Prion diseases include kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker disease (GSS), and fatal familia insomnia (FFI) of humans, as well as scrapie and bovine spongiform encephalopathy (BSE) of animals. 2. All these disorders involve conversion of the normal, cellular prion protein (PrPC) into the corresponding scrapie isoform (PrPSc). PrPC adopts a structure rich in alpha-helices and devoid of beta-sheet, in contrast to PrPSc, which has a high beta-sheet content and is resistant to limited digestion by proteases. That a conformational transition features in the conversion of PrPC into PrPSc implies that prion diseases are disorders of protein conformation. 3. This concept has been extended by our studies with heat shock proteins (Hsp), many of which are thought to function as molecular chaperones. We found that the induction of some Hsps but not others was profoundly altered in scrapie-infected cells and that the distribution of Hsp73 is unusual in these cells. 4. Whether the conversion of PrPC into PrPSc is assisted by molecular chaperones, or if the accumulation of the abnormally folded PrPSc is complexed with Hsps remains to be established.
