title: Myosin-Va regulates exocytosis through the submicromolar Ca2+-dependent binding of syntaxin-1A.
abstract: Myosin-Va is an actin-based processive motor that conveys intracellular cargoes. Synaptic vesicles are one of the most important cargoes for myosin-Va, but the role of mammalian myosin-Va in secretion is less clear than for its yeast homologue, Myo2p. In the current studies, we show that myosin-Va on synaptic vesicles interacts with syntaxin-1A, a t-SNARE involved in exocytosis, at or above 0.3 microM Ca2+. Interference with formation of the syntaxin-1A-myosin-Va complex reduces the exocytotic frequency in chromaffin cells. Surprisingly, the syntaxin-1A-binding site was not in the tail of myosin-Va but rather in the neck, a region that contains calmodulin-binding IQ-motifs. Furthermore, we found that syntaxin-1A binding by myosin-Va in the presence of Ca2+ depends on the release of calmodulin from the myosin-Va neck, allowing syntaxin-1A to occupy the vacant IQ-motif. Using an anti-myosin-Va neck antibody, which blocks this binding, we demonstrated that the step most important for the antibody's inhibitory activity is the late sustained phase, which is involved in supplying readily releasable vesicles. Our results demonstrate that the interaction between myosin-Va and syntaxin-1A is involved in exocytosis and suggest that the myosin-Va neck contributes not only to the large step size but also to the regulation of exocytosis by Ca2+.
authors: Division of Molecular and Cellular Biology, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Niigata 951-8510, Japan.
authors: Michitoshi
authors: M
authors: Watanabe
authors: Kazushige
authors: K
authors: Nomura
authors: Akihiro
authors: A
authors: Ohyama
authors: Ryoki
authors: R
authors: Ishikawa
authors: Yoshiaki
authors: Y
authors: Komiya
authors: Kohei
authors: K
authors: Hosaka
authors: Emiko
authors: E
authors: Yamauchi
authors: Hisaaki
authors: H
authors: Taniguchi
authors: Nobuyuki
authors: N
authors: Sasakawa
authors: Konosuke
authors: K
authors: Kumakura
authors: Tatsuo
authors: T
authors: Ushiki
authors: Osamu
authors: O
authors: Sato
authors: Mitsuo
authors: M
authors: Ikebe
authors: Michihiro
authors: M
authors: Igarashi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000378:metabolism / Q000648:ultrastructure; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D018625:Microscopy, Atomic Force; D008969:Molecular Sequence Data; D018995:Myosin Heavy Chains / Q000502:physiology* / Q000648:ultrastructure; D024701:Myosin Type V / Q000502:physiology* / Q000648:ultrastructure; D011485:Protein Binding; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism; D050827:Syntaxin 1 / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: C513081:Myo5a protein, rat; D050827:Syntaxin 1; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D002118:Calcium