|Prion Diseases (TSEs)|
|Classification and external resources|
Microscopic "holes" are characteristic in prion-affected tissue sections, causing the tissue to develop a "spongy" architecture.
A prion () is an infectious agent, specifically a protein in a misfolded form. The word prion, coined in 1982 by Stanley B. Prusiner, is derived from the words protein and infection. The protein itself, whether in its misfolded or its correctly folded form, can be referred to as the prion protein (PrP). A protein as an infectious agent stands in contrast to all other known infectious agents, like viruses, bacteria, fungi, or parasites—all of which must contain nucleic acids (either DNA, RNA, or both). Prions are responsible for mammalian transmissible spongiform encephalopathies, including bovine spongiform encephalopathy (BSE, also known as "mad cow disease") and scrapie in sheep. In humans, prions cause Creutzfeldt-Jakob Disease (CJD), variant Creutzfeldt-Jakob Disease (vCJD), Gerstmann–Sträussler–Scheinker syndrome, Fatal Familial Insomnia and kuru. All known prion diseases in mammals affect the structure of the brain or other neural tissue and all are currently untreatable and universally fatal. In 2013, a study revealed that 1 in 2,000 people in the United Kingdom might harbour the infectious prion protein that causes vCJD.
Prions are not considered living organisms but are misfolded protein molecules which may propagate by transmitting a
- UCSF Memory and Aging Center – medical center for diagnosis and care of people with prion disease and research into origin and treatment of prion diseases. (YouTube channel)
- 3D electron microscopy structures of Prions from the EM Data Bank(EMDB)
- Institute for Neurodegenerative Diseases – labs studying prion diseases, run by Stanley B. Prusiner, MD
- Prion Disease Database (PDDB) – Comprehensive transcriptome resource for systems biology research in prion diseases.
- Susan Lindquist's seminars: "The Surprising World of Prion Biology"
- http://www.prion.ucl.ac.uk/ MRC Prion Unit run by Professor John Collinge. Study of all forms of prion disease and development of therapies.
- Mammalian prion classification International Committee on Taxonomy of Viruses – ICTVdb
- Online Mendelian Inheritance in Man: Prion protein – PrP, inherited prion disease and transgenic animal models.
- The Surprising World of Prion Biology—A New Mechanism of Inheritance on-line lecture by Susan Lindquist
- The UK BSE Inquiry – Report of the UK public inquiry into BSE and variant CJD
- UK Spongiform Encephalopathy Advisory Committee (SEAC)
Reports and committees
- CDC – USA Centers for Disease Control and Prevention – information on prion diseases
- World Health Organisation – WHO information on prion diseases
- Deadly Feasts: The "Prion" Controversy and the Public's Health, Richard Rhodes, 1998, Touchstone, ISBN 0-684-84425-7
- The Pathological Protein: Mad Cow, Chronic Wasting, and Other Deadly Prion Diseases, Phillip Yam, 2003, Springer, ISBN 0-387-95508-9
- The Family That Couldn't Sleep by D. T. Max provides a history of prion diseases.
- The Prion Protein a special issue of the open-access journal Current Issues in Molecular Biology
- The Prion's Elusive Reason for Being Note: Behind a paywall.
- A prion lexicon (out of control). Paul Brown & Larisa Cervenakova The Lancet, Vol 365, No. 9454, p. 122, 8 January 2005.
- Ryan KJ, Ray CG, et al, ed. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 624–8.
- "Stanley B. Prusiner — Autobiography". NobelPrize.org. Retrieved 2007-01-02.
- Prusiner SB (1998). "Prions". Proceedings of the National Academy of Sciences of the United States of America 95 (23): 13363–83.
- Gill ON, Spencer Y, Richard-Loendt A, Kelly C, Dabaghian R, Boyes L, Linehan J, Simmons M, Webb P, Bellerby P, Andrews N, Hilton DA, Ironside JW, Beck J, Poulter M, Mead S, Brandner S (2013). "Prevalent abnormal prion protein in human appendixes after bovine spongiform encephalopathy epizootic: Large scale survey".
- Aguzzi A (2008). "Unraveling prion strains with cell biology and organic chemistry". Proceedings of the National Academy of Sciences of the United States of America 105 (1): 11–2.
- Masel J, Jansen VA, Nowak MA (March 1999). "Quantifying the kinetic parameters of prion replication". Biophysical Chemistry 77 (2–3): 139–152.
- Dobson CM (February 2001). "The structural basis of protein folding and its links with human disease" (PDF). Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 356 (1406): 133–45.
- Li J, Browning S, Mahal SP, Oelschlegel AM, Weissmann C (2010). "Darwinian evolution of prions in cell culture". Science 327 (5967): 869–72.
- Krull, Ira S.; Brian K. Nunnally (2004). Prions and mad cow disease. New York, N.Y: Marcel Dekker. p. 6.
- Laurén J, Gimbel DA, Nygaard HB, Gilbert JW, Strittmatter SM (February 2009). "Cellular prion protein mediates impairment of synaptic plasticity by amyloid-beta oligomers". Nature 457 (7233): 1128–32.
- Deleault NR, Harris BT, Rees JR, Supattapone S (2007). "Formation of native prions from minimal components in vitro". Proceedings of the National Academy of Sciences of the United States of America 104 (23): 9741–6.
- Lindquist S, Krobitsch S, Li L, Sondheimer N (February 2001). "Investigating protein conformation-based inheritance and disease in yeast". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 356 (1406): 169–76.
- Alper T, Cramp WA, Haig DA, Clarke MC (May 1967). "Does the agent of scrapie replicate without nucleic acid?". Nature 214 (5090): 764–6.
- Griffith JS (September 1967). "Self-replication and scrapie". Nature 215 (5105): 1043–4.
- Field EJ (1966). Br. Med. J 2 (564).
- Adams DH, Field EJ. "The Infective Process in Scrapie". The Lancet 292 (7570): 714–716.
- Field EJ, Farmer F, Caspary EA, Joyce G (Apr 5, 1969). "Susceptibility of scrapie agent to ionizing radiation.". Nature. 5188 222 (90): 1.
- Crick F (August 1970). "Central dogma of molecular biology". Nature 227 (5258): 561–3.
- "The Nobel Prize in Physiology or Medicine, 1997". NobelPrize.org. Retrieved 2010-02-28.
- Priola SA, Chesebro B, Caughey B (2003). "Biomedicine. A view from the top—prion diseases from 10,000 feet". Science 300 (5621): 917–9.
- Hegde RS, Mastrianni JA, Scott MR, DeFea KA, Tremblay P, Torchia M, DeArmond SJ, Prusiner SB, Lingappa VR (1998). "A transmembrane form of the prion protein in neurodegenerative disease". Science 279 (5352): 827–34.
- Brown DR, Qin K, Herms JW, Madlung A, Manson J, Strome R, Fraser PE, Kruck T, von Bohlen A, Schulz-Schaeffer W, Giese A, Westaway D, Kretzschmar H (1997). "The cellular prion protein binds copper in vivo". Nature 390 (6661): 684–7.
- Weissmann C (November 2004). "The state of the prion". Nature Reviews. Microbiology 2 (11): 861–71.
- Málaga-Trillo E, Solis GP, Schrock Y, Geiss C, Luncz L, Thomanetz V, Stuermer CA (March 2009). Weissmann, Charles, ed. "Regulation of embryonic cell adhesion by the prion protein". PLoS Biology 7 (3): e55.
- Pan KM, Baldwin M, Nguyen J, Gasset M, Serban A, Groth D, Mehlhorn I, Huang Z, Fletterick RJ, Cohen FE (December 1993). "Conversion of alpha-helices into beta-sheets features in the formation of the scrapie prion proteins". Proceedings of the National Academy of Sciences of the United States of America 90 (23): 10962–6.
- Baker, Harry F., and Rosalind M. Ridley, eds. Prion diseases. Totowa, N.J: Humana, 1996
- Cohen FE, Pan KM, Huang Z, Baldwin M, Fletterick RJ, Prusiner SB (1994). "Structural clues to prion replication". Science 265 (5178): 530–531.
- Eigen M (1996). "Prionics or the kinetic basis of prion diseases". Biophysical Chemistry 63 (1): A1–18.
- Bolton DC, Rudelli RD, Currie JR, Bendheim PE (1991). "Copurification of sp33-37 and scrapie agent from hamster brain prior to detectable histopathology and clinical-disease". Journal of General Virology 72 (12): 2905–2913.
- Jendroska K, Heinzel FP, Torchia M, Stowring L, Kretzschmar HA, Kon A, Stern A, Prusiner SB, DeArmond SJ (1991). "Proteinase-resistant prion protein accumulation in syrian-hamster brain correlates with regional pathology and scrapie infectivity". Neurology 41 (9): 1482–1490.
- Beekes M, Baldauf E, Diringer H (1996). "Sequential appearance and accumulation of pathognomonic markers in the central nervous system of hamsters orally infected with scrapie". Journal of General Virology 77 (8): 1925–1934.
- Bamborough P, Wille H, Telling GC, Yehiely F, Prusiner SB, Cohen FE (1996). "Prion protein structure and scrapie replication: theoretical, spectroscopic, and genetic investigations". Cold Spring Harbor Symposium on Quantitative Biology 61: 495–509.
- Knowles TP, Waudby CA, Devlin GL, Cohen SI, Aguzzi A, Vendruscolo M, Terentjev EM, Welland ME, Dobson CM (2009). "An Analytical Solution to the Kinetics of Breakable Filament Assembly". Science 326 (5959): 1533–1537.
- Masel J, Jansen VA (2000). "Designing drugs to stop the formation of prions and other amyloids". Biophysical Chemistry 88 (1–3): 47–59.
- Abbott A (2010-01-24). "Healthy prions protect nerves". Nature.
- Shorter J, Lindquist S (June 2005). "Prions as adaptive conduits of memory and inheritance". Nature Reviews. Genetics 6 (6): 435–50.
- Maglio LE, Perez MF, Martins VR, Brentani RR, Ramirez OA (2004). "Hippocampal synaptic plasticity in mice devoid of cellular prion protein". Brain Research. Molecular Brain Research 131 (1–2): 58–64.
- Caiati MD, Safiulina VF, Fattorini G, Sivakumaran S, Legname G, Cherubini E (2013). "PrPC Controls via Protein Kinase A the Direction of Synaptic Plasticity in the Immature Hippocampus". The Journal of Neuroscience 33 (7): 2973–83.
- Zhang CC, Steele AD, Lindquist S, Lodish HF (2006). "Prion protein is expressed on long-term repopulating hematopoietic stem cells and is important for their self-renewal". Proceedings of the National Academy of Sciences of the United States of America 103 (7): 2184–9.
- "90. Prions". ICTVdB Index of Viruses. U.S. National Institutes of Health website. 2002-02-14. Retrieved 2010-02-28.
- Hussein MF, Al-Mufarrej SI (2004). "Prion Diseases: A Review; II. Prion Diseases in Man and Animals" (PDF). Scientific Journal of King Faisal University (Basic and Applied Sciences) 5 (2): 139. Retrieved 2010-02-28.
- "BSE proteins may cause fatal insomnia.". BBC News. 1999-05-28. Retrieved 2010-02-28.
- Robbins SL, Cotran RS, Kumar V, Collins T, ed. (1999). Robbins pathologic basis of disease. Philadelphia: Saunders.
- Belay ED (1999). "Transmissible spongiform encephalopathies in humans". Annual Review of Microbiology 53: 283–314.
- "Prion Diseases". US Centers for Disease Control. 2006-01-26. Retrieved 2010-02-28.
- Gilch S, Winklhofer KF, Groschup MH, Nunziante M, Lucassen R, Spielhaupter C, Muranyi W, Riesner D, Tatzelt J, Schätzl HM (August 2001). "Intracellular re-routing of prion protein prevents propagation of PrP(Sc) and delays onset of prion disease". The EMBO Journal 20 (15): 3957–66.
- New York University Medical Center and School of Medicine (2005-05-14). "Active Vaccine Prevents Mice From Developing Prion Disease". Science Daily. Retrieved 2010-02-28.
Weiss, Rick (2007-01-01). "Scientists Announce Mad Cow Breakthrough.". The Washington Post. Retrieved 2010-02-28.
Scientists said yesterday that they have used genetic engineering techniques to produce the first cattle that may be biologically incapable of getting mad cow disease.
- Büeler H, Aguzzi A, Sailer A, Greiner RA, Autenried P, Aguet M, Weissmann C (1993). "Mice devoid of PrP are resistant to scrapie". Cell 73 (7): 1339–47.
- Collinge J (2001). "Prion diseases of humans and animals: their causes and molecular basis". Annual Review of Neuroscience 24: 519–50.
- Ironside JW (2006). "Variant Creutzfeldt-Jakob disease: risk of transmission by blood transfusion and blood therapies". Haemophilia : the Official Journal of the World Federation of Hemophilia. 12 Suppl 1: 8–15; discussion 26–8.
- Groschup MH, Kretzschmar HA, eds. (2001). Prion Diseases Diagnosis and Pathogeneis. Archives of Virology. Suppl 16 (New York: Springer).
- Telling GC, Scott M, Mastrianni J, Gabizon R, Torchia M, Cohen FE, DeArmond SJ, Prusiner SB (1995). "Prion propagation in mice expressing human and chimeric PrP transgenes implicates the interaction of cellular PrP with another protein". Cell 83 (1): 79–90.
- Johnson CJ, Pedersen JA, Chappell RJ, McKenzie D, Aiken JM (2007). "Oral transmissibility of prion disease is enhanced by binding to soil particles". PLoS Pathogens 3 (7): e93.
- Tamgüney G, Miller MW, Wolfe LL, Sirochman TM, Glidden DV, Palmer C, Lemus A, DeArmond SJ, Prusiner SB (9 September 2009). "Asymptomatic deer excrete infectious prions in faeces". Nature 461 (7263): 529–532.
- MacKenzie, Debora (13 January 2011). "Prion disease can spread through air". New Scientist (New Science Publications). Health.
- Van Dorsselaer A, Carapito C, Delalande F, Schaeffer-Reiss C, Thierse D, Diemer H, McNair DS, Krewski D, Cashman NR (2011). "Detection of prion protein in urine-derived injectable fertility products by a targeted proteomic approach". PLoS ONE 6 (3): e17815.
- Qin K, O'Donnell M, Zhao RY (August 2006). "Doppel: more rival than double to prion". Neuroscience 141 (1): 1–8.
- Race RE, Raymond GJ (2004). "Inactivation of transmissible spongiform encephalopathy (prion) agents by environ LpH". Journal of Virology 78 (4): 2164–5.
- Collins SJ, Lawson VA, Masters CL (2004). "Transmissible spongiform encephalopathies". Lancet 363 (9402): 51–61.
- Brown P, Rau EH, Johnson BK, Bacote AE, Gibbs CJ, Gajdusek DC (2000). "New studies on the heat resistance of hamster-adapted scrapie agent: threshold survival after ashing at 600 degrees C suggests an inorganic template of replication". Proceedings of the National Academy of Sciences of the United States of America 97 (7): 3418–21.
- "Ozone Sterilization". UK Health Protection Agency. 2005-04-14. Archived from the original on 2008-05-22. Retrieved 2010-02-28.
- Weissmann C, Enari M, Klöhn PC, Rossi D, Flechsig E (2002). "Transmission of prions". Proceedings of the National Academy of Sciences of the United States of America. 99 Suppl 4 (90004): 16378–83.
- Sutton JM, Dickinson J, Walker JT, Raven ND (September 2006). "Methods to minimize the risks of Creutzfeldt-Jakob disease transmission by surgical procedures: where to set the standard?". Clinical Infectious Diseases 43 (6): 757–64.
- Baker & Ridley (1996). Prion Disease. New Jersey: Humana Press.
- Oesch B, Westaway D, Wälchli M, McKinley MP, Kent SB, Aebersold R, Barry RA, Tempst P, Teplow DB, Hood LE (1985). "A cellular gene encodes scrapie PrP 27–30 protein". Cell 40 (4): 735–46.
- Goldmann W (2008). "PrP genetics in ruminant transmissible spongiform encephalopathies". Veterinary Research 39 (4): 30.
- Geissen M, Krasemann S, Matschke J, Glatzel M (2007). "Understanding the natural variability of prion diseases". Vaccine 25 (30): 5631–6.
- Supattapone S (2010). "What makes a prion infectious?". Science 327 (5969): 1091–2.
- Geoghegan JC, Valdes PA, Orem NR, Deleault NR, Williamson RA, Harris BT, Supattapone S (2007). "Selective incorporation of polyanionic molecules into hamster prions". The Journal of Biological Chemistry 282 (50): 36341–53.
- Wang F, Wang X, Yuan CG, Ma J (2010). "Generating a prion with bacterially expressed recombinant prion protein". Science 327 (5969): 1132–5.
- Legname G, Baskakov IV, Nguyen HO, Riesner D, Cohen FE, DeArmond SJ, Prusiner SB (2004). "Synthetic mammalian prions". Science 305 (5684): 673–6.
- Makarava N, Kovacs GG, Bocharova O, Savtchenko R, Alexeeva I, Budka H, Rohwer RG, Baskakov IV (2010). "Recombinant prion protein induces a new transmissible prion disease in wild-type animals". Acta Neuropathologica 119 (2): 177–87.
- Deleault NR, Piro JR, Walsh DJ, Wang F, Ma J, Geoghegan JC, Supattapone S (May 2012). "Isolation of phosphatidylethanolamine as a solitary cofactor for prion formation in the absence of nucleic acids". Proc. Natl. Acad. Sci. U.S.A. 109 (22): 8546–51.
- Deleault NR, Walsh DJ, Piro JR, Wang F, Wang X, Ma J, Rees JR, Supattapone S (July 2012). "Cofactor molecules maintain infectious conformation and restrict strain properties in purified prions". Proc. Natl. Acad. Sci. U.S.A. 109 (28): E1938–46.
- Singh N et al. (2010). "Prion Protein and Metal Interaction: Physiological and Pathological Implications". The Prion Protein. Savanna Press.
- Manuelidis L (March 2007). "A 25 nm virion is the likely cause of transmissible spongiform encephalopathies". Journal of Cellular Biochemistry 100 (4): 897–915.
- "Pathogenic Virus Found in Mad Cow Cells". Yale. 2007-02-02. Retrieved 2010-02-28.
- Manuelidis L, Yu ZX, Barquero N, Banquero N, Mullins B (2007). "Cells infected with scrapie and Creutzfeldt-Jakob disease agents produce intracellular 25-nm virus-like particles". Proceedings of the National Academy of Sciences of the United States of America 104 (6): 1965–70.
- Castilla J, Saá P, Hetz C, Soto C (2005). "In vitro generation of infectious scrapie prions". Cell 121 (2): 195–206.
- Dong J, Bloom JD, Goncharov V, Chattopadhyay M, Millhauser GL, Lynn DG, Scheibel T, Lindquist S (2007). "Probing the role of PrP repeats in conformational conversion and amyloid assembly of chimeric yeast prions". The Journal of Biological Chemistry 282 (47): 34204–12.
- Halfmann R, Alberti S, Lindquist S (2010). "Prions, protein homeostasis, and phenotypic diversity". Trends in Cell Biology 20 (3): 125–33.
- Nemecek J, Nakayashiki T, Wickner RB (2011). "Retraction for Nemecek et al.: A prion of yeast metacaspase homolog (Mca1p) detected by a genetic screen". Proc. Natl. Acad. Sci. U.S.A. 108 (24): 10022.
- Rogoza T, Goginashvili A, Rodionova S, Ivanov M, Viktorovskaya O, Rubel A, Volkov K, Mironova L (2010). "Non-Mendelian determinant ISP+ in yeast is a nuclear-residing prion form of the global transcriptional regulator Sfp". Proceedings of the National Academy of Sciences of the United States of America 107 (23): 10573–7.
- Kuwata K, Nishida N, Matsumoto T, Kamatari YO, Hosokawa-Muto J, Kodama K, Nakamura HK, Kimura K, Kawasaki M, Takakura Y, Shirabe S, Takata J, Kataoka Y, Katamine S (2007). "Hot spots in prion protein for pathogenic conversion". Proceedings of the National Academy of Sciences of the United States of America 104 (29): 11921–6.
- Jones DR, Taylor WA, Bate C, David M, Tayebi M (2010). Ma, Jiyan, ed. "A Camelid Anti-PrP Antibody Abrogates PrPSc Replication in Prion-Permissive Neuroblastoma Cell Lines". PLoS ONE 5 (3): e9804.
- Brown P, Meyer R, Cardone F, Pocchiari M (2003). "Ultra-high-pressure inactivation of prion infectivity in processed meat: A practical method to prevent human infection". Proceedings of the National Academy of Sciences 100 (10): 6093–6097.
- Johnson CJ, Bennett JP, Biro SM, Duque-Velasquez JC, Rodriguez CM, Bessen RA, Rocke TE (2011). "Degradation of the disease-associated prion protein by a serine protease from lichens". PLoS ONE 6 (5): e19836.
- Yam, Philip. "Natural Born Prion Killers: Lichens Degrade "Mad Cow" Related Brain Pathogen". Scientific American. Retrieved 20 May 2011.
- "Detecting Prions in Blood". Microbiology Today.: 195. August 2010. Retrieved 2011-08-21.
- in Brain and Blood"Sc"SOFIA: An Assay Platform for Ultrasensitive Detection of PrP. SUNY Downstate Medical Center. Retrieved 2011-08-19.
Astemizole has been found to have anti-prion activity.
In 2014 collaboration between Rocky Mountain Laboratories, Hamilton, Montana USA and the University of Verona, Italy developed for the first time a protocol for the detection of CJD in living patients. The RT-QuIC assay, a microplate reader-based prion detection method, was applied to nasal brushings obtained from the olfactory epithelium of living patients affected with CJD. The assay had a sensitivity of 97% and specificity of 100% for the detection of CJD. Though a preliminary study, researchers were for the first time able to diagnose Creutzfeldt-Jakob disease in living patients.
In 2010, a team from New York described detection of PrPSc even when initially present at only one part in a hundred billion (10−11) in brain tissue. The method combines amplification with a novel technology called Surround Optical Fiber Immunoassay (SOFIA) and some specific antibodies against PrPSc. After amplifying and then concentrating any PrPSc, the samples are labelled with a fluorescent dye using an antibody for specificity and then finally loaded into a micro-capillary tube. This tube is placed in a specially constructed apparatus so that it is totally surrounded by optical fibres to capture all light emitted once the dye is excited using a laser. The technique allowed detection of PrPSc after many fewer cycles of conversion than others have achieved, substantially reducing the possibility of artefacts, as well as speeding up the assay. The researchers also tested their method on blood samples from apparently healthy sheep that went on to develop scrapie. The animals’ brains were analysed once any symptoms became apparent. The researchers could, therefore, compare results from brain tissue and blood taken once the animals exhibited symptoms of the diseases, with blood obtained earlier in the animals’ lives, and from uninfected animals. The results showed very clearly that PrPSc could be detected in the blood of animals long before the symptoms appeared.
There continues to be a very practical problem with diagnosis of prion diseases, including BSE and CJD. They have an incubation period of months to decades, during which there are no symptoms, even though the pathway of converting the normal brain PrP protein into the toxic, disease-related PrPSc form has started. At present, there is virtually no way to detect PrPSc reliably except by examining the brain using neuropathological and immunohistochemical methods after death. Accumulation of the abnormally folded PrPSc form of the PrP protein is a characteristic of the disease, but it is present at very low levels in easily accessible body fluids like blood or urine. Researchers have tried to develop methods to measure PrPSc, but there are still no fully accepted methods for use in materials such as blood.
In 2011 it was discovered that prions could be degraded by lichens.
In the last decade, some progress dealing with ultra-high-pressure inactivation of prion infectivity in processed meat has been reported.
Advancements in computer modeling have allowed scientists to identify compounds that can treat prion-caused diseases, such as one compound found to bind a cavity in the PrPC and stabilize the conformation, reducing the amount of harmful PrPSc.
Potential treatments and diagnosis
|Protein||Natural host||Normal function||Prion state||Prion phenotype||Year identified|
|Ure2p||Saccharomyces cerevisiae||Nitrogen catabolite repressor||[URE3]||Growth on poor nitrogen sources||1994|
|Sup35p||S. cerevisiae||Translation termination factor||[PSI+]||Increased levels of nonsense suppression||1994|
|HET-S||Podospora anserina||Regulates heterokaryon incompatibility||[Het-s]||Heterokaryon formation between incompatible strains|
|Rnq1p||S. cerevisiae||Protein template factor||[RNQ+],[PIN+]||Promotes aggregation of other prions|
|Mca1||S. cerevisiae||Putative yeast caspase||[MCA+]||Unknown||2008|
|Swi1||S. cerevisiae||Chromatin remodeling||[SWI+]||Poor growth on some carbon sources||2008|
|Cyc8||S. cerevisiae||Transcriptional repressor||[OCT+]||Transcriptional derepression of multiple genes||2009|
|Mot3||S. cerevisiae||Nuclear transcription factor||[MOT3+]||Transcriptional derepression of anaerobic genes||2009|
|Sfp1||S. cerevisiae||Putative transcription factor||[ISP+]||Antisuppression||2010|
Research into fungal prions has given strong support to the protein-only concept, since purified protein extracted from cells with a prion state has been demonstrated to convert the normal form of the protein into a misfolded form in vitro, and in the process, preserve the information corresponding to different strains of the prion state. It has also shed some light on prion domains, which are regions in a protein that promote the conversion into a prion. Fungal prions have helped to suggest mechanisms of conversion that may apply to all prions, though fungal prions appear distinct from infectious mammalian prions in the lack of cofactor required for propagation. The characteristic prion domains may vary between species—e.g., characteristic fungal prion domains are not found in mammalian prions.
As of 2012, there are eight known prion proteins in fungi, seven in Saccharomyces cerevisiae (Sup35, Rnq1, Ure2, Swi1, Mot3, Cyc8, and Mod5) and one in Podospora anserina (HET-s). The article that reported the discovery of a prion form the Mca1 protein has recently been retracted due to the fact that the data could not be reproduced. Notably, most of the fungal prions are based on glutamine/asparagine-rich sequences, with the exception of HET-s and Mod5.
Fungal proteins exhibiting templated conformational change were discovered in the yeast Saccharomyces cerevisiae by Reed Wickner in the early 1990s. For their mechanistic similarity to mammalian prions, they were termed yeast prions. Subsequent to this, a prion has also been found in the fungus Podospora anserina. These prions behave similarly to PrP, but, in general, are nontoxic to their hosts. Susan Lindquist's group at the Whitehead Institute has argued some of the fungal prions are not associated with any disease state, but may have a useful role; however, researchers at the NIH have also provided arguments suggesting that fungal prions could be considered a diseased state. Thus, the issue of whether fungal proteins are diseases, or have evolved for some specific functions, still remains unresolved.
Recent studies propagating TSE infectivity in cell-free reactions and in purified component chemical reactions strongly suggest against TSE viral nature. More recently, using a similar defined recipe of multiple components (PrP, POPG lipid, RNA), Jiyan Ma and colleagues generated infectious prions from recombinant PrP expressed from E. coli, casting further doubt on the viral hypothesis.
- Strain variation: differences in prion infectivity, incubation, symptomology, and progression among species resembles that seen between viruses, especially RNA viruses
- The long incubation and rapid onset of symptoms resembles lentiviruses, such as HIV-induced AIDS
- Viral-like particles that do not appear to be composed of PrP have been found in some of the cells of scrapie- or CJD-infected cell lines.
Evidence in favor of a viral hypothesis includes:
The virion hypothesis states that TSEs are caused by a replicable informational molecule (which is likely to be a nucleic acid) bound to PrP. Many TSEs, including scrapie and BSE, show strains with specific and distinct biological properties, a feature that supporters of the virion hypothesis feel prions do not explain.
The protein-only hypothesis has been criticised by those maintaining that the simplest explanation of the evidence to date is viral. For more than a decade, Yale University neuropathologist Laura Manuelidis has been proposing that prion diseases are caused instead by an unidentified slow virus. In January 2007, she and her colleagues published an article reporting to have found a virus in 10%, or less, of their scrapie-infected cells in culture.
Recent reports suggest that imbalance of brain metal homeostasis is a significant cause of PrPSc-associated neurotoxicity, though the underlying mechanisms are difficult to explain based on existing information. Proposed hypotheses include a functional role for PrPC in metal metabolism, and loss of this function due to aggregation to the disease-associated PrPSc form as the cause of brain metal imbalance. Other views suggest gain of toxic function by PrPSc due to sequestration of PrPC-associated metals within the aggregates, resulting in the generation of redox-active PrPSc complexes. The physiological implications of some PrPC-metal interactions are known, while others are still unclear. The pathological implications of PrPC-metal interaction include metal-induced oxidative damage, and in some instances conversion of PrPC to a PrPSc-like form.
Heavy metal poisoning hypothesis
In 2012, Supattapone and colleagues purified the membrane lipid phosphatidylethanolamine as a solitary endogenous cofactor capable of facilitating the formation of high-titer recombinant prions derived from multiple prion strains. They also reported that the cofactor is essential for maintaining the infectious conformation of PrPSc, and that cofactor molecules dictate the strain properties of infectious prions.
In 2010, Jiyan Ma and colleagues at The Ohio State University produced infectious prions from a recipe of bacterially expressed recombinant PrP, POPG phospholipid, and RNA, further supporting the multi-component hypothesis. This finding is in contrast to studies that found minimally infectious prions produced from recombinant PrP alone.
In 2007, biochemist Surachai Supattapone and his colleagues at Dartmouth College produced purified infectious prions de novo from defined components (PrPC, co-purified lipids, and a synthetic polyanionic molecule). These researchers also showed that the polyanionic molecule required for prion formation was selectively incorporated into high-affinity complexes with PrP molecules, leading them to hypothesize that infectious prions may be composed of multiple host components, including PrP, lipid, and polyanionic molecules, rather than PrPSc alone.
Despite much effort, significant titers of prion infectivity have never been produced by refolding pure PrP molecules, raising doubt about the validity of the "protein only" hypothesis. In addition the "protein only" hypothesis fails to provide a molecular explanation for the ability of prion strains to target specific areas of the brain in distinct patterns. These shortcomings, along with additional experimental data, have given rise to the "multi-component" or "cofactor variation" hypothesis.
A gene for the normal protein has been identified: the PRNP gene. In all inherited cases of prion disease, there is a mutation in the PRNP gene. Many different PRNP mutations have been identified and these proteins are more likely to fold into abnormal prion. Although this discovery puts a hole in the general prion hypothesis, that prions can aggregate only proteins of identical amino acid make-up. These mutations can occur throughout the gene. Some mutations involve expansion of the octapeptide repeat region at the N-terminal of PrP. Other mutations that have been identified as a cause of inherited prion disease occur at positions 102, 117 & 198 (GSS), 178, 200, 210 & 232 (CJD) and 178 (Fatal Familial Insomnia, FFI). The cause of prion disease can be sporadic, genetic, and infectious, or a combination of these factors. For example, to have scrapie, both an infectious agent and a susceptible genotype must be present.
- No virus particles, bacteria, or fungi have been conclusively associated with prion diseases, although Saccharomyces cerevisiae has been known to be associated with infectious, yet non-lethal prions, such as Sup35p.
- No nucleic acid has been conclusively associated with infectivity; agent is resistant to ultraviolet radiation and nucleases.
- No immune response to infection.
- PrPSc experimentally transmitted between one species and another results in PrPSc with the amino-acid sequence of the recipient species, suggesting that replication of the donor agent does not occur.
- Familial prion disease occurs in families with a mutation in the PrP gene, and mice with PrP mutations develop prion disease despite controlled conditions where transmission is prevented.
- Animals lacking PrPC do not contract prion disease.
Evidence in favor of a protein-only hypothesis includes:
Prior to the discovery of prions, it was thought that all pathogens used nucleic acids to direct their replication. The "protein-only hypothesis" states that a protein structure can replicate without the use of nucleic acid. This was initially controversial as it contradicts the central dogma of molecular biology, which describes nucleic acid as the central form of replicative information.
Whether prions cause disease or are merely a symptom caused by a different agent is still debated by a minority of researchers. The following sections describe several hypotheses: Some pertain to the composition of the infectious agent (protein-only, protein with other components, virus, or other), while others pertain to its mechanism of reproduction.
- Immerse in a pan containing 1N NaOH and heat in a gravity-displacement autoclave at 121 °C for 30 minutes; clean; rinse in water; and then perform routine sterilization processes.
- Immerse in 1N NaClO (sodium hypochlorite) (20,000 parts per million available chlorine) for 1 hour; transfer instruments to water; heat in a gravity-displacement autoclave at 121 °C for 1 hour; clean; and then perform routine sterilization processes.
- Immerse in 1N NaOH or sodium hypochlorite (20,000 parts per million available chlorine) for 1 hour; remove and rinse in water, then transfer to an open pan and heat in a gravity-displacement (121 °C) or in a porous-load (134 °C) autoclave for 1 hour; clean; and then perform routine sterilization processes.
The World Health Organization recommends any of the following three procedures for the sterilization of all heat-resistant surgical instruments to ensure that they are not contaminated with prions:
Infectious particles possessing nucleic acid are dependent upon it to direct their continued replication. Prions, however, are infectious by their effect on normal versions of the protein. Sterilizing prions, therefore, requires the denaturation of the protein to a state in which the molecule is no longer able to induce the abnormal folding of normal proteins. In general, prions are quite resistant to proteases, heat, radiation, and formalin treatments, although their infectivity can be reduced by such treatments. Effective prion decontamination relies upon protein hydrolysis or reduction or destruction of protein tertiary structure. Examples include bleach, caustic soda, and strongly acidic detergents such as LpH. 134 °C (274 °F) for 18 minutes in a pressurized steam autoclave may not be enough to deactivate the agent of disease. Ozone sterilization is currently being studied as a potential method for prion denaturation and deactivation. Renaturation of a completely denatured prion to infectious status has not yet been achieved; however, partially denatured prions can be renatured to an infective status under certain artificial conditions.
A University of California research team, led by Nobel Prize winner Stanley Prusiner, has provided evidence for the theory that infection can occur from prions in manure. And, since manure is present in many areas surrounding water reservoirs, as well as used on many crop fields, it raises the possibility of widespread transmission. It was reported in January 2011 that researchers had discovered prions spreading through airborne transmission on aerosol particles, in an animal testing experiment focusing on scrapie infection in laboratory mice. Preliminary evidence supporting the notion that prions can be transmitted through use of urine-derived human menopausal gonadotropin, administered for the treatment of infertility, was published in 2011.
Current research suggests that the primary method of infection in animals is through ingestion. It is thought that prions may be deposited in the environment through the remains of dead animals and via urine, saliva, and other body fluids. They may then linger in the soil by binding to clay and other minerals.
It has been recognized that prion diseases can arise in three different ways: acquired, familial, or sporadic. It is often assumed that the diseased form directly interacts with the normal form to make it rearrange its structure. One idea, the "Protein X" hypothesis, is that an as-yet unidentified cellular protein (Protein X) enables the conversion of PrPC to PrPSc by bringing a molecule of each of the two together into a complex.
Many different mammalian species can be affected by prion diseases, as the prion protein (PrP) is very similar in all mammals. Due to small differences in PrP between different species it is unusual for a prion disease to transmit from one species to another. The human prion disease variant Creutzfeldt-Jakob disease, however, is believed caused by a prion that typically infects cattle, causing Bovine spongiform encephalopathy and is transmitted through infected meat.
All known prion diseases, collectively called transmissible spongiform encephalopathies (TSEs), are untreatable and fatal. However, a vaccine developed in mice may provide insight into providing a vaccine to resist prion infections in humans. Additionally, in 2006 scientists announced that they had genetically engineered cattle lacking a necessary gene for prion production – thus theoretically making them immune to BSE, building on research indicating that mice lacking normally occurring prion protein are resistant to infection by scrapie prion protein.
Prions cause neurodegenerative disease by aggregating extracellularly within the central nervous system to form plaques known as amyloid, which disrupt the normal tissue structure. This disruption is characterized by "holes" in the tissue with resultant spongy architecture due to the vacuole formation in the neurons. Other histological changes include astrogliosis and the absence of an inflammatory reaction. While the incubation period for prion diseases is relatively long (5 to 20 years), once symptoms appear the disease progresses rapidly, leading to brain damage and death. Neurodegenerative symptoms can include convulsions, dementia, ataxia (balance and coordination dysfunction), and behavioural or personality changes.
|cattle||Bovine spongiform encephalopathy (BSE), mad cow disease|
|mink||Transmissible mink encephalopathy (TME)|
|white-tailed deer, elk, mule deer, moose||Chronic wasting disease (CWD)|
|cat||Feline spongiform encephalopathy (FSE)|
|nyala, oryx, greater kudu||Exotic ungulate encephalopathy (EUE)|
(Has not been shown to be transmissible.)
|human||Creutzfeldt–Jakob disease (CJD)|
|Iatrogenic Creutzfeldt–Jakob disease (iCJD)|
|Variant Creutzfeldt–Jakob disease (vCJD)|
|Familial Creutzfeldt–Jakob disease (fCJD)|
|Sporadic Creutzfeldt–Jakob disease (sCJD)|
|Gerstmann–Sträussler–Scheinker syndrome (GSS)|
|Fatal familial insomnia (FFI)|
A 2006 article from the Whitehead Institute for Biomedical Research indicates that PrP expression on stem cells is necessary for an organism's self-renewal of bone marrow. The study showed that all long-term hematopoietic stem cells express PrP on their cell membrane and that hematopoietic tissues with PrP-null stem cells exhibit increased sensitivity to cell depletion.
PrP and stem cell renewal
A review of evidence in 2005 suggested that PrP may have a normal function in maintenance of long-term memory. As well, a 2004 study found that mice lacking genes for normal cellular PrP protein show altered hippocampal long-term potentiation.
PrP and long-term memory
The physiological function of the prion protein remains a controversial matter. While data from in vitro experiments suggest many dissimilar roles, studies on PrP knockout mice have provided only limited information because these animals exhibit only minor abnormalities. In recent research done in mice, it was found that the cleavage of PrP proteins in peripheral nerves causes the activation of myelin repair in Schwann Cells and that the lack of PrP proteins caused demyelination in those cells.
The mechanism of prion replication has implications for designing drugs. Since the incubation period of prion diseases is so long, an effective drug does not need to eliminate all prions, but simply needs to slow down the rate of exponential growth. Models predict that the most effective way to achieve this, using a drug with the lowest possible dose, is to find a drug that binds to fibril ends and blocks them from growing any further.
An alternative model assumes that PrPSc exists only as fibrils, and that fibril ends bind PrPC and convert it into PrPSc. If this were all, then the quantity of prions would increase linearly, forming ever longer fibrils. But exponential growth of both PrPSc and of the quantity of infectious particles is observed during prion disease. This can be explained by taking into account fibril breakage. A mathematical solution for the exponential growth rate resulting from the combination of fibril growth and fibril breakage has been found. The exponential growth rate depends largely on the square root of the PrPC concentration. The incubation period is determined by the exponential growth rate, and in vivo data on prion diseases in transgenic mice match this prediction. The same square root dependence is also seen in vitro in experiments with a variety of different amyloid proteins.
The first hypothesis that tried to explain how prions replicate in a protein-only manner was the heterodimer model. This model assumed that a single PrPSc molecule binds to a single PrPC molecule and catalyzes its conversion into PrPSc. The two PrPSc molecules then come apart and can go on to convert more PrPC. However, a model of prion replication must explain both how prions propagate, and why their spontaneous appearance is so rare. Manfred Eigen showed that the heterodimer model requires PrPSc to be an extraordinarily effective catalyst, increasing the rate of the conversion reaction by a factor of around 1015. This problem does not arise if PrPSc exists only in aggregated forms such as amyloid, where cooperativity may act as a barrier to spontaneous conversion. What is more, despite considerable effort, infectious monomeric PrPSc has never been isolated.
Prion replication mechanism
The infectious isoform of PrP, known as PrPSc, is able to convert normal PrPC proteins into the infectious isoform by changing their conformation, or shape; this, in turn, alters the way the proteins interconnect. PrPSc always causes prion disease. Although the exact 3D structure of PrPSc is not known, it has a higher proportion of β-sheet structure in place of the normal α-helix structure. Aggregations of these abnormal isoforms form highly structured amyloid fibers, which accumulate to form plaques. It is unclear as to whether these aggregates are the cause of cell damage or are simply a side-effect of the underlying disease process. The end of each fiber acts as a template onto which free protein molecules may attach, allowing the fiber to grow. Under most circumstances, only PrP molecules with an identical amino acid sequence to the infectious PrPSc are incorporated into the growing fiber. However, rare cross-species transmission is also possible.
An isoform of PrP known as PrPres because of its resistance to proteolytic digestion by Proteinase K, a surrogate marker of prion infectivity. PrPres may be infectious. This term is used to distinguish Proteinase K-resistant PrP isoforms that have been demonstrated to contain infectivity by transmission and those that have not been proven infectious. For example, PrPC can be denatured or fibrilized in vitro and these preparations may "convert" into Proteinase K-resistant isoforms. However, upon transmission into susceptible hosts, no prion disease develops.
PrPC is a normal protein found on the membranes of cells. It has 209 amino acids (in humans), one disulfide bond, a molecular mass of 35–36 kDa and a mainly alpha-helical structure. Several topological forms exist; one cell surface form anchored via glycolipid and two transmembrane forms. The normal protein is not sedimentable; meaning that it cannot be separated by centrifuging techniques. Its function is a complex issue that continues to be investigated. PrPC binds copper (II) ions with high affinity. The significance of this finding is not clear, but it is presumed to relate to PrP structure or function. PrPC is readily digested by proteinase K and can be liberated from the cell surface in vitro by the enzyme phosphoinositide phospholipase C (PI-PLC), which cleaves the glycophosphatidylinositol (GPI) glycolipid anchor. PrP has been reported to play important roles in cell-cell adhesion and intracellular signaling in vivo, and may therefore be involved in cell-cell communication in the brain.
The protein that prions are made of (PrP) is found throughout the body, even in healthy people and animals. However, PrP found in infectious material has a different structure and is resistant to proteases, the enzymes in the body that can normally break down proteins. The normal form of the protein is called PrPC, while the infectious form is called PrPSc — the C refers to 'cellular' PrP, while the Sc refers to 'scrapie', the prototypic prion disease, occurring in sheep. While PrPC is structurally well-defined, PrPSc is certainly polydisperse and defined at a relatively poor level. PrP can be induced to fold into other more-or-less well-defined isoforms in vitro, and their relationship to the form(s) that are pathogenic in vivo is not yet clear.
In 1982, Stanley B. Prusiner of the University of California, San Francisco announced that his team had purified the hypothetical infectious prion, and that the infectious agent consisted mainly of a specific protein – though they did not manage to isolate the protein until two years after Prusiner's announcement. While the infectious agent was named a prion, the specific protein that the prion was composed of is also known as the Prion Protein (PrP), though this protein may occur both in infectious and non-infectious forms. Prusiner won the Nobel Prize in Physiology or Medicine in 1997 for his research into prions.
Francis Crick recognized the potential importance of the Griffith protein-only hypothesis for scrapie propagation in the second edition of his "Central dogma of molecular biology" (1970): While asserting that the flow of sequence information from protein to protein, or from protein to RNA and DNA was "precluded", he noted that Griffith's hypothesis was a potential contradiction (although it was not so promoted by Griffith). The revised hypothesis was later formulated, in part, to accommodate reverse transcription (which both Howard Temin and David Baltimore discovered in 1970).
During the 1960s, two London-based researchers, radiation biologist Tikvah Alper and mathematician John Stanley Griffith, developed the hypothesis that some transmissible spongiform encephalopathies are caused by an infectious agent consisting solely of proteins. Earlier investigations by E. J. Field into scrapie and kuru had identified the transfer of pathologically inert polysaccharides that only become infectious in the host. Alper and Griffith wanted to account for the discovery that the mysterious infectious agent causing the diseases scrapie and Creutzfeldt–Jakob disease resisted ionizing radiation. (A single ionizing "hit" normally destroys an entire infectious particle, and the dose needed to hit half the particles depends on the size of the particles. The data suggested that the infectious agent was too small to be a virus.)
- Discovery 1
- PrPC 2.1.1
- PrPres 2.1.2
- PrPSc 2.1.3
- Isoforms 2.1
- Prion replication mechanism 3
PrP function 4
- PrP and long-term memory 4.1
- PrP and stem cell renewal 4.2
Prion disease 5
- Transmission 5.1
- Sterilization 5.2
- Protein-only hypothesis 5.3.1
- Genetic factors 5.3.2
- Multi-component hypothesis 5.3.3
- Heavy metal poisoning hypothesis 5.3.4
- Viral hypothesis 5.3.5
- Fungi 6
- Potential treatments and diagnosis 7
- See also 8
- References 9
- Further reading 10
External links 11
- General 11.1
- Reports and committees 11.2
- Genetics 11.3
- Research 11.4
- Other 11.5
All known mammalian prion diseases are caused by the so-called prion protein, PrP. The endogenous, properly folded form is denoted PrPC (for Common or Cellular), whereas the disease-linked, misfolded form is denoted PrPSc (for Scrapie, after one of the diseases first linked to prions and neurodegeneration.) The precise structure of the prion is not known, though they can be formed by combining PrPC, polyadenylic acid, and lipids in a Protein Misfolding Cyclic Amplification (PMCA) reaction. Proteins showing prion-type behavior are also found in some fungi, which has been useful in helping to understand mammalian prions. Fungal prions do not appear to cause disease in their hosts.
This altered structure is extremely stable and accumulates in infected tissue, causing tissue damage and cell death. This structural stability means that prions are resistant to denaturation by chemical and physical agents, making disposal and containment of these particles difficult. Prions come in different strains, each with a slightly different structure, and, most of the time, strains breed true. Prion replication is nevertheless subject to occasional epimutation and then natural selection just like other forms of replication.
(Note that the propagation of the prion depends on the presence of normally folded protein in which the prion can induce misfolding; animals that do not express the normal form of the prion protein can neither develop nor transmit the disease.)  rate associated with prion replication, which is a balance between the linear growth and the breakage of aggregates.exponential growth of prion diseases is determined by the incubation period. Amyloid aggregates are fibrils, growing at their ends, and replicating when breakage causes two growing ends to become four growing ends. The beta sheets fold, in which the protein polymerises into an aggregate consisting of tightly packed amyloid All known prions induce the formation of an