Separation of phosphorylated histone H1 variants by high-performance capillary electrophoresis

Application of CE-MS for the analysis of histones and histone modifications

The analysis, identification and quantification of histones and their post-translational modifications plays a central role in chromatin research and in studying epigenetic regulations during physiological processes. In the last decade analytical strategies based on mass spectrometry have been greatly improved for providing a global view of single modification abundances or to determine combinatorial patterns of modifications. Presented here is a newly developed strategy for histone protein analysis and a number of applications are illustrated with an emphasis on PTM characterization. Capillary electrophoresis is coupled to mass spectrometry (CE-MS) and has proven to be a very promising concept as it enables to study intact histones (top-down proteomics) as well as the analysis of enzymatically digested proteins (bottom-up proteomics). This technology combines highly efficient low-flow CE separations with ionization in a single device and offers an orthogonal separation principle to conventional LC-MS analysis, thus expanding the existing analytical repertoire in a perfect manner.

Investigating capillary electrophoresis-mass spectrometry for the analysis of common post-translational modifications

Capillary electrophoresis coupled to mass spectrometry is a very efficient analytical method for the analysis of post-translational modifications because of its high separation efficiency and high detection sensitivity. Here we applied CE-MS using three differently coated separation capillaries for in-depth analysis of a set of 70 synthetic post-translationally modified peptides (including phosphorylation, acetylation, methylation, and nitration). We evaluated the results in terms of peptide detection and separation characteristics and found that the use of a neutrally coated capillary resulted in highest overall signal intensity of singly modified peptides. In contrast, the use of a bare-fused silica capillary was superior in the identification of multi-phosphorylated peptides (12 out of 15 were identified). Fast separations of approximately 12 min could be achieved using a positively coated capillary, however, at the cost of separation efficiency. A comparison to nanoLC-MS revealed that multi-phosphorylated peptides interact with the RP material very poorly so that these peptides were either washed out or elute as very broad peaks from the nano column which results in a reduced peptide identification rate (7 out of 15). Moreover, the methods applied were found to be very well suited for the analysis of the acetylated, nitrated and methylated peptides. All 36 synthetic peptides, which exhibit one of those modifications, could be identified regardless of the method applied. As a final step in this study and as a proof of principle, the phosphoproteome enriched from PC-12 pheochromocytoma cells was analyzed by CE-MS resulting in 5686 identified and 4088 quantified phosphopeptides. We compared the characterized analytes to those identified by a nanoLC-MS proteomics study and found that less than one third of the phosphopeptides were identical, which demonstrates the benefit by combining different approaches quite impressively.

Separation of Methylated Histone Peptides via Host-Assisted Capillary Electrophoresis

Lysine methylation in protein is one important epigenetic mechanism that regulates diverse biological processes but is challenging to study due to the large variability in methylation levels and sites. Here, we show that supramolecular hosts such as calixarenes and cucurbiturils can be applied in the background electrolyte (BGE) of capillary electrophoresis (CE) for highly effective separation of post-translationally methylated histone peptides. The molecular recognition event causes a shift in the electrophoretic mobility of the peptide, allowing affinity measurement for binding between the synthetic receptor and various methylated lysine species. Successful separation of the H3 peptides carrying different methylation levels at the K9 position can be achieved using CX4 and CX6 as the BGE additives in CE, enabling monitoring of the activity of the histone lysine demethylase JMJD2E. This reveals the power of combining high resolution CE with synthetic hosts for study of protein methylation, and the method should be capable of analyzing complex biological samples for better understanding of the functions of histone methylation.

Quantitative proteomics using ultralow flow capillary electrophoresis-mass spectrometry

In this work, we evaluate the incorporation of an ultralow flow interface for coupling capillary electrophoresis (CE) and mass spectrometry (MS), in combination with reversed-phase high-pressure liquid chromatography (HPLC) fractionation as an alternate workflow for quantitative proteomics. Proteins, extracted from a SILAC (stable isotope labeling by amino acids in cell culture) labeled and an unlabeled yeast strain were mixed and digested enzymatically in solution. The resulting peptides were fractionated using RP-HPLC and analyzed by CE–MS yielding a total of 28 538 quantified peptides that correspond to 3 272 quantified proteins. CE–MS analysis was performed using a neutral capillary coating, providing the highest separation efficiency at ultralow flow conditions (<10 nL/min). Moreover, we were able to demonstrate that CE–MS is a powerful method for the identification of low-abundance modified peptides within the same sample. Without any further enrichment strategies, we succeeded in quantifying 1 371 phosphopeptides present in the CE–MS data set and found 49 phosphopeptides to be differentially regulated in the two yeast strains. Including acetylation, phosphorylation, deamidation, and oxidized forms, a total of 8 106 modified peptides could be identified in addition to 33 854 unique peptide sequences found. The work presented here shows the first quantitative proteomics approach that combines SILAC labeling with CE–MS analysis.

Comparing and combining capillary electrophoresis electrospray ionization mass spectrometry and nano-liquid chromatography electrospray ionization mass spectrometry for the characterization of post-translationally modified histones

We present the first comprehensive capillary electrophoresis electrospray ionization mass spectrometry (CESI-MS) analysis of post-translational modifications derived from H1 and core histones. Using a capillary electrophoresis system equipped with a sheathless high-sensitivity porous sprayer and nano-liquid chromatography electrospray ionization mass spectrometry (nano-LC-ESI-MS) as two complementary techniques, we characterized H1 histones isolated from rat testis. Without any pre-separation of the perchloric acid extraction, a total of 70 different modified peptides, including 50 phosphopeptides, were identified in the rat linker histones H1.0, H1a-H1e, and H1t. Out of the 70 modified H1 histone peptides, 27 peptides could be identified with CESI-MS only, and 11 solely with LC-ESI-MS. Immobilized metal-affinity chromatography enrichment prior to MS analysis yielded a total of 55 phosphopeptides; 22 of these peptides could be identified only by CESI-MS, and 19 only by LC-ESI-MS, showing the complementarity of the two techniques. We mapped 42 H1 modification sites, including 31 phosphorylation sites, of which 8 were novel sites. For the analysis of core histones, we chose a different strategy. In a first step, the sulfuric-acid-extracted core histones were pre-separated using reverse-phase high-performance liquid chromatography. Individual rat testis core histone fractions obtained in this way were digested and analyzed via bottom-up CESI-MS. This approach yielded the identification of 42 different modification sites including acetylation (lysine and N(α)-terminal); mono-, di-, and trimethylation; and phosphorylation. When we applied CESI-MS for the analysis of intact core histone subtypes from butyrate-treated mouse tumor cells, we were able to rapidly detect their degree of modification, and we found this method very useful for the separation of isobaric trimethyl and acetyl modifications. Taken together, our results highlight the need for additional techniques for the comprehensive analysis of post-translational modifications. CESI-MS is a promising new proteomics tool as demonstrated by this, the first comprehensive analysis of histone modifications, using rat testis as an example.

Histone H1 interphase phosphorylation becomes largely established in G1 or early S phase and differs in G1 between T-lymphoblastoid cells and normal T cells

Background

Histone H1 is an important constituent of chromatin, and is involved in regulation of its structure. During the cell cycle, chromatin becomes locally decondensed in S phase, highly condensed during metaphase, and again decondensed before re-entry into G₁. This has been connected to increasing phosphorylation of H1 histones through the cell cycle. However, many of these experiments have been performed using cell-synchronization techniques and cell cycle-arresting drugs. In this study, we investigated the H1 subtype composition and phosphorylation pattern in the cell cycle of normal human activated T cells and Jurkat T-lymphoblastoid cells by capillary electrophoresis after sorting of exponentially growing cells into G₁, S and G₂/M populations.

Results

We found that the relative amount of H1.5 protein increased significantly after T-cell activation. Serine phosphorylation of H1 subtypes occurred to a large extent in late G₁ or early S phase in both activated T cells and Jurkat cells. Furthermore, our data confirm that the H1 molecules newly synthesized during S phase achieve a similar phosphorylation pattern to the previous ones. Jurkat cells had more extended H1.5 phosphorylation in G₁ compared with T cells, a difference that can be explained by faster cell growth and/or the presence of enhanced H1 kinase activity in G₁ in Jurkat cells.

Conclusion

Our data are consistent with a model in which a major part of interphase H1 phosphorylation takes place in G₁ or early S phase. This implies that H1 serine phosphorylation may be coupled to changes in chromatin structure necessary for DNA replication. In addition, the increased H1 phosphorylation of malignant cells in G₁ may be affecting the G₁/S transition control and enabling facilitated S-phase entry as a result of relaxed chromatin condensation. Furthermore, increased H1.5 expression may be coupled to the proliferative capacity of growth-stimulated T cells.

The significance, development and progress of high-throughput combinatorial histone code analysis

The physiological state of eukaryotic DNA is chromatin. Nucleosomes, which consist of DNA in complex with histones, are the fundamental unit of chromatin. The post-translational modifications (PTMs) of histones play a critical role in the control of gene transcription, epigenetics and other DNA-templated processes. It has been known for several years that these PTMs function in concert to allow for the storage and transduction of highly specific signals through combinations of modifications. This code, the combinatorial histone code, functions much like a bar code or combination lock providing the potential for massive information content. The capacity to directly measure these combinatorial histone codes has mostly been laborious and challenging, thus limiting efforts often to one or two samples. Recently, progress has been made in determining such information quickly, quantitatively and sensitively. Here we review both the historical and recent progress toward routine and rapid combinatorial histone code analysis.

Analysis of histones, histone variants, and their post-translationally modified forms

For many years, histones were considered passive structural components of eukaryotic chromatin. Meanwhile it has been proven that histones also participate in gene regulation and repression via post-translational modification. The multitude of these post-translational modifications and the existence of numerous histone variants require particular separation strategies for their analysis, a prerequisite for studying biological processes. The most widely utilized techniques for the separation of histones, namely PAGE, HPCE, RP-HPLC, and hydrophilic Interaction LC, are reviewed here. Problems inherent to the analysis of histones owing to their unique physical and chemical properties along with advantages and shortcomings of particular methods are discussed.

Capillary electrophoresis analysis of poly(ethylene glycol) and ligand-modified polylysine gene delivery vectors

Cationic polymers including polylysine (PLL) and polyethylenimine are being widely tested as gene delivery vectors in various gene therapy applications. In many cases, the polymers were further modified by hydrophilic polymer grafting or ligand conjugation, which had been shown to greatly affect the vector stability, delivery efficiency and specificity. The characterization of modified polycation is particularly critical for quality control and vector development. Here several different separation modes using capillary electrophoresis for the analytical characterization of the modified polymers are described. PLL molecules were grafted with poly(ethylene glycol) (PEG) chain or conjugated with epidermal growth factor and analyzed under various analytical conditions. Poly(N,N'-dimethylacrylamide)-coated capillary was used to analyze the modified PLL to reduce the interaction between the samples and the capillary wall. PLLs containing different numbers of conjugated ligands were well separated with the coating method but, for PLL-g-PEG, the separation was poor under the same conditions. A method using low buffer pH and hydroxypropylmethyl cellulose additive was developed. These methods are useful to characterize various polycations and important for the quality control and application of potential gene delivery vectors.

Analyses of linker histone--chromatin interactions in situ

Recent studies, using cytometric techniques based on fluorescence microscopy, have provided new information on how linker histones interact with chromatin in vivo or in situ. In particular, the use of green fluorescent proteins (GFPs) has enabled detailed studies of how individual H1 subtypes, and specific motifs in them, interact with chromatin in vivo. Furthermore, the development of cytochemical methods to study the interaction between linker histones and chromatin using DNA-binding fluorochromes as indirect probes for linker histone affinity in situ, in combination with highly sensitive and specific analytical methods, has provided additional information on the interactions between linker histones and chromatin in several cell systems. Such results verified that linker histones have a substantially higher affinity for chromatin in mature chicken erythrocytes than in frog erythrocytes, and they also indicated that the affinity decreased during differentiation of the frog erythrocytes. Furthermore, in cultured human fibroblasts, the linker histones showed a relatively high affinity for chromatin in interphase, whereas it showed a significantly lower affinity in highly condensed metaphase chromosomes. This method also enables the analysis of linker histone affinity for chromatin in H1-depleted fibroblasts reconstituted with purified linker histones. No consistent correlation between linker histone affinity and chromatin condensation has so far been detected.

Chromatographic and electrophoretic characterization of protein variants

Almost all proteins are expressed in several variants, also known as isoforms. Individual protein variants differ by modifications of the individual amino acid side chains, or the N- or C-terminus. Typical modifications are glycosylation, phosphorylation, acetylation, methylation, deamidation or oxidation. It is of utmost interest to either get a quantitative picture of the variants of a particular protein or to separate the variants in order to be able to identify their molecular structure. Protein variants are present in native as well as in recombinant proteins. In the case of protein production it is interesting, how variants are generated during fermentation, purification processes, storage, and how present individual variants influence the biological activity. This review provides a comparison of chromatographic and electrophoretic separation methods to analyze and to prepare protein variants.

Characterization of sequence variations in human histone H1.2 and H1.4 subtypes

In humans, eight types of histone H1 exist (H1.1-H1.5, H1 degrees , H1t and H1oo), all consisting of a highly conserved globular domain and less conserved N- and C-terminal tails. Although the precise functions of these isoforms are not yet understood, and H1 subtypes have been found to be dispensable for mammalian development, it is now clear that specific functions may be assigned to certain individual H1 subtypes. Moreover, microsequence variations within the isoforms, such as polymorphisms or mutations, may have biological significance because of the high degree of sequence conservation of these proteins. This study used a hydrophilic interaction liquid chromatographic method to detect sequence variants within the subtypes. Two deviations from wild-type H1 sequences were found. In K562 erythroleukemic cells, alanine at position 17 in H1.2 was replaced by valine, and, in Raji B lymphoblastoid cells, lysine at position 173 in H1.4 was replaced by arginine. We confirmed these findings by DNA sequencing of the corresponding gene segments. In K562 cells, a homozygous GCC-->GTC shift was found at codon 18, giving rise to H1.2 Ala17Val because the initial methionine is removed in H1 histones. Raji cells showed a heterozygous AAA-->AGA codon change at position 174 in H1.4, corresponding to the Lys173Arg substitution. The allele frequency of these sequence variants in a normal Swedish population was found to be 6.8% for the H1.2 GCC-->GTC shift, indicating that this is a relatively frequent polymorphism. The AAA-->AGA codon change in H1.4 was detected only in Raji cells and was not present in a normal population or in six other cell lines derived from individuals suffering from Burkitt's lymphoma. The significance of these sequence variants is unclear, but increasing evidence indicates that minor sequence variations in linker histones may change their binding characteristics, influence chromatin remodeling, and specifically affect important cellular functions.

Role of the RB1 family in stabilizing histone methylation at constitutive heterochromatin

Here, we show a role for the RB1 family proteins in directing full heterochromatin formation. Mouse embryonic fibroblasts that are triply deficient for RB1 (retinoblastoma 1), RBL1 (retinoblastoma-like 1) and RBL2 (retinoblastoma-like 2) - known as TKO cells - show a marked genomic instability, which is coincidental with decreased DNA methylation, increased acetylation of histone H3 and decreased tri-methylation of histone H4 at lysine 20 (H4K20). Chromatin immunoprecipitation showed that H4K20 tri-methylation was specifically decreased at pericentric and telomeric chromatin. These defects are independent of E2F family function. Indeed, we show a direct interaction between the RB1 proteins and the H4K20 tri-methylating enzymes Suv4-20h1 and Suv4-20h2, indicating that the RB1 family has a role in controlling H4K20 tri-methylation by these histone methyltransferases. These observations indicate that the RB1 family is involved in maintaining overall chromatin structure and, in particular, that of constitutive heterochromatin, linking tumour suppression and the epigenetic definition of chromatin.

DNA methylation polymorphisms precede any histological sign of atherosclerosis in mice lacking apolipoprotein E

The present work investigates the occurrence and significance of aberrant DNA methylation patterns during early stages of atherosclerosis. To this end, we asked whether the genetically atherosclerosis-prone APOE-null mice show any changes in DNA methylation patterns before the appearance of histologically detectable vascular lesion. We exploited a combination of various techniques: DNA fingerprinting, in vitro methyl-accepting assay, 5-methylcytosine quantitation, histone post-translational modification analysis, Southern blotting, and PCR. Our results show that alterations in DNA methylation profiles, including both hyper- and hypomethylation, were present in aortas and PBMC of 4-week-old mutant mice with no detectable atherosclerotic lesion. Sequencing and expression analysis of 60 leukocytic polymorphisms revealed that epigenetic changes involve transcribed genic sequences, as well as repeated interspersed elements. Furthermore, we showed for the first time that atherogenic lipoproteins promote global DNA hypermethylation in a human monocyte cell line. Taken together, our results unequivocally show that alterations in DNA methylation profiles are early markers of atherosclerosis in a mouse model and may play a causative role in atherogenesis.

Linker histone subtype composition and affinity for chromatin in situ in nucleated mature erythrocytes

The replacement linker histones H1(0) and H5 are present in frog and chicken erythrocytes, respectively, and their accumulation coincides with cessation of proliferation and compaction of chromatin. These cells have been analyzed for the affinity of linker histones for chromatin with cytochemical and biochemical methods. Our results show a stronger association between linker histones and chromatin in chicken erythrocyte nuclei than in frog erythrocyte nuclei. Analyses of linker histones from chicken erythrocytes using capillary electrophoresis showed H5 to be the subtype strongest associated with chromatin. The corresponding analyses of frog erythrocyte linker histones using reverse-phase high performance liquid chromatography showed that H1(0) dissociated from chromatin at somewhat higher ionic strength than the three additional subtypes present in frog blood but at lower ionic strength than chicken H5. Which of the two H1(0) variants in frog is expressed in erythrocytes has thus far been unknown. Amino acid sequencing showed that H1(0)-2 is the only H1(0) subtype present in frog erythrocytes and that it is 100% acetylated at its N termini. In conclusion, our results show differences between frog and chicken linker histone affinity for chromatin probably caused by the specific subtype composition present in each cell type. Our data also indicate a lack of correlation between linker histone affinity and chromatin condensation.

Postsynthetic trimethylation of histone H4 at lysine 20 in mammalian tissues is associated with aging

Methylation of the N-terminal region of histones was first described more than 35 years ago, but its biological significance has remained unclear. Proposed functions range from transcriptional regulation to the higher order packing of chromatin in progress of mitotic condensation. Primarily because of the recent discovery of the SET domain-depending H3-specific histone methyltransferases SUV39H1 and Suv39h1, which selectively methylate lysine 9 of the H3 N terminus, this posttranslational modification has regained scientific interest. In the past, investigations concerning the biological significance of histone methylation were largely limited because of a lack of simple and sensitive analytical procedures for detecting this modification. The present work investigated the methylation pattern of histone H4 both in different mammalian organs of various ages and in cell lines by applying mass spectrometric analysis and a newly developed hydrophilic-interaction liquid chromatographic method enabling the simultaneous separation of methylated and acetylated forms, which obviates the need to work with radioactive materials. In rat kidney and liver the dimethylated lysine 20 was found to be the main methylation product, whereas the monomethyl derivative was present in much smaller amounts. In addition, for the first time a trimethylated form of lysine 20 of H4 was found in mammalian tissue. A significant increase in this trimethylated histone H4 was detected in organs of animals older than 30 days, whereas the amounts of mono- and dimethylated forms did not essentially change in organs from young (10 days old) or old animals (30 and 450 days old). Trimethylated H4 was also detected in transformed cells; although it was present in only trace amounts in logarithmically growing cells, we found an increase in trimethylated lysine 20 in cells in the stationary phase.

Analysis of histones by on-line capillary zone electrophoresis-electrospray ionisation mass spectrometry

The on-line combination of capillary electrophoresis and electrospray ionisation mass spectrometry was applied for the determination of some basic histones from calf thymus. The separation performance of those basic proteins was significantly improved by coating the capillaries with hydroxypropylmethylcellulose. The coating appeared to mask effectively the underlying silanol groups thus avoiding undesirable adsorption of the histones onto the capillary walls, while it was also shown to be an effective way to avoid contamination of the mass spectrometer. Finally, capillary electrophoresiselectrospray ionisation mass spectrometry with coaxial sheath liquid was successfully applied to the analysis of histones using a simple dialysis step of the sample as sample pretreatment.

Rapid dephosphorylation of H1 histones after apoptosis induction

H1 histones are involved in the formation of higher order chromatin structures and in the modulation of gene expression. Changes in chromatin structure are a characteristic initial feature of apoptosis. We therefore have investigated the histone H1 pattern of the human leukemic cell line HL60 undergoing programmed cell death, as induced by topoisomerase I inhibition. Histone H1 proteins were isolated and analyzed by high performance liquid chromatography and capillary zone electrophoresis. DNA fragmentation after apoptosis induction was monitored by agarose gel electrophoresis. The patterns of the three H1 histone subtypes extractable from apoptotic HL60 cells significantly differed from those of control cells in showing a decrease of phosphorylated H1 subtypes and an increase of the respective dephosphorylated forms. This dephosphorylation of H1 histones could be observed already 45 min after apoptosis induction and preceded internucleosomal DNA cleavage by approximately 2 h. We conclude that during apoptotic DNA fragmentation, the H1 histones become rapidly dephosphorylated by a yet unknown protein phosphatase.

Resolution of allelic and non-allelic variants of histone H1 by cation-exchange-hydrophilic-interaction chromatography

A mixed-mode high-performance liquid chromatography (HPLC) method that resolves the six known non-allelic variants of chicken erythrocyte histone H1 is described. Common, but previously unknown, allelic variants of H1 that comigrate in polyacrylamide gel electrophoresis are also resolved. The resolution of H1 variants achieved by this method should be useful in determining the functional significance of H1 sequence heterogeneity and in analyses of post-translational modification of H1. Furthermore, the principles behind the separation should be applicable to analyses of polymorphism in other proteins.

Capillary electrophoresis of histone H1 variants at neutral pH in dynamically modified fused- silica tubing

Existing methods for the analysis of histone H1 by capillary electrophoresis (CE) employ acidic buffers (pH <3.0) to suppress silanol ionization and minimize the loss of these extremely basic proteins by adsorption to capillary walls. Here we describe the use of Polybrene (PB) as a dynamic modification reagent in a simple procedure that facilitates the analysis of chicken H1 at neutral pH. PB is adsorbed to the inner surfaces of capillaries to render them cationic prior to use and a low concentration of PB is included in the electrolyte to replenish the coating during use. Inclusion of ethylenediaminetetraacetic acid (EDTA) in the electrolyte results in the assembly of a dynamic cation-exchange layer upon the immobilized PB that influences the relative mobilities of H1 variants. The six nonallelic variants of H1 known in this species as well as certain allelic variants are resolved. Because the procedure is effective in preventing the adsorption of proteins as basic as H1 at neutral pH, this strategy should facilitate CE analyses of many basic proteins under conditions that maintain their native conformation.

Normal spermatogenesis in mice lacking the testis-specific linker histone H1t

H1 histones bind to linker DNA and nucleosome core particles and facilitate the folding of chromatin into a more compact structure. Mammals contain seven nonallelic subtypes of H1, including testis-specific subtype H1t, which varies considerably in primary sequence from the other H1 subtypes. H1t is found only in pachytene spermatocytes and early, haploid spermatids, constituting as much as 55% of the linker histone associated with chromatin in these cell types. To investigate the role of H1t in spermatogenesis, we disrupted the H1t gene by homologous recombination in mouse embryonic stem cells. Mice homozygous for the mutation and completely lacking H1t protein in their germ cells were fertile and showed no detectable defect in spermatogenesis. Chromatin from H1t-deficient germ cells had a normal ratio of H1 to nucleosomes, indicating that other H1 subtypes are deposited in chromatin in place of H1t and presumably compensate for most or all H1t functions. The results indicate that despite the unique primary structure and regulated synthesis of H1t, it is not essential for proper development of mature, functional sperm.

In vitro binding of H1 histone subtypes to nucleosomal organized mouse mammary tumor virus long terminal repeat promotor

The binding of all known linker histones, named H1a through H1e, including H1(0) and H1t, to a model chromatin complex based on a DNA fragment containing the mouse mammary tumor virus long terminal repeat promotor was systematically studied. As for the histone subtype H1b, we found a dissociation constant of 8-16 nM to a single mononucleosome (210 base pairs), whereas the binding constant of all other subtypes varied between 2 and 4 nM. Most of the H1 histones, namely H1a, H1c, H1d/e, and H1(0), completely aggregate polynucleosomes (1.3 kilobase pairs, 6 nucleosomes) at 270-360 nM, corresponding to a molar ratio of six to eight H1 molecules per reconstituted nucleosome. To form aggregates with the histones H1t and H1b, however, greater amounts of protein were required. Furthermore, our results show that specific types of in vivo phosphorylation of the linker histone tails influence both the binding to mononucleosomes and the aggregation of polynucleosomes. S phase-specific phosphorylation with one to three phosphate groups at specific sites in the C terminus influences neither the binding to a mononucleosome nor the aggregation of polynucleosomes. In contrast, highly phosphorylated H1 histones with four to five phosphate groups in the C and N termini reveal a very high binding affinity to a mononucleosome but a low chromatin aggregation capability. These findings suggest that specific S phase or mitotic phosphorylation sites act independently and have distinct functional roles.

Buffer additives other than the surfactant sodium dodecyl sulfate for protein separations by capillary electrophoresis

The different compounds utilized as additives to the electrolyte solutions employed in protein capillary zone electrophoresis (CZE) for minimizing protein-capillary wall interactions, for improving selectivity and resolution and for controlling the electroosmotic flow are reviewed. The dependence of the electroosmotic flow on the different variables that can be affected by the incorporation of an additive into the electrolytic solution is discussed. A list of the most effective additives employed for protein separations by CZE is reported in Appendix A.

Application of hydrophilic-interaction liquid chromatography to the separation of phosphorylated H1 histones

A new two-step high-performance liquid chromatography (HPLC) procedure has been developed to separate modified histone H1 subtypes. Reversed-phase (RP) HPLC followed by hydrophilic-interaction liquid chromatography (HILIC) was used for analytical and semi-preparative scale fractionation of multi-phosphorylated H1 histone subtypes into their non-phosphorylated and distinct phosphorylated forms. The HILIC system utilizes the weak cation-exchange column PolyCAT A and an increasing sodium perchlorate gradient in a methanephosphonic acid-triethylamine buffer (pH 3.0) in the presence of 70% (v/v) acetonitrile. The identity and purity of the individual histone subfractions obtained was assayed by capillary electrophoretic analysis. The results demonstrate that application of the combined RP-HPLC-HILIC procedure to the analysis and isolation of modified H1 histone subtypes provides an innovative and important alternative to traditional separation techniques that will be extremely useful in studying the biological function of histone phosphorylation.

Effect of different surfactants on the separation by micellar electrokinetic chromatography of a complex mixture of dipeptides in urine of prolidase-deficient patients

Prolidase deficiency is a severe disorder characterized by massive excretion of metabolites with closely related structures. At present, micellar electrokinetic chromatography is the separation method which provides the highest selectivity of structurally similar solutes. However, the structure of a surfactant can greatly affect the selectivity of separation depending on factors such as the length of hydrophobic alkyl chain or the nature of the hydrophilic group. Here we investigated the effect of three non-ionic and four anionic detergents for obtaining the best separation conditions for resolving imidodipeptide mixtures. The effect on resolution of variables such as temperature, surfactant concentrations and organic solvents was also examined. The greatest resolution was obtained at the lowest temperature studied (10 degrees C) using 50 mM sodium borate, pH 9.3 containing 50 mM pentanesulfonate and 10% (v/v) methanol. Under these experimental conditions almost all excreted components were baseline separated and identified.

Complete resolution of imidodipeptide mixtures in urine of prolidase-deficient patients using micellar electrokinetic chromatography

The use of capillary zone electrophoresis as an efficient method for the identification of urinary imidodipeptides of prolidase-deficient patients has already been reported. However, owing to the complexity of the components excreted, the resolution of electrophoretic patterns obtained was poor. Here we examine the use of micellar electrokinetic chromatography to enhance peak resolution in order to obtain better insight into the electropherograms of patients' urine. The usefulness of sodium dodecyl sulphate as surfactant is reported: refined electropherograms were achieved using 35 mM sodium borate, pH 8.3 containing 65 mM sodium dodecyl sulphate. Almost all peaks were baseline separated, collected and sequenced. This allowed us to define the exact imidodipeptide composition of patients' urine. The possibility of identifying and thus quantifying each single peak means that comparison of urinary imidodipeptide excretion patterns from different patients can be made and the hypothesis that peptide patterns can be correlated with differing clinical severity can be investigated.

Effect of buffer composition on the migration order and separation of histone H1 subtypes

The effects of different buffer concentrations and compositions on the elution order and separation of H1 histone subtypes and their phosphorylated modifications isolated from several species was studied using high-performance capillary electrophoresis (CE). Various cations and anions were tested in an untreated silica capillary and low pH buffers, in the presence of the dynamic coating agent hydroxypropylmethyl cellulose. It was found that the cations and anions of buffers have a remarkable influence on both the efficiency and the selectivity of protein separations. A triethylammonium methanephosphonate system proved efficacious for the separation of rat histone subtype H1c from H1e and a perchlorate/triethylammonium phosphate system for the analysis of chicken and mouse linker histones. CE provides an attractive alternative to high-performance liquid chromatography and conventional gel electrophoresis.

Application of high-performance capillary electrophoresis to the analysis of H1 histones

High-performance capillary electrophoresis for the separation of rat testis H1 histone variants and their phosphorylated modifications is described. The influence of buffer pH, hydroxypropylmethyl cellulose, and buffer concentration has been investigated. Under optimized conditions (500 mM phosphate buffer, pH 2, 0.03% hydroxypropylmethyl cellulose) using an uncoated capillary, eight H1 histone subfractions, including two H1(0) histones and H1t and their phosphorylated modifications, are resolved. Application of capillary electrophoresis to the separation of H1 histones provides an important new alternative to high-performance liquid chromatography (HPLC) and traditional gel electrophoresis.