PROTEOLYSIS OF SNAP-25 BY TYPE-E AND TYPE-A BOTULINAL NEUROTOXINS

Clostridial neurotoxins, tetanus toxin (TeTx) and the seven related bu t serologically distinct botulinal neurotoxins (BoNT/A to BoNT/G), are potent inhibitors of synaptic vesicle exocytosis in nerve endings. Re cently it was reported that the light chains of clostridial neurotoxin s act as zinc-dependent metalloproteases which specifically cleave syn aptic target proteins such as synaptobrevin/VAMPs, HPC-1/syntaxin (BoN T/C1), and SNAP-25 (BoNT/A). We show here that BoNT/E, like BoNT/A, cl eaves SNAP-25, as generated by in vitro translation or by expression i n Escherichia coli. BoNT/E cleaves the Arg180-Ile181 bond. This site i s different from that of BoNT/A, which cleaves SNAP-25 between the ami no acid residues Gln197 and Arg198. These findings further support the view that clostridial neurotoxins have evolved from an ancestral prot ease recognizing the exocytotic fusion machinery of synaptic vesicles whereby individual toxins target different members of the membrane fus ion complex.