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 cau sed by scrapie form of prion protein (PrPSc), an abnormal, oligomeric isofo rm of the monomeric cellular prion protein (PrPC). One of the proposed func tions of PrPC in vivo is a Cu(II) binding activity. Previous studies reveal ed that Cu2+ binds to the unstructured N-terminal PrPC segment (residues 23 -120) through conserved histidine residues. Here we analyzed the Cu(ll) bin ding properties of full-length murine PrPC (mPrP), of its isolated C-termin al domain mPrP(121-231) and of the N-terminal fragment mPrP(58-91) in the r ange of pH 3-8 with electron paramagnetic resonance spectroscopy. We find t hat 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 s egment mPrP(58-91) binds Cu2+ only at pH values above 5.0, whereas both mPr P(121-231) and mPrP(23-231) already show identical Cu(ll) coordination in t he pH range 3-5. As the Cu2+-binding N-terminal segment 58-91 is not requir ed for prion propagation, our results open the possibility that Cu2+ ions b ound to the C-terminal domain are involved in the replication of prions, an d provide the basis for further analytical studies on the specificity of Cu (II) binding by PrP.