title: Structure, folding and stability of FimA, the main structural subunit of type 1 pili from uropathogenic Escherichia coli strains.
abstract: Filamentous type 1 pili are responsible for attachment of uropathogenic Escherichia coli strains to host cells. They consist of a linear tip fibrillum and a helical rod formed by up to 3000 copies of the main structural pilus subunit FimA. The subunits in the pilus interact via donor strand complementation, where the incomplete, immunoglobulin-like fold of each subunit is complemented by an N-terminal donor strand of the subsequent subunit. Here, we show that folding of FimA occurs at an extremely slow rate (half-life: 1.6 h) and is catalyzed more than 400-fold by the pilus chaperone FimC. Moreover, FimA is capable of intramolecular self-complementation via its own donor strand, as evidenced by the loss of folding competence upon donor strand deletion. Folded FimA is an assembly-incompetent monomer of low thermodynamic stability (-10.1 kJ mol(-1)) that can be rescued for pilus assembly at 37 °C because FimC selectively pulls the fraction of unfolded FimA molecules from the FimA folding equilibrium and allows FimA refolding on its surface. Elongation of FimA at the C-terminus by its own donor strand generated a self-complemented variant (FimAa) with alternative folding possibilities that spontaneously adopts the more stable conformation (-85.0 kJ mol(-1)) in which the C-terminal donor strand is inserted in the opposite orientation relative to that in FimA. The solved NMR structure of FimAa revealed extensive β-sheet hydrogen bonding between the FimA pilin domain and the C-terminal donor strand and provides the basis for reconstruction of an atomic model of the pilus rod.
authors.affiliation: ETH Zürich, Institute of Molecular Biology and Biophysics, 8093 Zurich, Switzerland.
authors.forename: Chasper
authors.initials: C
authors.lastname: Puorger
authors.forename: Michael
authors.initials: M
authors.lastname: Vetsch
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wider
authors.forename: Rudi
authors.initials: R
authors.lastname: Glockshuber
mesh_terms: D029968:Escherichia coli Proteins; D036781:Fimbriae Proteins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008958:Models, Molecular; D017510:Protein Folding; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D056689:Uropathogenic Escherichia coli / Q000737:chemistry*
chemical_list: D029968:Escherichia coli Proteins; D021122:Protein Subunits; C489721:fimC protein, E coli; C063055:fimbrillin; D036781:Fimbriae Proteins