PRNP and scrapie: Numerous studies have analyzed recombinant PrP, synthetic PrP, PrP fragments, and scrapie PrP (PrPSc) [16, 20, 22, 25, 26, 48, 49, 55], but the structural characterization of APrP from human brain tissues has proven difficult due to its insolubility and propensity to aggregate.