Stepping Mechanisms of Myosin Va on Various Actin Cytoskeleton Structures

Abstract

Myosin Va plays a central role in intracellular polarized transport through its actin-based processivity. Cargo transport by myosin Va has been intensively investigated. However, it is not known yet whether a myosin Va molecule moves over all the types of actin filaments in cells. To examine the effects of different types of actin filaments on myosin Va's processivity, we have used actin cytoskeleton structure in cells that were de-membraned by triton treatment. We then observed the movement behavior of single myosin Va molecules on these different areas of actin filaments which include stress fibers, filopodia, leading edges, and lamellipodia. The run-length, direction of step and step-size of myosin Va, at each region of cytoskeletal actin were measured.We found that myosin Va molecules moved well on stress fibers (run-length: 1.8 ± 0.35 μm), leading edge (run-length: 2.1 ± 0.43 μm), and filopodia (run-length: 1.6 ± 0.21 μm), but not at lamellipodia area (run-length: 0.54 ± 0.35 μm). The step-size of myosin Va molecule was 35.2 ± 8.2 nm at the stress fiber area, while it exhibited two peaks (Major peak: 34.6 ± 9.1nm, and Minor peak: 18.5 ± 5.5 nm) on filopodia. On the actin filaments at the leading edge, the distribution of myosin Va step-size was larger than others (35.5 ± 16.2 nm), suggesting that the myosin Va may take side-steps on actin filaments at the leading edges. We further investigate the movement and mechanism of myosin Va on a restricted subset of actin filaments.