Expression, purification and characterization of a three-domain Kazal-type inhibitor from silkworm pupae (Bombyx mori)

Expression patterns and antifungal function study of KaSPI in Mythimna separata

Kazal-type serine protease inhibitors (KaSPI) play important roles in insect growth, development, digestion, metabolism and immune defence. In this study, based on the transcriptome of Mythimna separata, the cDNA sequence of MsKaSPI with Kazal domain was uploaded to GenBank (MN931651). Spatial and temporal expression analysis showed that MsKaSPI was expressed at different developmental stages and different tissues, and it was induced by 20-hydroxyecdysone in third-instar larvae of M. separata. After 24 h infection by Beauveria bassiana, the expression level of MsKaSPI and the corresponding MsKaSPI content were significantly up-regulated, being 6.42-fold and 1.91-fold to the control group, respectively, while the activities of serine protease, trypsin and chymotrypsin were inhibited. After RNA interference interfered with MsKaSPI for 6 h, the expression decreased by 73.44%, the corresponding content of MsKaSPI protein decreased by 55.66% after 12 h, and the activities of serine protease and trypsin were significantly enhanced. Meanwhile, both the larval and pupal stages of M. separata were prolonged, the weights were reduced and the number of eggs per female decreased by 181. Beauveria bassiana infection also increased the mortality of MsKaSPI-silenced M. separata by 18.96%. These prove MsKaSPI can not only result in slow growth and low fecundity of M. separata by regulating the activity of related protease, but also participate in the resistance to pathogenic fungi by regulating the serine protease inhibitor content and the activities of related serine protease.

SPINK7 Recognizes Fungi and Initiates Hemocyte-Mediated Immune Defense Against Fungal Infections

Serine protease inhibitors of Kazal-type (SPINKs) were widely identified in vertebrates and invertebrates, and played regulatory roles in digestion, coagulation, and fibrinolysis. In this study, we reported the important role of SPINK7 in regulating immune defense of silkworm, Bombyx mori. SPINK7 contains three Kazal domains and has 6 conserved cysteine residues in each domain. Quantitative real-time PCR analyses revealed that SPINK7 was exclusively expressed in hemocytes and was upregulated after infection with two fungi, Saccharomyces cerevisiae and Candida albicans. Enzyme activity inhibition test showed that SPINK7 significantly inhibited the activity of proteinase K from C. albicans. Additionally, SPINK7 inhibited the growth of three fungal spores, including S. cerevisiae, C. albicans, and Beauveria bassiana. The pathogen-associated molecular patterns (PAMP) binding assays suggested that SPINK7 could bind to β-D-glucan and agglutinate B. bassiana and C. albicans. In vitro assays were performed using SPINK7-coated agarose beads, and indicated that SPINK7 promoted encapsulation and melanization of agarose beads by B. mori hemocytes. Furthermore, co-localization studies using immunofluorescence revealed that SPINK7 induced hemocytes to aggregate and entrap the fungi spores of B. bassiana and C. albicans. Our study revealed that SPINK7 could recognize fungal PAMP and induce the aggregation, melanization, and encapsulation of hemocytes, and provided valuable clues for understanding the innate immunity and cellular immunity in insects.

Proteo-Transcriptomic Characterization of Sirex nitobei (Hymenoptera: Siricidae) Venom

The wood-boring woodwasp Sirex nitobei is a native pest in Asia, infecting and weakening the host trees in numerous ecological and commercial coniferous forest plantations. In China, hosts of S. nitobei are diverse, so the pest has spread to several provinces of China, resulting in considerable economic and ecological damage. During female oviposition, S. nitobei venom along with arthrospores of the symbiotic fungus Amylostereum areolatum or A. chaetica is injected into host trees, and the combination of these two biological factors causes the death of xylem host trees. The presence of venom alone causes only the yellowing and wilting of needles. In this study, we constructed the venom gland transcriptome of S. nitobei for the first time and a total of 15,036 unigenes were acquired. From the unigenes, 11,560 ORFs were identified and 537 encoding protein sequences with signal peptides at the N-terminus. Then, we used the venomics approach to characterize the venom composition of female S. nitobei and predicted 1095 proteins by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. We focused on seven proteins that were both highly expressed in the venom gland transcriptome and predicted in the crude venom proteome. These seven proteins are laccase-2, laccase-3, a protein belonging to the Kazal family, chitooligosaccharidolytic β-N-acetylglucosaminidase, beta-galactosidase, icarapin-like protein, and waprin-Thr1-like protein. Using quantitative real-time PCR (qRT-PCR), we also proved that the genes related to these seven proteins are specifically expressed in the venom glands. Finally, we revealed the functional role of S. nitobei venom in the physiological response of host trees. It can not only promote the colonization of symbiotic fungus but contribute to the development of eggs and larvae. This study provides a deeper understanding of the molecular mechanism of the woodwasp–pine interaction.

An integrated transcriptomic and proteomic approach to identify the main Torymus sinensis venom components

During oviposition, ectoparasitoid wasps not only inject their eggs but also a complex mixture of proteins and peptides (venom) in order to regulate the host physiology to benefit their progeny. Although several endoparasitoid venom proteins have been identified, little is known about the components of ectoparasitoid venom. To characterize the protein composition of Torymus sinensis Kamijo (Hymenoptera: Torymidae) venom, we used an integrated transcriptomic and proteomic approach and identified 143 venom proteins. Moreover, focusing on venom gland transcriptome, we selected additional 52 transcripts encoding putative venom proteins. As in other parasitoid venoms, hydrolases, including proteases, phosphatases, esterases, and nucleases, constitute the most abundant families in T. sinensis venom, followed by protease inhibitors. These proteins are potentially involved in the complex parasitic syndrome, with different effects on the immune system, physiological processes and development of the host, and contribute to provide nutrients to the parasitoid progeny. Although additional in vivo studies are needed, initial findings offer important information about venom factors and their putative host effects, which are essential to ensure the success of parasitism.

DNA methylation in silkworm genome may provide insights into epigenetic regulation of response to Bombyx mori cypovirus infection

DNA methylation is an important epigenetic modification that regulates a wide range of biological processes including immune response. However, information on the epigenetics-mediated immune mechanisms in insects is limited. Therefore, in this study, we examined transcriptomes and DNA methylomes in the fat body and midgut tissues of silkworm, Bombyx mori with or without B. mori cytoplasmic polyhedrosis virus (BmCPV) infection. The transcriptional profile and the genomic DNA methylation patterns in the midgut and fat body were tissue-specific and dynamically altered after BmCPV challenge. KEGG pathway analysis revealed that differentially methylated genes (DMGs) could be involved in pathways of RNA transport, RNA degradation, nucleotide excision repair, DNA replication, etc. 27 genes were shown to have both differential expression and differential methylation in the midgut and fat body of infected larvae, respectively, indicating that the BmCPV infection-induced expression changes of these genes could be mediated by variations in DNA methylation. BS-PCR validated the hypomethylation of G2/M phase-specific E3 ubiquitin-protein ligase-like gene in the BmCPV infected midgut. These results demonstrated that epigenetic regulation may play roles in host-virus interaction in silkworm and would be potential value for further studies on mechanism of BmCPV epithelial-specific infection and epigenetic regulation in the silkworm.

Molecular characterization, expression and functional analysis of two Kazal-type serine protease inhibitors from Venerupis philippinarum

Kazal-type serine protease inhibitors (KSPIs) act as negative regulators in immune signaling pathway by controlling the extent of serine protease (SP) activities. In this study, the full-length cDNA of two KSPIs (designed as VpKSPI-1 and VpKSPI-2) were identified from Venerupis philippinarum by rapid amplification of cDNA ends (RACE) approaches. The open reading frame (ORF) of VpKSPI-1 and VpKSPI-2 was of 552 bp and 402 bp, encoding a polypeptide of 183 and 133 amino acids, respectively. The transcripts of VpKSPI-1 and VpKSPI-2 were ubiquitously expressed in all tissues tested with the highest expression level in hepatopancreas. After Vibrio anguillarum challenge, the relative mRNA expression of VpKSPI-1 and VpKSPI-2 in hepatopancreas was both up-regulated within 96 h. The recombinant VpKSPI-1 (rVpKSPI-1) displayed weak activities towards chymotrypsin, moderate inhibitory activity to trypsin, while rVpKSPI-2 showed significant inhibitory activities against chymotrypsin and trypsin. When the molar ratio of rVpKSPI-2 to chymotrypsin and trypsin reached 1:4 and 1:2, the protease activities could be almost entirely inhibited. All these results suggested that both VpKSPI-1 and VpKSPI-2 perhaps play a vital role in the innate immunity of V. philippinarum.

BIOINFORMATICS, TISSUE DISTRIBUTION, AND SUBCELLULAR LOCALIZATION ANALYSES OF FK506 BINDING PROTEIN 12B FROM SILKWORMS

FK506 binding proteins (FKBPs) are intracellular receptors of the immunosuppressant FK506 and play important roles in the correct folding of new proteins and the self-assembly of biological macromolecules. FKBP12 is a member of the FKBP family that is widely expressed and highly conserved in many species. In this study, we identified the complete cDNA sequence encoding the FKBP12 ortholog in Bombyx mori, named Bm-FKBP12B (GenBank accession no. DQ443423). Multiple-sequence alignment among different species revealed a high similarity among FKBP12 paralogs and orthologs. Bioinformatics analysis of the Bm-FKBP12B gene showed that it is located on chromosome 20 and consists of three exons and two introns. We cloned, expressed, and purified the Bm-FKBP12B protein in Escherichia coli and generated a specific polyclonal antibody against Bm-FKBP12B. The real-time quantitative reverse-transcription (qRT) PCR and Western blotting results showed that Bm-FKBP12B was present throughout all of the development stages, but it was abundant in the adult and embryo stages. Bm-FKBP12B expression was higher in the silk gland and gut, suggesting that it might play important roles in regulating gene expression in the silk gland and during silk fiber formation. Bm-FKBP12B protein was distributed in the cytoplasm, nucleus, and nuclear membrane.

Molecular Cloning and Functional Studies of Two Kazal-Type Serine Protease Inhibitors Specifically Expressed by Nasonia vitripennis Venom Apparatus

Two cDNA sequences of Kazal-type serine protease inhibitors (KSPIs) in Nasonia vitripennis, NvKSPI-1 and NvKSPI-2, were characterized and their open reading frames (ORFs) were 198 and 264 bp, respectively. Both NvKSPI-1 and NvKSPI-2 contained a typical Kazal-type domain. Real-time quantitative PCR (RT-qPCR) results revealed that NvKSPI-1 and NvKSPI-2 mRNAs were mostly detected specifically in the venom apparatus, while they were expressed at lower levels in the ovary and much lower levels in other tissues tested. In the venom apparatus, both NvKSPI-1 and NvKSPI-2 transcripts were highly expressed on the fourth day post eclosion and then declined gradually. The NvKSPI-1 and NvKSPI-2 genes were recombinantly expressed utilizing a pGEX-4T-2 vector, and the recombinant products fused with glutathione S-transferase were purified. Inhibition of recombinant GST-NvKSPI-1 and GST-NvKSPI-2 to three serine protease inhibitors (trypsin, chymotrypsin, and proteinase K) were tested and results showed that only NvKSPI-1 could inhibit the activity of trypsin. Meanwhile, we evaluated the influence of the recombinant GST-NvKSPI-1 and GST-NvKSPI-2 on the phenoloxidase (PO) activity and prophenoloxidase (PPO) activation of hemolymph from a host pupa, Musca domestica. Results showed PPO activation in host hemolymph was inhibited by both recombinant proteins; however, there was no significant inhibition on the PO activity. Our results suggested that NvKSPI-1 and NvKSPI-2 could inhibit PPO activation in host hemolymph and trypsin activity in vitro.

Involvement of a Serpin serine protease inhibitor (OoSerpin) from mollusc Octopus ocellatus in antibacterial response

Serpin is an important member of serine protease inhibitors (SPIs), which is capable of regulating proteolytic events and involving in a variety of physiological processes. In present study, a Serpin homolog was identified from Octopus ocellatus (designated as OoSerpin). Full-length cDNA of OoSerpin was of 1735 bp, containing a 5' untranslated region of 214 bp, a 3' UTR of 282 bp, and an open reading frame of 1239 bp. The open reading frame encoded a polypeptide of 412 amino acids which has a predicted molecular weight of 46.5 kDa and an isoelectric point of 8.52. The OoSerpin protein shares 37% sequence identity with other Serpins from Mus musculus (NP_941373) and Ixodes scapularis (XP_002407493). The existence of a conserved SERPIN domain strongly suggested that OoSerpin was a member of the Serpin subfamily. Expression patterns of OoSerpin, both in tissues and towards bacterial stimulation, were then characterized. The mRNA of OoSerpin was constitutively expressed at different levels in all tested tissues of untreated O. ocellatus, including mantle (lowest), muscle, renal sac, gill, hemocyte, gonad, systemic heart, and hepatopancreas (highest). The transcriptional level of OoSerpin was significantly up-regulated (P<0.01) in O. ocellatus upon bacterial challenges with Vibrio anguillarum and Micrococcus luteus, indicating its involvement in the antibacterial immune response. Furthermore, rOoSerpin, the recombinant protein of OoSerpin, exhibited strong abilities to inhibit proteinase activities of trypsin and chymotrypsin as well as the growth of Escherichia coli. Our results demonstrate that OoSerpin is a potential antibacterial factor involved in the immune response of O. ocellatus against bacterial infection.

Antimicrobial activity of a honeybee (Apis cerana) venom Kazal-type serine protease inhibitor

Insect-derived Kazal-type serine protease inhibitors exhibit thrombin, elastase, plasmin, proteinase K, or subtilisin A inhibition activity, but so far, no functional roles for bee-derived Kazal-type serine protease inhibitors have been identified. In this study, a bee (Apis cerana) venom Kazal-type serine protease inhibitor (AcKTSPI) that acts as a microbial serine protease inhibitor was identified. AcKTSPI contained a single Kazal domain that displayed six conserved cysteine residues and a P1 threonine residue. AcKTSPI was expressed in the venom gland and was present as a 10-kDa peptide in bee venom. Recombinant AcKTSPI Kazal domain (AcKTSPI-Kd) expressed in baculovirus-infected insect cells demonstrated inhibitory activity against subtilisin A (Ki 67.03 nM) and proteinase K (Ki 91.53 nM), but not against α-chymotrypsin or trypsin, which implies a role for AcKTSPI as a microbial serine protease inhibitor. However, AcKTSPI-Kd exhibited no detectable inhibitory effects on factor Xa, thrombin, tissue plasminogen activator, or elastase. Additionally, AcKTSPI-Kd bound directly to Bacillus subtilis, Bacillus thuringiensis, Beauveria bassiana, and Fusarium graminearum but not to Escherichia coli. Consistent with these findings, AcKTSPI-Kd showed antibacterial activity against Gram-positive bacteria and antifungal activity against both plant-pathogenic and entomopathogenic fungi. These findings constitute molecular evidence that AcKTSPI acts as an inhibitor of microbial serine proteases. This paper provides a novel view of the antimicrobial functions of a bee venom Kazal-type serine protease inhibitor.

Molecular characterization of two kazal-type serine proteinase inhibitor genes in the surf clam Mesodesma donacium exposed to Vibrio anguillarum

This study reports two kazal-type serine protease inhibitors (KPI) identified in a cDNA library from the surf clam Mesodesma donacium, and characterized through Rapid Amplification of cDNA Ends (RACE). The KPIs, denoted as MdSPI-1 and MdSPI-2, presented full sequences of 1139 bp and 781 bp respectively. MdSPI-1 had a 5'untranslated region (UTR) of 175 bp, a 3'UTR of 283 bp and an open reading frame (ORF) of 681 pb that encodes for 227 amino acids. MdSPI-2 showed a 5'UTR of 70 bp, a 3'UTR of 279 bp and an ORF of 432 bp that encodes for 144 amino acids. Both sequences presented two kazal-type tandem domains. Phylogenetic analysis of MdSPI-1 and MdSPI-2 shows a main clade composed by other bivalve species and closely related crustaceans. Real time PCR analysis showed that MdSPI-1 is mainly up-regulated in mantle, foot, gills and muscle tissues, while MdSPI-2 is expressed principally in foot tissue. Moreover, to evaluate the immune response of MdSPI-1 and MdSPI-2, infections with Vibrio anguillarum were performed. Herein, MdSPI-1 and MdSPI-2 transcription expression were significantly up-regulated at 2 and 8 h post-challenge. Our results suggest that MdSPI-1 and MdSPI-2 are important humoral factors of innate immunity in M. donacium.

Phylogenetic distribution of protease inhibitors of the Kazal-family within the Arthropoda

In mammalian pancreatic cells, the pancreatic secretory trypsin inhibitor (PSTI) belonging to the Kazal-family prevents the premature activation of digestive enzymes and thus plays an important role in a protective mechanism against tissue destruction by autophagy. Although a similar protective mechanism exists in Arthropoda, the distribution of these inhibitors in this phylum remains obscure. A comprehensive in silico search of nucleotide databases, revealed the presence of members of the Kazal-family in the four major subphyla of the Arthropoda. Especially in the Hexapoda and the Crustacea these inhibitors are widespread, while in the Chelicerata and Myriapoda only a few Kazal-like protease inhibitors were found. A sequence alignment of inhibitors retrieved in the digestive system of insects revealed a conservation of the PSTI characteristics and strong resemblance to vertebrate PSTI. A phylogenetic analysis of these inhibitors showed that they generally cluster according to their order. The results of this data mining study provide new evidence for the existence of an ancient protective mechanism in metazoan digestive systems. Kazal-like inhibitors, which play an important protective role in the pancreas of vertebrates, also seem to be present in Arthropoda.

A four-domain Kunitz-type proteinase inhibitor from Solen grandis is implicated in immune response

Serine proteinase inhibitor (SPI) serves as a negative regulator in immune signal pathway by restraining the activities of serine proteinase (SP) and plays an essential role in the innate immunity. In the present study, a Kunitz-type SPI was identified from the mollusk razor clam Solen grandis (designated as SgKunitz). The full-length cDNA of SgKunitz was of 1284 bp, containing an open reading frame (ORF) of 768 bp. The ORF encoded four Kunitz domains, and their amino acids were well conserved when compared with those in other Kunitz-type SPIs, especially the six cysteines involved in forming of three disulfide bridges in each domain. In addition, the tertiary structure of all the four domains adopted a typical model of Kunitz-type SPI family, indicating SgKunitz was a new member of Kunitz-type SPI superfamily. The mRNA transcripts of SgKunitz were detected in all tested tissues of razor clam, including muscle, mantle, gonad, gill, hepatopancreas and hemocytes, and with the highest expression level in gill. When the razor clams were stimulated by LPS, PGN or β-1, 3-glucan, the expression level of SgKunitz mRNA in hemocytes was significantly up-regulated (P < 0.01), suggesting SgKunitz might involved in the processes of inhibiting the activity of SPs during the immune responses triggered by various pathogens. Furthermore, the recombinant protein of SgKunitz could effectively inhibit the activities of SP trypsin and chymotrypsin in vitro. The present results suggested SgKunitz could serve as an inhibitor of SP involving in the immune response of S. grandis, and provided helpful evidences to understand the regulation mechanism of immune signal pathway in mollusk.

Kinetic analysis, expression pattern, and production of a recombinant fungal protease inhibitor of tasar silkworm Antheraea mylitta

Antheraea mylitta, a tasar silk-producing insect of Saturniidae family, expresses a fungal protease inhibitor named as A. mylitta fungal protease inhibitor-1 (AmFPI-1). AmFPI-1 inhibits alkaline protease of Aspergillus oryzae but its mechanism of action is not known. To understand the mode of inhibition of AmFPI-1 against the fungal protease, it was purified from the hemolymph of A. mylitta larvae and inhibitory activity against A. oryzae protease was studied. Kinetic analysis of purified AmFPI-1 on alkaline protease of A. oryzae showed that AmFPI-1 acts as a canonical-type competitive inhibitor with equilibrium dissociation constant (K ( i )) of 60 nM. Expression of AmFPI-1 in different body tissues of fifth instar A. mylitta larvae was determined by real-time PCR, and the highest expression was observed in fat body followed by integument, silk gland, and gut, indicating that AmFPI-1 has pleiotropic functions including protection from invading fungi. The cDNA of AmFPI-1 was expressed in Escherichia coli, and recombinant His-tagged fusion protein was purified by Ni-NTA chromatography. Recombinant AmFPI-1 showed inhibitory activity against A. oryzae protease and suggested its use in various biological applications to prevent proteolysis.

Peptidergic control of food intake and digestion in insects 1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Like all heterotrophic organisms, insects require a strict control of food intake and efficient digestion of food into nutrients to maintain homeostasis and to fulfill physiological tasks. Feeding and digestion are steered by both external and internal signals that are transduced by a multitude of regulatory factors, delivered either by neurons innervating the gut or mouthparts, or by midgut endocrine cells. The present review gives an overview of peptide regulators known to control feeding and digestion in insects. We describe the discovery and functional role in these processes for insect allatoregulatory peptides, diuretic hormones, FMRFamide-related peptides, (short) neuropeptide F, proctolin, saliva production stimulating peptides, kinins, and tachykinins. These peptides control either gut myoactivity, food intake, and (or) release of digestive enzymes. Some peptides exert their action at multiple levels, possibly having a biological function that depends on their site of delivery. Many regulatory peptides have been physically extracted from different insect species. However, multiple peptidomics, proteomics, transcriptomics, and genome sequencing projects have led to increased discovery and prediction of peptide (precursor) and receptor sequences. In combination with physiological experiments, these large-scale projects have already led to important steps forward in unraveling the physiology of feeding and digestion in insects.

Two Kazal-type protease inhibitors from Macrobrachium nipponense and Eriocheir sinensis: comparative analysis of structure and activities

Kazal-type inhibitors (KPIs) play important roles in many biological and physiological processes, such as blood clotting, the immune response and reproduction. In the present study, two male reproductive tract KPIs, termed Man-KPI and Ers-KPI, were identified in Macrobrachium nipponense and Eriocheir sinensis, respectively. The inhibitory activities of recombinant Man-KPI and Ers-KPI against chymotrypsin, elastase, trypsin and thrombin were determined. The results showed that both of them strongly inhibit chymotrypsin and elastase. Kinetic studies were performed to elucidate their inhibition mechanism. Furthermore, individual domains were also expressed to learn further which domain contributes to the inhibitory activities of intact KPIs. Only Man-KPI_domain3 is active in the inhibition of chymotrypsin and elastase. Meanwhile, Ers-KPI_domain2 and 3 are responsible for inhibition of chymotrypsin, and Ers-KPI_domains2, 3 and 4 are responsible for the inhibition of elastase. Meanwhile, the inhibitory activities of these two KPIs toward Macrobrachium rosenbergii, M. nipponense and E. sinensis sperm were compared with that of the Kazal-type peptidase inhibitor (MRPINK) characterized from the M. rosenbergii reproductive tract in a previous study. The results demonstrated that KPIs can completely inhibit the gelatinolytic activities of sperm proteases from their own species, while different levels of cross-inhibition were observed between KPI and proteases from different species. These results may provide new perspective to further clarify the mechanism of KPI-proteases interaction in the male reproductive system.

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.

Functional analysis of a pancreatic secretory trypsin inhibitor-like protein in insects: silencing effects resemble the human pancreatic autodigestion phenotype

INTRODUCTION

In mammalian pancreatic cells, the pancreatic secretory trypsin inhibitor (PSTI) prevents the premature activation of digestive enzymes and thus plays an important role in a protective mechanism against tissue destruction by autophagy, a process which may ultimately cause diseases such as pancreatitis and pancreatic cancer. Insects, however, lack a pancreas and so far no PSTI-like peptides are functionally characterized.

RESULTS

In several insect species protease inhibitors that structurally resemble the mammalian PSTI were predicted in silico. A putative PSTI-like protein (LmPSTI) was cloned and sequenced in the African migratory locust, Locusta migratoria. For the first time the expression of an insect derived PSTI-like inhibitor was shown to be restricted to the digestive enzyme-producing organs in insects (midgut and caeca). LmPSTI was produced via a bacterial expression system and was found to be a potent inhibitor of bovine trypsin as well as endogenous locust gut enzymes. In the caeca, RNAi-mediated knockdown of LmPSTI resulted in a significantly upregulated expression (2-fold) of locust ATG8 transcripts (an ubiquitin-like protein crucial for autophagosome formation). These findings were confirmed by an ultrastructural study on caeca, revealing the presence of autophagy-related structures in RNAi-treated animals.

CONCLUSION

The results of this study lead us to believe that LmPSTI plays an important role in controlling the proteolytic activity in the digestive system of L. migratoria. These findings provide new evidence for the existence of an ancient protective mechanism in metazoan digestive systems and open new perspectives for the study of autophagy-related diseases in the digestive tract.

Peptidase inhibitors in the MEROPS database

The MEROPS website (http://merops.sanger.ac.uk) includes information on peptidase inhibitors as well as on peptidases and their substrates. Displays have been put in place to link peptidases and inhibitors together. The classification of protein peptidase inhibitors is continually being revised, and currently inhibitors are grouped into 67 families based on comparisons of protein sequences. These families can be further grouped into 38 clans based on comparisons of tertiary structure. Small molecule inhibitors are important reagents for peptidase characterization and, with the increasing importance of peptidases as drug targets, they are also important to the pharmaceutical industry. Small molecule inhibitors are now included in MEROPS and over 160 summaries have been written.

Structure and function of invertebrate Kazal-type serine proteinase inhibitors

Proteinases and proteinase inhibitors are involved in several biological and physiological processes in all multicellular organisms. The proteinase inhibitors function as modulators for controlling the extent of deleterious proteinase activity. The Kazal-type proteinase inhibitors (KPIs) in family I1 are among the well-known families of proteinase inhibitors, widely found in mammals, avian and a variety of invertebrates. Like those classical KPIs, the invertebrate KPIs can be single or multiple domain proteins containing one or more Kazal inhibitory domains linked together by peptide spacers of variable length. All invertebrate Kazal domains of about 40-60 amino acids in length share a common structure which is dictated by six conserved cysteine residues forming three intra-domain disulfide cross-links despite the variability of amino acid sequences between the half-cystines. Invertebrate KPIs are strong inhibitors as shown by their extremely high association constant of 10(7)-10(13)M(-1). The inhibitory specificity of a Kazal domain varies widely with a different reactive P(1) amino acid. Different invertebrate KPI domains may arise from gene duplication but several KPI proteins can also be derived from alternative splicing. The invertebrate KPIs function as anticoagulants in blood-sucking animals such as leech, mosquitoes and ticks. Several KPIs are likely involved in protecting host from microbial proteinases while some from the parasitic protozoa help protecting the parasites from the host digestive proteinase enzymes. Silk moths produce KPIs to protect their cocoon from predators and microbial destruction.

Insights into the venom composition of the ectoparasitoid wasp Nasonia vitripennis from bioinformatic and proteomic studies

With the Nasonia vitripennis genome sequences available, we attempted to determine the proteins present in venom by two different approaches. First, we searched for the transcripts of venom proteins by a bioinformatic approach using amino acid sequences of known hymenopteran venom proteins. Second, we performed proteomic analyses of crude N. vitripennis venom removed from the venom reservoir, implementing both an off-line two-dimensional liquid chromatography matrix-assisted laser desorption/ ionization time-of-flight (2D-LC-MALDI-TOF) mass spectrometry (MS) and a two-dimensional liquid chromatography electrospray ionization Founer transform ion cyclotron resonance (2D-LC-ESI-FT-ICR) MS setup. This combination of bioinformatic and proteomic studies resulted in an extraordinary richness of identified venom constituents. Moreover, half of the 79 identified proteins were not yet associated with insect venoms: 16 proteins showed similarity only to known proteins from other tissues or secretions, and an additional 23 did not show similarity to any known protein. Serine proteases and their inhibitors were the most represented. Fifteen nonsecretory proteins were also identified by proteomic means and probably represent so-called 'venom trace elements'. The present study contributes greatly to the understanding of the biological diversity of the venom of parasitoid wasps at the molecular level.

High sequence variability among hemocyte-specific Kazal-type proteinase inhibitors in decapod crustaceans

Crustacean hemocytes were found to produce a large number of transcripts coding for Kazal-type proteinase inhibitors (KPIs). A detailed study performed with the crayfish Pacifastacus leniusculus and the shrimp Penaeus monodon revealed the presence of at least 26 and 20 different Kazal domains from the hemocyte KPIs, respectively. Comparisons with KPIs from other taxa indicate that the sequences of these domains evolve rapidly. A few conserved positions, e.g. six invariant cysteines were present in all domain sequences whereas the position of P1 amino acid, a determinant for substrate specificity, varied highly. A study with a single crayfish animal suggested that even at the individual level considerable sequence variability among hemocyte KPIs produced exist. Expression analysis of four crayfish KPI transcripts in hematopoietic tissue cells and different hemocyte types suggest that some of these KPIs are likely to be involved in hematopoiesis or hemocyte release as they were produced in particular hemocyte types or maturation stages only.

A three-domain Kazal-type serine proteinase inhibitor exhibiting domain inhibitory and bacteriostatic activities from freshwater crayfish Procambarus clarkii

In crustaceans, Kazal-type serine proteinase inhibitors in hemolymph are believed to function as regulators of the host-defense reactions or inhibitors against proteinases from microorganisms. In this study, we report a Kazal-type serine proteinase inhibitor, named hcPcSPI1, from freshwater crayfish (Procambarus clarkii). We found that hcPcSPI1 is composed of a putative signal peptide, an RGD motif, and three tandem Kazal-type domains with the domain P1 residues L, L and E, respectively. Mainly, hcPcSPI1 was detected in hemocytes as well as in the heart, gills, and intestine at both the mRNA and protein levels. Quantitative real-time PCR analysis showed that hcPcSPI1 in hemocytes was upregulated by the stimulation of Esherichia coli (8099) or became decreased after a white spot syndrome virus (WSSV) challenge. In addition, hcPcSPI1 and its three independent domains were overexpressed and purified to explore their potential functions. All four proteins inhibited subtilisin A and proteinase K, but not alpha-chymotypsin or trypsin. Recombinant hcPcSPI1 could firmly attach to Gram-negative bacteria E. coli and Klebsiella pneumoniae; Gram-positive bacteria Bacillus subtilis, Bacillus thuringiensis and Staphylococcus aureus; fungi Candida albicans and Saccharomyce cerevisiae, and only domain 1 was responsible for the binding to E. coli and S. aureus. In addition, recombinant hcPcSPI1 was also found to possess bacteriostatic activity against the B. subtilis and B. thuringiensis. Domains 2 and 3 contributed mainly to these bacteriostatic activities. All results suggested that hcPcSPI1 might play important roles in the innate immunity of crayfish.

Kazal-type serine proteinase inhibitors from the black tiger shrimp Penaeus monodon and the inhibitory activities of SPIPm4 and 5

Serine proteinase inhibitors (SPIs) play important roles in physiological and immunological processes involving proteinases in all multicellular organisms. In black tiger shrimp Penaeus monodon, nine different Kazal-type SPIs, namely SPIPm1-9, were identified from the cDNA libraries of hemocyte, hepatopancreas, hematopoietic tissue, ovary and lymphoid organ. They are multi-domain SPIs containing 2-7 and possibly more Kazal domains. Two interesting cDNA clones, SPIPm4 and SPIPm5 coding for two-domain Kazal-type SPIs, were identified from the heat-treated hemocyte cDNA libraries. The SPIPm4 and SPIPm5 consist of open reading frames of 387 and 399 bp coding for polypeptides of 128 and 132 amino acids with putative signal peptides of 21 and 19 amino acid residues and mature SPIs of 107 and 113 amino acid residues, respectively. Recombinant expression in an Escherichia coli expression system yielded recombinant proteins, rSPIPm4 and rSPIPm5, with molecular masses of 12.862 and 13.433 kDa, respectively. The inhibitory activities of SPIPm4 and SPIPm5 were tested against trypsin, chymotrypsin, subtilisin and elastase. The SPIPm4 exhibited potent inhibitory activity against subtilisin and weakly against chymotrypsin whereas the SPIPm5 strongly inhibited subtilisin and elastase. The inhibition was a competitive type with inhibition constants (K(i)) of 14.95 nM for SPIPm4 against subtilisin, 4.19 and 59.64 nM, respectively, for SPIPm5 against subtilisin and elastase. They had no bacteriostatic effect against Gram-positive bacteria: Bacillus subtilis, Bacillus megaterium, Staphylococcus aureus, and Gram-negative bacteria: Vibrio harveyi 639, E. coli JM109. Gene expression study revealed that the SPIPm5 gene was up-regulated in response to heat treatment suggesting the involvement of SPIs in stress responses.

Characterization, kinetics, and possible function of Kazal-type proteinase inhibitors of Chinese white shrimp, Fenneropenaeus chinensis

Serine proteinase inhibitor plays an essential role in arthropods by restraining the activities of endogenic or exogenic serine proteinases. Four Kazal-type serine proteinase inhibitors, Fcspi-1-4, from the hepatopancreas of Chinese white shrimp, Fenneropenaeus chinensis, were cloned and identified. The open reading frames (ORFs) of Fcspis are 1389, 1236, 1080, and 939 base pairs, encode the pre-proteins of 462, 411, 359, and 312 amino acids and form the 9, 8, 7, and 6 typical Kazal domains, respectively. When analyzing the amino acid sequences of the four inhibitors, it was found that they might have been derived from the same transcript, which was subjected to alternative splicing, and none of the Kazal domains were identical within each inhibitor. Multiple alignments showed that the Kazal inhibitors were homologous with a conserved motif of Cx(3)Cx(6)VCGSDGxTYx(3)CxLx(5)Cx(5)ITx(6)GC. The results from RT-PCR indicated that the expression of Fcspis as a whole was upregulated by bacterial challenge, no obvious change was noticed after viral challenge, and Fcspi-1 had a similar expression pattern with that of Fcspis. Recombinant FcSPIs were successfully expressed in bacteria and purified for further study. Recombinant FcSPI-1 was sensitive to DTT and had thermal stability. The inhibitory kinetics assay suggested that rFcSPI-1 was a mixed-type fast tight binding inhibitor with inhibitory activities against subtilisin A at a molar ratio of 1:1, 1:2 against proteinase K, and 2:1 against elastase. It can firmly bound to two Gram-positive and one Gram-negative bacteria but without anti-bacterial ability. In addition, it inhibited the activities of both bacterial-secreted proteinases and natural chymotrypsin of Chinese white shrimp, suggesting that FcSPI-1 may participate in the immune defence response by inhibition of bacterial pathogen proteinases and possibly be involved in the regulation of shrimp proteinase activity.

Domain inhibitory and bacteriostatic activities of the five-domain Kazal-type serine proteinase inhibitor from black tiger shrimp Penaeus monodon

Serine proteinase inhibitors (SPIs) in multi-cellular organisms are important modulators of proteinase activities in various biological processes. A five-domain Kazal-type SPI SPIPm2 from the black tiger shrimp Penaeus monodon is presumably involved in innate immune response. The SPIPm2 with the domain P1 residues T, A, E, K and E was isolated from the hemocyte cDNA libraries and found to strongly inhibit subtilisin and elastase, and weakly inhibit trypsin. To unravel further the inhibitory activity of each domain, we subcloned, over-expressed and purified each individual SPI domain. Their inhibitory specificities against trypsin, subtilisin and elastase were determined. Domain 1 was found to be inactive. Domains 2, 3 and 5 inhibited subtilisin. Domain 2 inhibited also elastase. Domain 4 weakly inhibited subtilisin and trypsin. The intact SPIPm2 inhibitor was found to possess bacteriostatic activity against the Bacillus subtilis but not the Bacillus megaterium, Staphylococcus aureus, Vibrio harveyi 639 and Escherichia coli JM109. Domains 2, 4 and 5 contributed to this bacteriostatic activity.

Inhibition mechanism and the effects of structure on activity of male reproduction-related peptidase inhibitor Kazal-type (MRPINK) of Macrobrachium rosenbergii

In our previous reports, a Kazal family serine protease inhibitor, male reproduction-related peptidase inhibitor Kazal-type (MRPINK) has been identified from the prawn, Macrobrachium rosenbergii, and discovered having an inhibitory effect on the sperm gelatinolytic activity. MRPINK was predicated to inhibit chymotrypsin since it contains leucine and proline at P(1) positions of the two domains, respectively. In this report, recombinant MRPINK was as expected found to specifically inhibit chymotrypsin, but no inhibition was detected against trypsin or thrombin. By the analysis of kinetic tests, the inhibition mechanism of MRPINK was determined to be typical competitive model with K (i) of 354 nM. To elucidate the effects of structure on activity of MRPINK, the mutants (domain-1 only, domain-2 only, MRPINK(P88I), MRPINK(L37K), MRPINK(L37A), and MRPINK(L37G)) were prepared and their inhibitory activities assayed. The results showed that domain-2 was the key contributor to the inhibition of chymotrypsin (K (i) of 416 nM) and P(1) Pro was crucial for the activity. Nevertheless, whether the P(1) amino acid residue was Leu, or even if it was replaced by Lys, Ala, or Gly, domain-1 was ineffective to the activity.