Human prion diseases are characterized by the conversion of the normal prion protein (PrP C ) into a pathogenic isomer (PrP Sc ). Distinct PrP Sc conformers are associated with different subtypes of prion diseases. PrP C binds copper and has antioxidation activity. Changes in metal-ion occupancy can lead to signi®cant decline of the antioxidation activity and changes in conformation of the protein. We studied the trace element status of brains from patients with sporadic Creutzfeldt±Jakob disease (sCJD). We found a decrease of up to 50% of copper and an increase in manganese of approximately 10-fold in the brain tissues from sCJD subjects. We have also studied the metal occupancy of PrP in sCJD patients. We observed striking elevation of manganese and, to a lesser extent, of zinc accompanied by signi®cant reduction of copper bound to puri®ed PrP in all sCJD variants, determined by the PrP genotype and PrP Sc type, combined.Both zinc and manganese were undetectable in PrP C preparations from controls. Copper and manganese changes were pronounced in sCJD subjects homozygous for methionine at codon 129 and carrying PrP Sc type-1. Anti-oxidation activity of puri®ed PrP was dramatically reduced by up to 85% in the sCJD variants, and correlated with increased in oxidative stress markers in sCJD brains. These results suggest that altered metal-ion occupancy of PrP plays a pivotal role in the pathogenesis of prion diseases. Since the metal changes differed in each sCJD variants, they may contribute to the diversity of PrP Sc and disease phenotype in sCJD. Finally, this study also presented two potential approaches in the diagnosis of CJD; the signi®cant increase in brain manganese makes it potentially detectable by MRI, and the binding of manganese by PrP in sCJD might represent a novel diagnostic marker.

We used ELISA and flow cytometry to study the binding of prion protein PrP to glycosaminoglycans (GAGs). We found that recombinant human PrP (rPrP) binds GAGs including chondroitin sulphate A, chondroitin sulphate B, hyaluronic acid, and heparin. rPrP binding to GAGs occurs via the N-terminus, a region known to bind divalent cations. Additionally, rPrP binding to GAGs is enhanced in the presence of Cu2+ and Zn2+, but not Ca2+ and Mn2+. rPrP binds heparin strongest, and the binding is inhibited by certain heparin analogues, including heparin disaccharide and sulphate-containing monosaccharides, but not by acetylated heparin. Full-length normal cellular prion protein (PrPC), but not N-terminally truncated PrPC species, from human brain bind GAGs in a similar Cu2+/Zn2+-enhanced fashion. We found that GAGs specifically bind to a synthetic peptide corresponding to amino acid residues 23-35 in the N-terminus of rPrP. We further demonstrated that while both wild-type PrPC and an octapeptide-repeat-deleted mutant PrP produced by transfected cells bound heparin at the cell surface, the PrP N-terminal deletion mutant and non-transfectant control failed to bind heparin. Binding of heparin to wild-type PrPC on the cell surface results in a reduction of the level of cell-surface PrPC. These results provide strong evidence that PrPC is a surface receptor for GAGs.

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Although minor abnormalities have been reported in prion protein (PrP) knock-out (Prnp 2/± ) mice, the normal physiological function of PrP, the causative agent implicated in transmissible spongiform encephalopathies (TSE), remains unresolved. Since there are increasing correlations between oxidative stress and amyloidoses, we decided to investigate whether PrP plays a role in oxidative modulation. We found higher levels of oxidative damage to proteins and lipids in the brain lysates of Prnp 2/± as compared to wild-type (WT) mice of the same genetic background. These two indicators, protein oxidation and lipid peroxidation, are hallmarks of cellular oxidative damage. Elevated levels of ubiquitin-protein conjugates were also observed in Prnp 2/± mice, a probable consequence of cellular attempts to remove the damaged proteins as indicated by increased proteasome activity. Taken together, these ®ndings are indicative of a role for PrP in oxidative homeostasis in vivo.