Multivalent protein-carbohydrate interactions. A new paradigm for supermolecular assembly and signal transduction

Glycosylation regulates Notch signalling

Intracellular post-translational modifications such as phosphorylation and ubiquitylation have been well studied for their roles in regulating diverse signalling pathways, but we are only just beginning to understand how differential glycosylation is used to regulate intercellular signalling. Recent studies make clear that extracellular post-translational modifications, in the form of glycosylation, are essential for the Notch signalling pathway, and that differences in the extent of glycosylation are a significant mechanism by which this pathway is regulated.

Computational analysis of multivalency in lectins: structures of garlic lectin-oligosaccharide complexes and their aggregates

Multivalency in lectins is a phenomenon that has been discussed at considerable length. The structural basis for the role of multivalency in garlic lectin has been investigated here through computational studies. Biochemical studies have shown that the binding affinity of garlic lectin for high mannose oligosaccharides is orders of magnitude greater than that for mannose. Modeling and energy calculations clearly indicate that such increase in affinity cannot be accounted for by binding of these oligosaccharides at any of the six sites of a garlic lectin dimer. These studies also indicate that a given oligosaccharide cannot bind simultaneously to more than one binding site on a lectin dimer. The possibility of a given oligosaccharide simultaneously binding to and hence linking two or more lectin molecules was therefore explored. This study showed that trimannosides and higher oligomers can cross-link lectin dimers, amplifying the protein-oligosaccharide interactions severalfold, thus explaining the role of multivalency in enhancing affinity. A comprehensive exploration of all possible cross-links posed a formidable computational problem. Even a partial exploration involving a carefully chosen region of the conformational space clearly showed that a given dimer pair can be cross-linked not only by a single oligosaccharide molecule but also simultaneously by two oligosaccharides. The number of such possible double cross-links, including those forming interesting tetrameric structures, generally increases with the size of the oligosaccharide, correlating with the biochemical data. In addition to their immediate relevance to garlic lectin, these studies are of general interest in relation to lectin-oligosaccharide interactions.

Development of carbohydrate-based scaffolds for restricted presentation of recognition groups. Extension to divalent ligands and implications for the structure of dimerized receptors

The solution structure of glycosyl amides has been studied by using NMR. A strong preference is displayed by tertiary aromatic glycosyl amides for E-anti structures in contrast with secondary aromatic glycosyl amides where Z-anti structures predominate. The structural diversity displayed by these classes of molecules would seem to be important as the directional properties of the aromatic ring, or groups attached to the aromatic ring, would be determined by choosing to have either a secondary or tertiary amide at the anomeric center and could be considered when designing bioactive molecules with carbohydrate scaffolds. The structural analysis was also carried out for related divalent secondary and tertiary glycosyl amides and these compounds display preferences similar to that of the monovalent compounds. The constrained divalent compounds have potential for promoting formation of clusters that will have restricted structure and thus have potential for novel studies of mechanisms of action of multivalent ligands. Possible applications of such compounds would be as scaffolds for the design and synthesis of ligands that will facilitate protein-protein or other receptor-receptor interactions. The affinity of restricted divalent (or higher order) ligands, designed to bind to proteins that recognize carbohydrates which would facilitate clustering and concomitantly promote protein-protein interactions, may be significantly higher than monovalent counterparts or multivalent ligands without these properties. This may be useful as a new approach in the development of therapeutics based on carbohydrates.

Stimulation of proliferation of rat hepatic stellate cells by galectin-1 and galectin-3 through different intracellular signaling pathways

We found that the expression of galectin-1 and galectin-3 was significantly up-regulated in hepatic stellate cells (HSCs) both in the course of their transdifferentiation into myofibroblasts, a process of "self-activation," and in the fibrosis of liver tissues. Recombinant galectin-1 and galectin-3 stimulated the proliferation of cultured HSCs via the MEK1/2-ERK1/2 signaling pathway. However, galectin-3 utilized protein kinases C and A to induce this process, whereas galectin-1 did not. We also found that thiodigalactoside, a potent inhibitor of beta-galactoside binding, attenuated the effects of both galectins. In addition, galectin-1, but not galectin-3, promoted the migration of HSCs. Thus, it appears that galectin-1 and galectin-3, generated by activated HSCs, could participate in beta-galactoside binding and induce different intracellular signaling pathways leading to the proliferation of HSCs.

The mystery of nonclassical protein secretion. A current view on cargo proteins and potential export routes

Most of the examples of protein translocation across a membrane (such as the import of classical secretory proteins into the endoplasmic reticulum, import of proteins into mitochondria and peroxisomes, as well as protein import into and export from the nucleus), are understood in great detail. In striking contrast, the phenomenon of unconventional protein secretion (also known as nonclassical protein export or ER/Golgi-independent protein secretion) from eukaryotic cells was discovered more than 10 years ago and yet the molecular mechanism and the molecular identity of machinery components that mediate this process remain elusive. This problem appears to be even more complex as several lines of evidence indicate that various kinds of mechanistically distinct nonclassical export routes may exist. In most cases these secretory mechanisms are gated in a tightly controlled fashion. This review aims to provide a comprehensive overview of our current knowledge as a basis for the development of new experimental strategies designed to unravel the molecular machineries mediating ER/Golgi-independent protein secretion. Beyond solving a fundamental problem in current cell biology, the molecular analysis of these processes is of major biomedical importance as these export routes are taken by proteins such as angiogenic growth factors, inflammatory cytokines, components of the extracellular matrix which regulate cell differentiation, proliferation and apoptosis, viral proteins, and parasite surface proteins potentially involved in host infection.

Negative regulation of T cell activation by placental protein 14 is mediated by the tyrosine phosphatase receptor CD45

CD45 is the major protein tyrosine phosphatase receptor on T cell surfaces that functions as both a positive and a negative regulator of T cell receptor (TCR) signaling. Although CD45 is required for the activation of TCR-associated Src family kinases, it also dephosphorylates phosphoproteins involved in the TCR-signaling cascade. This study links CD45 to the inhibitory activity of placental protein 14 (PP14), a major soluble protein of pregnancy that is now known to be a direct modulator of T cells and to function by desensitizing TCR signaling. PP14 and CD45 co-capped with each other, pointing to a physical linkage between the two. Interestingly, however, the binding of PP14 to T cell surfaces was not restricted to CD45 alone, with evidence showing that PP14 binds to other surface molecules in a carbohydrate-dependent fashion. Notwithstanding the broader molecular binding potential of PP14, its interaction with CD45 appeared to have special functional significance. Using transfected derivatives of the HPB. ALL mutant T cell line that differ in CD45 expression, we established that the inhibitory effects of PP14 are dependent upon the expression of intact CD45 on T cell surfaces. Based upon these findings, we propose a new immunoregulatory model for PP14, wherein one of its surface molecular targets, CD45, mediates its T cell inhibitory activity, accounting for the intriguing capacity of PP14 to elevate TCR activation thresholds and thereby down-regulate T cell activation.

Ah, sweet mystery of death! Galectins and control of cell fate

Control of cell death is critical in eukaryotic development, immune system homeostasis, and control of tumorigenesis. The galectin family of lectins is implicated in all of these processes. Other families of molecules function as death receptors or death effectors, but galectins are uniquely capable of acting both extracellularly and intracellularly to control cell death. Extracellularly, galectins cross-link glycan ligands to transduce signals that lead directly to death or that influence other signals regulating cell fate. Intracellular expression of galectins can modulate other signals controlling cell viability. Individual galectins can act on multiple cell types, and multiple galectins can act on the same cell. Understanding how galectins regulate cell viability and function will broaden our knowledge of the roles of galectins in basic biological processes and facilitate development of therapeutic applications for galectins in autoimmunity, transplant-related disease, and cancer.

Influencing receptor-ligand binding mechanisms with multivalent ligand architecture

Multivalent ligands can function as inhibitors or effectors of biological processes. Potent inhibitory activity can arise from the high functional affinities of multivalent ligand-receptor interactions. Effector functions, however, are influenced not only by apparent affinities but also by alternate factors, including the ability of a ligand to cluster receptors. Little is known about the molecular features of a multivalent ligand that determine whether it will function as an inhibitor or effector. We envisioned that, by altering multivalent ligand architecture, ligands with preferences for different binding mechanisms would be generated. To this end, a series of 28 ligands possessing structural diversity was synthesized. This series provides the means to explore the effects of ligand architecture on the inhibition and clustering of a model protein, the lectin concanavalin A (Con A). The structural parameters that were varied include scaffold shape, size, valency, and density of binding elements. We found that ligands with certain architectures are effective inhibitors, but others mediate receptor clustering. Specifically, high molecular weight, polydisperse polyvalent ligands are effective inhibitors of Con A binding, whereas linear oligomeric ligands generated by the ring-opening metathesis polymerization have structural properties that favor clustering. The shape of a multivalent ligand also influences specific aspects of receptor clustering. These include the rate at which the receptor is clustered, the number of receptors in the clusters, and the average interreceptor distance. Our results indicate that the architecture of a multivalent ligand is a key parameter in determining its activity as an inhibitor or effector. Diversity-oriented syntheses of multivalent ligands coupled with effective assays that can be used to compare the contributions of different binding parameters may afford ligands that function by specific mechanisms.

Regulation of notch signaling by o-linked fucose

Notch and its ligands are modified by a protein O-fucosyltransferase (OFUT1) that attaches fucose to a Serine or Threonine within EGF domains. By using RNAi to decrease Ofut1 expression in Drosophila, we demonstrate that O-linked fucose is positively required for Notch signaling, including both Fringe-dependent and Fringe-independent processes. The requirement for Ofut1 is cell autonomous, in the signal-receiving cell, and upstream of Notch activation. The transcription of Ofut1 is developmentally regulated, and surprisingly, overexpression of Ofut1 inhibits Notch signaling. Together, these results indicate that OFUT1 is a core component of the Notch pathway, which is required for the activation of Notch by its ligands, and whose regulation may contribute to the pattern of Notch activation during development.

Oligosaccharide specificity of galectins: a search by frontal affinity chromatography

Galectins are widely distributed sugar-binding proteins whose basic specificity for beta-galactosides is conserved by evolutionarily preserved carbohydrate-recognition domains (CRDs). Although they have long been believed to be involved in diverse biological phenomena critical for multicellular organisms, in only few a cases has it been proved that their in vivo functions are actually based on specific recognition of the complex carbohydrates expressed on cell surfaces. To obtain clues to understand the physiological roles of diverse members of the galectin family, detailed analysis of their sugar-binding specificity is necessary from a comparative viewpoint. For this purpose, we recently reinforced a conventional system for frontal affinity chromatography (FAC) [J. Chromatogr., B, Biomed. Sci. Appl. 771 (2002) 67-87]. By using this system, we quantitatively analyzed the interactions at 20 degrees C between 13 galectins including 16 CRDs originating from mammals, chick, nematode, sponge, and mushroom, with 41 pyridylaminated (PA) oligosaccharides. As a result, it was confirmed that galectins require three OH groups of N-acetyllactosamine, as had previously been denoted, i.e., 4-OH and 6-OH of Gal, and 3-OH of GlcNAc. As a matter of fact, no galectin could bind to glycolipid-type glycans (e.g., GM2, GA2, Gb3), complex-type N-glycans, of which both 6-OH groups are sialylated, nor Le-related antigens (e.g., Le(x), Le(a)). On the other hand, considerable diversity was observed for individual galectins in binding specificity in terms of (1) branching of N-glycans, (2) repeating of N-acetyllactosamine units, or (3) substitutions at 2-OH or 3-OH groups of nonreducing terminal Gal. Although most galectins showed moderately enhanced affinity for branched N-glycans or repeated N-acetyllactosamines, some of them had extremely enhanced affinity for either of these multivalent glycans. Some galectins also showed particular preference for alpha1-2Fuc-, alpha1-3Gal-, alpha1-3GalNAc-, or alpha2-3NeuAc-modified glycans. To summarize, galectins have evolved their sugar-binding specificity by enhancing affinity to either "branched", "repeated", or "substituted" glycans, while conserving their ability to recognize basic disaccharide units, Galbeta1-3/4GlcNAc. On these bases, they are considered to exert specialized functions in diverse biological phenomena, which may include formation of local cell-surface microdomains (raft) by sorting glycoconjugate members for each cell type.

Synthesis and applications of end-labeled neoglycopolymers

[reaction: see text] Neoglycopolymers that vary in length and contain a single fluorescent reporter group were synthesized using ring-opening metathesis polymerization (ROMP). The utility of these materials is demonstrated by the development of a cellular binding assay for L-selectin, a cell surface protein that plays a role in inflammation. The data reveal that these multivalent ligands interact with multiple copies of L-selectin.

Galectins and their ligands: amplifiers, silencers or tuners of the inflammatory response?

Recent evidence has implicated galectins and their ligands as master regulators of immune cell homeostasis. Whereas some members of this family, such as galectin-3, behave as amplifiers of the inflammatory cascade, others, such as galectin-1, trigger homeostatic signals to shut off T-cell effector functions. These carbohydrate-binding proteins, identified by shared consensus amino acid sequences and affinity for beta-galactoside-containing sugars, participate in the homeostasis of the inflammatory response, either by regulating cell survival and signaling, influencing cell growth and chemotaxis, interfering with cytokine secretion, mediating cell-cell and cell-matrix interactions or influencing tumor progression and metastasis. The current wealth of new information promises a future scenario in which individual members of the galectin family or their ligands will be used as powerful anti-inflammatory mediators and selective modulators of the immune response.

Specific recognition and cleavage of galectin-3 by Leishmania major through species-specific polygalactose epitope

Lipophosphoglycan is a major surface molecule of Leishmania, protozoa parasites, which are the causative agents of leishmaniasis, a disease that annually afflicts millions of people worldwide. The oligosaccharide structures of lipophosphoglycan varies among species, and epitopes of these species-specific oligosaccharides are suggested to be implicated in the interaction of Leishmania with macrophages as well as species-specific tissue tropism observed in leishmaniasis. The recognition of the species-specific variation of oligosaccharides is likely to be mediated by host carbohydrate-binding proteins, lectins, but the identities of the lectins remain elusive. Galectin-3 is a mammalian soluble beta-galactoside-binding lectin and is expressed in macrophages, dendritic cells, and keratinocytes, as well as fibroblasts, all of which are present in the site of Leishmania infection. In this paper, we found that galectin-3 binds to lipophosphoglycan of Leishmania major but not to those of Leishmania donovani through L. major-specific polygalactose epitopes. Association of galectin-3 with L. major led to the cleavage of galectin-3, resulting in truncated galectin-3 containing the C-terminal lectin domain but lacking the N-terminal domain implicated in lectin oligomerization. This cleavage was inhibited by the galectin-3 antagonist lactose, as well as 1,10-ortho-phenanthroline, suggesting that galectin-3 is cleaved by zinc metalloproteases after its binding to lipophosphoglycans. The modulation of various innate immunity reactions by galectin-3 is affected by its oligomerization; therefore, we propose the L. major-specific truncation of galectin-3 may contribute to the species-specific immune responses induced by Leishmania.

Peptide mimotopes as surrogate antigens of carbohydrates in vaccine discovery

Carbohydrate antigens are immune targets associated with a variety of pathogens and tumor cells. Unfortunately, most carbohydrates are intrinsically T cell-independent antigens, which diminishes their efficacy as immunogens. The conversion of carbohydrate epitopes to peptide mimotopes is one means to overcome the T cell-independent nature of carbohydrate antigens because peptides have an absolute requirement for T cells. Although such conversion has great potential for the development of veterinarian and human vaccines, there are issues related to the use of peptide-based immunogens as functional surrogates. Some of these issues are fundamental, pertaining to how mimicry comes about at the molecular level, and some are application oriented, directed at elucidating important immunological mechanisms. In this article the potential and caveats of this technology regarding its application in vaccine discovery are analyzed.

CD4+CD7- leukemic T cells from patients with Sézary syndrome are protected from galectin-1-triggered T cell death

In early stages of cutaneous T cell lymphoma (Sézary syndrome) both CD4+CD7- and CD4+CD7+ T cells clonally expand whereas in late stages of the disease CD7- cells are predominant in number, giving rise to the question whether CD7- T cells have a survival advantage in the skin. Galectin-1, a cell-bound lectin, was recently reported to trigger apoptosis in activated CD7+ T cells. Here, we demonstrate that in contrast to activated CD7(+) T cells, quiescent and activated CD69+ CD7- T cells from healthy donors and from Sézary patients are resistant to galectin-1-mediated cell death. CD7- T cells are apoptosis-resistant even during coculture with IFN-gamma-stimulated endothelial cells that constitutively express galectin-1 in high amounts. These data imply that resistance of CD7- T cells to galectin-1-induced apoptosis may contribute to the accumulation of CD7- Sézary T cells during progression of the disease.

Low micromolar inhibitors of galectin-3 based on 3'-derivatization of N-acetyllactosamine

A strategy for generating potential galectin inhibitors was devised based on derivatization at the C-3' atom in 3'-amino-N-acetyllactosamine by using structural knowledge of the galectin carbohydrate recognition site. A collection of 12 compounds was prepared by N-acylations or N-sulfonylations. Hydrophobic tagging of the O-3 atom in the N-acetylglucosamine residue with a stearic ester allowed rapid and simple product purification. The compounds were screened in a galectin-3 binding assay and three compounds with significantly higher inhibitory activities compared to the parent N-acetyllactosaminide were found. These three best inhibitors all carried an aromatic amide at the C-3' position of the galactose moiety, which indicates that favorable interactions were formed between the aromatic group and galectin-3. The best inhibitor had an IC50 value (4.4 microM) about 50 times better than the parent N-acetyllactosaminide, which implies that it has potential as a valuable tool for studying galectin-3 biological functions and also as a lead compound for the development of galectin-3-blocking pharmaceuticals.

Control of multivalent interactions by binding epitope density

Receptor clustering by multivalent ligands can activate signaling pathways. In principle, multivalent ligand features can control clustering and the downstream signals that result, but the influence of ligand structure on these processes is incompletely understood. Using a series of synthetic polymers that vary systematically, we studied the influence of multivalent ligand binding epitope density on the clustering of a model receptor, concanavalin A (Con A). We analyze three aspects of receptor clustering: the stoichiometry of the complex, rate of cluster formation, and receptor proximity. Our experiments reveal that the density of binding sites on a multivalent ligand strongly influences each of these parameters. In general, high binding epitope density results in greater numbers of receptors bound per polymer, faster rates of clustering, and reduced inter-receptor distances. Ligands with low binding epitope density, however, are the most efficient on a binding epitope basis. Our results provide insight into the design of ligands for controlling receptor-receptor interactions and can be used to illuminate mechanisms by which natural multivalent displays function.

Cell aggregation by scaffolded receptor clusters

The aggregation of cells by lectins or antibodies is important for biotechnological and therapeutic applications. One strategy to augment the avidity and aggregating properties of these mediators is to maximize the number of their ligand binding sites. The valency of lectins and antibodies, however, is limited by their quaternary structures. To overcome this limitation, we explored the use of polymers generated by ring-opening metathesis polymerization (ROMP) as scaffolds to noncovalently assemble multiple copies of a lectin, the tetravalent protein concanavalin A (Con A). We demonstrate that complexes between Con A and multivalent scaffolds aggregate cells of a T cell leukemia line (Jurkat) more effectively than Con A alone. We anticipate that synthetic scaffolds will offer a new means of facilitating processes that rely on cell aggregation, such as pathogen clearance and immune recognition.

Developing a taste for sweets

Lymphocytes are covered with sugars. Some of the oligosaccharides on lymphocytes may be recognized by specific lectins such as the selectins, but what other functions do all of these oligosaccharides serve? Two recent papers in Cell (Moody et al., 2001) and Immunity (Daniels et al., 2001) describe a novel role for glycosylation in the thymus--regulating the interaction of MHC class I molecules with CD8 during thymocyte maturation.

Distance mapping of protein-binding sites using spin-labeled oligosaccharide ligands

The binding of a nitroxide spin-labeled analog of N-acetyllactosamine to galectin-3, a mammalian lectin of 26 kD size, is studied to map the binding sites of this small oligosaccharide on the protein surface. Perturbation of intensities of cross-peaks in the (15)N heteronuclear single quantum coherence (HSQC) spectrum of full-length galectin-3 owing to the bound spin label is used qualitatively to identify protein residues proximate to the binding site for N-acetyllactosamine. A protocol for converting intensity measurements to a more quantitative determination of distances between discrete protein amide protons and the bound spin label is then described. This protocol is discussed as part of a drug design strategy in which subsequent perturbation of chemical shifts of distance mapped amide cross-peaks can be used effectively to screen a library of compounds for other ligands that bind to the target protein at distances suitable for chemical linkage to the primary ligand. This approach is novel in that it bypasses the need for structure determination and resonance assignment of the target protein.

The use of selective adsorbents in capillary electrophoresis-mass spectrometry for analyte preconcentration and microreactions: a powerful three-dimensional tool for multiple chemical and biological applications

Much attention has recently been directed to the development and application of online sample preconcentration and microreactions in capillary electrophoresis using selective adsorbents based on chemical or biological specificity. The basic principle involves two interacting chemical or biological systems with high selectivity and affinity for each other. These molecular interactions in nature usually involve noncovalent and reversible chemical processes. Properly bound to a solid support, an "affinity ligand" can selectively adsorb a "target analyte" found in a simple or complex mixture at a wide range of concentrations. As a result, the isolated analyte is enriched and highly purified. When this affinity technique, allowing noncovalent chemical interactions and biochemical reactions to occur, is coupled on-line to high-resolution capillary electrophoresis and mass spectrometry, a powerful tool of chemical and biological information is created. This paper describes the concept of biological recognition and affinity interaction on-line with high-resolution separation, the fabrication of an "analyte concentrator-microreactor", optimization conditions of adsorption and desorption, the coupling to mass spectrometry, and various applications of clinical and pharmaceutical interest.

Chemical deglycosylation can induce methylation, succinimide formation, and isomerization

Interpretation of deglycosylation studies relies heavily on the absence of modifications to the polypeptide chain. We have found that by using a common chemical deglycosylation technique, one can effect at least three changes in a peptide's structure: methylation, isomerization, and ring formation. It was determined that the conditions of chemical deglycosylation introduce a +14 Da shift in the masses of our model peptides, RKDVY, RKEVY, and horseradish peroxidase. This shift is localized to acidic functional groups and is interpreted as methylation of the free carboxylates in our models. An additional shift in mass of -18 Da is found in the model peptide RKDVY consistent with the loss of water associated with succinimide ring formation in this peptide. Chemical treatment induced isomerization of aspartyl residues to isoaspartyl residues in another model peptide, tetragastrin. These results indicate that one should use caution when interpreting the results of chemical deglycosylation experiments.

Negative regulation of neuroblastoma cell growth by carbohydrate-dependent surface binding of galectin-1 and functional divergence from galectin-3

The cell density-dependent growth inhibition of human SK-N-MC neuroblastoma cells is initiated by increased ganglioside sialidase activity leading to elevated cell surface presentation of ganglioside GM1, a ligand of galectin-1. We herein show that the extent of the cell surface expression of the galectin coincides with marked increases of the sialidase activity. Reverse transcriptase-polymerase chain reaction analysis excludes a regulation at the transcriptional level. Exposure of cells to purified galectin-1 reveals its carbohydrate-dependent activity to reduce cell proliferation. Assays to detect DNA fragmentation biochemically and cytometrically and to block caspases render it unlikely that galectin-1 acts as a classical proapoptotic factor on these cells. Because the chimeric galectin-3 shares binding sites and binding parameters with galectin-1 for these cells, we tested whether this galectin will elicit the same response as the homodimeric cross-linking galectin-1. Evidently, galectin-3 fails to affect cell growth by itself but interferes with galectin-1 upon coincubation. Its proteolytically truncated variant, the C-terminal lectin domain with impaired capacity to form aggregates when surface bound, has only weak binding properties. Thus, the way in which the galectin-1 interacts topologically with an apparently common set of ligands relative to galectin-3 is crucial for eliciting post-binding events. We conclude that galectin-1 is a probable effector in the sialidase-dependent growth control in this system. Moreover, the experiments with galectin-3 reveal functional divergence, most probably based on different topologies of presentation of homologous carbohydrate-binding sites.

Plant lectins: occurrence, biochemistry, functions and applications

Growing insights into the many roles of glycoconjugates in biorecognition as ligands for lectins indicates a need to compare plant and animal lectins. Furthermore, the popularity of plant lectins as laboratory tools for glycan detection and characterization is an incentive to start this review with a brief introduction to landmarks in the history of lectinology. Based on carbohydrate recognition by lectins, initially described for concanavalin A in 1936, the chemical nature of the ABH-blood group system was unraveled, which was a key factor in introducing the term lectin in 1954. How these versatile probes are produced in plants and how they are swiftly and efficiently purified are outlined, and insights into the diversity of plant lectin structures are also given. The current status of understanding their functions calls for dividing them into external activities, such as harmful effects on aggressors, and internal roles, for example in the transport and assembly of appropriate ligands, or in the targeting of enzymatic activities. As stated above, attention is given to intriguing parallels in structural/functional aspects of plant and animal lectins as well as to explaining caveats and concerns regarding their application in crop protection or in tumor therapy by immunomodulation. Integrating the research from these two lectin superfamilies, the concepts are discussed on the role of information-bearing glycan epitopes and functional consequences of lectin binding as translation of the sugar code (functional glycomics).