The scrapie fibril protein and its cellular isoform.

Proteins need help to fold and attain their functional conformation (Ellis and Hemmingsen 1989), and mechanisms have evolved to prevent the accumulation of misfolded protein aggregates within cells (Pelham 1988). These mechanisms fail to prevent the formation of protease-resistant, misfolded forms of PrP (ScPrP) during the development of scrapie and other transmissible spongiform encephalopathies, and ScPrP is a biochemical marker of these diseases. Much is now known about the structure and expression of the PrP gene, but the physiological function of the PrP protein and the mechanism by which the TDE pathogen replicates and specifically interferes with PrP metabolism remain a mystery--a mystery which will entertain prion-ophiliacs for some time yet.