Early stages of energy transduction by myosin: Roles of Arg in switch I, of Glu in switch II, and of the salt-bridge between them

On the basis of the crystallographic snapshots of Rayment and his collaborators [Fisher, A. J., Smith, C. A., Thoden, J. B., Smith, R., Sutoh, K., Holden, H. M., & Rayment, I. (1995) Biochemistry 34, 8960-8972], we have understood some basic principles about the early stages of myosin catalysis, namely, ATP is drawn into the active site, over which the cleft closes. Catalyzed hydrolysis occurs, and the first product (orthophosphate) is released from the backdoor of the cleft. In the cleft-closing process, the active site incidentally signals its movement to a particular remote tryptophan residue, Trp-512. In this work, we expand on some of these ideas to rationalize the behavior of a mutated system in action. From the behavior of recombinant myosin systems in which Arg-247 and Glu-470 were substituted in several ways, we draw the conclusions that (i) the force between Arg-247 and γ-phosphate of ATP may assist in closing the cleft, and incidentally in signaling to the remote Trp, and (ii) in catalysis, Glu-470 is involved in holding the lytic H₂O (w₁). We also propose that w₁ and also a second water, w₂, enter into a structure that bridges Glu-470 and the γ-phosphate of bound ATP, and at the same time positions w₁ for its in-line hydrolytic attack.