Development of an Atomistic Structure of Myosin-Bound Cardiac Thin Filament and Free Energy Determination of the Close-to-Open Transition

Abstract

Myosin represents a superfamily of motor proteins that is diverse both in homology as well as function and whose association with actin filaments in a ATP-dependent manner is often correlated with muscle contraction. With recent advances in Cryo-Electron Microscopy, high resolution images of various morphologies of myosin interacting with actin has allowed for the visualization of the specific interactions between myosin, actin, and tropomyosin, but little is still known how these interactions change as myosin progresses through its ATP hydrolysis cycle. Another issue is the lack of a high resolution structure of human cardiac myosin bound to actin where mutagenic changes in the myosin head have been associated with the development of cardiomyopathies within individuals. In the current study, we employ molecular dynamics (MD) simulations as well as other computational methods to study how the beta isoform of cardiac myosin (MYH7) interacts with the cardiac thin filament (CTF). Utilizing free energy calculations such as the adaptive biasing force (ABF) method, we will probe the mean force that a single myosin head must exert on tropomyosin to transition from the closed to open transition. With these simulations we hope to be able to evaluate the overall energetics of the transition, the possibility of a preferential, initial binding site of myosin on the thin filament, and the overall cooperative effect of myosin binding. Development of this novel atomistic myosin-CTF structure provides a unique insight into the specific structure and dynamics of cardiac myosin and allows for further studies of the development of cardiomyopathies as well as the dynamics of the cross-bridge cycle.