Mechanism of fibre assembly through the chaperone-usher pathway.
The chaperone-usher pathway directs the formation of adhesive surface fibres in numerous pathogenic Gram-negative bacteria. The fibres or pili consist exclusively of protein subunits that, before assembly, form transient complexes with a chaperone in the periplasm. In these chaperone:subunit complexes, the chaperone donates one beta-strand to complete the imperfect immunoglobulin-like fold of the subunit. During pilus assembly, the chaperone is replaced by a polypeptide extension of another subunit in a process termed 'donor strand exchange' (DSE). Here we show that DSE occurs in a concerted reaction in which a chaperone-bound acceptor subunit is attacked by another chaperone-bound donor subunit. We provide evidence that efficient DSE requires interactions between the reacting subunits in addition to those involving the attacking donor strand. Our results indicate that the pilus assembly platforms in the outer membrane, referred to as ushers, catalyse fibre formation by increasing the effective concentrations of donor and acceptor subunits.
Vetsch
Michael
M
Institute for Molecular Biology and Biophysics, ETH Zurich, Schafmattstrasse 20, 8093 Zurich, Switzerland.
Erilov
Denis
D
Molière
Noël
N
Nishiyama
Mireille
M
Ignatov
Oleksandr
O
Glockshuber
Rudi
R
D001422:Bacterial Adhesion / Q000502:physiology; D004926:Escherichia coli / Q000472:pathogenicity / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000502:physiology; D036781:Fimbriae Proteins / Q000737:chemistry / Q000502:physiology; D010861:Fimbriae, Bacterial / Q000502:physiology*; D008954:Models, Biological; D018832:Molecular Chaperones / Q000737:chemistry / Q000502:physiology*; D017434:Protein Structure, Tertiary
D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; C489721:fimC protein, E coli; C063055:fimbrillin; D036781:Fimbriae Proteins