Prions – (Wild Proteins) – [May be Viruses]
Why would you be interested in a newly discovered type of infectious agent? Because some forms of “hereditary” disease are really infections with 30 or more years to incubate in the body before showing their effect. Because some people have said, probably wrongly, that they could be a cause of old age, and because it challenges our ideas of what an infection is.
You’ve heard of bacteria, viruses, and protozoa (amoebae and such). Now we have prions. They can turn your brain to a sponge-like mush. What are they? The name is short for protein infectious particles. They are not viruses as they resist inactivation by procedures that modify nucleic acids. Scrapie, an itchy disease with muscular incoordination of sheep and goats, kuru (now eradicated), a muscular incoordination disease of Fore, New Guinea cannibals who ritually ate grandfather’s brain to gain wisdom, mad cow disease from contaminated feed which has killed over 150,000 cattle in recent years in Europe, Creutzfeldt-Jakob disease, a rare infectious dementia of men and women, and fatal familial insomnia are all believed to be caused by prions.
The discoverer of prions, Dr. Prusiner, just received the Lasker Award which often presages the Nobel Prize.
These prion diseases can be transmitted to apes and monkeys. They have been called slow virus diseases but are now known not to be caused by viruses. The prions contain little or no nucleic acid and they do not cause an immune or protective response.
The infectious agent is a sugar protein combination (called glycoprotein), Destruction of the protein part leads to loss of infectivity. It is called PrPSc (for Prion Protein Scrapie). Healthy cells have PrP-C (cellular) which has the same 253 amino acids. The bends and twists in the chain of amino acids are different. However, the abnormal protein is produced in nerve cells and causes empty spaces or vacuoles which eventually leads to microscopically visible brain holes called spongiform degeneration. These particles are not viruses but they do multiply. Is the normal necessary protein PrP-C converted into a malignant lethal molecule by contact with the prion? Are some so-called “inherited diseases” really caused by prions? These diseases have been transmitted by brain operations or by corneal transplants from infected donors.
Recently prion-protein (PrP-C) deprived mice have been shown to have an abnormal cellular docking site for gamma aminobutyric acid (GABA), one of the brain’s chemical messengers, the result is an electrical abnormality with involuntary jerks and, in some cases, seizures. This may be connected with lack of synapses (cellular connections ) without which most nerve cells die. There’s a lot to learn yet about these infectious proteins which so closely resemble normal intracellular proteins.
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