Molecular properties of complexes formed between the prion protein and synthetic peptides

Complexes of the Syrian hamster cellular prion protein (PrP(C)) and synthetic Syrian hamster PrP peptides were found to mimic many of the characteristics of Me scrapie PrP isoform (PrP(SC)). Either PrP(C) expressed in chinese hamster ovary (CHO) cells or a C-terminal fragment of 142 residues of recombinant PrP protein (rPrP) produced in Escherichia coli was mixed with an excess of a synthetic 56 amino acid peptide, denoted PrP(90-145). Complex formation required PrP(C) or rPrP to be destabilized by guanidine hydrochloride (GdnHCl) or urea and PrP(90-145) to be in a coil conformation; it was enhanced by an acidic environment, salt and detergent. If PrP(90-145) was in a β-sheet conformation, then no complexes were formed. While complex formation was rapid, acquisition' of protease resistance was a slow process. Amorphous aggregates with a PrP(C)/PrP(90-145) ratio of 1:1 were formed in phosphate buffer, whereas fibrils with a diameter of ~ 10 nm and a PrP(C)/PrP(90-145) ratio of 1:5 were formed in Tris buffer. The complexes were stable only in the presence of excess peptide in either the coil or β-sheet conformation; they dissociated rapidly after centrifugation and resuspension in buffer without peptide. Neither a peptide having a similar hydrophobicity profile/ charge distribution to PrP(90-145) nor a scrambled version, denoted hPrP(90-145) and sPrP(90-145), respectively, were able to induce complex formation. Although hPrP(90-145) could stabilize the PrP(C)/PrP(90-145) complexes, sPrP(90-145) could not. Studies of PrP(C)/peptide complexes may provide insights into how PrP(C) interacts with PrP(Sc) during the formation of a nascent PrP(Sc) molecule and into the process by which PrP(C) is converted into PrP(Sc).