Determining the Relative Susceptibility of Four Prion Protein Genotypes to Atypical Scrapie.

Abstract

Atypical scrapie is a sheep prion (PrP) disease whose epidemiology is consistent with a sporadic origin and is associated with specific polymorphisms of the normal cellular prion protein (PrP). To determine the relative amounts of PrP polymorphisms present in atypical scrapie, total PrP was digested with chymotrypsin to generate characteristic peptides spanning relevant polymorphisms at positions 136, 141, 154, 171, and 172 of sheep PrP. A multiple reaction monitoring method (MRM), employingN-labeled internal standards, was used to detect and quantify these polymorphisms present in both the PrPand PrPfrom heterozygous (ALRRY and ALHQY or ALRQD or AFRQY) atypical scrapie-infected or uninfected control sheep. Both polymorphisms of the full length and truncated (C1) natively expressed PrPare produced in equal amounts. The overall amount of PrPpresent in the infected or uninfected animals was similar. PrPisolated from heterozygotes was composed of significant amounts of both PrP polymorphisms, including the ALRRY polymorphism which is highly resistant to classical scrapie. Thus, an atypical scrapie infection does not result from an overexpression of sheep PrP. The replication of all atypical scrapie prions occurs at comparable rates, despite polymorphisms at positions 141, 154, 171, or 172.