Practice question

Myosin motor cycle couples ATP hydrolysis to filament sliding via conformational changes in conserved motor domain. In absence of ATP myosin head strongly bound to actin in rigor state, stereospecific binding between actin helix and myosin cardiomyopathy loop. Binding of ATP to P loop pocket between upper and lower 50 kilodalton subdomains induces opening of actin binding cleft reducing affinity thousand fold leading to detachment. While detached ATP hydrolyzed to ADP Pi mediated by Switch I Switch II closing around gamma phosphate, triggering recovery stroke where lever arm moves about 90 degrees to pre power stroke conformation storing elastic energy. Myosin ADP Pi rebinds actin weakly, phosphate release gates transition to strongly bound state closing cleft, producing power stroke large rotation of converter domain swinging lever arm 5 to 10 nanometer dragging actin. ADP release returns to rigor awaiting new ATP. Thus detachment powered by ATP binding, priming by hydrolysis, force generation by Pi release, not calcium influx, GTP hydrolysis, tail phosphorylation primary driver of movement.