Antimicrobial properties of arginine- and lysine-rich histones and involvement of bacterial outer membrane protease T in their differential mode of actions

There is growing evidence of the antimicrobial properties of histones and histone-derived peptides; however, most of them are specific to lysine (Lys)-rich histones (H1, H2A, and H2B). In the present study, we focused on arginine (Arg)-rich histones (H3 and H4) and investigated their antimicrobial properties in comparison with those of histone H2B. In a standard microdilution assay, calf thymus histones H2B, H3, and H4 showed growth inhibitory activity against the bacterial outer membrane protease T (OmpT) gene-expressing Escherichia coli strain JCM5491 with calculated 50% growth inhibitory concentrations of 3.8, 10, and 12.7 μM, respectively. A lysate prepared from the JCM5491 cells was capable of strongly, moderately, and slightly fragmenting histones H2B, H3, and H4, respectively. While the lysate prepared from the cells of the ompT-deleted E. coli strain BL21(DE3) did not digest these histones, the ompT-transformed BL21(DE3), termed BL21/OmpT⁺, cell lysate digested the histones more strongly than the JCM5491 cell lysate. Laser confocal and scanning electron microscopic analyses demonstrated that while histone H2B penetrated the cell membrane of JCM5491 or BL21/OmpT⁺ cells, histones H3 and H4 remained on the cell surface and subsequently disrupted the cell membrane structure with bleb formation in a manner similar to general antimicrobial peptides. The BL21(DE3) cells treated with each histone showed no bleb formation, but cell integrity was affected and the cell surface was corrugated. Consequently, it is suggested that OmpT is involved in the antimicrobial properties of Arg- and Lys-rich histones and that the modes of antimicrobial action of these histones are different.     

Identification of histone H2B as a regulated plasminogen receptor

Tethering of plasminogen to cell surfaces controls plasmin formation and, thereby, influences pericellular proteolysis and cell migration. Modulation of cellular plasminogen binding sites provides a mechanism for regulation of these events. In this study, two distinct models, phorbol ester-stimulated adhesion of U937 monocytoid cells and culturing of peripheral blood neutrophils, treatments which modulate plasminogen binding sites, have been examined to determine the molecular basis for the upregulation of plasminogen receptors. Membranes were isolated from cell populations, with and without upregulated plasminogen binding capacities, and analyzed by [(125)I]plasminogen ligand blotting of gel transfers. Approximately 15 different [(125)I]plasminogen-binding proteins were discerned in the membrane fractions, and only relatively minor differences in the intensities of individual bands were noted in the different cell populations. The notable exception was the presence of a 17 kDa band, which was selectively and markedly enhanced in the membranes from cells with enhanced plasminogen binding capacities. The 17 kDa protein was isolated from both cell types, and amino acid sequencing of peptide fragments identified the same protein, histone H2B. Increased expression of histone H2B was observed on stimulated U937 cells and cultured neutrophils by confocal microscopy with an antibody raised to the carboxy-terminal octopeptide sequence of histone H2B. This antibody or its Fab fragments substantially decreased the level of binding of plasminogen to these cultured neutrophils and stimulated U937 cells that exhibited elevated levels of binding but not to nonstimulated cells. Thus, histone H2B represents a regulated plasminogen receptor, which contributes significantly to the plasminogen binding capacity of cells.     

Structure-activity relations of parasin I, a histone H2A-derived antimicrobial peptide

The structure-activity relations and mechanism of action of parasin I, a 19-amino acid histone H2A-derived antimicrobial peptide, were investigated. Parasin I formed an amphipathic alpha-helical structure (residues 9-17) flanked by two random coil regions (residues 1-8 and 18-19) in helix-promoting environments. Deletion of the lysine residue at the N-terminal [Pa(2-19)] resulted in loss of antimicrobial activity, but did not affect the alpha-helical content of the peptide. The antimicrobial activity was recovered when the lysine residue was substituted with another basic residue, arginine ([R(1)]Pa), but not with polar, neutral, or acidic residues. Progressive deletions from the C-terminal [Pa(1-17), Pa(1-15)] slightly increased the antimicrobial activity (1-4 microg/ml) without affecting the alpha-helical content of the peptide. However, further deletion [Pa(1-14)] resulted in nearly complete loss of antimicrobial activity and alpha-helical structure. Confocal microscopic analysis and membrane permeabilization assays showed that parasin I and its analogs with comparable antimicrobial activities localized to the cell membrane and subsequently permeabilized the outer and cytoplasmic membranes. Pa(1-14) also localized to the cell membrane, but lost membrane-permeabilizing activity, whereas Pa(2-19) showed poor membrane-binding and -permeabilizing activities. The results indicate that the basic residue at the N-terminal is essential for the membrane-binding activity of parasin I, and among the membrane-binding parasin I analogs, the alpha-helical structure is necessary for the membrane-permeabilizing activity.     

Phosphorylation of histone H2B serine 32 is linked to cell transformation

Various types of post-translational modifications of the histone tails have been revealed, but a few modifications have been found within the histone core sequences. Histone core post-translational modifications have the potential to modulate nucleosome structure and DNA accessibility. Here, we studied the histone H2B core domain and found that phosphorylation of H2B serine 32 occurs in normal cycling and mitogen-stimulated cells. Notably, this phosphorylation is elevated in skin cancer cell lines and tissues compared with normal counterparts. The JB6 Cl41 mouse skin epidermal cell line is a well established model for tumor promoter-induced cell transformation and was used to study the function of H2B during EGF-induced carcinogenesis. Remarkably, cells overexpressing a nonphosphorylatable H2BS32A mutant exhibited suppressed growth and EGF-induced cell transformation, possibly because of decreased activation of activator protein-1, compared with control cells overexpressing wild type H2B. We identified ribosomal S6 kinase 2 (RSK2) as the kinase responsible for H2BS32 phosphorylation. Serum-starved JB6 cells contain very little endogenous H2BS32 phosphorylation, and EGF treatment induced this phosphorylation. The phosphorylation was attenuated in RSK2 knock-out MEFs and RSK2 knockdown JB6 cells. Taken together, our results demonstrate a novel role for H2B phosphorylation in cell transformation and show that H2BS32 phosphorylation is critical for controlling activator protein-1 activity, which is a major driver in cell transformation.     

Yeast histone H2A and H2B amino termini have interchangeable functions

The N-terminal ends of histones H2B and H2A have very different sequences and rates of evolution. However, they both extend from the nucleosome core and are positively charged. Short sequences at the C termini of both proteins also differ from each other and appear to be hydrophilic. Deletions at the N and C termini of yeast histones H2B2 and H2A1 do not obviously affect the cell's viability under normal growth conditions. However, deletions at the N termini of both H2B and H2A in the same cell are lethal or result in greatly reduced viability. Even switching portions of the N termini between H2B and H2A to create two chimeric histone proteins within the same cell has no obvious effect on viability. This supports the argument that the N-terminal end of one protein complements the function of the other.     

Antigenic structure of histone H2B

Antigenic determinants of histone H2B were localized using a series of 23 overlapping fragments of H2B obtained either by chemical and enzymatic cleavage of the histone or by solid-phase peptide synthesis. The ability of peptides to bind H2B antibodies was measured in an enzyme-linked immunosorbent assay, using antisera directed against calf thymus and chicken erythrocyte H2B as well as four anti H2B monoclonal antibodies obtained from autoimmune mice. Seven antigenic determinants were localized in the H2B molecule in the vicinity of residues 1-11, 6-18, 15-25, 26-35, 50-65, 94-113 and 114-125. Two of these determinants (residues 6-18 and 26-35) were revealed only through the binding properties of antibodies isolated from autoimmune mice. The usual correlation between hydrophilicity and antigenicity was found to hold for four of the epitopes, and the N- and C-termini of H2B were both antigenically active.     

Buforins: Histone H2A-derived antimicrobial peptides from toad stomach

Antimicrobial peptides (AMPs) constitute an important component of the innate immune system in a variety of organisms. Buforin I is a 39-amino acid AMP that was first isolated from the stomach tissue of the Asian toad Bufo bufo gargarizans. Buforin II is a 21-amino acid peptide that is derived from buforin I and displays an even more potent antimicrobial activity than its parent AMP. Both peptides share complete sequence identity with the N-terminal region of histone H2A that interacts directly with nucleic acids. Buforin I is generated from histone H2A by pepsin-directed proteolysis in the cytoplasm of gastric gland cells. After secretion into the gastric lumen, buforin I remains adhered to the mucous biofilm that lines the stomach, thus providing a protective antimicrobial coat. Buforins, which house a helix-hinge-helix domain, kill a microorganism by entering the cell without membrane permeabilization and thus binding to nucleic acids. The proline hinge is crucial for the cell penetrating activity of buforins. Buforins also are known to possess anti-endotoxin and anticancer activities, thus making these peptides attractive reagents for pharmaceutical applications. This review describes the role of buforins in innate host defense; future research paradigms; and use of these agents as human therapeutics.     

Primary structure of histone H2B from gonads of the starfish Asterias rubens. Identification of an N-dimethylproline residue at the amino-terminal

The complete amino acid sequence (121 residues) of histone H2B from gonads of the starfish Asterias rubens has been established from structural data obtained essentially from large fragments generated by cleavage of histone H2B at aspartyl residues and by limited hydrolysis of the dimer H2A-H2B with mouse submaxillary gland protease. No real sequence homology can be found between the amino-terminal sequence (residues 1-21) of starfish and calf H2B. One non-conservative substitution (serine-32 in calf----lysine-28 in starfish) leads to the presence of a cluster of eight basic residues (sequence 23-30) and to the disappearance of a potential site of phosphorylation. A particular structural feature of starfish histone H2B is the presence of N-dimethylproline at its amino-terminal end. By comparison with N-terminal acetylation, which is commonly found in histones, N-terminal methylation is rarely observed. At the present time the functional significance of the N-terminal methylation as well as that of the proline-rich nature of the amino-terminal sequence of the starfish histone H2B remain to be defined.     

The human H2A and H2B histone gene complement

Sequences and expression patterns of newly isolated human histone H2A and H2B genes and the respective proteins were compared with previously isolated human H2A and H2B genes and proteins. Altogether, 15 human H2A genes and 17 human H2B genes have been identified. 14 of these are organized as H2A/H2B gene pairs, while one H2A gene and three H2B genes are solitary genes. Two H2A genes and two H2B genes turned outto be pseudogenes. The 13 H2A genes code for at least 6 different amino acid sequences, and the 15 H2B genes encode 11 different H2B isoforms. Each H2A/H2B gene pair is controlled by a divergent promoter spanning 300 to 330 nucleotides between the coding regions of the two genes. The highly conserved divergent H2A/H2B promoters can be classified in two groups based on the patterns of consensus sequence elements. Group I promoters contain a TATA box for each gene, two Oct-1 factor binding sites, and three CCAAT boxes. Group II promoters contain the same elements as group I promoters and an additional CCAAT box, a binding motif for E2F and adjacent a highly conserved octanucleotide (CACAGCTT) that has not been described so far. Five of the 6 gene pairs and 4 solitary genes with group I promoters are localized in the large histone gene cluster at 6p21.3-6p22, and one gene pair is located at 1q21. All group II promoter associated genes are contained within the histone gene subcluster at D6S105, which is located at a distance of about 2 Mb from the major subcluster at 6p21.3-6p22 containing histone genes with group I promoters. Almost all group II H2A genes encode identical amino acid sequences, whereas group I H2A gene products vary at several positions. Using human cell lines, we have analyzed the expression patterns of functional human H2A/H2B gene pairs organized within the two histone gene clusters on the short arm of chromosome 6. The genes show varying expression patterns in different tumor cell lines.     

Nucleotide sequence and expression of two cDNA coding for two histone H2B variants of maize

The complete amino acid sequences of two variants of histone H2B of maize were deduced from the cDNAs isolated from a maize cDNA library. The two encoded proteins are 150 (H2B(1)) and 149 (H2B(2)) amino acids long and shows the classical organization of H2B histones. The hydrophobic C-terminal region is highly conserved as compared to that of the animal counterparts with only 21 changes (13 conservative) among the 90 residues. Between the N-terminal part and the C-terminal region we note the presence of a basic cluster (9 residues) characteristic of histones H2B. The N-terminal third is extended as compared to the animal consensus H2B and has the same size as the H2B histone of wheat. Up to 9 acidic residues and a five time repeated pentapeptide PA/KXE/KK are present in this region. Southern-blot hybrization showed that the H2B histones are encoded by a multigenic family like the other core histones (H3 and H4) of plants. The general expression pattern of these genes was not significantly different from that of the H3 and H4 genes neither in germinating seeds nor in different tissues of adult maize.     

The structure of ubiquitinated histone H2B.

Ubiquitinated histone H2B (uH2B) has been purified from both calf and pig thymus by exclusion chromatography in 7 M urea. Digestion of uH2B with Staphylococcus aureus V8 protease yielded the peptide 114-125 containing the ubiquitin moiety. Further digestion of this peptide with trypsin removed the ubiquitin and three H2B residues from the N-terminus. Edman degradations of both peptides established that ubiquitin is attached to the epsilon-amino group of lysine 120 in both calf and pig uH2B by an iso-peptide bond to the C-terminal glycine 76 of ubiquitin.     

Deimination of histone H2A and H4 at arginine 3 in HL-60 granulocytes

Interplay of various covalent modifications of histone tails has an essential role in regulation of chromatin function. Peptidylarginine deiminase (PADI) 4 deiminates protein arginine to citrulline in a Ca(2+)-dependent manner and is present in the nucleus of granulocyte-differentiated HL-60 cells. When these cells are treated with the calcium ionophore A23187, core histone deimination occurs. To determine the deimination sites of histones, histone species were purified by reverse-phase high-performance liquid chromatography (RP-HPLC) from the cells. Immunoblotting using antimodified citrulline antibody indicated that histones H2A, H3, and H4 but not H2B were deiminated. H2A and H4 were digested with Staphylococcus aureus V8 protease, and the digests were separated by RP-HPLC. Immuno dot-blotting and mass spectrometry showed that the deiminated residues were present in H2A (1-56) and H4 (1-52) regions but not in other regions. The H2A peptide (1-56) was digested with alpha-chymotrypsin, and the deiminated peptide was separated from the corresponding nondeiminated peptide by RP-HPLC. The deiminated residue was found to be limited to residues 1-23. Similarly, digestion of the H4 peptide (1-52) with endoproteinase Asp-N and separation of the deiminated peptide from the nondeiminated peptide indicated that the deiminated residue was limited to residues 1-23. Mass spectrometry of lysylendopeptidase digests of the H2A (1-23) and H4 (1-23) peptides showed that deimination occurred at arginine 3 of the N-terminal sequence Ac-SGRGK common to H2A and H4. These results suggest that PADI4 deiminates only a restricted site of target proteins in cells. Deimination of histones is discussed in relation to chromatin structure and function.     

Multiple forms of histone H2B from the nematode Caenorhabditis elegans.

The complete amino acid sequence of histone H2B from the nematode Caenorhabditis elegans was determined. The protein as obtained by us is a mixture of multiple forms. Approx. 90% of the molecules consist of a polypeptide chain of 122 amino acids with alanine as N-terminal residue and proline at the second position. In the remaining 10% alanine is lacking and the chain starts with proline. In addition to the heterogeneity of chain length, polymorphism occurs at the positions 7 (Ala/Lys), 14 (Ala/Lys) and 72 (Ala/Ser) of the major chain and at position 6 (Ala/Lys) of the shorter chain. In the N-terminal third of the molecule there is a high degree of sequence homology to the corresponding region in H2B from Drosophila (insect), Patella (mollusc) and Asterias (starfish). In contrast, this part of the molecule differs considerably from mammalian histone H2B.     

From the nucleus to the plasma membrane: translocation of the nuclear proteins histone H3 and lamin B1 in apoptotic microglia

Nuclear autoantibodies have been found in patients with autoimmune diseases. One possible source for nuclear antigens are apoptotic cells. However, the mechanism of how apoptotic cells make nuclear factors accessible to the immune system is still elusive. In the present study, we investigated the redistribution of nuclear components after UV irradiation in the microglial cell line BV-2 and in primary mouse microglia at the ultrastructural level. We used transmission electron microscopy-coupled electron energy loss spectroscopy (EELS) to measure phosphorus as an indicator for nucleic acids and immunogold labeling to detect histone H3 and lamin B1 in apoptotic cells. EELS revealed elevated concentrations of phosphorus in nuclear and cytoplasmic condensed chromatin compared to the remaining cytoplasm. Furthermore, immunolabeling of lamin B1 and histone H3 was detected in apoptotic microglia not only in the nucleus, but also in the cytoplasm, and even at the plasma membrane. Confocal images of apoptotic microglia, which were not previously permeabilized, showed patches of histone H3 and lamin B1 labeling at the cell surface. The pan-caspase inhibitor Z-VAD-FMK (carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoromethylketone) prevented the occurrence of cytoplasmic condensed chromatin in apoptotic microglia. Our findings indicate that nuclear components leak from the nucleus into the cytoplasm in apoptotic microglia. At least histone H3 and lamin B1 reach the cell surface, this may promote autoreactive processes.     

Upregulation in response to infection and antibacterial activity of oyster histone H4

Several histones and histone-derived peptides have been shown to have antimicrobial activity and a potential role in innate immune defenses. A histone H4 sequence was identified in a subtractive suppression library containing genes upregulated in American cupped oysters, Crassostrea virginica, in response to challenge with the protozoan parasite Perkinsus marinus. Oyster histone H4 protein levels significantly increased in hemocyte lysates and cell free hemolymph of oysters experimentally challenged with P. marinus. The complete histone H4 coding sequence of C. virginica was cloned into a Saccharomyces cerevisiae yeast expression system and recombinant expression was confirmed using SDS-PAGE analysis and western blot. Delivery of yeast cells expressing recombinant oyster histone H4 into the gut of brine shrimp, Artemia salinas, challenged with a streptomycin resistant strain of Vibrio anguillarum resulted in a significant and dose-dependent decrease in the load of V. anguillarum. Purified recombinant histone H4 showed antimicrobial activity against V. anguillarum and Escherichia coli at micromolar concentrations, but did not affect the viability of P. marinus in culture. These results support the role of histone H4 in the defense of oysters against bacterial infection and validate the use of a novel oyster antimicrobial H4 in a yeast feed-based delivery system for the treatment of bacterial infections in aquaculture applications.     

Multiple antibacterial histone H2B proteins are expressed in tissues of American oyster

We have previously identified a histone H2B isomer (cvH2B-1) from tissue extracts of the bivalve mollusk, the American oyster (Crassostrea virginica). In this paper, we isolate an additional three antibacterial proteins from acidified gill extract by preparative acid-urea-polyacrylamide gel electrophoresis and reversed-phase high performance liquid chromatography. Extraction of these proteins from tissue was best accomplished by briefly boiling the tissues in a weak acetic acid solution. Addition of protease inhibitors while boiling resulted in somewhat lower yields, with one protein being totally absent with this method. Via mass spectrometry, the masses of one of these purified proteins was 13607.0Da (peak 2), which is consistent with the molecular weight of histone H2B. In addition, via western-blotting using anti-calf histone H2B antibody, all three proteins were positive and were thus named cvH2B-2, cvH2B-3 and cvH2B-4. The antibacterial activity of cvH2B-2 was similar to that of cvH2B-1, with activity against a Gram-positive bacterium (Lactococcus lactis subsp. lactis; minimum effective concentration [MEC] 52-57μg/mL) but inactive against Staphylococcus aureus (MEC>250μg/mL). However, both proteins had relatively potent activity against the Gram-negative oyster pathogen Vibrio parahemolyticus (MEC 11.5-14μg/mL) as well as the human pathogen Vibrio vulnificus (MEC 21.3-25.3μg/mL). cvH2B-3 and cvH2B-4 also had similarly strong activity against Vibrio vulnificus. These data provide further evidence for the antimicrobial function of histone H2B isomers in modulating bacterial populations in oyster tissues. The combined estimated concentrations of these histone H2B isomers were far above the inhibitory concentrations for the tested vibrios, including human pathogens. Our results indicate that the highly conserved histone proteins might be important components not only of immune defenses in oysters but have the potential to influence the abundance of a ubiquitous microbial resident of oyster tissues that is the major source of seafood-borne illness in humans.     

人Src蛋白N端区段的表达、纯化和体外豆蔻酰化底物活性

利用RT PCR技术 ,从来源于人结肠癌Caco 2细胞总RNA中 ,扩增得到编码人Src蛋白N端 147氨基酸的DNA序列片段。进而构建T7启动子控制下的C端His tag融合的表达质粒pMF SrcHT ,并转化大肠杆菌BL2 1(DE3)。通过SDS PAGE等分析结果显示 ,在 37°C培养条件下经IPTG诱导 ,C端His tag融合的人Src蛋白N端区段 (命名为SrcHT ,2 1kD)得到高效表达 ,并且主要以可溶性形式存在。进一步利用Ni IDA亲和层析分离 ,从表达菌裂解上清液中一步纯化获得重组蛋白SrcHT ,SDS PAGE分析纯度达 95 %以上。在此基础上 ,以 [3H]豆蔻酰 CoA为同位素标记底物进行SrcHT的体外NMT豆蔻酰化反应测定。SDS PAGE分离和放射自显影分析结果表明 ,SrcHT蛋白可被NMT有效豆蔻酰化而具有NMT的底物活性。这些为深入详细研究Src蛋白豆蔻酰化作用和构建以Src蛋白豆蔻酰化为靶标的分子筛药体系等打下了重要基础。