Solution structure of moricin, an antibacterial peptide, isolated from the silkworm Bombyx mori

Insect Antimicrobial Peptides as Guardians of Immunity and Beyond: A Review

Antimicrobial peptides (AMPs), as immune effectors synthesized by a variety of organisms, not only constitute a robust defense mechanism against a broad spectrum of pathogens in the host but also show promising applications as effective antimicrobial agents. Notably, insects are significant reservoirs of natural AMPs. However, the complex array of variations in types, quantities, antimicrobial activities, and production pathways of AMPs, as well as evolution of AMPs across insect species, presents a significant challenge for immunity system understanding and AMP applications. This review covers insect AMP discoveries, classification, common properties, and mechanisms of action. Additionally, the types, quantities, and activities of immune-related AMPs in each model insect are also summarized. We conducted the first comprehensive investigation into the diversity, distribution, and evolution of 20 types of AMPs in model insects, employing phylogenetic analysis to describe their evolutionary relationships and shed light on conserved and distinctive AMP families. Furthermore, we summarize the regulatory pathways of AMP production through classical signaling pathways and additional pathways associated with Nitric Oxide, insulin-like signaling, and hormones. This review advances our understanding of AMPs as guardians in insect immunity systems and unlocks a gateway to insect AMP resources, facilitating the use of AMPs to address food safety concerns.

Antimicrobial peptide moricin induces ROS mediated caspase-dependent apoptosis in human triple-negative breast cancer via suppression of notch pathway

BACKGROUND

Breast cancer is the world's most prevalent cancer among women. Microorganisms have been the richest source of antibiotics as well as anticancer drugs. Moricin peptides have shown antibacterial properties; however, the anticancer potential and mechanistic insights into moricin peptide-induced cancer cell death have not yet been explored.

METHODS

An investigation through in silico analysis, analytical methods (Reverse Phase-High Performance Liquid Chromatography (RP-HPLC), mass spectroscopy (MS), circular dichroism (CD), and in vitro studies, has been carried out to delineate the mechanism(s) of moricin-induced cancer cell death. An in-silico analysis was performed to predict the anticancer potential of moricin in cancer cells using Anti CP and ACP servers based on a support vector machine (SVM). Molecular docking was performed to predict the binding interaction between moricin and peptide-related cancer signaling pathway(s) through the HawkDOCK web server. Further, in vitro anticancer activity of moricin was performed against MDA-MB-231 cells.

RESULTS

In silico observation revealed that moricin is a potential anticancer peptide, and protein-protein docking showed a strong binding interaction between moricin and signaling proteins. CD showed a predominant helical structure of moricin, and the MS result determined the observed molecular weight of moricin is 4544 Da. An in vitro study showed that moricin exposure to MDA-MB-231 cells caused dose dependent inhibition of cell viability with a high generation of reactive oxygen species (ROS). Molecular study revealed that moricin exposure caused downregulation in the expression of Notch-1, NF-ƙB and Bcl2 proteins while upregulating p53, Bax, caspase 3, and caspase 9, which results in caspase-dependent cell death in MDA-MB-231 cells.

CONCLUSIONS

In conclusion, this study reveals the anticancer potential and underlying mechanism of moricin peptide-induced cell death in triple negative cancer cells, which could be used in the development of an anticancer drug.

Diversity of Antimicrobial Peptides in Silkworm

Antimicrobial resistance is a phenomenon that the present-day world is witnessing that poses a serious threat to global health. The decline in the development of novel therapeutics over the last couple of decades has exacerbated the situation further. In this scenario, the pursuit of new alternative therapeutics to commonly used antibiotics has gained predominance amongst researchers across the world. Antimicrobial peptides (AMPs) from natural sources have drawn significant interest in the recent years as promising pharmacological substitutes over the conventional antibiotics. The most notable advantage of AMPs is that microorganisms cannot develop resistance to them. Insects represent one of the potential sources of AMPs, which are synthesized as part of an innate immune defence against invading pathogens. AMPs from different insects have been extensively studied, and silkworm is one of them. Diverse classes of AMPs (including attacins, cecropins, defensins, enbocins, gloverins, lebocins and moricins) were identified from silkworm that exhibit antimicrobial property against bacteria, fungi and viruses, indicating their potential therapeutic benefits. This review briefs about the immune responses of silkworm to invading pathogens, the isolation of AMPs from silkworms, AMPs reported in silkworms and their activity against various microorganisms.

Four antimicrobial peptides of Asian gypsy moth respond to infection of its viral pathogen, nucleopolyhedrovirus (LdMNPV)

Antimicrobial peptides (AMPs) play essential roles in defending against various invading pathogens. Although antibacterial or antifungal properties of AMPs have been well characterized, the contribution of AMPs to immune defenses against viruses especially baculoviruses is still unclear. In this study, four full-length AMP genes (Ldcec, Ldatt, Ldglo and Ldmor) that encode the cecropin, attacin, gloverin and moricin, respectively, were characterized in Lymantria dispar (Asian gypsy moth). All four AMPs were cationic peptides and exhibited hydrophilicity. Structural analysis showed that the Ldcec and Ldmor were α-helical peptides. Tissue-specific Ldcec expression was the highest in fat body, while expression of Ldatt, Ldglo and Ldmor was the highest in epidermis. All four AMP genes were expressed during all developmental stages with the highest expression in the pupa and adult. Compared to mock infection, expression of these four AMP genes were significantly induced following Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) challenge and sharply increased at 72 h post infection. After Ldglo gene silencing, the DNA replication levels of LdMNPV in L. dispar larvae significantly increased at 48 and 72 h post infection, indicating that the Ldglo could suppress the DNA replication of LdMNPV. Our results suggest that four AMPs of L. dispar may play important roles in antiviral immunity against LdMNPV.

Identification and Characterization of Antimicrobial Peptides From Butterflies: An Integrated Bioinformatics and Experimental Study

Butterflies represent one of the largest animal groups on Earth, yet antimicrobial peptides (AMPs) of this group are less studied in comparison with their moth counterparts. This study employed an integrated bioinformatics approach to survey natural AMPs from publicly available genomic datasets. Numerous AMPs, including cecropins, defensins, and moricins, were identified and subsequently used as templates for the design of a series of synthetic AMPs that mimicked the naturally occurring sequences. Despite differing biological effects among the various sequences, the synthetic AMPs exhibited potent antibacterial and antifungal activities in vitro and in vivo, without inducing hemolysis, which implied their therapeutic potential in infectious diseases. Electron and confocal fluorescence microscopies revealed that the AMPs induced distinct morphological and biophysical changes on microbial cell membranes and nuclei, suggesting that the antimicrobial effects were related to a mechanism of membrane penetration and nucleic acid binding by the peptides. In conclusion, this study not only offers insights into butterfly AMPs but also provides a practical strategy for high-throughput natural AMP discoveries that will have implications for future research in this area.

The rumen eukaryotome is a source of novel antimicrobial peptides with therapeutic potential

BACKGROUND

The rise of microbial antibiotic resistance is a leading threat to the health of the human population. As such, finding new approaches to tackle these microbes, including development of novel antibiotics is vital.

RESULTS

In this study, we mined a rumen eukaryotic metatranscriptomic library for novel Antimicrobial peptides (AMPs) using computational approaches and thereafter characterised the therapeutic potential of the AMPs. We identified a total of 208 potentially novel AMPs from the ruminal eukaryotome, and characterised one of those, namely Lubelisin. Lubelisin (GIVAWFWRLAR) is an α-helical peptide, 11 amino acid long with theoretical molecular weight of 1373.76 D. In the presence of Lubelisin, strains of methicillin-resistant Staphylococcus aureus (MRSA) USA300 and EMRSA-15 were killed within 30 min of exposure with ≥103 and 104 CFU/mL reduction in viable cells respectively. Cytotoxicity of Lubelisin against both human and sheep erythrocytes was low resulting in a therapeutic index of 0.43. Membrane permeabilisation assays using propidium iodide alongside transmission electron microscopy revealed that cytoplasmic membrane damage may contribute to the antimicrobial activities of Lubelisin.

CONCLUSIONS

We demonstrate that the rumen eukaryotome is a viable source for the discovery of antimicrobial molecules for the treatment of bacterial infections and further development of these may provide part of the potential solution to the ongoing problem of antimicrobial resistance. The role of these AMPs in the ecological warfare within the rumen is also currently unknown.

Identification of Candida glabrata Transcriptional Regulators That Govern Stress Resistance and Virulence

The mechanisms by which Candida glabrata resists host defense peptides and caspofungin are incompletely understood. To identify transcriptional regulators that enable C. glabrata to withstand these classes of stressors, a library of 215 C. glabrata transcriptional regulatory deletion mutants was screened for susceptibility to both protamine and caspofungin. We identified eight mutants that had increased susceptibility to both host defense peptides and caspofungin. Of these mutants, six were deleted for genes that were predicted to specify proteins involved in histone modification. These genes were ADA2, GCN5, SPT8, HOS2, RPD3, and SPP1 Deletion of ADA2, GCN5, and RPD3 also increased susceptibility to mammalian host defense peptides. The Δada2 and Δgcn5 mutants had increased susceptibility to other stressors, such as H₂O₂ and SDS. In the Galleria mellonella model of disseminated infection, the Δada2 and Δgcn5 mutants had attenuated virulence, whereas in neutropenic mice, the virulence of the Δada2 and Δrpd3 mutants was decreased. Thus, histone modification plays a central role in enabling C. glabrata to survive host defense peptides and caspofungin, and Ada2 and Rpd3 are essential for the maximal virulence of this organism during disseminated infection.

Antibacterial Mechanism of Silkworm Seroins

Seroin 1 and seroin 2 are abundant in silkworm cocoon silk and show strong antibacterial activities, and thus are thought to protect cocoon silk from damage by bacteria. In this study, we characterized the expression pattern of silkworm seroin 3, and found that seroin 3 is synthesized in the female ovary and secreted into egg to play its roles. After being infected, seroin 1, 2, and 3 were significantly up-regulated in the silkworm. We synthesized the full-length protein of seroin 1, 2, and 3 and their N/C-terminal domain (seroin-N/C), and compared the antimicrobial activities in vitro. All three seroins showed higher antibacterial activity against Gram-positive bacteria than against Gram-negative bacteria. Seroin 2 showed better antibacterial effect than seroin 1 and 3, whereas seroin 1/2/3-N was better than seroin 1/2/3-C. We found that seroin 2-C has stronger peptidoglycan binding ability than seroin 2-N per the ELISA test. The binding sites of seroin 2 with bacteria were blocked by peptidoglycan, which resulted in the loss of the antibacterial activity of seroin 2. Collectively, these findings suggest that seroin 1 and 2 play antibacterial roles in cocoon silk, whereas seroin 3 functions in the eggs. The three silkworm seroins have the same antibacterial mechanism, that is, binding to bacterial peptidoglycan by the C-terminal domain and inhibiting bacterial growth by the N-terminal domain.

Antimicrobial peptides fromBombyx mori: a splendid immune defense response in silkworms

Bombyx mori L., a primary producer of silk, is the main tool in the sericulture industry and provides the means of livelihood to a large number of people. Silk cocoon crop losses due to bacterial infection pose a major threat to the sericulture industry. Bombyx mori L., a silkworm of the mulberry type, has a sophisticated inherent innate immune mechanism to combat such invasive pathogens. Among all the components in this defense system, antimicrobial peptides (AMPs) are notable due to their specificity towards the invading pathogens without harming the normal host cells. Bombyx mori L. so far has had AMPs identified that belong to six different families, namely cecropin, defensin, moricin, gloverin, attacin and lebocin, which are produced by the Toll and immune deficiency (IMD) pathways. Their diverse modes of action depend on microbial pathogens and are still under investigation. This review examines the recent progress in understanding the immune defense mechanism of Bombyx mori based on AMPs.

AMPs produced by B. mori induced by microbial challenge in the fat body.

Curved or linear? Predicting the 3-dimensional structure of α-helical antimicrobial peptides in an amphipathic environment

α-Helical membrane-active antimicrobial peptides (AMPs) are known to act via a range of mechanisms, including the formation of barrel-stave and toroidal pores and the micellisation of the membrane (carpet mechanism). Different mechanisms imply that the peptides adopt different 3D structures when bound at the water-membrane interface, a highly amphipathic environment. Here, an evolutionary algorithm is used to predict the 3D structure of a range of α-helical membrane-active AMPs at the water-membrane interface by optimising amphipathicity. This amphipathic structure prediction (ASP) is capable of distinguishing between curved and linear peptides solved experimentally, potentially allowing the activity and mechanism of action of different membrane-active AMPs to be predicted. The ASP algorithm is accessible via a web interface at http://atb.uq.edu.au/asp/.

Molecular Identification of a Moricin Family Antimicrobial Peptide (Px-Mor) From Plutella xylostella With Activities Against the Opportunistic Human Pathogen Aureobasidium pullulans

Antimicrobial peptides (AMPs) represent the largest group of endogenous compounds and serves as a novel alternative to traditional antibiotics for the treatment of pathogenic microorganisms. Moricin is an important α-helical AMP plays a crucial role in insect humoral defense reactions. The present study was designed to identify and characterize novel AMP moricin (Px-Mor) from diamondback moth (Plutella xylostella) and tested its activity against bacterial and fungal infection including the opportunistic human pathogen Aureobasidium pullulans. Molecular cloning of Px-Mor using rapid amplification of cDNA ends revealed a 482 bp full length cDNA with 198 bp coding region. The deduced protein sequence contained 65 amino acids, and the mature peptides contained 42 amino acid residues with a molecular mass of 4.393 kDa. Expression analysis revealed that Px-Mor was expressed throughout the life cycle of P. xylostella with the highest level detectable in the fourth instar and prepupa stage. Tissue specific distribution showed that Px-Mor was highly expressed in fat body and hemocyte. In vitro, antimicrobial assays indicated that Px-Mor exhibited a broad antimicrobial spectrum against Gram positive bacteria (GPB), Gram negative bacteria (GNB) and fungi. Moreover, scanning electron microscopy and transmission electron microscopy (TEM) revealed that Px-Mor can cause obvious morphological alterations in A. pullulans, which demonstrated its powerful effect on the mycelia growth inhibition. Taken together, these results indicate that Px-Mor plays an important role in the immune responses of P. xylostella and can be further exploited as an antimicrobial agent against various diseases including for the treatment of A. pullulans infection.

The regulation of crecropin-A and gloverin 2 by the silkworm Toll-like gene 18 wheeler in immune response

The innate immune system is conserved among different insect species in its response to microorganism infection. The transmembrane receptors of the Toll superfamily play an important role in activating immune response, however, the function of silkworm Toll family member 18 Wheeler (18 W) remained unclear. Here, the 18w gene in silkworm was characterized. A relatively high transcription level of Bm18w mRNA was found in Malpighian tubules, and in eggs, larvae pre-molt to fourth instar, pupae and adults. When silkworm larvae were infected with E. coli or S. aureus, Bm18w showed a significant response, especially to E. coli, but did not have antibacterial activity. To further identify the downstream antimicrobial peptide genes of Bm18w, expression of Bm18w was knocked down with siRNA in vitro, resulting in significant decreases of cecropin-A, gloverin 2, and moricin B3. The overexpression of Bm18w was carried out using pIZT/V5-His-mCherry insect vector in BmN cells and significant upregulation of cecropin-A and gloverin 2 was detected, as well as upregulation of attacin and defensin. Based on the results, we concluded that Bm18w is involved in response to bacterial infection by selectively inducing the expression of antimicrobial peptide genes, especially cecropin-A and gloverin 2. This study provides valuable data to supplement understanding of the immune pathway of the silkworm.

Comparative Analysis of the Integument Transcriptomes between Stick Mutant and Wild-Type Silkworms

In insects, the integument provides mechanical support for the whole body and protects them from infections, physical and chemical injuries, and dehydration. Diversity in integument properties is often related to body shape, behavior, and survival rate. The stick (sk) silkworm is a spontaneous mutant with a stick-like larval body that is firm to the touch and, thus, less flexible. Analysis of the mechanical properties of the cuticles at day 3 of the fifth instar (L5D3) of sk larvae revealed higher storage modulus and lower loss tangent. Transcriptome sequencing identified a total of 19,969 transcripts that were expressed between wild-type Dazao and the sk mutant at L5D2, of which 11,596 transcripts were novel and detected in the integument. Differential expression analyses identified 710 upregulated genes and 1009 downregulated genes in the sk mutant. Gene Ontology (GO) enrichment analysis indicated that four chitin-binding peritrophin A domain genes and a chitinase gene were upregulated, whereas another four chitin-binding peritrophin A domain genes, a trehalase, and nine antimicrobial peptides were downregulated. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that two functional pathways, namely, fructose and mannose metabolism and tyrosine metabolism, were significantly enriched with differentially-expressed transcripts. This study provides a foundation for understanding the molecular mechanisms underlying the development of the stiff exoskeleton in the sk mutant.

Extensive characterization and differential analysis of endogenous peptides from Bombyx batryticatus using mass spectrometric approach

Bombyx batryticatus, the dried larva of Bombyx mori L. (4th-5th instars) infected with Beauveria bassiana Vuill, is an important animal-derived medicine effective against several diseases. The metamorphosis of silkworm can result insignificant changes in the levels of proteins and polypeptides in the 4^th and 5^th instar larvae. Here, we performed extensive characterization of Bombyx batryticatus peptides, including polypeptides containing cysteines, using an MS-based data mining strategy. A total of 779 peptides with various PTMs (post-translational modifications) were identified through database search and de novo sequencing. Some of these peptides might have important biological activities. Besides, the differential analysis of polypeptides between the head and body of Bombyx batryticatus was performed to provide a clinical basis for rational use of the drugs derived from it. This study illustrates the abundance and sequences of endogenous Bombyx batryticatus polypeptides, and thus, provides potential candidates for the screening of active compounds for future biological research and drug discovery studies.

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.

Functional Roles of Aromatic Residues and Helices of Papiliocin in its Antimicrobial and Anti-inflammatory Activities

A cecropin-like peptide, papiliocin, isolated from the swallowtail butterfly Papilio xuthus, possesses high selectivity against gram-negative bacteria. Since Trp(2) and Phe(5) are highly conserved residues in cecropin-like peptides, we investigated the role of Trp(2) and Phe(5) in antibacterial activity. Substitution of Trp(2) and Phe(5) in papiliocin with Ala (papiliocin-2A and papiliocin-5A) revealed that Trp(2) is a key residue in its antibacterial activities. In order to understand the structural requirements for papiliocin function and to design shorter, but more potent, peptide antibiotics, we designed papiliocin constructs, PapN (residues Arg(1)-Ala(22) from the N-terminal amphipathic helix). PapN exhibited significant broad-spectrum antibacterial activities without cytotoxicity. Bactericidal kinetics of peptides against E.coli showed that papiliocin completely and rapidly killed E.coli in less than 10 minutes at 2× MIC concentration, while papiliocin-2A and papiliocin-5A killed four times more slowly than papiliocin. The PapN series peptides permeabilized bacterial membranes less effectively than papiliocin, showing no antibacterial activities in an hour. The results imply that the Trp(2) and Phe(5) in the amphipathic N-terminal helix are important in the rapid permeabilization of the gram-negative bacterial membrane. The hydrophobic C-terminal residues permeabilize the hydrophobic bacterial cell membrane synergistically with these aromatic residues, providing selectivity against gram-negative bacteria.

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.

Properties and mechanisms of action of naturally occurring antifungal peptides

Antimicrobial peptides are a vital component of the innate immune system of all eukaryotic organisms and many of these peptides have potent antifungal activity. They have potential application in the control of fungal pathogens that are a serious threat to both human health and food security. Development of antifungal peptides as therapeutics requires an understanding of their mechanism of action on fungal cells. To date, most research on antimicrobial peptides has focused on their activity against bacteria. Several antimicrobial peptides specifically target fungal cells and are not active against bacteria. Others with broader specificity often have different mechanisms of action against bacteria and fungi. This review focuses on the mechanism of action of naturally occurring antifungal peptides from a diverse range of sources including plants, mammals, amphibians, insects, crabs, spiders, and fungi. While antimicrobial peptides were originally proposed to act via membrane permeabilization, the mechanism of antifungal activity for these peptides is generally more complex and often involves entry of the peptide into the cell.

Broad activity against porcine bacterial pathogens displayed by two insect antimicrobial peptides moricin and cecropin B

In response to infection, insects produce a variety of antimicrobial peptides (AMPs) to kill the invading pathogens. To study their physicochemical properties and bioactivities for clinical and commercial use in the porcine industry, we chemically synthesized the mature peptides Bombyx mori moricin and Hyalophora cecropia cecropin B. In this paper, we described the antimicrobial activity of the two AMPs. Moricin exhibited antimicrobial activity on eight strains tested with minimal inhibitory concentration values (MICs) ranging between 8 and 128 μg/ml, while cecropin B mainly showed antimicrobial activity against the Gramnegative strains with MICs ranging from 0.5 to 16 μg/ml. Compared to the potent antimicrobial activity these two AMPs displayed against most of the bacterial pathogens tested, they exhibited limited hemolytic activity against porcine red blood cells. The activities of moricin and cecropin B against Haemophilus parasuis SH 0165 were studied in further detail. Transmission electron microscopy (TEM) of moricin and cecropin B treated H. parasuis SH 0165 indicated extensive damage to the membranes of the bacteria. Insights into the probable mechanism utilized by moricin and cecropin B to eliminate pathogens are also presented. The observations from this study are important for the future application of AMPs in the porcine industry.

Inactivation of the budded virus of Autographa californica M nucleopolyhedrovirus by gloverin

Antimicrobial peptides are generated in insects exposed to pathogens for combating infection. Gloverin is a small cationic antibacterial protein whose expression is induced in the hemocytes and fat body cells of Trichoplusia ni larvae exposed to bacteria. The purpose of this study was to determine the role of gloverin during baculovirus infection. We found that gloverin expression is induced in T. ni systemically infected with the baculovirus Autographa californica M nucleopolyhedrovirus (AcMNPV). Two gloverin genes were cloned using RNA isolated from the hemocytes of T. ni larvae that were systemically infected with AcMNPV budded virus (BV) and C-terminal 6x-His and V5 epitope tags were incorporated to facilitate gloverin isolation, detection and functional studies. The supernatants of Sf9 cells stably transfected with the two gloverin expression plasmids and affinity purified gloverin proteins reduced the quantity of infectious AcMNPV BV as measured in vitro by plaque assay with untransfected Sf9 cells. Nanomolar concentrations of affinity column purified gloverin protein caused calcein to be rapidly released from unilamellar vesicles comprised of phosphatidylglycerol, but not from vesicles made up of phosphatidylcholine, suggesting that gloverin interaction with membranes is rapid and affected by membrane charge. Both the BV inactivation and calcein release activities of gloverin increased with higher concentrations of gloverin. These results demonstrate that gloverin is an antiviral protein that interacts with vesicle membranes to cause the contents to be released.

Manduca sexta moricin promoter elements can increase promoter activities of Drosophila melanogaster antimicrobial peptide genes

Insects produce a variety of antimicrobial peptides (AMPs). Induction of insect AMP genes is regulated by the Toll and IMD (immune deficiency) pathways via NF-κB and GATA factors. Little is known about species-specific regulation of AMP genes. In this report, we showed that activities of most Manduca sexta and Drosophila melanogaster AMP gene promoters were regulated in a species-specific manner in Drosophila (Dipteran) S2 cells and Spodoptera frugiperda (Lepidopteran) Sf9 cells. A κB-GATA element (22 bp) from M. sexta moricin (MsMoricin) promoter could significantly increase activities of Drosophila AMP gene promoters in S2 cells, and an MsMoricin promoter activating element (MPAE) (140 bp) could increase activity of drosomycin promoter specifically in Sf9 cells. However, κB and GATA factors alone were not sufficient for MsMoricin gene activation, suggesting that other co-regulators may be required to fully activate AMP genes. Our results suggest that induction of insect AMP genes may require a transcription complex composed of common nuclear factors (such as NF-κB and GATA factors) and species-related co-regulators, and it is the co-regulators that may confer species-specific regulation of AMP genes. In addition, we showed that activity of Drosophila drosomycin promoter could be activated cooperatively by the inserted exogenous κB-GATA element and the endogenous κB element. These findings revealed an approach of engineering AMP genes with enhanced activities, which may lead to broad applications.

Immunity in lepidopteran insects

Lepidopteran insects provide important model systems for innate immunity of insects, particularly for cell biology of hemocytes and biochemical analyses of plasma proteins. Caterpillars are also among the most serious agricultural pests, and understanding of their immune systems has potential practical significance. An early response to infection in lepidopteran larvae is the activation of hemocyte adhesion, leading to phagocytosis, nodule formation, or encapsulation. Plasmatocytes and granular cells are the hemocyte types involved in these responses. Infectious microorganisms are recognized by binding of hemolymph plasma proteins to microbial surface components. This "pattern recognition" triggers phagocytosis and nodule formation, activation of prophenoloxidase and melanization and the synthesis of antimicrobial proteins that are secreted into the hemolymph. Many hemolymph proteins that function in such innate immune responses of insects were first discovered in lepidopterans. Microbial proteinases and nucleic acids released from lysed host cells may also activate lepidopteran immune responses. Hemolymph antimicrobial peptides and proteins can reach high concentrations and may have activity against a broad spectrum of microorganisms, contributing significantly to clearing of infections. Serine proteinase cascade pathways triggered by microbial components interacting with pattern recognition proteins stimulate activation of the cytokine Spätzle, which initiates the Toll pathway for expression of antimicrobial peptides. A proteinase cascade also results inproteolytic activation of phenoloxidase and production of melanin coatings that trap and kill parasites and pathogens. The proteinases in hemolymph are regulated by specific inhibitors, including members of the serpin superfamily. New developments in lepidopteran functional genomics should lead to much more complete understanding of the immune systems of this insect group.

Functional divergence among silkworm antimicrobial peptide paralogs by the activities of recombinant proteins and the induced expression profiles

Antimicrobial peptides are small-molecule proteins that are usually encoded by multiple-gene families. They play crucial roles in the innate immune response, but reports on the functional divergence of antimicrobial peptide gene families are rare. In this study, 14 paralogs of antimicrobial peptides belonging to cecropin, moricin and gloverin families were recombinantly expressed in pET expression systems. By antimicrobial activity tests, peptides representing paralogs in the same family of cecropin and moricin families, displayed remarkable differences against 10 tested bacteria. The evolutionary rates were relatively fast in the two families, which presented obvious functional divergence among paralogs of each family. Four peptides of gloverin family had similar antimicrobial spectrum and activity against tested bacteria. The gloverin family showed similar antimicrobial function and slow evolutionary rates. By induced transcriptional activity, genes encoding active antimicrobial peptides were upregulated at obviously different levels when silkworm pupae were infected by three types of microbes. Association analysis of antimicrobial activities and induced transcriptional activities indicated that the antimicrobial activities might be positively correlated with induced transcriptional activities in the cecropin and moricin families. These results suggest that representative BmcecB6, BmcecD and Bmmor as the major effector genes have broad antimicrobial spectrum, strong antimicrobial activity and high microbe-induced expression among each family and maybe play crucial roles in eliminating microbial infection.

Trypanosoma cruzi: synergistic cytotoxicity of multiple amphipathic anti-microbial peptides to T. cruzi and potential bacterial hosts

The parasite Trypanasoma cruzi is responsible for Chagas disease and its triatomine vector, Rhodnius prolixus, has a symbiotic relationship with the soil bacterium, Rhodococcus rhodnii. R. rhodnii that was previously genetically engineered to produce the anti-microbial peptide, cecropin A was co-infected with T. cruzi into R. prolixus resulting in clearance of the infectious T. cruzi in 65% of the vectors. Similar anti-microbial peptides have been isolated elsewhere and were studied for differential toxicity against T. cruzi and R. rhodnii. Of the six anti-microbial peptides tested, apidaecin, magainin II, melittin, and cecropin A were deemed potential candidates for the Chagas paratransgenic system as they were capable of killing T.cruzi at concentrations that exhibit little or no toxic effects on R. rhodnii. Subsequent treatments of T. cruzi with these peptides in pair-wise combinations resulted in synergistic killing, indicating that improvement of the 65% parasite clearance seen in previous experiments may be possible utilizing combinations of different anti-microbial peptides.

Dermaseptins from Phyllomedusa oreades and Phyllomedusa distincta: Secondary structure, antimicrobial activity, and mammalian cell toxicity

The present study reports the structural characteristics, the biological activities, and preliminary clinical investigations of three synthetic members of the dermaseptin family of antimicrobial peptides. The three peptides showed similar tendencies to form alpha-helical structures in non-polar media. The antimicrobial activity towards bacteria and fungi was determined in the micromolar concentration and the peptides did not influenced peritoneal cells viability. One of the peptides was intravenously administered in mice at concentrations similar to those of antibiotics employed in bacterial/fungal infections and it did not cause any detectable changes in cells and tissues.

Solution structure, antibacterial activity, and expression profile of Manduca sexta moricin

In response to wounding or infection, insects produce a battery of antimicrobial peptides (AMPs) and other defense molecules to kill the invading pathogens. To study their structures, functions, and transcriptional regulation, we synthesized Manduca sexta moricin, a 42-residue peptide (GKIPVKAIKQAGKVIGKGLRAINIAGTTHDVVSFFRPKKKKH, 4539 Da). The compound exhibited potent antimicrobial activities against a broad spectrum of Gram-positive and Gram-negative bacteria with a minimum inhibitory concentration of 1.4 microM. The mRNA levels of M. sexta moricin increased substantially in fat body and hemocytes after the larvae were challenged with bacterial cells. We determined the solution structure of this AMP by two-dimensional 1H-1H -nuclear magnetic resonance spectroscopy. The tertiary structure is composed of an eight-turn alpha-helix spanning almost the entire peptide. Insights of relationships between the structure and function are also presented.

The discovery and analysis of a diverged family of novel antifungal moricin-like peptides in the wax moth Galleria mellonella

Screening for components with antifungal activity in the hemolymph of immune-stimulated Galleria mellonella larvae led to the identification of four novel moricin-like peptides (A, B, C3 and D). Subsequently, eight moricin-like peptide genes (A, B, C1-5 and D) were isolated and shown to code for seven unique peptides (mature C4 and C5 are identical). These genes contained single introns which varied from 180 to 1090bp. The moricin-like peptides were particularly active against filamentous fungi, preventing the growth of Fusarium graminearum at 3 microg/ml, and were also active against yeasts, gram positive bacteria and gram negative bacteria. Searches of the databases identified 30 moricin-like peptide genes which code for 23 unique mature peptides, all belonging to the Lepidoptera (moths and butterflies). The first comprehensive phylogenetic analysis of the moricin-like peptides suggested that they fall into two basic classes which diverged a long time ago. The peptides have since diversified extensively through a high level of gene duplication within species, as seen in G. mellonella and Bombyx mori. The restriction of moricin-like peptides to the Lepidoptera combined with their potent antifungal activity suggests that this diverse peptide family may play a role in the defence response of moths and butterflies.

Innate immunity: eggs of Manduca sexta are able to respond to parasitism by Trichogramma evanescens

So far, it was unknown whether immune responses of insect eggs are inducible or suppressed by parasitism. We investigated whether transcription of immune related genes in eggs of Manduca sexta changed in response to parasitism by Trichogramma evanescens. First, using DDRT-PCR, several cDNA elements known to represent immune related M. sexta genes inducible by bacterial challenge were isolated from eggs. In addition, two novel cDNAs were found: (a) immulectin-V (IML-V) suggested to be involved in recognition of foreign bodies, and (b) a new like-moricin protein with possible antimicrobial effects (L-Mor). Quantitative real time RT-PCR analyses revealed enhanced transcription in parasitized eggs compared to unparasitized ones for IML-V, prophenoloxidase (ProPO), prophenoloxidase activating protease I (PAP I), and proparalytic peptide (ProPP). No significant differences between parasitized and unparasitized eggs were detected for sequences encoding the antimicrobial peptides L-Mor, leureptin Leu, and attacin II Att II. Transcript levels of other antibacterial peptides were suppressed after parasitization for 3d (cecropin 6, Cec 6) and 2d (gloverin, Glov). While nearly 100% of the Manduca eggs contained Trichogramma specimens 1d after exposure to parasitoids, only 64% of the host eggs harbored parasitoid larvae 4d after parasitization. Our data demonstrate that the immune system of Manduca eggs shows differentiated responses to parasitization and suggest that insect eggs can defend against parasitization.

Advances in antimicrobial peptide immunobiology

Antimicrobial peptides are ancient components of the innate immune system and have been isolated from organisms spanning the phylogenetic spectrum. Over an evolutionary time span, these peptides have retained potency, in the face of highly mutable target microorganisms. This fact suggests important coevolutionary influences in the host-pathogen relationship. Despite their diverse origins, the majority of antimicrobial peptides have common biophysical parameters that are likely essential for activity, including small size, cationicity, and amphipathicity. Although more than 900 different antimicrobial peptides have been characterized, most can be grouped as belonging to one of three structural classes: (1) linear, often of alpha-helical propensity; (2) cysteine stabilized, most commonly conforming to beta-sheet structure; and (3) those with one or more predominant amino acid residues, but variable in structure. Interestingly, these biophysical and structural features are retained in ribosomally as well as nonribosomally synthesized peptides. Therefore, it appears that a relatively limited set of physicochemical features is required for antimicrobial peptide efficacy against a broad spectrum of microbial pathogens. During the past several years, a number of themes have emerged within the field of antimicrobial peptide immunobiology. One developing area expands upon known microbicidal mechanisms of antimicrobial peptides to include targets beyond the plasma membrane. Examples include antimicrobial peptide activity involving structures such as extracellular polysaccharide and cell wall components, as well as the identification of an increasing number of intracellular targets. Additional areas of interest include an expanding recognition of antimicrobial peptide multifunctionality, and the identification of large antimicrobial proteins, and antimicrobial peptide or protein fragments derived thereof. The following discussion highlights such recent developments in antimicrobial peptide immunobiology, with an emphasis on the biophysical aspects of host-defense polypeptide action and mechanisms of microbial resistance.

Structures, regulatory regions, and inductive expression patterns of antimicrobial peptide genes in the silkworm Bombyx mori

Antimicrobial peptides (AMPs) are a group of immune proteins that protect the host from infection. In Drosophila, seven groups of inducible AMPs have been identified, with activities against fungi and gram-positive and gram-negative bacteria. On the basis of the silkworm genome sequence and expressed sequence tags, we identified 35 AMP genes, mostly belonging to the cecropin, moricin, and gloverin gene families. We predicted the core promoters required for gene transcription and the cis-regulatory elements for NF-kappaB/Rel and GATA transcription factors. The expression profiles of these genes after an immune challenge with lipopolysaccharide were examined by reverse transcription PCR. Members of the cecropin B and gloverin A subfamilies were intensely expressed in the fat body after induction. In contrast, those of the moricin B subfamily were not expressed under the same conditions. Such results suggest that these regulatory elements and their positions in the upstream regions play an important role in regulating the transcription of these defense genes.

Isolation, gene expression and solution structure of a novel moricin analogue, antibacterial peptide from a lepidopteran insect, Spodoptera litura

An antibacterial peptide was isolated from a lepidopteran insect, Spodoptera litura. The molecular mass of this peptide was determined to be 4489.55 by matrix assisted laser desorption/ionization-time of flight mass (MALDI-TOF MS) spectrometry. The peptide consists of 42 amino acids and the sequence has 69-98% identity to those of moricin-related peptides, antibacterial peptides from lepidopetran insects. Thus, the peptide was designated S. litura (Sl) moricin. Sl moricin showed a broad antibacterial spectrum against Gram-positive and negative bacteria. Sl moricin gene was inducible by bacterial injection and expressed tissue-specifically in the fat body and hemocytes. Furthermore, the solution structure of Sl moricin was determined by two-dimensional (2D) 1H-nuclear magnetic resonance (NMR) spectroscopy and hybrid distance geometry-simulated annealing calculation. The tertiary structure revealed a long alpha-helix containing eight turns along nearly the full length of the peptide like that of moricin, confirming that Sl moricin is a new moricin-like antibacterial peptide. These results suggest that moricin is present not only in B. mori but also in other lepidopteran insects forming a gene family.

The relationship between peptide structure and antibacterial activity

Cationic antimicrobial peptides are a class of small, positively charged peptides known for their broad-spectrum antimicrobial activity. These peptides have also been shown to possess anti-viral and anti-cancer activity and, most recently, the ability to modulate the innate immune response. To date, a large number of antimicrobial peptides have been chemically characterized, however, few high-resolution structures are available. Structure-activity studies of these peptides reveal two main requirements for antimicrobial activity, (1) a cationic charge and (2) an induced amphipathic conformation. In addition to peptide conformation, the role of membrane lipid composition, specifically non-bilayer lipids, on peptide activity will also be discussed.