Sequence of three cDNAs encoding an alkaline midgut trypsin from Manduca sexta

Midgut serine proteinases participate in dietary adaptations of the castor (Eri) silkworm Samia ricini Anderson transferred from Ricinus communis to an ancestral host, Ailanthus excelsa Roxb

Dietary change influenced the life-history traits, nutritional utilization, and midgut serine proteinases in the larvae of the domesticated polyphagous S. ricini, transferred from R. communis (common name: castor; family Euphorbiaceae; the host plant implicated in its domestication) to A. excelsa (common name: Indian tree of heaven; family Simaroubaceae; an ancestral host of wild Samia species). Significantly higher values for fecundity and body weight were observed in larvae feeding on R. communis (Scr diet), and they took less time to reach pupation than insects feeding on A. excelsa (Scai diet). Nevertheless, the nutritional index for efficiency of conversion of digested matter (ECD) was similar for larvae feeding on the two plant species, suggesting the physiological adaptation of S. ricini (especially older instars) to an A. excelsa diet. In vitro protease assays and gelatinolytic zymograms using diagnostic substrates and protease inhibitors revealed significantly elevated levels (p ≤ 0.05) of digestive trypsins, which may be associated with the metabolic costs influencing slow growth in larvae feeding on A. excelsa. RT-PCR with semidegenerate serine proteinase gene-specific primers, and cloning and sequencing of 3' cDNA ends identified a large gene family comprising at least two groups of putative chymotrypsins (i.e., Sr I and Sr II) resembling invertebrate brachyurins/collagenases with wide substrate specificities, and five groups of putative trypsins (i.e., Sr III, Sr IV, Sr V, Sr VII, and Sr VIII). Quantitative RT-PCR indicated that transcripts belonging to the Sr I, Sr III, Sr IV, and Sr V groups, especially the Sr IV group (resembling achelase I from Lonomia achelous), were expressed differentially in the midguts of fourth instars reared on the two plant species. Sequence similarity indicated shared lineages with lepidopteran orthologs associated with expression in the gut, protein digestion, and phytophagy. The results obtained are discussed in the context of larval serine proteinases in dietary adaptations, domestication, and exploration of new host plant species for commercial rearing of S. ricini.

Culex quinquefasciatus Late Trypsin Biosynthesis Is Translationally Regulated by Trypsin Modulating Oostatic Factor

Trypsin is a serine protease that is synthesized by the gut epithelial cells of female mosquitoes; it is the enzyme that digests the blood meal. To study its molecular regulation, Culex quinquefasciatus late trypsin was purified by diethylaminoethyl (DEAE), affinity, and C₁₈ reverse-phase high performance liquid chromatography (HPLC) steps, and the N-terminal amino acid sequence was determined for molecular cloning. Five overlapping segments of the late trypsin cDNA were amplified by PCR, cloned, and the full sequence (855 bp) was characterized. Three-dimensional models of the pro-trypsin and activated trypsin were built and compared with other trypsin models. Trypsin modulating oostatic factor (TMOF) concentrations in the hemolymph were determined by ELISA and compared with trypsin activity in the gut after the blood meal. The results showed that there was an increase in TMOF concentrations circulating in the hemolymph which has correlated to the reduction of trypsin activity in the mosquito gut. Northern blot analysis of the trypsin transcripts after the blood meal indicated that trypsin activity also followed the increase and decrease of the trypsin transcript. Injections of different amounts of TMOF (0.025 to 50 μg) decreased the amounts of trypsin in the gut. However, Northern blot analysis showed that TMOF injections did not cause a decrease in trypsin transcript abundance, indicating that TMOF probably affected trypsin translation.

Cloning and reproductive regulation of a trypsin precursor gene in Adelphocorissuturalis

Adelphocoris suturalis is a major pest of cotton. Here, we identified a trypsin precursor gene (AsTryP) in A. suturali, which has an open reading frame region of 873 bp and belongs to the trypsin superfamily. The mRNA of the AsTryP gene was detectable in every life stage and different tissues of 8-day-old females, and the gene was highly expressed in fourth-instar nymphs and the thorax of 8-day-old females. Down-regulation of AsTryP by the injection of double-stranded RNA suppressed the ovarian development and female fertility. These results reveal that trypsin precursor is involved in the reproductive process of A. suturali, and may facilitate the development of new strategies for a better control of A. suturalis.

Juvenile hormone affects the splicing of Culex quinquefasciatus early trypsin messenger RNA

The full length of Culex quiquefasciatus early trypsin has been cloned and sequenced and a three-dimensional (3D) model of the enzyme was built showing that the enzyme has the canonical trypsin's active pocket containing H78, D123, S129, and D128. The biosynthesis of juvenile hormone (JH) III by the corpora allata (CA) in female Cx. quiquefasciatus is sugar-dependent. Females that were maintained on water after emergence synthesize very little JH III, JH III bisepoxide, and methyl farnesoate (MF) (3.8, 1.1, and 0.8 fmol/4 hr/CA, respectively). One hour after sugar feeding, the synthesis of JH III and JH III bisepoxide reached a maximum (11.3 and 5.9 fmol/4 hr/CA, respectively) whereas MF biosynthesis reached a maximum at 24 hr (5.2 fmol/4 hr/CA). The early trypsin is transcribed with a short intron (51 nt) is spliced when JH III biosynthesis is high in sugar fed and at 1 hr after the blood meal (22 and 15  fmol/4 hr/CA, respectively). We investigated the transcriptional and posttranscriptional regulation of the early trypsin gene showing that JH III concentrations influence splicing. In the absence JH III the unspliced transcript is linked by a phosphoamide bond at the 5'-end to RNA ribonuleoprotein (RNP). The biosynthesis of the early trypsin was followed in ligated abdomens (without CA) of newly emerged females that fed blood by enema. Our results show that the early trypsin biosynthesis depends on sugar and blood feeding, whereas the late trypsin biosynthesis does not depend on sugar feeding, or JH III biosynthesis. Downregulating the early trypsin transcript does not affect the late trypsin.

ER type I signal peptidase subunit (LmSPC1) is essential for the survival of Locusta migratoria manilensis and affects moulting, feeding, reproduction and embryonic development

The endoplasmic reticulum type I signal peptidase complex (ER SPC) is a conserved enzyme that cleaves the signal peptides of secretory or membrane preproteins. The deletion of this enzyme leads to the accumulation of uncleaved proteins in biomembranes and cell death. However, the physiological functions of ER SPC in insects are not fully understood. Here, a catalytic subunit gene of ER SPC, LmSPC1, was cloned from Locusta migratoria manilensis and its physiological functions were analysed by RNA interference (RNAi). The LmSPC1 open reading frame encoded a protein of 178 amino acids with all five conserved regions of signal peptidases. RNAi-mediated knockdown of LmSPC1 resulted in high mortality. Sixty-nine per cent of dead nymphs died of abnormal moulting, corresponding to decreased activity of moulting fluid protease. Moreover, insects in the RNAi group experienced a decline in food intake, and a decrease in the secretion of total protein and digestive enzymes from midgut tissues to the midgut lumen. Furthermore, the females produced fewer eggs and eggs with disrupted embryogenesis. These results indicate that LmSPC1 is required for the secretion of secretory proteins, affects physiological functions, including moulting, feeding, reproduction and embryonic development, and is essential for survival. Therefore, LmSPC1 may be a potential target for locust control.

Characterization and transcriptional analyses of cDNAs encoding three trypsin- and chymotrypsin-like proteinases in Cry1Ab-susceptible and Cry1Ab-resistant strains of sugarcane borer, Diatraea saccharalis

Diatraea saccharalis is a major corn borer pest. Midgut serine proteinases are essential for insect growth and development. Alteration of midgut proteinases is responsible for Bt resistance development in some species. To clone midgut trypsin and chymotrypsin cDNAs and to test if the Cry1Ab resistance in D. saccharalis is associated with changes in midgut proteinases, total midgut tryptic and chymotryptic activities, cDNA sequences, and gene expressions of three trypsin and three chymotrypsin genes were comparatively examined between Cry1Ab-susceptible (Cry1Ab-SS) and Cry1Ab-resistant (Cry1Ab-RR) strains. Full-length cDNAs encoding three trypsin- and three chymotrypsin-like proteinases were sequenced from Cry1Ab-SS and Cry1Ab-RR larvae. These cDNAs code for active forms of midgut serine proteinases with all functional motifs, including signal peptide, conserved His-Asp-Ser for the catalytic triad, three pairs of cysteines for disulfide bridge configurations, and conserved substrate specificity determination residues. In general, cDNA and putative protein sequences are highly similar between Cry1Ab-SS and Cry1Ab-RR strains, except for a few nucleotide and predicted amino acid substitutions, whose function need to be further clarified. Total trypsin and chymotrypsin activities were also similar between Cry1Ab-SS and Cry1Ab-RR strains. Transcriptional levels of the trypsin and chymotrypsin genes had numerical difference between Cry1Ab-SS and Cry1Ab-RR strains, but the difference was not statistically significant. Data suggest that the development of Cry1Ab resistance in D. saccharalis was not significantly associated with these trypsins and chymotrypsins. Results clarified the role of six midgut proteinases and provided a foundation for continuing examination of potential involvement of other midgut proteinases in Bt resistance development and other important biochemical processes.

Characterization of cDNAs encoding serine proteases and their transcriptional responses to Cry1Ab protoxin in the gut of Ostrinia nubilalis larvae

Serine proteases, such as trypsin and chymotrypsin, are the primary digestive enzymes in lepidopteran larvae, and are also involved in Bacillus thuringiensis (Bt) protoxin activation and protoxin/toxin degradation. We isolated and sequenced 34 cDNAs putatively encoding trypsins, chymotrypsins and their homologs from the European corn borer (Ostrinia nubilalis) larval gut. Our analyses of the cDNA-deduced amino acid sequences indicated that 12 were putative trypsins, 12 were putative chymotrypsins, and the remaining 10 were trypsin and chymotrypsin homologs that lack one or more conserved residues of typical trypsins and chymotrypsins. Reverse transcription PCR analysis indicated that all genes were highly expressed in gut tissues, but one group of phylogenetically-related trypsin genes, OnTry-G2, was highly expressed in larval foregut and midgut, whereas another group, OnTry-G3, was highly expressed in the midgut and hindgut. Real-time quantitative PCR analysis indicated that several trypsin genes (OnTry5 and OnTry6) were significantly up-regulated in the gut of third-instar larvae after feeding on Cry1Ab protoxin from 2 to 24 h, whereas one trypsin (OnTry2) was down-regulated at all time points. Four chymotrypsin and chymotrypsin homolog genes (OnCTP2, OnCTP5, OnCTP12 and OnCTP13) were up-regulated at least 2-fold in the gut of the larvae after feeding on Cry1Ab protoxin for 24 h. Our data represent the first in-depth study of gut transcripts encoding expanded families of protease genes in O. nubilalis larvae and demonstrate differential expression of protease genes that may be related to Cry1Ab intoxication and/or resistance.

Galactolipase, phospholipase and triacylglycerol lipase activities in the midgut of six species of lepidopteran larvae feeding on different lipid diets

Galactolipase, phospholipase and triacylglycerol lipase activities were measured from the midgut of six species of lepidopteran larvae, two folivores, Epiphyas postvittana (Tortricidae) and Helicoverpa armigera (Noctuidae); two granivores, Plodia interpunctella (Pyralidae) and Ephestia kuehniella (Pyrallidae); a presumptive carnivore, Galleria mellonella (Pyralidae); and a keratinophage, Tineola bisselliella (Tineidae). Galactolipase has not been previously reported in insects. Galactolipase and phospholipase activities were high in the folivores and triacylglycerol lipase activity was low, matching the high galactolipid content of leaves. Conversely, galactolipase and phospholipase activities were low, but not absent, and triacylglycerol lipase activity high in the four other non-folivorous species, matching the high acylglycerol content of their diets. These data suggest the utility of reclassification, for evolutionary studies, of phytophagous lepidoptera into two feeding classes; folivore and granivore, the latter having similarity to the fungivore line of feeders in terms of its lipase activities and ability to retrieve essential polyunsaturated long chain fatty acids from their diets. All the digestive lipases have alkaline pH optima for activity, matching the pH of the lepidopteran midgut and their amino acid content show modifications likely to stabilize the proteins in that environment.

A salivary serine protease of the haematophagous reduviid Panstrongylus megistus: sequence characterization, expression pattern and characterization of proteolytic activity

A cDNA encoding a trypsin-like protease from the salivary glands of the haematophagous reduviid Panstrongylus megistus was cloned and sequenced. The deduced protein sequence showed similarities to serine proteases of other hemipterans but with substitutions in the catalytic triad and the substrate binding site. The expression of the gene increased more than sixfold after feeding. Saliva showed the highest proteolytic activity at neutral to slightly basic pH. Substrate and inhibitor profiles and zymography indicated the presence of a trypsin-like protease with preference for Arg and Lys at P1. Using chromatography, a fibrinolytic enzyme was purified whose sequence was identified by tandem mass spectrometry as that encoded by the cDNA.

Characterization of midgut trypsinogen-like cDNA and enzymatic activity in Plutella xylostella parasitized by Cotesia vestalis or Diadegma semiclausum

Protein digestion in insects is a result of the action of a complex of proteinases present in the midgut. In this report we describe the cloning and sequencing of a trypsin cDNA from larvae of the lepidopteran herbivore Plutella xylostella. We investigated the expression of this gene and enzymatic activity of its translation product with N-a-benzoyl-l-arginine p-nitroanilide (BApNA) as substrate in P. xylostella larvae that were either unparasitized or parasitized by Cotesia vestalis or Diadegma semiclausum parasitoids. The full cDNA sequence consisted of an open reading frame (ORF) encoding 273 amino acid residues including 23 residues of a signal peptide, and the predicted mature trypsinogen-like enzyme had a molecular mass of 26.5 kDa. The amino acid sequence of this trypsinogen-like enzyme protein and phylogenetic relationship with other published trypsin enzyme proteins suggested that it may be a new proteinase in the trypsin protein family. Parasitism of D. semiclausum did not significantly change the mRNA transcript level or BApNAase activity in host larvae. By contrast, parasitization by C. vestalis induced higher transcript levels coupled with a higher level of BApNAase activity. The BApNAase activity in the midgut of nonparasitized or parasitized P. xylostella larvae increased to a maximum level at pH 12, and the parasitism by both C. vestalis and D. semiclausum increased sensitivity of the enzyme to pH values ranging from 2 to 9.5. These parasitoid-induced changes may represent host manipulation by the developing parasitoid larva.

Peritrophic membrane role in enhancing digestive efficiency. Theoretical and experimental models

The peritrophic membrane (PM) is an anatomical structure surrounding the food bolus in most insects. Rejecting the idea that PM has evolved from coating mucus to play the same protective role as it, novel functions were proposed and experimentally tested. The theoretical principles underlying the digestive enzyme recycling mechanism were described and used to develop an algorithm to calculate enzyme distributions along the midgut and to infer secretory and absorptive sites. The activity of a Spodoptera frugiperda microvillar aminopeptidase decreases by 50% if placed in the presence of midgut contents. S. frugiperda trypsin preparations placed into dialysis bags in stirred and unstirred media have activities of 210 and 160%, respectively, over the activities of samples in a test tube. The ectoperitrophic fluid (EF) present in the midgut caeca of Rhynchosciara americana may be collected. If the enzymes restricted to this fluid are assayed in the presence of PM contents (PMC) their activities decrease by at least 58%. The lack of PM caused by calcofluor feeding impairs growth due to an increase in the metabolic cost associated with the conversion of food into body mass. This probably results from an increase in digestive enzyme excretion and useless homeostatic attempt to reestablish destroyed midgut gradients. The experimental models support the view that PM enhances digestive efficiency by: (a) prevention of non-specific binding of undigested material onto cell surface; (b) prevention of excretion by allowing enzyme recycling powered by an ectoperitrophic counterflux of fluid; (c) removal from inside PM of the oligomeric molecules that may inhibit the enzymes involved in initial digestion; (d) restriction of oligomer hydrolases to ectoperitrophic space (ECS) to avoid probable partial inhibition by non-dispersed undigested food. Finally, PM functions are discussed regarding insects feeding on any diet.

Cloning and expression analysis of midgut chymotrypsin-like proteinases in the tobacco hornworm

Digestion of proteins in the midgut of lepidopteran larvae relies on different trypsin and chymotrypsin isoforms. In this study we describe three chymotrypsin-like proteinases (CTLP2-4) from the larval midgut of Manduca sexta, which are closely related to CTLP1 and less closely related to another chymotrypsin (CT), two previously described proteinases present in the larval midgut of M. sexta. CTLP1-4 fit perfectly into a novel subgroup of insect CTLPs by sequence similarity and by the replacement of GP by SA in the highly conserved GDSGGP motif. When we examined CTLP expression in different tissues, most of the proteinases were predominantly expressed in the anterior and median midgut, while some were found in the Malpighian tubules. When we examined CTLP expression at different physiological states, we observed that the CTLP mRNA amounts did not differ considerably in feeding and starving larvae except for CTLP2, whose mRNA dropped significantly upon starvation. During moulting, however, the mRNA amounts of all CTLPs dropped significantly. When we immunologically examined CTLP amounts, mature proteinases were only detectable in the gut lumen of feeding and re-fed larvae, but not in that of starving or moulting larvae, suggesting that CTLP secretion is suspended during starvation or moult.

Digestive duet: midgut digestive proteinases of Manduca sexta ingesting Nicotiana attenuata with manipulated trypsin proteinase inhibitor expression

BACKGROUND

The defensive effect of endogenous trypsin proteinase inhibitors (NaTPIs) on the herbivore Manduca sexta was demonstrated by genetically altering NaTPI production in M. sexta's host plant, Nicotiana attenuata. To understand how this defense works, we studied the effects of NaTPI on M. sexta gut proteinase activity levels in different larval instars of caterpillars feeding freely on untransformed and transformed plants.

METHODOLOGY/ PRINCIPAL FINDINGS

Second and third instars larvae that fed on NaTPI-producing (WT) genotypes were lighter and had less gut proteinase activity compared to those that fed on genotypes with either little or no NaTPI activity. Unexpectedly, NaTPI activity in vitro assays not only inhibited the trypsin sensitive fraction of gut proteinase activity but also halved the NaTPI-insensitive fraction in third-instar larvae. Unable to degrade NaTPI, larvae apparently lacked the means to adapt to NaTPI in their diet. However, caterpillars recovered at least part of their gut proteinase activity when they were transferred from NaTPI-producing host plants to NaTPI-free host plants. In addition extracts of basal leaves inhibited more gut proteinase activity than did extracts of middle stem leaves with the same protein content.

CONCLUSIONS/ SIGNIFICANCE

Although larvae can minimize the effects of high NaTPI levels by feeding on leaves with high protein and low NaTPI activity, the host plant's endogenous NaTPIs remain an effective defense against M. sexta, inhibiting gut proteinase and affecting larval performance.

Sequence variation in trypsin- and chymotrypsin-like cDNAs from the midgut of Ostrinia nubilalis: methods for allelic differentiation of candidate Bacillus thuringiensis resistance genes

Midgut expressed alkaline serine proteases of Lepidoptera function in conversion of Bacillus thuringiensis (Bt) protoxin to active toxin, and reduced level of transcript T23 is associated with Ostrinia nubilalis resistance to Dipel Bt formulations. Three groups of trypsin- (OnT25, OnT23, and OnT3) and two chymotrypsin-like (OnC1 and OnC2) cDNAs were isolated from O. nubilalis midgut tissue. Intraspecific groupings are based on cDNA similarity and peptide phylogeny. Derived serine proteases showed a catalytic triad (His, Asp, and Ser; except transcript OnT23a), three substrate specificity-determining residues, and three paired disulphide bonds. RT-PCR indicated all transcripts are expressed in the midgut. Mendelian-inherited genomic markers for loci OnT23, OnT3 and OnC1 will be useful for association of alleles with bioassayed Bt toxin resistance phenotypes.

Serine proteinases of the human body louse (Pediculus humanus): sequence characterization and expression patterns

After the previous characterization of one trypsin gene (Try1) of the human body louse Pediculus humanus, genes encoding a second trypsin (Try2) and a chymotrypsin (Chy1) have been cloned using degenerate serine proteinase primers and 5'- and 3'-RACE, and sequenced. The deduced 259 and 267 amino acid sequences of Try2 and Chy1 show an identity of 33%-40% to trypsinogens and chymotrypsinogens of other insects. Considering previously published partial sequences, P. humanus possesses at least one Try1 gene, five variants/isoforms of Try2 and six variants/isoforms of Chy1. The genomic DNA of Try2 contains three introns and Chy1 contains five introns. Using whole mount in situ hybridization, gene expression of Try1, Try2 and Chy1 has been localized not only in the distensible anterior region of the midgut of lice but sometimes also in the area following the distensible region. The Try2 gene was always expressed at much lower levels than Try1 or Chy1. This lower expression, the constitutive expression of Try1 and Chy1 at 1, 2, 6, 12 and 24 h after feeding of adults and the regional differences have been verified in quantitative real-time PCR.

Diversity of trypsins in the Mediterranean corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae), revealed by nucleic acid sequences and enzyme purification

The existence of a diverse trypsin gene family with a main role in the proteolytic digestion process has been proved in vertebrate and invertebrate organisms. In lepidopteran insects, a diversity of trypsin-like genes expressed in midgut has also been identified. Genomic DNA and cDNA trypsin-like sequences expressed in the Mediterranean corn Borer (MCB), Sesamia nonagrioides, midgut are reported in this paper. A phylogenetic analysis revealed that at least three types of trypsin-like enzymes putatively involved in digestion are conserved in MCB and other lepidopteran species. As expected, a diversity of sequences has been found, including four type-I (two subtypes), four type-II (two subtypes) and one type-III. In parallel, four different trypsins have been purified from midgut lumen of late instar MCB larvae. N-terminal sequencing and mass spectrometric analyses of purified trypsins have been performed in order to identify cDNAs coding for major trypsins among the diversity of trypsin-like sequences obtained. Thus, it is revealed that the four purified trypsins in MCB belong to the three well-defined phylogenetic groups of trypsin-like sequences detected in Lepidoptera. Major active trypsins present in late instar MCB lumen guts are trypsin-I (type-I), trypsin-IIA and trypsin-IIB (type-II), and trypsin-III (type-III). Trypsin-I, trypsin-IIA and trypsin-III showed preference for Arg over Lys, but responded differently to proteinaceous or synthetic inhibitors. As full-length cDNA clones coding for the purified trypsins were available, three-dimensional protein models were built in order to study the implication of specific residues on their response to inhibitors. Thus, it is predicted that Arg73, conserved in type-I lepidopteran trypsins, may favour reversible inhibition by the E-64. Indeed, the substitution of Val213Cys, unique for type-II lepidopteran trypsins, may be responsible for their specific inhibition by HgCl2. The implication of these results on the optimisation of the use of protease inhibitors for pest control, and on the identification of endoprotease-mediated resistance to Bacillus thuringiensis Cry-toxins is discussed.

Characterization of cDNAs encoding three trypsin-like proteinases and mRNA quantitative analysis in Bt-resistant and -susceptible strains of Ostrinia nubilalis

Our previous studies suggested that Bacillus thuringiensis (Bt) resistance in a Dipel-resistant strain of Ostrinia nubilalis was primarily due to reduced trypsin-like proteinase activity. In this study, we demonstrated a 254-fold resistance to Cry1Ab protoxin but only 12-fold to trypsin-activated Cry1Ab toxin in the Dipel-resistant strain. Significantly higher resistance to Cry1Ab protoxin than to trypsin-activated Cry1Ab toxin further supports the hypothesis that reduced trypsin-like proteinase activity leading to reduced activation of the Bt protoxin is a major resistance mechanism in the Dipel-resistant strain. To understand the molecular basis of reduced proteinase activity, three cDNAs, OnT2, OnT23, and OnT25, encoding full-length trypsin-like proteinases, were sequenced in Bt-resistant and -susceptible O. nubilalis larvae. Although a number of nucleotide differences were found in sequences from the Bt-resistant and -susceptible strains, the differences were not consistent with reduced trypsin-like activity in the Bt-resistant strain. However, the mRNA levels of OnT23 in the resistant strain were 2.7- and 3.8-fold lower than those of the susceptible strain as determined by northern blotting and real-time quantitative PCR, respectively. Thus, reduced trypsin-like activity may be attributed to reduced expression of OnT23 in Bt-resistant O. nubilalis. Our study provides new insights into Bt resistance management strategies, as resistance mediated by reduced Bt protoxin activation would be ineffective if resistant insects ingest a fully activated form of Cry1Ab toxin, either in spray formulations or transgenic Bt crops.

Regulation of chitin synthesis in the larval midgut of Manduca sexta

In insects, chitin is not only synthesized by ectodermal cells that form chitinous cuticles, but also by endodermal cells of the midgut that secrete a chitinous peritrophic matrix. Using anti-chitin synthase (CHS) antibodies, we previously demonstrated that in the midgut of Manduca sexta, CHS is expressed by two cell types, tracheal cells forming a basal tracheal network and columnar cells forming the apical brush border [Zimoch and Merzendorfer, 2002, Cell Tissue Res. 308, 287-297]. Now, we show that two different genes, MsCHS1 and MsCHS2, encode CHSs of midgut tracheae and columnar cells, respectively. To investigate MsCHS2 expression and activity in the course of the larval development, we monitored chitin synthesis, enzyme levels as well as mRNA amounts. All of the tested parameters were significantly reduced during molting and in the wandering stage when compared to the values obtained from intermolt feeding larvae. By contrast, MsCHS1 appeared to be inversely regulated because its mRNA was detectable only during the molt at the time when tracheal growth occurs at the basal site of the midgut. To further examine midgut chitin synthesis, we measured enzyme activity in crude midgut extracts and different membrane fractions. When we analysed trypsin-mediated proteolytic activation, a phenomenon previously reported for insect and fungal systems, we recognized that midgut chitin synthesis was only activated in crude extracts, but not in the 12,000 g membrane fraction. However, proteolytic activation by trypsin in the 12,000 g membrane fraction could be reconstituted by re-adding a soluble fraction, indicating that limited proteolysis affects an unknown soluble factor, a process that in turn activates chitin synthesis.

Serine proteinase over-expression in relation to deltamethrin resistance in Culex pipiens pallens

Two serine proteinase genes were isolated from Culex pipiens pallens as significantly up-regulated genes in a deltamethrin-resistant strain through a combination of suppression substractive hybridization and gene expression profiling by macroarrays. These two genes were found to be expressed at least threefold higher in the resistant strain than in the susceptible one. By using rapid amplification of cDNA ends to screen the constructed cDNA library, we cloned these two sequences. There were 909 bp with an open reading frame of 786 bp in the sequence of trypsin cDNA (GenBank/NCBI AF468495), the deduced protein had 261 amino acids, which was most similar to the trypsin gene of Anopheles gambiae. There were 992 bp with an open reading frame of 816 bp in the chymotrypsin cDNA (GenBank/NCBI AY034060), and its deduced amino acid sequence had 271 amino acids, which was most similar to the chymotrypsin-like protein from Aedes aegypti. The two genes were stably expressed in mosquito C6/36 cells, and the expected 29 and 30 kDa bands were shown with Western blot, respectively. In these cells, after deltamethrin treatment, they had protective effects on the viability. The results indicate that trypsin and chymotrypsin were more highly expressed in the deltamethrin-resistant strain, and was related to insecticide resistance in mosquitoes, Cx. pipiens pallens.

Characterization and cDNA cloning of midgut carboxypeptidases from Trichoplusia ni

Carboxypeptidase A and carboxypeptidase B activities from the midgut of Trichoplusia ni larvae were characterized. In the T. ni larval midgut, the primary digestive carboxypeptidase activity was attributed to carboxypeptidase A, which was eight times more active than carboxypeptidase B. Both the midgut carboxypeptidase A and carboxypeptidase B exhibited maximal activities at pH 8.0-8.5 and were similarly susceptible to inhibition by potato carboxypeptidase inhibitor and phenanthroline. The midgut carboxypeptidase activities were analyzed in T. ni larvae fed on various diet sources and the results indicated that midgut carboxypeptidase activities per milligram of gut were similar regardless of the amount of dietary proteins or amino acids. However, midgut carboxypeptidase A activity was significantly higher in larvae exposed to soybean trypsin inhibitor and was significantly lower in larvae fed on broccoli foliage. From the T. ni larval midgut, five putative carboxypeptidase cDNAs were cloned, demonstrating that midgut carboxypeptidase activities are composed of multiple carboxypeptidase types. Sequence analysis indicated that the midgut carboxypeptidases were produced as secreted proenzymes which could be activated after removal of an N-terminal activation fragment by a trypsin. Two cloned cDNAs are predicted to code for carboxypeptidase A and one cDNA is predicted to code for a putative carboxypeptidase B. The other two cDNAs are highly similar to carboxypeptidase A and carboxypeptidase B in sequences, but their activity was not predictable.

Manipulation of endogenous trypsin proteinase inhibitor production in Nicotiana attenuata demonstrates their function as antiherbivore defenses

Evidence for the in planta defensive function of trypsin protease inhibitors (TPIs) comes from observations of enhanced herbivore resistance after heterologous TPI expression or the manipulation of signal cascades that activate numerous defense responses, including TPI production; no studies have altered the expression of an endogenous pi gene to examine defensive function. We isolated two genes with seven- and six-repeat TPI domains from Nicotiana attenuata from the potato (Solanum tuberosum) PI-II family. To determine whether endogenous TPIs in N. attenuata function defensively against the native herbivores, hornworm (Manduca sexta) and mirids (Tupiocoris notatus), we expressed 175 bp of the seven-domain pi from N. attenuata in an antisense orientation in a TPI-producing genotype to reduce TPI expression and expressed the full-length seven-domain pi in a sense orientation under control of a constitutive promoter to restore TPI activity in a natural genotype from Arizona unable to produce TPIs. Constitutive and inducible TPI production in two antisense lines were diminished by 80% to 90% and 33% to 52%, respectively, and sense expression restored 67% of the activity found in the TPI-producing genotype after caterpillar attack in the TPI-deficient A genotype. Hornworm larvae fed on genotypes with low or no TPI activity grew faster, had higher survivorship, and produced heavier pupae than those that fed on genotypes with high TPI activity. T. notatus showed higher preference for genotypes with low or no TPI activity than for genotypes with high TPI levels. We conclude that endogenous TPIs are an effective defense against these native herbivores.

Molecular cloning of trypsin-like cDNAs and comparison of proteinase activities in the salivary glands and gut of the tarnished plant bug Lygus lineolaris (Heteroptera: Miridae)

Using specific proteinase inhibitors, we demonstrated that serine proteinases in the tarnished plant bug, Lygus lineolaris, are major proteinases in both salivary glands and gut tissues. Gut proteinases were less sensitive to inhibition than proteinases from the salivary glands. Up to 80% azocaseinase and 90% of BApNAse activities in the salivary glands were inhibited by aprotinin, benzamidine, and PMSF, whereas only 46% azocaseinase and 60% BApNAse activities in the gut were suppressed by benzamidine, leupeptin, and TLCK. The pH optima for azocaseinase activity in salivary glands ranged from 6.2 to 10.6, whereas the pH optima for gut proteinases was acidic for general and alkaline for tryptic proteinases. Zymogram analysis demonstrated that approximately 26-kDa proteinases from salivary glands were active against both gelatin and casein substrates. Three trypsin-like cDNAs, LlSgP2-4, and one trypsin-like cDNA, L1GtP1, were cloned from salivary glands and gut, respectively. Putative trypsin precursors from all cloned cDNAs contained a signal peptide, activation peptide, and conserved N-termini (IVGG). Other structural features included His, Asp, and Ser residues for the catalytic amino acid triad of serine proteinase active sites, residues for the binding pocket, and four pairs of cysteine residues for disulfide bridges. Deduced trypsin-like proteins from LlSgP2, LlSgP3, and LlGtP1 cDNAs shared 98-99% sequence identity with a previously reported trypsin-like precursor, whereas the trypsin-like protein of LlSgP4 shared only 44% sequence identity with all other trypsin-like proteins, indicating multi-trypsin forms are present in L. lineolaris.

Purification, properties and substrate specificity of a digestive trypsin from Periplaneta americana (Dictyoptera) adults

A digestive trypsin from the American cockroach (Periplaneta americana, Dictyoptera) males was purified by a combination of anionic chromatographies in low and high pressure systems. The yield was 70% with a final specific activity of 2,000 units per mg protein (substrate: benzoyl-Arg-p-nitroanilide, BRpNA). Chemical modification with TLCK (k(obs)=3.3 M(-1) s(-1); stoichiometry 1:1) and PMSF (k(obs)=0.18 M(-1) s(-1); stoichiometry 1:1) confirmed that this peptidase is a trypsin. This enzyme has a molecular weight of 29 kDa (SDS-PAGE), a pI of 6.0 and a pH optimum of 8.9. Kinetic parameters using different colorimetric, fluorimetric and internally-quenched substrates indicated that P. americana trypsin prefers to hydrolyze synthetic substrates containing more than one amino acid residue and with an arginine residue at P1 position and a hydrophobic residue at P2. This enzyme presented a Km of 120 microM for BRpNA and is competitively inhibited by benzamidine (Ki=0.25 microM). Soybean trypsin inhibitor is a tight-binding inhibitor presenting a K(D) of 0.4 nM. Differences in substrate specificity and in the reactivity of the trypsin active site groups can be related to adaptation of insects to different hosts. P. americana trypsin is an excellent model for comparison as a basal group on evolutionary studies of insect trypsins.

Thiol-activated serine proteinases from nymphal hemolymph of the African migratory locust, Locusta migratoria migratorioides

Two unique serine proteinase isoenzymes (LmHP-1 and LmHP-2) were isolated from the hemolymph of African migratory locust (Locusta migratoria migratorioides) nymphs. Both have a molecular mass of about 23 kDa and are activated by thiol-reducing agents. PMSF abolishes enzymes activity only after thiol activation, while the cysteine proteinase inhibitors E-64, iodoacetamide, and heavy metals fail to inhibit the thiol-activated enzymes. The N-terminal sequence was determined for the more-abundant LmHP-2 isoenzyme. It exhibits partial homology to that of other insect serine proteinases and similar substrate specificity and inhibition by the synthetic and protein trypsin inhibitors pABA, TLCK, BBI, and STI. The locust trypsins LmHP-1 and LmHP-2 constitute a new category of serine proteases wherein the active site of the enzyme is exposed by thiol activation without cleavage of peptide bonds.

An azurocidin-like protein is induced in Trichoplusia ni larval gut cells after bacterial challenge

Trichoplusia ni immune genes up-regulated in response to bacterial infection have been isolated using differential display polymerase chain reaction. Here we report the cloning and characterisation of a gut-specific immune gene encoding an azurocidin-like protein. The deduced protein is 317 amino acid residues long with a hydrophobic C-terminus and a predicted 17-residue signal peptide. The mature T. ni protein shows 30% identity to human azurocidin, an antibacterial protein. Like azurocidin, the T. ni protein contains two amino acid substitutions in the active site triad normally present in serine proteases. The T. ni protein was synthesised with a six-histidine C-terminal extension using the baculovirus expression system. Sequencing of the recombinant azurocidin-like protein confirmed the predicted cleavage of the signal peptide. Northern blots show that T. ni azurocidin-like protein is expressed solely in the larval gut and that expression is up-regulated by injecting or feeding bacteria. Expression reaches its highest level at 10 h after bacteria injection.

Characterization of the proteolytic enzymes in the midgut of the European Cockchafer, Melolontha melolontha (Coleoptera: Scarabaeidae)

In previous studies we showed that the resistance of the European Cockchafer, Melolontha melolontha, towards the Scarab specific Cry8C toxin of Bacillus thuringiensis japonensis strain Buibui is due to the complexity of proteinases in the midgut of the pest insect. In this study these proteinases were identified and characterized using a combination of synthetic substrates and specific inhibitors in zymograms, activity blots, and photometric/fluorometric assays. In the midgut juice three trypsin-like and three elastase-like serine proteinases are predominantly present. In addition, two metalloendoproteinases were detected. At least one of them is most likely to belong to the astacin family, proteinases which normally do not play a role in general protein digestion outside the decapod crustacean. Furthermore, a free aminopeptidase as well as a membrane-associated aminopeptidase, isolated from the brush boarder membrane vesicles (BBMV) of the midgut epithelium, were characterized.

Partial characterization of trypsin-like protease and molecular cloning of a trypsin-like precursor cDNA in salivary glands of Lygus lineolaris

Based on substrate specificity, an alkaline pH optimum, sensitivity to selected proteinase inhibitors, and molecular analysis, we provide evidence for the presence of a trypsin-like serine proteinase in the salivary gland complex (SGC) of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Heteroptera: Miridae). The predominant activity in extracts of the SGC against N(2)-benzoyl-L-arginine-p-nitroanilide (L-BApNA) was at pH 10, but a minor peak of activity also occurred at pH 5. The major BApNAase activity focused at 10.4 during preparative isoelectric focusing and was eluted with an apparent molecular weight of 23,000 from a calibrated gel filtration column. The BApNAase fraction gave a single major band when analyzed on a casein zymogram. The activity was completely suppressed by the serine protease inhibitors, phenylmethylsulfonyl fluoride (PMSF) and lima bean trypsin inhibitor. A cDNA coding for a trypsin-like protein in the salivary glands of L. lineolaris was cloned and sequenced. The 971bp cDNA contained an 873-nucleotide open reading frame encoding a 291-amino acid trypsin precursor. The encoded protein included amino acid sequence motifs that are conserved with four homologous serine proteases from other insects. Typical features of the putative trypsin-like protein from L. lineolaris included the serine protease active site (His(89), Asp(139), Ser(229)), conserved cysteine residues for disulfide bridges, the residues (Asp(223), Gly(252), Gly(262)) that determine trypsin specificity, and both zymogen signal and activation peptides. Cloning and sequencing of a trypsin-like precursor cDNA provided additional direct evidence for trypsin like enzymes in the salivary glands of L. lineolaris.

Compartmentalization of proteinases and amylases in Nauphoeta cinerea midgut

Compartmentalization of proteinases, amylases, and pH in the midgut of Nauphoeta cinerea Oliv. (Blattoptera:Blaberidae) was studied in order to understand the organization of protein and starch digestion. Total proteolytic activity measured with azocasein was maximal at pH 11.5 both in anterior (AM) and posterior (PM) halves of the midgut, but the bulk of activity (67%) was found in PM. Total AM and PM preparations were fractionated on a Sephadex G-50 column and further analysed by means of activity electrophoresis and specific inhibitors and activators. The major activity in PM was classified as an unusual SH-dependent proteinase with M(r) 24,000 and pH optimum with synthetic substrate BApNA at 10.0. The enzyme was 43-fold activated in the presence of 1 mM DTT, insensitive to synthetic inhibitors of serine (PMSF, TLCK, TPCK) and cysteine (IAA, E-64) proteinases, strongly inhibited by STI, and displayed four active bands on zymograms. In PM, activities of trypsin-like, chymotrypsin-like, subtilisin-like, and cysteine proteinases were observed. Aspartic and metalloproteinases were not detected. In AM, activity of unusual SH-dependent proteinase also dominated and activity of chymotrypsin-like proteinase was observed, but their levels were much lower than in PM. Distribution of amylase activity, exhibiting an optimum at pH 6.0, was quite the opposite. The major part of it (67%) was located in AM. Treatment of amylase preparation with proteinases from AM and PM reduced amylase activity twofold. pH of the midgut contents was 6.0-7.2 in AM, 6.4-7.6 in the first and 8.8-9.3 in the second halves of PM. Thus, pH in AM is in good agreement with the optimal pH of amylase, located in this compartment, but the activity of proteinases, including the ability to degrade amylase, in such an environment is low. Active proteolysis takes place in the second half of PM, where pH of the gut is close to the optimal pH of proteinases.

The origin and functions of the insect peritrophic membrane and peritrophic gel

There is a a fluid (peritrophic gel) or membranous (peritrophic membrane, PM) film surrounding the food bolus in most insects. The PM is composed of chitin and proteins, of which peritrophins are the most important. It is proposed here that, during evolution, midgut cells initially synthesized chitin and peritrophins derived from mucins by acquiring chitin-binding domains, thus permitting the formation of PM. Since PM compartmentalizes the midgut, new physiological roles were added to those of the ancestral mucus (protection against abrasion and microorganism invasion). These new roles are reviewed in the light of data on PM permeability and on enzyme compartmentalization, fluid fluxes, and ultrastructure of the midgut. The importance of the new roles in relation to those of protection is evaluated from data obtained with insects having disrupted PM. Finally, there is growing evidence suggesting that a peritrophic gel occurs when a highly permeable peritrophic structure is necessary or when chitin-binding molecules or chitinase are present in food.

Trypsinogen-like cDNAs and quantitative analysis of mRNA levels from the Indianmeal moth, Plodia interpunctella

Two cDNA fragments encoding full-length trypsinogen-like proteins were cloned from larvae of two strains (RC688s and HD198r) of the Indianmeal moth, Plodia interpunctella (Hübner), which differed in their sensitivity to Bacillus thuringiensis protoxins. One cDNA fragment contained 874 nucleotides, including a 780-nucleotide open reading frame that encoded a trypsinogen-like protein (PiT2b). Another cDNA fragment amplified from both P. interpunctella strains contained 864 nucleotides including a 780 bp open reading frame encoding a second trypsinogen-like protein (PiT2c). The cDNA sequence of PiT2b shared 89% sequence identity with PiT2a, a trypsinogen-like protein cloned previously from this species. The cDNA sequences of PiT2a and PiT2c shared 83% identity. The cDNA sequence identity between PiT2b and PiT2c was 80%. The cDNA for PiT2b from strain RC688s was different at six nucleotide positions from that of PiT2b from strain HD198r. Five nucleotide replacements occurred in the open reading frame leading to amino acid changes at all five positions. There were five nucleotide differences in the cDNAs for PiT2c trypsinogen-like proteins from the two strains. Two nucleotide substitutions in the open reading frame resulted in replacements of two amino acid residues in the deduced protein sequences. Amino acid sequences for PiT2a and PiT2b shared 84% identity, but only 50% identity was observed between PiT2c and the other two trypsinogen-like proteins. The deduced amino acid sequences for PiT2b and PiT2c included both signal and zymogen activation peptides and amino acid sequence motifs which are conserved in seven homologous trypsinogen-like proteins from other insects. Typical features of the putative trypsinogen-like proteins from P. interpunctella included the serine proteinase active site triad (His(81), Asp(133), and Ser(233)), three pairs of cysteine residues for disulfide bridges, and three residues, Asp(227), Gly(250), and Gly(260), that help to confer trypsin-like specificity to the enzymes. Quantitative RT-PCR analyses showed that, in fourth instar larvae, RC688s had 1.6-fold higher PiT2a trypsinogen-like mRNA than did HD198r. Expression of PiT2b mRNA was 3.4-fold higher in HD198r than in RC688s. Expression of PiT2c mRNA was 2.8-fold higher in RC688s than in HD198r. Mean accumulation levels of mRNAs for all three trypsinogen-like proteins were slightly higher in RC688s than in HD198r based on total RNA, and 1.3-fold higher in RC688s than in HD198r based on wet weight of larval body tissues.

Molecular cloning and characterization of a midgut chymotrypsin-like enzyme from the lesser grain borer, Rhyzopertha dominica

A cDNA encoding a chymotrypsinogen-like protein in midguts of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) was cloned and sequenced. The 901 bp cDNA contains an 816-nucleotide open reading frame encoding 272-amino acids. The predicted molecular mass and pI of the mature enzyme are 23.7 kDa and 4.64, respectively. The encoded protein includes amino acid sequence motifs that are conserved with 5 homologous chymotrypsinogen proteins from other insects. Features of the putative chymotrypsin-like protein from R. dominica include the serine proteinase active site (His(90), Asp(133), Ser(226)), conserved cysteine residues for disulfide bridges, the residues (Gly(220), Gly(243), Asp(252)) that determine chymotrypsin specificity, and both zymogen activation and signal peptides. A TPCK-sensitive caseinolytic protein (P6) with an estimated molecular mass of 24 kDa is present in midgut extracts of R. dominica and can be resolved by electrophoresis on 4-16% polyacrylamide gels. The molecular mass of this caseinolytic enzyme is similar to that of the chymotrypsin deduced from cDNA. Midgut extracts of R. dominica readily hydrolyzed azocasein and N-succinyl-alanine-alanine-proline-phenylalanine-p- nitroanilide (SAAPFpNA), a chymotrypsin-specific substrate. Properties of the enzymes responsible for these activities were partially characterized with respect to distribution in the gut, optimum pH, and sensitivity toward selected proteinase inhibitors. Optimal activity against both azocasein and SAAPFpNA occurs in a broad pH range from about 7 to 10. Both azocasein and SAAPFpNA activities, located primarily in the anterior midgut region, are inhibited by aprotinin, phenylmethyl sulphonylfluoride (PMSF), and soybean trypsin inhibitor (STI). TPCK (N-alpha-tosyl-L-phenylalanine chloromethyl ketone) and chymostatin inhibited more than 60% of SAAPFpNA but only about 10-20% of azocasein activity. These results provide additional evidence for the presence of serine proteinases, including chymotrypsin, in midguts of R. dominica. Arch. Insect Biochem. Physiol. 43:173-184, 2000.Published 2000 Wiley-Liss, Inc.

cDNA sequence, mRNA expression and genomic DNA of trypsinogen from the indianmeal moth, Plodia interpunctella

Trypsin-like enzymes are major insect gut enzymes that digest dietary proteins and proteolytically activate insecticidal proteins produced by the bacterium Bacillus thuringiensis (Bt). Resistance to Bt in a strain of the Indianmeal moth, Plodia interpunctella, was linked to the absence of a major trypsin-like proteinase (Oppert et al., 1997). In this study, trypsin-like proteinases, cDNA sequences, mRNA expression levels and genomic DNAs from Bt-susceptible and -resistant strains of the Indianmeal moth were compared. Proteinase activity blots of gut extracts indicated that the susceptible strain had two major trypsin-like proteinases, whereas the resistant strain had only one. Several trypsinogen-like cDNA clones were isolated and sequenced from cDNA libraries of both strains using a probe deduced from a conserved sequence for a serine proteinase active site. cDNAs of 852 nucleotides from the susceptible strain and 848 nucleotides from the resistant strain contained an open reading frame of 783 nucleotides which encoded a 261-amino acid trypsinogen-like protein. There was a single silent nucleotide difference between the two cDNAs in the open reading frame and the predicted amino acid sequence from the cDNA clones was most similar to sequences of trypsin-like proteinases from the spruce budworm, Choristoneura fumiferana, and the tobacco hornworm, Manduca sexta. The encoded protein included amino acid sequence motifs of serine proteinase active sites, conserved cysteine residues, and both zymogen activation and signal peptides. Northern blotting analysis showed no major difference between the two strains in mRNA expression in fourth-instar larvae, indicating that transcription was similar in the strains. Southern blotting analysis revealed that the restriction sites for the trypsinogen genes from the susceptible and resistant strains were different. Based on an enzyme size comparison, the cDNA isolated in this study corresponded to the gene for the smaller of two trypsin-like proteinases, which is found in both the Bt-susceptible and -resistant strains of the Indianmeal moth. The sequences reported in this paper have been deposited in the GenBank database (accession numbers AF064525 for the RC688 strain and AF064526 for HD198).

Characterisation of multiple trypsins from the midgut of Locusta migratoria

Three isoforms of trypsin were identified in midgut preparations from Locusta migratoria. Ammonium-sulphate-fractionated luminal contents of midguts were subjected to benzamidine affinity chromatography; proteins eluted by benzamidine were then separated by anion-exchange chromatography. Cationic (TRY 1) and anionic (TRY 2) trypsin activities were eluted from the DEAE column. TRY 1 was homogeneous, producing a single band of Mr 23,000 on SDS-PAGE. TRY 2 comprised two trypsins, TRY 2A (Mr 27,000) and TRY 2B (Mr 29,000). Following a subsequent chromatography step using a Bio-Rad UNO Q column, TRY 2A and TRY 2B were resolved to homogeneity. When homogenates of midgut caecae were the starting material for chromatography, SDS-PAGE of benzamidine-eluted proteins revealed an additional putative trypsin of Mr 17,000 (termed SERP 17) which had been absent from luminal enzyme preparations. Determination of the N-terminal 11 amino acid residues of each protein revealed unique, but similar sequences. The four sequences all began with IVGG, a motif which signifies all four proteins are serine proteases. TRY 1, TRY 2A and TRY 2B were shown to contain only trypsin activity and the preparations were sensitive to inhibition by AEBSF, PMSF, TLCK, benzamidine, leupeptin, SBTI, BPTI and E64.

Identification of novel serine proteinase gene transcripts in the midguts of two tropical insect pests, Scirpophaga incertulas (Wk.) and Helicoverpa armigera (Hb.)

We have used RT PCR and 3'RACE to identify diverse serine proteinase genes expressed in the midguts of the rice yellow stem borer (Scirpophaga incertulas) and Asian corn borer (Helicoverpa armigera). The RT-PCR primers encoded the conserved regions around the active site histidine57 and serine195 of Drosophila melanogaster alpha trypsin, including aspartate189 of the specificity pocket. These primers amplified three transcripts (SiP1-3) from midguts of S. incertulas, and two transcripts (HaP1-2) from midguts of H. armigera. The five RT PCR products were sequenced to permit design of gene-specific forward primers for use with anchored oligo dT primers in 3'RACE. Sequencing of the 3'RACE products indicated that SiP1, SiP2 and HaP1 encoded trypsin-like serine proteinases, while HaP2 encoded a chymotrypsin-like serine proteinases. The SiP3 transcript proved to be an abundant 960 nt mRNA encoding a trypsin-like protein in which the active site serine195 was replaced by aspartate. The possible functions of this unusual protein are discussed.

Characterization of midgut trypsin-like enzymes and three trypsinogen cDNAs from the lesser grain borer, Rhyzopertha dominica (Coleoptera: Bostrichidae)

Protein digestion in the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), results from the action of a complex of serine proteinases present in the midgut. In this study we partially characterized trypsin-like enzyme activity against N-alpha-benzoyl-L-arginine p-nitroanilide (BApNA) in midgut preparations and cloned and sequenced three cDNAs for trypsinogen-like proteins. BApNAase activity in R. dominica midgut was significantly reduced by serine proteinase inhibitors and specific inhibitors of trypsin, whereas BApNAase activity was not sensitive to specific inhibitors of chymotrypsin or aspartic proteinases. However, trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane (E-64) inhibited BApNAase activity by about 30%. BApNAase was most active in a broad pH range from about pH 7 to 9.5. The gut of R. dominica is a tubular tract approximately 2.5 mm in length. BApNAase activity was primarily located in the midgut region with about 1.5-fold more BApNAase activity in the anterior region compared to that in the posterior region. Proteinases with apparent molecular masses of 23-24 kDa that were visualized on casein zymograms following electrophoresis were inhibited by TLCK. Three cDNAs for trypsinogen-like proteins were cloned and sequenced from mRNA of R. dominica midgut. The full cDNA sequences consisted of open reading frames encoding 249, 293, and 255 amino acid residues for RdoT1, RdoT2, and RdoT3, respectively. cDNAs RdoT1, RdoT2, and RdoT3 shared 77-81% sequence identity. The three encoded trypsinogens shared 54-62% identity in their amino acid sequences and had 16-18 residues of signal peptides and 12-15 residues of activation peptides. The three predicted mature trypsin-like enzymes had molecular masses of 23.1, 28, and 23.8 kDa for RdoT1, RdoT2, and RdoT3, respectively. Typical features of these trypsin-like enzymes included the conserved N-terminal residues IVGG62-65, the catalytic amino acid triad of serine proteinase active sites (His109, Asp156, Ser257), three pairs of conserved cysteine residues for disulfide bridges, and the three residues (Asp251, Gly274, Gly284) that determine specificity in trypsin-like enzymes. In addition, RdoT2 has both a PEST-like sequence at the C-terminus and a free Cys158 near the active site, suggesting instability of this enzyme and/or sensitivity to thiol reagents. The sequences have been deposited in GenBank database (accession numbers AF130840 for RdoT1, AF130841 for RdoT2, and AF130842 for RdoT3).

Sequencing and characterization of the citrus weevil, Diaprepes abbreviatus, trypsin cDNA. Effect of Aedes trypsin modulating oostatic factor on trypsin biosynthesis

Trypsin mRNA from the citrus weevil, Diaprepes abbreviatus, was reverse transcribed and amplified by PCR. A cDNA species of 513 bp was cloned and sequenced. The 3' and 5' ends of the gene (262 bp and 237 bp, respectively) were amplified by rapid amplification of cDNA ends, cloned and sequenced. The deduced sequence of the trypsin cDNA (860 bp) encodes for 250 amino acids including 11 amino acids of activation and signal peptides and exhibited 16.8% identity to trypsin genes of selected Lepidoptera and Diptera. A three-dimensional model of Diaprepes trypsin contained two domains of beta-barrel sheets as has been found in Drosophila and Neobellieria. The catalytic active site is composed of the canonical triad of His41, Asp92 and Ser185 and a specificity pocket occupied by Asp179 with maximal activity at pH 10.4. Southern blot analysis indicated that at least two copies of the gene are encoded by Diaprepes midgut. Northern blot analysis detected a single RNA band below 1.35 kb at different larval ages (28-100 days old). The message increased with age and was most abundant at 100 days. Trypsin activity, on the other hand, reached a peak at 50 days and fell rapidly afterwards indicating that the trypsin message is probably regulated translationally. Feeding of soybean trypsin inhibitor and Aedes aegypti trypsin modulating oostatic factor affected trypsin activity and trypsin biosynthesis, respectively. These results indicate that Diaprepes regulates trypsin biosynthesis with a trypsin modulating oostatic factor-like signal.

Purification and characterization of the western spruce budworm larval midgut proteinases and comparison of gut activities of laboratory-reared and field-collected insects

Three proteolytic enzymes, trypsin, chymotrypsin, and aminopeptidase-N (APN), were purified from laboratory-reared western spruce budworm, Choristoneura occidentalis [Freeman], larvae. Budworm trypsin exhibited a high degree of substrate specificity, was inactivated by DFP and TLCK, and was inhibited by trypsin inhibitors. The western spruce budworm chymotrypsin hydrolyzed SAAPFpNA and SAAPLpNA, but not SFpNA, SGGFpNA, SGGLpNA or BTpNA. The chymotrypsin was inactivated by DFP, and was inhibited by chymostatin and the chymotrypsin inhibitor, POT-1. Purified budworm chymotrypsin exhibited little BTEE esterolytic activity and was insensitive to inhibition with TPCK. The N-terminal sequence of budworm trypsin, chymotrypsin, and APN were obtained. Similar levels of trypsin and APN gut activities were found in laboratory-reared and field-collected larvae. However, in comparison to laboratory-reared insects, considerably less chymotrypsin activity, and a much higher level of gut carboxypeptidase activity were found in field-collected western spruce budworm larvae.

Trypsin from Pacifastacus leniusculus hepatopancreas: purification and cDNA cloning of the synthesized zymogen

Trypsin was purified from crayfish, Pacifastacus leniusculus, hepatopancreas, and the gene that encoded this enzyme was cloned from a hepatopancreas cDNA library. Crayfish trypsin is synthesized as a zymogen according to the sequence of the putative precursor peptide. The authenticity of the trypsinogen is supported by the deduced amino acid sequence and confirmed by the N-terminal amino acid sequence of the mature protein. The enzyme has features characteristic of a trypsin, such as a specific binding pocket. Sequence comparison shows that crayfish trypsin is similar to those of other species, with the exception that six cysteine residues present in vertebrates are missing. Some structural characteristics, such as the length of the signal peptide and a calcium binding site, are similar to bacterial trypsin.

Isolation and characterization of two digestive trypsin-like proteinases from larvae of the stalk corn borer, Sesamia nonagrioides

Two digestive trypsin-like proteinases from Sesamia nonagrioides Lef. (Lepidoptera: Noctuidae) larvae were purified by benzamidine-Sepharose affinity chromatography. The purified enzymes showed molecular size of 27 (trypsin-I) and 24 KDa (trypsin-II). Amino acid analysis and N-terminal sequencing confirmed their relationship with other trypsins from lepidopteran larvae. However, trypsin-I presented one lysine at position 11, being the first report of this amino acid in the sequence of a lepidopteran digestive trypsin. Trypsin-I had an isoelectric point of 6.0, and a Km of 2.2 x 10(-4) M and 3.9 x 10(-5) M for BApNa and BAEE, respectively. Trypsin-II presented an isoelectric point of 8.7, and Km values of 1.7 x 10(-4) M (BApNa) and 3.8 x 10(-5) M (BAEE). Both enzymes were differentially inhibited by some proteinase inhibitors. In particular, trypsin-I was inhibited by E-64 (ID50 = 6 microM) but not by lima bean trypsin inhibitor (LBI), whereas trypsin-II was inhibited by LBI (ID50 = 1 microM) and poorly by E-64 (ID50 = 85 microM). Changes in the susceptibility of the trypsin-like activity of midgut extracts from different larval instars to these inhibitors suggest that the relative proportion of these two enzymes varied through larval development, being predominant in early instars trypsin-I and in late instars trypsin-II.

Midgut carboxypeptidase from Helicoverpa armigera (Lepidoptera: Noctuidae) larvae: enzyme characterisation, cDNA cloning and expression

Using synthetic substrates we have characterised carboxypeptidase activity in gut extracts from Helicoverpa armigera larvae. Carboxypeptidase A activity predominates, with only low levels of carboxypeptidase B activity present. Maximum carboxypeptidase A activity occurs over a broad pH range and is inhibited by phenanthroline and potato carboxypeptidase inhibitor. A cDNA clone encoding carboxypeptidase (the first such sequence from a lepidopteran insect) was isolated from a larval gut library. The sequence predicts a secreted polypeptide of Mr 46.6 k with homology to metallocarboxypeptidases from mammalian and invertebrate species. The presence of a serine residue at the active site suggests carboxypeptidase A activity. To further characterise the gene product, the complete cDNA sequence was expressed in insect cells using the baculovirus system. Culture supernatant from these cells contained carboxypeptidase A activity, with no activity against a carboxypeptidase B substrate; the carboxypeptidase B activity in gut extracts must thus be due to a separate enzyme. In agreement with this conclusion, the expressed carboxypeptidase cDNA is a member of a small multigene family. Chronic ingestion of soybean Kunitz trypsin inhibitor by H. armigera larvae results in increased accumulation of carboxypeptidase mRNA in the midgut cells, and an increase in carboxypeptidase A activity detected in gut extract.

cDNAs for a chymotrypsinogen-like protein from two strains of Plodia interpunctella

Gut proteinases are involved in the solubilization and activation of insecticidal toxins produced by Bacillus thuringiensis and may also be involved in resistance development. Approximately threefold lower chymotrypsin-like enzyme activity was observed in a Bt(entomocidus)-resistant strain of the Indianmeal moth, Plodia interpunctella, than that in the Bt-susceptible strain. Because chymotrypsin-like proteinases are involved in Bt protoxin activation in P. interpunctella, we compared cDNA sequences, mRNA expression levels, and genomic DNA for chymotrypsin-like enzymes in Bt-susceptible and Bt-resistant strains of P. interpunctella. To isolate cDNA coding for chymotrypsinogen-like proteinases, a probe was developed using polymerase chain reaction (PCR) amplification of a cDNA library from the Bt-susceptible strain using a vector primer and a degenerate primer corresponding to a conserved sequence in the active site of serine proteinases. This probe was used to screen cDNA libraries from resistant and susceptible strains. Predicted amino acid sequences from cDNA clones of each strain share similarity with sequences of chymotrypsin-like proteinases and are most similar to a chymotrypsin-like proteinase from the tobacco hornworm, Manduca sexta. cDNAs for putative chymotrypsinogen-like proteins, from both Bt-susceptible and Bt-resistant strains of P. interpunctella share an identical open reading frame of 846 nucleotides. The encoded proteins contain amino acid sequence motifs of serine proteinase active sites, disulfide-bridge cysteine residues, and both zymogen activation and signal peptides. A difference between these cDNAs was observed only in the untranslated region where a substitution of guanine for adenine occurred in the Bt-resistant strain. Southern and Northern blotting analyses indicated that there are no major differences in chymotrypsinogen-like genomic organization and mRNA expression in the two strains. These data suggest that chymotrypsinogen-like proteinase genes and their transcription are similar in the Bt-susceptible and Bt-resistant strains of P. interpunctella.

Characterization of major midgut proteinase cDNAs from Helicoverpa armigera larvae and changes in gene expression in response to four proteinase inhibitors in the diet

A Helicoverpa armigera larval midgut cDNA library from larvae raised on an artificial, protein-rich, inhibitor-free diet contained very large numbers of serine proteinase positive clones. DNA sequencing of six random positive cDNAs and 12 PCR derived products identified trypsin genes classifiable into three families, and chymotrypsin and elastase genes classifiable into a single family each. Genomic blots established that the most highly expressed of the trypsin families contained about 18 genes, and that the chymotrypsin and elastase families contained about 14 and 2 genes respectively. The levels of mRNA corresponding to the highly expressed trypsin and chymotrypsin families were determined following chronic ingestion of four proteinase inhibitors. Compared to insects on an inhibitor-free diet, chymotrypsin mRNA was increased by all inhibitors, and trypsin mRNA levels decreased. This occurred independent of whether the inhibitor was solely a trypsin inhibitor (aprotinin), an inhibitor of both trypsin and chymotrypsin (proteinase inhibitor II, soybean trypsin inhibitor) or predominantly a chymotrypsin inhibitor (proteinase inhibitor I). Changing the protein level of the diet did not affect trypsin mRNA levels, but chymotrypsin mRNA levels decreased with increasing dietary protein.

Differentially regulated inhibitor-sensitive and insensitive protease genes from the phytophagous insect pest, Helicoverpa armigera, are members of complex multigene families

Ingestion of soybean Kunitz trypsin inhibitor (SKTI) by larvae of the phytophagous insect pest Helicoverpa armigera induced production of inhibitor-insensitive protease activity. The induced activity was not due to proteolytic enzymes of different mechanistic classes, but rather to variants of the existing enzymes. Characterization of cDNAs showed that sequences encoding proteins of the serine protease family were abundant in gut tissue of both control and SKTI-fed insects. The majority of serine protease family cDNAs encode enzymes closely homologous to trypsin and chymotrypsin; comparison of these sequences shows variation in amino acid residues within the region which would be in contact with a protein protease inhibitor. More diverged sequences which may not encode active proteases are also present. All the cDNAs examined were found to derive from multigene families; at least 28 different genes are present in the serine protease family. Chronic ingestion of SKTI results in some serine protease-encoding mRNA species increasing in level, whereas others decrease. Chymotrypsin-encoding mRNAs tend to increase in level as a result of SKTI ingestion, but no clear trend is shown by trypsin-encoding mRNAs. It is suggested that multiple, varying protease-encoding genes are an adaptive mechanism for reducing the deleterious effects of plant protease inhibitors.