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Reglinski M, Monlezun L, Coulthurst SJ. The accessory protein TagV is required for full Type VI secretion system activity in Serratia marcescens. Mol Microbiol 2023; 119:326-339. [PMID: 36627840 PMCID: PMC7614798 DOI: 10.1111/mmi.15027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 12/21/2022] [Accepted: 01/06/2023] [Indexed: 01/12/2023]
Abstract
The bacterial Type VI secretion system (T6SS) is a dynamic macromolecular structure that promotes inter- and intra-species competition through the delivery of toxic effector proteins into neighbouring cells. The T6SS contains 14 well-characterised core proteins necessary for effector delivery (TssA-M, PAAR). In this study, we have identified a novel accessory component required for optimal T6SS activity in the opportunistic pathogen Serratia marcescens, which we name TagV. Deletion of tagV, which encodes an outer membrane lipoprotein, caused a reduction in the T6SS-dependent antibacterial activity of S. marcescens Db10. Mutants of S. marcescens lacking the core component TssJ, a distinct outer membrane lipoprotein previously considered essential for T6SS firing, retained a modest T6SS activity that could be abolished through deletion of tagV. TagV did not interact with the T6SS membrane complex proteins TssL or TssM, but is proposed to bind to peptidoglycan, indicating that the mechanism by which TagV promotes T6SS firing differs from that of TssJ. Homologues of tagV were identified in several other bacterial genera, suggesting that the accessory function of TagV is not restricted to S. marcescens. Together, our findings support the existence of a second, TssJ-independent mechanism for T6SS firing that is dependent upon the activity of TagV proteins.
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Affiliation(s)
- Mark Reglinski
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, UK
| | - Laura Monlezun
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, UK
| | - Sarah J Coulthurst
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, UK
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2
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Sun Y, Ding S, He M, Liu A, Long H, Guo W, Cao Z, Xie Z, Zhou Y. Construction and analysis of the immune effect of Vibrio harveyi subunit vaccine and DNA vaccine encoding TssJ antigen. FISH & SHELLFISH IMMUNOLOGY 2020; 98:45-51. [PMID: 31887410 DOI: 10.1016/j.fsi.2019.12.079] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 12/24/2019] [Accepted: 12/26/2019] [Indexed: 06/10/2023]
Abstract
Vibrio harveyi, a severe pathogen infects different kinds of sea animals, causes huge economic loss in aquaculture industry. In order to control the Vibriosis disease caused mainly by V. harveyi and other Vibrio spp., the best solution lies in developing corresponding efficient vaccines. In this study, we have cloned and analysed a putative antigen TssJ from the T6SS of V. harveyi, which has the potential as a vaccine against infection. The sequence analysis and western blotting experiments indicated that TssJ anchored in outer membrane and there were several antigenic determinants existed on its extracellular region. Two forms of universal vaccines, subunit vaccine and DNA vaccine, were developed based on TssJ and applied in Trachinotus ovatus. The results showed that both of the two vaccines could generate a moderate protection in fish against V. harveyi. The relative percentage survival (RPS) of subunit vaccine and DNA vaccine were 52.39% and 69.11%, respectively. Immunological analysis showed both subunit vaccine and DNA vaccine enhanced acid phosphatase, alkaline phosphatase, superoxide dismutase, and lysozyme activities. Specific serum antibodies against TssJ in the fish vaccinated with subunit vaccine was much higher than that in the DNA vaccine group. Several immune-related genes, i.e., IL10, C3, MHC Iα, MHC IIα, and IgM, were induced both by the two forms of vaccines. TNFα and Mx were only upregulated in the DNA vaccine group. However, the induction levels of these genes induced by DNA vaccine were higher than subunit vaccine. All these findings suggested that TssJ from V. harveyi had a potential application value in vaccine industry.
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Affiliation(s)
- Yun Sun
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China; Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China
| | - Susu Ding
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China; Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China
| | - Mingwang He
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China; Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China
| | - Anzhu Liu
- Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China
| | - Hao Long
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China
| | - Weiliang Guo
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China; Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China
| | - Zhenjie Cao
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China; Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China
| | - Zhenyu Xie
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China; Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China.
| | - Yongcan Zhou
- State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, PR China; Hainan Provincial Key Laboratory for Tropical Hydrobiology and Biotechnology, College of Marine Science, Hainan University, PR China.
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3
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Wang J, Brodmann M, Basler M. Assembly and Subcellular Localization of Bacterial Type VI Secretion Systems. Annu Rev Microbiol 2019; 73:621-638. [DOI: 10.1146/annurev-micro-020518-115420] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Bacteria need to deliver large molecules out of the cytosol to the extracellular space or even across membranes of neighboring cells to influence their environment, prevent predation, defeat competitors, or communicate. A variety of protein-secretion systems have evolved to make this process highly regulated and efficient. The type VI secretion system (T6SS) is one of the largest dynamic assemblies in gram-negative bacteria and allows for delivery of toxins into both bacterial and eukaryotic cells. The recent progress in structural biology and live-cell imaging shows the T6SS as a long contractile sheath assembled around a rigid tube with associated toxins anchored to a cell envelope by a baseplate and membrane complex. Rapid sheath contraction releases a large amount of energy used to push the tube and toxins through the membranes of neighboring target cells. Because reach of the T6SS is limited, some bacteria dynamically regulate its subcellular localization to precisely aim at their targets and thus increase efficiency of toxin translocation.
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Affiliation(s)
- Jing Wang
- Biozentrum, University of Basel, CH 4056 Basel, Switzerland
| | - Maj Brodmann
- Biozentrum, University of Basel, CH 4056 Basel, Switzerland
| | - Marek Basler
- Biozentrum, University of Basel, CH 4056 Basel, Switzerland
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Mariano G, Monlezun L, Coulthurst SJ. Dual Role for DsbA in Attacking and Targeted Bacterial Cells during Type VI Secretion System-Mediated Competition. Cell Rep 2019; 22:774-785. [PMID: 29346773 PMCID: PMC5792426 DOI: 10.1016/j.celrep.2017.12.075] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 12/15/2017] [Accepted: 12/21/2017] [Indexed: 01/23/2023] Open
Abstract
Incorporation of disulfide bonds into proteins can be critical for function or stability. In bacterial cells, the periplasmic enzyme DsbA is responsible for disulfide incorporation into many extra-cytoplasmic proteins. The type VI secretion system (T6SS) is a widely occurring nanomachine that delivers toxic effector proteins directly into rival bacterial cells, playing a key role in inter-bacterial competition. We report that two redundant DsbA proteins are required for virulence and for proper deployment of the T6SS in the opportunistic pathogen Serratia marcescens, with several T6SS components being subject to the action of DsbA in secreting cells. Importantly, we demonstrate that DsbA also plays a critical role in recipient target cells, being required for the toxicity of certain incoming effector proteins. Thus we reveal that target cell functions can be hijacked by T6SS effectors for effector activation, adding a further level of complexity to the T6SS-mediated inter-bacterial interactions which define varied microbial communities. Type VI secretion systems (T6SSs) are used by bacteria to attack competitors Disulfide bond formation by DsbA promotes assembly of an active T6SS in Serratia DsbA in the target cell is needed for activation of certain incoming T6SS effectors This work reveals that T6SS-delivered effectors can hijack target cell functions
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Affiliation(s)
- Giuseppina Mariano
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Laura Monlezun
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Sarah J Coulthurst
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
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Cherrak Y, Flaugnatti N, Durand E, Journet L, Cascales E. Structure and Activity of the Type VI Secretion System. Microbiol Spectr 2019; 7:10.1128/microbiolspec.psib-0031-2019. [PMID: 31298206 PMCID: PMC10957189 DOI: 10.1128/microbiolspec.psib-0031-2019] [Citation(s) in RCA: 80] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Indexed: 12/16/2022] Open
Abstract
The type VI secretion system (T6SS) is a multiprotein machine that uses a spring-like mechanism to inject effectors into target cells. The injection apparatus is composed of a baseplate on which is built a contractile tail tube/sheath complex. The inner tube, topped by the spike complex, is propelled outside of the cell by the contraction of the sheath. The injection system is anchored to the cell envelope and oriented towards the cell exterior by a trans-envelope complex. Effectors delivered by the T6SS are loaded within the inner tube or on the spike complex and can target prokaryotic and/or eukaryotic cells. Here we summarize the structure, assembly, and mechanism of action of the T6SS. We also review the function of effectors and their mode of recruitment and delivery.
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Affiliation(s)
- Yassine Cherrak
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), Aix-Marseille Université, CNRS, UMR 7255, 13402 Marseille Cedex 20, France
- Y.C. and N.F. contributed equally to this review
| | - Nicolas Flaugnatti
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), Aix-Marseille Université, CNRS, UMR 7255, 13402 Marseille Cedex 20, France
- Y.C. and N.F. contributed equally to this review
- Present address: Laboratory of Molecular Microbiology, Global Health Institute, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Eric Durand
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), Aix-Marseille Université, CNRS, UMR 7255, 13402 Marseille Cedex 20, France
| | - Laure Journet
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), Aix-Marseille Université, CNRS, UMR 7255, 13402 Marseille Cedex 20, France
| | - Eric Cascales
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), Aix-Marseille Université, CNRS, UMR 7255, 13402 Marseille Cedex 20, France
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Rapisarda C, Cherrak Y, Kooger R, Schmidt V, Pellarin R, Logger L, Cascales E, Pilhofer M, Durand E, Fronzes R. In situ and high-resolution cryo-EM structure of a bacterial type VI secretion system membrane complex. EMBO J 2019; 38:e100886. [PMID: 30877094 PMCID: PMC6517824 DOI: 10.15252/embj.2018100886] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Revised: 02/04/2019] [Accepted: 02/06/2019] [Indexed: 11/19/2022] Open
Abstract
Bacteria have evolved macromolecular machineries that secrete effectors and toxins to survive and thrive in diverse environments. The type VI secretion system (T6SS) is a contractile machine that is related to Myoviridae phages. It is composed of a phage tail-like structure inserted in the bacterial cell envelope by a membrane complex (MC) comprising the TssJ, TssL and TssM proteins. We previously reported the low-resolution negative-stain electron microscopy structure of the enteroaggregative Escherichia coli MC and proposed a rotational 5-fold symmetry with a TssJ:TssL:TssM stoichiometry of 2:2:2. Here, cryo-electron tomography analyses of the T6SS MC confirm the 5-fold symmetry in situ and identify the regions of the structure that insert into the bacterial membranes. A high-resolution model obtained by single-particle cryo-electron microscopy highlights new features: five additional copies of TssJ, yielding a TssJ:TssL:TssM stoichiometry of 3:2:2, an 11-residue loop in TssM, protruding inside the lumen of the MC and constituting a functionally important periplasmic gate, and hinge regions. Based on these data, we propose an updated model on MC structure and dynamics during T6SS assembly and function.
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Affiliation(s)
- Chiara Rapisarda
- CNRS UMR 5234 Microbiologie Fondamentale et Pathogénicité, Bordeaux, France
- Institut Européen de Chimie et Biologie, University of Bordeaux, Pessac, France
| | - Yassine Cherrak
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), UMR7255, Aix-Marseille Université - CNRS, Marseille, France
| | - Romain Kooger
- Institute of Molecular Biology & Biophysics, Eidgenössische Technische Hochschule Zürich, Zürich, Switzerland
| | - Victoria Schmidt
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), UMR7255, Aix-Marseille Université - CNRS, Marseille, France
| | - Riccardo Pellarin
- Institut Pasteur, Structural Bioinformatics Unit, Department of Structural Biology and Chemistry, CNRS UMR 3528, C3BI USR 3756, Paris, France
| | - Laureen Logger
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), UMR7255, Aix-Marseille Université - CNRS, Marseille, France
| | - Eric Cascales
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), UMR7255, Aix-Marseille Université - CNRS, Marseille, France
| | - Martin Pilhofer
- Institute of Molecular Biology & Biophysics, Eidgenössische Technische Hochschule Zürich, Zürich, Switzerland
| | - Eric Durand
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), Institut de Microbiologie de la Méditerranée (IMM), UMR7255, INSERM, Marseille, France
| | - Rémi Fronzes
- CNRS UMR 5234 Microbiologie Fondamentale et Pathogénicité, Bordeaux, France
- Institut Européen de Chimie et Biologie, University of Bordeaux, Pessac, France
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Clemens DL, Lee BY, Horwitz MA. The Francisella Type VI Secretion System. Front Cell Infect Microbiol 2018; 8:121. [PMID: 29740542 PMCID: PMC5924787 DOI: 10.3389/fcimb.2018.00121] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 04/03/2018] [Indexed: 12/27/2022] Open
Abstract
Francisella tularensisis subsp. tularensis is an intracellular bacterial pathogen and the causative agent of the life-threatening zoonotic disease tularemia. The Francisella Pathogenicity Island encodes a large secretion apparatus, known as a Type VI Secretion System (T6SS), which is essential for Francisella to escape from its phagosome and multiply within host macrophages and to cause disease in animals. The T6SS, found in one-quarter of Gram-negative bacteria including many highly pathogenic ones, is a recently discovered secretion system that is not yet fully understood. Nevertheless, there have been remarkable advances in our understanding of the structure, composition, and function of T6SSs of several bacteria in the past few years. The system operates like an inside-out headless contractile phage that is anchored to the bacterial membrane via a baseplate and membrane complex. The system injects effector molecules across the inner and outer bacterial membrane and into host prokaryotic or eukaryotic targets to kill, intoxicate, or in the case of Francisella, hijack the target cell. Recent advances include an atomic model of the contractile sheath, insights into the mechanics of sheath contraction, the composition of the baseplate and membrane complex, the process of assembly of the apparatus, and identification of numerous effector molecules and activities. While Francisella T6SS appears to be an outlier among T6SSs, with limited or no sequence homology with other systems, its structure and organization are strikingly similar to other systems. Nevertheless, we have only scratched the surface in uncovering the mysteries of the Francisella T6SS, and there are numerous questions that remain to be answered.
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Affiliation(s)
- Daniel L. Clemens
- Division of Infectious Diseases, Department of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | | | - Marcus A. Horwitz
- Division of Infectious Diseases, Department of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
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Tryptophan-mediated Dimerization of the TssL Transmembrane Anchor Is Required for Type VI Secretion System Activity. J Mol Biol 2018; 430:987-1003. [DOI: 10.1016/j.jmb.2018.02.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 01/29/2018] [Accepted: 02/11/2018] [Indexed: 11/23/2022]
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9
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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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Basler M. Type VI secretion system: secretion by a contractile nanomachine. Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2015.0021. [PMID: 26370934 PMCID: PMC4632598 DOI: 10.1098/rstb.2015.0021] [Citation(s) in RCA: 146] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The type VI secretion systems (T6SS) are present in about a quarter of all Gram-negative bacteria. Several key components of T6SS are evolutionarily related to components of contractile nanomachines such as phages and R-type pyocins. The T6SS assembly is initiated by formation of a membrane complex that binds a phage-like baseplate with a sharp spike, and this is followed by polymerization of a long rigid inner tube and an outer contractile sheath. Effectors are preloaded onto the spike or into the tube during the assembly by various mechanisms. Contraction of the sheath releases an unprecedented amount of energy, which is used to thrust the spike and tube with the associated effectors out of the effector cell and across membranes of both bacterial and eukaryotic target cells. Subunits of the contracted sheath are recycled by T6SS-specific unfoldase to allow for a new round of assembly. Live-cell imaging has shown that the assembly is highly dynamic and its subcellular localization is in certain bacteria regulated with a remarkable precision. Through the action of effectors, T6SS has mainly been shown to contribute to pathogenicity and competition between bacteria. This review summarizes the knowledge that has contributed to our current understanding of T6SS mode of action.
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Affiliation(s)
- Marek Basler
- Focal Area Infection Biology, Biozentrum, University of Basel, Basel, Switzerland
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11
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Aim, Load, Fire: The Type VI Secretion System, a Bacterial Nanoweapon. Trends Microbiol 2016; 24:51-62. [DOI: 10.1016/j.tim.2015.10.005] [Citation(s) in RCA: 267] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 09/30/2015] [Accepted: 10/09/2015] [Indexed: 12/31/2022]
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Intraspecies Competition in Serratia marcescens Is Mediated by Type VI-Secreted Rhs Effectors and a Conserved Effector-Associated Accessory Protein. J Bacteriol 2015; 197:2350-60. [PMID: 25939831 PMCID: PMC4524185 DOI: 10.1128/jb.00199-15] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Accepted: 04/24/2015] [Indexed: 12/27/2022] Open
Abstract
The type VI secretion system (T6SS) is widespread in Gram-negative bacteria and can deliver toxic effector proteins into eukaryotic cells or competitor bacteria. Antibacterial T6SSs are increasingly recognized as key mediators of interbacterial competition and may contribute to the outcome of many polymicrobial infections. Multiple antibacterial effectors can be delivered by these systems, with diverse activities against target cells and distinct modes of secretion. Polymorphic toxins containing Rhs repeat domains represent a recently identified and as-yet poorly characterized class of T6SS-dependent effectors. Previous work had revealed that the potent antibacterial T6SS of the opportunistic pathogen Serratia marcescens promotes intraspecies as well as interspecies competition (S. L. Murdoch, K. Trunk, G. English, M. J. Fritsch, E. Pourkarimi, and S. J. Coulthurst, J Bacteriol 193:6057–6069, 2011, http://dx.doi.org/10.1128/JB.05671-11). In this study, two new Rhs family antibacterial effectors delivered by this T6SS have been identified. One of these was shown to act as a DNase toxin, while the other contains a novel, cytoplasmic-acting toxin domain. Importantly, using S. marcescens, it has been demonstrated for the first time that Rhs proteins, rather than other T6SS-secreted effectors, can be the primary determinant of intraspecies competition. Furthermore, a new family of accessory proteins associated with T6SS effectors has been identified, exemplified by S. marcescens EagR1, which is specifically required for deployment of its associated Rhs effector. Together, these findings provide new insight into how bacteria can use the T6SS to deploy Rhs-family effectors and mediate different types of interbacterial interactions.
IMPORTANCE Infectious diseases caused by bacterial pathogens represent a continuing threat to health and economic prosperity. To counter this threat, we must understand how such organisms survive and prosper. The type VI secretion system is a weapon that many pathogens deploy to compete against rival bacterial cells by injecting multiple antibacterial toxins into them. The ability to compete is vital considering that bacteria generally live in mixed communities. We aimed to identify new toxins and understand their deployment and role in interbacterial competition. We describe two new type VI secretion system-delivered toxins of the Rhs class, demonstrate that this class can play a primary role in competition between closely related bacteria, and identify a new accessory factor needed for their delivery.
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Nguyen VS, Spinelli S, Desmyter A, Le TTH, Kellenberger C, Cascales E, Cambillau C, Roussel A. Production, crystallization and X-ray diffraction analysis of a complex between a fragment of the TssM T6SS protein and a camelid nanobody. Acta Crystallogr F Struct Biol Commun 2015; 71:266-71. [PMID: 25760699 PMCID: PMC4356300 DOI: 10.1107/s2053230x15000709] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2014] [Accepted: 01/13/2015] [Indexed: 11/10/2022] Open
Abstract
The type VI secretion system (T6SS) is a machine evolved by Gram-negative bacteria to deliver toxin effectors into target bacterial or eukaryotic cells. The T6SS is functionally and structurally similar to the contractile tail of the Myoviridae family of bacteriophages and can be viewed as a syringe anchored to the bacterial membrane by a transenvelope complex. The membrane complex is composed of three proteins: the TssM and TssL inner membrane components and the TssJ outer membrane lipoprotein. The TssM protein is central as it interacts with both TssL and TssJ, therefore linking the membranes. Using controlled trypsinolysis, a 32.4 kDa C-terminal fragment of enteroaggregative Escherichia coli TssM (TssM32Ct) was purified. A nanobody obtained from llama immunization, nb25, exhibited subnanomolar affinity for TssM32Ct. Crystals of the TssM32Ct-nb25 complex were obtained and diffracted to 1.9 Å resolution. The crystals belonged to space group P64, with unit-cell parameters a = b = 95.23, c = 172.95 Å. Molecular replacement with a model nanobody indicated the presence of a dimer of TssM32Ct-nb25 in the asymmetric unit.
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Affiliation(s)
- Van Son Nguyen
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Campus de Luminy, Case 932, 13288 Marseille, France
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille, France
| | - Silvia Spinelli
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Campus de Luminy, Case 932, 13288 Marseille, France
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille, France
| | - Aline Desmyter
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Campus de Luminy, Case 932, 13288 Marseille, France
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille, France
| | - Thi Thu Hang Le
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Campus de Luminy, Case 932, 13288 Marseille, France
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille, France
| | - Christine Kellenberger
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Campus de Luminy, Case 932, 13288 Marseille, France
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille, France
| | - Eric Cascales
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, Institut de Microbiologie de la Méditerranée, CNRS and Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseille, France
| | - Christian Cambillau
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Campus de Luminy, Case 932, 13288 Marseille, France
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille, France
| | - Alain Roussel
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Campus de Luminy, Case 932, 13288 Marseille, France
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Case 932, 13288 Marseille, France
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Biochemical analysis of TssK, a core component of the bacterial Type VI secretion system, reveals distinct oligomeric states of TssK and identifies a TssK-TssFG subcomplex. Biochem J 2014; 461:291-304. [PMID: 24779861 PMCID: PMC4072051 DOI: 10.1042/bj20131426] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Gram-negative bacteria use the Type VI secretion system (T6SS) to inject toxic proteins into rival bacteria or eukaryotic cells. However, the mechanism of the T6SS is incompletely understood. In the present study, we investigated a conserved component of the T6SS, TssK, using the antibacterial T6SS of Serratia marcescens as a model system. TssK was confirmed to be essential for effector secretion by the T6SS. The native protein, although not an integral membrane protein, appeared to localize to the inner membrane, consistent with its presence within a membrane-anchored assembly. Recombinant TssK purified from S. marcescens was found to exist in several stable oligomeric forms, namely trimer, hexamer and higher-order species. Native-level purification of TssK identified TssF and TssG as interacting proteins. TssF and TssG, conserved T6SS components of unknown function, were required for T6SS activity, but not for correct localization of TssK. A complex containing TssK, TssF and TssG was subsequently purified in vitro, confirming that these three proteins form a new subcomplex within the T6SS. Our findings provide new insight into the T6SS assembly, allowing us to propose a model whereby TssK recruits TssFG into the membrane-associated T6SS complex and different oligomeric states of TssK may contribute to the dynamic mechanism of the system. Genetic and biochemical analysis of TssK, an essential component of the bacterial Type VI secretion system, revealed that it forms a new subcomplex with two other core components, TssF and TssG, and displays several oligomerization states in vitro.
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Zoued A, Brunet YR, Durand E, Aschtgen MS, Logger L, Douzi B, Journet L, Cambillau C, Cascales E. Architecture and assembly of the Type VI secretion system. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1664-73. [PMID: 24681160 DOI: 10.1016/j.bbamcr.2014.03.018] [Citation(s) in RCA: 172] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 03/17/2014] [Accepted: 03/18/2014] [Indexed: 12/31/2022]
Abstract
The Type VI secretion system (T6SS) delivers protein effectors to diverse cell types including prokaryotic and eukaryotic cells, therefore it participates in inter-bacterial competition and pathogenesis. The T6SS is constituted of an envelope-spanning complex anchoring a cytoplasmic tubular edifice. This tubular structure is evolutionarily, functionally and structurally related to the tail of contractile phages. It is composed of an inner tube tipped by a spike complex, and engulfed within a sheath-like structure. This structure assembles onto a platform called "baseplate" that is connected to the membrane sub-complex. The T6SS functions as a nano-crossbow: upon contraction of the sheath, the inner tube is propelled towards the target cell, allowing effector delivery. This review focuses on the architecture and biogenesis of this fascinating secretion machine, highlighting recent advances regarding the assembly of the membrane or tail complexes. 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)
- Abdelrahim Zoued
- Laboratoire d'Ingeniérie des Systèmes Macromoléculaires, CNRS, Aix-Marseille Université, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Yannick R Brunet
- Laboratoire d'Ingeniérie des Systèmes Macromoléculaires, CNRS, Aix-Marseille Université, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Eric Durand
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Aix-Marseille Université, UMR 7257, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France
| | - Marie-Stéphanie Aschtgen
- Laboratoire d'Ingeniérie des Systèmes Macromoléculaires, CNRS, Aix-Marseille Université, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Laureen Logger
- Laboratoire d'Ingeniérie des Systèmes Macromoléculaires, CNRS, Aix-Marseille Université, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Badreddine Douzi
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Aix-Marseille Université, UMR 7257, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France
| | - Laure Journet
- Laboratoire d'Ingeniérie des Systèmes Macromoléculaires, CNRS, Aix-Marseille Université, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
| | - Christian Cambillau
- Architecture et Fonction des Macromolécules Biologiques, CNRS, Aix-Marseille Université, UMR 7257, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France
| | - Eric Cascales
- Laboratoire d'Ingeniérie des Systèmes Macromoléculaires, CNRS, Aix-Marseille Université, UMR 7255, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
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17
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Zhang XY, Brunet YR, Logger L, Douzi B, Cambillau C, Journet L, Cascales E. Dissection of the TssB-TssC interface during type VI secretion sheath complex formation. PLoS One 2013; 8:e81074. [PMID: 24282569 PMCID: PMC3840085 DOI: 10.1371/journal.pone.0081074] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 10/09/2013] [Indexed: 11/18/2022] Open
Abstract
The Type VI secretion system (T6SS) is a versatile machine that delivers toxins into either eukaryotic or bacterial cells. At a molecular level, the T6SS is composed of a membrane complex that anchors a long cytoplasmic tubular structure to the cell envelope. This structure is thought to resemble the tail of contractile bacteriophages. It is composed of the Hcp protein that assembles into hexameric rings stacked onto each other to form a tube similar to the phage tail tube. This tube is proposed to be wrapped by a structure called the sheath, composed of two proteins, TssB and TssC. It has been shown using fluorescence microscopy that the TssB and TssC proteins assemble into a tubular structure that cycles between long and short conformations suggesting that, similarly to the bacteriophage sheath, the T6SS sheath undergoes elongation and contraction events. The TssB and TssC proteins have been shown to interact and a specific α-helix of TssB is required for this interaction. Here, we confirm that the TssB and TssC proteins interact in enteroaggregative E. coli. We further show that this interaction requires the N-terminal region of TssC and the conserved α-helix of TssB. Using site-directed mutagenesis coupled to phenotypic analyses, we demonstrate that an hydrophobic motif located in the N-terminal region of this helix is required for interaction with TssC, sheath assembly and T6SS function.
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Affiliation(s)
- Xiang Y. Zhang
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Yannick R. Brunet
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Laureen Logger
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Badreddine Douzi
- Architecture et Fonction des Macromolécules Biologiques (AFMB, UMR 6098), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Christian Cambillau
- Architecture et Fonction des Macromolécules Biologiques (AFMB, UMR 6098), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Laure Journet
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Eric Cascales
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
- * E-mail: *
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18
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Rao VA, Shepherd SM, Owen R, Hunter WN. Structure of Pseudomonas aeruginosa inosine 5'-monophosphate dehydrogenase. Acta Crystallogr Sect F Struct Biol Cryst Commun 2013; 69:243-7. [PMID: 23519796 PMCID: PMC3606566 DOI: 10.1107/s1744309113002352] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 01/23/2013] [Indexed: 05/29/2023]
Abstract
Inosine 5'-monophosphate dehydrogenase (IMPDH) represents a potential antimicrobial drug target. The crystal structure of recombinant Pseudomonas aeruginosa IMPDH has been determined to a resolution of 2.25 Å. The structure is a homotetramer of subunits dominated by a (β/α)8-barrel fold, consistent with other known structures of IMPDH. Also in common with previous work, the cystathionine β-synthase domains, residues 92-204, are not present in the model owing to disorder. However, unlike the majority of available structures, clearly defined electron density exists for a loop that creates part of the active site. This loop, composed of residues 297-315, links α8 and β9 and carries the catalytic Cys304. P. aeruginosa IMPDH shares a high level of sequence identity with bacterial and protozoan homologues, with residues involved in binding substrate and the NAD+ cofactor being conserved. Specific differences that have been proven to contribute to selectivity against the human enzyme in a study of Cryptosporidium parvum IMPDH are also conserved, highlighting the potential value of IMPDH as a drug target.
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Affiliation(s)
- Vincenzo A. Rao
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland
| | - Sharon M. Shepherd
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland
| | - Richard Owen
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland
| | - William N. Hunter
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland
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19
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Moynie L, Schnell R, McMahon SA, Sandalova T, Boulkerou WA, Schmidberger JW, Alphey M, Cukier C, Duthie F, Kopec J, Liu H, Jacewicz A, Hunter WN, Naismith JH, Schneider G. The AEROPATH project targeting Pseudomonas aeruginosa: crystallographic studies for assessment of potential targets in early-stage drug discovery. Acta Crystallogr Sect F Struct Biol Cryst Commun 2013; 69:25-34. [PMID: 23295481 PMCID: PMC3539698 DOI: 10.1107/s1744309112044739] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Accepted: 10/29/2012] [Indexed: 12/25/2022]
Abstract
Bacterial infections are increasingly difficult to treat owing to the spread of antibiotic resistance. A major concern is Gram-negative bacteria, for which the discovery of new antimicrobial drugs has been particularly scarce. In an effort to accelerate early steps in drug discovery, the EU-funded AEROPATH project aims to identify novel targets in the opportunistic pathogen Pseudomonas aeruginosa by applying a multidisciplinary approach encompassing target validation, structural characterization, assay development and hit identification from small-molecule libraries. Here, the strategies used for target selection are described and progress in protein production and structure analysis is reported. Of the 102 selected targets, 84 could be produced in soluble form and the de novo structures of 39 proteins have been determined. The crystal structures of eight of these targets, ranging from hypothetical unknown proteins to metabolic enzymes from different functional classes (PA1645, PA1648, PA2169, PA3770, PA4098, PA4485, PA4992 and PA5259), are reported here. The structural information is expected to provide a firm basis for the improvement of hit compounds identified from fragment-based and high-throughput screening campaigns.
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Affiliation(s)
- Lucille Moynie
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, Scotland
| | - Robert Schnell
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Stephen A. McMahon
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, Scotland
| | - Tatyana Sandalova
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | | | - Jason W. Schmidberger
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Magnus Alphey
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, Scotland
| | - Cyprian Cukier
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Fraser Duthie
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, Scotland
| | - Jolanta Kopec
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Huanting Liu
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, Scotland
| | - Agata Jacewicz
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - William N. Hunter
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - James H. Naismith
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews KY16 9ST, Scotland
| | - Gunter Schneider
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
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20
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Shanks RMQ, Stella NA, Arena KE, Fender JE. Mutation of crp mediates Serratia marcescens serralysin and global secreted protein production. Res Microbiol 2012; 164:38-45. [PMID: 23072819 DOI: 10.1016/j.resmic.2012.10.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 09/27/2012] [Indexed: 12/13/2022]
Abstract
The bacterial species Serratia marcescens secretes both beneficial and cytotoxic proteins. Here we report that a crp mutant exhibited elevated secreted protease activity. A genetic screen revealed that the gene coding for the metalloprotease serralysin was necessary for the elevated proteolysis, and this was confirmed by western blot analysis. Proteomic analysis of secreted proteins corroborated increased secretion of serralysin protease by crp mutants compared to the wild type. The crp-mutant-secreted fractions also contained less chitinase and chitin binding protein. These data support the hypothesis that cAMP-CRP is an upstream indirect regulator of serralysin production and they provide novel insight into the S. marcescens secretome.
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Affiliation(s)
- Robert M Q Shanks
- The Charles T. Campbell Laboratory, UPMC Eye Center, Ophthalmology and Visual Sciences Research Center, Eye and Ear Institute, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15208, USA.
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21
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Lossi NS, Manoli E, Simpson P, Jones C, Hui K, Dajani R, Coulthurst SJ, Freemont P, Filloux A. The archetypePseudomonas aeruginosaproteins TssB and TagJ form a novel subcomplex in the bacterial type VI secretion system. Mol Microbiol 2012; 86:437-56. [DOI: 10.1111/j.1365-2958.2012.08204.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/04/2012] [Indexed: 12/25/2022]
Affiliation(s)
- Nadine S. Lossi
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Eleni Manoli
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Pete Simpson
- Division of Molecular Biosciences; Imperial College London; London; SW7 2AZ; UK
| | - Cerith Jones
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Kailyn Hui
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Rana Dajani
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Sarah J. Coulthurst
- Division of Molecular Microbiology; College of Life Sciences; University of Dundee; Dow Street; Dundee; DD1 5EH; UK
| | - Paul Freemont
- Division of Molecular Biosciences; Imperial College London; London; SW7 2AZ; UK
| | - Alain Filloux
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
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22
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Silverman JM, Brunet YR, Cascales E, Mougous JD. Structure and regulation of the type VI secretion system. Annu Rev Microbiol 2012; 66:453-72. [PMID: 22746332 DOI: 10.1146/annurev-micro-121809-151619] [Citation(s) in RCA: 272] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The type VI secretion system (T6SS) is a complex and widespread gram-negative bacterial export pathway with the capacity to translocate protein effectors into a diversity of target cell types. Current structural models of the T6SS indicate that the apparatus is composed of at least two complexes, a dynamic bacteriophage-like structure and a cell-envelope-spanning membrane-associated assembly. How these complexes interact to promote effector secretion and cell targeting remains a major question in the field. As a contact-dependent pathway with specific cellular targets, the T6SS is subject to tight regulation. Thus, the identification of regulatory elements that control T6S expression continues to shape our understanding of the environmental circumstances relevant to its function. This review discusses recent progress toward characterizing T6S structure and regulation.
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Affiliation(s)
- Julie M Silverman
- Department of Microbiology, University of Washington, Seattle, 98195, USA
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23
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Cascales E, Cambillau C. Structural biology of type VI secretion systems. Philos Trans R Soc Lond B Biol Sci 2012; 367:1102-11. [PMID: 22411981 DOI: 10.1098/rstb.2011.0209] [Citation(s) in RCA: 163] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Type VI secretion systems (T6SSs) are transenvelope complexes specialized in the transport of proteins or domains directly into target cells. These systems are versatile as they can target either eukaryotic host cells and therefore modulate the bacteria-host interaction and pathogenesis or bacterial cells and therefore facilitate access to a specific niche. These molecular machines comprise at least 13 proteins. Although recent years have witnessed advances in the role and function of these secretion systems, little is known about how these complexes assemble in the cell envelope. Interestingly, the current information converges to the idea that T6SSs are composed of two subassemblies, one resembling the contractile bacteriophage tail, whereas the other subunits are embedded in the inner and outer membranes and anchor the bacteriophage-like structure to the cell envelope. In this review, we summarize recent structural information on individual T6SS components emphasizing the fact that T6SSs are composite systems, adapting subunits from various origins.
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Affiliation(s)
- Eric Cascales
- CNRS, Laboratoire d'Ingénierie des Systèmes Macromoléculaires, UMR 7255, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
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24
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The structure of the conserved type six secretion protein TssL (DotU) from Francisella novicida. J Mol Biol 2012; 419:277-83. [PMID: 22504227 DOI: 10.1016/j.jmb.2012.04.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Revised: 04/02/2012] [Accepted: 04/03/2012] [Indexed: 01/11/2023]
Abstract
Type six secretion systems (T6SSs) are found in many Gram-negative bacteria and are important for their virulence or their ecological competitiveness. The multicomponent T6SSs are responsible for the translocation of effector molecules into target eukaryotic or prokaryotic cells. The Francisella pathogenicity island encodes a putative T6SS that Francisella novicida requires for intramacrophage growth and virulence during infection of rodents. Here, we present the X-ray crystal structure of the conserved type six secretion component TssL (DotU) from F. novicida. The structure of this protein, which is referred to as Ftn_TssL, revealed an all-α-helical fold that is a unique fusion of two 3-helix bundles. The sequence of Ftn_TssL shows low identity to presumed homologs that are found in most T6SSs. The structure of Ftn_TssL, however, has allowed us to provide bioinformatics evidence that the F. novicida TssL has a fold that is very likely representative for TssL forms from both T6SSs and from the distantly related B subclass of type four secretion systems. A map of sequence conservation on the TssL structure revealed a surface-exposed groove that may represent a functional site on the protein.
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25
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Durand E, Zoued A, Spinelli S, Watson PJH, Aschtgen MS, Journet L, Cambillau C, Cascales E. Structural characterization and oligomerization of the TssL protein, a component shared by bacterial type VI and type IVb secretion systems. J Biol Chem 2012; 287:14157-68. [PMID: 22371492 DOI: 10.1074/jbc.m111.338731] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Type VI secretion system (T6SS) is a macromolecular system distributed in Gram-negative bacteria, responsible for the secretion of effector proteins into target cells. The T6SS has a broad versatility as it can target both eukaryotic and prokaryotic cells. It is therefore involved in host pathogenesis or killing neighboring bacterial cells to colonize a new niche. At the architecture level, the T6SS core apparatus is composed of 13 proteins, which assemble in two subcomplexes. One of these subcomplexes, composed of subunits that share structural similarities with bacteriophage tail and baseplate components, is anchored to the cell envelope by the membrane subcomplex. This latter is constituted of at least three proteins, TssL, TssM, and TssJ. The crystal structure of the TssJ outer membrane lipoprotein and its interaction with the inner membrane TssM protein have been recently reported. TssL and TssM share sequence homology and characteristics with two components of the Type IVb secretion system (T4bSS), IcmH/DotU and IcmF, respectively. In this study, we report the crystal structure of the cytoplasmic domain of the TssL inner membrane protein from the enteroaggregative Escherichia coli Sci-1 T6SS. It folds as a hook-like structure composed of two three-helix bundles. Two TssL molecules associate to form a functional complex. Although the TssL trans-membrane segment is the main determinant of self-interaction, contacts between the cytoplasmic domains are required for TssL function. Based on sequence homology and secondary structure prediction, we propose that the TssL structure is the prototype for the members of the TssL and IcmH/DotU families.
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Affiliation(s)
- Eric Durand
- Aix-Marseille Université, Architecture et Fonction des Macromolécules Biologiques, Campus de Luminy, Case 932, 13288 Marseille Cedex 09, France
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