Scrapie infectivity is independent of amyloid staining properties of the N-terminally truncated prion protein

The (p) under bar rion (p) under bar rotein undergoes a profound conformati onal change when the (c) under bar ellular isoform (PrPC) is converted into the disease-causing form (PrPSc). Limited proteolysis of PrPSc produces Pr P 27-30, which readily polymerizes into amyloid. To study the relationship between PrP amyloid and infectivity, we employed organic solvents that pert urb protein conformation. Hexafluoro-2-propanol (HFIP), which promotes alph a-helix formation, modified the ultrastructure of PrP amyloid and decreased the beta-sheet content as well as prion infectivity, HFIP reversibly decre ased the binding of Congo red dye to the PrP amyloid rods while inactivatio n of prion infectivity was irreversible. In contrast, 1,1,1-trifluoro-2-pro panol (TFIP) did not inactivate prion infectivity but like HFIP, TFIP did a lter the morphology of the rods and abolished Congo red binding. Solubiliza tion using various solvents and detergents produced monomeric and dimeric P rP that lacked infectivity. Proteinase K resistance of detergent-treated Pr P 27-30 showed no correlation with scrapie infectivity. Our results separat e prion infectivity from the amyloid properties of PrP 27-30 and underscore the dependence of prion infectivity on PrPSc conformation. These findings also demonstrate that the specific beta-sheet-rich structures required for prion infectivity can be differentiated from those required for amyloid for mation. (C) 2000 Academic Press.