Potential involvement of copper and thiol-disulphide interchange in prion proteins' conformational conversion

The prion protein PrP(C) in transmissible spongiform encephalopathy converts to the pathogenic isoform PrP(Sc) containing less alpha-helical structure and a greater beta-pleated sheet content. The stability of PrP(C) protein is partly dependent on the disulphide bond between two alpha-helices designated B and C. Further stability could arise from ligand complexes of Cu(II) ions formed with carboxylic acid side chains in PrP(C). Electron spin resonance (E.S.R.) spectra and atomic absorption measurements have shown for alpha-keratin that the formation of ligands by Cu(II) is 10(2) more rapid than interaction of Cu(II) with ionised thiols X-S(-) which form X-S-Cu(+). X-S(-) destabilises disulphide bonds by thiol-disulphide interchange. When insufficient Cu(II) is present to form ligands with all available sites in PrP(C) then unblocked X-S(-) groups could potentially destabilise the disulphide bonds by thiol-disulphide interchange followed by reformation of the disulphide bond in the beta form of PrP(Sc) and the release of X-S(-) to interact with other PrP(C).