title: Structure of the mycobacterial ESX-5 type VII secretion system membrane complex by single-particle analysis.
abstract: Mycobacteria are characterized by their impermeable outer membrane, which is rich in mycolic acids1. To transport substrates across this complex cell envelope, mycobacteria rely on type VII (also known as ESX) secretion systems2. In Mycobacterium tuberculosis, these ESX systems are essential for growth and full virulence and therefore represent an attractive target for anti-tuberculosis drugs3. However, the molecular details underlying type VII secretion are largely unknown, due to a lack of structural information. Here, we report the molecular architecture of the ESX-5 membrane complex from Mycobacterium xenopi determined at 13 Å resolution by electron microscopy. The four core proteins of the ESX-5 complex (EccB5, EccC5, EccD5and EccE5) assemble with equimolar stoichiometry into an oligomeric assembly that displays six-fold symmetry. This membrane-associated complex seems to be embedded exclusively in the inner membrane, which indicates that additional components are required to translocate substrates across the mycobacterial outer membrane. Furthermore, the extended cytosolic domains of the EccC ATPase, which interact with secretion effectors, are highly flexible, suggesting an as yet unseen mode of substrate interaction. Comparison of our results with known structures of other bacterial secretion systems demonstrates that the architecture of type VII secretion system is fundamentally different, suggesting an alternative secretion mechanism.
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany.
authors.forename: Katherine S H
authors.identifier: http://orcid.org/0000-0002-4929-6119
authors.initials: KS
authors.lastname: Beckham
authors.affiliation: Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Campus-Vienna-Biocenter 1, 1030 Vienna, Austria.|Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria.|University Medical Centre Hamburg-Eppendorf (UKE), Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: Luciano
authors.initials: L
authors.lastname: Ciccarelli
authors.affiliation: Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands.
authors.forename: Catalin M
authors.initials: CM
authors.lastname: Bunduc
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany.
authors.forename: Haydyn D T
authors.initials: HD
authors.lastname: Mertens
authors.affiliation: VU University Medical Center, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands.
authors.forename: Roy
authors.initials: R
authors.lastname: Ummels
authors.affiliation: Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Campus-Vienna-Biocenter 1, 1030 Vienna, Austria.|Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria.|University Medical Centre Hamburg-Eppendorf (UKE), Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lugmayr
authors.affiliation: Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Campus-Vienna-Biocenter 1, 1030 Vienna, Austria.|Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria.|University Medical Centre Hamburg-Eppendorf (UKE), Martinistraße 52, 20246 Hamburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Mayr
authors.affiliation: European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany.
authors.forename: Mandy
authors.initials: M
authors.lastname: Rettel
authors.affiliation: European Molecular Biology Laboratory, Meyerhofstraße 1, 69117 Heidelberg, Germany.
authors.forename: Mikhail M
authors.initials: MM
authors.lastname: Savitski
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany.
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
authors.affiliation: Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands.|VU University Medical Center, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands.
authors.forename: Wilbert
authors.initials: W
authors.lastname: Bitter
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany.|University Medical Centre Hamburg-Eppendorf (UKE), Martinistraße 52, 20246 Hamburg, Germany.|Centre for Structural Systems Biology (CSSB), Notkestraße 85, 22607 Hamburg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Wilmanns
authors.affiliation: Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Campus-Vienna-Biocenter 1, 1030 Vienna, Austria.|Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria.|University Medical Centre Hamburg-Eppendorf (UKE), Martinistraße 52, 20246 Hamburg, Germany.|Centre for Structural Systems Biology (CSSB), Notkestraße 85, 22607 Hamburg, Germany.|Deutsches Elektronen-Synchrotron (DESY), Notkestraße 85, 22607 Hamburg, Germany.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Marlovits
authors.affiliation: European Molecular Biology Laboratory, Hamburg Unit, Notkestraße 85, 22607 Hamburg, Germany.
authors.forename: Annabel H A
authors.identifier: http://orcid.org/0000-0003-0635-8890
authors.initials: AH
authors.lastname: Parret
authors.affiliation: Vrije Universiteit Amsterdam, De Boelelaan 1108, 1081 HZ Amsterdam, The Netherlands.
authors.forename: Edith N G
authors.initials: EN
authors.lastname: Houben
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism; D000942:Antigens, Bacterial / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D055032:Electron Microscope Tomography; D009169:Mycobacterium tuberculosis / Q000737:chemistry* / Q000235:genetics / Q000472:pathogenicity; D000069377:Type VII Secretion Systems / Q000737:chemistry* / Q000235:genetics* / Q000648:ultrastructure
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D000069377:Type VII Secretion Systems; D000251:Adenosine Triphosphatases