Activated full-length myosin-X moves processively on filopodia with large steps toward diverse two-dimensional directions.

Myosin-X, (Myo 10), is an unconventional myosin that transports the specific cargos to filopodial tips, and is associated with the mechanism underlying filopodia formation and extension. To clarify the innate motor characteristic, we studied the single molecule movement of a full-length myosin-X construct with leucine zipper at the C-terminal end of the tail (M10LZ) and the tail-truncated myosin-X without artificial dimerization motif (BAP-M10HMM). M10LZ localizes at the tip of filopodia like myosin-X full-length (M10). M10LZ moves on actin filaments in the presence of PI(3,4,5)P, an activator of myosin-X. Single molecule motility analysis revealed that the step sizes of both M10LZ and BAP-M10HMM are widely distributed on single actin filaments that is consistent with electron microscopy observation. M10LZ moves on filopodial actin bundles of cells with a mean step size (36 nm), similar to the step size on single actin filaments (38 nm). Cartesian plot analysis revealed that M10LZ meandered on filopodial actin bundles to both x- and y- directions. These results suggest that the lever-arm of full-length myosin-X is flexible enough to processively steps on different actin filaments within the actin bundles of filopodia. This characteristic of myosin-X may facilitate actin filament convergence for filopodia production.