Understanding the Counterintuitive Phenomenon of Catch Bonds

Cells bind to each other and to surfaces using complementary receptor-ligand pairs as an essential part of their function. The mechanical forces that build up on these bonds was assumed to weaken them until three receptor-ligand complexes were shown to form catch bonds that are instead strengthened by mechanical force. This review analyzes the experimental data for these complexes to better understand this counterintuitive effect. Models of how force affects the energy landscapes of bonds are related to the behavior of various catch bonds when subjected to force. Structural explanations of how force affects molecular structure and function are also presented and related to simulations of the effect of force on structure and to the effect of point mutations on bond function. It can be concluded that catch bonds arise when force changes the angle or distance between two domains in a way that leads to enhanced binding. However, their mechanism through which the interdomain region can influence the lifetime of the distant binding site remains unsolved since more than one proposed mechanism can explain the data. It remains possible that different catch bonds work differently or even that multiple mechanism act in the same protein.