Mode of action of botulinum and tetanus neurotoxins

Clostridium botulinum and Clostridium tetani synthesize botulinum neurotoxins (A to G) and the tetanus toxin, which are responsible for botulism and tetanus, respectively. These toxins cause nervous disorders, either a flaccid paralysis (botulism) or a spastic paralysis (tetanus), which are severe and often lethal. Botulinum and tetanus neurotoxins prevent the release of neurotransmitters. Botulinum neurotoxins inhibit the release of acetylcholine at the neuromuscular junction, whereas tetanus toxin acts on the inhibitory interneurons in the central nervous system. They are metalloproteases, which cleave one of the three proteins in the SNARE complex, which plays a key role in neuroexocytosis. Although neurotoxins are potent poisons, they also are sometimes used as therapeutic agents; for instance, botulinum neurotoxins are largely used in the treatment of dystonia. SUMMARY