Abstract Body: Background: Cardiac myosin (MyHC) is the primary motor protein of the heart, converting chemical energy into mechanical force to drive cardiac contraction through its interaction with the thick filament protein cardiac myosin binding protein-C (cMyBP-C). The importance of this interaction is highlighted by the fact that mutations in the genes encoding MYH7 and MYBPC3 together account for approximately 70% of hypertrophic cardiomyopathy (HCM), a genetic disorder characterized by pathological thickening of the heart muscle. Despite its significance, the precise molecular mechanisms governing the interaction between MyHC and cMyBP-C remain incompletely understood.

Methods and Results: Using small peptides derived from myosin in combination with molecular dynamics simulations, we identified a region within the myosin S2 domain that interacts with the C1 domain of cMyBP-C. These peptides were subsequently evaluated for functional efficacy using pCa–force measurements in a skinned papillary muscle system. To assess the physiological relevance of this interaction in vivo, we generated a tamoxifen-inducible mouse model expressing a 126-amino-acid segment of the myosin S2 region (CAG-CAT-S2¹²⁶), demonstrating that inducible expression of this exogenous S2 fragment enhances cardiac function. To further investigate the pathological mechanisms of myosin S2 mutations in HCM, we generated a knock-in mouse model carrying the Myh6-E926K clinical variant and are currently evaluating its contribution to HCM pathogenesis. Finally, to determine whether modulation of cMyBP-C phosphorylation influences its interaction with mutant myosin S2, we crossed the Myh6 mutant mouse with cMyBP-C phospho-ablation and phospho-mimetic models. Our results show that inducible expression of the myosin S2 region enhances cardiac function in vivo. In addition, a 22-amino-acid sequence corresponding to a myopeptide (ID 27119) demonstrates strong binding to cMyBP-C and significantly improves maximal force generation in skinned cardiac papillary muscle in vitro. Ongoing studies are defining the molecular and functional mechanisms by which the Myh6-E926K clinical variant contributes to the development of an HCM phenotype.

Conclusions: These studies identify novel regulatory interactions between the MyHC S2 region and cMyBP-C that influence cardiac contractility. Targeting this interaction may provide a new therapeutic strategy to improve cardiac function in patients with HCM and heart failure.