title: Prion protein interaction with glycosaminoglycan occurs with the formation of oligomeric complexes stabilized by Cu(II) bridges.
abstract: Several lines of evidence have shown glycosaminoglycans (GAGs) to be physiological ligands of the prion protein (PrP), but the molecular and regulatory aspects of the interaction remain unknown. Using full-length recombinant prion protein and low molecular mass heparin and heparan sulfate as glycosaminoglycans, we have found that the interaction occurs with the formation of oligomeric complexes. Within the protein-glycosaminoglycan complexes, PrP exhibited an enhanced fluorescence emission and a reduced solvent exposure. The pH and ionic strength-dependence of the interaction reveals His residues as the main binding sites at acid pH. A synthetic peptide consisting of four octarepeats is able to reproduce the His-dependent binding of the protein, thus demonstrating the role of the octarepeats in the GAG interaction. Alternatively, PrP can bind GAGs through His-bound Cu(II). These Cu(II) bridges promote a tighter interaction, as shown by the increased resistance to ionic strength, to protease action, and to pH-induced cation release. Inspection of other cations shows that Zn(II) but not Ni(II) shares the interaction trend. Taken together, our data suggest that the octarepeat region constitutes a novel GAG-binding sequence and that His-bound Cu(II) may act as a cofactor for intermolecular recognition reactions, allowing the formation of PrP-Cu(II)-glycosaminoglycan assemblies that may be crucial entities in the PrP metabolism.
authors.affiliation: Insto Química-Física Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain.
authors.forename: Reinerio
authors.initials: R
authors.lastname: González-Iglesias
authors.forename: María A
authors.initials: MA
authors.lastname: Pajares
authors.forename: Carmen
authors.initials: C
authors.lastname: Ocal
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Espinosa
authors.forename: Bruno
authors.initials: B
authors.lastname: Oesch
authors.forename: María
authors.initials: M
authors.lastname: Gasset
mesh_terms: D000818:Animals; D002413:Cations, Divalent / Q000378:metabolism / Q000494:pharmacology; D002417:Cattle; D003300:Copper / Q000378:metabolism* / Q000494:pharmacology; D019286:Endopeptidase K / Q000378:metabolism; D006025:Glycosaminoglycans / Q000737:chemistry / Q000378:metabolism*; D006497:Heparan Sulfate / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008027:Light; D018625:Microscopy, Atomic Force; D009994:Osmolar Concentration; D011328:Prions / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding / Q000187:drug effects; D023302:Protein Footprinting; D020836:Protein Structure, Quaternary / Q000187:drug effects; D012542:Scattering, Radiation; D012995:Solubility; D012997:Solvents; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D002413:Cations, Divalent; D003300:Copper; D019286:Endopeptidase K; D006025:Glycosaminoglycans; D006497:Heparan Sulfate; D008024:Ligands; D011328:Prions; D012997:Solvents