DNA strand breakage induced by CuII and NiII, in the presence of peptide models of histone H2B.

In the present study we used the plasmid relaxation assay, a very sensitive method for detection of DNA strand breaks in vitro, in order to evaluate the role of peptide fragments of histone H2B in DNA strand breakage induced by copper and nickel. We have found that in the presence of peptides modeling the histone fold domain (H2B(32-62) and H2B(63-93)) as well as the N-terminal tail (H2B(1-31)) of histone H2B there is an increased DNA damage by Cu(2+)/H(2)O(2) and Ni(2+)/H(2)O(2) reaction mixtures. On the contrary, the C-terminal tail (H2B(94-125)) seems to have a protective role on the attack of ROS species to DNA.

Copper effective binding with 32-62 and 94-125 peptide fragments of histone H2B.

In an attempt to investigate the role of histone H2B in Cu(II) induced toxicity and carcinogenesis, we synthesized the terminally blocked peptides H2B(32-62) (SRKESYSVYVYKVLKQVH(48)PDTGISSKAMGIM) and Η2Β(94-125) (IQTAVRLLLPGELAKH(110)AVSEGTKAVTKYTSS), mimicking the N-terminal histone-fold domain and C-terminal tail of histone H2B, respectively and studied their interaction with Cu(II) ions by means of potentiometric titrations and spectroscopic techniques (UV-visible, CD and EPR). Both peptides, H2B(32-62) and H2B(94-125), interacted efficiently with Cu(II) ions, forming several species from pH 4 to 11, with His(48) and His(110) serving as anchors for metal binding. In H2B(32-62), the effective Cu(II) binding is emphasized by the formation of a soluble Cu(II)-H2B(32-62) complex, unlike the unbound peptide that precipitated over pH 7.

Kinetics and Mechanisms of the Chromium(III) Reactions with 2,4- and 2,5-Dihydroxybenzoic Acids in Weak Acidic Aqueous Solutions.

The reactions of 2,4- and 2,5-dihydroxybenzoic acids (dihydroxybenzoic acid, DHBA) with chromium(III) in weak acidic aqueous solutions have been shown to take place in at least two stages. The first stage of the reactions has an observed rate constant k(1(obs)) = k(1)[DHBA] + C and the corresponding activation parameters are DeltaH(1(2,4)) ( not equal) = 49, 5 kJ/mol(-1), DeltaS(1(2,4)) ( not equal) = -103, 7 J mol(-1) K(-1), DeltaH(1(2,5)) ( not equal) = 60, 3 kJ/mol(-1), and DeltaS(1(2,5)) ( not equal) = -68, 0 J mol(-1) K(-1). These are composite activation parameters and the breaking of the strong intramolecular hydrogen bonding in the two ligands is suggested to be the first step of the (composite) first stage of the reactions.

The possible role of 94-125 peptide fragment of histone H2B in nickel-induced carcinogenesis.

The molecular mechanism by which nickel carcinogenicity is exerted is not fully understood. However, it is believed to involve DNA damage and epigenetic effects in chromatin, resulting from metal binding to the cell nucleus. Histone nuclear proteins are the major candidates for metal binding not only due to their abundance but also due to the presence of strong binding sites within their sequence.

Coordination of Cu(2+)and Ni(2+) with the histone model peptide of H2B N-terminal tail (1-31 residues): A spectroscopic study.

The interaction of Cu(2+) and Ni(2+) with the N-terminal tail of histone H2B, the 31 amino acid peptide H2B(1-31) (Ac-PEPAKSAPAPKKG(13)SKKAVTKAQKKD(25)GKKRKR-NH(2)), studied by various spectroscopic techniques (UV/Vis, CD, EPR and NMR) are described. The results showed the formation of Cu(2+)-H2B(1-31) complexes above pH 7.3 most probably through the beta-carboxylate group of D25.

Interaction of histone H2B (fragment 63-93) with Ni(ii). An NMR study.

The behaviour of the 31 mer peptide (Ac-NSFVNDIFERIAG(13)EASRL(18)A(19)H(20)YNKRS(25)TITSRE-NH(2)), modelling the histone-fold domain (63 to 93 residues) of H2B, towards Ni(ii) was investigated by multidimensional NMR spectroscopy (1D, 2D TOCSY, NOESY and (13)C-HSQC). The coordination involved the imidazole of His20 and three amide nitrogens of His20, Ala19 and Leu18, similar to the one shown by the hexapeptide LAHYNK contained in the 31 mer peptide. The solution structure of the Ni(ii) complex with the tridecapeptide comprising histone's H2B 75-87 residues, was elucidated from the NOE cross correlations observed in the 2D-NOESY spectrum.

Reaction of chromium(III) with 3,4-dihydroxybenzoic acid: kinetics and mechanism in weak acidic aqueous solutions.

The interactions between chromium(III) and 3,4-dihydroxybenzoic acid (3,4-DHBA) were studied resulting in the formation of oxygen-bonded complexes upon substitution of water molecules in the chromium(III) coordination sphere. The experimental results show that the reaction takes place in at least three stages, involving various intermediates. The first stage was found to be linearly dependent on ligand concentration k(1(obs))' = k(0) + k(1(obs))[3, 4-DHBA], and the corresponding activation parameters were calculated as follows: DeltaH(1(obs)) ( not equal) = 51.

Interaction of Cu(II) and Ni(II) with the 63-93 fragment of histone H2B.

Chromatin proteins are believed to represent reactive sites for metal ion binding. We have synthesized the 31 amino acid peptide Ac-NSFVNDIFERIAGEASRLAHYNKRSTITSRE-NH2, corresponding to the 63-93 fragment of the histone H2B and studied its interaction with Cu(II) and Ni(II). Potentiometric and spectroscopic studies (UV-vis, CD, NMR and EPR) showed that histidine 21 acts as an anchoring binding site for the metal ion.