Membrane disruption by the prion protein with reduced disulfide bond

Transmissible spongeform encephalopathies including bovine spongeform encepalopathies and human Creutzfeldt-Jakob diseas are fatal neurodegenerative diseases. The protein-only hypothesis holds that structurally converted transmembrane prion proteins play a major role in the procedure of these diseases. According to this hypothesis, the wild type of prion protein (PrPC) is converted into the infectious form (PrPSC) under unknown conditions and thisPrPSc is believed to act as a seed for forming infectious fibril like oligomers of prion proteins.Between PrPC and PrPSc, there are no differences in sequences of deoxyribonucleic acids and amino acids but, only the structure is changed which leads PrPSc to obtain features of resistance to proteaseK and the increase of -β sheet contents than PrPC. In the present study, we focused on the mechanism how normal prion proteins are converted into infectious forms and assumed that the breakage of intra-disulfide bond of prion proteins by a reducing agent would make normal PrPC to tend to be like the infectious one. It is shown that the in vitroconverted PrPSc-like structure exhibits a binding affinity to membranes. Circular dichroism spectroscopy shows that the disulfide bond-broken PrPC has more β-sheet contents than normal PrPC in the presence of membrane. Membrane-encapsulated calcein, a self-quenching fluorophore, is released upon the treatment of both prion protein and reducing agent. The color ofpolydiacetylene biosenseor composed of PDA and phospholipid (25% negative charged) is shifted from blue to red when disulfide bond-defective PrPC is present. Results indicate that the prion protein gains membrane binding ability when the intramolecular disulfide bond is reduced, leating to membrane disruption.