title: Inter- and intra-octarepeat Cu(II) site geometries in the prion protein: implications in Cu(II) binding cooperativity and Cu(II)-mediated assemblies.
abstract: Cu(II) binding to the alpha prion protein (alphaPrP) can be both intramolecular and intermolecular. X-ray absorption spectroscopy at the copper K-edge has been used to explore the site geometry under each binding mode using both insoluble polymeric Cu(II).alphaBoPrP-(24-242) (bovine PrP) complexes and soluble Cu(II) complexes of peptides containing one, two, and four copies of the octarepeat. Analysis of the extended region of the spectra using a multiple scattering approach revealed two types of sites differing in the number of His residues in the first coordination shell of Cu(II). Peptides containing one and two-octarepeat copies in sub-stoichiometric Cu(II) complexes showed the direct binding of a single His in accord with crystallographic intra-repeat geometry. Alternatively, the polymeric Cu(II).alphaBoPrP-(24-242) complex and Cu(II) in its soluble complex with a four-octarepeat peptide at half-site-occupancy showed Cu(II) directly bound to two His residues, consistent with an inter-repeat binding mode. Increasing the Cu(II) site occupancy from 0.5 to 0.75 in the peptide containing four octarepeats resulted in spectral features that are intermediate to those of the inter- and intra-repeat modes. The transition from His-Cu-His (inter-repeat) to Cu-His (intra-repeat) on increasing Cu(II) saturation offers a structural basis for the positive cooperativity of the cation binding process and explains the capacity of alphaPrP to participate in Cu(II)-mediated intermolecular interactions.
authors.affiliation: Department of Physics, Universitá di Roma "Tor Vergata" and Istituto Nazionale per la Fisica della Materia, Via della Ricerca Scientifica 1, I-00133 Roma, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Morante
authors.forename: Reinerio
authors.initials: R
authors.lastname: González-Iglesias
authors.forename: Cristina
authors.initials: C
authors.lastname: Potrich
authors.forename: Carlo
authors.initials: C
authors.lastname: Meneghini
authors.forename: Wolfram
authors.initials: W
authors.lastname: Meyer-Klaucke
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Menestrina
authors.forename: María
authors.initials: M
authors.lastname: Gasset
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003300:Copper / Q000378:metabolism*; D008969:Molecular Sequence Data; D011328:Prions / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D020449:Repetitive Sequences, Amino Acid
chemical_list: D011328:Prions; D003300:Copper