Insect immunity: expression of the two major inducible antibacterial peptides, defensin and diptericin, in Phormia terranovae

In Vitro Evaluation of the Antibacterial Activity of the Peptide Fractions Extracted from the Hemolymph of Hermetia illucens (Diptera: Stratiomyidae)

Antimicrobial peptides (AMPs) are a chemically and structurally heterogeneous family of molecules produced by a large variety of living organisms, whose expression is predominant in the sites most exposed to microbial invasion. One of the richest natural sources of AMPs is insects which, over the course of their very long evolutionary history, have adapted to numerous and different habitats by developing a powerful innate immune system that has allowed them to survive but also to assert themselves in the new environment. Recently, due to the increase in antibiotic-resistant bacterial strains, interest in AMPs has risen. In this work, we detected AMPs in the hemolymph of Hermetia illucens (Diptera, Stratiomyidae) larvae, following infection with Escherichia coli (Gram negative) or Micrococcus flavus (Gram positive) and from uninfected larvae. Peptide component, isolated via organic solvent precipitation, was analyzed by microbiological techniques. Subsequent mass spectrometry analysis allowed us to specifically identify peptides expressed in basal condition and peptides differentially expressed after bacterial challenge. We identified 33 AMPs in all the analyzed samples, of which 13 are specifically stimulated by Gram negative and/or Gram positive bacterial challenge. AMPs mostly expressed after bacterial challenge could be responsible for a more specific activity.

Periplaneta americana L. a potential source of traditional medicine: chemometric analysis, in vitro and in silico study

'Mayurbhanj is the ethnic dominant tribal population district in Odisha, India. The triabl's of Mayurbhanj depends on traditional medicines since time immemorial for health-related issues. Due to the imperative ethnic claim of traditional healers, the financial stringency of the patient community and the necessity to produce a better therapeutic effect has led to investigate ethno zoological sources and to find out the biochemical moiety responsible for the healing process. Considering the ethnic communities' acceptability of the zoological source as traditional medicine, the current evidence-based research study is conducted to investigate the biochemical moiety present in Periplaneta americana, responsible for therapeutic activity. The whole powdered Periplaneta americana was extracted using maceration techniques with n-hexane and methanol as solvent. The obtained extracts were subjected to GC-MS analysis to identify the biochemical moiety. To check the potential biological activity, an in-vitro antimicrobial test was carried out in both turbidimetry and a viable count method against E. coli. Moreover, the obtained biochemical molecules were exposed to in silico studies for their binding modes and their affinity using Discovery studio software. The major compounds were found to be hexadecanoic acid, methyl ester, n-hexadecanoic acid, oleic acid, octadecanoic acid along with other minor constituents. The maximum inhibitory activity of n-hexane and methanol extract against S. aureus at a concentration of 400 µg/mL was found to be 89 and 87%, respectively. The binding models of almost all identified compounds confer very good binding affinities with some key and strong non-covalent interactions with various amino acid residues of receptor active site pocket, which predict the compounds to be potent inhibitors of various infectious bacteria. These findings suggested that the hexane extract of P. americana could be exploited as a potential natural source. Communicated by Ramaswamy H. Sarma.

The Battle Against Flystrike - Past Research and New Prospects Through Genomics

Flystrike, or cutaneous myiasis, is caused by blow fly larvae of the genus Lucilia. This disease is a major problem in countries with large sheep populations. In Australia, Lucilia cuprina (Wiedemann, 1830) is the principal fly involved in flystrike. While much research has been conducted on L. cuprina, including physical, chemical, immunological, genetic and biological investigations, the molecular biology of this fly is still poorly understood. The recent sequencing, assembly and annotation of the draft genome and analyses of selected transcriptomes of L. cuprina have given a first global glimpse of its molecular biology and insights into host-fly interactions, insecticide resistance genes and intervention targets. The present article introduces L. cuprina, flystrike and associated issues, details past control efforts and research foci, reviews salient aspects of the L. cuprina genome project and discusses how the new genomic and transcriptomic resources for this fly might accelerate fundamental molecular research of L. cuprina towards developing new methods for the treatment and control of flystrike.

Purification and characterization of a novel antibacterial peptide from black soldier fly (Hermetia illucens) larvae

In this study, we induced and purified a novel antimicrobial peptide exhibiting activity against Gram-positive bacteria from the immunized hemolymph of Hermetia illucens larvae. The immunized hemolymph was extracted, and the novel defensin-like peptide 4 (DLP4) was purified using solid-phase extraction and reverse-phase chromatography. The purified DLP4 demonstrated a molecular weight of 4267 Da, as determined using the matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) method. From analysis of DLP4 by N-terminal amino acid sequencing using Edman degradation, combined with MALDI-TOF and rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR), the amino acid sequence of the mature peptide was determined to be ATCDLLSPFKVGHAACAAHCIARGKRGGWCDKRAVCNCRK. In NCBI BLAST, the amino acid sequence of DPL4 was found to be 75% identical to the Phlebotomus duboscqi defensin. Analysis of the minimal inhibitory concentration (MIC) revealed that DLP4 have antibacterial effects against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). The expression of DLP4 transcripts in several tissues after bacterial challenge was measured by quantitative real-time PCR. Expression of the DLP4 gene hardly occurred throughout the body before immunization, but was mostly evident in the fat body after immunization.

Detection and preliminary physico-chemical properties of antimicrobial components in the native excretions/secretions of three species of Chrysomya (Diptera, Calliphoridae) in Brazil

Antibiotic-resistant bacteria in hospitals and communities increasingly threaten public health in Brazil and the rest of the World. There is an urgent need for additional antimicrobial drugs. Calliphorid blowfly larvae are a rich source of antimicrobial factors but the potential of Neotropical species has been neglected. This preliminary study evaluates the antimicrobial activity of the native excretions/secretions of larvae of three species of Brazilian calliphorids, Chrysomya megacephala, Chrysomya albiceps and Chrysomya putoria. Native excretions/secretions were collected from third instar larvae, sterile filtered and tested for antibacterial activity against Staphylococcus aureus 9518, Escherichia coli K12 4401 and Serratia marcescens 365. Turbidometric assays were made in micro-plates, using an ELISA reader, with readings taken up to 22 h. Bacterial suspensions at the start and end of each experiment were also serially diluted, spread on nutrient agar plates and then colony forming units counted. The physico-chemical characteristics of the native excretions/secretions were also tested by freezing/thawing, boiling, and protease digestion. The native excretions/secretions of larvae from these three Chrysomya species significantly inhibited bacterial growth. Therefore, Brazilian calliphorid flies could potentially provide new classes of antibiotics.

Insect antimicrobial peptides and their applications

Insects are one of the major sources of antimicrobial peptides/proteins (AMPs). Since observation of antimicrobial activity in the hemolymph of pupae from the giant silk moths Samia Cynthia and Hyalophora cecropia in 1974 and purification of first insect AMP (cecropin) from H. cecropia pupae in 1980, over 150 insect AMPs have been purified or identified. Most insect AMPs are small and cationic, and they show activities against bacteria and/or fungi, as well as some parasites and viruses. Insect AMPs can be classified into four families based on their structures or unique sequences: the α-helical peptides (cecropin and moricin), cysteine-rich peptides (insect defensin and drosomycin), proline-rich peptides (apidaecin, drosocin, and lebocin), and glycine-rich peptides/proteins (attacin and gloverin). Among insect AMPs, defensins, cecropins, proline-rich peptides, and attacins are common, while gloverins and moricins have been identified only in Lepidoptera. Most active AMPs are small peptides of 20-50 residues, which are generated from larger inactive precursor proteins or pro-proteins, but gloverins (~14 kDa) and attacins (~20 kDa) are large antimicrobial proteins. In this mini-review, we will discuss current knowledge and recent progress in several classes of insect AMPs, including insect defensins, cecropins, attacins, lebocins and other proline-rich peptides, gloverins, and moricins, with a focus on structural-functional relationships and their potential applications.

Biochemical characterization of novel bioactive protein from silkworm (Bombyx mori L) fecal matter

In this study, complete purification and biochemical characterization of protein is presented. The protein was purified by using Sephadex G-75 gel filtration column followed by reverse-phase high-performance liquid chromatography in a C18 column. The molecular weight of the protein was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, mass spectrum matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) and liquid chromatography-electrospray ionization tandem mass spectrometry. Protein was fragmented by trypsin based on the m/z values obtained by MALDI-TOF-MS analysis. The peptide fragments sequence showed homology with DEAD-box-ATP-dependent RNA helicase 45, present in a public domain, National Centre for Biotechnology Information. The protein exhibited antibacterial activity against selected Gram +/- bacteria. The analgesic activity was determined by conducting acetic-acid-induced writhing test in mice.

Insect natural products and processes: new treatments for human disease

In this overview, some of the more significant recent developments in bioengineering natural products from insects with use or potential use in modern medicine are described, as well as in utilisation of insects as models for studying essential mammalian processes such as immune responses to pathogens. To date, insects have been relatively neglected as sources of modern drugs although they have provided valuable natural products, including honey and silk, for at least 4-7000 years, and have featured in folklore medicine for thousands of years. Particular examples of Insect Folk Medicines will briefly be described which have subsequently led through the application of molecular and bioengineering techniques to the development of bioactive compounds with great potential as pharmaceuticals in modern medicine. Insect products reviewed have been derived from honey, venom, silk, cantharidin, whole insect extracts, maggots, and blood-sucking arthropods. Drug activities detected include powerful antimicrobials against antibiotic-resistant bacteria and HIV, as well as anti-cancer, anti-angiogenesis and anti-coagulant factors and wound healing agents. Finally, the many problems in developing these insect products as human therapeutic drugs are considered and the possible solutions emerging to these problems are described.

Induction of antibacterial activity in larvae of the blowfly Lucilia sericata by an infected environment

Maggot debridement therapy (MDT) is a method for the treatment of intractable, infected and necrotic wounds. In MDT, sterile larvae of Lucilia sericata Meigen (Diptera: Calliphoridae) are applied to infected wounds, where they exert antibacterial effects. Once the larvae are placed in the wound, they are no longer germ-free. This study analysed the influence of infected environments on larval antibacterial activities. Sterile larvae were mixed in a test tube containing a bacterial suspension of Staphylococcus aureus or Pseudomonas aeruginosa, transferred to liver puree agar, and incubated at 25 °C for set periods. To collect the larval extracts, the incubated larvae were transferred to a test tube containing phosphate buffered saline (PBS), cut into multiple pieces with scissors, and centrifuged. The supernatant was used to test antibacterial activities. The results showed that infected larvae had better antibacterial capacities than sterile larvae. Antibacterial activities were induced by pretreatment with a single bacterial species, S. aureus or P. aeruginosa, within 24 h and 12 h, respectively, and disappeared after 36 h. The activities were effective against S. aureus, but not against P. aeruginosa. This natural infection model is very similar to the clinical wound context in MDT and will be a powerful tool with which to study the antibacterial activities of L. sericata larvae in MDT.

A peptide with potent antifungal and antiproliferative activities from Nepalese large red beans

An antifungal defensin-like peptide with a molecular mass of 7.1kDa was isolated from dried Nepalese large red beans (Phaseolus angularis). The purification protocol employed included ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on SP-Sepharose, and gel filtration by fast protein liquid chromatography on Superdex 75. The antifungal peptide was unadsorbed on DEAE-cellulose, and adsorbed on Affi-gel blue gel and SP-Sepharose. The antifungal peptide inhibited mycelial growth in Fusarium oxysporum and Mycosphaerella arachidicola with an IC(50) value of 1.4 and 1.8 microM, respectively. It did not inhibit HIV-1 reverse transcriptase when tested up to 200 microM. It exerted an antiproliferative action on L1210 leukemia cells and MBL2 lymphoma cells with an IC(50) of 15 and 60 microM, respectively.

A defensin with highly potent antipathogenic activities from the seeds of purple pole bean

A 5443 Da peptide with sequence homology to defensins was purified from purple pole beans (Phaseolus vulgaris cv. 'Extra-long Purple Pole bean'). This peptide was isolated by adsorption on an affinity chromatographic medium Affi-Gel Blue gel and ion-exchange chromatographic media SP-Sepharose (sulfopropyl-Sepharose) and Mono S and by gel filtration on Superdex peptide. The peptide inhibited mycelial growth in Mycosphaerella arachidicola, Helminthosporium maydis, Fusarium oxysporum, Verticillium dahliae, Rhizoctonia solani, Candida albicans and Setosphaeria turcica with an IC50 of 0.8, 0.9, 2.3, 3.2, 4.3, 4.8 and 9.8 microM respectively. Its antifungal potency was higher than that of the plant defensin coccinin (IC50>50 microM). It induced membrane permeabilization in C. albicans as evidenced by SYTOX Green uptake, but did not affect erythrocyte membrane permeability. It inhibited growth in M. arachidicola by inducing chitin accumulation at hyphal tips as was shown by Congo Red staining. The antifungal activity was pH stable and thermostable. The peptide inhibited the proliferation of hepatoma (HepG2), breast cancer (MCF7), colon cancer (HT29) and cervical cancer (SiHa) cells but not that of human embryonic liver (WRL68) cells. Its anti-HepG2 activity (IC50=4.1+/-0.8 microM, n=3) was higher than that of another plant defensin, gymnin (IC50>50 microM). Its anti-MCF7 activity (IC50=8.3+/-0.3 microM, n=3) was similar to that of other plant defensins. It reduced the activity of HIV-1 reverse transcriptase with an IC50 of 0.5+/-0.1 microM, n=3, much more potently than other plant defensins (IC50>40 microM). There is the possibility of using the purple pole bean defensin for producing antifungal drugs and/or transgenic plants with fungal resistance.

Identification of a cis-regulatory element required for 20-hydroxyecdysone enhancement of antimicrobial peptide gene expression in Drosophila melanogaster

The antimicrobial peptide diptericin plays an important role in defence against microorganisms. Drosophila melanogaster diptericin mRNA levels showed an increase during the late final instar larval stage when the ecdysteroid titres increase to initiate metamorphosis. Deletion analysis in Drosophila melanogaster mbn2 (mbn2) cells identified a cis-regulatory element (AAGAAAGATCCCCTG) necessary for 20-hydroxyecdysone enhancement of peptidoglycan-induced expression of diptericin in the 3 kb diptericin promoter. Proteins extracted from mbn2 cells treated with peptidoglycan plus 20-hydroxyecdysone specifically bound to this element. 20-hydroxyecdysone also enhanced peptidoglycan-induced expression of four other antimicrobial peptide (AMP) genes--drosomycin, attacin-A, metchnikowin and cecropin A1. Moreover, in silico promoter analysis using the meme program showed that an eight-nucleotide region of the identified cis-regulatory element is present in the promoters of these four AMP genes. These studies suggest that 20-hydroxyecdysone regulates the expression of AMP genes through a conserved cis-regulatory element.

Two novel defensin-encoding genes of the Chagas disease vector Triatoma brasiliensis (Reduviidae, Triatominae): gene expression and peptide-structure modeling

Defensins are cysteine-rich peptides involved in the innate immunity of insects and many other organisms. In the present study, two novel defensin-encoding cDNAs and the respective genomic DNAs (def3 and def4) of Triatoma brasiliensis were identified and their tissue-specific and temporal expression was characterized. Both of the deduced mature peptides consisted of 43 amino acid residues and were highly similar to previously identified triatomine defensins (81.4-100%). Semi-quantitative RT-PCR data showed that def3 was constitutively expressed in the fat body and was induced in salivary glands and the small intestine at 5 and 3 days after feeding (daf), respectively. The def4 mRNA level was highly up-regulated in the stomach and fat-body tissues at 5 and 3 daf, respectively. The three-dimensional structures of these defensins were predicted using a homology modeling approach with Def-AAA, the defensin from Anopheles gambiae, as template (62-74% identity). A map of the electrostatic potential of these models revealed that, despite their similar folding patterns, mature Def2 and Def4 have a more cationic structure than is the case for Def1 and Def3. Such differences may orient the antimicrobial profile of these defensins against distinct targets in different organs of the insect.

Molecular cloning and characterization of a cDNA encoding a novel antibacterial peptide, defensin, from the mulberry longicorn beetle,Apriona germari

A full-length cDNA clone with high homology (62% mature peptide sequence identity) to an Acalolepta luxuriosa antibacterial gene, possessing a conserved cysteine-stabilized alphabeta motif, was cloned by screening an Apriona germari cDNA library. This gene (AgCRP) had a total length of 360 bp with an open reading frame of 207 bp, and encoded a predicted peptide of 69 amino acid residues. The mature AgCRP peptide was 27 amino acid residues long and had a cysteine-stabilized alphabeta motif of C...CXXXC...C...CXC consensus sequence, similar to insect defensins. Northern blot analysis revealed that the AgCRP exhibited fat body-specific expression and was up-regulated by wounding, bacterial or fungal challenge.

Comparative analysis of two attacin genes from Hyphantria cunea

A full-length clone corresponding to attacin was isolated from a cDNA library made from fat body of immunized Hyphantria cunea larvae. This newly isolated attacin B shows characteristics different from those previously reported for attacin A. The two attacin cDNAs encode precursor proteins of 233 and 248 amino acid residues, respectively. The two attacins show 45.9% identity at the amino acid level, and 35.2% identity at the nucleotide level. Attacins A and B of H. cunea show significant identities with the attacins of Lepidoptera. Attacin B is a typical glycine-rich protein, while attacin A is leucine-rich. Attacin B is expressed from last instar larvae to adult, while attacin A showed stage-specific expression during the prepupal and pupal stages. Attacins A and B are predicted to have different secondary structure in that attacin A has no tendency to form helices but attacin B contains a substantial number of helices. Attacin A is induced at a trace level in infected larvae, while attacin B is strongly induced against Gram-positive and negative bacteria, fungi, and viruses. The attacin B transcripts were detected in fat body, epidermis and hemocytes after injection with Escherichia coli, Citrobacter freundii, or Candida albicans, but not in the midgut and Malpighian tubule. Recombinant attacin A showed no antibacterial activity, while recombinant attacin B showed strong antibacterial activity in proportion to the amount of the protein injected.

Leptin-dependent toll-like receptor expression and responsiveness in preadipocytes and adipocytes

Leptin, an adipokine mainly produced by adipocytes, has been well characterized with regard to its regulatory function on immune cells. Thus the question occurred of how adipocytes and preadipocytes interact with the immune system and whether or not this communication is regulated by leptin. With the present study we evaluated the Toll-like receptor (TLR) expression and TLR ligand-specific activation of murine preadipocytes and adipocytes in the presence [wild type (WT), 3T3L1] or absence of leptin (ob/ob) or leptin signaling (db/db). The ob/ob as well as db/db adipocytes and preadipocytes were characterized by a significant up-regulation of TLR1 to -9 expression when compared with WT cells. In WT preadipocytes the TLR responsiveness increased during maturation to adipocytes; however, stimulation of ob/ob and db/db cells resulted in a 10- to 20-fold higher interleukin-6 production. Signaling studies revealed, in addition to the increased TLR expression, alterations in the phosphoinositide 3 kinase signaling cascade in ob/ob and db/db cells as an explanation for this increased responsiveness. In conclusion, the present study indicates the expression and responsiveness of TLR1 to -9 in murine preadipocytes as well as adipocytes, both of which are strongly regulated by the adipokine leptin. In summary, these data further emphasize the role of fat tissue in the immune system.

A mitogenic defensin from white cloud beans (Phaseolus vulgaris)

A peptide, with a molecular mass of 7458 Da, was purified from the seeds of white cloud beans (Phaseolus vulgaris cv. 'white cloud bean'). This peptide was isolated using a simple protocol consisting of affinity chromatography on Affi-gel blue gel and gel filtration on Superdex 75. The peptide had both antifungal and antibacterial activities. It reduced the activity of HIV-1 reverse transcriptase and it also inhibited translation in a cell-free rabbit reticulocyte lysate system. Its antifungal activity was retained after incubation with trypsin but was reduced when the ambient ionic strength was raised. The peptide elicited a mitogenic response from mouse splenocytes but did not stimulate nitric oxide production in mouse macrophages.

Detection and partial characterisation of two antibacterial factors from the excretions/secretions of the medicinal maggot Lucilia sericata and their activity against methicillin-resistant Staphylococcus aureus (MRSA)

Maggot therapy is a simple and highly successful method for cleansing infected and necrotic wounds. The use of maggots has become increasingly important in the treatment of non-healing wounds, particularly those infected with the multidrug-resistant pathogen, methicillin-resistant Staphylococcus aureus (MRSA). The increasing challenge concerning the treatment of MRSA infections and the recent finding of vancomycin-resistant strains of MRSA have elicited the search for novel antibacterial compounds and, in particular, investigations into the potent antibacterial mechanism(s) behind maggot therapy. In this study, we report that excretions/secretions (ES) from the blowfly, Lucilia sericata, exhibit potent, thermally stable, protease resistant antibacterial activity against MRSA in vitro. We describe the initial characterisation of two antibacterial factors from native ES of L. sericata. A small, <500 Da factor with significant antibacterial activity against MRSA was partially isolated using ultrafiltration techniques. The potent activity of this factor was comparable to that of native excretions/secretions. A larger, 0.5-3-kDa factor with significant activity against S. aureus was also partially characterised.

Ribosomally synthesized peptides with antimicrobial properties: biosynthesis, structure, function, and applications

Ribosomally synthesized peptides with antimicrobial properties (antimicrobial peptides-AMPs) are produced by eukaryotes and prokaryotes and represent crucial components of their defense systems against microorganisms. Although they differ in structure, they are nearly all cationic and very often amphiphilic, which reflects the fact that many of them attack their target cells by permeabilizing the cell membrane. They can be roughly categorized into those that have a high content of a certain amino acid, most often proline, those that contain intramolecular disulfide bridges, and those with an amphiphilic region in their molecule if they assume an alpha-helical structure. Most of the known ribosomally synthesized peptides with antimicrobial functions have been identified and studied during the last 20 years. As a result of these studies, new knowledge has been acquired into biology and biochemistry. It has become evident that these peptides may be developed into useful antimicrobial additives and drugs. The use of two-peptide antimicrobial peptides as replacement for clinical antibiotics is promising, though their applications in preservation of foods (safe and effective for use in meat, vegetables, and dairy products), in veterinary medicine, and in dentistry are more immediate. This review focuses on the current status of some of the main types of ribosomally synthesized AMPs produced by eucaryotes and procaryotes and discusses the novel antimicrobial functions, new developments, e.g. heterologous production of bacteriocins by lactic acid bacteria, or construction of multibacteriocinogenic strains, novel applications related to these peptides, and future research paradigms.

Wound dressings

There are currently hundreds of dressings on the market to aid in wound management. Before selecting a dressing for a particular wound, a practitioner must assess carefully the needs of the wound to understand which dressing would provide maximal benefit. Frequently, there is not one clear best choice, and it is crucial that the pros and cons of each dressing modality be understood. This article has provided a framework to assist in dressing assessment.

Purification, characterization and gene expression of a glycine and proline-rich antibacterial protein family from larvae of a beetle, Allomyrina dichotoma

Two structurally related antibacterial proteins were isolated from larvae of a beetle, Allomyrina dichotoma, immunized with Escherichia coli. The two proteins were designated A. dichotoma (A. d.) coleoptericin A and B. The mature portion of A. d. coleoptericins deduced from nucleotide sequences of the cDNAs consists of seventy-two amino acids without cysteine residues and is rich in glycine (11.1%) and proline (11.1%). Comparison of the amino acid sequences of the A. d. coleoptericins revealed that these antibacterial proteins have 94%, 75%, 50% and 43% similarity to rhinocerosin, holotricin 2, coleoptericin and acaloleptin A1. Recombinant A. d. coleoptericin A and B showed strong antibacterial activity against Staphylococcus aureus, methicillin resistant S. aureus (MRSA) and Bacillus subtilis. Recombinant A. d. coleoptericin A and B were shown to not form pores through bacterial membranes of E. coli, but to hamper cell division. Results of Northern blotting showed that A. d. coleoptericin genes are inducible by bacteria and are expressed strongly in the fat bodies and haemocytes, and weakly in the Malpighian tubules. Analysis of the evolutionary relationship of amino acid sequences among A. d. coleoptericins and other antibacterial proteins suggests that A. d. coleoptericins, rhinocerosin and holotricin 2 are closely related and form a gene family.

Two isoforms of a member of the arthropod defensin family from the soft tick, Ornithodoros moubata (Acari: Argasidae)

We previously purified and determined the partial amino acid sequence of a 4 kDa peptide having high homology with scorpion defensin from the hemolymph of adult fed female soft ticks, Ornithodoros moubata. In this study, the full length sequences of two defensin isoforms were obtained. Deduced amino acid sequences reveal a precursor protein of 73 amino acid residues with a mature portion consisting of 37 amino acid residues. This mature peptide contains six cysteine residues conserved in the same location as other invertebrate defensins. Phylogenetic analysis reveals that Ornithodoros defensin is most closely related to scorpion defensin and other more ancient arthropods. Ornithodoros defensin mRNA is constitutively expressed and up-regulated by blood-feeding and bacterial injection. Ornithodoros defensin gene expression occurs mainly in the midgut. This is the first report of the cloning and gene expression of an antibacterial peptide from the Acari.

The defensin peptide of the malaria vector mosquito Anopheles gambiae: antimicrobial activities and expression in adult mosquitoes

A recombinant Anopheles gambiae defensin peptide was used to define the antimicrobial activity spectrum against bacteria, filamentous fungi and yeast. Results showed that most of the Gram-positive bacterial species tested were sensitive to the recombinant peptide in a range of concentrations from 0.1 to 0.75 microM. No activity was detected against Gram-negative bacteria, with the exception of some E. coli strains. Growth inhibitory activity was detected against some species of filamentous fungi. Defensin was not active against yeast. The kinetics of bactericidal and fungicidal effects were determined for Micrococcus luteus and Neurospora crassa, respectively. Differential mass spectrometry analysis was used to demonstrate induction of defensin in the hemolymph of bacteria-infected adult female mosquitoes. Native peptide levels were quantitated in both hemolymph and midgut tissues. The polytene chromosome position of the defensin locus was mapped by in situ hybridization.

Insect immunity: molecular cloning, expression, and characterization of cDNAs and genomic DNA encoding three isoforms of insect defensin in Aedes aegypti

Aedes aegypti were immune activated by injection with bacteria, and the expression of insect defensins was measured over time. Northern analyses indicated that defensin transcriptional activity continued for at least 21 days after bacterial injection, and up to 10 days after saline inoculation. Mature defensin levels in the haemolymph reached approximately 45 microM at 24 h post inoculation. cDNAs encoding the preprodefensins of three previously described mature Ae. aegypti defensins were amplified by PCR, cloned and sequenced. Genomic clones were amplified using primers designed against the cDNA sequence. Sequence comparison indicates that there is significant inter- and intra-isoform variability in the signal peptide and prodefensin sequences of defensin genes. Preprodefensin sequences of isoforms A and B are very similar, consisting of a signal peptide region of twenty amino acids, a prodefensin region of thirty-eight amino acids and a forty amino acid mature peptide domain. The sequence encoding isoform C is significantly different, comprising a signal peptide region of twenty-three amino acids, a prodefensin region of thirty-six amino acids, and the mature protein domain of forty amino acids. Analysis of the genomic clones of each isoform revealed one intron spatially conserved in the prodefensin region of all sequences. The intron in isoforms A and B is 64 nt long, and except for a 4 nt substitution in one clone, these intron sequences are identical. The intron in isoform C is 76 nt long and does not share significant identity with the intron sequences of isoforms A or B. The defensin gene mapped to chromosome 3, between two known loci, blt and LF168.

Mosquito-Plasmodium interactions in response to immune activation of the vector

During the development of Plasmodium sp. within the mosquito midgut, the parasite undergoes a series of developmental changes. The elongated ookinete migrates through the layers of the midgut where it forms the oocyst under the basal lamina. We demonstrate here that if Aedes aegypti or Anopheles gambiae, normally susceptible to Plasmodium gallinaceum and P. berghei, respectively, are immune activated by the injection of bacteria into the hemocoel, and subsequently are fed on an infectious bloodmeal, there is a significant reduction in the prevalence and mean intensity of infection of oocysts on the midgut. Only those mosquitoes immune activated prior to, or immediately after, parasite ingestion exhibit this reduction in parasite development. Mosquitoes immune activated 2-5 days after bloodfeeding show no differences in parasite burdens compared with naive controls. Northern analyses reveal that transcriptional activity for mosquito defensins is not detected in the whole bodies of Ae. aegypti from 4 h to 10 days after ingesting P. gallinaceum, suggesting that parasite ingestion, passage from the food bolus through the midgut, oocyst formation, and subsequent release of sporozoites into the hemolymph do not induce the production of defensin. However, reverse transcriptase-PCR of RNA isolated solely from the midguts of Ae. aegypti indicates that transcription of mosquito defensins occurs in the midguts of naive mosquitoes and those ingesting an infectious or noninfectious bloodmeal. Bacteria-challenged Ae. aegypti showed high levels of mature defensin in the hemolymph that correlate with a lower prevalence and mean intensity of infection with oocysts. Because few oocysts were found on the midgut of immune-activated mosquitoes, the data suggest that some factor, induced by bacterial challenge, kills the parasite at a preoocyst stage.

Antimicrobial peptides: an emerging concept in cutaneous biology

Antimicrobial peptides are part of the host defense systems of plants, insects, fish, amphibia, birds, and mammals. These small proteins were previously thought of as an evolutionarily ancient system of immune protection with little relevance to the normal function of human skin. Recent developments have found that mammalian skin expresses these gene-encoded peptide antibiotics during inflammatory events such as wound repair, contact dermatitis, and psoriasis. The presence of these peptides in the skin forms a barrier for innate host protection against microbial pathogenesis. Furthermore, antimicrobial peptides also act on animal cells by stimulating them to change behaviors such as syndecan expression, chemotaxis, and chloride secretion. The combination of effects on host cells with antimicrobial action in a single molecule represents an efficient defense and response system against injury. Understanding the action of antimicrobial peptides in skin may yield further insight into the mechanism of innate cutaneous disease control and provide new approaches to therapy of wounds and inflammatory dermatitis.

Differential gene expression in insects: transcriptional control

Studies on transcriptional control of gene expression play a pivotal role in many areas of biology. In non-Drosophilid insects, the cuticle, chorion, immune response, silk gland, storage proteins, and vitellogenin are foci for advances in basic research on promoter elements and transcription factors. Insects offer other advantages for gene regulation studies, including the availability of applied problems. In non-Drosophilid insects, the most serious problem for transcriptional control studies is the lack of homologous in vivo expression systems. Once this deficiency is addressed, the full impact of research on transcription control will be realized throughout the field of entomology.

Midgut-specific immune molecules are produced by the blood-sucking insect Stomoxys calcitrans

We have cloned and sequenced two defensins, Smd1 and Smd2, from anterior midgut tissue of the blood-sucking fly Stomoxys calcitrans. The DNA and N-terminal protein sequences suggest both are produced as prepropeptides. Smd1 differs from the classic defensin pattern in having an unusual six-amino acid-long N-terminal sequence. Both Smd1 and Smd2 have lower pI points and charge than insect defensins derived from fat body/hemocytes. Northern analysis shows both of these defensin molecules are tissue specific; both are produced by the anterior midgut tissue and, unlike the other insect defensins reported to date, neither appears to be expressed in fat body or hemocytes. Northern analysis also shows that mRNAs for both defensins are constitutively produced in the anterior midgut tissues and that these transcripts are up-regulated in response to sterile as well as a lipopolysaccharide-containing blood meal. However, anti-Gram-negative biological activity in the midgut is substantially enhanced by lipopolysaccharide. These findings suggest that the insect midgut has its own tissue-specific immune mechanisms and that this invertebrate epithelium is, like several vertebrate epithelia, protected by specific antibacterial peptides.

Molecular population genetics of Drosophila immune system genes

A striking aspect of many vertebrate immune system is the exceptionally high level of polymorphism they harbor. A convincing case can be made that this polymorphism is driven by the diversity of pathogens that face selective pressures to evade attack by the host immune system. Different organisms accomplish a defense against diverse pathogens through mechanisms that differ widely in their requirements for specific recognition. It has recently been shown that innate defense mechanisms, which use proteins with broad-spectrum bactericidal properties, are common to both primitive and advanced organisms. In this study we characterize DNA sequence variation in six pathogen defense genes of Drosophila melanogaster and D. mauritiana, including Andropin; cecropin genes CecA1, CecA2, CecB, and CecC; and Diptericin. The necessity for protection against diverse pathogens, which themselves may evolve resistance to insect defenses, motivates a population-level analysis. Estimates of variation levels show that the genes are not exceptionally polymorphic, but Andropin and Diptericin have patterns of variation that differ significantly from neutrality. Patterns of interpopulation and interspecific differentiation also reveal differences among the genes in evolutionary forces.

Characterization and ion channel activities of novel antibacterial proteins from the skin mucosa of carp (Cyprinus carpio)

A detergent-solubilized fraction of skin mucus of carp (Cyprinus carpio) induced ion channels after reconstitution into planar lipid bilayers. A differential extraction using a non-ionic detergent followed by electrophoretic separation led to the isolation of two hydrophobic 31-kDa and 27-kDa proteins. In contrast to the 27-kDa protein, which was glycosylated, the 31-kDa did not bind to concanavalin A. The reconstitution of these proteins into a planar lipid bilayer restored the ionophore behavior already observed with the crude mucus. The main unit conductance levels were about 900 pS for the 27-kDa protein and 500 pS for the 31-kDa protein, and selectivity measurements gave Pcl/Pk ratios of 0.6 and 1.0, respectively. These proteins had large potent microbicidal activities (0.018-0.18 microM) against different strains of gram-negative and gram-positive bacteria. This behavior can be compared with insect defensins that are known to form large ion channels in the bacterial membrane. To exclude the eventuality of bacterial origin, the bacterial flora of the crude mucus were analysed and the following were identified: Pseudomonas cepacia; Micrococcus luteus; Micrococcus roseus; Flavobacterium sp.; Aeromonas hydrophila. Antibacterial assays with both proteins were performed against these specific strains and revealed good growth inhibition activities. Furthermore, microsequencing analysis showed that the 31-kDa protein was protected on its N-terminal extremity in contrast to the 27-kDa protein, which had a 19-amino-acid sequence. This last sequence, when compared with sequences in protein data banks, did not reveal any significant similarities to other proteins. These results suggest that these novel proteins could be involved in antibacterial defense processes in fish.

Cloning and characterization of cDNAs encoding the antibacterial peptide, defensin A, from the mosquito, Aedes aegypti

Insect defensins are cationic, inducible antibacterial peptides. Four full-length cDNAs encoding defensin A from the mosquito Aedes aegypti were cloned using polymerase chain reaction (PCR) and sequenced. All four cDNAs are 473 base pairs long, bearing an open reading frame of 98 amino acids with a few substitutions in the signal peptide domain. The deduced amino acid sequence of Aedes aegypti defensin (AaDef) contains a signal peptide sequence of 18 amino acids followed by a 40-amino acid putative propeptide domain and a 40-amino acid mature peptide domain. The mature peptide, with a predicted M(r) of 4148, shows 80% identity and 93% similarity to Phormia defensin A, and is identical to the peptide sequencing data for mosquito defensin A of Lowenberger et al. (1995) and B of Chalk et al. (1995). There are three potential phosphorylation sites but no glycosylation sites detected in AaDef. Three putative disulfide linkages between cysteines, characteristic of insect defensins, are conserved in AaDef. Aedes aegypti defensin mRNA is produced in response to a bacterial challenge; it is dramatically enhanced 6 h after bacterial injection, continues to increase through 24 h, and is maintained at high levels until at least 30 h post-bacterial injection.

Defensins

Defensins are a family of small cationic, antibiotic peptides that contain six cysteines in disulfide linkage. The peptides are abundant in phagocytes and small intestinal mucosa of humans and other mammals and in the hemolymph of insects. They contribute to host defense against microbes and may participate in tissue inflammation and endocrine regulation during infection. Bioengineered defensins are potentially useful as prophylactic and therapeutic agents in infections.

Characterization and transcriptional profiles of a Drosophila gene encoding an insect defensin. A study in insect immunity

Insect defensins are a family of 4-kDa, cationic, inducible antibacterial peptides which bear six cysteine residues engaged in three intramolecular disulfide bridges. They owe their name to certain sequence similarities with defensins from mammalian neutrophiles and macrophages. We report the characterization of a novel defensin isoform from Drosophila and the cloning of the gene encoding a preprodefensin. The gene, which is intronless and present in a single copy/haploid genome, maps at position 46CD on the right arm of the second chromosome. The analysis of the upstream region of the gene reveals the presence of multiple putative cis-regulatory sequences similar to mammalian regulatory motifs of acute-phase-response genes. Transcriptional profiles indicate that the Drosophila defensin gene is induced by bacterial challenge with acute-phase kinetics. It is also expressed in the absence of immune challenge during metamorphosis. These and other data on the Drosophila defensin gene lead us to suggest that insect and mammalian defensins have evolved independently.

Structure and induction of a lysozyme gene from the tobacco hornworm, Manduca sexta

Lysozyme is hypothesized to play a central role in initiating and maintaining the antibacterial defense response of Manduca sexta. We isolated a cDNA clone encoding a M. sexta lysozyme. Results of Northern blot analyses using this cDNA as a probe indicated that the abundance of lysozyme transcripts increased in seven tissues following treatment with peptidoglycan, with the highest level of accumulation occurring in the fat body. An analysis of the kinetics of accumulation of the transcripts in the fat body demonstrated low levels of transcripts in the naive larvae which increased rapidly after treatment and remained elevated over several days. A genomic fragment containing a lysozyme gene was also isolated and the nucleotide sequence and transcription start site of the gene was determined.

The inducible antibacterial peptides of insects

Insects respond to bacterial challenge by the rapid and transient synthesis of a large number of potent antibacterial peptides that are active against many different bacteria. Two families of inducible antibacterial peptides are well characterized: the cecropins and the insect defensins. A rapidly increasing number of proline- and glycine-rich peptides are reported from various insect species together with cecropins and insect defensins. In this review, Stéphane Cociancich, Philippe Bulet, Charles Hetru and Jules A. Hoffmann give an update of our current information on the induced antibacterial peptides.

Purification and primary structure of ceratotoxin A and B, two antibacterial peptides from the female reproductive accessory glands of the medfly Ceratitis capitata (Insecta:Diptera)

In the present article we report the purification and the amino acid sequence of two antibacterial peptides present in the secretion of the female reproductive accessory glands of the dipteran insect Ceratitis capitata. Both peptides consist of 29 amino acid residues, are heat stable, strongly basic and differ from each other for the substitution of two amino acids. Their primary sequence and predicted secondary structure are related to other families of peptides known to have lytic and/or antibacterial activity. We propose the name ceratotoxins (from Ceratitis) for these antibacterial peptides.

Antibiotic peptides and serine protease homologs in human polymorphonuclear leukocytes: defensins and azurocidin

The azurophil granule, a specialized lysosome of neutrophils, contains two families of antimicrobial proteins, each with four members. They are the defensins, comprising human neutrophil protein 1, -2, -3 and -4, on the one hand and the serprocidins, comprising cathepsin G, elastase, proteinase 3 and azurocidin, on the other. Defensins appear to contribute to mammalian as well as invertebrate immunity. Recent studies show that defensins and structurally related peptides are found not only in phagocytes but also in intestinal and respiratory cells. Aside from their antibiotic function, members of the defensin family may also act as hormonal agents. Within the serprocidin family the genes encoding the novel antibiotics and serine protease homologs azurocidin and proteinase 3 have been identified recently.

A novel insect defensin mediates the inducible antibacterial activity in larvae of the dragonfly Aeschna cyanea (Paleoptera, Odonata)

The injection of low doses of bacteria into the aquatic larvae of dragonflies (Aeschna cyanea, Odonata, Paleoptera) induces the appearance in their hemolymph of a potent antibacterial activity. We have isolated a 38-residue peptide from this hemolymph which is strongly active against Gram-positive bacteria and also shows activity against one of the Gram-negative bacteria which was tested. The peptide is a novel member of the insect defensin family of inducible antibacterial peptides, which had so far only been reported from the higher insect orders believed to have evolved 100 million years after the Paleoptera. Aeschna defensin is more potent than defensin from the dipteran Phormia, from which its structure differs in several interesting aspects, which are discussed in the paper.