Single-molecule mechanics of R403Q cardiac myosin isolated from the mouse model of familial hypertrophic cardiomyopathy

Familial hypertrophic cardiomyopathy (FHC) is an inherited cardiac disease that can result in sudden death in the absence of any overt symptoms. Many of the cases documented to date have been linked with missense mutations in the beta-myosin heavy chain gene. Here we present data detailing the funct ional impact of one of the most deadly mutations, R403Q, on myosin motor fu nction. Experiments were performed on whole cardiac myosin purified from a mouse model of FHC to eliminate potential uncertainties associated with pro tein expression systems. The R403Q mutant myosin demonstrated 2.3-fold high er actin-activated ATPase activity, 2.2-fold greater average force generati on, and 1.6-fold faster actin filament sliding in the motility assay. The f orce- and displacement-generating capacities of both the normal and mutant myosin were also characterized at the single molecule level in the laser tr ap assay. Both control and mutant generated similar unitary forces (approxi mate to 1 pN) and displacements (approximate to 7 nm) without any differenc es in event durations. On the basis of the distribution of mean unitary dis placements, this mutation may possibly perturb the mechanical coordination between the 2 heads of cardiac myosin. Any of these observations could, alo ne or possibly in combination, result in abnormal power output and potentia lly a stimulus for the hypertrophic response.