Brain myosin-V, a calmodulin-carrying myosin, binds to calmodulin-dependent protein kinase II and activates its kinase activity

Myosin-V, an unconventional myosin, has two notable structural features: (i ) a regulatory neck domain having six IQ motifs that bind calmodulin and li ght chains, and (ii) a structurally distinct tail domain likely responsible for its specific intracellular interactions. Myosin-V copurifies with syna ptic vesicles via its tail domain, which also is a substrate for calmodulin -dependent protein kinase II, We demonstrate here that myosin-V coimmunopre cipitates with CaM-kinase II from a Triton X-100-solubilized fraction of is olated nerve terminals, The purified proteins also coimmunoprecipitate from dilute solutions and bind in overlay experiments on Western blots. The bin ding region on myosin-V was mapped to its proximal and medial tail domains. Autophosphorylated CaM-kinase II binds to the tail domain of myosin-V with an apparent K-d of 7.7 nM. Surprisingly, myosin-V activates CaM-kinase II activity in a Ca2+-dependent manner, without the need for additional CaM, T he apparent activation constants for the autophosphorylation of CaM-kinase II were 10 and 26 nM, respectively, for myo sin-V versus CaM. The maximum i ncorporation of P-32 into CaM-kinase II activated by myosin-V was twice tha t for CaM, suggesting that myosin-V binding to CaM-kinase II entails altera tions in kinetic and/or phosphorylation site parameters. These data suggest that myosin-V, a calmodulin-carrying myosin, binds to and delivers CaM to CaM-kinase II, a calmodulin-dependent enzyme.