Biophysical Society Thematic Meeting | Canterbury 2023

Towards a More Perfect Union: Multi-Scale Models of Muscle and Their Experimental Validation

Tuesday Speaker Abstracts

MULTISCALE SIMULATIONS OF THE EFFECTS OF 2’-DEOXY-ATP AND MYOSIN MUTATIONS ON ACTOMYOSIN INTERACTIONS Marcus Hock 1 ; Matthew C Childers 3 ; Abigail Teitgen 1 ; Gary Huber 2 ; J. Andrew McCammon 2 ; Michael Regnier 3 ; Andrew D McCulloch 1 ; 1 University of California San Diego, Bioengineering, La Jolla, CA, USA 2 University of California San Diego, Chemistry and Biochemistry, La Jolla, CA, USA 3 University of Washington, Bioengineering, Seattle, WA, USA 2’-deoxy-ATP (dATP) is a myosin activator, which increases contractile force in cardiomyocytes even at low abundances in the nucleotide pool. dATP has therefore been proposed as a potential therapeutic for heart failure with reduced ejection fraction. Here, we use a novel combined molecular and Markov-Brownian dynamics model to investigate changes in acto-myosin dynamics due to dATP compared with ATP. As possible treatment targets, we also simulated two dilated cardiomyopathy causing mutations in β -myosin heavy chain myosin A223T and S532P, which have measured changes in cross-bridge kinetics and therefore expected changes in acto-myosin association. Molecular dynamics (MD) simulations of pre-powerstroke myosin were performed in four conditions: Wild Type (WT), A223T, and S532P myosin in the presence of ADP.Pi, and WT in the presence of dADP.Pi. The MD trajectories were clustered into microstates, before being coarse grained into a reduced Markov model consisting of 15 meta stable conformations, per each condition. By using multiple different metastable conformations from MD trajectories as inputs into the BD simulations, we expect these simulations will provide greater insights into protein-protein association kinetics. Furthermore, we have implemented geometric restraints into the Brownian dynamics simulations to better reflect the tethered natured of the myosin head to the thick filament. Analysis of the Markov models revealed that dADP.Pi reduces conformational variability of myosin head. Neither the A223T nor S532P mutations affected the rates of transitions between conformations. BD simulations showed that conformational variability leads to significant differences in association rates of myosin to actin, producing up to a threefold change between different conformations from a single MD trajectory. Overall comparisons between conditions demonstrate that dADP.Pi increases actin binding affinity of WT myosin by approximately twofold. The A223T + ADP.Pi and S532P + ADP.Pi conditions showed a 0.56x and 3.0x change in association relative to WT myosin, respectively.

39