Nickel binding sites in histone proteins: Spectroscopic and structural characterization (original) (raw)
Related papers
Nickel compounds are established human carcinogens. Their carcinogenic activity is consistently related to the ability of Ni(II) to access chromatin and cause multiple types of cellular nuclear damage via direct or indirect mechanisms. The mechanistic concepts proposed for nickel carcinogenesis include promutagenic DNA damage [1,2], epigenetic effects in chromatin [3-5], and impairment of DNA repair [6]. The core histone octamer (formed by two copies of histones H3, H4, H2A and H2B) together with the linker histone H1, package eukaryotic DNA into repeating nucleosomal units that are folded into higher order chromatin fibres. Due to its abundance inside the cell nucleus this histone octamer is a good target for nickel binding. We focused our interest on histone H4, first of all because it has been reported that nickel(II) is a potent suppressor of histone H4 acetylation, in both yeast and mammalian cells [7], and this may lead to transcription errors and subsequent DNA modifications [8]. Secondly, an anchoring binding site for nickel ion on the terminal part of this protein, specifically histidine H18, is close to sites for post-translational modifications involved in nickel toxicity. All this evidence points to the H4 tail as a candidate for Ni(II) binding on the histone octamer, and the study of its N-terminal tail as a model for metal coordination can supply useful information in the effort of unveiling the mechanisms of nickel carcinogenesis. We previously reported, by potentiometric and spectroscopic (NMR, Uv-Vis, CD) studies, about the interaction of Ni(II) with minimal models of the H4 tail: the two peptides with 6 amino acids Ac-AKRHRK-Am and with 22 amino acids Ac-SGRGKGGKGLGKGGAKRHRK VL-Am, respectively [9-11]. Here we present our recent results on the coordination ability of Ni(II) to the N-terminal tail of histone H4, the 30-amino acid peptide Ac-SGRGKGGKGLGKGGAKRH18RKVLRDNIQGITAm, achieved by the use of multidimensional NMR spectroscopy.
Molecular Mechanisms in Nickel Carcinogenesis: Modeling Ni(II) Binding Site in Histone H4
Environmental Health Perspectives, 2002
Ni(II) compounds are well known as human carcinogens, though the molecular events which are responsible for this are not yet fully understood. It has been proposed that the binding of N(II) ions within the cell nucleus is a crucial element in the mechanism of carcinogenesis. The most abundant proteins in the cell nucleus are histones, and this makes them the prime candidates for this role. This article is a review of our recent studies of histone H4 models of Ni(II) binding. We analyzed the sequence of the N-terminal tail of the histone H4, Ac-SGRGKGGKGLGKGG AKRH 18 RKVL-Am, for Ni(II) binding. This site has been proposed mainly because of the potent inhibitory effect of Ni(II) on the acetylation of lysine residues near the histidine H 18 , and also because of the accessibility of the H4 tail in the histone octamer. Combined potentiometric and spectroscopic studies showed that the histidine 18 acted as an anchoring binding site for metal ions in the peptide investigated. Comparison with the results for Cu(II) binding are also reported. The results allowed us to propose that the binding of Ni(II) is able to promote a secondary structure with organized side-chain orientation on the N-terminal tail of histone H4.
Chemical Research in Toxicology, 1998
A combined pH-metric and spectroscopic (UV/vis, CD, NMR) study of the Ni(II) binding to CH 3 CO-Thr-Glu-Ser-His-His-Lys-NH 2 (AcTESHHKam), a blocked hexapeptide modeling a part of the C-terminal sequence of the major variant of histone H2A (residues 120-125), revealed the formation of a pseudo-octahedral NiHL complex in weakly acidic and neutral solutions. Ni(II) is bound to the peptide through imidazole nitrogens on both of its histidine residues and the carboxylate of the side chain of glutamic acid. At higher pH, a series of square-planar complexes are formed. This process is accompanied by hydrolytic degradation of the peptide. At pH 7.4, the peptide hydrolyzes in a Ni(II)-assisted fashion, yielding the square-planar Ni-(II) complex of SHHKam as the sole product detected by CD, MALDI-TOF MS, and HPLC. Quantitative analysis of complex stabilities indicates that the-TESHHKmotif is a very likely binding site for carcinogenic Ni(II) ions in the cell nucleus. The Ni(II)-assisted hydrolysis of the C-terminal chain of histone H2A may provide a novel mechanism of genotoxicity combining the damage to the nucleosome with the generation of further toxic Ni(II) species.
Chemical Research in Toxicology, 2003
We have demonstrated previously that Ni(II) binds to the C-terminal-TESHHKAKGK motif of isolated bovine histone H2A. At physiological pH, the bound Ni(II) assists in hydrolysis of the E-S peptide bond in this motif that results in a cleavage of the terminal octapeptide SHHKAKGK off the histone's C-tail. To test if the hydrolysis could also occur in living cells, we cultured CHO (Chinese hamster ovary), NRK-52 (rat renal tubular epithelium), and HPL1D (human lung epithelium) cells with 0.1-1 mM Ni(II) for 3-7 days. As found by gel electrophoresis, Western blotting, and liquid chromatography/mass spectrometry, histones extracted from the cells contained a new fraction of histone H2A lacking the terminal octapeptide (q-H2A). The abundance of q-H2A increased with Ni(II) concentration and exposure time. It can be anticipated that the truncation of histone H2A may alter chromatin structure and affect gene expression. The present results provide evidence for novel mechanisms of epigenetic effects of Ni(II) that may be involved in nickel toxicity and carcinogenesis.
Chemical Research in Toxicology, 1995
Nickel(I1) compounds are established human carcinogens, but the molecular mechanisms underlying their activity are only partially known. One mechanism may include mediation by nickel of promutagenic oxidative DNA damage that depends on Ni(I1) binding to chromatin. To characterize such binding at the histone moiety of chromatin, we synthesized the peptide CH3CO-Cys-Ala-Ile-His-NH2 (L), a model of the evolutionarily conserved motif in histone H3 with expected affinity for transition metals, and evaluated its reactivity toward Ni(I1). Combined spectroscopic (W/vis, CD, NMR) and potentiometric measurements showed that, a t physiological pH, mixtures of Ni(I1) and L yielded unusual macrochelate complexes, NiL and NiL2, in which the metal cation was bound through Cys and His side chains in a squareplanar arrangement. Above pH 9, a NiH-3L complex was formed, structurally analogous to typical square-planar nickel complexes. These complexes are expected to catalyze oxidation reactions, and therefore, coordination of Ni(I1) by the L motif in core histone H3 may be a key event in oxidative DNA base damage observed in the process of Ni(I1)-induced carcinogenesis.
Alterations of histone modifications and transgene silencing by nickel chloride
Carcinogenesis, 2006
Although it has been well established that insoluble nickel compounds are potent carcinogens and soluble nickel compounds are less potent, the mechanisms remain unclear. Nickel compounds are weakly mutagenic, but cause epigenetic effects in cells. Previous studies have shown that insoluble nickel compounds enter cells by phagocytosis and silence gene expression, but the entry of soluble nickel compounds and their effects on gene silencing have not been well studied. Here, we have demonstrated, using a dye that fluoresces when nickel ions bind, that soluble nickel compounds were taken up by cells. Nickel ions localized initially in the cytoplasm, but later entered the nucleus and eventually silenced a transgene. In addition, we described three major changes in histone modification of cells exposed to soluble nickel compounds: (i) loss of acetylation of H2A, H2B, H3 and H4; (ii) increases of H3K9 dimethylation; and (iii) substantial increases of the ubiquitination of H2A and H2B. These effects were observed at nickel exposure conditions that had minimum effects on cell cytotoxicity. Moreover, we demonstrated that nickel-induced transgene silencing was associated with similar changes of histone modifications in their nuclesomes. This study is the first to show that nickel compounds increase histone ubiquitination in cells. These new findings will further our understanding of the epigenetic mechanisms of nickel-mediated carcinogenesis.
Molecular Mechanisms of Nickel Carcinogenesis
Annual Review of Pharmacology and Toxicology, 1991
Humans are exposed to carcinogenic nickel (Ni) compounds both occupationally and environmentally. In this paper, molecular mechanisms of nickel carcinogenesis are considered from the point-of-view of the uptake of nickel sulfide particles in cells, their dissolution and their effects on heterochromatin. Molecular mechanisms by which nickel induces gene silencing, DNA hypermethylation and inhibition of histone acetylation, will be discussed.
Nickel compounds are novel inhibitors of histone H4 acetylation
Cancer research, 2000
Environmental factors influence carcinogenesis by interfering with a variety of cellular targets. Carcinogenic nickel compounds, although generally inactive in most gene mutation assays, induce chromosomal damage in heterochromatic regions and cause silencing of reporter genes when they are located near telomere or heterochromatin in either yeast or mammalian cells. We studied the effects of nickel on the lysine acetylation status of the NH2-terminal region of histone H4. At nontoxic levels, nickel decreased the levels of histone H4 acetylation in vivo in both yeast and mammalian cells, affecting only lysine 12 in mammalian cells and all of the four lysine residues in yeast. In yeast, lysine 12 and 16 were more greatly affected than lysine 5 and 8. Interestingly, a histidine Ni2+ anchoring site is found at position 18 from the NH2-terminal tail of H4. Nickel was also found to inhibit the acetylation of H4 in vitro using purified recombinant histone acetyltransferase. To our knowledg...
Nickel Compounds Are Novel Inhibitors of Histone H4 Acetylation1
2000
Environmental factors influence carcinogenesis by interfering with a variety of cellular targets. Carcinogenic nickel compounds, although generally inactive in most gene mutation assays, induce chromosomal damage in heterochromatic regions and cause silencing of reporter genes when they are located near telomere or heterochromatin in either yeast or mammalian cells. We studied the effects of nickel on the lysine acetylation status of the NH 2 -terminal region of histone H4. At nontoxic levels, nickel decreased the levels of histone H4 acetylation in vivo in both yeast and mammalian cells, affecting only lysine 12 in mammalian cells and all of the four lysine residues in yeast. In yeast, lysine 12 and 16 were more greatly affected than lysine 5 and 8. Interestingly, a histidine Ni 2؉ anchoring site is found at position 18 from the NH 2 -terminal tail of H4. Nickel was also found to inhibit the acetylation of H4 in vitro using purified recombinant histone acetyltransferase. To our knowledge, this is the first agent shown to decrease histone H4 acetylation at nontoxic levels.
Nickel Binding Sites in Histone Proteins: Spectroscopic and Structural Characterization- short paper
Nickel compounds influence carcinogenesis by interfering with a variety of cellular targets. It has been found that nickel is a potent inhibitor in vivo of histone H4 acetylation, in both yeast and mammalian cells. It has preference to specific lysine residues in the H4 N-terminal -S 1 GRGK 5 GGK 8 GLGK 12 GGAK 16 RH 18 RKVL 22 tail, in which the sites of acetylation are clustered. About the nature of the structural changes induced by histone acetylation on H4, it has been recently demonstrated that acetylation promotes an increase in -helical conformation of the acetylated Nterminal tail of H4. This causes a shortening of the tail and such an effect may have an important structural and functional implication as a mechanism of transcriptional regulation. Here we report a study on the conformational changes induced by carcinogenic nickel compounds on the histone H4 protein. From a circular dichroism study we found that nickel is able to induce a secondary structure in the protein. In particular, nickel has the same effect as acetylation: it induces an increase in -helical conformation of the non-acetylated histone H4. The -helical increase occurring upon nickel interaction with histone H4 should decrease the ability of histone acetyl transferase to recognize and bind to the histone tail, and thus affect the ability of the enzyme to further modify the lysine residues. The shortening of the distance between adjacent amino acids, caused by the translation from an extended to a helical conformation, could disrupt the histone recognition motif; this may eventually compromise the entire "histone code".