Tetanus toxin light chain (tetX LC), in the cytosol of a target cell, catalyzes the removal of an aminoterminal peptide from vesicle-associated membrane protein 2 (VAMP2). tetX LC is a zinc metalloprotease (Foran et al. 1994; Schiavo et al. 1992). VAMP2 is associated with the cytosolic face of the target cell synaptic vesicle and is required for vesicle docking and exocytosis. Its cleavage by botulinum toxin blocks exocytosis and in vivo leads to a long-lasting spastic paralysis (Link et al. 1992).