Catch-to-Slip Bond Transition in Biological Bonds by Entropic and Energetic Elasticity

Abstract

It is revealed recently that the life time of some biological bonds increases in response to small and moderate external tensile forces, decreases with further increasing of tensile forces. Such biological bonds are termed ‘catch bonds’. This work aims to explain the dependence of bond life time on entropic and energetic factors which are controlled by external tensile forces. We count debonding events of a biological bond in a sphere surrounding the bonding complex. For simplicity, the surface is divided into two regions. Region (a) has a surface normal nearly parallel to a tensile force, and region (b) is the rest of the surface. The influence of a tensile force to dissociation in region (a) is by lowering the energy barrier to escape, and that to region (b) is by modifying accessible microstates for dissociation. The lifetime of the biological bond, due to the superimposition of two concurrent dissociation rates in each region, may grow with increasing tensile force to moderate amount and decrease with further increasing load. It is hypothesized that a catch-to-slip bond transition is a generic feature in biological bonds. The model also predicts that catch bonds in compliant molecular structure have longer lifetimes and lower bond strength. Here bond strength is defined as the critical force where the bond lifetime is maximized.