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PubMed2002

Antiviral and antitumor peptides from insects.

Insects can rapidly clear microbial infections by producing a variety of immune-induced molecules including antibacterial and/or antifungal peptides/polypeptides. In this report, we present the isolation, structural characterization, and biological properties of two variants of a group of bioactive, slightly cationic peptides, referred to as alloferons. Two peptides were isolated from the blood of an experimentally infected insect, the blow fly Calliphora vicina (Diptera), with the following amino acid sequences: HGVSGHGQHGVHG (alloferon 1) and GVSGHGQHGVHG (alloferon 2). Although these peptides have no clear homologies with known immune response modifiers, protein database searches established some structural similarities with proteins containing amino acid stretches similar to alloferon. In vitro experiments reveal that the synthetic version of alloferon has stimulatory activities on natural killer lymphocytes, whereas in vivo trials indicate induction of IFN production in mice after treatments with synthetic alloferon. Additional in vivo experiments in mice indicate that alloferon has antiviral and antitumoral capabilities. Taken together, these results suggest that this peptide, which has immunomodulatory properties, may have therapeutic capacities. The fact that insects may produce cytokine-like materials modulating basic mechanisms for human immunity suggests a source of anti-infection and antitumoral biopharmaceuticals.

Amino Acid Sequence↗
PubMed2003

Shade is the Drosophila P450 enzyme that mediates the hydroxylation of ecdysone to the steroid insect molting hormone 20-hydroxyecdysone.

The steroid 20-hydroxyecdysone (20E) is the primary regulatory hormone that mediates developmental transitions in insects and other arthropods. 20E is produced from ecdysone (E) by the action of a P450 monooxygenase that hydroxylates E at carbon 20. The gene coding for this key enzyme of ecdysteroidogenesis has not been identified definitively in any insect. We show here that the Drosophila E-20-monooxygenase (E20MO) is the product of the shade (shd) locus (cytochrome p450, CYP314a1). When shd is transfected into Drosophila S2 cells, extensive conversion of E to 20E is observed, whereas in sorted homozygous shd embryos, no E20MO activity is apparent either in vivo or in vitro. Mutations in shd lead to severe disruptions in late embryonic morphogenesis and exhibit phenotypes identical to those seen in disembodied (dib) and shadow (sad) mutants, two other genes of the Halloween class that code for P450 enzymes that catalyze the final two steps in the synthesis of E from 2,22-dideoxyecdysone. Unlike dib and sad, shd is not expressed in the ring gland but is expressed in peripheral tissues such as the epidermis, midgut, Malpighian tubules, and fat body, i.e., tissues known to be major sites of E20MO activity in a variety of insects. However, the tissue in which shd is expressed does not appear to be important for developmental function because misexpression of shd in the embryonic mesoderm instead of the epidermis, the normal embryonic tissue in which shd is expressed, rescues embryonic lethality.

Animals↗
PubMed1994

Drosophila mode of metamerization in the embryogenesis of the lepidopteran insect Manduca sexta.

Insect embryos have been classified as intermediate- and short-germ embryos, in which posterior segments are thought to be generated sequentially from an uncommitted growth zone, or as long-term embryos, such as Drosophila melanogaster, which develop primordia for all segments simultaneously. In Drosophila the coordinated activities among a three-tiered cascade of zygotic segmentation genes subdivide the embryo into progressively smaller units along the anterior-posterior axis. The mode of pattern specification in lepidopteran embryos has not been determined, although on morphological grounds they have been characterized as intermediate-germ insects. We have cloned orthologues of Drosophila segmentation genes from the tobacco hawkmoth Manduca sexta and have found that the blastoderm expression patterns of these genes show a molecular prepatterning typical of Drosophila. Thus, successive segment formation in Manduca embryos may not be due to sequential addition but rather may be the consequence of a lateral compression of the embryo proceeding in an anterior-to-posterior progression. These data challenge the view that the classification of insect development according to morphological criteria can serve as a reliable indicator of the molecular mechanisms underlying segmentation.

Amino Acid Sequence↗
PubMed1997

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

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

Amino Acid Sequence↗
PubMed1998

A protein with protective properties against the cellular defense reactions in insects.

The molecular mechanism of how insects recognize intruding microorganisms and parasites and distinguish them from own body structures is not well known. We explored evolutionary adaptations in an insect parasitoid host interaction to identify components that interfere with the recognition of foreign objects and cellular encapsulation. Because some parasitoids provide protection for the developing wasp in the absence of an overt suppression of the insect host defense, we analyzed the surface of eggs and symbiotic viruses for protective properties. Here we report on the molecular cloning of a 32-kDa protein (Crp32) that is one of the major protective components. It is produced in the calyx cells of the female wasp ovaries and attached to the surface of the egg and other particles including polydnaviruses. The recombinant protein confers protection to coated objects in a cellular encapsulation assay suggesting that a layer of Crp32 may prevent cellular encapsulation reactions by a local inactivation of the host defense system.

Amino Acid Sequence↗
PubMed1999

Solution structure of an insect growth factor, growth-blocking peptide.

Growth-blocking peptide (GBP) is an insect growth factor consisting of 25 amino acid residues that retards the development of lepidopteran larvae at high concentration while it stimulates larval growth at low concentration. In this study, we determined the solution structure of GBP by two-dimensional 1H NMR spectroscopy. The structure contains a short segment of double-stranded beta-sheet involving residues 11-13 and 19-21 and a type-II beta-turn in the loop region (residues 8-11), whereas the N and C termini are disordered. This is the first report of the three-dimensional structure of the peptiderigic insect growth factor, and the structure of the well defined region of GBP was found to share similarity with that of the C-terminal domain of the epidermal growth factor (EGF). Because GBP has been reported to stimulate DNA synthesis of not only insect cells but also human keratinocyte cells at the same level with EGF, the structural similarity between GBP and EGF may lead to the interaction of GBP to EGF receptor.

Amino Acid Sequence↗
PubMed1999

The putative bioactive surface of insect-selective scorpion excitatory neurotoxins.

Scorpion neurotoxins of the excitatory group show total specificity for insects and serve as invaluable probes for insect sodium channels. However, despite their significance and potential for application in insect-pest control, the structural basis for their bioactivity is still unknown. We isolated, characterized, and expressed an atypically long excitatory toxin, Bj-xtrIT, whose bioactive features resembled those of classical excitatory toxins, despite only 49% sequence identity. With the objective of clarifying the toxic site of this unique pharmacological group, Bj-xtrIT was employed in a genetic approach using point mutagenesis and biological and structural assays of the mutant products. A primary target for modification was the structurally unique C-terminal region. Sequential deletions of C-terminal residues suggested an inevitable significance of Ile73 and Ile74 for toxicity. Based on the bioactive role of the C-terminal region and a comparison of Bj-xtrIT with a Bj-xtrIT-based model of a classical excitatory toxin, AaHIT, a conserved surface comprising the C terminus is suggested to form the site of recognition with the sodium channel receptor.

Amino Acid Sequence↗
PubMed2001

Discovery and structure of a potent and highly specific blocker of insect calcium channels.

We have isolated a novel family of insect-selective neurotoxins that appear to be the most potent blockers of insect voltage-gated calcium channels reported to date. These toxins display exceptional phylogenetic specificity, with at least a 10,000-fold preference for insect versus vertebrate calcium channels. The structure of one of the toxins reveals a highly structured, disulfide-rich core and a structurally disordered C-terminal extension that is essential for channel blocking activity. Weak structural/functional homology with omega-agatoxin-IVA/B, the prototypic inhibitor of vertebrate P-type calcium channels, suggests that these two toxin families might share a similar mechanism of action despite their vastly different phylogenetic specificities.

Amino Acid Sequence↗
PubMed2003

Insect cytokine growth-blocking peptide triggers a termination system of cellular immunity by inducing its binding protein.

Growth-blocking peptide (GBP) is a 25-amino acid cytokine found in lepidopteran insects that possesses diverse biological activities such as stimulation of immune cells (plasmatocytes), cell proliferation, and larval growth regulation. We found another novel function of GBP that induces a hemolysis of another class of blood cells (oenocytoids). In the lysate of oenocytoids we identified a GBP-binding protein that shows a specific affinity for GBP. The characterization of purified GBP-binding protein and its cDNA demonstrated it as a 49.5-kDa novel protein with a C-terminal region displaying limited homology to several insect lipoproteins. Results of Northern and Western blotting indicated that the GBP-binding protein should be synthesized only in blood cells. Immunoelectron microscopic analyses confirmed that indirect immunoreactive signals were mostly localized in oenocytoids. Kinetic and biological analyses of interaction between GBP and the binding protein showed their strong binding was followed by clearance of GBP from hemolymph, thus indicating that this protein might function as an inhibitory factor against GBP. Based on these results, we propose that insect cytokine GBP shows multifunctions even in cellular immunity: it serves to stimulate immune cells and afterward silences its own action by inducing the binding protein through specific hemolysis.

Amino Acid Sequence↗
PubMed2004

The Gly-Gly linker region of the insect cytokine growth-blocking peptide is essential for activity.

Growth-blocking peptide (GBP) is a 25-amino acid cytokine isolated from the lepidopteran insect Pseudaletia separata. GBP exhibits various biological activities such as regulation of larval growth of insects, proliferation of a few kinds of cultured cells, and stimulation of a class of insect immune cells called plasmatocytes. The tertiary structure of GBP consists of a well structured core domain and disordered N and C termini. Our previous studies revealed that, in addition to the structured core, specific residues in the unstructured N-terminal region (Glu1 and Phe3) are also essential for the plasmatocyte-stimulating activity. In this study, a number of deletion, insertion, and site-directed mutants targeting the unstructured N-terminal residues of GBP were constructed to gain more detailed insight into the mode of interaction between the N-terminal region and GBP receptor. Alteration of the backbone length of the linker region between the core structure and N-terminal domain reduced plasmatocyte-stimulating activity. The substitutions of Gly5 or Gly6 in this linker region with more bulky residues, such as Phe and Pro, also remarkably reduced this activity. We conclude that the interaction of GBP with its receptor depends on the relative position of the N-terminal domain to the core structure, and therefore the backbone flexibility of Gly residues in the linker region is necessary for adoption of a proper conformation suited to receptor binding. Additionally, antagonistic experiments using deletion mutants confirmed that not only the core domain but also the N-terminal region of GBP are required for "receptor-binding," and furthermore Phe3 is a binding determinant of the N-terminal domain.

Amino Acid Motifs↗
PubMed2007

The xaxAB genes encoding a new apoptotic toxin from the insect pathogen Xenorhabdus nematophila are present in plant and human pathogens.

Xenorhabdus nematophila, a member of the Enterobacteriaceae, kills many species of insects by strongly depressing the immune system and colonizing the entire body. A peptide cytotoxin has been purified from X. nematophila broth growth, and the cytolytic effect on insect immunocytes and hemolytic effect on mammalian red blood cells of this toxin have been described (Ribeiro, C., Vignes, M., and Brehélin, M. (2003) J. Biol. Chem. 278, 3030-3039). We show here that this toxin, Xenorhabdus alpha-xenorhabdolysin (Xax), triggers apoptosis in both insect and mammalian cells. We also report the cloning and sequencing of two genes, xaxAB, encoding this toxin in X. nematophila. The expression of both genes in recombinant Escherichia coli led to the production of active cytotoxin/hemolysin. However, hemolytic activity was observed only if the two peptides were added in the appropriate order. Furthermore, we report here that inactivation of xaxAB genes in X. nematophila abolished the major cytotoxic activity present in broth growth, called C1. We also show that these genes are present in various entomopathogenic bacteria of the genera Xenorhabdus and Photorhabdus, in Pseudomonas entomophila, in the human pathogens Yersinia enterocolitica and Proteus mirabilis, and in the plant pathogen Pseudomonas syringae. This toxin cannot be classified in any known family of cytotoxins on the basis of amino acid sequences, locus organization, and activity features. It is, therefore, probably the prototype of a new family of binary toxins.

Animals↗
PubMed1993

Allergy to insect stings. A need for improved preventive management.

Allergy to insect venom is a major health problem for a significant number of people. Immunotherapy can reduce the risk of subsequent reaction from about 60% to less than 5%. Standard preventive care should include (1) advice concerning avoidance of insects, (2) prescription of an epinephrine kit or syringe for self-administration (unless medically contraindicated), and (3) referral for evaluation. Results of several studies from various regions of the country raise concern about the preventive care and advice given these patients and suggest a need for continuing medical education to improve preventive management of allergy to insect stings.

Anaphylaxis↗
PubMed1957

Lactic and alpha-glycerophosphate dehydrogenases in insects.

Different tissues, especially muscles, from insects belonging to various groups were extracted and studied for their lactic dehydrogenase (LDH) and alpha-glycerophosphate dehydrogenase (GDH I) activities from the comparative point of view. In all cases assays of flight muscle extracts showed extremely low values of LDH activity whereas the GDH activities were surprisingly high. The activities in leg muscles were generally lower. In some insects, however, a very active LDH was found; in these cases the GDH activity seemed to be decreased. GDH I was rather active in the fat bodies. The presence of particulate glycerophosphate dehydrogenase (GDH II) was also demonstrated in insect muscles. These results were interpreted as indicating a system by which there is accomplished immediate and direct breakdown of metabolites to supply large amounts of energy during flight and other activities without the accumulation of intermediate substances.

Animals↗
PubMed2006

Genome and EST analyses and expression of a gene family with putative functions in insect chemoreception.

Odorant-binding proteins (OBPs) are thought to be responsible for the transport of semiochemicals across hydrophobic interfaces to olfactory receptors. In insects, a second class of OBPs with four conserved cysteines has been variously named as sensory appendage proteins, olfactory segment-D proteins, and chemosensory proteins (CSPs). The physiological functions of these proteins have remained elusive. Here we report a comprehensive survey of both genome and expressed sequence tags (EST) databases. This showed that CSPs are apparently only present in the phylum, Arthropoda, and in two subphyla, Crustacea and Uniramia. This is the first report of a putative CSP in Crustacea and suggests that the origin of these genes predates the divergence of Uniramia and Crustacea. For the Uniramia, we identified 74 new genes encoding putative CSPs of insect species from 10 different orders. Using tissue-specific EST libraries, we have examined the relative expression of putative CSP genes in many tissues from 22 insect species suggesting that the genes are expressed widely. One Drosophila CSPs is expressed sixfold higher in head than other CSPs. One Bombyx mori CSPs was found at a very high level in pheromone gland, and for the first time, six CSPs were identified in B. mori compound eyes. The different frequencies of CSP transcripts were observed between solitary and gregarious EST libraries of Locusta migratoria.

Animals↗
PubMed2000

Two genes become one: the genes encoding heterochromatin protein Su(var)3-9 and translation initiation factor subunit eIF-2gamma are joined to a dicistronic unit in holometabolic insects.

The Drosophila suppressor of position-effect variegation Su(var)3-9 encodes a heterochromatin-associated protein that is evolutionarily conserved. In contrast to its yeast and mammalian orthologs, the Drosophila Su(var)3-9 gene is fused with the locus encoding the gamma subunit of translation initiation factor eIF2. Synthesis of the two unrelated proteins is resolved by alternative splicing. A similar dicistronic Su(var)3-9/eIF-2gamma transcription unit was found in Clytus arietis, Leptinotarsa decemlineata, and Scoliopterix libatrix, representing two different orders of holometabolic insects (Coleoptera and Lepidoptera). In all these species the N terminus of the eIF-2gamma, which is encoded by the first two exons, is fused to SU(VAR)3-9. In contrast to Drosophila melanogaster, RT-PCR analysis in the two coleopteran and the lepidopteran species demonstrated the usage of a nonconserved splice donor site located within the 3' end of the SU(VAR)3-9 ORF, resulting in removal of the Su(var)3-9-specific stop codon from the mRNA and complete in-frame fusion of the SU(VAR)3-9 and eIF-2gamma ORFs. In the centipede Lithobius forficatus eIF-2gamma and Su(var)3-9 are unconnected. Conservation of the dicistronic Su(var)3-9/eIF-2gamma transcription unit in the studied insects indicates its origin before radiation of holometabolic insects and represents a useful tool for molecular phylogenetic analysis in arthropods.

Amino Acid Sequence↗
PubMed1998

Comparison of three trap types for monitoring insect populations in stored grains.

Three trap types--probe, cone, and sticky--were used to monitor insect populations infesting shelled maize, Zea mays L., housed in galvanized steel storage bins. Sticky traps were suspended in the headspace 1 m above the grain mass, probe traps were inserted into the grain near the top and bottom of the grain mass, and cone traps were positioned at the surface of the grain mass. Although there was some overlap, each trap type was rather specific in the range of insect species trapped. Probe traps positioned near the grain surface trapped mostly Oryzaephilus surinamensis (L.), Tribolium castaneum (Herbst), and Cynaeus angustus (LeConte); whereas those positioned near the bottom of the grain mass trapped mostly Sitophilus zeamais Motschulsky. Cone traps caught mostly Typhaea stercorea (L.), Cryptolestes spp., and Ahasverus advena Waltl. Sticky traps caught primarily stored-product moths [Plodia interpunctella (Hübner) and Sitotroga cerealella (Olivier)] and A. advena. In addition to catching pest species, cone traps also caught hemipteran predators and hymenopteran parasitoids, and sticky traps caught large numbers of parasitoids. Although probe traps caught smaller numbers of several pest species than cone traps, these traps generally detected the presence of these species at the same time as cone traps, in addition to trapping other species that were not detected at all in cone traps. Therefore, a combination of sticky traps in the grain bin headspace and probe traps positioned just below the grain surface is probably most efficient for monitoring the presence of pest and beneficial insect species in grain storage. If pests cannot be eliminated from the space beneath the false floor of a grain bin, probe traps set at the bottom of the grain mass should provide the best early warning of infestation by species colonizing a grain mass by this route.

Animals↗
PubMed2003

Controlling the mealworm Alphitobius diaperinus (Coleoptera: Tenebrionidae) in broiler and turkey houses: field trials with a combined insecticide treatment: insect growth regulator and pyrethroid.

Trials were conducted during one year under field conditions to control the lesser mealworm, Alphitobius diaperinus (Panzer), in broiler and turkey houses. The tested combined treatment included an adulticidal compound (pyrethroid: cyfluthrin) and a larvicidal compound (insect growth regulator [IGR]: triflumuron). The combined insecticide treatment greatly reduced the adult and larval stocks throughout the different broiler growing periods, and control of A. diaperinus populations was achieved by the end of the second treatment. Control of the insect population in a turkey house was not similar. A reestablishment of the insect population was observed during the second turkey growing period in summer. Building characteristics and management practices of the breeding system (duration of the breeding period, management of the litter) interact with the combined insecticide treatment and lead to a different efficiency.

Animals↗
PubMed2003

Toxicity of fruit fly baits to beneficial insects in citrus.

Two fruit fly baits, Nu-Lure/malathion and GF-120 (Spinosad) were evaluated in the laboratory for non-target impacts on beneficial insects. Nu-Lure/malathion proved attractive and toxic to adults and larvae of the coccinellid species, Curinus coeruleus Mulsant, Cycloneda sanguinea L. and Harmonia axyridis Pallas, a lacewing species, Chrysoperla rufilabris Burmeister. The coccinellids Olla v-nigrum Mulsant, Scymnus sp. and nymphs of the insidious flower bug, Orius insidiosus (Say) did not succumb to Nu-Lure baits, even in no-choice situations. Nu-Lure was also attractive and lethal to adults of two aphidophagous flies; Leucopis sp. and the syrphid fly Pseudodorus clavatus (F.). Both Nu-Lure and GF-120 caused significant mortality to the parasitoid wasps, Aphytis melinus De Bach and Lysiphlebus testaceipes Cresson, within 24 h of exposure. However, GF-120 caused no significant mortality to any coccinellid in either choice or no-choice situations, despite considerable consumption of baits. Adults of P. clavatus tended to avoid GF-120, although mortality was significant in no-choice tests. Although larvae and adults of the lacewing C. rufilabris consumed GF-120, mortality was delayed; adults died 48 -96 h post-exposure and those exposed as larvae died two weeks later in the pupal stage. The Nu-Lure bait did not appear palatable to any of the insects, but the high concentration of malathion (195,000 ppm) caused rapid mortality to susceptible insects. Nu-Lure bait without malathion also caused significant mortality to flies and lacewings in cage trials. Although GF-120 bait appeared more benign overall, further research efforts are warranted to increase its selectivity for target fly species and reduce its attractiveness to parasitoids and lacewings. I conclude that the Florida "fly free zone" protocol in its current form is not compatible with an IPM approach to commercial citrus production.

Animals↗