Homo- and heterodimerization of synapsins.
In vertebrates, synapsins constitute a family of synaptic vesicle proteins encoded by three genes. Synapsins contain a central ATP-binding domain, the C-domain, that is highly homologous between synapsins and evolutionarily conserved in invertebrates. The crystal structure of the C-domain from synapsin I revealed that it constitutes a large (>300 amino ... acids), independently folded domain that forms a tight dimer with or without bound ATP. We now show that the C-domains of all synapsins form homodimers, and that in addition, C-domains from different synapsins associate into heterodimers. This conclusion is based on four findings: 1) in yeast two-hybrid screens with full-length synapsin IIa as a bait, the most frequently isolated prey cDNAs encoded the C-domain of synapsins; 2) quantitative yeast two-hybrid protein-protein binding assays demonstrated pairwise strong interactions between all synapsins; 3) immunoprecipitations from transfected COS cells confirmed that synapsin II heteromultimerizes with synapsins I and III in intact cells, and similar results were obtained with bacterial expression systems; and 4) quantification of the synapsin III level in synapsin I/II double knockout mice showed that the level of synapsin III is decreased by 50%, indicating that heteromultimerization of synapsin III with synapsins I or II occurs in vivo and is required for protein stabilization. These data suggest that synapsins coat the surface of synaptic vesicles as homo- and heterodimers in which the C-domains of the various subunits have distinct regulatory properties and are flanked by variable C-terminal sequences. The data also imply that synapsin III does not compensate for the loss of synapsins I and II in the double knockout mice.
Mesh Terms:
Animals, Antibody Specificity, Brain Chemistry, Cloning, Molecular, Dimerization, Mice, Mice, Knockout, Protein Binding, Protein Isoforms, Recombinant Proteins, Saccharomyces cerevisiae, Synapsins
Animals, Antibody Specificity, Brain Chemistry, Cloning, Molecular, Dimerization, Mice, Mice, Knockout, Protein Binding, Protein Isoforms, Recombinant Proteins, Saccharomyces cerevisiae, Synapsins
J. Biol. Chem.
Date: Jun. 11, 1999
PubMed ID: 10358015
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