Different mechanisms of inhibition of nerve terminals by botulinum and snake presynaptic neurotoxins.

The different mode of action on peripheral nerve terminals of the botulinum neurotoxins and of the snake presynaptic phospholipase A2 neurotoxins is reviewed here. These two groups of toxins are highly toxic because they are neurospecific and at the same time are enzymes that can modify many substrate molecules before being inactivated. The similarity of symptoms they cause in humans derives from the fact that both botulinum neurotoxins (seven serotypes named A-G) and snake presynaptic PLA2 neurotoxins block the nerve terminals and that peripheral cholinergic terminals are major targets. Given this general similarity of targets and clinical symptoms, the specific molecular and cellular mechanisms at the basis of their action are very different. This difference appears evident from the beginning of intoxication, i.e. neurotoxins binding to peripheral nerve terminals and proceeds with the different site of actions and molecular targets.