Identification and characterization of multiple novel Rab-myosin Va interactions.

Myosin Va is a widely expressed actin-based motor protein that binds members of the Rab GTPase family (3A, 8A, 10, 11A, 27A) and is implicated in many intracellular trafficking processes. To our knowledge, myosin Va has not been tested in a systematic screen for interactions with the entire Rab GTPase family. To that end, we report a yeast two-hybrid screen of all human Rabs for myosin Va-binding ability and reveal 10 novel interactions (3B, 3C, 3D, 6A, 6A', 6B, 11B, 14, 25, 39B), which include interactions with three new Rab subfamilies (Rab6, Rab14, Rab39B). Of interest, myosin Va interacts with only a subset of the Rabs associated with the endocytic recycling and post-Golgi secretory systems. We demonstrate that myosin Va has three distinct Rab-binding domains on disparate regions of the motor (central stalk, an alternatively spliced exon, and the globular tail). Although the total pool of myosin Va is shared by several Rabs, Rab10 and Rab11 appear to be the major determinants of its recruitment to intracellular membranes. We also present evidence that myosin Va is necessary for maintaining a peripheral distribution of Rab11- and Rab14-positive endosomes.