Proteolysis of synthetic peptides by type A botulinum neurotoxin.

Type A botulinum neurotoxin catalyzed the hydrolysis of synthetic peptides based on the sequence of the 25-kD synaptosomal protein SNAP-25. In each peptide, the toxin cleaved at a single glutaminyl-arginine bond corresponding to residues 197 and 198 of SNAP-25, confirming earlier reports on the enzymatic specificity of the toxin in synaptosomal preparations. Metal chelators inhibited catalysis, consistent with a metalloprotease activity. In contrast to tetanus toxin and other botulinum toxin serotypes, type A toxin hydrolyzed relatively short, 17- to 20-residue peptides. In the substrates, SNAP-25 residue 202 and one or more of residues 187-191 were required for efficient hydrolysis, but residues 167-186 and 203-206 were not. The highest rates of hydrolysis were found when the C-terminal residues of the peptides were amidated.