What is the molecular structure and proteolytic activity of botulinum toxin (BoNT)?

Updated: Oct 10, 2019
  • Author: Divakara Kedlaya, MBBS; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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The BoNT molecule is synthesized as a single chain (150 kD) and then cleaved to form the dichain molecule with a disulfide bridge (see image below).

Botulinum toxin structure (schematic diagram). Botulinum toxin structure (schematic diagram).

The light chain (~50 kD - amino acids 1-448) acts as a zinc (Zn2+) endopeptidase similar to tetanus toxin with proteolytic activity located at the N-terminal end (see image below). The heavy chain (~100 kD - amino acids 449-1280) provides cholinergic specificity and is responsible for binding the toxin to presynaptic receptors; it also promotes light-chain translocation across the endosomal membrane.

Proteolytic activity is located at the N-terminal Proteolytic activity is located at the N-terminal end of the light chain of botulinum toxin type A.

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