The native state of prion protein (PrP) directly inhibits formation of PrP-amyloid fibrils in vitro.

The conversion of globular proteins into amyloid fibrils is associated with a wide variety of human diseases. One example is the prion protein (PrP), which adopts an α-helical structure in the native state but its amyloid form is implicated in the pathogenesis of prion diseases. Previous evidence has suggested that destabilization of the native state promotes amyloid formation, but the underlying mechanism remains unknown. In this study, we report that the native state of PrP serves as a potent inhibitor in the formation of PrP amyloid fibrils. By monitoring the time courses of thioflavin T fluorescence, the kinetics of amyloid formation was studied in vitro under various concentrations of pre-formed amyloid, monomer, and denaturant. Quantitative analysis of the kinetic data using various models of enzyme kinetics suggested that the native state of PrP is either an uncompetitive or noncompetitive inhibitor of amyloid formation. This study highlights the significant role of the native state in inhibiting amyloid formation, which provides new insights into the pathogenesis of misfolding diseases.