Cu(II) induces small-size aggregates with amyloid characteristics in two alleles of recombinant ovine prion proteins

One of symptoms of transmissible spongiform encephalopathies is associated with the transformation of normal cellular prion protein, PrP, in its amyloid isoform resistant to proteolytic cleavage. The present study shows that interaction with copper ions converts both monomeric recombinant scrapie-susceptible PrP-VRQ and scrapie-resistant PrP-ARR variants into protease-resistant soluble oligomers with amyloid characteristics — dominant β-sheet secondary structure and interaction with thioflavine S. In contrast, binding of zinc ions resulting in the same resistance to proteolysis does not provoke transformation of α-helical monomeric structure of both PrP polymorphic variants. Cleavage of PrP N-terminus destabilises soluble form of such aggregates, and N-truncated PrPrec complexed with metal cations precipitate. N-truncated PrPrec complexed with Zn precipitated much faster than N-truncated PrPrec complexed with Cu. According to the hypothesis about the key role of small PrP oligomers in PrPC-PrPSc transformation, formation of soluble oligomers of PrP complexed with Cu can constitute an additional element in TSE propagation. Identical metal-chelating behaviour of two studied polymorphic PrPrec variants conferring different susceptibilities of sheep to scrapie could indicate their different capabilities to form fibrils. This could imply also that other factors than physico-chemical differences between PrP-VRQ and PrP-ARR and the differences in PrP transformation are responsible for the onset of TSE.