Small Ruminant Nor98 Prions Share Biochemical Features with Human Gerstmann-Sträussler-Scheinker Disease and Variably Protease-Sensitive Prionopathy

Prion diseases are classically characterized by the accumulation of pathological prion protein (PrP Sc ) with the protease resistant C-terminal fragment (PrP res ) of 27–30 kDa. However, in both humans and animals, prion diseases with atypical biochemical features, characterized by PK-resistant PrP internal fragments (PrP res ) cleaved at both the N and C termini, have been described. In this study we performed a detailed comparison of the biochemical features of PrP Sc from atypical prion diseases including human Gerstmann-Sträussler-Scheinker disease (GSS) and variably protease-sensitive prionopathy (VPSPr) and in small ruminant Nor98 or atypical scrapie. The kinetics of PrP res production and its cleavage sites after PK digestion were analyzed, along with the PrP Sc conformational stability, using a new method able to characterize both protease-resistant and protease-sensitive PrP Sc components. All these PrP Sc types shared common and distinctive biochemical features compared to PrP Sc from classical prion diseases such as sporadic Creutzfeldt-Jakob disease and scrapie. Notwithstanding, distinct biochemical signatures based on PrP res cleavage sites and PrP Sc conformational stability were identified in GSS A117V, GSS F198S, GSS P102L and VPSPr, which allowed their specific identification. Importantly, the biochemical properties of PrP Sc from Nor98 and GSS P102L largely overlapped, but were distinct from the other human prions investigated. Finally, our study paves the way towards more refined comparative approaches to the characterization of prions at the animal–human interface.