Oxidation of methionine residues in the prion protein by hydrogen peroxide

Reaction of H2O2 with the recombinant SHa(29–231) prion protein resulted in rapid oxidation of multiple methionine residues. Susceptibility to oxidation of individual residues, assessed by mass spectrometry after digestion with CNBr and lysC, was in general a function of solvent exposure. Met 109 and Met 112, situated in the highly flexible amino terminus, and key residues of the toxic peptide PrP (106–126), showed the greatest susceptibility. Met 129, a residue located in a polymorphic position in human PrP and modulating risk of prion disease, was also easily oxidized, as was Met 134. The structural effect of H2O2-induced methionine oxidation on PrP was studied by CD spectroscopy. As opposed to copper catalyzed oxidation, which results in extensive aggregation of PrP, this reaction led only to a modest increase in β-sheet structure. The high number of solvent exposed methionine residues in PrP suggests their possible role as protective endogenous antioxidants.