Prion protein does not redox-silence Cu 2+, but is a sacrificial quencher of hydroxyl radicals

Abstract

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 (PrP C). The precise physiological function of PrP C remains uncertain; however, Cu 2+ binds to PrP C in vivo, suggesting a role for PrP C in copper homeostasis. Here we examine the oxidative processes associated with PrP C and Cu 2+. 1H NMR was used to monitor chemical modifications of PrP fragments. Incubation of PrP fragments with ascorbate and CuCl 2 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 Cu 2+/+ redox cycling is not ‘silenced’ by Cu 2+ binding to PrP, as indicated by H 2O 2 production for full-length PrP. Surprisingly, although detection of Cu + indicates that the octarepeat region of PrP is capable of reducing Cu 2+ even in the absence of ascorbate, H 2O 2 is not generated unless ascorbate is present. Full-length PrP and fragments cause a dramatic reduction in detectable hydroxyl radicals in an ascorbate/Cu 2+/O 2 system; however, levels of H 2O 2 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 PrP C.