From force‐sensing to power generation – How force modulates the ATPase kinetics of myosin motors

Abstract

Myosins are motor proteins that hydrolyze ATP to power various cellular processes including muscle contraction, intracellular cargo transport, cytoskeletal anchoring, and signaling. Most members of the myosin family follow the same kinetic pathway for ATP hydrolysis, where force‐generating structural changes are linked to the release of inorganic phosphate and ADP. Interestingly, mechanical loads on myosins modulate the rate constants of key steps on the ATPase pathway, resulting in load‐dependent changes in velocity and power production. We investigated the load sensitivity of two members of the class‐1 family of myosins (Myo1b and Myo1c) using single molecule optical‐trap assays and ensemble biochemical techniques. We determined that the unloaded ATPase and transient kinetic rate constants of these two myosins are similar. Surprisingly, we found the kinetics of Myo1b to be substantially more sensitive to mechanical load than Myo1c. We also determined that load affects different biochemical steps in these two myosins, despite their having nearly identical unloaded kinetic properties. Understanding the different load sensitivities of these motors provides insights into their respective cellular roles (Myo1b is a tension‐sensing anchor and Myo1c is a power‐generating transporter) as well as the mechanisms of force sensing within the larger myosin family. Supported by NIH grant, PO1 GM087253.