Potentiometric and spectroscopic studies of the interaction of Cu(II) ions with the hexapeptides AcThrAlaSerHisHisLysNH2, AcThrGluAlaHisHisLysNH2, AcThrGluSerAlaHisLysNH2 and AcThrGluSerHisAlaLysNH2, models of C-terminal tail of histone H2A

The hexapeptides AcThrAlaSerHisHisLysNH2, AcThrGluAlaHisHisLysNH2, AcThrGluSerAlaHisLysNH2 and AcThrGluSerHisAlaLysNH2 which represent modifications of the 120–125 sequence of histone H2A were synthesized and their interactions with Cu(II) ions were studied with potentiometric and spectroscopic (UV–Vis, EPR and CD spectroscopy) studies. All peptides coordinate Cu(II) efficiently. At physiological pH, AcThrAlaSerHisHisLysNH2 forms dimeric species while the rest of the peptides form monomers. The dimer is formed when Cu(II) ions coordinate equatorially through the imidazole nitrogen of the His-4 residue and the amide nitrogens of the Ser-3 and His-4 residues, plus the imidazole nitrogen of the His-5 residue of a second peptide molecule after deprotonation. At higher pH peptides AcThrAlaSerHisHisLysNH2 and AcThrGluAlaHisHisLysNH2 are using the second histidine residue for coordination at the apical position while Cu(II) ions coordinate equatorially with the imidazole nitrogen of His-5 or His-4 and three amido nitrogens with the peptides AcThrGluSerAlaHisLysNH2 and AcThrGluSerHisAlaLysNH2.