title: Spa32 regulates a switch in substrate specificity of the type III secreton of Shigella flexneri from needle components to Ipa proteins.
abstract: Type III secretion systems (TTSS) are essential virulence determinants of many gram-negative bacteria and serve, upon physical contact with target cells, to translocate bacterial proteins directly across eukaryotic cell membranes. The Shigella TTSS is encoded by the mxi/spa loci located on its virulence plasmid. By electron microscopy secretons are visualized as tripartite with an external needle, a transmembrane domain, and a cytoplasmic bulb. In the present study, we generated a Shigella spa32 mutant and studied its phenotype. The spa32 gene shows low sequence homology to Salmonella TTSS1 invJ/spaN and to flagellar fliK. The spa32 mutant, like the wild-type strain, secreted the Ipas and IpgD, which are normally secreted via the TTSS, at low levels into the growth medium. However, unlike the wild-type strain, the spa32 mutant could neither be induced to secrete the Ipas and IpgD instantaneously upon addition of Congo red nor penetrate HeLa cells in vitro. Additionally, the Spa32 protein is secreted in large amounts by the TTSS during exponential growth but not upon Congo red induction. Interestingly, electron microscopy analysis of the spa32 mutant revealed that the needle of its secretons were up to 10 times longer than those of the wild type. In addition, in the absence of induction, the spa32 mutant secreted normal levels of MxiI but a large excess of MxiH. Taken together, our data indicate that the spa32 mutant presents a novel phenotype and that the primary defect of the mutant may be its inability to regulate or control secretion of MxiH.
authors.affiliation: Laboratoire de Bactériologie Moléculaire, Faculté de Médecine, Université Libre de Bruxelles, 1070 Brussels, Belgium.
authors.forename: Juana
authors.initials: J
authors.lastname: Magdalena
authors.forename: Abderrahman
authors.initials: A
authors.lastname: Hachani
authors.forename: Mustapha
authors.initials: M
authors.lastname: Chamekh
authors.forename: Noureddine
authors.initials: N
authors.lastname: Jouihri
authors.forename: Pierre
authors.initials: P
authors.lastname: Gounon
authors.forename: Ariel
authors.initials: A
authors.lastname: Blocker
authors.forename: Abdelmounaaïm
authors.initials: A
authors.lastname: Allaoui
mesh_terms: D018829:Adhesins, Bacterial; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004396:Coloring Agents / Q000378:metabolism; D003224:Congo Red / Q000378:metabolism; D006367:HeLa Cells / Q000382:microbiology; D006801:Humans; D008565:Membrane Proteins; D008854:Microscopy, Electron; D009154:Mutation; D012763:Shigella flexneri / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D013379:Substrate Specificity
chemical_list: D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D004396:Coloring Agents; D008565:Membrane Proteins; C413572:MxiH protein, Shigella; C459782:MxiI protein, Shigella flexneri; C450427:Spa32 protein, Shigella flexneri; C053476:invasin, Yersinia; D003224:Congo Red