Abstract 12207: S532P Mutation in Human β-Cardiac Myosin Heavy Chain Decreases Contractile Force by Decreasing the Intrinsic Force of the Myosin Motor
Dilated cardiomyopathy represents a major cause of morbidity and mortality in all age groups. Up to one third of patients with dilated cardiomyopathy have underlying causative genetic mutations and mutations in the beta-cardiac myosin heavy chain gene (MYH7) are among those more commonly associated with inherited dilated cardiomyopathy. However, the precise mechanisms by which MYH7 mutations cause inherited dilated cardiomyopathy are yet to be determined. Here, for the first time, we present the biomechanical analysis of the dilated cardiomyopathy-causing mutation, S532P, in the context of human beta-cardiac myosin. Using a dual beam optical trap, we found that the S532P mutation, located near the actin-binding region of the motor domain, causes a 20% decrease in the intrinsic force of the motor (1.1 ± 0.1 pN in mutant versus 1.4 ± 0.1 pN in wild-type, p≤0.05) without significantly changing its stroke size (6.8 ± 0.6 nm in mutant versus 5.8 ± 0.5 nm in wild-type, p≤0.2). The S532P mutation causes a 3-fold increase in the total ATPase cycle time of the motor (0.54 sec in mutant versus 0.18 sec in wild-type) and a 3-fold increase in the time the motor is strongly bound to the actin filament (19.0 msec in mutant versus 5.8 msec in wild-type). Therefore, the S532P mutation does not cause any change in the duty ratio (the time the motor is bound to the actin filament over the total ATPase cycle time of the motor). In addition, in vitro motility assays revealed a 3-fold decrease in actin velocity driven by myosin containing the S532P mutation (360 ± 10 nm/sec by mutant versus 990 ± 50 nm/sec by wild-type, p=0.0007), suggesting that power output is significantly decreased by this mutation. Overall, our study suggests that the S532P mutation causes a hypo-contractile state by decreasing intrinsic force and significantly decreasing the actin velocity of the myosin, resulting in reduced power production in the heart.
- © 2013 by American Heart Association, Inc.