Copper alters aggregation behavior of prion protein and induces novel interactions between its N-and C-terminal regions

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 prion protein. In this context, we set out to investigate the conformational consequences of Cu(²⁺)-binding to full-length prion protein (PrP) by ITC, NMR and small angle X-Ray scattering (SAXS). In the present 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 which contains the site H96/H111) 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.