Catch Bond Model Derived from Allostery Explains Force-Activated Bacterial Adhesion

¹ University of Washington
² Swiss Federal Institute of Technology (ETH)

^* To whom correspondence should be addressed. E-mail: wendyt{at}u.washington.edu.

Submitted on June 10, 2005
Revised on July 18, 2005
Accepted on 30 September 2005

	Abstract

High shear enhances the adhesion of Escherichia coli bacteria binding to mannose-coated surfaces via the protein FimH, raising the question as to whether FimH forms catch bonds that are stronger under tensile mechanical force. Here, we study the length of time that E. coli pause on mannosylated surfaces and report a double exponential decay in the duration of the pauses. This double exponential decay is unlike previous single molecule or whole cell data for other catch bonds, and indicates the existence of two distinct conformational states. We present a mathematical model, derived from the common notion of chemical allostery, which describes the lifetime of a catch bond in which mechanical force regulates the transitions between two conformational states which have different unbinding rates. The model explains these characteristics of the data: a double exponential decay, an increase in both the likelihood and lifetime of the high-binding state with shear stress, and a biphasic effect of force. The model parameters estimated from the data are consistent with the force-induced structural changes shown earlier in FimH. This strongly suggests that FimH forms allosteric catch bonds and advances our understanding of both catch bonds and the role of allostery in regulating protein activity.

Key Words: adhesion, allostery, mechanical force, model, shear stress

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