Reversible conversion of monomeric human prion protein between native and fibrilogenic conformations

Prion propagation involves the conversion of cellular prion protein (PrPc) into a disease-specific isomer, PrPSc, shifting from a predominantly alpha- helical to beta-sheet structure. Here, conditions were established in which recombinant human PrP could switch between the native a conformation, char acteristic of PrPc, and a compact, highly soluble, monomeric form rich in b eta structure. The soluble beta form (beta-PrP) exhibited partial resistanc e to proteinase kappa digestion, characteristic of PrPSc, and was a direct precursor of fibrillar structures closely similar to those isolated from di seased brains. The conversion of PrPc to beta-PrP in suitable cellular comp artments, and its subsequent stabilization by intermolecular association, p rovide a molecular mechanism for prion propagation.