A survey of diamagnetic probes for copper²⁺binding to the prion protein.¹H NMR solution structure of the palladium²⁺bound single octarepeat

Abstract

The prion protein (PrP C ) is a copper binding cell surface glycoprotein which when misfolded causes transmissible spongiform encephalopathies. The cooperative binding of Cu 2+ to an unstructured octarepeat sequence within PrP C causes profound folding of this region. The use of NMR to determine the solution structure of the octarepeat region of PrP with Cu 2+ bound has been hampered by the paramagnetic nature of the Cu 2+ ions. Using NMR we have investigated the binding of candidate diamagnetic replacement ions, to the octarepeat region of PrP. We show that Pd 2+ forms diamagnetic complexes with the peptides HGGG, HGGGW and QPHGGGWGQ with 1 : 1 stoichiometry. The 1 H NMR spectra indicate that these peptides are in slow-exchange between free and bound Pd 2+ on the chemical-shift time-scale. We demonstrate that the Pd-peptide complex forms slowly with a time taken to reach half-maximal signal of 3 hours. Other candidate metal ions, Ni 2+ , Pt 2+ and Au 3+ , were investigated but only the Pd 2+ complexes gave resolvable 1 H NMR spectra. We have determined the solution structure of the QPHGGGWGQ-Pd 1 : 1 complex using 71 NOE distance restraints. A backbone RMSD of 0.30 Å was observed over residues 3 to 7 in the final ensemble. The co-ordinating ligands consist of the histidine imidazole side chain Ne, the amide N of the second and third glycines with possibly H 2 O as the fourth ligand. The co-ordination geometry differs markedly from that of the HGGGW-Cu crystal structure. This survey of potential replacement metal ions to Cu 2+ provides insight into the metal specificity and co-ordination chemistry of the metal bound octarepeats.

Transition metal complexes of terminally protected peptides containing histidyl residues

“…The complexation with palladium(II) takes place at any pH values -even under strongly acidic conditions -suggesting that prion proteins have an outstanding affinity towards this metal ion. The most recent publication on the palladium(II) complexes of a single octarepeat came to similar conclusion [62]. The stoichiometries and binding modes of palladium(II) complexes, however, show a great variety depending on the metal ion to ligand ratio, pH and especially the presence of coordinating donor atoms in the side chains of peptide fragments.…”

Utilizing NMR and EPR spectroscopy to probe the role of copper in prion diseases

“…In a proton NMR experiment, Viles et al . replaced Cu(II) with Ni(II) to study the coordination of six copper ions with PrP at physiological concentrations . In a recent study, Ni(II) was used instead of paramagnetic Cu(II) ions to reinvestigate copper interactions with Met residues in the non‐octarepeat site of the huPrP .…”

Synthesis and characterization of Cu(II) paddlewheel complexes possessing fluorinated carboxylate ligands

“…This system was chosen because carboxylate residues (aspartate and/or glutamate) are known to directly bind metal ions in proteins and copper(II) coordination sites are found in a variety of biological enzymes. Copper binding is also believed to play a part in the pathogenesis of Cruetzfeldt-Jacob disease [11]. In addition to playing an important physiological role, copper carboxylate complexes have been investigated for a variety of other applications, including catalytic chemical bond activation [12], the preparation of metal oxide materials [13], the supra-molecular assembly of metal ions [14], and studying the fundamental nature of metal-metal interactions [15].…”