· D. Verger, E. Bullit, S. Hultgren, and G.
Waksman
Crystal structure of the P pilus rod
subunit PapA
PLoS Pathog. 3(5):674-682 (2007)
P pili are important adhesive fibres involved in kidney infection
by uropathogenic Escherichia coli strains. P pili are assembled by the conserved chaperone/usher
pathway, which involves the PapD chaperone and the PapC usher. During pilus assembly, subunits are
incorporated into the growing fiber via the donor-strand exchange mechanism,
whereby the chaperone’s G1 b-strand that complements the incomplete
immunoglobulin-fold of each subunit is displaced by the N-terminal extension
(Nte) of an incoming subunit. P
pili comprise a helical rod, a tip fibrillum and an adhesin at the distal end.
PapA is the rod subunit and is assembled into a super-helical right-handed
structure. Here we have solved the structure of a ternary complex of PapD bound
to PapA through donor-strand complementation, itself bound to another PapA subunit
through donor-strand exchange. This structure provides insight into the
structural basis of the donor-strand exchange reaction involving this important
pilus subunit. Using gel filtration chromatography and electron microscopy on a
number of PapA Nte mutants, we establish that PapA differs in its mode of
assembly compared to other Pap subunits, involving a much larger Nte that
encompasses not only the DSE region of the Nte but also the region N-terminal
to it.