Electron paramagnetic resonance evidence far binding of Cu2+ to the C-terminal domain of the murine prion protein

Transmissible spongiform encephalopathies in mammals are believed to be caused by scrapie form of prion protein (PrPSc), an abnormal, oligomeric isoform of the monomeric cellular prion protein (PrPC). One of the proposed functions of PrPC in vivo is a Cu(II) binding activity. Previous studies revealed that Cu2+ binds to the unstructured N-terminal PrPC segment (residues 23-120) through conserved histidine residues. Here we analyzed the Cu(ll) binding properties of full-length murine PrPC (mPrP), of its isolated C-terminal domain mPrP(121-231) and of the N-terminal fragment mPrP(58-91) in the range of pH 3-8 with electron paramagnetic resonance spectroscopy. We find that the C-terminal domain, both in its isolated form and in the context of the full-length protein, is capable of interacting with Cu2+. Three Cu(ll) coordination types are observed for the C-terminal domain. The N-terminal segment mPrP(58-91) binds Cu2+ only at pH values above 5.0, whereas both mPrP(121-231) and mPrP(23-231) already show identical Cu(ll) coordination in the pH range 3-5. As the Cu2+-binding N-terminal segment 58-91 is not required for prion propagation, our results open the possibility that Cu2+ ions bound to the C-terminal domain are involved in the replication of prions, and provide the basis for further analytical studies on the specificity of Cu(II) binding by PrP.