Structural polymorphism of bacterial adhesion pili

Abstract

BACTERIAL adhesion pili are designed to bind specifically and main-tain attachment of bacteria to target cells. Uropathogenic P-pili are sufficiently mechanically resilient to resist the cleansing action of urine flow that removes most other bacteria¹. P-pili are 68 Å in diameter and ˜1 um long², and are composed of ˜1,000 copies of the principal structural protein, PapA³. They are attached to the outer membrane by a minor structural protein, PapH⁴ and are terminated by an ˜20 Å diameter fibrillus composed of PapK, PapE and PapF, which presents the host-binding adhesin PapG^5–7. The amino-acid sequences of PapA^3,8, PapE⁹, and PapF⁹ are simi-lar, with highly conserved C-termini being responsible for binding to PapD^10–12, the periplasmic chaperone. Our three-dimensional reconstruction indicates that pili are formed by the tight winding of a much thinner structure. A structural transition allows the pilus to unravel without depolymerizing, producing a thin, extended structure five times the length of the original pilus.