Assembly of type 1 pili from Escherichia coli

Type 1 pili of Escherichia coli are large, heterooligomeric protein complexes anchored to the outer bacterial membrane and required for the attachment of the bacteria to host cell surfaces. The pili are critical virulence factors of uropathogenic E. coli strains and mediate the long-term survival of the bacteria within host cells. Type 1 pili are thus targets for the development of new antibiotics against infections of the urinary tract. Such drugs may etiher prevent pilus assembly or abolish their ability to bind to host cell surfaces.

A single E. coli cell may bear up to 500 type 1 pili, each being 7 nm wide and up to 2 micrometer long. Each pilus exclusively consists of protein, with an average number of about 1000 subunits per pilus. 98% of the pilus subunits are comprised of the main structural pilus subunit FimA, while the residual 2% of the subunits are composed of 4 additional subunits, namely FimF, FimG, FimI and the mannose-binding subunit FimH. Assembly of the pilus in vivo requires the assembly factor FimC, a soluble, periplasmic chaperone protein that is not a component of the pilus.