SYNAPTIC VESICLE MEMBRANE-FUSION COMPLEX - ACTION OF CLOSTRIDIAL NEUROTOXINS ON ASSEMBLY

Clostridial neurotoxins inhibit neurotransmitter release by selective and specific intracellular proteolysis of synaptobrevin/VAMP, synaptos omal-associated protein of 25 kDa (SNAP-25) or syntaxin. Here we show that in binary reactions synaptobrevin binds weakly to both SNAP-25 an d syntaxin, and SNAP-25 binds to syntaxin. In the presence of all thre e components, a dramatic increase in the interaction strengths occurs and a stable sodium dodecyl sulfate-resistant complex forms. Mapping o f the interacting sequences reveals that complex formation correlates with the presence of predicted cc-helical structures, suggesting that membrane fusion involves intermolecular interactions via coiled-coil s tructures. Most toxins only attack the free, and not the complexed, pr oteins, and proteolysis of the proteins by different clostridial neuro toxins has distinct inhibitory effects on the formation of synaptobrev in - syntaxin - SNAP-25 complexes. Our data suggest that synaptobrevin , syntaxin and SNAP-25 associate into a unique stable complex that fun ctions in synaptic vesicle exocytosis.