ABSTRACT
The prion protein is a glycoprotein expressed by neurones and other cells. In its holo-form it binds copper and exhibits superoxide dismutase activity. Studies in mice have led to the description of two distinct alleles. Differences in these alleles are linked to long and short incubation times following infection with scrapie. We studied recombinant mouse protein corresponding to the products of either allele and two intermediates carrying single amino-acid residue substitutions. The different forms of the prion protein exhibited differences in superoxide dismutase (SOD) activity and conformation. Intermediates with single substitutions were less stable than either allelic product. The findings provide insight into the differences between the two alleles and might have consequences for understanding differences in susceptibility to prion disease.
Subject(s)
Amyloid/genetics , Prions/genetics , Protein Precursors/genetics , Alleles , Amyloid/chemistry , Animals , Circular Dichroism , Copper/metabolism , Endopeptidase K/metabolism , Mice , Microscopy, Electron , Mutagenesis, Site-Directed , Prion Diseases/etiology , Prion Diseases/genetics , Prion Proteins , Prions/chemistry , Prions/ultrastructure , Protein Binding , Protein Conformation , Protein Folding , Protein Precursors/chemistry , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Superoxide Dismutase/metabolismABSTRACT
The prion protein (PrP) binds copper and has antioxidant activity enhancing the survival of neurones in culture. The ability of the PrP to bind other cations was tested and it was found that only manganese could substitute for copper. Although initially manganese-loaded PrP exhibited similar structure and activity to copper-loaded PrP, after aging, manganese-loaded PrP became proteinase resistant and lost function. It was also found that manganese could be incorporated into PrP expressed by astrocytes and that this PrP was partially proteinase resistant. These results show that it is possible to generate proteinase-resistant PrP from cells and suggest a possible mechanism for the formation of the scrapie isoform of the PrP as generated in sporadic prion disease.
