Histone H1 proteins act as receptors for the 987P fimbriae of enterotoxigenic Escherichia coli

From inside to outside: exploring extracellular antimicrobial histone-derived peptides as multi-talented molecules

The emergence of bacterial resistance to antibiotics poses a global health threat, necessitating innovative solutions. The contemporary challenge lies in bacterial resistance, impacting morbidity, mortality, and global economies. Antimicrobial peptides (AMPs) offer a promising avenue for addressing antibiotic resistance. The Antimicrobial Peptide Database catalogs 3569 peptides from various organisms, representing a rich resource for drug development. Histones, traditionally recognized for their role in nucleosome structures, have gained attention for their extracellular functions, including antimicrobial and immunomodulatory properties. This review aims to thoroughly investigate antimicrobial peptides derived from histones in various organisms, elucidating their mechanisms. In addition, it gives us clues about how extracellular histones might be used in drug delivery systems to fight bacterial infections. This comprehensive analysis emphasizes the importance of histone-derived peptides in developing innovative therapeutic strategies for evolving bacterial challenges.

siRNA targeting Atp5a1 gene encoding ATPase α, the ligand of Peg fimbriae, reduced Salmonella Enteritidis adhesion

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a zoonotic pathogen that can infect both humans and animals. Among the 13 types of fimbrial operons in S. Enteritidis, the highly conserved Peg fimbriae play a crucial role in the adhesion and invasion of S. Enteritidis into host cells but are not well studied. In this study, we identified the ATP synthase subunit alpha (ATPase α) as a ligand of Peg fimbriae using ligand blotting and mass spectrometry techniques. We confirmed the in vitro binding of ATPase α to the purified adhesion protein (PegD). Furthermore, we used siRNA to suppress the expression of ATPase α gene Atp5a1 in Leghorn male hepatoma (LMH) cells, which resulted in a significant reduction in the adhesion rate of S. Enteritidis to the cells (P < 0.05). The findings in this study provide insight into the mechanism of S. Enteritidis infection through Peg fimbriae and highlight the importance of ATPase α in the adhesion process.RESEARCH HIGHLIGHTS Ligand blotting was performed to screen the ligand of S. Enteritidis Peg fimbriae.Binding assay confirmed that ATPase α is the ligand of the Peg fimbriae.siRNA targeting ATPase α gene (Atp5a1) significantly reduced S. Enteritidis adhesion.

Contribution of Host Genetics to the Variation of Microbial Composition of Cecum Lumen and Feces in Pigs

Pigs are a perfect model for studying the interaction between host genetics and gut microbiome due to the high similarity of gastrointestine and digestive system with humans, and the easily controlled feeding conditions. In this study, two pig populations which were raised in uniformed farm conditions and provided with the same commercial formula diet were used as the experimental animals. A systematical investigation of host genetic effect on the gut microbial composition was separately performed in porcine cecum lumen and feces samples through the comparison of microbial composition among full-sibs, half-sibs and unrelated members, heritability estimate (h²), and genome-wide association study (GWAS). The results showed that full-sib members had a higher similarity of microbial composition than unrelated individuals. A significant correlation was observed between the microbial composition-based kinship and the host SNP-based kinship in both populations (P < 9.9 × 10^-5). We identified 81 and 67 microbial taxa having h² > 0.15 in fecal and cecum luminal samples, respectively, including 31 taxa with h² > 0.15 in both types of samples. GWAS identified 40 and 34 significant associations between host genomic loci and the abundance or presence/absence of bacterial taxa in the fecal and cecum luminal samples. Functional classifications of host candidate genes related to microbial taxa are mainly associated with metabolism, immunity functions and response, and signal transduction. The high similarity of heritable taxa and functional categories of candidate genes among pig, human and mouse suggests the similar mechanism of the host genetic effect on gut microbiome across mammalian species. The results from this study provided another evidence that host genetics contributes significantly to the gut microbiome.

Contribution of Host Genetics to the Variation of Microbial Composition of Cecum Lumen and Feces in Pigs

Pigs are a perfect model for studying the interaction between host genetics and gut microbiome due to the high similarity of gastrointestine and digestive system with humans, and the easily controlled feeding conditions. In this study, two pig populations which were raised in uniformed farm conditions and provided with the same commercial formula diet were used as the experimental animals. A systematical investigation of host genetic effect on the gut microbial composition was separately performed in porcine cecum lumen and feces samples through the comparison of microbial composition among full-sibs, half-sibs and unrelated members, heritability estimate (h ²), and genome-wide association study (GWAS). The results showed that full-sib members had a higher similarity of microbial composition than unrelated individuals. A significant correlation was observed between the microbial composition-based kinship and the host SNP-based kinship in both populations (P < 9.9 × 10^-5). We identified 81 and 67 microbial taxa having h ² > 0.15 in fecal and cecum luminal samples, respectively, including 31 taxa with h ² > 0.15 in both types of samples. GWAS identified 40 and 34 significant associations between host genomic loci and the abundance or presence/absence of bacterial taxa in the fecal and cecum luminal samples. Functional classifications of host candidate genes related to microbial taxa are mainly associated with metabolism, immunity functions and response, and signal transduction. The high similarity of heritable taxa and functional categories of candidate genes among pig, human and mouse suggests the similar mechanism of the host genetic effect on gut microbiome across mammalian species. The results from this study provided another evidence that host genetics contributes significantly to the gut microbiome.

Linker Histone in Diseases

The linker histone is a protein that binds with the nucleosome, which is generally considered to achieve chromatin condensation in the nucleus. Accumulating evidences suggest that the linker histone is essential in the pathogenesis of several diseases. In this review, we briefly introduce the current knowledge of the linker histone, including its structure, characteristics and functions. Also, we move forward to present the advances of the linker histone's association with certain diseases, such as cancer, Alzheimer's disease, infection, male infertility and aberrant immunity situations, focusing on the alteration of the linker histone under certain pathological conditions and its role in developing each disease.

Animal Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common cause of E. coli diarrhea in farm animals. ETEC are characterized by the ability to produce two types of virulence factors: adhesins that promote binding to specific enterocyte receptors for intestinal colonization and enterotoxins responsible for fluid secretion. The best-characterized adhesins are expressed in the context of fimbriae, such as the F4 (also designated K88), F5 (K99), F6 (987P), F17, and F18 fimbriae. Once established in the animal small intestine, ETEC produce enterotoxin(s) that lead to diarrhea. The enterotoxins belong to two major classes: heat-labile toxins that consist of one active and five binding subunits (LT), and heat-stable toxins that are small polypeptides (STa, STb, and EAST1). This review describes the disease and pathogenesis of animal ETEC, the corresponding virulence genes and protein products of these bacteria, their regulation and targets in animal hosts, as well as mechanisms of action. Furthermore, vaccines, inhibitors, probiotics, and the identification of potential new targets by genomics are presented in the context of animal ETEC.

Porcine intestinal glycosphingolipids recognized by F6-fimbriated enterotoxigenic Escherichia coli

One important virulence factor of enterotoxigenic Escherichia coli is their ability to adhere via fimbrial adhesins to specific receptors located on the intestinal mucosa. Here, the potential glycosphingolipid receptors of enterotoxigenic F6-fimbriated E. coli were examined by binding of purified F6 fimbriae, and F6-expressing bacteria, to glycosphingolipids on thin-layer chromatograms. When intestinal mucosal non-acid glycosphingolipids from single pigs were assayed for F6 binding capacity, a selective interaction with two glycosphingolipids was observed. The binding-active glycosphingolipids were isolated and characterized as lactotriaosylceramide (GlcNAcβ3Galβ4Glcβ1Cer) and lactotetraosylceramide (Galβ3GlcNAcβ3Galβ4Glcβ1Cer). Further binding assays using a panel of reference glycosphingolipids showed a specific interaction between the F6 fimbriae and a number of neolacto core chain (Galβ4GlcNAc) glycosphingolipids. In addition, an occasional binding of the F6 fimbriae to sulfatide, galactosylceramide, lactosylceramide with phytosphingosine and/or hydroxy fatty acids, isoglobotriaosylceramide, gangliotriaosylceramide, and gangliotetraosylceramide was obtained. From the results we conclude that lactotriaosylceramide and lactotetraosylceramide are major porcine intestinal receptors for F6-fimbriated E. coli.

The teleost acute-phase inflammatory response and caspase activation by a novel alarmin-like ligand

This study tested the hypothesis that NCAMP-1 has alarmin-like properties and activates the caspase-1-binding site in cells of the teleost bone marrow (equivalent). In mammals, alarmins have been studied extensively; however, in teleosts, little is known about their identity and functions. Similar to alarmins, NCAMP-1 has a broad spectrum of bacteriolytic activity. NCAMP-1 is constitutively present in CF serum, and levels were increased following infection with Edwardsiella ictaluri Binding to AK cells was determined with rNCAMP-1 and an anti-His-tag antibody. In vitro treatment of AK (bone marrow equivalent) or spleen cells with rNCAMP-1 increased the IL-1β message three- to fivefold at 3 h, 6 h, and 9 h post-treatment. The association of NCAMP-1 with the activities of alarmin ATP and the acute inflammatory response was demonstrated by NCAMP-1-induced P2X₇R pore opening and YO-PRO-1 cellular influx. The association of NCAMP-1 binding with inflammasome activation was demonstrated by NCAMP-1 activation of the caspase-1-binding site for tetrapeptide Z-YVAD-FMK. In competition assays, this tetrapeptide competitively inhibited subsequent binding by the pan-caspase substrate tripeptide FAM-VAD-FMK. Lymphocyte-like cells from the spleen were 16%⁺, and epithelial cells were also positive for NCAMP-1. IHC staining and confocal microscopy confirmed the cytosolic existence of NCAMP-1 in lymphoreticular tissue and IL-1β in AK cells. CF T cell lines G14D and 28S.3 expressed NCAMP-1 in the cytosol and in storage granules. These studies strongly suggested that NCAMP-1 is an alarmin-like ligand with similar but distinct activities to those of ATP and HMGB-1.

Role of sulfatide in normal and pathological cells and tissues

Sulfatide is 3-O-sulfogalactosylceramide that is synthesized by two transferases (ceramide galactosyltransferase and cerebroside sulfotransferase) from ceramide and is specifically degraded by a sulfatase (arylsulfatase A). Sulfatide is a multifunctional molecule for various biological fields including the nervous system, insulin secretion, immune system, hemostasis/thrombosis, bacterial infection, and virus infection. Therefore, abnormal metabolism or expression change of sulfatide could cause various diseases. Here, we discuss the important biological roles of sulfatide in the nervous system, insulin secretion, immune system, hemostasis/thrombosis, cancer, and microbial infections including human immunodeficiency virus and influenza A virus. Our review will be helpful to achieve a comprehensive understanding of sulfatide, which serves as a fundamental target of prevention of and therapy for nervous disorders, diabetes mellitus, immunological diseases, cancer, and infectious diseases.

Interaction of Rickettsia felis with histone H2B facilitates the infection of a tick cell line

Haematophagous arthropods are the primary vectors in the transmission of Rickettsia, yet the molecular mechanisms mediating the rickettsial infection of arthropods remain elusive. This study utilized a biotinylated protein pull-down assay together with LC-MS/MS to identify interaction between Ixodes scapularis histone H2B and Rickettsia felis. Co-immunoprecipitation of histone with rickettsial cell lysate demonstrated the association of H2B with R. felis proteins, including outer-membrane protein B (OmpB), a major rickettsial adhesin molecule. The rickettsial infection of tick ISE6 cells was reduced by approximately 25 % via RNA-mediated H2B-depletion or enzymic treatment of histones. The interaction of H2B with the rickettsial adhesin OmpB suggests a role for H2B in mediating R. felis internalization into ISE6 cells.

Design of novel histone-derived antimicrobial peptides

Previous studies have identified several naturally occurring antimicrobial peptides derived from histone proteins. This research aimed to design novel histone-derived antimicrobial peptides (HDAPs). To this end, three novel peptides (DesHDAP1, DesHDAP2, and DesHDAP3) were designed based on a histone-DNA crystal structure and structural properties of buforin II, the best characterized naturally occurring HDAP. Molecular dynamics simulations and circular dichroism spectroscopy were used to further support the predicted structure and potential nucleic acid interactions of these three designed peptides. The antibacterial activity of the three peptides was then verified experimentally against a series of bacterial strains using a radial diffusion assay. One of these peptides is the first known fragment of histone H3 with antibacterial properties. Optical density measurements of bacterial cells exposed to the designed peptides implied that at least two of the novel peptides can induce cell death without causing significant membrane permeabilization, as observed for buforin II. The antibacterial potency of these designed HDAPs does not appear to correlate with their overall alpha-helical content, unlike previous observations for analogs of buforin II. However, the most potent designed peptide, DesHDAP1, shares a markedly similar circular dichroism spectrum with buforin II. These results demonstrate the potential of using histone structures as a framework for designing novel antimicrobial peptides. As well, these studies represent an important starting point for a broader characterization of properties shared by HDAPs.

Evolution of the chaperone/usher assembly pathway: fimbrial classification goes Greek

Many Proteobacteria use the chaperone/usher pathway to assemble proteinaceous filaments on the bacterial surface. These filaments can curl into fimbrial or nonfimbrial surface structures (e.g., a capsule or spore coat). This article reviews the phylogeny of operons belonging to the chaperone/usher assembly class to explore the utility of establishing a scheme for subdividing them into clades of phylogenetically related gene clusters. Based on usher amino acid sequence comparisons, our analysis shows that the chaperone/usher assembly class is subdivided into six major phylogenetic clades, which we have termed alpha-, beta-, gamma-, kappa-, pi-, and sigma-fimbriae. Members of each clade share related operon structures and encode fimbrial subunits with similar protein domains. The proposed classification system offers a simple and convenient method for assigning newly discovered chaperone/usher systems to one of the six major phylogenetic groups.

Visualization of neutrophil extracellular traps in TEM

Neutrophil extracellular traps (NETs) have recently been described as an important innate defence mechanism in inflammation. However, routine electron microscopic staining techniques faintly stain NETs and are therefore insufficient for enabling a distinction between these and the host cell debris as well as proteins regularly present at the site of inflammation. In order to test suitable electron microscopic staining techniques, NETs induced ex vivo via phorbol myristate were absorbed on formvar. Four types of drop-on-grid positive staining were used: osmium tetroxide (Os), osmium tetroxide-uranyl acetate-lead citrate (Os-U-Pb), ruthenium red-osmium tetroxide (RR-OsO4), and cuprolinic blue enhanced by sodium tungstate (CB-WO4). We observed no staining of NETs using Os, faint staining with Os-U-Pb, better but still weak staining with CB-WO4 and outstanding staining with RR-OsO4. Furthermore, RR-OsO4 staining also enables the observation of bacterial fimbriae-mediated adhesion, which is possibly responsible for the ability of NETs to bind bacteria. Thus, the offered RR-OsO4 staining technique may facilitate the study of the NETs-bacterial interactions.

Possible role of histone H1 in the regulation of furin-dependent proprotein processing

Histone H1 and its C-terminal lysine rich fragments were recently found to be potent inhibitors of furin, a mammalian proprotein convertase. However, its role in the regulation of furin-dependent proprotein processing remains unclear. Here we report that histone H1 efficiently blocks furin-dependent pro-von Willebrand factor (pro-vWF) processing in a dose-dependent manner. Coimmunoprecipitation and immunofluorescence studies confirmed that histone H1 could interact with furin, and the interaction mainly took place on the cell surface. We noted that histone H1 was released from cells undergoing necrosis and apoptosis induced by H₂O₂. Our findings suggested that histone H1 might be involved in extracellular and/or intracellular furin regulation.

Beyond the walls of the nucleus: the role of histones in cellular signaling and innate immunity

Although they are one of the oldest family of proteins known (first described in 1884 by Kossel), histones continue to surprise researchers with their ever expanding roles in biology. In the past 25 years, the view of core histone octamers as a simple spool around which DNA in the nucleus is wound and linker histones as mere fasteners clipping it all together has transformed into the realization that histones play a vital role in transcriptional regulation. Through post-translational modifications, histones control the accessibility of transcription factors and a host of other proteins to multiple, conceivably thousands of, genes at once. While researchers have spent decades deciphering the role of histones in the overall structure of chromatin, it might surprise some to find that an entirely separate faction of scientists have focused on the role of histones beyond the confines of the nuclear envelope. In the past decade, there has been an accumulation of observations that suggest that histones can be found at the mitochondrion during the onset of apoptotic signaling and even at the cell surface, acting as a receptor for bacterial and viral proteins. More provocatively, immunologists are becoming convinced that they can also be found in the lumen of several tissues, acting as antimicrobial agents--critical components of an ancient innate immune system. Perhaps nowhere is this observation as dramatic as in the ability of neutrophils to entrap bacterial pathogens by casting out "nets" of DNA and histones that not only act as a physical barrier, but also display bactericidal activity. As our views regarding the role of histones inside and outside the cell evolve, some have begun to develop therapies that either utilize or target histones in the fight against cancer, microbial infection, and autoimmune disease. It is our goal here to begin the process of merging the dichotomous lives of histones both within and without the nuclear membrane.

The Psa fimbriae of Yersinia pestis interact with phosphatidylcholine on alveolar epithelial cells and pulmonary surfactant

The pH 6 antigen (Psa) of Yersinia pestis consists of fimbriae with adhesive properties of potential importance for the pathogenesis of plague, including pneumonic plague. The Psa fimbriae mediate bacterial binding to human alveolar epithelial cells. The Psa fimbriae bound mostly to one component present in the total lipid extract from type II alveolar epithelial cells of the cell line A549 separated by thin-layer chromatography (TLC). The Psa receptor was identified as phosphatidylcholine (PC) by TLC using alkali treatment, molybdenum blue staining, and Psa overlays. The Psa fimbriae bound to PC in a dose-dependent manner, and binding was inhibited by phosphorylcholine (ChoP) and choline. Binding inhibition was dose dependent, although only high concentrations of ChoP completely blocked Psa binding to PC. In contrast, less than 1 muM of a ChoP-polylysine polymer inhibited specifically the adhesion of Psa-fimbriated Escherichia coli to PC, and type I (WI-26 VA4) and type II alveolar epithelial cells. These results indicated that the homopolymeric Psa fimbriae are multimeric adhesins. Psa also bound to pulmonary surfactant, which covers the alveolar surface as a product of type II alveolar epithelial cells and includes PC as the major component. The observed dose-dependent interaction of Psa with pulmonary surfactant was blocked by ChoP. Interestingly, surfactant did not inhibit Psa-mediated bacterial binding to alveolar cells, suggesting that both surfactant and cell membrane PC retain Psa-fimbriated bacteria on the alveolar surface. Altogether, the results indicate that Psa uses the ChoP moiety of PC as a receptor to mediate bacterial binding to pulmonary surfactant and alveolar epithelial cells.

The potent inhibitory activity of histone H1.2 C-terminal fragments on furin

Many physiologically important proproteins, pathogenic bacterial exotoxins and viral envelope glycoproteins are activated by the proprotein convertase furin, which makes furin inhibitor a hot target for basic research and drug design. Although synthetic and bioengineered inhibitors of furin have been well characterized, its endogenous inhibitor has not been directly purified from mammalian tissues to date. In this study, three inhibitors were purified from the porcine liver by using a combination of chromatographic techniques, and identified to be the C-terminal truncated fragments with different sizes of histone H1.2. The gene of porcine histone H1.2 was cloned and sequenced, further confirming the determined sequences. These three C-terminal fragments inhibited furin with Ki values around 2 x 10(-7) m while the full-length histone H1.2 inhibited it with a lesser activity, suggesting that the inhibitory activity relies on the C-terminal lysine-rich domain. Though the inhibition was temporary, these inhibitors were specific, and the reactive site of one C-terminal fragment was identified. A 36 amino acid peptide around the reactive site was synthesized, which could still inhibit furin with a Ki of 5.2 x 10(-7) m.