Copper(II) coordination properties of GxG peptides: Key role of side chains of central residues on coordination of formed systems; combined potentiometric and ITC studies

Isothermal titration calorimetry (ITC) and potentiometric titration (PT) methods were used to study the interactions of copper(II) ions with GAG, GDG, GKG, and GHG peptides. The calorimetric measurements were run in a MES buffer with the pH value of 6.0 at 298.15 K. Based on the results of PT data supported by theoretical calculations, the dissociation constants were calculated for the investigated peptides. The quantification of the proton competition with the metal for the peptide and incorporation it into the ITC data analysis enabled to obtain the pH-independent parameters, namely the binding constants (K) and the free energy of binding (ΔG). Furthermore, the relationship between the proposed coordination modes of the considered peptides and the thermodynamic parameters (K, ΔG and ΔH) has been discussed.