Abstract 338: Motivating Myosin: 2 deoxy-ATP Induced Structural Alterations That Increase Myosin Activity

• Published in: Circulation research 2019-08, Vol.125 (Suppl_1)
• Main Author: Regnier, Michael
• Format: Article
• Language: English
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/res.125.suppl_1.338

Abstract only When 2-deoxy-ATP (dATP) replaces ATP as the contractile substrate, cardiac myosin binding to actin and the rate of cross-bridge cycling is increased. To understand the structural basis of this we employed low-angle x-ray diffraction and computational modeling. Molecular Dynamics (MD) simulations of pre-powerstroke myosin suggest dADP.Pi (vs. ADP.Pi) induces changes in contact pairs for nucleotide binding that translate to structural changes on the actin binding surface, exposing positive charge in regions that make electrostatic interactions with actin. Brownian Dynamics simulations suggest M.dADP.Pi binds more rapidly to actin at distances (angstrom) associated with weak binding. X-ray diffraction analysis of resting demembranated cardiac muscle indicated a large increase in the I 1,1 /I 1,0 intensity ratio for M.dADP.Pi, suggesting myosin moves towards thin filaments. This difference was eliminated at low ionic strength (100 vs. 170mM), where more protein surface charge is exposed, thus decreasing the electrostatic interaction advantage of M.dADP.Pi. The S M3 meridional reflection indicated spacing between myosin crowns was increased for M.dADP.Pi at rest, making it similar was to the activated position of M.ADP.Pi during contraction, with no change in axial ordering ( I M3 ).In intact soleus muscle of transgenic mice with 1% dATP (99% ATP), time-resolved x-ray structure indicates myosin dissociation from actin following tetanic contraction is slightly slower (vs WT) bu the first-order myosin layer line ( MLL1 ) intensity recovers faster, suggesting dATP increases the rate myosin heads return to an ordered resting state. At rest the radii to the center of mass of myosin heads (R m ) and I 1,1 /I 1,0 were larger, indicating myosin heads were closer to actin. MD simulations of post-powerstroke myosin showed greater dADP mobility in the binding pocket via altered interactions with key amino acids, resulting in altered conformation of residues on the actin binding surface in regions interacting with actin. Combined our results suggest that with dATP myosin moves closer to actin and S1 heads are more activated in resting muscle, staying primed for reactivation following relaxation, all via increased myosin-actin electrostatic interactions.