The Hypertrophic Cardiomyopathy Myosin Mutation R453C alters ATP-binding and hydrolysis of human cardiac {beta}-myosin [Enzymology]

December 16th, 2013 by Bloemink, M., Deacon, J., Langer, S., Vera, C., Combs, A., Leinwand, L., Geeves, M. A.

The human hypertrophic cardiomyopathy mutation R453C results in one of the more severe forms of the myopathy. R453 is found in a conserved surface loop of the upper 50-kDa domain of the myosin motor domain and lies between the nucleotide binding pocket and the actin binding site. It connects to the cardiomyopathy loop via a long alpha helix, helix O, and to Switch-2 via the 5th strand of the central β-sheet. The mutation is therefore in a position to perturb a wide range of myosin molecular activities. We report here the first detailed biochemical kinetic analysis of the motor domain of the human β-cardiac myosin carrying the R453C mutation. A recent report of the same mutation (Sommese et al. 2013 PNAS) found reduced ATPase and in vitro motility, but increased force production using an optical trap. Surprisingly, our results show that the mutation alters few biochemical kinetic parameters significantly. The exceptions are the rate constants for ATP binding to the motor domain (reduced by 35 %) and the ATP hydrolysis step/recovery stroke (slowed 3-fold) which could be the rate limiting step for the ATPase cycle. Effects of the mutation on the recovery stroke are consistent with a perturbation of Switch-2 closure which is required for the recovery stroke and the subsequent ATP hydrolysis.