Identification of lectin isoforms in juvenile freshwater prawns Macrobrachium rosenbergii (DeMan, 1879)

In vivo administration of LPS and β-glucan generates the expression of a serum lectin and its cellular receptor in Cherax quadricarinatus

In crustaceans, it has been suggested that specific protection against pathogens could be triggered by vaccines and biological response modifiers; although the specific mechanisms of this protection have not been clarified yet. In the crayfish Cherax quadricarinatus, a humoral lectin (CqL) binds its own granular hemocytes through a specific receptor (CqLR) and increases the production of reactive oxygen species (ROS). In the present study, we challenged in vivo crayfishes with immunostimulants, β-glucan (200 μg/kg) or LPS (20 μg/kg), and identified the participation of cellular and humoral mechanisms. The stimulants generated a complex modification in the total hemocytes count (THC), as well as in the proportion of hemocyte subsets. At 2 h after the challenge, the largest value in THC was observed in either challenged crayfishes. Furthermore, at the same time, hyaline hemocytes were the most abundant subset in the hemolymph; after 6 h, granular hemocytes (GH) were the most abundant hemocyte subset. It has been observed that a specific subset of GH possesses a CqLR that has been related to ROS production. After 2 and 6 h of the β-glucan challenge, a significant increase in CqLR expression was observed in the three circulating hemocyte subsets; also, an increased expression of CqL was detected in a granular hemocytes sub-population. After 2 and 6 h of stimulation, the specific activity of the serum lectin challenged with β-glucan was 250% and 160% higher than in the LPS-treated-group, respectively (P < 0.05). Hemocytes from challenged crayfishes were stimulated ex vivo with CqL, ROS production was 180% higher in hemocytes treated with β-glucan + CqL than in hemocytes treated with LPS + CqL (P < 0.05). The results evidence the effectivity of immune stimulators to activate specific crayfish defense mechanisms, the participation of CqL and its receptor (CqLR) could play an important role in the regulation of immune cellular functions, like ROS production, in Cherax quadricarinatus.

Characterization of a lectin from the craysfish Cherax quadricarinatus hemolymph and its effect on hemocytes

Lectins participate in the immune mechanisms of crustaceans. They have been considered as humoral receptors for pathogen-associated molecular patterns; however, some reports suggest that lectins could regulate crustacean cellular functions. In the present study, we purified and characterized a serum lectin (CqL) from the hemolymph of Cherax quadricarinatus by affinity chromatography and determined its participation in the regulation of hemocytes' oxidative burst. CqL is a 290-kDa lectin in native form, constituted by 108, 80, and 29-kDa subunits. It is mainly composed of glycine, alanine, and a minor proportion of methionine and histidine. It showed no carbohydrates in its structure. CqL is composed of several isoforms, as determined by 2D-electrophoresis, and shows no homology with any crustacean protein as determined by Lc/Ms mass spectrometry. CqL agglutinated mainly rat and rabbit erythrocytes and showed a broad specificity for monosaccharides such as galactose, glucose, and sialic acid, as well as for glycoproteins, such as porcine stomach and bovine submaxillary mucin and fetuin. It is a Mn(2+)-dependent lectin. CqL recognized 8% of crayfish granular hemocytes and increased 4.2-fold the production of hemocytes' superoxide anion in vitro assays when compared with non-treated hemocytes. This effect showed the same specificity for carbohydrates as hemagglutination; moreover, superoxide dismutase and diphenyleneiodonium chloride were effective inhibitors of CqL oxidative-activation. The CqL homoreceptor is a 120-kDa glycoprotein identified in the hemocytes lysate. Our results suggest that CqL participates actively in the regulation of the generation of superoxide anions in hemocytes using NADPH-dependent mechanisms.

Diversity and multiple functions of lectins in shrimp immunity

Lectins play important roles in many biological processes, including protein trafficking, cell signaling, pathogen recognition, as effector molecules, and so on, because of their capacity to bind carbohydrates. Presently, seven groups of lectins have been identified in shrimp: C-type, L-type, P-type, M-type, fibrinogen-like domain lectins, galectins, and calnexin/calreticulin. These lectins have different structures, diverse expression patterns, and multiple functions in the shrimp immune response. This review summarizes the research progress and analyzes the diversity of shrimp lectins, focusing mainly on the C-type lectin family. Shrimp C-type lectins show considerable diversity in their domain architectures, sugar substrates, tissue distributions, expression patterns responding to pathogen challenge and functions in shrimp immunity.

Purification and characterization of a lectin from the banana shrimp Fenneropenaeus merguiensis hemolymph

A lectin from the hemolymph of the banana shrimp Fenneropenaeus merguiensis was purified by affinity chromatography on a fetuin-agarose column following by gel filtration on a Superose-12 column. The native molecular mass of purified F. merguiensis lectin (FmL) determined by gel filtration was 316.2 kDa and its carbohydrate content was estimated to be 4.4%. By SDS-PAGE analysis, purified FmL consisted of 32.3 kDa and 30.9 kDa subunits. These data suggest that this lectin is an oligomer. Two-dimensional electrophoresis showed that it had a pI value of 6.0 and was mainly composed of glycine, serine, histidine, glutamic acids and glutamine, with relatively lower amounts of methionine and tyrosine. Purified FmL expressed higher agglutination activity against rabbit and rat erythrocytes than with those from human, and its activity was Ca(2+)-dependent. The hemagglutinating activity of FmL was stable up to 55 degrees C and at pH 7.5-8. N-acetylated sugars, such as ManNAc, GlcNAc, GalNAc, and NeuNAc were strong inhibitors of the FmL induced hemagglutinating activity with NeuNAc being most effective. Porcine stomach mucin and fetuin were the most potent inhibitors of FmL. Purified FmL caused selective agglutination of Vibrio harveyi, and Vibrio parahemolyticus both pathogens of this Penaeus species and to a lesser extent Vibrio vulnificus but had no effect on the non-pathogenic strains; Vibrio cholerae, Salmonella typhi and Escherichia coli. Its bacterial agglutination was also completely inhibited by NeuNAc, mucin, fetuin and also anti-FmL antibody. This observation indicates that FmL may contribute to the defense response of this species of penaeid shrimps to potentially pathogenic bacteria.

The effect of sugars and free amino acids from the freshwater prawn Macrobrachium rosenbergii hemolymph on lectin activity and on oxidative burst

We determined the effect of low molecular weight components (LMWC) from healthy juvenile and adult Macrobrachium rosenbergii hemolymph on lectin activity and oxidative burst (OB) in hemocytes. In an attempt to identify the LMWC that affect the lectin's hemagglutinating activity or oxidative burst, we determined the hemolymph carbohydrates and free amino acids (FAA) concentration. The LMWC (<2000 Da) were obtained after dialysis of the hemolymph. Our results showed that LMWC from juveniles exerted a greater inhibition on lectin than LMWC from adult hemolymph. Production of superoxide radicals by hemocytes was lower in the presence of juvenile (p<0.05) as compared to adult LMWC. FAA composition of the hemolymph and of LMWC from adults showed higher proportion of alanine (which corresponded to 25% of total FAA) and proline (>20%); whereas, in juveniles, the main FAA identified were glycine (>40%) and alanine (26%). N-Acetyl-D-glucosamine (GlcNAc) was the main sugar residue in the hemolymph and LMWC from juveniles; its concentration was 2.4 times higher than glucose (Glc), whereas, in adults, Glc was the main free sugar residue. Our results suggest that the proportion of FAA and carbohydrates in the hemolymph of M. rosenbergii seems to be correlated with the maturation process; furthermore, the high proportion of free GlcNAc and glycine regulate, in the juvenile stage, lectin activity and cellular oxidative mechanisms, respectively.

N-acetyl-d-galactosamine/N-acetyl-d-glucosamine – recognizing lectin from the snailCepaea hortensis: purification, chemical characterization, cloning and expression inE. coli

From the albumin gland of the snail Cepaea hortensis we isolated and characterized a new N-acetyl-D-galactosamine/N-acetyl-D-glucosamine (GalNAc/GlcNAc) specific lectin (CHA-II) which was purified by a combination of affinity chromatography on GalNAc-agarose and gel filtration. The purified native lectin was found to be a multimeric protein, as revealed by SDS-PAGE and MALDI-TOF analysis. In SDS-PAGE the denatured and reduced lectin showed two bands of molecular masses with 17 and 15.5 kDa which reacted equally with anti-CHA-II rabbit antiserum. The lectin was O- and N-glycosylated with [(Gal)2-Man]2-Man-GlcNAc-GlcNAc-Asn as a probable structure for the oligosaccharide. Isoelectric focusing revealed a heterogeneous protein of at least four bands around pH 8.7. Tryptic peptides of CHA-II were N-terminally sequenced and highly degenerated gene specific oligonucleotide primers (GSPs) had been constructed. Using total RNA isolated from albumin glands, cDNAs were produced by the running race technique. Specific PCR fragments were obtained by PCR using GSPs, the universal primer and 5'- or 3'-RACE-cDNAs. The amplified fragments were cloned into the vector pDrive and were sequenced. The resulting total cDNA sequence consisted of 496 base pairs including an open reading frame of 360 base pairs which encoded a protein of 120 amino acids. The protein carried a putative signal peptide. The mature protein was predicted to comprise 99 amino acid residues with a calculated molecular weight of 11,239 Da. The PCR fragment encoding the mature protein was cloned into the vector pQE30 and expressed in E. coli. Recombinant CHA-II lectin was produced as inclusion bodies and extracted by 6 M guanidine hydrochloride. After refolding, the recombinant CHA-II agglutinated specifically human red blood cells of groups A and AB. In immunodiffusion experiments using rabbit antiserum raised against the native lectin, the protein showed a precipitation line of identity with the native lectin.

Cloning and expression of a sialic acid-binding lectin from the snailCepaea hortensis

Highly degenerated gene-specific oligonucleotide primers (GSPs) were constructed from the amino acid sequence of tryptic fragments produced from the purified sialic acid-specific lectin of the garden snail Cepaea hortensis. From the albumin glands, the total RNA or the mRNA was prepared. Combination of a universal primer with the GSPs delivered gene-specific fragments of about 650, 620 and 280 bp by polymerase chain reaction (PCR). These fragments were cloned into the vector pDrive (Qiagen) and sequenced. The resulting cDNA sequence consisted of 744 bp, including an open reading frame of 480 bp. The encoded protein consists of 159 amino acids, including the putative signal sequence peptide. The mature protein should comprise 141 amino acid residues with a calculated molecular mass of 15,529 Da. The expression of the recombinant lectin in Escherichia coli resulted in a soluble protein reacting specifically with rabbit antiserum raised against the native lectin.

Sialylation is modulated through maturation in hemocytes from Macrobrachium rosenbergii

In this work we identified in adult and juvenile freshwater prawn, Macrobrachium rosenbergii, three major type of circulating hemocytes: fusiform; rounded; and large ovoid hemocytes. Rounded and large hemocytes represent the first defense line, since this type of cells exerts phagocytic activity as well as lectin synthesis. Considering that glycosylation plays important roles in cell communication and as a target for pathogenic microorganisms, in this report was also described the main glycosidic modifications that occur in the large and rounded hemocytes from the freshwater prawn during maturation as determined with lectins. Neu5Acalpha2,6Gal, was identified homogeneously distributed in the membrane in 90% of hemocytes from juvenile organisms. Maturation of the freshwater prawn induced a decrease or complete loss of Neu5Acalpha2,6Gal residues that were replaced with Neu5Acalpha2,3 molecules in practically all hemocytes from adult organisms. This change was paralleled by a diminution in 9-O-acetyl-neuraminic acid (Neu5,9Ac(2)) expression. T and Tn antigens (Galbetal,3 GalNAcalpha1-0-Ser/Thr or GalNAcalpha1-0-Ser/Thr, respectively), as well as N-glycosidically linked glycans, seem to be highly conserved throughout maturation. Our results show that sialylation of freshwater prawn hemocytes is modulated throughout the maturation process.