FimA is the main structural subunit of adhesive type 1 pili from uropathogenic Escherichia coli strains. Up to 3000 copies of FimA assemble to the helical pilus rod through a mechanism termed donor strand complementation, in which the incomplete immunoglobulin-like fold of each FimA subunit is complemented by the N-terminal extension (Nte) of the next subunit. The Nte of FimA, which exhibits a pseudo-palindromic sequence, is inserted in an antiparallel orientation relative to the last β-strand of the preceding subunit in the pilus.
