CmCatD, a cathepsin D-like protease has a potential role in insect defense against a phytocystatin

Deleterious effects of Schinus terebinthifolius Raddi seed flour on cowpea weevil, Callosobruchus maculatus (F.), larval development

Schinus terebinthifolius, Raddi, has been extensively studied due to its anti-inflammatory and antibiotic properties. S. terebinthifolius was also toxic to some insects, however little has been explored about the nature of its insecticide compounds or the toxicity of this plant to insect species. In this work, we investigate the toxicity of S. terebinthifolius seed flour against the insect C. maculatus. S. terebinthifolius seed flour interfered with the post hatch development of the C. maculatus larvae, decreasing larval survival, mass and length. Using DEAE-cellulose chromatography, five protein fractions were isolated, a non-retained fraction (NRF) and four retained fractions, eluted with 0.25, 0.5, 0.7 and 1.0 M NaCl. Proteins with varying molecular masses were observed in all fractions. The majority protein bands were identified by mass spectrometry analysis and among the main identified proteins are 11S globulins (such glycinin), lipoxygenase, chitinases, 7S globulins (vicilins, canavalin and β conglycinin), annexin, catalase and sucrose binding protein. All DEAE-protein fractions were toxic to the insect, interfering with the post hatch larval development and survival. Decreases greater than 90% were observed in the larval mass and length at 20 days after oviposition (DAO) for larvae raised on diet containing 0.5% of some fractions. Alterations in the level of proteins, glucose and in the activity of the enzymes lipases and cysteine proteases were also detected in these larvae. Our results show that seeds of S. terebinthifolius have an arsenal of toxic proteins with potential for the control of the insect C. maculatus.

Recruitment of lysosomal cathepsins B, L and D as digestive enzymes in Coleoptera

The recruitment of the lysosomal cathepsins B (CAB), L (CAL) and D (CAD) as luminal digestive enzymes was investigated in 3 species of beetles. Gene expression was determined by RNA-seq in different regions of the midgut and in the carcasses from the transcriptomes of Dermestes maculatus, Tenebrio molitor and Zabrotes subfasciatus. These data together with phylogenetic analyses, allowed us to identify the sequences of the gene coding for digestive and lysosomal CABs, CADs and CALs in T. molitor and Z. subfasciatus and observe the absence of digestive cathepsins in D. maculatus. Comparisons of structures based on the overall similarity of modelled structures were performed and subsite residues in the lysosomal and digestive CALs were identified by molecular docking. The data showed that S2 subsites are very variable, probably as an adaption to a luminal digestive role. The survey of sequences of the gene coding for cathepsins in the genomes of 13 beetle species from different phylogenetic groups showed that expansion of CAL and CAB genes occurred only in the Cucujiformia clade. Several digestive CABs have a reduced occluding loop, probably to act as digestive enzymes. Pollen-feeding was proposed to be the selective pressure to recruit cathepsins as digestive enzymes in Cucujiformia beetles.

Cloning, expression and characterization of arcelin and its impact on digestive enzymes of the stored product insect pest, Callosobruchus maculatus (F.)

The pulse beetle Callosobruchus maculatus causes potential damage to legume crops by infesting the seeds, leading to a reduction of total protein content. Arcelin found in the wild accessions of the common bean, is an insecticidal protein that has the potency to hamper the metabolism of the bruchid beetle. The arcelin gene from the wild accession of Phaseolus lunatus was isolated and the ORF encoding 158 amino acids was cloned in pET-45b (+) vector. The recombinant clones were transformed in BL21 STAR (DE3) pLysS cells, and the expressed arcelin was purified using Ni-NTA column. The recombinant protein was used in preparing an artificial diet, and the insecticidal activity was elucidated against the bruchid pest C. maculatus. Adult emergence and seed damage were drastically reduced in the treated groups. The response towards ingested diet by digestive enzymes involved in metabolism was elucidated through quantitative gene expression. The highest expression was observed in the aminopeptidase, followed by upregulation of alpha-amylase, glycoside hydrolase family 31 and cathepsin D-like aspartic protease, and downregulation of cathepsin L-like cysteine protease. The recombinant arcelin demonstrates effective insecticidal activity against the bruchid beetle. The changes in digestive enzymes to counteract the anti-nutritional nature of the protein were the strategies of the insect defense mechanism.

Proteases inhibitors-insensitive cysteine proteases allow Nezara viridula to feed on growing seeds of field-grown soybean

The southern green stink bug, Nezara viridula is one of the primary soybean pests and causes significant economic losses around the world. In spite of the high proteases inhibitor (PI) levels, N. viridula can feed on developing seeds of field-grown soybean and reduce crop yields. Although the PI-induced responses have been extensively investigated in many pest insects, there is lack of knowledge about the mechanisms that stink bugs employ to withstand cysteine PIs of soybean seeds. This study demonstrated that feeding on developing seeds of field-grown soybean inhibited total proteases activity of N. viridula, as result of inhibition of cathepsin B-like activity in the gut. In addition, from the 30 digestive cathepsins recognized in this study, 6 were identified as cathepsin B-like. Stink bugs that fed on growing seeds of field-grown soybean had similar gut pH to those reared in the laboratory, and both cathepsin B- and L-like had an optima pH of 6.5. Therefore, using specific proteases inhibitors we found that the main proteolytic activity in the gut is from cysteine proteases when N. viridula feeds on soybean crops. Since cathepsin L-like activity was not inhibited by soybean PIs, our results suggested that N. viridula relays on cathepsin L-like to feed on soybean. To our knowledge no study before has shown the impact of seed PIs of field-grown soybean on digestive proteases (cathepsin B- and L-like) of N. viridula. This study suggests that the activity of PI-insensitive cathepsins L-like in the gut would be part of an adaptive strategy to feed on developing soybean seeds. In agreement, the expansions of cathepsin L-like complement observed in pentatomids could confer to the insects a higher versatility to counteract the effects of different PIs.

Genetic Engineering Approaches for Enhanced Insect Pest Resistance in Sugarcane

Sugarcane (Saccharum officinarum), a sugar crop commonly grown for sugar production all over the world, is susceptible to several insect pests attack in addition to bacterial, fungal and viral infections leading to substantial reductions in its yield. The complex genetic makeup and lack of resistant genes in genome of sugarcane have made the conventional breeding a difficult and challenging task for breeders. Using pesticides for control of the attacking insects can harm beneficial insects, human and other animals and the environment as well. As alternative and effective strategy for control of insect pests, genetic engineering has been applied for overexpression of cry proteins, vegetative insecticidal proteins (vip), lectins and proteinase inhibitors (PI). In addition, the latest biotechnological tools such as host-induced gene silencing (HIGS) and CRISPR/Cas9 can be employed for sustainable control of insect pests in sugarcane. In this review overexpression of the cry, vip, lectins and PI genes in transgenic sugarcane and their disease resistance potential is described.

Cathepsins L and B in Dysdercus peruvianus, Rhodnius prolixus, and Mahanarva fimbriolata. Looking for enzyme adaptations to digestion

Cysteine peptidases (CP) play a role as digestive enzymes in hemipterans similar to serine peptidases in most other insects. There are two major CPs: cathepsin L (CAL), which is an endopeptidase and cathepsin B (CAB) that is both an exopeptidase and a minor endopeptidase. There are thirteen putative CALs in Dysdercus peruvianus, which in some cases were confirmed by cloning their encoding genes. RNA-seq data showed that DpCAL5 is mainly expressed in the anterior midgut (AM), DpCAL10 in carcass (whole body less midgut), suggesting it is a lysosomal enzyme, and the other DpCALs are expressed in middle (MM) and posterior (PM) midgut. The expression data were confirmed by qPCR and enzyme secretion to midgut lumen by a proteomic approach. Two CAL activities were isolated by chromatography from midgut samples with similar kinetic properties toward small substrates. Docking analysis of a long peptide with several DpCALs modeled with digestive Tenebrio molitor CAL (TmCAL3) as template showed that on adapting to luminal digestion DpCALs (chiefly DpCAL5) changed in relation to their ancestral lysosomal enzyme (DpCAL10) mainly at its S2 subsite. A similar conclusion arrived from structure alignment-based clustering of DpCALs based on structural similarity of the modeled structures. Changes mostly on S2 subsite could mean the enzymes turn out less peptide-bond selective, as described in TmCALs. R. prolixus CALs changed on adapting to luminal digestion, although less than DpCALs. Both D. peruvianus and R. prolixus have two digestive CABs which are expressed in the same extension as CALs, in the first digestive section of the midgut, but less than in the other midgut sections. Mahanarva fimbriolata does not seem to have digestive CALs and their digestive CABs are mainly expressed in the first digestive section of the midgut and do not diverge much from their lysosomal counterparts. The data suggest that CABs are necessary at the initial stage of digestion in CP-dependent Hemipterans, which action is completed by CALs with low peptide-bond selectivity in Heteroptera species. In M. fimbriolata protein digestion is supposed to be associated with the inactivation of sap noxious proteins, making CAB sufficient as digestive CP. Hemipteran genomes and transcriptome data showed that CALs have been recruited as digestive enzymes only in heteropterans, whereas digestive CABs occur in all hemipterans.

Proteolytic profile of larval developmental stages of Penaeus vannamei: An activity and mRNA expression approach

In arthropods, the cleavage of specific proteins by peptidases has pivotal roles in multiple physiological processes including oogenesis, immunity, nutrition, and parasitic infection. These enzymes are also key players in the larval development, and well-described triggers of molting and metamorphosis. In this work the peptidase complement throughout the larvae development of Penaeus vannamei was quantified at the transcript and activity level using qPCR and fluorogenic substrates designed to be hydrolyzed by class-specific peptidases respectively, providing a detailed identification of the proteolytic repertoire in P. vannamei larvae. Significant changes in the peptidase activity profile were observed. During the lecithotrophic naupliar instars, the dominant peptidase activity and expression derive from cysteine peptidases, suggesting that enzymes of this class hydrolyze the protein components of yolk as the primary amino acid source. At the first feeding instar, zoea, dominant serine peptidase activity was found where trypsin activity is particularly high, supporting previous observations that during zoea the breakdown of food protein is primarily enzymatic. At decapodid stages the peptidase expression and activity is more diverse indicating that a multienzyme network achieves food digestion. Our results suggest that proteolytic enzymes fulfill specific functions during P. vannamei larval development.

Protease inhibitors: recent advancement in its usage as a potential biocontrol agent for insect pest management

Plant-derived protease inhibitors (PIs) are a promising defensin for crop improvement and insect pest management. Although agronomist made significant efforts in utilizing PIs for managing insect pests, the potentials of PIs are still obscured. Insect ability to compensate nutrient starvation induced by dietary PI feeding using different strategies, that is, overexpression of PI-sensitive protease, expression of PI-insensitive proteases, degradation of PI, has made this innumerable collection of PIs worthless. A practical challenge for agronomist is to identify potent PI candidates, to limit insect compensatory responses and to elucidate insect compensatory and resistance mechanisms activated upon herbivory. This knowledge could be further efficiently utilized to identify potential targets for RNAi-mediated pest control. These vital genes of insects could be functionally annotated using the advanced gene-editing technique, CRISPR/Cas9. Contemporary research is exploiting different in silico and modern molecular biology techniques to utilize PIs in controlling insect pests efficiently. This review is structured to update recent advancements in this field, along with its chronological background.

Recruited lysosomal enzymes as major digestive enzymes in insects

The mass recruitment to the midgut contents of lysosomal proteolytic enzymes occurred in insects under three major selective pressures. Hemipteran (true bugs, aphids, and cicadas) ancestors lost their serine peptidases (SP) on adapting to feed on protein-free plant sap. When they returned to protein diets, their cathepsins L and B were recruited to replace their lost SP. Among beetles of the series Cucujiformia, cathepsins L were recruited to hydrolyze ingested plant inhibitors that affect their major SP and/or to deal with special seed proteins, such as prolamins. Larval flies have a very acid middle midgut and use cathepsin D to digest bacteria from their infected food. All the recruited enzymes originated from duplicated genes. The recruited digestive enzymes differ from their lysosomal counterparts in critical regions of their amino acid sequences that resulted in changes in substrate specificities and other kinetic properties. The discharge of digestive cathepsins in the midgut contents, instead of lysosomes, seems to be a consequence of their overexpression or the existence of new targeting signals. Their activation at the midgut contents occurs by an autoactivation mechanism or with the help of other enzymes or by a combination of both. The targeting to lysosomes of the insect lysosomal enzymes does not follow the mammalian mannose 6-phosphate route, but an incompletely known mechanism.

Purification and characterization of trypsin produced by gut bacteria from Anticarsia gemmatalis

Purification of active trypsin in the digestive process of insects is essential for the development of potent protease inhibitors (PIs) as an emerging pest control technology and research into insect adaptations to dietary PIs. An important aspect is the presence of proteolytic microorganisms, which contribute to host nutrition. Here, we purified trypsins produced by bacteria Bacillus cereus, Enterococcus mundtii, Enterococcus gallinarum, and Staphylococcus xylosus isolated from the midgut of Anticarsia gemmatalis. The trypsins had a molecular mass of approximately 25 kDa. The enzymes showed increased activity at 40°C, and they were active at pH values 7.5-10. Aprotinin, bis-benzamidine, and soybean Kunitz inhibitor (SKTI) significantly inhibited trypsin activity. The l-1-tosyl-amido-2-phenylethylchloromethyl ketone (TPCK), pepstatin A, E-64, ethylenediamine tetraacetic acid, and calcium ions did not affect the enzyme activity at the concentrations tested. We infer the purified trypsins do not require calcium ions, by which they differ from the trypsins of other microorganisms and the soluble and insoluble trypsins characterized from A. gemmatalis. These data suggest the existence of different isoforms of trypsin in the velvetbean caterpillar midguts.

Functional characterization of the aspartic proteinase cathepsin D in the beet armyworm (Spodoptera exigua)

In insects, proteolytic enzymes are involved in food digestion and the metamorphosis process. In the present study, the full-length cDNA of an aspartic proteinase, Spodoptera exigua cathepsin D (SeCatD), was cloned, and its functions in metamorphosis were characterized. SeCatD contains an open reading frame of 1152 nucleotides, encoding a 384-amino acid polypeptide including a signal peptide and two functional domains (family A1 propeptide of amino acids (19-45) and a cathepsin D-like domain of 327 amino acids (55-381)). Three-dimensional structure analysis indicated that Asp66 and Asp251 may play important role in hydrolysis. Recombinant SeCatD was expressed in Sf9 insect cells and verified via SDS-PAGE and Western blot, the molecular mass of the expressed SeCatD was approximately 42kDa. The enzyme had an optimal pH value of 3 for activity. In addition, the tissue expression profile of SeCatD during metamorphosis was obtained, and the data demonstrated that SeCatD was expressed increasingly in the fat body and midgut, but not in the epidermis. Finally, injection of dsRNA-SeCatD into the fifth-instar larvae significantly reduced SeCatD expression and larvae survival rate compared to a dsRNA-GFP treatment. These data imply that SeCatD may function during metamorphosis and may represent a target for insect control.

Oral transfer of chemical cues, growth proteins and hormones in social insects

Social insects frequently engage in oral fluid exchange - trophallaxis - between adults, and between adults and larvae. Although trophallaxis is widely considered a food-sharing mechanism, we hypothesized that endogenous components of this fluid might underlie a novel means of chemical communication between colony members. Through protein and small-molecule mass spectrometry and RNA sequencing, we found that trophallactic fluid in the ant Camponotus floridanus contains a set of specific digestion- and non-digestion related proteins, as well as hydrocarbons, microRNAs, and a key developmental regulator, juvenile hormone. When C. floridanus workers' food was supplemented with this hormone, the larvae they reared via trophallaxis were twice as likely to complete metamorphosis and became larger workers. Comparison of trophallactic fluid proteins across social insect species revealed that many are regulators of growth, development and behavioral maturation. These results suggest that trophallaxis plays previously unsuspected roles in communication and enables communal control of colony phenotypes.

Insect response to plant defensive protease inhibitors

Plant protease inhibitors (PIs) are natural plant defense proteins that inhibit proteases of invading insect herbivores. However, their anti-insect efficacy is determined not only by their potency toward a vulnerable insect system but also by the response of the insect to such a challenge. Through the long history of coevolution with their host plants, insects have developed sophisticated mechanisms to circumvent antinutritional effects of dietary challenges. Their response takes the form of changes in gene expression and the protein repertoire in cells lining the alimentary tract, the first line of defense. Research in insect digestive proteases has revealed the crucial roles they play in insect adaptation to plant PIs and has brought about a new appreciation of how phytophagous insects employ this group of molecules in both protein digestion and counterdefense. This review provides researchers in related fields an up-to-date summary of recent advances.

Partial venom gland transcriptome of a Drosophila parasitoid wasp, Leptopilina heterotoma, reveals novel and shared bioactive profiles with stinging Hymenoptera

Analysis of natural host-parasite relationships reveals the evolutionary forces that shape the delicate and unique specificity characteristic of such interactions. The accessory long gland-reservoir complex of the wasp Leptopilina heterotoma (Figitidae) produces venom with virus-like particles. Upon delivery, venom components delay host larval development and completely block host immune responses. The host range of this Drosophila endoparasitoid notably includes the highly-studied model organism, Drosophila melanogaster. Categorization of 827 unigenes, using similarity as an indicator of putative homology, reveals that approximately 25% are novel or classified as hypothetical proteins. Most of the remaining unigenes are related to processes involved in signaling, cell cycle, and cell physiology including detoxification, protein biogenesis, and hormone production. Analysis of L. heterotoma's predicted venom gland proteins demonstrates conservation among endo- and ectoparasitoids within the Apocrita (e.g., this wasp and the jewel wasp Nasonia vitripennis) and stinging aculeates (e.g., the honey bee and ants). Enzyme and KEGG pathway profiling predicts that kinases, esterases, and hydrolases may contribute to venom activity in this unique wasp. To our knowledge, this investigation is among the first functional genomic studies for a natural parasitic wasp of Drosophila. Our findings will help explain how L. heterotoma shuts down its hosts' immunity and shed light on the molecular basis of a natural arms race between these insects.

Differential gene expression profile of the calanoid copepod, Pseudodiaptomus annandalei, in response to nickel exposure

To better understand the underlying mechanisms of reactions of copepods exposed to elevated level of nickel, the suppression subtractive hybridization (SSH) was used to elucidate the response of the copepod Pseudodiaptomus annandalei to nickel exposure at the gene level. P. annandale is one of a few copepod species that can be cultured relatively easy under laboratory condition, and it is considered to be a potential model species for toxicity study. In the present study, P. annandalei were exposed to nickel at a concentration of 8.86 mgL(-1) for 24h, after which the RNA was prepared for SSH using unexposed P. annandalei as drivers. A total of 474 clones on the middle scale in the SSH library were sequenced. Among these genes, 129 potential functional genes were recognized based on the BLAST searches in NCBI and Uniprot databases. These genes were then categorized into nine groups in association with different biological processes using AmiGO against the Gene Ontology database. Of the 129 genes, 127 translatable DNA sequences were predicted to be proteins, and the putative amino acid sequences were searched for conserved domains (CD) and proteins using the CD-Search service and BLASTp. Among 129 genes, 119 (92.2%) were annotated to be involved in different biological processes, while 10 genes (7.8%) were classified as an unknown-function gene group. To further confirm the up-regulation of differentially expressed genes, the quantitative real time PCR were performed to test eight randomly selected genes, in which five of them, i.e. α-tubulin, ribosomal protein L13, ferritin, separase and Myohemerythrin-1, exhibited clear up-regulation after nickel exposure. In addition, MnSOD was further studied for the differential expression pattern after nickel exposure and the results showed that MnSOD had a time- and dose-dependent expression pattern in the copepod after nickel exposure. To the best of our knowledge, this is the first attempt to investigate the toxicity effects of nickel on a copepod at molecular level.

Antagonistic regulation, yet synergistic defense: effect of bergapten and protease inhibitor on development of cowpea bruchid Callosobruchus maculatus

The furanocoumarin compound bergapten is a plant secondary metabolite that has anti-insect function. When incorporated into artificial diet, it retarded cowpea bruchid development, decreased fecundity, and caused mortality at a sufficient dose. cDNA microarray analysis indicated that cowpea bruchid altered expression of 543 midgut genes in response to dietary bergapten. Among these bergapten-regulated genes, 225 have known functions; for instance, those encoding proteins related to nutrient transport and metabolism, development, detoxification, defense and various cellular functions. Such differential gene regulation presumably facilitates the bruchids' countering the negative effect of dietary bergapten. Many genes did not have homology (E-value cutoff 10(-6)) with known genes in a BlastX search (206), or had homology only with genes of unknown function (112). Interestingly, when compared with the transcriptomic profile of cowpea bruchids treated with dietary soybean cysteine protease inhibitor N (scN), 195 out of 200 coregulated midgut genes are oppositely regulated by the two compounds. Simultaneous administration of bergapten and scN attenuated magnitude of change in selected oppositely-regulated genes, as well as led to synergistic delay in insect development. Therefore, targeting insect vulnerable sites that may compromise each other's counter-defensive response has the potential to increase the efficacy of the anti-insect molecules.

Intestinal aspartate proteases TiCatD and TiCatD2 of the haematophagous bug Triatoma infestans (Reduviidae): sequence characterisation, expression pattern and characterisation of proteolytic activity

Two aspartate protease encoding complementary deoxyribonucleic acids (cDNA) were characterised from the small intestine (posterior midgut) of Triatoma infestans and the corresponding genes were named TiCatD and TiCatD2. The deduced 390 and 393 amino acid sequences of both enzymes contain two regions characteristic for cathepsin D proteases and the conserved catalytic aspartate residues forming the catalytic dyad, but only TiCatD2 possesses an entire C-terminal proline loop. The amino acid sequences of TiCatD and TiCatD2 show 51-58% similarity to other insect cathepsin D-like proteases and, respectively, 88 and 58% similarity to the aspartate protease ASP25 from T. infestans available in the GenBank database. In phylogenetic analysis, TiCatD and ASP25 clearly separate from cathepsin D-like sequences of other insects, TiCatD2 groups with cathepsin D-like proteases with proline loop. The activity of purified TiCatD and TiCatD2 was highest between pH 2 and 4, respectively, and hence, deviate from the pH values of the lumen of the small intestine, which varied in correlation with the time after feeding between pH 5.2 and 6.7 as determined by means of micro pH electrodes. Both cathepsins, TiCatD and TiCatD2, were purified from the lumen of the small intestine using pepstatin affinity chromatography and identified by nanoLC-ESI-MS/MS analysis as those encoded by the cDNAs. The proteolytic activity of the purified enzymes is highest at pH 3 and the respective genes are expressed in the both regions of the midgut, stomach (anterior midgut) and small intestine, not in the rectum, salivary glands, Malpighian tubules or haemocytes. The temporal expression pattern of both genes in the small intestine after feeding revealed a feeding dependent regulation for TiCatD but not for TiCatD2.

A complex of genes involved in adaptation of Leptinotarsa decemlineata larvae to induced potato defense

The Colorado potato beetle (Leptinotarsa decemlineata) is the most important pest of potato in many areas of the world. One of the main reasons for its success lies in the ability of its larvae to counteract plant defense compounds. Larvae adapt to protease inhibitors (PIs) produced in potato leaves through substitution of inhibitor-sensitive digestive cysteine proteases with inhibitor-insensitive cysteine proteases. To get a broader insight into the basis of larval adaptation to plant defenses, we created a "suppression subtractive hybridisation" library using cDNA from the gut of L. decemlineata larvae fed methyl jasmonate-induced or uninduced potato leaves. Four hundred clones, randomly selected from the library, were screened for their relevance to adaptation with DNA microarray hybridizations. Selected enzyme systems of beetle digestion were further inspected for changes in gene expression using quantitative PCR and enzyme activity measurements. We identified two new groups of digestive cysteine proteases, intestains D and intestains E. Intestains D represent a group of structurally distinct digestive cysteine proteases, of which the tested members are strongly upregulated in response to induced plant defenses. Moreover, we found that other digestive enzymes also participate in adaptation, namely, cellulases, serine proteases, and an endopolygalacturonase. In addition, juvenile hormone binding protein-like (JHBP-like) genes were upregulated. All studied genes were expressed specifically in larval guts. In contrast to earlier studies that reported experiments based on PI-enriched artificial diets, our results increase understanding of insect adaptation under natural conditions.

Identification and characterization of the cysteine protease inhibitor gene MdCPI from Musca domestica

Cysteine proteinase inhibitors (CPIs) are involved in many vital cellular processes such as signalling pathways, apoptosis, immune response and development; however, no CPIs have yet been reported from the housefly Musca domestica. Here we report the isolation and characterization of a housefly CPI gene designated MdCPI. The gene contains an open reading frame of 357 bp encoding a protein of 118 amino acid residues with a putative signal peptide of 17 amino acid residues. Protein alignment demonstrated a high homology to that of Sarcophaga crassipalpis (identity = 51%). Phylogenetic analysis suggested that all CPIs from dipterans, including the housefly, belong to the I25A family and may be descended from a single common ancestor. The gene was expressed in and purified from Escherichia coli. Biochemical studies showed that MdCPI exerts an inhibiting function on papain, which is a classical assay to confirm CPIs. Real-time quantitative PCR and immunolocalization analysis revealed that MdCPI is specifically expressed in haemocytes and fat bodies. It is highly down-regulated in larvae and markedly up-regulated in the pupal stage, suggesting that it may be related to development.

Changes in oxygen and carbon dioxide environment alter gene expression of cowpea bruchids

Hermetic storage is a widely adopted technique for preventing stored grain from being damaged by storage insect pests. In the air-tight container, insects consume oxygen through metabolism while concomitantly raising carbon dioxide concentrations through respiration. Previous studies on the impact of hypoxia and hypercapnia on feeding behavior of cowpea bruchids have shown that feeding activity gradually decreases in proportion to the changing gas concentrations and virtually ceases at approximately 3-6% (v/v) oxygen and 15-18% carbon dioxide. Further, a number of bruchid larvae are able to recover their feeding activity after days of low oxygen and high carbon dioxide, although extended exposure tends to reduce survival. In the current study, to gain insight into the molecular mechanism underpinning the hypoxia-coping response, we profiled transcriptomic responses to hypoxia/hypercapnia (3% oxygen, 17% carbon dioxide for 4 and 24h) using cDNA microarrays, followed by quantitative RT-PCR verification of selected gene expression changes. A total of 1046 hypoxia-responsive cDNAs were sequenced; these clustered into 765 contigs, of which 645 were singletons. Many (392) did not show homology with known genes, or had homology only with genes of unknown function in a BLAST search. The identified differentially-regulated sequences encoded proteins presumptively involved in nutrient transport and metabolism, cellular signaling and structure, development, and stress responses. Gene expression profiles suggested that insects compensate for lack of oxygen by coordinately reducing energy demand, shifting to anaerobic metabolism, and strengthening cellular structure and muscular contraction.

Isolation, biochemical characterization, and molecular modeling of American lobster digestive cathepsin D1

An aspartic proteinase was isolated from American lobster gastric fluid. The purified cathepsin D runs as a single band on native-PAGE displaying proteolytic activity on a zymogram at pH 3.0, with an isoelectric point of 4.7. Appearance of the protein in SDS-PAGE, depended on the conditions of the gel electrophoresis. SDS treatment by itself was not able to fully unfold the protein. Thus, in SDS-PAGE the protein appeared to be heterogeneous. A few minute of boiling the sample in the presence of SDS was necessary to fully denature the protein that then run in the gel as a single band of ~50 kDa. The protein sequence of lobster cathepsin D1, as deduced from its mRNA sequence, lacks a 'polyproline loop' and β-hairpin, which are characteristic of some of its structural homologues. A comparison of amino acid sequences of digestive and non-digestive cathepsin D-like enzymes from invertebrates showed that most cathepsin D enzymes involved in food digestion, lack the polyproline loop, whereas all non-digestive cathepsin Ds, including the American lobster cathepsin D2 paralog, contain the polyproline loop. We propose that the absence or presence of this loop may be characteristic of digestive and non-digestive aspartic proteinases, respectively.

Host-mediated induction of alpha-amylases by larvae of the Mexican bean weevil Zabrotes subfasciatus (Coleoptera: Chrysomelidae: Bruchinae) is irreversible and observed from the initiation of the feeding period

Larvae of Zabrotes subfasciatus secrete alpha-amylases that are insensitive to the alpha-amylase inhibitor found in seeds of Phaseolus vulgaris. By analyzing amylase activities during larval development on P. vulgaris, we detected activity of the constitutive amylase and the two inducible amylase isoforms at all stages. When larvae were transferred from the non alpha-amylase inhibitor containing seeds of Vigna unguiculata to P. vulgaris, the inducible alpha-amylases were expressed at the same level as in control larvae fed on P. vulgaris. Interestingly, when larvae were transferred from seeds of P. vulgaris to those of V. unguiculata, inducible alpha-amylases continued to be expressed at a level similar to that found in control larvae fed P. vulgaris continuously. When 10-day-old larvae were removed from seeds of V. unguiculata and transferred into capsules containing flour of P. vulgaris cotyledons, and thus maintained until completing 17 days (age when the larvae stopped feeding), we could detect higher activity of the inducible alpha-amylases. However, when larvae of the same age were transferred from P. vulgaris into capsules containing flour of V. unguiculata, the inducible alpha-amylases remained up-regulated. These results suggest that the larvae of Z. subfasciatus have the ability to induce insensitive amylases early in their development. A short period of feeding on P. vulgaris cotyledon flour was sufficient to irreversibly induce the inducible alpha-amylase isoforms. Incubations of brush border membrane vesicles with the alpha-amylase inhibitor 1 from P. vulgaris suggest that the inhibitor is recognized by putative receptors found in the midgut microvillar membranes.

Trophallaxis and prophylaxis: social immunity in the carpenter ant Camponotus pennsylvanicus

In social insects, group behaviour can increase disease resistance among nest-mates and generate social prophylaxis. Stomodeal trophallaxis, or mutual feeding through regurgitation, may boost colony-level immunocompetence. We provide evidence for increased trophallactic behaviour among immunized workers of the carpenter ant Camponotus pennsylvanicus, which, together with increased antimicrobial activity of the regurgitate droplet, help explain the improved survival of droplet recipient ants relative to controls following an immune challenge. We have identified a protein related to cathepsin D, a lysosomal protease, as a potential contributor to the antimicrobial activity. The combined behavioural and immunological responses to infection in these ants probably represent an effective mechanism underlying the social facilitation of disease resistance, which could potentially produce socially mediated colony-wide prophylaxis. The externalization and sharing of an individual's immune responses via trophallaxis could be an important component of social immunity, allowing insect colonies to thrive under high pathogenic pressures.

N-glycosylation at non-canonical Asn-X-Cys sequence of an insect recombinant cathepsin B-like counter-defense protein

CmCatB, a cowpea bruchid cathepsin B-like cysteine protease, facilitates insects coping with dietary protease inhibitor challenge. Expression of recombinant CmCatB using a Pichia pastoris system yielded an enzymatically active protein that was heterogeneously glycosylated, migrating as a smear of > or =50kDa on SDS-PAGE. Treatment with peptide:N-glycosidase F indicated that N-glycosylation was predominant. CmCatB contains three N-glycosylation Asn-X-Ser/Thr consensus sequences. Simultaneously replacing all three Asn residues with Gln via site-directed mutagenesis did not result in completely unglycosylated protein, suggesting the existence of additional atypical glycosylation sites. We subsequently investigated potential N-glycosylation at the two Asn-X-Cys sites (Asn(100) and Asn(236)) in CmCatB. Asn to Gln substitution at Asn(100)-X-Cys on the background of the double mutation at the canonical sites (m1m2, Asn(97)-->Gln and Asn(207)-->Gln) resulted in a single discrete band on the gel, namely m1m2c1 (Asn(97)-->Gln, Asn(207)-->Gln and Asn(100)-->Gln). However, another triple mutant protein m1m2c2 (Asn(97)-->Gln, Asn(207)-->Gln and Asn(236)-->Gln) and quadruple mutant protein m1m2c1c2 were unable to be expressed in Pichia cells. Thus Asn(236) appears necessary for protein expression while Asn(100) is responsible for non-canonical glycosylation. Removal of carbohydrate moieties, particularly at Asn(100), substantially enhanced proteolytic activity but compromised protein stability. Thus, glycosylation could significantly impact biochemical properties of CmCatB.