title: Structural and Functional Characterization of the Bacterial Type III Secretion Export Apparatus.
abstract: Bacterial type III protein secretion systems inject effector proteins into eukaryotic host cells in order to promote survival and colonization of Gram-negative pathogens and symbionts. Secretion across the bacterial cell envelope and injection into host cells is facilitated by a so-called injectisome. Its small hydrophobic export apparatus components SpaP and SpaR were shown to nucleate assembly of the needle complex and to form the central "cup" substructure of a Salmonella Typhimurium secretion system. However, the in vivo placement of these components in the needle complex and their function during the secretion process remained poorly defined. Here we present evidence that a SpaP pentamer forms a 15 Å wide pore and provide a detailed map of SpaP interactions with the export apparatus components SpaQ, SpaR, and SpaS. We further refine the current view of export apparatus assembly, consolidate transmembrane topology models for SpaP and SpaR, and present intimate interactions of the periplasmic domains of SpaP and SpaR with the inner rod protein PrgJ, indicating how export apparatus and needle filament are connected to create a continuous conduit for substrate translocation.
authors.affiliation: University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Section of Cellular and Molecular Microbiology, Tübingen, Germany.
authors.forename: Tobias
authors.identifier: http://orcid.org/0000-0002-7524-3520
authors.initials: T
authors.lastname: Dietsche
authors.affiliation: University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Section of Cellular and Molecular Microbiology, Tübingen, Germany.
authors.forename: Mehari
authors.initials: M
authors.lastname: Tesfazgi Mebrhatu
authors.affiliation: Center for Structural Systems Biology (CSSB), University Medical Center Hamburg-Eppendorf (UKE) and German Electron Synchrotron Centre (DESY), Hamburg, Germany.|Institute of Molecular Biotechnology (IMBA), Vienna Biocenter (VBC), Vienna, Austria.|Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria.
authors.forename: Matthias J
authors.initials: MJ
authors.lastname: Brunner
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
authors.forename: Patrizia
authors.identifier: http://orcid.org/0000-0002-9204-0856
authors.initials: P
authors.lastname: Abrusci
authors.affiliation: Department of Chemistry, University of Oxford, Oxford, United Kingdom.
authors.forename: Jun
authors.initials: J
authors.lastname: Yan
authors.affiliation: University of Tübingen, Proteome Center Tübingen, Tübingen, Germany.
authors.forename: Mirita
authors.initials: M
authors.lastname: Franz-Wachtel
authors.affiliation: University of Tübingen, Center for BioinformaticsTübingen, Germany.
authors.forename: Charlotta
authors.initials: C
authors.lastname: Schärfe
authors.affiliation: University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Section of Cellular and Molecular Microbiology, Tübingen, Germany.
authors.forename: Susann
authors.identifier: http://orcid.org/0000-0003-1403-399X
authors.initials: S
authors.lastname: Zilkenat
authors.affiliation: University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Section of Cellular and Molecular Microbiology, Tübingen, Germany.
authors.forename: Iwan
authors.initials: I
authors.lastname: Grin
authors.affiliation: Yale University School of Medicine, Department of Microbial Pathogenesis, New Haven, Connecticut, United States of America.
authors.forename: Jorge E
authors.initials: JE
authors.lastname: Galán
authors.affiliation: University of Tübingen, Center for BioinformaticsTübingen, Germany.|Max Planck Institute for Developmental Biology, Biomolecular Interactions, Tübingen, Germany.
authors.forename: Oliver
authors.identifier: http://orcid.org/0000-0003-1739-4598
authors.initials: O
authors.lastname: Kohlbacher
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
authors.forename: Susan
authors.identifier: http://orcid.org/0000-0001-9287-8053
authors.initials: S
authors.lastname: Lea
authors.affiliation: University of Tübingen, Proteome Center Tübingen, Tübingen, Germany.
authors.forename: Boris
authors.initials: B
authors.lastname: Macek
authors.affiliation: Center for Structural Systems Biology (CSSB), University Medical Center Hamburg-Eppendorf (UKE) and German Electron Synchrotron Centre (DESY), Hamburg, Germany.|Institute of Molecular Biotechnology (IMBA), Vienna Biocenter (VBC), Vienna, Austria.|Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Marlovits
authors.affiliation: Department of Chemistry, University of Oxford, Oxford, United Kingdom.
authors.forename: Carol V
authors.initials: CV
authors.lastname: Robinson
authors.affiliation: University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Section of Cellular and Molecular Microbiology, Tübingen, Germany.|German Center for Infection Research (DZIF), Partner-site Tübingen, Tübingen, Germany.
authors.forename: Samuel
authors.identifier: http://orcid.org/0000-0003-1808-3556
authors.initials: S
authors.lastname: Wagner
mesh_terms: D002850:Chromatography, Gel; D007091:Image Processing, Computer-Assisted; D015151:Immunoblotting; D013058:Mass Spectrometry; D008854:Microscopy, Electron; D012486:Salmonella typhimurium / Q000378:metabolism* / Q000648:ultrastructure*; D000069296:Type III Secretion Systems / Q000378:metabolism* / Q000648:ultrastructure*
chemical_list: D000069296:Type III Secretion Systems