title: The needle component of the type III secreton of Shigella regulates the activity of the secretion apparatus.
abstract: Gram-negative bacteria commonly interact with eukaryotic host cells by using type III secretion systems (TTSSs or secretons). TTSSs serve to transfer bacterial proteins into host cells. Two translocators, IpaB and IpaC, are first inserted with the aid of IpaD by Shigella into the host cell membrane. Then at least two supplementary effectors of cell invasion, IpaA and IpgD, are transferred into the host cytoplasm. How TTSSs are induced to secrete is unknown, but their activation appears to require direct contact of the external distal tip of the apparatus with the host cell. The extracellular domain of the TTSS is a hollow needle protruding 60 nm beyond the bacterial surface. The monomeric unit of the Shigella flexneri needle, MxiH, forms a superhelical assembly. To probe the role of the needle in the activation of the TTSS for secretion, we examined the structure-function relationship of MxiH by mutagenesis. Most point mutations led to normal needle assembly, but some led to polymerization or possible length control defects. In other mutants, secretion was constitutively turned "on." In a further set, it was "constitutively on" but experimentally "uninducible." Finally, upon induction of secretion, some mutants released only the translocators and not the effectors. Most types of mutants were defective in interactions with host cells. Together, these data indicate that the needle directly controls the activity of the TTSS and suggest that it may be used to "sense" host cells.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom.
authors.forename: Roma
authors.initials: R
authors.lastname: Kenjale
authors.forename: Justin
authors.initials: J
authors.lastname: Wilson
authors.forename: Sebastian F
authors.initials: SF
authors.lastname: Zenk
authors.forename: Saroj
authors.initials: S
authors.lastname: Saurya
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Picking
authors.forename: William D
authors.initials: WD
authors.lastname: Picking
authors.forename: Ariel
authors.initials: A
authors.lastname: Blocker
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005408:Flagellin / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D010641:Phenotype; D017354:Point Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid; D012763:Shigella flexneri / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C095770:IpaD protein, Shigella flexneri; C413572:MxiH protein, Shigella; C087447:ipaB protein, Shigella; C092342:IpaC protein, Shigella; D005408:Flagellin