Myosin-Va regulates exocytosis through the submicromolar Ca 2+-dependent binding of syntaxin-1A

Michitoshi Watanabe, Kazushige Nomura, Akihiro Ohyama, Ryoki Ishikawa, Yoshiaki Komiya, Kohei Hosaka, Emiko Yamauchi, Hisaaki Taniguchi, Nobuyuki Sasakawa, Konosuke Kumakura, Tatsuo Ushiki, Osamu Sato, Mitsuo Ikebe, Michihiro Igarashi

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77 Citations (Scopus)


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 μM 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 Ca 2+.

Original languageEnglish
Pages (from-to)4519-4530
Number of pages12
JournalMolecular biology of the cell
Issue number10
Publication statusPublished - 2005 Oct
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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