Internalization Tetanus neurotoxin

Botulinum neurotoxins (seven serotypes, A-G) are relatively large water soluble proteins (150 kDa) produced by the Clostridium botulinum. Each protein has two polypeptide chains (a 100 kDa heavy chain and a 50 kDa light chain) linked through a disulfide bond (Fig. 2). In the proposed mode of action of botulinum and tetanus neurotoxins (Simpson, 1986, 1989), the C-terminal half of the heavy chain binds to the nerve membrane leading to internalization of the neurotoxin in the nerve cell through endocytosis. Subsequently, the pH of the endosome is lowered causing the heavy chain to get integrated in the membrane... 

Rossetto O, Seveso M, Caccin P, Schiavo G, Montecucco C (2001b) Tetanus and botulinum neurotoxins turning bad guys into good by research. Toxicon 39 27—41 Rossetto O, Morbiato L, Rossetto et al. 2006 Caccin P, Rigoni M, Montecucco C (2006) Presynaptic enzymatic neurotoxins. J Neurochem 97 1534—4 5 Roux S, Colasante C, Saint Clomcnt C, Barbier J, Curie T et al. (2005) Internalization of a GFP-tetanus toxin C-terminal fragment fusion protein at mature mouse neuromuscular junctions. Mol Cell Neurosci 30 572-82... 

Future important discoveries will be the identification of the neuron-specific receptors of CNTs and of the mode of internalization and membrane translocation of the neurotoxins. Another important line of research is aimed at finding specific inhibitors of these metallo-proteinases. Inhibitors which can cross the neuronal plasmalemma into the cytosol would be potential therapeutic agents in the treatment of tetanus and botulism. The modification of BoNTs to prolong their life time inside the NMJs would be an important research goal to improve the treatment of dystonias. The determination of the three-dimensional structure of these neurotoxins will greatly accelerate the research on these fronts. 

Primary cultures of spinal cord represent a convenient and sensitive system to study mechanisms of neurotransmitters release [11,12]. Internalized neurotransmitters by spinal cord neurons in culture were released quantitatively in response to depolarization and Ca2+. This release is inhibited by tetanus toxin and bot-ulinum neurotoxins in a concentration- and time-dependent manner [13-17]. Therefore, this system serves as a suitable model to examine the efficacy of prospective BoNT countermeasures. Sheridan and Adler indicated that the evoked release of neurotransmitters, notably glycine, in this system was time-dependently increased [18]. In our studies, there was a pronounced time-dependent increase of the drug carrier separation from DDV, which paralleled an enhancement of transmitter release. 

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