A very-high-density lipoprotein with clotting ability from hemolymph of sand crayfish, Ibacus ciliatus

Identification of key immune and stress related genes and pathways by comparative analysis of the gene expression profile under multiple environmental stressors in pacific white shrimp (Litopenaeus vannamei)

Water salinity, pH, and nitrite concentration are considered environmental factors affecting the growth rate, survival, health, and physiological conditions of aquatic animals. The identification of key genes that are involved in the response to environmental stressors is essential for controlling stress in aquatic animals and sustainable aquaculture. In this study, RNA sequencing was performed to identify the differentially expressed genes (DEGs) and biological pathways that are involved in the response of the hepatopancreas to environmental stressors, including low salinity stress, nitrite stress, low pH stress, and high pH stress. The DEGs were enriched in biological pathways related to immune response, energy metabolism, oxidative stress response, hemostasis, and enzymatic activity of the hepatopancreas. In addition to the identification of DEGs related to each stressor, some DEGs were found to be expressed among all groups. The most important overlapping DEGs under multiple stressors were juvenile hormone esterase-like protein 2 (JHE-like), myosin light chain, C-type lectin 2, myosin-9-like, anti-lipopolysaccharide factor 1 (ALF-1), peroxisomal acyl-coenzyme An oxidase 1-like (ACX1), hepatic lectin-like, venom phosphodiesterase 2-like, hemolymph clottable protein-like (CP), cathepsin L, and Ras-like protein 2. The results of the present study provide additional information regarding the transcriptional response of the hepatopancreas to low salinity, nitrite, low pH, and high pH stress. Moreover, the discovery of several overlapping DEGs among different stressors provided a better understanding of the molecular function of the hepatopancreas.

Immuno-stimulatory effect and toxicology studies of salt pan bacteria as probiotics to combat shrimp diseases in aquaculture

The shrimp aquaculture industry has experienced serious economic losses due to diseases caused by Vibrio species. The application of antibiotics to combat diseases has led to environmental hazards, antibiotic-resistance in pathogens and accumulation of antibiotics in tissues. This study explores the use of probiotics as an alternative to antibiotics. A probiotic consortium SFSK4 (comprising salt pan bacteria Bacillus licheniformis TSK71, Bacillus amyloliquefaciens SK27, Bacillus subtilis SK07, Pseudomonas sp. ABSK55) was used as a water additive during shrimp culture. It significantly increased shrimp (Litopenaeus vannamei) immunity i.e. total hemocyte count, phagocytosis, total plasma protein, respiratory burst and bactericidal activity as compared to the control. It also stimulated the phenoloxidase activity by two-fold. Proteomic analysis revealed the differential expression of 50 immune proteins (39 up-regulated and 11 down-regulated) in SFSK4 treated shrimps. Four major immune modulation proteins viz. Caspase2, GTPase activating protein, Hemocyanin and Glucan pattern-recognition lipoprotein involved in cell mediated immune response were identified in SFSK4 treated shrimp hemolymph. SFSK4 decreased shrimp mortality by more than 50% against pathogens. Toxicology studies revealed that administration of the highest dose of probiotic (10¹² CFU/mL) showed no adverse effect on shrimp survival (LC₅₀ analysis) and neither exhibited cytotoxicity. Genotoxicity study confirmed that the probiotic did not cause DNA damage in shrimps. The findings suggest that the probiotic SFSK4 is an eco-friendly water additive to enhance shrimp immunity against diseases in aquaculture, which could help curtail environmental hazards as an effective alternative to antibiotics.

Crustacean Hemolymph Lipoproteins

Lipoproteins mediate the transport of apolar lipids in the hydrophilic environment of physiological fluids such as the vertebrate blood and the arthropod hemolymph. In this overview, we will focus on the hemolymph lipoproteins in Crustacea that have received most attention during the last years: the high density lipoprotein/β-glucan binding proteins (HDL-BGBPs), the vitellogenins (VGs), the clotting proteins (CPs) and the more recently discovered large discoidal lipoproteins (dLPs). VGs are female specific lipoproteins which supply both proteins and lipids as storage material for the oocyte for later use by the developing embryo. Unusual within the invertebrates, the crustacean yolk proteins-formerly designated VGs-are more related to the ApoB type lipoproteins of vertebrates and are now termed apolipocrustaceins. The CPs on the other hand, which are present in both sexes, are related to the (sex specific) VGs of insects and vertebrates. CPs serve in hemostasis and wound closure but also as storage proteins in the oocyte. The HDL-BGBPs are the main lipid transporters, but are also involved in immune defense. Most crustacean lipoproteins belong to the family of the large lipid transfer proteins (LLTPs) such as the intracellular microsomal triglyceride transfer protein, the VGs, CPs and the dLPs. In contrast, the HDL-BGBPs do not belong to the LLTPs and their relationship with other lipoproteins is unknown. However, they originate from a common precursor with the dLPs, whose functions are as yet unknown. The majority of lipoprotein studies have focused on decapod crustaceans, especially shrimps, due to their economic importance. However, we will present evidence that the HDL-BGBPs are restricted to the decapod crustaceans which raises the question as to the main lipid transporting proteins of the other crustacean groups. The diversity of crustaceans lipoproteins thus appears to be more complex than reflected by the present state of knowledge.

The clotting system in decapod crustaceans: History, current knowledge and what we need to know beyond the models

Hemolymph coagulation is among the major arms of the humoral immune response in crustaceans. According to the current model, hemolymph clotting in decapod crustacean relies mostly on the polymerization of the plasmatic clotting protein (CP) which is directly promoted by calcium-depended transglutaminase (TGase) released from hemocytes upon microbial stimulus or injury. However, the type of hemocytes containing TGase, and hence how the TGase is released, might vary among species. Thus, we discourse here about possible mechanisms for clotting initiation. On the other hand, the initiation of coagulation reaction in the absence of microbial elicitors is poorly understood and seems to involve hemocytes lability, yet the mechanism remains unknown. A cellular clottable protein called coagulogen, different to the plasma CP, occurs in several species and could be related with the immune response, but the biological relevance of this protein is unknown. It is also demonstrated that the clotting response is actively involved in defense against pathogens. In addition, both TGase and the CP show pleiotropic functions, and although both proteins are relatively conserved, some of their physic-chemical properties vary significantly. The occurrence of differences in the clotting system in crustaceans is conceivable given the high number of species and their diverse ecology. Results from still non-studied decapods may provide explanation for some of the issues presented here from an evolutionary perspective.

Impact of ammonia exposure on coagulation in white shrimp, Litopenaeus vannamei

Ammonia (un-ionized plus ionized ammonia as nitrogen), the end product of protein catabolism, is produced by decomposing organic matter. In aquaculture, shrimp are commonly exposed to high concentrations of ammonia that induces immunological and histological changes. The purpose of this study was to evaluate the effects on hemolymph coagulation time, transglutaminase (TG) activity as well as TG and clottable protein (CP) genes expressions in Litopenaeus vannamei when exposed to ambient ammonia-nitrogen (N) at 0, 1, 5, and 10mg/L for 0, 2, and 7 days. The actual concentrations in control and tests solution were 0.001, 1.15, 5.11, and 11.68mg/L for ammonia-N, and 7×10(-5), 0.080, 0.357, and 0.815mg/L for NH3-N (unionized ammonia). Delayed coagulation time following exposure to 5 and 10mg/L of ambient ammonia-N for 7 days, and increased transglutaminase (TG) activity following exposure to 5 and 1mg/L of ambient ammonia-N for 2 and 7 days, respectively, were observed. Downregulated TG expression and upregulated clottable protein (CP) expression in the hemocytes of L. vannamei exposed to 10 and 5mg/L of ambient ammonia-N for 2 and 7 days, respectively, were shown. These results indicated that ambient ammonia-N (>5mg/L) and NH3-N (>0.357mg/L) interrupted coagulation and down-regulated TG gene expression in L. vannamei, which caused ecotoxicity on immune deficiencies and may contribute the increased susceptibility to infection by pathogens.

Molecular and immunological responses of the giant freshwater prawn, Macrobrachium rosenbergii, to the organophosphorus insecticide, trichlorfon

Trichlorfon is an organophosphorus (OP) insecticide that is used as an agriculture pesticide to destroy insects, a human medicine to combat internal parasites, and an ectoparasiticide in the livestock and aquaculture industries, but which has caused aquatic toxicity in the prawn industry. The aim of this study was to investigate the effects of trichlorfon on molecular and enzymatic processes of the immunological response of the giant freshwater prawn, Macrobrachium rosenbergii, at 0, 0.2, and 0.4mgL(-1) with 0, 3, 6, 12, and 24h of exposure. The total hemocyte count (THC), respiratory bursts (RBs), phenoloxidase (PO) activity, and superoxide dismutase (SOD) activity were examined to evaluate immunological responses and oxidative stress. Results showed that THCs of the prawn exposed to trichlorfon at both concentrations (0.2 and 0.4mgL(-1)) had increased after 12 and 24h; SOD and PO activities had significantly increased at 3h, whereas production of RBs had dramatically increased as oxidative stress at each sampling time after exposure to trichlorfon compared to the control. A potential biomarker of OPs, acetylcholinesterase (AChE) revealed a significant decrease after exposure for 6h, and showed a time-dependent tendency. Immune gene expressions, including prophenoloxidase (proPO), the lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP), peroxinectin (PE), α2-macroglubulin (α2M), transglutaminase (TG), and copper, zinc (Cu,Zn)-SOD, of prawns exposed to trichlorfon at 0, 0.2, and 0.4mgL(-1) for 0, 6, and 24h were further evaluated. Expressions of all of the immune genes significantly decreased when prawns were exposed to 0.4mgL(-1) trichlorfon for 24h, and among them, an increase in SOD expression was seen after exposure to 0.4mgL(-1) for 6h. Prawns exposed to trichlorfon within 24h exhibited the decrease of circulating hemocytes, and also the induction of oxidative stress, which caused subsequent damage to DNA formation of immune genes. From these results, we concluded that immunological responses and immune gene expressions of prawn exposed to trichlorfon at 0.4mgL(-1) for 24h were perturbed, thus causing a deficiency in immunity and subsequent increased susceptibility to pathogen infections.

Proteomic identification of the related immune-enhancing proteins in shrimp Litopenaeus vannamei stimulated with vitamin C and Chinese herbs

Recently, strong interest has been focused on immunostimulants to reducing the diseases in shrimp aquaculture. However, information regarding to the related immune-enhancing proteins in shrimps is not available yet. In this study, vitamin C (Vc), Chinese herbs (CH), and the mixture of vitamin C and Chinese herbs (Mix) were tested for their enhancement on shrimp's immune activity. Compared with those in the control group, values of phenoloxidase (PO), superoxide dismutase (SOD) and antibacterial (Ua) activity in the Mix-treated group were improved significantly 12 or 24 days after the treatment. The cumulative mortality was also lower in the Mix-treated group after infection with Vibrio parahemolyticus. Furthermore, comparative proteomic approach was used to assess the protein expression profile in shrimps. Approximately 220-290 and 300-400 protein spots were observed in the 2-DE gels. Among them, 29 and 28 altered proteins from hemocytes and hepatopancreas, respectively, were subjected to matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS) analysis. The results revealed that the main altered proteins showed high homologies with Litopenaeus vannamei hemocyanin, hemolymph clottable protein, hemoglobin beta, cytosolic MnSOD, trypsin, cathepsin I(L) and zinc proteinase Mpc1. Together, these studies found Vc and CH were suitable immunostimulants to shrimp L. vannamei, and 7 altered proteins could be involved in the enhanced immune activities.

Insect hemolymph clotting

The clot's appearance in different large-bodied insects has been described, but until recently, little was known about any insect clot's molecular makeup, and few experiments could directly test its function. Techniques have been developed in Drosophila (fruit fly) larvae to identify clotting factors that can then be tested for effects on hemostasis, healing, and immunity. This has revealed unanticipated complexity in the hemostatic mechanisms in these larvae. While the clot's molecular structure is not yet fully understood, progress is being made, and the loss of clotting factors has been shown to cause subtle immune defects. The few similarities between coagulation in different insect species and life stages, and the current state of knowledge about coagulation in insects are discussed.

Expression of clottable protein of tiger shrimp (Penaeus monodon) in gonads and its possible role as nutrient source for the embryo

We have investigated the expression of clottable protein (CP) in gonad of tiger shrimp (Penaeus monodon) and extent of its phosphorylation. Polyclonal antibodies against purified CP were prepared from rabbit serum. Using this anti-CP antiserum, the temporal expression of CP in gonads of tiger shrimp was analyzed. It was found that the CP occurs only in mature ovaries but not in immature ovaries and testes. Results of RT-PCR confirmed that these tissues expressed low levels of CP mRNA transcripts. Upon eyestalk-ablation, the ovaries in female shrimps were induced to develop, and the CP expression levels in ovaries were traced chronically by RT-PCR analyses. The expression level peaked on day 3 with an increase of about 40 folds relative to the basal level and returned to normal level (as the control shrimp) at day 12. The shrimp embryos at different intervals from spawning to 16h post-spawning were also collected, and it was found that CP contents were gradually decreased in the embryos until the nauplii were hatched. In addition, purified CP was shown to react with specific anti-phosphoserine, anti-phosphothreonine, and anti-phosphotyrosine antibodies suggesting that CP is a phosphoprotein with all types of phosphorylations. Taken together the results suggest that expression of CP in shrimp ovaries is coupled to ovarian development and CP possibly supply nutrition for shrimp embryo.

Cloning and characterization of hemolymph clottable proteins of kuruma prawn (Marsupenaeus japonicus) and white shrimp (Litopenaeus vannamei)

The hemolymph clottable protein (CP) of Marsupenaeus japonica (designated as Mj-CP) was purified by a DEAE anion-exchanger and a Sepharose CL-6B gel filtration column. In the presence of Ca(2+), it formed stable clots in vitro upon the addition of the hemocytes lysate containing transglutaminase. Results of gel filtration chromatography and SDS-PAGE indicated that Mj-CP mainly existed as disulfide-linked homodimers of 390 kDa. Specific primers were designed; PCR as well as RACE help to clone and sequence Mj-CP cDNA of 5660 bp. The predicted CP-precursor contains a signal peptide followed by a subunit of 1671 amino acids (isoelectric point 5.6), including two RGD motifs and three potential N-glycosylation sites. Mj-CP is structurally 80% and 38% identical to the CPs of tiger shrimp and crayfish, respectively. Likewise, CP cDNA of white shrimp (Litopenaeus vannamei) was also cloned and sequenced; the predicted CP has 1666 amino acid residues and an isoelectric point of 5.2. Both CPs bear potential transglutaminase cross-linking sites, i.e. seven Ser-Lys-Thr repeats near the N-terminus, a Ser- and Gln-rich region in the middle, and polyGln (n=8-11) near the C-terminus. Phylogenetic analyses of crustacean CPs and vitellogenins revealed divergent evolution of the two protein families. By RT-PCR, the sub-cuticular epidermis was identified as one of the major tissues that express CP in M. japonica.

Tissue-specific expression and regulation of the haemolymph clottable protein of tiger shrimp (Penaeus monodon)

The clottable protein (CP) involved in Penaeus monodon haemolymph coagulation has previously been characterized and cloned. Polyclonal antibodies against purified CP were also prepared from rabbit serum. By Western blot analyses, we showed occurrence of CP in the shrimp central nervous system, gill, and lymphoid organ. Results of RT-PCR further indicated that the central nervous system, gill, and lymphoid organ transcribed more CP, heart and hepatopancreas transcribed less, while the haemocytes and the muscle did not. We further analyzed the CP distribution within shrimp lymphoid organ by immunohistochemical method, CP was found to localise in stromal cells of lymphoid organ rather than in the developing haemocytes. In addition, concentrations and regulation of the plasma CP under normal and artificially traumatic conditions were studied with rocket immunoelectrophoresis. The average plasma CP concentration in normal intermolt shrimps was elevated from 3 mg ml(-1) to above 12 mg ml(-1) after successive blood-withdrawing for a week. The production and secretion of CP apparently were increased more than 4 folds to compensate its loss. Our result also suggested that the shrimp sinus gland endocrine system is not directly required for the expression and up-regulation of CP.

Hemolymph clotting in crustaceans: Implications for neuropeptide extraction from invertebrate hemolymph

The hemolymph of invertebrates contains factors that facilitate clotting as a defense mechanism for injury. However, the clotting process may impair the measurement of hormone titers by interfering with the extraction of peptides. Using hemolymph from freshwater crayfish, our results demonstrate that hemolymph clotting appears to reduce both the amount of an endogenous peptide(s) (Dippu-AST 11-like) extracted from hemolymph, as well as the amount of spiked peptide tracer ([125I]-Dippu-AST 11) recovered from hemolymph. The efficacy of peptide extraction from hemolymph was improved by collecting the hemolymph into a variety of different media prior to hemolymph coagulation. Hemolymph samples collected into media containing the anticoagulant, citrate, had the highest amount of endogenous Dippu-AST 11-like peptide extracted as well as the highest percent recovery of spiked tracer.

Purification and partial characterization of the plasma clotting protein from the pink shrimp Farfantepenaeus paulensis

A clotting protein (CP) was purified from the plasma of the pink shrimp Farfantepenaeus paulensis by sequential anion-exchange chromatography. The shrimp CP was able to form stable clots in vitro in the presence of hemocyte lysate and Ca2+, suggesting that the clotting reaction is catalyzed by a Ca2+-dependent transglutaminase present in shrimp hemocytes. Dansylcadaverine was incorporated into the shrimp CP in the presence of endogenous transglutaminase (hemocyte lysate), confirming that the shrimp purified CP is the substrate for the transglutaminase enzyme. The molecular mass of the CP was determined by gel filtration to be 341 kDa and 170 kDa by SDS-PAGE under reducing conditions. These results suggest that the shrimp CP consists of two identical subunits, covalently linked by disulphide bonds. The amino acid sequence at the N-terminus was 100% identical to that of the penaeids Litopenaeus vannamei and Penaeus monodon and 66% to 80% identical to the CPs of other decapods. This is the first report of a CP characterization in an Atlantic penaeid species. Further studies, including a molecular cloning approach would enable to detect which tissues express the gene of the clotting protein. It would be also useful to understand the mechanism by which the coagulation time is delayed in shrimps under stress conditions.

Starvation and diet composition affect mRNA levels of the high density-lipoprotein-β glucan binding protein in the shrimp Litopenaeus vannamei

A high density lipoprotein-beta glucan binding protein (HDL-BGBP) is synthesized in the hepatopancreas of the white shrimp Litopenaeus vannamei and secreted to the hemolymph. Recently, we reported the HDL-BGBP full length cDNA sequence and found that the predicted polypeptide is larger than the mature protein and also, that it contains a long 5'- and 3'-UTRs that may be involved in transcript level regulation. To test whether starvation and feeding may play a role in regulating HDL-BGBP mRNA levels, two different stimuli were evaluated: starvation and composition of diets. After 24 h, the steady state HDL-BGBP mRNA levels of starved shrimp decreased, suggesting that synthesis of the lipoprotein is less required in the absence of food. When shrimp were fed with diets containing different concentrations of protein and lipids, changes in HDL-BGBP mRNA levels were also detected. Shrimp fed the lower concentration of protein and lipid feed accumulated higher levels of HDL-BGBP mRNA. These results indicate that feeding influences HDL-BGBP transcript levels in the hepatopancreas.

Response of Penaeus indicus females at two different stages of ovarian development to a lethal infection with Vibrio penaeicida

An association between vitellogenesis and the immune system was suggested in crustaceans from studies on plasma lipoproteins. The present research studies the effect of an experimentally induced bacterial infection on vitellogenesis in females of the shrimp Penaeus indicus, as a model for penaeid species. Pre-vitellogenic and vitellogenic P. indicus females were experimentally infected with an extremely pathogenic bacterium, Vibrio penaeicida. The peak in mortality occurred earlier in pre-vitellogenic animals than in vitellogenic ones, although the final mortality level ( approximately 64-74%) 52h post-infection was nearly the same for the two groups. Twenty hours after infection, the total number of haemocytes was significantly reduced in vitellogenic females while there was no change in the pre-vitellogenic group. Protein synthesis in ovaries was not significantly affected by infection, at the two stages of ovarian development. No differences were found in mRNA levels of shrimp ovarian peritrophin protein (SOP), but preliminary results showed that mRNA expression of vitellin (VT) was reduced in a heavily infected vitellogenic female. The total amount of lipids in the haemolymph of vitellogenic females was almost twice higher than that of pre-vitellogenic ones. However, there was no change in the total content of lipids, lipid classes and fatty acid distribution in haemolymph or hepatopancreas following infection. Although vitellogenic and pre-vitellogenic females probably respond differently to a lethal bacterial infection, physiological differences may be concealed by the rapid onset of mortality.

Molecular characterization of the bifunctional VHDL-CP from the hemolymph of white shrimp Penaeus vannamei

A very high-density lipoprotein (VHDL) purified from the hemolymph of the white shrimp Penaeus vannamei is shown to be identical to the clotting protein (CP) previously reported from the same organism based on size, subunits and N-terminal amino acid sequence. The approximately 440-kDa protein, a homodimer of approximately 200-kDa subunits, was present in KBr gradient fractions ranging in density from 1.155 to 1.212 g/ml. Samples of VHDL after purification by strong cation exchange chromatography were subjected to electrophoresis on native polyacrylamide gels. Lipids associated with the VHDL were detected by Sudan Black and Oil Red O staining and comprise 9-15% of the purified protein. Circular dichroism of VHDL-CP indicates that the alpha-helix content of the VHDL-CP is 32%, while beta-sheets correspond to 33%, closely resembling the secondary structure of CP from the shrimp Penaeus monodon and, remarkably, the secondary structure of very high-density lipophorin E (VHDLpE) from the tobacco hornworm, Manduca sexta.

A transglutaminase involved in the coagulation system of the freshwater crayfish, Pacifastacus leniusculus. Tissue localisation and cDNA cloning

The crayfish haemolymph can form stable and insoluble clots by a transglutaminase (TGase)-catalysed crosslinking reaction between the soluble clotting protein molecules from the plasma. The crayfish haemocytes, both semigranular and granular cells, as well as the muscle tissue, contain TGase activity, whereas the hepatopancreas and plasma have no TGase activity. A 3199 bp cDNA encoding a TGase was isolated from a crayfish haemocyte cDNA library. The deduced protein comprises 766 amino acid residues and has a calculated molecular mass of between 85,930 and 86,034 kDa due to four amino acid variations. This gene is expressed as a single 4.9 kb transcript exclusively in the haemocytes and at very low levels in muscle and the hepatopancreas. Sequence comparison shows that this TGase has significant similarities to other TGases from invertebrates and mammals.

Proteinase activity in the white shrimp (Penaeus vannamei) clotting protein

The clottable protein (CP) was isolated from white shrimp, Penaeus vannamei plasma as a 400-kDa protein that splits to two identical 200-kDa subunits when it is reduced with 2-ME. However, using DTT as reducing agent, four main bands were observed; two of them (179 and 125 kDa) had the same N-terminus sequence of the intact CP, indicating that most fragmentation occurs in the carboxy-terminus. The proteinase activity of reduced CP was detected using azoalbumin as substrate. Proteinase activity was only detected in the reduced, but not alkylated protein. Trypsin and papain, as well as soybean trypsin inhibitor and E64, were included for comparison. Proteolytic activity of reduced CP was inhibited by E64, but not by STI, indicating that such activity corresponds to a cysteine type proteinase.

Partial characterization of vitellin and localization of vitellogenin production in the terrestrial isopod, Armadillidium vulgare

Vitellins were purified separately from ovaries and eggs of the isopod, Armadillidium vulgare. Ovarian vitellin consisted of at least six proteins with relative molecular masses of 205, 200, 185, 180, 122 and 112 kDa. The larger four proteins disappeared in eggs within a week after oviposition and a 59-kDa protein appeared thereafter. The amino-terminal amino acid sequences of these vitellin proteins were identical except for the ovarian 112 kDa, egg 112 kDa and 59 kDa proteins, and showed considerable similarity to those of known vitellogenins from other animals. Comparison of tryptic peptide maps of the 122 and 112 kDa proteins from eggs on reversed-phase HPLC and sequence identification of two randomly selected peaks having the same retention times indicated that two peptides were mostly similar in sequence. PCR-assisted cloning of the 5' region of a cDNA (591 bp) encoding vitellogenin revealed the presence of a signal peptide consisting of 16 amino acid residues and clarified the structural relationship among the protein components except for the ovarian 112 kDa and the egg 59 kDa proteins. Northern blot analysis revealed that the fat body is the main vitellogenin producing organ.

Molecular cloning and characterization of a hemolymph clottable protein from tiger shrimp (Penaeus monodon)

To investigate the coagulation system in crustacean decapoda, a homodimeric glycoprotein of 380 kDa was purified from the hemolymph of tiger shrimp (Penaeus monodon) by sequential DEAE anion exchange chromatography. The purified protein was coagulated by the shrimp hemocyte transglutaminase in the presence of Ca2+. The clottable protein contains 44% alpha helices and 26% beta sheets as determined by circular dichroism spectra. Its conformation is stable in buffer of pH 4-9. To solve its primary structure, partial sequences of the purified polypeptides from cyanogen bromide cleavage and endopeptidase digestion were also determined. A shrimp cDNA expression library was constructed. By combination with antibody screening, reverse transcriptase PCR using degenerate primers from determined amino acid sequences and cDNA library screening with digoxigenin-labeled DNA probes, the entire cDNA of 6124 bp was obtained. This cDNA encodes a protein of 1670 amino acids, including a 14-amino acid signal peptide. With four potential N-glycosylation sites, the clottable protein was found to contain 3.8% high-mannose glycan; and Man8GlcNAc and Man9GlcNAc were released upon endo-beta-N-acetylglucosaminidase hydrolysis. Upon conducting a protein sequence database survey, the shrimp clottable protein shows 36% identities to the crayfish clotting protein and lower similarities to members of insect vitellogenins, apolipoprotein B and mammalian von Willebrand factor. Notably, a region rich in Gln residues, a polyGln motif and five Ser-Lys-Thr-Ser repeats are present in the shrimp protein, suggesting this protein might be a transglutaminase substrate. Northern blot analysis revealed that the clottable protein is expressed in most of the shrimp tissues but not in the mature hemocytes.

The crayfish plasma clotting protein: a vitellogenin-related protein responsible for clot formation in crustacean blood

Coagulation in crayfish blood is based on the transglutaminase-mediated crosslinking of a specific plasma clotting protein. Here we report the cloning of the subunit of this clotting protein from a crayfish hepatopancreas cDNA library. The ORF encodes a protein of 1,721 amino acids, including a signal peptide of 15 amino acids. Sequence analysis reveals that the clotting protein is homologous to vitellogenins, which are proteins found in vitellogenic females of egg-laying animals. The clotting protein and vitellogenins are all lipoproteins and share a limited sequence similarity to certain other lipoproteins (e.g., mammalian apolipoprotein B and microsomal triglyceride transfer protein) and contain a stretch with similarity to the D domain of mammalian von Willebrand factor. The crayfish clotting protein is present in both sexes, unlike the female-specific vitellogenins. Electron microscopy was used to visualize individual clotting protein molecules and to study the transglutaminase-mediated clotting reaction. In the presence of an endogenous transglutaminase, the purified clotting protein molecules rapidly assemble into long, flexible chains that occasionally branch.