Investigating the spatial distribution of the super-relaxed state of myosin in cardiac myofibrils using single-molecule microscopy

Muscle contraction is a mechanism regulated primarily by the thick and thin filaments of the sarcomere, the smallest contractile unit of the muscle. Using single-molecule imaging we were able to investigate the ATP turnover rates of SRX myosin, a myosin state understood to be essential for maintaining contractile regulation. Our results revealed ATP turnover rates for the SRX state of myosin of ~ 0.006 s -1, consistent with literature. We also developed a high-resolution imaging technique to spatially resolve ATP binding events, creating a map of myosin activity across the sarcomere. Our findings confirm the precision of these techniques and the potential for their use in providing a deeper understanding of contractile regulation within the cardiac myofibril. This work also provides the foundation for the comparison of ATP turnover rates and distribution of SRX myosin in cardiomyopathy mutated samples.