Interactions of Zn(II) ions with three His-containing peptide models of histone H2A

The interactions of Zn(II) ions with the blocked hexapeptide models -TESHHK-, -TASHHK- and -TEAHHK- of the -ESHH- motif of the C-terminal of histone H2A were studied by using potentiometric and H-1-NMR techniques. The first step of these studies was to compare the pK(a) values of the two His residues inside each hexapeptide calculated by potentiometric or H-1-NMR titrations. Hereafter, the potentiometric titrations in the pH range 5-11 suggest the formation of several monomeric Zn(II) complexes. It was found that all hexapeptides bind to Zn(II) ions initially through both imidazole nitrogens in weakly acidic and neutral solutions forming slightly distorted octahedral complexes. At higher pH values, the combination of potentiometric titrations and one and two dimensional NMR suggested no amide coordination in the coordination sphere of Zn(II) ions. Obviously, these studies support that the -ESHH- sequence of histone H2A is a potential binding site for Zn(II) ions similarly with the Cu(II) and Ni(II) ions, presented in previous papers.