2-deoxy-ATP Alters Myosin Structure to Enhance Cross-Bridge Cycling and Improve Cardiac Function

Abstract

We previously reported that increased cellular 2-deoxy-ATP (dATP) augments contraction, enhancing the rate and magnitude of both contraction and relaxation in intact cardiomyocytes, force production in skinned cardiac muscle, and fractional shortening of the whole heart. To better understand the mechanism by which dATP enhances cardiac function, we used molecular dynamics (MD) simulations to study the pre- and post-powerstroke states of myosin (PDB ID: 1VOM and 1MMA) bound to either Mg2+.(d)ADP.Pi (pre-powerstroke) or Mg2+.(d)ADP (post-powerstroke) for 50ns. In both states, dATP binding to myosin alters the conformation of the nucleotide binding pocket and the actin binding surface. In the pre-powerstroke state, myosin made fewer contacts with dADP than with ADP and this structural change translated to increased exposure of polar residues on the actin-binding surface of myosin. Since the initial acto-myosin interaction is primarily electrostatic, the affinity of myosin for actin may thus be enhanced with dADP.Pi. In post-powerstroke simulations, dADP binding reduced the exposure of actin binding residues on myosin somewhat. This may translate into improved ability for myosin detachment from actin at the end of the powerstroke in the presence of dADP vs. ADP. Furthermore, stopped-flow spectroscopy demonstrated that myosin has 40-80% weaker binding affinity for dADP than ADP, which may also contribute to faster myosin detachment. Together, these data demonstrate that dADP binding to myosin significantly alters the conformation of myosin, which may translate to faster cross-bridge cycling due to both enhanced myosin binding in the pre-powerstroke state and faster myosin detachment from actin in the post-powerstroke state. Ongoing studies examining the effect of enhanced cross-bridge cycling with elevated dATP in infarcted hearts suggest that dATP may reduce the loss of systolic function. Supported by HL111197 (MR), WT085309 (MAG), GM50789 (VD) and T32EB001650 (SGN).