Modulation of Cardiac Myosin by a Small Molecule Agent that Targets the Regulatory Light Chain

Abstract

A small molecule modulator of cardiac myosin enzymatic function has been identified (refered to as compound-A) and our characterization demonstrates that this agent exerts its effect through the regulatory light chain (RLC) of myosin. Compound A inhibited the actin activated ATPase activity of cardiac heavy meromyosin (HMM, derived from bovine heart), which contains both the essential and regulatory light chains, whereas no inhibition was seen with bovine cardiac myosin subfragment-1 which does not contain the regulatory light chain in our preparations. The regulatory light chain from full length cardiac myosin was removed and the extent of inhibition was dramatically reduced. Binding of this small molecule to the RLC was assessed using differential scanning fluorimetry (DSF) and found that binding occurs to the RLC. Compound A was further characterized in permeabilized rat cardiac muscle fibers and a dose-dependent decrease in maximal tension was observed. It has been demonstrated in animal studies that a small molecule modulator of myosin has applicability in treating hypertrophic cardiomyopathy, the identified regulatory light chain modulator described here suggests that the RLC may be a potential new target for therapeutic applications in hypertrophic cardiomyopathies.