Quantitative profiling of PrP^Sc peptides by high-performance liquid chromatography mass spectrometry to investigate the diversity of prions

Prions are proteins that can exist in two (or more) folding states, a normal or cellular form and a series of infectious or prion forms, which are prone to aggregate. The prion form can induce conversion of the cellular form and so transmit phenotypic effects of this structural rearrangement within and between cells and organisms. The conversion of PrP^C, the mammalian prion glycoprotein, to its prion form, PrP^Sc, in the brain is a precursor to progressive neurological degeneration, and the various folded forms of PrP^Sc (defined by the size and glycosylation of protease-resistant core peptides of the PrP aggregates, PrP^res) are characteristic of a particular neurodegenerative phenotype or prion disease. Here, quantitative multiplex mass spectrometry was used for N-terminal amino acid profiling (N-TAAP) of PrP^res from sheep affected by scrapie, the prion disease of small ruminants, to rapidly assess the diversity of prions within particular flocks. In 29 cases, PrP^res concentrations varied from below the limit of detection (350 fmol/g) to 15 pmol/g wet brain. Although most had a single N-TAAP profile, two novel variants were identified: one common to the ARH/ARQ animals in this study and one in an animal of the wild-type sheep PrP genotype (ARQ/ARQ).