Copper Alters Aggregation Behavior of Prion Protein and Induces Novel Interactions between Its N- and C-terminal Regions

Copper is reported to promote and prevent aggregation of prion protein. Conformational and functional consequences of Cu2+-binding to prion protein (PrP) are not well understood largely because most of the Cu2+-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 Cu2+-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 Cu2+. At physiological temperature, Cu2+ did not promote aggregation suggesting that Cu2+ may not play a role in the aggregation of PrP at physiological temperature (37 degrees C). However, Cu2+-bound PrP aggregated at lower temperatures. This temperature-dependent process is reversible. Our results show two novel intraprotein interactions upon Cu2+-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 Cu2+. 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 Cu2+-binding. 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.