Tracking of displacement steps generated by single myosin ID and myosin II molecules

Myosins are actin-based molecular motors which are believed to generate nanometer-sized displacements by amplifying small movements in the motor domain via a lever arm mechanism. Strong evidence in favor of this mechanism has been presented for myosin II molecules from muscle, however, previous step size measurements from other myosins did not relate directly to the proposed mechanism. In this study we analyzed the single molecule step size from rat myosin ID in more detail. Varying the length of the light chain binding domain of myosin ID resulted in a proportional change of the step size, similar to our observations for experiments on myosin II. However, the step sizes of myosin ID are much larger than those of myosin II at comparable length of the proposed lever arm domain. Based on these results we conclude, that both motors employ the same mechanism for generating displacements and suggest that differences in the step sizes of different myosins are not only determined by the length of the lever arm, but are also based on substantial differences in the degree of the lever arm rotation.