A family of bacteria-regulated, cecropin D-like peptides from Manduca sexta

Mosquito pericardial cells upregulate Cecropin expression after an immune challenge

Most mosquito-transmitted pathogens grow or replicate in the midgut before invading the salivary glands. Pathogens are exposed to several immunological factors along the way. Recently, it was shown that hemocytes gather near the periostial region of the heart to efficiently phagocytose pathogens circulating in the hemolymph. Nerveless, not all pathogens can be phagocyted by hemocytes and eliminated by lysis. Interestingly, some studies have shown that pericardial cells (PCs) surrounding periostial regions, may produce humoral factors, such as lysozymes. Our current work provides evidence that Anopheles albimanus PCs are a major producer of Cecropin 1 (Cec1). Furthermore, our findings reveal that after an immunological challenge, PCs upregulate Cec1 expression. We conclude that PCs are positioned in a strategic location that could allow releasing humoral components, such as cecropin, to lyse pathogens on the heart or circulating in the hemolymph, implying that PCs could play a significant role in the systemic immune response.

Screening and Functional Analyses of Novel Cecropins from Insect Transcriptome

Antibiotic resistance is a significant and growing threat to global public health. However, antimicrobial peptides (AMPs) have shown promise as they exhibit a broad spectrum of antibacterial activities with low potential for resistance development. Insects, which inhabit a wide range of environments and are incredibly diverse, remain largely unexplored as a source of novel AMPs. To address this, we conducted a screening of the representative transcriptomes from the 1000 Insect Transcriptome Evolution (1KITE) dataset, focusing on the homologous reference genes of Cecropins, the first identified AMPs in insects known for its high efficiency. Our analysis identified 108 Cecropin genes from 105 insect transcriptomes, covering all major hexapod lineages. We validated the gene sequences and synthesized mature peptides for three identified Cecropin genes. Through minimal inhibition concentration and agar diffusion assays, we confirmed that these peptides exhibited antimicrobial activities against Gram-negative bacteria. Similar to the known Cecropin, the three Cecropins adopted an alpha-helical conformation in membrane-like environments, efficiently disrupting bacterial membranes through permeabilization. Importantly, none of the three Cecropins demonstrated cytotoxicity in erythrocyte hemolysis tests, suggesting their safety in real-world applications. Overall, this newly developed methodology provides a high-throughput bioinformatic pipeline for the discovery of AMP, taking advantage of the expanding genomic resources available for diverse organisms.

A zone-of-inhibition assay to screen for humoral antimicrobial activity in mosquito hemolymph

In insects, antibacterial immunity largely depends on the activation of downstream signaling and effector responses, leading to the synthesis and secretion of soluble effector molecules, such as antimicrobial peptides (AMPs). AMPs are acute infection response peptides secreted into the hemolymph upon bacterial stimulation. The transcription of innate immunity genes encoding for AMPs is highly dependent on several signaling cascade pathways, such as the Toll pathway. In the African malaria mosquito, Anopheles gambiae, AMPs hold a special interest as their upregulation have been shown to limit the growth of malaria parasites, bacteria, and fungi. Most of the current knowledge on the regulation of insect AMPs in microbial infection have been obtained from Drosophila. However, largely due to the lack of convenient assays, the regulation of antimicrobial activity in mosquito hemolymph is still not completely understood. In this study, we report a zone of inhibition assay to identify the contribution of AMPs and components of the Toll pathway to the antimicrobial activity of A. gambiae hemolymph. As a proof of principle, we demonstrate that Micrococcus luteus challenge induces antimicrobial activity in the adult female mosquito hemolymph, which is largely dependent on defensin 1. Moreover, by using RNAi to silence Cactus, REL1, and MyD88, we showed that Cactus kd induces antimicrobial activity in the mosquito hemolymph, whereas the antimicrobial activity in REL1 kd and MyD88 kd is reduced after challenge. Finally, while injection itself is not sufficient to induce antimicrobial activity, our results show that it primes the response to bacterial challenge. Our study provides information that increases our knowledge of the regulation of antimicrobial activity in response to microbial infections in mosquitoes. Furthermore, this assay represents an ex vivo medium throughput assay that can be used to determine the upstream regulatory elements of antimicrobial activity in A. gambiae hemolymph.

Functional Characterization of Outer Membrane Proteins (OMPs) in Xenorhabdus nematophila and Photorhabdus luminescens through Insect Immune Defense Reactions

Xenorhabdus nematophila and Photorhabdusluminescens are entomopathogenic bacterial symbionts that produce toxic proteins that can interfere with the immune system of insects. Herein, we show that outer membrane proteins (OMPs) could be involved as bacterial virulence factors. Purified totals OMPs of both bacterial species were injected into fifth instar larvae of Spodopteraexigua Hübner. Larvae were surveyed for cellular defenses fluctuations in total haemocyte counts (THC) and granulocyte percentage and for the humoral defenses protease, phospholipase A2 (PLA₂), and phenoloxidase (PO) activities at specific time intervals. Changes in the expression of the three inducible antimicrobial peptides (AMPs), cecropin, attacin, and spodoptericin, were also measured. Larvae treated with OMPs of both bacterial species had more haemocytes than did the negative controls. OMPs of X. nematophila caused more haemocyte destruction than did the OMPs of P. luminescens. The OMPs of both bacterial species initially activated insect defensive enzymes post-injection, the degree of activation varying with enzyme type. The AMPs, attacin, cecropin, and spodoptericin were up-regulated by OMP injections compared with the normal larvae. The expression of these three AMPs was maximal at four hours post injection (hpi) with P. luminescens OMPs treatment. Expression of the three AMPs in X. nematophila treated insects was irregular and lower than in the P. luminescens OMPs treatment. These findings provide insights into the role of OMPs of entomopathogenic nematode bacterial symbionts in countering the physiological defenses of insects.

Innate immune responses in the Chinese oak silkworm, Antheraea pernyi

Innate immunity, the evolutionarily conserved defense system, has been extensively analyzed in insect models over recent decades. The significant progress in this area has formed our dominant conceptual framework of the innate immune system, but critical advances in other insects have had a profound impact on our insights into the mystery of innate immunity. In recent years, we focused on the immune responses in Antheraea pernyi, an important commercial silkworm species reared in China. Here, we review the immune responses of A. pernyi based on immune-related gene-encoded proteins that are divided into five categories, namely pattern recognition receptors, hemolymph proteinases and their inhibitors, prophenoloxidase, Toll pathway factors and antimicrobial peptides, and others. Although the summarized information is limited since the research on A. pernyi immunity is in its infancy, we hope to provide evidence for further exploration of innate immune mechanisms.

The role of pilin protein of Xenorhabdus nematophila against immune defense reactions of insects

Xenorhabdus nematophila is a symbiotic bacterium of the entomopathogenic nematode Steinernema carpocapsae (Weiser). It produces several toxic proteins which interfere with the immune system of insects. The current study shows that purified pilin protein could be a virulence trait of X. nematophila. The fifth instar larvae of Spodoptera exigua (Hübner) was injected with purified pilin. Changes in the cellular defenses in terms of total haemocyte counts and granulocyte percentage and humoral factors including total protease, phospholipase A₂, and phenoloxidase activities (humoral defense) as well as the expression of the three main antimicrobial peptides attacin, cecropin, and spodoptericin were measured at specific times. The level of THC and granulocytes in larvae with different concentrations of pilin protein were less than the negative control. Also agglutination of haemocytes was observed 8-16h post-injection. The pilin protein activated phenoloxidase in the initial hour post-injection, by 2hpi, activity was stable. The activities of phospholipase A2 and protease activities reached maximum levels at 12 and 4hpi, respectively, and then decreased. The expressions of attacin, cecropin, and spodoptericin in larvae treated with pilin protein were up-regulated above that of the normal sample. The overexpression of cecropin was greater than the other antimicrobial protein mRNA transcripts. The spodoptericin expression had an irregular trend while expressions of attacin and cecropin reached maximum levels at 4hpi and then decreased. Generally, after the injection of pilin protein, the cellular and humoral immune system of S. exigua is activated but this toxin was able to inhibit them. This is the first report of the role of pilin protein when the bacterial symbiont of S. carpocapsae encounters the humoral defense of an insect.

Differential Change Patterns of Main Antimicrobial Peptide Genes During Infection of Entomopathogenic Nematodes and Their Symbiotic Bacteria

The expression of antimicrobial peptides (AMPs) as the main humoral defense reactions of insects during infection by entomopathogenic nematodes (EPNs) and their symbiont is addressed herein. Three AMPs, attacin, cecropin, and spodoptericin, were evaluated in the fifth instar larvae of Spodoptera exigua Hübner (beet armyworm) when challenged with Steinernema carpocapsae or Heterorhabditis bacteriophora. The results indicated that attacin was expressed to a greater extent than either cecropin or spodoptericin. While spodoptericin was expressed to a much lesser extent, this AMP was induced against Gram-positive bacteria, and thus not expressed after penetration of Xenorhabdus nematophila and Photorhabdus luminescens. Attacin and cecropin in the larvae treated with S. carpocapsae at 8 hr post-injection (PI) attained the maximum expression levels and were 138.42-fold and 65.84-fold greater than those of larvae infected with H. bacteriophora, respectively. Generally, the ability of H. bacteriophora to suppress attacin, cecropin, and spodoptericin was greater than that of S. carpocapsae. According to the results, the expression of AMPs by Sp. exigua larvae against S. carpocapsae was determined in the 4 statuses of monoxenic nematode, axenic nematode, live symbiotic bacterium, and dead symbiotic bacterium. The expression of attacin in larvae treated with a monoxenic nematode and live bacterium at 8 and 2 hr PI, respectively, were increased to the maximum amount. Live X. nematophila was the strongest agent for the suppression of attacin. The expression of cecropin against monoxenic nematodes and live symbiotic bacteria at 8 and 4 hr PI, respectively, reached the maximum amount while the expression levels of attacin and cecropin for axenic nematodes were lesser and stable. The results highlighted that the ability of P. luminescens in AMPs suppression was much more than X. nematophila. The results also showed that the effect of symbiotic bacterium in suppressing attacin and cecropin expression was greater than that of a monoxenic nematode; this result provided deep insight into the expression pattern parallels and fluctuations of the main AMPs during nematode infection.

Characterization and regulation of expression of an antifungal peptide from hemolymph of an insect, Manduca sexta

Insects secrete antimicrobial peptides as part of the innate immune response. Most antimicrobial peptides from insects have antibacterial but not antifungal activity. We have characterized an antifungal peptide, diapausin-1 from hemolymph of a lepidopteran insect, Manduca sexta (tobacco hornworm). Diapausin-1 was isolated by size exclusion chromatography from hemolymph plasma of larvae that were previously injected with a yeast, Saccharomyces cerevisiae. Fractions containing activity against S. cerevisiae were analyzed by SDS-PAGE and MALDI-TOF MS/MS and found to contain a 45-residue peptide that was encoded by sequences identified in M. sexta transcriptome and genome databases. A cDNA for diapausin-1 was cloned from cDNA prepared from fat body RNA. Diapausin-1 is a member of the diapausin family of peptides, which includes members known to have antifungal activity. The M. sexta genome contains 14 genes with high similarity to diapausin-1, each with 6 conserved Cys residues. Diapausin-1 was produced as a recombinant protein in Escherichia coli. Purified recombinant diapausin-1 was active against S. cerevisiae, with IC50 of 12 μM, but had no detectable activity against bacteria. Spores of some plant fungal pathogens treated with diapausin-1 had curled germination tubes or reduced and branched hyphal growth. Diapausin-1 mRNA level in fat body strongly increased after larvae were injected with yeast or with Micrococcus luteus. In addition, diapausin-1 mRNA levels increased in midgut and fat body at the wandering larval stage prior to pupation, suggesting developmental regulation of the gene. Our results indicate that synthesis of diapausin-1 is part of an antifungal innate immune response to infection in M. sexta.

A genome-wide analysis of antimicrobial effector genes and their transcription patterns in Manduca sexta

Antimicrobial proteins/peptides (AMPs) are effectors of innate immune systems against pathogen infection in multicellular organisms. Over half of the AMPs reported so far come from insects, and these effectors act in concert to suppress or kill bacteria, fungi, viruses, and parasites. In this work, we have identified 86 AMP genes in the Manduca sexta genome, most of which seem likely to be functional. They encode 15 cecropins, 6 moricins, 6 defensins, 3 gallerimycins, 4 X-tox splicing variants, 14 diapausins, 15 whey acidic protein homologs, 11 attacins, 1 gloverin, 4 lebocins, 6 lysozyme-related proteins, and 4 transferrins. Some of these genes (e.g. attacins, cecropins) constitute large clusters, likely arising after rounds of gene duplication. We compared the amino acid sequences of M. sexta AMPs with their homologs in other insects to reveal conserved structural features and phylogenetic relationships. Expression data showed that many of them are synthesized in fat body and midgut during the larval-pupal molt. Certain genes contain one or more predicted κB binding sites and other regulatory elements in their promoter regions, which may account for the dramatic mRNA level increases in fat body and hemocytes after an immune challenge. Consistent with these strong mRNA increases, many AMPs become highly abundant in the larval plasma at 24 h after the challenge, as demonstrated in our previous peptidomic study. Taken together, these data suggest the existence of a large repertoire of AMPs in M. sexta, whose expression is up-regulated via immune signaling pathways to fight off invading pathogens in a coordinated manner.

cDNA CLONING AND TRANSCRIPTIONAL REGULATION OF THE CECROPIN AND ATTACIN FROM THE ORIENTAL FRUIT FLY, Bactrocera dorsalis (DIPTERA: TEPHRITIDAE)

We described the cDNA cloning of two antimicrobial peptides (AMPs), cecropin (BdCec), and attacin C (BdAttC), from the oriental fruit fly, Bactrocera dorsalis (Hendel), a serious insect pest of fruit trees. Using rapid amplification of cDNA ends, fragments encompassing the entire open reading frames of BdCec and BdAttC were cloned and sequenced. The complete 425 bp cDNA of BdCec encodes a protein of 64 amino acids with a predicted molecular weight of 6.84 kDa. The 931 bp cDNA of BdAttC encodes a protein of 239 residues with a predicted molecular weight of 24.97 kDa. Real-time quantitative RT-PCR demonstrated that the developmental transcription profiles of BdCec and BdAttC were similar in each larvae, pupae, and adults. The constitutive expression levels of both AMPs were high in the first-instar and late third-instar larvae, suggesting that their antimicrobial activity is active in the newly hatched larvae and just before pupation. The basal expression levels were not significant different in adult fat bodies. The expression of BdCec and BdAttC was upregulated after bacterial challenge in adult fat bodies. The ratio of inducible expression to constitutive expression was lower in males compared to females.

Identification of a cuticle protein with unique repeated motifs in the silkworm, Bombyx mori

The insect cuticle is non-cellular matrix secreted from a monolayer of epidermal cells. After abrasion of the larval cuticle of the silkworm, Bombyx mori, a protein with molecular mass of 135 kDa is newly detected in the cuticle. Mass spectrometric analysis of the tryptic fragments from this protein revealed that the 135-kDa protein is encoded by the Cb10 gene. In the predicted amino acid sequence of Cb10, three repeated motifs with [YxGGFGGppG(L/V)L] sequence are found in the C-terminal region. In addition to the repeated motifs, Cb10 has seventeen CxxxxC motifs randomly distributed throughout the polypeptide chain and serine rich region at the N-terminal region. The Cb10 gene is strongly expressed in epidermal cells after pupal ecdysis, and its expression in the larval epidermal cells is induced not only by cuticular abrasion, but also by bacterial infection. These expression patterns suggest some specific roles of this protein in pupal cuticle formation and defense reactions.

Secretion and activity of antimicrobial peptide cecropin D expressed in Pichia pastoris

To express the antimicrobial peptide cecropin D in Pichia pastoris and determine the activity of the expressed product, four oligonucleotide fragments were synthesized in accordance with the available cecropin D sequences and a codon bias suitable for Pichia pastoris. Sequence fragments were phosphorylated, annealed, linked and cloned into the expression vector pGAPZαA and the yeast α-mating factor signal peptide was used as the signal sequence. The P. pastoris SMD1168 cells were transformed by electroporation using the constructed recombinant plasmid pGAPZαA-cecropin D. We were able to demonstrate by PCR that the cecropin D sequence had integrated into the P. pastoris genome. The expressed and secreted product was identified using Tricine-SDS-PAGE. Antibacterial activity was demonstrated using an agarose diffusion test and turbidimetry. The molecular mass of the recombinant cecropin D was estimated to be 3,900 Da. The recombinant cecropin D exhibited antibacterial activity for both Gram-positive and Gram-negative bacteria, suggesting that cecropin D was successfully expressed in P. pastoris. This approach holds great promise for antibacterial drug development.

Predicting antimicrobial peptides from eukaryotic genomes: in silico strategies to develop antibiotics

A remarkable and intriguing challenge for the modern medicine consists in the development of alternative therapies to avoid the problem of microbial resistance. The cationic antimicrobial peptides present a promise to be used to develop more efficient drugs applied to human health. The in silico analysis of genomic databases is a strategy utilized to predict peptides of therapeutic interest. Once the main antimicrobial peptides' physical-chemical properties are already known, the correlation of those features to search on these databases is a tool to shorten identifying new antibiotics. This study reports the identification of antimicrobial peptides by theoretical analyses by scanning the Paracoccidioides brasiliensis transcriptome and the human genome databases. The identified sequences were synthesized and investigated for hemocompatibility and also antimicrobial activity. Two peptides presented antifungal activity against Candida albicans. Furthermore, three peptides exhibited antibacterial effects against Staphylococcus aureus and Escherichia coli; finally one of them presented high potential to kill both pathogens with superior activity in comparison to chloramphenicol. None of them showed toxicity to mammalian cells. In silico structural analyses were performed in order to better understand function-structure relation, clearly demonstrating the necessity of cationic peptide surfaces and the exposition of hydrophobic amino acid residues. In summary, our results suggest that the use of computational programs in order to identify and evaluate antimicrobial peptides from genomic databases is a remarkable tool that could be used to abbreviate the search of peptides with biotechnological potential from natural resources.

Cecropins as a marker of Spodoptera frugiperda immunosuppression during entomopathogenic bacterial challenge

An antimicrobial peptide (AMP) of the cecropin family was isolated by HPLC from plasma of the insect pest, Spodoptera frugiperda. Its molecular mass is 3910.9 Da as determined by mass spectrometry. Thanks to the EST database Spodobase, we were able to describe 13 cDNAs encoding six different cecropins which belong to the sub-families CecA, CecB, CecC and CecD. The purified peptide identified as CecB1 was chemically synthesized (syCecB1). It was shown to be active against Gram-positive and Gram-negative bacteria as well as fungi. Two closely related entomopathogenic bacteria, Xenorhabdus nematophila F1 and Xenorhabdus mauleonii VC01(T) showed different susceptibility to syCecB1. Indeed, X. nematophila was sensitive to syCecB1 whereas X. mauleonii had a minimal inhibitory concentration (MIC) eight times higher. Interestingly, injection of live X. nematophila into insects did not induce the expression of AMPs in hemolymph. This effect was not observed when this bacterium was heat-killed before injection. On the opposite, both live and heat-killed X. mauleonii induced the expression of AMPs in the hemolymph of S. frugiperda. The same phenomenon was observed for another immune-related protein lacking antimicrobial activity. Altogether, our data suggest that Xenorhabdus strains have developed different strategies to supplant the humoral defense mechanisms of S. frugiperda, either by increasing their resistance to AMPs or by preventing their expression during such host-pathogen interaction.

Functional analysis of two lebocin-related proteins from Manduca sexta

Insects produce a group of antimicrobial peptides (AMPs) in response to microbial infections. Most AMPs are synthesized as inactive precursors/pro-proteins and require proteolytic processing to generate small active peptides. Here we report identification and functional analysis of two lebocin-related proteins (Leb-B and Leb-C) from the tobacco hornworm, Manduca sexta. The mRNA levels of Leb-B and Leb-C increased significantly in larval fat body and hemocytes after injection of Escherichia coli, Micrococcus luteus and Saccharomyces cerevisiae. Western blotting using rabbit polyclonal antibody to Leb-B showed accumulation of large protein(s) and small peptide(s) in larval hemolymph after microbial injection. This result and the presence of RXXR motifs in the deduced amino acid sequences led to our postulation that Leb-B/C may be inactive precursors that are processed in larval hemolymph to generate short active peptides. To test this hypothesis, we expressed and purified full-length and various fragments of Leb-B and Leb-C as thioredoxin (TRX) fusion proteins. We found that fusion proteins could be cleaved by induced larval plasma, and the cleavage sites were determined by protein sequencing. Antibacterial activity of peptide fragments was also verified using synthetic peptides, and active M. sexta lebocin peptides were located at the N-termini of Leb-B/C, which are different from Bombyx mori lebocins 1-4 that are located close to the C-termini. In addition, we found that synthetic Leb-B(22-48) peptide not only had higher antibacterial activity but also caused agglutination of E. coli cells. Our results provide valuable information for studying processing of lebocin precursors in lepidopteran insects.

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.

Functional analysis of four processing products from multiple precursors encoded by a lebocin-related gene from Manduca sexta

Antimicrobial peptides (AMPs) are a crucial component of the natural immune system in insects. Five types of AMPs have been identified in the tobacco hornworm Manduca sexta, including attacin, cecropin, moricin, gloverin, and lebocin. Here we report the isolation of lebocin-related cDNA clones and antibacterial activity of their processed protein products. The 17 cDNA sequences are composed of a constant 5' end and a variable 3' region containing 3-16 copies of an 81-nucleotide repeat. The sequence of the corresponding gene isolated from a M. sexta genomic library and Southern blotting results indicated that the gene lacks introns and exists as a single copy in the genome. The genomic sequence contained 13 complete and one partial copy of the 81-nucleotide repeat. Northern blot analysis revealed multiple transcripts with major size differences. The mRNA level of M. sexta lebocin increased substantially in fat body after larvae had been injected with bacteria. The RXXR motifs in the protein sequences led us to postulate that the precursors are processed by an intracellular convertase to form four bioactive peptides. To test this hypothesis, we chemically synthesized the peptides and examined their antibacterial activity. Peptide 1 killed Gram-positive and Gram-negative bacteria. Peptide 2, similar in sequence to a Galleria mellonella AMP, did not affect the bacterial growth. Peptide 3 was inactive but peptide 3 with an extra Arg at the carboxyl terminus was active against Escherichia coli at a high minimum inhibitory concentration. Peptide 4, encoded by the 81-bp repeat, was inactive in the antibacterial tests. The hypothesis that posttranslational processing of the precursor proteins produces multiple bioactive peptides for defense purposes was validated by identification of peptides 1, 2, and 3 from larval hemolymph via liquid chromatography and tandem mass spectrometry. Comparison with the orthologs from other lepidopteran insects indicates that the same mechanism may be used to generate several functional products from a single precursor.

Generation and characterization of the antibacterial activity of a novel hybrid antimicrobial peptide comprising functional domains from different insect cecropins

The search for new antimicrobial compounds involves finding novel sources of chemotherapeutic compounds or manipulating and combining structures from existing molecules. Small antimicrobial peptides (AMPs) are components of innate immune defenses characterized in greatest detail in insect-derived AMPs. We have generated hybrid AMPs (hAMPs) by combining functional motifs from different insect AMPs as a proof of principle that we can generate molecules with lower minimum inhibitory concentrations, and with different activity and target specificity than either parent molecule. A two-helix, cecropin-like hAMP was created by linking the N-terminal alpha helix of cecropin A from Aedes aegypti to the C-terminal alpha helix of cecropin A1 from Drosophila melanogaster. This molecule exhibits antibacterial activity at sub-micromolar concentrations with a target specificity that differs from either parent molecule. Antibacterial activity of the hybrid molecule was found to be greater against Gram-negative than Gram-positive bacteria. No hemolysis was observed in sheep red blood cells exposed to concentrations up to 50 micromol/L, suggesting the peptide is not detrimental to eukaryotic cells.

CpxRA contributes to Xenorhabdus nematophila virulence through regulation of lrhA and modulation of insect immunity

The gammaproteobacterium Xenorhabdus nematophila is a blood pathogen of insects that requires the CpxRA signal transduction system for full virulence (E. E. Herbert et al., Appl. Environ. Microbiol. 73:7826-7836, 2007). We show here that the DeltacpxR1 mutant has altered localization, growth, and immune suppressive activities relative to its wild-type parent during infection of Manduca sexta insects. In contrast to wild-type X. nematophila, which were recovered throughout infection, DeltacpxR1 cells did not accumulate in hemolymph until after insect death. In vivo imaging of fluorescently labeled bacteria within live insects showed that DeltacpxR1 displayed delayed accumulation and also occasionally were present in isolated nodes rather than systemically throughout the insect as was wild-type X. nematophila. In addition, in contrast to its wild-type parent, the DeltacpxR1 mutant elicited transcription of an insect antimicrobial peptide, cecropin. Relative to phosphate-buffered saline-injected insects, cecropin transcript was induced 21-fold more in insects injected with DeltacpxR1 and 2-fold more in insects injected with wild-type X. nematophila. These data suggest that the DeltacpxR1 mutant has a defect in immune suppression or has an increased propensity to activate M. sexta immunity. CpxR regulates, directly or indirectly, genes known or predicted to be involved in virulence (E. E. Herbert et al., Appl. Environ. Microbiol. 73:7826-7836, 2007), including lrhA, encoding a transcription factor necessary for X. nematophila virulence, motility, and lipase production (G. R. Richards et al., J. Bacteriol. 190:4870-4879, 2008). CpxR positively regulates lrhA transcript, and we have shown that altered regulation of lrhA in the DeltacpxR1 mutant causes this strain's virulence defect. The DeltacpxR1 mutant expressing lrhA from a constitutive lac promoter showed wild-type virulence in M. sexta. These data suggest that CpxR contributes to X. nematophila virulence through the regulation of lrhA, immune suppression, and growth in Insecta.

Antibacterial activity in vivo and in vitro in the hemolymph of Galleria mellonella infected with Pseudomonas aeruginosa

The antibacterial activity of hemolymph from Galleria mellonella infected with entomopathogenic strain of Pseudomonas aeruginosa and non-pathogenic bacterium Escherichia coli was studied. In vivo, the antimicrobial activity appeared shortly after P. aeruginosa infection, reached the maximum level 18 h postinjection, while 30 h later only trace activity was noted. The activity induced by E. coli sustained on the high level until 48 h after infection. We also noted that the antimicrobial activity level induced by the non-pathogenic bacterium was higher in comparison to that measured in insects infected with the pathogenic strain of P. aeruginosa. The results of our in vitro studies indicated that inducible antimicrobial peptides of G. mellonella larvae were digested by P. aeruginosa elastase B. After 1 h incubation of cell-free hemolymph of immune-challenged larvae with elastase B, no antibacterial activity was observed. It was also shown that elastase B degraded synthetic cecropin B while in the presence of 6 mM EDTA antibacterial activity of cell-free hemolymph as well as cecropin B, was not changed which confirmed that the activity was abolished by the metalloprotease.

Design and analysis of structure-activity relationship of novel antimicrobial peptides derived from the conserved sequence of cecropin

We have de novo designed four antimicrobial peptides AMP-A/B/C/D, the 51-residues peptides, which are based on the conserved sequence of cecropin. In the present study, the four peptides were chemically synthesized and their activities assayed. Their secondary structure, amphipathic property, electric field distribution and transmembrane domain were subsequently predicted by bioinformatics tools. Finally, the structure-activity relationship was analyzed from the results of activity experiments and prediction. The results of activity experiments indicated that AMP-B/C/D clearly possessed excellent broad-spectrum activity against bacteria, whereas AMP-A was almost inactive against most of the bacterial strains tested. AMP-B/C/D showed more potent activity against Gram-positive bacteria than against Gram-negative bacteria. By utilizing bioinformatics analysis tools, we found that the secondary structure of the four cation peptides was mainly alpha-helix, and the result of CD spectrum also displayed that all the peptides had considerable alpha-helix in the presence of either 50% TFE or SDS micelles. AMP-C showed much better activity than other peptides against most of the bacteria tested, owing to its remarkable cation property and the amphipathic character of its N-terminal. The study of structure-activity relationship of the designed peptides confirmed that amphipathic structure and high net positive charge were prerequisites for maintaining their activities.

Expression of antimicrobial peptide genes encoding Enbocin and Gloverin isoforms in the silkworm, Bombyx mori

Antimicrobial peptides, Enbocin and Gloverin isoforms from the silkworm Bombyx mori, were analyzed for expression of these peptide genes. Tissue-specific expression of Enbocin and Bmgloverin isoform genes was observed mainly in the fat body upon injection of Escherichia coli. Peptidoglycan and lipopolysaccharide triggered expression of these genes in vivo. On the other hand, lipid A activated Bmgloverin isoform genes but not Enbocin isoform genes. These results illustrate the fact that expression of Enbocin and Bmgloverin isoform genes is inducible by bacteria and that the effects of bacterial cell wall components on the activation of these peptide genes are not necessarily the same. In addition, selective activation of the Enbocin2, Bmgloverin2, and Bmgloverin4 genes by BmRelB rather than BmRelA was observed, providing additional evidence for the occurrence of selective activation of antimicrobial peptide genes by a Rel protein. These results suggest complex regulatory mechanisms in insect antimicrobial peptide genes by bacterial cell wall components.

Characterization and expression of a cecropin-like gene from Helicoverpa armigera

A cDNA encoding a cecropin-like antibacterial peptide was obtained by RT-PCR from cotton budworm (Helicoverpa armigera). The cloned cDNA consists of 773 nucleotides with a 192 bp open reading frame encoding a peptide of 63 aa, which is comprised of a 21 aa signal peptide and a 42 amino acids mature peptide. The amino acid sequence of the mature peptide is highly similar to those D-type cecropins. The peptide was named as HacD. RT-PCR revealed that the transcript of HacD gene was inducible and could be detected in fatbodies, midguts, hemocytes and Malpighian tubules. HacD was highly expressed in E. coli M15 by fusing with green fluorescent protein (GFP). After purification, desalting and cleavage with factor Xa, HacD was released and showed antibacterial activity to both Gram-positive and Gram-negative bacteria. The genomic DNA of HacD was amplified by TAIL-PCR. NF-kappaB and NF-IL6 binding sites were found in the 5'-upstream regulatory region of HacD gene. EMSA (electrophoretic mobility shift assay) revealed that nuclear proteins from the immunized larvae could bind to the NF-kappaB site, but no nuclear proteins were found to bind to the NF-IL6 site. It was proposed that the NF-kappaB site might contribute to the expression of HacD.

Purification and characterization of eight peptides from Galleria mellonella immune hemolymph

Defense peptides play a crucial role in insect innate immunity against invading pathogens. From the hemolymph of immune-challenged greater wax moth, Galleria mellonella (Gm) larvae, eight peptides were isolated and characterized. Purified Gm peptides differ considerably in amino acid sequences, isoelectric point values and antimicrobial activity spectrum. Five of them, Gm proline-rich peptide 2, Gm defensin-like peptide, Gm anionic peptides 1 and 2 and Gm apolipophoricin, were not described earlier in G. mellonella. Three others, Gm proline-rich peptide 1, Gm cecropin D-like peptide and Galleria defensin, were identical with known G. mellonella peptides. Gm proline-rich peptides 1 and 2 and Gm anionic peptide 2, had unique amino acid sequences and no homologs have been found for these peptides. Antimicrobial activity of purified peptides was tested against gram-negative and gram-positive bacteria, yeast and filamentous fungi. The most effective was Gm defensin-like peptide which inhibited fungal and sensitive bacteria growth in a concentration of 2.9 and 1.9 microM, respectively. This is the first report describing at least a part of defense peptide repertoire of G. mellonella immune hemolymph.

Analysis of the immune-inducible genes of Plutella xylostella using expressed sequence tags and cDNA microarray

In the present study, the complex gene expression responses of Plutella xylostella to microbial challenges and injury were surveyed using a newly constructed expressed sequence tag (EST) clone collection and cDNA microarray analysis. A total of 1132 P. xylostella ESTs were cloned, annotated and categorized by their putative functions; these included proteases, protease inhibitors, recognition molecules and anti-microbial peptides. GeneOntology revealed that 4% of the P. xylostella ESTs corresponded to immunity-related genes potentially involved in innate immunity. We then used microarray analysis to identify 44 genes that were differentially expressed with at least a two-fold expression difference in P. xylostella before and after pathogen challenge. Together, our EST categorization and microarray profiling analyses allowed us to identify 70 genes that should be considered candidate immune response genes, providing important new insights into the molecular events that occur during the innate immune response in P. xylostella.

Expression and characterization of a housefly cecropin gene in the methylotrophic yeast, Pichia pastoris

A 371 bp full-length cDNA (GenBank Accession No. DQ232774) was obtained from housefly Musca domestica by using degenerate primers and subsequent amplification by 5'- and 3'-RACE. The cecropin gene, Mdcec and Mdcec/6His, was cloned into expression pPICZalpha-A vector and was expressed in the methylotrophic yeast, Pichia pastoris. The recombinant Mdcec was purified using cationic exchange chromatography and 1.2mg pure active Mdcec was obtained from 100ml culture broth supernatant. To facilitate purification of Mdcec, the C-terminal 6His-tagged Mdcec was also expressed in P. pastoris. The recombinant Mdcec/6His was purified to homogeneity by a nickel chelating sepharose column and 2.0mg pure active Mdcec/6His was obtained from 100ml culture broth supernatant. Anti-microbial assays demonstrated that Mdcec had broad spectrum of antimicrobial property against fungi, as well as Gram-positive and Gram-negative bacteria. Mdcec/6His showed a similar activity to Mdcec against bacteria, but a slight higher activity against fungi. These results indicate that the 6His-tag can enhance the cationic nature and stability of Mdcec. This is the first report on the heterologous expression of a cecropin and cecropin with a 6His tag in P. pastoris. Our results suggest that the P. pastoris expression system can be used to produce large quantities of fully functional M. domestica cecropin for both research and industrial purpose.

Characterization and cDNA cloning of hinnavin II, a cecropin family antibacterial peptide from the cabbage butterfly, Artogeia rapae

Hinnavins, together with lysozymes, are the main types of antibacterial peptides/proteins previously isolated from the larval haemolymph of the cabbage butterfly, Artogeia rapae as part of the humoral immune response to a bacterial invasion. One of these antibacterial peptides, named hinnavin II, was purified and characterized after cDNA cloning. The purified hinnavin II was more active against Gram negative than against Gram positive bacteria. Hinnavin II also showed a powerful synergistic effect on the inhibition of bacterial growth with purified lysozyme. The cDNA has a total length of 186 bp with a 114 coding region. The deduced protein sequence contains 38 amino acids with a coding capacity of 4142.8 Da. The result of a multiple sequence alignment and phylogenetic analysis with Clustal W indicated that mature hinnavin II showed an approximately 78.9% amino acid sequence identity with cecropin A and originated from a group containing mostly lepidopteran cecropins.

Peptide-membrane interactions and mechanisms of membrane destruction by amphipathic alpha-helical antimicrobial peptides

Antimicrobial peptides (AMPs) have received considerable interest as a source of new antibiotics with the potential for treatment of multiple-drug resistant infections. An important class of AMPs is composed of linear, cationic peptides that form amphipathic alpha-helices. Among the most potent of these are the cecropins and synthetic peptides that are hybrids of cecropin and the bee venom peptide, mellitin. Both cecropins and cecropin-mellitin hybrids exist in solution as unstructured monomers, folding into predominantly alpha-helical structures upon membrane binding with their long helical axis parallel to the bilayer surface. Studies using model membranes have shown that these peptides intercalate into the lipid bilayer just below the level of the phospholipid glycerol backbone in a location that requires expansion of the outer leaflet of the bilayer, and evidence from a variety of experimental approaches indicates that expansion and thinning of the bilayer are common characteristics during the early stages of antimicrobial peptide-membrane interactions. Subsequent disruption of the membrane permeability barrier may occur by a variety of mechanisms, leading ultimately to loss of cytoplasmic membrane integrity and cell death.

Purification and cDNA cloning of a cecropin from the longicorn beetle, Acalolepta luxuriosa

We have cloned and characterized a novel antibacterial peptide from the hemolymph of the coleopteran insect Acalolepta luxuriosa, of the superfamily Cerambyocidea. This peptide is active against Micrococcus luteus and Escherichia coli, and the amino acid sequence deduced by cloning of the cDNA identifies it as a coleopteran cecropin. Sequence comparisons and phylogenetic analyses performed using Clustal X suggest that this cecropin is evolutionarily intermediate between dipteran and lepidopteran cecropins. The results of MALDI-TOF mass spectrometry indicate that the mature form of this antibacterial peptide is 35 amino acid residues in length and has an amidated C-terminal isoleucine. This report is the first description of a cecropin from a coleopteran insect.

Innate immune responses of a lepidopteran insect, Manduca sexta

Many innate immune mechanisms are conserved throughout the animal kingdom. Manduca sexta, a widely used model for insect biochemical research, employs these mechanisms to defend against invading pathogens and parasites. We have isolated from M. sexta hemolymph a group of proteins (hemolin, peptidoglycan recognition proteins, beta-1,3-glucan recognition proteins, and C-type lectins), which serve as a surveillance mechanism by binding to microbial surface molecules (e.g. peptidoglycan, lipopolysaccharide, lipoteichoic acid, and beta-1,3-glucan). The binding triggers diverse responses such as phagocytosis, nodule formation, encapsulation, melanization, and synthesis of anti-microbial peptides/proteins. Some of these responses are mediated and coordinated by serine proteinase cascades, analogous to the complement system in mammals. Our current research is focused on the proteolytic activation of prophenoloxidase (proPO)--a reaction implicated in melanotic encapsulation, wound healing, and protein cross-linking. We have isolated three proPO-activating proteinases, each of which requires serine proteinase homologs as a cofactor for generating active phenoloxidase. The proteinases and proteinase-like molecules, containing one to two clip domains at their amino-terminus, are acute-phase proteins induced upon an immune challenge. Inhibitory regulation of the proteinases by serpins and association of the proteinase homologs with a bacteria-binding lectin are important for ensuring a localized defense response. Additional serine proteinases expressed in M. sexta hemocytes and fat body have been discovered. Future research efforts will be aimed at elucidating the proteinase cascade for proPO activation and investigating the roles of proteinases in other immune responses such as processing of plasmatocyte-spreading peptide.

Induced immunity in Antheraea assama Ww larvae against flacherie causing Pseudomonas aeruginosa AC-3

This study reports for the first time the induction of immunity in Antheraea assama Ww larvae against bacterial flacherie. In silkworms group of disease caused by bacteria are collectively called "flacherie." This refers to the flaccid condition of the larvae due to the infections of bacterial strains pathogenic to muga silkworm. Antibacterial activity against pathogenic Pseudomonas aeruginosa AC-3 causing flacherie, was induced by injection of heat-killed cells of the same strain. Experiments on larval survivability and viable cell count revealed peak immune response on third day. Comparison of the amount of food ingested, excreta produced and larval weight of the saline-injected control, live bacteria-challenged larvae and heat-killed bacteria-injected larvae "(vaccinated)" confirmed the development of immunity against bacterial infection in the "vaccinated" set. The haemolymph of A. assama larvae was analyzed for proteins associated with bacterial infection. Out of the total 32 detected proteins, eleven (A1-2, A15-20, A22-23, and A29) were constitutively synthesized in both the control and live bacteria-injected larvae. Four inducible proteins A4, A9-10, and A21 were detected in the haemolymph of the live bacteria-injected larvae. Synthesis of rest of the proteins varied between the control and their live bacteria-injected counterparts. General protein profile of "vaccinated" larvae injected with live bacteria were found to be similar to that of the saline-injected control.

Identification by subtractive suppression hybridization of bacteria-induced genes expressed in Manduca sexta fat body

Insect immune processes are mediated by programs of differential gene expression. To understand the molecular regulation of the immune response in the tobacco hornworm, Manduca sexta, the relevant subset of differentially expressed genes of interest must be identified, cloned and studied in detail. In this study, suppression subtractive hybridization, a PCR-based method for cDNA subtraction was performed to identify mRNAs from fat body of immunized larvae that are not present (or present at a low level) in control larvae. A subtracted cDNA library enriched in immune-inducible genes was constructed. Northern blot analysis of a sample of clones from our subtracted library indicated that >90% of the clones randomly selected from the subtracted library are immune inducible. Sequence analysis of 238 expressed sequence tags (ESTs) revealed that 120 ESTs, representing 54 distinct genes or gene families, had sequences identical or similar to previously characterized genes, some of which have been confirmed to be involved in innate immunity. These ESTs were categorized into seven groups, including pattern recognition proteins, serine proteinases and their inhibitors, and antimicrobial proteins. 112 ESTs, about 47.5% of the library, showed no significant similarity to any known genes. The sequences identified in this M. sexta library reflect our knowledge of insect immune strategies and may facilitate better understanding of insect immune responses.

cDNA cloning and antibacterial activities of cecropin D-like peptides from Agrius convolvuli

We have characterized full-length cDNAs encoding two isoforms of agriusin, cecropin D-like antibacterial peptide, present in the hemolymph of the immunized Agrius convolvuli larvae. The cloned cDNAs of agriusins 1 and 2 contain 331 and 329 bp, respectively. The nucleotide sequencing of cDNAs showed that they encode 62 amino acids, whose mature portion was deduced to consist of 38 amino acid residues with over 94% sequence identity. In the sequence homology search, mature agriusin 1 showed over 86 and 71% amino acid sequence homology with bactericidin 4 from Manduca sexta and cecropin D from Hyalophora cecropia, respectively. Since it was demonstrated from the deduced amino acid sequences that the C-terminal residues of agriusins are followed by a Gly residue, two types of synthetic agriusin 1 (syn-agriusin 1 amide and acid) were prepared to verify if natural agriusin 1 is C-terminally amidated. From acid-urea PAGE and reversed phase HPLC profiles to compare two synthetic peptides, we could confirm that the C-terminal amino acid residue of natural agriusin 1, like several cecropins so far identified, is amidated. Finally, our antibacterial assay performed with two syn-agriusins 1 revealed that there is little difference between antibacterial activities of both peptides against Gram-positive and Gram-negative bacteria.

Antibacterial peptides isolated from insects

Insects are amazingly resistant to bacterial infections. To combat pathogens, insects rely on cellular and humoral mechanisms, innate immunity being dominant in the latter category. Upon detection of bacteria, a complex genetic cascade is activated, which ultimately results in the synthesis of a battery of antibacterial peptides and their release into the haemolymph. The peptides are usually basic in character and are composed of 20-40 amino acid residues, although some smaller proteins are also included in the antimicrobial repertoire. While the proline-rich peptides and the glycine-rich peptides are predominantly active against Gram-negative strains, the defensins selectively kill Gram-positive bacteria and the cecropins are active against both types. The insect antibacterial peptides are very potent: their IC50 (50% of the bacterial growth inhibition) hovers in the submicromolar or low micromolar range. The majority of the peptides act through disintegrating the bacterial membrane or interfering with membrane assembly, with the exception of drosocin, apidaecin and pyrrhocoricin which appear to deactivate a bacterial protein in a stereospecific manner. In accordance with their biological function, the membrane-active peptides form ordered structures, e.g. alpha-helices or beta-pleated sheets and often cast permeable ion-pores. Their cytotoxic properties were exploited in in vivo studies targeting tumour progression. Although the native peptides degrade quickly in biological fluids other than insect haemolymph, structural modifications render the peptides resistant against proteases without sacrificing biological activity. Indeed, a pyrrhocoricin analogue shows lack of toxicity in vitro and in vivo and protects mice against experimental Escherichia coli infection. Careful selection of lead molecules based on the insect antibacterial peptides may extend their utility and produce viable alternatives to the conventional antimicrobial compounds for mammalian therapy.

Antimicrobial activity spectrum, cDNA cloning, and mRNA expression of a newly isolated member of the cecropin family from the mosquito vector Aedes aegypti

An antimicrobial peptide belonging to the cecropin family was isolated from the hemolymph of bacteria-challenged adult Aedes aegypti. This new peptide, named cecropin A, was purified to homogeneity and fully characterized after cDNA cloning. The 34-residue A. aegypti cecropin A is different from the majority of reported insect cecropins in that it is devoid of a tryptophan residue and C-terminal amidation. The importance of these two structural features on the activity spectrum was investigated using a chemically synthesized peptide. A comparison of the antimicrobial activity spectrum of A. aegypti and Drosophila cecropin A showed a lower activity for the mosquito molecule. A. aegypti cecropin mRNA expression was not detected by Northern blot or reverse transcription-polymerase chain reaction analysis in any immature stage of the mosquito, nor in naïve adults, but it was observed in challenged adults 6 h after bacteria inoculation, and it continued over 7-10 days.

Cecropin D-like antibacterial peptides from the sphingid moth, Agrius convolvuli

Two major antibacterial peptides were isolated and purified from immunized larval hemolymph of Agrius convolvuli. Acid extraction, gel filtration, ultrafiltration, and reversed-phase FPLC were used for purification of peptides. These peptides had similar molecular mass and amino acid composition. Moreover, 21 of the first 23 N terminal residues were identical. The peptides were highly homologous with cecropin D in size and primary sequence, and named Agrius cecropin D1 and D2. The molecular masses of Agrius cecropin D1 and D2 were 3,879.39 and 3,839.27, respectively. In antibacterial and hemolytic assays, Agrius cecropin D showed potent antibacterial activities against a panel of Gram positive and negative bacteria without hemolytic activity against human red blood cells. Notably, our antibacterial assay revealed Agrius cecropin D possessed stronger or at least equivalent activities against B. megaterium than cecropin A. It suggests that Agrius cecropin D, which has an alternative structure from cecropin D, could be the model for the development of peptide antibiotics. Arch.

Peptide sequence of an antibiotic cecropin from the vector mosquito, Aedes albopictus

We have identified a 35-amino acid antibiotic cecropin secreted by an established mosquito cell line. C7-10 cells from the vector mosquito, Aedes albopictus, were incubated with heat-killed Escherichia coli, and materials secreted into the cell culture supernatant were recovered by acid precipitation. Following batch elution from Sep-Pak C18 cartridges and further purification by reverse phase high performance liquid chromatography (RP-HPLC) a predominant peak of antibacterial activity was characterized by mass spectrometry, amino acid composition analysis, and Edman degradation, yielding the sequence GGLKKLGKKLEGVGKRVFKASEKALPVAVGIKALG. Unlike other cecropins, the peptide was not amidated at the C-terminus. Aedes albopictus Cecropin A (AalCecA) is the first cecropin to be described from a mosquito vector of human disease. Consistent with the classification of mosquitoes among the Dipteran suborder Nematocera, AalCecA shares only 36% amino acid identity with cecropins from Drosophila melanogaster and other Cyclorrhaphid flies, whose mature cecropins share 80% to 100% amino acid identity.

Cloning and expression of a novel gene encoding a new antibacterial peptide from silkworm, Bombyx mori

We differentially screened a novel gene encoding a new antibacterial peptide from the immunized Bombyx mori cDNA library. The gene showed a similar structure to that of cecropin-family, encoding 59 amino acids including a putative leader peptide and mature peptide. The deduced peptide, named Enbocin, had conserved amino acid residues which have been known to play an important role in the antibacterial activities. Enbocin genomic sequence revealed that the transcription unit of Enbocin gene was about 1.2 kb, and the coding sequence was interrupted by an intron of 660 bases. Recombinant Enbocin, expressed under the control of the baculovirus polyhedrin promoter, demonstrated a broad range of antibacterial activities against gram positive and gram negative bacteria.

Protein purification and cDNA cloning of a cecropin-like peptide from the larvae of fall webworm (Hyphantria cunea)

A proteinous antimicrobial substance was purified from the bacteria-challenged larvae of the fall webworm, Hyphantria cunea. It is a cecropin-like antibacterial peptide which exhibits antibacterial activity against Gram-negative and Gram-positive bacteria, and known as Hyphantria cecropin A. The cDNA clones corresponding to this peptide were isolated from a cDNA library constructed from the bacteria-challenged larvae and obtained complete nucleotide sequences. In addition to the Hyphantria cecropin A sequence, we obtained three other cDNAs exhibiting high sequence similarity with Hyphantria cecropin A. We synthesized the C-terminally amidated peptide of 35 residues based on the deduced sequence of the isolated cDNA of Hyphantria cecropin A. The synthetic peptide exhibited strong antibacterial activity against several microbes including medically important bacteria such as Salmonella, Shigella, and fungus such as Candida. A Southern blot experiment using these cloned cDNAs as probes predicted the existence of multiple forms of Hyphantria cecropin genes.

cDNA cloning of three cecropin-like antimicrobial peptides (Styelins) from the tunicate, Styela clava

We cloned precursors of three new antimicrobial peptides, Styelins C, D and E, from a pharyngeal cDNA library of a tunicate, Styela clava. Preprostyelins resembled dipteran preprocecropins, while the mature domain of Styelin C resembled Cecropin P1, an antimicrobial peptide purified from the porcine intestine. Beginning with the last 6 residues of their signal sequences, Styelin C and Cecropin 1 from Drosophila virilis had 8/11 identical amino acids (72.7%). Moreover, 4 of the last 6 residues of their mature peptide domains were also identical. Styelins were shorter, by 8 residues, than dipteran cecropins and preprostyelins contained a conserved, polyanionic C-terminal extension that was absent in preprocecropins. Delineation of cecropin-like antimicrobial peptides in a protochordate supports the antiquity of this family as effectors of innate immunity in animals and it increases the likelihood that additional cecropin-like peptides will be found among other evolutionary descendants of protochordates--vertebrates.

Biological mediators of insect immunity

Infection in insects stimulates a complex defensive response. Recognition of pathogens may be accomplished by plasma or hemocyte b1p4eins that bind specifically to bacterial or fungal polysaccharides. Several morphologically distinct hemocyte cell types cooperate in the immune response. Hemocytes attach to invading organisms and then isolate them by phagocytosis, by trapping them in hemocyte aggregates called nodules, or by forming an organized multicellular capsule around large parasites. These responses are often accompanied by proteolytic activation of the phenoloxidase zymogen that is present in the hemolymph. A component of insect immune responses to bacteria is the synthesis by fat body and hemocytes of a variety of antibacterial proteins and peptides, which are secreted into the hemolymph. These molecules attack bacteria by several mechanisms. Inducible antifungal proteins have also been recently discovered in insect hemolymph. The promoters for several antibacterial protein genes in insects are regulated by transcription factors similar to those involved in mammalian acute phase responses.

Presence in Pieris rapae of cytotoxic activity against human carcinoma cells

Cytotoxic activity in extracts of pupae and adults of various kinds of butterflies and moths was tested in vitro against the human gastric carcinoma cell line, TMK-1, which was chosen as an example of human carcinoma cells. Among the species examined, cytotoxicity was limited to Pieris rapae, Pieris napi and Pieris brassicae. Activity was found down to a dilution of 1/10(4), while with the other butterflies and moths no activity was observed, even at 1/10(2). When the cytotoxicity of the three developmental stages, larvae, pupae and adults, of Pieris rapae was compared, the pupae showed the strongest activity, the IC50 against TMK-1 cells being at the 1/10(6) dilution. For larvae and adults, the respective IC50 values were at the 1/10(5) and 5/10(5) dilutions. The active principle in the pupae of Pieris rapae was found to be heat-labile and not extractable with organic solvents, but precipitated with ammonium sulfate and digested by proteases, suggesting that it is a protein. This cytotoxic factor was named pierisin.

Formation of pores in Escherichia coli cell membranes by a cecropin isolated from hemolymph of Heliothis virescens larvae

The insect humoral defense system produces antibacterial peptides called cecropins. Cecropins were initially isolated from Hyalophora cecropia pupae and have since been isolated and identified in various insects. In this study, we have isolated and identified a cecropin from Heliothis virescens larvae. Rabbit IgG were raised against synthetic cecropin B. Affinity chromatography with the rabbit anti-(cecropin B) IgG was used to isolate a cecropin from hemolymph of H. virescens larvae. Acid gel electrophoresis followed by a bacterial-overlay analysis showed that Heliothis cecropin is a basic peptide of low molecular mass with bactericidal activity against Escherichia coli K12 D31. Heliothis cecropin is therefore analogous to synthetic cecropin B. One unresolved issue concerning cecropins and other antibiotic peptides is the mode of action by which they kill bacteria. By means of electron microscopy and immunocytochemistry with gold-labeled rabbit anti-cecropin IgG, binding of purified and synthetic cecropin to the cell membranes of E. coli K12 D31 cells was observed. Small lesions in the cell membrane were seen that had a diameter of 9.6 nm and internal pore of 4.2 nm. The Heliothis cecropin was found to be a pore-forming molecule that causes lesions in the cell membrane of E. coli K12 D31. The lesions lead to leakage of cytoplasmic contents and death of bacteria.

Cloning of mRNA sequences for two antibacterial peptides in a hemipteran insect, Riptortus clavatus

Escherichia coli injection rapidly induced bactericidal activity in the hemolymph of a hemipteran insect, Riptortus clavatus. This activity reached its maximum at 9 hr after injection and thereafter declined slowly. Two types of cDNA clones involved in this response were isolated by differential screening. The predominant type encoded for an open reading frame of 678 amino acids, which consisted of fourteen tandem repeats. Each repeat was rich in charged residues and had a proline-rich region which had striking sequence similarities to proline-rich antibacterial peptides from other insect species, indicating these clones encode a multipeptide precursor of antibacterial peptides. The other type encoded for a glycine-rich peptide similar to a known antibacterial peptide as well. Northern blot analyses revealed rapid induction of mRNAs corresponding to these clones after the injection. To our knowledge, this is the first report on the mRNA sequences of antibacterial peptides of hemimetabolous insects, and the second report on the occurrence of multipeptide precursor structure in insect antibacterial peptides.

Isolation and characterization of the lysozyme-encoding gene from the silkworm Bombyx mori

We have isolated and characterized a Bombyx mori (Bm) cDNA encoding a lysozyme (Lyz). A 90-bp DNA fragment was amplified by PCR using degenerate oligodeoxyribonucleotide primers derived from the known amino acid (aa) sequence of the Bm Lyz. These PCR fragments were used to screen a fat body cDNA library. A clone containing the complete lys cDNA (1294 bp) was isolated and completely sequenced. The deduced 137-aa sequence showed high homology with other chicken-type Lyz. Bm lys gene expression was constitutive in fat body, cuticular epidermal tissue and at a very low level in hemocytes. This gene expression was up-regulated in fat body, hemocytes and cuticular epidermal tissue following the injection of Gram+ bacteria.

Processing of chromogranin B in bovine adrenal medulla. Identification of secretolytin, the endogenous C-terminal fragment of residues 614-626 with antibacterial activity

Chromogranins constitute a family of acidic soluble proteins widely distributed in endocrine cells and neurons. Chromogranin A, the major soluble component in bovine adrenal medullary secretory granules in chromaffin cells, has been shown to be actively processed to peptide fragments [Metz-Boutigue, M. H., Garcia-Sablone, P., Hogue-Angeletti, R. & Aunis, D. (1993) Eur. J. Biochem. 217, 247-257]. In the present paper, the structural features of the proteolytic degradation mechanism of chromogranin B/secretogranin I have been characterized with regard to the possible function of this protein as a precursor of biologically active peptides. Chromogranin-B-derived fragments present in bovine chromaffin granules were identified by microsequencing after separation by two-dimensional gel electrophoresis or high-performance liquid chromatography. A similar approach was performed to characterize chromogranin-B-derived fragments released into the extracellular space from depolarized bovine cultured chromaffin cells. In chromogranin B, 18 cleavage sites were identified along the protein chain and chromogranin B/secretogranin I fragments were generated by proteolytic attack at both the N-terminus and C-terminus. A major fragment corresponding to residues 614-626 of the C-terminal sequence, was identified in the extracellular space; this peptide was found to share sequence and structural similarities with the lytic domain of cecropins and, as expected from this similarity, to display potent antibacterial properties. Endogenous and synthetic peptides were active on Micrococus luteus, killing bacteria in the micromolar concentration range. The synthetic peptide slows the growth of Bacillus megaterium and was inactive towards Escherichia coli. In addition, the synthetic peptide was unable to induce hemolytic activity. This antibacterial function might be of biological significance in the neuroendocrine system of living organisms. We propose to name this peptide secretolytin.

Characterization of a Bombyx mori cDNA encoding a novel member of the attacin family of insect antibacterial proteins

A Bombyx mori cDNA was cloned that hybridized with Hyalophora cecropia attacin probe and its nucleotide sequence was determined. This cDNA consisted of 846 nucleotides and the deduced amino acid sequence showed that the cDNA encodes an attacin precursor protein. The putative mature protein of B. mori attacin had 70.4, 68.3 and 18.8% identity in amino acid sequences with that of H. cecropia acidic and basic attacins and Sarcophaga peregrina sarcotoxin IIA, respectively. B. mori and H. cecropia attacins and S. peregrina sarcotoxin IIA had two subdomains in each G domain, suggesting that common amino acid residues in the subdomains are conserved during evolution and plays an important role in the activity of the antibacterial proteins. Expression of B. mori attacin gene was rapidly induced by the injection of Escherichia coli cells into B. mori larvae and continued at least for 48 h mainly in fat bodies and hemocytes.