  Uropathogenic Escherichia coli (UPEC) express various kinds of organelles,
so-called pili or fimbriae, that mediate adhesion to host tissue in the urinary
tract through specific receptor-adhesin interactions. The biomechanical
properties of these pili have been considered important for the ability of
bacteria to withstand shear forces from rinsing urine flows. Force measuring
optical tweezers have been used to characterize individual organelles of F1C
type expressed by UPEC bacteria with respect to such properties. Qualitatively,
the force-vs.-elongation response was found to be similar to that of other
types of helix-like pili expressed by UPEC, i.e. type 1, P, and S, with
force-induced elongation in three regions of which one represents the important
uncoiling mechanism of the helix-like quaternary structure. Quantitatively, the
steady-state uncoiling force was assessed to 26.4(1.4) pN, which is similar to
those of other pili (which range from 21 pN for SI to 30 pN for type 1). The
corner velocity for dynamic response (1400 nm/s) was found to be larger than
those of the other pili (400 -700 nm/s for S and P pili, and 6 nm/s for type
1). The kinetics were found to be faster, with a thermal opening rate of 17 Hz,
a few times higher than S and P pili, and three orders of magnitude times
higher than type 1. These data suggest that F1C pili are, like P and S pili,
evolutionary-selected to primarily withstand the conditions expressed in the
upper urinary tract.
