title: Role of synaptotagmin, a Ca2+ and inositol polyphosphate binding protein, in neurotransmitter release and neurite outgrowth.
abstract: Synaptotagmin I (or II), a possible Ca(2+)-sensor of synaptic vesicles, has two functionally distinct C2 domains: the C2A domain binds Ca2+ and the C2B domain binds inositol high polyphosphates (IP4, IP5, and IP6). Ca(2+)-regulated exocytosis of secretory vesicles is proposed to be activated by Ca2+ binding to the C2A domain and inhibited by inositol polyphosphate binding to the C2B domain. Synaptotagmins now constitute a large family and are thought to be involved in both regulated and constitutive vesicular trafficking. They are classified from their distribution as neuronal (synaptotagmin I-V, X, and XI) and the ubiquitous type (synaptotagmin VI-IX). Among them, synaptotagmins III, V, VI and X are deficient in IP4 binding activity due to the amino acid substitutions in the C-terminal region of the C2B domain, suggesting that these isoforms can work for vesicular trafficking even in the presence of inositol high polyphosphates. Synaptotagmin I is also known to be present in neuronal growth cone vesicles. Antibody against the C2A domain (anti-C2A) that inhibits Ca(2+)-regulated exocytosis also blocked neurite outgrowth of the chick dorsal root ganglion (DRG) neuron, suggesting that Ca(2+)-dependent synaptotagmin activation is also crucial for neurite outgrowth.
authors.affiliation: Department of Molecular Neurobiology, University of Tokyo, Japan. mikosiba@ims.u-tokyo.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Mikoshiba
authors.forename: M
authors.initials: M
authors.lastname: Fukuda
authors.forename: K
authors.initials: K
authors.lastname: Ibata
authors.forename: H
authors.initials: H
authors.lastname: Kabayama
authors.forename: A
authors.initials: A
authors.lastname: Mizutani
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D005089:Exocytosis; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D016501:Neurites / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000502:physiology; D016415:Sequence Alignment; D050863:Synaptotagmin I; D050857:Synaptotagmins
chemical_list: D002135:Calcium-Binding Proteins; D007295:Inositol Phosphates; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C494310:SYT1 protein, human; C494298:SYT6 protein, human; D050863:Synaptotagmin I; D050857:Synaptotagmins; D002118:Calcium