State Dependent Dynamic Coupling In Myo1b During The Force Sensitive Transition And Mgadp Release

Myosins adjust their power outputs in response to mechanical loads in an isoform-dependent manner, resulting in their ability to dynamically adapt to a range of motile challenges. We recently resolved the near-atomic resolution structures of one rigor (AM) and two ADP-bound states (AM.ADPA, AM.ADPB) of myosin-IB (myo1b) bound to actin, determined by cryo-electron microscopy (cryo-EM) to understand the mechanism of mechanical force-sensing by myo1b. Atomic models of myo1b flexibly fit with molecular dynamics simulations (MD) were stable over 200 ns for all three states. The time averaged synthetic cryo-EM maps generated from MD overlapped well with the cryo-EM data, including the gradual decrease in resolution going from the actin binding interface to the end of the lever arm helix (LAH). Residue-residue cross correlation analysis from MD based on the myo1b C-alpha atoms, together with network analysis of correlated motions, were used to create a dynamic protein structure network depicting the internal dynamic coordination within myo1b. This coordination differs among AM.ADPA, AM.ADPB and AM states. Among key structural elements associated with the nucleotide binding site [i.e. P-loop, switch-I, switch-II, and helix-loop-helix motif (HH, HF helices, Loop-1)], major communication changes occur only within the helix-loop-helix motif. At the interface of the N- terminal subdomain, converter and LAH, only the interactions of loop-5 with the N-terminal extension and the LAH change substantially. Our results provide new details regarding the allosteric coupling critical for myosin motor domain function that are involved in Mg.ADP release.