Copper-ion interaction with the 106–113 domain of the prion protein: a solution-equilibria study on model peptides

Abstract

Prion diseases are characterized by a structural modification of the regular prion protein (PrP(C)) to its isoform, termed PrP(Sc)(scrapie). Such a modification involves the secondary and tertiary structure of the protein; the amino acidic sequence remains unchanged. PrP(Sc) is almost insoluble in non-denaturing solvents, resistant to proteases and it loses its redox activity. PrP(C) is able to bind copper and other metal ions: these complexes have been suggested to play an important role in the protein refolding leading to PrP(Sc). It is well-known that at least one relatively strong copper-binding site is located in the PrP(92--126) domain, where two His residues (96 and 111) are present. However, in the same domain, other amino acidic residues bear potentially donating atoms, i.e. Met, Asn and Lys residues. In order to shed light on the role of the side chains of such potentially tridentate amino acids on copper complexation, the polypeptide Ac-KTNMKHMA-NH(2), corresponding to the PrP(106--113) fragment, and some synthetic analogues have been investigated as ligands for the copper ion, by means of both thermodynamic and spectroscopic techniques. The pivotal role of imidazolic side chain of His in "anchoring" the metal ion has been confirmed. On the other hand, no clue was found on the participation of sulfur atom of Met or side amino-group of Lys residues to copper complex-formation.

Copper(II) coordination properties of the integrin ligand sequence PHSRN and its new β-cyclodextrin conjugates

“…The pK value obtained (Table 1) is in agreement with value reported for analogous peptides containing only one histidine [40,41].…”

Cross‐Talk Between the Octarepeat Domain and the Fifth Binding Site of Prion Protein Driven by the Interaction of Copper(II) with the N‐terminus

“…[72,73,75,90,91,108] (N im ,N À ,N À ) is the main metal-binding mode experienced by Cu 2+ , although there is no general agreement on the contribution of additional donor atoms. [72,74,89,90,[93][94][95][96][97][98][109][110][111] Structural rearrangement of the N-terminus caused by copper(II) binding has also been studied but conflicting results have been reported for peptides that contain different domains. [112,113] The majority of studies with PrP peptide fragments allowed the assessment of the copper(II) coordination modes, but the results represented a simplified model of the copper-binding chemistry and did not consider important aspects of the metal-PrP interactions because protein folding and interregion interactions were not accounted for.…”

“…Metal binding to His111 is further supported by limited proteolysis experiments with trypsin, for which copper(II) has no reported effect on enzyme activity. [104] Three peptide fragments were produced after complete trypsin digestion of AcPrP [ Figure 1], namely, AcPr(P60-106), PrP (107)(108)(109)(110) and PrP (111)(112)(113)(114) [Figure 8 a]. In the absence of Cu 2+ , the peptide was digested after 30 min.…”

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

“…Surprisingly, the EPR results ruled out any interaction with Met residues in the metal complexation, [278] contradicting the proton NMR data collected by the same group [274] and the conclusion reported by Rizzarelli and co-workers. [277,279,282] Although different research groups confirmed no involvement of Met 109 or Met 112, [269,[283][284][285] Shearer et al proposed that both Met residues could participate in copper-PrP complexation at pH 7.4. [103,286] Rivillas-Acevedo et al employed EPR spectroscopy along with other spectroscopic techniques to evaluate Met binding with .…”