Phosphorylation Modulates the Dynamics of the N-Terminal Tail in Cardiac RLC

Abstract

Background: Phosphorylation of the Regulatory Light Chain (RLC) in cardiac myosin has been shown to be critical for the normal heart performance. In particular, different cardiomyopathy-related mutations have been found to be associated with decreased levels of RLC phosphorylation. RLC is part of the myosin lever arm, whose power stroke is the result of the amplification of conformational changes occurring in the motor domain during the contractile cycle. Several findings indicate that RLC phosphorylation can have significant effects on myosin mechanics. However, the associated molecular events are still unknown.Methods and Results: Here, we use computational methods to model the dynamics of human cardiac RLC bound to a fragment of myosin heavy chain (MyBS). Molecular Dynamics simulations are used to explore the space of conformations accessible to the N-terminal tail, which contains the RLC phosphorylation site. The conformational free energy landscape is reconstructed and the dynamic behaviour is analysed in terms of probability distributions of key residues of the tail around RLC and MyBS. Remarkably, simulations of phosphorylated RLC show significantly modified tail distributions, associated with a shifting in the population of the preferred tail conformations.Results from simulations are compared with experimental NMR data and the effects of mutations implicated in the pathogenesis of hypertrophic cardiomyopathy (HCM) are discussed.Conclusions: Molecular Dynamics simulations of cardiac RLC reveal phosphorylation-induced changes in the dynamics of the N-terminal tail and in its interaction with the rest of the molecule. These modifications can potentially regulate the interactions between RLC and other myosin components and interactors.This research is supported by the British Heart Foundation.