Solution structure of myosin-ADP-MgFn ternary complex by fluorescent probes and small-angle synchrotron X-ray scattering

In the presence of excess amounts of fluorine, a physiological divalent cat ion, magnesium (Mg2+), forms a novel phosphate analogue, magnesium fluoride (MgFn). Park ct at [Biochim. Biophys. Acta 1430, 127-140 (1999)] previousl y demonstrated that MgADP MgFn forms a complex with myosin subfragment-1 (S -1), and the S-1 ADP MgFn ternary complex mimics a transient state in the a ctivity cycle of ATPase, In the present study, localized conformations in t he regions of highly reactive cysteine and lysine residues, Cys 707 (SH1), Cys 697 (SH2), and Lys 83 (RLR), which change their conformations markedly during ATP hydrolysis, were studied using fluorescent probes and chemical m odification. The global shape of the complex was also studied using small a ngle X-ray solution scattering and compared it with other previously report ed myosin . ADP . fluorometal ternary complexes. The results suggest that t he overall conformation and localized functional regions of the complex are quite similar to those in the presence of ATP, indicating that the complex mimics the M**. ADP . P-i steady state.