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PRIONS

PRIONS. Kalina Estrada TA: Yu-Chen Hwang Thursday, 7-8pm. Background. PRIONS ARE NOT VIRUSES- they don’t contain genetic material

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PRIONS

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  1. PRIONS Kalina Estrada TA: Yu-Chen Hwang Thursday, 7-8pm

  2. Background • PRIONS ARE NOT VIRUSES- they don’t contain genetic material • “Prion” - short for proteinaceous infectious particle (coined by Prusiner), made ONLY of protein. Therefore, they are resistent to nucleases, but not proteases. • The specific protein that the prion was made of was named PrP, an abbreviation for "prion-related protein".

  3. History • 1730’s: 1st appearance in Sheep • 1950’s: High levels of Kuru appear among the Fore people of New Guinea. • 1960’s: found to be contagious • 1980’s: 60 people died from CJD, after being infected by contaminated surgical instruments • 1982: Prusiner found these diseases to be caused by a protein • 1985: Scientists found that uninfected individuals produce the normal PrP genes • 1987: Mad Cow Disease. By 2000, approx. 180,000 cattle were found infected, and most were killed (to prevent further contamination) • 1996: Mad Cow beef proves to be fatal to people. By April 2005, 155 U.K. resisdents died.

  4. Structure • There are two forms of PrP (for the most part made up of the same amino acids): • PrP-sen (on the left): is produced by normal healthy cells. Sen stands for “sensitive” because it is sensitive to being broken down • PrP-res (on the right): is an isoform- the disease causing form. Res stands for “resistant” because it is resistent to being broken down.

  5. Replication • Unlike other infectious particles or viruses, Prions do not contain a nucleic acid genome. However, once a prion has infected, it can replicate • Although it has not been confirmed, evidence shows that when PrP-sen comes into contact with PrP-res it is converted to PrP-res, by dimerizing. This results in a chain reaction of PrP-sen isforming into PrP-res.

  6. How they infect… • Because of their abnormal shape, PrP-res proteins tend to stick to each other. Over time, the PrP-res molecules stack up to form long chains called “amyloid fibers”. • Amyloid fibers are toxic to cells, and ultimately kill them. • Astrocytes crawl through the brain digesting the dead neurons, leaving holes where neurons used to be. The amyloid fibers remain. • This causes holes in the brain which can ultimately lead to death.

  7. Prions are contracted in a few different ways: • Eating tissue infected with PrP-res • An inherited mutation in the gene that encodes for normal PrP • Spontaneous formation of PrP-res (rare)

  8. Transmission Cycle PrP-BSE PrP-Scr PrP-vCJD

  9. Some Examples of Prions (spongiform diseases): • Scrapie (sheep- PrP-Scr) • Bovine Spongiform Encephalopathy (BSE, a.k.a. Mad Cow Disease,1987) • Kuru (transmitted through consumption of human brain tissue) • Creutzfeld-Jakob disease in humans (CJD) • Encephalopathy of mink

  10. Any treatment? • There is no immune response to pathogen • Spongiform diseases are contagious and have a long incubation period • Spongiform diseases are fatal and untreatable • There are no effective treatments • Symptoms vary depending on the concentrated area

  11. Prevention • Do not eat infected tissue • Make sure when undergoing or performing surgical procedures, to use sterile utensils. • Prions are not easily destroyed. The use of boiling techniques, alcohol , acid, standard autoclaving methods, or radiation will not kill them. • “ In fact, infected brains that have been sitting in formaldehyde for decades can still transmit spongiform disease.”- University of Utah, 2006 • Cooking your burger until it's well done will not get rid of the prions!!

  12. References • University of Utah, Genetic Science learning center, 2006 http://gslc.genetics.utah.edu/features/prions/kuru.cfm • Research in the News: Prions - Puzzling Infectious Proteins, National Institutes of Health, 1997 http://science-education.nih.gov/home2.nsf/Educational+Resources/Resource+Formats/Online+Resources/+High+School/D07612181A4E785B85256CCD0064857B

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