Crystal structure of the ternary FimC–FimF t–FimD N complex indicates conserved pilus chaperone–subunit complex recognition by the usher FimD

Abstract

Type 1 pili, anchored to the outer membrane protein FimD, enable uropathogenic Escherichia coli to attach to host cells. During pilus biogenesis, the N-terminal periplasmic domain of FimD (FimD N) binds complexes between the chaperone FimC and pilus subunits via its partly disordered N-terminal segment, as recently shown for the FimC–FimH P–FimD N ternary complex. We report the structure of a new ternary complex (FimC–FimF t–FimD N) with the subunit FimF t instead of FimH p. FimD N recognizes FimC–FimF t and FimC–FimH P very similarly, predominantly through hydrophobic interactions. The conserved binding mode at a “hot spot” on the chaperone surface could guide the design of pilus assembly inhibitors.