MOLECULAR-PROPERTIES OF COMPLEXES FORMED BETWEEN THE PRION PROTEIN AND SYNTHETIC PEPTIDES

Complexes of the Syrian hamster cellular prion protein (PrPc) and synt hetic Syrian hamster PrP peptides were found to mimic many of the char acteristics of the scrapie PrP isoform (PrPSc). Either PrPc expressed in chinese hamster ovary (CHO) cells or a C-terminal fragment of 142 r esidues of recombinant PrP protein (rPrP) produced in Escherichia coli was mixed with an excess of a synthetic 56 amino acid peptide, denote d PrP(90-145). Complex formation required PrPc or rPrP to be destabili zed 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 beta-sheet conformation, then no complexes were formed. While complex formation was rapid, acquisiti on of protease resistance was a slow process. Amorphous aggregates wit h a PrPc/PrP(90-145) ratio of 1:1 were formed in phosphate buffer, whe reas fibrils with a diameter of similar to 10 nm and a PrPc/PrP(90-145 ) ratio of 1:5 were formed in Tris buffer. The complexes were stable o nly in the presence of excess peptide in either the coil or beta-sheet conformation; they dissociated rapidly after centrifugation and resus pension in buffer without peptide. Neither a peptide having a similar hydrophobicity profile/charge distribution to PrP(90-145) nor a scramb led version denoted hPrP(90-145) and sPrP(90-145), respectively, were able to induce complex formation. Although hPrP(90-145) could stabiliz e the PrPc/PrP(90-145) complexes, sPrP(90-145) could not. Studies of P rPc/peptide complexes may provide insights into how PrPc interacts wit h PrPSc during the formation of a nascent PrPSc molecule and into the process by which PrPc is converted into PrPSc. (C) 1997 Academic Press Limited.