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Type three secretion system in Salmonella Typhimurium: the key to infection. Genes Genomics 2020; 42:495-506. [PMID: 32112371 DOI: 10.1007/s13258-020-00918-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2019] [Accepted: 02/12/2020] [Indexed: 11/27/2022]
Abstract
BACKGROUND Type Three Secretion Systems (T3SS) are nanomachine complexes, which display the ability to inject effector proteins directly into host cells. This skill allows for gram-negative bacteria to modulate several host cell responses, such as cytoskeleton rearrangement, signal transduction, and cytokine production, which in turn increase the pathogenicity of these bacteria. The Salmonella enterica subsp. enterica serovar Typhimurium (ST) T3SS has been the most characterized so far. Among gram-negative bacterium, ST is one of enterica groups predicted to have two T3SSs activated during different phases of infection. OBJECTIVE To comprise current information about ST T3SS structure and function as well as an overview of its assembly and hierarchical regulation. METHODS With a brief and straightforward reading, this review summarized aspects of both ST T3SS, such as its structure and function. That was possible due to the development of novel techniques, such as X-ray crystallography, cryoelectron microscopy, and nano-gold labelling, which also elucidated the mechanisms behind T3SS assembly and regulation, which was addressed in this review. CONCLUSION This paper provided fundamental overview of ST T3SS assembly and regulation, besides summarized the structure and function of this complex. Due to T3SS relevance in ST pathogenicity, this complex could become a potential target in therapeutic studies as this nanomachine modulates the infection process.
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2
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Majewski DD, Worrall LJ, Strynadka NCJ. Secretins revealed: structural insights into the giant gated outer membrane portals of bacteria. Curr Opin Struct Biol 2018; 51:61-72. [DOI: 10.1016/j.sbi.2018.02.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 02/28/2018] [Indexed: 01/19/2023]
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3
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Billerbeck S. Small Functional Peptides and Their Application in Superfunctionalizing Proteins. Synth Biol (Oxf) 2018. [DOI: 10.1002/9783527688104.ch11] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Affiliation(s)
- Sonja Billerbeck
- Columbia University; Department of Chemistry; 550 West 120th Street New York NY 10027 USA
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4
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Unraveling the Self-Assembly of the Pseudomonas aeruginosa XcpQ Secretin Periplasmic Domain Provides New Molecular Insights into Type II Secretion System Secreton Architecture and Dynamics. mBio 2017; 8:mBio.01185-17. [PMID: 29042493 PMCID: PMC5646246 DOI: 10.1128/mbio.01185-17] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The type II secretion system (T2SS) releases large folded exoproteins across the envelope of many Gram-negative pathogens. This secretion process therefore requires specific gating, interacting, and dynamics properties mainly operated by a bipartite outer membrane channel called secretin. We have a good understanding of the structure-function relationship of the pore-forming C-terminal domain of secretins. In contrast, the high flexibility of their periplasmic N-terminal domain has been an obstacle in obtaining the detailed structural information required to uncover its molecular function. In Pseudomonas aeruginosa, the Xcp T2SS plays an important role in bacterial virulence by its capacity to deliver a large panel of toxins and degradative enzymes into the surrounding environment. Here, we revealed that the N-terminal domain of XcpQ secretin spontaneously self-assembled into a hexamer of dimers independently of its C-terminal domain. Furthermore, and by using multidisciplinary approaches, we elucidate the structural organization of the XcpQ N domain and demonstrate that secretin flexibility at interdimer interfaces is mandatory for its function. Bacterial secretins are large homooligomeric proteins constituting the outer membrane pore-forming element of several envelope-embedded nanomachines essential in bacterial survival and pathogenicity. They comprise a well-defined membrane-embedded C-terminal domain and a modular periplasmic N-terminal domain involved in substrate recruitment and connection with inner membrane components. We are studying the XcpQ secretin of the T2SS present in the pathogenic bacterium Pseudomonas aeruginosa. Our data highlight the ability of the XcpQ N-terminal domain to spontaneously oligomerize into a hexamer of dimers. Further in vivo experiments revealed that this domain adopts different conformations essential for the T2SS secretion process. These findings provide new insights into the functional understanding of bacterial T2SS secretins.
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Thomassin JL, Santos Moreno J, Guilvout I, Tran Van Nhieu G, Francetic O. The trans-envelope architecture and function of the type 2 secretion system: new insights raising new questions. Mol Microbiol 2017; 105:211-226. [DOI: 10.1111/mmi.13704] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/04/2017] [Indexed: 12/21/2022]
Affiliation(s)
- Jenny-Lee Thomassin
- Department of structural biology and chemistry, Biochemistry of Macromolecular Interactions Unit; Institut Pasteur; 28 rue du Dr Roux 75724 Paris Cedex 15 France
- Centre National de la Recherche Scientifique (CNRS); ERL6002 75724 Paris France
| | - Javier Santos Moreno
- Université Paris Diderot (Paris 7) Sorbonne Paris Cité; Paris France
- Laboratory of Intercellular Communication and Microbial Infections; CIRB, Collège de France; 11 Place Marcelin Berthelot 75005 Paris France
- Institut National de la Santé et de la Recherche Médicale (Inserm) U1050; 75005 Paris France
- Centre National de la Recherche Scientifique (CNRS), UMR7241; 75005 Paris France
- MEMOLIFE Laboratory of Excellence and Paris Sciences et Lettres; 75005 Paris France
| | - Ingrid Guilvout
- Department of structural biology and chemistry, Biochemistry of Macromolecular Interactions Unit; Institut Pasteur; 28 rue du Dr Roux 75724 Paris Cedex 15 France
- Centre National de la Recherche Scientifique (CNRS); ERL6002 75724 Paris France
| | - Guy Tran Van Nhieu
- Laboratory of Intercellular Communication and Microbial Infections; CIRB, Collège de France; 11 Place Marcelin Berthelot 75005 Paris France
- Institut National de la Santé et de la Recherche Médicale (Inserm) U1050; 75005 Paris France
- Centre National de la Recherche Scientifique (CNRS), UMR7241; 75005 Paris France
- MEMOLIFE Laboratory of Excellence and Paris Sciences et Lettres; 75005 Paris France
| | - Olivera Francetic
- Department of structural biology and chemistry, Biochemistry of Macromolecular Interactions Unit; Institut Pasteur; 28 rue du Dr Roux 75724 Paris Cedex 15 France
- Centre National de la Recherche Scientifique (CNRS); ERL6002 75724 Paris France
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6
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Guilvout I, Brier S, Chami M, Hourdel V, Francetic O, Pugsley AP, Chamot-Rooke J, Huysmans GHM. Prepore Stability Controls Productive Folding of the BAM-independent Multimeric Outer Membrane Secretin PulD. J Biol Chem 2016; 292:328-338. [PMID: 27903652 DOI: 10.1074/jbc.m116.759498] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Revised: 11/21/2016] [Indexed: 12/19/2022] Open
Abstract
Members of a group of multimeric secretion pores that assemble independently of any known membrane-embedded insertase in Gram-negative bacteria fold into a prepore before membrane-insertion occurs. The mechanisms and the energetics that drive the folding of these proteins are poorly understood. Here, equilibrium unfolding and hydrogen/deuterium exchange monitored by mass spectrometry indicated that a loss of 4-5 kJ/mol/protomer in the N3 domain that is peripheral to the membrane-spanning C domain in the dodecameric secretin PulD, the founding member of this class, prevents pore formation by destabilizing the prepore into a poorly structured dodecamer as visualized by electron microscopy. Formation of native PulD-multimers by mixing protomers that differ in N3 domain stability, suggested that the N3 domain forms a thermodynamic seal onto the prepore. This highlights the role of modest free energy changes in the folding of pre-integration forms of a hyperstable outer membrane complex and reveals a key driving force for assembly independently of the β-barrel assembly machinery.
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Affiliation(s)
- Ingrid Guilvout
- From the Molecular Genetics Unit, CNRS ERL 3526.,Laboratory of Macromolecular Systems and Signaling and
| | - Sébastien Brier
- Structural Mass Spectrometry and Proteomics Unit, CNRS UMR 3528, Institut Pasteur, 75724 Paris Cedex 15, France and
| | - Mohamed Chami
- the BioEM lab, Biozentrum, University of Basel, CH 4058 Basel, Switzerland
| | - Véronique Hourdel
- Structural Mass Spectrometry and Proteomics Unit, CNRS UMR 3528, Institut Pasteur, 75724 Paris Cedex 15, France and
| | - Olivera Francetic
- From the Molecular Genetics Unit, CNRS ERL 3526.,Laboratory of Macromolecular Systems and Signaling and
| | | | - Julia Chamot-Rooke
- Structural Mass Spectrometry and Proteomics Unit, CNRS UMR 3528, Institut Pasteur, 75724 Paris Cedex 15, France and
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Salzer R, D'Imprima E, Gold VAM, Rose I, Drechsler M, Vonck J, Averhoff B. Topology and Structure/Function Correlation of Ring- and Gate-forming Domains in the Dynamic Secretin Complex of Thermus thermophilus. J Biol Chem 2016; 291:14448-56. [PMID: 27226590 DOI: 10.1074/jbc.m116.724153] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Indexed: 11/06/2022] Open
Abstract
Secretins are versatile outer membrane pores used by many bacteria to secrete proteins, toxins, or filamentous phages; extrude type IV pili (T4P); or take up DNA. Extrusion of T4P and natural transformation of DNA in the thermophilic bacterium Thermus thermophilus requires a unique secretin complex comprising six stacked rings, a membrane-embedded cone structure, and two gates that open and close a central channel. To investigate the role of distinct domains in ring and gate formation, we examined a set of deletion derivatives by cryomicroscopy techniques. Here we report that maintaining the N0 ring in the deletion derivatives led to stable PilQ complexes. Analyses of the variants unraveled that an N-terminal domain comprising a unique βββαβ fold is essential for the formation of gate 2. Furthermore, we identified four βαββα domains essential for the formation of the N2 to N5 rings. Mutant studies revealed that deletion of individual ring domains significantly reduces piliation. The N1, N2, N4, and N5 deletion mutants were significantly impaired in T4P-mediated twitching motility, whereas the motility of the N3 mutant was comparable with that of wild-type cells. This indicates that the deletion of the N3 ring leads to increased pilus dynamics, thereby compensating for the reduced number of pili of the N3 mutant. All mutants exhibit a wild-type natural transformation phenotype, leading to the conclusion that DNA uptake is independent of functional T4P.
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Affiliation(s)
- Ralf Salzer
- From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and
| | - Edoardo D'Imprima
- the Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Vicki A M Gold
- the Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Ilona Rose
- From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and
| | - Moritz Drechsler
- From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and
| | - Janet Vonck
- the Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Beate Averhoff
- From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and
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8
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Lipids assist the membrane insertion of a BAM-independent outer membrane protein. Sci Rep 2015; 5:15068. [PMID: 26463896 PMCID: PMC4604470 DOI: 10.1038/srep15068] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 09/14/2015] [Indexed: 02/04/2023] Open
Abstract
Like several other large, multimeric bacterial outer membrane proteins (OMPs), the assembly of the Klebsiella oxytoca OMP PulD does not rely on the universally conserved β-barrel assembly machinery (BAM) that catalyses outer membrane insertion. The only other factor known to interact with PulD prior to or during outer membrane targeting and assembly is the cognate chaperone PulS. Here, in vitro translation-transcription coupled PulD folding demonstrated that PulS does not act during the membrane insertion of PulD, and engineered in vivo site-specific cross-linking between PulD and PulS showed that PulS binding does not prevent membrane insertion. In vitro folding kinetics revealed that PulD is atypical compared to BAM-dependent OMPs by inserting more rapidly into membranes containing E. coli phospholipids than into membranes containing lecithin. PulD folding was fast in diC14:0-phosphatidylethanolamine liposomes but not diC14:0-phosphatidylglycerol liposomes, and in diC18:1-phosphatidylcholine liposomes but not in diC14:1-phosphatidylcholine liposomes. These results suggest that PulD efficiently exploits the membrane composition to complete final steps in insertion and explain how PulD can assemble independently of any protein-assembly machinery. Lipid-assisted assembly in this manner might apply to other large OMPs whose assembly is BAM-independent.
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9
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Dunstan RA, Hay ID, Wilksch JJ, Schittenhelm RB, Purcell AW, Clark J, Costin A, Ramm G, Strugnell RA, Lithgow T. Assembly of the secretion pores GspD, Wza and CsgG into bacterial outer membranes does not require the Omp85 proteins BamA or TamA. Mol Microbiol 2015; 97:616-29. [DOI: 10.1111/mmi.13055] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/08/2015] [Indexed: 01/07/2023]
Affiliation(s)
- Rhys A. Dunstan
- Department of Microbiology; Monash University; Clayton Vic. 3800 Australia
- Department of Biochemistry and Molecular Biology; Monash University; Clayton Vic. 3800 Australia
| | - Iain D. Hay
- Department of Microbiology; Monash University; Clayton Vic. 3800 Australia
| | - Jonathan J. Wilksch
- Department of Microbiology & Immunology; The Peter Doherty Institute for Infection and Immunity; University of Melbourne; Parkville Vic. 3052 Australia
| | - Ralf B. Schittenhelm
- Department of Biochemistry and Molecular Biology; Monash University; Clayton Vic. 3800 Australia
| | - Anthony W. Purcell
- Department of Biochemistry and Molecular Biology; Monash University; Clayton Vic. 3800 Australia
| | - Joan Clark
- Department of Biochemistry and Molecular Biology; Monash University; Clayton Vic. 3800 Australia
| | - Adam Costin
- Department of Biochemistry and Molecular Biology; Monash University; Clayton Vic. 3800 Australia
| | - Georg Ramm
- Department of Biochemistry and Molecular Biology; Monash University; Clayton Vic. 3800 Australia
| | - Richard A. Strugnell
- Department of Microbiology & Immunology; The Peter Doherty Institute for Infection and Immunity; University of Melbourne; Parkville Vic. 3052 Australia
| | - Trevor Lithgow
- Department of Microbiology; Monash University; Clayton Vic. 3800 Australia
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10
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Abstract
UNLABELLED Type IV pili (T4Ps) are surface appendages used by Gram-negative and Gram-positive pathogens for motility and attachment to epithelial surfaces. In Gram-negative bacteria, such as the important pediatric pathogen enteropathogenic Escherichia coli (EPEC), during extension and retraction, the pilus passes through an outer membrane (OM) pore formed by the multimeric secretin complex. The secretin is common to Gram-negative assemblies, including the related type 2 secretion (T2S) system and the type 3 secretion (T3S) system. The N termini of the secretin monomers are periplasmic and in some systems have been shown to mediate substrate specificity. In this study, we mapped the topology of BfpB, the T4P secretin from EPEC, using a combination of biochemical and biophysical techniques that allowed selective identification of periplasmic and extracellular residues. We applied rules based on solved atomic structures of outer membrane proteins (OMPs) to generate our topology model, combining the experimental results with secondary structure prediction algorithms and direct inspection of the primary sequence. Surprisingly, the C terminus of BfpB is extracellular, a result confirmed by flow cytometry for BfpB and a distantly related T4P secretin, PilQ, from Pseudomonas aeruginosa. Keeping with prior evidence, the C termini of two T2S secretins and one T3S secretin were not detected on the extracellular surface. On the basis of our data and structural constraints, we propose that BfpB forms a beta barrel with 16 transmembrane beta strands. We propose that the T4P secretins have a C-terminal segment that passes through the center of each monomer. IMPORTANCE Secretins are multimeric proteins that allow the passage of secreted toxins and surface structures through the outer membranes (OMs) of Gram-negative bacteria. To date, there have been no atomic structures of the C-terminal region of a secretin, although electron microscopy (EM) structures of the complex are available. This work provides a detailed topology prediction of the membrane-spanning domain of a type IV pilus (T4P) secretin. Our study used innovative techniques to provide new and comprehensive information on secretin topology, highlighting similarities and differences among secretin subfamilies. Additionally, the techniques used in this study may prove useful for the study of other OM proteins.
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11
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Secretion of bacterial lipoproteins: through the cytoplasmic membrane, the periplasm and beyond. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1509-16. [PMID: 24780125 DOI: 10.1016/j.bbamcr.2014.04.022] [Citation(s) in RCA: 150] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 04/16/2014] [Accepted: 04/18/2014] [Indexed: 11/20/2022]
Abstract
Bacterial lipoproteins are peripherally anchored membrane proteins that play a variety of roles in bacterial physiology and virulence in monoderm (single membrane-enveloped, e.g., gram-positive) and diderm (double membrane-enveloped, e.g., gram-negative) bacteria. After export of prolipoproteins through the cytoplasmic membrane, which occurs predominantly but not exclusively via the general secretory or Sec pathway, the proteins are lipid-modified at the cytoplasmic membrane in a multistep process that involves sequential modification of a cysteine residue and cleavage of the signal peptide by the signal II peptidase Lsp. In both monoderms and diderms, signal peptide processing is preceded by acylation with a diacylglycerol through preprolipoprotein diacylglycerol transferase (Lgt). In diderms but also some monoderms, lipoproteins are further modified with a third acyl chain through lipoprotein N-acyl transferase (Lnt). Fully modified lipoproteins that are destined to be anchored in the inner leaflet of the outer membrane (OM) are selected, transported and inserted by the Lol (lipoprotein outer membrane localization) pathway machinery, which consists of the inner-membrane (IM) ABC transporter-like LolCDE complex, the periplasmic LolA chaperone and the OM LolB lipoprotein receptor. Retention of lipoproteins in the cytoplasmic membrane results from Lol avoidance signals that were originally described as the "+2 rule". Surface localization of lipoproteins in diderms is rare in most bacteria, with the exception of several spirochetal species. Type 2 (T2SS) and type 5 (T5SS) secretion systems are involved in secretion of specific surface lipoproteins of γ-proteobacteria. In the model spirochete Borrelia burgdorferi, surface lipoprotein secretion does not follow established sorting rules, but remains dependent on N-terminal peptide sequences. Secretion through the outer membrane requires maintenance of lipoproteins in a translocation-competent unfolded conformation, likely through interaction with a periplasmic holding chaperone, which delivers the proteins to an outer membrane lipoprotein flippase. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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12
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Guilvout I, Chami M, Disconzi E, Bayan N, Pugsley AP, Huysmans GHM. Independent domain assembly in a trapped folding intermediate of multimeric outer membrane secretins. Structure 2014; 22:582-9. [PMID: 24657091 DOI: 10.1016/j.str.2014.02.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Revised: 01/27/2014] [Accepted: 02/11/2014] [Indexed: 11/28/2022]
Abstract
The outer membrane portal of the Klebsiella oxytoca type II secretion system, PulD, is a prototype of a family of proteins, the secretins, which are essential components of many bacterial secretion and pilus assembly machines. PulD is a homododecamer with a periplasmic vestibule and an outer chamber on either side of a membrane-spanning region that is poorly resolved by electron microscopy. Membrane insertion involves the formation of a dodecameric membrane-embedded intermediate. Here, we describe an amino acid substitution in PulD that blocks its assembly at this intermediate "prepore" stage. Electron microscopy indicated that the prepore has an apparently normal periplasmic vestibule but a poorly organized outer chamber. A peptide loop around this amino acid appears to be important for the formation/stability of the fully folded complex. A similar assembly intermediate results from creation of the same amino acid substitution in the Pseudomonas aeruginosa secretin XcpQ.
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Affiliation(s)
- Ingrid Guilvout
- Molecular Genetics Unit, Departments of Microbiology and of Structural Biology and Chemistry, Institut Pasteur, rue du Dr. Roux, 75724 Paris Cedex 15, France; CNRS ERL3526, rue du Dr. Roux, 75724 Paris Cedex 15, France
| | - Mohamed Chami
- C-CINA Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, 4058 Basel, Switzerland
| | - Elena Disconzi
- Molecular Genetics Unit, Departments of Microbiology and of Structural Biology and Chemistry, Institut Pasteur, rue du Dr. Roux, 75724 Paris Cedex 15, France; CNRS ERL3526, rue du Dr. Roux, 75724 Paris Cedex 15, France; Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Université de Paris-Sud, 91405 Orsay, France; CNRS UMR 8619, 91405 Orsay, France
| | - Nicolas Bayan
- Institut de Biochimie et de Biophysique Moléculaire et Cellulaire, Université de Paris-Sud, 91405 Orsay, France; CNRS UMR 8619, 91405 Orsay, France
| | - Anthony P Pugsley
- Molecular Genetics Unit, Departments of Microbiology and of Structural Biology and Chemistry, Institut Pasteur, rue du Dr. Roux, 75724 Paris Cedex 15, France; CNRS ERL3526, rue du Dr. Roux, 75724 Paris Cedex 15, France.
| | - Gerard H M Huysmans
- Molecular Genetics Unit, Departments of Microbiology and of Structural Biology and Chemistry, Institut Pasteur, rue du Dr. Roux, 75724 Paris Cedex 15, France; CNRS ERL3526, rue du Dr. Roux, 75724 Paris Cedex 15, France.
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Huysmans GHM, Guilvout I, Pugsley AP. Sequential steps in the assembly of the multimeric outer membrane secretin PulD. J Biol Chem 2013; 288:30700-30707. [PMID: 24019525 DOI: 10.1074/jbc.m113.489112] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Investigations into protein folding are largely dominated by studies on monomeric proteins. However, the transmembrane domain of an important group of membrane proteins is only formed upon multimerization. Here, we use in vitro translation-coupled folding and insertion into artificial liposomes to investigate kinetic steps in the assembly of one such protein, the outer membrane secretin PulD of the bacterial type II secretion system. Analysis of the folding kinetics, measured by the acquisition of distinct determinants of the native state, provides unprecedented evidence for a sequential multistep process initiated by membrane-driven oligomerization. The effects of varying the lipid composition of the liposomes indicate that PulD first forms a "prepore" structure that attains the native state via a conformational switch.
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Affiliation(s)
- Gerard H M Huysmans
- From the Molecular Genetics Unit, Departments of Microbiology and Structural Biology and Chemistry, and CNRS ERL3526, Institut Pasteur, rue du Dr. Roux, 75724 Paris Cedex 15, France
| | - Ingrid Guilvout
- From the Molecular Genetics Unit, Departments of Microbiology and Structural Biology and Chemistry, and CNRS ERL3526, Institut Pasteur, rue du Dr. Roux, 75724 Paris Cedex 15, France
| | - Anthony P Pugsley
- From the Molecular Genetics Unit, Departments of Microbiology and Structural Biology and Chemistry, and CNRS ERL3526, Institut Pasteur, rue du Dr. Roux, 75724 Paris Cedex 15, France.
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14
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Collin S, Krehenbrink M, Guilvout I, Pugsley AP. The targeting, docking and anti-proteolysis functions of the secretin chaperone PulS. Res Microbiol 2013; 164:390-6. [PMID: 23567323 DOI: 10.1016/j.resmic.2013.03.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Accepted: 03/20/2013] [Indexed: 01/09/2023]
Abstract
The Klebsiella oxytoca lipoprotein PulS might function as either or both a pilot and a docking factor in the outer membrane targeting and assembly of the Type II secretion system secretin PulD. In the piloting model, PulS binds to PulD monomers and targets them to the outer membrane via the lipoprotein sorting pathway components LolA and LolB. In this model, PulS also protects the PulD monomers from proteolysis during transit through the periplasm. In the docking model, PulS is targeted alone to the outer membrane, where it acts as a receptor for PulD monomers, allowing them to accumulate and assemble specifically in this membrane. PulS was shown to dissociate from and/or re-associate freely with PulD multimers in zwitterionic detergent, making it difficult to determine whether PulS remains associated with PulD dodecamers in the outer membrane by co-purification. However, PulD protomers in the dodecamer were shown to be stable in the absence of PulS, indicating that PulS is only required to protect the protease-susceptible monomer. DegP was identified as one of the proteases that could contribute to PulD degradation in the absence of PulS. Studies on the in vitro assembly and targeting of PulD into Escherichia coli membrane vesicles demonstrated its strong preference to insert into the inner membrane, as is the case in vivo in the absence of PulS. However, PulD could be targeted to outer membrane fragments in vitro if they were preloaded with PulS, indicating the technical feasibility of the docking model. We conclude that both modes of action might contribute to efficient outer membrane targeting of PulD in vivo, although the piloting function is likely to predominate.
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Affiliation(s)
- Séverine Collin
- Institut Pasteur, Molecular Genetics Unit, 25 rue du Dr. Roux, 70105 Paris, France
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15
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Dunstan RA, Heinz E, Wijeyewickrema LC, Pike RN, Purcell AW, Evans TJ, Praszkier J, Robins-Browne RM, Strugnell RA, Korotkov KV, Lithgow T. Assembly of the type II secretion system such as found in Vibrio cholerae depends on the novel Pilotin AspS. PLoS Pathog 2013; 9:e1003117. [PMID: 23326233 PMCID: PMC3542185 DOI: 10.1371/journal.ppat.1003117] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 11/20/2012] [Indexed: 12/18/2022] Open
Abstract
The Type II Secretion System (T2SS) is a molecular machine that drives the secretion of fully-folded protein substrates across the bacterial outer membrane. A key element in the machinery is the secretin: an integral, multimeric outer membrane protein that forms the secretion pore. We show that three distinct forms of T2SSs can be distinguished based on the sequence characteristics of their secretin pores. Detailed comparative analysis of two of these, the Klebsiella-type and Vibrio-type, showed them to be further distinguished by the pilotin that mediates their transport and assembly into the outer membrane. We have determined the crystal structure of the novel pilotin AspS from Vibrio cholerae, demonstrating convergent evolution wherein AspS is functionally equivalent and yet structurally unrelated to the pilotins found in Klebsiella and other bacteria. AspS binds to a specific targeting sequence in the Vibrio-type secretins, enhances the kinetics of secretin assembly, and homologs of AspS are found in all species of Vibrio as well those few strains of Escherichia and Shigella that have acquired a Vibrio-type T2SS. The type 2 secretion system (T2SS) is a sophisticated, multi-component molecular machine that drives the secretion of fully-folded protein substrates across the bacterial outer membrane. In Vibrio cholerae, for example, the T2SS mediates the secretion of cholera toxin. We find that there are three distinct forms of T2SS, based on the sequence characteristics of the secretin. A targeting paradigm, developed for the Klebsiella-type secretin PulD, could not previously be applied to the T2SS in Vibrio cholerae and many other bacterial species whose genomes encode no homolog of the crucial targeting factor PulS (also called OutS, EtpO or GspS). Using bioinformatics we find, remarkably, that these bacteria have instead evolved a structurally distinct protein to serve in place of PulS. We crystallized and solved the structure of this distinct factor, AspS, measured its activity in novel assays for T2SS assembly, and show that the protein is essential for the function of the Vibrio-type T2SS. A structural homolog of AspS found here in Pseudomonas suggests widespread use of the pilotin-secretin targeting paradigm for T2SS assembly.
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Affiliation(s)
- Rhys A. Dunstan
- Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia
| | - Eva Heinz
- Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia
- Victorian Bioinformatics Consortium, Monash University, Melbourne, Australia
| | | | - Robert N. Pike
- Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia
| | - Anthony W. Purcell
- Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia
| | - Timothy J. Evans
- Department of Molecular and Cellular Biochemistry and Center for Structural Biology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Judyta Praszkier
- Department of Microbiology and Immunology, The University of Melbourne, Melbourne, Australia
- Monash Institute of Medical Research, Melbourne, Australia
| | - Roy M. Robins-Browne
- Department of Microbiology and Immunology, The University of Melbourne, Melbourne, Australia
- Murdoch Childrens Research Institute, Royal Children's Hospital, Melbourne, Australia
| | - Richard A. Strugnell
- Department of Microbiology and Immunology, The University of Melbourne, Melbourne, Australia
| | - Konstantin V. Korotkov
- Department of Molecular and Cellular Biochemistry and Center for Structural Biology, University of Kentucky, Lexington, Kentucky, United States of America
- * E-mail: (KVK); (TL)
| | - Trevor Lithgow
- Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Australia
- * E-mail: (KVK); (TL)
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16
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Berry JL, Phelan MM, Collins RF, Adomavicius T, Tønjum T, Frye SA, Bird L, Owens R, Ford RC, Lian LY, Derrick JP. Structure and assembly of a trans-periplasmic channel for type IV pili in Neisseria meningitidis. PLoS Pathog 2012; 8:e1002923. [PMID: 23028322 PMCID: PMC3441751 DOI: 10.1371/journal.ppat.1002923] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2012] [Accepted: 08/07/2012] [Indexed: 01/24/2023] Open
Abstract
Type IV pili are polymeric fibers which protrude from the cell surface and play a critical role in adhesion and invasion by pathogenic bacteria. The secretion of pili across the periplasm and outer membrane is mediated by a specialized secretin protein, PilQ, but the way in which this large channel is formed is unknown. Using NMR, we derived the structures of the periplasmic domains from N. meningitidis PilQ: the N-terminus is shown to consist of two β-domains, which are unique to the type IV pilus-dependent secretins. The structure of the second β-domain revealed an eight-stranded β-sandwich structure which is a novel variant of the HSP20-like fold. The central part of PilQ consists of two α/β fold domains: the structure of the first of these is similar to domains from other secretins, but with an additional α-helix which links it to the second α/β domain. We also determined the structure of the entire PilQ dodecamer by cryoelectron microscopy: it forms a cage-like structure, enclosing a cavity which is approximately 55 Å in internal diameter at its largest extent. Specific regions were identified in the density map which corresponded to the individual PilQ domains: this allowed us to dock them into the cryoelectron microscopy density map, and hence reconstruct the entire PilQ assembly which spans the periplasm. We also show that the C-terminal domain from the lipoprotein PilP, which is essential for pilus assembly, binds specifically to the first α/β domain in PilQ and use NMR chemical shift mapping to generate a model for the PilP:PilQ complex. We conclude that passage of the pilus fiber requires disassembly of both the membrane-spanning and the β-domain regions in PilQ, and that PilP plays an important role in stabilising the PilQ assembly during secretion, through its anchorage in the inner membrane.
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Affiliation(s)
- Jamie-Lee Berry
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Marie M. Phelan
- Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Richard F. Collins
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Tomas Adomavicius
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Tone Tønjum
- Centre for Molecular Biology and Neuroscience, University of Oslo, Oslo, Norway
| | - Stefan A. Frye
- Centre for Molecular Biology and Neuroscience, University of Oslo, Oslo, Norway
| | - Louise Bird
- Oxford Protein Production Facility, Research Complex at Harwell, Harwell, Oxford, United Kingdom
| | - Ray Owens
- Oxford Protein Production Facility, Research Complex at Harwell, Harwell, Oxford, United Kingdom
| | - Robert C. Ford
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Lu-Yun Lian
- Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Jeremy P. Derrick
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
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17
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The type II secretion system: biogenesis, molecular architecture and mechanism. Nat Rev Microbiol 2012; 10:336-51. [PMID: 22466878 DOI: 10.1038/nrmicro2762] [Citation(s) in RCA: 347] [Impact Index Per Article: 28.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Many gram-negative bacteria use the sophisticated type II secretion system (T2SS) to translocate a wide range of proteins from the periplasm across the outer membrane. The inner-membrane platform of the T2SS is the nexus of the system and orchestrates the secretion process through its interactions with the periplasmic filamentous pseudopilus, the dodecameric outer-membrane complex and a cytoplasmic secretion ATPase. Here, recent structural and biochemical information is reviewed to describe our current knowledge of the biogenesis and architecture of the T2SS and its mechanism of action.
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18
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Nickerson NN, Tosi T, Dessen A, Baron B, Raynal B, England P, Pugsley AP. Outer membrane targeting of secretin PulD protein relies on disordered domain recognition by a dedicated chaperone. J Biol Chem 2011; 286:38833-43. [PMID: 21878629 PMCID: PMC3234708 DOI: 10.1074/jbc.m111.279851] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Revised: 08/26/2011] [Indexed: 12/29/2022] Open
Abstract
Interaction of bacterial outer membrane secretin PulD with its dedicated lipoprotein chaperone PulS relies on a disorder-to-order transition of the chaperone binding (S) domain near the PulD C terminus. PulS interacts with purified S domain to form a 1:1 complex. Circular dichroism, one-dimensional NMR, and hydrodynamic measurements indicate that the S domain is elongated and intrinsically disordered but gains secondary structure upon binding to PulS. Limited proteolysis and mass spectrometry identified the 28 C-terminal residues of the S domain as a minimal binding site with low nanomolar affinity for PulS in vitro that is sufficient for outer membrane targeting of PulD in vivo. The region upstream of this binding site is not required for targeting or multimerization and does not interact with PulS, but it is required for secretin function in type II secretion. Although other secretin chaperones differ substantially from PulS in sequence and secondary structure, they have all adopted at least superficially similar mechanisms of interaction with their cognate secretins, suggesting that intrinsically disordered regions facilitate rapid interaction between secretins and their chaperones.
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Affiliation(s)
- Nicholas N. Nickerson
- From the Institut Pasteur, Molecular Genetics Unit, Microbiology Department, rue du Dr. Roux, 75015 Paris
- the CNRS URA2172, rue du Dr. Roux, 75015 Paris
| | - Tommaso Tosi
- the Institut de Biologie Structurale, Bacterial Pathogenesis Group, Université de Grenoble I, Rue Jules Horowitz, 38027 Grenoble
- the CNRS UMR 5075, Rue Jules Horowitz, 38027 Grenoble
- the Commissariat à l'Enérgie Atomique, Rue Jules Horowitz, 38027 Grenoble
| | - Andréa Dessen
- the Institut de Biologie Structurale, Bacterial Pathogenesis Group, Université de Grenoble I, Rue Jules Horowitz, 38027 Grenoble
- the CNRS UMR 5075, Rue Jules Horowitz, 38027 Grenoble
- the Commissariat à l'Enérgie Atomique, Rue Jules Horowitz, 38027 Grenoble
| | - Bruno Baron
- the Institut Pasteur, Biophysics of Macromolecules and their Interactions Platform, Proteopole and Structural Biology and Chemistry Department, rue du Dr. Roux, 75015 Paris, and
- the CNRS URA2185, rue du Dr. Roux, 75015 Paris, France
| | - Bertrand Raynal
- the Institut Pasteur, Biophysics of Macromolecules and their Interactions Platform, Proteopole and Structural Biology and Chemistry Department, rue du Dr. Roux, 75015 Paris, and
- the CNRS URA2185, rue du Dr. Roux, 75015 Paris, France
| | - Patrick England
- the Institut Pasteur, Biophysics of Macromolecules and their Interactions Platform, Proteopole and Structural Biology and Chemistry Department, rue du Dr. Roux, 75015 Paris, and
- the CNRS URA2185, rue du Dr. Roux, 75015 Paris, France
| | - Anthony P. Pugsley
- From the Institut Pasteur, Molecular Genetics Unit, Microbiology Department, rue du Dr. Roux, 75015 Paris
- the CNRS URA2172, rue du Dr. Roux, 75015 Paris
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19
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Korotkov KV, Johnson TL, Jobling MG, Pruneda J, Pardon E, Héroux A, Turley S, Steyaert J, Holmes RK, Sandkvist M, Hol WGJ. Structural and functional studies on the interaction of GspC and GspD in the type II secretion system. PLoS Pathog 2011; 7:e1002228. [PMID: 21931548 PMCID: PMC3169554 DOI: 10.1371/journal.ppat.1002228] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Accepted: 07/21/2011] [Indexed: 12/02/2022] Open
Abstract
Type II secretion systems (T2SSs) are critical for secretion of many proteins from Gram-negative bacteria. In the T2SS, the outer membrane secretin GspD forms a multimeric pore for translocation of secreted proteins. GspD and the inner membrane protein GspC interact with each other via periplasmic domains. Three different crystal structures of the homology region domain of GspC (GspCHR) in complex with either two or three domains of the N-terminal region of GspD from enterotoxigenic Escherichia coli show that GspCHR adopts an all-β topology. N-terminal β-strands of GspC and the N0 domain of GspD are major components of the interface between these inner and outer membrane proteins from the T2SS. The biological relevance of the observed GspC–GspD interface is shown by analysis of variant proteins in two-hybrid studies and by the effect of mutations in homologous genes on extracellular secretion and subcellular distribution of GspC in Vibrio cholerae. Substitutions of interface residues of GspD have a dramatic effect on the focal distribution of GspC in V. cholerae. These studies indicate that the GspCHR–GspDN0 interactions observed in the crystal structure are essential for T2SS function. Possible implications of our structures for the stoichiometry of the T2SS and exoprotein secretion are discussed. Many bacterial pathogens affecting humans, animals and plants export diverse proteins across the cell membranes into the medium surrounding the bacteria. Some of these secreted proteins are involved in pathogenesis. One example is cholera toxin secreted by the bacterium Vibrio cholerae, a causative agent of cholera. The sophisticated type II secretion system is responsible for moving this toxin, and several other proteins, across the outer membrane. Here, we studied the interaction between the outer membrane pore of the type II secretion system, the secretin GspD, and the inner membrane protein GspC. We have solved three crystal structures of complexes between the interacting domains and identified critical contacts in the GspC–GspD interface. We also showed the importance of these contacts for assembly of the secretion system and for secretion of proteins by V. cholerae. Our studies provide a major piece in the puzzle of how the type II secretion system is assembled and how it functions. One day this knowledge might allow us to design compounds which interfere with this secretion process. Such compounds would be useful in the battle against bacteria affecting human health.
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Affiliation(s)
- Konstantin V. Korotkov
- Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, Washington, United States of America
| | - Tanya L. Johnson
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Michael G. Jobling
- Department of Microbiology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Jonathan Pruneda
- Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, Washington, United States of America
| | - Els Pardon
- Department of Molecular and Cellular Interactions, VIB, Brussels, Belgium
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
| | - Annie Héroux
- National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States of America
| | - Stewart Turley
- Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, Washington, United States of America
| | - Jan Steyaert
- Department of Molecular and Cellular Interactions, VIB, Brussels, Belgium
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
| | - Randall K. Holmes
- Department of Microbiology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Maria Sandkvist
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
| | - Wim G. J. Hol
- Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, Washington, United States of America
- * E-mail:
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20
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Tarry M, Jääskeläinen M, Paino A, Tuominen H, Ihalin R, Högbom M. The extra-membranous domains of the competence protein HofQ show DNA binding, flexibility and a shared fold with type I KH domains. J Mol Biol 2011; 409:642-53. [PMID: 21530539 DOI: 10.1016/j.jmb.2011.04.034] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 04/08/2011] [Accepted: 04/12/2011] [Indexed: 10/18/2022]
Abstract
Secretins form large oligomeric assemblies in the membrane that control both macromolecular secretion and uptake. Several Pasteurellaceae are naturally competent for transformation, but the mechanism for DNA assimilation is largely unknown. In Haemophilus influenzae, the secretin ComE has been demonstrated to be essential for DNA uptake. In closely related Aggregatibacter actinomycetemcomitans, an opportunistic pathogen in periodontitis, the ComE homolog HofQ is believed to be the outer membrane DNA translocase. Here, we report the structure of the extra-membranous domains of HofQ at 2.3 Å resolution by X-ray crystallography. We also show that the extra-membranous domains of HofQ are capable of DNA binding. The structure reveals two secretin-like folds, the first of which is formed by means of a domain swap. The second domain displays extensive structural similarity to K homology (KH) domains, including the presence of a GxxG motif, which is essential for the nucleotide-binding function of KH domains, suggesting a possible mechanism for DNA binding by HofQ. The data indicate a direct involvement in DNA acquisition and provide insight into the molecular basis for natural competence.
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Affiliation(s)
- Michael Tarry
- Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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21
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Collin S, Guilvout I, Nickerson NN, Pugsley AP. Sorting of an integral outer membrane protein via the lipoprotein-specific Lol pathway and a dedicated lipoprotein pilotin. Mol Microbiol 2011; 80:655-65. [PMID: 21338419 DOI: 10.1111/j.1365-2958.2011.07596.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The lipoprotein PulS is a dedicated chaperone that is required to target the secretin PulD to the outer membrane in Klebsiella or Escherichia coli, and to protect it from proteolysis. Here, we present indirect evidence that PulD protomers do not assemble into the secretin dodecamer before they reach the outer membrane, and that PulS reaches the outer membrane in a soluble heterodimer with the general lipoprotein chaperone LolA. However, we could not find any direct evidence for PulD protomer association with the PulS-LolA heterodimer. Instead, in cells producing PulD and a permanently locked PulS-LolA dimer (in which LolA carries an R43L substitution that prevents lipoprotein transfer to LolB in the outer membrane), LolAR43L was found in the inner membrane, probably still associated with PulS bound to PulD that had been incorrectly targeted because of the LolAR43L substitution. It is speculated that PulD protomers normally cross the periplasm together with PulS bound to LolA but when the latter cannot be separated (due to the mutation in lolA), the PulD protomers form dodecamers that insert into the inner membrane.
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Affiliation(s)
- Séverine Collin
- Institut Pasteur, Molecular Genetics Unit, Microbiology Department, 75015 Paris, France
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22
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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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23
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Burkhardt J, Vonck J, Averhoff B. Structure and function of PilQ, a secretin of the DNA transporter from the thermophilic bacterium Thermus thermophilus HB27. J Biol Chem 2011; 286:9977-84. [PMID: 21285351 DOI: 10.1074/jbc.m110.212688] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Secretins are a family of large bacterial outer membrane protein complexes mediating the transport of complex structures, such as type IV pili, DNA and filamentous phage, or various proteins, such as extracellular enzymes and pathogenicity determinants. PilQ of the thermophilic bacterium Thermus thermophilus HB27 is a member of the secretin family required for natural transformation. Here we report the isolation, structural, and functional analyses of a unique PilQ from T. thermophilus. Native PAGE, gel filtration chromatography, and electrophoretic mobility shift analyses indicated that PilQ forms a macromolecular homopolymeric complex that binds dsDNA. Electron microscopy showed that the PilQ complex is 15 nm wide and 34 nm long and consists of an extraordinary stable "cone" and "cup" structure and five ring structures with a large central channel. Moreover, the electron microscopic images together with secondary structure analyses combined with structural data of type II protein secretion system and type III protein secretion system secretins suggest that the individual rings are formed by conserved domains of alternating α-helices and β-sheets. The unprecedented length of the PilQ complex correlated well with the distance between the inner and outer membrane of T. thermophilus. Indeed, PilQ was found immunologically in both membranes, indicating that the PilQ complex spans the entire cell periphery of T. thermophilus. This is consistent with the hypothesis that PilQ accommodates a PilA4 comprising pseudopilus mediating DNA transport across the outer membrane and periplasmic space in a single-step process.
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Affiliation(s)
- Janin Burkhardt
- Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University, Max-von-Laue-Strasse 9, D-60438 Frankfurt/Main, Germany
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24
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Outer membrane translocons: structural insights into channel formation. Trends Microbiol 2010; 19:40-8. [PMID: 21130656 DOI: 10.1016/j.tim.2010.10.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 10/18/2010] [Accepted: 10/29/2010] [Indexed: 01/26/2023]
Abstract
Gram-negative bacteria need to maintain the integrity of their outer membrane while also regulating the secretion of toxins and other macromolecules. A variety of dedicated outer membrane proteins (OMPs) facilitate this process. Recent structural work has shown that some of these proteins adopt classical β-barrel transmembrane structures and rely on structural changes within the barrel lumen to allow passage of substrate proteins. Other secretion systems have OMP components which use transmembrane α-helices and appear to function in a different way. Here we review a selection of recent structural studies which have major ramifications for our understanding of the passage of macromolecules across the outer membrane.
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25
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Ayers M, Howell PL, Burrows LL. Architecture of the type II secretion and type IV pilus machineries. Future Microbiol 2010; 5:1203-18. [PMID: 20722599 DOI: 10.2217/fmb.10.76] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Motility and protein secretion are key processes contributing to bacterial virulence. A wealth of phylogenetic, biochemical and structural evidence support the hypothesis that the widely distributed type IV pilus (T4P) system, involved in twitching motility, and the type II secretion (T2S) system, involved in exoprotein release, are descended from a common progenitor. Both are composed of dedicated but dynamic assemblages, which have been proposed to function through alternate polymerization and depolymerization or degradation of pilin-like subunits. While ongoing studies aimed at understanding the details of assembly and function of these systems are leading to new insights, there are still large knowledge gaps with respect to several fundamental aspects of their biology, including the localization and stoichiometry of critical assembly components, and the nature of their interactions. This article highlights recent advances in understanding the architectures of the T4P and T2S systems, and the organization of their inner and outer membrane components. As structural data accumulates, it is becoming increasingly apparent that even components with little-to-no sequence similarity have similar folds, further supporting the idea that both systems function by a similar mechanism.
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Affiliation(s)
- Melissa Ayers
- Department of Biochemistry & Biomedical Sciences and the Michael G. DeGroote Institute for Infectious Diseases Research, McMaster University, Hamilton, ON, Canada
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26
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Abstract
The type II secretion system (T2SS) is used by Escherichia coli and other gram-negative bacteria to translocate many proteins, including toxins and proteases, across the outer membrane of the cell and into the extracellular space. Depending on the bacterial species, between 12 and 15 genes have been identified that make up a T2SS operon. T2SSs are widespread among gram-negative bacteria, and most E. coli appear to possess one or two complete T2SS operons. Once expressed, the multiple protein components that form the T2S system are localized in both the inner and outer membranes, where they assemble into an apparatus that spans the cell envelope. This apparatus supports the secretion of numerous virulence factors; and therefore secretion via this pathway is regarded in many organisms as a major virulence mechanism. Here, we review several of the known E. coli T2S substrates that have proven to be critical for the survival and pathogenicity of these bacteria. Recent structural and biochemical information is also reviewed that has improved our current understanding of how the T2S apparatus functions; also reviewed is the role that individual proteins play in this complex system.
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27
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Spagnuolo J, Opalka N, Wen WX, Gagic D, Chabaud E, Bellini P, Bennett MD, Norris GE, Darst SA, Russel M, Rakonjac J. Identification of the gate regions in the primary structure of the secretin pIV. Mol Microbiol 2010; 76:133-50. [DOI: 10.1111/j.1365-2958.2010.07085.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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28
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Login FH, Fries M, Wang X, Pickersgill RW, Shevchik VE. A 20-residue peptide of the inner membrane protein OutC mediates interaction with two distinct sites of the outer membrane secretin OutD and is essential for the functional type II secretion system in Erwinia chrysanthemi. Mol Microbiol 2010; 76:944-55. [PMID: 20444086 DOI: 10.1111/j.1365-2958.2010.07149.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The type II secretion system (T2SS) is widely exploited by proteobacteria to secrete enzymes and toxins involved in bacterial survival and pathogenesis. The outer membrane pore formed by the secretin OutD and the inner membrane protein OutC are two key components of the secretion complex, involved in secretion specificity. Here, we show that the periplasmic regions of OutC and OutD interact directly and map the interaction site of OutC to a 20-residue peptide named OutCsip (secretin interacting peptide, residues 139-158). This peptide interacts in vitro with two distinct sites of the periplasmic region of OutD, one located on the N0 subdomain and another overlapping the N2-N3' subdomains. The two interaction sites of OutD have different modes of binding to OutCsip. A single substitution, V143S, located within OutCsip prevents its interaction with one of the two binding sites of OutD and fully inactivates the T2SS. We show that the N0 subdomain of OutD interacts also with a second binding site within OutC located in the region proximal to the transmembrane segment. We suggest that successive interactions between these distinct regions of OutC and OutD may have functional importance in switching the secretion machine.
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Affiliation(s)
- Frédéric H Login
- Université de Lyon, F-69003, Université Lyon 1, Lyon, F-69622, INSA-Lyon, Villeurbanne, F-69621, CNRS, UMR5240, Microbiologie Adaptation et Pathogénie, Lyon, F-69622, France
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29
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Structure-function relationships of the outer membrane translocon Wza investigated by cryo-electron microscopy and mutagenesis. J Struct Biol 2009; 166:172-82. [PMID: 19236919 DOI: 10.1016/j.jsb.2009.02.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 01/23/2009] [Accepted: 02/15/2009] [Indexed: 11/21/2022]
Abstract
The outer membrane protein Wza, from Escherichia coli K30, forms an octameric complex that is essential for capsular polysaccharide export. Homologs of Wza are widespread in gram-negative bacterial pathogens where capsules are critical virulence determinants. Wza is unusual in that it spans the outer membrane using a barrel composed of amphipathic alpha-helices, rather than being a beta-barrel like almost all other outer membrane channels. The transmembrane helical barrel of Wza also forms the external opening to a hydrophilic translocation pathway that spans the periplasm. Here, we have probed the structure and function of the Wza complex using both cryo-electron microscopy and mutagenesis. The helical barrel structure is stable in detergent micelles under mildly acidic conditions but is destabilized at basic pH, although the overall quaternary structure is retained. Truncation of the C-terminal region that forms the helical barrel by 4 residues has no effect on the ability of Wza to oligomerize and support capsule export, but larger truncations of 18, 24 or 35 amino acids abolish its function. The bulk of the C-terminal domain is essential for the stability and assembly of the E. coli Wza complex.
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Meng G, Fronzes R, Chandran V, Remaut H, Waksman G. Protein oligomerization in the bacterial outer membrane (Review). Mol Membr Biol 2009; 26:136-45. [PMID: 19225986 DOI: 10.1080/09687680802712422] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The formation of homo-oligomeric assemblies is a well-established characteristic of many soluble proteins and enzymes. Oligomerization has been shown to increase protein stability, allow allosteric cooperativity, shape reaction compartments and provide multivalent interaction sites in soluble proteins. In comparison, our understanding of the prevalence and reasons behind protein oligomerization in membrane proteins is relatively sparse. Recent progress in structural biology of bacterial outer membrane proteins has suggested that oligomerization may be as common and versatile as in soluble proteins. Here we review the current understanding of oligomerization in the bacterial outer membrane from a structural and functional point of view.
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Affiliation(s)
- Guoyu Meng
- Institute of Structural and Molecular Biology, University College London and Birkbeck College, London, UK
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31
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Korotkov KV, Pardon E, Steyaert J, Hol WG. Crystal structure of the N-terminal domain of the secretin GspD from ETEC determined with the assistance of a nanobody. Structure 2009; 17:255-65. [PMID: 19217396 PMCID: PMC2662362 DOI: 10.1016/j.str.2008.11.011] [Citation(s) in RCA: 157] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Revised: 11/24/2008] [Accepted: 11/24/2008] [Indexed: 01/07/2023]
Abstract
Secretins are among the largest bacterial outer membrane proteins known. Here we report the crystal structure of the periplasmic N-terminal domain of GspD (peri-GspD) from the type 2 secretion system (T2SS) secretin in complex with a nanobody, the VHH domain of a heavy-chain camelid antibody. Two different crystal forms contained the same compact peri-GspD:nanobody heterotetramer. The nanobody contacts peri-GspD mainly via CDR3 and framework residues. The peri-GspD structure reveals three subdomains, with the second and third subdomains exhibiting the KH fold which also occurs in ring-forming proteins of the type 3 secretion system. The first subdomain of GspD is related to domains in phage tail proteins and outer membrane TonB-dependent receptors. A dodecameric peri-GspD model is proposed in which a solvent-accessible beta strand of the first subdomain interacts with secreted proteins and/or T2SS partner proteins by beta strand complementation.
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Affiliation(s)
- Konstantin V. Korotkov
- Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, WA 98195, USA
| | - Els Pardon
- Department of Molecular and Cellular Interactions, VIB, B-1050 Brussels, Belgium,Structural Biology Brussels, Vrije Universiteit Brussel, B-1050 Brussels, Belgium
| | - Jan Steyaert
- Department of Molecular and Cellular Interactions, VIB, B-1050 Brussels, Belgium,Structural Biology Brussels, Vrije Universiteit Brussel, B-1050 Brussels, Belgium
| | - Wim G.J. Hol
- Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, WA 98195, USA
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32
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Sharpe ML, Gao C, Kendall SL, Baker EN, Lott JS. The Structure and Unusual Protein Chemistry of Hypoxic Response Protein 1, a Latency Antigen and Highly Expressed Member of the DosR Regulon in Mycobacterium tuberculosis. J Mol Biol 2008; 383:822-36. [DOI: 10.1016/j.jmb.2008.07.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Revised: 06/30/2008] [Accepted: 07/02/2008] [Indexed: 01/20/2023]
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Type II secretion system secretin PulD localizes in clusters in the Escherichia coli outer membrane. J Bacteriol 2008; 191:161-8. [PMID: 18978053 DOI: 10.1128/jb.01138-08] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cellular localization of a chimera formed by fusing a monomeric red fluorescent protein to the C terminus of the Klebsiella oxytoca type II secretion system outer membrane secretin PulD (PulD-mCherry) in Escherichia coli was determined in vivo by fluorescence microscopy. Like PulD, PulD-mCherry formed sodium dodecyl sulfate- and heat-resistant multimers and was functional in pullulanase secretion. Chromosome-encoded PulD-mCherry formed fluorescent foci on the periphery of the cell in the presence of high (plasmid-encoded) levels of its cognate chaperone, the pilotin PulS. Subcellular fractionation demonstrated that the chimera was located exclusively in the outer membrane under these circumstances. A similar localization pattern was observed by fluorescence microscopy of fixed cells treated with green fluorescent protein-tagged affitin, which binds with high affinity to an epitope in the N-terminal region of PulD. At lower levels of (chromosome-encoded) PulS, PulD-mCherry was less stable, was located mainly in the inner membrane, from which it could not be solubilized with urea, and did not induce the phage shock response, unlike PulD in the absence of PulS. The fluorescence pattern of PulD-mCherry under these conditions was similar to that observed when PulS levels were high. The complete absence of PulS caused the appearance of bright and almost exclusively polar fluorescent foci.
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Felise HB, Nguyen HV, Pfuetzner RA, Barry KC, Jackson SR, Blanc MP, Bronstein PA, Kline T, Miller SI. An inhibitor of gram-negative bacterial virulence protein secretion. Cell Host Microbe 2008; 4:325-36. [PMID: 18854237 PMCID: PMC2646588 DOI: 10.1016/j.chom.2008.08.001] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2008] [Revised: 05/15/2008] [Accepted: 08/06/2008] [Indexed: 12/14/2022]
Abstract
Bacterial virulence mechanisms are attractive targets for antibiotic development because they are required for the pathogenesis of numerous global infectious disease agents. The bacterial secretion systems used to assemble the surface structures that promote adherence and deliver protein virulence effectors to host cells could comprise one such therapeutic target. In this study, we developed and performed a high-throughput screen of small molecule libraries and identified one compound, a 2-imino-5-arylidene thiazolidinone that blocked secretion and virulence functions of a wide array of animal and plant Gram-negative bacterial pathogens. This compound inhibited type III secretion-dependent functions, with the exception of flagellar motility, and type II secretion-dependent functions, suggesting that its target could be an outer membrane component conserved between these two secretion systems. This work provides a proof of concept that compounds with a broad spectrum of activity against Gram-negative bacterial secretion systems could be developed to prevent and treat bacterial diseases.
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Affiliation(s)
- Heather B Felise
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
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35
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Guilvout I, Chami M, Berrier C, Ghazi A, Engel A, Pugsley AP, Bayan N. In Vitro Multimerization and Membrane Insertion of Bacterial Outer Membrane Secretin PulD. J Mol Biol 2008; 382:13-23. [DOI: 10.1016/j.jmb.2008.06.055] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2008] [Revised: 06/19/2008] [Accepted: 06/23/2008] [Indexed: 11/26/2022]
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Remodeling a DNA-binding protein as a specific in vivo inhibitor of bacterial secretin PulD. Proc Natl Acad Sci U S A 2007; 104:17983-8. [PMID: 17984049 DOI: 10.1073/pnas.0702963104] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We engineered a class of proteins that binds selected polypeptides with high specificity and affinity. Use of the protein scaffold of Sac7d, belonging to a protein family that binds various ligands, overcomes limitations inherent in the use of antibodies as intracellular inhibitors: it lacks disulfide bridges, is small and stable, and can be produced in large amounts. An in vitro combinatorial/selection approach generated specific, high-affinity (up to 140 pM) binders against bacterial outer membrane secretin PulD. When exported to the Escherichia coli periplasm, they inhibited PulD oligomerization, thereby blocking the type II secretion pathway of which PulD is part. Thus, high-affinity inhibitors of protein function can be derived from Sac7d and can be exported to, and function in, a cell compartment other than that in which they are produced.
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Abstract
The experimental problems associated with in vivo studies of essential proteins or integral membrane proteins have triggered geneticists to generate novel approaches that have often led to insights of general relevance (Shuman and Silhavy, 2003). In order to extend the experimental portfolio, we developed target-directed proteolysis (TDP), an in vivo method allowing structural and functional characterization of target proteins in living cells. TDP is based on the activity of the highly sequence-specific NIa protease from tobacco etch virus. When its recognition site of seven residues is engineered into target proteins and NIa protease is expressed under tight promoter control, substrates can be conditionally processed while other cellular proteins remain unaffected. Applications include conditional inactivation as well as functional characterization of target proteins.
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Affiliation(s)
- Markus Eser
- School of Biosciences, Cardiff University, Cardiff, Wales, UK
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Frye SA, Assalkhou R, Collins RF, Ford RC, Petersson C, Derrick JP, Tønjum T. Topology of the outer-membrane secretin PilQ from Neisseria meningitidis. MICROBIOLOGY-SGM 2007; 152:3751-3764. [PMID: 17159226 DOI: 10.1099/mic.0.2006/000315-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Neisseria meningitidis is the causative agent of epidemic meningococcal meningitis and septicaemia. Type IV pili are surface organelles that mediate a variety of functions, including adhesion, twitching motility, and competence for DNA binding and uptake in transformation. The secretin PilQ is required for type IV pilus expression at the cell surface, and forms a dodecameric cage-like macromolecular complex in the meningococcal outer membrane. PilQ-null mutants are devoid of surface pili, and prevailing evidence suggests that the PilQ complex facilitates extrusion and retraction of type IV pili across the outer membrane. Defining the orientation of the meningococcal PilQ complex in the membrane is a prerequisite for understanding the structure-function relationships of this important protein in pilus biology. In order to begin to define the topology of the PilQ complex in the outer membrane, polyhistidine insertions in N- and C-terminal regions of PilQ were constructed, and their subcellular locations examined. Notably, the insertion epitopes at residues 205 and 678 were located within the periplasm, whereas residue 656 was exposed at the outer surface of the outer membrane. Using electron microscopy with Ni-NTA gold labelling, it was demonstrated that the insertion at residue 205 within the N-terminus mapped to a site on the arm-like features of the 3D structure of the PilQ multimer. Interestingly, mutation of the same region gave rise to an increase in vancomycin permeability through the PilQ complex. The results yield novel information on the PilQ N-terminal location and function in the periplasm, and reveal a complex organization of the membrane-spanning secretin in vivo.
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Affiliation(s)
- Stephan A Frye
- Centre for Molecular Biology and Neuroscience and Institute of Microbiology, Rikshospitalet-Radiumhospitalet Medical Centre, Norway
- Centre for Molecular Biology and Neuroscience and Institute of Microbiology, University of Oslo, Norway
| | - Reza Assalkhou
- Centre for Molecular Biology and Neuroscience and Institute of Microbiology, University of Oslo, Norway
| | - Richard F Collins
- Faculty of Life Sciences, The University of Manchester, Sackville Street, PO Box 88, Manchester M60 1QD, UK
| | - Robert C Ford
- Faculty of Life Sciences, The University of Manchester, Sackville Street, PO Box 88, Manchester M60 1QD, UK
| | - Christoffer Petersson
- Division of Medical Microbiology, Department of Molecular and Clinical Medicine, Faculty of Health Sciences, Linköping University, Sweden
| | - Jeremy P Derrick
- Faculty of Life Sciences, The University of Manchester, Sackville Street, PO Box 88, Manchester M60 1QD, UK
| | - Tone Tønjum
- Centre for Molecular Biology and Neuroscience and Institute of Microbiology, Rikshospitalet-Radiumhospitalet Medical Centre, Norway
- Centre for Molecular Biology and Neuroscience and Institute of Microbiology, University of Oslo, Norway
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Collins RF, Derrick JP. Wza: a new structural paradigm for outer membrane secretory proteins? Trends Microbiol 2007; 15:96-100. [PMID: 17275308 DOI: 10.1016/j.tim.2007.01.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2006] [Revised: 01/05/2007] [Accepted: 01/19/2007] [Indexed: 11/17/2022]
Abstract
Gram-negative bacteria need to be able to transport a large variety of macromolecules across their outer membranes. In Escherichia coli, the passage of the group 1 capsular polysaccharide is mediated by an integral outer membrane protein, Wza. The crystal structure of Wza, determined recently, reveals a novel transmembrane alpha-helical barrel and a large central cavity within the core of the vase-shaped protein complex. The structure has similarities with that of the secretin protein, PilQ, which mediates the transition of type IV pili across the outer membrane. We propose that the large internal chamber, which can accommodate the secreted assembled macromolecule, is likely to be a common feature found in other outer membrane proteins involved in secretion processes.
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Affiliation(s)
- Richard F Collins
- Faculty of Engineering and Physical Sciences, Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester, M1 7DN, UK
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40
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Guilvout I, Chami M, Engel A, Pugsley AP, Bayan N. Bacterial outer membrane secretin PulD assembles and inserts into the inner membrane in the absence of its pilotin. EMBO J 2006; 25:5241-9. [PMID: 17082772 PMCID: PMC1636608 DOI: 10.1038/sj.emboj.7601402] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2006] [Accepted: 09/29/2006] [Indexed: 11/09/2022] Open
Abstract
Dodecamerization and insertion of the outer membrane secretin PulD is entirely determined by the C-terminal half of the polypeptide (PulD-CS). In the absence of its cognate chaperone PulS, PulD-CS and PulD mislocalize to the inner membrane, from which they are extractable with detergents but not urea. Electron microscopy of PulD-CS purified from the inner membrane revealed apparently normal dodecameric complexes. Electron microscopy of PulD-CS and PulD in inner membrane vesicles revealed inserted secretin complexes. Mislocalization of PulD or PulD-CS to this membrane induces the phage shock response, probably as a result of a decreased membrane electrochemical potential. Production of PulD in the absence of the phage shock response protein PspA and PulS caused a substantial drop in membrane potential and was lethal. Thus, PulD-CS and PulD assemble in the inner membrane if they do not associate with PulS. We propose that PulS prevents premature multimerization of PulD and accompanies it through the periplasm to the outer membrane. PulD is the first bacterial outer membrane protein with demonstrated ability to insert efficiently into the inner membrane.
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Affiliation(s)
- Ingrid Guilvout
- Molecular Genetics Unit and CNRS URA2172, Institut Pasteur, Paris, France
| | - Mohamed Chami
- ME Müller Institute, Biozentrum, University of Basel, Basel, Switzerland
| | - Andreas Engel
- ME Müller Institute, Biozentrum, University of Basel, Basel, Switzerland
| | - Anthony P Pugsley
- Molecular Genetics Unit and CNRS URA2172, Institut Pasteur, Paris, France
- Molecular Genetics Unit, Institut Pasteur, 25, rue du Dr Roux, 75724 Paris Cedex 15, France. Tel.: +33 1 4568 8494; Fax: +33 1 4568 8960; E-mail:
| | - Nicolas Bayan
- Molecular Genetics Unit and CNRS URA2172, Institut Pasteur, Paris, France
- CNRS UMR8619, Université de Paris Sud, Orsay, France
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41
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Rumszauer J, Schwarzenlander C, Averhoff B. Identification, subcellular localization and functional interactions of PilMNOWQ and PilA4 involved in transformation competency and pilus biogenesis in the thermophilic bacterium Thermus thermophilus HB27. FEBS J 2006; 273:3261-72. [PMID: 16857013 DOI: 10.1111/j.1742-4658.2006.05335.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The natural transformation system of the thermophilic bacterium Thermus thermophilus HB27 comprises at least 16 distinct competence proteins encoded by seven distinct loci. In this article, we present for the first time biochemical analyses of the Thermus thermophilus competence proteins PilMNOWQ and PilA4, and demonstrate that the pilMNOWQ genes are each essential for natural transformation. We identified three different forms of PilA4, one with an apparent molecular mass of 14 kDa, which correlates with that of the deduced protein, an 18-kDa form and a 23-kDa form; the last was found to be glycosylated. We demonstrate that PilM, PilN and PilO are located in the inner membrane, whereas PilW, PilQ and PilA4 are located in the inner and outer membranes. These data show that PilMNOWQ and PilA4 are components of a DNA translocator structure that spans the inner and outer membranes. We further show that PilA4 and PilQ both copurify with pilus structures. Possible functions of PilQ and PilA4 in DNA translocation and in pilus biogenesis are discussed. Comparative mutant studies revealed that mutations in either pilW or pilQ significantly affect the location of the other protein in the outer membrane. Furthermore, no PilA4 was present in the outer membranes of these mutants. From these findings, we conclude that the abilities of PilW, PilQ and PilA4 to stably localize or accumulate in the outer membrane fraction are strongly dependent on one another, which is in accord with an outer membrane DNA translocator complex comprising PilW, PilQ, and PilA4.
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Affiliation(s)
- Judit Rumszauer
- Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt/Main, Germany
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42
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Abstract
The type IV pilus filament of Myxococcus xanthus penetrates the outer membrane through a gated channel--the PilQ secretin. Assembly of the channel and formation of PilQ multimeric complexes that resist disassembly in heated detergent is correlated with the release of a 50 kDa fragment of PilQ. Tgl lipoprotein is required for PilQ assembly in M. xanthus, because PilQ monomers but no heat and detergent-resistant complexes are present in a strain from which tgl has been deleted. PilQ protein is often found in single patches at both poles of the cell. Tgl, however, is found in a patch at only one pole that most likely identifies the piliated cell pole. Tgl protein that has been transferred from another cell by contact stimulation leads to secretin assembly in the recipient. Pilus proteins PilQ, PilG, PilM, PilN, PilO and PilP are also required for the donation of Tgl by contact stimulation to a stimulation recipient. We suggest that these proteins are parts of a polar superstructure that holds PilQ monomers in a cluster and ready for Tgl to bring about secretin assembly.
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Affiliation(s)
- Eric Nudleman
- Department of Developmental Biology, Stanford University School of Medicine, B300 Beckman Center, 279 Campus Drive, Stanford, CA 94305, USA
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43
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Francetić O, Pugsley AP. Towards the identification of type II secretion signals in a nonacylated variant of pullulanase from Klebsiella oxytoca. J Bacteriol 2005; 187:7045-55. [PMID: 16199575 PMCID: PMC1251600 DOI: 10.1128/jb.187.20.7045-7055.2005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pullulanase (PulA) from the gram-negative bacterium Klebsiella oxytoca is a 116-kDa surface-anchored lipoprotein of the isoamylase family that allows growth on branched maltodextrin polymers. PulA is specifically secreted via a type II secretion system. PelBsp-PulA, a nonacylated variant of PulA made by replacing the lipoprotein signal peptide (sp) with the signal peptide of pectate lyase PelB from Erwinia chrysanthemi, was efficiently secreted into the medium. Two 80-amino-acid regions of PulA, designated A and B, were previously shown to promote secretion of beta-lactamase (BlaM) and endoglucanase CelZ fused to the C terminus. We show that A and B fused to the PelB signal peptide can also promote secretion of BlaM and CelZ but not that of nuclease NucB or several other reporter proteins. However, the deletion of most of region A or all of region B, either individually or together, had only a minor effect on PelBsp-PulA secretion. Four independent linker insertions between amino acids 234 and 324 in PelBsp-PulA abolished secretion. This part of PulA, region C, could contain part of the PulA secretion signal or be important for its correct presentation. Deletion of region C abolished PelBsp-PulA secretion without dramatically affecting its stability. PelBsp-PulA-NucB chimeras were secreted only if the PulA-NucB fusion point was located downstream from region C. The data show that at least three regions of PulA contain information that influences its secretion, depending on their context, and that some reporter proteins might contribute to the secretion of chimeras of which they are a part.
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Affiliation(s)
- Olivera Francetić
- Molecular Genetics Unit, CNRS URA2172, Institut Pasteur, 25, rue du Dr. Roux, 75724 Paris CEDEX 15, France
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Chami M, Guilvout I, Gregorini M, Rémigy HW, Müller SA, Valerio M, Engel A, Pugsley AP, Bayan N. Structural insights into the secretin PulD and its trypsin-resistant core. J Biol Chem 2005; 280:37732-41. [PMID: 16129681 DOI: 10.1074/jbc.m504463200] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Limited proteolysis, secondary structure and biochemical analyses, mass spectrometry, and mass measurements by scanning transmission electron microscopy were combined with cryo-electron microscopy to generate a three-dimensional model of the homomultimeric complex formed by the outer membrane secretin PulD, an essential channel-forming component of the type II secretion system from Klebsiella oxytoca. The complex is a dodecameric structure composed of two rings that sandwich a closed disc. The two rings form chambers on either side of a central plug that is part of the middle disc. The PulD polypeptide comprises two major, structurally quite distinct domains; an N domain, which forms the walls of one of the chambers, and a trypsin-resistant C domain, which contributes to the outer chamber, the central disc, and the plug. The C domain contains a lower proportion of potentially transmembrane beta-structure than classical outer membrane proteins, suggesting that only a small part of it is embedded within the outer membrane. Indeed, the C domain probably extends well beyond the confines of the outer membrane bilayer, forming a centrally plugged channel that penetrates both the peptidoglycan on the periplasmic side and the lipopolysaccharide and capsule layers on the cell surface. The inner chamber is proposed to constitute a docking site for the secreted exoprotein pullulanase, whereas the outer chamber could allow displacement of the plug to open the channel and permit the exoprotein to escape.
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Affiliation(s)
- Mohamed Chami
- ME Müller Institute, Biozentrum, University of Basel, Switzerland
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Jakubowski SJ, Cascales E, Krishnamoorthy V, Christie PJ. Agrobacterium tumefaciens VirB9, an outer-membrane-associated component of a type IV secretion system, regulates substrate selection and T-pilus biogenesis. J Bacteriol 2005; 187:3486-95. [PMID: 15866936 PMCID: PMC1112014 DOI: 10.1128/jb.187.10.3486-3495.2005] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Agrobacterium tumefaciens translocates DNA and protein substrates between cells via a type IV secretion system (T4SS) whose channel subunits include the VirD4 coupling protein, VirB11 ATPase, VirB6, VirB8, VirB2, and VirB9. In this study, we used linker insertion mutagenesis to characterize the contribution of the outer-membrane-associated VirB9 to assembly and function of the VirB/D4 T4SS. Twenty-five dipeptide insertion mutations were classified as permissive for intercellular substrate transfer (Tra+), completely transfer defective (Tra-), or substrate discriminating, e.g., selectively permissive for transfer only of the oncogenic transfer DNA and the VirE2 protein substrates or of a mobilizable IncQ plasmid substrate. Mutations inhibiting transfer of DNA substrates did not affect formation of close contacts of the substrate with inner membrane channel subunits but blocked formation of contacts with the VirB2 and VirB9 channel subunits, which is indicative of a defect in assembly or function of the distal portion of the secretion channel. Several mutations in the N- and C-terminal regions disrupted VirB9 complex formation with the outer-membrane-associated lipoprotein VirB7 or the inner membrane energy sensor VirB10. Several VirB9.i2-producing Tra+ strains failed to elaborate T pilus at detectable levels (Pil-), and three such Tra+ Pil- mutant strains were rendered Tra- upon deletion of virB2, indicating that the cellular form of pilin protein is essential for substrate translocation. Our findings, together with computer-based analyses, support a model in which distinct domains of VirB9 contribute to substrate selection and translocation, establishment of channel subunit contacts, and T-pilus biogenesis.
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Affiliation(s)
- Simon J Jakubowski
- Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston, 6431 Fannin, Houston, TX 77030, USA
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46
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Collins RF, Frye SA, Balasingham S, Ford RC, Tønjum T, Derrick JP. Interaction with type IV pili induces structural changes in the bacterial outer membrane secretin PilQ. J Biol Chem 2005; 280:18923-30. [PMID: 15753075 DOI: 10.1074/jbc.m411603200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Type IV pili are cell surface organelles found on many Gram-negative bacteria. They mediate a variety of functions, including adhesion, twitching motility, and competence for DNA uptake. The type IV pilus is a helical polymer of pilin protein subunits and is capable of rapid polymerization or depolymerization, generating large motor forces in the process. Here we show that a specific interaction between the outer membrane secretin PilQ and the type IV pilus fiber can be detected by far-Western analysis and sucrose density gradient centrifugation. Transmission electron microscopy of preparations of purified pili, to which the purified PilQ oligomer had been added, showed that PilQ was uniquely located at one end of the pilus fiber, effectively forming a "mallet-type" structure. Determination of the three-dimensional structure of the PilQ-type IV pilus complex at 26-angstroms resolution showed that the cavity within the protein complex was filled. Comparison with a previously determined structure of PilQ at 12-angstroms resolution indicated that binding of the pilus fiber induced a dissociation of the "cap" feature and lateral movement of the "arms" of the PilQ oligomer. The results demonstrate that the PilQ structure exhibits a dynamic response to the binding of its transported substrate and suggest that the secretin could play an active role in type IV pilus assembly as well as secretion.
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Affiliation(s)
- Richard F Collins
- Faculty of Life Sciences, The University of Manchester, Faculty of Life Sciences, Sackville Street, P. O. Box 88, Manchester M60 1QD, United Kingdom
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Filloux A. The underlying mechanisms of type II protein secretion. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1694:163-79. [DOI: 10.1016/j.bbamcr.2004.05.003] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2003] [Accepted: 05/07/2004] [Indexed: 10/26/2022]
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Burghout P, van Boxtel R, Van Gelder P, Ringler P, Müller SA, Tommassen J, Koster M. Structure and electrophysiological properties of the YscC secretin from the type III secretion system of Yersinia enterocolitica. J Bacteriol 2004; 186:4645-54. [PMID: 15231798 PMCID: PMC438636 DOI: 10.1128/jb.186.14.4645-4654.2004] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
YscC is the integral outer membrane component of the type III protein secretion machinery of Yersinia enterocolitica and belongs to the family of secretins. This group of proteins forms stable ring-like oligomers in the outer membrane, which are thought to function as transport channels for macromolecules. The YscC oligomer was purified after solubilization from the membrane with a nonionic detergent. Sodium dodecyl sulfate did not dissociate the oligomer, but it caused a change in electrophoretic mobility and an increase in protease susceptibility, indicating partial denaturation of the subunits within the oligomer. The mass of the homo-oligomer, as determined by scanning transmission electron microscopy, was approximately 1 MDa. Analysis of the angular power spectrum from averaged top views of negatively stained YscC oligomers revealed a 13-fold angular order, suggesting that the oligomer consists of 13 subunits. Reconstituted in planar lipid bilayers, the YscC oligomer displayed a constant voltage-independent conductance of approximately 3 nS, thus forming a stable pore. However, in vivo, the expression of YscC did not lead to an increased permeability of the outer membrane. Electron microscopy revealed that the YscC oligomer is composed of three domains, two stacked rings attached to a conical domain. This structure is consistent with the notion that the secretin forms the upper part of the basal body of the needle structure of the type III secreton.
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Affiliation(s)
- Peter Burghout
- Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands
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Abstract
Pullulan degrading enzymes belong to a group of glycosylhydrolases that are widely distributed in nature and are produced by an extremely wide variety of species. Among them the thermophilic and mesophilic bacteria are a rich source of these enzymes. There are many biotechnological applications for these enzymes and a rapidly growing amount of information about their diversity, genetic as well as biochemical and biophysical characteristics. The properties of these enzymes vary and are somewhat linked to the natural environment inhabited by the producing organisms. Genes for these enzymes have been cloned from several strains and their amino acid sequences show highly conserved regions common to the enzymes of the amylase family. Molecular studies have greatly extended our knowledge on pullulan degrading enzymes and their biosynthesis. However, enzyme production levels have usually not been as high as had been assumed possible, and the properties of some enzymes are less than optimal for their industrial applications. Some of these problems can be overcome with the use of good producer organisms, optimized expression/secretion vectors, and site-directed mutagenesis. The molecular biology of pullulan degrading enzymes has been and continues to be a valuable system for studying basic questions of cell biology, such as mechanisms of gene regulation and secretion, and the structure-function relationships of proteins.
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Abstract
Type IV pili are an efficient and versatile device for bacterial surface motility. They are widespread among the beta-, gamma-, and delta-proteobacteria and the cyanobacteria. Within that diversity, there is a core of conserved proteins that includes the pilin (PilA), the motors PilB and PilT, and various components of pilus biogenesis and assembly, PilC, PilD, PilM, PilN, PilO, PilP, and PilQ. Progress has been made in understanding the motor and the secretory functions. PilT is a motor protein that catalyzes pilus retraction; PilB may play a similar role in pilus extension. Type IV pili are multifunctional complexes that can act as bacterial virulence factors because pilus-based motility is used to spread pathogens over the surface of a tissue, or to build multicellular structures such as biofilms and fruiting bodies.
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Affiliation(s)
- Eric Nudleman
- Stanford University, Departments of Biochemistry and of Developmental Biology, Stanford, California 94305, USA
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