PURIFICATION AND PARTIAL CHARACTERIZATION OF A LECTIN FROM THE SEEDS OF DIOCLEA GUIANENSIS

Plant lectins as potent Anti-coronaviruses, Anti-inflammatory, antinociceptive and antiulcer agents

Lectins are defined as carbohydrate-binding proteins/glycoproteins of none immune origin, they are ubiquitous in nature, exist from bacteria to human cells. And due to their carbohydrate-binding recognition capacity, they have been a useful biological tool for the purification of glycoproteins and their subsequent characterization. Some plant lectins have also been revealed to own antinociceptive, antiulcer, and anti-inflammatory properties, where these features, in many instances, depending on the lectin carbohydrate-binding site. Coronavirus disease of 2019 (COVID-19) is a respiratory disease that struck the entire world leaving millions of people dead and more infected. Although COVID-19 vaccines have been made available, and quite a large number of world populations have already been immunized, the viral infection rates remained in acceleration, which continues to provoke major concern about the vaccines' efficacy. The belief in the ineffectiveness of the vaccine has been attributed in part to the recurrent mutations that occur in the epitope determinant fragments of the virus. Coronavirus envelope surface is extensively glycosylated being covered by more than sixty N-linked oligomannose, composite, and hybrid glycans with a core of Man3GlcNAc2Asn. In addition some O-linked glycans are also detected. Of these glyco-chains, many have also been exposed to several mutations, and a few remained conserved. Therefore, numerous plant lectins with a specificity directed towards these viral envelope sugars have been found to interact preferentially with them and are suggested to be scrutinized as a possible future tool to combat coronaviruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through blocking the viral attachment to the host cells. In this review, we will discuss the possible applications of plant lectins as anti-coronaviruses including SARS-CoV-2, antinociceptive, anti-inflammatory, and antiulcer agents with the proposed mechanism of their actions.

Purification and characterization of a highly thermostable GlcNAc-binding lectin from Collaea speciosa seeds

Lectins from plants of the Diocleinae subtribe often exhibit specificity towards mannose/glucose and derived sugars, with some plants also displaying a second lectin specific to lactose/GalNAc. Here, we present a novel lectin from Collaea speciosa, named CsL, that displays specificity for GlcNAc/glucose. The lectin was extracted from Collaea speciosa seeds and purified by a single chromatographic step on a Sephadex G-50 matrix. In solution, the lectin appears as a dimeric protein composed of 25 kDa monomers. The protein is stable at pH 7-8 and dependent on divalent cations. CsL maintained its agglutination activity after heating to 90 °C for 1 h. Glycan array studies revealed that CsL binds to N-glycans with terminal GlcNAc residues, chitobiose and chitotriose moieties. The partial amino acid sequence of the lectin is similar to that of some lactose-specific lectins from the same subtribe. In contrast to other ConA-like lectins, CsL is not toxic to Artemia. Because of its remarkably different properties and specificity, this lectin could be the first member of a new group inside the Diocleinae lectins.

Fruticulosin: A novel type 2 ribosome-inactivating protein from Abrus fruticulosus seeds that exhibits toxic and antileishmanial activity

Plant ribosome-inactivating proteins (RIPs) are a family of toxins that inhibit protein synthesis. In this study, we have isolated a novel type 2 ribosome-inactivating protein (RIP) present in seeds of the Abrus fruticulosus, named of fruticulosin. Fruticulosin, shows characteristics common to other type 2 RIPs, as specificity by galactosides (d-galactose, N-acetyl-d-galactosamine, and d-lactose), mass of approximately 60 kDa and presence of the of disulfide bonds. The N-terminal amino acid sequence (26 residues) of A-chain fruticulosin, determined by Edman degradation, revealed high similarity of the A-chain with those of other type 2 RIPs. The secondary structure of fruticulosin was analysed by circular dichroism, which showed that fruticulosin contains α-helices (22.3%), β-sheets (43.5%), and random coils and corners (34.2%). Furthermore, fruticulosin showed high toxicity in Artemia sp. (3.12 μg/mL), inhibited in vitro protein synthesis by a cell-free system and showed RNA N-glycosidase activity. Fruticulosin presented biological activities such as agglutination and antileishmanial activity on promastigote forms of Leishmania major.

Differential recognition of natural and remodeled glycotopes by three Diocleae lectins

The carbohydrate specificities of Dioclea grandiflora lectins DGL-I¹ and DGL-II, and Galactia lindenii lectin II (GLL-II) were explored by use of remodeled glycoproteins as well as by the lectin hemagglutinating activity against erythrocytes from various species with different glycomic profiles. The three lectins exhibited differences in glycan binding specificity but also showed overlapping recognition of some glycotopes (i.e. Tα glycotope for the three lectins; IIβ glycotope for DGL-II and GLL-II lectins); in many cases the interaction with distinct glycotopes was influenced by the structural context, i.e., by the neighbouring sugar residues. Our data complement and expand the existing knowledge about the binding specificity of these three Diocleae lectins, and taken together with results of previous studies, allow us to suggest a functional map of the carbohydrate recognition which illustrate the impact of modification of basic glycotopes enhancing, permiting, or inhibiting their recognition by each lectin.

Effect of algae and plant lectins on planktonic growth and biofilm formation in clinically relevant bacteria and yeasts

This study aimed to evaluate the abilities of plant and algae lectins to inhibit planktonic growth and biofilm formation in bacteria and yeasts. Initially, ten lectins were tested on Staphylococcus epidermidis, Staphylococcus aureus, Klebsiella oxytoca, Pseudomonas aeruginosa, Candida albicans, and C. tropicalis at concentrations of 31.25 to 250 μg/mL. The lectins from Cratylia floribunda (CFL), Vatairea macrocarpa (VML), Bauhinia bauhinioides (BBL), Bryothamnion seaforthii (BSL), and Hypnea musciformis (HML) showed activities against at least one microorganism. Biofilm formation in the presence of the lectins was also evaluated; after 24 h of incubation with the lectins, the biofilms were analyzed by quantifying the biomass (by crystal violet staining) and by enumerating the viable cells (colony-forming units). The lectins reduced the biofilm biomass and/or the number of viable cells to differing degrees depending on the microorganism tested, demonstrating the different characteristics of the lectins. These findings indicate that the lectins tested in this study may be natural alternative antimicrobial agents; however, further studies are required to better elucidate the functional use of these proteins.

Toxicity and binding profile of lectins from the Genus canavalia on brine shrimp

Lectins are sugar-binding proteins widely distributed in nature with many biological functions. Although many lectins have a remarkable biotechnological potential, some of them can be cytotoxic. Thus, the aim of this study was to assess the toxicity of five lectins, purified from seeds of different species of Canavalia genus. In order to determine the toxicity, assays with Artemia nauplii were performed. In addition, a fluorescence assay was carried out to evaluate the binding of lectins to Artemia nauplii. In order to verify the relationship between the structure of lectins and their cytotoxic effect, structural analysis was carried out to evaluate the volume of the carbohydrate recognition domain (CRD) of each lectin. The results showed that all lectins exhibited different toxicities and bound to a similar area in the digestive tract of Artemia nauplii. Concerning the structural analysis, differences in spatial arrangement and volume of CRD may explain the variation of the toxicity exhibited by each lectin. To this date, this is the first study that establishes a link between toxicity and structure of CRD from Diocleinae lectins.

Purification, partial characterization and immobilization of a mannose-specific lectin from seeds of Dioclea lasiophylla mart

Lectin from the seeds of Dioclea lasiophylla (DlyL) was purified in a single step by affinity chromatography on a Sephadex^® G-50 column. DlyL strongly agglutinated rabbit erythrocytes and was inhibited by monosaccharides (_D-mannose and α-methyl-d-mannoside) and glycoproteins (ovalbumin and fetuin). Similar to other Diocleinae lectins, DlyL has three chains, α, β and γ, with mass of 25,569 ± 2, 12,998 ± 1 and 12,588 ± 1 Da, respectively, and has no disulfide bonds. The hemagglutinating activity of DlyL was optimal in pH 8.0, stable at a temperature of 70 °C and decreased in EDTA solution, indicating that lectin activity is dependent on divalent metals. DlyL exhibited low toxicity on Artemia sp. nauplii, but this effect was dependent on the concentration of lectin in solution. DlyL immobilized on cyanogen bromide-activated Sepharose^® 4B bound 0.917 mg of ovalbumin per cycle, showing the ability to become a tool for glycoproteomics studies.

Crystallization and characterization of an inflammatory lectin purified from the seeds of Dioclea wilsonii

DwL, a lectin extracted from the seeds of Dioclea wilsonii, is a metalloprotein with strong agglutinating activity against rabbit and ABO erythrocytes, inhibited by glucose and mannose. DwL was purified by affinity chromatography on a Sephadex G-50 column and ion exchange chromatography on a HiTrap SP XL column. SDS-PAGE revealed three electrophoretic bands corresponding to the α (25,634 ± 2 Da), β (12,873 ± 2 Da) and γ (12,779 ± 2 Da) chains. Protein sequencing was done by Tandem Mass Spectrometry. The primary sequence featured 237 amino acids and was highly homologous to other reported Diocleinae lectins. A complete X-ray dataset was collected at 2.0 Å for X-Man-complexed DWL crystals produced by the vapor diffusion method. The crystals were orthorhombic and belonged to the space group I222, with the unit-cell parameters a = 59.6, b = 67.9 and c = 109.0 Å. DWL differed in potency from other ConA-like lectins and was found to induce neutrophil migration in rats, making it particularly useful in structural/functional studies of this class of proteins.

Composição química e antinutrientes presentes nas amêndoas cruas e torradas de chicha (Sterculia striata A. St. Hill & Naudin)

OBJETIVO: Analisar os componentes químicos e antinutrientes antes e após torrefação da amêndoa de chichá da espécie Sterculia striata A. St. Hill & Naudin, oriunda de Corrente, Piauí. MÉTODOS: Foram realizadas análises: centesimal, perfil de ácidos graxos, antinutrientes (taninos, inibidor de tripsina, inibidor de amilase, lectina, fitatos), compostos fenólicos e atividade de peroxidase e polifenoloxidase. RESULTADOS: Os resultados da análise centesimal da amêndoa crua e torrada foram: lipídeos de 25,1% e 26,2%, carboidratos de 44,4% e 45,6%, proteína de 20,8% e 22,1%, cinzas de 3,7% e 4,0%, fibra alimentar total de 12,3% e 10,4%, respectivamente. Nas amêndoas cruas e torradas não foram encontradas lectinas, taninos, inibidores de tripsina e alfa-amilase. Verificou-se a ausência de peroxidase e polifenoloxidase e conteúdo de compostos fenólicos de 107,7mg/100g e 108,9mg/100g para amêndoas cruas e torradas, respectivamente. CONCLUSÃO: A torrefação realizada a 205°C por 11 minutos diminuiu o teor de fitatos de 10,6mg/g para 5,5mg/g. Por fim, as amêndoas de chichá, cruas e torradas, apresentam alto teor de proteínas, fibras, ácidos graxos monoinsaturados e saturados.

A ConA-like lectin from Dioclea guianensis Benth. has antifungal activity against Colletotrichum gloeosporioides, unlike its homologues, ConM and ConA

This study reports on the antifungal activity of Dgui, a ConA-like lectin from Dioclea guianensis seeds. Dgui inhibited conidial germination but not mycelial growth of Colletotrichum gloeosporioides. The lectins ConA and ConM from Canavalia ensiformis and Canavalia maritima, respectively, share high levels of amino acid sequence similarity (>84%) with Dgui and have the same specificity toward glucose/mannose but had no effect on the fungus. Fluorescence microscopy showed that both Dgui and ConM bind to C. gloeosporioides ungerminated conidia. However, Dgui did not bind to C. gloeosporioides germinated conidia and germ tubes and was not inhibitory to mycelial growth. Because only Dgui inhibited germination of the fungus, C. gloeosporioides conidia might have surface-specific germination targets recognized by Dgui but not by its homologues, ConM and ConA. Therefore, Dgui is a candidate for biotechnological approaches for improving the resistance of various nutritionally and commercially important crops that are affected by C. gloeosporioides.

Potential immunomodulatory effects of plant lectins in Schistosoma mansoni infection

Lectins are sugar-binding glycoproteins that can stimulate, in a non-antigen-specific fashion, lymphocytes, leading to proliferation and cytokine production. Some lectins are utilized as in vitro mitogenic lymphocyte stimulators and their use as immunomodulators against infectious diseases has been evaluated experimentally. In the experimental murine model, the immune response to schistosomiasis is Th1-like during the initial stage of infection, with a shift towards a Th2-like response after oviposition. We report the response of schistosomiasis patients' (n=37) peripheral blood mononuclear cells (PBMC) to stimulation by lectins, including newly isolated lectins from Brazilian flora, and by Schistosomamansoni soluble egg antigens (SEA). Cytokine production upon lectin stimulation ex vivo was assessed in PBMC supernatants, collected at 24 and 72 h, by sandwich ELISA to IL-5, IL-10, TNF-alpha and IFN-gamma. In PBMC from infected patients all but one of the lectins induced a Th2-like cytokine response, characterized by elevated IL-5 production that was higher than that induced by SEA stimulation alone. Our results show that the Th2 environment present during schistosomiasis is not affected and that it may be further stimulated by the presence of lectins.

Differential effect of plant lectins on mast cells of different origins

Histamine release induced by plant lectins was studied with emphasis on the carbohydrate specificity, external calcium requirement, metal binding sites, and mast cell heterogeneity and on the importance of antibodies bound to the mast cell membrane to the lectin effect. Peritoneal mast cells were obtained by direct lavage of the rat peritoneal cavity and guinea pig intestine and hamster cheek pouch mast cells were obtained by dispersion with collagenase type IA. Histamine release was induced with concanavalin A (Con A), lectins from Canavalia brasiliensis, mannose-specific Cymbosema roseum, Maackia amurensis, Parkia platycephala, Triticum vulgaris (WGA), and demetallized Con A and C. brasiliensis, using 1-300 microg/ml lectin concentrations applied to Wistar rat peritoneal mast cells, peaking on 26.9, 21.0, 29.1, 24.9, 17.2, 10.7, 19.9, and 41.5%, respectively. This effect was inhibited in the absence of extracellular calcium. The lectins were also active on hamster cheek pouch mast cells (except demetallized Con A) and on Rowett nude rat (animal free of immunoglobulins) peritoneal mast cells (except for mannose-specific C. roseum, P. platycephala and WGA). No effect was observed in guinea pig intestine mast cells. Glucose-saturated Con A and C. brasiliensis also released histamine from Wistar rat peritoneal mast cells. These results suggest that histamine release induced by lectins is influenced by the heterogeneity of mast cells and depends on extracellular calcium. The results also suggest that this histamine release might occur by alternative mechanisms, because the usual mechanism of lectins is related to their binding properties to metals from which depend the binding to sugars, which would be their sites to bind to immunoglobulins. In the present study, we show that the histamine release by lectins was also induced by demetallized lectins and by sugar-saturated lectins (which would avoid their binding to other sugars). Additionally, the lectins also released histamine from Rowett nude mast cells that are free of immunoglobulins.

Crystal structure of native and Cd/Cd-substituted Dioclea guianensis seed lectin. A novel manganese-binding site and structural basis of dimer-tetramer association

Diocleinae legume lectins are a group of oligomeric proteins whose subunits display a high degree of primary structure and tertiary fold conservation but exhibit considerable diversity in their oligomerisation modes. To elucidate the structural determinants underlaying Diocleinae lectin oligomerisation, we have determined the crystal structures of native and cadmium-substituted Dioclea guianensis (Dguia) seed lectin. These structures have been solved by molecular replacement using concanavalin (ConA) coordinates as the starting model, and refined against data to 2.0 A resolution. In the native (Mn/Ca-Dguia) crystal form (P4(3)2(1)2), the asymmetric unit contains two monomers arranged into a canonical legume lectin dimer, and the tetramer is formed with a symmetry-related dimer. In the Cd/Cd-substituted form (I4(1)22), the asymmetric unit is occupied by a monomer. In both crystal forms, the tetrameric association is achieved by the corresponding symmetry operators. Like other legume lectins, native D. guianensis lectin contains manganese and calcium ions bound in the vicinity of the saccharide-combining site. The architecture of these metal-binding sites (S1 and S2) changed only slightly in the cadmium/cadmium-substituted form. A highly ordered calcium (native lectin) or cadmium (Cd/Cd-substituted lectin) ion is coordinated at the interface between dimers that are not tetrameric partners in a similar manner as the previously identified Cd(2+) in site S3 of a Cd/Ca-ConA. An additional Mn(2+) coordination site (called S5), whose presence has not been reported in crystal structures of any other homologous lectin, is present in both, the Mn/Ca and the Cd/Cd-substituted D. guianensis lectin forms. On the other hand, comparison of the primary and quaternary crystal structures of seed lectins from D. guianensis and Dioclea grandiflora (1DGL) indicates that the loop comprising residues 117-123 is ordered to make interdimer contacts in the D. grandiflora lectin structure, while this loop is disordered in the D. guianensis lectin structure. A single amino acid difference at position 131 (histidine in D. grandiflora and asparagine in D. guianensis) drastically reduces interdimer contacts, accounting for the disordered loop. Further, this amino acid change yields a conformation that may explain why a pH-dependent dimer-tetramer equilibrium exists for the D. guianensis lectin but not for the D. grandiflora lectin.

Nutritional study of two Brazilian soybean (Glycine max) cultivars differing in the contents of antinutritional and toxic proteins

The research was conducted with two different recently released Brazilian soybean cultivars (Rio Balsas and Bays) to evaluate whether there is any correlation between the different levels of antinutritional and/or toxic proteins in the cultivars and their nutritive value as sources of protein for monogastric animals (rats). Furthermore, it is discussed, for the first time, the role of the dietary soyatoxin on the performance of rats fed on diets containing soyatoxin-rich (cv. Bays) and soyatoxin-free (cv. Rio Balsas) soybean cultivars. Feeding rats with diets containing raw soybean cultivars showed a lower growth rate, net protein utilization and digestibility, a much higher dry matter and nitrogen excretion and macroscopic alterations in internal organs when compared to rats fed on egg-white protein. The nutritional parameters measured for the diet based on raw Bays cultivar were poorer than those of the diet prepared with Rio Balsas. In the raw soybeans, trypsin inhibitor and lectin, and urease to a lesser extent, significantly affected at different fashion the soybean protein utilization. Heating treatment of the Bays seeds increased the growth rate, NPU, in vivo protein digestibility and practically eliminated or attenuated all the organ alterations observed. This study might be helpful in the choice of safe and nutritious soybean cultivars.

Purification of a novel antibacterial and haemagglutinating protein from the purple gland of the sea hare, Aplysia dactylomela rang, 1828

Physicochemical characterisation and antibacterial and haemagglutinating properties of a new protein isolated from purple fluid of the Aplysia dactylomela are reported. The purification procedure consisted basically of ammonium sulphate fractionation, ion exchange, exclusion molecular and hydrophobic interaction chromatography. The highly purified protein, designated dactylomelin-P, is a single chain protein of 60,000 Da by SDS-polyacrylamide gel electrophoresis and 56,200 Da by gel filtration on calibrated Superose column at pH 7.5 and contains less than 0.05% of its weight in neutral carbohydrates. Dactylomelin-P has two biological activities, antibacterial and haemagglutinating. The antibacterial action is bacteriostatic but not bactericidal. The haemagglutinating activity is preferentially against rabbit erythrocytes. The glycoprotein fetuin was able to abolish the haemagglutinating activity but not the antibacterial one even when used at concentrations 10 fold higher. This is the first time that a chimeroprotein is described in the purple fluid of sea hares, which may be involved in the chemical defence mechanism of these organisms.

Thermodynamic binding studies of lectins from the diocleinae subtribe to deoxy analogs of the core trimannoside of asparagine-linked oligosaccharides

Lectins from seven different species of the Diocleinae subtribe have been recently isolated and characterized in terms of their carbohydrate binding specificities (Dam, T. K., Cavada, B. S., Grangeiro, T. B., Santos, C. F., de Sousa, F. A. M., Oscarson, S., and Brewer, C. F. (1998) J. Biol. Chem. 273, 12082-12088). The lectins included those from Canavalia brasiliensis, Cratylia floribunda, Dioclea rostrata, Dioclea virgata, Dioclea violacea, and Dioclea guianensis. All of the lectins exhibited specificity for Man and Glc residues, but much higher affinities for the branched chain trimannoside, 3,6-di-O-(alpha-d-mannopyranosyl)-d-mannose, which is found in the core region of all asparagine-linked carbohydrates. In the present study, isothermal titration microcalorimetry is used to determine the binding thermodynamics of the above lectins, including a new lectin from Canavalia grandiflora, to a complete series of monodeoxy analogs of the core trimannoside. From losses in the affinity constants and enthalpies of binding of certain deoxy analogs, assignments are made of the hydroxyl epitopes on the trimannoside that are involved in binding to the lectins. The pattern of binding of the deoxy analogs is similar for all seven lectins, and similar to that of concanavalin A which is also a member of the Diocleinae subtribe. However, differences in the magnitude of the thermodynamic binding parameters of the lectins are observed, even though the lectins possess conserved contact residues in many cases, and highly conserved primary sequences. The results indicate that non-contact residues in the lectins, even those distant from the binding sites, modulate their thermodynamic binding parameters.

Demonstration of a conserved histidine and two water ligands at the Mn2+ site in Diocleinae lectins by pulsed EPR spectroscopy

Lectins from the Diocleinae subtribe, including Canavalia brasiliensis, Canavalia bonariensis, Canavalia grandiflora, Cratylia floribunda, Dioclea grandiflora, Dioclea guianensis, Dioclea rostrata, Dioclea violacea, and Dioclea virgata, have been recently isolated and characterized in terms of their carbohydrate binding specificities. Although all of the lectins are Man/Glc specific, they possess different biological activities. In the present study, electron paramagnetic resonance (EPR) spectroscopy demonstrates that all nine Diocleinae lectins contain Mn2+. The spectra of C. floribunda and D. rostrata suggest Mn2+ site symmetry different from that of the other seven lectins. However, electron spin-echo envelope modulation (ESEEM) spectroscopy indicates that all nine lectins are coordinated to a histidyl imidazole, with similar electron-nuclear coupling to the Mn2+-bound imidazole nitrogen. ESEEM also demonstrates ligation of two water molecules to Mn2+ in all nine Diocleinae lectins. Thus, the EPR and ESEEM data indicate the presence of a Mn2+ binding site in the above Diocleinae lectins with a conserved histidine residue and two water ligands.

Molecular characterization and crystallization of Diocleinae lectins

Molecular characterization of seven Diocleinae lectins was assessed by sequence analysis, determination of molecular masses by mass spectrometry, and analytical ultracentrifugation equilibrium sedimentation. The lectins show distinct pH-dependent dimer-tetramer equilibria, which we hypothesize are due to small primary structure differences at key positions. Lectins from Dioclea guianensis, Dioclea virgata, and Cratylia floribunda seeds have been crystallized and preliminary X-ray diffraction analyses are reported.

Toxic, antimicrobial and hemagglutinating activities of the purple fluid of the sea hare Aplysia dactylomela Rang, 1828

The antimicrobial, hemagglutinating and toxic activities of the purple fluid of the sea hare Aplysia dactylomela are described. Intact or dialyzed purple fluid inhibited the growth of species of Gram-positive and Gram-negative bacteria and the action was not bactericidal but bacteriostatic. The active factor or factors were heat labile and sensitive to extreme pH values. The fluid preferentially agglutinated rabbit erythrocytes and, to a lesser extent, human blood cells, and this activity was inhibited by the glycoprotein fetuin, a fact suggesting the presence of a lectin. The fluid was also toxic to brine shrimp nauplii (LD50 141.25 micrograms protein/ml) and to mice injected intraperitoneally (LD50 201.8 +/- 8.6 mg protein/kg), in a dose-dependent fashion. These toxic activities were abolished when the fluid was heated. Taken together, the data suggest that the activities of the purple fluid are due primarily to substance(s) of a protein nature which may be involved in the chemical defense mechanism of this sea hare.

Diocleinae lectins are a group of proteins with conserved binding sites for the core trimannoside of asparagine-linked oligosaccharides and differential specificities for complex carbohydrates

The seed lectin from Dioclea grandiflora and jack bean lectin concanavalin A (ConA) are both members of the Diocleinae subtribe of Leguminosae lectins. Both lectins have recently been shown to possess enhanced affinities and extended binding sites for the trisaccharide, 3,6-di-O-(alpha-D-mannopyranosyl)-D-mannose, which is present in the core region of all asparagine-linked carbohydrates (Gupta, D., Oscarson, S., Raju, S., Stanley, P. Toone, E. J. and Brewer, C. F. (1996) Eur. J. Biochem. 242, 320-326). In the present study, the binding specificities of seven other lectins from the Diocleinae subtribe have been investigated by hemagglutination inhibition and isothermal titration microcalorimetry (ITC). The lectins are from Canavalia brasiliensis, Canavalia bonariensis, Cratylia floribunda, Dioclea rostrata, Dioclea virgata, Dioclea violacea, and Dioclea guianensis. Hemagglutination inhibition and ITC experiments show that all seven lectins are Man/Glc-specific and have high affinities for the core trimannoside, like ConA and D. grandiflora lectin. All seven lectins also exhibit the same pattern of binding to a series of monodeoxy analogs and a tetradeoxy analog of the trimannoside, similar to that of ConA and D. grandiflora lectin. However, C. bonariensis, C. floribunda, D. rostrata, and D. violacea, like D. grandiflora, show substantially reduced affinities for a biantennary complex carbohydrate with terminal GlcNAc residues, while C. brasiliensis, D. guianensis, and D. virgata, like ConA, exhibit affinities for the oligosaccharide comparable with that of the trimannoside. Thermodynamic data obtained by ITC indicate different energetic mechanisms of binding of the above two groups of lectins to the complex carbohydrate. The ability of the lectins to induce histamine release from rat peritoneal mast cells is shown to correlate with the relative affinities of the proteins for the biantennary carbohydrate.

Isolation and partial characterisation of highly toxic lectins from Abrus pulchellus seeds

The seeds of Abrus pulchellus, sub-specie tenuiflorus, belonging to the Leguminosae, subfamily Papilionoideae contain highly toxic lectins exhibiting specificity for galactose and galactose-containing structures. The toxins which agglutinate rabbit erythrocytes, present a highly toxic activity in vivo when injected in the peritoneal cavity of mice (LD50=31 microg x kg(-1)) or when tested with the microcrustacean Arthemia salina (LD50=3.5 microg x ml(-1)). The active fraction was purified in a single step, by affinity chromatography on a Sepharose-4B column. The purified toxins migrated as two single bands of Mr 63000 and 61500 Da (SDS-PAGE) and Mr 31500 and 29000 Da (SDS-PAGE with 2-mercaptoethanol), respectively, suggesting the presence of disulphide-bridge interchains as occurs in other plant toxins. The antibodies anti-A. pulchellus toxins did not recognize ricin preparation and only partial identity was observed to A. precatorius toxic lectins prepared in a similar way to ricin and A. pulchellus toxins.

Histamine release induced by glucose (mannose)-specific lectins isolated from Brazilian beans. Comparison with concanavalin A

The histamine releasing properties of glucose (mannose)-specific lectins isolated from Brazilian beans was examined. The Canavalia brasiliensis, Dioclea rostrata, and Dioclea virgata lectins induced histamine release in rat peritoneal mast cells similar to concanavalin A. Less potency and efficacy was observed for Canavalia maritima, Dioclea guianensis, and Dioclea violacea while very low activities were seen for the lectins from Dioclea grandiflora, Canavalia bonariensis, and Cratylia floribunda. The histamine releasing effect was quenched by higher doses of D. virgata lectin similar to what was reported for concanavalin A. This effect was abrogated by increasing the concentration of calcium in the incubating medium. As these above proteins have sites that bind calcium, higher doses of the lectins might withdraw the calcium which is essential for the mast cell secretion.

Human lymphocyte stimulation by legume lectins from the Diocleae tribe

Lectins from eight leguminous seeds from the Diocleae tribe were compared to Concanavalin A (Con A), a well known T cell mitogen, on the stimulation of lymphocyte proliferation and Interferon gamma (IFN-gamma) production by peripheral blood mononuclear cells (PBMC) from normal volunteers. Lectins from Canavalia brasiliensis and Dioclea virgata induced the highest lymphocyte proliferation, both much higher than levels obtained with Con A, whereas lectins from Dioclea guianensis var. lasiophylla and from Canavalia bonariensis induced the lowest stimulation. Lectins from Dioclea rostrata, D. grandiflora, D. violacea and Cratylia floribunda induced intermediate levels of proliferation. The highest stimulation for IFN-gamma production was obtained with the lectin from D. rostrata, followed by those of C. floribunda and C. brasiliensis; only the lectins from D. virgata and C. bonariensis induced an IFN-gamma production lower than the one obtained by Con A-stimulation. Since all these legumes belong to the same tribe of C. ensiformis (Con A), and all are supposed to exhibit very similar lectins, it is interesting the high variation in the stimulation of lymphocyte proliferation. It is also noteworthy the dissociation between this parameter and IFN-gamma production in the case of D. virgata. A detailed analysis on the structure of such lectins, and their ligand sugars on lymphocyte surface is necessary to further explore such differences.