CONFORMATIONAL-CHANGES OF THE MYOSIN HEADS DURING HYDROLYSIS OF ATP AS ANALYZED BY X-RAY SOLUTION SCATTERING

We have shown for the first time that the myosin head (subfragment-1, S1), the energy-transducing component in the actomyosin motor system undergoes a distinct shape change during hydrolysis of ATP using x-ray solution scattering techniques. Among various analogs for intermediate states of the St ATPase cycle, the complexes with MgADP and vanadate (S1.ADP.V-i), MgADP and beryllium fluoride (S1.ADP.BeF3), or MgADP and aluminum fluoride (S1.ADP.AlF4) showed a shape change similar to that in the presence of MgATP, but the complexes with ATP gamma S (S1.ADP gamma S) and MgADP trapped by crosslinking with pPDM (S1.ADP-pPDM) seemed to have a shape similar to that of nucleotide-free S1. These results indicate that the shape of an S1**.ADP.P-i state is more rounded or bent than in other intermediate states of the S1 ATPase cycle. Such changes occur in light chain 2-deficient St and also in smooth muscle S1. However, MgADP-fluoride complexes with smooth muscle S1 (without phosphorylation of a regulatory light chain) seemed to have a structure similar to that of nucleotide-free St. Analysis of x-ray scattering data indicated that a conformational change of S1 in the presence of MgATP might be caused by a hinge-like bending movement between the catalytic and regulatory domains. The global change of S1 is correlated with some specific changes of a nucleotide-binding moiety.