Protein refolding is required for assembly of the type three secretion needle.
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.
Poyraz
Omer
O
Max-Planck-Institute for Infection Biology, Cellular Microbiology, Berlin, Germany.
Schmidt
Holger
H
Seidel
Karsten
K
Delissen
Friedmar
F
Ader
Christian
C
Tenenboim
Hezi
H
Goosmann
Christian
C
Laube
Britta
B
Thünemann
Andreas F
AF
Zychlinsky
Arturo
A
Baldus
Marc
M
Lange
Adam
A
Griesinger
Christian
C
Kolbe
Michael
M
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*
D001426:Bacterial Proteins; C413572:MxiH protein, Shigella