Thioredoxin converts the Syrian hamster (29-231) recombinant prion proteinto an insoluble form

The prion protein (PrP) is an essential, and probably the only, component o f the infectious agent responsible for the transmissible spongiform encepha lopathies. In its cellular (PrPC) form, it is a soluble, a-helix-rich prote in of yet unknown function attached to the outer membrane of neurons throug h a glycosylphosphatidyl inositol anchor. In its pathogenic, "scrapie" form (PrPSc), it appears as an aggregate showing no detectable covalent modific ations but displaying a profoundly altered conformation enriched in P-sheet structure. Reduction of the single disulfide bridge in the prion protein w ith millimolar concentrations of dithiothreitol results in transformation o f the alpha -helix-rich to the P-sheet-rich conformation, with concomitant decrease in solubility. We report here that thioredoxin coupled with thiore doxin reductase and NADPH efficiently reduces recombinant Syrian hamster (2 9-231) prion protein under physiologically relevant conditions. The reduced prion protein immediately becomes insoluble and precipitates, although it does not gain significant resistance to proteinase K. The thioredoxin/thior edoxin reductase system is similar to 7000 times more efficient than dithio threitol. (C) 2001 Elsevier Science Inc.