The occurrence in nature of erythrocyte-agglutinating proteins has been known since the turn of the 19th century. By the 1960s it became apparent that such proteins also agglutinate other types of cells, and that many of them are sugar-specific. These cell-agglutinating and sugar-specific proteins have been named lectins. Although shown to occur widely in plants and to some extent also in invertebrates, very few lectins had been isolated until the early 1970s, and they had attracted little attention. This attitude changed with the demonstration that lectins are extremely useful tools for the investigation of carbohydrates on cell surfaces, in particular of the changes that the latter undergo in malignancy, as well as for the isolation and characterization of glycoproteins. In subsequent years numerous lectins have been isolated from plants as well as from microorganisms and animals, and during the past two decades the structures of hundreds of them have been established. Concurrently, it was shown that lectins function as recognition molecules in cell-molecule and cell-cell interactions in a variety of biological systems. Here we present a brief account of 100-plus years of lectin research and show how these proteins have become the focus of intense interest for biologists and in particular for the glycobiologists among them.

Six leguminous lectins from the seeds of plants of the Erythrina genus, namely E. caffra (ECafL), E. cristagalli (ECL), E. flabelliformis (EFL), E. lysistemon (ELysL), E. rubrinerva (ERL), and E. vespertilio (EVL), were examined to establish their sequence homology and to determine the structure and sites of attachment of their glycans. Tryptic digests of these lectins were analyzed by capillary electrophoresis coupled to electrospray mass spectrometry (CE-ESMS). Assignments were made by comparing the molecular masses of the observed tryptic peptides with those of Erythrina corallodendron lectin (ECorL), the sequence of which had been established previously. Glycan structure and genetic variations in the amino acid sequence were probed by tandem mass spectrometry. Small differences were found between the sequences of the various lectins examined and all of them exhibited C-terminal processing resulting in proteins with a C-terminal Asn residue. The major glycan of these glycoproteins was shown to be the heptasaccharide Man(3)XylFucGlcNAc(2), consistent with previous investigations on ECL and ECorL. A minor glycan heterogeneity was observed for most lectins examined except for that of ECafL and ECorL where an extra hexose residue was observed on the reducing GlcNAc residue of the heptasaccharide.

1. Different carbohydrate-specific proteins, such as lectins, may combine with the same monosaccharide or oligosaccharide by different H-bonding and hydrophobic side chains. 2. Homologous proteins with distinct specificities may bind different monosaccharides (e.g., for glucose and galactose that differ in the configuration of a single hydroxyl) by the same set of invariant residues that are identically positioned in their tertiary structures. 3. The energetics of protein-carbohydrate interactions cannot be derived from structural information. 4. Nature solves in a variety of different ways the problem of constructing combining sites for carbohydrates, just as it provides diverse solutions for other functions of proteins.

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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLectins: Carbohydrate-Specific Proteins That Mediate Cellular Recognition†Halina Lis and Nathan SharonView Author Information Department of Membrane Research and Biophysics, The Weizmann Institute of Science, Rehovot 76100, Israel Cite this: Chem. Rev. 1998, 98, 2, 637–674Publication Date (Web):March 19, 1998Publication History Received25 July 1997Revised20 January 1998Published online19 March 1998Published inissue 1 April 1998https://pubs.acs.org/doi/10.1021/cr940413ghttps://doi.org/10.1021/cr940413gresearch-articleACS PublicationsCopyright © 1998 American Chemical SocietyRequest reuse permissionsArticle Views8096Altmetric-Citations1460LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Carbohydrates,Ligands,Monomers,Oligosaccharides,Peptides and proteins Get e-Alerts

Glycophorin A (GPA) of human erythrocytes contains a minor number of unsubstituted GalNAc residues (Tn receptors) which are recognized by Moluccella laevis lectin (MLL). The lectin reacts better with blood group N‐ than M‐type of GPA which suggests a higher number of Tn receptors in GPA‐N than in GPA‐M. To find out whether this difference is restricted to a defined domain of GPA, the N‐terminal tryptic glycopeptides of GPA‐M and GPA‐N (a.a. residues 1–39) and their fragments obtained by degradation with CNBr (a.a. residues 1–8 and 9–39) were analyzed. The untreated and desialylated glycopeptides were tested as inhibitors of MLL in ELISA, and the content of GalNAc‐ol was determined in the products of β‐elimination of the asialoglycopeptides by gas‐liquid chromatography/mass spectrometry. The asialoglycopeptides 1–39 and 1–8 derived from GPA‐N showed about 2 and 4 times higher content of non‐galactosylated GalNAc residues, respectively, and higher reactivity with MLL than their counterparts derived from GPA‐M, while asialoglycopeptides 9–39 of GPA‐M and GPA‐N did not show such differences. These results demonstrate that higher expression of non‐galactosylated GalNAc in GPA‐N than in GPA‐M is confined to GalNAc residues located in the amino‐terminal portion of GPA polypeptide chain, between the blood group M‐ and N‐specific amino acid residues 1 and 5.

This chapter focuses on the purification of lectins and determination of their carbohydrate specificity. A number of procedures employed for the purification of the different lectins are basically similar. A common to virtually all lectin purification schemes is affinity chromatography on immobilized sugars, which exploits the ability of lectins to combine with carbohydrates specifically and reversibly. Hemagglutination is routinely assayed with native or modified erythrocytes from humans or other animals, usually rabbits and sometimes sheep. Blood group-specific lectins are tested with a panel of typed human erythrocytes. In plants, lectins often occur as a group of closely related proteins with the same carbohydrate specificity, or isolectins. Different molecular species of the lectin may also result from intramolecular aggregation, possibly occurring during purification.

Telltale surface sugars enable cells to identify and interact with one another. New drugs aimed at those carbohydrates could stop infection and inflammation.

During the last decade, there have been enormous advances in our knowledge of glycoproteins and the stage has been set for the biotechnological production of many of them for therapeutic use. These advances are reviewed, with special emphasis on the structure and function of the glycoproteins (excluding the proteoglycans). Current methods for structural analysis of glycoproteins are surveyed, as are novel carbohydrate-peptide linking groups, and mono- and oligo-saccharide constituents found in these macromolecules. The possible roles of the carbohydrate units in modulating the physicochemical and biological properties of the parent proteins are discussed, and evidence is presented on their roles as recognition determinants between molecules and cells, or cell and cells. Finally, examples are given of changes that occur in the carbohydrates of soluble and cell-surface glycoproteins during differentiation, growth and malignancy, which further highlight the important role of these substances in health and disease.

The lectin from Moluccella laevis seeds agglutinates specifically blood-type-A and -N erythrocytes, and both activities are inhibited by micromolar concentrations of N-acetyl-D-galactosamine. The lectin consists of three subunits: a 67 kDa heterodimer, made up of two S-S-linked polypeptides of 28 and 46 kDa, and two non-covalently linked moieties of 26 and 42 kDa, the latter migrating after reduction with an apparent molecular mass of 46 kDa. Here we demonstrate that affinity chromatography of a crude protein fraction from M. laevis seeds on immobilized D-galactose in the presence of 8 M-urea affords a fully active lectin practically devoid of the 42 kDa subunit. We also present data showing that the 26 kDa subunit is devoid of cysteine residues, that the 28 kDa subunit contains two cysteine residues engaged in S-S bonds with the 46 kDa subunit, and that the latter has, in addition, two intramolecular cystine residues. Gel filtration on Sephadex G-150 in 8 M-urea/0.2 M-D-galactose of the lectin, affinity-purified in the presence of urea, afforded a pure 26 kDa subunit which exhibited both anti-A and anti-N activity, as well as high specificity for N-acetyl-D-galactosamine. In addition to demonstrating that the lectin is unusually stable and retains its carbohydrate-binding activity in 8 M-urea, our findings also show that the activity for different blood groups resides in the same subunit.

The specificity of the anti A+N lectin of Moluccella laevis (MLL) was examined by hemagglutination experiments with enzyme-modified human erythrocytes and by inhibition of hemagglutination. In addition, binding to various glycoproteins and inhibition by different sugars and glycoproteins were examined by enzyme immunoassay with antibodies to the lectin. Treatment of AMM erythrocytes with proteolytic enzymes increased their agglutinability by MLL 4-16-fold; similar treatment of ONN cells decreased their agglutinability 8-16-fold. This is in line with the known location and enzyme sensitivity of A and N specificity determinants. Treatment of the erythrocytes with sialidase increased their agglutinability and abolished the distinction between N and M cells. Hapten inhibition of hemagglutination of AMM and ONN erythrocytes by the lectin, and its binding to glycoproteins measured by enzyme immunoassay, confirmed the high specificity of MLL for N-acetyl-D-galactosamine (200-500 times more than for D-galactose) and suggested the presence of hydrophobic interactions around HO-2 of the D-galactose unit. The methyl alpha-glycosides of D-galactose and of N-acetyl-D-galactosamine were better inhibitors than the corresponding beta-glycosides; this preference was abolished, and sometimes reversed, when the p-nitrophenyl glycosides of the same monosaccharides were tested, stressing again the importance of hydrophobic interactions in the binding of carbohydrates to MLL. The lectin reacted well with ONN substance and with glycophorin A of the N phenotype (GPAN), but did not react with OMM substance or GPAM. The strongest inhibitor was asialo ovine submaxillary mucin, which contains many unsubstituted alpha-D-GalpNAc-(1-->3)-Ser/Thr residues; calculated per N-acetyl-D-galactosamine residue, it was 1500 stronger than free N-acetyl-D-galactosamine. In accordance with this result, it was found that the lectin strongly agglutinates Tn cells. The specificity of MLL can, thus, be defined as anti-Tn, crossreactive with blood types A and N, and with sialosyl-Tn. The N-specificity can best be explained by assuming that GPAN contains a small number of unsubstituted or partially sialylated alpha-D-GalpNAc-(1-->3)-Ser/Thr residues, which are present in smaller proportions, if at all, in GPAM.