A hypothesis about myosin catalysis

When ATP binds to the active site of myosin heads, Switch II undergoes a large conformational change and the cleft surrounding the bound γ-phosphate closes. In the closed state, Glu470 in Switch II comes together with Arg247 in Switch I to form a salt-bridge. Here, the functional significance of the two bridging residues was tested by using site-directed mutagenesis. We conclude from such tests that (a) the attractive force between Arg247 and the γ-phosphate of ATP moves the cleft to close, and (b) during hydrolysis, Glu470 is intimately involved in positioning the lytic water for the attack on the γ-phosphorus. We also speculate on how the salt-bridge between Arg247 and Glu470 is related to hydrolysis.