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Wimmi S, Fleck M, Helbig C, Brianceau C, Langenfeld K, Szymanski WG, Angelidou G, Glatter T, Diepold A. Pilotins are mobile T3SS components involved in assembly and substrate specificity of the bacterial type III secretion system. Mol Microbiol 2024; 121:304-323. [PMID: 38178634 DOI: 10.1111/mmi.15223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 12/17/2023] [Accepted: 12/20/2023] [Indexed: 01/06/2024]
Abstract
In animal pathogens, assembly of the type III secretion system injectisome requires the presence of so-called pilotins, small lipoproteins that assist the formation of the secretin ring in the outer membrane. Using a combination of functional assays, interaction studies, proteomics, and live-cell microscopy, we determined the contribution of the pilotin to the assembly, function, and substrate selectivity of the T3SS and identified potential new downstream roles of pilotin proteins. In absence of its pilotin SctG, Yersinia enterocolitica forms few, largely polar injectisome sorting platforms and needles. Accordingly, most export apparatus subcomplexes are mobile in these strains, suggesting the absence of fully assembled injectisomes. Remarkably, while absence of the pilotin all but prevents export of early T3SS substrates, such as the needle subunits, it has little effect on secretion of late T3SS substrates, including the virulence effectors. We found that although pilotins interact with other injectisome components such as the secretin in the outer membrane, they mostly localize in transient mobile clusters in the bacterial membrane. Together, these findings provide a new view on the role of pilotins in the assembly and function of type III secretion injectisomes.
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Affiliation(s)
- Stephan Wimmi
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Moritz Fleck
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Carlos Helbig
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Corentin Brianceau
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Katja Langenfeld
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Witold G Szymanski
- Mass Spectrometry and Proteomics Facility, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Georgia Angelidou
- Mass Spectrometry and Proteomics Facility, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Timo Glatter
- Mass Spectrometry and Proteomics Facility, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Andreas Diepold
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
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2
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Herfurth M, Pérez-Burgos M, Søgaard-Andersen L. The mechanism for polar localization of the type IVa pilus machine in Myxococcus xanthus. mBio 2023; 14:e0159323. [PMID: 37754549 PMCID: PMC10653833 DOI: 10.1128/mbio.01593-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 07/31/2023] [Indexed: 09/28/2023] Open
Abstract
IMPORTANCE Type IVa pili (T4aP) are widespread bacterial cell surface structures with important functions in motility, surface adhesion, biofilm formation, and virulence. Different bacteria have adapted different piliation patterns. To address how these patterns are established, we focused on the bipolar localization of the T4aP machine in the model organism Myxococcus xanthus by studying the localization of the PilQ secretin, the first component of this machine that assembles at the poles. Based on experiments using a combination of fluorescence microscopy, biochemistry, and computational structural analysis, we propose that PilQ, and specifically its AMIN domains, binds septal and polar peptidoglycan, thereby enabling polar Tgl localization, which then stimulates PilQ multimerization in the outer membrane. We also propose that the presence and absence of AMIN domains in T4aP secretins contribute to the different piliation patterns across bacteria.
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Affiliation(s)
- Marco Herfurth
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - María Pérez-Burgos
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Lotte Søgaard-Andersen
- Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
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3
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Barbat B, Douzi B, Voulhoux R. Structural lessons on bacterial secretins. Biochimie 2023; 205:110-116. [PMID: 36096236 DOI: 10.1016/j.biochi.2022.08.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 07/26/2022] [Accepted: 08/31/2022] [Indexed: 11/30/2022]
Abstract
To exchange and communicate with their surroundings, bacteria have evolved multiple active and passive mechanisms for trans-envelope transport. Among the pore-forming complexes found in the outer membrane of Gram-negative bacteria, secretins are distinctive homo-oligomeric channels dedicated to the active translocation of voluminous structures such as folded proteins, assembled fibers, virus particles or DNA. Members of the bacterial secretin family share a common cylinder-shaped structure with a gated pore-forming part inserted in the outer membrane, and a periplasmic channel connected to the inner membrane components of the corresponding nanomachine. In this mini-review, we will present what recently determined 3D structures have told us about the mechanisms of translocation through secretins of large substrates to the bacterial surface or in the extracellular milieu.
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Affiliation(s)
- Brice Barbat
- LCB-UMR7283, CNRS, Aix Marseille Université, IMM, 13009, Marseille, France
| | | | - Romé Voulhoux
- LCB-UMR7283, CNRS, Aix Marseille Université, IMM, 13009, Marseille, France.
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4
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Scaffolding Protein GspB/OutB Facilitates Assembly of the Dickeya dadantii Type 2 Secretion System by Anchoring the Outer Membrane Secretin Pore to the Inner Membrane and to the Peptidoglycan Cell Wall. mBio 2022; 13:e0025322. [PMID: 35546537 PMCID: PMC9239104 DOI: 10.1128/mbio.00253-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The phytopathogenic proteobacterium Dickeya dadantii secretes an array of plant cell wall-degrading enzymes and other virulence factors via the type 2 secretion system (T2SS). T2SSs are widespread among important plant, animal, and human bacterial pathogens. This multiprotein complex spans the double membrane cell envelope and secretes fully folded proteins through a large outer membrane pore formed by 15 subunits of the secretin GspD. Secretins are also found in the type 3 secretion system and the type 4 pili. Usually, specialized lipoproteins termed pilotins assist the targeting and assembly of secretins into the outer membrane. Here, we show that in D. dadantii, the pilotin acts in concert with the scaffolding protein GspB. Deletion of gspB profoundly impacts secretin assembly, pectinase secretion, and virulence. Structural studies reveal that GspB possesses a conserved periplasmic homology region domain that interacts directly with the N-terminal secretin domain. Site-specific photo-cross-linking unravels molecular details of the GspB-GspD complex in vivo. We show that GspB facilitates outer membrane targeting and assembly of the secretin pores and anchors them to the inner membrane while the C-terminal extension of GspB provides a scaffold for the secretin channel in the peptidoglycan cell wall. Phylogenetic analysis shows that in other bacteria, GspB homologs vary in length and domain composition and act in concert with either a cognate ATPase GspA or the pilotin GspS.
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5
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BonA from Acinetobacter baumannii Forms a Divisome-Localized Decamer That Supports Outer Envelope Function. mBio 2021; 12:e0148021. [PMID: 34311571 PMCID: PMC8406262 DOI: 10.1128/mbio.01480-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Acinetobacter baumannii is a high-risk pathogen due to the rapid global spread of multidrug-resistant lineages. Its phylogenetic divergence from other ESKAPE pathogens means that determinants of its antimicrobial resistance can be difficult to extrapolate from other widely studied bacteria. A recent study showed that A. baumannii upregulates production of an outer membrane lipoprotein, which we designate BonA, in response to challenge with polymyxins. Here, we show that BonA has limited sequence similarity and distinct structural features compared to lipoproteins from other bacterial species. Analyses through X-ray crystallography, small-angle X-ray scattering, electron microscopy, and multiangle light scattering demonstrate that BonA has a dual BON (Bacterial OsmY and Nodulation) domain architecture and forms a decamer via an unusual oligomerization mechanism. This analysis also indicates this decamer is transient, suggesting dynamic oligomerization plays a role in BonA function. Antisera recognizing BonA shows it is an outer membrane protein localized to the divisome. Loss of BonA modulates the density of the outer membrane, consistent with a change in its structure or link to the peptidoglycan, and prevents motility in a clinical strain (ATCC 17978). Consistent with these findings, the dimensions of the BonA decamer are sufficient to permeate the peptidoglycan layer, with the potential to form a membrane-spanning complex during cell division. IMPORTANCE The pathogen Acinetobacter baumannii is considered an urgent threat to human health. A. baumannii is highly resistant to treatment with antibiotics, in part due to its protective cell envelope. This bacterium is only distantly related to other bacterial pathogens, so its cell envelope has distinct properties and contains components distinct from those of other bacteria that support its function. Here, we report the discovery of BonA, a protein that supports A. baumannii outer envelope function and is required for cell motility. We determine the atomic structure of BonA and show that it forms part of the cell division machinery and functions by forming a complex, features that mirror those of distantly related homologs from other bacteria. By improving our understanding of the A. baumannii cell envelope this work will assist in treating this pathogen.
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6
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Majewski DD, Okon M, Heinkel F, Robb CS, Vuckovic M, McIntosh LP, Strynadka NCJ. Characterization of the Pilotin-Secretin Complex from the Salmonella enterica Type III Secretion System Using Hybrid Structural Methods. Structure 2020; 29:125-138.e5. [PMID: 32877645 DOI: 10.1016/j.str.2020.08.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 07/21/2020] [Accepted: 08/11/2020] [Indexed: 12/01/2022]
Abstract
The type III secretion system (T3SS) is a multi-membrane-spanning protein channel used by Gram-negative pathogenic bacteria to secrete effectors directly into the host cell cytoplasm. In the many species reliant on the T3SS for pathogenicity, proper assembly of the outer membrane secretin pore depends on a diverse family of lipoproteins called pilotins. We present structural and biochemical data on the Salmonella enterica pilotin InvH and the S domain of its cognate secretin InvG. Characterization of InvH by X-ray crystallography revealed a dimerized, α-helical pilotin. Size-exclusion-coupled multi-angle light scattering and small-angle X-ray scattering provide supporting evidence for the formation of an InvH homodimer in solution. Structures of the InvH-InvG heterodimeric complex determined by X-ray crystallography and NMR spectroscopy indicate a predominantly hydrophobic interface. Knowledge of the interaction between InvH and InvG brings us closer to understanding the mechanisms by which pilotins assemble the secretin pore.
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Affiliation(s)
- Dorothy D Majewski
- Department of Biochemistry and Molecular Biology and the Center for Blood Research, University of British Columbia, Vancouver, BC, Canada
| | - Mark Okon
- Michael Smith Laboratories, Department of Biochemistry and Molecular Biology, and Department of Chemistry, University of British Columbia, Vancouver, BC, Canada
| | - Florian Heinkel
- Michael Smith Laboratories, Department of Biochemistry and Molecular Biology, and Department of Chemistry, University of British Columbia, Vancouver, BC, Canada
| | - Craig S Robb
- Department of Biochemistry and Molecular Biology and the Center for Blood Research, University of British Columbia, Vancouver, BC, Canada
| | - Marija Vuckovic
- Department of Biochemistry and Molecular Biology and the Center for Blood Research, University of British Columbia, Vancouver, BC, Canada
| | - Lawrence P McIntosh
- Michael Smith Laboratories, Department of Biochemistry and Molecular Biology, and Department of Chemistry, University of British Columbia, Vancouver, BC, Canada.
| | - Natalie C J Strynadka
- Department of Biochemistry and Molecular Biology and the Center for Blood Research, University of British Columbia, Vancouver, BC, Canada.
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7
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Silva YRDO, Contreras-Martel C, Macheboeuf P, Dessen A. Bacterial secretins: Mechanisms of assembly and membrane targeting. Protein Sci 2020; 29:893-904. [PMID: 32020694 DOI: 10.1002/pro.3835] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 01/25/2020] [Accepted: 01/28/2020] [Indexed: 12/20/2022]
Abstract
Secretion systems are employed by bacteria to transport macromolecules across membranes without compromising their integrities. Processes including virulence, colonization, and motility are highly dependent on the secretion of effector molecules toward the immediate cellular environment, and in some cases, into the host cytoplasm. In Type II and Type III secretion systems, as well as in Type IV pili, homomultimeric complexes known as secretins form large pores in the outer bacterial membrane, and the localization and assembly of such 1 MDa molecules often relies on pilotins or accessory proteins. Significant progress has been made toward understanding details of interactions between secretins and their partner proteins using approaches ranging from bacterial genetics to cryo electron microscopy. This review provides an overview of the mode of action of pilotins and accessory proteins for T2SS, T3SS, and T4PS secretins, highlighting recent near-atomic resolution cryo-EM secretin complex structures and underlining the importance of these interactions for secretin functionality.
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Affiliation(s)
- Yuri Rafael de Oliveira Silva
- Brazilian Biosciences National Laboratory (LNBio), CNPEM, Campinas, São Paulo, Brazil.,Departamento de Genética, Evolução, Microbiologia e Imunologia, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), Campinas, São Paulo, Brazil
| | - Carlos Contreras-Martel
- Université Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Pauline Macheboeuf
- Université Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Andréa Dessen
- Brazilian Biosciences National Laboratory (LNBio), CNPEM, Campinas, São Paulo, Brazil.,Université Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
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8
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Natarajan J, Moitra A, Zabel S, Singh N, Wagner S, Rapaport D. Yeast can express and assemble bacterial secretins in the mitochondrial outer membrane. MICROBIAL CELL 2019; 7:15-27. [PMID: 31921930 PMCID: PMC6946019 DOI: 10.15698/mic2020.01.703] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Secretins form large multimeric pores in the outer membrane (OM) of Gram-negative bacteria. These pores are part of type II and III secretion systems (T2SS and T3SS, respectively) and are crucial for pathogenicity. Recent structural studies indicate that secretins form a structure rich in β-strands. However, little is known about the mechanism by which secretins assemble into the OM. Based on the conservation of the biogenesis of β-barrel proteins in bacteria and mitochondria, we used yeast cells as a model system to study the assembly process of secretins. To that end, we analyzed the biogenesis of PulD (T2SS), SsaC (T3SS) and InvG (T3SS) in wild type cells or in cells mutated for known mitochondrial import and assembly factors. Our results suggest that secretins can be expressed in yeast cells, where they are enriched in the mitochondrial fraction. Interestingly, deletion of mitochondrial import receptors like Tom20 and Tom70 reduces the mitochondrial association of PulD but does not affect that of InvG. SsaC shows another dependency pattern and its membrane assembly is enhanced by the absence of Tom70 and compromised in cells lacking Tom20 or the topogenesis of outer membrane β-barrel proteins (TOB) complex component, Mas37. Collectively, these findings suggest that various secretins can follow different pathways to assemble into the bacterial OM.
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Affiliation(s)
- Janani Natarajan
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany
| | - Anasuya Moitra
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany
| | - Sussanne Zabel
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany.,Current address: Center for Bioinformatics (ZBIT), University of Tübingen, Tübingen, Germany
| | - Nidhi Singh
- Interfaculty Institute of Microbiology and Infection Medicine (IMIT), University of Tübingen, Tübingen, Germany
| | - Samuel Wagner
- Interfaculty Institute of Microbiology and Infection Medicine (IMIT), University of Tübingen, Tübingen, Germany.,German Center for Infection Research (DZIF), partner-site Tübingen, Tübingen, Germany
| | - Doron Rapaport
- Interfaculty Institute of Biochemistry, University of Tübingen, Tübingen, Germany
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9
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Abstract
The type II secretion system (T2SS) delivers toxins and a range of hydrolytic enzymes, including proteases, lipases, and carbohydrate-active enzymes, to the cell surface or extracellular space of Gram-negative bacteria. Its contribution to survival of both extracellular and intracellular pathogens as well as environmental species of proteobacteria is evident. This dynamic, multicomponent machinery spans the entire cell envelope and consists of a cytoplasmic ATPase, several inner membrane proteins, a periplasmic pseudopilus, and a secretin pore embedded in the outer membrane. Despite the trans-envelope configuration of the T2S nanomachine, proteins to be secreted engage with the system first once they enter the periplasmic compartment via the Sec or TAT export system. Thus, the T2SS is specifically dedicated to their outer membrane translocation. The many sequence and structural similarities between the T2SS and type IV pili suggest a common origin and argue for a pilus-mediated mechanism of secretion. This minireview describes the structures, functions, and interactions of the individual T2SS components and the general architecture of the assembled T2SS machinery and briefly summarizes the transport and function of a growing list of T2SS exoproteins. Recent advances in cryo-electron microscopy, which have led to an increased understanding of the structure-function relationship of the secretin channel and the pseudopilus, are emphasized.
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10
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Natarajan J, Singh N, Rapaport D. Assembly and targeting of secretins in the bacterial outer membrane. Int J Med Microbiol 2019; 309:151322. [PMID: 31262642 DOI: 10.1016/j.ijmm.2019.06.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 06/04/2019] [Accepted: 06/18/2019] [Indexed: 11/20/2022] Open
Abstract
In Gram-negative bacteria, secretion of toxins ensure the survival of the bacterium. Such toxins are secreted by sophisticated multiprotein systems. The most conserved part in some of these secretion systems are components, called secretins, which form the outer membrane ring in these systems. Recent structural studies shed some light on the oligomeric organization of secretins. However, the mechanisms by which these proteins are targeted to the outer membrane and assemble there into ring structures are still not fully understood. This review discusses the various species-specific targeting and assembly pathways that are taken by secretins in order to form their functional oligomers.
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Affiliation(s)
- Janani Natarajan
- Interfaculty Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany.
| | - Nidhi Singh
- Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str.6, 72076 Tübingen, Germany
| | - Doron Rapaport
- Interfaculty Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Str. 4, 72076 Tübingen, Germany
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11
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Howard SP, Estrozi LF, Bertrand Q, Contreras-Martel C, Strozen T, Job V, Martins A, Fenel D, Schoehn G, Dessen A. Structure and assembly of pilotin-dependent and -independent secretins of the type II secretion system. PLoS Pathog 2019; 15:e1007731. [PMID: 31083688 PMCID: PMC6532946 DOI: 10.1371/journal.ppat.1007731] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Revised: 05/23/2019] [Accepted: 03/26/2019] [Indexed: 01/09/2023] Open
Abstract
The type II secretion system (T2SS) is a cell envelope-spanning macromolecular complex that is prevalent in Gram-negative bacterial species. It serves as the predominant virulence mechanism of many bacteria including those of the emerging human pathogens Vibrio vulnificus and Aeromonas hydrophila. The system is composed of a core set of highly conserved proteins that assemble an inner membrane platform, a periplasmic pseudopilus and an outer membrane complex termed the secretin. Localization and assembly of secretins in the outer membrane requires recognition of secretin monomers by two different partner systems: an inner membrane accessory complex or a highly sequence-diverse outer membrane lipoprotein, termed the pilotin. In this study, we addressed the question of differential secretin assembly mechanisms by using cryo-electron microscopy to determine the structures of the secretins from A. hydrophila (pilotin-independent ExeD) and V. vulnificus (pilotin-dependent EpsD). These structures, at approximately 3.5 Å resolution, reveal pentadecameric stoichiometries and C-terminal regions that carry a signature motif in the case of a pilotin-dependent assembly mechanism. We solved the crystal structure of the V. vulnificus EpsS pilotin and confirmed the importance of the signature motif for pilotin-dependent secretin assembly by performing modelling with the C-terminus of EpsD. We also show that secretin assembly is essential for membrane integrity and toxin secretion in V. vulnificus and establish that EpsD requires the coordinated activity of both the accessory complex EpsAB and the pilotin EpsS for full assembly and T2SS function. In contrast, mutation of the region of the S-domain that is normally the site of pilotin interactions has little effect on assembly or function of the ExeD secretin. Since secretins are essential outer membrane channels present in a variety of secretion systems, these results provide a structural and functional basis for understanding the key assembly steps for different members of this vast pore-forming family of proteins.
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Affiliation(s)
- S. Peter Howard
- Dept. Biochemistry, Microbiology and Immunology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Leandro F. Estrozi
- Univ Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Quentin Bertrand
- Univ Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | | | - Timothy Strozen
- Dept. Biochemistry, Microbiology and Immunology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Viviana Job
- Univ Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Alexandre Martins
- Univ Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Daphna Fenel
- Univ Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Guy Schoehn
- Univ Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
| | - Andréa Dessen
- Univ Grenoble Alpes, CNRS, CEA, Institut de Biologie Structurale (IBS), Grenoble, France
- Brazilian Biosciences National Laboratory (LNBio), CNPEM, Campinas, São Paulo, Brazil
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12
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Gregson BH, Metodieva G, Metodiev MV, Golyshin PN, McKew BA. Differential Protein Expression During Growth on Medium Versus Long-Chain Alkanes in the Obligate Marine Hydrocarbon-Degrading Bacterium Thalassolituus oleivorans MIL-1. Front Microbiol 2018; 9:3130. [PMID: 30619200 PMCID: PMC6304351 DOI: 10.3389/fmicb.2018.03130] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 12/04/2018] [Indexed: 02/02/2023] Open
Abstract
The marine obligate hydrocarbonoclastic bacterium Thalassolituus oleivorans MIL-1 metabolizes a broad range of aliphatic hydrocarbons almost exclusively as carbon and energy sources. We used LC-MS/MS shotgun proteomics to identify proteins involved in aerobic alkane degradation during growth on medium- (n-C14) or long-chain (n-C28) alkanes. During growth on n-C14, T. oleivorans expresses an alkane monooxygenase system involved in terminal oxidation including two alkane 1-monooxygenases, a ferredoxin, a ferredoxin reductase and an aldehyde dehydrogenase. In contrast, during growth on long-chain alkanes (n-C28), T. oleivorans may switch to a subterminal alkane oxidation pathway evidenced by significant upregulation of Baeyer-Villiger monooxygenase and an esterase, proteins catalyzing ketone and ester metabolism, respectively. The metabolite (primary alcohol) generated from terminal oxidation of an alkane was detected during growth on n-C14 but not on n-C28 also suggesting alternative metabolic pathways. Expression of both active and passive transport systems involved in uptake of long-chain alkanes was higher when compared to the non-hydrocarbon control, including a TonB-dependent receptor, a FadL homolog and a specialized porin. Also, an inner membrane transport protein involved in the export of an outer membrane protein was expressed. This study has demonstrated the substrate range of T. oleivorans is larger than previously reported with growth from n-C10 up to n-C32. It has also greatly enhanced our understanding of the fundamental physiology of T. oleivorans, a key bacterium that plays a significant role in natural attenuation of marine oil pollution, by identifying key enzymes expressed during the catabolism of n-alkanes.
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Affiliation(s)
- Benjamin H Gregson
- School of Biological Sciences, University of Essex, Colchester, United Kingdom
| | - Gergana Metodieva
- School of Biological Sciences, University of Essex, Colchester, United Kingdom
| | - Metodi V Metodiev
- School of Biological Sciences, University of Essex, Colchester, United Kingdom
| | - Peter N Golyshin
- School of Biological Sciences, Bangor University, Bangor, United Kingdom.,School of Natural Sciences, College of Environmental Sciences and Engineering, Bangor University, Bangor, United Kingdom
| | - Boyd A McKew
- School of Biological Sciences, University of Essex, Colchester, United Kingdom
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13
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Wagner S, Grin I, Malmsheimer S, Singh N, Torres-Vargas CE, Westerhausen S. Bacterial type III secretion systems: a complex device for the delivery of bacterial effector proteins into eukaryotic host cells. FEMS Microbiol Lett 2018; 365:5068689. [PMID: 30107569 PMCID: PMC6140923 DOI: 10.1093/femsle/fny201] [Citation(s) in RCA: 112] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 08/08/2018] [Indexed: 12/21/2022] Open
Abstract
Virulence-associated type III secretion systems (T3SS) serve the injection of bacterial effector proteins into eukaryotic host cells. They are able to secrete a great diversity of substrate proteins in order to modulate host cell function, and have evolved to sense host cell contact and to inject their substrates through a translocon pore in the host cell membrane. T3SS substrates contain an N-terminal signal sequence and often a chaperone-binding domain for cognate T3SS chaperones. These signals guide the substrates to the machine where substrates are unfolded and handed over to the secretion channel formed by the transmembrane domains of the export apparatus components and by the needle filament. Secretion itself is driven by the proton motive force across the bacterial inner membrane. The needle filament measures 20-150 nm in length and is crowned by a needle tip that mediates host-cell sensing. Secretion through T3SS is a highly regulated process with early, intermediate and late substrates. A strict secretion hierarchy is required to build an injectisome capable of reaching, sensing and penetrating the host cell membrane, before host cell-acting effector proteins are deployed. Here, we review the recent progress on elucidating the assembly, structure and function of T3SS injectisomes.
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Affiliation(s)
- Samuel Wagner
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
- German Center for Infection Research (DZIF), partner-site Tübingen, Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Iwan Grin
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Silke Malmsheimer
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Nidhi Singh
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Claudia E Torres-Vargas
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
| | - Sibel Westerhausen
- University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Elfriede-Aulhorn-Str. 6, 72076 Tübingen, Germany
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14
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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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15
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Structural insight into the assembly of the type II secretion system pilotin–secretin complex from enterotoxigenic Escherichia coli. Nat Microbiol 2018; 3:581-587. [DOI: 10.1038/s41564-018-0148-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 03/07/2018] [Indexed: 12/29/2022]
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16
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Gu S, Shevchik VE, Shaw R, Pickersgill RW, Garnett JA. The role of intrinsic disorder and dynamics in the assembly and function of the type II secretion system. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:1255-1266. [PMID: 28733198 DOI: 10.1016/j.bbapap.2017.07.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 07/02/2017] [Accepted: 07/17/2017] [Indexed: 10/19/2022]
Abstract
Many Gram-negative commensal and pathogenic bacteria use a type II secretion system (T2SS) to transport proteins out of the cell. These exported proteins or substrates play a major role in toxin delivery, maintaining biofilms, replication in the host and subversion of host immune responses to infection. We review the current structural and functional work on this system and argue that intrinsically disordered regions and protein dynamics are central for assembly, exo-protein recognition, and secretion competence of the T2SS. The central role of intrinsic disorder-order transitions in these processes may be a particular feature of type II secretion.
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Affiliation(s)
- Shuang Gu
- Queen Mary University of London, School of Biological and Chemical Sciences, London E1 4NS, United Kingdom
| | - Vladimir E Shevchik
- 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
| | - Rosie Shaw
- Queen Mary University of London, School of Biological and Chemical Sciences, London E1 4NS, United Kingdom
| | - Richard W Pickersgill
- Queen Mary University of London, School of Biological and Chemical Sciences, London E1 4NS, United Kingdom.
| | - James A Garnett
- Queen Mary University of London, School of Biological and Chemical Sciences, London E1 4NS, United Kingdom.
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17
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Defining Lipoprotein Localisation by Fluorescence Microscopy. Methods Mol Biol 2017. [PMID: 28667602 DOI: 10.1007/978-1-4939-7033-9_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
In recent years it has become evident that lipoproteins play crucial roles in the assembly of bacterial envelope-embedded nanomachineries and in the processes of protein export/secretion. In this chapter we describe a method to determine their precise localisation, for example inner versus outer membrane, in Gram-negative bacteria using human opportunistic pathogen Pseudomonas aeruginosa as a model. A fusion protein between a given putative lipoprotein and the red fluorescent protein mCherry must be created and expressed in a strain expressing cytoplasmic green fluorescent protein (GFP). Then the peripheral localisation of the fusion protein in the cell can be examined by treating cells with lysozyme to create spheroplasts and monitoring fluorescence under a confocal microscope. Mutants in the signal peptide can be engineered to study the association with the membrane and efficiency of transport. This protocol can be adapted to monitor lipoprotein localisation in other Gram-negative bacteria.
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18
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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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19
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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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20
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De Geyter J, Tsirigotaki A, Orfanoudaki G, Zorzini V, Economou A, Karamanou S. Protein folding in the cell envelope of Escherichia coli. Nat Microbiol 2016; 1:16107. [PMID: 27573113 DOI: 10.1038/nmicrobiol.2016.107] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Accepted: 06/02/2016] [Indexed: 11/09/2022]
Abstract
While the entire proteome is synthesized on cytoplasmic ribosomes, almost half associates with, localizes in or crosses the bacterial cell envelope. In Escherichia coli a variety of mechanisms are important for taking these polypeptides into or across the plasma membrane, maintaining them in soluble form, trafficking them to their correct cell envelope locations and then folding them into the right structures. The fidelity of these processes must be maintained under various environmental conditions including during stress; if this fails, proteases are called in to degrade mislocalized or aggregated proteins. Various soluble, diffusible chaperones (acting as holdases, foldases or pilotins) and folding catalysts are also utilized to restore proteostasis. These responses can be general, dealing with multiple polypeptides, with functional overlaps and operating within redundant networks. Other chaperones are specialized factors, dealing only with a few exported proteins. Several complex machineries have evolved to deal with binding to, integration in and crossing of the outer membrane. This complex protein network is responsible for fundamental cellular processes such as cell wall biogenesis; cell division; the export, uptake and degradation of molecules; and resistance against exogenous toxic factors. The underlying processes, contributing to our fundamental understanding of proteostasis, are a treasure trove for the development of novel antibiotics, biopharmaceuticals and vaccines.
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Affiliation(s)
- Jozefien De Geyter
- KU Leuven-University of Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, B-3000 Leuven, Belgium
| | - Alexandra Tsirigotaki
- KU Leuven-University of Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, B-3000 Leuven, Belgium
| | - Georgia Orfanoudaki
- Institute of Molecular Biology and Biotechnology, FORTH and Department of Biology, University of Crete, PO Box 1385, GR-711 10 Iraklio, Crete, Greece
| | - Valentina Zorzini
- KU Leuven-University of Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, B-3000 Leuven, Belgium
| | - Anastassios Economou
- KU Leuven-University of Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, B-3000 Leuven, Belgium.,Institute of Molecular Biology and Biotechnology, FORTH and Department of Biology, University of Crete, PO Box 1385, GR-711 10 Iraklio, Crete, Greece
| | - Spyridoula Karamanou
- KU Leuven-University of Leuven, Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Molecular Bacteriology, B-3000 Leuven, Belgium
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21
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Folding outer membrane proteins independently of the β-barrel assembly machinery: an assembly pathway for multimeric complexes? Biochem Soc Trans 2016; 44:845-50. [DOI: 10.1042/bst20160003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Indexed: 11/17/2022]
Abstract
Since the discovery of the essential role of the β-barrel assembly machinery (BAM) for the membrane insertion of outer membrane proteins (OMPs) that are unrelated in sequence, members of this universally conserved family dominate discussions on OMP assembly in bacteria, mitochondria and chloroplasts. However, several multimeric bacterial OMPs assemble independently of the catalyzing BAM-component BamA. Recent progress on this alternative pathway is reviewed here, and a model for BAM-independent assembly for multimeric OMPs is proposed in which monomer delivery to the membrane and stable prepore formation are key steps towards productive membrane insertion.
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22
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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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23
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Jeeves M, Knowles TJ. A novel pathway for outer membrane protein biogenesis in Gram-negative bacteria. Mol Microbiol 2015; 97:607-11. [PMID: 26059329 PMCID: PMC4973683 DOI: 10.1111/mmi.13082] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/03/2015] [Indexed: 02/04/2023]
Abstract
The understanding of the biogenesis of the outer membrane of Gram‐negative bacteria is of critical importance due to the emergence of bacteria that are becoming resistant to available antibiotics. A problem that is most serious for Gram‐negative bacteria, with essentially few antibiotics under development or likely to be available for clinical use in the near future. The understanding of the Gram‐negative bacterial outer membrane is therefore critical to developing new antimicrobial agents, as this membrane makes direct contact with the external milieu, and the proteins present within this membrane are the instruments of microbial warfare, playing key roles in microbial pathogenesis, virulence and multidrug resistance. To date, a single outer membrane complex has been identified as essential for the folding and insertion of proteins into the outer membrane, this is the β‐barrel assembly machine (BAM) complex, which in some cases is supplemented by the Translocation and Assembly Module (TAM). In this issue of Molecular Microbiology, Dunstan et al. have identified a novel pathway for the insertion of a subset of integral membrane proteins into the Gram‐negative outer membrane that is independent of the BAM complex and TAM.
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Affiliation(s)
- Mark Jeeves
- School of Cancer Sciences, University of Birmingham, Birmingham, B15 2TT, UK
| | - Timothy J Knowles
- School of Cancer Sciences, University of Birmingham, Birmingham, B15 2TT, UK
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24
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Gazi AD. Commentary: The absence of protein Y4yS affects negatively the abundance of T3SS Mesorhizobium loti secretin, RhcC2, in bacterial membranes. Front Microbiol 2015; 6:710. [PMID: 26236295 PMCID: PMC4500985 DOI: 10.3389/fmicb.2015.00710] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Accepted: 06/29/2015] [Indexed: 11/20/2022] Open
Affiliation(s)
- Anastasia D Gazi
- Laboratoire d'Enzymologie et Biochimie Structurales, Centre National de la Recherche Scientifique Gif-sur-Yvette, France
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25
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Identification of YsaP, the Pilotin of the Yersinia enterocolitica Ysa Type III Secretion System. J Bacteriol 2015; 197:2770-9. [PMID: 26078446 DOI: 10.1128/jb.00238-15] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Accepted: 06/09/2015] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Secretins are multimeric outer membrane pore-forming proteins found in complex export systems in Gram-negative bacteria. All type III secretion systems (T3SSs) have a secretin, and one of these is the YsaC secretin of the chromosomally encoded Ysa T3SS of Yersinia enterocolitica. In some cases, pilotin proteins, which are outer membrane lipoproteins, are required for their cognate secretins to multimerize and/or localize to the outer membrane. However, if secretin multimers mislocalize to the inner membrane, this can trigger the protective phage shock protein (Psp) stress response. During a screen for mutations that suppress YsaC toxicity to a psp null strain, we isolated several independent mutations predicted to increase expression of the YE3559 gene within the Ysa pathogenicity island. YE3559, which we have named ysaP, is predicted to encode a small outer membrane lipoprotein, and this location was confirmed by membrane fractionation. Elevated ysaP expression increased the steady-state level of YsaC but made it less toxic to a psp null strain, and it also decreased YsaC-dependent induction of psp gene expression. Subsequent experiments showed that YsaP was not required for YsaC multimerization but was required for the multimers to localize to the outer membrane. Consistent with this, a ysaP null mutation compromised protein export by the Ysa T3SS. All these observations suggest that YsaP is the pilotin for the YsaC secretin. This is only the second pilotin to be characterized for Yersinia and one of only a small number of pilotins described for all bacteria. IMPORTANCE Secretins are essential for the virulence of many bacterial pathogens and also play roles in surface attachment, motility, and competence. This has generated considerable interest in understanding how secretins function. However, their fundamental differences from typical outer membrane proteins have raised various questions about secretins, including how they are assembled into outer membrane multimers. Pilotin proteins facilitate the assembly of some secretins, but only a small number of pilotins have been identified, slowing efforts to understand common and distinct features of secretin assembly. This study provides an important advance by identifying a novel member of the pilotin family and also demonstrating a method of pilotin discovery that could be broadly applied.
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26
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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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27
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Mercante V, Duarte CM, Sánchez CM, Zalguizuri A, Caetano-Anollés G, Lepek VC. The absence of protein Y4yS affects negatively the abundance of T3SS Mesorhizobium loti secretin, RhcC2, in bacterial membranes. FRONTIERS IN PLANT SCIENCE 2015; 6:12. [PMID: 25688250 PMCID: PMC4311626 DOI: 10.3389/fpls.2015.00012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 01/06/2015] [Indexed: 06/04/2023]
Abstract
Mesorhizobium loti MAFF303099 has a functional type III secretion system (T3SS) that is involved in the determination of nodulation competitiveness on Lotus. The M. loti T3SS cluster contains gene y4yS (mlr8765) that codes for a protein of unknown function (Y4yS). A mutation in the y4yS gene favors the M. loti symbiotic competitive ability on Lotus tenuis cv. Esmeralda and affects negatively the secretion of proteins through T3SS. Here we localize Y4yS in the bacterial membrane using a translational reporter peptide fusion. In silico analysis indicated that this protein presents a tetratricopeptide repeat (TPR) domain, a signal peptide and a canonical lipobox LGCC in the N-terminal sequence. These features that are shared with proteins required for the formation of the secretin complex in type IV secretion systems and in the Tad system, together with its localization, suggest that the y4yS-encoded protein is required for the formation of the M. loti T3SS secretin (RhcC2) complex. Remarkably, analysis of RhcC2 in the wild-type and M. loti y4yS mutant strains indicated that the absence of Y4yS affects negatively the accumulation of normal levels of RhcC2 in the membrane.
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Affiliation(s)
- Virginia Mercante
- Instituto de Investigaciones Biotecnológicas “Dr. Rodolfo A. Ugalde,” Universidad Nacional de San MartínBuenos Aires, Argentina
| | - Cecilia M. Duarte
- Instituto de Investigaciones Biotecnológicas “Dr. Rodolfo A. Ugalde,” Universidad Nacional de San MartínBuenos Aires, Argentina
| | - Cintia M. Sánchez
- Instituto de Investigaciones Biotecnológicas “Dr. Rodolfo A. Ugalde,” Universidad Nacional de San MartínBuenos Aires, Argentina
| | - Andrés Zalguizuri
- Instituto de Investigaciones Biotecnológicas “Dr. Rodolfo A. Ugalde,” Universidad Nacional de San MartínBuenos Aires, Argentina
| | - Gustavo Caetano-Anollés
- Evolutionary Bioinformatics Laboratory, Department of Crop Sciences, University of IllinoisUrbana-Champaign, USA
| | - Viviana C. Lepek
- Instituto de Investigaciones Biotecnológicas “Dr. Rodolfo A. Ugalde,” Universidad Nacional de San MartínBuenos Aires, Argentina
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28
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Type II secretion system: A magic beanstalk or a protein escalator. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1568-77. [DOI: 10.1016/j.bbamcr.2013.12.020] [Citation(s) in RCA: 129] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Revised: 12/13/2013] [Accepted: 12/23/2013] [Indexed: 12/12/2022]
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29
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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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30
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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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31
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Rehman S, Gu S, Shevchik VE, Pickersgill RW. Anatomy of secretin binding to theDickeya dadantiitype II secretion system pilotin. ACTA CRYSTALLOGRAPHICA SECTION D: BIOLOGICAL CRYSTALLOGRAPHY 2013; 69:1381-6. [DOI: 10.1107/s0907444913007658] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 03/19/2013] [Indexed: 01/01/2023]
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32
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Koo J, Tang T, Harvey H, Tammam S, Sampaleanu L, Burrows LL, Howell PL. Functional Mapping of PilF and PilQ in the Pseudomonas aeruginosa Type IV Pilus System. Biochemistry 2013; 52:2914-23. [DOI: 10.1021/bi3015345] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Jason Koo
- Program in Molecular Structure and
Function, Research Institute, Hospital for Sick Children, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Tim Tang
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Hanjeong Harvey
- Department
of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
| | - Stephanie Tammam
- Program in Molecular Structure and
Function, Research Institute, Hospital for Sick Children, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
| | - Liliana Sampaleanu
- Program in Molecular Structure and
Function, Research Institute, Hospital for Sick Children, Toronto, ON, Canada
| | - Lori L. Burrows
- Department
of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
| | - P. Lynne Howell
- Program in Molecular Structure and
Function, Research Institute, Hospital for Sick Children, Toronto, ON, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, Canada
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33
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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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34
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Abstract
The type II secretion system is utilized by many Gram-negative bacteria to export folded proteins to the surface and/or the extracellular environment of the cell. Although the function of the system is to move proteins from the periplasm to the outside of the cell, it is a large trans-envelope structure composed of more than a dozen different proteins present in multiple copies, including peripheral, integral inner membrane and integral outer membrane proteins plus a pseudopilus stretching between them. The establishment of this structure as an integral component of the entire envelope including the peptidoglycan layer between the two membranes requires assembly. Many of the participants and processes involved in this assembly have now been established, while other aspects remain to be discovered or more fully understood.
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Affiliation(s)
- S Peter Howard
- Department of Microbiology and Immunology, University of Saskatchewan, Health Sciences Building, Room 2D01, 107 Wiggins Road, Saskatoon, Saskatchewan, Canada S7N 5E5.
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35
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Rondelet A, Condemine G. Type II secretion: the substrates that won't go away. Res Microbiol 2013; 164:556-61. [PMID: 23538405 DOI: 10.1016/j.resmic.2013.03.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Accepted: 02/05/2013] [Indexed: 02/06/2023]
Abstract
Type II secretion systems (T2SSs) generally release their substrates into the culture medium. A few T2SS substrates remain anchored to or bound at the surface of the bacteria after secretion. Since they handle already folded proteins, T2SSs are the best way for bacteria to target, at their surface, proteins containing a cofactor, proteins that have to be folded in the cytoplasm or in the periplasm, or multimeric proteins. However, how a T2SS deals with membrane-anchored proteins is not yet understood. While this type of protein has until now been overlooked, new proteomic approaches will facilitate its identification.
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Affiliation(s)
- Arnaud Rondelet
- Université de Lyon, F69003, Université Lyon 1, F69622, INSA-Lyon, F69621, CNRS UMR5240, Microbiologie Adaptation et Pathogénie, 10 rue Dubois, Bât. Lwoff, 69622 Villeurbanne, France
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36
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Crystal structure of the pilotin from the enterohemorrhagic Escherichia coli type II secretion system. J Struct Biol 2013; 182:186-91. [PMID: 23458689 DOI: 10.1016/j.jsb.2013.02.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2012] [Revised: 02/06/2013] [Accepted: 02/18/2013] [Indexed: 12/17/2022]
Abstract
Bacteria contain several sophisticated macromolecular machineries responsible for translocating proteins across the cell envelope. One prominent example is the type II secretion system (T2SS), which contains a large outer membrane channel, called the secretin. These gated channels require specialized proteins, so-called pilotins, to reach and assemble in the outer membrane. Here we report the crystal structure of the pilotin GspS from the T2SS of enterohemorrhagic Escherichia coli (EHEC), an important pathogen that can cause severe disease in cases of food poisoning. In this four-helix protein, the straight helix α2, the curved helix α3 and the bent helix α4 surround the central N-terminal helix α1. The helices of GspS create a prominent groove, mainly formed by side chains of helices α1, α2 and α3. In the EHEC GspS structure this groove is occupied by extra electron density which is reminiscent of an α-helix and corresponds well with a binding site observed in a homologous pilotin. The residues forming the groove are well conserved among homologs, pointing to a key role of this groove in this class of T2SS pilotins. At the same time, T2SS pilotins in different species can be entirely different in structure, and the pilotins for secretins in non-T2SS machineries have yet again unrelated folds, despite a common function. It is striking that a common complex function, such as targeting and assembling an outer membrane multimeric channel, can be performed by proteins with entirely different folds.
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37
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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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38
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A Single Amino Acid Substitution Changes the Self-Assembly Status of a Type IV Piliation Secretin. J Bacteriol 2012; 194:4951-8. [PMID: 22773793 DOI: 10.1128/jb.00798-12] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Secretins form large multimeric complexes in the outer membranes of many Gram-negative bacteria, where they function as dedicated gateways that allow proteins to access the extracellular environment. Despite their overall relatedness, different secretins use different specific and general mechanisms for their targeting, assembly, and membrane insertion. We report that all tested secretins from several type II secretion systems and from the filamentous bacteriophage f1 can spontaneously multimerize and insert into liposomes in an in vitro transcription-translation system. Phylogenetic analyses indicate that these secretins form a group distinct from the secretins of the type IV piliation and type III secretion systems, which do not autoassemble in vitro. A mutation causing a proline-to-leucine substitution allowed PilQ secretins from two different type IV piliation systems to assemble in vitro, albeit with very low efficiency, suggesting that autoassembly is an inherent property of all secretins.
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39
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YghG (GspSβ) is a novel pilot protein required for localization of the GspSβ type II secretion system secretin of enterotoxigenic Escherichia coli. Infect Immun 2012; 80:2608-22. [PMID: 22585966 DOI: 10.1128/iai.06394-11] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The enterotoxigenic Escherichia coli (ETEC) pathotype, characterized by the prototypical strain H10407, is a leading cause of morbidity and mortality in the developing world. A major virulence factor of ETEC is the type II secretion system (T2SS) responsible for secretion of the diarrheagenic heat-labile enterotoxin (LT). In this study, we have characterized the two type II secretion systems, designated alpha (T2SS(α)) and beta (T2SS(β)), encoded in the H10407 genome and describe the prevalence of both systems in other E. coli pathotypes. Under laboratory conditions, the T2SS(β) is assembled and functional in the secretion of LT into culture supernatant, whereas the T2SS(α) is not. Insertional inactivation of the three genes located upstream of gspC(β) (yghJ, pppA, and yghG) in the atypical T2SS(β) operon revealed that YghJ is not required for assembly of the GspD(β) secretin or secretion of LT, that PppA is likely the prepilin peptidase required for the function of T2SS(β), and that YghG is required for assembly of the GspD(β) secretin and thus function of the T2SS(β). Mutational and physiological analysis further demonstrated that YghG (redesignated GspS(β)) is a novel outer membrane pilotin protein that is integral for assembly of the T2SS(β) by localizing GspD(β) to the outer membrane, whereupon GspD(β) forms the macromolecular secretin multimer through which T2SS(β) substrates are translocated.
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40
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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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41
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Outer membrane targeting, ultrastructure, and single molecule localization of the enteropathogenic Escherichia coli type IV pilus secretin BfpB. J Bacteriol 2012; 194:1646-58. [PMID: 22247509 DOI: 10.1128/jb.06330-11] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type IV pili (T4P) are filamentous surface appendages required for tissue adherence, motility, aggregation, and transformation in a wide array of bacteria and archaea. The bundle-forming pilus (BFP) of enteropathogenic Escherichia coli (EPEC) is a prototypical T4P and confirmed virulence factor. T4P fibers are assembled by a complex biogenesis machine that extrudes pili through an outer membrane (OM) pore formed by the secretin protein. Secretins constitute a superfamily of proteins that assemble into multimers and support the transport of macromolecules by four evolutionarily ancient secretion systems: T4P, type II secretion, type III secretion, and phage assembly. Here, we determine that the lipoprotein transport pathway is not required for targeting the BfpB secretin protein of the EPEC T4P to the OM and describe the ultrastructure of the single particle averaged structures of the assembled complex by transmission electron microscopy. Furthermore, we use photoactivated localization microscopy to determine the distribution of single BfpB molecules fused to photoactivated mCherry. In contrast to findings in other T4P systems, we found that BFP components predominantly have an uneven distribution through the cell envelope and are only found at one or both poles in a minority of cells. In addition, we report that concurrent mutation of both the T4bP secretin and the retraction ATPase can result in viable cells and found that these cells display paradoxically low levels of cell envelope stress response activity. These results imply that secretins can direct their own targeting, have complex distributions and provide feedback information on the state of pilus biogenesis.
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42
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Koo J, Burrows LL, Lynne Howell P. Decoding the roles of pilotins and accessory proteins in secretin escort services. FEMS Microbiol Lett 2011; 328:1-12. [DOI: 10.1111/j.1574-6968.2011.02464.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Revised: 10/28/2011] [Accepted: 11/11/2011] [Indexed: 12/19/2022] Open
Affiliation(s)
| | - Lori L. Burrows
- Department of Biochemistry and Biomedical Sciences; McMaster University; Hamilton; ON; Canada
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43
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Outer membrane targeting of Pseudomonas aeruginosa proteins shows variable dependence on the components of Bam and Lol machineries. mBio 2011; 2:mBio.00246-11. [PMID: 22147293 PMCID: PMC3230066 DOI: 10.1128/mbio.00246-11] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
In Gram-negative bacteria, the Lol and Bam machineries direct the targeting of lipidated and nonlipidated proteins, respectively, to the outer membrane (OM). Using Pseudomonas aeruginosa strains with depleted levels of specific Bam and Lol proteins, we demonstrated a variable dependence of different OM proteins on these targeting pathways. Reduction in the level of BamA significantly affected the ability of the β-barrel membrane protein OprF to localize to the OM, while the targeting of three secretins that are functionally related OM proteins was less affected (PilQ and PscC) or not at all affected (XcpQ). Depletion of LolB affected all lipoproteins examined and had a variable effect on the nonlipidated proteins. While the levels of OprF, PilQ, and PscC were significantly reduced by LolB depletion, XcpQ was unaffected and was correctly localized to the OM. These results suggest that certain β-barrel proteins such as OprF primarily utilize the complete Bam machinery. The Lol machinery participates in the OM targeting of secretins to variable degrees, likely through its involvement in the assembly of lipidated Bam components. XcpQ, but not PilQ or PscC, was shown to assemble spontaneously into liposomes as multimers. This work raises the possibility that there is a gradient of utilization of Bam and Lol insertion and targeting machineries. Structural features of individual proteins, including their β-barrel content, may determine the propensity of these proteins for folding (or misfolding) during periplasmic transit and OM insertion, thereby influencing the extent of utilization of the Bam targeting machinery, respectively. Targeting of lipidated and nonlipidated proteins to the outer membrane (OM) compartment in Gram-negative bacteria involves the transfer across the periplasm utilizing the Lol and Bam machineries, respectively. We show that depletion of Bam and Lol components in Pseudomonas aeruginosa does not lead to a general OM protein translocation defect, but the severity (and therefore, Lol and Bam dependence), varies with individual proteins. XcpQ, the secretin component of the type II secretion apparatus, is translocated into the OM without the assistance of Bam or Lol machineries. The hypothesis that XcpQ, after secretion across the cytoplasmic membrane, does not utilize the OM targeting machineries was supported by demonstrating that in vitro-synthesized XcpQ (but not the other P. aeruginosa secretins) can spontaneously incorporate into lipid vesicles. Therefore, the requirement for ancillary factors appears to be, in certain instances, dictated by the intrinsic properties of individual OM proteins, conceivably reflecting their propensities to misfold during periplasmic transit.
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44
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Tosi T, Nickerson NN, Mollica L, Jensen MR, Blackledge M, Baron B, England P, Pugsley AP, Dessen A. Pilotin-secretin recognition in the type II secretion system of Klebsiella oxytoca. Mol Microbiol 2011; 82:1422-32. [PMID: 22098633 DOI: 10.1111/j.1365-2958.2011.07896.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A crucial aspect of the functionality of bacterial type II secretion systems is the targeting and assembly of the outer membrane secretin. In the Klebsiella oxytoca type II secretion system, the lipoprotein PulS, a pilotin, targets secretin PulD monomers through the periplasm to the outer membrane. We present the crystal structure of PulS, an all-helical bundle that is structurally distinct from proteins with similar functions. Replacement of valine at position 42 in a charged groove of PulS abolished complex formation between a non-lipidated variant of PulS and a peptide corresponding to the unfolded region of PulD to which PulS binds (the S-domain), in vitro, as well as PulS function in vivo. Substitutions of other residues in the groove also diminished the interaction with the S-domain in vitro but exerted less marked effects in vivo. We propose that the interaction between PulS and the S-domain is maintained through a structural adaptation of the two proteins that could be influenced by cis factors such as the fatty acyl groups on PulS, as well as periplasmic trans-acting factors, which represents a possible paradigm for chaperone-target protein interactions.
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Affiliation(s)
- Tommaso Tosi
- Institut de Biologie Structurale, Bacterial Pathogenesis Group, Université Grenoble I, 41 rue Jules Horowitz, 38027 Grenoble, France
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45
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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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46
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Ricci DP, Silhavy TJ. The Bam machine: a molecular cooper. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1067-84. [PMID: 21893027 DOI: 10.1016/j.bbamem.2011.08.020] [Citation(s) in RCA: 134] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 08/08/2011] [Accepted: 08/15/2011] [Indexed: 11/24/2022]
Abstract
The bacterial outer membrane (OM) is an exceptional biological structure with a unique composition that contributes significantly to the resiliency of Gram-negative bacteria. Since all OM components are synthesized in the cytosol, the cell must efficiently transport OM-specific lipids and proteins across the cell envelope and stably integrate them into a growing membrane. In this review, we discuss the challenges associated with these processes and detail the elegant solutions that cells have evolved to address the topological problem of OM biogenesis. Special attention will be paid to the Bam machine, a highly conserved multiprotein complex that facilitates OM β-barrel folding. This article is part of a Special Issue entitled: Protein Folding in Membranes.
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Affiliation(s)
- Dante P Ricci
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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47
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Structure/function analysis of Neisseria meningitidis PilW, a conserved protein that plays multiple roles in type IV pilus biology. Infect Immun 2011; 79:3028-35. [PMID: 21646452 DOI: 10.1128/iai.05313-11] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type IV pili (Tfp) are widespread filamentous bacterial organelles that mediate multiple functions and play a key role in pathogenesis in several important human pathogens, including Neisseria meningitidis. Tfp biology remains poorly understood at a molecular level because the roles of the numerous proteins that are involved remain mostly obscure. Guided by the high-resolution crystal structure we recently reported for N. meningitidis PilW, a widely conserved protein essential for Tfp biogenesis, we have performed a structure/function analysis by targeting a series of key residues through site-directed mutagenesis and analyzing the corresponding variants using an array of phenotypic assays. Here we show that PilW's involvement in the functionality of Tfp can be genetically uncoupled from its concurrent role in the assembly/stabilization of the secretin channels through which Tfp emerge on the bacterial surface. These findings suggest that PilW is a multifunctional protein.
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