Tetanus toxin
Tetanus toxin | |||||||
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UniProt P04958 | | ||||||
Other data | |||||||
Chromosome | Genomic: 0.07 - 0.07 Mb | ||||||
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Tentoxilysin | |||||||||
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Identifiers | |||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
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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. It is also called spasmogenic toxin, tentoxilysin, tetanospasmin or, tetanus neurotoxin. The LD50 of this toxin has been measured to be approximately 2.5–3 ng/kg,[2][3] making it second only to the related botulinum toxin (LD50 2 ng/kg)[4] 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.[5]
Distribution
Tetanus toxin spreads through tissue spaces into the
Structure
The tetanus toxin
- The B-chain binds to disialogangliosides (GD2 and GD1b) on the neuronal membrane and contains a translocation domain which aids the movement of the protein across that membrane and into the neuron.
- The A-chain, an M27-family zinc endopeptidase, attacks the vesicle-associated membrane protein (VAMP).
The TetX gene encoding this protein is located on the PE88 plasmid.[8][9]
Several structures of the binding domain and the peptidase domain have been solved by X-ray crystallography and deposited in the PDB.[10]
Mechanism of action
The mechanism of TeNT action can be broken down and discussed in these different steps:
- Transport
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- Specific binding in the periphery neurons
- Retrograde axonal transport to the CNS inhibitory interneurons
- Transcytosis from the axon into the inhibitory interneurons
- Action
The first three steps outline the travel of tetanus toxin from the peripheral nervous system to where it is taken up to the CNS and has its final effect. The last three steps document the changes necessary for the final mechanism of the neurotoxin.
Transport to the CNS inhibitory interneurons begins with the B-chain mediating the neurospecific binding of TeNT to the nerve terminal membrane. It binds to GT1b polysialo
Once the vesicle is in the inhibitory interneuron, its translocation is mediated by pH and temperature, specifically a low or acidic pH in the vesicle and standard physiological temperatures.
Clinical significance
The clinical manifestations of tetanus are caused when tetanus toxin blocks inhibitory impulses, by interfering with the release of
Tetanic spasms can occur in a distinctive form called
Immunity and vaccination
Due to its extreme potency, even a lethal dose of tetanospasmin may be insufficient to provoke an immune response. Naturally acquired tetanus infections thus do not usually provide immunity to subsequent infections. Immunization (which is impermanent and must be repeated periodically) instead uses the less deadly
Evolution
Very little has been written or researched on how and why tetanospasmin evolved in animals. The toxin is highly specific to muscular neurons in higher animals and is carried by a plasmid which implies that the host bacterium acquired the plasmid through horizontal gene transfer from another source organism as is the case of most plasmid based toxins such as shigatoxin. Although tetanospasmin is now classified as an extremely potent neurotoxin, its evolutionary origins may indicate it may have served an entirely different function in early animal life. It is routinely carried by anaerobic organisms and early life on earth was typically capable of both aerobic and anaerobic respiration. Human DNA still contains all the genes necessary for anaerobic respiration and one example is the lens cells of the human eye, which still operate in anaerobic mode.[24]
Most lower animals, and even some mammals are capable of anaerobic respiration during their hibernation phases. The spasms typically caused by this toxin mimic cardiac rhythms in skeletal muscles in most reptiles exposed to the toxin and would provide an evolutionary advantage to a hibernating reptile by keeping blood moving slowly around the organism while in hibernation mode if the organism switched to anaerobic respiration. This theory is supported by the fact that tetanus bacteria use a "pump and dump" strategy by secreting the toxin inside a plasmid membrane then exocysing the plasmid vacuole into target tissue. The toxin is not immediately released typically. [25] Higher mammals host this bacteria as a common component of intestinal gut flora and mouth bacteria without any ill effects and it only becomes a problem in anaerobic conditions.[26]
It has no currently known function in the bacterium's host environment which is soil and manure and is harmless to any competing organisms. It only affects higher animals which have neuro muscular junctions which makes its very existence a mystery to modern science.
References
- ^ "Tetanospasmin" at Dorland's Medical Dictionary
- ^ "Pinkbook | Tetanus | Epidemiology of Vaccine Preventable Diseases". CDC. Retrieved 2017-01-18.
- ^ "Toxin Table". Environmental Health & Safety » University of Florida. Archived from the original on 2017-01-18. Retrieved 2017-01-18.
- ^ "Botulism". World Health Organization. Retrieved 2017-01-18.
- ISBN 978-0-07-337523-6.
- PMID 10945801.
- PMID 14576357.
- PMID 3536478.
- PMID 22514279.
- ^ "Advanced Search for UniProt ID P04958". Protein Databank in Europe (PDBe).
- PMID 11716521.
- ^ a b
Winter A, Ulrich WP, Wetterich F, Weller U, Galla HJ (June 1996). "Gangliosides in phospholipid bilayer membranes: interaction with tetanus toxin". Chemistry and Physics of Lipids. 81 (1): 21–34. PMID 9450318.
- PMID 21124874.
- PMID 23200837.
- PMID 24973217.
- PMID 23178719.[permanent dead link]
- PMID 7588600.
- ^ Kumar V, Abbas AK, Fausto N, Aster JC. Robbins and Cotran Pathologic Basis of Disease (Professional: Expert Consult - Online Kindle ed.). Elsevier Health.
- PMID 6308220.
- S2CID 4241066.
- ^ Todar K (2005). "Pathogenic Clostridia, including Botulism and Tetanus". Todar's Online Textbook of Bacteriology. Retrieved 24 June 2018.
- ISBN 978-0-07-146633-2.
- ^ Yabes Jr JM, McLaughlin R. Brusch JL (ed.). "Tetanus in Emergency Medicine". Emedicine. Retrieved 2011-09-01.
- ISBN 0-7506-7152-1.
- PMID 32070229.
- PMID 34181568.
Further reading
- Pellizzari R, Rossetto O, Schiavo G, Montecucco C (February 1999). "Tetanus and botulinum neurotoxins: mechanism of action and therapeutic uses". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 354 (1381): 259–268. PMID 10212474.
- Rossetto O, Scorzeto M, Megighian A, Montecucco C (May 2013). "Tetanus neurotoxin". Toxicon : Official Journal of the International Society on Toxinology. 66: 59–63. PMID 23419592.
- Lalli G, Bohnert S, Deinhardt K, Verastegui C, Schiavo G (September 2003). "The journey of tetanus and botulinum neurotoxins in neurons". Trends in Microbiology. 11 (9): 431–7. PMID 13678859.
- Montecucco C (August 1986). "How do tetanus and botulinum toxins bind to neuronal membranes?". Trends in Biochemical Sciences. 11 (8): 314–317. .
External links
- tetanospasmin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Tentoxilysin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Media related to Tetanus neurotoxin at Wikimedia Commons