Pepsin-mediated processing of the cytoplasmic histone H2A to strong antimicrobial peptide buforin I

Short Antimicrobial Peptide Derived from the Venom Gland Transcriptome of Pamphobeteus verdolaga Increases Gentamicin Susceptibility of Multidrug-Resistant Klebsiella pneumoniae

Infectious diseases account for nine percent of annual human deaths, and the widespread emergence of antimicrobial resistances threatens to significantly increase this number in the coming decades. The prospect of antimicrobial peptides (AMPs) derived from venomous animals presents an interesting alternative for developing novel active pharmaceutical ingredients (APIs). Small, cationic and amphiphilic peptides were predicted from the venom gland transcriptome of Pamphobeteus verdolaga using a custom database of the arthropod's AMPs. Ninety-four candidates were chemically synthesized and screened against ATCC® strains of Escherichia coli and Staphylococcus aureus. Among them, one AMP, named PvAMP66, showed broad-spectrum antimicrobial properties with selectivity towards Gram-negative bacteria. It also exhibited activity against Pseudomonas aeruginosa, as well as both an ATCC® and a clinically isolated multidrug-resistant (MDR) strain of K. pneumoniae. The scanning electron microscopy analysis revealed that PvAMP66 induced morphological changes of the MDR K. pneumoniae strain suggesting a potential "carpet model" mechanism of action. The isobologram analysis showed an additive interaction between PvAMP66 and gentamicin in inhibiting the growth of MDR K. pneumoniae, leading to a ten-fold reduction in gentamicin's effective concentration. A cytotoxicity against erythrocytes or peripheral blood mononuclear cells was observed at concentrations three to thirteen-fold higher than those exhibited against the evaluated bacterial strains. This evidence suggests that PvAMP66 can serve as a template for the development of AMPs with enhanced activity and deserves further pre-clinical studies as an API in combination therapy.

Revealing Natural Intracellular Peptides in Gills of Seahorse Hippocampus reidi

The seahorse is a marine teleost fish member of the Syngnathidae family that displays a complex variety of morphological and reproductive behavior innovations and has been recognized for its medicinal importance. In the Brazilian ichthyofauna, the seahorse Hippocampus reidi is among the three fish species most used by the population in traditional medicine. In this study, a protocol was performed based on fast heat inactivation of proteases plus liquid chromatography coupled to mass spectrometry to identify native peptides in gills of seahorse H. reidi. The MS/MS spectra obtained from gills allowed the identification of 1080 peptides, of which 1013 peptides were present in all samples and 67 peptide sequences were identified in an additional LC-MS/MS run from an alkylated and reduced pool of samples. The majority of peptides were fragments of the internal region of the amino acid sequence of the precursor proteins (67%), and N- and C-terminal represented 18% and 15%, respectively. Many peptide sequences presented ribosomal proteins, histones and hemoglobin as precursor proteins. In addition, peptide fragments from moronecidin-like protein, described with antimicrobial activity, were found in all gill samples of H. reidi. The identified sequences may reveal new bioactive peptides.

Functional characterization of a histone H2A derived antimicrobial peptide HARRIOTTIN-1 from sicklefin chimaera, Neoharriotta pinnata

Antimicrobial peptides (AMPs) are gene encoded short peptides which play an important role in the innate immunity of almost all living organisms ranging from bacteria to mammals. Histones play a very important role in defense as precursors to bioactive peptides. The present study is an attempt to decipher the antimicrobial activity of a histone H2A derived peptide, Harriottin-1 from sicklefin chimaera, Neoharriotta pinnata. Analysis in silico predicted the molecule with potent antibacterial and anticancer property. The Harriottin-1 was recombinantly produced and the recombinant peptide rHar-1 demonstrated potent antibacterial activity at 25 μM besides anticancer activity. The study strongly suggests the importance of histone H2A derived peptides as a model for the design and synthesis of potent peptide drugs.

Dual Roles of Extracellular Histone H3 in Host Defense: Its Differential Regions Responsible for Antimicrobial and Cytotoxic Properties and Their Modes of Action

Extracellular histones play a dual role—antimicrobial and cytotoxic—in host defense. In this study, we evaluated the antimicrobial and cytotoxic activities of histone H3 and identified the responsible molecular regions for these properties. Broth microdilution assays indicated that histone H3 exhibits growth inhibitory activity against not only Gram-negative and -positive bacteria but also fungi. Observations under scanning electron microscopy (SEM) revealed that histone H3 induced morphological abnormalities on the cell surface of a wide range of reference pathogens. MTT assays and SEM observations indicated that histone H3 has strong cytotoxic and cell lytic effects on mammalian normal, immortal, and tumor cell lines. Assays using synthetic peptides corresponding to fragments 1–34 (H3DP1), 35–68 (H3DP2), 69–102 (H3DP3), and 103–135 (H3DP4) of histone H3 molecule demonstrated that its antimicrobial activity and cytotoxicity are elicited by the H3DP2 and H3DP3 protein regions, respectively. Enzyme-linked endotoxin binding assays indicated that histones H3 and H3DP1, H3DP2, and H3DP4, but not H3DP3, exhibited high affinities toward lipopolysaccharide and lipoteichoic acid. Our findings are expected to contribute to the development of new histone H3-based peptide antibiotics that are not cytotoxic.

Buforin I an alternative to conventional antibiotics: Evaluation of the antimicrobial properties, stability, and safety

Cationic antimicrobial peptides are being developed as a promising class of antimicrobial sub-stances. The introduction of a new antibiotic component requires a comprehensive study of its properties so that it can be relied upon to continue laboratory procedures and clinical trials on laboratory animals or human volunteers. Antimicrobial activity of buforin I was evaluated against 15 of the most important pathogenic bacterial and fungal strains. This was followed by assessing anti-biofilm activity, time-dependent inhibitory, thermal stability, plas-ma stability, hemolysis, and cytotoxic activities. The range of obtained MICs was between 4 and 16 μg/mL. The most resistant and most sensitive microbial strains were S. salivarius and C. perfringens, respectively. Buforin I not only inhibited biofilm formation, but also showed a high biofilm radiation activity. Buforin I was stable in human plasma and also at different temperatures including 40, 60, and 80 °C. Although no significant anti-cancer properties were observed for buforin I, the lack of cytotoxicity as well as the lack of hemolytic activity confirm its safety. The high therapeutic index indicated that buforin I has a considerable pharmaceutical potential and can be a reasonable candidate to replace antibiotics or administered in combination with antibiotics to increase the effectiveness as well as reduce the dose of antibiotics.

Interplay between membrane active host defense peptides and heme modulates their assemblies and in vitro activity

In the emerging era of antimicrobial resistance, the susceptibility to co-infections of patients suffering from either acquired or inherited hemolytic disorders can lead to dramatic increase in mortality rates. Closely related, heme liberated during hemolysis is one of the major sources of iron, which is vital for both host and invading microorganisms. While recent intensive research in the field has demonstrated that heme exerts diverse local effects including impairment of immune cells functions, it is almost completely unknown how it may compromise key molecules of our innate immune system, such as antimicrobial host defense peptides (HDPs). Since HDPs hold great promise as natural therapeutic agents against antibiotic-resistant microbes, understanding the effects that may modulate their action in microbial infection is crucial. Here we explore how hemin can interact directly with selected HDPs and influence their structure and membrane activity. It is revealed that induced helical folding, large assembly formation, and altered membrane activity is promoted by hemin. However, these effects showed variations depending mainly on peptide selectivity toward charged lipids, and the affinity of the peptide and hemin to lipid bilayers. Hemin-peptide complexes are sought to form semi-folded co-assemblies, which are present even with model membranes resembling mammalian or bacterial lipid compositions. In vitro cell-based toxicity assays supported that toxic effects of HDPs could be attenuated due to their assembly formation. These results are in line with our previous findings on peptide-lipid-small molecule systems suggesting that small molecules present in the complex in vivo milieu can regulate HDP function. Inversely, diverse effects of endogenous compounds could also be manipulated by HDPs.

Evaluation of Antimicrobial Activity of Buforin I and Nisin and Synergistic Effect of the Combination of them as a Novel Antimicrobial Preservative

One of the most effective methods for increasing the antimicrobial activity of a substance is to combine it with one or more other antimicrobial agents. The aim of the present study was to evaluate the antimicrobial effect of buforin I and nisin alone and investigate the synergistic action of these compounds against the most important food spoilage microorganisms in clouding B. subtilis, S. epidermidis, L. innocua, E. coli, S. Enteritidis, A. oryzae, R. glutinis and G. candidum. The results of MIC and MBC/MFC examinations showed that buforin I had higher antimicrobial activity than nisin on all the microbial strains used in this study (p≤0.5). E.coli was the most resistant to both antimicrobial agents, while Listeria innocua and Staphylococcus epidermidis were the most sensitive to nisin and buforin I, respectively. The results of synergistic interaction between buforin I and nisin indicated that the combination of buforin I and nisin on B. subtilis, S. epidermidis and A. oryzae showed synergistic effect, while it had no effect on S. Enteritidis and Geotrichum candidum. The combination of buforin I and nisin showed partial synergistic effect on Listeria innocua, Escherichia coli, Rhodotorula glutinis. Assessment of viability of the microorganisms under the antimicrobial agents alone and in combination with each other at MICs and FICs indicated that use of these antimicrobial agents in combination enhances antimicrobial activity at lower concentrations of both agents. The present study investigated the antimicrobial properties of buforin I against food spoilage microorganisms for the first time and suggests that its use alone or in combination with nisin may provide a clear horizon for the application of antimicrobial peptides as natural preservatives. Thus, the combination of antimicrobial peptides and traditional antimicrobial food preservative could be a promising option for the prevention of contamination, spoilage, and infestation of food and beverage products.

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.

Putative Antimicrobial Peptides of the Posterior Salivary Glands from the Cephalopod Octopus vulgaris Revealed by Exploring a Composite Protein Database

Cephalopods, successful predators, can use a mixture of substances to subdue their prey, becoming interesting sources of bioactive compounds. In addition to neurotoxins and enzymes, the presence of antimicrobial compounds has been reported. Recently, the transcriptome and the whole proteome of the Octopus vulgaris salivary apparatus were released, but the role of some compounds—e.g., histones, antimicrobial peptides (AMPs), and toxins—remains unclear. Herein, we profiled the proteome of the posterior salivary glands (PSGs) of O. vulgaris using two sample preparation protocols combined with a shotgun-proteomics approach. Protein identification was performed against a composite database comprising data from the UniProtKB, all transcriptomes available from the cephalopods’ PSGs, and a comprehensive non-redundant AMPs database. Out of the 10,075 proteins clustered in 1868 protein groups, 90 clusters corresponded to venom protein toxin families. Additionally, we detected putative AMPs clustered with histones previously found as abundant proteins in the saliva of O. vulgaris. Some of these histones, such as H2A and H2B, are involved in systemic inflammatory responses and their antimicrobial effects have been demonstrated. These results not only confirm the production of enzymes and toxins by the O. vulgaris PSGs but also suggest their involvement in the first line of defense against microbes.

Gastrointestinal stress as innate defence against microbial attack

The human gastrointestinal (GI) tract has been bestowed with the most difficult task of protecting the underlying biological compartments from the resident commensal flora and the potential pathogens in transit through the GI tract. It has a unique environment in which several defence tactics are at play while maintaining homeostasis and health. The GI tract shows myriad number of environmental extremes, which includes pH variations, anaerobic conditions, nutrient limitations, elevated osmolarity etc., which puts a check to colonization and growth of nonfriendly microbial strains. The GI tract acts as a highly selective barrier/platform for ingested food and is the primary playground for balance between the resident and uninvited organisms. This review focuses on antimicrobial defense mechanisms of different sections of human GI tract. In addition, the protective mechanisms used by microbes to combat the human GI defence systems are also discussed. The ability to survive this innate defence mechanism determines the capability of probiotic or pathogen strains to confer health benefits or induce clinical events respectively.

Overview of Host Defense Peptides and Their Applications for Plastic and Reconstructive Surgeons

BACKGROUND

Host defense peptides are a family of endogenous short peptides that are found in all living beings and play a critical role in innate immunity against infection.

METHODS

A nonsystematic review of host defense peptides was conducted with specific interest in properties and applications relevant to plastic and reconstructive surgery.

RESULTS

In addition to their direct antimicrobial actions against pathogens, including multidrug-resistant bacteria, they also demonstrate important functions in immunomodulation, tumor cell lysis, and tissue regeneration. These properties have made them a topic of clinical interest for plastic surgeons because of their potential applications as novel antibiotics, wound healing medications, and cancer therapies. The rising clinical interest has led to a robust body of literature describing host defense peptides in great depth and breadth. Numerous mechanisms have been observed to explain their diverse functions, which rely on specific structural characteristics. However, these peptides remain mostly experimental, with limited translation to clinical practice because of numerous failures to achieve acceptable results in human trials.

CONCLUSIONS

Despite the broad ranging potential of these peptides for use in the field of plastic and reconstructive surgery, they are rarely discussed in the literature or at scientific meetings. In this review, the authors provide a summary of the background, structure, function, bacterial resistance, and clinical applications of host defense peptides with the goal of stimulating host defense peptide-based innovation within the field of plastic and reconstructive surgery.

Cystic Fibrosis Defective Response to Infection Involves Autophagy and Lipid Metabolism

Cystic fibrosis (CF) is a hereditary disease, with 70% of patients developing a proteinopathy related to the deletion of phenylalanine 508. CF is associated with multiple organ dysfunction, chronic inflammation, and recurrent lung infections. CF is characterized by defective autophagy, lipid metabolism, and immune response. Intracellular lipid accumulation favors microbial infection, and autophagy deficiency impairs internalized pathogen clearance. Myriocin, an inhibitor of sphingolipid synthesis, significantly reduces inflammation, promotes microbial clearance in the lungs, and induces autophagy and lipid oxidation. RNA-seq was performed in Aspergillusfumigatus-infected and myriocin-treated CF patients’ derived monocytes and in a CF bronchial epithelial cell line. Fungal clearance was also evaluated in CF monocytes. Myriocin enhanced CF patients’ monocytes killing of A. fumigatus. CF patients’ monocytes and cell line responded to infection with a profound transcriptional change; myriocin regulates genes that are involved in inflammation, autophagy, lipid storage, and metabolism, including histones and heat shock proteins whose activity is related to the response to infection. We conclude that the regulation of sphingolipid synthesis induces a metabolism drift by promoting autophagy and lipid consumption. This process is driven by a transcriptional program that corrects part of the differences between CF and control samples, therefore ameliorating the infection response and pathogen clearance in the CF cell line and in CF peripheral blood monocytes.

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.

High-Throughput Identification of Putative Antimicrobial Peptides from Multi-Omics Data of the Lined Seahorse (Hippocampus erectus)

Lined seahorse (Hippocampus erectus), the most widely cultivated seahorse in China, has been in short supply because of its important medicinal value; meanwhile, unnatural deaths caused by various diseases (especially enteritis) have limited their practical large-scale aquaculture. Antimicrobial peptides (AMPs), as the best alternative to antibiotics, have been extensively applied in agricultural practices. In this study, we identified 290 putative AMP sequences from our previously published genome and transcriptome data of the lined seahorse. Among them, 267 are novel, and 118 were validated by our proteome data generated in the present study. It seems that there is a tissue preference in the distribution of AMP/AMP precursor transcripts, such as lectins in the male pouch. In addition, their transcription levels usually varied during development. Interestingly, the representative lectins kept extremely high levels at the pre-pregnancy stage while at relatively lower levels at other stages. Especially Lectin25, with the highest transcription levels and significant developmental changes, has been reported to be involved in seahorse and human pregnancy. The comparison of transcriptome data between one-day and three-month juveniles indicated that Hemoglobin2 (Hemo2) was significantly upregulated in the body, haslet, and brain. Our proteome data of female and male individuals revealed three putative AMP precursors with sexual specificity, including two male-biased cyclin-dependent kinases (CDK-like16 and CDK-like23) and one female-biased bovine pancreatic trypsin inhibitor 2 (BPTI2). In conclusion, our present high-throughput identification of putative AMP sequences from multi-omics (including genomics, transcriptomics, and proteomics) data provides an overview of AMPs in the popular lined seahorse, which lays a solid foundation for further development of AMP-based fish food additives and human drugs.

Production and Function of Different Regions from Mytichitin-1 of Mytilus coruscus

Chitinase is an important enzyme for many physiological processes. Mytichitin-1 is a chitinase-like protein in Mytilus coruscus, and its C-terminal 55-AA fragment (mytichitin-CB) is a novel antimicrobial peptide, suggesting a new immune process in which chitinase is involved; mytichtin-1 may have various forms in the different biological processes of M. coruscus. Thus, the study of mytichitin-1 will be helpful for understanding the mechanism of mussel immune biology and the functional diversity of chitinase. In this study, mytichitin-1 was recombinantly expressed with different lengths, full-length mytichtin-1 (rMchi-F) and the N-terminal region (rMchi-N) in Escherichia coli BL21 with codon optimization. The results of SDS-PAGE, Western blotting, and mass spectrometry confirmed that the two forms of mytichitin-1 had been successfully recombinant expressed with a yield of 40 mg purified enzyme per L culture. In addition, the 55-AA fragment of mytichitin-CB was chemically synthesized (sMchi-CB). After purification and oxidation, the functions of the three protein products were analysed, including chitin degradation, chitin binding, and antimicrobial activities. Both rMchi-F and rMchi-N displayed enzymatic activity with the optimum pH of 4.0 and optimum temperature of 40 °C, and rMchi-N showed a stronger activity than rMchi-F. Enzymatic activities of rMchi-F and rMchi-N were stimulated by the metal ions Fe²⁺, Ba²⁺, and Na⁺ and partially inhibited by Cu²⁺, Ni²⁺ and Zn²⁺. rMchi-F, rMchi-N, and sMchi-CB had the ability to combine with colloid chitin. The antimicrobial activities of these proteins were tested against bacteria and fungi, and the results indicated the strongest activity for sMchi-CB and the weakest activity for rMchi-N. Using a prepared anti-rMchi-F polyclonal antibody, immunohistochemistry and immunoprecipitation were performed and the results revealed the location of mytichitin-1 in mantle, digestive gland and blood cells. In addition, two forms of mytichitin-1, mytichitin-CB (6 kD) and full-length mytichitin-1 (48 kD), were detected, and a 35 kD protein was identified as the third form of mytichitin-1, existing in various tissues of M. coruscus. These findings suggest that mytichitin-1 may play different roles, with at least three forms, in different M. coruscus tissues.

Acellular vascular matrix grafts from human placenta chorion: Impact of ECM preservation on graft characteristics, protein composition and in vivo performance

Small diameter vascular grafts from human placenta, decellularized with either Triton X-100 (Triton) or SDS and crosslinked with heparin were constructed and characterized. Graft biochemical properties, residual DNA, and protein composition were evaluated to compare the effect of the two detergents on graft matrix composition and structural alterations. Biocompatibility was tested in vitro by culturing the grafts with primary human macrophages and in vivo by subcutaneous implantation of graft conduits (n = 7 per group) into the flanks of nude rats. Subsequently, graft performance was evaluated using an aortic implantation model in Sprague Dawley rats (one month, n = 14). In situ graft imaging was performed using MRI angiography. Retrieved specimens were analyzed by electromyography, scanning electron microscopy, histology and immunohistochemistry to evaluate cell migration and the degree of functional tissue remodeling. Both decellularization methods resulted in grafts of excellent biocompatibility in vitro and in vivo, with low immunogenic potential. Proteomic data revealed removal of cytoplasmic proteins with relative enrichment of ECM proteins in decelluarized specimens of both groups. Noteworthy, LC-Mass Spectrometry analysis revealed that 16 proteins were exclusively preserved in Triton decellularized specimens in comparison to SDS-treated specimens. Aortic grafts showed high patency rates, no signs of thrombus formation, aneurysms or rupture. Conduits of both groups revealed tissue-specific cell migration indicative of functional remodeling. This study strongly suggests that decellularized allogenic grafts from the human placenta have the potential to be used as vascular replacement materials. Both detergents produced grafts with low residual immunogenicity and appropriate mechanical properties. Observed differences in graft characteristics due to preservation method had no impact on successful in vivo performance in the rodent model.

A truncated Sph12-38 with potent antimicrobial activity showing resistance against bacterial challenge in Oryzias melastigma

Antimicrobial peptides (AMPs) represent an efficient part of innate immunity and are found in a variety of life. Among them Histone 2A (H2A), as a promising class of AMPs, attracts great attention, but the in vivo mechanism of H2A derived AMP is still less known. Based on the acquisition of Sphistin, a synthetic 38-amino acid H2A derived peptide from Scylla paramamosain, as reported in our previous study, was truncated into three short fragments (Sph_12-38, Sph_20-38 and Sph_30-38) and further investigated for its possible functional domains. The antimicrobial activities of these analogs against different Gram-positive bacteria, Gram-negative bacteria and fungi were illustrated. Among the analogs, Sph_12-38 showed a stronger activity with a much lower minimum inhibitory concentration (3 μM) against Staphylococcus aureus, Corynebacterium glutamicum, Micrococcus lysodeikticus Fleming, Bacillus subtilis, Pseudomonas fluorescens, Aeromonas hydrophila and A. sobria in comparison with the reported Sphistin. A leakage of intracellular content was described in E. coli treated with Sph_12-38. Unlike Sphistin which mainly disrupts the membrane integrity, Sph_12-38 could also combine the A. sobria genomic DNA with a minimum concentration of 6 μM and was located intracellularly in cells observed under confocal laser scanning microscope imaging. In comparison with the control group of Oryzias melastigma injected with A. sobria alone, the group treated with a mixture of Sph_12-38 and A. sobria showed a higher survival rate 7 days post-injection. Furthermore, in a pretreatment assay at 6 h, a higher survival rate was observed in the group injected with the mixture of Sph_12-38 and A. sobria. Taken together, the synthetic peptide of Sph_12-38 had a potent antimicrobial activity against bacteria. However, Sph_12-38 had no cytotoxicity towards the hemolymph of S. paramamosain. Our study suggested that, as with Sph_12-38, the H2A derived peptides were more likely prone to exert their activities in vivo through the truncated fragments while defending against different species of pathogens.

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.

A novel role for β2-microglobulin: a precursor of antibacterial chemokine in respiratory epithelial cells

We analyzed a panel of cationic molecules secreted in the culture medium of human respiratory epithelial cells (REC) upon activation by IL-1β and different pathogen-associated molecular patterns. A 9 kDa fragment derived from β2-microglobulin (B2M) was identified and named shed 9 kDa B2M (sB2M-9). The primary structure of sB2M-9 was revealed to increase its pI value that potentially could play an important role in innate defense. sB2M-9 exhibits antibacterial activity against Gram positive Staphylococcus aureus (SA) but not against Gram negative Klebsiella pneumonia (KP). Upon its binding to SA, sB2M-9 induces clumps, a phenomenon not observed with B2M. Migration of THP-1 monocytes exposed to SA clumps was significantly greater than that to SA without clumps. sB2M-9 binds to SA, more likely as a chemokine, to facilitate THP-1 migration. As a whole, we demonstrated that REC release a novel chemokine with antibacterial activity that is shed from B2M to facilitate THP-1 migration.

The New Antimicrobial Peptide SpHyastatin from the Mud Crab Scylla paramamosain with Multiple Antimicrobial Mechanisms and High Effect on Bacterial Infection

SpHyastatin was first identified as a new cationic antimicrobial peptide in hemocytes of the mud crab Scylla paramamosain. Based on the amino acid sequences deduced, it was predicted that this peptide was composed of two different functional domains, a proline-rich domain (PRD) and a cysteine-rich domain (CRD). The recombinant product of SpHyastatin displayed potent antimicrobial activities against the human pathogen Staphylococcus aureus and the aquatic animal pathogens Aeromonas hydrophila and Pseudomonas fluorescens. Compared with the CRD of SpHyastatin, the PRD presented better antimicrobial and chitin binding activities, but both regions were essential for allowing SpHyastatin complete antimicrobial activity. The binding properties of SpHyastatin to different microbial surface molecules suggested that this might be an initial and crucial step for performing its antimicrobial activities. Evaluated using propidium iodide uptake assays and scanning electron microscopy images, the antimicrobial mechanism of SpHyastatin was found to be prone to disrupt cell membrane integrity. Interestingly, SpHyastatin exerted its role specifically on the surface of S. aureus and Pichia pastoris whereas it directly killed P. fluorescens through simultaneous targeting the membrane and the cytoplasm, indicating that SpHyastatin could use different antimicrobial mechanisms to kill different species of microbes. As expected, the recombinant SpHyastatin increased the survival rate of crabs challenged with Vibrio parahaemolyticus. In addition, SpHyastatin could modulate some V. parahaemolyticus-responsive genes in S. paramamosain.

Mechanism study on a new antimicrobial peptide Sphistin derived from the N-terminus of crab histone H2A identified in haemolymphs of Scylla paramamosain

Histone H2A is known to participate in host immune defense through generating special antimicrobial peptides (AMPs), for which it has been an interesting research focus to characterize this kind of peptides in vertebrates and invertebrates. Although thousands of AMPs have been reported in variety of life species, only several AMPs are known in crabs and in particular no H2A-derived AMP has yet been reported. In the present study, a 38-amino acid peptide with antimicrobial activity was determined based on the sequence analysis of a histone H2A identified from the mud crab Scylla paramamosain. The histone H2A derived peptide was an AMP-like molecule and designated as Sphistin. Sphistin showed typical features of AMPs such as amphiphilic α-helical second structrue and positive charge net. The synthetic Sphistin exerted high antimicrobial activity against Gram-positive, Gram-negative bacteria and yeast, among which Aeromonas hydrophila, Pseudomonas fluorescens and Pseudomonas stutzeri are important aquatic pathogens. Leakage of the cell content and disruption of the cell surface were observed in bacterial cells treated with Sphistin using scanning electron microscopy. It was proved that the increasing cytoplasmic membrane permeability of Escherichia coli was caused by Sphistin. Further observation under confocal microscopy showed that Sphistin could combine onto the membrane of Staphylococcus aureus, E. coli MC1061 and Pichia pastoris but not translocate into the cytoplasm. Moreover, the affinity of Sphistin with either LPS or LTA was also testified that there was an interaction between Sphistin and cell membrane. Thus, the antimicrobial mechanism of this peptide likely exerted via adsorption and subsequently permeabilization of the bacterial cell membranes other than penetrating cell membrane. In addition, synthetic Sphistin exhibited no cytotoxicity to primary cultured crab haemolymphs and mammalian cells even at a high concentration of 100 μg/mL for 24 h. This is the first report of a histone-derived Sphistin identified from S. paramamosain with a specific antimicrobial activity and mechanism, which could be a new candidate for future application in aquaculture and veterinary medicine.

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.

Isolation, identification and functional profile of excretory-secretory peptides from Onchocerca ochengi

Parasitic helminths excrete or secrete a variety of functional molecules into the internal milieu of their mammalian hosts and arthropod vectors which reveal distinct immunomodulatory and other biological activities. We identified and initially characterized the low molecular weight peptide composition of the secretome from the filarial parasite Onchocerca ochengi. A total of 85 peptides were purified by liquid chromatography and further characterized by mass spectrometry. 72 of these peptides were derived from already described Onchocerca proteins and 13 peptide sequences are included in the sequence of uncharacterized proteins. Three peptides, similar to host defense peptides, revealed antibacterial activity. The present analysis confirms the putative involvement of low molecular weight compounds in the parasite-host cross-talk.

Sequence diversity and evolution of antimicrobial peptides in invertebrates

Antimicrobial peptides (AMPs) are evolutionarily ancient molecules that act as the key components in the invertebrate innate immunity against invading pathogens. Several AMPs have been identified and characterized in invertebrates, and found to display considerable diversity in their amino acid sequence, structure and biological activity. AMP genes appear to have rapidly evolved, which might have arisen from the co-evolutionary arms race between host and pathogens, and enabled organisms to survive in different microbial environments. Here, the sequence diversity of invertebrate AMPs (defensins, cecropins, crustins and anti-lipopolysaccharide factors) are presented to provide a better understanding of the evolution pattern of these peptides that play a major role in host defense mechanisms.

Characterization of a novel antimicrobial peptide with chitin-biding domain from Mytilus coruscus

Using reverse phase high performance liquid chromatography (RP-HPLC), a novel antimicrobial peptide with 55 amino acid residues was isolated from the hemolymph of Mytilus coruscus. This new antimicrobial peptide displays predominant antimicrobial activity against fungi and Gram-positive bacteria. The molecular mass and the N-terminal sequence of this peptide were analyzed by Mass Spectrometry and Edman degradation, respectively. This antimicrobial peptide, with molecular mass of 6621.55 Da, is characterized by a chitin-biding domain and by 6 Cysteine residues engaged in three intra-molecular disulfide bridges. The full-length of cDNA sequence of this new peptide was obtained by rapid amplification of cDNA ends (RACE) and the encoded precursor was turn out to be a chitotriosidase-like protein. Therefore, we named the precursor with mytichitin-1 and the new antimicrobial peptide (designated as mytichitin-CB) is the carboxyl-terminal part of mytichitin-1. The mRNA transcripts of mytichitin-1 are mainly detected in gonad and the expression level of mytichitin-1 in gonad was up-regulated and reached the highest level at 12 h after bacterial challenge, which was 9-fold increase compared to that of the control group. These results indicated that mytichitin-1 was involved in the host immune response against bacterial infection and might contribute to the clearance of invading bacteria.

Environmental responses mediated by histone variants

Fluctuations in the ambient environment can trigger chromatin disruptions, involving replacement of nucleosomes or exchange of their histone subunits. Unlike canonical histones, which are available only during S-phase, replication-independent histone variants are present throughout the cell cycle and are adapted for chromatin repair. The H2A.Z variant mediates responses to environmental perturbations including fluctuations in temperature and seasonal variation. Phosphorylation of histone H2A.X rapidly marks double-strand DNA breaks for chromatin repair, which is mediated by both H2A and H3 histone variants. Other histones are used as weapons in conflicts between parasites and their hosts, which suggests broad involvement of histone variants in environmental responses beyond chromatin repair.

Differential mode of antimicrobial actions of arginine-rich and lysine-rich histones against Gram-positive Staphylococcus aureus

We previously reported the activities and modes of action of arginine (Arg)-rich histones H3 and H4 against Gram-negative bacteria. In the present study, we investigated the properties of the Arg-rich histones against Gram-positive bacteria in comparison with those of lysine (Lys)-rich histone H2B. In a standard microdilution assay, calf thymus histones H2B, H3, and H4 showed growth inhibitory activity against Staphylococcus aureus with minimum effective concentration values of 4.0, 4.0, and 5.6 μM, respectively. Laser confocal microscopic analyses revealed that both the Arg-rich and Lys-rich histones associated with the surface of S. aureus. However, while the morphology of S. aureus treated with histone H2B appeared intact, those treated with the histones H3 and H4 closely resembled each other, and the cells were blurred. Electrophoretic mobility shift assay results revealed these histones have binding affinity to lipoteichoic acid (LTA), one of major cell surface components of Gram-positive bacteria. Scanning electron microscopic analyses demonstrated that while histone H2B elicited no obvious changes in cell morphology, histones H3 and H4 disrupted the cell membrane structure with bleb formation in a manner similar to general antimicrobial peptides. Consequently, our results suggest that bacterial cell surface LTA initially attracts both the Arg- and Lys-rich histones, but the modes of antimicrobial action of these histones are different; the former involves cell membrane disruption and the latter involves the cell integrity disruption.

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.

Rifaximin-mediated changes to the epithelial cell proteome: 2-D gel analysis

Rifaximin is a semi-synthetic rifamycin derivative that is used to treat different conditions including bacterial diarrhea and hepatic encephalopathy. Rifaximin is of particular interest because it is poorly adsorbed in the intestines and has minimal effect on colonic microflora. We previously demonstrated that rifaximin affected epithelial cell physiology by altering infectivity by enteric pathogens and baseline inflammation suggesting that rifaximin conferred cytoprotection against colonization and infection. Effects of rifaximin on epithelial cells were further examined by comparing the protein expression profile of cells pretreated with rifaximin, rifampin (control antibiotic), or media (untreated). Two-dimensional (2-D) gel electrophoresis identified 36 protein spots that were up- or down-regulated by over 1.7-fold in rifaximin treated cells compared to controls. 15 of these spots were down-regulated, including annexin A5, intestinal-type alkaline phosphatase, histone H4, and histone-binding protein RbbP4. 21 spots were up-regulated, including heat shock protein (HSP) 90α and fascin. Many of the identified proteins are associated with cell structure and cytoskeleton, transcription and translation, and cellular metabolism. These data suggested that in addition to its antimicrobial properties, rifaximin may alter host cell physiology that provides cytoprotective effects against bacterial pathogens.

Characterization of Histone H2A Derived Antimicrobial Peptides, Harriottins, from Sicklefin Chimaera Neoharriotta pinnata (Schnakenbeck, 1931) and Its Evolutionary Divergence with respect to CO1 and Histone H2A

Antimicrobial peptides (AMPs) are humoral innate immune components of fishes that provide protection against pathogenic infections. Histone derived antimicrobial peptides are reported to actively participate in the immune defenses of fishes. Present study deals with identification of putative antimicrobial sequences from the histone H2A of sicklefin chimaera, Neoharriotta pinnata. A 52 amino acid residue termed Harriottin-1, a 40 amino acid Harriottin-2, and a 21 mer Harriottin-3 were identified to possess antimicrobial sequence motif. Physicochemical properties and molecular structure of Harriottins are in agreement with the characteristic features of antimicrobial peptides, indicating its potential role in innate immunity of sicklefin chimaera. The histone H2A sequence of sicklefin chimera was found to differ from previously reported histone H2A sequences. Phylogenetic analysis based on histone H2A and cytochrome oxidase subunit-1 (CO1) gene revealed N. pinnata to occupy an intermediate position with respect to invertebrates and vertebrates.

A novel role for lipid droplets in the organismal antibacterial response

We previously discovered histones bound to cytosolic lipid droplets (LDs); here we show that this forms a cellular antibacterial defense system. Sequestered on droplets under normal conditions, in the presence of bacterial lipopolysaccharide (LPS) or lipoteichoic acid (LTA), histones are released from the droplets and kill bacteria efficiently in vitro. Droplet-bound histones also function in vivo: when injected into Drosophila embryos lacking droplet-bound histones, bacteria grow rapidly. In contrast, bacteria injected into embryos with droplet-bound histones die. Embryos with droplet-bound histones displayed more than a fourfold survival advantage when challenged with four different bacterial species. Our data suggests that this intracellular antibacterial defense system may function in adult flies, and also potentially in mice.DOI:http://dx.doi.org/10.7554/eLife.00003.001.

Pathophysiology, staging and therapy of severe sepsis in baboon models

We review our baboon models of Escherichia coli sepsis that mimic, respectively, the shock/disseminated intravascular coagulation (DIC) and organ failure variants of severe sepsis, and analyse the pathophysiologic processes that are unique to each. The multi-stage, multi-factorial characteristics of severe sepsis develop as a result of the initial insult, which - depending on its intensity - activates components of the intravascular compartment leading to overwhelming shock/DIC; or initiates a sequence of events involving both the intra- and extravascular (tissues) compartments that lead to organ failure. In the latter case, the disorder passes through two stages: an initial inflammatory/coagulopathic intravascular first stage triggered by E. coli, followed by an extravascular second stage, involving components unique to each organ and triggered by ischemia/reperfusion (oxidative stress and histone release). Although a myriad of overlapping cellular and molecular components are involved, it is the context in which these components are brought into play that determine whether shock/DIC or organ failure predominate. For example, inflammatory and thrombotic responses amplified by thrombin in the first case whereas similar responses are amplified by complement activation products in the second. Rather than blocking specific mediators, we found that attenuation of the thrombin and complement amplification pathways can effectively reverse the shock/DIC and organ failure exhibited by the LD(100) and LD(50) E. coli models of severe sepsis, respectively. Translation of these concepts to successful intervention in the respective baboon models of E. coli sepsis and the application to their clinical counterparts is described.

Identification and Molecular Characterization of Molluskin, a Histone-H2A-Derived Antimicrobial Peptide from Molluscs

Antimicrobial peptides are humoral innate immune components of molluscs that provide protection against pathogenic microorganisms. Among these, histone-H2A-derived antimicrobial peptides are known to actively participate in host defense responses of molluscs. Present study deals with identification of putative antimicrobial sequences from the histone-H2A of back-water oyster Crassostrea madrasensis, rock oyster Saccostrea cucullata, grey clam Meretrix casta, fig shell Ficus gracilis, and ribbon bullia Bullia vittata. A 75 bp fragment encoding 25 amino acid residues was amplified from cDNA of these five bivalves and was named “Molluskin.” The 25 amino acid peptide exhibited high similarity to previously reported histone-H2A-derived AMPs from invertebrates indicating the presence of an antimicrobial sequence motif. Physicochemical properties of the peptides are in agreement with the characteristic features of antimicrobial peptides, indicating their potential role in innate immunity of molluscs.

Defending the cornea with antibacterial fragments of keratin

In addition to its role in refraction, the cornea forms a barrier between the eye and environmental and infectious insults. Corneal infections are surprisingly rare, suggesting that multiple aspects of the immune system are at play in mediating protection. In this issue of the JCI, Tam et al. describe the unexpected role of a structural protein, cytokeratin 6A, in this process.

Identification of a histone derived, putative antimicrobial peptide Himanturin from round whip ray Himantura pastinacoides and its phylogenetic significance

Histone H2A participates in host defense responses by producing antimicrobial peptides (AMPs). The present study deals with identification of a putative antimicrobial sequence, Himanturin from the histone H2A of Round Whip Ray, Himantura pastinacoides. A 204 bp fragment encoding 68 amino acid residues was amplified from cDNA of Round Whip Ray, H. pastinacoides. Himanturin exhibited high similarity to previously reported histone H2A derived AMPs indicating the presence of an antimicrobial sequence motif. Physicochemical properties of Himanturin suggest it to be a potential antimicrobial candidate.

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.

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.

Identification of novel host defense peptides and the absence of alpha-defensins in the bovine genome

Host defense peptides (historically called antimicrobial peptides, AMPs) are key components in the mammalian innate immune system, and are responsible for both direct killing and immunomodulatory effects in host defense against pathogenic organisms. In order to identify novel host defense peptides by sequence analysis, we constructed the AMPer resource (http://www.cnbi2.com/cgi-bin/amp.pl) that utilizes hidden Markov models to recognize sequences of antimicrobial peptides. In the current work, we utilized the AMPer resource to search bovine expressed sequence tags from the NCBI dbEST project and the bovine genome sequence for novel host defense peptides. Of the 34 known bovine AMPs, 27 were identified with high confidence in the AMPs predicted from ESTs. A further potential 68 AMPs predicted from the EST data were found that appear to be novel giving a total estimate of 102 AMPs present in the genome. Two of these were cathelicidins and selected for experimental verification in RNA derived from bovine tissue. One predicted AMP, most similar to rabbit '15 kDa protein' AMP, was confirmed to be present in infected bovine intestinal tissue using PCR. These findings demonstrated the practical applicability of the developed bioinformatics approach and laid a foundation for future discoveries of gene-coded AMPs. No members of the alpha-defensin family were found in the bovine sequences. Since we could find no technical reasons these would be missed and no references to bovine alpha-defensins in the literature, this suggests that cattle lack this important family of host defense peptides.

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.

Antimicrobial effects of H4-(86-100), histogranin and related compounds--possible involvement of DNA gyrase

Histone-derived antimicrobial peptides have been identified in various organisms from plants to humans. The rat histone H4 mRNA variants, H4-v.1 and rat histogranin (HNr) mRNAs, were recently reported to be involved in the synthesis of H4-(86-100) and its related peptide HNr, respectively. Herein, the two peptides were investigated for putative antimicrobial activity and found to inhibit growth of gram-negative (Escherichia coli, Pseudomonas aeruginosa) and gram-positive (Bacillus subtilis, Staphylococcus aureus) bacteria. Their inhibitory potencies in E. coli (LD(50): 3.48 and 4.34 microg x mL(-1)) are comparable to that of the antimicrobial peptide LL-37 (LD(50): 4.10 microg x mL(-1)). The antimicrobial activities of H4-(86-100) and HNr depend upon the integrity of the molecules, as precursors [H4-(84-102), pro-HNr] and fragments [bovine histogranin (HNb)-(1-13), HNb-(3-13), H4-(89-102) or OGP] are at least five times less potent than the parent peptides. Among various HN-like compounds, cyclo-(-Gly-pCl-Phe-Tyr-D-Arg) (compound 3) and N-5-guanidino pentanamide-(2R)-yl-2-N-(p-hydroxyphenylacetyl)-4-(p-chlorobenzoyl)-phenylene diamine (compound 8) display antimicrobial activities comparable to that of HNr. Interestingly, the antimicrobial activities of H4-(86-100), HNr and compound 3, like those of quinolone antibiotics acting as DNA gyrase poisons, are potentiated by ATP (1 mM) and coumermycin A1 (a DNA gyrase-linked ATPase inhibitor) and blocked by 2,4-dinitrophenol (DNP, an uncoupler of oxidative phosphorylation) and fluoroacetic acid (a metabolic poison). Finally, in vitro experiments indicate that H4-(86-100), HNr, compound 3 and compound 8, but not HNb-(1-13) or HNb-(3-13), inhibit DNA gyrase-mediated supercoiling of pBR322 DNA. These data indicate that the naturally occurring H4-(86-100) and HNr display antimicrobial effects that involve a modulation of ATP-dependent DNA gyrase.

Antimicrobial action of histone H2B in Escherichia coli: evidence for membrane translocation and DNA-binding of a histone H2B fragment after proteolytic cleavage by outer membrane proteinase T

Previous studies have led to the isolation of histone H2B with antibacterial properties from an extract of the skin of the Schlegel's green tree frog Rhacophorus schlegelii and it is now demonstrated that the intact peptide is released into norepinephrine-stimulated skin secretions. In order to investigate the mechanism of action of this peptide, a maltose-binding protein (MBP)-fused histone H2B (MBP-H2B) conjugate was prepared and subjected to antimicrobial assay. The fusion protein showed bacteriostatic activity against Escherichia coli strain JCM5491 with a minimum inhibitory concentration of 11 microM. The lysate prepared from JCM5491 cells was capable of fragmenting MBP-H2B within the histone H2B region, but the lysate from the outer membrane proteinase T (OmpT) gene-deleted BL21(DE3) cells was not. FITC-labeled MBP-H2B (FITC-MBP-H2B) penetrated into the bacterial cell membrane of JCM5491 and ompT-transformed BL21(DE3) cells, but not into ompT-deleted BL21(DE3) cells. Gel retardation assay using MBP-H2B-deletion mutants indicated that MBP-H2B bound to DNA at a site within the N-terminal region of histone H2B. Consequently, it is proposed that the antimicrobial action of histone H2B involves, at least in part, penetration of an OmpT-produced N-terminal histone H2B fragment into the bacterial cell membrane with subsequent inhibition of cell functions.