title: Rab3C is a synaptic vesicle protein that dissociates from synaptic vesicles after stimulation of exocytosis.
abstract: Rab3 proteins are small GTP-binding proteins of the Ras superfamily. Four highly homologous Rab3 proteins termed Rab3A, Rab3B, Rab3C, and Rab3D have been described. Rab3A has previously been shown to be a constituent of synaptic vesicles in neurons that undergoes membrane dissociation-association cycles during synaptic vesicle recycling. Here we report that Rab3C copurifies with Rab3A during the isolation of synaptic vesicles. Organelles immunoisolated with monoclonal antibodies directed against Rab3A led to a coenrichment of Rab3A and Rab3C, demonstrating that both Rab3 proteins are colocalized on the same organelle. In isolated nerve terminals, stimulation of neurotransmitter release resulted in a dissociation of Rab3C from synaptic vesicle and/or recycling membranes. This dissociation parallels that of Rab3A observed under the same conditions. In contrast, no change was observed in the membrane-association of Rab5, a Rab protein localized on early endosomes. We conclude that in the nervous system Rab3C is localized on synaptic vesicles and, like Rab3A, cycles on and off the synaptic vesicle membrane in parallel with exocytotic release of neurotransmitter.
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: G
authors.initials: G
authors.lastname: Fischer von Mollard
authors.forename: B
authors.initials: B
authors.lastname: Stahl
authors.forename: A
authors.initials: A
authors.lastname: Khokhlatchev
authors.forename: T C
authors.initials: TC
authors.lastname: Südhof
authors.forename: R
authors.initials: R
authors.lastname: Jahn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D001483:Base Sequence; D002460:Cell Line; D002540:Cerebral Cortex / Q000378:metabolism*; D003001:Cloning, Molecular; D017931:DNA Primers; D005089:Exocytosis; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D015151:Immunoblotting; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D015388:Organelles / Q000378:metabolism; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D016133:Polymerase Chain Reaction; D011817:Rabbits / Q000276:immunology; D051381:Rats; D013572:Synaptic Vesicles / Q000378:metabolism*; D014162:Transfection; D020692:rab3 GTP-Binding Proteins
chemical_list: D000906:Antibodies; D017931:DNA Primers; D009419:Nerve Tissue Proteins; D010455:Peptides; D019204:GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins