Altered Domain Structure of the Prion Protein Caused by Cu2+ Binding and Functionally Relevant Mutations: Analysis by Cross-Linking, MS/MS, and NMR.

The cellular isoform of the prion protein (PrPC) serves as precursor to the infectious isoform (PrPSc), and as a cell-surface receptor, which binds misfolded protein oligomers as well as physiological ligands such as Cu2+ ions. PrPC consists of two domains: a flexible N-terminal domain and a structured C-terminal domain. Both the physiological and pathological functions of PrP depend on intramolecular interactions between these two domains, but the specific amino acid residues involved have proven challenging to define. Here, we employ a combination of chemical cross-linking, mass spectrometry, NMR, molecular dynamics simulations, and functional assays to identify residue-level contacts between the N- and C-terminal domains of PrPC. We also determine how these interdomain contacts are altered by binding of Cu2+ ions and by functionally relevant mutations. Our results provide a structural basis for interpreting both the normal and toxic activities of PrP.