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PLoS Pathog. 2016 Dec 15;12(12):e1006071. doi: 10.1371/journal.ppat.1006071. eCollection 2016 Dec.

Structural and Functional Characterization of the Bacterial Type III Secretion Export Apparatus.

Author information

1
University of Tübingen, Interfaculty Institute of Microbiology and Infection Medicine (IMIT), Section of Cellular and Molecular Microbiology, Tübingen, Germany.
2
Center for Structural Systems Biology (CSSB), University Medical Center Hamburg-Eppendorf (UKE) and German Electron Synchrotron Centre (DESY), Hamburg, Germany.
3
Institute of Molecular Biotechnology (IMBA), Vienna Biocenter (VBC), Vienna, Austria.
4
Research Institute of Molecular Pathology (IMP), Vienna Biocenter (VBC), Vienna, Austria.
5
Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
6
Department of Chemistry, University of Oxford, Oxford, United Kingdom.
7
University of Tübingen, Proteome Center Tübingen, Tübingen, Germany.
8
University of Tübingen, Center for BioinformaticsTübingen, Germany.
9
Yale University School of Medicine, Department of Microbial Pathogenesis, New Haven, Connecticut, United States of America.
10
Max Planck Institute for Developmental Biology, Biomolecular Interactions, Tübingen, Germany.
11
German Center for Infection Research (DZIF), Partner-site Tübingen, Tübingen, Germany.

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.

PMID:
27977800
PMCID:
PMC5158082
DOI:
10.1371/journal.ppat.1006071
[Indexed for MEDLINE]
Free PMC Article

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