Coupling of Bond Breaking With State Transition Leads to High Apparent Detachment Rates of a Single Myosin

Abstract

Quantifying interactions between motors and filaments is important for the understanding of intriguing emergent behaviors of motor–filament systems, which play critical roles in various biological processes. Recently, unusually high detachment rates of a myosin from actin were obtained with a force spectroscopy technique of an unprecedented spatial–temporal resolution. Here, we suggest that these high apparent detachment rates may be due to the inherent coupling between bond breaking and state transition, which can be common in protein–protein interactions. Based on a kinetic model for the chemomechanical cycle of single myosin, rates of bond breaking between myosin and actin at different nucleotide states are systematically calculated. These quantitative results indicate that myosins may adopt much higher transition rates than bond breaking rates at different nucleotide states under physiological conditions when applied forces are relatively low. This work also indicates that accurate biophysical models considering both protein unbinding dynamics and protein state transitions are required in order to properly interpret the experimental data when the ultrafast forceclamp spectroscopy technique is employed to study, for example, the DNA–protein interactions.