title: Cast: a novel protein of the cytomatrix at the active zone of synapses that forms a ternary complex with RIM1 and munc13-1.
abstract: The cytomatrix at the active zone (CAZ) has been implicated in defining the site of Ca2+-dependent exocytosis of neurotransmitter. We have identified here a novel CAZ protein of approximately 120 kD from rat brain and named it CAST (CAZ-associated structural protein). CAST had no transmembrane segment, but had four coiled-coil domains and a putative COOH-terminal consensus motif for binding to PDZ domains. CAST was localized at the CAZ of conventional synapses of mouse brain. CAST bound directly RIM1 and indirectly Munc13-1, presumably through RIM1, forming a ternary complex. RIM1 and Munc13-1 are CAZ proteins implicated in Ca2+-dependent exocytosis of neurotansmitters. Bassoon, another CAZ protein, was also associated with this ternary complex. These results suggest that a network of protein-protein interactions among the CAZ proteins exists at the CAZ. At the early stages of synapse formation, CAST was expressed and partly colocalized with bassoon in the axon shaft and the growth cone. The vesicles immunoisolated by antibassoon antibody-coupled beads contained not only bassoon but also CAST and RIM1. These results suggest that these CAZ proteins are at least partly transported on the same vesicles during synapse formation.
authors.affiliation: KAN Research Institute Inc., Kyoto 600-8815, Japan. t-ohtsuka@kan.gr.jp
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Ohtsuka
authors.forename: Etsuko
authors.initials: E
authors.lastname: Takao-Rikitsu
authors.forename: Eiji
authors.initials: E
authors.lastname: Inoue
authors.forename: Marie
authors.initials: M
authors.lastname: Inoue
authors.forename: Masakazu
authors.initials: M
authors.lastname: Takeuchi
authors.forename: Kaho
authors.initials: K
authors.lastname: Matsubara
authors.forename: Maki
authors.initials: M
authors.lastname: Deguchi-Tawarada
authors.forename: Keiko
authors.initials: K
authors.lastname: Satoh
authors.forename: Koji
authors.initials: K
authors.lastname: Morimoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakanishi
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Takai
mesh_terms: D000375:Aging / Q000378:metabolism; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D001921:Brain / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D002451:Cell Compartmentation / Q000502:physiology; D002454:Cell Differentiation; D002478:Cells, Cultured; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism* / Q000648:ultrastructure; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D019204:GTP-Binding Proteins; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism* / Q000648:ultrastructure; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D013570:Synaptic Membranes / Q000378:metabolism* / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology; D016708:Synaptophysin / Q000378:metabolism
chemical_list: C498440:BSN protein, human; C498441:Bsn protein, mouse; C113688:Bsn protein, rat; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C491492:RIMS1 protein, human; C107293:Rim protein, mammalian; C491490:Rims1 protein, mouse; C491489:Rims1 protein, rat; D016708:Synaptophysin; C485548:UNC13B protein, human; C103912:Unc13a protein, rat; C485549:Unc13b protein, mouse; C033652:postsynaptic density proteins; C464860:synaptic CAST protein, human; D019204:GTP-Binding Proteins