Synaptic vesicle fusion complex contains unc-18 homologue bound to syntaxin.
Three synaptic proteins, syntaxin, SNAP-25 and synaptobrevin, were recently identified as targets of clostridial neurotoxins that irreversibly inhibit synaptic vesicle fusion. Experiments searching for membrane receptors for N-ethylmaleimide-sensitive fusion protein (NSF), which has an important role in membrane fusion, revealed an ATP-dependent interaction of the same three synaptic proteins with NSF and its soluble attachment proteins. Thus, two independent approaches identify syntaxin, synaptobrevin and SNAP-25 as components of the synaptic vesicle fusion machinery, but their mode of action is unclear. We have now discovered a brain protein of relative molecular mass 67,000 (67K) which binds stably to syntaxin. Amino-acid sequencing and complementary DNA cloning revealed that the 67K protein is encoded by the mammalian homologue of the Caenorhabditis elegans gene unc-18. In C. elegans, unc-18 belongs to a group of genes defined by mutations with a paralytic phenotype and accumulations of acetylcholine, suggesting a defect in neurotransmitter release. The binding of the mammalian homologue of unc-18 (Munc-18) to syntaxin requires the N terminus of syntaxin whereas that of SNAP-25 involves a more C-terminal sequence. Our data suggest that Munc-18 is a previously unidentified essential component of the synaptic vesicle fusion protein complex.
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Howard Hughes Medical Institute, University of Texas Southwestern Medical School, Dallas 75235.
Slaughter
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Südhof
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TC
D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D001483:Base Sequence; D001923:Brain Chemistry; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D002417:Cattle; D015801:Helminth Proteins / Q000737:chemistry; D008561:Membrane Fusion / Q000502:physiology*; D008969:Molecular Sequence Data; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000502:physiology*; D010750:Phosphoproteins; D011485:Protein Binding; D051381:Rats; D011993:Recombinant Fusion Proteins; D017386:Sequence Homology, Amino Acid; D013572:Synaptic Vesicles / Q000502:physiology*; D050827:Syntaxin 1; D033921:Vesicular Transport Proteins
D000954:Antigens, Surface; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D015801:Helminth Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D050827:Syntaxin 1; C082636:Unc-18 protein, C elegans; D033921:Vesicular Transport Proteins