NMR study of Nickel binding to N-tail of Histone H4

The molecular mechanisms of nickel-induced carcinogenesis include interactions of this metal with major chromatin components causing alterations in gene expression rather than by direct DNA damage [1,2]. We have previously reported that nickel is a potent suppressor in vivo of histone H4 acetylation, in both yeast and mammalian cells [3]. Acetylation induces an increase in a-helical content in the histone tails of the nucleosome, particularly in the N-terminal domain of histone H4. It causes a shortening of the tail and, such effect, may have important structural and functional implication as a mechanism of transcriptional regulation. In our study we found that also nickel can cause conformational changes on the histone H4 protein and the same as acetylation it induces an increase in the a-helical conformation of the histone H4. In order to focus the conformational changes in the a-helical-inducted region and the role exhibit by the side-chain in the complex stability, the interactions between Ni(II) and the N-terminal region of histone H4, Ac-SGRGKGGKGLGKGGAKRHRKVLRDNIQGIT-Am, were studied using NMR spectroscopy. A series of 1D and 2D Tocsy and Noesy 1H-NMR spectra of the peptide-ligand with increasing of nickel concentration to the final molar ratio 1:1, were acquired. The complex was studied at pH 9, a the maximum level 4N of metal coordination to the peptide, with respect the our potentiometric analysis previous reported [4,5].