Prion

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A prion is an infectious protein. It is the only infectious agent that contains no nucleic acids (such as DNA or RNA).

Prions are proteins that in their normal form are made of amino acids that are in a mainly α-helix structure. This form is known as PrPC.[1]

The normal form is found in cell membranes and thought to be involved in maintaining long term memories in the hippocampus.[2]

The abnormal disease causing form is the result of a misfolded protein PrPSc, in this form much of the structure is replaced by β-sheets.[3]

These β-sheets combine to form helical fibres called amyloid. Amyloid fibres grow at the ends of proteins and as normal protein subunits bind to these ends they misfold and become a part of the amyloid[4]. This β-sheets confirmation leads to gradual accumulation proteins which creates a stable amyloid fibril. This property builds a positive feedback loop conformation to spread rapidly from cell to cell in the central neuron system. Amyloid fibril in brain eventually leads to damage on tissue and cell death.[5]

An isoform of the normal protein (PrPC) has been found to catalyse normal protein into the abnormal PrPSc form.This is why prions are classed as infectious agents.[6] 

Prions occur in a multitude of organisms including humans. They are responsible for may neurodegenerative diseases and all prions found in mammals affect the brain or any other type of neural tissue. All diseases caused by prions are currently untreatable and result in the death of the affected individual[7]. An example of a disease that is caused by infectious prions is BSE (bovine spongiform encephalopathy), which is also known as mad cow disease[8]. This degenerative disease occurs in humans when they eat a part of an infected cow. 

Another feature that set prions apart from other infectious agents are the fact they are resistant to the normals strategies used in the destruction of infective agents.

They are resistant to denaturation by chemical and physical agents.[9]Including bleach, radiation and heat which is often used to sterilise medical equipment.

Contents

Notable Prion Diseases

BSE (bovine spongiform encephalopathy),

This is also known as mad cow disease[10]. This degenerative disease occurs in humans when they eat a part of an infected cow.

Kuru

This disease is a human prion disease and is endemic to tribal regions of Papua New Guinea.[11] The disease is spread by ingestion of the prions during funerary cannibalism [12]. This involves ingestion of the brain matter of a deceased tribe member as part of their funeral rites.

Research for treatment

All notable prion diseases in mammals have significant adverse effects on brain or other neural tissues. There is no treatment or cure at the moment.[13] However, many trials to find treatment are ongoing.

Congo Red Derivative 

Congo red is a dye for detecting prion proteins by binding to them, however, it cannot be utilised for medical treatment due to its toxicity.[14]

References

  1. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  2. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  3. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  4. Alberts, B Johnson, A Lewis, J Raff, M Roberts, K Walter, P (2008). Molecular Biology of the Cell. 5th ed. New York: Garland Science. 1499.
  5. Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K., . . . Hunt, T. (2015). Molecular biology of the cell (6th ed.). New York, NY: Garland Science, Taylor and Francis Group.
  6. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  7. Prusiner SB (1998). "Prions". Proceedings of the National Academy of Sciences of the United States of America 95 (23): 13363–83.
  8. Alberts, B Johnson, A Lewis, J Raff, M Roberts, K Walter, P (2008). Molecular Biology of the Cell. 5th ed. New York: Garland Science. 1498.
  9. Naish, J., Court, D.S. and Revest, P. (2009) Medical Sciences. Elsevier Health Sciences UK. 239.
  10. Alberts, B Johnson, A Lewis, J Raff, M Roberts, K Walter, P (2008). Molecular Biology of the Cell. 5th ed. New York: Garland Science. 1498.
  11. Wadsworth JD, Joiner S, Linehan JM, et al. (March 2008). "Kuru prions and sporadic Creutzfeldt-Jakob disease prions have equivalent transmission properties in transgenic and wild-type mice". Proc. Natl. Acad. Sci. U.S.A. 105 (10): 3885–90
  12. Lindenbaum S (November 2008). "Review. Understanding kuru: the contribution of anthropology and medicine". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 363 (1510): 3715–20
  13. Prusiner SB (November 1998). "Prions". Proceedings of the National Academy of Sciences of the United States of America. 95 (23): 13363–83. Bibcode:1998PNAS...9513363P. doi:10.1073/pnas.95.23.13363. PMC 33918. PMID 9811807.
  14. LibreTexts Biology,Prions, 2016, https://bio.libretexts.org/TextMaps/Introductory_and_General_Biology/Supplemental_Modules_(Molecular_Biology)/Prions (accessed 08/12/2018)
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