A prion’s pathogenic character is enciphered in its conformation. Additionally, conformation defines the chemical environments of its component amino acids and their reactivity. Mammalian cells express methionine sulfoxide-reducing enzymes (Msr A and B) to maintain surface exposed methionines in their naturally reduced state. Natively expressed mammalian proteins are largely devoid of methionine oxidation and, therefore, possess little background oxidation. Quantifying the oxidation of a prion’s methionines resulting from experimental chemical oxidation permits researchers to identify surface exposed methionines and, thereby, reveal conformation-dependent information. Oxidizing a prion’s methionines does not substantially reduce its infectivity, implying that a prion’s structure is not perturbed when its methionines are oxidized. We identified a set of methionine-containing peptides derived from the tryptic, chymotryptic or tryptic/chymotryptic digestion of recombinant hamster PrP (rPrP). We developed a multiple reaction monitoring (MRM) based method of quantifying the extent of the methionine oxidation in those peptides. We used our MRM method to quantify the extent of the methionine oxidation in rPrP and the Sc237 strain of hamster-adapted scrapie after experimental oxidation. Conformation-dependent differences in susceptibility of methionines to oxidation was observed. Such information can be used to distinguish among prion strains and to guide modelers in developing computation-based prion structures.

Oxidizing methionine to map a prion’s surface and reveal conformational differences

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.