title: Prion protein does not redox-silence Cu2+, 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+). (1)H 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(2)O(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(2)O(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(2)O(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).
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Nadal
authors.forename: Salama R
authors.initials: SR
authors.lastname: Abdelraheim
authors.forename: Marcus W
authors.initials: MW
authors.lastname: Brazier
authors.forename: Stephen E J
authors.initials: SE
authors.lastname: Rigby
authors.forename: David R
authors.initials: DR
authors.lastname: Brown
authors.forename: John H
authors.initials: JH
authors.lastname: Viles
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D016166:Free Radical Scavengers / Q000737:chemistry / Q000378:metabolism*; D006639:Histidine / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000378:metabolism; D017665:Hydroxyl Radical / Q000737:chemistry / Q000378:metabolism*; D008715:Methionine / Q000737:chemistry; D051379:Mice; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D011328:Prions / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017382:Reactive Oxygen Species / Q000737:chemistry / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism
chemical_list: D016166:Free Radical Scavengers; D010446:Peptide Fragments; D011328:Prions; D017382:Reactive Oxygen Species; D017392:Thiobarbituric Acid Reactive Substances; C428437:prion protein (23-231); D017665:Hydroxyl Radical; D006639:Histidine; D003300:Copper; D008715:Methionine; D006861:Hydrogen Peroxide; D001205:Ascorbic Acid