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Lafrance AE, Chimalapati S, Garcia Rodriguez N, Kinch LN, Kaval KG, Orth K. Enzymatic Specificity of Conserved Rho GTPase Deamidases Promotes Invasion of Vibrio parahaemolyticus at the Expense of Infection. mBio 2022; 13:e0162922. [PMID: 35862776 PMCID: PMC9426531 DOI: 10.1128/mbio.01629-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 06/17/2022] [Indexed: 11/23/2022] Open
Abstract
Vibrio parahaemolyticus is among the leading causes of bacterial seafood-borne acute gastroenteritis. Like many intracellular pathogens, V. parahaemolyticus invades host cells during infection by deamidating host small Rho GTPases. The Rho GTPase deamidating activity of VopC, a type 3 secretion system (T3SS) translocated effector, drives V. parahaemolyticus invasion. The intracellular pathogen uropathogenic Escherichia coli (UPEC) invades host cells by secreting a VopC homolog, the secreted toxin cytotoxic necrotizing factor 1 (CNF1). Because of the homology between VopC and CNF1, we hypothesized that topical application of CNF1 during V. parahaemolyticus infection could supplement VopC activity. Here, we demonstrate that CNF1 improves the efficiency of V. parahaemolyticus invasion, a bottleneck in V. parahaemolyticus infection, across a range of doses. CNF1 increases V. parahaemolyticus invasion independent of both VopC and the T3SS altogether but leaves a disproportionate fraction of intracellular bacteria unable to escape the endosome and complete their infection cycle. This phenomenon holds true in the presence or absence of VopC but is particularly pronounced in the absence of a T3SS. The native VopC, by contrast, promotes a far less efficient invasion but permits the majority of internalized bacteria to escape the endosome and complete their infection cycle. These studies highlight the significance of enzymatic specificity during infection, as virulence factors (VopC and CNF1 in this instance) with similarities in function (bacterial uptake), catalytic activity (deamidation), and substrates (Rho GTPases) are not sufficiently interchangeable for mediating a successful invasion for neighboring bacterial pathogens. IMPORTANCE Many species of intracellular bacterial pathogens target host small Rho GTPases to initiate invasion, including the human pathogens Vibrio parahaemolyticus and uropathogenic Escherichia coli (UPEC). The type three secretion system (T3SS) effector VopC of V. parahaemolyticus promotes invasion through the deamidation of Rac1 and CDC42 in the host, whereas the secreted toxin cytotoxic necrotizing factor 1 (CNF1) drives UPEC's internalization through the deamidation of Rac1, CDC42, and RhoA. Despite these similarities in the catalytic activity of CNF1 and VopC, we observed that the two enzymes were not interchangeable. Although CNF1 increased V. parahaemolyticus endosomal invasion, most intracellular V. parahaemolyticus aborted their infection cycle and remained trapped in endosomes. Our findings illuminate how the precise biochemical fine-tuning of T3SS effectors is essential for efficacious pathogenesis. Moreover, they pave the way for future investigations into the biochemical mechanisms underpinning V. parahaemolyticus endosomal escape and, more broadly, the regulation of successful pathogenesis.
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Affiliation(s)
- Alexander E. Lafrance
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Suneeta Chimalapati
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Nalleli Garcia Rodriguez
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Lisa N. Kinch
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Karan Gautam Kaval
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Kim Orth
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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Rahmatelahi H, El-Matbouli M, Menanteau-Ledouble S. Delivering the pain: an overview of the type III secretion system with special consideration for aquatic pathogens. Vet Res 2021; 52:146. [PMID: 34924019 PMCID: PMC8684695 DOI: 10.1186/s13567-021-01015-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 11/08/2021] [Indexed: 11/10/2022] Open
Abstract
Gram-negative bacteria are known to subvert eukaryotic cell physiological mechanisms using a wide array of virulence factors, among which the type three-secretion system (T3SS) is often one of the most important. The T3SS constitutes a needle-like apparatus that the bacterium uses to inject a diverse set of effector proteins directly into the cytoplasm of the host cells where they can hamper the host cellular machinery for a variety of purposes. While the structure of the T3SS is somewhat conserved and well described, effector proteins are much more diverse and specific for each pathogen. The T3SS can remodel the cytoskeleton integrity to promote intracellular invasion, as well as silence specific eukaryotic cell signals, notably to hinder or elude the immune response and cause apoptosis. This is also the case in aquatic bacterial pathogens where the T3SS can often play a central role in the establishment of disease, although it remains understudied in several species of important fish pathogens, notably in Yersinia ruckeri. In the present review, we summarise what is known of the T3SS, with a special focus on aquatic pathogens and suggest some possible avenues for research including the potential to target the T3SS for the development of new anti-virulence drugs.
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Affiliation(s)
- Hadis Rahmatelahi
- Clinical Division of Fish Medicine, University of Veterinary Medicine, 1210, Vienna, Austria
| | - Mansour El-Matbouli
- Clinical Division of Fish Medicine, University of Veterinary Medicine, 1210, Vienna, Austria
| | - Simon Menanteau-Ledouble
- Clinical Division of Fish Medicine, University of Veterinary Medicine, 1210, Vienna, Austria.
- Department of Chemistry and Bioscience, Aalborg University, Fredrik Bajers Vej 7H, 9220, Aalborg Ø, Denmark.
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Manera K, Kamal F, Burkinshaw B, Dong TG. Essential functions of chaperones and adaptors of protein secretion systems in Gram-negative bacteria. FEBS J 2021; 289:4704-4717. [PMID: 34092034 DOI: 10.1111/febs.16056] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/18/2021] [Accepted: 06/04/2021] [Indexed: 01/02/2023]
Abstract
Equipped with a plethora of secreted toxic effectors, protein secretion systems are essential for bacteria to interact with and manipulate their neighboring environment to survive in host microbiota and other highly competitive communities. While effectors have received spotlight attention in secretion system studies, many require accessory chaperone and adaptor proteins for proper folding/unfolding and stability throughout the secretion process. Here, we review the functions of chaperones and adaptors of three protein secretions systems, type 3 secretion system (T3SS), type 4 secretion system (T4SS), and type 6 secretion system (T6SS), which are employed by many Gram-negative bacterial pathogens to deliver toxins to bacterial, plant, and mammalian host cells through direct contact. Since chaperone and adaptor functions of the T3SS and the T4SS are relatively well studied, we discuss in detail the methods of chaperone-facilitated effector secretion by the T6SS and highlight commonalities between the effector chaperone/adaptor proteins of these diverse secretion systems. While the chaperones and adaptors are generally referred to as accessory proteins as they are not directly involved in toxicities to target cells, they are nonetheless vital for the biological functions of the secretion systems. Future research on biochemical and structural properties of these chaperones will not only elucidate the mechanisms of chaperone-effector binding and release process but also facilitate custom design of cargo effectors to be translocated by these widespread secretion systems for biotechnological applications.
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Affiliation(s)
- Kevin Manera
- Department of Ecosystem and Public Health, University of Calgary, Canada
| | - Fatima Kamal
- Department of Ecosystem and Public Health, University of Calgary, Canada
| | | | - Tao G Dong
- Department of Ecosystem and Public Health, University of Calgary, Canada.,State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, China
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Ng Ang A PN, Ebner JK, Plessner M, Aktories K, Schmidt G. Engineering Photorhabdus luminescens toxin complex (PTC) into a recombinant injection nanomachine. Life Sci Alliance 2019; 2:e201900485. [PMID: 31540947 PMCID: PMC6756610 DOI: 10.26508/lsa.201900485] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Revised: 09/10/2019] [Accepted: 09/10/2019] [Indexed: 12/15/2022] Open
Abstract
Engineering delivery systems for proteins and peptides into mammalian cells is an ongoing challenge for cell biological studies as well as for therapeutic approaches. Photorhabdus luminescens toxin complex (PTC) is a heterotrimeric protein complex able to deliver diverse protein toxins into mammalian cells. We engineered the syringe-like nanomachine for delivery of protein toxins from different species. In addition, we loaded the highly active copepod luciferase Metridia longa M-Luc7 for accurate quantification of injected molecules. We suggest that besides the probable size limitation, the charge of the cargo also influences the efficiency of packing and transport into mammalian cells. Our data show that the PTC constitutes a powerful system to inject recombinant proteins, peptides, and potentially, other molecules into mammalian cells. In addition, in contrast to other protein transporters based on pore formation, the closed, compact structure of the PTC may protect cargo from degradation.
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Affiliation(s)
- Peter Njenga Ng Ang A
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
- Spemann Graduate School for Biology and Medicine, University of Freiburg, Freiburg, Germany
| | - Julia K Ebner
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- Faculty of Biology, University of Freiburg, Freiburg, Germany
- Spemann Graduate School for Biology and Medicine, University of Freiburg, Freiburg, Germany
| | - Matthias Plessner
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Klaus Aktories
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
- BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany
| | - Gudula Schmidt
- Institute for Experimental and Clinical Pharmacology and Toxicology, Faculty of Medicine, University of Freiburg, Freiburg, Germany
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Molecular basis of binding between the global post-transcriptional regulator CsrA and the T3SS chaperone CesT. Nat Commun 2018; 9:1196. [PMID: 29567971 PMCID: PMC5864733 DOI: 10.1038/s41467-018-03625-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Accepted: 03/01/2018] [Indexed: 02/05/2023] Open
Abstract
The T3SS chaperone CesT is recently shown to interact with the post-transcriptional regulator CsrA to modulate post-attachment signaling in enteropathogenic and enterohemorrhagic Escherichia coli. The molecular basis of the CesT/CsrA binding, however, remains elusive. Here, we show that CesT and CsrA both created two ligand binding sites in their homodimers, forming irregular multimeric complexes in solution. Through construction of a recombinant CsrA-dimer (Re-CsrA) that contains a single CesT binding site, the atomic binding features between CesT and CsrA are delineated via the structure of the CesT/Re-CsrA complex. In contrast to a previously reported N-terminally swapped dimer-form, CesT adopts a dimeric architecture with a swapped C-terminal helix for CsrA engagement. In CsrA, CesT binds to a surface patch that extensively overlaps with its mRNA binding site. The binding mode therefore justifies a mechanism of CsrA-modulation by CesT via competitive inhibition of the CsrA/mRNA interactions. CesT is a type III secretion system chaperone that interacts with the post-transcriptional regulator CsrA, which is important for the modulation of post-attachment signaling in enteropathogenic and enterohemorrhagic Escherichia coli. Here the authors present the structure of the CsrA/CesT complex and propose a mechanism for CsrA-modulation by CesT.
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Burkinshaw BJ, Strynadka NCJ. Assembly and structure of the T3SS. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1649-63. [PMID: 24512838 DOI: 10.1016/j.bbamcr.2014.01.035] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Revised: 01/27/2014] [Accepted: 01/29/2014] [Indexed: 02/06/2023]
Abstract
The Type III Secretion System (T3SS) is a multi-mega Dalton apparatus assembled from more than twenty components and is found in many species of animal and plant bacterial pathogens. The T3SS creates a contiguous channel through the bacterial and host membranes, allowing injection of specialized bacterial effector proteins directly to the host cell. In this review, we discuss our current understanding of T3SS assembly and structure, as well as highlight structurally characterized Salmonella effectors. 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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Affiliation(s)
- Brianne J Burkinshaw
- Department of Biochemistry and Molecular Biology, Center for Blood Research, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
| | - Natalie C J Strynadka
- Department of Biochemistry and Molecular Biology, Center for Blood Research, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
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Dey S, Datta S. Interfacial residues of SpcS chaperone affects binding of effector toxin ExoT in Pseudomonas aeruginosa: novel insights from structural and computational studies. FEBS J 2014; 281:1267-80. [PMID: 24387107 DOI: 10.1111/febs.12704] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Revised: 12/06/2013] [Accepted: 12/23/2013] [Indexed: 12/12/2022]
Abstract
ExoT belongs to the family of type 3 secretion system (T3SS) effector toxins in Pseudomonas aeruginosa, known to be one of the major virulence determinant toxins that cause chronic and acute infections in immuno-compromised individuals, burn victims and cystic fibrosis patients. Here, we report the X-ray crystal structure of the amino terminal fragment of effector toxin ExoT, in complex with full-length homodimeric chaperone SpcS at 2.1 Å resolution. The full-length dimeric chaperone SpcS has the conserved α-β-β-β-α-β-β-α fold of class I chaperones, the characteristic hydrophobic patches for binding effector proteins and a conserved polar cavity at the dimeric interface. The stable crystallized amino terminal fragment of ExoT consists of a chaperone binding domain and a membrane localization domain that wraps around the dimeric chaperone. Site-directed mutagenesis experiments and a molecular dynamics study complement each other in revealing Asn65, Phe67 and Trp88 as critical dimeric interfacial residues that can strongly influence the effector-chaperone interactions.
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Affiliation(s)
- Supratim Dey
- Department of Structural Biology and Bioinformatics, Indian Institute of Chemical Biology, Kolkata, India
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8
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Lohou D, Lonjon F, Genin S, Vailleau F. Type III chaperones & Co in bacterial plant pathogens: a set of specialized bodyguards mediating effector delivery. FRONTIERS IN PLANT SCIENCE 2013; 4:435. [PMID: 24319448 PMCID: PMC3837300 DOI: 10.3389/fpls.2013.00435] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Accepted: 10/12/2013] [Indexed: 05/19/2023]
Abstract
Gram-negative plant pathogenic bacteria possess a type III secretion system (T3SS) to inject bacterial proteins, called type III effectors (T3Es), into host cells through a specialized syringe structure. T3Es are virulence factors that can suppress plant immunity but they can also conversely be recognized by the plant and trigger specific resistance mechanisms. The T3SS and injected T3Es play a central role in determining the outcome of a host-pathogen interaction. Still little is known in plant pathogens on the assembly of the T3SS and the regulatory mechanisms involved in the temporal control of its biosynthesis and T3E translocation. However, recent insights point out the role of several proteins as prime candidates in the role of regulators of the type III secretion (T3S) process. In this review we report on the most recent advances on the regulation of the T3S by focusing on protein players involved in secretion/translocation regulations, including type III chaperones (T3Cs), type III secretion substrate specificity switch (T3S4) proteins and other T3S orchestrators.
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Affiliation(s)
- David Lohou
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
| | - Fabien Lonjon
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
| | - Stéphane Genin
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
| | - Fabienne Vailleau
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Institut National Polytechnique, École Nationale Supérieure Agronomique de Toulouse, Université de ToulouseCastanet-Tolosan, France
- *Correspondence: Fabienne Vailleau, Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-Microorganismes, CS 52627, 24 Chemin de Borde Rouge-Auzeville, Castanet-Tolosan cedex 31326, France e-mail:
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9
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Norais C, Servant P, Bouthier-de-la-Tour C, Coureux PD, Ithurbide S, Vannier F, Guerin PP, Dulberger CL, Satyshur KA, Keck JL, Armengaud J, Cox MM, Sommer S. The Deinococcus radiodurans DR1245 protein, a DdrB partner homologous to YbjN proteins and reminiscent of type III secretion system chaperones. PLoS One 2013; 8:e56558. [PMID: 23441204 PMCID: PMC3575483 DOI: 10.1371/journal.pone.0056558] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Accepted: 01/04/2013] [Indexed: 11/18/2022] Open
Abstract
The bacterium Deinococcus radiodurans exhibits an extreme resistance to ionizing radiation. A small subset of Deinococcus genus-specific genes were shown to be up-regulated upon exposure to ionizing radiation and to play a role in genome reconstitution. These genes include an SSB-like protein called DdrB. Here, we identified a novel protein encoded by the dr1245 gene as an interacting partner of DdrB. A strain devoid of the DR1245 protein is impaired in growth, exhibiting a generation time approximately threefold that of the wild type strain while radioresistance is not affected. We determined the three-dimensional structure of DR1245, revealing a relationship with type III secretion system chaperones and YbjN family proteins. Thus, DR1245 may display some chaperone activity towards DdrB and possibly other substrates.
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Affiliation(s)
- Cédric Norais
- Department of Biochemistry, University of Wisconsin College of Agriculture and Life Sciences, Madison, Wisconsin, United States of America
- Ecole polytechnique, Laboratoire de Biochimie, Centre national de la recherche scientifique, Palaiseau, France
| | - Pascale Servant
- Univ. Paris-Sud, Institut de Génétique et Microbiologie (Bât. 409), UMR8621, Orsay, France
- Centre national de la recherche scientifique, Orsay, France
| | - Claire Bouthier-de-la-Tour
- Univ. Paris-Sud, Institut de Génétique et Microbiologie (Bât. 409), UMR8621, Orsay, France
- Centre national de la recherche scientifique, Orsay, France
| | - Pierre-Damien Coureux
- Ecole polytechnique, Laboratoire de Biochimie, Centre national de la recherche scientifique, Palaiseau, France
| | - Solenne Ithurbide
- Univ. Paris-Sud, Institut de Génétique et Microbiologie (Bât. 409), UMR8621, Orsay, France
- Centre national de la recherche scientifique, Orsay, France
| | - Françoise Vannier
- Univ. Paris-Sud, Institut de Génétique et Microbiologie (Bât. 409), UMR8621, Orsay, France
- Centre national de la recherche scientifique, Orsay, France
| | - Philippe P. Guerin
- Commissariat à l’énergie atomique et aux énergies alternatives, Direction des Sciences du Vivant, Institut de Biologie Environnementale et Biotechnologie, Lab Biochim System Perturb, Bagnols-sur-Cèze, France
| | - Charles L. Dulberger
- Department of Biochemistry, University of Wisconsin College of Agriculture and Life Sciences, Madison, Wisconsin, United States of America
| | - Kenneth A. Satyshur
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - James L. Keck
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, United States of America
| | - Jean Armengaud
- Commissariat à l’énergie atomique et aux énergies alternatives, Direction des Sciences du Vivant, Institut de Biologie Environnementale et Biotechnologie, Lab Biochim System Perturb, Bagnols-sur-Cèze, France
| | - Michael M. Cox
- Department of Biochemistry, University of Wisconsin College of Agriculture and Life Sciences, Madison, Wisconsin, United States of America
| | - Suzanne Sommer
- Univ. Paris-Sud, Institut de Génétique et Microbiologie (Bât. 409), UMR8621, Orsay, France
- Centre national de la recherche scientifique, Orsay, France
- * E-mail:
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Protein export according to schedule: architecture, assembly, and regulation of type III secretion systems from plant- and animal-pathogenic bacteria. Microbiol Mol Biol Rev 2012; 76:262-310. [PMID: 22688814 DOI: 10.1128/mmbr.05017-11] [Citation(s) in RCA: 304] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Flagellar and translocation-associated type III secretion (T3S) systems are present in most gram-negative plant- and animal-pathogenic bacteria and are often essential for bacterial motility or pathogenicity. The architectures of the complex membrane-spanning secretion apparatuses of both systems are similar, but they are associated with different extracellular appendages, including the flagellar hook and filament or the needle/pilus structures of translocation-associated T3S systems. The needle/pilus is connected to a bacterial translocon that is inserted into the host plasma membrane and mediates the transkingdom transport of bacterial effector proteins into eukaryotic cells. During the last 3 to 5 years, significant progress has been made in the characterization of membrane-associated core components and extracellular structures of T3S systems. Furthermore, transcriptional and posttranscriptional regulators that control T3S gene expression and substrate specificity have been described. Given the architecture of the T3S system, it is assumed that extracellular components of the secretion apparatus are secreted prior to effector proteins, suggesting that there is a hierarchy in T3S. The aim of this review is to summarize our current knowledge of T3S system components and associated control proteins from both plant- and animal-pathogenic bacteria.
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11
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Schmidt G. Yersinia enterocolitica outer protein T (YopT). Eur J Cell Biol 2011; 90:955-8. [DOI: 10.1016/j.ejcb.2010.12.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Revised: 12/23/2010] [Accepted: 12/23/2010] [Indexed: 01/18/2023] Open
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Brinkworth AJ, Malcolm DS, Pedrosa AT, Roguska K, Shahbazian S, Graham JE, Hayward RD, Carabeo RA. Chlamydia trachomatis Slc1 is a type III secretion chaperone that enhances the translocation of its invasion effector substrate TARP. Mol Microbiol 2011; 82:131-44. [PMID: 21883523 DOI: 10.1111/j.1365-2958.2011.07802.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Bacterial type III secretion system (T3SS) chaperones pilot substrates to the export apparatus in a secretion-competent state, and are consequently central to the translocation of effectors into target cells. Chlamydia trachomatis is a genetically intractable obligate intracellular pathogen that utilizes T3SS effectors to trigger its entry into mammalian cells. The only well-characterized T3SS effector is TARP (translocated actin recruitment protein), but its chaperone is unknown. Here we exploited a known structural signature to screen for putative type III secretion chaperones encoded within the C. trachomatis genome. Using bacterial two-hybrid, co-precipitation, cross-linking and size exclusion chromatography we show that Slc1 (SycE-like chaperone 1; CT043) specifically interacts with a 200-amino-acid residue N-terminal region of TARP (TARP¹⁻²⁰⁰). Slc1 formed homodimers in vitro, as shown in cross-linking and gel filtration experiments. Biochemical analysis of an isolated Slc1-TARP¹⁻²⁰⁰ complex was consistent with a characteristic 2:1 chaperone-effector stoichiometry. Furthermore, Slc1 was co-immunoprecipitated with TARP from C. trachomatis elementary bodies. Also, coexpression of Slc1 specifically enhanced host cell translocation of TARP by a heterologous Yersinia enterocolitica T3SS. Taken together, we propose Slc1 as a chaperone of the C. trachomatis T3SS effector TARP.
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Affiliation(s)
- Amanda J Brinkworth
- Centre for Molecular Microbiology and Infection, Division of Cell and Molecular Biology, Imperial College, London SW72AZ, UK
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Cendron L, Zanotti G. Structural and functional aspects of unique type IV secretory components in the Helicobacter pylori cag-pathogenicity island. FEBS J 2011; 278:1223-31. [PMID: 21284804 DOI: 10.1111/j.1742-4658.2011.08038.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Helicobacter pylori cytotoxin-associated gene-pathogenicity island (cagPAI) is responsible for the secretion of the CagA effector through a type IV secretion system (T4SS) apparatus, as well as of peptidoglycan and possibly other not yet identified factors. Twenty-nine different polypeptide chains are encoded by this cluster of genes, although only some of them show a significant similarity with the constitutive elements of well characterized secretion systems from other bacteria. The other cagPAI components represent almost unique proteins in this scenario. The majority of the T4SS include approximately fifteen components, taking into account either the transmembrane complex subunits, ATPases or substrate factors. The composition of the cagPAI is very complex: it includes proteins most likely involved at different levels in the pilus assembly, stabilization and processing of secreted substrate, as well as regulatory particles possibly involved in the control of the entire apparatus. Despite recent findings with respect to components that play a role in the interaction with the host cell, the function of several cagPAI proteins remains unclear or unknown. This is particularly true for those that represent unique members with no clear similarity to those of other T4SS and no obvious evidence of involvement in the secretion of CagA or induction of pro-inflammatory responses. We summarize what is known about these accessory components, both from a molecular and structural point of view, as well as their putative physiological role.
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Affiliation(s)
- Laura Cendron
- Department of Biological Chemistry, University of Padua, Padua, Italy
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A solvent-exposed patch in chaperone-bound YopE is required for translocation by the type III secretion system. J Bacteriol 2010; 192:3114-22. [PMID: 20382763 DOI: 10.1128/jb.00113-10] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Most effector proteins of bacterial type III secretion (T3S) systems require chaperone proteins for translocation into host cells. Such effectors are bound by chaperones in a conserved and characteristic manner, with the chaperone-binding (Cb) region of the effector wound around the chaperone in a highly extended conformation. This conformation has been suggested to serve as a translocation signal in promoting the association between the chaperone-effector complex and a bacterial component required for translocation. We sought to test a prediction of this model by identifying a potential association site for the Yersinia pseudotuberculosis chaperone-effector pair SycE-YopE. We identified a set of residues in the YopE Cb region that are required for translocation but are dispensable for expression, SycE binding, secretion into the extrabacterial milieu, and stability in mammalian cells. These residues form a solvent-exposed patch on the surface of the chaperone-bound Cb region, and thus their effect on translocation is consistent with the structure of the chaperone-bound Cb region serving as a signal for translocation.
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15
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Arnold R, Jehl A, Rattei T. Targeting effectors: the molecular recognition of Type III secreted proteins. Microbes Infect 2010; 12:346-58. [PMID: 20178857 DOI: 10.1016/j.micinf.2010.02.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2010] [Accepted: 02/10/2010] [Indexed: 01/01/2023]
Abstract
The Type III secretion system (TTSS) facilitates the export of effector proteins from pathogenic and symbiotic Gram-negative bacteria into the cytosol of eukaryotic host cells. The current functional and evolutionary knowledge on the molecular recognition of TTSS substrates and computational models of the secretion signal are discussed in this review.
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Affiliation(s)
- Roland Arnold
- Department of Genome Oriented Bioinformatics, Technische Universität München, Wissenschaftszentrum Weihenstephan, 85350 Freising, Germany
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16
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The Helicobacter pylori CagD (HP0545, Cag24) protein is essential for CagA translocation and maximal induction of interleukin-8 secretion. J Mol Biol 2008; 386:204-17. [PMID: 19109970 DOI: 10.1016/j.jmb.2008.12.018] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2008] [Revised: 12/01/2008] [Accepted: 12/06/2008] [Indexed: 12/16/2022]
Abstract
Pathogenic strains of Helicobacter pylori use a type IV secretion system (T4SS) to deliver the toxin CagA into human host cells. The T4SS, along with the toxin itself, is coded into a genomic insert, which is termed the cag pathogenicity island. The cag pathogenicity island contains about 30 open-reading frames, for most of which the exact function is not well characterized or totally unknown. We have determined the crystal structure of one of the proteins coded by the cag genes, CagD, in two crystal forms. We show that the protein is a covalent dimer in which each monomer folds as a single domain that is composed of five beta-strands and three alpha-helices. Our data show that in addition to a cytosolic pool, CagD partially associates with the inner membrane, where it may be exposed to the periplasmic space. Furthermore, CagA tyrosine phosphorylation and interleukin-8 assays identified CagD as a crucial component of the T4SS that is involved in CagA translocation into host epithelial cells; however, it does not seem absolutely necessary for pilus assembly. We have also identified significant amounts of CagD in culture supernatants, which are not a result of general bacterial lysis. Since this localization was independent of the various tested cag mutants, our findings may indicate that CagD is released into the supernatant during host cell infection and then binds to the host cell surface or is incorporated in the pilus structure. Overall, our results suggest that CagD may serve as a unique multifunctional component of the T4SS that may be involved in CagA secretion at the inner membrane and may localize outside the bacteria to promote additional effects on the host cell.
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17
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Rodgers L, Gamez A, Riek R, Ghosh P. The type III secretion chaperone SycE promotes a localized disorder-to-order transition in the natively unfolded effector YopE. J Biol Chem 2008; 283:20857-63. [PMID: 18502763 DOI: 10.1074/jbc.m802339200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Many virulence-related, bacterial effector proteins are translocated directly into the cytosol of host cells by the type III secretion (TTS) system. Translocation of most TTS effectors requires binding by specific chaperones in the bacterial cytosol, although how chaperones promote translocation is unclear. To provide insight into the action of such chaperones, we studied the consequences of binding by the Yersinia chaperone SycE to the effector YopE by NMR. These studies examined the intact form of the effector, whereas prior studies have been limited to well ordered fragments. We found that YopE had the characteristics of a natively unfolded protein, with its N-terminal 100 residues, including its chaperone-binding (Cb) region, flexible and disordered in the absence of SycE. SycE binding caused a pronounced disorder-to-order transition in the Cb region of YopE. The effect of SycE was strictly localized to the Cb region, with other portions of YopE being unperturbed. These results provide stringent limits on models of chaperone action and are consistent with the chaperone promoting formation of a three-dimensional targeting signal in the Cb region of the effector. The target of this putative signal is unknown but appears to be a bacterial component other than the TTS ATPase YscN.
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Affiliation(s)
- Loren Rodgers
- Section of Molecular Biology, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
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18
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The Yersinia enterocolitica type three secretion chaperone SycO is integrated into the Yop regulatory network and binds to the Yop secretion protein YscM1. BMC Microbiol 2007; 7:67. [PMID: 17612396 PMCID: PMC1933539 DOI: 10.1186/1471-2180-7-67] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2006] [Accepted: 07/05/2007] [Indexed: 01/09/2023] Open
Abstract
Background Pathogenic yersiniae (Y. pestis, Y. pseudotuberculosis, Y. enterocolitica) share a virulence plasmid encoding a type three secretion system (T3SS). This T3SS comprises more than 40 constituents. Among these are the transport substrates called Yops (Yersinia outer proteins), the specific Yop chaperones (Sycs), and the Ysc (Yop secretion) proteins which form the transport machinery. The effectors YopO and YopP are encoded on an operon together with SycO, the chaperone of YopO. The characterization of SycO is the focus of this study. Results We have established the large-scale production of recombinant SycO in its outright form. We confirm that Y. enterocolitica SycO forms homodimers which is typical for Syc chaperones. SycO overproduction in Y. enterocolitica decreases secretion of Yops into the culture supernatant suggesting a regulatory role of SycO in type III secretion. We demonstrate that in vitro SycO interacts with YscM1, a negative regulator of Yop expression in Y. enterocolitica. However, the SycO overproduction phenotype was not mediated by YscM1, YscM2, YopO or YopP as revealed by analysis of isogenic deletion mutants. Conclusion We present evidence that SycO is integrated into the regulatory network of the Yersinia T3SS. Our picture of the Yersinia T3SS interactome is supplemented by identification of the SycO/YscM1 interaction. Further, our results suggest that at least one additional interaction partner of SycO has to be identified.
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19
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Abstract
The type III secretion injectisome is a complex nanomachine that allows bacteria to deliver protein effectors across eukaryotic cellular membranes. In recent years, significant progress has been made in our understanding of its structure, assembly and mode of operation. The principal structural components of the injectisome, from the base located in the bacterial cytosol to the tip of the needle protruding from the cell surface, have been investigated in detail. The structures of several constituent proteins were solved at the atomic level and important insights into the assembly process have been gained. However, despite the ongoing concerted efforts of molecular and structural biologists, the role of many of the constituent components of this nanomachine remain unknown.
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Affiliation(s)
- Guy R Cornelis
- Biozentrum der Universität Basel, Klingelbergstrasse 50, CH-4056, Basel, Switzerland.
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20
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Knodler LA, Bertero M, Yip C, Strynadka NCJ, Steele-Mortimer O. Structure-based mutagenesis of SigE verifies the importance of hydrophobic and electrostatic residues in type III chaperone function. Mol Microbiol 2006; 62:928-40. [PMID: 17038123 DOI: 10.1111/j.1365-2958.2006.05418.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Despite sharing little sequence identity, most type III chaperones display a similar homodimeric structure characterized by negative charges distributed broadly over their entire surface, interspersed with hydrophobic patches. Here we have used SigE from Salmonella as a model for class IA type III chaperones to investigate the role of these surface-exposed residues in chaperone function. SigE is essential for the stability, secretion and translocation of its cognate effector, SopB (SigD). We analysed the effect of mutating nine conserved hydrophobic and electronegative surface-exposed amino acids of SigE on SopB binding, stability, secretion and translocation. Six of these mutations affected some aspect of SigE function (Leu14, Asp20, Leu22, Leu23, Ile25 and Asp51) and three were without effect (Leu54, Glu92 and Glu99). Our results highlight that both hydrophobic and electronegative surfaces are required for the function of SigE and provide an important basis for the prediction of side-chain requirements for other chaperone-effector pairs.
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Affiliation(s)
- Leigh A Knodler
- Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, NIAID, NIH, Hamilton, MT 59840, USA.
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21
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Schmid A, Dittmann S, Grimminger V, Walter S, Heesemann J, Wilharm G. Yersinia enterocolitica type III secretion chaperone SycD: Recombinant expression, purification and characterization of a homodimer. Protein Expr Purif 2006; 49:176-82. [PMID: 16750393 DOI: 10.1016/j.pep.2006.04.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2006] [Revised: 04/21/2006] [Accepted: 04/23/2006] [Indexed: 01/15/2023]
Abstract
Yersinia species pathogenic to human benefit from a protein transport machinery, a type three secretion system (T3SS), which enables the bacteria to inject effector proteins into host cells. Several of the transport substrates of the Yersinia T3SS, called Yops (Yersinia outer proteins), are assisted by specific chaperones (Syc for specific Yop chaperone) prior to transport. Yersinia enterocolitica SycD (LcrH in Yersinia pestis and Yersinia pseudotuberculosis) is a chaperone dedicated to the assistance of the translocator proteins YopB and YopD, which are assumed to form a pore in the host cell membrane. In an attempt to make SycD amenable to structural investigations we recombinantly expressed SycD with a hexahistidine tag in Escherichia coli. Combining immobilized nickel affinity chromatography and gel filtration we obtained purified SycD with an exceptional yield of 120mg per liter of culture and homogeneity above 95%. Analytical gel filtration and cross-linking experiments revealed the formation of homodimers in solution. Secondary structure analysis based on circular dichroism suggests that SycD is mainly composed of alpha-helical elements. To prove functionality of purified SycD previously suggested interactions of SycD with Yop secretion protein M2 (YscM2), and low calcium response protein V (LcrV), respectively, were reinvestigated.
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Affiliation(s)
- Annika Schmid
- Max von Pettenkofer-Institut, Lehrstuhl für Bakteriologie, Ludwig-Maximilians-Universität München, Pettenkoferstr. 9a, D-80336 München, Germany
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22
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Letzelter M, Sorg I, Mota LJ, Meyer S, Stalder J, Feldman M, Kuhn M, Callebaut I, Cornelis GR. The discovery of SycO highlights a new function for type III secretion effector chaperones. EMBO J 2006; 25:3223-33. [PMID: 16794578 PMCID: PMC1500984 DOI: 10.1038/sj.emboj.7601202] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2006] [Accepted: 05/29/2006] [Indexed: 12/13/2022] Open
Abstract
Bacterial injectisomes deliver effector proteins straight into the cytosol of eukaryotic cells (type III secretion, T3S). Many effectors are associated with a specific chaperone that remains inside the bacterium when the effector is delivered. The structure of such chaperones and the way they interact with their substrate is well characterized but their main function remains elusive. Here, we describe and characterize SycO, a new chaperone for the Yersinia effector kinase YopO. The chaperone-binding domain (CBD) within YopO coincides with the membrane localization domain (MLD) targeting YopO to the host cell membrane. The CBD/MLD causes intrabacterial YopO insolubility and the binding of SycO prevents this insolubility but not folding and activity of the kinase. Similarly, SycE masks the MLD of YopE and SycT covers an aggregation-prone domain of YopT, presumably corresponding to its MLD. Thus, SycO, SycE and most likely SycT mask, inside the bacterium, a domain needed for proper localization of their cognate effector in the host cell. We propose that covering an MLD might be an essential function of T3S effector chaperones.
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Affiliation(s)
| | - Isabel Sorg
- Biozentrum der Universität Basel, Basel, Switzerland
| | | | - Salome Meyer
- Biozentrum der Universität Basel, Basel, Switzerland
| | | | - Mario Feldman
- Biozentrum der Universität Basel, Basel, Switzerland
| | - Marina Kuhn
- Biozentrum der Universität Basel, Basel, Switzerland
| | - Isabelle Callebaut
- Département de Biologie Structurale, Institut de Minéralogie et de Physique des Milieux Condensés (CNRS/UMR 7590) Universités Paris 6 & Paris 7, Paris, France
| | - Guy R Cornelis
- Biozentrum der Universität Basel, Basel, Switzerland
- Biozentrum, Klingelbergstrasse 50, 4056 Basel, Switzerland. Tel.: +41 61 267 2110; Fax: +41 61 267 2118; E-mail:
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23
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Edqvist PJ, Bröms JE, Betts HJ, Forsberg A, Pallen MJ, Francis MS. Tetratricopeptide repeats in the type III secretion chaperone, LcrH: their role in substrate binding and secretion. Mol Microbiol 2006; 59:31-44. [PMID: 16359316 DOI: 10.1111/j.1365-2958.2005.04923.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Non-flagellar type III secretion systems (T3SSs) transport proteins across the bacterial cell and into eukaryotic cells. Targeting of proteins into host cells requires a dedicated translocation apparatus. Efficient secretion of the translocator proteins that make up this apparatus depends on molecular chaperones. Chaperones of the translocators (also called class-II chaperones) are characterized by the possession of three tandem tetratricopeptide repeats (TPRs). We wished to dissect the relations between chaperone structure and function and to validate a structural model using site-directed mutagenesis. Drawing on a number of experimental approaches and focusing on LcrH, a class-II chaperone from the Yersinia Ysc-Yop T3SS, we examined the contributions of different residues, residue classes and regions of the protein to chaperone stability, chaperone-substrate binding, substrate stability and secretion and regulation of Yop protein synthesis. We confirmed the expected role of the conserved canonical residues from the TPRs to chaperone stability and function. Eleven mutations specifically abrogated YopB binding or secretion while three mutations led to a specific loss of YopD secretion. These are the first mutations described for any class-II chaperone that allow interactions with one translocator to be dissociated from interactions with the other. Strikingly, all mutations affecting the interaction with YopB mapped to residues with side chains projecting from the inner, concave surface of the modelled TPR structure, defining a YopB interaction site. Conversely, all mutations preventing YopD secretion affect residues that lie on the outer, convex surface of the triple-TPR cluster in our model, suggesting that this region of the molecule represents a distinct interaction site for YopD. Intriguingly, one of the LcrH double mutants, Y40A/F44A, was able to maintain stable substrates inside bacteria, but unable to secrete them, suggesting that these two residues might influence delivery of substrates to the secretion apparatus.
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Affiliation(s)
- Petra J Edqvist
- Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden
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24
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Büttner D, Lorenz C, Weber E, Bonas U. Targeting of two effector protein classes to the type III secretion system by a HpaC- and HpaB-dependent protein complex fromXanthomonas campestrispv.vesicatoria. Mol Microbiol 2005; 59:513-27. [PMID: 16390446 DOI: 10.1111/j.1365-2958.2005.04924.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The Gram-negative plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria translocates effector proteins via a specialized type III secretion (TTS) system into the host cell cytosol. The efficient secretion of many effector proteins depends on the global TTS chaperone HpaB. Here, we identified a novel export control protein, HpaC, which significantly contributes to bacterial pathogenicity. Deletion of hpaC leads to a severe reduction in secretion of effector proteins and the putative type III translocon proteins HrpF and XopA. By contrast, secretion of the TTS pilus protein HrpE is not affected. We provide experimental evidence that HpaC differentiates between two classes of effector proteins. Using an in vivo reporter assay, we found that HpaC specifically promotes the translocation of the effector proteins XopJ and XopF1 into the plant cell, whereas AvrBs3 and XopC are efficiently translocated even in the absence of HpaC. Similar findings were obtained for HpaB. Inhibition of protein synthesis suggests that HpaB is involved in the secretion of stored effector proteins. Furthermore, protein-protein interaction studies revealed that HpaB and HpaC form an oligomeric protein complex and that they interact with members of both effector protein classes and the conserved TTS system component HrcV. Taken together, our data indicate that HpaB and HpaC play a central role in recruiting TTS substrates to the secretion apparatus.
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Affiliation(s)
- Daniela Büttner
- Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle, Saale, Germany.
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25
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Johnson S, Deane JE, Lea SM. The type III needle and the damage done. Curr Opin Struct Biol 2005; 15:700-7. [PMID: 16263265 DOI: 10.1016/j.sbi.2005.10.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Revised: 09/14/2005] [Accepted: 10/20/2005] [Indexed: 12/30/2022]
Abstract
Many Gram-negative pathogens translocate virulence proteins directly into host cells using a type III secretion system. This complex secretion machinery is composed of approximately 25 different proteins that assemble to span both bacterial membranes, and contact the host cell to form a direct channel between the bacterial and host cell cytoplasms. Assembly of the system and efficient secretion of virulence proteins through this apparatus require specific chaperones. Although the machinery is morphologically conserved among all bacteria, the secreted proteins vary widely and are responsible for the range of diseases caused by bacterial pathogens. Recent structures have given insights into important chaperone and effector proteins, as well as revealing the first atomic structures of portions of the secretion machinery itself.
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Affiliation(s)
- Steven Johnson
- Laboratory of Molecular Biophysics, Department of Biochemistry, South Parks Road, Oxford OX1 3QU, UK
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