Clostridial neurotoxins synaptic vesicles

Tetanus is a disease caused by the release of neurotoxins from the anaerobic, spore-forming rod Clostridium tetani. The clostridial protein, tetanus toxin, possesses a protease activity which selectively degrades the pre-synaptic vesicle protein synaptobrevin, resulting in a block of glycine and y-aminobutyric acid (GABA) release from presynaptic terminals. Consistent with the loss of neurogenic motor inhibition, symptoms of tetanus include muscular rigidity and hyperreflexia. The clinical course is characterized by increased muscle tone and spasms, which first affect the masseter muscle and the muscles of the throat, neck and shoulders. Death occurs by respiratory failure or heart failure. 

Rizzoli SO, Betz WJ (2005) Synaptic vesicle pools. Nat Rev Neurosci 6 57-69 Rossetto O, Montecucco C (2004) Clostridial neurotoxins. In Proft C (ed) Microbial toxins, molecular and cellular biology. Horizon Scientific Press, Norfolk, UK, pp 149-78 Rossetto O, Montecucco C (2007) Peculiar binding of botulinum neurotoxins. ACS Chem Biol 2 96-8... 

Hoyoshi T, McMahon H, Yamasaki S, BinzT, Hata Y, Sodhof TC, Niemann H (1994) Synaptic vesicles membrane fusion complex action of clostridial neurotoxins on assembly. In EMBOJ. 13 5051-61... 

If there is any problem with protein detection, enriched synaptic protein preparations (synaptosomes, presynaptic plasma membrane of synaptic vesicle preparations, depending of the toxin and the substrate) can be better starting material than brain homogenate to check the proteolytic activity of clostridial neurotoxins L chains. 

Pellegrini LL, Oconnor V, Lottspeich F ef al. (1995) Clostridial neurotoxins compromise the stability of a low-energy SNARE complex mediating NSF activation of synaptic vesicle fusion EMBOJ. 14 4705-13. 

Demonstration of this activity was initially difficult because the toxins are very specific for their substrates. However, it is now clear that (a) the clostridial neurotoxins express proteolytic activity and (b) this activity is absolutely required for toxicity.30 The substrate proteins for this action appear to be part of a hetero-oligomeric assembly associated with the synaptic vesicles. Interestingly, the specific target site for cleavage seems to be different for each serotype of the botulinum toxins in some cases, different locations on the same protein in others, different proteins of the assembly.30 The basis of this marked specificity is not yet clear and remains fascinating to scientists interested in neurosecretion. 

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