Fig. 4.

Myosin-5a head motion during processive stepping. (A) iSCAT tracking results: distance traveled as a function of time for a single-motor domain labeled with a 20-nm gold particle at its N-terminus and the corresponding 2D-trajectory, which is shown to the right of the time trace. The arrows indicate ~40 nm off-axis side position of the unbound motor domain (transient state). Inset: schematic of myosin-5a labeling and movement. Imaging speed: 1000 frames per second. (B) Contour map of a two-dimensional histogram with a 10 × 10-nm² bin width obtained from the transient state of the unbound head x–y trajectories (number of steps=486). All contributing steps were aligned and those to the right of the filament when viewed in the direction of motion were mirrored. (C) The data lead to a hand-over-hand spinning model (shown schematically), in which each step proceeds via a single, spatially constrained transient state of the detached head (Andrecka et al., 2015).