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

Comparative proteomic analysis reveals insights into the response of Cryptolaemus montrouzieri to bottom-up transfer of cadmium and lead across a multi-trophic food chain

Contamination of agro-ecosystems with heavy metals can affect the development and reproduction of insect natural enemies. This study reports a detailed Tandem Mass Tag based quantitative proteomic analysis of underlying mechanisms responsible for stress response of Cryptolaemus montrouzieri against heavy metals (cadmium (Cd) and lead (Pb)) transported across a multi-trophic food chain. A total of 6639 proteins were detected under Cd as well as Pb stress. In Pb versus the control cluster, 69 proteins (28 up-regulated and 41 down-regulated) were differentially expressed whereas 268 proteins were differentially expressed under Cd versus the control cluster, having 198 proteins up-regulated and 70 down-regulated proteins. The analysis of differentially expressed proteins showed that 27 proteins overlapped in both clusters representing the core proteome to Pb and Cd stress. The bioinformatics analysis demonstrated that these proteins were mapped to 57 and 99 pathways in Pb versus control and Cd versus control clusters, respectively. The functional classification by COG, GO and KEGG databases showed significant changes in protein expression by C. montrouzieri under Pb and Cd stress. The heavy metal stress (Pb and Cd) induced significant changes in expression of proteins like hexokinase (HK), succinyl-CoA, trypsin like proteins, cysteine proteases, cell division cycle proteins, and yellow gene proteins. The results provide detailed information on the protein expression levels of C. montrouzieri and will serve as basic information for future proteomic studies on heavy metal responses of insect predators within a multi-trophic food chain.

Alkaline serine proteases from Helicoverpa armigera: potential candidates for industrial applications

We characterized trypsin- and chymotrypsin-like serine alkaline proteases from cotton bollworm, Helicoverpa armigera, for their probable potential application as additives in various bio-formulations. Purification was achieved by using hydroxylapatite, DEAE sephadex and CM sephadex columns, which resulted in increased enzyme activity by 13.76- and 14.05-fold for trypsin and chymotrypsin, respectively. Michaelis-Menten constants (K_m ) for substrates of trypsin and chymotrypsin, BApNA and SAAPFpNA, were found to be 1.25 and 0.085 mM, correspondingly. Fluorescent zymogram analysis indicated the presence of five trypsin bands with molecular masses of ∼21, 25, 38, 40, and 66 kDa and two chymotrypsin bands with molecular masses of ∼29 and 34 kDa in SDS-PAGE. The optimum pH was 10.0 and optimum temperature was 50°C for proteolytic activity for the purified proteases. The proteases were inhibited by synthetic inhibitors such as PMSF, aprotonin, leupeptin, pefabloc, and antipain. TLCK and TPCK inhibited about 94 and 90% of trypsin and chymotrypsin activity, respectively, while EDTA, EGTA, E64, pepstatin, idoacetamide, and bestatin did not affect the enzymes. The purified enzymes exhibited high stability and compatibility with metal ions; oxidizing, reducing, and bleaching agents; organic solvents; and commercial detergents. Short life cycles, voracious feeding behavior, and production of multiple forms of proteases in the midgut with rapid catalytic activity and chemostability can serve H. armigera as an excellent alternative source of industrially important proteases for use as additives in stain removers, detergents, and other bio-formulations. Identification of enzymes with essential industrial properties from insect species could be a bioresource.

Physiology of digestion and the molecular characterization of the major digestive enzymes from Periplaneta americana

Cockroaches are among the first insects to appear in the fossil record. This work is part of ongoing research on insects at critical points in the evolutionary tree to disclose evolutionary trends in the digestive characteristics of insects. A transcriptome (454 Roche platform) of the midgut of Periplanetaamericana was searched for sequences of digestive enzymes. The selected sequences were manually curated. The complete or nearly complete sequences showing all characteristic motifs and highly expressed (reads counting) had their predicted sequences checked by cloning and Sanger sequencing. There are two chitinases (lacking mucin and chitin-binding domains), one amylase, two α- and three β-glucosidases, one β-galactosidase, two aminopeptidases (none of the N-group), one chymotrypsin, 5 trypsins, and none β-glucanase. Electrophoretic and enzymological data agreed with transcriptome data in showing that there is a single β-galactosidase, two α-glucosidases, one preferring as substrate maltase and the other aryl α-glucoside, and two β-glucosidases. Chromatographic and enzymological data identified 4 trypsins, one chymotrypsin (also found in the transcriptome), and one non-identified proteinase. The major digestive trypsin is identifiable to a major P. americana allergen (Per a 10). The lack of β-glucanase expression in midguts was confirmed, thus lending support to claims that those enzymes are salivary. A salivary amylase was molecularly cloned and shown to be different from the one from the midgut. Enzyme distribution showed that most digestion occurs under the action of salivary and midgut enzymes in the foregut and anterior midgut, except the posterior terminal digestion of proteins. A counter-flux of fluid may be functional in the midgut of the cockroach to explain the low excretory rate of digestive enzymes. Ultrastructural and immunocytochemical localization data showed that amylase and trypsin are released by both merocrine and apocrine secretion mainly from gastric caeca. Finally, a discussion on Polyneoptera digestive physiology is provided.

Purification of a serine protease and evidence for a protein C activator from the saliva of the tick, Ixodes scapularis

The saliva of ticks is critical to their survival as parasites and hematophagous animals. In this study, we have purified an enzyme with trypsin-like activity from the saliva of the tick vector of Lyme Disease, Ixodes scapularis. This enzyme, named as IXOSP (I. scapularis salivary serine protease), is a 29.9 kDa molecule with N-terminus FPxMVxLRIKxR. A BLAST search identified IXOSP as a secreted serine protease (AAY66740) with a conserved catalytic triad His, Asp, and Ser. In vitro studies demonstrated that IXOSP cleaves chromogenic substrates with arginine in the P1 position, by a mechanism inhibited by PMSF or aprotinin. Gene expression studies revealed that IXOSP is expressed at different tick developmental stages, including eggs, and unfed or fed adult tick salivary glands, but not in nymphs or in the midgut. While the physiological substrate for IXOSP remains to be identified, we demonstrated that I. scapularis saliva activate protein C (PC) resulting in the production of activated PC, a potent anticoagulant that also regulates a myriad of inflammatory responses through protease activated receptors. In contrast, the salivary glands of Anopheles gambiae, Anopheles stephensi, Anopheles albimanus, Aedes aegypti, Lutzomyia longipalpis, and Phlebotomus ariasi did not activate protein C. These discoveries are discussed in the context of blood coagulation, inflammation and vector-host interactions.

Characterization of a chemostable serine alkaline protease from Periplaneta americana

BACKGROUND

Proteases are important enzymes involved in numerous essential physiological processes and hold a strong potential for industrial applications. The proteolytic activity of insects' gut is endowed by many isoforms with diverse properties and specificities. Thus, insect proteases can act as a tool in industrial processes.

RESULTS

In the present study, purification and properties of a serine alkaline protease from Periplaneta americana and its potential application as an additive in various bio-formulations are reported. The enzyme was purified near to homogeneity by using acetone precipitation and Sephadex G-100 gel filtration chromatography. Enzyme activity was increased up to 4.2 fold after gel filtration chromatography. The purified enzyme appeared as single protein-band with a molecular mass of ~ 27.8 kDa in SDS-PAGE. The optimum pH and temperature for the proteolytic activity for purified protein were found around pH 8.0 and 60°C respectively. Complete inhibition of the purified enzyme by phenylmethylsulfonyl fluoride confirmed that the protease was of serine-type. The purified enzyme revealed high stability and compatibility towards detergents, oxidizing, reducing, and bleaching agents. In addition, enzyme also showed stability towards organic solvents and commercial detergents.

CONCLUSION

Several important properties of a serine protease from P. Americana were revealed. Moreover, insects can serve as excellent and alternative source of industrially important proteases with unique properties, which can be utilized as additives in detergents, stain removers and other bio-formulations. Properties of the P. americana protease accounted in the present investigation can be exploited further in various industrial processes. As an industrial prospective, identification of enzymes with varying essential properties from different insect species might be good approach and bioresource.

The first pacifastin elastase inhibitor characterized from a blood sucking animal

Pacifastin-like protease inhibitors belong to a recent classified protease inhibitor family and they are the smallest protease inhibitors described in animals. In this work, we purified and characterized, for the first time, two neutrophil elastase inhibitors belonging to the pacifastin family from the blood sucking insect Triatoma infestans eggs. The inhibitors showed the same N-terminal sequences, molecular masses of 4257 and 4024Da by MALDI-TOF mass spectrometry and dissociation constants (Ki) for neutrophil elastase of 0.52 and 0.29nM, respectively. Using a fat body cDNA library, we cloned a pacifastin precursor containing two protease inhibitor domains similar to locust pacifastins. The first pacifastin domain translated to T. infestans purified protein, named TIPI1. Recombinant TIPI1 expressed in Pichia pastoris system showed similar inhibitory activities compared to the native inhibitor. Its precursor, called TiPP1, is mainly expressed in fat body, and it is up-regulated after blood feeding. The immune challenges of 1(a) instar T. infestans nymph with bacteria or dsRNA strongly stimulated TiPP1 expression in fat body, suggesting a possible role of TiPP1 in T. infestans immunity. This work is the first to characterize a blood feeding insect pacifastin inhibitor.

Insect chymotrypsins: chloromethyl ketone inactivation and substrate specificity relative to possible coevolutional adaptation of insects and plants

Insect digestive chymotrypsins are present in a large variety of insect orders but their substrate specificity still remains unclear. Four insect chymotrypsins from 3 different insect orders (Dictyoptera, Coleoptera, and two Lepidoptera) were isolated using affinity chromatography. Enzymes presented molecular masses in the range of 20 to 31 kDa and pH optima in the range of 7.5 to 10.0. Kinetic characterization using different colorimetric and fluorescent substrates indicated that insect chymotrypsins differ from bovine chymotrypsin in their primary specificity toward small substrates (like N-benzoyl-L-Tyr p-nitroanilide) rather than on their preference for large substrates (exemplified by Succynil-Ala-Ala-Pro-Phe p-nitroanilide). Chloromethyl ketones (TPCK, N- alpha-tosyl-L-Phe chloromethyl ketone and Z-GGF-CK, N- carbobenzoxy-Gly-Gly-Phe-CK) inactivated all chymotrypsins tested. Inactivation rates follow apparent first-order kinetics with variable second order rates (TPCK, 42 to 130 M(-1) s(-1); Z-GGF-CK, 150 to 450 M(-1) s(-1)) that may be remarkably low for S. frugiperda chymotrypsin (TPCK, 6 M(-1) s(-1); Z-GGF-CK, 6.1 M(-1) s(-1)). Homology modelling and sequence alignment showed that in lepidopteran chymotrypsins, differences in the amino acid residues in the neighborhood of the catalytic His 57 may affect its pKa value. This is proposed as the cause of the decrease in His 57 reactivity toward chloromethyl ketones. Such amino acid replacement in the active site is proposed to be an adaptation to the presence of dietary ketones.

Morphology and three-dimensional reconstruction of the digestive system of Periplaneta americana

A three-dimensional (3-D) model of the digestive system of Periplaneta americana was built for the first time based on hematoxylin and eosin (H&E) staining, the study of multiple cross-sections of the larval cockroach, and 3-D reconstruction technology. The digestive system of P. americana includes the foregut, midgut, and hindgut and takes up most of the celom. The foregut comprises almost one half of the digestive system (43.57%). The midgut, the critical region for digestion and absorption, has the second highest volume ratio (35.21%). The hindgut, with the lowest volume ratio (21.22%), includes the ileum, colon, and rectum. After the ileal valve is the colon. The 3-D model presented in this paper provides a stereoscopic view for studying the adjacent relationship and arrangement of different gut sections of P. americana.

A set of serine proteinase paralogs are required for blood-digestion in the ixodid tick Haemaphysalis longicornis

We present evidence demonstrating that genes encoding enzymes essential for successful blood-feeding are differentially induced in the midgut of the hard tick Haemaphysalis longicornis. Three serine proteinase genes (HlSP, HlSP2 and HlSP3) isolated from H. longicornis midgut exhibit protein sequence similarity with other trypsin-like serine proteinases reported from arthropods and vertebrate animal species. The endogenous enzymes were mainly detected in the midgut epithelial cells and in the lumen of an adult tick. The recombinant enzymes expressed in Escherichia coli efficiently hydrolyzed synthetic substrates specific for serine proteinases over a broad range of pH and temperature values. Notably, the transcript levels of HlSP2 and HlSP3 were detected to significantly increase at 96 h post infestation, while the transcript of HlSP was induced in the earlier stage of blood-feeding. Further, silencing of HlSP, HlSP2 and HlSP3 genes by RNA interference led to a significant reductions in the engorged tick body weight, suggesting synergetic roles of these serine proteinases in blood-feeding and digestion.

Identification of a serine protease as a major allergen (Per a 10) of Periplaneta americana

BACKGROUND

Cockroach allergens are associated with the development of asthma, but none of these has been characterized for proteolytic activity. This study was undertaken to isolate and characterize a protease from Periplaneta americana and determine its allergenicity.

METHODS

A serine protease was isolated from P. americana extract using benzamidine sepharose column and characterized by immunobiochemical methods. Allergenicity of the protease was assessed by enzyme-linked immunosorbent assay, immunoblot, intradermal testing, histamine release and peripheral blood mononuclear cells (PBMCs) proliferation.

RESULTS

Affinity purified protein of approximately 28 kDa (Per a 10) showed a single band of activity in gelatin zymogram and agarose plate assay. N-terminal sequence (IVGGRPAQI) revealed similarity with mite serine protease allergens and insect trypsins. It demonstrated proteolytic activity with azocollagen > gelatin > defatted-milk > casein including serine protease specific substrate, N-benzoyl-arginine-ethyl-ester-hydrochloride. It was inhibited by serine protease inhibitors, namely aprotinin > pefabloc > AEBSF > PMSF > benzamidine > antipain > leupeptin and trypsin-specific inhibitor (tosyl-lysyl-chloromethyl-ketone) suggesting it to be a trypsin-like serine protease. Per a 10 was recognized as a major allergen, showing IgE reactivity with >80% of cockroach sensitized patients by skin tests and immunoblot. It could induce significant histamine release (P < 0.05) in blood and secretion of interleukin-4 (IL-4) (P < 0.05) and IL-5 (P < 0.05) in culture supernatant of PBMCs from cockroach hypersensitive patients, suggesting a strong allergenic potency.

CONCLUSION

A serine protease isolated from P. americana was demonstrated to be a major allergen (Per a 10). It has a potential for component-based diagnosis of allergy and will be useful in elucidating the mechanism of allergy.

Subsite substrate specificity of midgut insect chymotrypsins

Insect chymotrypsins are distinctively sensitive to plant protein inhibitors, suggesting that they differ in subsite architecture and hence in substrate specificities. Purified digestive chymotrypsins from insects of three different orders were assayed with internally quenched fluorescent oligopeptides with three different amino acids at P1 (Tyr, Phe, and Leu) and 13 amino acid replacements in positions P1', P2, and P3. The binding energy (DeltaG(s), calculated from K(m) values) and the activation energy (DeltaG(T)++, determined from k(cat)/K(m) values) were calculated. The hydrophobicities of each subsite were calculated from the efficiency of hydrolysis of the different amino acid replacements at that subsite. The results showed that except for S1, the other subsites (S2, S3, and S1') vary among chymotrypsins. This result contrasts with insect trypsin data that revealed a trend along evolution, putatively associated with resistance to plant inhibitors. In spite of those differences, the data suggested that in lepidopteran chymotrypsins S2 and S1' bind the substrate ground state, whereas only S1' binds the transition state, supporting aspects of the present accepted mechanism of catalysis.

Proteinase, amylase, and proteinase-inhibitor activities in the gut of six cockroach species

Representative species, two from each of the cockroach families Blattidae, Blattellidae, and Blaberidae, have similar morphology of the digestive tract but differ in the physiology of digestion. The pH of crop and along the midgut varies in different species from 5.9 to 9.0 and the redox parameter from 10.1 to 12.9. Activities of proteinases and amylases in comparable gut regions differ among the species up to 100 times. Proteolytic activity is high in the midgut and moderate in the crop of Blattidae; in the other species, it is very low in the crop and increases to a moderate level in the posterior half of midgut (PM). The level of amylolytic activity is similar in the examined gut compartments of Blattidae and Blattellidae but low in the PM of Blaberidae. Blaberidae are also characterized by a high potential of the salivary glands, crop, and midgut to inhibit subtilisin, trypsin, and chymotrypsin. Inhibition of these proteinases by the extracts of salivary glands and gut is several orders of magnitude lower and often undetectable in the representatives of Blattidae and Blattellidae.

The full-length cDNA of anticoagulant protein infestin revealed a novel releasable Kazal domain, a neutrophil elastase inhibitor lacking anticoagulant activity

Infestins are Kazal-type serine proteinase inhibitors found in the midgut of the Chagas' disease vector, Triatoma infestans. In previous studies, we characterized two double-headed infestins with potent anticoagulant activity; infestin 1-2, which inhibits thrombin and infestin 3-4, a factor XIIa inhibitor. In the present work, we have cloned the full-length cDNA of infestins' precursor. The translated cDNA predicted a polypeptide containing a signal peptide and seven Kazal-type domains, four domains from infestin 1-2 and infestin 3-4, and three new domains. Northern blot analysis confirmed that infestins are synthesized in a single transcript (approximately 1,800 bp) in the insect midgut, but not in salivary glands. Based on the cDNA sequence, the three new Kazal domains were named infestin 1R, 2R and 3R. Infestin 2R-3R has 77% amino acid sequence identity to infestin 1-2 and the same basic amino acid residue at P1 position in the inhibitory reactive site suggesting that these two proteins have a similar inhibitory specificity. In contrast, infestin 1R has two different characteristics when compared to the other infestins: i) a hydrophobic amino acid residue at P1 position in the inhibitory reactive site and ii) a prediction to be processed as a single Kazal domain. These two characteristics were experimentally demonstrated by the purification of native infestin 1R from T. infestans midgut. Native infestin 1R was shown to be processed as a single Kazal domain by mass spectrometry and it was able to inhibit neutrophil elastase, subtilisin A and chymotrypsin. To further characterize infestin 1R inhibitory activity, it was expressed as a recombinant protein in bacteria. Recombinant infestin 1R inhibited neutrophil elastase with the same K(i) of the native inhibitor. Moreover, it inhibited subtilisin A, chymotrypsin and proteinase K but did inhibit neither thrombin nor coagulation assays. In conclusion, unlike the other described infestins, infestin 1R did not present anticoagulant activity and is processed as a single Kazal domain with inhibitory specificity towards proteases that hydrolyze peptide bonds after hydrophobic amino acid residues.

Substrate specificity of insect trypsins and the role of their subsites in catalysis

Trypsins have high sequence similarity, although the responses of insect trypsins to chemical and natural inhibitors suggest they differ in specificities. Purified digestive trypsins from insects of four different orders were assayed with internally quenched fluorescent oligopeptides with two different amino acids at P1 (Arg/Lys) and 15 amino acid replacements in positions P1', P2', P2, and P3. The binding energy (deltaG(s), calculated from Km values) and the activation energy (deltaG(T)(double dagger), determined from kcat/Km values) were calculated. Dictyoptera, Coleoptera and Diptera trypsins hydrolyze peptides with Arg at P1 at least 3 times more efficiently than peptides with Lys at P1, whereas Lepidoptera trypsins have no preference between Arg and Lys at that position. The hydrophobicities of each subsite were calculated from the efficiency of hydrolysis of the different amino acid replacements at that subsite. The results suggested that insect trypsin subsites become progressively more hydrophobic along evolution. Apparently, this is an adaptation to resist plant protein inhibitors, which usually have polar residues at their reactive sites. Results also suggested that, at least in lepidopteran trypsins, S3, S2, S1', and S2' significantly bind the substrate ground state, whereas in the transition state only S1' and S2' do that, supporting aspects of the presently accepted mechanism of trypsin catalysis. Homology modeling showed differences among those trypsins that may account for the varied kinetic properties.

Cloning and expression of trypsin-encoding cDNA from Blattella germanica and its possibility as an allergen

In this study, the trypsin gene (bgtryp-1) from the German cockroach, Blattella germanica, was cloned via the immunoscreening of patients with allergies to cockroaches. Nucleotide sequence analysis predicted an 863 bp open reading frame which encodes for 257 amino acids. The deduced amino acid sequence exhibited 42-57% homology with the serine protease from dust mites, and consisted of a conserved catalytic domain (GDSGGPLV). bgtryp-1 was determined by both Northern and Southern analysis to be a 0.9 kb, single-copy gene. SDS-PAGE and Western blotting analyses of the recombinant protein (Bgtryp-1) over-expressed in Escherichia coli revealed that the molecular mass of the expressed protein was 35 kDa, and the expressed protein was capable of reacting with the sera of cockroach allergy patients. We also discussed the possibility that trypsin excreted by the digestive system of the German cockroach not only functions as an allergen, but also may perform a vital role in the activation of PAR-2.

Unraveling biochemical properties of cockroach (Periplaneta americana) proteinases with a gel X-ray film contact print method

Eleven proteinase activity bands were detected in American cockroach (Periplaneta americana) gut. These were partially purified and characterized using a gel X-ray film contact print method. Cockroach gut proteinases (CGPs) show activity over a broad range of pH with maximum activity between pH 6 and 10, and optimal activity at 50-70 degrees C. CGPs were partially purified by preparative gel electrophoresis and analyzed using synthetic substrates and inhibitors. Four of the proteases exhibited chymotrypsin-like (C1 to C4) activity and seven trypsin-like (T1 to T7) activity. Accuracy of the gel X-ray film contact print method is confirmed by including bovine chymotrypsin in CGP analysis. Inhibition of CGPs with different plant proteinaceous proteinase inhibitors allowed identification of potential CGP inhibitors. Our results imply that presence of several CGP activity bands, and their stability and activity over a broad pH and temperature range might contribute to adaptation of P. americana to extreme environmental conditions and the polyphagous nature of the species.

Characterization of two midgut proteinases of Helicoverpa armigera and their interaction with proteinase inhibitors

Two serine proteinases from the midgut of Helicoverpa armigera have been partially purified and characterized. One proteinase, HGP-1, was capable of hydrolyzing a synthetic substrate of elastase and was inhibited by elastatinal. The second proteinase, HGP-2, was inhibited by a trypsin inhibitor. Molecular weights of HGP-1 and HGP-2 were approximately 26.0 and 29.0kDa, respectively. Both the proteinases exhibited alkaline pH optima in the range of 10-11. Furthermore, interaction of HGP-1 and HGP-2 with proteinase inhibitors (PIs) from host and non-host plants was studied. HGP-1 was not only insensitive to a PI from chickpea (host) but was also able to degrade it. The same PI from chickpea was able to inhibit over 50% activity of HGP-2. On the contrary, PIs from potato (non-host) showed strong inhibition of both, HGP-1 and HGP-2 and also demonstrated protection of chickpea seed proteins from digestion by both the HGPs. These results could provide important clues in designing strategies for sustainable use of plant PIs in developing insect-tolerant transgenic plants.

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

Trypsin-like proteases from the midgut of Anticarsia gemmatalis Hubner (Lepidoptera: Noctuidae) were purified on an aprotinin-agarose column equilibrated with 0.01 M Tris-HCl containing 5 mM CaCl2 (pH 7.5). The yield was 66.7% with a purification factor of 107 and a final specific activity of 6.88 mM/min/mg protein with the substrate N-alpha-benzoyl-L-Arg-p-nitroanilide (L-BApNA). The purified fraction showed three bands with proteolytic activity and molecular weights of 66,000, 71,000 and 91,000 (sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis (PAGE)). Enzyme specificity assays were carried out using seven synthetic peptides containing 13 amino acid residues, but differing only on the 5th residue (K, R, Y, L, W or P). Peptide cleavage takes place only with amino acids K or R at the 5th position, which is typical of trypsin. The partially purified enzymes hydrolyzed casein and the synthetic trypsin substrates L-BApNA and N-alpha-p-tosyl-L-Arg methyl ester (L-TAME). Higher activity was observed at pH 8.5 and 35 degrees C when using L-BApNA as substrate and at pH 8.0 and 30 degrees C when using L-TAME. Maximum enzyme activity against L-BApNA was obtained with 20 mM CaCl2 in the reaction mixture. The partially purified enzymes showing trypsin activity were sensitive to inhibition by ethylenediaminetetraacetic acid (EDTA), phenylmethyl sulphonyl fluoride (PMSF), N-alpha-tosyl-L-lysine chloromethyl ketone (TLCK), benzamidine and aprotinin. Highest inhibition was obtained with TLCK and benzamidine. KM values obtained were 0.32 mM for L-BApNA and 52.5 microM for L-TAME.

Digestive proteinases of yellow mealworm (Tenebrio molitor) larvae: Purification and characterization of a trypsin-like proteinase

A new trypsin-like proteinase was purified to homogeneity from the posterior midgut of Tenebrio molitor larvae by ion-exchange chromatography on DEAE-Sephadex A-50 and gel filtration on Superdex-75. The isolated enzyme had molecular mass of 25.5 kD and pI 7.4. The enzyme was also characterized by temperature optimum at 55 degrees C, pH optimum at 8.5, and K(m) value of 0.04 mM (for hydrolysis of Bz-Arg-pNA). According to inhibitor analysis the enzyme is a trypsin-like serine proteinase stable within the pH range of 5.0-9.5. The enzyme hydrolyzes peptide bonds formed by Arg or Lys residues in the P1 position with a preference for relatively long peptide substrates. The N-terminal amino acid sequence, IVGGSSISISSVPXQIXLQY, shares 50-72% identity with other insect trypsin-like proteinases, and 44-50% identity to mammalian trypsins. The isolated enzyme is sensitive to inhibition by plant proteinase inhibitors and it can serve as a suitable target for control of digestion in this stored product pest.

Cloning and molecular characterization of a cubilin-related serine proteinase from the hard tick Haemaphysalis longicornis

Serine proteinases are one of the largest proteolytic families of enzymes, and have diverse cellular activities in mammalian tissues. We report here the cloning and molecular characterization of a cDNA encoding the serine proteinase of the hard tick Haemaphysalis longicornis (HlSP). The HlSP cDNA is 1570 bp long and the deduced precursor protein consists of 464 amino acids with a predicted molecular mass of 50.4 kDa and a pI of 8.2. The preprotein, consisting of 443 amino acids, was predicted to include a complement C1r/C1s, Uegf, and bone morphogenic protein-1 domain, a low-density lipoprotein receptor class A domain, and a catalytic domain. HlSP sequence analysis showed high similarity to serine proteinases reported from arthropods and vertebrate animal species. Two-dimensional immunoblot analysis revealed endogenous HlSP in adult tick extracts at 50 kDa. Endogenous HlSP was also expressed in all lifecycle stages of H. longicornis. Immunohistochemical studies detected the endogenous enzyme in the midgut epithelial cells of an adult tick. The Escherichia coli-expressed recombinant HlSP was demonstrated to degrade bovine serum albumin and hydrolyze the substrate Bz-L-Arg-pNA at the rate of 30.2 micromol/min/mg protein. Further, HlSP expression was up-regulated during a blood-feeding process, indicating its involvement in the digestion of host blood components.

Coevolution of insect trypsins and inhibitors

Many plant proteinase inhibitors have lysine at the P1 position, presumably to avoid hydrolysis by insect trypsins. Lepidopteran trypsins appear to have adapted to resist proteinase inhibitors through increased inhibitor hydrolysis and decreased binding to inhibitor hydrophilic reactive sites. Lepidopteran digestive trypsins prefer lysine at the P1 position and have substrate binding subsites more hydrophobic than trypsins from insects in other orders. All available sequences of sensitive and inhibitor-insensitive insect trypsins were aligned with porcine trypsin, for which interactions with Kunitz and Bowman-Birk inhibitor are known. After discounting conserved positions and positions not typical of sensitive or insensitive trypsins, the following residues were considered important to insect trypsin-PI interactions (chymotrypsin numbering): 60, 94, 97, 98, 99, 188, 190, 213, 215, 217, 219, 228. These residues support the Neighbor Joining analysis tree branches separating sensitive and insensitive trypsin sequences. Primary sequences interacting with PIs are around the active site, with some forming part of the S1 (188, 217, 219 and 228) or S4 (99, 215) pockets.