How the Load and the Nucleotide State Affect the Actin Filament Binding Mode of the Molecular Motor Myosin V.

The interaction between actin and myosin V has been probed by measuring the unbinding force of individual actomyosin complexes using optical tweezers. Surprisingly, we found that in both the nucleotide-free and ADP-bound states single- and double-headed binding occurs with approximately the same probability. Estimation of the spring constant of individual actomyosin complexes confirmed that in each of the nucleotide states two distinct populations exist. These results confirm that optical nanometry can be used to reliably study the mechanism of how cytoskeleton molecular motors interact with their associated polymer lattices under solution conditions more closely resembling the intracellular environment.