Mavacamten inhibits myosin activity by stabilizing the myosin interacting-heads motif and stalling motor force...

Most sudden cardiac deaths in young people arise from hypertrophic cardiomyopathy, a genetic heart muscle disease. Treatment has until recently been limited to symptomatic relief or invasive procedures. Small-molecule modulators of cardiac myosin are promising therapeutic options to target disease progression. Mavacamten, the first Food and Drug Administration-approved example, has an unclear mechanism. To address this, we solved cryo-electron microscopy (cryo-EM) structures of beta-cardiac heavy meromyosin in three adenosine 5'-diphosphate and inorganic phosphate (ADP.P_i)-bound states, the primed motor domain with and without mavacamten and the autoinhibited interacting-heads motif (IHM) with mavacamten, to 2.9, 3.4, and 3.7 Å global resolution, respectively. Together with quantitative cross-linking mass spectrometry analysis, these structures reveal how mavacamten inhibits myosin. Mavacamten stabilizes ADP.P_i binding, stalling the motor domain in a primed state, reducing motor dynamics required for actin-binding cleft closure, and slowing progression through the force generation cycle. These effects propagate within the two-headed molecule, stabilizing the IHM through increased motor-motor contacts. While this promotes diastolic relaxation, it also reduces systolic contractile output.