The biomechanical properties of F1C pili

TL;DR

This study characterizes the biomechanical properties of F1C pili in Uropathogenic Escherichia coli, revealing their force response and uncoiling behavior, which are similar to other pili and adapted for urinary tract conditions.

Contribution

It provides the first detailed biomechanical analysis of F1C pili, comparing their properties to other known pili types and highlighting their evolutionary adaptation.

Findings

F1C pili have a steady-state uncoiling force of ~26.4 pN.

F1C pili exhibit faster kinetics and higher corner velocity than other pili.

F1C pili are adapted to withstand shear forces in the urinary tract.

Abstract

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.