Molecular Dynamics Studies of Myosin Structure with 2-Deoxy-ADP

Abstract

Myosin uses ATP catalysis to drive muscle contraction by facilitating cross-bridge cycling. During the cross-bridge powerstroke, coordinated release of the byproducts of nucleotide catalysis (Pi, ADP) triggers a series of conformational changes in myosin that alter its interactions with actin and ultimately generate force. In addition to ATP, myosins can utilize other nucleotides, such as the naturally occurring 2-deoxy-ATP (dATP), to catalyze the powerstroke. We have reported that dATP enhances cross-bridge binding and cycling dynamics, resulting in stronger, faster contraction especially in cardiac muscle. In a recent study (Nowakowski 2017, Protein Sci 26:749-62) our simulations of myosin in the pre-powerstroke state showed that dADP induces conformational changes that expose polar residues and enhance its affinity for actin. In a current study using x-ray structural analysis, we found that dATP increases the rate of myosin detachment following tetanic contraction. To understand the molecular basis for the enhanced rate of detachment in the presence of elevated dATP, we performed molecular dynamics simulations of the myosin motor domain modeled in the post-powerstroke conformation in the presence of Mg2+ and either ADP or dADP. We found that dADP was more flexible than ADP, more mobile within the nucleotide binding pocket and had different interactions with myosin relative to ADP. Furthermore, changes in the interactions between dADP and myosin were transmitted to the actin binding surface. Additionally, we observed partial release of the nucleotides from the binding pocket and have delineated the molecular mechanisms by which regulatory loops in myosin control nucleotide release. Our results have revealed molecular mechanisms underlying dATP-enhanced cross-bridge cycling dynamics. More generally they have yielded insights for the development of novel myosin-targeted therapies for cardiomyopathies based the structural advantages produced by dATP in resting and contracting muscle.