Screening single nucleotide changes to tropomyosin to identify novel cardiomyopathy mutants.

Inherited cardiomyopathy is a broad class of heart disease that includes pathological cardiac remodeling such as hypertrophic and dilated cardiomyopathy, affecting 1/250-1/500 people worldwide. In many cases, mutations in proteins that make up the sarcomere, the basic subcellular unit of contraction, alter thin filament regulation and are the root cause of hypertrophic and dilated cardiomyopathy. Initially, compensations can maintain cardiac function, so patients may remain asymptomatic for years before a major cardiac episode. Early therapeutic intervention could rescue the deleterious effects of mutations thereby avoiding pathological remodeling, so prediction of potential outcomes and severity of as yet uncharacterized and known mutants of uncertain significance is critical. To accomplish this goal, we begin with the structure of the thin filament containing actin, tropomyosin, and troponin in its regulatory B- and C-states, incorporate all potential single nucleotide mutations to the tropomyosin sequence (over 1700 unique mutations), and then measure the interaction energy between tropomyosin and actin after energy minimization. Analysis of the database thus generated shows the tropomyosin residues resulting in large changes in tropomyosin-actin interaction, and therefore most likely to be deleterious to function. Some of these mutants have been observed in human patients, whereas others are novel. Global analysis further refines hotspots of mutation-sensitive, coiled-coil tropomyosin residues affecting actin interactions. Altogether, the database will allow research to focus in great depth on key candidates for functional analysis, for instance, by assaying in vitro motility and engineered heart tissue mechanics and assessing outcomes in animal models.