Nitration of the tyrosine in histone F1 in salt solutions and in F1-polyanion complexes

The emerging role of chromatin remodelers in neurodevelopmental disorders: a developmental perspective

Neurodevelopmental disorders (NDDs), including intellectual disability (ID) and autism spectrum disorders (ASD), are a large group of disorders in which early insults during brain development result in a wide and heterogeneous spectrum of clinical diagnoses. Mutations in genes coding for chromatin remodelers are overrepresented in NDD cohorts, pointing towards epigenetics as a convergent pathogenic pathway between these disorders. In this review we detail the role of NDD-associated chromatin remodelers during the developmental continuum of progenitor expansion, differentiation, cell-type specification, migration and maturation. We discuss how defects in chromatin remodelling during these early developmental time points compound over time and result in impaired brain circuit establishment. In particular, we focus on their role in the three largest cell populations: glutamatergic neurons, GABAergic neurons, and glia cells. An in-depth understanding of the spatiotemporal role of chromatin remodelers during neurodevelopment can contribute to the identification of molecular targets for treatment strategies.

Oxidative post-translational modifications in histones

Epigenetic regulation is attracting much attention because it explains many of the effects that the external environment induces in organisms. Changes in the cellular redox status and even more specifically in its nuclear redox compartment is one of these examples. Redox changes can induce modulation of the epigenetic regulation in cells. Here we present a few cases where reactive oxygen or nitrogen species induces epigenetic marks in histones. Posttranslational modification of these proteins like histone nitrosylation, carbonylation, or glutathionylation together with other mechanisms not reviewed here are the cornerstones of redox-related epigenetic regulation. We currently face a new field of research with potential important consequences for the treatment of many pathologies.

The secondary structure of histone IV and its stability

The secondary structure within histone IV and its fragments obtained by cyanogen bromide (CNBr) and cleavage at Met 84 has been examined by circular dichroism and spectophotometric pH titration measurements. These studies have confirmed the existence of stable secondary structure within the C-terminal fragment of histone IV (C-peptide which can be perturbed only by 6M urea at pH greater than 8 or 8 M guanidine-HCL. In contrast, the N-terminal fragment (N-peptide) appears to lack significant secondary structure at low ionic strengths but acquires approximately 15% betasheet conformation and 5% alpha-helix upon aggregation at ionic strengths larger than or equal to 0.4. The rates of nitration of the N- and C-peptides by tetranitromethane (TNM) have also been measured as a function of ionic strengths. Under comparable conditions, the rate constant for nitration of the N-peptide was found to be about six times greater than that for the C-peptide, further evidence in support of the presence of stable secondary structure within the C-terminal region of histone IV. After binding these histone IV fragments to DNA, however, the nitration reaction rate constants for the N- and C-peptide in the bound form are found to be 2% and 27% of the corresponding free peptides. Reconstituted nucleohistone IV is about 10% as reactive to TNM as histone IV at comparable ionic strength.

Histone H1.2 is a substrate for denitrase, an activity that reduces nitrotyrosine immunoreactivity in proteins

Several reports have described an activity that modifies nitrotyrosine-containing proteins and their immunoreactivity to nitrotyrosine Abs. Without knowing the product of the reaction, this new activity has been called a "denitrase." In those studies, some nonspecific proteins, which have multiple tyrosine residues, e.g., albumin, were used as a substrate. Therefore, the studies were based on an unknown mechanism of reaction and potentially a high background. To solve these problems, one of the most important things is to find a more suitable substrate for assay of the enzyme. We developed an assay strategy for determining the substrate for denitrase combining 2D-gel electrophoresis and an on-blot enzyme assay. The resulting substrate from RAW 264.7 cells was Histone H1.2, an isoform protein of linker histone. Histone H1.2 has only one tyrosine residue in the entire molecule, which ensures the exact position of the substrate to be involved. It has been reported that Histones are the most prominent nitrated proteins in cancer tissues. It was also demonstrated that tyrosine nitration of Histone H1 occurs in vivo. These findings lead us to the idea that Histone H1.2 might be an intrinsic substrate for denitrase. We nitrated recombinant and purified Histone H1.2 chemically and subjected it to an on-blot enzyme assay to characterize the activity. Denitrase activity behaved as an enzymatic activity because the reaction was time dependent and was destroyed by heat or trypsin treatment. The activity was shown to be specific for Histone H1.2, to differ from proteasome activity, and to require no additional cofactors.

Selective nitration of histone tyrosine residues in vivo in mutatect tumors

Nitric oxide-derived reactive species have been implicated in many disorders. Protein nitrotyrosine is often used as a stable marker of these reactive species. Using immunohistochemistry, we have previously detected nitrotyrosine in murine Mutatect tumors, where neutrophils are the principal source of nitric oxide. We now report on the identification of several prominent nitrotyrosine-containing proteins. Using Western blot analysis, nitrotyrosine in higher molecular mass proteins (>20 kDa) was detected in tumors containing a high number of neutrophils but not in tumors with fewer neutrophils. Staining for nitrotyrosine was consistently seen in low molecular mass proteins (< or =15 kDa), regardless of the level of neutrophils. Protein nitrotyrosine was not seen in Mutatect cells growing in vitro. Treatment with nitric oxide donors produced nitration of < or =15-kDa proteins, but only after extended periods. These small proteins, both from tumors and cultured cells, were identified by mass spectrometry to be histones. Only a subset of tyrosine residues was nitrated. Selective nitration may reflect differential accessibility of different tyrosine residues and the influence of neighboring residues within the nucleosome. The prominence of histone nitration may reflect its relative stability, making this post-translational modification a potentially useful marker of extended exposure of cells or tissues to nitric oxide-derived reactive species.

Role of tyrosine residues on structure-function of fructose-1,6-biphosphate aldolase from Ceratitis capitata

Tyrosine contributions to the structure-function relationship in the fructose-1, 6-biphospate aldolase from C. capitata have been investigated. There are three well defined groups of tyrosine residues with different roles in the structure of the insect aldolase. C-terminal tyrosine residues are essential for the maintenance of the catalytic conformation. Releasing of these residues by carboxypeptidase A treatment results in complex conformational changes according to CD studies. Another tyrosine residue group is located at the active site, and the substrate, fructose-1, 6-biphosphate, protects it upon nitration. Chemical modification of this residue results in enzyme activity changes similar to those induced by carboxypeptidase digestion. Enzyme-substrate interaction results in a change of the microenvironment of at least three tyrosine residues per subunit with different accessibility for tetranitromethane.

Fatty acid synthetase complex from the insect Ceratitis capitata. Structural studies

The involvement of lipids in the structure and the activity of the fatty acid synthetase from the insect Ceratitis capitata has been previously established. Lipid-protein interactions were examined by circular dichroism. A thermal transition for both the structure and the activity of the enzyme complex takes place at about 50 degrees C; as the temperature is raised alpha-helix content decreases considerably and, concomitantly, the enzyme undergoes a marked inactivation. After 180 min at 37 degrees C, the secondary structure of the enzyme complex is 20% alpha-helix, 33% beta structure and 47% of not ordered structure against 43%, 26% and 31% as respective percentages for the native form of the complex. Lipolytic digestion of the complex was carried out with either lipase or phospholipase A2 or a mixture of both enzymes. Any of the lipolytic treatments induces a decrease of [theta]220 and the simultaneous digestion with lipase plus phospholipase during 90 min account for a limit structure with 8% of alpha-helix. The secondary structure of the complex after treatment with proteolytic enzymes, trypsin or chymotrypsin, had 15% alpha-helix, 20% beta structure and 57% of not ordered structure. The preservation of the alpha-helix content indicates that lipids protect certain of the bonds cleavable in the absence of lipids. The structural organization of the complex was studied through sequences of lipolytic and proteolytic treatments; final organization was dependent on the initial lipolytic digestion in agreement with the peptide bond shielding by the lipid component. Nitration of the complex with tetranitromethane modified almost completely all tyrosine residues of the polypeptide chains.

Conformational changes in subfractions of calf thymus histone H1

This paper presents the first study of conformational changes in the subfractions of calf thymus H1. H1 was fractionated by the method of Kincade and Cole (Kincade, J. M., and Cole, R.D. (1966), J. Biol. Chem. 241. 5790) using a very shallow Gdn-HC1 gradient. A possible new H1 subfraction, about 5--8% of the H1, has been found and characterized by amino acid analysis and electrophoresis. The effects of salt concentration and pH on the conformation of each of the four major subfractions have been studied by measuring the fluorescence anisotropy of the tyrosine emission and the circular dichroism (CD) of the peptide bond. Upon the addition of salt to aqueous solutions at neutral pH, all four subfractions show an instantaneous change in fluorescence anisotropy, fluorescence intensity, tyrosine absorbance, and CD. The folding associated with this instantaneous change is highly cooperative, and involves the region of the molecule containing the lone tyrosine, which becomes buried in the folded form. The folding of subfraction 3a is more sensitive to salt than the other major subfractions. Upon folding, approximately 13% of the residues of subfractions 1b and 2 form alpha and beta structure; 3a and 3b have approximately 16% of the residues in alpha and beta structures. There is no evidence for interactions between the subfractions. In salt-free solutions, each of the four major subfractions show very little change in conformation in going from low to neutral pH, but each shows a very sharp transition near pH 9. This transition gives rise to a marked increase in fluorescence anisotropy and fluorescence intensity, and involves the formation of both alpha and beta strucute in a manner similar to that of the salt-induced state.

The solubility of calf thymus chromatin in sodium chloride

The solubility of calf thymus chromatin and chromatin depleted of F1-histone has been examined under various conditions in sodium chloride. F1-depleted DNH was more soluble than native DNH at low concentrations but this difference became small at high concentrations (1mg/ml). Both exhibited minimum solubility in 0.15M -NaCl. The effect of pH and of maleylation of the mino acid side chains on the solubility implied that electrostatic interactions dominated the precipitation reaction. Urea had no effect on the solubility of either complex. N.m.r. studies showed that the chromatin behaved as a rigid complex at all salt concentrations less than 0.6 molar.