Mutant sheep scrapie prion lacks a stretch of amino acids that may be essential for infection For the first time, scientists have isolated a mutated prion protein that can multiply in the lab but not in living animals, according to a PLOS Pathogens study. The new open-access article is titled “Isolation of a Defective Prion Mutant from Natural Scrapie.” The mutant prion provides new insights into the mechanisms that make prions infectious, say co-author Ilaria Vanni of the Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, and colleagues. Prions are cellular proteins that have become mis-folded and can trigger other proteins to mis-fold, aggregate into dense protein structures, and cause brain damage. Prions are responsible for several infectious fatal neurodegenerative disorders, including Creutzfeldt-Jakob disease in humans and "mad cow disease" in cattle. Previous research has shown that, under certain conditions, prion strains can mutate--change their conformation. In the new study, Vanni's team induced the emergence of a prion mutant while working with highly diluted natural prions obtained from sheep suffering from a prion disease called scrapie. Like other prions, the mutant scrapie prion was able to multiply in the lab outside of an animal, in vitro. However, when the researchers infected bank voles with the mutant protein, none of the voles showed signs of disease. In contrast, the natural, un-mutated form of the prion was able to successfully infect bank voles.mThe mutant prion's inability to infect voles may be due to its missing a stretch of amino acids that is present in the un-mutated form. The researchers hypothesize that this region is essential for animal infection, but not for in vitro multiplication.
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