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PubMed2006

Effect of hybridization of the Quercus crassifolia x Quercus crassipes complex on the community structure of endophagous insects.

In a previous study, we showed that the geographic proximity of hybrid plants to the allopatric areas of parental species increases their morphological and genetic similarity with them. In the present work, we explored whether the endophagous fauna of hybrid plants show the same pattern. We studied the canopy species richness, diversity and composition of leaf-mining moths (Lepidoptera: Tischeridae, Citheraniidae) and gall-forming wasps (Hymenoptera: Cynipidae) associated with two species of red oaks (Quercus crassifolia and Quercus crassipes) and their interspecific hybrid (Quercusxdysophylla Benth pro sp.) in seven hybrid zones in central Mexico, during four seasons in 2 years. The study was conducted on 194 oak trees with known genetic status [identified by leaf morphology and molecular markers (random amplified polymorphic DNAs)], and the results indicate a bidirectional pattern of gene flow. Hybrid plants supported intermediate levels of infestation of gall-forming and leaf-mining insects compared to their putative parental species. The infestation level of leaf-mining insects varied significantly following the pattern: Q. crassifolia>hybrids>Q. crassipes, whereas the gall-forming insects showed an inverse pattern. A negative and significant relationship was found between these two types of insect guilds in each host taxa, when the infestation percentage was evaluated. It was found that 31.5% (n=11) of the endophagous insects were specific to Q. crassipes, 22.9% (n=8) to Q. crassifolia, and 8.6% (n=3) to hybrid individuals. The hybrid bridge hypothesis was supported in the case of 25.7% (n=9) of insects, which suggests that the presence of a hybrid intermediary plant may favor a host herbivore shift from one plant species to another. Greater genetic diversity in a hybrid zone is associated with greater diversity in the endophagous community. The geographic proximity of hybrid plants to the allopatric site of a parental species increases their similarity in terms of endophagous insects and the Eje Neovolcánico acts as a corridor favoring this pattern.

Animals↗
PubMed2007

Insect sodium channels and insecticide resistance.

Voltage-gated sodium channels are essential for the generation and propagation of action potentials (i.e., electrical impulses) in excitable cells. Although most of our knowledge about sodium channels is derived from decades of studies of mammalian isoforms, research on insect sodium channels is revealing both common and unique aspects of sodium channel biology. In particular, our understanding of the molecular dynamics and pharmacology of insect sodium channels has advanced greatly in recent years, thanks to successful functional expression of insect sodium channels in Xenopus oocytes and intensive efforts to elucidate the molecular basis of insect resistance to insecticides that target sodium channels. In this review, I discuss recent literature on insect sodium channels with emphases on the prominent role of alternative splicing and RNA editing in the generation of functionally diverse sodium channels in insects and the current understanding of the interactions between insect sodium channels and insecticides.

Action Potentials↗
PubMed2004

Insect olfactory receptors: contributions of molecular biology to chemical ecology.

Our understanding of the molecular basis of chemical signal recognition in insects has been greatly expanded by the recent discovery of olfactory receptors (Ors). Since the discovery of the complete repertoire of Drosophila melanogaster Ors, candidate Ors have been identified from at least 12 insect species from four orders (Coleoptera, Lepidoptera, Diptera, and Hymenoptera), including species of economic or medical importance. Although all Ors share the same G-protein coupled receptor structure with seven transmembrane domains, they present poor sequence homologies within and between species, and have been identified mainly through genomic data analyses. To date, D. melanogaster remains the only insect species where Ors have been extensively studied, from expression pattern establishment to functional investigations. These studies have confirmed several observations made in vertebrates: one Or type is selectively expressed in a subtype of olfactory receptor neurons, and one olfactory neuron expresses only one type of Or. In addition, all olfactory neurons expressing one Or type converge to the same glomerulus in the antennal lobe. The olfactory mechanism, thus, appears to be conserved between insects and vertebrates. Although Or functional studies are in their initial stages in insects (mainly Drosophila), insects appear to be good models to establish fundamental concepts of olfaction with the development of powerful genetic, imaging, and behavioral tools. This new field of study will greatly contribute to the understanding of insect chemical communication mechanisms, particularly with agricultural pests and disease vectors, and could result in future strategies to reduce their negative effects.

Animals↗
PubMed1990

Extramitochondrial release of hydrogen peroxide from insect and mouse liver mitochondria using the respiratory inhibitors phosphine, myxothiazol, and antimycin and spectral analysis of inhibited cytochromes.

The fumigant insecticide phosphine (PH3) is known to inhibit cytochrome c oxidase in vitro. Inhibition of the respiratory chain at this site has been shown to stimulate the generation of superoxide radicals (O2-), which dismutate to form hydrogen peroxide (H2O2). This study was performed in order to investigate the production of H2O2 by mitochondria isolated from granary weevil (Sitophilus granarius) and mouse liver on exposure to PH3. Other respiratory inhibitors, antimycin, myxothiazol, and rotenone were used with insect mitochondria. Hydrogen peroxide was measured spectrophotometrically using yeast cytochrome c peroxidase as an indicator. Insect and mouse liver mitochondria, utilizing endogenous substrate, both produced H2O2 after inhibition by PH3. Insect organelles released threefold more H2O2 than did mouse organelles, when exposed to PH3. Production of H2O2 by PH3-treated insect mitochondria was increased significantly on addition of the substrate alpha-glycerophosphate. Succinate did not enhance H2O2 production, however, indicating that the H2O2 did not result from the autoxidation of ubiquinone. NAD(+)-linked substrates, malate and pyruvate also had no effect on H2O2 production, suggesting that NADH-dehydrogenase was not the source of H2O2. Data obtained using antimycin and myxothiazol, both of which stimulated the release of H2O2 from insect mitochondria, lead to the conclusion that glycerophosphate dehydrogenase is a source of H2O2. The effect of combining PH3, antimycin, and myxothiazol on cytochrome spectra in insect mitochondria was also recorded. It was observed that PH3 reduces cytochrome c oxidase but none of the other cytochromes in the electron transport chain. There was no movement of electrons to cytochrome b when insect mitochondria are inhibited with PH3. The spectral data show that the inhibitors interact with the respiratory chain in a way that would allow the production of H2O2 from the sites proposed previously.

Animals↗
PubMed1987

Re-examination of the specificity of the scorpion Androctonus australis hector insect toxin towards arthropods.

The toxicity of the insect toxin from the venom of the scorpion Androctonus australis Hector has been studied in six species of insects, three species of crustaceans (two terrestrial and one aquatic) and in mice. Paralysing and lethal effects were observed not only in insects but also on the three crustacean species. For insects the LD50 varies from 2 to 1310 ng per 100 mg of insect, according to the species. On crustaceans doses up to 3-9 micrograms per 100 mg of animal induced a paralysing or lethal effect. In mice injections of 0.05 and 1 mg of the toxin intracerebroventricularly and s.c. resulted in no apparent symptoms of intoxication. These results demonstrate that the insect toxin of Androctonus australis Hector has no toxicity for the mouse, but also that it is not absolutely specific for insects.

Animals↗
PubMed1995

Gluconeogenesis and effect of nutritional status on TCA cycle activity in the insect Manduca sexta.

Gluconeogenesis from isotopically substituted (3-13C)alanine (Ala) was demonstrated in the last larval instar of an insect, Manduca sexta, when maintained on low carbohydrate diets. 13C was incorporated into all carbons of the blood sugar trehalose (Tre), but enrichments of C1 and C6, and C2 and C5 were greatest. Relative to the amount of [3-13C]Ala metabolized, larvae maintained on a low carbohydrate diet supplemented with casein displayed the greatest enrichment of Tre. Very little de novo synthesis of Tre was observed in larvae maintained on a complete-balanced diet containing calorically equivalent amounts of sucrose and casein. Starvation failed to induce gluconeogenesis and 13C was not incorporated into Tre in starved insects. Activity of the TCA cycle contributed approximately 10% of the 13C incorporated into Tre in larvae on low carbohydrate diets, while the TCA cycle contribution in larvae on the complete diet approached 70%. The pattern of 13C enrichment of glucose in larvae on the low carbohydrate diets indicated that cytoplasmic carboxylation, possibly due to 'malic enzyme'-like activity, contributed significantly to the synthesis of Tre. The pentose phosphate pathway was evidenced in insects on all diets. Glucose labelling ratios indicated a pentose cycling flux of 10 to 20% in insects on the low carbohydrate diets and 50% in larvae on the complete diet. Glutamine together with lesser amounts of glutamate and glutathione were also products of the labelled Ala. The distribution of label in these products under different dietary conditions demonstrated shifts in the relative contribution of pyruvate carboxylase and pyruvate dehydrogenase activities for providing substrate to the TCA cycle. In the expected fashion starved insects and insects on the low carbohydrate diets incorporated a greater proportion of 13C into the TCA cycle via carboxylation while incorporation by the two pathways was similar in insects on the complete diet. The significance of these findings with regard to the regulation of gluconeogenesis in M. sexta and comparison of the present results with those obtained from studies of hepatic gluconeogenesis are discussed.

Alanine↗
PubMed1991

Production scale insect cell culture.

Insect cells in culture are currently commanding great interest as superior hosts for the efficient production of biologicals with applications in health care and in agriculture. Insect cell culture is ripe for scale-up technologies, in order to meet future projected production requirements of (a) insect viruses used as bioinsecticides and (b) recombinant proteins of therapeutic potential for humans and animals. The single most prominent system used in research-based and in commercial insect cell culture today involves lepidopteran cells transfected with baculovirus expression vectors for abundant formation of recombinant biologicals. However, dipteran insect cell lines also are beginning to emerge as useful tools in biotechnology. Current practices in bioprocess development using insect cell culture, advances in media formulation and in insect cell bioreactor design, and emerging trends are presented and critically evaluated.

Journal Article↗
PubMed2005

Lipoprotein-mediated lipid transport in insects: analogy to the mammalian lipid carrier system and novel concepts for the functioning of LDL receptor family members.

In all animals, lipoproteins are used to transport lipids through the aqueous circulation. Lipids are delivered to mammalian cells by two different mechanisms: via endocytic uptake of the complete lipoprotein particle mediated by members of the low density lipoprotein (LDL) receptor (LDLR) family, or by selective delivery of lipoprotein-carried lipids at the cell surface, such as lipid uptake following the action of a lipoprotein lipase. Although many structural elements of the lipid transport system of insects are similar to those of mammals, insect lipoprotein-mediated lipid transport was thought to apply only to the latter concept, since the single lipoprotein acts as a reusable lipid shuttle. However, the recent identification of lipoprotein receptors of the LDLR family in insects suggests that lipid transport in these animals may also adopt the first concept. Yet, the endocytic properties of the insect LDLR homologue appear to deviate from those of the mammalian LDLR family members, resulting in the recycling of endocytosed lipoprotein in a transferrin-like manner. This indicates that a hitherto unknown as well as unexpected function can be added to the plethora of functions of LDLR family members. Analysis of the molecular mechanism of the ligand-recycling function of the insect receptor provides also new insight into the possible functioning of the mammalian family members. In the last several years, mammalian and insect lipoprotein-mediated lipid transport systems have been reviewed separately with respect to functioning and lipid delivery. This review, in which new and important developments in the insect field with respect to our understanding of lipid delivery are discussed with a particular focus on the involvement of the LDLR homologue, aims at comparing the two systems, also from an evolutionary biological perspective, and proposes that the two systems are more similar than assumed previously.

Amino Acid Sequence↗
PubMed2004

Zinc-metalloproteases in insects: ACE and ECE.

Research on the angiotensin-converting enzyme (ACE) in insects has substantially advanced during the recent decade. The cloning of this enzyme in many insect species, the determination of the 3D-structure and several molecular and physiological studies have contributed to the characterization of insect ACE as we know it today: a functional enzyme with a putative role in reproduction, development and defense. The discovery of the endothelin-converting enzyme in insects occurred more recently and cloning of the corresponding cDNA has been carried out in only one insect species so far. However, activity studies and analysis of insect genomes indicate that this enzyme is also widely distributed among insect species. Making hypotheses about its putative function would be preliminary, but its wide tissue distribution suggests a major and diverse biological role.

Amino Acid Sequence↗
PubMed2004

Tn5 as an insect gene vector.

The purpose of this study was to explore alternatives to insect-derived transposable elements as insect gene vectors with the intention of improving existing insect transgenesis methods. The mobility properties of the bacterial transposon, Tn5, were tested in mosquitoes using a transient transposable element mobility assay and by attempting to create transgenic insects. Tn5 synaptic complexes were assembled in vitro in the absence of Mg(2+) and co-injected with a target plasmid into developing yellow fever mosquito, Aedes aegypti, embryos. Target plasmids recovered from embryos a day later were screened for the presence of Tn5. Recombinants (transposition events) were found at a frequency of 1.2 x 10(-3). Some transposition events did not appear to be associated with canonical 9 bp direct duplications at the site of insertion and also were associated with either deletions or rearrangements. A Tn5 element containing the brain-specific transgene, 3 x P3DsRed, was assembled into synaptic complexes in vitro and injected into pre-blastoderm embryos of Ae. aegypti. Of the approximately 900 embryos surviving injection and developing into adults, two produced transgenic progeny. Both transgenic events involved the co-integrations of approximately five elements resulting in nested and tandem arrayed Tn5::3 x P3DsRed elements. This study extends the known host range of Tn5 to insects and makes available to insect biologists and others another eukaryotic genome-manipulation tool. The hyperactivity of synaptic complexes may be responsible for the unusual clustering of elements and managing this aspect of the element's behavior will be important in future applications of this technology to insects.

Aedes↗
PubMed2006

Dynamics of carbon dioxide release from insects infected with entomopathogenic nematodes.

The quality of an insect as a host to an entomopathogenic nematode infective juvenile depends in part on whether or not the insect is already infected and on the stage of that infection. Previous research has shown that nematode response to hosts can change after infection and that, for uninfected hosts, CO(2) can be an important cue used by infective stage juveniles during attraction. We hypothesized that CO(2) production from an insect changes after it is infected, and that these changes could influence nematode infection decisions. Changes in CO(2) released by two insect species (Galleria mellonella and Tenebrio molitor) after infection by one of four nematode species (Steinernema carpocapsae, Steinernema feltiae, Steinernema glaseri, or Steinernema riobrave) were measured. Measurements were taken every 2h from time of initial exposure to nematodes up to 224 h after infection. Dead (freeze-killed) and live uninfected insects were used as controls. Infected G. mellonella showed two distinct peaks of CO(2) production: one between 20 and 30 h and the other between 70 and 115 h after exposure to the nematodes. Peaks were up to two times higher than levels produced by uninfected insects. Infected T. molitor showed only one peak between 25 and 50h. We found differences in peak height and timing among nematode and insect species combinations. The influence of these changes in CO(2) production on IJ attraction and infection behavior remains to be determined.

Animals↗
PubMed2006

Exploring the pharmacological properties of insect nicotinic acetylcholine receptors.

Insect nicotinic acetylcholine (nACh) receptors are molecular targets of insecticides such as neonicotinoids that are used to control disease-carrying insects and agricultural pests. To date, several insect nACh receptor subunits have been identified, indicating different nACh receptor subtypes and pharmacological profiles. Because of the difficulty in expressing functional insect nACh receptors in heterologous systems, new research tools are needed. Studies on insects resistant to the insecticide imidacloprid and on laboratory-generated hybrid and chimaeric nACh receptors in vitro have provided information about the molecular basis of receptor diversity, neonicotinoid resistance and selectivity. Additionally, recent results indicate that the sensitivity of insect nACh receptors to imidacloprid can be modulated by intracellular phosphorylation mechanisms, which offers a new approach to studying insect nACh receptor pharmacology.

Animals↗
PubMed2006

Plant-mediated effects in insect-pathogen interactions.

Interactions between insect herbivores and their pathogens can be modulated by host plants. Inter- and intraspecific differences in plant chemistry and structure can alter the susceptibility of insects to infection and the production and environmental persistence of pathogens. Whether plants can manipulate insect pathogens to act as "bodyguards" and increase their own fitness remains to be shown. Reduced insect performance owing to poor plant quality can enhance the susceptibility of an insect to disease while these same phytochemicals can also reduce the effectiveness of entomopathogens in killing the host. As we discuss here, plants have an important role in the evolution of insect-pathogen relationships and a tritrophic perspective should thus be incorporated into the study of insects and their pathogens.

Animals↗
PubMed2000

Interactions of dietary protein and carbohydrate determine blood sugar level and regulate nutrient selection in the insect Manduca sexta L.

The non-homeostatic regulation of blood sugar concentration in the insect Manduca sexta L. was affected by nutritional status. Larvae maintained on diets lacking sucrose displayed low concentrations of trehalose, the blood sugar of insects, which varied from 5 to 15 mM with increasing dietary casein level between 12.5 and 75 g/l. These insects were glucogenic, as demonstrated by the selective 13C enrichment of trehalose synthesized from [3-13C]alanine, and de novo synthesis was the sole source of blood sugar. The distribution of 13C in glutamine established that following transamination of the 13C substituted substrate, [3-13C]pyruvate carboxylation rather than decarboxylation was the principal pathway of Pyr metabolism. The mean blood trehalose level was higher in insects maintained on diets with sucrose. At the lowest dietary casein level blood trehalose was approximately 50 mM, and declined to 20 mM at the highest casein level. Gluconeogenesis was detected in insects maintained on sucrose-free diets at the higher protein levels examined, but [3-13C]pyruvate decarboxylation and TCA cycle metabolism was the principal fate of [3-13C]alanine following transamination, and dietary carbohydrate was the principal source of glucose for trehalose synthesis. Feeding studies established a relationship between nutritional status, blood sugar level and dietary self-selection. Insects preconditioned by feeding on diets without sucrose had low blood sugar levels regardless of dietary casein level, and when subsequently given a choice between a sucrose diet or a casein diet, selected the former. Larvae preconditioned on a diet containing sucrose and the lowest level of casein had high blood sugar levels and subsequently selected the casein diet. Larvae maintained on the sucrose diet with the highest casein level had low blood sugar and self-selected the sucrose diet. When preconditioned on diets with sucrose and intermediate levels of casein, insects selected more equally between the sucrose and the casein diets. It is concluded that blood sugar level may be intimately involved in dietary self-selection by M. sexta larvae, and that in the absence of dietary carbohydrate, gluconeogenesis provides sufficient blood sugar to ensure that larvae choose a diet or diets that produce an optimal intake of dietary protein and carbohydrate.

Alanine↗
PubMed2002

The glucogenic response of a parasitized insect Manduca sexta L. is partially mediated by differential nutrient intake.

Induction of gluconeogenesis is accelerated in larvae of the insect Manduca sexta L. parasitized by Cotesia congregata (Say), maintaining the concentration of the blood sugar trehalose, an important nutrient for parasite development. Investigation has demonstrated that when host larvae are offered a choice of diets with varying levels of sucrose and casein, parasitized insects consume a different balance of these nutrients, principally due to a decrease in protein consumption. The result is metabolic homeostasis, with normal unparasitized and parasitized larvae exhibiting similar levels of gluconeogenesis and blood sugar level. In the present study, normal unparasitized and parasitized larvae were maintained on individual chemically defined diets having the balance of protein and carbohydrate consumed by each when offered a dietary choice. Total dietary nutrient, the sum of carbohydrate and protein, was provided at six levels, composed of three pairs of diets. Each diet pair consisting of diets having equivalent overall nutrient ratios of 2:1 and 1:1 casein/sucrose. Host growth and diet consumption were significantly affected by dietary nutrient level and the magnitude of these effects was influenced by parasitism. Due to the effects of dietary nutrient level on diet consumption, none of the unparasitized and parasitized larvae within any of the three diet pairs consumed protein and carbohydrate at the levels predicted by the earlier choice experiments. Among insects on all of the diets, however, two groups of unparasitized and parasitized larvae consumed the expected levels of protein and carbohydrate. In each case, gluconeogenesis, as measured by 13C nuclear magnetic resonance spectroscopy (NMR) analysis of pyruvate cycling and trehalose synthesis from [2-13C]pyruvate, was evident in unparasitized and parasitized insects, confirming the conclusions of the earlier experiments. Generally, all larvae that consumed less than approximately 250 mg of sucrose over the 3-day feeding period, were gluconeogenic, regardless of diet. Differential carbohydrate consumption, therefore, was an important factor in inducing gluconeogenesis in both unparasitized and parasitized insects. The selective 13C enrichment in trehalose displayed by non-gluconeogenic larvae on some diets demonstrated trehalose formation from [2]pyruvate. The absence of net carbohydrate synthesis in these insects was likely due to an elevation of glycolysis. There was no significant effect of diet consumption or parasitism on blood trehalose level. Parasitized larvae displayed higher levels of gluconeogenesis than did unparasitized insects, a finding consistent with the conclusion that blood sugar is rapidly sequestered by developing parasites. The parasite burden, the total number of parasites developing within host larvae, as well as the number of parasites emerging from host larvae to complete development, was significantly less at the lowest dietary nutrient level, but was otherwise similar at all dietary nutrient levels. Moreover, the number of parasites that emerged increased with increasing diet consumption as reflected by host final weight.

Animals↗
PubMed1997

Glucogenesis in an insect, Manduca sexta L., estimated from the 13C isotopomer distribution in trehalose synthesized from [1,3-13C2]glycerol.

Glucogenesis from [3-13C]alanine and [1,3-13C2]glycerol was demonstrated in the insect Manduca sexta by examining the 13C enrichment of trehalose, a non-reducing disaccharide of glucose synthesized in the insect fat body and released into the blood or hemolymph. In insects maintained on a low carbohydrate diet, trehalose synthesized from [3-13C]alanine was selectively enriched at C1 and C6, and C2 and C5. The 13C-labelling pattern indicated the carboxylation of [3-13C]pyruvate, formed by transamination of the [3-13C]alanine followed by randomization of the label at the fumarate step of the tricarboxylic acid cycle and glucose synthesis via the gluconeogenic pathway. 13C enrichment of trehalose was absent in similarly maintained insect larvae administered 3-mercaptopicolinic acid, an inhibitor of hepatic phosphoenolpyruvate carboxykinase. Insects on the low carbohydrate diet also synthesized trehalose from [1,3-13C2]glycerol. 13C multiplets were observed in trehalose C3 and C4 demonstrating the synthesis of three 13C enriched glucose isotopomers from the 13C-labelled glycerol. The relative contributions of 13C-labelled glycerol and unlabelled 3 carbon substrates to the synthesis of the 13C enriched trehalose isotopomers were determined from the multiplet structure at C3, and calculation of minimal rates of glucogenesis were based on the 13C enrichment of C4. The C4/C3 13C enrichment ratio in trehalose synthesized from [1,3-13C2]glycerol was close to unity, and total glucogenesis was calculated after estimation of the expected contribution of unlabelled trehalose synthesis from 3 carbon substrates by comparison of the ratio of unlabelled and labelled contributions to the 13C enriched trehalose isotopomers with the 13C enrichment of [1,3-13C2]glycerol-3-phosphate. The estimated total rates of glucogenesis varied from 0.33 to 2.80 micromol glucose/g fresh weight/h. The blood sugar level of M. sexta was also highly variable. Although the potential importance of glucogenesis from 3 carbon substrates to the maintenance of blood sugar was not established by the present investigation, insects maintained on the low carbohydrate diet had similar blood trehalose levels to those previously reported by others for insects maintained on a natural food.

Animals↗
PubMed1998

Insect cytochromes P450: diversity, insecticide resistance and tolerance to plant toxins.

In the last decade, studies of individual insect P450s have blossomed. This new information has furthered our understanding of P450 diversity, insecticide resistance and tolerance to plant toxins. Insect P450s can be adult specific, larval specific or life stage independent. Similarly, insect P450s vary as to the tissues where they are expressed and in their response to inducers. Insect P450s can now be rapidly sequenced using degenerate PCR primers. Given the huge diversity represented by the Class Insecta, this technique will provide vast amounts of new information about insect P450s and the evolution of the P450 gene superfamily. CYP6D1 is responsible for monooxygenase-mediated resistance to pyrethroid insecticides in the house fly. CYP6D1 is ubiquitously expressed in adults with 10-fold higher levels found in the resistant strain compared to susceptible strains. CYP6D1 is on autosome 1 in house fly. The high level of expression found in the resistant strain is due to genes on autosomes 1 and 2. Whether or not the different CYP6D1 alleles found in resistant and susceptible strains have any role in resistance remains to be elucidated. The CYP6B gene subfamily is involved in the metabolism of host plant toxins (i.e. furanocoumarins). CYP6B gene transcripts in two Papilio (swallowtail) species have been shown to be induced by host plant toxins and in turn to metabolize these toxins. CYP6B P450s play a critical role in allowing Papilio to adapt to furanocoumarin-containing host plants. Similarities in structural and promoter regions of the CYP6B genes suggest that they are derived from a common ancestral gene. Although the P450 monooxygenases of insects are important for the metabolism of hormones and phermones, no individual P450 has yet been shown to metabolize an endogenous compound. Advances in this area are critical because they will provide important new information about insect physiology, biochemistry and development.

Animals↗
PubMed1990

Neurotoxins active on insects: amino acid sequences, chemical modifications, and secondary structure estimation by circular dichroism of toxins from the scorpion Androctonus australis Hector.

Two scorpion neurotoxins active only on insects, the insect toxins AaH IT1 and AaH IT2, were purified from the venom of scorpions Androctonus australis Hector collected in Tozeur (Tunisia) and characterized. AaH IT2 was sequenced and found to differ in four amino acid positions from AaH IT, the single previously sequenced insect toxin [Darbon, H., Zlotkin, E., Kopeyan, C., Van Rietschoten, J., & Rochat, H. (1982) Int. J. Pept. Protein Res. 20, 320-330] which possessed an equal potential for paralyzing fly larvae. The basic amino acid residues of AaH IT1, which differs from AaH IT by one amino acid residue, were selectively chemically modified. Six derivatives were characterized. Their toxicity toward fly larvae and cockroach was determined, and their affinity for the AaH IT1 synaptosomal receptor from cockroach nerve cord was measured. Modification of His-30, Lys-34, and Arg-60 showed no significant effect on biological activity. However, the modification of Lys-28 or Lys-51 demonstrated that these two amino acids are important for toxicity. Furthermore, simultaneous modifications of both Lys-28 and Lys-51 led to a cumulative decrease in biological activity. AaH IT1 and AaH IT2 show similar CD spectra. The secondary structures content of AaH IT2 was estimated from circular dichroism data. Results showed that this class of toxin should possess an additional alpha-helical region and a beta-sheet strand, not found in toxins active on mammals. Attempts to localize these secondary structural features in the amino acid sequence of AaH IT2 indicated that these two regions would be located within the last 20 C-terminal amino acid residues. From these studies on secondary structures, it is possible to consider that toxins active on insects are more structurally constrained than those active on mammals; a decreased molecular flexibility may be, at least partially, responsible for the observed specificity of these toxins for the insect sodium channel. Furthermore, the two alpha-helices found in insect toxins enclosed the two conserved Lys-28 and Lys-51 and might thus be implicated in the toxic site of insect toxins.

Amino Acid Sequence↗