1
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Bunduc CM, Ding Y, Kuijl C, Marlovits TC, Bitter W, Houben ENG. Reconstitution of a minimal ESX-5 type VII secretion system suggests a role for PPE proteins in the outer membrane transport of proteins. mSphere 2023; 8:e0040223. [PMID: 37747201 PMCID: PMC10597459 DOI: 10.1128/msphere.00402-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 08/03/2023] [Indexed: 09/26/2023] Open
Abstract
Mycobacteria utilize type VII secretion systems (T7SSs) to secrete proteins across their highly hydrophobic and diderm cell envelope. Pathogenic mycobacteria have up to five different T7SSs, called ESX-1 to ESX-5, which are crucial for growth and virulence. Here, we use a functionally reconstituted ESX-5 system in the avirulent species Mycobacterium smegmatis that lacks ESX-5, to define the role of each esx-5 gene in system functionality. By creating an array of gene deletions and assessing protein levels of components and membrane complex assembly, we observed that only the five components of the inner membrane complex are required for its assembly. However, in addition to these five core components, active secretion also depends on both the Esx and PE/PPE substrates. Tagging the PPE substrates followed by subcellular fractionation, surface labeling and membrane extraction showed that these proteins localize to the mycobacterial outer membrane. This indicates that they could play a role in secretion across this enigmatic outer barrier. These results provide the first full overview of the role of each esx-5 gene in T7SS functionality. IMPORTANCE Pathogenic mycobacteria, such as the notorious Mycobacterium tuberculosis, are highly successful as pathogens, in part due to their specific and diderm cell envelope, with a mycolic acid-containing outer membrane. The architecture of this highly impermeable membrane is little understood and the proteins that populate it even less so. To transport proteins across their cell envelope, mycobacteria employ a specialized transport pathway called type VII secretion. While recent studies have elucidated the type VII secretion membrane channel that mediates transport across the inner membrane, the identity of the outer membrane channel remains a black box. Here, we show evidence that specific substrates of the type VII pathway could form these channels. Elucidating the pathway and mechanism of protein secretion through the mycobacterial outer membrane will allow its exploitation for the development of novel mycobacterial therapeutics.
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Affiliation(s)
- C. M. Bunduc
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
- Centre for Structural Systems Biology, Notkestraße, Hamburg, Germany
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Notkestraße, Hamburg, Germany
- German Electron Synchrotron Centre, Notkestraße, Hamburg, Germany
| | - Y. Ding
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
| | - C. Kuijl
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Amsterdam, The Netherlands
| | - T. C. Marlovits
- Centre for Structural Systems Biology, Notkestraße, Hamburg, Germany
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Notkestraße, Hamburg, Germany
- German Electron Synchrotron Centre, Notkestraße, Hamburg, Germany
| | - W. Bitter
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Amsterdam, The Netherlands
| | - E. N. G. Houben
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
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2
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Famelis N, Geibel S, van Tol D. Mycobacterial type VII secretion systems. Biol Chem 2023; 0:hsz-2022-0350. [PMID: 37276364 DOI: 10.1515/hsz-2022-0350] [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: 12/17/2022] [Accepted: 05/22/2023] [Indexed: 06/07/2023]
Abstract
Mycobacteria, such as the pathogen M. tuberculosis, utilize up to five paralogous type VII secretion systems to transport proteins across their cell envelope. Since these proteins associate in pairs that depend on each other for transport to a different extent, the secretion pathway to the bacterial surface remained challenging to address. Structural characterization of the inner-membrane embedded secretion machineries along with recent advances on the substrates' co-dependencies for transport allow for the first time more detailed and testable models for secretion.
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Affiliation(s)
- Nikolaos Famelis
- Institute for Molecular Infection Biology, Julius Maximilian University of Würzburg, D-97080 Würzburg, Germany
| | - Sebastian Geibel
- Leiden Institute of Chemistry, Leiden University, NL-2333 CC Leiden, Netherlands
| | - Daan van Tol
- Leiden Institute of Chemistry, Leiden University, NL-2333 CC Leiden, Netherlands
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3
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D'Souza C, Kishore U, Tsolaki AG. The PE-PPE Family of Mycobacterium tuberculosis: Proteins in Disguise. Immunobiology 2023; 228:152321. [PMID: 36805109 DOI: 10.1016/j.imbio.2022.152321] [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: 06/28/2022] [Revised: 12/22/2022] [Accepted: 12/27/2022] [Indexed: 12/31/2022]
Abstract
Mycobacterium tuberculosis has thrived in parallel with humans for millennia, and despite our efforts, M. tuberculosis continues to plague us, currently infecting a third of the world's population. The success of M. tuberculosis has recently been attributed, in part, to the PE-PPE family; a unique collection of 168 proteins fundamentally involved in the pathogenesis of M. tuberculosis. The PE-PPE family proteins have been at the forefront of intense research efforts since their discovery in 1998 and whilst our knowledge and understanding has significantly advanced over the last two decades, many important questions remain to be elucidated. This review consolidates and examines the vast body of existing literature regarding the PE-PPE family proteins, with respect to the latest developments in elucidating their evolution, structure, subcellular localisation, function, and immunogenicity. This review also highlights significant inconsistencies and contradictions within the field. Additionally, possible explanations for these knowledge gaps are explored. Lastly, this review poses many important questions, which need to be addressed to complete our understanding of the PE-PPE family, as well as highlighting the challenges associated with studying this enigmatic family of proteins. Further research into the PE-PPE family, together with technological advancements in genomics and proteomics, will undoubtedly improve our understanding of the pathogenesis of M. tuberculosis, as well as identify key targets/candidates for the development of novel drugs, diagnostics, and vaccines.
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Affiliation(s)
- Christopher D'Souza
- Biosciences, Department of Life Sciences, College of Health, Medicine and Life Sciences, Brunel University London, Uxbridge UB8 3PH, United Kingdom
| | - Uday Kishore
- Department of Veterinary Medicine, United Arab Emirates University, Al Ain, United Arab Emirates
| | - Anthony G Tsolaki
- Biosciences, Department of Life Sciences, College of Health, Medicine and Life Sciences, Brunel University London, Uxbridge UB8 3PH, United Kingdom.
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4
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The ESX-1 Substrate PPE68 Has a Key Function in ESX-1-Mediated Secretion in Mycobacterium marinum. mBio 2022; 13:e0281922. [PMID: 36409073 PMCID: PMC9765416 DOI: 10.1128/mbio.02819-22] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Mycobacteria use specialized type VII secretion systems (T7SSs) to secrete proteins across their diderm cell envelope. One of the T7SS subtypes, named ESX-1, is a major virulence determinant in pathogenic species such as Mycobacterium tuberculosis and the fish pathogen Mycobacterium marinum. ESX-1 secretes a variety of substrates, called Esx, PE, PPE, and Esp proteins, at least some of which are folded heterodimers. Investigation into the functions of these substrates is problematic, because of the intricate network of codependent secretion between several ESX-1 substrates. Here, we describe the ESX-1 substrate PPE68 as essential for secretion of the highly immunogenic substrates EsxA and EspE via the ESX-1 system in M. marinum. While secreted PPE68 is processed on the cell surface, the majority of cell-associated PPE68 of M. marinum and M. tuberculosis is present in a cytosolic complex with its PE partner and the EspG1 chaperone. Interfering with the binding of EspG1 to PPE68 blocked its export and the secretion of EsxA and EspE. In contrast, esxA was not required for the secretion of PPE68, revealing a hierarchy in codependent secretion. Remarkably, the final 10 residues of PPE68, a negatively charged domain, seem essential for EspE secretion, but not for the secretion of EsxA and of PPE68 itself. This indicates that distinctive domains of PPE68 are involved in secretion of the different ESX-1 substrates. Based on these findings, we propose a mechanistic model for the central role of PPE68 in ESX-1-mediated secretion and substrate codependence. IMPORTANCE Pathogenic mycobacteria, such Mycobacterium tuberculosis and Mycobacterium marinum, use a type VII secretion system (T7SS) subtype, called ESX-1, to mediate intracellular survival via phagosomal rupture and subsequent translocation of the mycobacterium to the host cytosol. Identifying the ESX-1 substrate that is responsible for this process is problematic because of the intricate network of codependent secretion between ESX-1 substrates. Here, we show the central role of the ESX-1 substrate PPE68 for the secretion of ESX-1 substrates in Mycobacterium marinum. Unravelling the mechanism of codependent secretion will aid the functional understanding of T7SSs and will allow the analysis of the individual roles of ESX-1 substrates in the virulence caused by the significant human pathogen Mycobacterium tuberculosis.
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5
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De Maio F, Salustri A, Battah B, Palucci I, Marchionni F, Bellesi S, Palmieri V, Papi M, Kramarska E, Sanguinetti M, Sali M, Berisio R, Delogu G. PE_PGRS3 ensures provision of the vital phospholipids cardiolipin and phosphatidylinositols by promoting the interaction between M. tuberculosis and host cells. Virulence 2021; 12:868-884. [PMID: 33757409 PMCID: PMC8007152 DOI: 10.1080/21505594.2021.1897247] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 01/23/2021] [Accepted: 02/21/2021] [Indexed: 12/12/2022] Open
Abstract
PE_PGRS proteins of Mycobacterium tuberculosis (Mtb) constitute a large family of complex modular proteins whose role is still unclear. Among those, we have previously shown, using the heterologous expression in Mycobacterium smegmatis, that PE_PGRS3 containing a unique arginine-rich C-terminal domain, promotes adhesion to host cells. In this study, we investigate the role of PE_PGRS3 and its C-terminal domain directly in Mtb using functional deletion mutants. The results obtained here show that PE_PGRS3 is localized on the mycobacterial cell wall and its arginine-rich C-terminal region protrudes from the mycobacterial membrane and mediates Mtb entry into epithelial cells. Most importantly, this positively charged helical domain specifically binds phosphorylated phosphatidylinositols and cardiolipin, whereas it is unable to bind other phospholipids. Interestingly, administration of cardiolipin and phosphatidylinositol but no other phospholipids was able to turn-off expression of pe_pgrs3 activated by phosphate starvation conditions. These findings suggest that PE_PGRS3 has the key role to serve as a bridge between mycobacteria and host cells by interacting with specific host phospholipids and extracting them from host cells, for their direct integration or as a source of phosphate, during phases of TB pathogenesis when Mtb is short of phosphate supply.
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Affiliation(s)
- Flavio De Maio
- Dipartimento di Scienze di Laboratorio e Infettivologiche, Fondazione Policlinico Universitario “A. Gemelli”, Rome, Italy
- Dipartimento di Scienze biotecnologiche di base, cliniche intensivologiche e perioperatorie – Sezione di Microbiologia, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Alessandro Salustri
- Dipartimento di Scienze biotecnologiche di base, cliniche intensivologiche e perioperatorie – Sezione di Microbiologia, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Basem Battah
- Dipartimento di Scienze biotecnologiche di base, cliniche intensivologiche e perioperatorie – Sezione di Microbiologia, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Ivana Palucci
- Dipartimento di Scienze di Laboratorio e Infettivologiche, Fondazione Policlinico Universitario “A. Gemelli”, Rome, Italy
- Dipartimento di Scienze biotecnologiche di base, cliniche intensivologiche e perioperatorie – Sezione di Microbiologia, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Federica Marchionni
- Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, Rome, Italy
| | - Silvia Bellesi
- Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, Rome, Italy
| | - Valentina Palmieri
- Dipartimento di Neuroscienze, Università Cattolica del Sacro Cuore, Roma, Italy
| | - Massimiliano Papi
- Dipartimento di Neuroscienze, Università Cattolica del Sacro Cuore, Roma, Italy
- Fondazione Policlinico Universitario “A. Gemelli”, Rome, Italy
| | - Eliza Kramarska
- Institute of Biostructures and Bioimaging - CNR-IBB, Naples, Italy
| | - Maurizio Sanguinetti
- Dipartimento di Scienze di Laboratorio e Infettivologiche, Fondazione Policlinico Universitario “A. Gemelli”, Rome, Italy
- Dipartimento di Scienze biotecnologiche di base, cliniche intensivologiche e perioperatorie – Sezione di Microbiologia, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Michela Sali
- Dipartimento di Scienze di Laboratorio e Infettivologiche, Fondazione Policlinico Universitario “A. Gemelli”, Rome, Italy
- Dipartimento di Scienze biotecnologiche di base, cliniche intensivologiche e perioperatorie – Sezione di Microbiologia, Università Cattolica del Sacro Cuore, Rome, Italy
| | - Rita Berisio
- Institute of Biostructures and Bioimaging - CNR-IBB, Naples, Italy
| | - Giovanni Delogu
- Dipartimento di Scienze di Laboratorio e Infettivologiche, Fondazione Policlinico Universitario “A. Gemelli”, Rome, Italy
- Mater Olbia Hospital, Olbia, Italy
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6
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Pajuelo D, Tak U, Zhang L, Danilchanka O, Tischler AD, Niederweis M. Toxin secretion and trafficking by Mycobacterium tuberculosis. Nat Commun 2021; 12:6592. [PMID: 34782620 PMCID: PMC8593097 DOI: 10.1038/s41467-021-26925-1] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 10/27/2021] [Indexed: 12/30/2022] Open
Abstract
The tuberculosis necrotizing toxin (TNT) is the major cytotoxicity factor of Mycobacterium tuberculosis (Mtb) in macrophages. TNT is the C-terminal domain of the outer membrane protein CpnT and gains access to the cytosol to kill macrophages infected with Mtb. However, molecular mechanisms of TNT secretion and trafficking are largely unknown. A comprehensive analysis of the five type VII secretion systems of Mtb revealed that the ESX-4 system is required for export of CpnT and surface accessibility of TNT. Furthermore, the ESX-2 and ESX-4 systems are required for permeabilization of the phagosomal membrane in addition to the ESX-1 system. Thus, these three ESX systems need to act in concert to enable trafficking of TNT into the cytosol of Mtb-infected macrophages. These discoveries establish new molecular roles for the two previously uncharacterized type VII secretion systems ESX-2 and ESX-4 and reveal an intricate link between toxin secretion and phagosomal permeabilization by Mtb. The tuberculosis necrotizing toxin (TNT) is the major cytotoxicity factor of M. tuberculosis (Mtb). Mtb possesses five type VII secretion systems (ESX). Pajuelo et al. show that the ESX-4 system is required for TNT secretion and that ESX-2 and ESX-4 systems work in concert with ESX-1 to permeabilize the phagosomal membrane and enable trafficking of TNT into the cytoplasm of macrophages infected with Mtb.
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Affiliation(s)
- David Pajuelo
- Department of Microbiology, University of Alabama at Birmingham, 609 Bevill Biomedical Research Building, 845 19th Street South, Birmingham, AL, 35294, USA
| | - Uday Tak
- Department of Microbiology, University of Alabama at Birmingham, 609 Bevill Biomedical Research Building, 845 19th Street South, Birmingham, AL, 35294, USA.,University of Colorado Boulder, Jennie Smoly Caruthers Biotechnology Building B255, 3415 Colorado Avenue, Boulder, CO, 80303, USA
| | - Lei Zhang
- Department of Microbiology, University of Alabama at Birmingham, 609 Bevill Biomedical Research Building, 845 19th Street South, Birmingham, AL, 35294, USA
| | - Olga Danilchanka
- Department of Microbiology, University of Alabama at Birmingham, 609 Bevill Biomedical Research Building, 845 19th Street South, Birmingham, AL, 35294, USA.,Merck & Co., Inc., Cambridge, MA, 02141, USA
| | - Anna D Tischler
- Department of Microbiology and Immunology, University of Minnesota Twin Cities, Minneapolis, MN, 55455, USA
| | - Michael Niederweis
- Department of Microbiology, University of Alabama at Birmingham, 609 Bevill Biomedical Research Building, 845 19th Street South, Birmingham, AL, 35294, USA.
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7
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Rivera-Calzada A, Famelis N, Llorca O, Geibel S. Type VII secretion systems: structure, functions and transport models. Nat Rev Microbiol 2021; 19:567-584. [PMID: 34040228 DOI: 10.1038/s41579-021-00560-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/09/2021] [Indexed: 02/07/2023]
Abstract
Type VII secretion systems (T7SSs) have a key role in the secretion of effector proteins in non-pathogenic mycobacteria and pathogenic mycobacteria such as Mycobacterium tuberculosis, the main causative agent of tuberculosis. Tuberculosis-causing mycobacteria, still accounting for 1.4 million deaths annually, rely on paralogous T7SSs to survive in the host and efficiently evade its immune response. Although it is still unknown how effector proteins of T7SSs cross the outer membrane of the diderm mycobacterial cell envelope, recent advances in the structural characterization of these secretion systems have revealed the intricate network of interactions of conserved components in the plasma membrane. This structural information, added to recent advances in the molecular biology and regulation of mycobacterial T7SSs as well as progress in our understanding of their secreted effector proteins, is shedding light on the inner working of the T7SS machinery. In this Review, we highlight the implications of these studies and the derived transport models, which provide new scenarios for targeting the deathly human pathogen M. tuberculosis.
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Affiliation(s)
- Angel Rivera-Calzada
- Structural Biology Programme, Spanish National Cancer Research Centre (CNIO), Madrid, Spain.
| | - Nikolaos Famelis
- Institute for Molecular Infection Biology, Julius-Maximilian University of Würzburg, Würzburg, Germany.,Rudolf Virchow Center for Integrative and Translational Biomedicine, Julius-Maximilian University of Würzburg, Würzburg, Germany
| | - Oscar Llorca
- Structural Biology Programme, Spanish National Cancer Research Centre (CNIO), Madrid, Spain
| | - Sebastian Geibel
- Institute for Molecular Infection Biology, Julius-Maximilian University of Würzburg, Würzburg, Germany. .,Rudolf Virchow Center for Integrative and Translational Biomedicine, Julius-Maximilian University of Würzburg, Würzburg, Germany.
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8
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Lagune M, Petit C, Sotomayor FV, Johansen MD, Beckham KSH, Ritter C, Girard-Misguich F, Wilmanns M, Kremer L, Maurer FP, Herrmann JL. Conserved and specialized functions of Type VII secretion systems in non-tuberculous mycobacteria. MICROBIOLOGY-SGM 2021; 167. [PMID: 34224347 DOI: 10.1099/mic.0.001054] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Non-tuberculous mycobacteria (NTM) are a large group of micro-organisms comprising more than 200 individual species. Most NTM are saprophytic organisms and are found mainly in terrestrial and aquatic environments. In recent years, NTM have been increasingly associated with infections in both immunocompetent and immunocompromised individuals, prompting significant efforts to understand the diverse pathogenic and signalling traits of these emerging pathogens. Since the discovery of Type VII secretion systems (T7SS), there have been significant developments regarding the role of these complex systems in mycobacteria. These specialised systems, also known as Early Antigenic Secretion (ESX) systems, are employed to secrete proteins across the inner membrane. They also play an essential role in virulence, nutrient uptake and conjugation. Our understanding of T7SS in mycobacteria has significantly benefited over the last few years, from the resolution of ESX-3 structure in Mycobacterium smegmatis, to ESX-5 structures in Mycobacterium xenopi and Mycobacterium tuberculosis. In addition, ESX-4, considered until recently as a non-functional system in both pathogenic and non-pathogenic mycobacteria, has been proposed to play an important role in the virulence of Mycobacterium abscessus; an increasingly recognized opportunistic NTM causing severe lung diseases. These major findings have led to important new insights into the functional mechanisms of these biological systems, their implication in virulence, nutrient acquisitions and cell wall shaping, and will be discussed in this review.
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Affiliation(s)
- Marion Lagune
- Université Paris-Saclay, UVSQ, Inserm, Infection et inflammation, 78180, Montigny-Le-Bretonneux, France
| | - Cecile Petit
- European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany
| | - Flor Vásquez Sotomayor
- National and WHO Supranational Reference Center for Mycobacteria, Research Center Borstel, Leibniz Lung Center, Borstel, Germany
| | - Matt D Johansen
- Centre National de la Recherche Scientifique UMR 9004, Institut de Recherche en Infectiologie de Montpellier (IRIM), Université de Montpellier, 1919 route de Mende, 34293, Montpellier, France.,Present address: Centre for Inflammation, Centenary Institute and University of Technology Sydney, Faculty of Science, Sydney, NSW, Australia
| | - Kathrine S H Beckham
- European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany
| | - Christina Ritter
- European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany
| | - Fabienne Girard-Misguich
- Université Paris-Saclay, UVSQ, Inserm, Infection et inflammation, 78180, Montigny-Le-Bretonneux, France
| | - Matthias Wilmanns
- European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany.,University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20251 Hamburg, Germany
| | - Laurent Kremer
- Centre National de la Recherche Scientifique UMR 9004, Institut de Recherche en Infectiologie de Montpellier (IRIM), Université de Montpellier, 1919 route de Mende, 34293, Montpellier, France.,INSERM, IRIM, 34293 Montpellier, France
| | - Florian P Maurer
- National and WHO Supranational Reference Center for Mycobacteria, Research Center Borstel, Leibniz Lung Center, Borstel, Germany.,Institute of Medical Microbiology, Virology and Hospital Hygiene, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Jean-Louis Herrmann
- Université Paris-Saclay, UVSQ, Inserm, Infection et inflammation, 78180, Montigny-Le-Bretonneux, France.,APHP, GHU Paris-Saclay, Hôpital Raymond Poincaré, Service de Microbiologie, Garches, France
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9
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Abstract
The type VII protein secretion system (T7SS) of Staphylococcus aureus is encoded at the ess locus. T7 substrate recognition and protein transport are mediated by EssC, a membrane-bound multidomain ATPase. Four EssC sequence variants have been identified across S. aureus strains, each accompanied by a specific suite of substrate proteins. The ess genes are upregulated during persistent infection, and the secretion system contributes to virulence in disease models. It also plays a key role in intraspecies competition, secreting nuclease and membrane-depolarizing toxins that inhibit the growth of strains lacking neutralizing immunity proteins. A genomic survey indicates that the T7SS is widely conserved across staphylococci and is encoded in clusters that contain diverse arrays of toxin and immunity genes. The presence of genomic islands encoding multiple immunity proteins in species such as Staphylococcus warneri that lack the T7SS points to a major role for the secretion system in bacterial antagonism. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Lisa Bowman
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom; ,
| | - Tracy Palmer
- Microbes in Health and Disease Theme, Newcastle University Biosciences Institute, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom; ,
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10
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Bunduc CM, Fahrenkamp D, Wald J, Ummels R, Bitter W, Houben ENG, Marlovits TC. Structure and dynamics of a mycobacterial type VII secretion system. Nature 2021; 593:445-448. [PMID: 33981042 PMCID: PMC8131196 DOI: 10.1038/s41586-021-03517-z] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 04/06/2021] [Indexed: 11/20/2022]
Abstract
Mycobacterium tuberculosis is the cause of one of the most important infectious diseases in humans, which leads to 1.4 million deaths every year1. Specialized protein transport systems-known as type VII secretion systems (T7SSs)-are central to the virulence of this pathogen, and are also crucial for nutrient and metabolite transport across the mycobacterial cell envelope2,3. Here we present the structure of an intact T7SS inner-membrane complex of M. tuberculosis. We show how the 2.32-MDa ESX-5 assembly, which contains 165 transmembrane helices, is restructured and stabilized as a trimer of dimers by the MycP5 protease. A trimer of MycP5 caps a central periplasmic dome-like chamber that is formed by three EccB5 dimers, with the proteolytic sites of MycP5 facing towards the cavity. This chamber suggests a central secretion and processing conduit. Complexes without MycP5 show disruption of the EccB5 periplasmic assembly and increased flexibility, which highlights the importance of MycP5 for complex integrity. Beneath the EccB5-MycP5 chamber, dimers of the EccC5 ATPase assemble into three bundles of four transmembrane helices each, which together seal the potential central secretion channel. Individual cytoplasmic EccC5 domains adopt two distinctive conformations that probably reflect different secretion states. Our work suggests a previously undescribed mechanism of protein transport and provides a structural scaffold to aid in the development of drugs against this major human pathogen.
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Affiliation(s)
- Catalin M Bunduc
- Centre for Structural Systems Biology, Hamburg, Germany
- Institute of Structural and Systems Biology, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany
- Deutsches Elektron Synchrotron DESY, Hamburg, Germany
- Molecular Microbiology Section, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Dirk Fahrenkamp
- Centre for Structural Systems Biology, Hamburg, Germany
- Institute of Structural and Systems Biology, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany
- Deutsches Elektron Synchrotron DESY, Hamburg, Germany
| | - Jiri Wald
- Centre for Structural Systems Biology, Hamburg, Germany
- Institute of Structural and Systems Biology, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany
- Deutsches Elektron Synchrotron DESY, Hamburg, Germany
| | - Roy Ummels
- Department of Medical Microbiology and Infection Control, Amsterdam Infection and Immunity Institute, Amsterdam UMC, Amsterdam, The Netherlands
| | - Wilbert Bitter
- Molecular Microbiology Section, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
- Department of Medical Microbiology and Infection Control, Amsterdam Infection and Immunity Institute, Amsterdam UMC, Amsterdam, The Netherlands
| | - Edith N G Houben
- Molecular Microbiology Section, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Thomas C Marlovits
- Centre for Structural Systems Biology, Hamburg, Germany.
- Institute of Structural and Systems Biology, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.
- Deutsches Elektron Synchrotron DESY, Hamburg, Germany.
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11
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Tran HKR, Grebenc DW, Klein TA, Whitney JC. Bacterial type VII secretion: An important player in host-microbe and microbe-microbe interactions. Mol Microbiol 2021; 115:478-489. [PMID: 33410158 DOI: 10.1111/mmi.14680] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2020] [Revised: 01/03/2021] [Accepted: 01/04/2021] [Indexed: 12/19/2022]
Abstract
Type VII secretion systems (T7SSs) are poorly understood protein export apparatuses found in mycobacteria and many species of Gram-positive bacteria. To date, this pathway has predominantly been studied in Mycobacterium tuberculosis, where it has been shown to play an essential role in virulence; however, much less studied is an evolutionarily divergent subfamily of T7SSs referred to as the T7SSb. The T7SSb is found in the major Gram-positive phylum Firmicutes where it was recently shown to target both eukaryotic and prokaryotic cells, suggesting a dual role for this pathway in host-microbe and microbe-microbe interactions. In this review, we compare the current understanding of the molecular architectures and substrate repertoires of the well-studied mycobacterial T7SSa systems to that of recently characterized T7SSb pathways and highlight how these differences may explain the observed biological functions of this understudied protein export machine.
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Affiliation(s)
- Hiu-Ki R Tran
- Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, ON, Canada.,Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
| | - Dirk W Grebenc
- Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, ON, Canada.,Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
| | - Timothy A Klein
- Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, ON, Canada.,Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada
| | - John C Whitney
- Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, ON, Canada.,Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada.,David Braley Centre for Antibiotic Discovery, McMaster University, Hamilton, ON, Canada
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Bunduc CM, Bitter W, Houben E. Structure and Function of the Mycobacterial Type VII Secretion Systems. Annu Rev Microbiol 2020; 74:315-335. [DOI: 10.1146/annurev-micro-012420-081657] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Bacteria have evolved intricate secretion machineries for the successful delivery of large molecules across their cell envelopes. Such specialized secretion systems allow a variety of bacteria to thrive in specific host environments. In mycobacteria, type VII secretion systems (T7SSs) are dedicated protein transport machineries that fulfill diverse and crucial roles, ranging from metabolite uptake to immune evasion and subversion to conjugation. Since the discovery of mycobacterial T7SSs about 15 y ago, genetic, structural, and functional studies have provided insight into the roles and functioning of these secretion machineries. Here, we focus on recent advances in the elucidation of the structure and mechanism of mycobacterial T7SSs in protein secretion. As many of these systems are essential for mycobacterial growth or virulence, they provide opportunities for the development of novel therapies to combat a number of relevant mycobacterial diseases.
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Affiliation(s)
- Catalin M. Bunduc
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HZ Amsterdam, The Netherlands
| | - W. Bitter
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HZ Amsterdam, The Netherlands
- Department of Medical Microbiology and Infection Control, Amsterdam Infection and Immunity Institute, Amsterdam University Medical Centers, 1007 MB Amsterdam, The Netherlands
| | - E.N.G. Houben
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HZ Amsterdam, The Netherlands
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13
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Damen MPM, Phan TH, Ummels R, Rubio-Canalejas A, Bitter W, Houben ENG. Modification of a PE/PPE substrate pair reroutes an Esx substrate pair from the mycobacterial ESX-1 type VII secretion system to the ESX-5 system. J Biol Chem 2020; 295:5960-5969. [PMID: 32184351 DOI: 10.1074/jbc.ra119.011682] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 03/13/2020] [Indexed: 01/20/2023] Open
Abstract
Bacterial type VII secretion systems secrete a wide range of extracellular proteins that play important roles in bacterial viability and in interactions of pathogenic mycobacteria with their hosts. Mycobacterial type VII secretion systems consist of five subtypes, ESX-1-5, and have four substrate classes, namely, Esx, PE, PPE, and Esp proteins. At least some of these substrates are secreted as heterodimers. Each ESX system mediates the secretion of a specific set of Esx, PE, and PPE proteins, raising the question of how these substrates are recognized in a system-specific fashion. For the PE/PPE heterodimers, it has been shown that they interact with their cognate EspG chaperone and that this chaperone determines the designated secretion pathway. However, both structural and pulldown analyses have suggested that EspG cannot interact with the Esx proteins. Therefore, the determining factor for system specificity of the Esx proteins remains unknown. Here, we investigated the secretion specificity of the ESX-1 substrate pair EsxB_1/EsxA_1 in Mycobacterium marinum Although this substrate pair was hardly secreted when homologously expressed, it was secreted when co-expressed together with the PE35/PPE68_1 pair, indicating that this pair could stimulate secretion of the EsxB_1/EsxA_1 pair. Surprisingly, co-expression of EsxB_1/EsxA_1 with a modified PE35/PPE68_1 version that carried the EspG5 chaperone-binding domain, previously shown to redirect this substrate pair to the ESX-5 system, also resulted in redirection and co-secretion of the Esx pair via ESX-5. Our results suggest a secretion model in which PE35/PPE68_1 determines the system-specific secretion of EsxB_1/EsxA_1.
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Affiliation(s)
- Merel P M Damen
- Section Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Trang H Phan
- Section Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Roy Ummels
- Department of Medical Microbiology and Infection Control, Amsterdam Infection & Immunity Institute, Amsterdam University Medical Centers, 1081 HV Amsterdam, The Netherlands
| | - Alba Rubio-Canalejas
- Section Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands
| | - Wilbert Bitter
- Department of Medical Microbiology and Infection Control, Amsterdam Infection & Immunity Institute, Amsterdam University Medical Centers, 1081 HV Amsterdam, The Netherlands
| | - Edith N G Houben
- Section Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands.
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Bunduc CM, Ummels R, Bitter W, Houben ENG. Species-specific secretion of ESX-5 type VII substrates is determined by the linker 2 of EccC 5. Mol Microbiol 2020; 114:66-76. [PMID: 32096294 PMCID: PMC7384006 DOI: 10.1111/mmi.14496] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Revised: 02/21/2020] [Indexed: 12/20/2022]
Abstract
Mycobacteria use type VII secretion systems (T7SSs) to translocate a wide range of proteins across their diderm cell envelope. These systems, also called ESX systems, are crucial for the viability and/or virulence of mycobacterial pathogens, including Mycobacterium tuberculosis and the fish pathogen Mycobacterium marinum. We have previously shown that the M. tuberculosis ESX-5 system is unable to fully complement secretion in an M. marinum esx-5 mutant, suggesting species specificity in secretion. In this study, we elaborated on this observation and established that the membrane ATPase EccC5 , possessing four (putative) nucleotide-binding domains (NBDs), is responsible for this. By creating M. marinum-M. tuberculosis EccC5 chimeras, we observed both in M. marinum and in M. tuberculosis that secretion specificity of PE_PGRS proteins depends on the presence of the cognate linker 2 domain of EccC5 . This region connects NBD1 and NBD2 of EccC5 and is responsible for keeping NBD1 in an inhibited state. Notably, the ESX-5 substrate EsxN, predicted to bind to NBD3 on EccC5 , showed a distinct secretion profile. These results indicate that linker 2 is involved in species-specific substrate recognition and might therefore be an additional substrate recognition site of EccC5 .
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Affiliation(s)
- Catalin M Bunduc
- Section Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Roy Ummels
- Department of Medical Microbiology and Infection Control, Amsterdam Infection & Immunity Institute, Amsterdam UMC, Amsterdam, The Netherlands
| | - Wilbert Bitter
- Section Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.,Department of Medical Microbiology and Infection Control, Amsterdam Infection & Immunity Institute, Amsterdam UMC, Amsterdam, The Netherlands
| | - Edith N G Houben
- Section Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
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