Abstract
Copper is reported to promote and prevent aggregation of prion protein. Conformational and functional consequences of Cu(2+)-binding to prion protein (PrP) are not well understood largely because most of the Cu(2+)-binding studies have been performed on fragments and truncated variants of the prion protein. In this context, we set out to investigate the conformational consequences of Cu(2+)-binding to full-length prion protein (PrP) by isothermal calorimetry, NMR, and small angle x-ray scattering. In this study, we report altered aggregation behavior of full-length PrP upon binding to Cu(2+). At physiological temperature, Cu(2+) did not promote aggregation suggesting that Cu(2+) may not play a role in the aggregation of PrP at physiological temperature (37 °C). However, Cu(2+)-bound PrP aggregated at lower temperatures. This temperature-dependent process is reversible. Our results show two novel intra-protein interactions upon Cu(2+)-binding. The N-terminal region (residues 90-120 that contain the site His-96/His-111) becomes proximal to helix-1 (residues 144-147) and its nearby loop region (residues 139-143), which may be important in preventing amyloid fibril formation in the presence of Cu(2+). In addition, we observed another novel interaction between the N-terminal region comprising the octapeptide repeats (residues 60-91) and helix-2 (residues 174-185) of PrP. Small angle x-ray scattering studies of full-length PrP show significant compactness upon Cu(2+)-binding. Our results demonstrate novel long range inter-domain interactions of the N- and C-terminal regions of PrP upon Cu(2+)-binding, which might have physiological significance.
Highlights
Role of copper as an attenuator or facilitator in prion diseases is controversial
We have observed temperature-dependent reversible aggregation of Cu2ϩ-bound prion protein (PrP)[23–231]; it aggregates at lower temperatures and resolubilizes at physiological temperature
We believe that a novel interaction between helix-2 and the octapeptide repeats region of PrP[23–231] is involved in this reversible aggregation
Summary
Results: Copper-bound PrP does not aggregate at physiological temperature and shows two novel interactions between its Nand C-terminal domains. Conclusion: Copper may act as an attenuator in prion diseases and induces novel long range inter-domain interactions in PrP. Our results demonstrate novel long range inter-domain interactions of the N- and C-terminal regions of PrP upon Cu2؉binding, which might have physiological significance. Prion protein (PrP) is involved in transmissible spongiform encephalopathies, a group of diseases such as Creutzfeldt-Jakob disease, Kuru, Fatal Familial Insomnia, and GerstmannStraussler-Scheinker syndrome, characterized by neurodegeneration, spongiform cerebral tissue, and amyloid plaques Such diseases are caused by the conformational transition of ␣-helixrich cellular prion protein (PrPC) to the -sheet-rich scrapie prion protein (PrPSC) [1]. Cu2ϩ is shown to convert PrPC from brain homogenates [2] and aged recombinant PrP [17] to protease-resistant and detergent-insoluble aggregates These aggregates are structurally distinct from the scrapie prion protein (PrPSC).
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