Interactions of transition metal ions with His-containing peptide models of histone H2A Marios Mylonas a , Artur Kre ˛ yel b , John C. Plakatouras a, * , Nick Hadjiliadis a, * , Wojciech Bal c a University of Ioannina, Department of Chemistry, Ioannina 45110, Greece b Faculty of Chemistry, University of Wroclaw, 50-383 Wroclaw, Poland c Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02-106 Warsaw, Poland Available online 11 September 2004 Abstract The coordination properties of Ni(II), Cu(II) and Zn(II) ions towards the terminally blocked (CH 3 CONH– and –CONH 2 ) hexapeptides – TESHHK–, –TASHHK–, –TEAHHK–, –TESAHK– and –TESHAK–, which are all models of the C-terminal btailQ (–ESHH–) of histone H2A, were studied by potentiometric and several spectroscopic techniques (UV/Vis, CD, NMR, EPR). The peptides were chosen in such a way as to compare the effect of Glu, Ser and His residues on the stability, the coordination and hydrolytic abilities of the complexes formed. It was found that all peptides bind to the metal ions initially through one or two imidazole nitrogens in weakly acidic and neutral solutions forming slightly distorted octahedral complexes. At higher pH values, a series of square-planar complexes are formed with Ni(II), which binds simultaneously through an imidazole and three amide nitrogens in an equatorial plane. This proposed conformation includes the participation of only one imidazole nitrogen, in the case of all peptides, in the coordination sphere of Ni(II) ions. Additionally, all peptides coordinate Cu(II) efficiently. At higher pH values, Cu(II) ions coordinate equatorially with the imidazole nitrogen of His-5 or His-4 and three amido nitrogens of the peptides –TESAHK– and – TESHAK–, while the second histidine residue of the peptides –TESHHK–, –TASHHK– and –TEAHHK– is additionally bound in the apical position. In contrast, the combination of potentiometric titrations and one- and two-dimensional 1 H-NMR suggested no amide coordination in the coordination sphere of Zn(II) ions, over a wide range of pH. In basic solutions, the peptides –TASHHK– and –TESAHK– were hydrolyzed in a Ni(II)-assisted fashion, while no hydrolytic processes were noticed in peptides –TEAHHK– and –TESHAK– where the Ser or His-5 residues are replaced with the Ala residue. Moreover, CuH 1 L complex with –TESHHK– reacts with H 2 O 2 and the resulting reactive oxygen intermediate efficiently oxidizes 2V-deoxyguanosine. D 2004 Elsevier B.V. All rights reserved. Keywords: Histone H2A; Hexapeptides; Eukaryotic cells 1. Introduction It is well known that several metals have been found to be carcinogenic to humans and animals [1,2]. Nevertheless, the molecular mechanism by which metal carcinogenicity is exerted is not fully understood. Studies of several years support that neoplastic transformation of cells results from a heritable alteration in the genetic code, concluding that any molecule which can bind with constituents of the cell nuclei may affect the genetic code. Thus, it is believed that metal ions may cause changes to the genetic code by their binding to the proteins and DNA. Particularly, the abundance of histones inside the cell nuclei makes them the prime expectants for that role. In all eukaryotic cells, histone basic proteins provide a scaffold for DNA double helix and are organized in repeating units called nucleosomes. The nucleosome is composed of a histone octamer (containing two copies of each of histones H2A, H2B, H3 and H4) and a 170 base pairs DNA stretches [3]. The elucidation of metal’s toxicity and carcinogenicity can be approached by studying their interactions with model histone peptides. In this respect, the interaction of Ni(II) 0167-7322/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.molliq.2004.07.025 * Corresponding authors. E-mail address: iplakatu@cc.uoi.gr (J.C. Plakatouras). Journal of Molecular Liquids 118 (2005) 119– 129 www.elsevier.com/locate/molliq