title: Shigella Spa33 is an essential C-ring component of type III secretion machinery.
abstract: Type III secretion machinery (TTSM), composed of a needle, a basal body, and a C-ring compartment, delivers a subset of effectors into host cells. Here, we show that Shigella Spa33 is an essential component of the C-ring compartment involved in mediating the transit of various TTSM-associated translocated proteins. Electron microscopic analysis and pull-down assay revealed Spa33 to be localized beneath the TTSM via interaction with MxiG and MxiJ (basal body components). Spa33 is also capable of interacting with Spa47 (TTSM ATPase), MxiK, MxiN (required for the transit of MxiH, the needle component), Spa32 (required for determining needle length), and several effectors. Genetic and functional analyses of the Spa33 C-terminal region, which is highly conserved in the SpaO-YscQ-HrcQ(B)-FliN family, indicate that some of the conserved residues are crucial for needle formation via interactions with MxiN. Thus, Spa33 plays a central role as the C-ring component in recruiting/exporting TTSM-associated proteins.
authors.affiliation: Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, International Research Center for Infectious Diseases, 4-6-1, Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Morita-Ishihara
authors.forename: Michinaga
authors.initials: M
authors.lastname: Ogawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sagara
authors.forename: Mitutaka
authors.initials: M
authors.lastname: Yoshida
authors.forename: Eisaku
authors.initials: E
authors.lastname: Katayama
authors.forename: Chihiro
authors.initials: C
authors.lastname: Sasakawa
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012763:Shigella flexneri / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure*
chemical_list: D001426:Bacterial Proteins; D000251:Adenosine Triphosphatases; C478167:Spa47 protein, Shigella flexneri