A zinc-protease specific domain in botulinum and tetanus neurotoxins.

Neurotoxins produced by Clostridium botulinum are classified into groups (A to G) based on their serological nature. They consist of two subunits, heavy and light chains, linked by one or more disulphide bridges. The light chain is responsible for the blocking of acetylcholine release. Amino acid sequences of light chains have already been reported for botulinum toxins types A, C, D and E. Five highly homologous regions are found between these four toxins. One of these homologous regions, sequence HELIHSL, shows strong similarity with the active site of zinc-proteases. We suggest that inhibition of acetylcholine release might be associated with this protease activity.