Molecular cloning and characterization of lipopolysaccharide- and beta-1,3-glucan-binding protein from the giant freshwater prawn Macrobrachium rosenbergii and its transcription in relation to foreign material injection and the molt stage

Characterization of a Lipopolysaccharide- and Beta-1,3-Glucan Binding Protein (LGBP) from the Hepatopancreas of Freshwater Prawn, Macrobrachium rosenbergii, Possessing Lectin-Like Activity

The study focuses on the isolation, characterization, and expression analysis of a lectin from the hepatopancreas of Macrobrachium rosenbergii. The protein was isolated by affinity chromatography on a melibiose-agarose column. The molecular weight of the native protein was found to be ~120 kDa which consists of a single polypeptide of ~39.5 kDa. On mass spectrometric analysis, the protein was identified as lipopolysaccharide- and beta-1,3-glucan binding protein (LGBP). LGBP showed hemagglutination with rabbit RBC like a lectin and its carbohydrate-binding specificity was determined by the hemagglutination inhibition test. The protein also showed antibacterial activity against two Gram-negative bacteria Vibrio harveyi and Aeromonas sobria, and one Gram positive bacteria Bacillus cereus in the disc diffusion test. Rabbit antiserum was raised against the purified LGBP and used to develop a sandwich ELISA system for quantitation of the protein in hepatopancreas and serum samples of M. rosenbergii. The expression of the LGBP transcripts in muscle, hepatopancreas, and gill tissues from M. rosenbergii juveniles at 72 h post-challenge of V. harveyi was not modulated as noticed in qPCR analysis. However, significant increases in the concentrations of LGBP protein in hepatopancreas (5.23 ± 0.45 against 3.43 ± 0.43 mg/g tissue in control) and serum (1.08 ± 0.14 against 0.61 ± 0.08 µg/ml in control) were observed in the challenged group of prawns in ELISA suggesting its putative role against bacterial infections. The study for the first time characterized the native LGBP of M. rosenbergii showing a multifunctional role in immunity.

Dietary supplementation of host‐associated lactic acid bacteria modulates growth, metabolic activities, and immune‐related gene expression in giant freshwater prawn, Macrobrachium rosenbergii

The present study was carried out to evaluate the dietary effects of host‐associated lactic acid bacteria on growth performance, metabolic enzyme activities, and immune response of Macrobrachium rosenbergii juveniles. To formulate the test diets, a control (Con) diet was supplemented with a commercial probiotic and three host‐derived bacteria Enterococcus faecalis (EC), Lactococcus lactis I (LC‐I), and L. lactis II (LC‐II), which were previously isolated from the gastrointestinal tract of adult individuals of M. rosenbergii. Juvenile M. rosenbergii (0.65 ± 0.008 g) were randomly stocked at 20 individuals/100 L of fiberglass tanks with three replications for each test diet. After 50 days, juveniles fed the diets LC‐I and LC‐II showed significantly higher (p < .05) weight gain, specific growth rate, and the lowest feed conversion ratio. The analyses of glutamic oxaloacetate transaminase and glutamic pyruvate transaminase in muscle and hepatopancreas revealed significantly (p < .05) reduced values in LC‐I fed juveniles. The total hemocyte count and phenoloxidase activity were significantly increased (p < .05) in LC‐I and LC‐II fed juveniles. The relative mRNA expression patterns of immune‐related α2‐M, LGBP, ProPO, Cu, Zn‐SOD, TG, PE, AKP, and ACP genes were significantly (p < .05) upregulated in juveniles fed with LC‐I followed by the diet LC‐II. Finally, the study suggests that the growth performance and immune response of M. rosenbergii can be improved through supplementation of host‐associated L. lactis bacteria for its higher production.

Research progress in innate immunity of freshwater crustaceans

Invertebrates lack adaptive immunity and innate immunity plays important roles in combating foreign invasive pathogens. Freshwater crustaceans, which are invertebrates, depend completely on their innate immune system. In recent years, many immune-related molecules in freshwater crustaceans, as well as their functions, have been identified. Three main immune signaling pathways, namely, Toll, immune deficiency (IMD), and Janus kinase-signal transducer activator of transcription (JAK/STAT) pathways, were found in freshwater crustaceans. A series of pattern recognition receptors (PRRs), including Toll receptors, lectins, lipopolysaccharide and β-1,3-glucan binding protein, scavenger receptors, Down syndrome cell adhesion molecules, and thioester-containing proteins, were reported. Prophenoloxidase activation system and antimicrobial peptide synthesis are two important immune effector systems. These components are involved in the innate immunity of freshwater crustaceans, and they function in the innate immune defense against invading pathogens. This review mainly summarizes innate immune signaling pathways, PRRs, and effector molecules in freshwater crustaceans.

Alginate from Sargassum siliquosum Simultaneously Stimulates Innate Immunity, Upregulates Immune Genes, and Enhances Resistance of Pacific White Shrimp (Litopenaeus vannamei) Against White Spot Syndrome Virus (WSSV)

Although alginate is known as an immunostimulant in shrimp, the comprehensive and simultaneous study on its activity to resolve the relationship of the hematological parameters, upregulation of immune-related gene expression, and resistance to pathogen has not been found in shrimp. We performed experiments to evaluate the effect and mechanism of alginate from S. siliquosum on Pacific white shrimp immune system. Hematological parameters were examined after oral administration of Na alginate in the shrimp. White spot syndrome virus (WSSV) was injected to the shrimp at 14 days, and its copy number was examined quantitatively (qRT-PCR). Immune-related gene expression was evaluated by qRT-PCR. Alginate increased some hematological immune parameters of shrimp. Before WSSV infection, expression levels of Toll and lectin genes were upregulated. The lectin gene were upregulated post infection, and the Toll gene in all the treatments were downregulated, except the shrimps fed with alginate at 6.0 g kg-1 at 48 h post infection (hpi). The shrimps fed with alginate at 6.0 g kg-1 were the most resistant and gave the least WSSV copy number at 48 hpi. Resistance of shrimps fed the alginate-supplemented diets against WSSV was significantly higher compared to that of the control treatment with 56% and 10% of survival rates, respectively. Oral administration of alginate did not affect the growth and total protein plasma. At 120 h post challenge, alginate treatment at 6.0 g kg-1 exhibited the highest survival rate. It is concluded that oral administration of alginate enhanced the innate immunity by upregulating immune-related gene expression. Consequently, the enhancement of the shrimp innate immunity improves the resistance against WSSV infection.

Expression of Macrobrachium rosenbergii lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) in Saccharomyces cerevisiae and evaluation of its immune function

Pattern recognition proteins (PRPs) activate the innate immune system in invertebrates, and lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) is an important PRP with various biological functions. Here, the open reading frame (ORF) of Macrobrachium rosenbergii LGBP (MrLGBP) was cloned into plasmid vector pHAC181, then integrated into downstream of the GAL1 promoter of Saccharomyces cerevisiae strain GAL1-ScRCH1 via homologous recombination, followed by its expression in the yeast eukaryotic system. The resulting recombinant LGBP contained a 3 × HA-tag at its C terminus and had a molecular weight of about 45 kDa, as evaluated by western blot analysis. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were ranged from 0.340 to 0.802 and 1.189-1.810 μM, respectively. The recombinant MrLGBP protein agglutinated almost all tested bacteria except Bacillus thuringiensis and Staphylococcus aureus. These results revealed that this recombinant protein exhibited antimicrobial activity against some Gram-positive and Gram-negative bacteria. M. rosenbergii prawns were fed with the recombinant yeast strain MrLGBP for 1 month and challenged with the most common crustacean pathogen, Vibrio parahaemolyticus. These prawns showed lower mortality and higher enzymatic activity and expression levels of immunity genes than did the control groups. All these results suggest that MrLGBP may play important roles in the innate immunity of crustaceans, and recombinant strain S. cerevisiae MrLGBP may be useful for the development of an effective immune feed additive in the future.

Lipopolysaccharide- and β-1,3-glucan-binding protein from Litopenaeus vannamei: Purification, cloning and contribution in shrimp defense immunity via phenoloxidase activation

Lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) existed in diversity of invertebrates including shrimp plays a crucial role in an innate immunity via mediating the recognition of invading pathogens. In this study, LGBP was cloned and characterized from the hepatopancreas of Litopenaeus vannamei, named as LvLGBP. Its full-length cDNA of 1282 bp contained an open reading frame (1101 bp) encoding a peptide of 367 amino acids. The LGBP primary structure contained a glycosyl hydrolase domain, two integrin binding motifs, two kinase C phosphorylation sites, and two polysaccharide recognition motifs which were identified as a polysaccharide binding motif and a β-1,3-glucan recognition motif. The LvLGBP transcripts were expressed mainly in the hepatopancreas. Upon challenge with Vibrio parahaemolyticus or white spot syndrome virus (WSSV), the LvLGBP mRNA expression was significantly up-regulated to reach a maximum at 48 h post injection. Its expression was also induced by lipopolysaccharide (LPS) or β-1,3-glucan stimulation. RNAi-based silencing resulted in the critical suppression of LvLGBP expression. Knockdown of LvLGBP gene with co-inoculation by V. parahaemolyticus or WSSV led to increase in the cumulative mortality and reduce in the median lethal time. Native LGBP was detected only in the hepatopancreas as verified by Western blotting. Purified LGBP from the hepatopancreas exhibited the agglutinating and binding activity towards Gram-negative bacterium V. parahaemolyticus with calcium-dependence. Its agglutinating activity was dominantly inhibited by LPS with higher potential than β-1,3-glucan. Purified LvLGBP could significantly activate the hemocyte phenoloxidase activity in the presence of LPS (12.9 folds), while slight activation was detected with β-1,3-glucan (2.0 folds). It could enhance the encapsulation by hemocytes but did not have antibacterial activity. These results provided evidence that LvLGBP might act as a pathogenic recognition protein to activate shrimp immune defense against invading pathogens via the agglutination, binding and enhancing encapsulation and phenoloxidase activity of the hemocytes.

The transcription of atypical protein kinase C in hemocytes of the giant freshwater prawn, Macrobrachium rosenbergii, during the molt stage and injection of pathogen-associated compounds

Protein kinase C (PKC), which is involved in cell signaling pathways, comprises a family of serine/threonine kinases ubiquitously present in animals and its members are grouped on the basis of structural and activation characteristics into novel, classical, and atypical PKC forms. In this study, an atypical PKC of Macrobrachium rosenbergii, designated MraPKC, was successfully cloned, and its protein comprised structural domains similar to those of atypical PKC homologues, including the Phox and Bem1 (PB1) domain, a zinc finger phorbol-ester/DAG-type signature, protein kinase signatures, and a cAMP-dependent, cGMP-dependent, and PKC (AGC) kinase C-terminal domain. Phylogenetic analyses revealed a close evolutionary relationship between MraPKC and aPKCs of insects. MraPKC transcripts were detected in all tissues examined through an RT-PCR, with the highest level detected in muscles. A quantitative real-time PCR was used to evaluate MraPKC expression in hemocytes of M. rosenbergii in various molt stages, and in prawn challenged with Vibrio alginolyticus, Lactococcus garvieae, and white spot syndrome virus (WSSV) as well as in prawns injected with pathogen-associated molecular patterns (PAMPs), including lipopolysaccharide (LPS), peptidoglycan (PG), and polyinosinic:polycytidylic acid (Poly:IC). Results revealed that the expression pattern of MraPKC was distinctly modulated during molting, with significant enhancement in the C stage. MraPKC transcripts significantly increased in hemocytes of prawns infected with L. garvieae at 6-24 h and those injected with PG at 12-24 h. In contrast, significantly decreased expression of MraPKC was observed in hemocytes of prawns injected with V. alginolyticus and LPS for 3 and 12 h, respectively, and a similar phenomenon was observed in hemocytes of those injected with WSSV and Poly:IC for 12 h each. Therefore, MraPKC might play crucial roles in biological processes, and it may mediate the signaling pathway induced by varied pathogens for the potential regulation of host innate defense.

Lipopolysaccharide- and β-1,3-glucan-binding protein from Fenneropenaeus merguiensis functions as a pattern recognition receptor with a broad specificity for diverse pathogens in the defense against microorganisms

In crustaceans, lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) plays an important role in innate immunity by mediating the recognition of pathogens to host cells. Hereby, LGBP was cloned from Fenneropenaeus merguiensis hepatopancreas. Its full-length cDNA (1280 bp) had an open reading frame of 1101 bp, encoding a peptide of 366 amino acids. The LGBP primary structure comprises a recognition motif for β-1,3-linkage of polysaccharides, two integrin binding motifs, a kinase C phosphorylation site and a bacterial glucanase motif. The LGBP mRNA was strongly expressed in hepatopancreas and significantly up-regulated to get the maximum at 12 h upon Vibrio harveyi challenge. Recombinant LGBP (rLGBP) could agglutinate Gram-negative and Gram-positive bacteria including yeast with Ca²⁺-dependence. V. harveyi agglutination induced by rLGBP was intensively inhibited by lipoteichoic acid, less in order were lipopolysaccharide, β-1,3-glucan and N-acetyl neuraminic acid. Western blotting revealed that rLGBP bound widely to Gram-negative and Gram-positive bacteria and also yeast. By ELISA quantification, rLGBP could bind to β-1,3-glucan better than to lipopolysaccharide and lipoteichoic acid. These findings suggest that LGBP may function as a receptor which recognizes invading diverse pathogens and contribute in F. merguiensis immune response.

A first insight into temperature stress-induced neuroendocrine and immunological changes in giant freshwater prawn, Macrobrachium rosenbergii

Haemolymph norepinephrine (NE); total haemocyte count (THC); respiratory bursts (RBs); superoxide dismutase (SOD), phenoloxidase (PO), and phagocytic activity; and prophenoloxidase (proPO)-system-related genes (lipopolysaccharide- and β-1,3-glucan-binding protein: LGBP, proPO, peroxinectin: PE, and α2-macroglobulin: α2-M) in haemocytes of Macrobrachium rosenbergii were investigated after transferring them from 28 °C to 22 °C, 28 °C, and 34 °C respectively. The results revealed that haemolymph NE, hyaline cells (HCs), and PO activity per granulocyte increased from 30 to 120 min of exposure, and however, RBs and phagocytic activity significantly decreased from 30 to 120 min of exposure as well as granular cells (GCs), semigranular cells (SGCs), and SOD activity decreased from 60 to 120 min of exposure for the prawns subjected to temperature stress. The proPO-system-related gene expression markedly increased with 60-120 min of exposure for the prawns transferred from 28 °C to 22 °C and 34 °C, except α2M at 120 min. These results provide a first insight into the effects of temperature stress on haemolymph NE level and immune functions in prawns and suggest that temperature-stress-induced acute modulation in immunity is associated with the release of haemolymph NE in M. rosenbergii.

PtLGBP, a pattern recognition receptor in Portunus trituberculatus involved in the immune response against different challenges

Lipopolysaccharide and b-1,3-glucan binding protein (LGBP) is a pattern recognition receptor that can recognize and bind LPS and b-1,3-glucan. LGBP has crucial roles in innate immune defense against Gram-negative bacteria and fungi. In this study, LGBP functions in Portunus trituberculatus innate immunity were analyzed. First, the mRNA expression of PtLGBP in hemocytes, hepatopancreas, and muscle toward three typical pathogen-associated molecular patterns (PAMPs) stimulations were examined using real-time PCR. Results show that the overall trend of relative expressions of the LGBP gene in three tissues is consistent, showing up-down trend. In each group, the highest expression of the LGBP gene was at 3 and 12 h post-injection. The LGBP gene is also expressed significantly higher in the hemocytes and hepatopancreas than in the muscle. The highest level of LGBP was in the lipopolysaccharides (LPS) and glucan-injected group, whereas the lowest level was in the PGN-injected group. Furthermore, bacterial agglutination assay with polyclonal antibody specifically for PtLGBP proved that the recombinant PtLGBP (designated as rPtLGBP) could exhibit obvious agglutination activity toward Gram-negative bacteria Escherichia coli, Vibrio parahaemolyticus, and V. alginolyticus; Gram-positive bacteria Bacillus subtilis; and fungi Saccharomyces cerevisiae. LGBP in Portunus trituberculatus possibly served as a multi-functional PRR. In addition, LGBP is not only involved in the immune response against Gram-negative and fungi, as manifested in other invertebrates, but also has a significant role in anti-Gram-positive bacteria infection.

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.

Particularity and universality of a putative Gram-negative bacteria-binding protein (GNBP) gene from amphioxus (Branchiostoma belcheri): insights into the function and evolution of GNBP

Gram-negative bacteria-binding proteins (GNBPs) are important pattern recognition proteins (PRPs), which can initiate host defense in response to pathogen surface molecules. The roles of GNBP in innate immunity of arthropods and molluscs have recently been reported. However, the GNBP gene has not been characterized in the species of higher evolutionary status yet. In this study, we identified and characterized an amphioxus GNBP gene (designated as AmphiGNBP). First, we identified and cloned the AmphiGNBP and found that the AmphiGNBP encodes a putative protein with 558 amino acids, which contains a conserved β-1, 3-glucan recognizing and binding domain. Second, we found that the AmphiGNBP encodes two extra WSC (cell Wall integrity and Stress response Component) domains, which are unique in AmphiGNBP protein. The two WSC domains of AmphiGNBP protein coupled with the expansion of amphioxus immunity repertoire might undergo intensive domain shuffling during the age of the Cambrian explosion. Finally, we found that the AmphiGNBP was mainly expressed in immune tissues, such as hepatic cecum and intestine, and the expression of AmphiGNBP was affected after LPS stimulation. In conclusion, our findings disclose the particularity and universality of AmphiGNBP and provide profound insights into the function and evolution of GNBP.

Association of CfLGBP gene polymorphism with disease susceptibility/resistance of Zhikong scallop (Chlamys farreri) to Listonella anguillarum

Lipopolysaccharide and β-1, 3-glucan binding protein (LGBP) is a pattern recognition receptor (PRR) recognizing and binding both LPS and β-1, 3-glucan, playing important roles in innate immunity. In the present study, the single nucleotide polymorphisms (SNPs) were assessed in LGBP gene from scallop Chlamys farreri (designated CfLGBP), and eight SNPs were found in its potential LPS and glucanase binding motif. The locus +7679 with the transition of G-A, which produced an amino acid substitution at codon 360 from a non polar Glycine to polar Serine, was selected to inspect their association with disease resistance/susceptibility to Listonella anguillarum. Three genotypes G/G, G/A and A/A, were revealed at locus +7679, and their frequencies were 89.7%, 7.7% and 2.6% in the resistant stock, while 63.2%, 34.2% and 2.6% in the susceptible stock, respectively. The frequency of genotypes G/G and G/A were significantly different (P < 0.05) between the two stocks. The pathogen-associated molecular patterns (PAMP) binding activity of two recombinant proteins, rCfLGBP (G) with G variant at locus +7679 and rCfLGBP (S) with A variant at locus +7679, were elucidated by ELISA assay. The binding affinities of both LPS and β-glucan binding affinity were varied in a dose-dependent manner, where the binding affinity of rCfLGBP (G) was significantly higher than that of rCfLGBP (S) (P < 0.05). The results collectively suggested that the polymorphism of +7679 G/G in CfLGBP possibly enhances the binding activity of LPS and β-glucan, and was associated to disease resistance of scallop against L. anguillarum, which could be a potential marker applied in future selection of scallop with enhanced resistance to L. anguillarum.