Diversity of lectins in Macrobrachium rosenbergii and their expression patterns under spiroplasma MR-1008 stimulation

Isolation and characterization of a lectin-like chitinase from the hepatopancreas of freshwater prawn, Macrobrachium rosenbergii

A lectin was isolated from the hepatopancreas of freshwater prawn, Macrobrachium rosenbergii by affinity chromatography using mucin-sepharose matrix. The purity of the isolated lectin was confirmed in native gradient PAGE that showed a single protein band of ∼37.9 kDa. In SDS-PAGE also one band of ∼43.3 kDa molecular weight was observed that indicated the protein to be a monomer. The band from the SDS-PAGE gel was identified through mass spectrometry as chitinase 1. The purified chitinase (50 μg/ml) hemagglutinated rabbit RBCs and, mucin and glucose inhibited hemagglutination with minimum concentrations of 0.1 mg/ml and 100 mM, respectively. Bacterial agglutination with Gram -ve Vibrio harveyi, Aeromonas sobria and Escherichia coli was also observed by this protein. Thus, chitinase 1 showed lectin-like properties besides its chitin hydrolytic activity. In western blot with hepatopancreas sample, rabbit antiserum against chitinase 1 cross-reacted to two additional proteins namely, chitinase 1C and obstructor E (a chitin-binding protein, CBP), besides its specific reactivity. An indirect ELISA was developed with the antiserum to quantify chitinases/CBP in hepatopancreas and serum samples of M. rosenbergii. The assay was used in samples from juvenile prawns following V. harveyi challenge. At 72 h post-challenge, significantly higher levels of chitinases/CBP were quantified in the hepatopancreas of the challenged group (1.8 ± 0.2 mg/g tissue) compared to the control (1.2 ± 0.1 mg/g tissue). This study suggests that the chitinase 1 protein with lectin-like properties is possibly induced at the protein level and can be putatively involved in the innate immune response of M. rosenbergii.

Identification and characterization of an L-type lectin from obscure puffer Takifugu obscurus in response to bacterial infection

L-type lectins (LTLs) contain a carbohydrate recognition domain homologous to leguminous lectins, and have functions in selective protein trafficking, sorting and targeting in the secretory pathway of animals. In this study, a novel LTL, designated as ToERGIC-53, was cloned and identified from obscure puffer Takifugu obscurus. The open reading frame of ToERGIC-53 contained 1554 nucleotides encoding 517 amino acid residues. The deduced ToERGIC-53 protein consisted of a signal peptide, a leguminous lectin domain (LTLD), a coiled-coil region, and a transmembrane region. Quantitative real-time PCR showed that ToERGIC-53 was expressed in all examined tissues, with the highest expression level in the liver. The expression of ToERGIC-53 was significantly upregulated after infection with Vibrio harveyi and Staphylococcus aureus. Recombinant ToERGIC-53-LTLD (rToERGIC-53-LTLD) protein could not only agglutinate and bind to one Gram-positive bacterium (S. aureus) and three Gram-negative bacteria (V. harveyi, V. parahaemolyticus and Aeromonas hydrophila), but also bind to glycoconjugates on the surface of bacteria such as lipopolysaccharide, peptidoglycan, mannose and galactose. In addition, rToERGIC-53-LTLD inhibited the growth of bacteria in vitro. All these results suggested that ToERGIC-53 might be a pattern recognition receptor involved in antibacterial immune response of T. obscurus.

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.

Molecular cloning, sequence characterization, and expression analysis of C-type lectin (CTL) and ER-Golgi intermediate compartment 53-kDa protein (ERGIC-53) homologs from the freshwater prawn, Macrobrachium rosenbergii

Lectin protein families are diverse and multi-functional in crustaceans. The carbohydrate-binding domains (CRDs) of lectins recognize the molecular patterns associated with pathogens and orchestrate important roles in crustacean defense. In this study, two lectin homologs, a single CRD containing C-type lectin (CTL) and an L-type lectin (LTL) domain containing endoplasmic reticulum Golgi intermediate compartment 53 kDa protein (ERGIC-53) were identified from the freshwater prawn, Macrobrachium rosenbergii. The open reading frames of MrCTL and MrERGIC-53 were 654 and 1,515 bp, encoding polypeptides of 217 and 504 amino acids, respectively. Further, MrCTL showed a 20-amino acid transmembrane helix region and 10 carbohydrate-binding residues within the CRD. MrERGIC-53 showed a signal peptide region, a type-I transmembrane region, and a coiled-coil region at the C-terminus. Phylogenetic analysis revealed a close relationship between MrCTL and MrLectin and M. nipponense CTL (MnCTL), whereas MrERGIC-53 shared high sequence identity with Eriocheir sinensis ERGIC-53 and Penaeus vannamei MBL-1. A homology-based model predicted small carbohydrate-combining sites with a metal-binding site for ligand binding (Ca²⁺ binding site) in MrCTL and beta-sheets connected by short loops and beta-bends forming a dome-shaped beta-barrel structure representing the LTL domain of MrERGIC-53. Quantitative real-time polymerase chain reaction detected MrCTL and MrERGIC-53 transcripts in all examined tissues, with particularly high levels observed in hemocytes, hepatopancreas, and mucosal-associated tissues, such as the stomach and intestine. Further, the expression levels of MrCTL and MrERGIC-53 transcripts were remarkably altered after V. harveyi challenge, suggesting putative function in host innate immunity.

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The online version contains supplementary material available at 10.1007/s10499-022-00845-3.

Lectin-Like Activity of Hemocyanin in Freshwater Prawn, Macrobrachium rosenbergii

Lectins are proteins that bind to the carbohydrate moieties on surface of bacteria, erythrocytes and other cells of invertebrates causing agglutination and mediate in recognition of foreign substances. In the present study, we isolated and characterized a lectin molecule present in the hemolymph of Macrobrachium rosenbergii, an important cultured freshwater prawn. Lectin in serum samples of adult prawns was assessed through hemagglutination (HA) test using rabbit RBC that showed a titre ranging from 16 to 64. This serum hemagglutinin was confirmed as a C-type lectin based on its dependency on calcium ions towards binding to rabbit RBCs. The hemagglutinin was also found to be stable at the pH range of 5.0-10.0 and temperature range of 10-40 °C. Of various sugars and glycoproteins tested in hemagglutination inhibition assay, the serum lectin was found specific only to N-acetylneuraminic acid and fetuin with respective minimum inhibitory concentrations at 50 mM and 0.31 mg/ml. Further, the lectin was purified by affinity chromatography on rabbit erythrocyte stroma, which showed hemagglutination with rabbit RBC. In electrophoretic analyses, the purified lectin showed one band with molecular weight of ~ 427 kDa in native gradient PAGE, and its two constituent polypeptide chains of ~ 81 and ~ 73 kDa in SDS-PAGE. These polypeptides were analysed in MALDI-TOF/TOF mass spectrometry and identified as hemocyanins. It was hence, concluded that hemocyanin in M. rosenbergii possesses lectin-like activity.

Full-length transcriptome analysis of Litopenaeus vannamei reveals transcript variants involved in the innate immune system

To better understand the immune system of shrimp, this study combined PacBio isoform sequencing (Iso-Seq) and Illumina paired-end short reads sequencing methods to discover full-length immune-related molecules of the Pacific white shrimp, Litopenaeus vannamei. A total of 72,648 nonredundant full-length transcripts (unigenes) were generated with an average length of 2545 bp from five main tissues, including the hepatopancreas, cardiac stomach, heart, muscle, and pyloric stomach. These unigenes exhibited a high annotation rate (62,164, 85.57%) when compared against NR, NT, Swiss-Prot, Pfam, GO, KEGG and COG databases. A total of 7544 putative long noncoding RNAs (lncRNAs) were detected and 1164 nonredundant full-length transcripts (449 UniTransModels) participated in the alternative splicing (AS) events. Importantly, a total of 5279 nonredundant full-length unigenes were successfully identified, which were involved in the innate immune system, including 9 immune-related processes, 19 immune-related pathways and 10 other immune-related systems. We also found wide transcript variants, which increased the number and function complexity of immune molecules; for example, toll-like receptors (TLRs) and interferon regulatory factors (IRFs). The 480 differentially expressed genes (DEGs) were significantly higher or tissue-specific expression patterns in the hepatopancreas compared with that in other four tested tissues (FDR <0.05). Furthermore, the expression levels of six selected immune-related DEGs and putative IRFs were validated using real-time PCR technology, substantiating the reliability of the PacBio Iso-seq results. In conclusion, our results provide new genetic resources of long-read full-length transcripts data and information for identifying immune-related genes, which are an invaluable transcriptomic resource as genomic reference, especially for further exploration of the innate immune and defense mechanisms of shrimp.

Characterisation and functional analysis of an L-type lectin from the swimming crab Portunus trituberculatus

L-type lectins are involved in glycoprotein secretion and are associated with immune responses. Herein, an L-type lectin was identified in swimming crab (Portunus trituberculatus). The 1347 bp PtLTL cDNA includes a 26 bp 5'-untranslated region (UTR), a 547 bp 3'-UTR with a poly(A) tail, and a 774 bp open reading frame encoding a 257 amino acid protein with a putative 21 residue signalling peptide. The protein includes an L-type lectin carbohydrate recognition domain containing four conserved cysteines. The 714 bp cDNA fragment encoding the mature peptide of PtLTL1 was recombined into pET-21a (+) with a C-terminally hexa-histidine tag fused in-frame and expressed in Escherichia coli Origami (DE3). Recombinant PtLTL1 caused agglutination of all three Gram-positive and Gram-negative bacterial strains tested. In addition, erythrocyte agglutination and LPS-binding activity were observed. PtLTL1 mRNA transcripts were most abundant in P. trituberculatus hepatopancreas and hemocytes, and expression was up-regulated in hemocytes challenged with Vibrio alginolyticus, suggesting PtLTL functions in the immune response against bacterial pathogens.

Impacts of environmental and biological stressors on immune system of Macrobrachium rosenbergii

Macrobrachium rosenbergii commonly called giant freshwater prawn is a widely farmed crustacean in freshwater. Similar to other aquatic organisms, their growth and well‐being is influenced by various physical, chemical and biological factors. We discuss about the critical growth limiting factors as well as disease causing agents and the potential immune molecules of M. rosenbergii that are proved to involve in preventing and/or responding to those limiting factors.

Immune response and survival of Circulifer haematoceps to Spiroplasma citri infection requires expression of the gene hexamerin

Spiroplasma citri is a cell wall-less bacterium that infects plants. It is transmitted by the leafhopper Circulifer haematoceps, which hosts this bacterium in the haemocel and insect tissues. Bacterial factors involved in spiroplasma colonization of the insect host have been identified, but the immune response of the leafhopper to S. citri infection remains unknown. In this study, we showed that C. haematoceps activates both humoral and cellular immune responses when challenged with bacteria. When infected by S. citri, C. haematoceps displayed a specific immune response, evidenced by activation of phagocytosis and upregulation of a gene encoding the protein hexamerin. S. citri infection also resulted in decreased phenoloxidase-like activity. Inhibition of hexamerin by RNA interference resulted in a significant reduction in phenoloxidase-like activity and increased mortality of infected leafhoppers. Therefore, the gene hexamerin is involved in S. citri control by interfering with insect phenoloxidase activity.

Cloning and characterization of two different L-type lectin genes from the Chinese mitten crab Eriocheir sinensis

L-type lectins contain a leguminous lectin domain and bind to high-mannose type oligosaccharides. In the secretory pathway, L-type lectins play crucial functions in the trafficking, sorting, and targeting of maturing glycoproteins. This study identified two novel L-type lectins, designated as EsERGIC-53 and EsVIP36, from the Chinese mitten crab Eriocheir sinensis. The complete nucleotide sequence of ERGIC-53 cDNA was 1955 bp, containing a 1506 bp open reading frame (ORF) encoding a putative protein of 501 deduced amino acids. The full-length cDNA of VIP36 was 3474 bp with a 984 bp ORF encoding a 327-amino acid peptide. The deduced ERGIC-53 and VIP36 proteins contained a putative signal peptide and an L-type lectin-like domain. Phylogenetic analysis showed that ERGIC-53 and VIP36 belonged to different clades of L-type lectin family. Reverse transcription PCR showed that ERGIC-53 and VIP36 were expressed in all tested tissues. Quantitative real-time RT-PCR analysis revealed that ERGIC-53 and VIP36 transcripts in hepatopancreas were significantly induced at various time points after infection with lipopolysaccharide (LPS), peptidoglycan (PGN), Staphylococcus aureus, Vibrio parahaemolyticus, and Aeromonas hydrophila. A bacterium-binding experiment showed that both ERGIC-53 and VIP36 could bind to different microbes. Sugar binding assay revealed that these lectins could also bind to the glycoconjugates of bacteria surface, such as LPS, PGN, d-Mannose, and N-Acetyl-d-mannosamine. Moreover, these two L-type lectins agglutinated bacteria in a calcium-dependent manner, and both exerted the ability of facilitating the clearance of injected bacteria V. parahaemolyticus in the crab. Our results suggested that ERGIC-53 and VIP36 functioned as pattern recognition receptors in the immune system of E. sinensis.

An LDLa domain-containing C-type lectin is involved in the innate immunity of Eriocheir sinensis

C-type lectins (CTLs) have crucial functions in recognizing and eliminating pathogens in innate immunity. This study identified a novel low-density lipoprotein receptor class A (LDLa) domain-containing CTL, designated as EsCTLDcp, from the Chinese mitten crab Eriocheir sinensis. The EsCTLDcp cDNA is 1258 bp long, with a 975 bp open reading frame that encodes a 324-amino acid protein. EsCTLDcp contains a signal peptide, an LDLa, and a single C-type lectin-like domain. EsCTLDcp was only expressed in the hepatopancreas of normal crabs, and its expression was regulated following crab challenge with pathogen-associated molecular patterns and with bacteria. The recombinant EsCTLDcp agglutinates Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Vibrio parahaemolyticus and Aeromonas hydrophila) in the presence of calcium. rEsCTLDcp also binds to various bacteria including S. aureus, Bacillus thuringiensis, Bacillus subtilis, Escherichia coli, Vibrio natriegens, V. parahaemolyticus, and A. hydrophila. The rEsCTLDcp protein helped the crabs clear the virulent Gram-negative bacterium V. parahaemolyticus in vivo, as well as interacted with VP24, an envelope protein of white spot syndrome virus (WSSV). These data suggest that EsCTLDcp functions as a pattern-recognition receptor involved in the innate immunity of E. sinensis.