Mapping the antigenicity of copper-treated cellular prion protein with the scrapie isoform

Abstract:

When recombinant and cellular prion protein (PrP^C) binds copper, it acquires properties resembling the scrapie isoform (PrP^Sc), namely protease resistance, detergent insolubility and increased β sheet content. However, whether the conformations of PrP^C induced by copper and PrP^Sc are similar has not been studied in great detail. Here, we use a panel of seven monoclonal antibodies to decipher the epitopes on full-length mouse PrP^C that are affected by exogenous copper, and to compare the antigenicity of the copper-treated full-length PrP^C with the full-length PrP^Sc present in scrapie-infected mouse brains. In the presence of copper, we found that epitopes along residues 115–130 and 153–165 become more accessible on PrP^C. These regions correspond to the two β sheet strands in recombinant PrP and they were proposed to be important for prion conversion. However, when we compared the antibody-binding patterns between full-length PrP^C with full-length PrP^Sc and between copper-treated full-length PrP^C with full-length PrP^Sc, antibody binding to residues 143–155 and 175–185 was consistently increased on PrP^Sc. Collectively, our results suggest that copper-treated full-length PrP^C does not resemble full-length PrP^Sc, despite acquiring PrP^Sc-like properties. In addition, since each full-length protein reacts distinctively to some of the antibodies, this binding pattern could discriminate between PrP^C and PrP^Sc.