Mavacamten stabilizes an autoinhibited state of two-headed cardiac myosin

Significance Small-molecule allosteric effectors designed to target and modulate striated and smooth myosin isoforms for the treatment of disease show promise in preclinical and clinical trials. Beta-cardiac myosin is an especially important target, as heart disease remains a primary cause of death in the United States. One prevalent type of heart disease is hypertrophic cardiomyopathy (HCM), which is hypothesized to result from dysregulated force generation by cardiac myosin. Mavacamten is a potent cardiac myosin ATPase activity inhibitor that improves cardiac output in HCM animal models. Our results show that mavacamten selectively stabilizes a two-headed–dependent, autoinhibited state of cardiac myosin in solution. The kinetics and energetics of this state are consistent with the autoinhibited superrelaxed state previously observed only in intact sarcomeres.