Review: The multiple roles of plant lectins

For decades, the biological roles of plant lectins remained obscure and subject to speculation. With the advent of technological and scientific progress, researchers have compiled a vast amount of information regarding the structure, biological activities and functionality of hundreds of plant lectins. Data mining of genomes and transcriptome sequencing and high-throughput analyses have resulted in new insights. This review aims to provide an overview of what is presently known about plant lectins, highlighting their versatility and the importance of plant lectins for a multitude of biological processes, such as plant development, immunity, stress signaling and regulation of gene expression. Though lectins primarily act as readers of the glycocode, the multiple roles of plant lectins suggest that their functionality goes beyond carbohydrate-recognition.

Immunostimulatory and anti-allergic potential of novel heterotrimeric lectin from seeds of Zizyphus mauritiana Lam

Zizyphus mauritiana Lam. seeds (ZMS) have been used medicinally as sedative or hypnotic drugs in most of Asian countries. ZMS has significant benefits to the human health. Therefore, we have evaluated immunomodulatory effect of lectin extracted from these ZMSL in both in vitro and in vivo study. Anaphylaxis is a severe life-threatening allergic reaction and Arthus reaction is deposition of immune complex and complement system activation, so we hypothesized that if ZMSL can protect these severe allergic diseases. We have studied the effect of ZMSL on macrophages and Wistar albino rats and confirmed its protective effect against anaphylaxis and Arthus reaction. Results of this study suggest ZMSL have immunostimulatory and antiallergic activity.

Bioaccessibility and In Vitro Intestinal Permeability of a Recombinant Lectin from Tepary Bean (Phaseolus acutifolius) Using the Everted Intestine Assay

Tepary bean (Phaseolus acutifolius) lectins exhibit differential in vitro and in vivo biological effects, but their gastrointestinal interactions and digestion have not yet been assessed. This work aimed to evaluate the changes of a recombinant Tepary bean lectin (rTBL-1) through an in vitro and ex vivo gastrointestinal process. A polyclonal antibody was developed to selectively detect rTBL-1 by Western blot (WB) and immunohistochemical analysis. Everted gut sac viability was confirmed until 60 min, where protein bioaccessibility, apparent permeability coefficient, and efflux ratio showed rTBL-1 partial digestion and absorption. Immunoblot assays suggested rTBL-1 internalization, since the lectin was detected in the digestible fraction. The immunohistochemical assay detected rTBL-1 presence at the apical side of the small intestine, potentially due to the interaction with the intestinal cell membrane. The in silico interactions between rTBL-1 and some saccharides or derivatives showed high binding affinity to sialic acid (-6.70 kcal/mol) and N-acetylglucosamine (-6.10 kcal/mol). The ultra-high-performance liquid chromatography-electron spray ionization-quantitative time-of-flight coupled to mass spectrometry (UHPLC-ESI-QTOF/MS) analysis showed rTBL-1 presence in the gastric content and the non-digestible fraction after intestinal simulation conditions. The results indicated that rTBL-1 partially resisted the digestive conditions and interacted with the intestinal membrane, whereas its digestion allowed the absorption or internalization of the protein or the derivative peptides. Further purification of digestion samples should be conducted to identify intact rTBL-1 protein and digested peptides to assess their physiological effects.

Protection of the intestinal epithelium of poultry against deleterious effects of dietary lectins by a multi-strain bacterial supplement

The intake of antinutritional factors produce impairment on the intestinal digestive function, impeding the efficient use of nutrients. Probiotics could be useful in poultry breeding to prevent negative effects of antinutritional factors, like the dietary lectins soybean agglutinin (SBA) and wheat germ agglutinin (WGA). Therefore, this investigation aimed to verify that SBA and wheat, which contains WGA, exert harmful effects on the intestinal mucosa and the digestive system of young poultry, and determine if the administration of probiotics able to capture lectins could counteract their effects. The trials performed demonstrated that a mixture of Bifidobacterium infantis CRL 1395, Enterococcus faecium LET 301, Lactobacillus salivarius LET 201, L. reuteri LET 210, and Propionibacterium acidipropionici LET 103, strains with ex vivo ability to interfere with the interaction of lectins and epithelial cells, has no negative effect on young chickens health. Middle levels of SBA, as well as wheat as a source of WGA, resulted in lower activities of intestinal and brush border enzymes and alterations in the integrity and morphological parameters of the chicks jejunal mucosa. The bacteria blend increased the activity of several digestive enzymes and the intestinal maturation marker alkaline phosphatase in birds fed with a conventional diet. Besides, it partially countered the deleterious effects of increased content of SBA, as well as the negative effect of a dietary source of WGA, on digestive enzymes activity and intestinal mucosa integrity. The results highlight the capability of multifunctional bacterial mixtures to protect the digestive system of avian against residual dietary lectins.

Tepary bean (Phaseolus acutifolius) lectin fraction provokes reversible adverse effects on rats' digestive tract

The Tepary bean (Phaseolus acutifolius) lectin fraction (TBLF) exhibits differential cytotoxicity on colon cancer cells and inhibition of early tumorigenesis in the colon (50 mg/kg, three times per week, for 6 weeks). TBLF showed low toxicity with the ability to activate the immune system; however, some adverse effects are the loss in body weight gain, intestinal atrophy, and pancreatic hyperplasia. After a recovery period of 2 weeks after treatment, reversion of pancreatic hyperplasia but no recovery of intestinal atrophy was observed. As TBLF has shown anticancer effects on the colon, it is important to characterize the adverse effects and how they can be reversed. Sprague Dawley rats were administered with TBLF (50 mg/kg) for 6 weeks, three times per week, and then allowed to recover for 6 weeks post-treatment. After TBLF administration, small intestine atrophy, villus atrophy, and cryptic hyperplasia were confirmed, as well as increased intestinal mucus production, increased permeability and a decrease in the apparent ileal digestibility of crude proteins. The colon showed damage in the simple prismatic tissue and decreased crypt depth, and changes in microbiota and a decrease in the apparent fecal digestibility of crude protein were determined. Our results show that the adverse effects provoked by TBLF were partially reversed after 6 weeks of recovery post-treatment, suggesting that increasing the recovery period it could be possible to reverse all adverse effects observed.

MytiLec-1 Shows Glycan-Dependent Toxicity against Brine Shrimp Artemia and Induces Apoptotic Death of Ehrlich Ascites Carcinoma Cells In Vivo

MytiLec-1, a 17 kDa lectin with β-trefoil folding that was isolated from the Mediterranean mussel (Mytilus galloprovincialis) bound to the disaccharide melibiose, Galα(1,6) Glc, and the trisaccharide globotriose, Galα(1,4) Galβ(1,4) Glc. Toxicity of the lectin was found to be low with an LC₅₀ value of 384.53 μg/mL, determined using the Artemia nauplii lethality assay. A fluorescence assay was carried out to evaluate the glycan-dependent binding of MytiLec-1 to Artemia nauplii. The lectin strongly agglutinated Ehrlich ascites carcinoma (EAC) cells cultured in vivo in Swiss albino mice. When injected intraperitoneally to the mice at doses of 1.0 mg/kg/day and 2.0 mg/kg/day for five consecutive days, MytiLec-1 inhibited 27.62% and 48.57% of cancer cell growth, respectively. Antiproliferative activity of the lectin against U937 and HeLa cells was studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in vitro in RPMI-1640 medium. MytiLec-1 internalized into U937 cells and 50 μg/mL of the lectin inhibited their growth of to 62.70% whereas 53.59% cell growth inhibition was observed against EAC cells when incubated for 24 h. Cell morphological study and expression of apoptosis-related genes (p53, Bax, Bcl-X, and NF-κB) showed that the lectin possibly triggered apoptosis in these cells.

Lectin Isolated from Japanese Red Sword Beans (Canavalia gladiata) as a Potential Cancer Chemopreventive Agent

In this study, we investigated the chemical and biological profile of lectin isolated from Japanese red sword beans (Canavalia gladiata; RSBs). RSB lectin was purified using maltamyl-Sepharose 4B and subjected to amino acid composition and partial amino acid sequencing analyses, and evaluated for blood and carbohydrate specificity, mitogenic activity, splenic natural killer (NK) cell activity, and its effect on B16 melanoma cell proliferation, compared with Concanavalin A (Con A). The amino acid composition and sequences of RSB lectin were similar to those of Con A. RSB lectin showed specificity to mannose, glucose, maltose, methyl-D-mannoside, and thyroglobulin, but not rhamnose, using mouse, sheep, and rabbit erythrocytes. Compared with Con A, RSB lectin showed low resistance to proteases and to temperatures greater than 70 °C, but high mitogenic activity for mouse splenic cells. Notably, while treatment with RSB lectin and Con A (0.01 and 0.1 μg/mL) promoted similar levels of splenic NK cell activity, which were higher than that observed in the control (0 μg/mL) and interleukin 2 (IL-2) (25 U)-treated populations, RBS lectin exerted a significantly stronger anti-proliferative effect than Con A at a concentration of 125.0 μg per well. Overall, our results show that RSB lectin might exert immunological effects on mouse splenic cells and could thus be used as a potential cancer chemopreventive agent.

PRACTICAL APPLICATION

Japanese red sword bean (RSB) is a tropical perennial legume consumed in many Asian countries. RSB lectin shows specificity to mannose, glucose, maltose, methyl-d-mannoside, and thyroglobulin, but not to rhamnose, using mouse, sheep, and rabbit erythrocytes. RSB lectin exhibits similarities to Concanavalin A in amino acid composition and sequence, shows mitogenic activity for mouse splenic cells and strong anti-proliferative activity for B16 melanoma cells, and also enhances the activity of splenic natural killer (NK) cells against YAC-1 cells. Thus, RSB lectin has the potential to be used as a bioactive protein in medical research.

Effects of intragastrically-administered Tepary bean lectins on digestive and immune organs: Preclinical evaluation

Previous work showed that Tepary bean (Phaseolus acutifolius) lectins exhibit differential cytotoxic effects on cancer cell lines by apoptosis induction. In vivo studies using a Tepary bean lectin fraction (TBLF, 50 mg/kg of body weight) after colon cancer induction in rats showed that TBLF inhibited early precancerous lesions without systemic toxicity however, loss of body weight gain and activation of immune cells were observed. In order to know more about the possible adverse effects, we evaluated the administration of TBLF on digestive and immune organs. Sprague Dawley rats were administered TBLF for six weeks and allowed to recover for two weeks. Immune activation was observed through an increased lymphocyte-granulocyte ratio, an increased number of lymphoid follicles in intestinal Peyer's patches and a slight expansion of the splenic white pulp. Atrophy was observed in small intestine villi and crypt foci of the colon without normalization after the recovery period. Pancreas histopathology showed hypertrophy after the six-week administration period, particularly vacuolation and trabecular widening; but after the two-week recovery period atrophy was observed, suggesting a partial compensatory type process. Our results show that TBLF activates the immune system and affects digestive organs through direct interaction with intestinal epithelium, and indirectly by producing pancreatic hyperfunction. Further work will focus in longer recuperation periods after TBLF treatment.

Plant Lectins as Medical Tools against Digestive System Cancers

Digestive system cancers-those of the esophagus, stomach, small intestine, colon-rectum, liver, and pancreas-are highly related to genetics and lifestyle. Most are considered highly mortal due to the frequency of late diagnosis, usually in advanced stages, caused by the absence of symptoms or masked by other pathologies. Different tools are being investigated in the search of a more precise diagnosis and treatment. Plant lectins have been studied because of their ability to recognize and bind to carbohydrates, exerting a variety of biological activities on animal cells, including anticancer activities. The present report integrates existing information on the activity of plant lectins on various types of digestive system cancers, and surveys the current state of research into their properties for diagnosis and selective treatment.

Effect of feeding soybean meal and differently processed peas on the gut mucosal immune system of broilers

Peas are traditionally used as a protein source for poultry. However, peas contain antinutritional factors (ANF), which are associated with the initiation of local and systemic immune reactions. The current study examined the effect of feeding raw or differently processed peas in comparison with feeding a soybean meal (SBM) based control diet (C) on the gut mucosal immune system of broilers in a 35 day feeding trial. In six replicates, a total of 360 one-day-old male broilers were randomly allocated to four different groups receiving C, or three treatment diets containing raw, fermented, and enzymatically pre-digested peas, each supplying 30% of required crude protein. After slaughtering, jejunal samples were taken for immunohistochemical, flow cytometric, and gene expression analyses. Investigations were focused on the topological distribution of intraepithelial leukocytes (villus tip, villus mid, and crypt region) as well as on the further characterization of the different intraepithelial lymphocytes (IEL) and concomitant pro- and anti-inflammatory cytokines. Broilers receiving the raw or processed pea diets had higher numbers of intraepithelial CD45+ leukocytes in the tip (P = 0.004) and mid region (P < 0.001) of villi than birds fed C. Higher numbers of intraepithelial CD3+ lymphocytes were found in the villus tip (P = 0.002) and mid region (P = 0.003) of birds fed raw or processed pea containing diets in comparison with those fed C. The flow cytometric phenotyping showed a similar relative distribution of IEL among the feeding groups. The expression of intestinal pro- and anti-inflammatory cytokines was affected by feeding the different diets only to a minor extent. To conclude, feeding of diets formulated with raw and processed peas in comparison with feeding a SBM control diet initiated mucosal immune responses in the jejunum of broilers indicated by a quantitative increase of intraepithelial T cells. Further research is needed in order to ascertain the specific factors which are responsible for observed local immune reactions and how these local reactions might affect the immune status and health of broilers.

Isolation of Rice Bran Lectins and Characterization of Their Unique Behavior in Caco-2 Cells

Rice bran lectins, named as RBA1 and RBA2, were isolated from Oryza sativa in two chromatography steps: affinity chromatography and cation-exchange chromatography. RBA1 was found to be composed of a covalently linked heterodimer of 20- and 12-kDa subunits, and RBA2 was a noncovalently linked dimer of 12-kDa subunits. Both RBA1 and RBA2 bound to desialylated complex glycoproteins such as fetuin, α1-acid glycoprotein, and transferrin, and agalactosylated complex glycoproteins such as agalacto fetuin, agalacto-α1-acid glycoprotein, and agalacto-transferrin, in addition to chitooligosacchrides. RBAs were heat stable up to 80 °C and stable at pH 4–10. RBA1 increased the transport of the fluorescent marker, rhodamine 123, which is known to be transported via the P-glycoprotein-mediated efflux pathway across human intestinal Caco-2 cell monolayers. Furthermore, RBA1 itself was transported to the basolateral side of the monolayers via an endocytotic pathway.

Effect of chum salmon egg lectin on tight junctions in Caco-2 cell monolayers

The effect of a chum salmon egg lectin (CSL3) on tight junction (TJ) of Caco-2 cell monolayers was investigated. The lectin opened TJ as indicated by the decrease of the transepithelial electrical resistance (TER) value and the increase of the permeation of lucifer yellow, which is transported via the TJ-mediated paracellular pathway. The effects of CSL3 were inhibited by the addition of 10 mM L-rhamnose or D-galactose which were specific sugars for CSL3. The lectin increased the intracellular Ca2+ of Caco-2 cell monolayers, that could be inhibited by the addition of L-rhamnose. The fluorescence immunostaining of β-actin in Caco-2 cell monolayers revealed that the cytoskeleton was changed by the CSL3 treatment, suggesting that CSL3 depolymerized β-actin to cause reversible TJ structural and functional disruption. Although Japanese jack bean lectin and wheat germ lectin showed similar effects in the decrease of the TER values and the increase of the intracellular Ca2+, they could not be inhibited by the same concentrations of simple sugars, such as D-glucose and N-acetyl-D-glucosamine.

Dietary supplement of banana (Musa acuminata) peels hot-water extract to enhance the growth, anti-hypothermal stress, immunity and disease resistance of the giant freshwater prawn, Macrobrachium rosenbergii

In the present study, Macrobrachium rosenbergii were fed with diets containing extracts of banana, Musa acuminate, fruit's peel (banana peels extract, BPE) at 0, 1.0, 3.0 and 6.0 g kg(-1). The non-specific immune parameters, disease resistance and anti-hypothermal stress were evaluated at 2, 4, 8, 16 and 32 days of post feeding. Also, we demonstrated the percent weight gain (PWG), percent length gain (PLG), feeding efficiency (FE), and survival rate of giant freshwater prawn at 30, 60, 90, and 120 days of post feeding. The PWG, PLG, FE and survival rate of prawns fed at 0, 1.0, 3.0 and 6.0 g kg(-1) BPE-containing diets after 120 days were 69.5%, 75.4%, 77.8% and 83.3%; 21.8%, 23.6%, 27.8% and 33.9%; 0.60, 0.72, 0.75 and 0.90; and 55.4%, 62.2%, 62.3% and 75.3%, respectively. After 32 days of post feeding, a significant increase in total haemocyte count (THC), different haemocyte count (DHC), respiratory bursts (RBs), superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, phenoloxidase (PO) activity and transglutaminase (TG) activity, and meanwhile, a decreased haemolymph coagulation time was observed. Furthermore, phagocytic activity and clearance efficiency of prawns against Lactococcus garvieae infection were significantly increased. Prawns challenged with L. garvieae after 32 days of feeding at 1.0, 3.0 and 6.0 g kg(-1) had a significantly higher survival rate (33.3%, 40.0% and 56.7%) than those fed with the control diet. Subsequently, hypothermal (14 °C) stress was 43.4%, 50.0% and 50.0%, respectively. Altogether, we therefore recommend the dietary BPE administration at 6.0 g kg(-1) promotes growth, anti-hypothermal stress, and enhance immunity and resistance against L. garvieae in M. rosenbergii.

Towards the control of necrotic enteritis in broiler chickens with in-feed antibiotics phasing-out worldwide

Poultry production has undergone a substantial increase compared to the livestock industries since 1970. However, the industry worldwide is now facing challenges with the removal of in-feed antibiotics completely or gradually, as the once well-controlled poultry diseases have re-emerged to cause tremendous loss of production. Necrotic enteritis (NE) is one of the most important diseases which costs the industry over two billion dollars annually. In this paper, we review the progress on the etiology of NE and its control through dietary modifications, pre- and probiotics, short chain fatty acids, and vaccination. The other likely measures resulted in the most advances in the toxin characterization are also discussed. Vaccine strategies may have greater potential for the control of NE mainly due to clearer etiology of NE having been elucidated in recent years with the identification of necrotic enteritis toxin B-like (NetB) toxin. Therefore, the use of alternatives to in-feed antibiotics with a better understanding of the relationship between nutrition and NE, and limiting exposure to infectious agents through biosecurity and vaccination, might be a tool to reduce the incidence of NE and to improve gut health in the absence of in-feed antibiotics. More importantly, the combinations of different measures may achieve greater protection of birds against the disease. Among all the alternatives investigated, prebiotics, organic acids and vaccination have shown improved gastrointestinal health and thus, have potential for the control of NE.

Distribution patterns of carbohydrates in murine glycocalyx

Enterocytes are unique cells governing an array of processes. They are covered by the gut glycocalyx, which is an extraneous carbohydrate-rich coat and an integral part of the plasma membrane. The intestinal glycocalyx and secreted mucins constitute a glycosylated milieu which has a number of physiological and protective functions. One of the important functions of the glycocalyx is its barrier function against microbial adherence to different membrane glycolipids. Thus, the glycocalyx is an important part of the mucosal immune system in newborns. The aim of our study was to identify the carbohydrates in the small bowel glycocalyx of Balb/c mice at different ages. We used plant lectins with different sugar specificities. Fluorescein-labelled lectins binding different carbohydrate moieties were detected using confocal laser scanning microscopy. Biotinilated lectins were used for transmission electron microscopy observations of the constituents of the gut glycocalyx at different periods of postnatal development in mice. Different carbohydrate moieties that were identified in the murine intestinal glycocalyx followed different distribution patterns and characteristics. Carbohydrates present on the mucus surface depended on tissue localization, cell type and stage of development. The distribution and mucins glycosylation could be of interest in analysing the response of the mucosal barrier to intestinal pathogens causing infection or inflammation.

Isolation and biochemical characterization of Apios tuber lectin

Apios tuber lectin, named ATL, was isolated from Apios americana Medikus by two chromatography steps, hydrophobic chromatography and anion-exchange chromatography. The minimum concentration required for the hemagglutination activity toward rabbit erythrocytes of ATL was 4 μg/mL. ATL was composed of a homodimer of 28.4 kDa subunits. The amino acid sequence of ATL was similar to those of other legume lectins. The lectin showed moderate stability toward heating and acidic pH, and the binding affinity against several monosaccharides, such as D-glucosamine and D-galactosamine. ATL also bound to desialylated or agalactosylated glycoproteins such as asialo and agalacto transferrin. ATL decreased the transepithelial electrical resistance across human intestinal Caco-2 cell monolayers, suggesting the effect on the tight junction-mediated paracellular transport.

Tolerability assessment of a lectin fraction from Tepary bean seeds (Phaseolus acutifolius) orally administered to rats

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We examine the toxicological profile of Tepary Bean lectins by oral route.

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Tepary bean lectins showed digestion resistance up to 72 h.

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Tepary bean lectins induce granulocyte increase after 24 h treatment.

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A reduction in body weight gain was observed after 6 weeks treatment.

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No toxicity was observed for Tepary bean lectins after 6 weeks.

Our previous studies have shown that a lectin rich fraction (TBLF) extracted from Tepary bean seeds differentially inhibits cancer cells proliferation in vitro. Before testing the in vivo anticancer effect, the acute and subchronic toxicological assays in rats were conducted, where an oral dose of 50 mg/body weight kg was determined as the NOAEL. This study evaluated the resistance to digestion and complete blood count (CBC) after 24 h of the orally administered 50 mg/kg TBLF. The digestion resistance test showed lectins activity retention after 72 h and the CBC study showed a high level of eosinophils, suggesting an allergic-like response. Tolerability was assayed after 6 weeks of treatment by dosing with an intragastric cannula every third day per week. It was observed a transient reduction in food intake and body weight in the first weeks, resulting in body weight gain reduction of 10% respect to the control group at the end of the study. Additionally, organs weight, histopathological analysis and blood markers for nutritional status and for liver, pancreas and renal function were not affected. Our results suggest that 50 mg/kg TBLF administered by oral route, exhibit no toxicity in rats and it was well tolerated. Further studies will focus on long-term studies.

Effects of hot-water extract of banana (Musa acuminata) fruit's peel on the antibacterial activity, and anti-hypothermal stress, immune responses and disease resistance of the giant freshwater prawn, Macrobrachium rosenbegii

The hot-extracts isolated from fruit's peel of banana, Musa acuminata, was evaluated on the antibacterial activity to pathogens from aquatic animals, and immunostimulating potential, disease resistance and anti-hypothermal stress in giant freshwater prawn, Macrobrachium rosenbergii through injection administration. The banana peel extract (BPE) showed good activity against 1 Gram-positive and 3 Gram-negative pathogens, including Lactococcus garvieae, Photobacteria damsella, Vibrio alginolyticus and Vibrio parahemolyticus especially in prawn pathogen of L. garvieae strain, which were carried out by a disk diffusion method. Prawn received BPE via injection administration at 1-6 μg (g prawn)(-1) significantly increased total haemocyte count (THC), hyaline cell (HC), granular cell (GC), phenoloxidase (PO) activity and phagocytic activity against L. garvieae from 3 to 6 days, and significantly increased clearance efficiency against L. garvieae and a significantly decreased coagulation time of prawn from 1 to 6 days. Prawn injected with BPE at 6.0 μg (g prawn)(-1) for 6 days showed significantly increased superoxide dismutase (SOD) activity, but significantly decreased respiratory bursts (RBs) of per haemocyte. Survival rates of M. rosenbergii injected with BPE at concentrations of 1, 3 and 6 μg (g prawn)(-1) were significantly higher than those injected with saline control after challenge with L. garvieae for 4-6 days, and the respective relative survival percentages of prawn were 28.6%, 38.1%, and 47.8%, respectively at 6 days. The sublethal time of prawns that had received saline and BPE at 1, 3 and 6 μg (g prawn)(-1) for 6 days and then were transferred from 28 °C to 14 °C were 69.4, 79.8, 83.6, and 90.2 h, respectively. It was concluded that the BPE can be used as the bacteriostat, and immunostimulant and physiological regulator for prawn through injection administration to enhance immunity, physiological responses, and resistance against L. garvieae.

The "white kidney bean incident" in Japan

Lectin poisoning occurred in Japan in 2006 after a TV broadcast that introduced a new diet of eating staple foods with powdered toasted white kidney beans, seeds of Phaseolus vulgaris. Although the method is based on the action of a heat-stable α-amylase inhibitor in the beans, phaseolamin, more than 1,000 viewers who tried the method suffered from acute intestinal symptoms and 100 people were hospitalized. Lectins in the white kidney beans were suspected to be the cause of the trouble. We were asked to investigate the lectin activity remaining in the beans after the heat treatment recommended on the TV program. The test suggested that the heat treatment was insufficient to inactivate the lectin activity, which, combined with our ignorance of carbohydrate signaling in the intestine, was the cause of the problem.

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.

Plant as a plenteous reserve of lectin

Lectins are clusters of glycoproteins of nonimmune foundation that combine specifically and reversibly to carbohydrates, mainly the sugar moiety of glycoconjugates, resulting in cell agglutination and precipitation of glycoconjugates. They are universally distributed in nature, being established in plants, fungi, viruses, bacteria, crustacea, insects, and animals, but leguminacae plants are rich source of lectins. The present review reveals the structure, biological properties, and application of plant lectins.

Compatible interaction with its rice host leads to enhanced expression of the gamma subunit of oligosaccharyl transferase in the Asian rice gall midge, Orseolia oryzae

The Asian rice gall midge, Orseolia oryzae, is a fast evolving, damaging pest of rice. Understanding the underlying molecular mechanism of interaction between the gall midge and rice will help in devising strategies to control and manage the pest. The present study aims to identify rice-responsive genes in the gall midge that aid pest survival. The abundance of transcripts coding for enzymes related to glycosylation, in a cDNA library prepared from maggots of the rice gall midge feeding on susceptible hosts, indicated their probable involvement in the gall midge-rice interaction. Hence, a full-length transcript for a gamma subunit of the oligosaccharyl transferase gene (OoOST) from the gall midge was cloned and characterized. It has 72% similarity to its orthologue cloned from Aedes aegypti. Tissue-specific analysis of the expression of OoOST revealed an increase (> sevenfold) in the transcripts of the gene in the salivary glands of maggots in susceptible plants when compared with the transcript level in the salivary glands of maggots feeding on resistant hosts. Using quantitative PCR, performed on different developmental stages of the maggots in two susceptible and two resistant hosts, we observed similar expression patterns (i.e. overexpression in the compatible interaction). These results indicate the involvement of OoOST in maggot survival and establishment in the susceptible host. In order to identify polymorphism in the gene, OoOST was cloned from three gall midge biotypes GMB1, GMB4 and GMB4M.

Stimulation of IFN-γ production by garlic lectin in mouse spleen cells: involvement of IL-12 via activation of p38 MAPK and ERK in macrophages

Several lectins, present in beans and edible plant products, have immuno-potentiating and anti-tumor activities. We here report the effects of garlic lectin purified from garlic bulbs on the production of cytokines such as interleukin-12 (IL-12) and interferon-γ (IFN-γ) in the mouse. Garlic lectin induced IFN-γ production in spleen cells in a bell-shaped time (24-60 h)- and concentration (0.25-2.0 mg/ml)-dependent manner. The maximal enhancement was observed at 36 h with 0.5 mg/ml of garlic lectin. The stimulatory effect of garlic lectin on IFN-γ production was completely inhibited by both actinomycin D and cycloheximide, an inhibitor of ribosomal protein synthesis and DNA-dependent RNA polymerase, respectively, and was associated with an increase in IFN-γ mRNA level. Garlic lectin also induced IL-12 production in mouse peritoneal macrophages in a concentration (0.25-1.0 mg/ml)- and bell-shaped time (3-24 h)-dependent manner. The lectin increased the phosphorylation of extracellular signal-regulated kinases (ERK) and p38 mitogen-activated protein kinase (p38 MAPK) in macrophages. Furthermore, specific pharmacological inhibitors of ERK kinase (U0126) and p38 MAPK (SB203580) also suppressed the production of IL-12 induced by garlic lectin. The present findings suggest that garlic lectin induces IL-12 production via activation of p38 MAPK and ERK in mouse macrophages, which, in turn, stimulates IFN-γ production through an increase in IFN-γ mRNA in the spleen cells.

Possible immune functions of congerin, a mucosal galectin, in the intestinal lumen of Japanese conger eel

Congerin, a mucosal galectin of the Japanese conger eel, provides chemical fortification through its agglutinating and opsonizing activity. Congerin is produced in the epidermis, and the epithelia of the oral cavity to the esophagus, but not in the stomach or intestine. We hypothesized that congerin secreted from the upper digestive tract can reach and function in the intestinal lumen. We found that congerin possessed marked resistance against digestion by gastric and enteric enzymes of conger eel. It was not degraded until 6h of incubation with stomach extract or intestinal digestion juice. Western blotting demonstrated that congerin essentially remained in the intestinal mucus. The mucus agglutinated rabbit erythrocytes, and the agglutination was hampered by anti-congerin antibody. Furthermore, congerin could bind to some enteric bacteria. These results support the above hypothesis.

A novel wheat gene encoding a putative chitin-binding lectin is associated with resistance against Hessian fly

SUMMARY The gene-for-gene interaction triggering resistance of wheat against first-instar Hessian fly larvae utilizes specialized defence response genes not previously identified in other interactions with pests or pathogens. We characterized the expression of Hfr-3, a novel gene encoding a lectin-like protein with 68-70% identity to the wheat germ agglutinins. Within each of the four predicted chitin-binding hevein domains, the HFR-3 translated protein sequence contained five conserved saccharide-binding amino acids. Quantification of Hfr-3 mRNA levels confirmed a rapid response and gradual increase, up to 3000-fold above the uninfested control in the incompatible interaction 3 days after egg hatch. Hfr-3 mRNA abundance was influenced by the number of larvae per plant, suggesting that resistance is localized rather than systemic. In addition, Hfr-3 was responsive to another sucking insect, the bird cherry-oat aphid, but not to fall armyworm attack, wounding or exogenous application of methyl jasmonate, salicylic acid or abscisic acid. Western blot analysis demonstrated that HFR-3 protein increased in parallel to mRNA levels in crown tissues during incompatible interactions. HFR-3 protein was detected in both virulent and avirulent larvae, indicating ingestion. Anti-nutritional proteins, such as lectins, may be responsible for the apparent starvation of avirulent first-instar Hessian fly larvae during the initial few days of incompatible interactions with resistant wheat plants.

SLICK − Scoring and Energy Functions for Protein−Carbohydrate Interactions

Protein-carbohydrate interactions are increasingly being recognized as essential for many important biomolecular recognition processes. From these, numerous biomedical applications arise in areas as diverse as drug design, immunology, or drug transport. We introduce SLICK, a package containing a scoring and an energy function, which were specifically designed to predict binding modes and free energies of sugars and sugarlike compounds to proteins. SLICK accounts for van der Waals interactions, solvation effects, electrostatics, hydrogen bonds, and CH...pi interactions, the latter being a particular feature of most protein-carbohydrate interactions. Parameters for the empirical energy function were calibrated on a set of high-resolution crystal structures of protein-sugar complexes with known experimental binding free energies. We show that SLICK predicts the binding free energies of predicted complexes (through molecular docking) with high accuracy. SLICK is available as part of our molecular modeling package BALL (www.ball-project.org).

Response of Turkey Poults to Soybean Lectin Levels Typically Encountered in Commercial Diets. 2. Effect on Intestinal Development and Lymphoid Organs

Lectins are capable of altering intestinal morphology by binding to and disrupting the intestinal brush border membrane. They are also known to alter the weight of lymphoid organs. Therefore, we evaluated the effect of soybean lectin (SBL) on intestinal morphology and lymphoid organ weights of poults fed diets containing SBL. Dietary treatments evaluated in this study included a cornstarch and casein-based control (lectin-free) semipurified diet (PD) and semipurified diets containing 0.024 or 0.048% SBL (PDL and PDH, respectively). Experimental diets were fed from hatch to 14 d. Morphological evaluation of the intestine involved measurement of the villi height and perimeter, crypt depth, villus:crypt, and thickness of the muscle layer in the jejunum. Intestinal physical characteristics were also determined by measuring intestinal weight, length, and volume. Results indicated that 0.048% SBL in PDH increased villus:crypt and reduced total intestinal length in turkey poults. In addition, both the 0.024 and 0.048% dietary SBL levels reduced thymus weights. It was concluded that dietary SBL up to 0.048% enhanced intestinal development by increasing villus:crypt, but might alter the structural integrity of lymphoid organs.

Novel Carbohydrate-binding Activity of Pancreatic Trypsins to N-Linked Glycans of Glycoproteins

How glycosylation affects the reactivity of proteins to trypsin is not well understood. Bovine and porcine pancreatic trypsins were discovered to bind to alpha-Man, Neu5Acalpha2,6Galbeta1,4Glc, and alpha-galactose sequences by binding studies with biotinylated sugar-polymers. Quantitative kinetic studies supported that phenylmethylsulfonyl fluoride (PMSF)-treated trypsin binds to glycolipid analogues possessing alpha-Man or alpha-NeuAc but not to those possessing beta-galactose or beta-GlcNAc residue. Enzyme-linked immunosorbent assay (ELISA) showed that trypsin binds to six kinds of biotinylated glycoproteins possessing high mannose-type and complex-type N-glycans but not to bovine submaxillary mucin, which possesses only O-glycans. Further, the binding of trypsin to glycoproteins was differentially changed by treatments with sequential exoglycosidases, endoglycosidase H, or N-glycosidase F. Quantitative kinetic studies indicated that PMSF-treated trypsin binds with bovine thyroglobulin with the affinity constant of 10(10) m(-1), which was the highest among the glycoproteins examined, and that alpha-galactosidase treatment decreased it to 10(5) m(-1). PMSF-treated trypsin bound to other glycoproteins, including ovomucoid, a trypsin inhibitor, with the affinity constants of 10(8)-10(5) mol(-1) and were markedly changed by glycosidase treatments in manners consistent with the sugar-binding specificities suggested by ELISA. Thus, the binding site for glycans was shown to be distinct from the catalytic site, allowing trypsin to function as an uncompetitive activator in the hydrolysis of a synthetic peptide substrate. Correspondingly the carbohydrate-binding activities of trypsin were unaffected by treatment with PMSF or soybean trypsin inhibitor. The results indicate the presence of an allosteric regulatory site on trypsin that sugar-specifically interacts with glycoproteins in addition to the proteolytic catalytic site.

Effect of lectins on the transport of food factors in caco-2 cell monolayers

The effect of three plant lectins, soybean lectin (SBA), Japanese jack bean lectin (CGA), and wheat germ lectin (WGA), on the transport of various food factors, such as isoflavones, quercetin, dipeptides, and calcium ions, were investigated by use of an intestinal tract model, Caco-2 cell monolayers. The lectins increased the isoflavone transport but had no effect on aglycon transport. SBA increased the transport of quercetin glycosides, whereas CGA and WGA had no effect. The lectins increased the transport of calcium ions but showed no effect on the transport of dipeptides, carnosine, and anserine. Although SBA did not change the transepithelial electrical resistance (TER) value of the Caco-2 cell monolayers, CGA and WGA decreased the TER value. These results indicate that plant lectins affect the transport of food factors in different manners, presumably due to their specific sugar binding activity.

Grain legume proteins and nutraceutical properties

Grain legumes are a valuable source of food proteins. Their exploitation is expected to grow in relation of a growing world's food needs. Moreover, it is currently taking place a reappraisal of the beneficial effects of legume seed dietary intake, which are the basis for various health claims. Proteins and peptides concur to the observed biological activities of legume seeds, but their effect(s) has(ve) not completely been disclosed. Aims of this review are: to report the most relevant putative positive effects of grain legumes on human health and to give an account of the current knowledge on the demonstrated legume seed protein biological activities. Specific effects on the prevention and treatment of various diseases, mostly of which are typical of the affluent countries, are reported. Examples of studies at molecular level aimed at elucidating of the underlying mechanism(s) are given. The prospects on targeted legume protein exploitation in the nutraceutical area, including the biotechnological approaches, are also considered.

Effect of feed particle size and feed processing on morphological characteristics in the small and large intestine of pigs and on adhesion of Salmonella enterica serovar Typhimurium DT12 in the ileum in vitro1

A 2 x 2 factorial experiment with pigs was undertaken to investigate the effect of particle size (fine and coarse) and feed processing (pelleted and nonpelleted) on morphological characteristics in the small intestine, cecum, and colon of pigs and on the adhesion of Salmonella enterica serovar Typhimurium DT12 to the ileum in vitro. Ninety-six pigs (average BW = 33 +/- 7 kg) were fed the experimental diets. After 4 wk, 24 pigs were selected (six pigs per diet) and euthanized, and tissue samples were taken from the mid and distal small intestine, cecum, and distal colon. The effects of particle size and feed processing on villus height and crypt depth in the small intestine were minor. Feeding coarse diets increased (P = 0.05) the crypt depth in the colon. The crypt depth was 420 +/- 12 and 449 +/- 12 microm in pigs fed finely and coarsely ground feed, respectively. Pigs fed pelleted diets had a larger (P = 0.01) staining area for neutral mucins, as well as for acidic and sulfomucins on the villi of the distal small intestine than pigs fed nonpelleted diets. The area was 41, 46, and 33% larger for neutral, acidic, and sulfomucins, respectively. The mucin-staining areas of the crypts in the cecum and the colon were not affected by the experimental diets. Examination of lectin binding characteristics of the distal small intestine and the cecum did not reveal any differences between the experimental diets. Using a pig intestine organ culture model, Salmonella adhered less (P < 0.05) to the ileal tissue of pigs fed the nonpelleted diets than to those fed pelleted diets; the adherence was 60% less in these pigs. Results of this study suggest that pigs fed pelleted diets secrete mucins that are capable of binding Salmonella enterica serovar Typhimurium DT12 and thereby allowing for colonization. Therefore, pigs fed a nonpelleted diet are better protected against Salmonella infections than pigs fed a pelleted diet.

Antinutritional properties of plant lectins

Lectins are carbohydrate binding (glyco)proteins which are ubiquitous in nature. In plants, they are distributed in various families and hence ingested daily in appreciable amounts by both humans and animals. One of the most nutritionally important features of plant lectins is their ability to survive digestion by the gastrointestinal tract of consumers. This allows the lectins to bind to membrane glycosyl groups of the cells lining the digestive tract. As a result of this interaction a series of harmful local and systemic reactions are triggered placing this class of molecules as antinutritive and/or toxic substances. Locally, they can affect the turnover and loss of gut epithelial cells, damage the luminal membranes of the epithelium, interfere with nutrient digestion and absorption, stimulate shifts in the bacterial flora and modulate the immune state of the digestive tract. Systemically, they can disrupt lipid, carbohydrate and protein metabolism, promote enlargement and/or atrophy of key internal organs and tissues and alter the hormonal and immunological status. At high intakes, lectins can seriously threaten the growth and health of consuming animals. They are also detrimental to numerous insect pests of crop plants although less is presently known about their insecticidal mechanisms of action. This current review surveys the recent knowledge on the antinutritional/toxic effects of plant lectins on higher animals and insects.

Constitutive apical membrane recycling in Aplysia enterocytes

In Aplysia californica enterocytes, alanine-stimulated Na+ absorption increases both apical membrane exocytosis and fractional capacitance (fCa; a measure of relative apical membrane surface area). These increases are thought to reduce membrane tension during periods of nutrient absorption that cause the enterocytes to swell osmotically. In the absence of alanine, exocytosis and fCa are constant. These findings imply equal rates of constitutive endocytosis and exocytosis and constitutive recycling of the apical plasma membrane. Thus, the purpose of this study was to confirm and determine the relative extent of constitutive apical membrane recycling in Aplysia enterocytes. Biotinylated lectins are commonly used to label plasma membranes and to investigate plasma membrane recycling. Of fourteen biotinylated lectins tested, biotinylated wheat germ agglutinin (bWGA) bound preferentially to the enterocytes apical surface. Therefore, we used bWGA, avidin D (which binds tightly to biotin), and the UV fluorophore 7-amino-4-methylcoumarin-3-acetic acid (AMCA)-conjugated avidin D to assess the extent of constitutive apical membrane recycling. A temperature-dependent (20 vs. 4 degrees C) experimental protocol employed the use of two tissues from each of five snails and resulted in a approximately 60% difference in apical surface fluorescence intensity. Because the extent of membrane recycling is proportional to the difference in surface fluorescence intensity, this difference reveals a relatively high rate of constitutive apical membrane recycling in Aplysia enterocytes.

Response of turkey poults to soybean lectin levels typically encountered in commercial diets. 1. Effect on growth and nutrient digestibility

Lectins are known to bind to the intestinal brush border membrane and induce antinutritional effects such as disruption of the brush border membrane (BBM) and reduced nutrient digestibility in laboratory rodents. Because soybean lectin (SBL) is usually present in poult starter diets, 2 similar experiments with starting turkey poults were conducted to investigate the effects of purified SBL on growth performance and nutrient digestibility. Experimental diets were a corn starch-casein based control (lectin-free) semipurified diet (PD), semipurified diets containing 0.024 or 0.048% soybean lectin (PDL, PDH), and a corn-soybean meal diet (SBD). Experimental diets were fed from hatch to 14 d. Antibodies specific for soybean lectin were detected in the serum of poults fed the PDL and PDH diets, implying that the SBL in these diets remained active in the digestive tract. Poults fed the control PD or SBD grew equally well. The 0.024% SBL level in PDL had no significant detrimental effect on any parameters assessed in the 2 experiments. In contrast, the 0.048% SBL level in the PDH gave inconsistent results for feed efficiency (FE) and brush border enzyme levels. For instance, on d 6 in experiment 2, poults fed the PDH had poorer FE (P < 0.05) compared with the control PD treatment, but had similar FE to poults fed the PD in experiment 1. In conclusion, SBL present at levels up to 0.024% of the diet would not cause antinutritional effect in turkey poults up to 2 wk of age.