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Publication Abstract from PubMed

P pili are important adhesive fibres that are assembled by the conserved chaperone-usher pathway. During pilus assembly, the subunits are incorporated into the growing fibre by the donor-strand exchange mechanism, whereby the beta-strand of the chaperone, which complements the incomplete immunoglobulin fold of each subunit, is displaced by the amino-terminal extension of an incoming subunit in a zip-in-zip-out exchange process that is initiated at the P5 pocket, an exposed hydrophobic pocket in the groove of the subunit. In vivo, termination of P pilus growth requires a specialized subunit, PapH. Here, we show that PapH is incorporated at the base of the growing pilus, where it is unable to undergo donor-strand exchange. This inability is not due to a stronger PapD-PapH interaction, but to a lack of a P5 initiator pocket in the PapH structure, suggesting that PapH terminates pilus growth because it is lacking the initiation point by which donor-strand exchange proceeds.

Molecular mechanism of P pilus termination in uropathogenic Escherichia coli.,Verger D, Miller E, Remaut H, Waksman G, Hultgren S EMBO Rep. 2006 Dec;7(12):1228-32. Epub 2006 Nov 3. PMID:17082819^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.