title: IpaD is localized at the tip of the Shigella flexneri type III secretion apparatus.
abstract: Type III secretion (T3S) systems are used by numerous Gram-negative pathogenic bacteria to inject virulence proteins into animal and plant host cells. The core of the T3S apparatus, known as the needle complex, is composed of a basal body transversing both bacterial membranes and a needle protruding above the bacterial surface. In Shigella flexneri, IpaD is required to inhibit the activity of the T3S apparatus prior to contact of bacteria with host and has been proposed to assist translocation of bacterial proteins into host cells. We investigated the localization of IpaD by electron microscopy analysis of cross-linked bacteria and mildly purified needle complexes. This analysis revealed the presence of a distinct density at the needle tip. A combination of single particle analysis, immuno-labeling and biochemical analysis, demonstrated that IpaD forms part of the structure at the needle tip. Anti-IpaD antibodies were shown to block entry of bacteria into epithelial cells.
authors.affiliation: Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. m.sani@rug.nl
authors.forename: Musa
authors.initials: M
authors.lastname: Sani
authors.forename: Anne
authors.initials: A
authors.lastname: Botteaux
authors.forename: Claude
authors.initials: C
authors.lastname: Parsot
authors.forename: Philippe
authors.initials: P
authors.lastname: Sansonetti
authors.forename: Egbert J
authors.initials: EJ
authors.lastname: Boekema
authors.forename: Abdelmounaaïm
authors.initials: A
authors.lastname: Allaoui
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D000942:Antigens, Bacterial / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism* / Q000648:ultrastructure; D004847:Epithelial Cells / Q000382:microbiology*; D006801:Humans; D008854:Microscopy, Electron; D012763:Shigella flexneri / Q000378:metabolism / Q000472:pathogenicity / Q000648:ultrastructure; D014774:Virulence
chemical_list: D000906:Antibodies; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C095770:IpaD protein, Shigella flexneri