Functional Analysis of the Mutations in the Human Cardiac b -Myosin that Are Responsible for Familial Hypertrophic Cardiomyopathy

More than 30 missense mutations in the b -cardiac myosin heavy chain gene have been shown to be responsible for familial hypertrophic cardiomyopathy. To clarify the effects of these point mutations on myosin motor function, we expressed wild-type and mutant human b -cardiac myosin heavy chains in insect cells with human cardiac light chains. The wild-type myosin was well purified with similar enzymatic and motor activities to those of the naturally isolated V3 cardiac myosin. Arg 249 → Gln and Arg 453 → Cys mutations resulted in decreased actin translocating activity (61 and 23% of the wild-type, respectively) with decreased intrinsic ATPase activity. Arg 403 → Gln mutation greatly decreased actin translocating activity (27% of wild type) with a 3.3fold increased dissociation constant for actin, while intrinsic ATPase activity was unchanged. Val 606 → Met mutation only mildly affected the actin translocating activity as well as ATPase activity of myosin. The degree of deterioration by each mutation was closely correlated with the prognosis of the affected kindreds, indicating that myosin dysfunction caused by the point mutations is responsible for the pathogenesis of the disease. Structure/function relationship of myosin is discussed. ( J. Clin. Invest. 1996 . 98:2866–2873.)