Tetanus toxin
Tetanus toxin is an extremely potent neurotoxin produced by the vegetative cell of Clostridium tetani in anaerobic conditions, causing tetanus. It has no known function for clostridia in the soil environment where they are normally encountered. It is also called spasmogenic toxin, or TeNT. The LD50 of this toxin has been measured to be approximately 2.5-3 ng/kg, making it second only to Botulinum toxin (LD50 2 ng/kg) as the deadliest toxin in the world. However, these tests are conducted solely on mice which may react to the toxin differently from humans and other animals.
C. tetani also produces the exotoxin tetanolysin, a hemolysin, that causes destruction of tissues.
Tetanus toxin spreads through tissue spaces into the lymphatic and vascular systems. It enters the nervous system at the neuromuscular junctions and migrates through nerve trunks and into the central nervous system (CNS) by retrograde axonal transport by using dyneins.
The tetanus toxin protein has a molecular weight of 150kDa. It is translated from the tetX gene as one protein which is subsequently cleaved into two parts: a 100kDa heavy or B-chain and a 50kDa light or A-chain. The chains are connected by a disulfide bond.
The TetX gene encoding this protein is located on the PE88 plasmid.
The sequence of this protein has been deposited in Uniprot with accession P04958
Several structures of the binding domain and the peptidase domain have been solved by X-ray crystallography and deposited in the PDB. A summary of these structures is available using the UniPDB application at PDBe, for example 1z7h or 3hmy.
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