# The G256E HCM mutation prolongs cardiac muscle relaxation via altered nucleotide handling

## TL;DR

This study shows how the G256E mutation in myosin causes heart muscle relaxation issues by affecting ADP release during contraction.

## Contribution

The study reveals that the G256E mutation causes slower ADP release, contributing to HCM pathology through altered nucleotide handling.

## Key findings

- G256E increases the work needed to displace ADP.Mg2+ from the actomyosin complex.
- ADP affinity for actomyosin is increased, and ADP sensitivity during relaxation is reduced.
- Slower ADP release is a key factor in the pathological contractile behavior of G256E.

## Abstract

Mutations in myosin alter its motor functions in diverse ways by affecting different structural and chemo-mechanical events. Multidisciplinary strategies can be used to understand how varying alterations in motor function converge to common phenotypes like hypercontractility and hypertrophic cardiomyopathy (HCM). Here, we combined molecular dynamics (MD) simulations with protein biochemical and myofibril mechanical analyses to study the HCM-causing myosin variant G256E. MD simulations demonstrated that G256E induces structural changes that increase the work required to displace ADP.Mg2+ from actomyosin complex. Stopped-flow biochemical analysis demonstrated increased ADP affinity for actomyosin and single myofibril mechanics analysis demonstrated increased force generation and reduced ADP sensitivity of the early, slow phase of relaxation. Together, these results demonstrate that slower ADP release from myosin during contraction is a significant contributor to pathological contractile nature of the G256E mutation. This study highlights the importance of detailed chemo-mechanical analysis of mutations associated with hereditary cardiac diseases.