The Two-Pathway Model of the Biological Catch-Bond as a Limit of the Allosteric Model

Abstract

Recent years have witnessed great interest in the biophysics of receptor-ligand complexes, such as FimH/mannose, P,L,E-selectin/PSGL-1, etc., showing unusual dependence of complex lifetime on the strength of an applied external force. In contrast to the expected decrease in the lifetime with increasing force strength, the lifetimes of these complexes showed an initial growth, which was followed by the expected decay. This low force phenomenon was called catch-binding, and the transition between the unexpected low force behavior and the expected high force limit was called the catch-slip transition. We discuss various models for the catch-slip anomaly and show that the two-state allostery model [Thomas, W et al., Biophys. J. 90, 753 (2006); Pereverzev, YV et al., Phys. Rev. E 79, 051913 (2009)] can be transformed into the two-pathway model [Pereverzev, YV et al., Biophys. J. 89, 1446 (2005)]. We demonstrate that such transformation is possible when the relaxation time of the allostery site is much smaller than the characteristic decay time of the bound complex. This transition is considered for P-selectin/PSGL-1 and FimH/mannose complexes exposed to both constant and time-dependent forces. Good agreement between theory and experiment is obtained, and the relevant biophysical parameters of the catch-bonds are found.