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Mechanism of action of tetanospasmin. Tetanus toxin (TeNT) is an extremely potent neurotoxin produced by the vegetative cell of Clostridium tetani [ 1 ] in anaerobic conditions, causing tetanus. It has no known function for clostridia in the soil environment where they are normally encountered.
There are four main steps in tetanus's mechanism of action: binding to the neuron, internalization of the toxin, membrane translocation, and cleavage of the target VAMP. [36]
The mechanisms of binding to and inhibition of neural cells are related to specific portions of the tetanus toxin molecule. Tetanus toxin is produced initially as an inactive polypeptide chain by actively growing organisms. This synthesis is controlled by genes located in an intracellular plasmid.
Tetanus is caused by the action of a highly potent neurotoxin, tetanospasmin, which is produced during the growth of the anaerobic bacterium Clostridium tetani. C. tetani is not an invasive organism; infection with C. tetani remains localized.
Tetanus and botulinum neurotoxins cause the neuroparalytic syndromes of tetanus and botulism, respectively, by delivering inside different types of neurons, metalloproteases specifically cleaving the SNARE proteins that are essential for the release of neurotransmitters.
Tetanus neurotoxin binds specifically to peripheral motoneuron nerve terminals at the neuromuscular junction and is endocytosed within vesicles, which transport the toxin retroaxonally to the spinal cord.
Tetanus neurotoxin acts mainly at the CNS synapse, while the seven botulinum neurotoxins act peripherally. Clostridial neurotoxins share a similar mechanism of cell intoxication: they block the release of neurotransmitters. They are composed of two disulfide-linked polypeptide chains.
Tetanus and botulinum neurotoxins intoxicate central and peripheral neurons respectively, via a four-step mechanism. TeNT and BoNTs bind to the neuromuscular junction.
The recent comprehen-sion of the biochemical mechanism of action inside neuronal cells have established these toxins as useful tools in studying the processes of fusion of vesicles with target membranes within the cell (Rappuoli & Montecucco 1997).
The clostridial neurotoxins responsible for tetanus and botulism are proteins consisting of three domains endowed with different functions: neurospecific binding, membrane translocation and proteolysis for specific components of the neuroexocytosis apparatus.