β-MYHC Mutations Linked to Early-Onset HCM and DCM Show Differences in Pre-Steady and Steady State Kinetic Parameters

Abstract

Hypertrophic Cardiomyopathy (HCM) is the leading cause of sudden cardiac death in young athletes and has an incidence of 1 in 500 people. Dilated cardiomyopathy (DCM) has a prevalence of 1 in 2000 people. Both diseases can be inherited, with HCM being autosomal dominant, and DCM having different genotypic profiles. There are over 400 mutations in cardiac myosin (MYH7) that have been linked to both diseases. Also noteworthy, early-onset HCM and DCM patients typically have a worse prognosis than adult-onset patients. The only intervention for these pediatric patients is a heart transplant. Here we describe the kinetic analysis of several cardiac myosin mutations that have been identified to be unique to early-onset patients. One set of mutations has been identified in pediatric HCM and the other set is DCM. Steady-state characterization of ATP hydrolysis for both mutant sets using an NADH coupled ATPase assay is reported. Additionally, transient kinetic analysis for several mutants was conducted illustrating differences in the cross-bridge kinetics between HCM and DCM mutants, namely ATP-induced dissociation, ADP release, and the binding constants of actin and the different nucleotide states. This data suggests that the motor activity is different among mutants and may provide insight into the mechanistic defects that can lead to both diseases.