Partial purification and characterization of digestive trypsin-like proteases from the velvet bean caterpillar, Anticarsia gemmatalis

Bovine pancreatic trypsin inhibitor and soybean Kunitz trypsin inhibitor: Differential effects on proteases and larval development of the soybean pest Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Pest management is challenged with resistant herbivores and problems regarding human health and environmental issues. Indeed, the greatest challenge to modern agriculture is to protect crops from pests and still maintain environmental quality. This study aimed to analyze by in silico, in vitro, and in vivo approaches to the feasibility of using the inhibitory protein extracted from mammals - Bovine Pancreatic Trypsin Inhibitor (BPTI) as a potential inhibitor of digestive trypsins from the pest Anticarsia gemmatalis and comparing the results with the host-plant inhibitor - Soybean Kunitz Trypsin Inhibitor (SKTI). BPTI and SKTI interacts with A. gemmatalis trypsin-like enzyme competitively, through hydrogen and hydrophobic bonds. A. gemmatalis larvae exposed to BPTI did not show two common adaptative mechanisms i.e., proteolytic degradation and overproduction of proteases, presenting highly reduced trypsin-like activity. On the other hand, SKTI-fed larvae did not show reduced trypsin-like activity, presenting overproduction of proteases and SKTI digestion. In addition, the larval survival was reduced by BPTI similarly to SKTI, and additionally caused a decrease in pupal weight. The non-plant protease inhibitor BPTI presents intriguing element to compose biopesticide formulations to help decrease the use of conventional refractory pesticides into integrated pest management programs.

Arginine-containing dipeptides decrease affinity of gut trypsins and compromise soybean pest development

The design and production of molecules capable of mimicking the binding or/and functional sites of proteins inhibitors represent a promising strategy for the exploration and modulation of gut trypsin function in insect pests, specifically Lepidoptera. Here, for the first time, we characterized the trypsin activity present in the gut, performance and development of Anticarsia gemmatalis (Lepidoptera: Noctuidae) larvae when exposed to arginine-containing dipeptides. In silico assessment showed that arginine-containing dipeptides have a greater affinity for the active site of A. gemmatalis trypsins than lysine-containing peptides due to the presence of the double-charged guanidinium group that enhances the interaction at the S1 subsite of trypsins. Furthermore, the inhibitory and anti-insect potential of the peptides was demonstrated through kinetic and larval life cycle parameters, respectively. These dipeptides showed structural stability, binding to the active site, corroborated in vitro (competitive inhibition), and significant reduction of trypsin enzyme activity in the gut, survival, and weight of the A. gemmatalis larvae. Our findings reinforce the idea that small peptides are promising candidates for lepidopteran pest management. The optimization of DI2 and DI1 peptides, enhancing uptake and affinity to trypsins, may turn the use of these molecules feasible in agriculture.

Differential defense responses of tropical grasses to Mahanarva spectabilis (Hemiptera: Cercopidae) infestation

The spittlebugs Mahanarva spectabilis economically challenges cattle production of neotropical regions, due to its voracious feeding on tropical grasses. Here, we evaluated biochemical responses of the interaction between M. spectabilis and the widely cultivated tropical grasses Brachiaria spp. (i.e., brizantha and decumbens) and elephant grasses (cvs. Roxo de Botucatu and Pioneiro), regarding lipoxygenases, protease inhibitors, phytohormones, and proteolytic activities in the midgut of M. spectabilis. The M. spectabilis-infested grasses increased lipoxygenases activity, except for cv. Pioneiro. The levels of the phytohormones jasmonic and abscisic acids were similarly low in all genotypes and increased under herbivory. Furthermore, salicylic acid concentration was constitutively higher in Brachiaria sp., increasing only in spittlebug-infested B. decumbens. M. spectabilis infestations did not induce increases of protease inhibitors in any forage grass type. The trypsin activity remained unaltered, and the total proteolytic activity increased only in B. decumbens-fed insects. Our findings revealed that most forage grasses exposed to spittlebugs activate the lipoxygenases pathway, resulting in increased abscisic and jasmonic acids. However, greater amounts of these hormones do not induce protease inhibitory activity in response to spittlebug attack. This knowledge certainly helps to guide future projects aiming at reducing the impact of spittlebugs on forage production.

Small peptides inhibit gut trypsin-like proteases and impair Anticarsia gemmatalis (Lepidoptera: Noctuidae) survival and development

BACKGROUND

Anticarsia gemmatalis larvae are key defoliating pests of soybean plants. Inorganic insecticides, harmful to the environment and human health, are the main molecules used in the control of this pest. To apply more sustainable management methods, organic molecules with high specificities, such as proteinaceous protease inhibitors, have been sought. Thus, molecular docking studies, kinetics assays, and biological tests were performed to evaluate the inhibitory activity of two peptides (GORE1 and GORE2) rationally designed to inhibit trypsin-like enzymes, which are the main proteases of A. gemmatalis midgut.

RESULTS

The molecular docking simulations revealed critical hydrogen bonding patterns of the peptides with key active site residues of trypsin-like proteases of A. gemmatalis and other Lepidopteran insects. The negative values of binding energy indicate that hydrogen bonds potentiate the tight binding of the peptides with trypsin-like proteases, predicting an effective inhibition. The inhibition's rate constants (Ki) were 0.49 and 0.10 mM for GORE1 and GORE2, resulting in effective inhibition of the activity trypsin on the L-BApNA substrate in the in vitro tests, indicating that the peptide GORE2 has higher inhibitory capacity on the A. gemmatalis trypsins. In addition, the two peptides were determined to be reversible competitive inhibitors. The in vivo test demonstrated that the peptides harm the survival and development of A. gemmatalis larvae.

CONCLUSION

These results suggest that these peptides are potential candidates in the management of A. gemmatalis larvae and provide baseline information for the design of new trypsin-like inhibitors based on peptidomimetic tools. © 2020 Society of Chemical Industry.

Leaf metabolic profiles of two soybean genotypes differentially affect the survival and the digestibility of Anticarsia gemmatalis caterpillars

Insect pests such as Anticarsia gemmatalis cause defoliation and yield losses. Soybean breeding has obtained resistant genotypes, however the mechanism remains unknown. Studies indicated the presence of deterrents compounds in the resistant genotype IAC17, and their leaf metabolite profiles were compared to the susceptible genotype UFV105, which was elicited or not by caterpillar infestation. Cluster analysis indicated a significative distinction between these profiles as well as differences in plant defense pathways. Methylquercetins were constitutively present in the largest concentrations, specifically in the IAC17. Relationship between the resistance and the levels of phytohormones jasmonic acid, abscisic acid and salicylic acid was not observed. However, 1-aminocyclopropane -1carboxylic acid levels indicated that the ethylene may be involved in the constitutive biosynthesis of bioactive compounds. Extracts were added to the diets at three different concentrations to evaluate the effect on caterpillar survival. Lowest survival rates were observed when extracts from the resistant IAC 17 were used, at the lowest concentrations. Survival rates were not higher when IAC 17 infested by caterpillars were used. On the other hand, when extracts from the susceptible were used, the survival reductions were only observed in the highest extract concentrations. These supplementations of the diet reduced the digestive capacity, agreeing with the proteolytic activities, whereas malformations of the intestinal cells were dose dependent. The inhibitory effects persisted in higher dilutions only for the IAC17. Constitutive resistance was also explained by higher levels of protease inhibition. These results can be useful to elucidate the genes and cascades controlling the resistance.

Inhibition kinetics of digestive proteases for Anticarsia gemmatalis

Anticarsia gemmatalis Hübner, 1818 (Lepidoptera) is a major pest of soybean in the Brazil. It is known that the reduction of proteolytic activity by the ingestion of protease inhibitors reduces digestion and larval development of the insects. Control via inhibition of the digestive enzymes necessitates deeper knowledge of the enzyme kinetics and the characterization of the inhibition kinetics of these proteases, for better understanding of the active centers and action mechanisms of this enzyme. Trypsin-like proteases found in the gut of Anticarsia gemmatalis were purified in a p-aminobenzamidine agarose column. Kinetic characterization showed KM 0.503 mM for the L-BApNA substrate; Vmax= 46.650 nM s-1; Vmax/[E]= 9.256 nM s-1 mg L-1 and Vmax/[E]/KM= 18.402 nM s-1 mg L-1 mM. The Ki values for the inhibitors benzamidine, berenil, SKTI and SBBI were 11.2 µM, 32.4 µM, 0.25 nM and 1.4 nM, respectively, and all revealed linear competitive inhibition. The SKTI showed the greatest inhibition, which makes it a promising subject for future research to manufacture peptide mimetic inhibitors.

Larval development and proteolytic activity of Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae) exposed to different soybean protease inhibitors

Anticarsia gemmatalis represents a relevant factor for lowering soybean and other legume crop productivities. Protease inhibitors affect protein degradation and reduce the availability of amino acids, impairing the development and survival of insect pests. To evaluate the possible use of proteinaceous protease inhibitors in the management of this pest, the activities of midgut proteases and the growth and development of A. gemmatalis larvae exposed to soybean Bowman-Birk trypsin-chymotrypsin inhibitor (SBBI) and soybean Kunitz trypsin inhibitor (SKTI) were determined. The survival curves obtained using Kaplan-Meier estimators indicated that SKTI and SBBI stimulated larval survival. However, the development of A. gemmatalis was delayed, and prepupal weight decreased in the presence of both inhibitors. The results showed that SKTI and SBBI inhibited the trypsin-like and total proteolytic activities of larvae on the 12th day after eclosion. On the 15th day after eclosion, larvae exposed to SKTI increased the activities of trypsin and total proteases. Although SKTI and SBBI did not affect the survival of the insect, they had effects on midgut proteases in a stage wherein A. gemmatalis fed voraciously, increased the larval cycle, and decreased prepupal weight. These findings provide baseline information about the potential of proteinaceous protease inhibitors to manage the velvetbean caterpillar, avoiding chemical pesticides.

Intestinal proteolytic profile changes during larval development of Anticarsia gemmatalis caterpillars

Soybean is one of most consumed and produced grains in the world, and Anticarsia gemmatalis is a pest that causes great damage to this crop due to severe defoliation during its larval phase. Plants have mechanisms that lead to the inhibition of proteases in the intestine of these herbivores, hampering their development. Understanding this complex protease inhibitor is important for pest control. The objective of this study was to evaluate the enzymatic profiles of the intestinal proteases of the soybean caterpillar at different instars. For this, the proteolytic profile of the gut in the third, fourth, and fifth instars were analyzed. Irreversible inhibitors of proteases were separately incubated with A. gemmatalis enzyme extracts at the third, fourth, and fifth instar to assess the contribution of these proteases to total proteolytic activity. The enzymatic extracts were also evaluated with specific substrates to confirm changes in the specific activities of trypsin-like, chymotrypsin-like, and cysteine proteases at different instars. The results showed that the protease profile of A. gemmatalis gut changes throughout its larval development. The activity of cysteine proteases was more intense in the first instar. On the contrary, the serine proteases showed major activities in the late stages of the larval phase. Zymogram analysis and protein identification by liquid chromatography-mass spectrometry indicated serine protease as the main protease class expressed in the fifth instar. These results may shift the focus from the rational development of the protease inhibitor to A. gemmatalis and other Lepidoptera, as the expression of major proteases is not constant.

Biochemical characterization of digestive membrane-associated alkaline phosphatase from the velvet bean caterpillar Anticarsia gemmatalis

In Brazil, the use of transgenic plants expressing the insect-toxic Bacillus thuringiensis endotoxin has been successfully used as pest control management since 2013 in transgenic soybean lineages against pest caterpillars such as Helicoverpa armigera. These toxins, endogenously expressed by the plants or sprayed over the crops, are ingested by the insect and bind to receptors in the midgut of these animals, resulting in disruption of digestion and lower insect survival rates. Here, we identified and characterized a membrane-associated alkaline phosphatase (ALP) in the midgut of Anticarsia gemmatalis, the main soybean defoliator pest in Brazil, and data suggested that it binds to Cry1Ac toxin in vitro. Our data showed a peak of ALP activity in homogenate samples of the midgut dissected from the 4th and 5th instars larvae. The brush border membrane vesicles obtained from the midgut of these larvae were used to purify a 60 kDa ALP, as detected by in-gel activity and in vitro biochemical characterization using pharmacological inhibitors and mass spectrometry. When Cry1Ac toxin was supplied to the diet, it was efficient in decreasing larval weight gain and survival. Indeed, in vitro incubation of Cry1Ac toxin with the purified ALP resulted in a 43% decrease in ALP specific activity and enzyme-linked immunosorbent assay showed that ALP interacts with Cry1Ac toxin in vitro, thus suggesting that ALP could function as a Cry toxin ligand. This is a first report characterizing an ALP in A. gemmatalis.

Purification and characterization of a propanol-tolerant neutral protease from Bacillus sp. ZG20

A propanol-tolerant neutral protease was purified and characterized from Bacillus sp. ZG20 in this study. This protease was purified to homogeneity with a specific activity of 26,655 U/mg. The recovery rate and purification fold of the protease were 13.7% and 31.5, respectively. The SDS-PAGE results showed that the molecular weight of the protease was about 29 kDa. The optimal temperature and pH of the protease were 45 °C and 7.0, respectively. The protease exhibited a good thermal- and pH stability, and was tolerant to 50% propanol. Mg²⁺, Zn²⁺, K⁺, Na⁺ and Tween-80 could improve its activity. The calculated K_m and V_max values of the protease towards α-casein were 12.74 mg/mL and 28.57 µg/(min mL), respectively. This study lays a good foundation for the future use of the neutral protease from Bacillus sp. ZG20.

Biochemical characterization a digestive trypsin in the midgut of large cabbage white butterfly, Pieris brassicae L. (Lepidoptera: Pieridae)

A comprehensive study on digestive trypsin was undertaken in the larval midgut of Pieris brassicae L. Results of enzymatic compartmentalization showed a significantly higher activity of crude trypsin in the anterior larval midgut rather than posterior-midgut. Using Diethylaminoethyl cellulose fast flow column chromatography a purified trypsin was obtained by specific activity of 21 U mg-1 protein, recovery of 22%, purification fold of 28-fold and molecular weight of 25 kDa. This purified enzyme showed the highest activity at pH 8 and the corresponding temperature of 40°C. However, the specific inhibitors used including 4-(2-Aminoethyl) benzenesulfonyl fluroride hydrochloride, N-p-Tosyl-L-lysine methyl ester hydrochloride and Soybean Trypsin Inhibitor significantly lowered the activity of the purified enzyme in vitro. Moreover, the activity of trypsin and likewise the nutritional indices were significantly altered in the larval midgut feeding upon the leaves treated by 1 mM concentration of each inhibitor in comparison with control. Determination of enzymatic characteristics of insect trypsins is crucial in paving the path for controlling pests by potential natural compounds via transgenic plants.

Bacterial Symbionts in Lepidoptera: Their Diversity, Transmission, and Impact on the Host

The insect’s microbiota is well acknowledged as a “hidden” player influencing essential insect traits. The gut microbiome of butterflies and moths (Lepidoptera) has been shown to be highly variable between and within species, resulting in a controversy on the functional relevance of gut microbes in this insect order. Here, we aim to (i) review current knowledge on the composition of gut microbial communities across Lepidoptera and (ii) elucidate the drivers of the variability in the lepidopteran gut microbiome and provide an overview on (iii) routes of transfer and (iv) the putative functions of microbes in Lepidoptera. To find out whether Lepidopterans possess a core gut microbiome, we compared studies of the microbiome from 30 lepidopteran species. Gut bacteria of the Enterobacteriaceae, Bacillaceae, and Pseudomonadaceae families were the most widespread across species, with Pseudomonas, Bacillus, Staphylococcus, Enterobacter, and Enterococcus being the most common genera. Several studies indicate that habitat, food plant, and age of the host insect can greatly impact the gut microbiome, which contributes to digestion, detoxification, or defense against natural enemies. We mainly focus on the gut microbiome, but we also include some examples of intracellular endosymbionts. These symbionts are present across a broad range of insect taxa and are known to exert different effects on their host, mostly including nutrition and reproductive manipulation. Only two intracellular bacteria genera (Wolbachia and Spiroplasma) have been reported to colonize reproductive tissues of Lepidoptera, affecting their host’s reproduction. We explore routes of transmission of both gut microbiota and intracellular symbionts and have found that these microbes may be horizontally transmitted through the host plant, but also vertically via the egg stage. More detailed knowledge about the functions and plasticity of the microbiome in Lepidoptera may provide novel leads for the control of lepidopteran pest species.

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.

Purification and biochemical characterization of a novel fibrinolytic enzyme, PSLTro01, from a medicinal animal Porcellio scaber Latreille

A novel protease, named PSLTro01, with fibrinolytic and anticoagulant activity was isolated from Porcellio scaber Latreille and was purified by a combination of hollow fibre membrane molecular weight cut-off (MWCO), ammonium sulfate fractionation, gel filtration and ion-exchange chromatography. PSLTro01 is a single-chain protein with a molecular mass of 38,497 Da as estimated by non-reduced SDS-PAGE and MALDI-TOF MS spectrometry, and its N-terminal 15 amino acid sequence was determined as DINGGGATLPQPLYQ. PSLTro01 is stable in the range of 20-40 °C and pH 6.0-10.0, with a maximum fibrinolytic activity at 40 °C and pH 7.0. The PSLTro01-induced fibrinolytic activity was not influenced by K(+) or Na(+) but was slightly increased by Mg(2+) and completely inhibited by aprotinin and pepstatin A. Fibrin plate assays revealed that PSLTro01 could not directly degrade fibrin but was a plasminogen activator. PSLTro01 exhibited high specificity for the substrate S-2251 for plasmin, followed by S-2238 for thrombin and S-2444 for urokinase. Moreover, the fibrinogenolysis pattern of PSLTro01 was Aα-chains>Bβ-chains>γ-chain. Tail-thrombus of the enzyme treated group was significantly shorter than the physiological saline treated group and the thrombus decrement was correlated with the enzyme dose. PSLTro01 prolongs both thrombin time (TT) and activated partial thromboplastin time (APTT). These results indicate that PSLTro01 may have potential applications in the prevention and treatment of thrombosis.

Identification and partial characterization of proteases in larval preparations of the cereal leaf beetle (Oulema melanopus, Chrysomelidae, Coleoptera)

We determined some biochemical properties of Oulema melanopus larval gut proteases. We found adult midgut enzyme preparations yielded results similar to whole-larval preparations, permitting studies of the very small whole-larval preparations. Protein preparations were analyzed using FITC-casein as a substrate. Acidic pH is optimal for proteolytic activity (range 3.0-4.0). Cysteine protease activity increased at acidic pH and in the presence of β-mercaptoethanol. Protease activities at all pH values were maximal at 45°C. Enzyme activity in larval preparations was inhibited by addition of Fe(2+) , Ca(2+) , Mg(2+) , Zn(2+) , and K(+) (10 mM). Fe(2+) and Zn(2+) significantly decreased enzyme activity at all pH values, Ca(2+) and Mg(2+) at pH 6.2 and Mg(2+) at pH 4.0. Inhibitors, including pepstatin A, showed the greatest inhibition at pH 4.0; phenylmethylsulfonyl fluoride, N-p-tosyl-l-phenylalanine chloromethyl ketone at pH 6.2; and phenylmethylsulfonyl fluoride, Nα -tosyl-l-lysine chloromethyl ketone hydrochloride, N-p-tosyl-l-phenylalanine chloromethyl ketone, trans-epoxysuccinyl-l-leucylamido-(4-guanidino) butane at pH of 7.6. Inhibition assays indicated that cysteine, aspartyl (cathepsin D), serine (trypsin, chymotrypsin-like) proteases and metalloproteases act in cereal leaf beetle digestion.

Peptidases and peptidase inhibitors in gut of caterpillars and in the latex of their host plants

Studies investigating the resistance-susceptibility of crop insects to proteins found in latex fluids have been reported. However, latex-bearing plants also host insects. In this study, the gut proteolytic system of Pseudosphinx tetrio, which feeds on Plumeria rubra leaves, was characterized and further challenged against the latex proteolytic system of its own host plant and those of other latex-bearing plants. The gut proteolytic system of Danaus plexippus (monarch) and the latex proteolytic system of its host plant (Calotropis procera) were also studied. The latex proteins underwent extensive hydrolysis when mixed with the corresponding gut homogenates of the hosted insects. The gut homogenates partially digested the latex proteins of foreign plants. The fifth instar of D. plexippus that were fed diets containing foreign latex developed as well as those individuals who were fed diets containing latex proteins from their host plant. In vitro assays detected serine and cysteine peptidase inhibitors in both the gut homogenates and the latex fluids. Curiously, the peptidase inhibitors of caterpillars did not inhibit the latex peptidases of their host plants. However, the peptidase inhibitors of laticifer origin inhibited the proteolysis of gut homogenates. In vivo analyses of the peritrophic membrane proteins of D. plexippus demonstrate resistance against latex peptidases. Only discrete changes were observed when the peritrophic membrane was directly treated with purified latex peptidases in vitro. This study concludes that peptidase inhibitors are involved in the defensive systems of both caterpillars and their host plants. Although latex peptidase inhibitors inhibit gut peptidases (in vitro), the ability of gut peptidases to digest latex proteins (in vivo) regardless of their origin seems to be important in governing the resistance-susceptibility of caterpillars.

Biochemical responses of Anticarsia gemmatalis (Lepidoptera: Noctuidae) in soybean cultivars sprayed with the protease inhibitor berenil

The damage caused by Anticarsia gemmatalis motivates this study on the adaptive mechanisms of the insect to soybean. The lipoxygenase pathway produces and releases jasmonic acid, involved in the regulation of the plant defense genes, which encodes protease inhibitor (PI) production. Three soybean cultivars IAC-18, IAC-24, and Foscarin-31 were sprayed with water and berenil, a synthetic inhibitor, at 0.60 and 1.0% (w/v) and then infested with A. gemmatalis larvae. The lipoxygenase (LOX) activity increased in the leaves of Foscarin-31, IAC-18, and IAC-24 by 87, 81, and 78%, respectively, after 24 h of A. gemmatalis damage. IAC-18 revealed the lowest increase in PI when compared to the other cultivars. Protease, amidase, and esterase activities in soybean larvae dropped drastically after berenil application. PIs may be included in the control strategies of A. gemmatalis in soybean by lowering the digestive enzyme activity in the larval midgut, thus affecting insect growth and development.

Proteolytic activity of gut bacteria isolated from the velvet bean caterpillar Anticarsia gemmatalis

The development of proteinase inhibitors as potential insect control agents has been constrained by insect adaptation to these compounds. The velvet bean caterpillar (Anticarsia gemmatalis) is a key soybean pest species that is well-adapted to proteinase inhibitors, particularly serine-proteinase inhibitors, which are abundant in the caterpillar host. The expression of diverse proteolytic enzymes by gut symbionts may allow the velvet bean caterpillar to circumvent proteinase inhibitors produced by the host plant. In this study, we characterized the proteolytic activity of the four nonpathogenic species of gut bacteria isolated from the velvet bean caterpillar-Bacillus cereus, Enterococcus gallinarum, Enterococcus mundtii and Staphylococcus xylosus. Two proteinase substrates, N-α-benzoyl-L-Arg-p-nitroanilide (L-BApNA) and N-α-p-tosyl-L-Arg methyl ester (L-TAME) and five proteinase inhibitors [aprotinin, E-64, ethylenediamine tetraacetic acid (EDTA), pepstatin and N-α-tosyl-L-lysine chloromethyl ketone (TLCK)] as well as CaCl2, pH and temperature profiles were used to characterize the expressed proteolytic activity of these bacterial strains in vitro. Kinetic parameters for proteolytic activity were also estimated. The results of these experiments indicated that serine- and cysteine-proteinase activities were expressed by all four gut bacteria symbionts of the velvet bean caterpillar. The cysteine- and serine-proteinase activities of these gut symbionts were distinct and different from that of gut proteinases of the caterpillar itself. This finding provides support for the potential involvement of gut symbionts in the mitigation of the negative effects of serine-proteinase inhibitors in the velvet bean caterpillar.

An amino acid substitution inhibits specialist herbivore production of an antagonist effector and recovers insect-induced plant defenses

Plants respond to insect herbivory through the production of biochemicals that function as either direct defenses or indirect defenses via the attraction of natural enemies. While attack by closely related insect pests can result in distinctive levels of induced plant defenses, precise biochemical mechanisms responsible for differing responses remain largely unknown. Cowpea (Vigna unguiculata) responds to Fall armyworm (Spodoptera frugiperda) herbivory through the detection of fragments of chloroplastic ATP synthase γ-subunit proteins, termed inceptin-related peptides, present in larval oral secretions (OS). In contrast to generalists like Fall armyworm, OS of the legume-specializing velvetbean caterpillar (VBC; Anticarsia gemmatalis) do not elicit ethylene production and demonstrate significantly lower induced volatile emission in direct herbivory comparisons. Unlike all other Lepidoptera OS examined, which preferentially contain inceptin (Vu-In; +ICDINGVCVDA-), VBC OS contain predominantly a C-terminal truncated peptide, Vu-In(-A) (+ICDINGVCVD-). Vu-In(-A) is both inactive and functions as a potent naturally occurring antagonist of Vu-In-induced responses. To block antagonist production, amino acid substitutions at the C terminus were screened for differences in VBC gut proteolysis. A valine-substituted peptide (Vu-In(ΔV); +ICDINGVCVDV-) retaining full elicitor activity was found to accumulate in VBC OS. Compared with the native polypeptide, VBC that previously ingested 500 pmol of the valine-modified chloroplastic ATP synthase γ-subunit precursor elicited significantly stronger plant responses in herbivory assays. We demonstrate that a specialist herbivore minimizes the activation of defenses by converting an elicitor into an antagonist effector and identify an amino acid substitution that recovers these induced plant defenses to a level observed with generalist herbivores.

Enzymatic response of the eucalypt defoliator Thyrinteina arnobia (Stoll) (Lepidoptera: Geometridae) to a bis-benzamidine proteinase Inhibitor. i

Ingestion of proteinase inhibitors leads to hyperproduction of digestive proteinases, limiting the bioavailability of essential amino acids for protein synthesis, which affects insect growth and development. However, the effects of proteinase inhibitors on digestive enzymes can lead to an adaptive response by the insect. In here, we assessed the biochemical response of midgut proteinases from the eucalypt defoliator Thyrinteina arnobia (Stoll) to different concentrations of berenil, a bis-benzamidine proteinase inhibitor, on eucalyptus. Eucalyptus leaves were immersed in berenil solutions at different concentrations and fed to larvae of T. arnobia. Mortality was assessed daily. The proteolytic activity in the midgut of T. arnobia was assessed after feeding on plants sprayed with aqueous solutions of berenil, fed to fifth instars of T. arnobia for 48 h before midgut removal for enzymatic assays. Larvae of T. arnobia were able to overcome the effects of the lowest berenil concentrations by increasing their trypsin-like activity, but not as berenil concentration increased, despite the fact that the highest berenil concentration resulted in overproduction of trypsin-like proteinases. Berenil also prevented the increase of the cysteine proteinases activity in response to trypsin inhibition.

Structural and functional comparison of proteolytic enzymes from plant latex and snake venoms

This work describes classification, functions, location, inhibition, activation, and therapeutic applications of proteases from snake venoms and vegetables. Snake venoms and vegetables can present toxins that unchain necrosis or proteolysis due to the direct cytotoxic action of venom proteases. These proteases are potential tools in the development of drugs for the prevention and treatment of several illnesses. We report herein mainly fibrinogenolytic metallo proteases and serine proteases ("thrombin-like"). These enzymes are extensively used in the treatment and prevention of thrombotic disorders, since they serve as defibrinogenating agents. The therapeutic uses of fibrin(ogen)olytic metallo proteases hold promise for clinical application due to potential in reversing the effects of thrombosis; this has been shown to be an alternative approach to the prevention and treatment of cardiovascular disorders, which are among the most prominent causes of mortality around the world. Plant proteases can be utilized for many cellular and molecular activities, in antibacterial and anticancer therapies, and in the treatment of snakebites, inhibiting snake venom activities such as blood-clotting, defibrinogenation, and fibrin(ogen)olytic and hemorrhagic actions. These toxins also display potential for clinical use in the treatment of hemostatic disorders.

Characterization and identification of proteolytic bacteria from the gut of the velvetbean caterpillar (Lepidoptera: Noctuidae)

The characterization and identification of proteolytic bacteria from the gut of the velvetbean caterpillar (Anticarsia gemmatalis) were the objectives of this study. Twelve aerobic and anaerobic isolates of proteolytic bacteria were obtained from the caterpillar gut in calcium caseinate agar. The number of colony forming units (CFUs) of proteolytic bacteria was higher when the bacteria were extracted from caterpillars reared on artificial diet rather than on soybean leaves (1.73 +/- 0.35 x 10(3) and 0.55 +/- 0.22 x 10(3) CFU/mg gut, respectively). The isolated bacteria were divided into five distinct groups, according to their polymerase chain reaction-restriction fragment-length polymorphism profiles. After molecular analysis, biochemical tests and fatty acid profile determination, the bacteria were identified as Bacillus subtilis, Bacillus cereus, Enterococcus gallinarum, Enterococcus mundtii, and Staphylococcus xylosus. Bacterial proteolytic activity was assessed through in vitro colorimetric assays for (general) proteases, serine proteases, and cysteine proteases. The isolated bacteria were able of hydrolyzing all tested substrates, except Staphylococcus xylosus, which did not exhibit serine protease activity. This study provides support for the hypothesis that gut proteases from velvetbean caterpillar are not exclusively secreted by the insect cells but also by their symbiotic gut bacteria. The proteolytic activity from gut symbionts of the velvetbean caterpillar is suggestive of their potential role minimizing the potentially harmful consequences of protease inhibitors from some of this insect host plants, such as soybean, with implications for the management of this insect pest species.

Contribution of gut bacteria to digestion and development of the velvetbean caterpillar, Anticarsia gemmatalis

Bacteria colonies from gut homogenates of fifth instar velvetbean caterpillars (Lepidoptera: Noctuidae) were subjected to antibiotic sensitivity experiments using discs containing 22 antibiotics. The antibiotic tetracycline provided the best results, followed by chloramphenicol. Tetracycline also provided higher inhibition of colony forming units than chloramphenicol and was therefore provided to the caterpillars in increasing diet concentrations to assess the contribution of gut bacteria to their digestion and development. The activity of proteases (general), serine-proteinases and lipases were significantly suppressed by tetracycline. Concentration-inhibition curves were successfully established for tetracycline and this antibiotic was effective in suppressing them, particularly serine-proteinases, suggesting that gut bacteria may significantly contribute with lipid- and mainly protein-digestion in velvetbean caterpillars. Increased diet concentrations of tetracycline led only to mild increase in insect mortality (ca. 20%), with the surviving insects showing faster development (< or =4 days) and higher pupa weight (<0.04 mg) with increased concentrations of tetracycline. Therefore, the gut bacteria inhibited by tetracycline does not seem to play a crucial role in the survival and development of the velvetbean caterpillar, but may be important in the adaptation of this pest species to hosts rich in protease inhibitors, such as soybean.

Trypsin cleavage of the baculovirus occlusion-derived virus attachment protein P74 is prerequisite in per os infection

Baculovirus occlusion-derived virions (ODVs) contain a number of infectivity factors essential for the initiation of infection in larval midgut cells. Deletion of any of these factors neutralizes infectivity by the per os route. We have observed that P74 of the group I alphabaculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is N-terminally cleaved when a soluble form of the protein was incubated with insect midgut tissues under alkaline conditions and that cleavage was prevented by soybean trypsin inhibitor (SBTI). Presently, biological assays were carried out that suggest SBTI inhibits and trypsin enhances baculovirus per os infectivity. We developed a method to rescue per os infectivity of a P74 null virus involving co-transfection of viral DNA with a plasmid that transiently expresses p74. We used this plasmid rescue method to functionally characterize P74. A series of site-directed mutants were generated at the N terminus to evaluate if trypsin cleavage sites were necessary for function. Mutagenesis of R195, R196 and R199 compromised per os infectivity and rendered P74 resistant to midgut trypsin.

Midgut pH profile and protein digestion in the larvae of Lutzomyia longipalpis (Diptera: Psychodidae)

The sand fly Lutzomyia longipalpis is the vector of Leishmania infantum, the etiological agent of American visceral leishmaniasis. Despite its importance, until now the internal anatomy of the immature forms has never been described and little is known about their digestive processes. In nature, sand fly larvae feed on organic detritus in the soil, constantly ingesting large amounts of material. The objective of this study was to describe the anatomy of the gut and the pH of the gut lumen, as well as to investigate the proteases responsible for protein digestion. The larvae have a short gut with a prominent, well-developed midgut. Ingestion of food containing indicator dyes permitted the gut pH to be measured. A pH gradient was observed, varying from >9 in the anterior midgut to 6.5-7.0, in the posterior midgut. The endoproteolytic enzymes are secreted in the anterior midgut and are able to digest azocasein over a large pH range, specially at pH 11. Studies with various inhibitors indicated that the digestive endoproteases are trypsin- and chymotrypsin-like enzymes. These results were confirmed by using the substrates BApNA and N-CBZ-L-PpNA, specific for trypsin and chymotrypsin, respectively. Aminopeptidases were also investigated with p-nitroaniline-derived substrates. These enzymes are located in the posterior midgut, bound to the membranes and functioning at an optimal pH of 6.5-8.0. The results presented here are consistent with the current proposal that proteins are digested to peptides in the anterior midgut inside the endoperitrophic space and subsequently undergo digestion in the ectoperitrophic space of the posterior midgut.

Perspectives of digestive pest control with proteinase inhibitors that mainly affect the trypsin-like activity of Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae)

The present study describes the main characteristics of the proteolytic activities of the velvetbean caterpillar, Anticarsia gemmatalis Hübner, and their sensitivity to proteinase inhibitors and activators. Midguts of last instar larvae reared on an artificial diet were homogenized in 0.15 M NaCl and centrifuged at 14,000 g for 10 min at 4 degrees C and the supernatants were used in enzymatic assays at 30 degrees C, pH 10.0. Basal total proteolytic activity (azocasein hydrolysis) was 1.14 +/- 0.15 absorbance variation min(-1) mg protein(-1), at 420 nm; basal trypsin-like activity (N-benzoyl-L-arginine-p-nitroanilide, BApNA, hydrolysis) was 0.217 +/- 0.02 mmol p-nitroaniline min(-1) mg protein(-1). The maximum proteolytic activities were observed at pH 10.5 using azocasein and at pH 10.0 using BApNA, this pH being identical to the midgut pH of 10.0. The maximum trypsin-like activity occurred at 50 degrees C, a temperature that reduces enzyme stability to 80 and 60% of the original, when pre-incubated for 5 and 30 min, respectively. Phenylmethylsulfonyl fluoride inhibited the proteolytic activities with an IC50 of 0.39 mM for azocasein hydrolysis and of 1.35 mM for BApNA hydrolysis. Benzamidine inhibited the hydrolysis with an IC50 of 0.69 and 0.076 mM for azocasein and BApNA, respectively. The absence of cysteine-proteinases is indicated by the fact that 2-mercaptoethanol and L-cysteine did not increase the rate of azocasein hydrolysis. These results demonstrate the presence of serine-proteinases and the predominance of trypsin-like activity in the midgut of Lepidoptera insects, now also detected in A. gemmatalis, and suggest this enzyme as a major target for pest control based on disruption of protein metabolism using proteinase inhibitors.