteins), the hydrophobic residues in these regions are preferentially buried. This is expected to lead to the compact structural organization of the loops, which is transferred to the TM helices, causing them to assemble. We argue that a soluble protein complexed with a membrane protein similarly promotes compactness; other properties of such complexes are also studied. We calculate complementary attractive interactions between helices, including hydrogen bonds and van der Waals interactions of sequential motifs, such as GXXXG. The relative and combined effects of all these factors on the association of the TM helices are discussed and protein structures with only a few of these factors are analyzed. Our study emphasizes the need for classifying membrane proteins into groups according to structural organization. This classification should be considered when procedures for structural analysis or prediction are developed and applied. Detailed analysis of each structure is provided at http://flan.blm.cs.cmu.edu/memloop/
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Affiliation(s)
- Oznur Tastan
- Language Technologies Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
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229
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Kutik S, Stroud DA, Wiedemann N, Pfanner N. Evolution of mitochondrial protein biogenesis. Biochim Biophys Acta Gen Subj 2009; 1790:409-15. [DOI: 10.1016/j.bbagen.2009.04.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2008] [Revised: 04/02/2009] [Accepted: 04/06/2009] [Indexed: 02/08/2023]
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230
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Remmert M, Linke D, Lupas AN, Söding J. HHomp--prediction and classification of outer membrane proteins. Nucleic Acids Res 2009; 37:W446-51. [PMID: 19429691 PMCID: PMC2703889 DOI: 10.1093/nar/gkp325] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Outer membrane proteins (OMPs) are the transmembrane proteins found in the outer membranes of Gram-negative bacteria, mitochondria and plastids. Most prediction methods have focused on analogous features, such as alternating hydrophobicity patterns. Here, we start from the observation that almost all beta-barrel OMPs are related by common ancestry. We identify proteins as OMPs by detecting their homologous relationships to known OMPs using sequence similarity. Given an input sequence, HHomp builds a profile hidden Markov model (HMM) and compares it with an OMP database by pairwise HMM comparison, integrating OMP predictions by PROFtmb. A crucial ingredient is the OMP database, which contains profile HMMs for over 20,000 putative OMP sequences. These were collected with the exhaustive, transitive homology detection method HHsenser, starting from 23 representative OMPs in the PDB database. In a benchmark on TransportDB, HHomp detects 63.5% of the true positives before including the first false positive. This is 70% more than PROFtmb, four times more than BOMP and 10 times more than TMB-Hunt. In Escherichia coli, HHomp identifies 57 out of 59 known OMPs and correctly assigns them to their functional subgroups. HHomp can be accessed at http://toolkit.tuebingen.mpg.de/hhomp.
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Affiliation(s)
- Michael Remmert
- Department of Protein Evolution, Max-Planck-Institute for Developmental Biology, Spemannstrasse 35, 72076 Tübingen, Germany
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231
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Pivotal roles of the outer membrane polysaccharide export and polysaccharide copolymerase protein families in export of extracellular polysaccharides in gram-negative bacteria. Microbiol Mol Biol Rev 2009; 73:155-77. [PMID: 19258536 PMCID: PMC2650888 DOI: 10.1128/mmbr.00024-08] [Citation(s) in RCA: 185] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Many bacteria export extracellular polysaccharides (EPS) and capsular polysaccharides (CPS). These polymers exhibit remarkably diverse structures and play important roles in the biology of free-living, commensal, and pathogenic bacteria. EPS and CPS production represents a major challenge because these high-molecular-weight hydrophilic polymers must be assembled and exported in a process spanning the envelope, without compromising the essential barrier properties of the envelope. Emerging evidence points to the existence of molecular scaffolds that perform these critical polymer-trafficking functions. Two major pathways with different polymer biosynthesis strategies are involved in the assembly of most EPS/CPS: the Wzy-dependent and ATP-binding cassette (ABC) transporter-dependent pathways. They converge in an outer membrane export step mediated by a member of the outer membrane auxiliary (OMA) protein family. OMA proteins form outer membrane efflux channels for the polymers, and here we propose the revised name outer membrane polysaccharide export (OPX) proteins. Proteins in the polysaccharide copolymerase (PCP) family have been implicated in several aspects of polymer biogenesis, but there is unequivocal evidence for some systems that PCP and OPX proteins interact to form a trans-envelope scaffold for polymer export. Understanding of the precise functions of the OPX and PCP proteins has been advanced by recent findings from biochemistry and structural biology approaches and by parallel studies of other macromolecular trafficking events. Phylogenetic analyses reported here also contribute important new insight into the distribution, structural relationships, and function of the OPX and PCP proteins. This review is intended as an update on progress in this important area of microbial cell biology.
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232
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A conserved structural motif mediates formation of the periplasmic rings in the type III secretion system. Nat Struct Mol Biol 2009; 16:468-76. [PMID: 19396170 DOI: 10.1038/nsmb.1603] [Citation(s) in RCA: 157] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Accepted: 04/08/2009] [Indexed: 11/09/2022]
Abstract
The type III secretion system (T3SS) is a macromolecular 'injectisome' that allows bacterial pathogens to transport virulence proteins into the eukaryotic host cell. This macromolecular complex is composed of connected ring-like structures that span both bacterial membranes. The crystal structures of the periplasmic domain of the outer membrane secretin EscC and the inner membrane protein PrgH reveal the conservation of a modular fold among the three proteins that form the outer membrane and inner membrane rings of the T3SS. This leads to the hypothesis that this conserved fold provides a common ring-building motif that allows for the assembly of the variably sized outer membrane and inner membrane rings characteristic of the T3SS. Using an integrated structural and experimental approach, we generated ring models for the periplasmic domain of EscC and placed them in the context of the assembled T3SS, providing evidence for direct interaction between the outer membrane and inner membrane ring components and an unprecedented span of the outer membrane secretin.
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233
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Hagelueken G, Ingledew W, Huang H, Petrovic-Stojanovska B, Whitfield C, ElMkami H, Schiemann O, Naismith J. PELDOR Spectroscopy Distance Fingerprinting of the Octameric Outer-Membrane Protein Wza fromEscherichia coli. Angew Chem Int Ed Engl 2009. [DOI: 10.1002/ange.200805758] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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234
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Structure-function relationships of the outer membrane translocon Wza investigated by cryo-electron microscopy and mutagenesis. J Struct Biol 2009; 166:172-82. [PMID: 19236919 DOI: 10.1016/j.jsb.2009.02.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 01/23/2009] [Accepted: 02/15/2009] [Indexed: 11/21/2022]
Abstract
The outer membrane protein Wza, from Escherichia coli K30, forms an octameric complex that is essential for capsular polysaccharide export. Homologs of Wza are widespread in gram-negative bacterial pathogens where capsules are critical virulence determinants. Wza is unusual in that it spans the outer membrane using a barrel composed of amphipathic alpha-helices, rather than being a beta-barrel like almost all other outer membrane channels. The transmembrane helical barrel of Wza also forms the external opening to a hydrophilic translocation pathway that spans the periplasm. Here, we have probed the structure and function of the Wza complex using both cryo-electron microscopy and mutagenesis. The helical barrel structure is stable in detergent micelles under mildly acidic conditions but is destabilized at basic pH, although the overall quaternary structure is retained. Truncation of the C-terminal region that forms the helical barrel by 4 residues has no effect on the ability of Wza to oligomerize and support capsule export, but larger truncations of 18, 24 or 35 amino acids abolish its function. The bulk of the C-terminal domain is essential for the stability and assembly of the E. coli Wza complex.
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235
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Meng G, Fronzes R, Chandran V, Remaut H, Waksman G. Protein oligomerization in the bacterial outer membrane (Review). Mol Membr Biol 2009; 26:136-45. [PMID: 19225986 DOI: 10.1080/09687680802712422] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The formation of homo-oligomeric assemblies is a well-established characteristic of many soluble proteins and enzymes. Oligomerization has been shown to increase protein stability, allow allosteric cooperativity, shape reaction compartments and provide multivalent interaction sites in soluble proteins. In comparison, our understanding of the prevalence and reasons behind protein oligomerization in membrane proteins is relatively sparse. Recent progress in structural biology of bacterial outer membrane proteins has suggested that oligomerization may be as common and versatile as in soluble proteins. Here we review the current understanding of oligomerization in the bacterial outer membrane from a structural and functional point of view.
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Affiliation(s)
- Guoyu Meng
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, London, UK
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236
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Hagelueken G, Ingledew WJ, Huang H, Petrovic-Stojanovska B, Whitfield C, ElMkami H, Schiemann O, Naismith JH. PELDOR spectroscopy distance fingerprinting of the octameric outer-membrane protein Wza from Escherichia coli. Angew Chem Int Ed Engl 2009; 48:2904-6. [PMID: 19294709 PMCID: PMC3312575 DOI: 10.1002/anie.200805758] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Distance fingerprinting: Pulsed electron-electron double resonance spectroscopy (PELDOR) is applied to the octameric membrane protein complex Wza of E. coli. The data yielded a detailed distance fingerprint of its periplasmic region that compares favorably to the crystal structure. These results provide the foundation to study conformation changes from interaction with partner proteins.
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Affiliation(s)
- Gregor Hagelueken
- Centre for Biomolecular Sciences The University of St. Andrews Fife KY16 9RH, UK
| | - W. John Ingledew
- Centre for Biomolecular Sciences The University of St. Andrews Fife KY16 9RH, UK
| | - Hexian Huang
- Centre for Biomolecular Sciences The University of St. Andrews Fife KY16 9RH, UK
| | | | - Chris Whitfield
- Department of Molecular and Cellular Biology University of Guelph Ontario N1G 2W1, Canada
| | - Hassane ElMkami
- School of Physics and Astronomy University of St Andrews Fife KY16 9SS, UK
| | - Olav Schiemann
- Centre for Biomolecular Sciences The University of St. Andrews Fife KY16 9RH, UK
| | - James H. Naismith
- Centre for Biomolecular Sciences The University of St. Andrews Fife KY16 9RH, UK
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237
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238
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Morona R, Purins L, Tocilj A, Matte A, Cygler M. Sequence-structure relationships in polysaccharide co-polymerase (PCP) proteins. Trends Biochem Sci 2008; 34:78-84. [PMID: 19058968 DOI: 10.1016/j.tibs.2008.11.001] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2008] [Revised: 10/30/2008] [Accepted: 11/03/2008] [Indexed: 10/21/2022]
Abstract
Polysaccharides are ubiquitously distributed on the cell surface of bacteria. These polymers are involved in many processes, including immune avoidance and bacteria-host interactions, which are especially important for pathogenic organisms. In many instances, the lengths of these polysaccharides are not random, but rather distribute around some mean value, termed the modal length. A large family of proteins, called polysaccharide co-polymerases (PCPs), found in both Gram-negative and Gram-positive species regulate polysaccharide modal length. Recent crystal structures of Wzz proteins from Escherichia coli and Salmonella typhimurium provide the first atomic-resolution information for one family of PCPs, the PCP1 group. These crystal structures have important implications for the structures of other PCP families.
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Affiliation(s)
- Renato Morona
- Australian Bacterial Pathogenesis Program, School of Molecular and Biomedical Science, Discipline of Microbiology and Immunology, University of Adelaide, North Terrace, Adelaide, SA 5005, Australia.
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239
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Affiliation(s)
- Dale Kaiser
- Departments of Biochemistry and of Developmental Biology, Stanford University School of Medicine, Stanford, California, 94305;
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240
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Kutik S, Stojanovski D, Becker T, Stroud DA, Becker L, Meinecke M, Krüger V, Prinz C, Guiard B, Wagner R, Meisinger C, Pfanner N, Wiedemann N. Response: The Mitochondrial β-Signal and Protein Sorting. Cell 2008. [DOI: 10.1016/j.cell.2008.12.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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241
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NEWSTEAD SIMON, HOBBS JEANETTE, JORDAN DAVINA, CARPENTER ELISABETHP, IWATA SO. Insights into outer membrane protein crystallization. Mol Membr Biol 2008; 25:631-8. [PMID: 19023694 PMCID: PMC2885437 DOI: 10.1080/09687680802526574] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Outer membrane proteins are structurally distinct from those that reside in the inner membrane and play important roles in bacterial pathogenicity and human metabolism. X-ray crystallography studies on >40 different outer membrane proteins have revealed that the transmembrane portion of these proteins can be constructed from either beta-sheets or less commonly from alpha-helices. The most common architecture is the beta-barrel, which can be formed from either a single anti-parallel sheet, fused at both ends to form a barrel or from multiple peptide chains. Outer membrane proteins exhibit considerable rigidity and stability, making their study through x-ray crystallography particularly tractable. As the number of structures of outer membrane proteins increases a more rational approach to their crystallization can be made. Herein we analyse the crystallization data from 53 outer membrane proteins and compare the results to those obtained for inner membrane proteins. A targeted sparse matrix screen for outer membrane protein crystallization is presented based on the present analysis.
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Affiliation(s)
- SIMON NEWSTEAD
- Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
| | - JEANETTE HOBBS
- Molecular Dimensions Ltd, Unit 7 Acorn Business Centre, Oaks Drive, Newmarket, Suffolk, CB8 7SY, UK
| | - DAVINA JORDAN
- Molecular Dimensions Ltd, Unit 7 Acorn Business Centre, Oaks Drive, Newmarket, Suffolk, CB8 7SY, UK
| | - ELISABETH P. CARPENTER
- Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
- Membrane Protein Laboratory, Diamond Light Source Ltd, Harwell Science and Innovation Campus, Chilton, Didcot, OX11 ODE, UK
| | - SO IWATA
- Division of Molecular Biosciences, Membrane Protein Crystallography Group, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
- Membrane Protein Laboratory, Diamond Light Source Ltd, Harwell Science and Innovation Campus, Chilton, Didcot, OX11 ODE, UK
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242
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Díaz-Mejía JJ, Babu M, Emili A. Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome. FEMS Microbiol Rev 2008; 33:66-97. [PMID: 19054114 PMCID: PMC2704936 DOI: 10.1111/j.1574-6976.2008.00141.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The bacterial cell-envelope consists of a complex arrangement of lipids, proteins and carbohydrates that serves as the interface between a microorganism and its environment or, with pathogens, a human host. Escherichia coli has long been investigated as a leading model system to elucidate the fundamental mechanisms underlying microbial cell-envelope biology. This includes extensive descriptions of the molecular identities, biochemical activities and evolutionary trajectories of integral transmembrane proteins, many of which play critical roles in infectious disease and antibiotic resistance. Strikingly, however, only half of the c. 1200 putative cell-envelope-related proteins of E. coli currently have experimentally attributed functions, indicating an opportunity for discovery. In this review, we summarize the state of the art of computational and proteomic approaches for determining the components of the E. coli cell-envelope proteome, as well as exploring the physical and functional interactions that underlie its biogenesis and functionality. We also provide a comprehensive comparative benchmarking analysis on the performance of different bioinformatic and proteomic methods commonly used to determine the subcellular localization of bacterial proteins.
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Affiliation(s)
- Juan Javier Díaz-Mejía
- Banting and Best Department of Medical Research, Terrence Donnelly Center for Cellular and Biomolecular Research, University of Toronto, Toronto, ON, Canada
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243
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Outer membrane permeability and antibiotic resistance. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1794:808-16. [PMID: 19100346 DOI: 10.1016/j.bbapap.2008.11.005] [Citation(s) in RCA: 995] [Impact Index Per Article: 62.2] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 09/19/2008] [Revised: 11/12/2008] [Accepted: 11/13/2008] [Indexed: 01/19/2023]
Abstract
To date most antibiotics are targeted at intracellular processes, and must be able to penetrate the bacterial cell envelope. In particular, the outer membrane of gram-negative bacteria provides a formidable barrier that must be overcome. There are essentially two pathways that antibiotics can take through the outer membrane: a lipid-mediated pathway for hydrophobic antibiotics, and general diffusion porins for hydrophilic antibiotics. The lipid and protein compositions of the outer membrane have a strong impact on the sensitivity of bacteria to many types of antibiotics, and drug resistance involving modifications of these macromolecules is common. This review will describe the molecular mechanisms for permeation of antibiotics through the outer membrane, and the strategies that bacteria have deployed to resist antibiotics by modifications of these pathways.
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244
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Spatial clustering of the curlin secretion lipoprotein requires curli fiber assembly. J Bacteriol 2008; 191:608-15. [PMID: 19011034 DOI: 10.1128/jb.01244-08] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Gram-negative bacteria assemble functional amyloid surface fibers called curli. CsgB nucleates the major curli subunit protein, CsgA, into a self-propagating amyloid fiber on the cell surface. The CsgG lipoprotein is sufficient for curlin transport across the outer membrane and is hypothesized to be the central molecule of the curli fiber secretion and assembly complex. We tested the hypothesis that the curli secretion protein, CsgG, was restricted to certain areas of the cell to promote the interaction of CsgA and CsgB during curli assembly. Here, electron microscopic analysis of curli-producing strains showed that relatively few cells in the population contacted curli fibers and that curli emanated from spatially discrete points on the cell surface. Microscopic analysis revealed that CsgG was surface exposed and spatially clustered around curli fibers. CsgG localization to the outer membrane and exposure of the surface domain were not dependent on any other csg-encoded protein, but the clustering of CsgG required the csg-encoded proteins CsgE, CsgF, CsgA, and CsgB. CsgG formed stable oligomers in all the csg mutant strains, but these oligomers were distinct from the CsgG complexes assembled in wild-type cells. Finally, we found that efficient fiber assembly was required for the spatial clustering of CsgG. These results suggest a new model where curli fiber formation is spatially coordinated with the CsgG assembly apparatus.
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245
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Modifications and applications of the Acinetobacter venetianus RAG-1 exopolysaccharide, the emulsan complex and its components. Appl Microbiol Biotechnol 2008; 81:201-10. [DOI: 10.1007/s00253-008-1664-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2008] [Revised: 08/06/2008] [Accepted: 08/08/2008] [Indexed: 11/28/2022]
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246
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Faridmoayer A, Fentabil MA, Haurat MF, Yi W, Woodward R, Wang PG, Feldman MF. Extreme substrate promiscuity of the Neisseria oligosaccharyl transferase involved in protein O-glycosylation. J Biol Chem 2008; 283:34596-604. [PMID: 18930921 DOI: 10.1074/jbc.m807113200] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Neisseria meningitidis PglL belongs to a novel family of bacterial oligosaccharyltransferases (OTases) responsible for O-glycosylation of type IV pilins. Although members of this family are widespread among pathogenic bacteria, there is little known about their mechanism. Understanding the O-glycosylation process may uncover potential targets for therapeutic intervention, and can open new avenues for the exploitation of these pathways for biotechnological purposes. In this work, we demonstrate that PglL is able to transfer virtually any glycan from the undecaprenyl pyrophosphate (UndPP) carrier to pilin in engineered Escherichia coli and Salmonella cells. Surprisingly, PglL was also able to interfere with the peptidoglycan biosynthetic machinery and transfer peptidoglycan subunits to pilin. This represents a previously unknown post-translational modification in bacteria. Given the wide range of glycans transferred by PglL, we reasoned that substrate specificity of PglL lies in the lipid carrier. To test this hypothesis we developed an in vitro glycosylation system that employed purified PglL, pilin, and the lipid farnesyl pyrophosphate (FarPP) carrying a pentasaccharide that had been synthesized by successive chemical and enzymatic steps. Although FarPP has different stereochemistry and a significantly shorter aliphatic chain than the natural lipid substrate, the pentasaccharide was still transferred to pilin in our system. We propose that the primary roles of the lipid carrier during O-glycosylation are the translocation of the glycan into the periplasm, and the positioning of the pyrophosphate linker and glycan adjacent to PglL. The unique characteristics of PglL make this enzyme a promising tool for glycoengineering novel glycan-based vaccines and therapeutics.
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Affiliation(s)
- Amirreza Faridmoayer
- Department of Biological Sciences, Alberta Ingenuity Centre for Carbohydrate Science, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
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Olivares-Illana V, Meyer P, Bechet E, Gueguen-Chaignon V, Soulat D, Lazereg-Riquier S, Mijakovic I, Deutscher J, Cozzone AJ, Laprévote O, Morera S, Grangeasse C, Nessler S. Structural basis for the regulation mechanism of the tyrosine kinase CapB from Staphylococcus aureus. PLoS Biol 2008; 6:e143. [PMID: 18547145 PMCID: PMC2422856 DOI: 10.1371/journal.pbio.0060143] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Accepted: 04/28/2008] [Indexed: 12/19/2022] Open
Abstract
Bacteria were thought to be devoid of tyrosine-phosphorylating enzymes. However, several tyrosine kinases without similarity to their eukaryotic counterparts have recently been identified in bacteria. They are involved in many physiological processes, but their accurate functions remain poorly understood due to slow progress in their structural characterization. They have been best characterized as copolymerases involved in the synthesis and export of extracellular polysaccharides. These compounds play critical roles in the virulence of pathogenic bacteria, and bacterial tyrosine kinases can thus be considered as potential therapeutic targets. Here, we present the crystal structures of the phosphorylated and unphosphorylated states of the tyrosine kinase CapB from the human pathogen Staphylococcus aureus together with the activator domain of its cognate transmembrane modulator CapA. This first high-resolution structure of a bacterial tyrosine kinase reveals a 230-kDa ring-shaped octamer that dissociates upon intermolecular autophosphorylation. These observations provide a molecular basis for the regulation mechanism of the bacterial tyrosine kinases and give insights into their copolymerase function. An idiosyncratic new class of bacterial enzymes, bacterial tyrosine-kinases (BY-kinases), has been characterized. These enzymes, which are involved in an increasing number of physiological processes ranging from stress resistance to pathogenicity, share no sequence similarities with eukaryotic kinases, and their function remains largely unknown. They have nevertheless been described to undergo autophosphorylation on a C-terminal tyrosine cluster and to phosphorylate endogenous protein substrates. We describe here the first crystal structure of a bacterial tyrosine kinase, namely CapB from the pathogen Staphylococcus aureus, in complex with the cytoplasmic domain of the transmembrane stimulatory protein CapA. Our data explain the activation mechanism of CapB by CapA and allow us to propose a regulatory mechanism based on intermolecular autophosphorylation. These results also give new insights onto the phosphorylation of the endogenous substrate CapO, an enzyme involved in the synthesis of polysaccharide precursors. CapA and CapB, among others, are involved as copolymerases in the synthesis of extracellular polysaccharides that are thought to be potent virulence factors. Thus, these structural data provide the basis for designing specific inhibitors for these enzymes, which constitute an original and attractive target for the development of new drugs to treat infectious diseases. Structural analysis of a conserved bacterial tyrosine kinase fromStaphylococcus aureus provides the basis for deciphering its regulatory mechanism, leading to a model for its implication in extracellular polysaccharide synthesis.
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Affiliation(s)
| | - Philippe Meyer
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Gif sur Yvette, France
| | - Emmanuelle Bechet
- Institut de Biologie et Chimie des Protéines, CNRS, Université Lyon 1, Université de Lyon, Lyon, France
| | | | - Didier Soulat
- Institut de Biologie et Chimie des Protéines, CNRS, Université Lyon 1, Université de Lyon, Lyon, France
| | | | - Ivan Mijakovic
- Center for Microbial Biotechnology, BioCentrum, Technical University of Denmark, Lyngby, Denmark
| | - Josef Deutscher
- Laboratory of Microbiology and Molecular Genetics, AgroParisTech, CNRS, INRA, Thiverval-Grignon, France
| | - Alain J Cozzone
- Institut de Biologie et Chimie des Protéines, CNRS, Université Lyon 1, Université de Lyon, Lyon, France
| | - Olivier Laprévote
- Institut de Chimie des Substances Naturelles, CNRS, Gif sur Yvette, France
| | - Solange Morera
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Gif sur Yvette, France
| | - Christophe Grangeasse
- Institut de Biologie et Chimie des Protéines, CNRS, Université Lyon 1, Université de Lyon, Lyon, France
- * To whom correspondence should be addressed. E-mail: (CG); (SN)
| | - Sylvie Nessler
- Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Gif sur Yvette, France
- * To whom correspondence should be addressed. E-mail: (CG); (SN)
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248
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SciN is an outer membrane lipoprotein required for type VI secretion in enteroaggregative Escherichia coli. J Bacteriol 2008; 190:7523-31. [PMID: 18805985 DOI: 10.1128/jb.00945-08] [Citation(s) in RCA: 182] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Enteroaggregative Escherichia coli (EAEC) is a pathogen implicated in several infant diarrhea or diarrheal outbreaks in areas of endemicity. Although multiple genes involved in EAEC pathogenesis have been identified, the overall mechanism of virulence is not well understood. Recently, a novel secretion system, called type VI secretion (T6S) system (T6SS), has been identified in EAEC and most animal or plant gram-negative pathogens. T6SSs are multicomponent cell envelope machines responsible for the secretion of at least two putative substrates, Hcp and VgrG. In EAEC, two copies of T6S gene clusters, called sci-1 and sci-2, are present on the pheU pathogenicity island. In this study, we focused our work on the sci-1 gene cluster. The Sci-1 apparatus is probably composed of all, or a subset of, the 21 gene products encoded on the cluster. Among these subunits, some are shared by all T6SSs identified to date, including a ClpV-type AAA(+) ATPase (SciG) and an IcmF (SciS) and an IcmH (SciP) homologue, as well as a putative lipoprotein (SciN). In this study, we demonstrate that sciN is a critical gene necessary for T6S-dependent secretion of the Hcp-like SciD protein and for biofilm formation. We further show that SciN is a lipoprotein, as shown by the inhibition of its processing by globomycin and in vivo labeling with [(3)H]palmitic acid. SciN is tethered to the outer membrane and exposed in the periplasm. Sequestration of SciN at the inner membrane by targeting the +2 residue responsible for lipoprotein localization (Gly2Asp) fails to complement an sciN mutant for SciD secretion and biofilm formation. Together, these results support a model in which SciN is an outer membrane lipoprotein exposed in the periplasm and essential for the Sci-1 apparatus function.
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249
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Marczak M, Mazur A, Gruszecki WI, Skorupska A. PssO, a unique extracellular protein important for exopolysaccharide synthesis in Rhizobium leguminosarum bv. trifolii. Biochimie 2008; 90:1781-90. [PMID: 18835420 DOI: 10.1016/j.biochi.2008.08.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Accepted: 08/25/2008] [Indexed: 11/29/2022]
Abstract
Synthesis and secretion of polysaccharides by Gram-negative bacteria are a result of a concerted action of enzymatic and channel-forming proteins localized in different compartments of the cell. The presented work comprises functional characterization of PssO protein encoded within the previously identified, chromosomal exopolysaccharide (EPS) biosynthesis region (Pss-I) of symbiotic bacterium Rhizobium leguminosarum bv. trifolii TA1 (RtTA1). pssO gene localization between pssN and pssP genes encoding proteins engaged in exopolysaccharide synthesis and transport, suggested its role in EPS synthesis and/or secretion. RtTA1 pssO deletion mutant and the PssO protein overproducing strains were constructed. The mutant strain was EPS-deficient, however, this mutation was not complemented. The PssO-overproducing strain was characterized by increase in EPS secretion. Subcellular fractionation, pssO-phoA/lacZ translational fusion analyses and immunolocalisation of PssO on RtTA1 cell surface by electron microscopy demonstrated that PssO is secreted to the extracellular medium and remains attached to the cell. Western blotting analysis revealed the presence of immunologically related proteins within the species R. leguminosarum bv. trifolii, bv. viciae and Rhizobium etli. The secondary structure of PssO-His(6), as determined by FTIR spectroscopy, consists of at least 32% alpha-helical and 12% beta-sheet structures. A putative function of PssO in EPS synthesis and/or transport is discussed in the context of its cellular localization and the phenotypes of the deletion mutant and pssO-overexpressing strain.
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Affiliation(s)
- M Marczak
- Department of Genetics and Microbiology, Institute of Microbiology and Biotechnology, Maria Curie-Skłodowska University, Lublin, Poland
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250
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Wang W, Black SS, Edwards MD, Miller S, Morrison EL, Bartlett W, Dong C, Naismith JH, Booth IR. The structure of an open form of an E. coli mechanosensitive channel at 3.45 A resolution. Science 2008; 321:1179-83. [PMID: 18755969 DOI: 10.1126/science.1159262] [Citation(s) in RCA: 165] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
How ion channels are gated to regulate ion flux in and out of cells is the subject of intense interest. The Escherichia coli mechanosensitive channel, MscS, opens to allow rapid ion efflux, relieving the turgor pressure that would otherwise destroy the cell. We present a 3.45 angstrom-resolution structure for the MscS channel in an open conformation. This structure has a pore diameter of approximately 13 angstroms created by substantial rotational rearrangement of the three transmembrane helices. The structure suggests a molecular mechanism that underlies MscS gating and its decay of conductivity during prolonged activation. Support for this mechanism is provided by single-channel analysis of mutants with altered gating characteristics.
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Affiliation(s)
- Wenjian Wang
- Centre for Biomolecular Sciences, The North Haugh, University of St. Andrews, KY16 9ST, Scotland, UK
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