Interaction between liposomes and sarcotoxin IA, a potent antibacterial protein of Sarcophaga peregrina (flesh fly)

Appressoria Formation in Phytopathogenic Fungi Suppressed by Antimicrobial Peptides and Hybrid Peptides from Black Soldier Flies

Antimicrobial peptides (AMPs) from black solider flies (Hermetia illucens, BSF) exhibiting broad-spectrum antimicrobial activity are the most promising green substitutes for preventing the infection of phytopathogenic fungi; therefore, AMPs have been a focal topic of research. Recently, many studies have focused on the antibacterial activities of BSF AMPs against animal pathogens; however, currently, their antifungal activities against phytopathogenic fungi remain unclear. In this study, 7 AMPs selected from 34 predicted AMPs based on BSF metagenomics were artificially synthesized. When conidia from the hemibiotrophic phytopathogenic fungi Magnaporthe oryzae and Colletotrichum acutatum were treated with the selected AMPs, three selected AMPs-CAD1, CAD5, and CAD7-showed high appressorium formation inhibited by lengthened germ tubes. Additionally, the MIC₅₀ concentrations of the inhibited appressorium formations were 40 μM, 43 μM, and 43 μM for M. oryzae, while 51 μM, 49 μM, and 44 μM were observed for C. acutatum, respectively. A tandem hybrid AMP named CAD-Con comprising CAD1, CAD5, and CAD7 significantly enhanced antifungal activities, and the MIC₅₀ concentrations against M. oryzae and C. acutatum were 15 μM and 22 μM, respectively. In comparison with the wild type, they were both significantly reduced in terms of virulence when infection assays were performed using the treated conidia of M. oryzae or C. acutatum by CAD1, CAD5, CAD7, or CAD-Con. Meanwhile, their expression levels of CAD1, CAD5, and CAD7 could also be activated and significantly increased after the BSF larvae were treated with the conidia of M. oryzae or C. acutatum, respectively. To our knowledge, the antifungal activities of BSF AMPs against plant pathogenic fungi, which help us to seek potential AMPs with antifungal activities, provide proof of the effectiveness of green control strategies for crop production.

Transgenic Sweet Orange Expressing the Sarcotoxin IA Gene Produces High-Quality Fruit and Shows Tolerance to ‘Candidatus Liberibacter asiaticus’

Huanglongbing (otherwise known as HLB or greening) is currently the most devastating citrus disease worldwide. HLB is primarily associated with the phloem-inhabiting bacterium ‘Candidatus Liberibacter asiaticus’ (CLas). Currently, there are no citrus species resistant to CLas. Genetic transformation is one of the most effective approaches used to induce resistance against plant diseases. Antimicrobial peptides (AMPs) have shown potential breakthroughs to improve resistance to bacterial diseases in plants. In this paper, we confirm the Agrobacterium-mediated transformation of Pera sweet orange expressing the AMP sarcotoxin IA (stx IA) gene isolated from the flesh fly Sarcophaga peregrina and its reaction to CLas, involving plant performance and fruit quality assessments. Four independent transgenic lines, STX-5, STX-11, STX-12, and STX-13, and a non-transgenic control, were graft-inoculated with CLas. Based on our findings, none of the transgenic plants were immune to CLas. However, the STX-5 and STX-11 lines showed reduced susceptibility to HLB with mild disease symptoms and low incidence of plants with the presence of CLas. Fruit and juice quality were not affected by the genetic transformation. Further, no residues of the sarcotoxin IA protein were found in the juice of the STX-11 and STX-12 fruits, though detected in the juice of the STX-5 and STX-13 lines, as revealed by the immunoblotting test. However, juices from all transgenic lines showed low traces of sarcotoxin IA peptide in its composition. The accumulation of this peptide did not cause any deleterious effects on plants or in fruit/juice. Our findings reinforce the challenges of identifying novel approaches to managing HLB.

The black soldier fly, Hermetia illucens - a promising source for sustainable production of proteins, lipids and bioactive substances

The growing demand worldwide for proteins and lipids cannot be met by the intensive use of agricultural land currently available. Insect mass cultures as a source for proteins and lipids have been in focus for various reasons. An insect with many positive properties is the black soldier fly, Hermetia illucens, whose larvae could be used for the sustainable production of proteins and lipids. Furthermore, the larvae produce bioactive substances which could potentially be used for human and animal welfare.

Linear Analogues of the Lipopeptide Battacin With Potent In Vitro Activity Against S. aureus

Eight linear analogues of the lipopeptide battacin were evaluated for their antibacterial activity against the Gram-positive Staphylococcus aureus. Of this library, the enantiomeric lipopeptide analogue 9.4 exhibited nanomolar inhibitory activity (MIC=200nmol) against S. aureus. Furthermore, this lipopeptide was resilient toward degradation conditions when exposed to rat serum proteases for up to 8h.

A potent anti-inflammatory peptide from the salivary glands of horsefly

Background

A diverse group of physiologically active peptides/proteins are present in the salivary glands of horsefly Tabanus yao (Diptera, Tabanidae) that facilitate acquisition of blood meal. However, their roles in the regulation of local inflammation remains poorly understood.

Methods

Induction expression profiles of immune-related molecules in the salivary glands of T. yao was analyzed by quantitative PCR (qPCR) after bacterial feeding. A significantly up-regulated molecule (cecropin-TY1) was selected for anti-inflammatory assay in lipopolysaccharide (LPS)-stimulated mouse peritoneal macrophages. The transcription levels of inducible NO synthase (iNOS) and pro-inflammatory cytokines were quantified by qPCR. Nitric oxide (NO) production was determined by Griess reagent. Pro-inflammatory cytokine production was determined by an enzyme-linked immunosorbent assay (ELISA). The inflammatory signals were assayed by Western blotting analysis. The secondary structure of cecropin-TY1 was measured by Circular dichroism (CD) spectroscopy. Interaction of cecropin-TY1 with LPS was evaluated by the dissociation of fluorescein isothiocyanate (FITC)-conjugated LPS aggregates and neutralization of LPS determined by a quantitative Chromogenic End-point Tachypleus amebocyte lysate (TAL) assay kit. Homology modeled structure analysis and mutation of key residues/structures were performed to understand its structure-activity relationship.

Results

Cecropin-TY1 was demonstrated to possess high anti-inflammatory activity and low cytotoxicity toward mouse macrophages. In LPS-stimulated mouse peritoneal macrophage, addition of cecropin-TY1 significantly inhibited the production of nitric oxide (NO) and pro-inflammatory cytokines. Further study revealed that cecropin-TY1 inhibited inflammatory cytokine production by blocking activation of mitogen-activated protein kinases (MAPKs) and transcriptional nuclear factor-κB (NF-κB) signals. Cecropin-TY1 even interacted with LPS and neutralized LPS. The secondary structure analysis revealed that cecropin-TY1 adopted unordered structures in hydrophobic environment but converted to α-helical confirmation in membrane mimetic environments. Homology modeled structure analysis demonstrated that cecropin-TY1 adopted two α-helices (Leu3-Thr24, Ile27-Leu38) linked by a hinge (Leu25-Pro26) and the structure surface was partly positively charged. Structure-activity relationship analysis indicated that several key residues/structures are crucial for its anti-inflammatory activity including α-helices, aromatic residue Trp2, positively charged residues Lys and Arg, hinge residue Pro26 and N-terminal amidation.

Conclusions

We found a novel anti-inflammatory function of horsefly-derived cecropin-TY1 peptide, laying groundwork for better understanding the ectoparasite-host interaction of horsefly with host and highlighting its potency in anti-inflammatory therapy for sepsis and endotoxin shock caused by Gram-negative bacterial infections.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1149-y) contains supplementary material, which is available to authorized users.

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.

Stable isotope-assisted NMR characterization of interaction between lipid A and sarcotoxin IA, a cecropin-type antibacterial peptide

Sarcotoxin IA is a 39-residue cecropin-type peptide from Sarcophaga peregrina. This peptide exhibits antibacterial activity against Gram-negative bacteria through its interaction with lipid A, a core component of lipopolysaccharides. To acquire detailed structural information on this specific interaction, we performed NMR analysis using bacterially expressed sarcotoxin IA analogs with (13)C- and (15)N-labeling along with lipid A-embedding micelles composed of dodecylphosphocholine. By inspecting the stable isotope-assisted NMR data, we revealed that the N-terminal segment (Leu3-Arg18) of sarcotoxin IA formed an amphiphilic α-helix upon its interaction with the aqueous micelles. Furthermore, chemical shift perturbation data indicated that the amino acid residues displayed on this α-helix were involved in the specific interaction with lipid A. On the basis of these data, we successfully identified Lys4 and Lys5 as key residues in the interaction with lipid A and the consequent antibacterial activity. Therefore, these results provide unique information for designing chemotherapeutics based on antibacterial peptide structures.

Fly immunity: recognition of pathogens and induction of immune responses

Despite the lack of adaptive immunity based on gene rearrangement such as that in higher vertebrates, flies are able to defend themselves from a wide array of pathogens using multiple innate immune responses whose molecular mechanisms are strikingly similar to those of the innate immune responses of other multicellular organisms, including humans. Invading pathogens passing through the epithelial barriers, the first line of self-defense, are detected by pattern recognition receptors that identify pathogen-associated molecular patterns in the hemolymph or on the immune cell surface and are eliminated by humoral and cellular responses. Some pathogens escape recognition and elimination in the hemolymphby invading the host cell cytoplasm. Some of these intracellular pathogens, however, such as Listeria monocytogenes, are identified by pattern recognition receptors in the cytoplasm and are eliminated by intracellular responses, including autophagy, an intracellular degradation system. Although some of these pattern recognition receptors are encoded in the germ-line as protein families, another type of receptor in the immunoglobulin-superfamily is extensively diversified by alternative splicing in somatic immune cells in Drosophila.

Helical membrane peptides to modulate cell function

In recent years there has been an abundance of research into the potential of helical peptides to influence cell function. These peptides have been used to achieve a variety of different outcomes from cell repair to cell death, depending upon the peptide sequence and the nature of its interactions with cell membranes and membrane proteins. In this critical review, we summarise several mechanisms by which helical peptides, acting as either transporters, inhibitors, agonists or antibiotics, can have significant effects on cell membranes and can radically affect the internal mechanisms of the cell. The various approaches to peptide design are discussed, including the role of naturally-occurring proteins in the design of these helical peptides and current breakthroughs in the use of non-natural (and therefore more stable) peptide scaffolds. Most importantly, the current successful applications of these peptides, and their potential uses in the field of medicine, are reviewed (131 references).

Molecules participating in insect immunity of Sarcophaga peregrina

Pricking the body wall of Sarcophaga peregrina (flesh fly) larvae with a needle activated the immune system of this insect and induced various immune molecules, including antibacterial proteins, in the hemolymph. In this review, I summarize and discuss the functions of these immune molecules, with particular emphasis on the dual roles of some of these molecules in defense and development.

Engineering host resistance against parasitic weeds with RNA interference

Host genetic resistance is a key component of integrated pest management. The present authors and others are investigating the use of RNA interference (RNAi) as a genetic tool for engineering host resistance against parasitic weeds. The general approach is to transform a host plant with a plasmid encoding a double stranded hairpin RNA (hpRNA) targeted against one or more vital parasite genes. When the hpRNAs are specifically designed against parasite gene sequences, the hpRNA should have no phenotypic effect on the host. They will, however, have a dramatic effect on the parasites that have taken up the parasite-specific RNAi from the host via the haustorium. The current status of using RNAi technology for controlling parasitic weeds is reviewed. A key component to success with RNAi technology is identifying the best parasite genes to silence. Some of the criteria for RNAi targets are discussed, the existing status of parasitic plant sequence databases is described and internet access points to the parasite genome data are highlighted. Sequence information obtained from different parasite species can be used to clone the homologous gene from a particular pest or can be directly transformed into crop plants.

AMPed up immunity: how antimicrobial peptides have multiple roles in immune defense

Antimicrobial peptides (AMPs) are widely expressed and rapidly induced at epithelial surfaces to repel assault from diverse infectious agents including bacteria, viruses, fungi and parasites. Much information suggests that AMPs act by mechanisms that extend beyond their capacity to serve as gene-encoded antibiotics. For example, some AMPs alter the properties of the mammalian membrane or interact with its receptors to influence diverse cellular processes including cytokine release, chemotaxis, antigen presentation, angiogenesis and wound healing. These functions complement their antimicrobial action and favor resolution of infection and repair of damaged epithelia. Opposing this, some microbes have evolved mechanisms to inactivate or avoid AMPs and subsequently become pathogens. Thus, AMPs are multifunctional molecules that have a central role in infection and inflammation.

Small changes in the primary structure of transportan 10 alter the thermodynamics and kinetics of its interaction with phospholipid vesicles

The kinetics and thermodynamics of binding of transportan 10 (tp10) and four of its variants to phospholipid vesicles, and the kinetics of peptide-induced dye efflux, were compared. Tp10 is a 21-residue, amphipathic, cationic, cell-penetrating peptide similar to helical antimicrobial peptides. The tp10 variants examined include amidated and free peptides, and replacements of tyrosine by tryptophan. Carboxy-terminal amidation or substitution of tryptophan for tyrosine enhance binding and activity. The Gibbs energies of peptide binding to membranes determined experimentally and calculated from the interfacial hydrophobicity scale are in good agreement. The Gibbs energy for insertion into the bilayer core was calculated using hydrophobicity scales of residue transfer from water to octanol and to the membrane/water interface. Peptide-induced efflux becomes faster as the Gibbs energies for binding and insertion of the tp10 variants decrease. If anionic lipids are included, binding and efflux rate increase, as expected because all tp10 variants are cationic and an electrostatic component is added. Whether the most important effect of peptide amidation is the change in charge or an enhancement of helical structure, however, still needs to be established. Nevertheless, it is clear that the changes in efflux rate reflect the differences in the thermodynamics of binding and insertion of the free and amidated peptide groups.

Function of antimicrobial proteins in insects

We have isolated and characterized various antimicrobial proteins from the haemolymph of Sarcophaga peregrina (flesh fly) larvae. Of these the sarcotoxin I family is a group of proteins mainly active against Gram-negative bacteria whereas sapecin is active mainly against Gram-positive bacteria. In addition to its function in defence, sapecin also plays a role in insect development. Recently, we identified a hendecapeptide of the sapecin homologue sapecin B that has the same antibacterial activity as the original sapecin B. Both sarcotoxin I and sapecin are inducible proteins synthesized de novo by the fat body and/or haemocytes and secreted into the haemolymph when the insect is in the acute phase response to bacterial infection. Antifungal protein (AFP) is constitutively present in the haemolymph and is active against certain fungi but not bacteria. These various antimicrobial proteins interact with microbial membranes. Sarcotoxin I interferes with membrane functions such as ATP synthesis and amino acid transport. The fungicidal activity of AFP is enhanced synergistically by sarcotoxin I, although sarcotoxin I alone has no appreciable antifungal activity. It is clear that the flesh fly has the ability to mount a potent defence response against microbial parasites by mobilizing several antimicrobial proteins.

Drosophila as a model system for antibacterial peptides

As a defence against bacteria, infected insects synthesize cecropins and a large number of other bactericidal proteins and peptides. To understand this response and its possible relationship with similar systems in mammals, we need to characterize the induced components and how they act, as well as how this antibacterial response is initiated. To study the molecular basis for this response we cloned the genes for cecropins and other bactericidal peptides from Drosophila, 14 genes in total. The cecropin genes were selected as convenient markers for the immune response because they are strongly induced by different microbial substances. In contrast the lysozyme gene family is constitutively expressed in the digestive tract. We have developed an inducible blood cell line from Drosophila for studying the immune response in vitro. Using this system we are now investigating the function of membrane proteins and signal pathways in the transcriptional activation of immune genes in Drosophila.

Recognition and elimination of diversified pathogens in insect defense systems

The elimination of infectious non-self by the host defense systems of multicellular organisms requires a variety of recognition and effector molecules. The diversity is generated in somatic cells or encoded in the germ-line. In adaptive immunity in jawed vertebrates, the diversity of immunoglobulins and antigen receptors is generated by gene rearrangements in somatic cells. In innate immunity, various effector molecules and pattern recognition receptors, such as antimicrobial peptides and peptidoglycan recognition proteins, are encoded in the germ-line of multicellular organisms, including insects and jawed vertebrates. In the present review, we discuss how insect host defense systems recognize and eliminate a multitude of microbes via germ-line-encoded molecules, including recent findings that a Drosophila member of the immunoglobulin superfamily is extensively diversified by alternative splicing in somatic immune cells and participates in the elimination of bacteria.

Detergent-like actions of linear amphipathic cationic antimicrobial peptides

Antimicrobial peptides have raised much interest as pathogens become resistant against conventional antibiotics. We review biophysical studies that have been performed to better understand the interactions of linear amphipathic cationic peptides such as magainins, cecropins, dermaseptin, delta-lysin or melittin. The amphipathic character of these peptides and their interactions with membranes resemble the properties of detergent molecules and analogies between membrane-active peptide and detergents are presented. Several models have been suggested to explain the pore-forming, membrane-lytic and antibiotic activities of these peptides. Here we suggest that these might be 'special cases' within complicated phase diagrams describing the morphological plasticity of peptide/lipid supramolecular assemblies.

Expression of sarcotoxin IA gene via a root-specific tob promoter enhanced host resistance against parasitic weeds in tomato plants

We have developed a simple genetic engineering strategy for conferring resistance against parasitic weeds on host plants. Transgenic tomato plants expressing the sarcotoxin IA gene were grown either in polyethylene bags (PE) or in pots inoculated with Orobanche aegyptiaca seeds. The results indicate that transgenic plants exhibited strong inhibition of parasite growth and significantly increased yield as compared with non-transgenic ones. In both PE and pot systems most of the parasite tubercles attached to the transgenic root plants turned necrotic and developed abnormally. Integration and expression of the gene were confirmed by Southern blot, RT-PCR and Western blot analysis. Our results indicate that the insect gene produced in the plant cells was selectively toxic to the parasite and non-toxic to the host plant.

Expression and purification of antimicrobial peptide adenoregulin with C-amidated terminus in Escherichia coli

Adenoregulin is a 33 amino acid antimicrobial peptide isolated from the skin of the arboreal frog Phyllomedusa bicolor. Natural adenoregulin is synthesized with an amidated valine residue at C-terminus and shows lethal effects against filamentous fungi, as well as a broad spectrum of pathogenic microorganisms. A synthetic gene for adenoregulin (ADR) with an additional amino acid glutamine at C-terminus was cloned into pET32a vector to allow expression of ADR as a Trx fusion protein in Escherichia coli BL21(DE3). The resulting expression level of the fusion protein could reach up to 20% of the total cell proteins. The fusion protein could be purified effectively by Ni2+-chelating chromatography. Released from the fusion protein by enterokinase cleavage and purified to homogeneity, the recombinant ADR displayed antimicrobial activity similar to that of the synthetic ADR reported earlier. Comparing the antimicrobial activities of the recombinant adenoregulin with C-amidated terminus to that without an amidated C-terminus, we found that the amide of glutamine at C-terminus of ADR improved its potency on certain microorganisms such as Tritirachium album and Saccharomyces cerevisiae.

A peptide from insects protects transgenic tobacco from a parasitic weed

Parasitic plants present some of the most intractable weed problems for agriculture in much of the world. Species of root parasites such as Orobanche can cause enormous yield losses, yet few control measures are effective and affordable. An ideal solution to this problem is the development of parasite-resistant crops, but this goal has been elusive for most susceptible crops. Here we report a mechanism for resistance to the parasitic angiosperm Orobanche based on expression of sarcotoxin IA in transgenic tobacco. Sarcotoxin IA is a 40-residue peptide with antibiotic activity, originally isolated from the fly, Sarcophaga peregrina. The sarcotoxin IA gene was fused to an Orobanche-inducible promoter, HMG2, which is induced locally in the host root at the point of contact with the parasite, and used to transform tobacco. The resulting transgenic plants accumulated more biomass than non-transformed plants in the presence of parasites. Furthermore, plants expressing sarcotoxin IA showed enhanced resistance to O. aegyptiaca as evidenced by abnormal parasite development and higher parasite mortality after attachment as compared to non-transformed plants. The transgenic plants were similar in appearance to non-transformed plants suggesting that sarcotoxin IA is not detrimental to the host.

Insights into the anti-microbial defense of marine invertebrates: the penaeid shrimps and the oyster Crassostrea gigas

Research on innate immunity of the penaeid shrimps and the oyster Crassostrea gigas is motivated greatly by economical necessities. Indeed, the aquaculture of these organisms is now limited by the development of infectious diseases. Studying anti-microbial peptides/proteins (AMPs), which are effector molecules of the host defense, is particularly attractive not only for progressing basic knowledge on immunity but also because they offer various possible applications for disease management in aquaculture. AMPs are explored with a global approach,considering their structure, properties, function, gene expression, and tissue distribution during the response to infections. In shrimp, investigations of the penaeidins, which are constitutively expressed peptides, have highlighted the importance of hemocytes and hematopoiesis as major elements of the immune response, providing both local and systemic reactions. The activation of hematopoiesis must be regarded as a regulatory way for the expression and distribution of constitutively expressed immune effectors. As complementary approaches, genomics and gene profiling are promising to deepen our understanding of the anti-microbial defense of the oyster and the shrimp. However, real progress will depend also on the characterization of hemocyte lineages and hematopoiesis of these marine invertebrates as well as on the ontogenesis of their immune systems.

A novel antimicrobial peptide from the sea hare Dolabella auricularia

The sea hare Dolabella auricularia is a marine shell-less gastropod. Four cytotoxic glycoproteins named dolabellanin A, C, E and P were found in the animal previously. An antimicrobial factor was newly isolated from the sea hare's body-wall including skin and mucus. This factor is a novel peptide which consists of 33 amino acid residues, and is called dolabellanin B2. Dolabellanin B2 was cytotoxically effective against some pathogenic microorganisms at a concentration of 2.5-100 microg/ml.

Expression of the recombinant antibacterial peptide sarcotoxin IA in Escherichia coli cells

Sarcotoxin IA is an antibacterial peptide that is secreted by a meat-fly Sarcophaga peregrina larva in response to a hypodermic injury or bacterial infection. This peptide is highly toxic against a broad spectrum of both Gram-positive and Gram-negative bacteria and lethal to microbes even at nanomolar concentrations. However, research needs as well as its potential use in medicine require substantial amounts of highly purified sarcotoxin. Because heterologous expression systems proved to be inefficient due to sarcotoxin sensitivity to intracellular proteases, here we propose the biosynthesis of sarcotoxin precursors in Escherichia coli cells that are highly sensitive to the mature peptide. To optimize its biosynthesis, sarcotoxin was translationally fused with proteins highly expressed in E. coli. A fusion partner and the position of sarcotoxin in the chimeric polypeptide were crucial for protecting the sarcotoxin portion of the fusion protein from proteolysis. Released after chemical cleavage of the fusion protein and purified to homogeneity, sarcotoxin displayed antibacterial activity comparable to that previously reported for the natural peptide.

Behavior of silkworm yolk protein on phospholipid membranes

During early development, the plasma membrane of silkworm (Bombyx mori) eggs undergoes a superficial cleavage that separates the blastodermal protoplasm and the yolk. To test whether the blastoderm absorbs yolk through the plasma membrane in B. mori, we studied the interaction of phospholipid membranes and yolk using a phospholipid planar bilayer membrane (PBM) and liposomes. In addition, egg-specific protein (ESP; 225 kDa), a yolk protein that is specific to B. mori eggs, was collected by fractionating the eggs. Liposomes were mixed with either B. mori yolk or ESP, and observed under an electron microscope. This showed that the phospholipid membrane was spanned by fine particles 10-20 nm in diameter. Both yolk and ESP caused the PBM to become extraordinarily leaky, with a membrane potential of -70 mV for yolk and -198 mV for ESP. These results suggest that although it is a water-soluble protein, ESP permeates the phospholipid membrane without the help of enzymes.

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.

Induced expression of sarcotoxin IA enhanced host resistance against both bacterial and fungal pathogens in transgenic tobacco

We demonstrate here that induced expression of sarcotoxin IA, a bactericidal peptide from Sarcophaga peregrina, enhanced the resistance of transgenic tobacco plants to both bacterial and fungal pathogens. The peptide was produced with a modified PR1a promoter, which is further activated by salicylic acid treatment and necrotic lesion formation by pathogen infection. Host resistance to infection of bacteria Erwinia carotovora subsp. carotovora and Pseudomonas syringae pv. tabaci was shown to be dependent on the amounts of sarcotoxin IA expressed. Since we found antifungal activity of the peptide in vitro, transgenic seedlings were also inoculated with fungal pathogens Rhizoctonia solani and Pythium aphanidermatum. Transgenic plants expressing higher levels of sarcotoxin were able to withstand fungal infection and remained healthy even after 4 weeks, while control plants were dead by fungal infection after 2 weeks.

The structure, dynamics and orientation of antimicrobial peptides in membranes by multidimensional solid-state NMR spectroscopy

Linear peptide antibiotics have been isolated from amphibians, insects and humans and used as templates to design cheaper and more potent analogues for medical applications. Peptides such as cecropins or magainins are < or = 40 amino acids in length. Many of them have been prepared by solid-phase peptide synthesis with isotopic labels incorporated at selected sites. Structural analysis by solid-state NMR spectroscopy and other biophysical techniques indicates that these peptide antibiotics strongly interact with lipid membranes. In bilayer environments they exhibit amphipathic alpha-helical conformations and alignments of the helix axis parallel to the membrane surface. This contrasts the transmembrane orientations observed for alamethicin or gramicidin A. Models that have been proposed to explain the antibiotic and pore-forming activities of membrane-associated peptides, as well as other experimental results, include transmembrane helical bundles, wormholes, carpets, detergent-like effects or the in-plane diffusion of peptide-induced bilayer instabilities.

The terminal structure plays an important role in the biological activity of cecropin CMIV

Antibacterial peptides have received increasing attention as a new pharmaceutical substance. But the molecular mechanism of lysis is still poorly understood. CMIV gene and mutant CMIV gene in GST fusion system were expressed. After cleaving with different cleavage reagents, the peptide with an excess of N-terminus and with an un-amidated C-terminus stopped the activity while the peptide with an excess Asn at the C-terminus had the activity level the same as natural CMIV. The results showed that the terminal structure of cecropin CMIV played an important role in its biological activity.

Epithelial peptide antibiotics

Surfaces of higher eukaryotes such as plants, invertebrates, and vertebrates, including humans, are normally covered with microorganisms but usually are not infected by them. The reason, apart from physical barriers, is the production of gene-encoded antimicrobial peptides by epithelial cells. Many novel antimicrobial peptides have been discovered recently in the epithelia of plants, insects, amphibians, and cattle, and, more recently, also in humans. In situ hybridization studies indicate a rather organ-specific expression of the genes for peptide antibiotics, which, due to their antimicrobial spectrum and conditions of expression, may also define the physiologic microflora. Some epithelial antimicrobial peptides are constitutively expressed; others are inducible, either by the presence of microorganisms via as of yet not well characterized elicitor receptors or by endogenous proinflammatory cytokines. Most antimicrobial peptides kill microorganisms by forming pores in the cell membrane, and the sensitivity of some peptide antibiotics towards cholesterol, a major mammalian cell membrane constituent, may indicate why these peptide antibiotics are not toxic for mammalian cells. Thus, it seems to be difficult for microorganisms to acquire resistance, making these peptides very attractive for therapeutic use as antibiotics. The first clinical studies are very promising, and after solving the problems of a large-scale biotechnical synthesis, which is more complicated due to the principally suicidal activity of these peptides, a number of new natural structure-based peptides may be developed. Furthermore, discovery of the inducibility of many antimicrobial peptides may also lead to the development of compounds that elicit epithelial defense reactions by stimulating the synthesis of endogenous peptide antibiotics.

Antibacterial activity of a novel 26-kDa serine protease in the yellow body of Sarcophaga peregrina (flesh fly) pupae

We have reported a novel serine protease produced by Sarcophaga peregrina (Nakajima et al., J. Biol. Chem. 272 (1997) 23805-23810). This 26-kDa protease showed antibacterial activity against several bacteria. This activity was an intrinsic characteristic of the enzyme protein and not directly related to its protease activity, because treating the 26-kDa protease with diisopropyl fluorophosphate had no appreciable effect on its antibacterial activity. Unlike bovine trypsin, the 26-kDa protease interacted with acidic phospholipids, suggesting that its antibacterial activity is attributable to interaction with bacterial membranes.

Pore formation by the cytotoxic islet amyloid peptide amylin

Amylin is a 37-amino acid cytotoxic constituent of amyloid deposits found in the islets of Langerhans of patients with type II diabetes. Extracellular accumulation of this peptide results in damage to insulin-producing beta cell membranes and cell death. We report here that at cytotoxic concentrations, amylin forms voltage-dependent, relatively nonselective, ion-permeable channels in planar phospholipid bilayer membranes. Channel formation is dependent upon lipid membrane composition, ionic strength, and membrane potential. At 1-10 microM, cytotoxic human amylin dramatically increases the conductance of lipid bilayer membranes, while non-cytotoxic rat amylin does not. We suggest that channel formation may be the mechanism of cytotoxicity of human amylin.

Structure-activity studies on magainins and other host defense peptides

Host defense peptides are widely distributed in nature, being found in species from bacteria to humans. The structures of these peptides from insects, horseshoe crabs, frogs, and mammals are known to have the common features of a net cationic charge due to the presence of multiple Arg and Lys residues and in most cases the ability to form amphipathic structures. These properties are important for the mechanism of action that is thought to be a nonreceptor-mediated interaction with the anionic phospholipids of the target cell followed by incorporation into the membrane and disruption of the membrane structure. Host defense peptides have been shown to have broad spectrum antimicrobial activity, able to kill most strains of bacteria as well as some fungi, protozoa, and in addition, many types of tumor cells. Specificity for pathogenic cells over host cells is thought to be due to the composition of the cell membranes, with an increased proportion of anionic phospholipids making the pathogen more susceptible and the presence of cholesterol making the host membranes more resistant. Structure-activity relationship studies have been performed on insect cecropins and apidaecins, horseshoe crab tachyplesins and polyphemusins, and the frog magainins, CPFs (caerulein precursor fragments) and PGLa. In general, changes that increased the basicity and stabilized the amphipathic structure have increased the antimicrobial activity; however, as the peptides become more hydrophobic the degree of specificity decreases. One magainin-2 analogue, MSI-78, has been developed by Magainin Pharmaceuticals as a topical antiinfective and is presently in clinical trials for the treatment of infected diabetic foot ulcers.

Magainin oligomers reversibly dissipate delta microH+ in cytochrome oxidase liposomes

Magainin peptides present in the skin of Xenopus laevis and identified as antimicrobial agents are shown to decrease the membrane potential in cytochrome oxidase liposomes. They also released respiratory control with a third or higher order concentration dependence. Respiratory control was restored by proteolytic digestion of the added magainin. The amount of magainin required for half-maximal stimulation of respiration was proportional to lipid concentration. At appreciably higher concentrations magainins inhibited uncoupled respiration. The results are discussed in terms of a model in which most of the added magainin adsorbs as a monomer to the membranes but equilibrates with a multimeric pore that causes rather general permeability of membranes. The ensuing ion permeation dissipates membrane potential and stimulates respiration.

Expression of post-translational processing of preprocecropin A using a baculovirus vector

A cDNA fragment encoding preprocecropin A was inserted into the baculovirus Autographa californica nuclear polyhedrosis virus downstream of the polyhedrin promoter. The gene was expressed in recombinant-infected last instar larvae of Trichoplusia ni and in diapausing pupae of Hyalophora cecropia. The identity of the recombinant product was established by electrophoresis with detection of antibacterial activity and mass spectrometry. The prepropeptide had been correctly processed including removal of signal peptide and pro-part. Biologically active and amidated cecropin A was exported to the hemolymph. The yield of recombinant protein in H. cecropia reached a level of 600 micrograms/ml hemolymph and about 70% of the material was amidated.

Insect immunity. Isolation of cDNA clones corresponding to diptericin, an inducible antibacterial peptide from Phormia terranovae (Diptera). Transcriptional profiles during immunization

We have previously isolated and characterized a family of novel 8-kDa cationic antibacterial peptides synthesized by larvae of Phormia terranovae (Diptera) in response to various injuries. These molecules have been named diptericins. The peptide sequence of diptericin A was used to prepare oligonucleotides for screening cDNA libraries and we report in the present paper the isolation of several cDNA clones encoding diptericin. The analysis of the nucleotide sequences indicates that diptericin is synthesized as a prepeptide which is matured in two steps: (a) cleavage of a signal peptide and (b) amidation of the C-terminal residue. Interestingly, the 3' untranslated region of the mRNA contains a consensus sequence TTATTTAT which is also observed in the mRNA of another insect antibacterial peptide (attacin-related sarcotoxin IIA) and in mRNAs encoding proteins related to the inflammatory response in mammals. Our data illustrate that diptericins form a polymorphic family of immune peptides. The transcription of the diptericin genes is rapidly induced in the fat body after inoculation of bacteria, as evidenced by the transcriptional profile.

Effects of a purified cecropin D from a Chinese silk moth on growth, function and differentiation of murine hemopoietic cells

The effects of cecropin D, a small basic peptide isolated from a Chinese oak silk moth, on the functions or differentiation of mammalian hemopoietic cells are described in the present paper. This peptide suppressed lectin-induced DNA synthesis of murine splenocytes in a dose-dependent manner without any significant cytotoxic effects. It also exhibited inhibitory effects on antibody production in lipopolysaccharide-stimulated lymphocytes and on colony formation of hemopoietic progenitor cells in plasma clots culture. These results indicate that cecropin D can regulate growth, function and differentiation of murine hemopoietic cells. The biological significance of this finding is discussed from the comparative immunological point of view.

Novel feature of expression of the sarcotoxin IA gene in development of Sarcophaga peregrina

The expressions of the sarcotoxin IA and IIA genes were investigated. Although both these antibacterial proteins were synthesized by the fat body and secreted into the hemolymph in the same way when the body wall of third instar larvae of Sarcophaga peregrina was injured, the expressions of their genes during development of this insect were different. The sarcotoxin IA gene was activated transiently in the embryonic and pupal stages, whereas the sarcotoxin IIA gene was totally inactive in these stages. These results suggest that sarcotoxin IA plays a role in the development as well as the defence mechanism of Sarcophaga.