Purification and characterization of a rhamnose-binding lectin with immunoenhancing activity from grass carp (Ctenopharyngodon idellus) ovaries

New Data on the Rhamnose-Binding Lectin from the Colonial Ascidian Botryllus schlosseri: Subcellular Distribution, Secretion Mode and Effects on the Cyclical Generation Change

Botryllus schlosseri in a cosmopolitan ascidian, considered a reliable model organism for studies on the evolution of the immune system. B. schlosseri rhamnose-binding lectin (BsRBL) is synthesised by circulating phagocytes and behaves as an opsonin by interacting with foreign cells or particles and acting as a molecular bridge between them and the phagocyte surface. Although described in previous works, many aspects and roles of this lectin in Botryllus biology remain unknown. Here, we studied the subcellular distribution of BsRBL during immune responses using light and electron microscopy. In addition, following the hints from extant data, suggesting a possible role of BsRBL in the process of cyclical generation change or takeover, we investigated the effects of interfering with this protein, by injecting a specific antibody in the colonial circulation, starting one day before the generation change. Results confirm the requirement of the lectin for a correct generation change and open new queries on the roles of this lectin in Botryllus biology.

Immunological characterization and function analysis of L-type lectin from spotted knifejaw, Oplegnathus punctatus

Lily-type lectin (LTL) plays significant roles in innate immune response against pathogen infection. LTL in animals and plants has received widespread attention. In the present study, an LTL (OppLTL) was identified from spotted knifejaw Oplegnathus punctatus. The OppLTL encoded a typical Ca²⁺-dependent carbohydrate-binding protein containing a CRD domain. The qRT-PCR showed that it was mainly expressed in the gill and was significantly upregulated after Vibrio anguillarum challenge. The agglutination analysis showed that the recombinant OppLTL could bind and agglutinate Gram-negative and Gram-positive bacteria in a Ca²⁺-dependent manner. However, the binding activity was different. Meanwhile, the recombinant OppLTL could hemagglutinate mammalian and teleost erythrocytes. Subcellular localization revealed that OppLTL was mainly detected in the cytoplasm of HEK293T cells. The dual-luciferase analysis revealed that OppLTL could inhibit the activity of the NF-κB signal pathway in HEK293T cells after OppLTL overexpression. These findings collectively demonstrated that OppLTL could be involved in host innate immune response and defense against bacterial infection in spotted knifejaw.

Proliferative Effect of Tilapia Fish (Oreochromis niloticus) Lectin on BALB/c Mice Splenocytes

BACKGROUND

Lectins have been studied in recent years due to their immunomodulatory activities.

OBJECTIVE

We purified a lectin named OniL from tilapia fish (Oreochromis niloticus) and here we analyzed the cell proliferation and cytokine production in Balb/c mice splenocytes.

METHODS

Cells were stimulated in vitro in 24, 48, 72 hours and 6 days with different concentrations of OniL and Con A. Evaluation of cell proliferation was performed through [3H]-thymidine incorporation, cytokines were investigated using ELISA assay and cell viability assay was performed by investigation of damage through signals of apoptosis and necrosis.

RESULTS

OniL did not promote significant cell death, induced high mitogenic activity in relation to control and Con A and stimulated the cells to release high IL-2 and IL-6 cytokines.

CONCLUSION

These findings suggest that, like Con A, OniL lectin can be used as a mitogenic agent in immunostimulatory assays.

l-rhamnose-binding lectins (RBLs) in turbot (Scophthalmus maximus L.): Characterization and expression profiling in mucosal tissues

Rhamnose-binding lectin (RBL) were mostly identified from egg cortex and ovary cells from vertebrates and invertebrates, with the specific binding activities to l-rhamnose or d-galactose. Previously, we found that a RBL gene was dramatically down-regulated (-11.90 fold at 1 h, -48.95 fold at 4 h, -905.94 fold at 12 h) in the intestine of turbot following Vibrio anguillarum challenge using RNA-seq expression analysis. In this regard, we sought here to identify RBLs in turbot, as well as the analysis of genomic structure, phylogenetic relationships, basal tissue distribution and the expression patterns following different bacteria challenge in mucosal tissues. In this study, two RBLs were captured in turbot with two conserved type 5 CRD5s, which were belong to type IIIc RBL. In phylogenetic tree analysis, turbot RBLs were clustered with tilapia, European sea bass and snakehead. In addition, in comparison of genomic architecture of turbot RBLs with the available published RBL genes revealed a high degree of conservation in the exon/intron organization among the teleost species. Moreover, both RBLs were significantly up-regulated in mucosal tissues following V. anguillarum and Streptococcus iniae challenge, indicated their critical roles in turbot mucosal immunity. Further studies are needed to expand functional characterization of detailed mechanisms of RBLs in fish innate immunity.

Lectins, Interconnecting Proteins with Biotechnological/Pharmacological and Therapeutic Applications

Lectins are proteins extensively used in biomedical applications with property to recognize carbohydrates through carbohydrate-binding sites, which identify glycans attached to cell surfaces, glycoconjugates, or free sugars, detecting abnormal cells and biomarkers related to diseases. These lectin abilities promoted interesting results in experimental treatments of immunological diseases, wounds, and cancer. Lectins obtained from virus, microorganisms, algae, animals, and plants were reported as modulators and tool markers in vivo and in vitro; these molecules also play a role in the induction of mitosis and immune responses, contributing for resolution of infections and inflammations. Lectins revealed healing effect through induction of reepithelialization and cicatrization of wounds. Some lectins have been efficient agents against virus, fungi, bacteria, and helminths at low concentrations. Lectin-mediated bioadhesion has been an interesting characteristic for development of drug delivery systems. Lectin histochemistry and lectin-based biosensors are useful to detect transformed tissues and biomarkers related to disease occurrence; antitumor lectins reported are promising for cancer therapy. Here, we address lectins from distinct sources with some biological effect and biotechnological potential in the diagnosis and therapeutic of diseases, highlighting many advances in this growing field.

Three novel B-type mannose-specific lectins of Cynoglossus semilaevis possess varied antibacterial activities against Gram-negative and Gram-positive bacteria

Lectins are a group of sugar-binding proteins that are important factors of the innate immune system. In this study, we examined, in a comparative manner, the expression and function of three Bulb-type (B-type) mannose-specific lectins (named CsBML1, CsBML2, and CsBML3) from tongue sole. All three lectins possess three repeats of the conserved mannose binding motif QXDXNXVXY. Expression of CsBML1, CsBML2, and CsBML3 was most abundant in liver and upregulated by bacterial infection. Recombinant (r) CsBML1, CsBML2, and CsBML3 bound to a wide arrange of bacteria in a dose-dependent manner and with different affinities. All three lectins displayed mannose-specific and calcium-dependent agglutinating capacities but differed in agglutinating profiles. rCsBML1 and rCsBML2, but not rCsBML3, killed target bacteria in vitro and inhibited bacterial dissemination in fish tissues in vivo. These results indicate for the first time that in teleost, different members of B-type mannose-specific lectins likely play different roles in antibacterial immunity.

Marine lectins and their medicinal applications

Marine organisms have been extensively explored for the last several decades as potential sources of novel biologically active compounds, and extensive research has been conducted on lectins. Lectins derived from marine organisms are structurally diverse and also differ from those identified from terrestrial organisms. Marine lectins appear to be particularly useful in some biological applications. They seem to induce negligible immunogenicity because they have a relatively small size, are more stable due to extensive disulfide bridge formation, and have high specificity for complex glyco-conjugates and carbohydrates instead of simple sugars. It is clear that many of them have not yet been extensively studied when compared with their terrestrial counterparts. Marine lectins can be used to design and develop new potentially useful therapeutic agents. This review encompasses recent research on the isolation and identification of marine lectins with potential value in medicinal applications.

A rhamnose-binding lectin from sea bass (Dicentrarchus labrax) plasma agglutinates and opsonizes pathogenic bacteria

The discovery of rhamnose-binding lectins (RBLs) in teleost fish eggs led to the identification of a novel lectin family characterized by a unique sequence motif and a structural fold, and initially proposed to modulate fertilization. Further studies of the RBL tissue localization and gene organization were also suggestive of role(s) in innate immunity. Here we describe the purification, and biochemical and functional characterization of a novel RBL (DlRBL) from sea bass (Dicentrarchus labrax) serum. The purified DlRBL had electrophoretic mobilities corresponding to 24 kDa and 100 kDa under reducing and non-reducing conditions, respectively, suggesting that in plasma the DlRBL is present as a physiological homotetramer. DlRBL subunit transcripts revealed an open reading frame encoding 212 amino acid residues that included two tandemly-arrayed carbohydrate-recognition domains, and an 18-residue signal sequence at the N-terminus. The deduced size of 24.1 kDa for the mature protein was in good agreement with the subunit size of the isolated lectin. Binding activity of DlRBL for rabbit erythrocytes could be inhibited in the presence of rhamnose or galactose, did not require calcium, and was optimal at around 20°C and within the pH 6.5-8.0 range. DlRBL agglutinated Gram positive and Gram negative bacteria, and exposure of formalin-killed Escherichia coli to DlRBL enhanced their phagocytosis by D. labrax peritoneal macrophages relative to the unexposed controls. Taken together, the results suggest that plasma DlRBL may play a role in immune recognition of microbial pathogens and facilitate their clearance by phagocytosis.

L-Rhamnose-binding lectins (RBLs) in channel catfish, Ictalurus punctatus: Characterization and expression profiling in mucosal tissues

Rhamnose-binding lectins (RBLs) have recently emerged as important molecules in the context of innate immunity in teleost fishes. Previously, using RNA-seq technology, we observed marked up-regulation of a RBL in channel catfish (Ictalurus punctatus) gill following a challenge with the bacterial pathogen Flavobacterium columnare. Furthermore, the magnitude of RBL up-regulation positively correlated with disease susceptibility. Moving forward from these findings, we wished to more broadly understand RBL function, diversity, and expression kinetics in channel catfish. Therefore, in the present study we characterized the RBL gene family present in select channel catfish tissues and profiled family member expression after challenge with two different Gram-negative bacterial pathogens. Here, six RBLs were identified from channel catfish and were designated IpRBL1a, IpRBL1b, IpRBL1c, IpRBL3a, IpRBL3b, and IpRBL5a. These RBLs contained carbohydrate recognition domains (CRD) ranging from one to three domains and each CRD contained the conserved motifs of -YGR- and -DPC-. Despite a level of structural conservation, the catfish RBLs showed low full-length identity with RBLs from outside the order Siluriformes. IpRBL expression after bacterial infection varied depending on both pathogen and tissue type, suggesting that IpRBLs may exert disparate functions or exhibit distinct tissue-selective roles in the host immune response to bacterial pathogens.

Rachycentron canadum (cobia) lectin promoted mitogenic response in mice BALB/c splenocytes

The mitogenic lectins are invaluable tools to study the biochemical changes associated with lymphocyte activation and proliferation of various immune cells. Rachycentron canadum lectin (RcaL) was detected and purified from serum of cobia fish. The aim of this study was to evaluate the proliferative response and cytokine production in splenocytes of mice in vitro stimulated with RcaL lectin; Canavalia ensiformis lectin (Con A) was used as positive control. A high proliferation index was induced by RcaL in relation to control cells. Furthermore, RcaL induced higher IL-2 and IL-6 production in relation to control. The cell viability was 90% in splenocytes treated with RcaL lectin, but RcaL promoted significant late apoptosis after 24 and 48 h in relation to control. RcaL induced proliferative responses suggesting that this lectin can be used as a mitogenic agent in immunostimulatory assays.

Structural characterization and antitumor and mitogenic activity of a lectin from the gill of bighead carp (Aristichthys nobilis)

In this study, we investigated the gross structure, secondary structure, and antitumor and mitogenic activity of GANL, a lectin from the gill of bighead carp (Aristichthys nobilis). We used infrared spectroscopy, β-elimination, and circular dichroism spectroscopy to determine the structure of GANL. We measured antiproliferation activity against six human tumor cell lines and mitogenic activity against murine splenocytes using the MTT assay. Based on infrared spectroscopy and β-elimination, we conclude that GANL is a glycoprotein. The protein and carbohydrate moieties are joined by O-glycosidic linkage. A circular dichroism spectroscopic analysis revealed that the secondary structure of GANL consists of α-helices (34.8 %), β-sheets (12.1 %), β-turns (24.5 %), and unordered structures (33.0 %). GANL exerted potent antitumor activity against the HeLa cell line (IC(50) = 11.86 μg/mL) and a mitogenic effect on murine splenocytes in the MTT assay. GANL, a lectin that is isolated from the gills of bighead carp, is a glycoprotein with potent antitumor and mitogenic activity.

Immunomodulatory response of mice splenocytes induced by RcaL, a lectin isolated from cobia fish (Rachycentron canadum) serum

This work reports the isolation of a serum lectin from cobia fish (Rachycentron canadum) named RcaL. Immunomodulatory activity on mice splenocyte experimental cultures through cytotoxic assays and cytokine production were also performed. RcaL was obtained through precipitation with ammonium sulphate and affinity chromatography on a Concanavalin A-Sepharose 4B column. The ammonium sulphate fraction F3 showed the highest specific hemagglutinating activity and was applied to affinity chromatography. The lectin was eluted with methyl-α-D-mannopyranoside. RcaL showed highest affinity for methyl-α-D-mannopyranoside and D-mannose; eluted fractions of RcaL agglutinated rabbit erythrocytes (titre, 128(-1)) retained 66 % of chromatographed lectin activity, and the obtained purification factor was 1.14. Under reducing conditions, a polypeptide band of 19.2 kDa was revealed in sodium dodecyl sulphate polyacrylamide gel electrophoresis (PAGE). PAGE confirmed RcaL as an acidic protein revealed in a single band. Cytotoxic and immunomodulatory assays with RcaL in mice splenocyte cultures showed that the lectin was not cytotoxic and induced higher interferon gamma and nitric oxide production in splenocyte cultures. Purified RcaL induced preferential Th1 response, suggesting that it acts as an immunomodulatory compound.

Purification and characterization of a lectin with high hemagglutination property isolated from Allium altaicum

A lectin was purified from the leaves of Allium altaicum and corresponding gene was cloned. The lectin namely Allium altaicum agglutinin (AAA) was ~24 kDa homodimeric protein and similar to a typical garlic leaf lectin. It was synthesized as 177 amino acid residues pre-proprotein, which consisted of 28 and 43 amino acid long N and C-terminal signal peptides, respectively. The plant expressed this protein more in scapes and flowers in comparison to the bulbs and leaves. Hemagglutination activity (with rabbit erythrocytes) was 1,428 fold higher as compared to Allium sativum leaf agglutinin (ASAL) although, the insecticidal activity against cotton aphid (Aphis gossypii) was relatively low. Glycan array revealed that AAA had higher affinity towards GlcAb1-3Galb as compared to ASAL. Homology analysis showed 57-94% similarity with other Allium lectins. The mature protein was expressed in E. coli as a fusion with SUMO peptide in soluble and biologically active form. Recombinant protein retained high hemagglutination activity.

Purification and characterization of a mannose recognition lectin from Oreochromis niloticus (tilapia fish): cytokine production in mice splenocytes

The aim of this work was to purify and partially characterize a mannose recognition lectin from Nile tilapia (Oreochromis niloticus) serum, named OniL. OniL was isolated through precipitation with ammonium sulfate and affinity chromatography (Concanavalin A-Sepharose 4B). In addition, we evaluated carbohydrate specificity, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) profiles, and in vitro immunomodulatory activity on mice splenocyte experimental cultures through cytotoxic assays and cytokine production. The ammonium sulfate fraction F2 showed the highest specific hemagglutinating activity (331) and was applied to affinity matrix. Adsorbed proteins (OniL) were eluted with methyl-α-D: -mannopyranoside. OniL, a 17-kDa protein by SDS-PAGE constituted by subunits of 11 and 6.6 kDa, showed highest affinity for methyl-α-D: -mannopyranoside and D: -mannose. Immunological assays, in vitro, showed that OniL did not show cytotoxicity against splenocytes, induced higher IFN-γ production and lower IL-10 as well as nitrite release. In conclusion, OniL lectin was successfully purified and showed a preferential Th1 response in mice splenocytes.

Purification and characterization of a rhamnose-binding chinook salmon roe lectin with antiproliferative activity toward tumor cells and nitric oxide-inducing activity toward murine macrophages

In this study, a rhamnose-binding lectin from the roe of chinook salmon (Oncorhynchus tshawytscha) was purified and characterized, and its biological activities were examined in several model systems. Chinook salmon roe lectin had a molecular mass of 30 kDa and agglutinated rabbit and bovine erythrocytes. The hemagglutination activity of the lectin was not affected by metal ions. The lectin was stable up to 70 °C and between pH 4 and pH 11. Chinook salmon roe lectin did not exert antifungal activity toward the fungal species tested and did not exhibit mitogenic response toward mouse splenocytes up to a concentration of 5 mg/mL. The lectin had selective antiproliferative activity toward human breast cancer MCF-7 cells and hepatoma Hep G2 cells. It also induced the production of nitric oxide from mouse peritoneal macrophages. This is the first report that demonstrates these biological activities from chinook salmon roe lectin.

Molecular cloning of rhamnose-binding lectin gene and its promoter region from snakehead Channa argus

Lectins are sugar-binding proteins that mediate pathogen recognition and cell-cell interactions. A rhamnose-binding lectin (RBL) gene and its promoter region have been cloned and characterized from snakehead Channa argus. From the transcription initiation site, snakehead rhamnose-binding lectin (SHL) gene extends 2,382 bp to the end of the 3' untranslated region (UTR), and contains nine exons and eight introns. The open reading frame (ORF) of the SHL transcript has 675 bp which encodes 224 amino acids. The molecular structure of SHL is composed of two tandem repeat carbohydrate recognition domains (CRD) with 35% internal identity. Analysis of the gene organization of SHL indicates that the ancestral gene of RBL may diverge and evolve by exon shuffling and gene duplication, producing new forms to play their own roles in various organisms. The characteristics of SHL gene 5' flanking region are the presence of consensus nuclear factor of interleukin 6 (NF-IL6) and IFN-gamma activation (GAS) sites. The results provide indirect evidence that up-regulation of SHL expression may be induced in response to inflammatory stimuli, such as lipopolysaccharide (LPS), interleukin 6 (IL-6), and interferon gamma (IFN-gamma). The transcript of SHL mRNA was expressed in the head kidney, posterior kidney, spleen, liver, intestine, heart, muscle, and ovary. No tissue-specific expressive pattern is different from reported STLs, WCLs, and PFLs, suggesting that different types of RBLs exist in species-specific fish that have evolved and adapted to their surroundings.

A haemagglutinin from the medicinal fungus Cordyceps militaris

There are only a few reports on agglutinins from ascomycete and medicinal fungi. An HA (haemagglutinin), with an N-terminal amino acid sequence different from those of known lectins, was isolated in the present study from dried fruiting bodies of the medicinal ascomycete fungus Cordyceps militaris. The purification protocol consisted of affinity chromatography, ion-exchange chromatography and gel filtration. The haemagglutinating activity of the HA could not be inhibited by simple sugars or heparin, and was stable over the pH range 2–13 and up to 60°C. Chemical modification of tryptophan and tyrosine residues had no effect. The HA exhibited some antiproliferative activity towards hepatoma (HepG2) cells and inhibited HIV-1 reverse transcriptase (IC50=10 μM). However, it did not exhibit antifungal activity, mitogenic activity towards splenocytes, nitric oxide-inducing activity towards macrophages or RNase activity. The results of the present study add to the meagre information pertaining to agglutinins from ascomycete and medicinal mushrooms. It is revealed in this study that C. militaris HA differs from other ascomycete mushroom HAs in a variety of biochemical characteristics.

Isolation and characterization of l-rhamnose-binding lectin, which binds to microsporidian Glugea plecoglossi, from ayu (Plecoglossus altivelis) eggs

A rhamnose-binding lectin, named SFL, was isolated from the eggs of ayu (sweet fish, Plecoglossus altivelis) by affinity and ion-exchange chromatographies. SFL revealed 287 amino acid residues with 3 tandemly repeated domains, and contained 8 half-Cys residues in each domain. The lectin was shown to have a highly specific binding affinity to globotriaosylceramide (Gb3) by frontal affinity chromatography using 100 oligosaccharides. SFL was localized in several tissues and serum of both male and female ayu, such as gill, liver, ovary, testis, intestine, stomach, brain, kidney and serum. The lectin agglutinated the spores of the microsporidian Glugea plecoglossi, which is a pathogen of ayu. Although SFL bound to glycoproteins and glycolipids of G. plecoglossi spores, Gb3 could not be detected in either of them. The results suggest that SFL could interact with various glycoconjugates of pathogens to play a role in the adhesion of microorganisms invading in the body.

Purification, cloning and characterization of egg lectins from the teleost Tribolodon brandti

Three L-rhamnose-binding egg lectins, TBL1, TBL2 and TBL3, were isolated from the eggs of the Far East dace Tribolodon brandti by a combination of affinity chromatography on L-rhamnose-Sepharose 6B gel and reversed-phase HPLC. L-rhamnose is a common inhibitor of the purified lectins and strongly inhibited the hemagglutinating activity of TBL2 and TBL3, but less weakly that of TBL1. L-arabinose, which has the same hydroxyl group orientation at C2 and C4 as L-rhamnose, and D-galactose showed no inhibitory activity against TBL1 but showed weak inhibitory activity against TBL2 and TBL3. The open reading frames of the cDNAs of TBL1, TBL2 and TBL3 encoded for mature proteins of 207, 189, and 293 amino acid residues, respectively. A BLAST homology search showed that the TBLs have about 40% homology to the carbohydrate recognition domains of rhamnose-binding lectins in salmonid eggs. The tandem repeated domains present in TBL1, TBL2 and TBL3 were two, two and three, respectively. TBL2 was exclusively expressed in ovary, while TBL1 and TBL3 were expressed mainly in ovary and weakly in various tissues including gill, heart, kidney, liver, spleen and testis.

Structural characterization of a rhamnose-binding glycoprotein (lectin) from Spanish mackerel (Scomberomorous niphonius) eggs

A rhamnose-binding glycoprotein (lectin), named SML, was isolated from the eggs of Spanish mackerel (Scomberomorous niphonius) by affinity and ion-exchange chromatographies. SML was composed of a non-covalently linked homodimer. The SML subunit was composed of 201 amino acid residues with two tandemly repeated domains, and contained 8 half-Cys residues in each domain, which is highly homologous to the N-terminal lectin domain of calcium-independent alpha-latrotoxin receptor in mammalian brains. Each domain has the same disulfide bonding pattern; Cys10-Cys40, Cys20-Cys99, Cys54-Cys86 and Cys67-Cys73 were located in the N-terminal domain, and Cys108-Cys138, Cys117-Cys195, Cys152-Cys182 and Cys163-Cys169 were in the C-terminal domain. SML was N-glycosylated at Asn168 in the C-terminal domain. The structure of the sugar chain was determined to be NeuAc-Galbeta1-4GlcNAcbeta1-2Manalpha1-6-(NeuAc-Galbeta1-4GlcNAcbeta1-2Manalpha1-3)Manbeta1-4GlcNAcbeta1-4GlcNAc-Asn.

A mannose-specific tetrameric lectin with mitogenic and antibacterial activities from the ovary of a teleost, the cobia (Rachycentron canadum)

A tetrameric lectin, with hemagglutinating activity toward rabbit erythrocytes and with specificity toward D-mannosamine and D(+)-mannose, was isolated from the ovaries of a teleost, the cobia Rachycentron canadum. The isolation protocol comprised ion exchange chromatography on CM-cellulose and Q-Sepharose, ion exchange chromatography by fast protein liquid chromatography (FPLC) on Mono Q, and finally gel filtration by FPLC on Superose 12. The lectin was adsorbed on all ion exchangers used. It exhibited a molecular mass of 180 kDa in gel filtration on Superose 12 and a single 45-kDa band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating that it is a tetrameric protein. The hemagglutinating activity of the lectin was stable up to 40 degrees C and between pH 4 and pH 10. All hemagglutinating activity disappeared at 60 degrees C and at pH 1 and pH 13. The hemagglutinating activity was doubled in the presence of 0.1 microM FeCl3. The lectin exerted antibacterial activity against Escherichia coli with 50% inhibition at 250 microg. There was no antifungal activity toward Coprinus comatus, Fusarium oxysporum, Mycosphaerella arachidicola, and Rhizoctonia solani at a dose of 300 microg. The lectin exhibited maximal mitogenic response from mouse splenocytes at a concentration of 14 microM.

A lectin with some unique characteristics from the samta tomato

A lectin, with a molecular mass of 79 kDa, and with specificity toward rhamnose and O-nitrophenyl-beta-D-galactopyranoside, was isolated from samta tomato fruits. The procedure entailed ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on CM-cellulose and gel filtration by fast protein liquid chromatography on Superdex 75. The lectin was unadsorbed on DEAE-cellulose but adsorbed on Affi-gel blue gel and CM-cellulose. The lectin was stable up to 70 degrees C. The lectin activity was potentiated by NaOH solutions (25-100 mM), but was reduced by 50 and 100 mM HCl solutions. The activity of the lectin was reduced in the presence of CaCl(2), MgCl(2) and ZnCl(2), but was potentiated by 5 and 10 mM AlCl(3) solutions. The lectin stimulated the mitogenic response in mouse splenocytes and inhibited human immunodeficiency virus-1 reverse transcriptase with an IC(50) of 6.2 microM.

Evidence for lectin activity of a plant receptor-like protein kinase by application of neoglycoproteins and bioinformatic algorithms

Detection of genes for putative receptor-like protein kinases, which contain an extracellular domain related to leguminous lectins, in plant genomes inspired the hypothesis that this part acts as sensor. Initial support for this concept came from proof for protein kinase activity. The next step, focusing on the protein of lombardy poplar (Populus nigra var. italica), is scrutiny for lectin activity. Consequently, we first pinpointed sets of high-scoring sequence pairs by extensive databank search. The calculations resulted in P-values in the range from 10(-14) to 10(-18) exclusively for leguminous lectins, the Pterocarpus angolensis agglutinin being front runner with P=3 x 10(-18) and thus most suitable template for modeling. The superimposition of the two folds gave notable similarity in the region responsible for binding carbohydrate and Ca(2+)/Mn(2+)-ions. Binding activity toward carbohydrates was detected by assaying a panel of (neo)glycoproteins as polyvalent probes, especially for alpha-l-rhamnose and glycans of asialofetuin. It was strictly dependent on Ca(2+)-ions, enhanced by Mn(2+)-ions and reached a K(D)-value of 34.3 nM for the neoglycoprotein with rhamnose as ligand. These results give further research direction to define physiological ligands, plant/bacterial rhamnose-containing saccharides and rhamnose-mimetic glycans or peptides being potential candidates.

Isolation and characterization of a glucose/mannose/rhamnose-specific lectin from the knife bean Canavalia gladiata

A lectin with specificity toward mannose, glucose, and rhamnose has been isolated from the legumes of the knife bean Canavalia gladiata. The lectin is composed of two identical 30-kDa subunits with substantial N-terminal sequence similarity to Concanavalin A (Con A). It was purified by affinity chromatography on Affi-gel blue gel, ion exchange chromatography on Mono S, and gel filtration by fast protein liquid chromatography on Superdex 200. Compared with Con A, knife bean lectin started to stimulate [methyl-(3)H]thymidine uptake by mouse splenocytes at a lower concentration, and more potently inhibited proliferation of L1210 leukemia cells. In contrast to Con A, the mitogenic activity of knife bean lectin toward mouse splenocytes, but not its antiproliferative activity toward tumor cells, could be abrogated by 250 mM glucose. Both mitogenic and antiproliferative activities of Con A were abolished by glucose. The lectin inhibited HIV-1 reverse transcriptase with an IC(50) of 35 microM and cell-free translation in a rabbit reticulocyte lysate system with an IC(50) of 2.08 microM. The lectin did not exhibit antifungal activity.

Characterization of a galactose binding serum lectin from the Indian catfish, Clarias batrachus: possible involvement of fish lectins in differential recognition of pathogens

A lectin with molecular mass around 200 kDa was isolated from the serum of the Indian catfish Clarias batrachus. The bioactivity of this serum lectin was Ca2+ and pH dependent. The lectin appeared to be specific for alpha-methyl galactose and sialoglycoproteins like porcine and bovine submaxillary mucin and could agglutinate human, rabbit, mice, rat and chicken erythrocytes. This fish lectin was able to specifically agglutinate different gram negative bacteria. When it was checked against different strains of the fish pathogen Aeromonas sp., it significantly altered the viability and pathogenicity of the bacteria. Binding of the lectin to Aeromonas sp., resulted in a dose dependent increase in the bactericidal activity of fish macrophages. However, when the lectin was checked against different gram positive bacteria it could not agglutinate or affect the viability of those strains and also failed to bring about any significant change in the bactericidal potential of fish macrophages. The lectin was able to induce the proliferation of head kidney lymphocytes of Clarias and helped in the release of 'IL-1' like cytokines from head kidney macrophages.

The male seahorse synthesizes and secretes a novel C-type lectin into the brood pouch during early pregnancy

The male seahorse incubates its young in a manner resembling that of a mammalian pregnancy. After the female deposits her eggs into the male's brood pouch they are fertilized and the embryos develop and grow for several weeks until they are able to withstand the external environmental conditions independently, at which point they are irreversibly released. Although the precise function of the brood pouch is not clear, it is probably related to providing a suitable protective and osmotic environment for the young. The aim of this project was to construct and characterize a cDNA library made from the tissue lining the pouch, in order to help understand the molecular mechanisms regulating its development and function. The library profile indicates expression of genes encoding proteins involved in metabolism and transport, as well as structural proteins, gene regulatory proteins, and other proteins whose function is unknown. However, a large portion of the library contained genes encoding C-type lectins (CTLs), of which three full-length proteins were identified and found to contain a signal peptide and a single C-lectin domain, possessing all the conserved structural elements. We have produced recombinant protein for one of these and raised antisera; we have shown, using Western analysis and 2D electrophoresis, that this protein is secreted in significant quantities into the pouch fluid specifically during early pregnancy. Preliminary functional studies indicate that this CTL causes erythrocyte agglutination and may help to repress bacterial growth.

Purification and characterization of four isoforms of Himalayan mistletoe ribosome-inactivating protein from Viscum album having unique sugar affinity

Ribosome-inactivating proteins having antitumor and immunomodulatory properties constitute the active principle of widely used mistletoe therapy in Europe. This is the first report of the four isoforms of Himalayan mistletoe ribosome-inactivating proteins (HmRips) from Viscum album parasitized on wild apple inhabiting NW Himalayas. HmRips were purified by affinity chromatography and four isoforms were separated by ion-exchange chromatography. HmRip 1, 2, 3, and 4 have isoelectric points of 6.6, 6.1, 5.2, and 4.7, respectively. Disulfide linked toxin and lectin subunits of HmRip 1 and 2 isoforms have molecular weights of 28 and 34kDa while those of HmRip 3 and 4 have 28 and 32kDa. The isoforms lacked blood group specificity and showed positive activity with seven mammalian erythrocyte types but did not show any activity with avian erythrocyte type. Lectin activity of HmRips remained unchanged for a wide range of temperatures (0-65 degrees C) and pH (3-9). Unlike other type II Rips, the HmRip 1, 2, and 4 showed unique affinity towards l-rhamnose, meso-inositol, and l-arabinose while HmRip 3 has specificity to gal/galNAc. Sugar binding studies with 22 sugars also suggested that the C-4 hydroxyl of galactose might be the critical site involved in sugar binding of HmRips. Type II Rips are known to be galactoside specific and do not have affinity for l-rhamnose and meso-inositol. However, HmRip 1, 2, and 4 having equal affinity for galactose and l-rhamnose do not strictly fit into any of the four structural classes of the lectins and represent a new class of type II Rips and plant lectins.

The immunostimulatory activity and stability of grass carp (Ctenopharyngodon idellus) roe lectin

A hexameric rhamnose-specific lectin with a molecular mass of 205kDa and exhibiting some N-terminal sequence similarity to other fish lectins was isolated from roe of the grass carp (Ctenopharyngodon idellus) by affinity chromatography on rhamnose-Sepharose and ion exchange chromatography by fast protein liquid chromatography on a Mono S column. The lectin exhibited mitogenic activity toward murine splenocytes with a potency lower than that of the plant lectin ConA. It exerted a stimulatory effect at a concentration of 10 micro g/ml on the phagocytic activity of seabream (Sparus sarba) macrophages. It was unstable toward heat (temperature > or =40 degrees C), acid (0.1M HCl), alkali (0.1M NaOH), trypsin and succinylation.