cDNA cloning and characterization of buforin I, an antimicrobial peptide: a cleavage product of histone H2A

Fish Skin Mucus Extracts: An Underexplored Source of Antimicrobial Agents

The slow discovery of new antibiotics combined with the alarming emergence of antibiotic-resistant bacteria underscores the need for alternative treatments. In this regard, fish skin mucus has been demonstrated to contain a diverse array of bioactive molecules with antimicrobial properties, including peptides, proteins, and other metabolites. This review aims to provide an overview of the antimicrobial molecules found in fish skin mucus and its reported in vitro antimicrobial capacity against bacteria, fungi, and viruses. Additionally, the different methods of mucus extraction, which can be grouped as aqueous, organic, and acidic extractions, are presented. Finally, omic techniques (genomics, transcriptomics, proteomics, metabolomics, and multiomics) are described as key tools for the identification and isolation of new antimicrobial compounds. Overall, this study provides valuable insight into the potential of fish skin mucus as a promising source for the discovery of new antimicrobial agents.

Immunoprotective Effects of Two Histone H2A Variants in the Grass Carp Against Flavobacterium columnare Infection

In teleost fish, the nucleotide polymorphisms of histone H2A significantly affect the resistance or susceptibility of zebrafish to Edwardsiella piscicida infection. Whether histone H2A variants can enhance the resistance of grass carp to Flavobacterium columnare infection remains unclear. Here, the effects of 7 previously obtained variants (gcH2A-1~gcH2A-7) and 5 novel histone H2A variants (gcH2A-11, gcH2A-13~gcH2A-16) in response to F. columnare infection were investigated. It was found that these histone H2A variants could be divided into type I and II. Among them, 5 histone H2A variants had no any effects on the F. columnare infection, however 7 histone H2A variants had antibacterial activity against F. columnare infection. The gcH2A-4 and gcH2A-11, whose antibacterial activity was the strongest in type I and II histone H2A variants respectively, were picked out for yeast expression. Transcriptome data for the samples from the intestines of grass carp immunized with the engineered Saccharomyces cerevisiae expressing PYD1, gcH2A-4 or gcH2A-11 revealed that 5 and 12 immune-related signaling pathways were significantly enriched by gcH2A-4 or gcH2A-11, respectively. For the engineered S. cerevisiae expressing gcH2A-4, NOD-like receptor and Toll-like receptor signaling pathways were enriched for up-regulated DEGs. Besides NOD-like receptor and Toll-like receptor signaling pathways, the engineered S. cerevisiae expressing gcH2A-11 also activated Cytosolic DNA-sensing pathway, RIG-I-like receptor signaling pathway and C-type lectin receptor signaling pathway. Furthermore, grass carp were immunized with the engineered S. cerevisiae expressing PYD1, gcH2A-4 or gcH2A-11 for 1 month and challenged with F. columnare. These grass carp immunized with gcH2A-4 or gcH2A-11 showed lower mortality and fewer numbers of F. columnare than did the control group. All these results suggest that gcH2A-4 and gcH2A-11 play important roles in evoking the innate immune responses and enhancing disease resistance of grass carp against F. columnare infection.

Sex-dependent acrolein sensitivity in mice is associated with differential lung cell, protein, and transcript changes

Acrolein is a reactive inhalation hazard. Acrolein's initial interaction, which in itself can be function-altering, is followed by time-dependent cascade of complex cellular and pulmonary responses that dictate the severity of the injury. To investigate the pathophysiological progression of sex-dependent acrolein-induced acute lung injury, C57BL/6J mice were exposed for 30 min to sublethal, but toxic, and lethal acrolein. Male mice were more sensitive than female mice. Acrolein of 50 ppm was sublethal to female but lethal to male mice, and 75 ppm was lethal to female mice. Lethal and sublethal acrolein exposure decreased bronchoalveolar lavage (BAL) total cell number at 3 h after exposure. The cell number decrease was followed by progressive total cell and neutrophil number and protein increases. The BAL total cell number in female mice exposed to a sublethal, but not lethal dose, returned to control levels at 16 h. In contrast, BAL protein content and neutrophil number were higher in mice exposed to lethal compared to sublethal acrolein. RNASeq pathway analysis identified greater increased lung neutrophil, glutathione metabolism, oxidative stress responses, and CCL7 (aka MCP-3), CXCL10 (aka IP-10), and IL6 transcripts in males than females, whereas IL10 increased more in female than male mice. Thus, the IL6:IL10 ratio, an indicator of disease severity, was greater in males than females. Further, H3.3 histone B (H3F3B) and pro-platelet basic protein (PPBP aka CXCL7), transcripts increased in acrolein exposed mouse BAL and plasma at 3 h, while H3F3B protein that is associated with neutrophil extracellular traps formation increased at 12 h. These results suggest that H3F3B and PPBP transcripts increase may contribute to extracellular H3F3B and PPBP proteins increase.

A histone H2A-derived antimicrobial peptide, Hipposin from mangrove whip ray, Himantura walga: Molecular and functional characterisation

Antimicrobial peptides (AMPs) are biologically dynamic molecules produced by all type of organisms as a fundamental component of their innate immune system. The present study deals with the identification of a histone H2A-derived antimicrobial peptide, Hipposin from mangrove whip ray, Himantura walga. A 243 base pair fragment encoding 81 amino acid residues amplified from complementary DNA was identified as Hipposin and termed as Hw-Hip. Homologous analysis showed that Hw-Hip belongs to the Histone H2A superfamily and shares sequence identity with other histone-derived AMPs from fishes. Phylogenetic analysis of Hw-Hip displayed clustering with the fish H2A histones. Secondary structure analysis showed the presence of three α-helices and four random coils with a prominent proline hinge. The physicochemical properties of Hw-Hip are in agreement with the properties of antimicrobial peptides. A 39-mer active peptide sequence was released by proteolytic cleavage in silico. Functional characterisation of active peptide in silico revealed antibacterial, anticancer and antibiofilm activities making Hw-Hip a promising candidate for further exploration.

Neutrophil Extracellular Traps and Liver Disease

Neutrophil extracellular traps, or NETs, are heterogenous, filamentous structures which consist of extracellular DNA, granular proteins, and histones. NETs are extruded by a neutrophil in response to various stimuli. Although NETs were initially implicated in immune defense, subsequent studies have implicated NETs in a spectrum of disease processes, including autoimmune disease, thrombosis, and cancer. NETs also contribute to the pathogenesis of several common liver diseases, including alcohol-associated liver disease and portal hypertension. Although there is much interest in the therapeutic potential of NET inhibition, future clinical applications must be balanced against potential increased risk of infection.

Cathelicidin-DM is an Antimicrobial Peptide from Duttaphrynus melanostictus and Has Wound-Healing Therapeutic Potential

Antimicrobial peptides (AMPs) are a class of templates with application potential for drug development. Amphibians are important sources of AMPs. Duttaphrynus melanostictus is the main source of traditional Chinese medicine "Chansu", which has anti-infection effect while without a clear mechanism. This study aimed to find the cathelicidin peptide in D. melanostictus and then investigate the activity in vivo and in vitro, and an AMP-encoding gene (cathelicidin-DM, GenBank: KJ820824.1) was obtained from the constructed cDNA library of D. melanostictus. The MIC test and SYTOX Green uptake were used for the evaluation of the bactericidal capacity and mechanisms. The serum stability tests were used for the evaluation of the application potential. The skin wound infection model and in vivo imaging were used for in vitro application of possibility evaluation. The results showed that cathelicidin-DM was a 37 amino acid AMP with good bactericidal ability, which was similar to melittin: both can kill bacteria within 15 min. Moreover, cathelicidin-DM exhibits good therapeutic potential in the mouse wound infection model, and it can be enriched to the site of infection for treatment. Thus, cathelicidin-DM could be a new template for antimicrobial drug development given its good antibacterial activity in vivo and in vitro.

The First Genome Survey of the Antarctic Krill (Euphausia superba) Provides a Valuable Genetic Resource for Polar Biomedical Research

The world-famous Antarctic krill (Euphausia superba) plays a fundamental role in the Antarctic food chain. It resides in cold environments with the most abundant biomass to support the Antarctic ecology and fisheries. Here, we performed the first genome survey of the Antarctic krill, with genomic evidence for its estimated genome size of 42.1 gigabases (Gb). Such a large genome, however, is beyond our present capability to obtain a good assembly, although our sequencing data are a valuable genetic resource for subsequent polar biomedical research. We extracted 13 typical protein-coding gene sequences of the mitochondrial genome and analyzed simple sequence repeats (SSRs), which are useful for species identification and origin determination. Meanwhile, we conducted a high-throughput comparative identification of putative antimicrobial peptides (AMPs) and antihypertensive peptides (AHTPs) from whole-body transcriptomes of the Antarctic krill and its well-known counterpart, the whiteleg shrimp (Penaeus vannamei; resident in warm waters). Related data revealed that AMPs/AMP precursors and AHTPs were generally conserved, with interesting variations between the two crustacean species. In summary, as the first report of estimated genome size of the Antarctic krill, our present genome survey data provide a foundation for further biological research into this polar species. Our preliminary investigations on bioactive peptides will bring a new perspective for the in-depth development of novel marine drugs.

Characterization, expression, and antimicrobial activity of histones from Japanese flounder Paralichthys olivaceus

Histone proteins are not only structurally important for chromosomal DNA packaging but also involved in the regulation of gene expression and the immune response of host against pathogens. Japanese flounder (Paralichthys olivaceus) as one of the most important marine flatfish, suffered from widespread outbreaks of diseases, and its immunological functioning remained to be elucidated. In the present study, we reported the expression patterns of four histones (H1, H2A, H3, and H3.3) and functional characterization of the histone H3.3 from flounder. Quantitative real time RT-PCR (RT-qPCR) analysis showed that expression of the four histones occurred in multiple tissues, but their levels of expression were relatively high in immune organs, and inducible in response to pathogens infection. Infection with extracellular and intracellular bacterial pathogens and viral pathogen regulated the expression of histones in a manner that depended on tissue type, pathogen, and infection stage. Specifically, H1 expression was highly induced by intracellular viral pathogens; H2AX and H3 expressions were highly induced by intracellular bacterial pathogen; dissimilarly, H3.3 expression was slightly induced by extracellular bacterial pathogen, but was inhibited by intracellular bacterial and viral pathogens. To further investigate H3.3 function, recombinant H3.3 (rH3.3) was obtained, and in vitro experiments showed rH3.3 possessed the capability of binding to both Gram-negative and Gram-positive bacteria and inhibiting the growth of some target bacteria. Consistently, In vivo results showed that overexpression of H3.3 promoted the host defense against invading pathogenic microorganism and regulated the expressions of several cytokines. These results suggested that flounder histones exhibit different expression patterns in response to the infection of different microbial pathogens, and H3.3 serves as an immune-related protein and plays an important role in antimicrobial immunity of Japanese flounder. Taken together, this study is the first report about the expression profile of different histones upon different kind of pathogens and anti-infectious immunity of H3.3 in teleost, which offered new insights into the immunological function of histones in teleost.

Physical Mechanisms of Bacterial Killing by Histones

Antibiotic resistance is a global epidemic, becoming increasingly pressing due to its rapid spread. There is thus a critical need to develop new therapeutic approaches. In addition to searching for new antibiotics, looking into existing mechanisms of natural host defense may enable researchers to improve existing defense mechanisms, and to develop effective, synthetic drugs guided by natural principles. Histones, primarily known for their role in condensing mammalian DNA, are antimicrobial and share biochemical similarities with antimicrobial peptides (AMPs); however, the mechanism by which histones kill bacteria is largely unknown. Both AMPs and histones are similar in size, cationic, contain a high proportion of hydrophobic amino acids, and possess the ability to form alpha helices. AMPs, which mostly kill bacteria through permeabilization or disruption of the biological membrane, have recently garnered significant attention for playing a key role in host defenses. This chapter outlines the structure and function of histone proteins as they compare to AMPs and provides an overview of their role in innate immune responses, especially regarding the action of specific histones against microorganisms and their potential mechanism of action against microbial pathogens.

White spot syndrome virus down-regulates expression of histones H2A and H4 of Penaeus vannamei to promote viral replication

The white spot syndrome virus (WSSV) is a highly lethal and contagious pathogen to most cultivated shrimp species. The WSSV genome contains the ICP11 gene and its encoded protein acts as a multifunctinal DNA mimic protein that disrupts the nucleosome assembly by binding to the histone proteins H2A and H3. In addition, WSSV provokes severe nuclear hypertrophy and DNA damage. However, little is known about the influence of WSSV on the expression of the host's genes encoding for histones. Therefore, we investigated the effect of WSSV infection on the expression of the genes encoding histones in shrimp Penaeus vannamei. An RT-qPCR assay was performed to evaluate the temporal expression of H2A and H4 transcripts in the shrimp. Significant changes were observed in the expression of these genes, which coincided with the dynamics of replication of the virus. H2A reached its maximum expression levels at 12 hpi. Thus, it may be suggested that this is a viral strategy to evade the host's immune response in order to promote viral replication.

Histone H2A cooperates with RIP2 to induce the expression of antibacterial genes and MHC related genes

An octamer consisting of two copies of histones H2A, H2B, H3 and H4 is the nucleosome core. It is well established that histone derived antimicrobial peptides (AMPs) have anti-microbial properties in various invertebrate and vertebrate species. Different from well-known histone H2A-derived AMPs, the antimicrobial properties of the complete histone H2A are rather limited. In the present study, we report the functional characterization of the complete histone H2A from zebrafish. The expression of zebrafish histone H2A was higher in embryos than in larvae, and inducible in response to bacterial infection. Furthermore, the expression of zebrafish histone H2A was decreased by RIP2 deficiency with and/or without bacterial infection. During Edwardsiella piscicida infection, the overexpression of zebrafish histone H2A inhibited bacterial proliferation and increased the survival rate of zebrafish larvae. The overexpression of zebrafish histone H2A demonstrated an increased transcription of many antibacterial genes and MHC related genes, which was dependent on RIP2, an adaptor protein for signal propagation of the NLRs-mediated antibacterial immune response. In line with this, zebrafish histone H2A cooperated with RIP2 to induce the transcription of many antibacterial genes and MHC related genes. All together, these results firstly demonstrate the antibacterial property of the complete histone H2A against gram-negative bacteria E. piscicida in vivo and the correlation between zebrafish histone H2A and RIP2 adaptor protein on the transcriptional regulation of antibacterial genes and MHC related genes.

A histone H2A derived antimicrobial peptide, Fi-Histin from the Indian White shrimp, Fenneropenaeus indicus: Molecular and functional characterization

Antimicrobial peptides (AMPs) derived from histone proteins form an important category of peptide antibiotics. Present study deals with the molecular and functional characterization of a 27-amino acid histone H2A derived AMP from the Indian White shrimp, Fenneropenaeus indicus designated as Fi-Histin. This peptide displayed distinctive features of AMPs such as amphiphilic alpha helical structure and a net charge of +6. The synthetic peptide exhibited significant antimicrobial activity against Gram-negative and Gram-positive bacteria especially against V. vulnificus, P. aeruginosa, V. parahaemolyticus, V. cholera and S. aureus. Disruption of cell membrane and cell content leakage were observed in peptide treated V. vulnificus using scanning electron microscopy. The synthetic peptide Fi-His_1-21 exhibited DNA binding activity and found to be non-haemolytic at the tested concentrations. Peptide was also found to possess anticancer activity against NCI-H460 and HEp-2 cell lines with an IC₅₀ of 22.670 ± 13.939 μM and 31.274 ± 24.531 μM respectively. This is the first report of a histone H2A derived peptide from F. indicus with a specific antimicrobial activity and anticancer activity, which could be a new candidate for future applications in aquaculture and medicine.

H2A and Ca-L-hipposin gene: Characteristic analysis and expression responses to Aeromonas hydrophila infection in Carassius aurutus

Antimicrobial peptide is an important component of the host innate immune system and thus serves a crucial function in host defense against microbial invasion. In this study, H2A and derived antimicrobial peptide Ca-L-hipposin were cloned and characterized in Carassius aurutus. The gene H2A full-length cDNA is 908 bp and includes a 5'-terminal untranslated region (UTR) of 55 bp and a 3'-terminal UTR of 466 bp with a canonical polyadenylation signal sequence AATAA, as well as an open reading frame (ORF) of 387 bp encoding a polypeptide of 128 amino acids, with a molecular weight of 13.7 kDa, an isoelectric point of 10.7, and 94% homology with Danio rerio H2A. The secondary structure of H2A includes the α-spiral with 51 amino acids with a composition ratio of 39.8%, as well as a β-corner with 15 amino acids in a composition ratio of 11.7%. The online software ExPaSy predicted that a peptide sequence with 51 amino acids from the 2nd to 52nd amino acids in histone H2A can be produced through hydrolization by protease chymotrypsin, which indicates a difference of only three amino acids, compared with the antimicrobial peptide hipposin in Hippoglossus hippoglossus with a homology of 94%. Ca-L-hipposin includes 51 amino acids with a molecular weight of 5.4 kDa and an isoelectric point of 12.0, the secondary structure of which contains an α-helix of 17 amino acids accounting for 33.3% and a β-corner of 8 amino acids accounting for 15.7%. H2A was extensively expressed in the mRNA levels of various tissues, with higher expression levels in kidney and spleen. After C. aurutus was challenged with Aeromonas hydrophila, the mRNA expression levels of H2A were upregulated in the kidney, spleen, and liver. H2A serves an important function in the defense against the invasion of A. hydrophila. In addition, sequence characteristics reveal that Ca-L-hipposin could be a potential antimicrobial peptide for use in killing pathogenic bacteria in aquaculture.

Antibacterial Peptides: Opportunities for the Prevention and Treatment of Dental Caries

Dental caries is a multifactorial disease that is a growing and costly global health concern. The onset of disease is a consequence of an ecological imbalance within the dental plaque biofilm that favors specific acidogenic and aciduric caries pathogens, namely Streptococcus mutans and Streptococcus sobrinus. It is now recognized by the scientific and medical community that it is neither possible nor desirable to totally eliminate dental plaque. Conversely, the chemical biocides most commonly used for caries prevention and treatment indiscriminately attack all plaque microorganisms. These treatments also suffer from other drawbacks such as bad taste, irritability, and staining. Furthermore, the public demand for safe and natural personal hygiene products continues to rise. Therefore, there are opportunities that exist to develop new strategies for the treatment of this disease. As an alternative to conventional antibiotics, antibacterial peptides have been explored greatly over the last three decades for many different therapeutic uses. There are currently tens of hundreds of antibacterial peptides characterized across the evolutionary spectrum, and among these, many demonstrate physical and/or biological properties that may be suitable for a more targeted approach to the selective control or elimination of putative caries pathogens. Additionally, many peptides, such as nisin, are odorless, colorless, and tasteless and do not cause irritation or staining. This review focuses on antibacterial peptides for their potential role in the treatment and prevention of dental caries and suggests candidates that need to be explored further. Practical considerations for the development of antibacterial peptides as oral treatments are also discussed.

Antimicrobial proteins: From old proteins, new tricks

This review describes the main types of antimicrobial peptides (AMPs) synthesised by crustaceans, primarily those identified in shrimp, crayfish, crab and lobster. It includes an overview of their range of microbicidal activities and the current landscape of our understanding of their gene expression patterns in different body tissues. It further summarises how their expression might change following various types of immune challenges. The review further considers proteins or protein fragments from crustaceans that have antimicrobial properties but are more usually associated with other biological functions, or are derived from such proteins. It discusses how these unconventional AMPs might be generated at, or delivered to, sites of infection and how they might contribute to crustacean host defence in vivo. It also highlights recent work that is starting to reveal the extent of multi-functionality displayed by some decapod AMPs, particularly their participation in other aspects of host protection. Examples of such activities include proteinase inhibition, phagocytosis, antiviral activity and haematopoiesis.

Arginine-rich histones have strong antiviral activity for influenza A viruses

While histones are best known for DNA binding and transcription-regulating properties, they also have antimicrobial activity against a broad range of potentially pathogenic organisms. Histones are abundant in neutrophil extracellular traps, where they play an important role in NET-mediated antimicrobial killing. Here, we show anti-influenza activity of histones against both seasonal H3N2 and H1N1, but not pandemic H1N1. The arginine rich histones, H3 and H4, had greater neutralizing and viral aggregating activity than the lysine rich histones, H2A and H2B. Of all core histones, histone H4 is most potent in neutralizing IAV, and incubation with IAV with histone H4 results in a decrease in uptake and viral replication by epithelial cells when measured by qRT-PCR. The antiviral activity of histone H4 is mediated principally by direct effects on viral particles. Histone H4 binds to IAV as assessed by ELISA and co-sedimentation of H4 with IAV. H4 also induces aggregation, as assessed by confocal microscopy and light transmission assays. Despite strong antiviral activity against the seasonal IAV strains, H4 was inactive against pandemic H1N1. These findings indicate a possible role for histones in the innate immune response against IAV.

Proteomic analysis of pure human airway gland mucus reveals a large component of protective proteins

Airway submucosal glands contribute to innate immunity and protect the lungs by secreting mucus, which is required for mucociliary clearance and which also contains antimicrobial, anti-inflammatory, anti-proteolytic and anti-oxidant proteins. We stimulated glands in tracheal trimmings from three lung donors and collected droplets of uncontaminated mucus as they formed at the gland orifices under an oil layer. We analyzed the mucus using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Analysis identified 5486 peptides and 441 proteins from across the 3 samples (269-319 proteins per subject). We focused on 269 proteins common to at least 2 0f 3 subjects, of which 102 (38%) had protective or innate immunity functions. While many of these have long been known to play such roles, for many others their cellular protective functions have only recently been appreciated in addition to their well-studied biologic functions (e.g. annexins, apolipoproteins, gelsolin, hemoglobin, histones, keratins, and lumican). A minority of the identified proteins are known to be secreted via conventional exocytosis, suggesting that glandular secretion occurs via multiple mechanisms. Two of the observed protective proteins, major vault protein and prohibitin, have not been observed in fluid from human epithelial cultures or in fluid from nasal or bronchoalveolar lavage. Further proteomic analysis of pure gland mucus may help clarify how healthy airways maintain a sterile environment.

FAF and SufA: proteins of Finegoldia magna that modulate the antibacterial activity of histones

Many bacterial pathogens have developed methods to overcome the defences of the host innate immune system. One such defence is the release of antimicrobial peptides (AMPs). Histones have been found to function as AMPs, in addition to their main biological function of packaging and organising DNA into nucleosomes. In this study, the Gram-positive anaerobic coccus Finegoldia magna was found to bind histones by Western blot and immunoprecipitation analysis. F. magna, which is normally a commensal of the skin and mucous membranes, is also known to act as an opportunistic pathogen and has been isolated from various clinical infection sites. It was found to bind to histones extracted from human skin epidermis through its surface and extracellular adhesion protein FAF. Through FAF binding, F. magna was protected from histone bactericidal activity. Furthermore, the histones were found to be degraded by SufA, a subtilisin-like extracellular serine protease of F. magna. Hence, the results of the present study will give more insight into how F. magna persists both as a commensal organism at the basement membrane of the skin and as an opportunistic pathogen during infection.

An unconventional antimicrobial protein histone from freshwater prawn Macrobrachium rosenbergii: analysis of immune properties

In this study, we have reported the first histone characterized at molecular level from freshwater prawn Macrobrachium rosenbergii (MrHis). A full length cDNA of MrHis (751 base pairs) was identified from an established M. rosenbergii cDNA library using GS-FLX technique. It encodes 137 amino acid residues with a calculated molecular mass of 15 kDa and an isoelectric point of 10.5. MrHis peptide contains a histone H2A signature between 21 and 27 amino acids. Homologous analysis showed that MrHis had a significant sequence identity (99%) with other known histone H2A groups especially from Penaeus monodon. Phylogenetic analysis of MrHis showed a strong relationship with other amino acid sequences from histone H2A arthropod groups. Further phylogenetic analysis showed that the MrHis belongs to histone H2A superfamily and H2A1A sub-family. Secondary structure of MrHis showed that the protein contains 50.36% α-helical region and 49.64% coils. The 3D model of MrHis was predicted by I-Tasser program and the model was evaluated for quality analysis including C-score analysis, Ramachandran plot analysis and RMSD analysis. The surface view analysis of MrHis showed the active domain at the N terminal. The antimicrobial property of MrHis protein was confirmed by the helical structure and the total hydrophobic surface along with its net charge. The MFE of the predicted RNA structure of MrHis is -128.62 kcal/mol, shows its mRNA stability. Schiffer-Edmundson helical wheel analysis of the N-terminal of MrHis showed a perfect amphipathic nature of the peptide. Significantly (P < 0.05) highest gene expression was noticed in the hemocyte and is induced with viral (WSBV and MrNV) and bacteria (A eromonas hydrophila and Vibrio harveyi) infections. The coding sequence of recombinant MrHis protein was expressed in a pMAL vector and purified to study the antimicrobial properties. The recombinant product showed antimicrobial activity against both Gram negative and Gram positive bacteria. In this study, the recombinant MrHis protein displayed antimicrobial activity in its entirety. Hence, it is possible to suggest that the activity may be due to the direct defense role of histone or its N-terminal antimicrobial property. However, this remains to be verified by detailed investigations.

O-antigen protects gram-negative bacteria from histone killing

Beyond their traditional role of wrapping DNA, histones display antibacterial activity to Gram-negative and -positive bacteria. To identify bacterial components that allow survival to a histone challenge, we selected resistant bacteria from homologous Escherichia coli libraries that harbor plasmids carrying pieces of the chromosome in different sizes. We identified genes required for exopolysaccharide production and for the synthesis of the polysaccharide domain of the lipopolysaccharide, called O-antigen. Indeed, O-antigen and exopolysaccharide conferred further resistance to histones. Notably, O-antigen also conferred resistance to histones in the pathogens Shigella flexneri and Klebsiella pneumoniae.

Extracellular histone H1 is neurotoxic and drives a pro-inflammatory response in microglia

In neurodegenerative conditions and following brain trauma it is not understood why neurons die while astrocytes and microglia survive and adopt pro-inflammatory phenotypes. We show here that the damaged adult brain releases diffusible factors that can kill cortical neurons and we have identified histone H1 as a major extracellular candidate that causes neurotoxicity and activation of the innate immune system. Extracellular core histones H2A, H2B H3 and H4 were not neurotoxic. Innate immunity in the central nervous system is mediated through microglial cells and we show here for the first time that histone H1 promotes their survival, up-regulates MHC class II antigen expression and is a powerful microglial chemoattractant. We propose that when the central nervous system is degenerating, histone H1 drives a positive feedback loop that drives further degeneration and activation of immune defences which can themselves be damaging. We suggest that histone H1 acts as an antimicrobial peptide and kills neurons through mitochondrial damage and apoptosis.

Antimicrobial peptides from amphibians

Increased prevalence of multi-drug resistance in pathogens has encouraged researchers to focus on finding novel forms of anti-infective agents. Antimicrobial peptides (AMPs) found in animal secretions are components of host innate immune response and have survived eons of pathogen evolution. Thus, they are likely to be active against pathogens and even those that are resistant to conventional drugs. Many peptides have been isolated and shown to be effective against multi-drug resistant pathogens. More than 500 AMPs have been identified from amphibians. The abundance of AMPs in frog skin is remarkable and constitutes a rich source for design of novel pharmaceutical molecules. Expression and post-translational modifications, discovery, activities and probable therapeutic application prospects of amphibian AMPs will be discussed in this article.

Transcriptional response in the peripheral blood of patients infected with Salmonella enterica serovar Typhi

We used microarrays and transcriptional profiling of peripheral blood to investigate the host response of 29 individuals who contracted typhoid fever in the Mekong Delta region of Vietnam. Samples were taken over a nine month period encompassing acute disease, convalescence, and recovery. We found that typhoid fever induced a distinct and highly reproducible signature in the peripheral blood that changed during treatment and convalescence, returning in the majority of cases to the "normal" profile as measured in healthy uninfected controls. Unexpectedly, there was a strong, distinct signature of convalescence present at day 9 after infection that remained virtually unchanged one month after acute infection and in some cases persisted as long as nine months despite a complete clinical recovery in all patients. Patients who retain the convalescent signature may be genetically or temporarily incapable of developing an effective immune response and may be more susceptible to reinfection, relapse, or the establishment of a carrier state.

A theoretical approach to spot active regions in antimicrobial proteins

Background

Much effort goes into identifying new antimicrobial compounds able to evade the increasing resistance of microorganisms to antibiotics. One strategy relies on antimicrobial peptides, either derived from fragments released by proteolytic cleavage of proteins or designed from known antimicrobial protein regions.

Results

To identify these antimicrobial determinants, we developed a theoretical approach that predicts antimicrobial proteins from their amino acid sequence in addition to determining their antimicrobial regions. A bactericidal propensity index has been calculated for each amino acid, using the experimental data reported from a high-throughput screening assay as reference. Scanning profiles were performed for protein sequences and potentially active stretches were identified by the best selected threshold parameters. The method was corroborated against positive and negative datasets. This successful approach means that we can spot active sequences previously reported in the literature from experimental data for most of the antimicrobial proteins examined.

Conclusion

The method presented can correctly identify antimicrobial proteins with an accuracy of 85% and a sensitivity of 90%. The method can also predict their key active regions, making this a tool for the design of new antimicrobial drugs.

Abhisin: a potential antimicrobial peptide derived from histone H2A of disk abalone (Haliotis discus discus)

Antimicrobial peptides (AMPs) play an important role in the immune defense against pathogenic microorganisms. In this study, a histone H2A full-length cDNA was cloned from disk abalone Haliotis discus discus. We identified a 40-amino acid AMP designated as abhisin from the N-terminus of the abalone histone H2A sequence. Abhisin shows the characteristic features of AMPs including net positive charge (+13), higher hydrophobic residues (27%) and 2.82 kcal/mol protein binding potential. Abhisin shares 80% amino acid identity with the buforin I peptide that is derived from Asian toad histone H2A. We synthesized the synthetic peptide of abhisin, and characterized its antimicrobial activities. Our results showed the growth inhibition of Gram positive (G+) Listeria monocytogenes, Gram negative (G-) Vibrio ichthyoenteri bacteria, and fungi (yeast) Pityrosporum ovale by abhisin treatment at 250 microg/mL. However, stronger activity was displayed against the G+ than G- bacteria. Additionally, scanning electron microscope (SEM) observation results confirmed that P. ovale cells were damaged by abhisin treatment. Interestingly, abhisin treatment (50 microg/mL) decreased the viability of THP-1 leukemia cancer cells approximately by 25% but there was no effect on the normal vero cells, suggesting that abhisin has cytotoxicity against cancer cells but not normal cells. Quantitative real time RT-PCR results revealed that histone H2A transcription was significantly induced at 3 h post-infection with bacteria in abalone gills and digestive tract. These results suggest that abhisin is a potential antimicrobial agent, and its precursor histone H2A may be involved in the innate immune defense system in abalone.

The Toxicogenomic Multiverse: Convergent Recruitment of Proteins Into Animal Venoms

Throughout evolution, numerous proteins have been convergently recruited into the venoms of various animals, including centipedes, cephalopods, cone snails, fish, insects (several independent venom systems), platypus, scorpions, shrews, spiders, toxicoferan reptiles (lizards and snakes), and sea anemones. The protein scaffolds utilized convergently have included AVIT/colipase/prokineticin, CAP, chitinase, cystatin, defensins, hyaluronidase, Kunitz, lectin, lipocalin, natriuretic peptide, peptidase S1, phospholipase A2, sphingomyelinase D, and SPRY. Many of these same venom protein types have also been convergently recruited for use in the hematophagous gland secretions of invertebrates (e.g., fleas, leeches, kissing bugs, mosquitoes, and ticks) and vertebrates (e.g., vampire bats). Here, we discuss a number of overarching structural, functional, and evolutionary generalities of the protein families from which these toxins have been frequently recruited and propose a revised and expanded working definition for venom. Given the large number of striking similarities between the protein compositions of conventional venoms and hematophagous secretions, we argue that the latter should also fall under the same definition.

Solution NMR studies of amphibian antimicrobial peptides: linking structure to function?

The high-resolution three-dimensional structure of an antimicrobial peptide has implications for the mechanism of its antimicrobial activity, as the conformation of the peptide provides insights into the intermolecular interactions that govern the binding to its biological target. For many cationic antimicrobial peptides the negatively charged membranes surrounding the bacterial cell appear to be a main target. In contrast to what has been found for other classes of antimicrobial peptides, solution NMR studies have revealed that in spite of the wide diversity in the amino acid sequences of amphibian antimicrobial peptides (AAMPs), they all adopt amphipathic alpha-helical structures in the presence of membrane-mimetic micelles, bicelles or organic solvent mixtures. In some cases the amphipathic AAMP structures are directly membrane-perturbing (e.g. magainin, aurein and the rana-box peptides), in other instances the peptide spontaneously passes through the membrane and acts on intracellular targets (e.g. buforin). Armed with a high-resolution structure, it is possible to relate the peptide structure to other relevant biophysical and biological data to elucidate a mechanism of action. While many linear AAMPs have significant antimicrobial activity of their own, mixtures of peptides sometimes have vastly improved antibiotic effects. Thus, synergy among antimicrobial peptides is an avenue of research that has recently attracted considerable attention. While synergistic relationships between AAMPs are well described, it is becoming increasingly evident that analyzing the intermolecular interactions between these peptides will be essential for understanding the increased antimicrobial effect. NMR structure determination of hybrid peptides composed of known antimicrobial peptides can shed light on these intricate synergistic relationships. In this work, we present the first NMR solution structure of a hybrid peptide composed of magainin 2 and PGLa bound to SDS and DPC micelles. The hybrid peptide adopts a largely helical conformation and some information regarding the inter-helix organization of this molecule is reported. The solution structure of the micelle associated MG2-PGLa hybrid peptide highlights the importance of examining structural contributions to the synergistic relationships but it also demonstrates the limitations in the resolution of the currently used solution NMR techniques for probing such interactions. Future studies of antimicrobial peptide synergy will likely require stable isotope-labeling strategies, similar to those used in NMR studies of proteins.

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.

Identification of heparin/heparan sulfate interacting protein as a major broad-spectrum antimicrobial protein in lung and small intestine

The lungs are continuously exposed to a broad array of microbes through inhalation, and microorganisms that escape clearance by the upper airway mucociliary motion will deposit in the alveolar compartment of the lower airways. The pulmonary epithelium in the alveolar compartment is covered by a thin aqueous layer that contains surfactant proteins but also microbicidal components. We have here identified the epithelial cell surface-expressed heparin/heparan sulfate interacting protein (HIP/RPL29) by high-performance liquid chromatography-fractionation, N-terminal sequencing, and mass spectrometry analysis as a major antimicrobial component in extracts of mouse lung tissue. HIP/RPL29 was also detected in extracts of mouse small intestinal tissue. HIP/RPL29 exhibited broad antibacterial activity, notably against Pseudomonas aeruginosa strains. Human recombinant HIP/RPL29 exhibited killing activity in the same order of magnitude. The HIP/RPL29 protein was demonstrated to be localized to the epithelial cells and cell surface of the lungs and intestines by immunohistochemistry. We suggest that HIP/RPL29 fulfills a function as an abundant antibacterial factor of the epithelial innate defense shield against invading bacteria in both the lungs and the small intestine.

Characterization of a hemolytic protein, identified as histone H4, from the skin of the Japanese tree frog Hyla japonica (Hylidae)

An extract of the skin of the Japanese tree frog, Hyla japonica Günther, 1859 (Anura: Hylidae) did not inhibit the growth of the bacteria Escherichia coli or Staphylococcus aureus, but contained a protein that was strongly hemolytic against human erythrocytes. The protein was purified to near homogeneity by reverse-phase HPLC, and its N-terminal amino acid sequence (SGRGKGGKGL...) identified it as histone H4. The complete primary structure of the 102-amino-acid-residue histone H4 was determined by a combination of molecular cloning of genomic and complementary DNAs encoding the protein. The molecular mass of the purified histone H4 determined by electrospray mass spectrometry was 71+/-2 Daltons greater than that predicted from the deduced amino acid sequence of the protein. The +71 mass units is consistent with the proposal that the protein isolated from the skin was post-translationally modified by addition of one acetyl and two methyl groups. The stem-loop structure at the 3' flanking region of the H. japonica histone H4 gene, which acts as a transcription termination signal, contained a nucleotide sequence (5'-GGCTCTCCTCAGAGCC-3') with unusual structural features not seen in other histone genes.

Beneficial suicide: why neutrophils die to make NETs

Neutrophils are one of the main types of effector cell in the innate immune system and were first shown to effectively kill microorganisms by phagocytosis more than 100 years ago. Recently, however, it has been found that stimulated neutrophils can also produce extracellular structures called neutrophil extracellular traps (NETs) that capture and kill microorganisms. This Progress article gives an overview of the structure, function and generation of NETs, and their role in infections.

Preliminary study on a potential antibacterial peptide derived from histone H2A in hemocytes of scallop Chlamys farreri

Histone H2A is reported to participate in host defense response through producing novel antimicrobial peptides (AMPs) from its N-terminus in vertebrates and invertebrates, while the AMPs derived from H2A have not to our knowledge been reported in mollusca. In the present study, gene cloning, mRNA expression of H2A from scallop Chlamys farreri, and the recombinant expression of its N-terminus were conducted to investigate whether a similar mechanism exists in mollusca. The full-length DNA of H2A was identified by the techniques of homology cloning and genomic DNA walking. The full-length DNA of the scallop H2A was 696bp long, including a 5'-terminal untranslated region (UTR) of 90bp, a 3'-terminal UTR of 228bp with a stem-loop structure and a canonical polyadenylation signal sequence AATAAA, and an open reading frame of 375bp encoding a polypeptide of 125 amino acids. The mRNA expression of H2A in the hemocytes of scallop challenged by microbe was measured by semi-quantitative RT-PCR. The expression of H2A was not upregulated after stimulation, suggesting that H2A did not participate in immunity response directly. The DNA fragment of 117bp encoding 39 amino acids corresponding to the N-terminus of scallop H2A, which was homologous to buforin I in vertebrates, was cloned into Pichia pastoris GS115. The transformants (His(+) Mut(+)) containing multi-copy gene insertion were selected with increasing concentration of antibiotic G418. The peptide of 39 amino acids was expressed by induction of 0.5% methanol. The recombinant product exerted antibacterial activity against both Gram-positive (G(+)) and Gram-negative (G(-)) bacteria. The antibacterial activity toward G(+) bacteria was 2.5 times more than that against G(-) bacteria. The results elucidated that N-terminus of H2A was a potential AMP and provided a promising candidate for a new antibiotic screening. However, whether H2A is really involved in scallop immune response mechanisms needs to be further investigated.

Lysosomal killing of Mycobacterium mediated by ubiquitin-derived peptides is enhanced by autophagy

Mycobacterium tuberculosis parasitizes resting macrophages yet is killed by activated macrophages through both oxidative and nonoxidative mechanisms. Nonoxidative mechanisms are linked to the maturation of the bacteria-containing phagosome into an acidified, hydrolytically active compartment. We describe here a mechanism for killing Mycobacteria in the lysosomal compartment through the activity of peptides generated by the hydrolysis of ubiquitin. The induction of autophagy in infected macrophages enhanced the delivery of ubiquitin conjugates to the lysosome and increased the bactericidal capacity of the lysosomal soluble fraction. The accumulation of ubiquitinated proteins in the autophagolysosome provides one possible mechanism behind the antimicrobial activities observed for a range of pathogens in autophagous host cells.

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.

Characterization, localization and possible anti-inflammatory function of rat histone H4 mRNA variants

Two histone H4 mRNA variants, H4-v.1 and histogranin mRNAs, were detected in the rat genome and measured in various tissues and isolated alveolar macrophages. Medium to high levels of both mRNAs were present in the liver, adrenal glands, thymus, bone marrow and alveolar macrophages. H4-v.1 cDNA contained an open reading frame that coded for unmodified whole histone H4, whereas histogranin cDNA lacked the first ATG codon and contained an open reading frame that coded for modified (Thr89) H4-(84-102). The two genes displayed a sequence homologous (> 80%) to the open reading frame of core H4 somatic (H4s) and H4 germinal (H4g) and their variant nature was supported by the absence of histone consensus palindromic and purine-rich sequences in the proximal 3'UTR, and the presence of a polyadenylation signal in the distal 3'UTR and of specific upstream transcription factor-binding sites. H4-v.1 and histogranin transcripts, but not H4s transcript, were selectively induced by lipopolysaccharide and/or interferon gamma in alveolar macrophages. In vitro transcription/translation experiments with H4-v.1 and histogranin cDNA pCMV constructs produced peptides with the molecular mass (2 kDa) of the alternative histone H4 translation product which, like synthetic H4-(86-100) and [Thr89]H4-(86-100) or rat histogranin, inhibited lipopolysaccharide-induced prostaglandin E(2) release from rat alveolar macrophages. The synthetic peptides also inhibited the secretion of the CXC chemokine interleukin-8 (GRO/CINC-1) in response to lipopolysaccharide. The presence of H4-v.1 and histogranin mRNAs in tissues wherein immune reactions take place and the inhibitory effects of their translation products on prostaglandin E(2) and interkeukin-8 secretion by activated alveolar macrophages suggest an anti-inflammatory function.

Correlation between the expression of the histone H4 mRNA variant H4-v.1 and the levels of histone H4-(86-100) and H4-(89-102) (OGP) in various rat tissues and alveolar macrophages

We studied the expression of the osteogenic and antinociceptive C-terminal histone H4-related peptide fragments, H4-(89-102) (OGP) and H4-(86-100), respectively, within various rat tissues and isolated alveolar macrophages (AM) by radioimmunoassay (RIA). OGP was located mainly within the bone marrow, spleen, thymus, and lungs whereas H4-(86-100) was more concentrated within the bone marrow, lymph nodes, spinal cord, pituitaries and thymus. The expression pattern of the two peptides showed similarities with the tissue expression pattern of the histone H4 mRNA variant H4-v.1. In rat AM, OGP and H4-(86-100) levels were significantly stimulated (2.6- and 1.9-fold, respectively) by LPS (1 microg/ml), along with H4-v.1 mRNA (4.1-fold), but not whole histone H4 (1.1-fold) nor total histone H4 mRNA (1.1-fold). The results suggest that H4-v.1 mRNA may play a role in the synthesis of the naturally occurring peptides H4-(86-100) and OGP via the alternative translation product H4-(84-102), but not whole histone H4.

Evolution of innate immune systems*

Innate immunity is the oldest form of defense and is found to some degree in all species. It predates the adaptive immune system, consisting of antibodies, B cells, T cells, and the major histocompatibility antigens. These are found only in higher vertebrates and have been the focus of the majority of immunological research, particularly in mice and humans, over the years. Knowledge of immunity in lower vertebrate and invertebrate species is now increasing rapidly, shedding light on the evolution of immunity and in many cases adding to our understanding of the mammalian system. Several recurring structural, genetic, and developmental mechanisms are common features in these processes in both the cellular and the molecular aspects of innate immunity.

Anti-microbial peptides: from invertebrates to vertebrates

Gene-encoded anti-microbial peptides (AMPs) are widespread in nature, as they are synthesized by microorganisms as well as by multicellular organisms from both the vegetal and the animal kingdoms. These naturally occurring AMPs form a first line of host defense against pathogens and are involved in innate immunity. Depending on their tissue distribution, AMPs ensure either a systemic or a local protection of the organism against environmental pathogens. They are classified into three major groups: (i) peptides with an alpha-helical conformation (insect cecropins, magainins, etc.), (ii) cyclic and open-ended cyclic peptides with pairs of cysteine residues (defensins, protegrin, etc.), and (iii) peptides with an over-representation of some amino acids (proline rich, histidine rich, etc.). Most AMPs display hydrophobic and cationic properties, have a molecular mass below 25-30 kDa, and adopt an amphipathic structure (alpha-helix, beta-hairpin-like beta-sheet, beta-sheet, or alpha-helix/beta-sheet mixed structures) that is believed to be essential to their anti-microbial action. Interestingly, in recent years, a series of novel AMPs have been discovered as processed forms of large proteins. Despite the extreme diversity in their primary and secondary structures, all natural AMPs have the in vitro particularity to affect a large number of microorganisms (bacteria, fungi, yeast, virus, etc.) with identical or complementary activity spectra. This review focuses on AMPs forming alpha-helices, beta-hairpin-like beta-sheets, beta-sheets, or alpha-helix/beta-sheet mixed structures from invertebrate and vertebrate origins. These molecules show some promise for therapeutic use.

Neutrophil extracellular traps kill bacteria

Neutrophils engulf and kill bacteria when their antimicrobial granules fuse with the phagosome. Here, we describe that, upon activation, neutrophils release granule proteins and chromatin that together form extracellular fibers that bind Gram-positive and -negative bacteria. These neutrophil extracellular traps (NETs) degrade virulence factors and kill bacteria. NETs are abundant in vivo in experimental dysentery and spontaneous human appendicitis, two examples of acute inflammation. NETs appear to be a form of innate response that binds microorganisms, prevents them from spreading, and ensures a high local concentration of antimicrobial agents to degrade virulence factors and kill bacteria.

A protein with antimicrobial activity in the skin of Schlegel’s green tree frog Rhacophorus schlegelii (Rhacophoridae) identified as histone H2B

An extract of the skin of Schlegel's green tree frog, Rhacophorus schlegelii (Anura: Rhacophoridae), contained a protein that inhibited the growth of the Gram-negative bacterium Escherichia coli but was inactive against the Gram-positive bacterium Staphylococcus aureus. The protein was purified to near homogeneity by reverse-phase HPLC and amino acid sequence analysis of the products of an endoproteinase Glu-C digest identified the protein as histone H2B. The complete primary structure of the 125 amino acid residue Rhacophorus histone H2B was determined by nucleotide sequence analysis of a cloned cDNA encoding the protein. Mass spectrometry demonstrated that the protein isolated from the skin was not post-translationally modified. Histone fragments with antimicrobial activity were not identified in the Rhacophorus skin extract nor were cationic, alpha-helical antimicrobial peptides of the kind isolated from the skins of several other frog families. The data provide further evidence that histones play a role in the defense against microorganisms.

Hipposin, a histone-derived antimicrobial peptide in Atlantic halibut (Hippoglossus hippoglossus L.)

A novel 51-residue antimicrobial peptide (AMP) from the skin mucus of Atlantic halibut (Hippoglossus hippoglossus L.) was isolated using acid extraction, and cationic exchange and reversed phase chromatography. The complete amino acid sequence of the AMP, termed hipposin, was determined by automated Edman degradation and mass spectrometry to be SGRGKTGGKARAKAKTRSSRAGLQFPVGRVHRLLRKGNYAHRVGAGAPVYL. The N-terminal amino group was acetylated. The theoretical mass of hipposin was calculated to be 5458.4 Da, which was in good agreement with the mass of 5459 Da determined by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). Hipposin was shown to be derived from histone H2A by PCR amplifying the encoding sequences from Atlantic halibut genomic DNA. The peptide showed sequence similarity with the 39-mer AMP buforin I of Asian toad and the 19-mer AMP parasin I of catfish. Fifty of the fifty-one residues in hipposin were identical to the N-terminal region of histone H2A from rainbow trout. Hipposin showed strong antimicrobial activity against several Gram-positive and Gram-negative bacteria and activity could be detected down to hipposin concentrations of 0.3 microM (1.6 microg/ml). Hipposin without N-terminal acetylation was prepared by solid-phase peptide synthesis and shown to have the same antimicrobial activity as the natural acetylated peptide. Thus, hipposin is a new broad-spectrum histone-derived AMP found in the skin mucus of Atlantic halibut.

Antimicrobial peptide buforin I inhibits tissue factor-initiated coagulation

The enhanced extrinsic blood coagulation following septic shock often manifests cardiovascular complications. The upregulated monocytic tissue factor (mTF) was shown to be a primary contributor to the extrinsic hypercoagulation following acute bacterial endotoxin (LPS) infection. A single-stage clotting assay monitors TF-initiated coagulation. We herein demonstrate a novel anticoagulant activity of antimicrobial peptide Buforin I (BF I) in offsetting LPS-induced mTF hypercoagulation in THP-1 cells, which was confirmed in a cell-free in vitro model, showing that BF I effectively blocked rabbit brain thromboplastin (rbTF) procoagulant activity. Upon inclusion of 25 microM BF I into human plasma, the prolonged prothrombin time (PT) was consistent with the depressed TF-initiated coagulation. In a two-stage chromogenic assay monitoring S-2288 hydrolysis, BF I significantly inhibited not only mTF- but also rbTF-catalyzed FVII activation accompanied by the diminished FVIIa formation. The inhibition by BF I of FVII activation accounted for its novel anticoagulant activity in offsetting mTF-initiated hypercoagulation.

Histone H1: an antimicrobial protein of Atlantic salmon (Salmo salar)

Antimicrobial activity was detected in acid extracts of liver, intestine, and stomach of healthy Atlantic salmon (Salmo salar). An antimicrobial protein was isolated from salmon liver using acid extraction followed by ammonium sulfate precipitation, large-scale gel filtration chromatography, reverse-phase HPLC, and size exclusion HPLC. The salmon antimicrobial (SAM) protein was found to have a molecular mass of 20,734 Da by MALDI TOF mass spectrometry. Peptide mass fingerprinting and partial sequencing by tandem nanoelectrospray mass spectrometry identified the protein as histone H1. The protein had a minimal inhibitory concentration of 31 microg/mL against E. coli D31 in a plate clearing assay. The effect of the SAM protein on bacterial morphology was indistinguishable from that of (Ala-(8,13,18))-magainin II, as shown by scanning electron microscopy, which suggests that the protein disrupts E. coli membranes in a manner similar to that of most antimicrobial peptides. This protein may act as an antimicrobial in vivo through active secretion or by release from cells during infection-related apoptosis.

Antimicrobial peptides: properties and applicability

All organisms need protection against microorganisms, e. g. bacteria, viruses and fungi. For many years, attention has been focused on adaptive immunity as the main antimicrobial defense system. However, the adaptive immune system, with its network of humoral and cellular responses is only found in higher animals, while innate immunity is encountered in all living creatures. The turning point in the appreciation of the innate immunity was the discovery of antimicrobial peptides in the early eighties. In general these peptides act by disrupting the structural integrity of the microbial membranes. It has become clear that membrane-active peptides and proteins play a crucial role in both the innate and the adaptive immune system as antimicrobial agents. This review is focused on the functional and structural features of the naturally occurring antimicrobial peptides, and discusses their potential as therapeutics.