title: Three-dimensional reconstruction of the Shigella T3SS transmembrane regions reveals 12-fold symmetry and novel features throughout.
abstract: Type III secretion systems (T3SSs) mediate bacterial protein translocation into eukaryotic cells, a process essential for virulence of many Gram-negative pathogens. They are composed of a cytoplasmic secretion machinery and a base that bridges both bacterial membranes, into which a hollow, external needle is embedded. When isolated, the latter two parts are termed the 'needle complex'. An incomplete understanding of the structure of the needle complex has hampered studies of T3SS function. To estimate the stoichiometry of its components, we measured the mass of its subdomains by scanning transmission electron microscopy (STEM). We determined subunit symmetries by analysis of top and side views within negatively stained samples in low-dose transmission electron microscopy (TEM). Application of 12-fold symmetry allowed generation of a 21-25-A resolution, three-dimensional reconstruction of the needle complex base, revealing many new features and permitting tentative docking of the crystal structure of EscJ, an inner membrane component.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, UK.
authors.forename: Julie L
authors.initials: JL
authors.lastname: Hodgkinson
authors.forename: Ashley
authors.initials: A
authors.lastname: Horsley
authors.forename: David
authors.initials: D
authors.lastname: Stabat
authors.forename: Martha
authors.initials: M
authors.lastname: Simon
authors.forename: Steven
authors.initials: S
authors.lastname: Johnson
authors.forename: Paula C A
authors.initials: PC
authors.lastname: da Fonseca
authors.forename: Edward P
authors.initials: EP
authors.lastname: Morris
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Wall
authors.forename: Susan M
authors.initials: SM
authors.lastname: Lea
authors.forename: Ariel J
authors.initials: AJ
authors.lastname: Blocker
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002462:Cell Membrane / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D017348:Microscopy, Electron, Scanning Transmission; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D012633:Secretin / Q000737:chemistry / Q000378:metabolism; D012763:Shigella flexneri / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D012633:Secretin