Botulinum toxin

Botulinum toxin is a neurotoxic protein produced by Clostridium botulinum. The heavy chain of botulinum toxin first binds to synaptotagmin and gangliosides on the presynaptic membrane of nerve terminals, after which it enters the neuron via endocytosis. Once inside the cell, the light chain functions as a Zn²⁺-dependent endopeptidase that cleaves different SNARE proteins depending on the toxin type, such as SNAP-25, synaptobrevin/VAMP, or syntaxin. This prevents synaptic vesicles from fusing with the neuronal membrane, blocks acetylcholine (ACh) release, deprives muscles of contraction signals, disrupts neuromuscular transmission, and leads to phenomena associated with flaccid paralysis.