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PubMed1998

Plant lectins - more than just tools for glycoscientists: occurrence, structure, and possible functions of plant lectins.

Plant lectins are easily available, fairly stable and suitable for many kinds of chemical modification. Thus, they have become important tools in glycosciences. In the present review, it is attempted to throw light upon aspects of lectinology that deal with their natural occurrence, biosynthesis, structure, binding specificities and hypotheses about their biological functions.

Binding Sites↗
PubMed1992

The mannose-specific plant lectins from Cymbidium hybrid and Epipactis helleborine and the (N-acetylglucosamine)n-specific plant lectin from Urtica dioica are potent and selective inhibitors of human immunodeficiency virus and cytomegalovirus replication in vitro.

A series of four mannose(Man)-, three N-acetylglucosamine (GlcNAc)n-, ten N-acetylgalactosamine/galactose(GalNAc/Gal)-, one 5-acetylneuraminic acid (alpha-2,3-Gal/GalNAc)- and one 5-acetylneuroaminic acid(alpha-2,6-Gal/Gal-NAc)-specific plant agglutinins were evaluated for their antiviral activity in vitro. the mannose-specific lectins from the orchid species Cymbidium hybrid (CA), Epipactis helleborine (EHA) and Listera ovata (LOA) were highly inhibitory to human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) in MT-4, and showed a marked anti-human cytomegalovirus (CMV), respiratory syncytial virus (RSV) and influenza A virus activity in HEL, HeLa and MDCK cells, respectively. The 50% effective concentration (EC50) of CA and EHA for HIV ranged from 0.04 to 0.08 micrograms/ml, that is about 3 orders of magnitude below their toxicity threshold (50% inhibitory concentration for MT-4 cell growth: 54 to 60 micrograms/ml). Also, the (GlcNAc)n-specific lectin from Urtica dioica (UDA) was inhibitory to HIV-1-, HIV-2-, CMV-, RSV- and influenza A virus-induced cytopathicity at an EC50 ranging from 0.3 to 9 micrograms/ml. The GalNAc/Gal-, alpha-2,3-Gal/GalNAc- or alpha-2,6-Gal/GalNAc-specific lectins were not inhibitory to HIV or CMV at non-toxic concentrations. CA, EHA and UDA proved to be potent inhibitors of syncytium formation between persistently HIV-1- and HIV-2-infected HUT-78 cells and CD4+ Molt/4 (clone 8) cells (EC50: 0.2-2 micrograms/ml). Unlike dextran sulfate, the plant lectins CA, EHA and UDA did not interfere with HIV-1 adsorption to MT-4 cells and RSV- and influenza A virus adsorption to HeLa and MDCK cells, respectively. They presumably interact at the level of virion fusion with the target cell.

Acetylglucosamine↗
PubMed1992

Cross-linking activity of the 14-kilodalton beta-galactoside-specific vertebrate lectin with asialofetuin: comparison with several galactose-specific plant lectins.

We have previously shown that plant lectins with a wide range of carbohydrate binding specificities can bind and cross-link (precipitate) specific multiantennary oligosaccharides and glycopeptides [cf. Bhattacharyya, L., Fant, J., Lonn, H., & Brewer, C. F. (1990) Biochemistry 29, 7523-7530]. This leads to a new source of binding specificity: namely, the formation of homogeneous cross-linked lattices between lectins and carbohydrates. Recently, we have demonstrated the existence of highly ordered cross-linked lattices that form between the D-Man/D-Glc-specific plant lectin concanavalin A and the soybean agglutinin which is a tetrameric glycoprotein possessing a single Man9 oligomannose chain per monomer [Khan, M. I., Mandal, D. K., & Brewer, C. F. (1991) Carbohydr. Res. 213, 69-77]. In the present study, we have compared the ability of the 14-kDa beta-galactoside-specific lectin from calf spleen, a dimeric S-type animal lectin, and several galactose-specific plant lectins from Erythrina indica, Erythrina cristagalli, and Glycine max (soybean agglutinin) to form specific cross-linked complexes with asialofetuin (ASF), a 48-kDa monomeric glycoprotein, using quantitative precipitation analyses. The results show the formation of 1:9 and 1:3 stoichiometric cross-linked complexes (per monomer) of ASF to the 14-kDa lectin, depending on their relative ratio in solution. Evidence indicates that the three triantennary N-linked complex-type oligosaccharide chains of ASF mediate the cross-linking interactions and that each chain expresses either trivalency in the 1:9 cross-linked complex or univalency in the 1:3 complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

[Plant lectin and its application in insect-resistant plant genetic engineering].

Plant lectins are proteins possessing at least one non-catalytic domain that binds reversibly to specific mono-or oligosaccharides. They distinguish themselves from other plant proteins by the ability of carbohydrate binding. Most plant lectins are directed to bind foreign polysaccharide. Plant lectin is believed to take part in the defense responses against invader. In this paper we presented a review on the classification, characters, functions, crystal structure and,functions related to the carbohydrate binding activity. The status and prospect of plant lectins utilization were also discussed.

English Abstract↗
PubMed1986

Characterization of the carbohydrate moiety of Clerodendron trichotomum lectins. Its structure and reactivity toward plant lectins.

Lectins were isolated from fruits and leaves of Clerodendron trichotomum by affinity chromatography on lactamyl-Sepharose. The purified lectins (C. trichotomum agglutinin: CTA) were homogeneous on SDS/polyacrylamide gel electrophoresis, and the carbohydrate moiety was characterized by physicochemical and immunochemical methods. The asparagine-linked oligosaccharides were released by treatment with N-oligosaccharide glycopeptidase (almond, EC 3.5.1.52) of peptic glycopeptides obtained from fruit CTA, and separated by gel filtration and thin-layer chromatography. The structure of the predominant oligosaccharide was determined as Xyl beta 1----2 (Man alpha 1----6)(Man alpha 1----3)Man beta 1----4GlcNAc beta 1----4(Fuc alpha 1----3)GlcNAc by high-performance liquid chromatography, sugar analysis and 1H-NMR spectroscopy. The reactivity of the carbohydrate moiety of CTA toward various lectins was studied. Fruit and leaf CTAs were applied to polyacrylamide gel electrophoresis, transferred to nitrocellulose sheets and detected with horseradish-peroxidase-conjugated lectins. Concanavalin A, lentil lectin, pea lectin, Vicia faba lectin and Ulex europeus agglutinin I, but not wheat germ lectin, bound to fruit CTA. The results indicate new binding properties of these plant lectins: a beta-xylosyl residue substituted at C-2 of the beta-mannosyl residue of N-linked oligosaccharide does not affect the binding with mannose-specific lectins, lentil, pea and Vicia faba lectins can bind to N-linked oligosaccharides containing an alpha-L-fucosyl residue attached to C-3 of the asparagine-linked N-acetyl-D-glucosamine residue, and Ulex europeus agglutinin I can bind to the (alpha 1----3)-linked fucose residue of the N-linked oligosaccharide.

Carbohydrates↗
PubMed2004

Profile of resistance of human immunodeficiency virus to mannose-specific plant lectins.

The mannose-specific plant lectins from the Amaryllidaceae family (e.g., Hippeastrum sp. hybrid and Galanthus nivalis) inhibit human immunodeficiency virus (HIV) infection of human lymphocytic cells in the higher nanogram per milliliter range and suppress syncytium formation between persistently HIV type 1 (HIV-1)-infected cells and uninfected CD4(+) T cells. These lectins inhibit virus entry. When exposed to escalating concentrations of G. nivalis and Hippeastrum sp. hybrid agglutinin, a variety of HIV-1(III(B)) strains were isolated after 20 to 40 subcultivations which showed a decreased sensitivity to the plant lectins. Several amino acid changes in the envelope glycoprotein gp120, but not in gp41, of the mutant virus isolates were observed. The vast majority of the amino acid changes occurred at the N glycosylation sites and at the S or T residues that are part of the N glycosylation motif. The degree of resistance to the plant lectins was invariably correlated with an increasing number of mutated glycosylation sites in gp120. The nature of these mutations was entirely different from that of mutations that are known to appear in HIV-1 gp120 under the pressure of other viral entry inhibitors such as dextran sulfate, bicyclams (i.e., AMD3100), and chicoric acid, which also explains the lack of cross-resistance of plant lectin-resistant viruses to any other HIV inhibitor including T-20 and the blue-green algae (cyanobacteria)-derived mannose-specific cyanovirin. The plant lectins represent a well-defined class of anti-HIV (microbicidal) drugs with a novel HIV drug resistance profile different from those of other existing anti-HIV drugs.

Amino Acid Substitution↗
PubMed2000

Synthesis and binding to plant lectins of sulfur-containing analogues of betaGal1,3 alphaGalNAc (T-antigen).

Analogues of the tumor-associated T-antigen (betaGal1,3 alphaGalNAc) containing 4,6-epidithio and 4,6-thietan modifications were synthesized from the alpha-allyl glycoside of betaGal alpha1,3GlcNAc via suitable thiocyanate derivatives. Binding to three leguminous lectins as model systems was investigated in an enzyme-linked lectin assay (ELLA) and IC50 values comparable to the corresponding natural disaccharides T-antigen, lactose and N-acetyllactosamine were found.

Antigens, Viral, Tumor↗
PubMed1985

Interactions of brain muscarinic acetylcholine receptors with plant lectins.

We previously reported that muscarinic acetylcholine receptors (mAChRs) from porcine brains are glycoproteins. When porcine brain membranes were solubilized with digitonin or 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS), approximately 20% of the receptors were solubilized, most (90% or more) of which bound to Sepharose 4B conjugated with wheat germ agglutinin (WGA). In contrast, when membranes were solubilized with Lubrol PX, a much larger fraction (approximately 60%) of the receptors were solubilized. However, about a third of this solubilized receptor population remained unbound to WGA-Sepharose even in the presence of an excess amount of the lectin-Sepharose. These results suggested a structural heterogeneity of the mAChR in terms of its carbohydrate moiety. The effects of lectins on the ligand binding properties of mAChRs were also studied. WGA or concanavalin A (ConA) was found to cause a 2- to 3-fold increase in the affinity of membrane-bound receptors to an antagonist [3H]quinuclidinyl benzylate [( 3H]QNB) without affecting the maximum number of sites, whereas the lectins had no significant effects on the binding of the agonist [3H]cis-methyldioxolane. When the membranes were dissolved with detergents, lectin did not increase the [3H]QNB affinity: These lectins caused an approximately 2 fold decrease in the affinity of digitonin-solubilized receptors for [3H]QNB. Thus the lectins exert differential effects on agonist and antagonist binding to the brain membrane mAChRs, most likely by modulating some intermolecular interactions.

Animals↗
PubMed1981

Effects of plant lectins on the adhesive properties of baby hamster kidney cells.

We studied the effects of different lectins on the adhesive properties of baby hamster kidney (BHK) cells. The purpose of these studies was to learn more about the cell surface receptors involved in cell adhesion. Three adhesive phenomena were analyzed: 1) the adhesion of BHK cells to lectin-coated substrata; 2) the effects of lectins on the adhesion of cells to substrata coated by plasma fibronectin (pFN); and 3) the effects of lectins on the binding of pFN-coated beads to cells. Initial experiments with fluorescein-conjugated lectins indicated that concanavalin A (Con A), ricinus communis agglutinin I (RCA I), and wheat germ agglutinin (WGA) bound to BHK cells but peanut agglutinin (PNA), soybean agglutinin (SBA), and ulex europaeus agglutinin I (UEA I) dod not bind. All three of the lectins which bound to the cells promoted cell spreading on lectin substrata, and the morphology of the spread cells was similar to that observed with cells spread on pFN substrata. Protease treatment of the cells, however, was found to inhibit cell spreading on pFN substrata or WGA substrata more than on Con A substrata or RCA I substrata. In the experiment of cells with Con A or WGA inhibited cell spreading on pFN substrata, but RCA I treatment had no effect. Finally, treatment of cells with WGA inhibited binding to cells of pFN beads, but neither Con A nor RCA I affected this interaction. These results indicate that the lectins modify cellular adhesion in different ways, probably by interacting with different surface receptors. The possibility that the pFN receptor is a WGA receptor is discussed.

Animals↗
PubMedDate not supplied

Relevance of plant lectins in human cell biology and immunology.

Protein-carbohydrate interactions are used for intercellular communication. Mammalian cells are known to bear a variety of glycoconjugates. Lectins, first discovered in plants, are proteins which can specifically bind carbohydrates. Given the high affinity of plant lectins for carbohydrates, they have always been important as molecular tools in the identification, purification and stimulation of specific glycoproteins on human cells. Lectins have provided important clues to the repertoire of carbohydrate structures in animal cells. The discovery of plant lectins gave a great impulse to modern glycobiology. They represent important biochemical reagents for numerous applications in the biomedical field and in research. Sequence determinations and structural characterization helped to understand the mechanism of action in many biologic systems. Plant lectins have been fundamental in human immunological studies because some of them are mitogenic/activating to lymphocytes. Understanding the molecular basis of lectin-carbohydrate interactions and of the intracellular signalling evoked holds promise for the design of novel drugs for the treatment of infectious, inflammatory and malignant diseases. It may also be of help for the structural and functional investigation of glycoconjugates and their changes during physiological and pathological processes.

Biomedical Research↗
PubMed1990

Comparison of the lectin-like activity of pertussis toxin with two plant lectins that have differential specificities for alpha (2-6) and alpha (2-3)-linked sialic acid.

In this report we have compared the lectin-like properties of Pertussis toxin with two plant lectins which are known to possess different specificities towards terminal Neu5Ac Gal linkages on glycoconjugates. The hemagglutinin from elderberry bark (Sambucus nigra) has a binding specificity for terminal Neu5Ac alpha (2-6) Gal sequences and was found to bind a series of glycoconjugates with a similar specificity as Pertussis toxin. The binding specificity of Pertussis toxin was different from that of the leukoagglutinin from the seeds of Maackia amurensis which preferentially binds terminal Neu5Ac alpha (2-3) Gal sequences. These observations confirm the specificity of Pertussis toxin for Neu5Ac alpha (2-6) Gal glycoconjugate sequences.

Binding, Competitive↗
PubMed1997

Antitumor effect of plant lectins.

This review examines the literature data concerning the biological activity of plant lectins. Numerous studies have reported that these substances possess toxic, cytotoxic, antitumor, and anticarcinogenic properties. A brief description of the biological properties of plant lectins, as well as the effect of plant lectins on normal and malignant cells and the antitumor properties of these lectins in vivo and in vitro, are included. These findings are interpreted and possible mechanisms of the antitumor effect of plant lectins are discussed.

Animals↗
PubMed1995

Structure of mannose-specific snowdrop (Galanthus nivalis) lectin is representative of a new plant lectin family.

Tetrameric Galanthus nivalis agglutinin (50,000 M(r)) belongs to a super-family of alpha-D-mannose-specific plant bulb lectins known to be potent inhibitors of retroviruses. The 2.3 A crystal structure of this lectin complexed with methyl alpha-D-mannose reveals a novel three-fold symmetric beta-sheet polypeptide fold. Three antiparallel four-stranded beta-sheets, each with a conserved mannose-binding site, are arranged as a 12-stranded beta-barrel. The tetramer displays 222 symmetry. Pairs of monomers form stable dimers through C-terminal strand exchange. The so formed hybrid beta-sheets are the sites for high affinity mannose binding in the dimer interface. Occupancy observed at corresponding sites in other beta-sheets suggests a potential for twelve sites per tetramer.

Amino Acid Sequence↗
PubMed1998

Lectin-mediated bioadhesion: binding characteristics of plant lectins on the enterocyte-like cell lines Caco-2, HT-29 and HCT-8.

In order to take advantage of the biorecognition between lectins and specific carbohydrates for targeted drug delivery, fluorescein-labelled lectins of different carbohydrate specificities were screened for binding to human colorectal carcinoma cell lines by flow cytometry and confocal microscopy. The lectin-binding rate increased as follows: Dolichos biflorus agglutinin, DBA<peanut agglutinin, PNA<Lens culinaris agglutinin, LCA<Solanum tuberosum lectin, STL<Ulex europaeus isoagglutinin I, UEA-I<wheat germ agglutinin, WGA (Caco-2); PNA<UEA-I<WGA (HT-29); DBA<UEA-I<WGA (HCT-8), thus reflecting the glycosylation pattern of the cells. Compared to the BSA-binding capacity of the cells, the extent of nonspecific binding was strongly dependent on the type of cell line and lectin under investigation being lower than 2% in the case of WGA, STL and UEA-I/Caco-2 and HT-29 cells. Whereas 50% of DBA was bound nonspecifically to Caco-2 cells, the interactions DBA/HCT-8 and PNA/HT-29 were due to nonspecific binding. By competitive inhibition of lectin-adhesion to the cells upon addition of the complementary carbohydrate, specificity of lectin-binding was confirmed except for the interaction of DBA/HCT-8 and PNA/HT-29. Following on from this work, we consider WGA-, STL- and UEA-I-mediated drug delivery to be a promising approach for peroral bioadhesive formulations adhering to absorptive enterocytes.

Caco-2 Cells↗