Prion protein does not redox-silence Cu2+, but is a sacrificial quencher of hydroxyl radicals

Oxidative stress is believed to play a central role in the pathogenesis of prion diseases, a group of fatal neurodegenerative disorders associated with a conformational change in the prion protein (PrPC). The precise physiological function of PrPC remains uncertain; however, Cu2+ binds to PrPC in vivo, suggesting a role for PrPC in copper homeostasis. Here we examine the oxidative processes associated with PrPC and Cu2+. H-1 NMR was used to monitor chemical modifications of PrP fragments. Incubation of PrP fragments with ascorbate and CuCl, showed specific metal-catalyzed oxidation of histidine residues, His(96/111), and the methionine residues, Met(109/112). The octarepeat region protects His(96/111) and Met(109/112) from oxidation, suggesting that PrP(90-231) might be more prone to chemical modification. We show that Cu2+/+ redox cycling is not 'silenced' by Cu2+ binding to PrP, as indicated by H2O2 production for full-length PrP. Surprisingly, although detection of Cu+ indicates that the octarepeat region of PrP is capable of reducing Cu2+ even in the absence of ascorbate, H2O2 is not generated unless ascorbate is present. Full-length PrP and fragments cause a dramatic reduction in detectable hydroxyl radicals in an ascorbate/Cu2+/O-2 system; however, levels of H2O2 production are unaffected. This suggests that PrP does not affect levels of hydroxyl radical production via Fentons cycling, but the radicals cause highly localized chemical modification of PrPC. (c) 2006 Elsevier Inc. All rights reserved.