Model for kinetics of myosin-V molecular motors.

A hand-over-hand model is presented for the processive movement of myosin-V based on previous biochemical experimental results and structural observations of nucleotide-dependent conformational changes of single-headed myosins. The model shows that the ADP-release rate of the trailing head is much higher than that of the leading head, thus giving a 1:1 mechanochemical coupling for the processive movement of the motor. It explains well the previous finding that some 36-nm steps consist of two substeps, while other 36-nm steps consist of no substeps. Using the model, the calculated kinetic behaviors of myosin-V such as the main and intermediate dwell time distributions, the load dependence of the average main and intermediate dwell time and the load dependence of occurrence frequency of the intermediate state under various nucleotide conditions show good quantitative agreement with previous experimental results.