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].