POISONING BY BOTULINUM NEUROTOXIN-A DOES NOT INHIBIT FORMATION OR DISASSEMBLY OF THE SYNAPTOSOMAL FUSION COMPLEX

We investigated the effect of poisoning rat brain synaptosomes with bo tulinum neurotoxin A on the NSF-mediated disassembly of a complex cons isting of syntaxin, SNAP-25 and synaptobrevin (fusion complex). Botuli num neurotoxin A specifically removes 9 amino acids from the C-terminu s of SNAP-25 and efficiently blocks KCl-evoked glutamate release from synaptosomes. We report that truncated SNAP-25 is incorporated into th e fusion complex of poisoned synaptosomes. The presence of truncated S NAP-25 does not interfere with the NSF-induced disassembly of the fusi on complex. Also, the release of truncated SNAP-25 from the fusion com plex is similar to that of the native SNAP-25. Since neither the forma tion of the complex nor its disassembly seems to be affected by the SN AP-25 fragment, this fragment is likely to block exocytosis by disrupt ing events between disassembly of the synaptosomal fusion complex and membrane fusion itself. (C) 1995 Academic Press, Inc.