Truncation of vertebrate striated muscle myosin light chains disturbs calcium-induced structural transitions in synthetic myosin filaments

Electron microscopy and negative staining techniques have been used to show that the proteolytic removal of 13 amino acids from the N-terminus of esse ntial light chain 1 and 19 amino acids from the N-terminus of the regulator y light chain of rabbit skeletal and cardiac muscle myosins destroys Ca2+- induced reversible movement of subfragment-2 (S2) with heads (S1) away from the backbone of synthetic myosin filaments observed for control assemblies of the myosin under near physiological conditions. This is the direct demo nstration of the contribution of the S2 movement to the Ca2+-sensitive stru ctural behavior of rabbit cardiac and skeletal myosin filaments and of the necessity of intact light chains for this movement. In muscle, such a mobil ity might play an. important role in proper functioning of the myosin filam ents. The impairment of the Ca2+-dependent structural behavior of S2 with S 1 on the surface of the synthetic myosin filaments observed by us may be of direct relevance to some cardiomyopathies, which are accompanied by proteo lytic breakdown or dissociation of myosin light chains. (C) 2000 Academic P ress.