Purification and characterization of a group of five novel peptide serine protease inhibitors from ovaries of the desert locust, Schistocerca gregaria

Proteins with Anti-apoptotic Action in the Hemolymph of Caterpillars of the Megalopygidae Family Acts by Maintaining the Structure of the Cellular Cytoskeleton

Brazil has a very large biological variety, which is an almost inexhaustible source of substances of pharmacological and biotechnological interest. Several studies have demonstrated the presence of bioactive peptides in insect hemolymph and their potential use as therapeutic agents. However, few data are available regarding molecules extracted from insects with anti-apoptotic action. The objective of this work was to identify the presence of proteins from the hemolymph of caterpillars of the Megalopygidae family with pharmacological and biotechnological interest. This study provides preliminary and innovative information on a new substance that inhibits cellular apoptopsis and stabilizes the tested cells, impacting the cytoskeleton, maintaining cellular structure and its functions. To this, two species of Megalopygidae family were studied, Podalia sp. and Megalopyge albicolis. Cytotoxicity tests on Vero and Sf-9 cells revealed that the hemolymph of both caterpillars was cytotoxic only at concentrations greater than 5%v/v. In the anti-apoptotic activity assays, it was verified that the supplementation of cell cultures with only 1% of hemolymph v/v is sufficient to inhibit cell death by apoptosis induced by different inducers such as terbutyl, actinomycin D, hydrogen peroxide, or even by nutrient depletion. For this study, cells were stained with trypan blue, crystal violet, and fluorescent markers to cytoskeleton (actin and tubulin), mitochondria membrane electric potential (JC-1), and apoptosis marker (acridine orange and ethidium). The protein responsible for anti-apoptotic action was isolated through gel filtration chromatography, using an AKTA purifier high-resolution liquid chromatography system. The hemolymph was fractionated into 3 pools for Podalia sp. and 6 pools for M. abicolis. In the antiapoptotic tests, semi-purified hemolymph from both caterpillars showed anti-apoptotic effect in VERO and SF-9 cells, pre-treated with only 1% v/v of hemolymph and induced to death by different and apoptotic inductors. Was observed that the molecule with anti-apoptotic effect is present in pool 3 in both hemolymphs. This protector effect blocked and attenuated the disruption of the cytoskeleton (actin filaments), being that the protective effect also was observed on the integrity of the mitochondrial membrane of SF-9 cells pre-treated with both hemolymphs and treated with the apoptosis inducer Terbutil at concentrations of 25 to 100 µM. By acting on the mitochondrial pathway of death by apoptosis, and by maintaining the structure of the cytoskeleton and cellular functions, pathway that can cause disorders and diseases neurodegenerative, the substances present in the hemolymph of these and other caterpillars could be good candidates in studies for the treatment of neurodegenerative diseases such as Parkinson's disease and Alzheimer's.

Structural and Biophysical Characterization of Cajanus cajan Protease Inhibitor

CONTEXT

A large number of studies have proven that Protease inhibitors (PIs), specifically serine protease inhibitors, show immense divergence in regulation of proteolysis by targeting their specific proteases and hence, they play a key role in healthcare.

OBJECTIVE

We aimed to access in-vitro anticancer potential of PI from Cajanus cajan (CCPI). Also, crystallization of CCPI was targetted alongwith structure determination and its structure-function relationship.

MATERIALS AND METHODS

CCPI was purified from Cajanus cajan seeds by chromatographic techniques. The purity and molecular mass was determined by SDS-PAGE. Anticancer potential of CCPI was determined by MTT assay in normal HEK and cancerous A549 cells. The crystallization screening of CCPI was performed by commercially available screens. CCPI sequence was subject to BLASTp with homologous PIs. Progressive multiple alignment was performed using clustalw2 and was modelled using ab initio protocol of I-TASSER.

RESULTS

The results showed ~14kDa CCPI was purified in homogeneity. Also, CCPI showed low cytotoxic effects of in HEK i.e., 27% as compared with 51% cytotoxicity in A549 cells. CCPI crystallized at 16°C using 15% PEG 6000 in 0.1M potassium phosphate buffer (pH 6.0) in 2-3weeks as rod or needles visualized as clusters under the microscope. The molecular modelling revealed that it contains 3 beta sheets, 3 beta hairpins, 2 β-bulges, 6 strands, 3 helices, 1helix-helix interaction, 41 β-turns and 27 γ-turns.

DISCUSSION AND CONCLUSION

The results indicate that CCPI may help to treat cancer in vivo aswell. Also, this is the first report on preliminary crystallization and structural studies of CCPI.

Improved replication of the baculovirus Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV) in vitro using proteins from Lonomia obliqua hemolymph

The baculovirus Anticarsia gemmatalis nucleopolyhedrovirus (AgMNPV), a member of the family Baculoviridae, has been widely applied as a biopesticide for the control of the velvetbean caterpillar, a pest of soybean crop field. Baculoviruses are considered safe and efficient agents for this purpose, because they do not infect vertebrates, being safe for the health of humans and animals, as well as to the environment. The objective of this work was to identify proteins obtained from Lonomia obliqua hemolymph with potential application in the optimization of baculovirus AgMNPV replication in Sf9 insect cell culture. In this work the improvement of the cell culture and viral replication of the AgMNPV baculovirus was observed when Grace medium was supplemented with 10 % (v/v) Fetal Bovine Serum (FBS), 1 % (v/v) hemolymph extract, or 3 % (v/v) of hemolymph fractions or hemolymph sub-fractions obtained by purifying hemolymph through High Performance Liquid Chromatography. Hemolymph presented a positive effect on the synthesis of polyhedra and enhanced baculovirus replication in Spodoptera frugiperda (Sf9) cells (TCID50/mL), and led to Sf9 cell culture improvement. Grace medium supplemented with 10 % (v/v) FBS and 1 % (v/v) hemolymph provided an increase of baculovirus replication, when the cells were infected with multiplicity of infection of 1. In this case, the baculovirus replication was 6,443.91 times greater than that obtained with the control: Grace medium supplemented with 10 % (v/v) FBS. In addition, this work suggests that hemolymph from L. obliqua could have an interesting application in biotechnology, due to an increase in the viability of the cells and virus replication.

Identification of immune response-related genes in the Chinese oak silkworm, Antheraea pernyi by suppression subtractive hybridization

Insects possess an innate immune system that responds to invading microorganisms. In this study, a subtractive cDNA library was constructed to screen for immune response-related genes in the fat bodies of Antheraea pernyi (Lepidoptera: Saturniidae) pupa challenged with Escherichia coli. Four hundred putative EST clones were identified by suppression subtractive hybridization (SSH), including 50 immune response-related genes, three cytoskeleton genes, eight cell cycle and apoptosis genes, five respiration and energy metabolism genes, five transport genes, 40 metabolism genes, ten stress response genes, four transcription and translation regulation genes and 77 unknown genes. To verify the reliability of the SSH data, the transcription of a set of randomly selected immune response-related genes were confirmed by semi-quantitative reverse transcription-PCR (RT-PCR) and real-time quantitative reverse transcription-PCR (qRT-PCR). These identified immune response-related genes provide insight into understanding the innate immunity in A. pernyi.

Uses of phage display in agriculture: a review of food-related protein-protein interactions discovered by biopanning over diverse baits

This review highlights discoveries made using phage display that impact the use of agricultural products. The contribution phage display made to our fundamental understanding of how various protective molecules serve to safeguard plants and seeds from herbivores and microbes is discussed. The utility of phage display for directed evolution of enzymes with enhanced capacities to degrade the complex polymers of the cell wall into molecules useful for biofuel production is surveyed. Food allergies are often directed against components of seeds; this review emphasizes how phage display has been employed to determine the seed component(s) contributing most to the allergenic reaction and how it has played a central role in novel approaches to mitigate patient response. Finally, an overview of the use of phage display in identifying the mature seed proteome protection and repair mechanisms is provided. The identification of specific classes of proteins preferentially bound by such protection and repair proteins leads to hypotheses concerning the importance of safeguarding the translational apparatus from damage during seed quiescence and environmental perturbations during germination. These examples, it is hoped, will spur the use of phage display in future plant science examining protein-ligand interactions.

A hemocyte-derived Kunitz-BPTI-type chymotrypsin inhibitor, HlChI, from the ixodid tick Haemaphysalis longicornis, plays regulatory functions in tick blood-feeding processes

Inhibitors of proteases play key roles in the biological processes of vertebrate and invertebrate animals, including arthropod parasites. Here, we describe a cDNA that encodes a functionally active chymotrypsin inhibitor of the BPTI/Kunitz family of serine protease inhibitors from the hemocytes of the ixodid tick, Haemaphysalis longicornis, herein called HlChI. HlChI sequence is evolutionarily conserved and contains six cysteine residues and three disulfide bonds with a calculated molecular weight of 9.1 kDa. HlChI-specific mRNA was expressed in all developmental stages of ticks and the expression was up-regulated by host's blood-feeding processes. Endogenous HlChI was localized mainly in the hemocytes. HlChI potently inhibited bovine pancreatic α-chymotrypsin for hydrolyzing the fluorogenic substrate (IC(50) 8.32 nM, K(d) 5.35 ± 1.01 nM) and bovine casein digestion. However, HlChI weakly inhibited bovine pancreatic trypsin and could not affect the porcine elastase activity, suggesting its narrow specificity to chymotrypsin. HlChI was stable over the pH range 2-11 and heating up to 70 °C at pH 8. HlChI was highly stable to 8 M urea and 2% SDS at pH 8.0, when treated for 24 h at 37 °C. However, 0.2 M 2-mercaptoethanol caused complete but reversible inactivation of HlChI. Knockdown of HlChI gene by RNA interference (RNAi) caused death of the feeding ticks, failure of ticks to engorge and significantly reduced body weight gain. RNAi also resulted in significantly decreased egg conversion ratio and fecundity. These results suggest that HlChI is a chymotrypsin-specific inhibitor with high stability and may play regulatory functions in host's blood-feeding processes and tick reproduction.

SERINE proteinase like activity in apolipophorin III from the hemolymph of desert locust, Schistocerca gregaria

Apolipophorin III (apoLp-III) has been known as a lipid transport protein of insects. Recent studies indicated the involvement of apoLp-III in immune reactions and in the control of cell destruction, but no enzymatic activity has so far been detected. In the present study, a protease from the hemolymph of Schistocerca gregaria was purified to homogeneity and its enzymatic activity was examined. Identity as chymotrypsin-like proteinase was established by its high affinity toward bulky aromatic substrates and its catalytic specificity for amide or ester bonds on the synthetic substrates, Suc-Ala-Ala-Pro-Xaa-AMC (where Xaa was Phe, Tyr, Trp, and Lys, and AMC is 7-amino-4-methyl-coumarin) and thiolbenzyl ester substrate Suc-Ala-Ala-Pro-Phe-SBzl. The sensitivity for serine protease and chymotrypsin-specific covalent inhibitors, PMSF, TPCK, and noncovalent inhibitors SGCI, showed that it is a chymotrypsin-like proteinase. It showed its maximum activity at pH 8.0 and 55°C for the hydrolysis of Suc-Ala-Ala-Pro-Tyr-AMC. According to similarities in the amino terminal sequence, molar mass (19 kDa) and retention on reversed-phase analytical high-performance liquid chromatography (HPLC) column, this protein is S. gregaria homologue of Locusta migratoria apoLp-III. Our data suggest that apoLp-III also has an inherent proteolytic activity. Results indicated that S. gregaria apoLp-III is a good catalyst and could be used as a biotechnological tool in food processing and in agricultural biotechnology.

Genome-wide identification and immune response analysis of serine protease inhibitor genes in the silkworm, Bombyx mori

In most insect species, a variety of serine protease inhibitors (SPIs) have been found in multiple tissues, including integument, gonad, salivary gland, and hemolymph, and are required for preventing unwanted proteolysis. These SPIs belong to different families and have distinct inhibitory mechanisms. Herein, we predicted and characterized potential SPI genes based on the genome sequences of silkworm, Bombyx mori. As a result, a total of eighty SPI genes were identified in B. mori. These SPI genes contain 10 kinds of SPI domains, including serpin, Kunitz_BPTI, Kazal, TIL, amfpi, Bowman-Birk, Antistasin, WAP, Pacifastin, and alpha-macroglobulin. Sixty-three SPIs contain single SPI domain while the others have at least two inhibitor units. Some SPIs also contain non-inhibitor domains for protein-protein interactions, including EGF, ADAM_spacer, spondin_N, reeler, TSP_1 and other modules. Microarray analysis showed that fourteen SPI genes from lineage-specific TIL family and Group F of serpin family had enriched expression in the silk gland. The roles of SPIs in resisting pathogens were investigated in silkworms when they were infected by four pathogens. Microarray and qRT-PCR experiments revealed obvious up-regulation of 8, 4, 3 and 3 SPI genes after infection with Escherichia coli, Bacillus bombysepticus, Beauveria bassiana or B. mori nuclear polyhedrosis virus (BmNPV), respectively. On the contrary, 4, 11, 7 and 9 SPI genes were down-regulated after infection with E. coli, B. bombysepticus, B. bassiana or BmNPV, respectively. These results suggested that these SPI genes may be involved in resistance to pathogenic microorganisms. These findings may provide valuable information for further clarifying the roles of SPIs in the development, immune defence, and efficient synthesis of silk gland protein.

The first homolog of pacifastin-related precursor in the swimming crab (Portunus trituberculatus): characterization and potential role in immune response to bacteria and fungi

Among all the serine proteinase inhibitor families (SPIs), the pacifastin-related inhibitor is seldom isolated. A pacifastin-related SPI named as PtPLC was identified from the swimming crab Portunus trituberculatus in this study. The full-length of PtPLC was cloned from haemocytes cDNA library by the combination of homology cloning and rapid amplification of cDNA ends (RACE). The PtPLC contained an open reading frame (ORF) of 1098 bp encoding a putative pacifastin-related precursor of 365 amino acids, a 5'-untranslated region (UTR) of 33 bp, and a 3'-UTR of 524 bp. The estimated molecular weight of mature PtPLC was 40.51 kDa and its isoelectric point was 5.04. Eight PLD domains in PtPLC shared a common characteristic of conserved array of six cysteine residues (Cys-Xaa(9-12)-Cys-Asn-Xaa-Cys-Xaa- Cys-Xaa(2-3)-Gly-Xaa(3-4)-Cys-Thr-Xaa(3)-Cys). The mRNA expression of PtPLC transcripts was highly detected in haemocytes, gill, hepatopancreas and stomach. The temporal expression levels of PtPLC transcripts in haemocytes showed different expression patterns after challenged by Gram-negative bacteria Vibrio alginolyticus, Gram-positive bacteria Micrococcus luteus and fungus Pichia pastoris. There were two peaks in the mRNA expression profile after M. luteus stimulation. And after V. alginolyticus and P. pastoris stimulation, there were three peaks in the mRNA expression profiles. These findings suggest that PtPLC is involved in the antibacterial defense mechanism of P. tritubercualtus.

Role of proteases in extra-oral digestion of a predatory bug, Andrallus spinidens

Roles of salivary proteases in the extra-oral digestion of the predatory bug, Andrallus spinidens Fabricius (Hemiptera: Pentatomidae) were studied by using 2% azocasein as a general substrate and specific protease substrates, as well as synthetic and endogenous inhibitors. It was found that salivary glands of A. spinidens have two anterior, two lateral, and two posterior lobes. Azocasein was used to measure the activity of general proteases in the salivary glands using different buffer solutions. The enzyme had the highest activity at pH 8. General protease activity was highest at 40 °C and was stable for 6-16 hours. The use of specific substrates showed that trypsin-like, chymotrypsin-like, aminopeptidase, and carboxypeptidase are the active proteases present in salivary glands, by the maximum activity of trypsin-like protease in addition to their optimal pH between 8-9. Ca(2+) and Mg(2+) increased proteolytic activity about 216%, while other ions decreased it. Specific inhibitors including SBTI, PMSF, TLCK, and TPCK significantly decreased enzyme activity, as well as the specific inhibitors of methalloproteases including phenanthroline, EGTA, and TTHA. Extracted endogenous trypsin inhibitors extracted from potential prey, Chilo suppressalis, Naranga aenescens, Pieris brassicae, Hyphantria cunea, and Ephestia kuhniella, had different effects on trypsin-like protease activity of A. spinidens salivary glands. With the exception of C. suppressalis, the endogenous inhibitors significantly decreased enzyme activity in A. spinidens.

High affinity small protein inhibitors of human chymotrypsin C (CTRC) selected by phage display reveal unusual preference for P4' acidic residues

Human chymotrypsin C (CTRC) is a pancreatic protease that participates in the regulation of intestinal digestive enzyme activity. Other chymotrypsins and elastases are inactive on the regulatory sites cleaved by CTRC, suggesting that CTRC recognizes unique sequence patterns. To characterize the molecular determinants underlying CTRC specificity, we selected high affinity substrate-like small protein inhibitors against CTRC from a phage library displaying variants of SGPI-2, a natural chymotrypsin inhibitor from Schistocerca gregaria. On the basis of the sequence pattern selected, we designed eight inhibitor variants in which amino acid residues in the reactive loop at P1 (Met or Leu), P2' (Leu or Asp), and P4' (Glu, Asp, or Ala) were varied. Binding experiments with CTRC revealed that (i) inhibitors with Leu at P1 bind 10-fold stronger than those with P1 Met; (ii) Asp at P2' (versus Leu) decreases affinity but increases selectivity, and (iii) Glu or Asp at P4' (versus Ala) increase affinity 10-fold. The highest affinity SGPI-2 variant (K(D) 20 pm) bound to CTRC 575-fold tighter than the parent molecule. The most selective inhibitor variant exhibited a K(D) of 110 pm and a selectivity ranging from 225- to 112,664-fold against other human chymotrypsins and elastases. Homology modeling and mutagenesis identified a cluster of basic amino acid residues (Lys(51), Arg(56), and Arg(80)) on the surface of human CTRC that interact with the P4' acidic residue of the inhibitor. The acidic preference of CTRC at P4' is unique among pancreatic proteases and might contribute to the high specificity of CTRC-mediated digestive enzyme regulation.

In vitro activity of pacifastin-like inhibitors in relation to their structural characteristics

Information on the structural characteristics and inhibitory activity of the pacifastin family is restricted to a handful of locust pacifastin-related inhibitors. In this report the optimization of a bacterial recombinant expression system is described, resulting in the high yield production of pacifastin-like inhibitors of the desert locust. Subsequently, the relative inhibitory activity of these peptides towards mammalian, locust and caterpillar digestive peptidases has been compared. In general, the enzyme specificity of locust pacifastin-like inhibitors towards trypsin- or chymotrypsin-like peptidases corresponds to the nature of the P1-residue at the reactive site. In addition, other structural characteristics, including specific core interactions, have been reported to result in a different affinity of pacifastin members towards digestive trypsin-like enzymes from mammals and arthropods. One remarkable observation in this study is a specifically designed pacifastin-like peptidase inhibitor, which, unlike other inhibitors of the same family, does not display this specificity and selectivity towards digestive enzymes from different animals.

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.

Exogenous and endogenous protease inhibitors in the gut of the fall armyworm larvae, Spodoptera frugiperda

A dose-dependent inhibition of endogenous trypsin and aminopeptidase occurs in the lumen of Spodoptera frugiperda after feeding L6 larvae exogenous inhibitors soybean trypsin inhibitor (SBTI), tosyl-L-lysine chloromethyl ketone-HCl (TLCK), or bestatin, respectively, for 3 days. TLCK inhibits trypsin in tissue extracts and in secretions more strongly than SBTI. The aminopeptidase released into the lumen (containing the peritrophic membrane) is strongly inhibited by bestatin, but the membrane-bound enzyme is not. A bound enzyme may be more resistant to an inhibitor than unbound. A cross-class elevation of aminopeptidase activity occurs in response to ingested trypsin inhibitor, but there was no cross-class effect of aminopeptidase inhibitor (bestatin) on trypsin activity. An endogenous trypsin and aminopeptidase inhibitor is present in the lumen and ventricular cells. The strength of the endogenous trypsin inhibition seems to be in the same range as that resulting from ingestion of the exogenous inhibitor SBTI. In some insect species, considerable trypsin secretion occurs in unfed as well as in fed animals, and endogenous protease inhibitors might function to protect the ventricular epithelium by inactivation of trypsin when less food is available.

Study of kinetic parameters for the production of recombinant rabies virus glycoprotein

Gene expression in insect cells is an advantageous system for recombinant protein production, mainly because of its capacity to produce complex proteins with correct post-translational modifications. Recently, we identified and purified a protein from Lonomia obliqua hemolymph able to increase the production of rabies virus glycoprotein, expressed in Drosophila melanogaster cells, by about 60%. In this work, the kinetic parameters for cell growth and recombinant rabies virus glycoprotein production were determined in cultures of transfected Drosophila melanogaster Schneider 2 (S2) cells expressing recombinant rabies virus glycoprotein (rRVGP), enriched and non-enriched with the hemolymph of Lonomia obliqua (Hb). The highest concentration of rRVGP was achieved at the beginning of the culture enriched with Hb, indicating that the cells produce greater amounts of rRVGP per cell (specific rRVGP concentration) at the early exponential growth phase. After day 8, a decrease in the concentration of rRVGP (ng/mL) was observed, probably due to protein decomposition. The average specific rRVGP production rate (mu(rRVGP)) was 30 ng rRVGP/10(7)cell.day, higher than that observed in the non-enriched culture.

Characterization of two novel pacifastin-like peptide precursor isoforms in the desert locust (Schistocerca gregaria): cDNA cloning, functional analysis and real-time RT-PCR gene expression studies

In the last decade, a new serine protease inhibitor family has been described in arthropods. Eight members of the family were purified from locusts and share a conserved cysteine array (Cys-Xaa(9-12)-Cys-Asn-Xaa-Cys-Xaa-Cys-Xaa(2-3)-Gly-Xaa(3-6)-Cys-Thr-Xaa3-Cys) with nine inhibitory domains of the light chain of the crayfish protease inhibitor, pacifastin (PLDs; pacifastin light chain domains). Using cDNA cloning, several pacifastin-related precursors have been identified, encoding additional PLD-related peptides in different insect species. In the present study, two isoforms of a novel pacifastin-related precursor (SGPP-4) have been identified in the desert locust, predicting the previously identified SGPI-5 (Schistocerca gregaria PLD-related inhibitor-5) peptide and two novel PLD-related peptide sequences. One novel peptide (SGPI-5A) was synthesized chemically, and its inhibitory activity was assessed in vitro. Although proteases from a locust midgut extract were very sensitive to SGPI-5A, the same peptide proved to be a relatively poor inhibitor of bovine trypsin. By an in silico datamining approach, a novel pacifastin-related precursor with seven PLD-related domains was identified in the mosquito, Aedes aegypti. As in other insect pacifastin-related precursors, the Aedes precursor showed a particular domain architecture that is not encountered in other serine protease inhibitor families. Finally, a comparative real-time RT-PCR analysis of SGPP-4 transcripts in different tissues of isolated- (solitarious) and crowded-reared (gregarious) locusts was performed. This showed that SGPP-4 mRNA levels are higher in the brain, testes and fat body of gregarious males than of solitarious males. These results have been compared with data from a similar study on SGPP-1-3 transcripts and discussed with respect to a differential regulation of serine-protease-dependent pathways as a possible mechanism underlying locust phase polymorphism.

A lepidopteran pacifastin member: cloning, gene structure, recombinant production, transcript profiling and in vitro activity

Members of the pacifastin family have been characterized as serine peptidase inhibitors (PI), but their target enzyme(s) are unknown in insects. So far, the structural and biochemical characteristics of pacifastin-like PI have only been studied in locusts. Here we report the molecular identification and functional characterization of a pacifastin-like precursor in a lepidopteran insect, i.e. the silkworm Bombyx mori. The bmpp-1 gene contains 17 exons and codes for two pacifastin-related precursors of different length. The longest splice variant encodes 13 inhibitor domains, more than any other pacifastin-like precursor in arthropods. The second transcript lacks two exons and codes for 11 inhibitor domains. By studying the expression profile of the Bombyx pacifastin-like gene a different expression pattern for the two variants was observed suggesting functional diversification. Next, several PI domains of BMPP-1 were produced and, contrary to locust pacifastin peptides, they were found to be potent inhibitors of both bovine trypsin and chymotrypsin. Surprisingly, the same Bombyx PI are only weak inhibitors of endogenous digestive peptidases, indicating that other peptidases are the in vivo targets. Interestingly, the Bombyx PI inhibit a fungal trypsin-like cuticle degrading enzyme, suggesting a protective function for BMPP-1 against entomopathogenic fungi.

Endocrinology of reproduction and phase transition in locusts

In the last decade, important progress has been made in the experimental analysis of the endocrine mechanisms controlling reproduction and phase transition in locusts. Phase transition is a very fascinating, but complex, phenomenon of phenotypic plasticity that is triggered by changes in population density and can lead to the formation of extremely devastating hopper bands and adult gregarious locust swarms. While some phase characteristics change within hours, others appear more gradually in the next stage(s), or even in the next generation(s). In adults, the phase status also has a major influence on the process of reproduction. A better understanding of how solitarious locusts become gregarious and how this switch affects reproductive physiology may result in novel strategies to fight locust plagues. In this paper, we will review the current knowledge concerning this close interaction between locust phase polyphenism and reproduction.

Identification, distribution and molecular evolution of the pacifastin gene family in Metazoa

BACKGROUND

Members of the pacifastin family are serine peptidase inhibitors, most of which are produced as multi domain precursor proteins. Structural and biochemical characteristics of insect pacifastin-like peptides have been studied intensively, but only one inhibitor has been functionally characterised. Recent sequencing projects of metazoan genomes have created an unprecedented opportunity to explore the distribution, evolution and functional diversification of pacifastin genes in the animal kingdom.

RESULTS

A large scale in silico data mining search led to the identification of 83 pacifastin members with 284 inhibitor domains, distributed over 55 species from three metazoan phyla. In contrast to previous assumptions, members of this family were also found in other phyla than Arthropoda, including the sister phylum Onychophora and the 'primitive', non-bilaterian Placozoa. In Arthropoda, pacifastin members were found to be distributed among insect families of nearly all insect orders and for the first time also among crustacean species other than crayfish and the Chinese mitten crab. Contrary to precursors from Crustacea, the majority of insect pacifastin members contain dibasic cleavage sites, indicative for posttranslational processing into numerous inhibitor peptides. Whereas some insect species have lost the pacifastin gene, others were found to have several (often clustered) paralogous genes. Amino acids corresponding to the reactive site or involved in the folding of the inhibitor domain were analysed as a basis for the biochemical properties.

CONCLUSION

The absence of the pacifastin gene in some insect genomes and the extensive gene expansion in other insects are indicative for the rapid (adaptive) evolution of this gene family. In addition, differential processing mechanisms and a high variability in the reactive site residues and the inner core interactions contribute to a broad functional diversification of inhibitor peptides, indicating wide ranging roles in different physiological processes. Based on the observation of a pacifastin gene in Placozoa, it can be hypothesized that the ancestral pacifastin gene has occurred before the divergence of bilaterian animals. However, considering differences in gene structure between the placozoan and other pacifastin genes and the existence of a 'pacifastin gene gap' between Placozoa and Onychophora/Arthropoda, it cannot be excluded that the pacifastin signature originated twice by convergent evolution.

Pacifastin-related peptides: structural and functional characteristics of a family of serine peptidase inhibitors

Members of the pacifastin family are serine peptidase inhibitors, found in arthropods and have many members within different insect orders. Based on their structural characteristics, inhibitors of this peptide family are divided into two groups (I and II). Members of both groups exhibit specificity towards different types of serine peptidases. In addition, group I inhibitors display species selectivity. The specificity and selectivity of these inhibitors depends on the nature of their P1 residue and on additional interaction sites at the inhibitor's surface. Functional analysis studies have shown that crustacean pacifastin plays a key role in the immune response, whereas insect pacifastin-like peptides have multiple regulatory functions in processes involved in immunity, reproduction, phase transition, etc.

Quantitative RT-PCR analysis of pacifastin-related precursor transcripts during the reproductive cycle of solitarious and gregarious desert locusts

In locusts, little is known about the physiological and biochemical mechanisms regulating complex processes, such as reproduction and phase transition. The pacifastin family constitutes a family of peptidic inhibitors of serine proteases that are considered to be important regulators of several physiological processes in arthropods. We have performed a detailed transcript profiling analysis of two pacifastin-related peptide precursors, SGPP-2 and SGPP-4, during the reproductive cycle of adult desert locusts (Schistocerca gregaria). This quantitative real-time (RT)-PCR analysis revealed a temporal regulation of both transcripts, which is paralleled by several events that occur during the reproductive cycle of adult locusts. The observed temporal transcript profiles display a strong tissue-, gender- and phase-dependence. In addition, a partial regregarization experiment suggests that both transcript levels are regulated during phase transition and can be employed as molecular markers of the gregarization process.

Enhancing effect of a protein from Lonomia obliqua hemolymph on recombinant protein production

Gene expression in animal cells allows large scale production of proteins used for either structure and function studies or therapeutic purposes. Maximizing recombinant protein production is necessary to optimize cell growth and protein expression. Some studies have demonstrated the presence of pharmacologically active substances in insect hemolymph. In this work, we have identified and purified a protein from Lonomia obliqua hemolymph able to increase the production of the rabies virus glycoprotein, expressed in Drosophila melanogaster S2 cells, by about 59%.

Localization of the phase-related 6-kDa peptide (PRP) in different tissues of the desert locust Schistocerca gregaria--immunocytochemical and mass spectrometric approach

A 6-kDa phase-related peptide (PRP) was recently identified from the hemolymph of the desert locust Schistocerca gregaria. Its presence in much higher concentrations in the crowd-reared (gregarious) phase than in the isolated-reared (solitarious) one suggests a role in phase polyphenism. However, when tested in a variety of classical bioassays, no activity could be found. We hoped that uncovering its site(s) of synthesis might yield hints as to possible functions. An antiserum was raised against the C-terminal 16 aa part of PRP for use in immunocytochemistry. No immunoreactivity was recorded in the fat body, midgut, or Malpighian tubules. The strongest positive immunostaining was observed in the follicle cells of the ovary and in the seminal vesicle tubes of the male accessory gland complex. Also, positive were a pair of large neurosecretory cells in the subesophageal ganglion, the storage part of the corpora cardiaca and some nerve fibers in the brain- and abdominal regions. An additional mass spectrometric analysis was successfully done in combination with a BLAST search to detect possible false positive staining. This confirmed the presence of genuine PRP in most of the immunopositive tissues. Additional experiments are needed to unravel the role of PRP.

The role of hemocytes, serine protease inhibitors and pathogen-associated patterns in prophenoloxidase activation in the desert locust, Schistocerca gregaria

The prophenoloxidase-activating system is an important component of the innate immune response of insects, involved in wound healing and melanotic encapsulation. In this paper we show that in the desert locust, Schistocerca gregaria, hemocytes, challenged with microbial elicitors, are indispensable for the limited proteolytic activation of prophenoloxidase (proPO) in plasma. In addition, we assessed the influence of serine protease inhibitors on the induction of PO-activity in plasma. While soybean Bowman-Birk inhibitor (SBBI) inhibited the PO activation by laminarin-treated hemocytes, the endogenous pacifastin-related inhibitors, SGPI-1 (S. gregaria pacifastin-related inhibitor-1) and SGPI-2 did not affect the PO-activity under similar conditions. On the other hand, real-time PCR analysis revealed that the transcripts, encoding SGPI-1-3, were more abundant in the fat body of immune challenged animals, as compared to control animals.

Insect gonadotropic peptide hormones: some recent developments

Gonadotropic peptides are a new generation of peptide hormone regulators of insect reproduction. They have been isolated from ovaries, oviducts, or brains of insects. The subject of this paper is insect peptides that exert stimulatory or inhibitory effects on ovarian development and oocyte maturation. On the basis of the literature data and the results of our investigations, the structure and biological properties of different groups of peptides are presented.

When the Surface Tells What Lies Beneath: Combinatorial Phage-display Mutagenesis Reveals Complex Networks of Surface–Core Interactions in the Pacifastin Protease Inhibitor Family

Pacifastin protease inhibitors are small cysteine-rich motifs of approximately 35 residues that were discovered in arthropods. The family is divided into two related groups on the basis of the composition of their minimalist inner core. In group I, the core is governed by a Lys10-Trp26 interaction, while in group II it is organized around Phe10. Group I inhibitors exhibit intriguing taxon specificity: potent arthropod-trypsin inhibitors from this group are almost inactive against vertebrate enzymes. The group I member SGPI-1 and the group II member SGPI-2 are extensively studied inhibitors. SGPI-1 is taxon-selective, while SGPI-2 is not. Individual mutations failed to explain the causes underlying this difference. We deciphered this phenomenon using comprehensive combinatorial mutagenesis and phage display. We produced a complete chimeric SGPI-1 / SGPI-2 inhibitor-phage library, in which the two sequences were shuffled at the highest possible resolution of individual residues. The library was selected for binding to bovine trypsin and crayfish trypsin. Sequence analysis of the selectants revealed that taxon specificity is due to an intra-molecular functional coupling between a surface loop and the Lys10-Trp26 core. Five SGPI-2 surface residues transplanted into SGPI-1 resulted in a variant that retained the "taxon-specific" core, but potently inhibited both vertebrate and arthropod enzymes. An additional rational point mutation resulted in a picomolar inhibitor of both trypsins. Our results challenge the generally accepted view that surface residues are the exclusive source of selectivity for canonical inhibitors. Moreover, we provide important insights into general principles underlying the structure-function properties of small disulfide-rich polypeptides, molecules that exist at the borderline between peptides and proteins.

A novel locust (Schistocerca gregaria) serine protease inhibitor with a high affinity for neutrophil elastase

We have purified to homogeneity two forms of a new serine protease inhibitor specific for elastase/chymotrypsin from the ovary gland of the desert locust Schistocerca gregaria. This protein, greglin, has 83 amino acid residues and bears putative phosphorylation sites. Amino acid sequence alignments revealed no homology with pacifastin insect inhibitors and only a distant relationship with Kazal-type inhibitors. This was confirmed by computer-based structural studies. The most closely related homologue is a putative gene product from Ciona intestinalis with which it shares 38% sequence homology. Greglin is a fast-acting and tight binding inhibitor of human neutrophil elastase (k(ass)=1.2x10(7) M(-1) x s(-1), K(i)=3.6 nM) and subtilisin. It also binds neutrophil cathepsin G, pancreatic elastase and chymotrypsin with a lower affinity (26 nM< or =K(i)< or =153 nM), but does not inhibit neutrophil protease 3 or pancreatic trypsin. The capacity of greglin to inhibit neutrophil elastase was not significantly affected by exposure to acetonitrile, high temperature (90 degrees C), low or high pH (2.5-11.0), N-chlorosuccinimide-mediated oxidation or the proteolytic enzymes trypsin, papain and pseudolysin from Pseudomonas aeruginosa. Greglin efficiently inhibits the neutrophil elastase activity of sputum supernatants from cystic fibrosis patients. Its biological function in the locust ovary gland is currently unknown, but its physicochemical properties suggest that it can be used as a template to design a new generation of highly resistant elastase inhibitors for treating inflammatory diseases.

Annotation of novel neuropeptide precursors in the migratory locust based on transcript screening of a public EST database and mass spectrometry

Background

For holometabolous insects there has been an explosion of proteomic and peptidomic information thanks to large genome sequencing projects. Heterometabolous insects, although comprising many important species, have been far less studied. The migratory locust Locusta migratoria, a heterometabolous insect, is one of the most infamous agricultural pests. They undergo a well-known and profound phase transition from the relatively harmless solitary form to a ferocious gregarious form. The underlying regulatory mechanisms of this phase transition are not fully understood, but it is undoubtedly that neuropeptides are involved. However, neuropeptide research in locusts is hampered by the absence of genomic information.

Results

Recently, EST (Expressed Sequence Tag) databases from Locusta migratoria were constructed. Using bioinformatical tools, we searched these EST databases specifically for neuropeptide precursors. Based on known locust neuropeptide sequences, we confirmed the sequence of several previously identified neuropeptide precursors (i.e. pacifastin-related peptides), which consolidated our method. In addition, we found two novel neuroparsin precursors and annotated the hitherto unknown tachykinin precursor. Besides one of the known tachykinin peptides, this EST contained an additional tachykinin-like sequence. Using neuropeptide precursors from Drosophila melanogaster as a query, we succeeded in annotating the Locusta neuropeptide F, allatostatin-C and ecdysis-triggering hormone precursor, which until now had not been identified in locusts or in any other heterometabolous insect. For the tachykinin precursor, the ecdysis-triggering hormone precursor and the allatostatin-C precursor, translation of the predicted neuropeptides in neural tissues was confirmed with mass spectrometric techniques.

Conclusion

In this study we describe the annotation of 6 novel neuropeptide precursors and the neuropeptides they encode from the migratory locust, Locusta migratoria. By combining the manual annotation of neuropeptides with experimental evidence provided by mass spectrometry, we demonstrate that the genes are not only transcribed but also translated into precursor proteins. In addition, we show which neuropeptides are cleaved from these precursor proteins and how they are post-translationally modified.

Local binding with globally distributed changes in a small protease inhibitor upon enzyme binding

Complexation of the small serine protease inhibitor Schistocerca gregaria chymotrypsin inhibitor (SGCI), a member of the pacifastin inhibitor family, with bovine chymotrypsin was followed by NMR spectroscopy. (1)H-(15)N correlation (HSQC) spectra of the inhibitor with increasing amounts of the enzyme reveal tight and specific binding in agreement with biochemical data. Unexpectedly, and unparalleled among canonical serine protease inhibitors, not only residues in the protease-binding loop of the inhibitor, but also some segments of it located spatially far from the substrate-binding cleft of the enzyme were affected by complexation. However, besides changes, some of the dynamical features of the free inhibitor are retained in the complex. Comparison of the free and complexed inhibitor structures revealed that most, but not all, of the observed chemical shift changes can be attributed to minor structural transitions. We suggest that the classical 'scaffold + binding loop' model of canonical inhibitors might not be fully valid for the inhibitor family studied. In our view, this feature allows for the emergence of both taxon-specific and nontaxon-specific inhibitors in this group of small proteins.

Enzyme:substrate hydrogen bond shortening during the acylation phase of serine protease catalysis

Atomic resolution (<or=1.2 A) serine protease intermediate structures revealed that the strength of the hydrogen bonds between the enzyme and the substrate changed during catalysis. The well-conserved hydrogen bonds of antiparallel beta-sheet between the enzyme and the substrate become significantly shorter in the transition from a Michaelis complex analogue (Pontastacus leptodactylus (narrow-fingered crayfish) trypsin (CFT) in complex with Schistocerca gregaria (desert locust) trypsin inhibitor (SGTI) at 1.2 A resolution) to an acyl-enzyme intermediate (N-acetyl-Asn-Pro-Ile acyl-enzyme intermediate of porcine pancreatic elastase at 0.95 A resolution) presumably synchronously with the nucleophilic attack on the carbonyl carbon atom of the scissile peptide bond. This is interpreted as an active mechanism that utilizes the energy released from the stronger hydrogen bonds to overcome the energetic barrier of the nucleophilic attack by the hydroxyl group of the catalytic serine. In the CFT:SGTI complex this hydrogen bond shortening may be hindered by the 27I-32I disulfide bridge and Asn-15I of SGTI. The position of the catalytic histidine changes slightly as it adapts to the different nucleophilic attacker during the transition from the Michaelis complex to the acyl-enzyme state, and simultaneously its interaction with Asp-102 and Ser-214 becomes stronger. The oxyanion hole hydrogen bonds provide additional stabilization for acyl-ester bond in the acyl-enzyme than for scissile peptide bond of the Michaelis complex. Significant deviation from planarity is not observed in the reactive bonds of either the Michaelis complex or the acyl-enzyme. In the Michaelis complex the electron distribution of the carbonyl bond is distorted toward the oxygen atom compared to other peptide bonds in the structure, which indicates the polarization effect of the oxyanion hole.

Bacterial production and purification of SGPI-1 and SGPI-2, two peptidic serine protease inhibitors from the desert locust, Schistocerca gregaria

The last decade, a new serine protease inhibitor family has been described in arthropods. Eight members were purified from the locusts Locusta migratoria (LMPI-1-2 and HI) and Schistocerca gregaria (SGPI-1-5) and 11 additional locust peptides were identified by cDNA cloning. Furthermore, the light chain of the 155-kDa heterodimeric protease inhibitor pacifastin, from the freshwater crayfish Pacifastacus leniusculus, was found to be composed of nine consecutive inhibitory domains (PLDs). These domains share a pattern of 6 conserved cysteine residues (Cys-Xaa(9-12)-Cys-Asn-Xaa-Cys-Xaa-Cys-Xaa(2-3)-Gly-Xaa(3-4)-Cys-Thr-Xaa3-Cys) with the locust inhibitors. So far, for most of the PLD-related peptides the biological functions remain obscure. To obtain sufficient amounts of material to perform physiological experiments, we have optimised the production of SGPI-1-2 via a bacterial (Escherichia coli) expression system. The cDNA sequences encoding these peptides were inserted in the pMAL-2pX vector, downstream of the gene encoding the maltose-binding protein (including a signal peptide). As a consequence, both peptides were expressed as fusion proteins (2-3 mg/l) and targeted to the periplasmic space. Following a one-step affinity purification, both fusion proteins were successfully cleaved by Factor Xa and after a methanol extraction, it took only one additional RP-HPLC run to purify both peptides to homogeneity. Finally, the formation of the disulphide bridges and the biological activity of the recombinant peptides were verified by mass spectrometry and a spectrophotometric protease inhibitor assay, respectively.

Molecular identification of SGPP-5, a novel pacifastin-like peptide precursor in the desert locust

Recently, a new serine protease inhibitor family has been described in arthropods. Eight members were purified from locusts and 13 peptides have been identified by cDNA cloning. The peptides share a conserved cysteine array (Cys-Xaa(9-12)-Cys-Asn-Xaa-Cys-Xaa-Cys-Xaa(2-3)-Gly-Xaa(3-6)-Cys-Thr-Xaa(3)-Cys) with nine inhibitory domains (PLDs) of the light chain of the crayfish protease inhibitor, pacifastin. A molecular identification of a pacifastin-related precursor (SGPP-5) with three novel PLD-related peptides is presented in this study. This is a first report, identifying the presence of a SGPP-transcript in the brain, fore- and hindgut, including a 100-fold difference in fat body SGPP-transcript level of male as compared with female locust.

Transcript profiling of pacifastin-like peptide precursors in crowd- and isolated-reared desert locusts

Locusts have fascinated researchers for several decades, because they have the remarkable ability to undergo phase transition from the harmless solitary to the swarm-forming gregarious phase. However, the physiological and endocrine mechanisms, underlying phase polymorphism, are only partially unravelled. Nevertheless, besides the 'classical' hormones, pacifastin-related peptides have been suggested to play a role in phase transition. Here, we present the first quantitative and comparative analysis of locust transcripts, in particular pacifastin-related precursor (SGPP-1-3) mRNAs, between isolated-reared (solitary) and crowd-reared (gregarious) desert locusts, revealing a phase-dependent transcriptional regulation of the corresponding genes. While the SGPP-1 and SGPP-3 transcripts were most abundant in fat body from crowd-reared males, corresponding to significantly higher levels than in isolated-reared males, the SGPP-2 transcript was detected most abundantly in brain from crowd-reared male locusts. Furthermore, SGPP-2 transcript levels in brain, testes, fat body, and accessory glands from crowd-reared males significantly exceeded the levels in solitary locusts.

Protein purification, cDNA cloning and characterization of a protease inhibitor from the Indian tasar silkworm, Antheraea mylitta

An inhibitor of Aspergillus oryzae fungal protease was purified to homogeneity from the hemolymph of fifth instar larvae of Antheraea mylitta by ammonium sulfate precipitation, anion exchange and gel filtration (FPLC) chromatography, and termed as AmFPI-1. The extent of purification was checked by two-dimensional gel electrophoresis, and the molecular weight of purified inhibitor was determined by SDS-PAGE as 10.4 kDa. Fifteen N-terminal amino acid sequences of this protein were determined, and degenerate oligonucleotides were synthesized on the basis of these sequences. A cDNA library of A. mylitta integument was constructed, and protease inhibitor cDNA was partially amplified by PCR using degenerate oligonucleotides and CDS primers. A full-length inhibitor cDNA clone obtained by screening the library with PCR amplified DNA as probe was sequenced. The cDNA consists of 543 nucleotides with an ORF of 315 bp and encodes a protein of 105 amino acids. The sequence exhibits similarity to several Bombyx mori ESTs, and in particular to N-terminal amino acid sequence of an inducible serine protease inhibitor (ISPI-1) from Galleria mellonella indicating its relatedness to ISPI-1 of G. mellonella. The presence of this protease inhibitor in the hemolymph may play an important role as a natural defense system against invading microorganisms.

Genomics, evolution and biological functions of the pacifastin peptide family: a conserved serine protease inhibitor family in arthropods

The last decade, a new serine protease inhibitor family has been described in arthropods. Eight members were purified from the locusts Locusta migratoria (LMPI-1-2 and HI) and Schistocerca gregaria (SGPI-1-5). The light chain of the heterodimeric protease inhibitor pacifastin, from the freshwater crayfish Pacifastacus leniusculus, was found to be composed of nine consecutive inhibitory domains (PLDs). These domains share a pattern of six conserved cysteine residues (Cys-Xaa(9-12)-Cys-Asn-Xaa-Cys-Xaa-Cys-Xaa(2-3)-Gly-Xaa(3-6)-Cys-Thr-Xaa(3)-Cys) with the locust inhibitors. Via cDNA cloning, eight pacifastin-related precursors have been identified in locusts. Interestingly, additional pacifastin-related precursors have been identified in Diptera, Lepidoptera and Coleoptera utilising an in silico data mining approach.

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.

Search for peptidic molecular markers in hemolymph of crowd-(gregarious) and isolated-reared (solitary) desert locusts, Schistocerca gregaria

An HPLC analysis of hemolymph extracts was undertaken to uncover differences between desert locusts, Schistocerca gregaria, reared under either crowded or isolated conditions. Some differences in the chromatographic pattern could be detected. One of the major peaks in the hemolymph of crowd-reared adults was found to be a minor one in isolated-reared individuals, whereas other peaks increased after solitarization. The differences became even more pronounced after several generations of isolated rearing. The dominant chromatographic peak in hemolymph extracts of the crowd-reared animals was identified as a novel peptide with a molecular mass of 6080Da. Edman degradation in combination with enzymatic fragmentation and quadrupole-time of flight (Q-Tof) mass spectrometry revealed the full sequence: DNADEDTICVAADNKFYLYANSLKLYTCYNQLPKVYVVKPKSQCRSSLSDCPTS. This 54 aa-peptide is very abundant in hemolymph of crowd-reared adults. Its concentration in hemolymph amounts to 0.1mM. To uncover the function, its effects were investigated in several bioassays, so far without positive results. One of the other peaks differentially expressed in the individuals of the two phases was identified as SGPI-2 (MW=3794Da), which is a serine protease inhibitor in locusts.

Cloning of two cDNAs encoding isoforms of a pacifastin-related precursor polypeptide in the desert locust, Schistocerca gregaria: analysis of stage- and tissue-dependent expression

A novel serine protease inhibitor peptide family, designated as the 'pacifastin family', has recently been described in insects (locusts, lepidopterans) and crustaceans (crayfish). This study presents the cDNA cloning of two isoforms of SGPP-3, a novel pacifastin-related precursor in the desert locust, Schistocerca gregaria, which codes for three putative inhibitor peptides. The precursor isoforms differ at a single amino acid position in the third, C-terminal peptide. Northern blot analysis confirmed the presence of two different transcripts (0.75 and 0.90 kb). Both transcripts are most abundant in the fat body and appear to be strongly regulated during the moulting cycle. In addition, the amount of transcript proved to be strictly regulated in the ovaries during the female reproductive cycle.

cDNA cloning of two different serine protease inhibitor precursors in the migratory locust, Locusta migratoria

Recently, a novel serine protease-inhibiting peptide family, designated as the 'pacifastin family', has been described in locusts and crayfish. All members of this family possess a characteristic cysteine-rich domain. The present study describes the cDNA cloning, sequencing and transcript distribution of two novel pacifastin-related peptide precursors in the migratory locust, Locusta migratoria. Only one of the encoded peptides (HI) was identified previously, whereas six others represent new members of the pacifastin family. Northern blot analysis showed that both precursor transcripts are present in adult locust fat body. These could not be detected in the midgut. Interestingly, an in silico data mining approach of the expressed sequence tags (EST) database revealed the existence of Manduca sexta and Bombyx mori cDNAs that display pronounced sequence similarities with these locust pacifastin-related transcripts.

Structural and functional properties of a novel serine protease inhibiting peptide family in arthropods

Recently, several arthropod peptides that belong to a new serine protease inhibitor family were discovered. Three members (HI, PMP-D2=LMCI-1 and PMP-C=LMCI-2) were isolated from the migratory locust, Locusta migratoria. Five additional members (SGPI-1-5) were identified in the desert locust Schistocerca gregaria, and a heterodimeric serine protease inhibitor (pacifastin) was isolated from the hemolymph of the crayfish Pacifastacus leniusculus. The light chain of pacifastin constitutes the inhibitory subunit that has nine cysteine-rich domains (PLDs) that are homologous with the locust inhibitors. These locust inhibitors and PLDs share a conserved array of six cysteine residues (Cys-Xaa(9-12)-Cys-Asn-Xaa-Cys-Xaa-Cys-Xaa(2-3)-Gly-Xaa(3-4)-Cys-Thr-Xaa(3)-Cys), which are involved in an identical disulfide bridge pattern (Cys(1)-Cys(4), Cys(2)-Cys(6), Cys(3)-Cys(5)). The solution structures of LMCI-1 and LMCI-2 showed a similar, compact, globular folding, which is unique within the group of the small 'canonical' inhibitors. Moreover, the reactive site, including the P1-P'1 bond was thoroughly investigated by means of synthetic variants. However, the biological function(s) of the locust inhibitors is (are) not fully understood. LMCI-1 and LMCI-2 were shown to inhibit the endogenous proteolytic activating cascade of prophenoloxidase. Northern blot analysis indicated that the genes encoding the SGPI precursors are differentially expressed in a time-, stage- and hormone-dependent manner.

Peptide differential display: a novel approach for phase transition in locusts

Today, the question of the physiological cause of phase transition, the transition from the solitary to the gregarious phase, in locusts remains unanswered. We hereby present a novel approach by which we have attempted to determine whether different phases express or release different peptides in similar physiological conditions. For this purpose, a peptidomic analysis of the corpora cardiaca and hemolymph of crowded and isolated locusts of Schistocerca gregaria was performed using high performance liquid chromatography and matrix-assisted laser desorption ionisation time of flight mass spectrometry. A comparison between the two conditions reveals differences in the number and amount of peptides present in the corpora cardiaca and the hemolymph. Further research will have to identify these phase specific differences and their role in locust phase polymorphism.

Remarkable phylum selectivity of a Schistocerca gregaria trypsin inhibitor: the possible role of enzyme-inhibitor flexibility

A 35-mer polypeptide isolated from the hemolymph of desert locust Schistocerca gregaria (SG) proved to be a canonical inhibitor of bovine trypsin (K(i) = 0.2 microM). Despite having a trypsin-specific arginine at the primary specificity P(1) site, it inhibits bovine chymotrypsin almost as well (K(i) = 2 microM). Furthermore, while the latter reactivity improves 10(4)-fold by the single replacement of P(1) Arg by Leu, changing P(1)' from Lys to Met only moderately improves trypsin affinity (K(i) = 30 nM). The apparent low compatibility to trypsin, however, is not observed vs two arthropodal trypsins: SG peptides with P(1) Arg inhibit crayfish and shrimp trypsins with K(i) values in the picomolar range. This unprecedented high discrimination between orthologous enzymes is postulated to derive from flexibility differences in the protein-protein interaction. The more than four orders of magnitude phylum selectivity makes these peptides prospective candidates for agricultural use.

Complexation of two proteic insect inhibitors to the active site of chymotrypsin suggests decoupled roles for binding and selectivity

The crystal structures of two homologous inhibitors (PMP-C and PMP-D2v) from the insect Locusta migratoria have been determined in complex with bovine alpha-chymotrypsin at 2.1- and 3.0-A resolution, respectively. PMP-C is a potent bovine alpha-chymotrypsin inhibitor whereas native PMP-D2 is a weak inhibitor of bovine trypsin. One unique mutation at the P1 position converts PMP-D2 into a potent bovine alpha-chymotrypsin inhibitor. The two peptides have a similar overall conformation, which consists of a triple-stranded antiparallel beta-sheet connected by three disulfide bridges, thus defining a novel family of serine protease inhibitors. They have in common the protease interaction site, which is composed of the classical protease binding loop (position P5 to P'4, corresponding to residues 26-34) and of an internal segment (residues 15-18), held together by two disulfide bridges. Structural divergences between the two inhibitors result in an additional interaction site between PMP-D2v (position P10 to P6, residues 21-25) and the residues 172-175 of alpha-chymotrypsin. This unusual interaction may be responsible for species selectivity. A careful comparison of data on bound and free inhibitors (from this study and previous NMR studies, respectively) suggests that complexation to the protease stabilizes the flexible binding loop (from P5 to P'4).

Purification and characterization of two serine protease inhibitors from the hemolymph of Mythimna unipuncta

Two serine protease inhibitors, trypsin inhibitor and alpha-chymotrypsin inhibitor, were isolated from the hemolymph of Mythimna unipuncta. Mythimna trypsin and alpha-chymotrypsin inhibitors were purified by gel filtration and anion-exchange chromatography. They displayed molecular masses of 52 kDa and 43 kDa, respectively, as determined by electrophoresis under reducing and non-reducing conditions on denaturing polyacrylamide gels. Their isoelectric points were evaluated by isoelectric focusing and two-dimensional electrophoresis. Their N-terminal sequences have been analyzed as APSDTTIAETLTITEEFFPD and FDESFGFQGPSTYEKTPLGEP, respectively. The role of these inhibitors in the regulation of the defense reaction of the insect is discussed.

Insect silk contains both a Kunitz-type and a unique Kazal-type proteinase inhibitor

Insect silk is made up of structural fibrous (fibroins) and sticky (sericins) proteins, and contains a few small peptides of hitherto unknown functions. We demonstrate that two of these peptides inhibit bacterial and fungal proteinases (subtilisin, proteinase K and pronase). These 'silk proteinase inhibitors' 1 and 2 (SPI 1 and 2) are produced in the middle section of the silk-secreting glands prior to cocoon spinning and their production is controlled at transcription level. The full length cDNA of pre-SPI 1 contains 443 nucleotides and encodes a peptide of 76 amino-acid residues, of which 20 make up a signal sequence. The mature SPI 1 (6056.7 Da, 56 residues) is a typical thermostable Kunitz-type proteinase inhibitor with Arg in P1 position. The cDNA of pre-SPI 2 consists of 260 nucleotides and yields a putative secretory peptide of 58 amino-acid residues. The functional SPI 2 (3993 Da, 36 residues) is a single-domain Kazal-type proteinase inhibitor with unique structural features: free segment of the N-terminus is reduced to a single amino-acid residue, lack of CysI and CysV precludes formation of the A-ring and provides increased flexibility to the C-ring, and absence of several residues around the normal position of CysV shortens and changes the alpha helix segment of the protein. The structure reveals that the length and arrangement of the B-ring, including exposure of the P1 residue, and the position of the C-terminus relative to the B-loop, are essential for the activity of the Kazal-type inhibitors.

Low molecular weight serine protease inhibitors from insects are proteins with highly conserved sequences

A low molecular weight protease inhibitor peptide found in ovaries of the desert locust Schistocerca gregaria (SGPI-2), was purified from plasma of the same locust and sequenced. It was named SGCI. It was found active towards chymotrypsin and human leukocyte elastase. SGCI was synthesized using a solid-phase procedure and the sequence of its reactive site for chymotrypsin was determined. Compared with an inhibitor purified earlier from another locust species, the total sequence of SGCI showed 88% identity. In particular, the sequence of the reactive site of these inhibitors was identical. Our search for a closely related peptide in an insect species far removed from locusts, the lepidopteran Spodoptera littoralis, was unfruitful but a different chymotrypsin inhibitor, belonging to the Kazal family, was found whose mass is greater than that of SGCI (20 vs 3.6 kDa). Its N-terminal sequence shares 80% identity with that of a chymotrypsin inhibitor purified earlier from the haemolymph of another lepidopteran. Conservation of the amino acid sequence in the reactive site seems to be an exception among protease inhibitors.

Proteinase inhibitors from desert locust, Schistocerca gregaria: engineering of both P(1) and P(1)' residues converts a potent chymotrypsin inhibitor to a potent trypsin inhibitor

Two peptides, SGCI and SGTI, that inhibited chymotrypsin and trypsin, respectively, were isolated from the haemolymph of Schistocerca gregaria. Their primary structures were found to be identical with SGP-2 and SGP-1, two of a series of peptides isolated from ovaries of the same species (A. Hamdaoui et al., FEBS Lett. 422 (1998) 74-78). All these peptides are composed of 35-36 amino acid residues and contain three homologous disulfide bridges. The residues imparting specificity to SGCI and SGTI were identified as Leu-30 and Arg-29, respectively. The peptides were synthesised by solid-phase peptide synthesis, and the synthetic ones displayed the same inhibition as the natural forms: SGCI is a strong inhibitor of chymotrypsin (K(i) = 6.2 x 10(-12) M), and SGTI is a rather weak inhibitor of trypsin (K(i) = 2.1 x 10(-7) M). The replacement of P(1) then P(1)' residues of SGCI with trypsin-specific residues increased affinity towards trypsin 3600- and 1100-fold, respectively, thus SGCI was converted to a strong trypsin inhibitor (K(i) = 5.0 x 10(-12) M) that retained some inhibitory affinity towards chymotrypsin (K(i) = 3.5 x 10(-8) M). The documented role of both P(1) and P(1)' highlights the importance of S(1)'P(1)' interactions in enzyme-inhibitor complexes.

Serine proteinase inhibitors in arthropod immunity

Arthropod hemolymph contains proteins with serine proteinase inhibitory activity. These inhibitors may exist in plasma or in hemocyte granules. Serine proteinase inhibitors from the Kazal, Kunitz, alpha-macroglobulin, and serpin families have been identified in arthropod hemolymph and have been characterized biochemically. Two new families of low molecular weight serine proteinase inhibitors have recently been discovered: one in silkworms (the Bombyx family) and another in locusts and a crayfish. The serine proteinase inhibitors in arthropod hemolymph are likely to function in protecting their hosts from infection by pathogens or parasites. Some may inhibit fungal or bacterial proteinases. Others probably have roles in regulating endogenous proteinases involved in coagulation, prophenol oxidase activation, or cytokine activation.