Molecular Pharmacology of Botulinum Toxin and Tetanus Toxin

Abstract

Botulinum toxin is a term that has been used to describe eight different substances designated types A, B, Cb C2, D, E, F, and G. For many years it was assumed that these eight substances acted at the neuromuscular junction to block acetylcholine release. It is now known that this assumption is not entirely correct. Seven Of the substances do act at cholinergic junctions (types A, B, C b D, E, F, and G), and they are properly referred to as botulinum neurotoxins. The eighth substance (type C2) is unique in its structure and pharmacological actions. It is called the botulinum binary toxin. Tetanus toxin is a term that has been used to describe a single substance that acts mainly in the central nervous system to block inhibitory transmission. There are many similarities between tetanus toxin and botulinum neurotoxin, including a common origin, a closely related structure, and perhaps the same subcellular mechanism of action. The similarities between tetanus toxin and the botulinum binary toxin are less clear. The purpose of the present review is to discuss the proposed mechanism( s) of action of the three groups of clostridial toxins. Recent findings suggest that research is moving quickly toward a full determination of the cellular and subcellular actions of these substances. This is an encouraging tum of events, because the clostridial toxins are generally regarded as the most poisonous substances known to mankind.