ABSTRACT
1. Myosin-V from vertebrate brain is a novel molecular motor with a myosin-like head domain, a calmodulin-binding neck region and a unique tail domain of unknown function. Previous studies showed brain myosin-V to be a phosphoprotein substrate for Ca2+/calmodulin-dependent protein kinase associated with actomyosin. In the present study we describe the preparation of a specific actin-cytoskeletal fraction which is enriched in brain myosin-V. 2. We show that Ca2+/calmodulin-dependent protein kinase activity is also associated with this preparation and phosphorylates brain myosin-V. 3. Calpain, a Ca(2+)-dependent protease, generates a M(r) 80,000 fragment from the COOH terminal region of brain myosin-V containing most or all of the phosphorylation sites. 4. These results suggest that the unique tail domain of this novel myosin is subject to Ca2+ control via phosphorylation by kinase activity associated with the actin cytoskeleton