Carrier-immobilized derivatized lysoganglioside GM1 is a ligand for specific binding sites in various human tumor cell types and peripheral blood lymphocytes and monocytes

Glycan Chains of Gangliosides: Functional Ligands for Tissue Lectins (Siglecs/Galectins)

Molecular signals on the cell surface are responsible for adhesion and communication. Of relevance in this respect, their chemical properties endow carbohydrates with the capacity to store a maximum of information in a minimum of space. One way to present glycans on the cell surface is their covalent conjugation to a ceramide anchor. Among the resulting glycosphingolipids, gangliosides are special due to the presence of at least one sialic acid in the glycan chains. Their spatial accessibility and the dynamic regulation of their profile are factors that argue in favor of a role of glycans of gangliosides as ligands (counterreceptors) for carbohydrate-binding proteins (lectins). Indeed, as discovered first for a bacterial toxin, tissue lectins bind gangliosides and mediate contact formation (trans) and signaling (cis). While siglecs have a preference for higher sialylated glycans, certain galectins also target the monosialylated pentasaccharide of ganglioside GM1. Enzymatic interconversion of ganglioside glycans by sialidase action, relevant for neuroblastoma cell differentiation and growth control in vitro, for axonogenesis and axon regeneration, as well as for proper communication between effector and regulatory T cells, changes lectin-binding affinity profoundly. The GD1a-to-GM1 "editing" is recognized by such lectins, for example, myelin-associated glycoprotein (siglec-4) losing affinity and galectin-1 gaining reactivity, and then translated into postbinding signaling. Orchestrations of loss/gain of affinity, of ganglioside/lectin expression, and of lectin presence in a network offer ample opportunities for fine-tuning. Thus glycans of gangliosides such as GD1a and GM1 are functional counterreceptors by a pairing with tissue lectins, an emerging aspect of ganglioside and lectin functionality.

Sweet complementarity: the functional pairing of glycans with lectins

Carbohydrates establish the third alphabet of life. As part of cellular glycoconjugates, the glycans generate a multitude of signals in a minimum of space. The presence of distinct glycotopes and the glycome diversity are mapped by sugar receptors (antibodies and lectins). Endogenous (tissue) lectins can read the sugar-encoded information and translate it into functional aspects of cell sociology. Illustrated by instructive examples, each glycan has its own ligand properties. Lectins with different folds can converge to target the same epitope, while intrafamily diversification enables functional cooperation and antagonism. The emerging evidence for the concept of a network calls for a detailed fingerprinting. Due to the high degree of plasticity and dynamics of the display of genes for lectins the validity of extrapolations between different organisms of the phylogenetic tree yet is inevitably limited.

A guide into glycosciences: How chemistry, biochemistry and biology cooperate to crack the sugar code

BACKGROUND

The most demanding challenge in research on molecular aspects within the flow of biological information is posed by the complex carbohydrates (glycan part of cellular glycoconjugates). How the 'message' encoded in carbohydrate 'letters' is 'read' and 'translated' can only be unraveled by interdisciplinary efforts.

SCOPE OF REVIEW

This review provides a didactic step-by-step survey of the concept of the sugar code and the way strategic combination of experimental approaches characterizes structure-function relationships, with resources for teaching.

MAJOR CONCLUSIONS

The unsurpassed coding capacity of glycans is an ideal platform for generating a broad range of molecular 'messages'. Structural and functional analyses of complex carbohydrates have been made possible by advances in chemical synthesis, rendering production of oligosaccharides, glycoclusters and neoglycoconjugates possible. This availability facilitates to test the glycans as ligands for natural sugar receptors (lectins). Their interaction is a means to turn sugar-encoded information into cellular effects. Glycan/lectin structures and their spatial modes of presentation underlie the exquisite specificity of the endogenous lectins in counterreceptor selection, that is, to home in on certain cellular glycoproteins or glycolipids.

GENERAL SIGNIFICANCE

Understanding how sugar-encoded 'messages' are 'read' and 'translated' by lectins provides insights into fundamental mechanisms of life, with potential for medical applications.

Determination of structural and functional overlap/divergence of five proto-type galectins by analysis of the growth-regulatory interaction with ganglioside GM1in silicoandin vitroon human neuroblastoma cells

The growth-regulatory interplay between ganglioside GM1 on human SK-N-MC neuroblastoma cells and an endogenous lectin provides a telling example for glycan (polysaccharide) functionality. Galectin-1 is the essential link between the sugar signal and the intracellular response. The emerging intrafamily complexity of galectins raises the question on defining extent of their structural and functional overlap/divergence. We address this problem for proto-type galectins in this system: ganglioside GM1 as ligand, neuroblastoma cells as target. Using the way human galectin-1 interacts with this complex natural ligand as template, we first defined equivalent positioning for distinct substitutions in the other tested proto-type galectins, e.g., Lys63 vs. Leu60/Gln72 in galectins-2 and -5. As predicted from our in silico work, the tested proto-type galectins have affinity for the pentasaccharide of ganglioside GM1. In contrast to solid-phase assays, cell surface presentation of the ganglioside did not support binding of galectin-5, revealing the first level of regulation. Next, a monomeric proto-type galectin (CG-14) can impair galectin-1-dependent negative growth control by competitively blocking access to the shared ligand without acting as effector. Thus, the quaternary structure of proto-type galectins is an efficient means to give rise to functional divergence. The identification of this second level of regulation is relevant for diagnostic monitoring. It might be exploited therapeutically by producing galectin variants tailored to interfere with galectin activities associated with the malignant phenotype. Moreover, the given strategy for comparative computational analysis of extended binding sites has implications for the rational design of galectin-type-specific ligands.

Unique Conformer Selection of Human Growth-Regulatory Lectin Galectin-1 for Ganglioside GM1 versus Bacterial Toxins,

Endogenous lectins induce effects on cell growth by binding to antennae of natural glycoconjugates. These complex carbohydrates often present more than one potential lectin-binding site in a single chain. Using the growth-regulatory interaction of the pentasaccharide of ganglioside GM(1) with homodimeric galectin-1 on neuroblastoma cell surfaces as a model, we present a suitable strategy for addressing this issue. The approach combines NMR spectroscopic and computational methods and does not require isotope-labeled glycans. It involves conformational analysis of the two building blocks of the GM(1) glycan, i.e., the disaccharide Galbeta1-3GalNAc and the trisaccharide Neu5Acalpha2-3Galbeta1-4Glc. Their bound-state conformations were determined by transferred nuclear Overhauser enhancement spectroscopy. Next, measurements on the lectin-pentasaccharide complex revealed differential conformer selection regarding the sialylgalactose linkage in the tri- versus pentasaccharide (Phi and Psi value of -70 degrees and 15 degrees vs 70 degrees and 15 degrees, respectively). To proceed in the structural analysis, the characteristic experimentally detected spatial vicinity of a galactose unit and Trp68 in the galectin's binding site offered a means, exploiting saturation transfer from protein to carbohydrate protons. Indeed, we detected two signals unambiguously assigned to the terminal Gal and the GalNAc residues. Computational docking and interaction energy analyses of the entire set of ligands supported and added to experimental results. The finding that the ganglioside's carbohydrate chain is subject to differential conformer selection at the sialylgalactose linkage by galectin-1 and GM(1)-binding cholera toxin (Phi and Psi values of -172 degrees and -26 degrees, respectively) is relevant for toxin-directed drug design. In principle, our methodology can be applied in studies aimed at blocking galectin functionality in malignancy and beyond glycosciences.

Homodimeric galectin-7 (p53-induced gene 1) is a negative growth regulator for human neuroblastoma cells

The extracellular functions of galectin-7 (p53-induced gene 1) are largely unknown. On the surface of neuroblastoma cells (SK-N-MC), the increased GM1 density, a result of upregulated ganglioside sialidase activity, is a key factor for the switch from proliferation to differentiation. We show by solid-phase and cell assays that the sugar chain of this ganglioside is a ligand for galectin-7. In serum-supplemented proliferation assays, galectin-7 reduced neuroblastoma cell growth without the appearance of features characteristic for classical apoptosis. The presence of galectin-3 blocked this effect, which mechanistically resembles that of galectin-1. By virtue of carbohydrate binding, galectin-7 thus exerts neuroblastoma growth control similar to galectin-1 despite their structural differences. In addition to p53-linked proapoptotic activity intracellularly, galectin-7, acting as a lectin on the cell surface, appears to be capable of reducing cancer cell proliferation in susceptible systems.

Involvement of the Galbeta1 - 3GalNAcbeta structure in the recognition of apoptotic bodies by THP-1 cells

A specific apoptotic glycosylation pattern may play an assistant or even a causative role in phagocytosis of apoptotic bodies. To elucidate the role of macrophages in lectin-mediated phagocytosis, an experimental system was used, where monocyte-derived THP-1 cells engulf the apoptotic bodies from the melanoma cell line MELJUSO. A flow cytometry assay was performed to reveal lectin expression and quantify the phagocytosis of apoptotic bodies. Taking into account that siglecs, a mannose receptor and galectins expressed on macrophages could be involved in engulfment of apoptotic bodies we studied their potential expression on THP-1 cells by means of polyacrylamide glycoconjugates. A strong binding of the cells to siglec ligands (3'SiaLac, 6'SiaLac, [Neu5Acalpha2-8]2) and galectin ligands (LacNAc, GalNAcbeta1 - 4GlcNAc, Galbeta1 - 3GalNAcbeta and asialoGM1) was observed. To reveal the corresponding targets on apoptotic bodies, the carbohydrate pattern of MELJUSO cells was analyzed. The apoptotic membrane was characterized by a high level of glycans terminated by galactose or sialic acid. To study lectin-mediated phagocytosis of apoptotic bodies by THP-1 cells, an inhibitory phagocytosis assay was performed. Binding of Galbeta1 - 3GalNAc- or LacNAc-specific reagents (lectins and antibodies) to apoptotic bodies abolished their engulfment by the THP-1 cells whereas blocking of Neu5Acalpha2 - 6 or Neu5Acalpha2 - 3 sites by the corresponding lectins was not effective. Furthermore, Galbeta1 - 3GalNAcbeta-PAA or asialoGM1-PAA binding to the THP-1 cells decreased phagocytosis, whereas two other potent THP-1-binding probes, LacNAc-PAA and GalNAcbeta1 - 4GlcNAc-PAA did not inhibit phagocytosis. Thus, Galbeta1 - 3GalNAcbeta-terminated chains represented on the apoptotic bodies but not the other tested galectin ligands appear to be a target for THP-1 cells.

Glyco- and immunohistochemical refinement of the differential diagnosis between mesothelioma and metastatic carcinoma and survival analysis of patients

The aim of this study was to analyse the diagnostic value of selected glyco- and immunohistochemical probes for discrimination between mesotheliomas and metastatic carcinomas within the pleura, and to evaluate prognostic indicators in the tested panel. A panel of nine markers (five antibodies, two neoglycoproteins, and labelled hyaluronic acid) was applied to a total of 264 specimens with mesotheliomas (118 cases) and metastatic carcinomas in the pleura (146 cases); the material consisted exclusively of surgical specimens. The diagnosis obtained by standard procedures was further substantiated through a detailed follow-up and clear-cut descriptions of primary sites. The metastatic tumours originated from the lung (82 cases), breast (47 cases), colon (three cases), and kidney (two cases); in 12 cases, however, the tumour origin could not be ascertained. In detail, the probes tested included antibodies against carcinoembryonic antigen (CEA), vimentin, calretinin, mesothelial cells (HBME-1), calcyclin and keratin-5; and also biotinylated neoglycoproteins with ganglioside GM1 and N-acetyl-D-glucosamine (GlcNAc) as the ligand part, and hyaluronic acid. Carrier-immobilized ganglioside GM1 and hyaluronic acid displayed the highest specificity and sensitivity for mesotheliomas, followed by calretinin and HBME-1, whereas keratin-5 and vimentin were of low specificity (43% and 52%, respectively). Metastatic carcinomas could be discerned by CEA detection and application of GlcNAc-bearing neoglycoprotein with similar sensitivity (76% and 72%, respectively) and specificity (91% and 86%, respectively). In cases of breast carcinoma, the maximum specificity (59%) and sensitivity (67%) were low for all markers. Patients with mesothelioma survived longer than those with metastatic carcinoma, especially those with detectable binding sites for hyaluronic acid. No association of tumour type and binding properties of the other applied probes with survival of the patients could be found at a statistically significant level. It is concluded that in routine practice, the application of carrier-immobilized GM1, hyaluronic acid, and antibodies against calretinin and HBME-1 is useful for confirmation of mesothelioma, whereas the detection of CEA and GlcNAc-specific binding sites is useful for distinguishing metastatic carcinoma from mesothelioma. Despite the rather infrequent occurrence of mesotheliomas in women, particular attention should be given to exclude or confirm metastatic breast carcinoma in cases of unknown history or long metastatic interval.

Galectin-1 is a major receptor for ganglioside GM1, a product of the growth-controlling activity of a cell surface ganglioside sialidase, on human neuroblastoma cells in culture

Cell density-dependent inhibition of growth and neural differentiation in the human neuroblastoma cell line SK-N-MC are associated with a ganglioside sialidase-mediated increase of GM1 and lactosylceramide at the cell surface. Because these glycolipids expose galactose residues, we have initiated the study of the potential role of galectins in such cellular events. Using specific antibodies, galectin-1 but not galectin-3 was found to be present at the cell surface. Assessment of carbohydrate-dependent binding revealed a saturable amount of ligand sites approaching 2.6 x 10(6) galectin-1 molecules bound/cell. Presence during cell culture of the sialidase inhibitor 2-deoxy-2,3-dehydro-N-acetylneuraminic acid or of the GM1-binding cholera toxin B subunit effected a decrease of the presentation of galectin-1 ligands by 30-50%. The assumption that GM1 is a major ligand for galectin-1 was reinforced by the correlation between the number of carbohydrate-dependent 125I-iodinated GM1-neoganglioprotein binding sites and the amount of immunoreactive surface galectin-1, the marked sensitivity of probe binding to the presence of anti-galectin-1 antibody, and the inhibition of cell adhesion to surface-immobilized GM1 by the antibody. The results open the possibility that the carbohydrate-dependent interaction between ganglioside GM1 and galectin-1 may relay sialidase-dependent alterations in this cell system.

Polyacrylamide-based glycoconjugates as tools in glycobiology

This review describes the synthesis, physicochemical characteristics and application for studying carbohydrate-binding proteins of polyacrylamide (PAA) type neoglycoconjugates. An approach to the synthesis of conjugates based on the interaction of activated polyacrylic acid with omega-aminoalkyl glycosides has been developed. Both the molecules of Glyc-PAA and the conjugates bearing various labels and effectors, as well as sorbents, and glycosurfaces can be designed using this method. Examples of the application of the conjugates as tools for the study of lectins, antibodies, and glycosyltransferases in glycobiology, cytochemistry and histochemistry are described along with the prospects of the further development of the presented approach in glycotechnology and medicine.

Neoglycoproteins with the synthetic complex biantennary nonasaccharide or its alpha 2,3/alpha 2,6-sialylated derivatives: their preparation, assessment of their ligand properties for purified lectins, for tumor cells in vitro, and in tissue sections, and their biodistribution in tumor-bearing mice

Neoglycoproteins were prepared with chemoenzymatically synthesized complex biantennary N-glycan derivatives the nonreducing ends of which bear typical sequences found in glycoproteins. A chemically obtained biantennary heptasaccharide-azide was reduced and acylated with a 6-aminohexanoyl spacer. Elongation of the deprotected heptasaccharide using glycosyltransferases yielded a biantennary nonasaccharide with terminal galactose residues and two undecasaccharides terminating with alpha 2,6- or alpha 2,3-linked sialic acid. The free amino group of the spacer of these oligosaccharides was converted into an isothiocyanate. Its subsequent coupling to bovine serum albumin gave neoglycoproteins with a yield of 2.4-3.6 glycan chains per carrier molecule. This versatile synthetic pathway allows employment of a wide variety of complex-type glycans, which can be introduced to various test systems in vitro and in vivo to evaluate potential biomedical applications. Solid-phase assays with biotinylated sugar receptors revealed discriminatory binding properties of the three neoglycoproteins, especially for the mistletoe lectin. This direct assay system is preferable to the measurement of inhibitory capacities with respect to model ligands. Ligand type- and cell type-dependent quantitative differences in the binding properties of the probes were detected by FACScan analyses with a panel of tumor cell lines and by monitoring of staining in tissue sections for small cell and non-small-cell lung cancer and mesotheliomas. Biodistribution of iodinated neoglycoproteins in mice gave a prolonged presence of the sialylated probes in serum. Relative to the nonasaccharide, the uptake, especially of the iodinated neoglycoprotein with alpha 2,3-sialylated ligand chains, was clearly elevated in mice for kidneys and Ehrlich tumors. On the basis of the documented feasibility of these applications, it is concluded that the further elaboration of glycan chain variants by the described synthetic approach in combination with the given test panel is warranted to evaluate the potential of complex glycan chain-carrying neoglycoproteins for diagnostic and therapeutic purposes.

Animal lectins

Protein and lipid glycosylation is no longer considered as a topic whose appeal is restricted to a limited number of analytical experts perseveringly pursuing the comprehensive cataloguing of structural variants. It is in fact arousing curiosity in various areas of basic and applied bioscience. Well founded by the conspicuous coding potential of the sugar part of cellular glycoconjugates which surpasses the storage capacity of oligonucleotide- or oligopeptide-based code systems, recognition of distinct oligosaccharide ligands by endogenous receptors, i.e. lectins and sugar-binding enzymes or antibodies, is increasingly being discovered to play salient roles in animal physiology. Having inevitably started with a descriptive stage, research on animal lectins has now undubitably reached maturity. Besides listing the current categories for lectin classification and providing presentations of the individual families and their presently delineated physiological significance, this review places special emphasis on tracing common structural and functional themes which appear to reverberate in nominally separated lectin and animal categories as well as lines of research which may come to fruition for medical sciences.

Binding capacities of two immunomodulatory lectins, carrier-immobilized glycoligands and steroid hormones in lung cancer and the concentration of nitrite/nitrate in pleural effusions

Combined analysis of the binding properties of inflammatory and tumor cells in pleural effusion, and tumor imprints for various carrier-immobilized types of ligands and lectins, and of a biochemical feature of the effusions is performed to extend the characterization of these cells and their activity. In detail, the binding of Viscum album agglutinin (VAA), Urtica dioica agglutinin (UDA), and of carrier-immobilized N-acetyl-D-glucosamine (GlcNAc), lysoganglioside GM1, estradiol, progesterone, testosterone, and hydrocortisone to native specimens consisting of 46 tumor imprints from surgically treated patients with lung cancer and 74 smears of pleural effusion (PE) cells from cancer or non-cancer patients was studied using fluorescence microscopy with Texas red-labeled streptavidin. Among the tested ligands, VAA was found to provide the most effective staining of cells (60-78.1% of positive cases). When compared with inflammatory cells from PE, cancer cells were seen to bind more frequently only two ligands, namely UDA and estradiol. Significant (P < 0.001) difference between patients with bronchial carcinoma and non-cancer patients were found, when the content of NO2-/NO3- in PE fluids was measured. Whereas the level of NO2-/NO3- in PE of non-cancer patients was 12.6 +/- 10.7 microM (n = 12), it was 37.7 +/- 19.4 microM (n = 14) in cancer patients without pleural metastases and 37.5 +/- 16.0 microM (n = 26) in patients with pleural metastases. The level of NO2-/NO3- in PE appeared to correlate with extent of staining with GM1 and GlcNAc: in non-cancer patient groups it was significantly higher (P = 0.032) for negative subjects than those binding the ligand GlcNAc, whereas in the patient group with adenocarcinoma it was significantly lower (P = 0.032) for patients without binding capacities for GlcNAc and GM1. The results obtained suggest that the combined analysis of increased levels of NO2-/NO3- in PE and of glycohistochemical properties of cancer and inflammatory cells may be useful in exploring the interrelationship of functionally important cellular characteristics.

Ganglioside binding proteins of calf brain with ubiquitin-like N-terminals

Two ganglioside-associated protein components I and II have been isolated from crude ganglioside preparations of calf brain by DEAE-Sephadex ion-exchange chromatography. Both components exhibited binding capacity in aqueous media for gangliosides of the 'ganglio' series but not for neutral glycosphingolipids (polyglycosylceramides) and only a low capacity for sialosylparagloboside. Each protein bound individual gangliosides with different efficiency. Upon prolonged incubation of component I with gangliosides, complexes with high (30:1) and low (6:1) glycolipid/protein molar ratios were formed. The latter but not the former complex was able to penetrate Sephadex G-200 beads. Both components inhibited plating efficiency of cultured mouse N2a neuroblastoma cells. The molecular masses of components I and II were determined by SDS/PAGE to be 11-12 kDa and 28 kDa, respectively. Carbohydrates (fucose, mannose, galactose, N-acetylglucosamine, N-acetylgalactosamine, and some sialic acid) were found only in component II. When examined by reverse-phase HPLC each component separated into two major closely migrating peaks which were subsequently examined by Edman degradation. Amino acid sequences of the N-terminal portions of three of these peaks (one peak from component I and both peaks from component II) showed, as far as the sequences were established, identity with the sequence of ubiquitin. It is hypothesized that the proteins may be instrumental in intracellular trafficking of gangliosides.

Oligosaccharide-binding molecules on the surface of human hemopoietic and lymphoid cells

High oligosaccharide specificity for binding carbohydrate probes (biotinylated polyacrylamide with carbohydrates attached) with human hemopoietic and lymphoid cells is shown. Of 15 probes studied those bearing blood group trisaccharides, A and B, bound most intensely. In addition, transformed (leukemic and lymphoid) cells interacted more strongly than normal ones.

Carbohydrate-binding specificity of calcyclin and its expression in human tissues and leukemic cells

Binding of biotinylated fetuin in a solid-phase assay served as activity assay for purification of calcyclin, the product of a cell growth-related cDNA with homologies to Ca(2+)-binding proteins. Asialofetuin failed to bind to calcyclin, emphasizing the importance of sialic acids. Binding of fetuin was most effectively reduced by N-glycolylneuraminic acid within a panel of mostly negatively charged sugars. Bovine submaxillary mucin and the ganglioside GM1, but not asialo-GM1, proved more effective than neoglycoproteins, carrying negatively charged carbohydrate moieties. Extension of N-acetyl-neuraminic acid to its lactosyl derivative increased its inhibitory potency. Among charge-free carbohydrate residues, only N-acetylglucosamine, lactose, and mannose, but not fucose, melibiose, or N-acetylgalactosamine affected fetuin binding, substantiating the inherent selectivity. Chemical modification with group-specific reagents revealed that lysine and arginine residues appear to be involved in ligand binding that is optimal in the presence of Ca2+, but not Zn2+ and stable up to 1 m NaCl. Biotinylation of calcyclin by modification of carboxyl groups facilitated performance of solid-phase assays with calcyclin in solution, yielding similar results with (neo)glycoproteins in relation to assays with immobilized calcyclin, thereby excluding an impact of binding to nitrocellulose on calcyclin's specificity. Subcellular fractionation disclosed the presence of fetuin-binding activity in all fractions, the specific activity decreasing from the nuclear to the particulate cytoplasmic fraction and the cytoplasmic supernatant. Affinity-purified antibodies were employed to detect high levels of calcyclin expression in acute lymphoblastic, myelogenous, and monocytic leukemia cell lines, but not in myeloma or lymphoblastoid cells. In comparison, most cells were nearly devoid of an O-acetylsialic acid-specific protein that is more abundant in various tissue types than calcyclin.

Glycopeptide-albumin derivative: it preparation and histochemical ligand properties

Carrier-immobilized mono- or disaccharides and other carbohydrate structures, derived by custom-made chemical synthesis, have already proven to be valuable ligands for localizing carbohydrate-binding proteins in tissue sections. Defined purified glycopeptides, as components of neoglycoproteins, offer the possibility of increasing their structural complexity and, thereby, their receptor selectivity. To test the feasibility of this approach, the glycopeptide man6-glcNAc2-asparagine derived from ovalbumin was purified after pronase digestion. It was coupled to bovine serum albumin as carrier protein with the homobifunctional linking agent bis-(sulphosuccinimidyl)suberate to yield the diglycosylated concanavalin A-reactive product. Following biotinylation, it was used to detect mannose-specific binding sites in fixed cells of seven human leukemia or lymphoma lines and in fixed, paraffin-embedded sections of human breast cancer. In comparison to chemically mannosylated bovine serum albumin with ten sites of glycosylation or to ovalbumin, this derivative produced a similar pattern of reaction with a quantitatively lower extent of staining in most cases. Remarkably, the presence of potential endogenous ligands for the detected receptor sites was ascertained using the plant lectin concanavalin A. Thus, the conjugation of a purified, deliberately selected glycopeptide to a suitable carrier produces a histochemical tool for detecting glycopeptide-specific binding sites.

[Tumor lectinology--status and perspectives of clinical application]

A detailed knowledge of the mechanisms of molecular recognition is a prerequisite to rationally improved diagnostic and therapeutic procedures in diseases. In addition to sequences of amino acids, carbohydrate structures apparently store biological information that is thought to be relevant for physiologically important processes. Such ligands, namely the carbohydrate part of cellular glycoconjugates, can be recognized by specific endogenous binding proteins like lectins. If their presence can be reliably ascertained and correlated to the clinical course of the disease, e.g. in oncology, lectinology may help to define a yet undisclosed role for this class of proteins in tumor progression and spread.