Myosin binding to actin filaments in the lattice setting. 

 

We have demonstrated the effect of the thick and thin filament lattice on myosin binding, which corroborate and extends similar experiments carried out by Chase and colleagues. This was achieved by using longitudinal and azimuthal selection rules for mapping heads to target zones of adjacent actin sites and by using mean-field approximation to generate independent state probabilities for myosin. We also developed a more rigorous approach to binding by involving azimuthal selection of actin sites on F-actin by unbound myosin heads within a 3D sarcomere lattice and a Monte Carlo simulation defining the transition between actomyosin states. Azimuthal probabilities are defined via reasonable but somewhat arbitrary weight functions. In the proposed project period, we will use an energetic approach based on Brownian dynamics which incorporates the compliance of S2 into bending (rotation axis perpendicular to plane of S2 and F-actin), shearing (rotation axis parallel to F-actin), and long range electrostatic interactions. We believe that this approach will refine our estimates of binding and will be compatible with the 3-site target zones used in our present approach.