title: Protein refolding is required for assembly of the type three secretion needle.
abstract: Pathogenic Gram-negative bacteria use a type three secretion system (TTSS) to deliver virulence factors into host cells. Although the order in which proteins incorporate into the growing TTSS is well described, the underlying assembly mechanisms are still unclear. Here we show that the TTSS needle protomer refolds spontaneously to extend the needle from the distal end. We developed a functional mutant of the needle protomer from Shigella flexneri and Salmonella typhimurium to study its assembly in vitro. We show that the protomer partially refolds from alpha-helix into beta-strand conformation to form the TTSS needle. Reconstitution experiments show that needle growth does not require ATP. Thus, like the structurally related flagellar systems, the needle elongates by subunit polymerization at the distal end but requires protomer refolding. Our studies provide a starting point to understand the molecular assembly mechanisms and the structure of the TTSS at atomic level.
authors.affiliation: Max-Planck-Institute for Infection Biology, Cellular Microbiology, Berlin, Germany.
authors.forename: Omer
authors.initials: O
authors.lastname: Poyraz
authors.forename: Holger
authors.initials: H
authors.lastname: Schmidt
authors.forename: Karsten
authors.initials: K
authors.lastname: Seidel
authors.forename: Friedmar
authors.initials: F
authors.lastname: Delissen
authors.forename: Christian
authors.initials: C
authors.lastname: Ader
authors.forename: Hezi
authors.initials: H
authors.lastname: Tenenboim
authors.forename: Christian
authors.initials: C
authors.lastname: Goosmann
authors.forename: Britta
authors.initials: B
authors.lastname: Laube
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Thünemann
authors.forename: Arturo
authors.initials: A
authors.lastname: Zychlinsky
authors.forename: Marc
authors.initials: M
authors.lastname: Baldus
authors.forename: Adam
authors.initials: A
authors.lastname: Lange
authors.forename: Christian
authors.initials: C
authors.lastname: Griesinger
authors.forename: Michael
authors.initials: M
authors.lastname: Kolbe
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012486:Salmonella typhimurium / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D012763:Shigella flexneri / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; C413572:MxiH protein, Shigella