251
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Tame JR. Autotransporter protein secretion. Biomol Concepts 2011; 2:525-36. [DOI: 10.1515/bmc.2011.045] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 09/16/2011] [Indexed: 11/15/2022] Open
Abstract
AbstractAutotransporter proteins are a large family of virulence factors secreted from Gram-negative bacteria by a unique mechanism. First described in the 1980s, these proteins have a C-terminal region that folds into a β-barrel in the bacterial outer membrane. The so-called passenger domain attached to this barrel projects away from the cell surface and may be liberated from the cell by self-cleavage or surface proteases. Although the majority of passenger domains have a similar β-helical structure, they carry a variety of subdomains, allowing them to carry out widely differing functions related to pathogenesis. Considerable biochemical and structural characterisation of the barrel domain has shown that ‘autotransporters’ in fact require a conserved and essential protein complex in the outer membrane for correct folding. Although the globular domains of this complex projecting into the periplasmic space have also been structurally characterised, the overall secretion pathway of the autotransporters remains highly puzzling. It was presumed for many years that the passenger domain passed through the centre of the barrel domain to reach the cell surface, driven at least in part by folding. This picture is complicated by conflicting data, and there is currently little hard information on the true nature of the secretion intermediates. As well as their medical importance therefore, autotransporters are proving to be an excellent system to study the folding and membrane insertion of outer membrane proteins in general. This review focuses on structural aspects of autotransporters; their many functions in pathogenesis are beyond its scope.
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Affiliation(s)
- Jeremy R.H. Tame
- 1Yokohama City University, Suehiro 1-7-29, Tsurumi, Yokohama 230-0045, Japan
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252
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Interaction between bacterial outer membrane proteins and periplasmic quality control factors: a kinetic partitioning mechanism. Biochem J 2011; 438:505-11. [PMID: 21671888 DOI: 10.1042/bj20110264] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The OMPs (outer membrane proteins) of Gram-negative bacteria have to be translocated through the periplasmic space before reaching their final destination. The aqueous environment of the periplasmic space and high permeability of the outer membrane engender such a translocation process inevitably challenging. In Escherichia coli, although SurA, Skp and DegP have been identified to function in translocating OMPs across the periplasm, their precise roles and their relationship remain to be elucidated. In the present paper, by using fluorescence resonance energy transfer and single-molecule detection, we have studied the interaction between the OMP OmpC and these periplasmic quality control factors. The results of the present study reveal that the binding rate of OmpC to SurA or Skp is much faster than that to DegP, which may lead to sequential interaction between OMPs and different quality control factors. Such a kinetic partitioning mechanism for the chaperone-substrate interaction may be essential for the quality control of the biogenesis of OMPs.
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253
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Genetic interaction maps in Escherichia coli reveal functional crosstalk among cell envelope biogenesis pathways. PLoS Genet 2011; 7:e1002377. [PMID: 22125496 PMCID: PMC3219608 DOI: 10.1371/journal.pgen.1002377] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Accepted: 09/24/2011] [Indexed: 12/28/2022] Open
Abstract
As the interface between a microbe and its environment, the bacterial cell envelope has broad biological and clinical significance. While numerous biosynthesis genes and pathways have been identified and studied in isolation, how these intersect functionally to ensure envelope integrity during adaptive responses to environmental challenge remains unclear. To this end, we performed high-density synthetic genetic screens to generate quantitative functional association maps encompassing virtually the entire cell envelope biosynthetic machinery of Escherichia coli under both auxotrophic (rich medium) and prototrophic (minimal medium) culture conditions. The differential patterns of genetic interactions detected among >235,000 digenic mutant combinations tested reveal unexpected condition-specific functional crosstalk and genetic backup mechanisms that ensure stress-resistant envelope assembly and maintenance. These networks also provide insights into the global systems connectivity and dynamic functional reorganization of a universal bacterial structure that is both broadly conserved among eubacteria (including pathogens) and an important target. Proper assembly of the cell envelope is essential for bacterial growth, environmental adaptation, and drug resistance. Yet, while the biological roles of the many genes and pathways involved in biosynthesis of the cell envelope have been studied extensively in isolation, how the myriad components intersect functionally to maintain envelope integrity under different growth conditions has not been explored systematically. Genome-scale genetic interaction screens have increasingly been performed to great impact in yeast; no analogous comprehensive studies have yet been reported for bacteria despite their prominence in human health and disease. We addressed this by using a synthetic genetic array technology to generate quantitative maps of genetic interactions encompassing virtually all the components of the cell envelope biosynthetic machinery of the classic model bacterium E. coli in two common laboratory growth conditions (rich and minimal medium). From the resulting networks of high-confidence genetic interactions, we identify condition-specific functional dependencies underlying envelope assembly and global remodeling of genetic backup mechanisms that ensure envelope integrity under environmental challenge.
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254
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Kim KH, Aulakh S, Tan W, Paetzel M. Crystallographic analysis of the C-terminal domain of the Escherichia coli lipoprotein BamC. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:1350-8. [PMID: 22102230 DOI: 10.1107/s174430911103363x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Accepted: 08/18/2011] [Indexed: 11/10/2022]
Abstract
In Gram-negative bacteria, the BAM complex catalyzes the essential process of assembling outer membrane proteins. The BAM complex in Escherichia coli consists of five proteins: one β-barrel membrane protein, BamA, and four lipoproteins, BamB, BamC, BamD and BamE. Here, the crystal structure of the C-terminal domain of E. coli BamC (BamC(C): Ala224-Ser343) refined to 1.5 Å resolution in space group H3 is reported. BamC(C) consists of a six-stranded antiparallel β-sheet, three α-helices and one 3(10)-helix. Sequence and surface analysis reveals that most of the conserved residues within BamC(C) are localized to form a continuous negatively charged groove that is involved in a major crystalline lattice contact in which a helix from a neighbouring BamC(C) binds against this surface. This interaction is topologically and architecturally similar to those seen in the substrate-binding grooves of other proteins with BamC-like folds. Taken together, these results suggest that an identified surface on the C-terminal domain of BamC may serve as an important protein-binding surface for interaction with other BAM-complex components or substrates.
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Affiliation(s)
- Kelly H Kim
- Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
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255
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Evans ML, Schmidt JC, Ilbert M, Doyle SM, Quan S, Bardwell JCA, Jakob U, Wickner S, Chapman MR. E. coli chaperones DnaK, Hsp33 and Spy inhibit bacterial functional amyloid assembly. Prion 2011; 5:323-34. [PMID: 22156728 PMCID: PMC3821533 DOI: 10.4161/pri.18555] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Revised: 10/24/2011] [Accepted: 10/27/2011] [Indexed: 01/17/2023] Open
Abstract
Amyloid formation is an ordered aggregation process, where β-sheet rich polymers are assembled from unstructured or partially folded monomers. We examined how two Escherichia coli cytosolic chaperones, DnaK and Hsp33, and a more recently characterized periplasmic chaperone, Spy, modulate the aggregation of a functional amyloid protein, CsgA. We found that DnaK, the Hsp70 homologue in E. coli, and Hsp33, a redox-regulated holdase, potently inhibited CsgA amyloidogenesis. The Hsp33 anti-amyloidogenesis activity was oxidation dependent, as oxidized Hsp33 was significantly more efficient than reduced Hsp33 at preventing CsgA aggregation. When soluble CsgA was seeded with preformed amyloid fibers, neither Hsp33 nor DnaK were able to efficiently prevent soluble CsgA from adopting the amyloid conformation. Moreover, both DnaK and Hsp33 increased the time that CsgA was reactive with the amyloid oligomer conformation-specific A11 antibody. Since CsgA must also pass through the periplasm during secretion, we assessed the ability of the periplasmic chaperone Spy to inhibit CsgA polymerization. Like DnaK and Hsp33, Spy also inhibited CsgA polymerization in vitro. Overexpression of Spy resulted in increased chaperone activity in periplasmic extracts and in reduced curli biogenesis in vivo. We propose that DnaK, Hsp33 and Spy exert their effects during the nucleation stages of CsgA fibrillation. Thus, both housekeeping and stress induced cytosolic and periplasmic chaperones may be involved in discouraging premature CsgA interactions during curli biogenesis.
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Affiliation(s)
- Margery L Evans
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
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256
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Evans ML, Schmidt JC, Ilbert M, Doyle SM, Quan S, Bardwell JCA, Jakob U, Wickner S, Chapman MR. E. coli chaperones DnaK, Hsp33 and Spy inhibit bacterial functional amyloid assembly. Prion 2011. [PMID: 22156728 DOI: 10.4161/pri.5.4.18555] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/28/2022] Open
Abstract
Amyloid formation is an ordered aggregation process, where β-sheet rich polymers are assembled from unstructured or partially folded monomers. We examined how two Escherichia coli cytosolic chaperones, DnaK and Hsp33, and a more recently characterized periplasmic chaperone, Spy, modulate the aggregation of a functional amyloid protein, CsgA. We found that DnaK, the Hsp70 homologue in E. coli, and Hsp33, a redox-regulated holdase, potently inhibited CsgA amyloidogenesis. The Hsp33 anti-amyloidogenesis activity was oxidation dependent, as oxidized Hsp33 was significantly more efficient than reduced Hsp33 at preventing CsgA aggregation. When soluble CsgA was seeded with preformed amyloid fibers, neither Hsp33 nor DnaK were able to efficiently prevent soluble CsgA from adopting the amyloid conformation. Moreover, both DnaK and Hsp33 increased the time that CsgA was reactive with the amyloid oligomer conformation-specific A11 antibody. Since CsgA must also pass through the periplasm during secretion, we assessed the ability of the periplasmic chaperone Spy to inhibit CsgA polymerization. Like DnaK and Hsp33, Spy also inhibited CsgA polymerization in vitro. Overexpression of Spy resulted in increased chaperone activity in periplasmic extracts and in reduced curli biogenesis in vivo. We propose that DnaK, Hsp33 and Spy exert their effects during the nucleation stages of CsgA fibrillation. Thus, both housekeeping and stress induced cytosolic and periplasmic chaperones may be involved in discouraging premature CsgA interactions during curli biogenesis.
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Affiliation(s)
- Margery L Evans
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
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257
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Probing the Borrelia burgdorferi surface lipoprotein secretion pathway using a conditionally folding protein domain. J Bacteriol 2011; 193:6724-32. [PMID: 21965569 DOI: 10.1128/jb.06042-11] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Surface lipoproteins of Borrelia spirochetes are important virulence determinants in the transmission and pathogenesis of Lyme disease and relapsing fever. To further define the conformational secretion requirements and to identify potential lipoprotein translocation intermediates associated with the bacterial outer membrane (OM), we generated constructs in which Borrelia burgdorferi outer surface lipoprotein A (OspA) was fused to calmodulin (CaM), a conserved eukaryotic protein undergoing calcium-dependent folding. Protein localization assays showed that constructs in which CaM was fused to full-length wild-type (wt) OspA or to an intact OspA N-terminal "tether" peptide retained their competence for OM translocation even in the presence of calcium. In contrast, constructs in which CaM was fused to truncated or mutant OspA N-terminal tether peptides were targeted to the periplasmic leaflet of the OM in the presence of calcium but could be flipped to the bacterial surface upon calcium chelation. This indicated that in the absence of an intact tether peptide, unfolding of the CaM moiety was required in order to facilitate OM traversal. Together, these data further support a periplasmic tether peptide-mediated mechanism to prevent premature folding of B. burgdorferi surface lipoproteins. The specific shift in the OM topology of sequence-identical lipopeptides due to a single-variable change in environmental conditions also indicates that surface-bound Borrelia lipoproteins can localize transiently to the periplasmic leaflet of the OM.
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258
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Varying dependency of periplasmic peptidylprolyl cis–trans isomerases in promoting Yersinia pseudotuberculosis stress tolerance and pathogenicity. Biochem J 2011; 439:321-32. [DOI: 10.1042/bj20110767] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Periplasmic PPIases (peptidylprolyl cis–trans isomerases) catalyse the cis–trans isomerization of peptidyl-prolyl bonds, which is a rate-limiting step during protein folding. We demonstrate that the surA, ppiA, ppiD, fkpA and fklB alleles each encode a periplasmic PPIase in the bacterial pathogen Yersinia pseudotuberculosis. Of these, four were purified to homogeneity. Purified SurA, FkpA and FklB, but not PpiD, displayed detectable PPIase activity in vitro. Significantly, only Y. pseudotuberculosis lacking surA caused drastic alterations to the outer membrane protein profile and FA (fatty acid) composition. They also exhibited aberrant cellular morphology, leaking LPS (lipopolysaccharide) into the extracellular environment. The SurA PPIase is therefore most critical for maintaining Y. pseudotuberculosis envelope integrity during routine culturing. On the other hand, bacteria lacking either surA or all of the genes ppiA, ppiD, fkpA and fklB were sensitive to hydrogen peroxide and were attenuated in mice infections. Thus Y. pseudotuberculosis exhibits both SurA-dependent and -independent requirements for periplasmic PPIase activity to ensure in vivo survival and a full virulence effect in a mammalian host.
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259
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Bæk KT, Vegge CS, Brøndsted L. HtrA chaperone activity contributes to host cell binding in Campylobacter jejuni. Gut Pathog 2011; 3:13. [PMID: 21939552 PMCID: PMC3260087 DOI: 10.1186/1757-4749-3-13] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Accepted: 09/22/2011] [Indexed: 11/25/2022] Open
Abstract
Background Acute gastroenteritis caused by the food-borne pathogen Campylobacter jejuni is associated with attachment of bacteria to the intestinal epithelium and subsequent invasion of epithelial cells. In C. jejuni, the periplasmic protein HtrA is required for efficient binding to epithelial cells. HtrA has both protease and chaperone activity, and is important for virulence of several bacterial pathogens. Results The aim of this study was to determine the role of the dual activities of HtrA in host cell interaction of C. jejuni by comparing an htrA mutant lacking protease activity, but retaining chaperone activity, with a ΔhtrA mutant and the wild type strain. Binding of C. jejuni to both epithelial cells and macrophages was facilitated mainly by HtrA chaperone activity that may be involved in folding of outer membrane adhesins. In contrast, HtrA protease activity played only a minor role in interaction with host cells. Conclusion We show that HtrA protease and chaperone activities contribute differently to C. jejuni's interaction with mammalian host cells, with the chaperone activity playing the major role in host cell binding.
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Affiliation(s)
- Kristoffer T Bæk
- Department of Veterinary Disease Biology, University Copenhagen, Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark.
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260
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Zhang M, Lin S, Song X, Liu J, Fu Y, Ge X, Fu X, Chang Z, Chen PR. A genetically incorporated crosslinker reveals chaperone cooperation in acid resistance. Nat Chem Biol 2011; 7:671-7. [DOI: 10.1038/nchembio.644] [Citation(s) in RCA: 190] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Accepted: 07/05/2011] [Indexed: 12/20/2022]
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261
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Ricci DP, Silhavy TJ. The Bam machine: a molecular cooper. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1067-84. [PMID: 21893027 DOI: 10.1016/j.bbamem.2011.08.020] [Citation(s) in RCA: 134] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 08/08/2011] [Accepted: 08/15/2011] [Indexed: 11/24/2022]
Abstract
The bacterial outer membrane (OM) is an exceptional biological structure with a unique composition that contributes significantly to the resiliency of Gram-negative bacteria. Since all OM components are synthesized in the cytosol, the cell must efficiently transport OM-specific lipids and proteins across the cell envelope and stably integrate them into a growing membrane. In this review, we discuss the challenges associated with these processes and detail the elegant solutions that cells have evolved to address the topological problem of OM biogenesis. Special attention will be paid to the Bam machine, a highly conserved multiprotein complex that facilitates OM β-barrel folding. This article is part of a Special Issue entitled: Protein Folding in Membranes.
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Affiliation(s)
- Dante P Ricci
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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262
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Hagan CL, Kahne D. The reconstituted Escherichia coli Bam complex catalyzes multiple rounds of β-barrel assembly. Biochemistry 2011; 50:7444-6. [PMID: 21823654 DOI: 10.1021/bi2010784] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
β-Barrel proteins are folded and inserted into the outer membranes of Escherichia coli by the Bam complex. The Bam complex has been purified and functionally reconstituted in vitro. We report conditions for reconstitution that increase the folding yield 10-fold and allow us to monitor the time course of folding directly. We use these conditions to analyze the effect of a mutation in the Bam complex and to demonstrate the ability of the reconstituted complex to catalyze more than one round of substrate assembly.
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Affiliation(s)
- Christine L Hagan
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States
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263
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Expression of OmpATb is dependent on small membrane proteins in Mycobacterium bovis BCG. Tuberculosis (Edinb) 2011; 91:544-8. [PMID: 21802366 DOI: 10.1016/j.tube.2011.06.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 05/26/2011] [Accepted: 06/22/2011] [Indexed: 11/21/2022]
Abstract
Small membrane proteins emerge as a novel class of regulatory molecules in bacteria. Experiments carried out in Mycobacterium bovis BCG indicate that the ompATb gene (Rv0899), encoding a major outer membrane protein, is organized in operon with Rv0900 and Rv0901, encoding two small proteins with a predicted transmembrane domain. Fractioning experiment confirmed the association of Rv0901 with the membrane fraction. To investigate the role of Rv0900 and Rv0901 in M. bovis BCG, we have constructed a strain deleted for the whole operon as well as complemented strains carrying a deletion of Rv0900 or a frameshift mutation in either Rv0900 or Rv0901. Importantly, mutations in Rv0900 and/or Rv0901 strongly altered OmpATb expression, demonstrating that Rv0900 and Rv0901 play a regulatory role, which appears to occur at a post-transcriptional level.
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264
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The fimbrial usher FimD follows the SurA-BamB pathway for its assembly in the outer membrane of Escherichia coli. J Bacteriol 2011; 193:5222-30. [PMID: 21784935 DOI: 10.1128/jb.05585-11] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fimbrial ushers are the largest β-barrel outer membrane proteins (OMPs) known to date, which function in the polymerization of fimbriae and their translocation to the bacterial surface. Folding and assembly of these complex OMPs are not characterized. Here, we investigate the role of periplasmic chaperones (SurA, Skp, DegP, and FkpA) and individual components of the β-barrel assembly machinery (BAM) complex (BamA, BamB, BamC, and BamE) in the folding of the Escherichia coli FimD usher. The FimD level is dramatically reduced (∼30-fold) in a surA null mutant, but a strong cell envelope stress is constitutively activated with upregulation of DegP (∼10-fold). To demonstrate a direct role of SurA, FimD folding was analyzed in a conditional surA mutant in which SurA expression was controlled. In this strain, FimD is depleted from bacteria in parallel to SurA without significant upregulation of DegP. Interestingly, the dependency on SurA is higher for FimD than for other OMPs. We also demonstrate that a functional BAM complex is needed for folding of FimD. In addition, FimD levels were strongly reduced (∼5-fold) in a mutant lacking the accessory lipoprotein BamB. The critical role of BamB for FimD folding was confirmed by complementation and BamB depletion experiments. Similar to SurA dependency, FimD showed a stronger dependency on BamB than OMPs. On the other hand, folding of FimD was only marginally affected in bamC and bamE mutants. Collectively, our results indicate that FimD usher follows the SurA-BamB pathway for its assembly. The preferential use of this pathway for the folding of OMPs with large β-barrels is discussed.
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265
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Affiliation(s)
- Christine L. Hagan
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
| | - Thomas J. Silhavy
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544;
| | - Daniel Kahne
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115; ,
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266
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The soluble, periplasmic domain of OmpA folds as an independent unit and displays chaperone activity by reducing the self-association propensity of the unfolded OmpA transmembrane β-barrel. Biophys Chem 2011; 159:194-204. [PMID: 21782315 DOI: 10.1016/j.bpc.2011.06.013] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Revised: 06/13/2011] [Accepted: 06/20/2011] [Indexed: 11/22/2022]
Abstract
OmpA is one of only a few transmembrane proteins whose folding and stability have been investigated in detail. However, only half of the OmpA mass encodes its transmembrane β-barrel; the remaining sequence is a soluble domain that is localized to the periplasmic side of the outer membrane. To understand how the OmpA periplasmic domain contributes to the stability and folding of the full-length OmpA protein, we cloned, expressed, purified and studied the OmpA periplasmic domain independently of the OmpA transmembrane β-barrel region. Our experiments showed that the OmpA periplasmic domain exists as an independent folding unit with a free energy of folding equal to -6.2 (±0.1) kcal mol(-1) at 25°C. Using circular dichroism, we determined that the OmpA periplasmic domain adopts a mixed alpha/beta secondary structure, a conformation that has previously been used to describe the partially folded non-native state of the full-length OmpA. We further discovered that the OmpA periplasmic domain reduces the self-association propensity of the unfolded barrel domain, but only when covalently attached (in cis). In vitro folding experiments showed that self-association competes with β-barrel folding when allowed to occur before the addition of membranes, and the periplasmic domain enhances the folding efficiency of the full-length protein by reducing its self-association. These results identify a novel chaperone function for the periplasmic domain of OmpA that may be relevant for folding in vivo. We have also extensively investigated the properties of the self-association reaction of unfolded OmpA and found that the transmembrane region must form a critical nucleus comprised of three molecules before undergoing further oligomerization to form large molecular weight species. Finally, we studied the conformation of the unfolded OmpA monomer and found that the folding-competent form of the transmembrane region adopts an expanded conformation, which is in contrast to previous studies that have suggested a collapsed unfolded state.
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267
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Zhang H, Gao ZQ, Hou HF, Xu JH, Li LF, Su XD, Dong YH. High-resolution structure of a new crystal form of BamA POTRA4-5 from Escherichia coli. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:734-8. [PMID: 21795783 PMCID: PMC3144785 DOI: 10.1107/s1744309111014254] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2011] [Accepted: 04/15/2011] [Indexed: 11/11/2022]
Abstract
In Escherichia coli, the BAM complex is employed to mediate correct folding of the outer membrane (OM) proteins into β-barrels and their insertion into the OM. BamA, which is an essential component of the complex, consists of a C-terminal transmembrane region and five N-terminal polypeptide transport-associated (POTRA) domains. Although deletion studies have shown that each of the POTRA domains plays an important role in the process of BAM complex formation, only POTRA5 is essential for cell viability. Here, the crystal structure of POTRA4-5 has been determined to 1.50 Å resolution with an R factor of 14.7% and an Rfree of 18.9%.
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Affiliation(s)
- Heng Zhang
- National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Science, Peking University, Beijing 100871, People's Republic of China
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268
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Leichert LI. Proteomic methods unravel the protein quality control in Escherichia coli. Proteomics 2011; 11:3023-35. [DOI: 10.1002/pmic.201100082] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 03/22/2011] [Accepted: 03/28/2011] [Indexed: 11/10/2022]
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269
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Kale A, Phansopa C, Suwannachart C, Craven CJ, Rafferty JB, Kelly DJ. The virulence factor PEB4 (Cj0596) and the periplasmic protein Cj1289 are two structurally related SurA-like chaperones in the human pathogen Campylobacter jejuni. J Biol Chem 2011; 286:21254-65. [PMID: 21524997 PMCID: PMC3122185 DOI: 10.1074/jbc.m111.220442] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Revised: 04/08/2011] [Indexed: 11/06/2022] Open
Abstract
The PEB4 protein is an antigenic virulence factor implicated in host cell adhesion, invasion, and colonization in the food-borne pathogen Campylobacter jejuni. peb4 mutants have defects in outer membrane protein assembly and PEB4 is thought to act as a periplasmic chaperone. The crystallographic structure of PEB4 at 2.2-Å resolution reveals a dimer with distinct SurA-like chaperone and peptidyl-prolyl cis/trans isomerase (PPIase) domains encasing a large central cavity. Unlike SurA, the chaperone domain is formed by interlocking helices from each monomer, creating a domain-swapped architecture. PEB4 stimulated the rate of proline isomerization limited refolding of denatured RNase T(1) in a juglone-sensitive manner, consistent with parvulin-like PPIase domains. Refolding and aggregation of denatured rhodanese was significantly retarded in the presence of PEB4 or of an engineered variant specifically lacking the PPIase domain, suggesting the chaperone domain possesses a holdase activity. Using bioinformatics approaches, we identified two other SurA-like proteins (Cj1289 and Cj0694) in C. jejuni. The 2.3-Å structure of Cj1289 does not have the domain-swapped architecture of PEB4 and thus more resembles SurA. Purified Cj1289 also enhanced RNase T(1) refolding, although poorly compared with PEB4, but did not retard the refolding of denatured rhodanese. Structurally, Cj1289 is the most similar protein to SurA in C. jejuni, whereas PEB4 has most structural similarity to the Par27 protein of Bordetella pertussis. Our analysis predicts that Cj0694 is equivalent to the membrane-anchored chaperone PpiD. These results provide the first structural insights into the periplasmic assembly of outer membrane proteins in C. jejuni.
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Affiliation(s)
- Avinash Kale
- From the Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
| | - Chatchawal Phansopa
- From the Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
| | - Chatrudee Suwannachart
- From the Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
| | - C. Jeremy Craven
- From the Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
| | - John B. Rafferty
- From the Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
| | - David J. Kelly
- From the Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom
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270
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Sequential and spatially restricted interactions of assembly factors with an autotransporter beta domain. Proc Natl Acad Sci U S A 2011; 108:E383-91. [PMID: 21646511 DOI: 10.1073/pnas.1103827108] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Autotransporters are bacterial virulence factors that consist of an N-terminal extracellular ("passenger") domain and a C-terminal β barrel domain ("β domain") that resides in the outer membrane. Here we used an in vivo site-specific photocrosslinking approach to gain insight into the mechanism by which the β domain is integrated into the outer membrane and the relationship between β domain assembly and passenger domain secretion. We found that periplasmic chaperones and specific components of the β barrel assembly machinery (Bam) complex interact with the β domain of the Escherichia coli O157:H7 autotransporter extracellular serine protease P (EspP) in a temporally and spatially regulated fashion. Although the chaperone Skp initially interacted with the entire β domain, BamA, BamB, and BamD subsequently interacted with discrete β domain regions. BamB and BamD remained bound to the β domain longer than BamA and therefore appeared to function at a later stage of assembly. Interestingly, we obtained evidence that the completion of β domain assembly is regulated by an intrinsic checkpoint mechanism that requires the completion of passenger domain secretion. In addition to leading to a detailed model of autotransporter biogenesis, our results suggest that the lipoprotein components of the Bam complex play a direct role in the membrane integration of β barrel proteins.
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271
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Desrosiers DC, Anand A, Luthra A, Dunham-Ems SM, LeDoyt M, Cummings MAD, Eshghi A, Cameron CE, Cruz AR, Salazar JC, Caimano MJ, Radolf JD. TP0326, a Treponema pallidum β-barrel assembly machinery A (BamA) orthologue and rare outer membrane protein. Mol Microbiol 2011; 80:1496-515. [PMID: 21488980 PMCID: PMC3115443 DOI: 10.1111/j.1365-2958.2011.07662.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Definitive identification of Treponema pallidum rare outer membrane proteins (OMPs) has long eluded researchers. TP0326, the sole protein in T. pallidum with sequence homology to a Gram-negative OMP, belongs to the BamA family of proteins essential for OM biogenesis. Structural modelling predicted that five polypeptide transport-associated (POTRA) domains comprise the N-terminus of TP0326, while the C-terminus forms an 18-stranded amphipathic β-barrel. Circular dichroism, heat modifiability by SDS-PAGE, Triton X-114 phase partitioning and liposome incorporation supported these topological predictions and confirmed that the β-barrel is responsible for the native protein's amphiphilicity. Expression analyses revealed that native TP0326 is expressed at low abundance, while a protease-surface accessibility assay confirmed surface exposure. Size-exclusion chromatography and blue native polyacrylamide gel electrophoresis revealed a modular Bam complex in T. pallidum larger than that of Escherichia coli. Non-orthologous ancillary factors and self-association of TP0326 via its β-barrel may both contribute to the Bam complex. T. pallidum-infected rabbits mount a vigorous antibody response to both POTRA and β-barrel portions of TP0326, whereas humans with secondary syphilis respond predominantly to POTRA. The syphilis spirochaete appears to have devised a stratagem for harnessing the Bam pathway while satisfying its need to limit surface antigenicity.
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Affiliation(s)
- Daniel C. Desrosiers
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030
| | - Arvind Anand
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030
| | - Amit Luthra
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030
| | - Star M Dunham-Ems
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030
| | - Morgan LeDoyt
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030
| | - Michael A. D. Cummings
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
| | - Azad Eshghi
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
| | - Caroline E. Cameron
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
| | - Adriana R. Cruz
- Centro Internacional de Entrenamiento e Investigaciones Médicas (CIDEIM), Cali, Colombia
| | - Juan C. Salazar
- Centro Internacional de Entrenamiento e Investigaciones Médicas (CIDEIM), Cali, Colombia
- Department of Pediatrics, Connecticut Children's Medical Center, Division of Pediatric Infectious Diseases, Hartford, CT 06106
| | - Melissa J. Caimano
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030
| | - Justin D. Radolf
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030
- Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030
- Department of Pediatrics, Connecticut Children's Medical Center, Division of Pediatric Infectious Diseases, Hartford, CT 06106
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272
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Kim S, Grant RA, Sauer RT. Covalent linkage of distinct substrate degrons controls assembly and disassembly of DegP proteolytic cages. Cell 2011; 145:67-78. [PMID: 21458668 DOI: 10.1016/j.cell.2011.02.024] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Revised: 12/03/2010] [Accepted: 02/07/2011] [Indexed: 11/17/2022]
Abstract
Protein quality control requires careful regulation of intracellular proteolysis. For DegP, a periplasmic protease, substrates promote assembly of inactive hexamers into proteolytically active cages with 12, 18, 24, or 30 subunits. Here, we show that sensitive activation and cage assembly require covalent linkage of distinct substrate sequences that affect degradation (degrons). One degron binds the DegP active site, and another degron binds a separate tethering site in PDZ1 in the crystal structure of a substrate-bound DegP dodecamer. FRET experiments demonstrate that active cages assemble rapidly in a reaction that is positively cooperative in substrate concentration, remain stably assembled while uncleaved substrate is present, and dissociate once degradation is complete. Thus, the energy of binding of linked substrate degrons drives assembly of the proteolytic machine responsible for subsequent degradation. Substrate cleavage and depletion results in disassembly, ensuring that DegP is proteolytically active only when sufficient quantities of protein substrates are present.
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Affiliation(s)
- Seokhee Kim
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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273
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Folding studies of purified LamB protein, the maltoporin from the Escherichia coli outer membrane: trimer dissociation can be separated from unfolding. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2206-13. [PMID: 21640073 DOI: 10.1016/j.bbamem.2011.05.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Revised: 04/29/2011] [Accepted: 05/16/2011] [Indexed: 11/20/2022]
Abstract
The folding mechanisms for β-barrel membrane proteins present unique challenges because acquisition of both secondary and tertiary structure is coupled with insertion into the bilayer. For the porins in Escherichia coli outer membrane, the assembly pathway also includes association into homotrimers. We study the folding pathway for purified LamB protein in detergent and observe extreme hysteresis in unfolding and refolding, as indicated by the shift in intrinsic fluorescence. The strong hysteresis is not seen in unfolding and refolding a mutant LamB protein lacking the disulfide bond, as it unfolds at much lower denaturant concentrations than wild type LamB protein. The disulfide bond is proposed to stabilize the structure of LamB protein by clasping together the two sides of Loop 1 as it lines the inner cavity of the barrel. In addition we find that low pH promotes dissociation of the LamB trimer to folded monomers, which run at about one third the size of the native trimer during SDS PAGE and are much more resistant to trypsin than the unfolded protein. We postulate the loss at low pH of two salt bridges between Loop 2 of the neighboring subunit and the inner wall of the monomer barrel destabilizes the quaternary structure.
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274
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Mykytczuk NCS, Trevors JT, Foote SJ, Leduc LG, Ferroni GD, Twine SM. Proteomic insights into cold adaptation of psychrotrophic and mesophilic Acidithiobacillus ferrooxidans strains. Antonie Van Leeuwenhoek 2011; 100:259-77. [DOI: 10.1007/s10482-011-9584-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2011] [Accepted: 04/29/2011] [Indexed: 11/29/2022]
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275
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Baud C, Gutsche I, Willery E, de Paepe D, Drobecq H, Gilleron M, Locht C, Jamin M, Jacob-Dubuisson F. Membrane-associated DegP in Bordetella chaperones a repeat-rich secretory protein. Mol Microbiol 2011; 80:1625-36. [DOI: 10.1111/j.1365-2958.2011.07672.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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276
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Roles of cysteine proteases Cwp84 and Cwp13 in biogenesis of the cell wall of Clostridium difficile. J Bacteriol 2011; 193:3276-85. [PMID: 21531808 DOI: 10.1128/jb.00248-11] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Clostridium difficile expresses a number of cell wall proteins, including the abundant high-molecular-weight and low-molecular-weight S-layer proteins (SLPs). These proteins are generated by posttranslational cleavage of the precursor SlpA by the cysteine protease Cwp84. We compared the phenotypes of C. difficile strains containing insertional mutations in either cwp84 or its paralog cwp13 and complemented with plasmids expressing wild-type or mutant forms of their genes. We show that the presence of uncleaved SlpA in the cell wall of the cwp84 mutant results in aberrant retention of other cell wall proteins at the cell surface, as demonstrated by secretion of the proteins Cwp66 and Cwp2 into the growth medium. These phenotypes are restored by complementation with a plasmid expressing wild-type Cwp84 enzyme but not with one encoding a Cys116Ala substitution in the active site. The cwp13 mutant cleaved the SlpA precursor normally and had a wild-type-like colony phenotype. Both Cwp84 and Cwp13 are produced as proenzymes which are processed by cleavage to produce mature enzymes. In the case of Cwp84, this cleavage does not appear to be autocatalytic, whereas in Cwp13 autocatalysis was demonstrated as a Cys109Ala mutant did not undergo processing. Cwp13 appears to have a role in processing of Cwp84 but is not essential for Cwp84 activity. Cwp13 cleaves SlpA in the HMW SLP domain, which we suggest may reflect a role in cleavage and degradation of misfolded proteins at the cell surface.
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277
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Sandoval CM, Baker SL, Jansen K, Metzner SI, Sousa MC. Crystal structure of BamD: an essential component of the β-Barrel assembly machinery of gram-negative bacteria. J Mol Biol 2011; 409:348-57. [PMID: 21463635 DOI: 10.1016/j.jmb.2011.03.035] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 03/15/2011] [Accepted: 03/16/2011] [Indexed: 01/28/2023]
Abstract
Folding and insertion of integral β-barrel proteins in the outer membrane (OM) is an essential process for Gram-negative bacteria that requires the β-barrel assembly machinery (BAM). Efficient OM protein (OMP) folding and insertion appears to require a consensus C-terminal signal in OMPs characterized by terminal F or W residues. The BAM complex is embedded in the OM and, in Escherichia coli, consists of the β-barrel BamA and four lipoproteins BamBCDE. BamA and BamD are broadly distributed across all species of Gram-negative bacteria, whereas the other components are present in only a subset of species. BamA and BamD are also essential for viability, suggesting that these two proteins constitute the functional core of the bacterial BAM complex. Here, we present the crystal structure of BamD from the thermophilic bacteria Rhodothermus marinus refined to 2.15 Å resolution. The protein contains five tetratricopeptide repeats (TPRs) organized into two offset tandems, each capped by a terminal helix. The N-terminal domain contains three TPRs and displays remarkable structural similarity with proteins that recognize targeting signals in extended conformations. The C-terminal domain harbors the remaining two TPRs and previously described mutations that impair binding to other BAM components map to this domain. Therefore, the structure suggests a model where the C-terminal domain provides a scaffold for interaction with BAM components, while the N-terminal domain participates in interaction with the substrates, either recognizing the C-terminal consensus sequence or binding unfolded OMP intermediates.
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Affiliation(s)
- Cristina M Sandoval
- Department of Chemistry and Biochemistry, University of Colorado at Boulder, USA
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278
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Balamurugan S, Dugan MER. Growth temperature associated protein expression and membrane fatty acid composition profiles of Salmonella enterica serovar Typhimurium. J Basic Microbiol 2011; 50:507-18. [PMID: 20806250 DOI: 10.1002/jobm.201000037] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Total cellular proteins and fatty acid composition profiles of mid-log phase cells of Salmonella enterica serovar Typhimurium grown at 8, 25, 37 or 42 °C were separated by 2D-PAGE and FAME analysis. Growth temperature associated protein expression can be grouped into 3 thermal classes which include proteins whose expression is: I) optimal at 37 °C, meaning their expression peaked at 37 °C; II) up-regulated with an increase in growth temperature; III) down-regulated with increase in growth temperature; meaning their expression peaked at 8 °C. At higher growth temperatures, proteins belonging to the functional groups of amino acid transport and metabolism, nucleotide metabolism, energy metabolism and post-translation modifications (chaperones) are present in substantially higher amounts. This increase in abundance is regulated in a temperature dependent manner. It is important to point out that proteins involved in energy metabolism observed in higher amounts at higher growth temperatures all belong to the glycolysis pathway, while at 8 °C they belonged to the TCA cycle. Increase in growth temperatures results in a decrease in membrane fatty acid unsaturation and an increase in saturated and cyclic fatty acids. These results provide an insight into the dynamic molecular and physiological responses of Salmonella Typhimurium during growth at different temperatures.
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279
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Bennion D, Charlson ES, Coon E, Misra R. Dissection of β-barrel outer membrane protein assembly pathways through characterizing BamA POTRA 1 mutants of Escherichia coli. Mol Microbiol 2011; 77:1153-71. [PMID: 20598079 DOI: 10.1111/j.1365-2958.2010.07280.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BamA of Escherichia coli is an essential component of the hetero-oligomeric machinery that mediates β-barrel outer membrane protein (OMP) assembly. The C- and N-termini of BamA fold into trans-membrane β-barrel and five soluble POTRA domains respectively. Detailed characterization of BamA POTRA 1 missense and deletion mutants revealed two competing OMP assembly pathways, one of which is followed by the archetypal trimeric β-barrel OMPs, OmpF and LamB, and is dependent on POTRA 1. Interestingly, our data suggest that BamA also requires its POTRA 1 domain for proper assembly. The second pathway is independent of POTRA 1 and is exemplified by TolC. Site-specific cross-linking analysis revealed that the POTRA 1 domain of BamA interacts with SurA, a periplasmic chaperone required for the assembly of OmpF and LamB, but not that of TolC and BamA. The data suggest that SurA and BamA POTRA 1 domain function in concert to assist folding and assembly of most β-barrel OMPs except for TolC, which folds into a unique soluble α-helical barrel and an OM-anchored β-barrel. The two assembly pathways finally merge at some step beyond POTRA 1 but presumably before membrane insertion, which is thought to be catalysed by the trans-membrane β-barrel domain of BamA.
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Affiliation(s)
- Drew Bennion
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
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280
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Role of the periplasmic chaperones Skp, SurA, and DegQ in outer membrane protein biogenesis in Neisseria meningitidis. J Bacteriol 2011; 193:1612-21. [PMID: 21296967 DOI: 10.1128/jb.00532-10] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The periplasmic chaperones Skp, SurA, and DegP are implicated in the biogenesis of outer membrane proteins (OMPs) in Escherichia coli. Here, we investigated whether these chaperones exert similar functions in Neisseria meningitidis. Although N. meningitidis does not contain a homolog of the protease/chaperone DegP, it does possess a homolog of another E. coli protein, DegQ, which can functionally replace DegP when overproduced. Hence, we examined whether in N. meningitidis, DegQ acts as a functional homolog of DegP. Single skp, surA, and degQ mutants were easily obtained, showing that none of these chaperones is essential in N. meningitidis. Furthermore, all combinations of double mutants were generated and no synthetic lethality was observed. The absence of SurA or DegQ did not affect OMP biogenesis. In contrast, the absence of Skp resulted in severely lower levels of the porins PorA and PorB but not of other OMPs. These decreased levels were not due to proteolytic activity of DegQ, since porin levels remained low in a skp degQ double mutant, indicating that neisserial DegQ is not a functional homolog of E. coli DegP. The absence of Skp resulted in lower expression of the porB gene, as shown by using a P(porB)-lacZ fusion. We found no cross-species complementation when Skp of E. coli or N. meningitidis was heterologously expressed in skp mutants, indicating that Skp functions in a species-specific manner. Our results demonstrate an important role for Skp but not for SurA or DegQ in OMP biogenesis in N. meningitidis.
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281
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Guilvout I, Nickerson NN, Chami M, Pugsley AP. Multimerization-defective variants of dodecameric secretin PulD. Res Microbiol 2011; 162:180-90. [DOI: 10.1016/j.resmic.2011.01.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Revised: 01/14/2011] [Indexed: 10/18/2022]
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282
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Heuck A, Schleiffer A, Clausen T. Augmenting β-augmentation: structural basis of how BamB binds BamA and may support folding of outer membrane proteins. J Mol Biol 2011; 406:659-66. [PMID: 21236263 DOI: 10.1016/j.jmb.2011.01.002] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Accepted: 01/04/2011] [Indexed: 10/18/2022]
Abstract
β-Barrel proteins are frequently found in the outer membrane of mitochondria, chloroplasts and Gram-negative bacteria. In Escherichia coli, these proteins are inserted in the outer membrane by the Bam (β-barrel assembly machinery) complex, a multiprotein machinery formed by the β-barrel protein BamA and the four peripheral membrane proteins BamB, BamC, BamD and BamE. The periplasmic part of BamA binds prefolded β-barrel proteins by a β-augmentation mechanism, thereby stabilizing the precursors prior to their membrane insertion. However, the role of the associated proteins within the Bam complex remains unknown. Here, we describe the crystal structure of BamB, a nonessential component of the Bam complex. The structure shows a typical eight-bladed β-propeller fold. Two sequence stretches of BamB were previously identified to be important for interaction with BamA. In our structure, both motifs are located in close proximity to each other and contribute to a conserved region forming a narrow groove on the top of the propeller. Moreover, crystal contacts reveal two interaction modes of how BamB might bind unfolded β-barrel proteins. In the crystal lattice, BamB binds to exposed β-strands by β-augmentation, whereas peptide stretches rich in aromatic residues can be accommodated in hydrophobic pockets located at the bottom of the propeller. Thus, BamB could simultaneously bind to BamA and prefolded β-barrel proteins, thereby enhancing the folding and membrane insertion capability of the Bam complex.
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Affiliation(s)
- Alexander Heuck
- Research Institute of Molecular Pathology, Dr. Bohrgasse 7, A-1030 Vienna, Austria
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283
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Crozat E, Hindré T, Kühn L, Garin J, Lenski RE, Schneider D. Altered regulation of the OmpF porin by Fis in Escherichia coli during an evolution experiment and between B and K-12 strains. J Bacteriol 2011; 193:429-40. [PMID: 21097626 PMCID: PMC3019833 DOI: 10.1128/jb.01341-10] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2010] [Accepted: 11/08/2010] [Indexed: 12/19/2022] Open
Abstract
The phenotypic plasticity of global regulatory networks provides bacteria with rapid acclimation to a wide range of environmental conditions, while genetic changes in those networks provide additional flexibility as bacteria evolve across long time scales. We previously identified mutations in the global regulator-encoding gene fis that enhanced organismal fitness during a long-term evolution experiment with Escherichia coli. To gain insight into the effects of these mutations, we produced two-dimensional protein gels with strains carrying different fis alleles, including a beneficial evolved allele and one with an in-frame deletion. We found that Fis controls the expression of the major porin-encoding gene ompF in the E. coli B-derived ancestral strain used in the evolution experiment, a relationship that has not been described before. We further showed that this regulatory connection evolved over two different time scales, perhaps explaining why it was not observed before. On the longer time scale, we showed that this regulation of ompF by Fis is absent from the more widely studied K-12 strain and thus is specific to the B strain. On a shorter time scale, this regulatory linkage was lost during 20,000 generations of experimental evolution of the B strain. Finally, we mapped the Fis binding sites in the ompF regulatory region, and we present a hypothetical model of ompF expression that includes its other known regulators.
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Affiliation(s)
- Estelle Crozat
- Laboratoire Adaptation et Pathogénie des Micro-organismes, CNRS UMR 5163, Université Joseph Fourier, Grenoble 1, BP 170, F-38042 Grenoble Cedex 9, France, CEA, DSV, iRTSV, Laboratoire d'Etude de la Dynamique des Protéomes, INSERM, U880, F-38042 Grenoble Cedex 9, France, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824
| | - Thomas Hindré
- Laboratoire Adaptation et Pathogénie des Micro-organismes, CNRS UMR 5163, Université Joseph Fourier, Grenoble 1, BP 170, F-38042 Grenoble Cedex 9, France, CEA, DSV, iRTSV, Laboratoire d'Etude de la Dynamique des Protéomes, INSERM, U880, F-38042 Grenoble Cedex 9, France, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824
| | - Lauriane Kühn
- Laboratoire Adaptation et Pathogénie des Micro-organismes, CNRS UMR 5163, Université Joseph Fourier, Grenoble 1, BP 170, F-38042 Grenoble Cedex 9, France, CEA, DSV, iRTSV, Laboratoire d'Etude de la Dynamique des Protéomes, INSERM, U880, F-38042 Grenoble Cedex 9, France, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824
| | - Jérome Garin
- Laboratoire Adaptation et Pathogénie des Micro-organismes, CNRS UMR 5163, Université Joseph Fourier, Grenoble 1, BP 170, F-38042 Grenoble Cedex 9, France, CEA, DSV, iRTSV, Laboratoire d'Etude de la Dynamique des Protéomes, INSERM, U880, F-38042 Grenoble Cedex 9, France, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824
| | - Richard E. Lenski
- Laboratoire Adaptation et Pathogénie des Micro-organismes, CNRS UMR 5163, Université Joseph Fourier, Grenoble 1, BP 170, F-38042 Grenoble Cedex 9, France, CEA, DSV, iRTSV, Laboratoire d'Etude de la Dynamique des Protéomes, INSERM, U880, F-38042 Grenoble Cedex 9, France, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824
| | - Dominique Schneider
- Laboratoire Adaptation et Pathogénie des Micro-organismes, CNRS UMR 5163, Université Joseph Fourier, Grenoble 1, BP 170, F-38042 Grenoble Cedex 9, France, CEA, DSV, iRTSV, Laboratoire d'Etude de la Dynamique des Protéomes, INSERM, U880, F-38042 Grenoble Cedex 9, France, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824
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284
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van Ulsen P. Protein folding in bacterial adhesion: secretion and folding of classical monomeric autotransporters. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2011; 715:125-42. [PMID: 21557061 DOI: 10.1007/978-94-007-0940-9_8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Bacterial adhesins mediate the attachment of bacteria to their niches, such as the tissue of an infected host. Adhesins have to be transported across the cell envelope to become active and during this secretion process they fold into their final conformation. This chapter focuses on the biogenesis of the classical monomeric autotransporter proteins, which are the most ubiquitous class of secreted proteins in Gram-negative bacteria. They may function as adhesins, but other functions are also known. Autotransporter proteins have a modular structure and consist of an N-terminal signal peptide and a C-terminal translocator domain with in between the secreted passenger domain that harbours the functions. The signal peptide directs the transport across the inner membrane to the periplasm via the Sec machinery. The translocator domain inserts into the outer membrane and facilitates the transport of the passenger to the cell surface. In this chapter, I will review our current knowledge of the secretion of classical monomeric autotransporters and the methods that have been used to assess their folding during the translocation, both in vitro and in vivo.
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Affiliation(s)
- Peter van Ulsen
- Section Molecular Microbiology, Department of Molecular Cell Biology, VU University Amsterdam, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands.
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285
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Involvement of the Shewanella oneidensis decaheme cytochrome MtrA in the periplasmic stability of the beta-barrel protein MtrB. Appl Environ Microbiol 2010; 77:1520-3. [PMID: 21169449 DOI: 10.1128/aem.01201-10] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Shewanella oneidensis outer membrane β-barrel protein MtrB is part of a membrane-spanning protein complex (MtrABC) which is necessary for dissimilatory iron reduction. Quantitative PCR, heterologous gene expression, and mutant studies indicated that MtrA is required for periplasmic stability of MtrB. DegP depletion compensated for this MtrA dependence.
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286
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New insights into the Lpt machinery for lipopolysaccharide transport to the cell surface: LptA-LptC interaction and LptA stability as sensors of a properly assembled transenvelope complex. J Bacteriol 2010; 193:1042-53. [PMID: 21169485 DOI: 10.1128/jb.01037-10] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lipopolysaccharide (LPS) is a major glycolipid present in the outer membrane (OM) of Gram-negative bacteria. The peculiar permeability barrier of the OM is due to the presence of LPS at the outer leaflet of this membrane that prevents many toxic compounds from entering the cell. In Escherichia coli LPS synthesized inside the cell is first translocated over the inner membrane (IM) by the essential MsbA flippase; then, seven essential Lpt proteins located in the IM (LptBCDF), in the periplasm (LptA), and in the OM (LptDE) are responsible for LPS transport across the periplasmic space and its assembly at the cell surface. The Lpt proteins constitute a transenvelope complex spanning IM and OM that appears to operate as a single device. We show here that in vivo LptA and LptC physically interact, forming a stable complex and, based on the analysis of loss-of-function mutations in LptC, we suggest that the C-terminal region of LptC is implicated in LptA binding. Moreover, we show that defects in Lpt components of either IM or OM result in LptA degradation; thus, LptA abundance in the cell appears to be a marker of properly bridged IM and OM. Collectively, our data support the recently proposed transenvelope model for LPS transport.
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287
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Helbig S, Patzer SI, Schiene-Fischer C, Zeth K, Braun V. Activation of colicin M by the FkpA prolyl cis-trans isomerase/chaperone. J Biol Chem 2010; 286:6280-90. [PMID: 21149455 PMCID: PMC3057819 DOI: 10.1074/jbc.m110.165274] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Colicin M (Cma) is specifically imported into the periplasm of Escherichia coli and kills the cells. Killing depends on the periplasmic peptidyl prolyl cis-trans isomerase/chaperone FkpA. To identify the Cma prolyl bonds targeted by FkpA, we replaced the 15 proline residues individually with alanine. Seven mutant proteins were fully active; Cma(P129A), Cma(P176A), and Cma(P260A) displayed 1%, and Cma(P107A) displayed 10% of the wild-type activity. Cma(P107A), Cma(P129A), and Cma(P260A), but not Cma(P176A), killed cells after entering the periplasm via osmotic shock, indicating that the former mutants were translocation-deficient; Cma(P129A) did not bind to the FhuA outer membrane receptor. The crystal structures of Cma and Cma(P176A) were identical, excluding inactivation of the activity domain located far from Pro-176. In a new peptidyl prolyl cis-trans isomerase assay, FkpA isomerized the Cma prolyl bond in peptide Phe-Pro-176 at a high rate, but Lys-Pro-107 and Leu-Pro-260 isomerized at only <10% of that rate. The four mutant proteins secreted into the periplasm via a fused signal sequence were toxic but much less than wild-type Cma. Wild-type and mutant Cma proteins secreted or translocated across the outer membrane by energy-coupled import or unspecific osmotic shock were only active in the presence of FkpA. We propose that Cma unfolds during transfer across the outer or cytoplasmic membrane and refolds to the active form in the periplasm assisted by FkpA. Weak refolding of Cma(P176A) would explain its low activity in all assays. Of the four proline residues identified as being important for Cma activity, Phe-Pro-176 is most likely targeted by FkpA.
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Affiliation(s)
- Stephanie Helbig
- Max Planck Institute for Developmental Biology, Spemannstrasse 35, 72076 Tübingen, Germany
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288
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Rowley G, Skovierova H, Stevenson A, Rezuchova B, Homerova D, Lewis C, Sherry A, Kormanec J, Roberts M. The periplasmic chaperone Skp is required for successful Salmonella Typhimurium infection in a murine typhoid model. MICROBIOLOGY-SGM 2010; 157:848-858. [PMID: 21148205 DOI: 10.1099/mic.0.046011-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The alternative sigma factor σ(E) (rpoE) is essential for survival in vivo of Salmonella Typhimurium but is dispensable during growth in the laboratory. We have been identifying σ(E)-regulated genes and studying their regulation and function to elucidate their potential role in the severe attenuation of S. Typhimurium rpoE mutants. In this study we identify five promoters that control the rseP, yaeT (bamA), skp region. A confirmed σ(E)-dependent promoter, yaeTp1, and a second downstream promoter, yaeTp2, are located within the upstream gene rseP and direct expression of the downstream genes. The only known function of RseP is σ(E) activation, and it is therefore not expected to be essential for S. Typhimurium in vitro. However, it proved impossible to delete the entire rseP gene due to the presence of internal promoters that regulate the essential gene yaeT. We could inactivate rseP by deleting the first third of the gene, leaving the yaeT promoters intact. Like the rpoE mutant, the rseP mutant exhibited severe attenuation in vivo. We were able to delete the entire coding sequence of skp, which encodes a periplasmic chaperone involved in targeting misfolded outer-membrane proteins to the β-barrel assembly machinery. The skp mutant was attenuated in mice after oral and parenteral infection. Virulence could be complemented by providing skp in trans but only by linking it to a heterologous σ(E)-regulated promoter. The reason the skp mutant is attenuated is currently enigmatic, but we know it is not through increased sensitivity to a variety of RpoE-activating host stresses, such as H(2)O(2), polymyxin B and high temperature, or through altered secretion of effector proteins by either the Salmonella pathogenicity island (SPI)-1 or the SPI-2 type III secretion system.
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Affiliation(s)
- Gary Rowley
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Henrieta Skovierova
- Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 845 51 Bratislava, Slovak Republik
| | - Andrew Stevenson
- Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow G61 1QH, UK
| | - Bronislava Rezuchova
- Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 845 51 Bratislava, Slovak Republik
| | - Dagmar Homerova
- Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 845 51 Bratislava, Slovak Republik
| | - Claire Lewis
- Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow G61 1QH, UK
| | - Aileen Sherry
- Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow G61 1QH, UK
| | - Jan Kormanec
- Institute of Molecular Biology, Slovak Academy of Sciences, Dubravska cesta 21, 845 51 Bratislava, Slovak Republik
| | - Mark Roberts
- Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow G61 1QH, UK
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289
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Constitutive expression of the maltoporin LamB in the absence of OmpR damages the cell envelope. J Bacteriol 2010; 193:842-53. [PMID: 21131484 DOI: 10.1128/jb.01004-10] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cells experience multiple environmental stimuli simultaneously. To survive, they must respond accordingly. Unfortunately, the proper response to one stress easily could make the cell more susceptible to a second coexistent stress. To deal with such a problem, a cell must possess a mechanism that balances the need to respond simultaneously to both stresses. Our recent studies of ompR malT(Con) double mutants show that elevated expression of LamB, the outer membrane porin responsible for maltose uptake, causes cell death when the osmoregulator OmpR is disabled. To obtain insight into the nature of the death experienced by ompR malT(Con) mutants, we described the death process. On the basis of microscopic and biochemical approaches, we conclude that death results from a loss of membrane integrity. On the basis of an unbiased genome-wide search for suppressor mutations, we conclude that this loss of membrane integrity results from a LamB-induced envelope stress that the cells do not sufficiently perceive and thus do not adequately accommodate. Finally, we conclude that this envelope stress involves an imbalance in the lipopolysaccharide/porin composition of the outer membrane and an increased requirement for inorganic phosphate.
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290
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Different contributions of HtrA protease and chaperone activities to Campylobacter jejuni stress tolerance and physiology. Appl Environ Microbiol 2010; 77:57-66. [PMID: 21075890 DOI: 10.1128/aem.01603-10] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The microaerophilic bacterium Campylobacter jejuni is the most common cause of bacterial food-borne infections in the developed world. Tolerance to environmental stress relies on proteases and chaperones in the cell envelope, such as HtrA and SurA. HtrA displays both chaperone and protease activities, but little is known about how each of these activities contributes to stress tolerance in bacteria. In vitro experiments showed temperature-dependent protease and chaperone activities of C. jejuni HtrA. A C. jejuni mutant lacking only the protease activity of HtrA was used to show that the HtrA chaperone activity is sufficient for growth at high temperature or under oxidative stress, whereas the HtrA protease activity is essential only under conditions close to the growth limit for C. jejuni. However, the protease activity was required to prevent induction of the cytoplasmic heat shock response even under optimal growth conditions. Interestingly, the requirement of HtrA at high temperatures was found to depend on the oxygen level, and our data suggest that HtrA may protect oxidatively damaged proteins. Finally, protease activity stimulates HtrA production and oligomer formation, suggesting that a regulatory role depends on the protease activity of HtrA. Studying a microaerophilic organism encoding only two known periplasmic chaperones (HtrA and SurA) revealed an efficient HtrA chaperone activity and proposed multiple roles of the protease activity, increasing our understanding of HtrA in bacterial physiology.
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291
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Gatzeva-Topalova PZ, Warner LR, Pardi A, Sousa MC. Structure and flexibility of the complete periplasmic domain of BamA: the protein insertion machine of the outer membrane. Structure 2010; 18:1492-501. [PMID: 21070948 PMCID: PMC2991101 DOI: 10.1016/j.str.2010.08.012] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2010] [Revised: 08/16/2010] [Accepted: 08/17/2010] [Indexed: 11/30/2022]
Abstract
Folding and insertion of β-barrel outer membrane proteins (OMPs) is essential for Gram-negative bacteria. This process is mediated by the multiprotein complex BAM, composed of the essential β-barrel OMP BamA and four lipoproteins (BamBCDE). The periplasmic domain of BamA is key for its function and contains five "polypeptide transport-associated" (POTRA) repeats. Here, we report the crystal structure of the POTRA4-5 tandem, containing the essential for BAM complex formation and cell viability POTRA5. The domain orientation observed in the crystal is validated by solution NMR and SAXS. Using previously determined structures of BamA POTRA1-4, we present a spliced model of the entire BamA periplasmic domain validated by SAXS. Solution scattering shows that conformational flexibility between POTRA2 and 3 gives rise to compact and extended conformations. The length of BamA in its extended conformation suggests that the protein may bridge the inner and outer membranes across the periplasmic space.
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292
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Giuseppe PO, Von Atzingen M, Nascimento ALTO, Zanchin NIT, Guimarães BG. The crystal structure of the leptospiral hypothetical protein LIC12922 reveals homology with the periplasmic chaperone SurA. J Struct Biol 2010; 173:312-22. [PMID: 20970503 DOI: 10.1016/j.jsb.2010.10.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Revised: 10/11/2010] [Accepted: 10/18/2010] [Indexed: 12/22/2022]
Abstract
Leptospirosis is a world spread zoonosis caused by members of the genus Leptospira. Although leptospires were identified as the causal agent of leptospirosis almost 100 years ago, little is known about their biology, which hinders the development of new treatment and prevention strategies. One of the several aspects of the leptospiral biology not yet elucidated is the process by which outer membrane proteins (OMPs) traverse the periplasm and are inserted into the outer membrane. The crystal structure determination of the conserved hypothetical protein LIC12922 from Leptospira interrogans revealed a two domain protein homologous to the Escherichia coli periplasmic chaperone SurA. The LIC12922 NC-domain is structurally related to the chaperone modules of E. coli SurA and trigger factor, whereas the parvulin domain is devoid of peptidyl prolyl cis-trans isomerase activity. Phylogenetic analyses suggest a relationship between LIC12922 and the chaperones PrsA, PpiD and SurA. Based on our structural and evolutionary analyses, we postulate that LIC12922 is a periplasmic chaperone involved in OMPs biogenesis in Leptospira spp. Since LIC12922 homologs were identified in all spirochetal genomes sequenced to date, this assumption may have implications for the OMPs biogenesis studies not only in leptospires but in the entire Phylum Spirochaetes.
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Affiliation(s)
- Priscila O Giuseppe
- Brazilian Biosciences National Laboratory (LNBio), Brazilian Center of Research in Energy and Materials (CNPEM), Giuseppe Máximo Scolfaro 10000, 13083-970 Campinas, SP, Brazil
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293
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Bohnsack MT, Schleiff E. The evolution of protein targeting and translocation systems. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:1115-30. [DOI: 10.1016/j.bbamcr.2010.06.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2010] [Revised: 05/26/2010] [Accepted: 06/11/2010] [Indexed: 11/28/2022]
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294
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Jong WSP, Saurí A, Luirink J. Extracellular production of recombinant proteins using bacterial autotransporters. Curr Opin Biotechnol 2010; 21:646-52. [DOI: 10.1016/j.copbio.2010.07.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2010] [Accepted: 07/15/2010] [Indexed: 01/29/2023]
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295
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Knowles TJ, Sridhar P, Rajesh S, Manoli E, Overduin M, Henderson IR. Secondary structure and 1H, 13C and 15N resonance assignments of BamE, a component of the outer membrane protein assembly machinery in Escherichia coli. BIOMOLECULAR NMR ASSIGNMENTS 2010; 4:179-181. [PMID: 20526702 DOI: 10.1007/s12104-010-9236-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2010] [Accepted: 05/20/2010] [Indexed: 05/29/2023]
Abstract
We report the (1)H, (13)C and (15)N backbone and side chain chemical shift assignments and secondary structure of the Escherichia coli protein BamE, a subunit of the BAM (Omp85) complex, the β-barrel assembly machinery present in all Gram-negative bacteria, mitochondria and chloroplasts and is essential for viability.
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Affiliation(s)
- Timothy J Knowles
- School of Cancer Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
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296
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Matern Y, Barion B, Behrens-Kneip S. PpiD is a player in the network of periplasmic chaperones in Escherichia coli. BMC Microbiol 2010; 10:251. [PMID: 20920237 PMCID: PMC2956729 DOI: 10.1186/1471-2180-10-251] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Accepted: 09/29/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The inner membrane-anchored periplasmic folding factor PpiD is described as a parvulin-like peptidyl prolyl isomerase (PPIase) that assists in the maturation of the major beta-barrel outer membrane proteins (OMPs) of Escherichia coli. More recent work however, calls these findings into question. Here, we re-examined the role of PpiD in the E. coli periplasm by analyzing its functional interplay with other folding factors that influence OMP maturation as well as general protein folding in the periplasmic compartment of the cell, such as SurA, Skp, and DegP. RESULTS The analysis of the effects of both deletion and overexpression of ppiD on cell envelope phenotypes revealed that PpiD in contrast to prior observations plays only a minor role, if any, in the maturation of OMPs and cannot compensate for the lack of SurA in the periplasm. On the other hand, our results show that overproduction of PpiD rescues a surA skp double mutant from lethality. In the presence of increased PpiD levels surA skp cells show reduced activities of both the SigmaE-dependent and the Cpx envelope stress responses, and contain increased amounts of folded species of the major OMP OmpA. These effects require the anchoring of PpiD in the inner membrane but are independent of its parvulin-like PPIase domain. Moreover, a PpiD protein lacking the PPIase domain also complements the growth defects of an fkpA ppiD surA triple PPIase mutant and exhibits chaperone activity in vitro. In addition, PpiD appears to collaborate with DegP, as deletion of ppiD confers a temperature-dependent conditional synthetic phenotype in a degP mutant. CONCLUSIONS This study provides first direct evidence that PpiD functions as a chaperone and contributes to the network of periplasmic chaperone activities without being specifically involved in OMP maturation. Consistent with previous work, our data support a model in which the chaperone function of PpiD is used to aid in the early periplasmic folding of many newly translocated proteins.
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Affiliation(s)
- Yvonne Matern
- Abteilung Molekulare Genetik und Präparative Molekularbiologie, Institut für Mikrobiologie und Genetik, Georg-August-Universität Göttingen, Grisebachstr, 8, D-37077 Göttingen, Germany
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297
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Denoncin K, Vertommen D, Paek E, Collet JF. The protein-disulfide isomerase DsbC cooperates with SurA and DsbA in the assembly of the essential β-barrel protein LptD. J Biol Chem 2010; 285:29425-33. [PMID: 20615876 PMCID: PMC2937975 DOI: 10.1074/jbc.m110.119321] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2010] [Revised: 06/23/2010] [Indexed: 11/06/2022] Open
Abstract
The assembly of the β-barrel proteins present in the outer membrane (OM) of Gram-negative bacteria is poorly characterized. After translocation across the inner membrane, unfolded β-barrel proteins are escorted across the periplasm by chaperones that reside within this compartment. Two partially redundant chaperones, SurA and Skp, are considered to transport the bulk mass of β-barrel proteins. We found that the periplasmic disulfide isomerase DsbC cooperates with SurA and the thiol oxidase DsbA in the folding of the essential β-barrel protein LptD. LptD inserts lipopolysaccharides in the OM. It is also the only β-barrel protein with more than two cysteine residues. We found that surAdsbC mutants, but not skpdsbC mutants, exhibit a synthetic phenotype. They have a decreased OM integrity, which is due to the lack of the isomerase activity of DsbC. We also isolated DsbC in a mixed disulfide complex with LptD. As such, LptD is identified as the first substrate of DsbC that is localized in the OM. Thus, electrons flowing from the cytoplasmic thioredoxin system maintain the integrity of the OM by assisting the folding of one of the most important β-barrel proteins.
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Affiliation(s)
- Katleen Denoncin
- From the de Duve Institute, Université catholique de Louvain and
- the Brussels Center for Redox Biology, B-1200 Brussels, Belgium and
| | - Didier Vertommen
- From the de Duve Institute, Université catholique de Louvain and
| | - Eunok Paek
- the Department of Mechanical and Information Engineering, University of Seoul, Seoul 130–743, Korea
| | - Jean-François Collet
- From the de Duve Institute, Université catholique de Louvain and
- the Brussels Center for Redox Biology, B-1200 Brussels, Belgium and
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298
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Listeria monocytogenes PrsA2 is required for virulence factor secretion and bacterial viability within the host cell cytosol. Infect Immun 2010; 78:4944-57. [PMID: 20823208 DOI: 10.1128/iai.00532-10] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the course of establishing its replication niche within the cytosol of infected host cells, the facultative intracellular bacterial pathogen Listeria monocytogenes must efficiently regulate the secretion and activity of multiple virulence factors. L. monocytogenes encodes two predicted posttranslocation secretion chaperones, PrsA1 and PrsA2, and evidence suggests that PrsA2 has been specifically adapted for bacterial pathogenesis. PrsA-like chaperones have been identified in a number of Gram-positive bacteria, where they are reported to function at the bacterial membrane-cell wall interface to assist in the folding of proteins translocated across the membrane; in some cases, these proteins have been found to be essential for bacterial viability. In this study, the contributions of PrsA2 and PrsA1 to L. monocytogenes growth and protein secretion were investigated in vitro and in vivo. Neither PrsA2 nor PrsA1 was found to be essential for L. monocytogenes growth in broth culture; however, optimal bacterial viability was found to be dependent upon PrsA2 for L. monocytogenes located within the cytosol of host cells. Proteomic analyses of prsA2 mutant strains in the presence of a mutationally activated allele of the virulence regulator PrfA revealed a critical requirement for PrsA2 activity under conditions of PrfA activation, an event which normally takes place within the host cell cytosol. Despite a high degree of amino acid similarity, no detectable degree of functional overlap was observed between PrsA2 and PrsA1. Our results indicate a critical requirement for PrsA2 under conditions relevant to host cell infection.
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299
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Tommassen J. Assembly of outer-membrane proteins in bacteria and mitochondria. Microbiology (Reading) 2010; 156:2587-2596. [DOI: 10.1099/mic.0.042689-0] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The cell envelope of Gram-negative bacteria consists of two membranes separated by the periplasm. In contrast with most integral membrane proteins, which span the membrane in the form of hydrophobicα-helices, integral outer-membrane proteins (OMPs) formβ-barrels. Similarβ-barrel proteins are found in the outer membranes of mitochondria and chloroplasts, probably reflecting the endosymbiont origin of these eukaryotic cell organelles. How theseβ-barrel proteins are assembled into the outer membrane has remained enigmatic for a long time. In recent years, much progress has been reached in this field by the identification of the components of the OMP assembly machinery. The central component of this machinery, called Omp85 or BamA, is an essential and highly conserved bacterial protein that recognizes a signature sequence at the C terminus of its substrate OMPs. A homologue of this protein is also found in mitochondria, where it is required for the assembly ofβ-barrel proteins into the outer membrane as well. Although accessory components of the machineries are different between bacteria and mitochondria, a mitochondrialβ-barrel OMP can be assembled into the bacterial outer membrane and, vice versa, bacterial OMPs expressed in yeast are assembled into the mitochondrial outer membrane. These observations indicate that the basic mechanism of OMP assembly is evolutionarily highly conserved.
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Affiliation(s)
- Jan Tommassen
- Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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300
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Minor modifications and major adaptations: the evolution of molecular machines driving mitochondrial protein import. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:947-54. [PMID: 20659421 DOI: 10.1016/j.bbamem.2010.07.019] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2010] [Revised: 07/17/2010] [Accepted: 07/20/2010] [Indexed: 11/23/2022]
Abstract
Bacterial endosymbionts gave rise to mitochondria in a process that depended on the acquisition of protein import pathways. Modification and in some cases major re-tooling of the endosymbiont's cellular machinery produced these pathways, establishing mitochondria as organelles common to all eukaryotic cells. The legacy of this evolutionary tinkering can be seen in the homologies and structural similarities between mitochondrial protein import machinery and modern day bacterial proteins. Comparative analysis of these systems is revealing both possible routes for the evolution of the mitochondrial membrane translocases and a greater understanding of the mechanisms behind mitochondrial protein import. This article is part of a Special Issue entitled Protein translocation across or insertion into membranes.
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