The Clostridial neurotoxin, botulinum, is a zinc endoprotease that cleaves synaptobrevin (VAMP) in cholinergic neurons. Synaptobrevin is a vesicle docking protein; it essential for vesicle fusion with the presynaptic membrane and neurotransmitter release. See Gordon Shepherd's Neurobiology (1994). I hope this helps. G. Ballough