Plant lectins: the ties that bind in root symbiosis and plant defense

Lectins are a diverse group of carbohydrate-binding proteins that are found within and associated with organisms from all kingdoms of life. Several different classes of plant lectins serve a diverse array of functions. The most prominent of these include participation in plant defense against predators and pathogens and involvement in symbiotic interactions between host plants and symbiotic microbes, including mycorrhizal fungi and nitrogen-fixing rhizobia. Extensive biological, biochemical, and molecular studies have shed light on the functions of plant lectins, and a plethora of uncharacterized lectin genes are being revealed at the genomic scale, suggesting unexplored and novel diversity in plant lectin structure and function. Integration of the results from these different types of research is beginning to yield a more detailed understanding of the function of lectins in symbiosis, defense, and plant biology in general.     

Plant lectins: targeting programmed cell death pathways as antitumor agents

Lectins, a group of highly diverse, carbohydrate-binding proteins of non-immune origin that are ubiquitously distributed in plants, animals and fungi, are well-characterized to have numerous links a wide range of pathological processes, most notably cancer. In this review, we present a brief outline of the representative plant lectins including Ricin-B family, proteins with legume lectin domains and GNA family that can induce cancer cell death via targeting programmed cell death pathways. Amongst these above-mentioned lectins, we demonstrate that mistletoe lectins (MLs), Ricin, Concanavalin A (ConA) and Polygonatum cyrtonema lectin (PCL) can lead to cancer cell programmed death via targeting apoptotic pathways. In addition, we show that ConA and PCL can also result in cancer cell programmed death by targeting autophagic pathways. Moreover, we summarize the possible anti-cancer therapeutic implications of plant lectins such as ConA, Phaseolus vulgaris lectin (PHA) and MLs that have been utilized at different stages of preclinical and clinical trials. Together, these findings can provide a comprehensive perspective for further elucidating the roles of plant lectins that may target programmed cell death pathways in cancer pathogenesis and therapeutics. And, this research may, in turn, ultimately help cancer biologists and clinicians to exploit lectins as potential novel antitumor drugs in the future.     

Current trends of lectins from microfungi

Lectins are widespread in nature and have been isolated from plants, animals, microorganisms, and viruses. Although several lectins have been reported from microfungi, many more genera still remain unexplored and their physiological role is also uncertain. Microfungal lectins show wide disparity regarding their specificity to erythrocytes. Only a few lectins display specificity to particular human blood types. In addition, they also show agglutination to various animal erythrocytes. Many lectins from microfungi exhibit stringent specificity to animal glycoproteins, while a few have much more simplified sugar binding properties. The role of few microfungal lectins in host-parasite interactions, as storage proteins, and in growth and morphogenesis has been proposed. The current review focuses on an overview of lectins from microfungi, their specificity towards erythrocytes and carbohydrates, physicochemical characteristics, and their possible role and applications.     

Current trends of lectins from microfungi

Lectins are widespread in nature and have been isolated from plants, animals, microorganisms, and viruses. Although several lectins have been reported from microfungi, many more genera still remain unexplored and their physiological role is also uncertain. Microfungal lectins show wide disparity regarding their specificity to erythrocytes. Only a few lectins display specificity to particular human blood types. In addition, they also show agglutination to various animal erythrocytes. Many lectins from microfungi exhibit stringent specificity to animal glycoproteins, while a few have much more simplified sugar binding properties. The role of few microfungal lectins in host-parasite interactions, as storage proteins, and in growth and morphogenesis has been proposed. The current review focuses on an overview of lectins from microfungi, their specificity towards erythrocytes and carbohydrates, physicochemical characteristics, and their possible role and applications.     

Characteristics of yeast lectins and their role in cell-cell interactions

Lectins are ubiquitous proteins with the ability to induce cell agglutination and, mediate cellular and molecular recognition processes in a variety of biological interactions. Fungi display exquisite specificity for target tissues and attach to host glycoconjugates via these sugar-binding proteins. Although only few reports are available on lectin activity of yeasts, these sugar binding proteins have been embraced for their role in cell flocculation, a commercially beneficial property, that simplifies downstream recovery operations in yeast fermentations. The lectins bind to cell wall mannans of the neighboring cells via hydrogen bonds leading to the formation of cell aggregates which get interrupted in the presence of specific sugars. Attachment of pathogenic yeasts to host cell surface is also a consequence of lectin-mediated recognition process. This review provides a brief overview of yeast lectins, with an insight to lectin-mediated cellular recognition phenomenon in yeasts.     

Carbohydrate-binding proteins of marine invertebrates

The information on the carbohydrate specificity and molecular organization of some carbohydrate-binding proteins (lectins) of marine invertebrates is reported. Antiviral activity of some of the lectins against human immunodeficiency virus has been studied. Lectins of marine invertebrates are promising tools for studying natural glycoconjugates and cell effectors in vitro.     

Carbohydrate-binding proteins of marine invertebrates

The information on the carbohydrate specificity and molecular organization of some carbohydrate-binding proteins (lectins) of marine invertebrates is reported. Antiviral activity of some of the lectins against human immunodeficiency virus has been studied. Lectins of marine invertebrates are promising tools for studying natural glycoconjugates and cell effectors in vitro.     

黄瓜苋科凝集素基因的表达分析与逆境调控

凝集素是一类具有特异性糖结合活性的蛋白质,通常具有1个或多个非催化的糖结合结构域。凝集素在植物对病原菌的防御反应中发挥重要作用。由于其抗细菌、真菌、病毒和昆虫等的活性,凝集素在农业和生物医药领域都具有很大的应用潜力。作为最小的凝集素家族之一,苋科凝集素的研究较少。该文通过对重要经济作物黄瓜(Cucumis sativu...     

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.     

Novel effect of plant lectins on the inhibition of Streptococcus mutans biofilm formation on saliva-coated surface

Aims:  Dental caries is caused by the disturbance in oral homeostasis, marked by a notable increase in the population of Streptococcus mutans . Lectins are a group of plant proteins that are capable of recognizing the glycoconjugates present on the bacterial surface. The aim of this study was to evaluate the effect of seven plant lectins on the growth and initial adhesion of S. mutans .
Methods and Results:  Lectins of different carbohydrate specificities were isolated from plant sources by conventional methods of protein purification. The effect on growth of S. mutans was evaluated following CLSI guidelines. None of the lectins used in this study inhibited the bacterial growth and multiplication. The adherence and biofilm formation of bacteria to saliva-coated polystyrene plates was tested in the presence of plant lectins. All the plant lectins tested, inhibited both the adherence and biofilm in a concentration dependent manner. Confocal microscopy and scanning electron microscopy were employed to assess the biofilm formation in the presence of plant lectin (glucose/mannose-specific) at sub-minimal inhibitory concentrations. These evaluations revealed that lectins inhibited the clumping and attachment of S. mutans .
Conclusions:  Lectins tested here inhibited initial biofilm formation by S. mutans. Glucose/Mannose-specific lectin altered the adhesion arrangement of the bacteria on the saliva-coated surfaces.
Significance and Impact of the Study:  The plant lectins used in this study may offer a novel strategy to reduce development of dental caries by inhibiting the initial adhesion and subsequent biofilm formation of S. mutans.     

Lectin-like proteins in model organisms: implications for evolution of carbohydrate-binding activity.

Classes of intracellular lectins that recognize core-type structures and mediate intracellular glycoprotein trafficking are present in vertebrates, model invertebrates such as Caenorhabditis elegans and Drosophila melanogaster, plants, and yeasts. Lectins that recognize more complex structures at the cell surface, such as C-type lectins and galectins, are also found in invertebrate organisms as well as vertebrates, but the functions of these proteins have evolved differently in different animal lineages.     

Fucose-specific lectins disclose perpetuation of root primordia in callus cultures of maize (Zea mays L.)

Fucose-specific, fluorochrome-coupled lectins bind to the periphery of cryosectioned root tips of a Zea mays F1 hybrid. Differentiating and differentiated root cap cells, the mucilage in which the root cap cells are embedded, and the epidermis below the root hair region bind the lectin. Procedures were developed to locate binding sites for the lectins in callus growing on nutrient medium with the auxin 2,4-dichlorophenoxyacetic acid. Lectins applied to cryosectioned callus capable of root regeneration, bound strongly to the peripheral cells and the surrounding mucous matrix which invariably covers such callus. The overall staining patterns confirm that the callus cultures were suppressed, teratomatous primordia rather than a population of “dedifferentiated, unspecialized” cells.     

植物凝集素的超级家族

凝集素是一类专一、可逆地和糖类结合的蛋白质,迄今已经分离纯化并测定了氨基酸序列的凝集素已有不少,一些凝集素以及它们与配体糖相互结合的复合物的高级结构也已经给出,许多工作已深入到基因水平．就目前已有的知识,说明植物凝集素是一个庞大的蛋白质家族．     

Analysis of lectin concentrations in different Rhizoctonia solani strains

Lectins are carbohydrate-binding proteins that contain at least one carbohydrate binding domain which can bind to a specific mono- or oligosaccharide. These proteins are widely distributed in plants. However, over the last decade evidence is accumulating that lectins occur also in numerous fungi belonging to both the Ascomycota and Basiodiomycota. Rhizoctonia solani is known to be an important pathogen to a wide range of host plants. In this study, isolates of R. solani from different anastomosis groups have been screened for the presence of lectin using agglutination assays to detect and quantitate lectin activity. The evaluation included determination of the lectin content in mycelium as well as in sclerotia. The amount of lectin in the sclerotia was higher than in the mycelium of the same strains. The R. solani strains with the highest amounts of lectin have been selected for cultivation, extraction and purification of the lectin.     

Oligosaccharide structure determination of glycoconjugates using lectins

Lectins, the divalent or polyvalent (glyco) proteins of non-immune origin of the cells agglutinate cells or other materials, that display more than one saccharide of sufficient complementarity. Lectins considered ‘identical’ in terms of mono-and disaccharide specificity can be differentiated by their ability to recognise the fine differences in more complex structures. The present review discusses the interaction of lectins with various oligosaccharides and their resultant separations due to structural variations.     

Receptors of Garlic (Allium sativum) Lectins and Their Role in Insecticidal Action

Garlic (Allium sativum) lectins are promising candidate molecules for the protection against chewing (lepidopteran) as well as sap sucking (homopteran) insect pests. Molecular mechanism of toxicity and interaction of lectins with midgut receptor proteins has been described in many reports. Lectins show its effect right from sensory receptors of mouth parts by disrupting the membrane integrity and food detection ability. Subsequently, enter into the gut lumen and interact with midgut glycosylated proteins like alkaline phosphatase (ALP), aminopeptidase-N (APN), cadherin-like proteins, polycalins, sucrase, symbionin and others. These proteins play critical role in life cycle of insect directly or indirectly. Lectins interfere with the activity of these proteins and causes physiological disorders leading to the death of insects. Lectins further transported across the insect gut, accumulated in various body parts (like haemolymph and ovary) and interact with intracellular proteins like symbionin and cytochrome p450. Binding with cytochrome p450 (which involve in ecdysone synthesis) might interfere in the development of insects, which results in growth retardation and pre-mature death.     

Mushroom lectins: Current status and future perspectives

Lectins are nonimmune proteins or glycoproteins that bind specifically to cell surface carbohydrates, culminating in cell agglutination. These are known to play key roles in host defense system and also in metastasis. Many new sources have been explored for the occurrence of lectins during the last few years. Numerous novel lectins with unique specificities and exploitable properties have been discovered. Mushrooms have attracted a number of researchers in food and pharmaceuticals. Many species have long been used in traditional Chinese medicines or functional foods in Japan and other Asian countries. A number of bioactive constituents have been isolated from mushrooms including polysaccharides, polysaccharopeptides, polysaccharide–protein complexes, proteases, ribonucleases, ribosome inactivating proteins, antifungal proteins, immunomodulatory proteins, enzymes, lectins, etc. Mushroom lectins are endowed with mitogenic, antiproliferative, antitumor, antiviral, and immunestimulating potential. In this review, an attempt has been made to collate the information on mushroom lectins, their blood group and sugar specificities, with an emphasis on their biomedical potential and future perspectives.     

Exquisite specificity of mitogenic lectin from <Emphasis Type="Italic">Cephalosporium curvulum</Emphasis> to core fucosylated N-glycans

Lectins are carbohydrate binding proteins that are gaining attention as important tools for the identification of specific glycan markers expressed during different stages of the cancer. We earlier reported the purification of a mitogenic lectin from human pathogenic fungus Cephalosporium curvulum (CSL) that has complex sugar specificity when analysed by hapten inhibition assay. In the present study, we report the fine sugar specificity of CSL as determined by glycan array analysis. The results revealed that CSL has exquisite specificity towards core fucosylated N-glycans. Fucosylated trimannosyl core is the basic structure required for the binding of CSL. The presence of fucose in the side chain further enhances the avidity of CSL towards such glycans. The affinity of CSL is drastically reduced towards the non-core fucosylated glycans, in spite of their side chain fucosylation. CSL showed no binding to the tested O-glycans and monosaccharides. These observations suggest the unique specificity of CSL towards core fucosylated N-glycans, which was further validated by binding of CSL to human colon cancer epithelial and hepatocarcinoma cell lines namely HT29 and HepG2, respectively, that are known to express core fucosylated N-glycans, using AOL and LCA as positive controls. LCA and AOL are fucose specific lectins that are currently being used clinically for the diagnosis of hepatocellular carcinomas. Most of the gastrointestinal markers express core fucosylated N-glycans. The high affinity and exclusive specificity of CSL towards α1-6 linkage of core fucosylated glycans compared to other fucose specific lectins, makes it a promising molecule that needs to be further explored for its application in the diagnosis of gastrointestinal cancer.