THE 26-MER PEPTIDE RELEASED FROM SNAP-25 CLEAVAGE BY BOTULINUM NEUROTOXIN-E INHIBITS VESICLE DOCKING

Botulinum neurotoxin E (BoNT E) cleaves SNAP-25 at the C-terminal doma in releasing a 26-mer peptide. This peptide product may act as an exci tation-secretion uncoupling peptide (ESUP) to inhibit vesicle fusion a nd thus contribute to the efficacy of BoNT E in disabling neurosecreti on, We have addressed this question using a synthetic 26-mer peptide w hich mimics the amino acid sequence of the naturally released peptide, and is hereafter denoted as ESUP E, This synthetic peptide is a poten t inhibitor of Ca2+-evoked exocytosis in permeabilized chromaffin cell s and reduces neurotransmitter release from identified cholinergic syn apses in in vitro buccal ganglia of Aplysia californica. In chromaffin cells, both ESUP E and BoNT E abrogate the slow component of secretio n without affecting the fast, Ca2+-mediated fusion event, Analysis of immunoprecipitates of the synaptic ternary complex involving SNAP-25, VAMP and syntaxin demonstrates that ESUP E interferes with the assembl y of the docking complex, Thus, the efficacy of BoNTs as inhibitors of neurosecretion may arise from the synergistic action of cleaving the substrate and releasing peptide products that disable the fusion proce ss by blocking specific steps of the exocytotic cascade, (C) 1998 Fede ration of European Biochemical Societies.