Copper(II) Interaction with Prion Peptide Fragments Encompassing Histidine Residues Within and Outside the Octarepeat Domain: Speciation, Stability Constants and Binding Details

Abstract

A 31-mer polypeptide, which encompasses residues 84-114 of human prion protein HuPrP(84-114) and contains three histidyl residues, namely one from the octarepeat (His85) and two histidyl residues from outside the octarepeat region (His96 and His111), and its mutants with two histidyl residues HuPrP(84-114)His85Ala, HuPrP(84-114) His96Ala, HuPrP(84-114)His111Ala and HuPrP(91-115) have been synthesised and their Cu2+ complexes studied by potentiometric and spectroscopic (UV/Vis, CD, EPR, ESI-MS) techniques. The results revealed a high Cu2+-binding affinity of all peptides, and the spectroscopic studies made it possible to clarify the coordination mode of the peptides in the different complex species. The imidazole nitrogen donor atoms of histidyl residues are the exclusive metal-binding sites below pH 5.5, and they have a preference for macrochelate structure formation. The deprotonation and metal-ion coordination of amide functions take place by increasing the pH; all of the histidines can be considered to be independent metal-binding sites in these species. As a consequence, di- and trinuclear complexes can be present even in equimolar samples of the metal ion and peptides, but the ratios of polynuclear species do not exceed the statistically expected ones; this excludes the possibility of cooperative Cu2+ binding. The species with a (N(im),N,N)-binding mode are favoured around pH 7, and their stability is enhanced by the macrochelation from another histidyl residue in the mononuclear complexes. The independence of the histidyl sites results in the existence of coordination isomers and the preference for metal binding follows the order of: His111>His96>His85. Deprotonation and metal-ion coordination of the third amide functions were detected in slightly alkaline solutions at each of the metal-binding sites; all had a (N(im),N,N,N)-coordination mode. Spectroscopic measurements also made it clear that the four lysyl amino groups of the peptides are not metal-binding sites in any cases.

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

“…[67,70,72,73,75,76,[88][89][90][91][92][93][94][95][96] Although there is no general consensus, most of the results obtained so far indicate His111 as the preferential, if not exclusive, copper(II) binding site. [67,72,73,75,76,90,91,95,96] Our systematic studies carried out on small peptide fragments of PrP led to the same conclusions, and the high copper(II) binding affinities of the His96, [97] His111, [98] and even His187 [99] residues have unambiguously been demonstrated. A comparison of the thermodynamic stabilities of the histidinecontaining fragments revealed that the peptides that encompass the amino acid sequences outside the octarepeat domain are even more efficient chelators of copper(II) than the single octarepeat fragments.…”

Tuning the coordination properties of multi-histidine peptides by using a tripodal scaffold: solution chemical study and catechol oxidase mimicking

“…Although the protonation processes of L 1 are strongly overlapped, the first three pK values are mostly related to deprotonation of the imidazole rings, while pK 4 , pK 5 also increases the acidity of imidazolium rings.…”

“…Linear peptides have long since been used to mimic the metal binding sites of metalloproteins [1][2][3][4][5][6][7] and metalloenzymes. [8][9][10][11][12] Previously, we also studied some histidine-rich peptides in order to create similar metal ion environment to native enzymes.…”

A minimalist chemical model of matrix metalloproteinases — Can small peptides mimic the more rigid metal binding sites of proteins?

“…Such metal binding sites are obviously difficult to mimic by small peptides. However, a number of proteins possess relatively short histidine-rich sequences with strong metal binding ability, which substantially contributes to the function of the given macromolecule [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Beside the well known human serum albumin (HSA) [1], probably the prion proteins (PrP) [2] are the most studied examples of such sequences.…”

“…Beside the well known human serum albumin (HSA) [1], probably the prion proteins (PrP) [2] are the most studied examples of such sequences. Studies on the metal ion binding of peptides related to the N-terminal of HSA [3][4][5], and those mimicking the octarepeat region of PrP [6][7][8] demonstrated the usefulness of such studies. Besides, several peptides copying the putative metal binding sequences of e.g.…”