MUTATIONS IN EITHER THE ESSENTIAL OR REGULATORY LIGHT-CHAINS OF MYOSIN ARE ASSOCIATED WITH A RARE MYOPATHY IN HUMAN HEART AND SKELETAL-MUSCLE

The muscle myosins are hexomeric proteins consisting of two heavy chai ns and two pairs of light chains, the latter called essential (ELC) an d regulatory (RLC). The light chains stabilize the long alpha helical neck of the myosin head. Their function in striated muscle, however, i s only partially understood. We report here the identification of dist inct missense mutations in a skeletal/ventricular ELC and RLC, each of which are associated with a rare variant of cardiac hypertrophy as we ll as abnormal skeletal muscle. We show that myosin containing the mut ant ELC has abnormal function, map the mutant residues on the three-di mensional structure of myosin and suggest that the mutations disrupt t he stretch activation response of the cardiac papillary muscles.