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In this chapter, we describe the key procedures for isolation of the oligosaccharides and the preparation of neoglycolipid probes together with expression of malectin that have enabled the discovery of the highly selective binding of this newly described protein in the endoplasmic reticulum (ER) to a diglucosyl high-mannose N-glycan. This is the first indication of a bioactivity for a diglucosyl high-mannose N-glycan of the type that occurs in the ER of eukaryotic cells and which is an intermediate in the early steps of the N-glycosylation pathway of nascent proteins. The malectin story is an example of a powerful convergence of disciplines in biological sciences: (i) developmental biology, (ii) bioinformatics, (iii) recombinant protein expression, (iv) protein structural studies, (v) glucan biochemistry, and (vi) drug-assisted engineering of oligosaccharide biosynthesis, culminating in (vii) oligosaccharide "designer" microarrays, to clinch the remarkable selectivity of the binding of this newly discovered ER protein. Thus, the way is open to the identification of the role of malectin in the N-glycosylation pathway., (Copyright (c) 2010 Elsevier Inc. All rights reserved.)

This study was aimed at investigating the efficacy of presentation of biotinylated oligosaccharides on streptavidin-coated microwells for interactions with (a) three monoclonal antibodies directed at sialyl-Lewisa (Le(a)) or sulfo-Le(a)-related sequences, and (b) the endothelium-leukocyte adhesion molecules, the E-, L- and P-selectins which recognize both the sulfo- and sialyl-Le(a) series. With the antibodies it was observed that if the biotinylated oligosaccharide incorporated the entire antigenic determinant, and additional saccharide length was not included, the biotinyl tag spacer length was a critical factor in the strength of the binding signal. If oligosaccharide chain beyond the determinant was included, the biotinyl tag spacer length was less important. The E-selectin binding data with the biotinylated sialyl- and sulfo-oligosaccharides were in overall accord with previous knowledge. With the L- and P-selectins, however, unexpectedly low binding signals were elicited by biotinyl sulfo-Le(a) sequences relative to those with the sialyl-analogs. This suppression was more pronounced with the rodent than the human L-selectin. Such differential availabilities of oligosaccharides displayed on streptavidin may relate to biological situations, such as the differential reactivities of the three selectins with a given oligosaccharide ligand presented on different carrier proteins, or on different O-glycan cores on mucin-type glycoproteins.

Biotinyl-oligosaccharides are a relatively new generation of saccharide probes that enable immobilization of desired oligosaccharides on streptavidin matrices for studies of carbohydrate-protein interactions. Here we describe the facile preparation of biotinyl-l-3-(2-naphthyl)-alanine hydrazide (BNAH) derivatives of oligosaccharides, containing a strong UV absorbing and fluorescent group, in which the ring of the reducing-end monosaccharide is nonreduced. We evaluate reactivities of immobilized BNAH- N -glycans with plant lectins that recognize aspects of the oligosaccharide core or outer-arms. We make some comparisons with 2-amino-6-amidobiotinyl-pyridine (BAP) derivatives obtained by reductive amination, and 6-(biotinyl)-aminocaproyl-hydrazide (BACH) derivatives which have a longer spacer-arm. N -Glycan-BNAH and-BAP derivatives have, overall, comparable reactivities with lectins which recognize N -glycan outer-arms or the trimannosyl core, but only BNAH and BACH derivatives are bound by lectins which recognize the non-reduced core. Moreover, with Pisum sativum agglutinin (PSA) which additionally requires the fucosyl- N- glycan-asparaginyl core for high affinity binding, the immobilized BNAH derivative (which is an alanine hydrazide beta-glycoside) can substitute for the natural beta-glycosylasparaginyl core, whereas the BACH derivative (aminocaproyl-hydrazide-beta-glycoside) is less effective. BNAH is a derivatization reagent of choice, therefore, for solid phase carbohydrate-binding experiments with immobilized N -glycans.

This communication is concerned with the binding specificity of the leukocyte-adhesion molecule L-selectin (leukocyte homing receptor) towards structurally defined sulphated oligosaccharides of the blood group Le(a) and Le(x) series, and of the glycosaminoglycan series heparin, chondroitin sulphate and keratan sulphate. The recombinant soluble form of the rat L-selectin (L-selectin-IgG Fc chimera) investigated here was shown previously to bind to lipid-linked oligosaccharides 3-O, 4-O and 6-O sulphated at galactose, such as sulphatides and a mixture of 3-sulphated Le(a)/Le(x) type tetrasaccharides isolated from ovarian cystadenoma, as well as to the HNK-1 glycolipid with 3-O sulphated glucuronic acid. In the present study, the L-selectin investigated in both chromatogram binding and plastic microwell binding experiments using neoglycolipids was found to bind to the individual 3-sulphated Le(a) and Le(x) sequences (penta-, tetra- and trisaccharides), and with somewhat lower intensities to their non-fucosylated analogues. Glycosaminoglycan disaccharides of keratan sulphate, heparin and chondroitin sulphate types were also bound by L-selectin in one or both assay systems, leading to the conclusion that clustered glycosaminoglycan oligosaccharides with 6-O sulphation of N-acetylgalactosamine, N-acetylglucosamine or glucosamine, 4-O sulphation of N-acetylgalactosamine, 2-O sulphation of uronic acid, N-sulphation of glucosamine and, to a lesser extent, the non-sulphated uronic acid-containing disaccharides, can support L-selectin adhesion. As inflammatory chemokines (short-range stimulators of lymphocyte migration which trigger integrin activation) are known to bind to endothelial glycosaminoglycans, we propose that the binding of the lymphocyte membrane L-selectin to endothelial glycosaminoglycans may provide a link between the selectin-mediated and integrin-mediated adhesion systems in leukocyte extravasation cascades. The possibility is also raised that lymphocyte L-selectin interactions with glycosaminoglycans may contribute to pathologies of glycosaminoglycan-rich tissues, e.g. cartilage loss in rheumatoid arthritis and inflammatory lesions of the cornea.

A diversity of high-affinity oligosaccharide ligands are identified for NKR-P1, a membrane protein on natural killer (NK) cells which contains an extracellular Ca(2+)-dependent lectin domain. Interactions of such oligosaccharides on the target cell surface with NKR-P1 on the killer cell surface are crucial both for target cell recognition and for delivery of stimulatory or inhibitory signals linked to the NK cytolytic machinery. NK-resistant tumour cells are rendered susceptible by preincubation with liposomes expressing NKR-P1 ligands, suggesting that purging of tumour or virally infected cells in vivo may be a therapeutic possibility.

Carbohydrate recognition by the human endothelial-leukocyte adhesion molecule, E-selectin, has been investigated by binding studies using 3H-labeled Chinese hamster ovary cells expressing different levels of the transfected full-length adhesion molecule and a series of structurally defined oligosaccharides linked to the lipid phosphatidylethanolamine dipalmitoate (neoglycolipids) and synthetic glycolipids chromatographed on silica gel plates or immobilized on plastic wells. Evidence is presented for density-dependent binding of the membrane-associated E-selectin not only to 3'-sialyl-lacto-N-fucopentaose II (3'-S-LNFP-II) and 3'-sialyl-lacto-N-fucopentaose III (3'-S-LNFP-III) which express the sialyl Le(a) and sialyl Le(x) antigens, respectively, but also to the nonsialylated analogue LNFP-II; there is a threshold density of E-selectin required for binding to these sialylated sequences, and binding to the nonsialylated analogue is a property only of cells with the highest density of E-selectin expression. The presence of fucose linked to subterminal rather than to an internal N-acetylglucosamine is shown to be a requirement for E-selectin binding, and although the presence of sialic acid 3-linked to the terminal galactose of the LNFP-II or LNFP-III sequences substantially enhances E-selectin binding, the presence of 6-linked sialic acid abolishes binding. E-selectin binding is unaffected in the presence of the blood group H fucose (alpha 1-2 linked to galactose to form the Le(b) antigen). However, the binding is abolished when in addition alpha 1-3-linked N-acetylgalactosamine to the galactose (blood group A antigen) is present. These results indicate that some E-selectin-mediated adhesive events may be influenced by blood group status.

Two different mannose-binding proteins (MBP-A and MBP-C), which show 56% sequence identity, are present in rat serum and liver. It has previously been shown that MBP-A binds to a range of monosaccharide-bovine serum albumin conjugates, and that, among oligosaccharide ligands tested, preferential binding is to terminal nonreducing N-acetylglucosamine residues of complex type N-linked oligosaccharides. In order to compare the binding specificity of MBP-C, an expression system has been developed for production of a fragment of this protein which contains the COOH-terminal carbohydrate-recognition domain. After radioiodination, the domain has been used to probe natural glycoproteins, neoglycoproteins, and neoglycolipids. Like MBP-A, MBP-C binds several different monosaccharides conjugated to bovine serum albumin, including mannose, fucose, and N-acetylglucosamine, although binding to the last of these is relatively weaker than observed for MBP-A. The results of binding to natural glycoproteins and to neoglycolipids containing oligosaccharides derived from these proteins are most compatible with the interpretation that MBP-C interacts primarily with the trimannosyl core of complex N-linked oligosaccharides, with additional ligands being terminal fucose and perhaps also peripheral mannose residues of high mannose type oligosaccharides. This binding specificity is thus quite distinct from that of MBP-A. The presence of multiple MBPs with distinct binding specificities in preparations derived from serum and liver explains conflicting conclusions which have been reached about carbohydrate recognition by these proteins.

In this study carbohydrate-mediated interactions of the envelope glycoprotein, gp120, of HIV-1 were investigated. Oligosaccharide probes (neoglycolipids), prepared from the N-glycosidically-linked chains of the natural and recombinant forms of gp120, were used in conjunction with the intact glycoprotein to investigate reactivities with a soluble carbohydrate-binding protein (lectin) known as mannose-binding protein in human serum. Evidence is presented that the high-mannose-type oligosaccharides with seven, eight and nine mannose residues from both forms of gp120 are recognized by the serum lectin, and that these reactivities are unrelated to CD4 recognition. Reactivities of the two forms of envelope glycoprotein with macrophages derived from human blood monocytes and with the mannose-specific macrophage endocytosis receptor isolated from human placental membranes were also investigated. Evidence is presented that both forms of gp120 bind to the macrophage surface by multiple interactions in addition to CD4 binding, and that among these interactions is a carbohydrate-mediated binding to the endocytosis receptor. We propose that such carbohydrate-mediated interactions could form the basis of viral attachment to a variety of healthy and diseased tissues.

Conditions have been established for the rapid and efficient conjugation of reducing oligosaccharides (di- to deca-saccharides) to dipalmitoyl phosphatidylethanolamine. The resulting neoglycolipids derived from several naturally occurring oligosaccharides and a series of N-linked high-mannose-type oligosaccharides released by hydrazinolysis from RNAase B showed specific and potent reactivities, as appropriate, with monoclonal antibodies to blood group Lewis(b), blood group A or a stage-specific embryonic (SSEA-1) antigen, or the lectin concanavalin A.

Desialylated human blood group O erythrocyte glycopeptides were digested with the endo-beta-galactosidase of Bacteroides fragilis and the enzyme-released products reduced with NaBH4 and purified by Bio-Gel P-4 chromatography. Three linear and six branched oligosaccharides of poly(N-acetylllactosamine) type, which together accounted for 90% of the oligosaccharide alditols, were characterised by fast-atom-bombardment mass spectrometry and gas-liquid chromatography/mass spectrometry. Linkage and composition data were obtained for the remaining material. The salient findings were (a) the branched oligosaccharide alditols each contained the sequence: (Formula: see text) and (b) there was no evidence for the terminal branch-point sequence: (Formula: see text). Together these observations indicate that, as with erythrocyte glycolipids described previously [Scudder, P., Hanfland, P., Uemura, K. & Feizi, T. (1984) J. Biol. Chem. 259, 6586-6592], the endo-beta-galactosidase of Bacteroides fragilis cannot hydrolyse branch-point beta-galactosidic linkages on erythrocyte membrane glycopeptides.

Oligosaccharide recognition by three mammalian mannose-binding proteins was investigated by using as probes a series of structurally characterized neoglycolipids in t.l.c. binding assays. The neoglycolipids were derived from N-linked oligosaccharides of complex, high-mannose and hybrid types and from human milk oligosaccharides and simple di- and tri-saccharides. The three proteins, namely the recombinant carbohydrate-recognition domain of rat mannose-binding Protein A and the multi-subunit forms of rat and human serum mannose-binding proteins, were shown to have in common reactivity with oligosaccharide probes containing one or more non-reducing terminal N-acetylglucosamine residue(s). Substitution with galactose masks reactivity. The three proteins also bound to non-reducing terminal mannose residues in high-mannose-type oligosaccharides, non-reducing terminal fucose residues in the sequence Fuc alpha 1-4(Gal beta 1-3)GlcNAc and non-reducing terminal glucose residues in dextran oligomers; the recombinant binding domain gave consistently weaker binding. The relative reactivities with the various probes differ for each protein. Overall, the reaction patterns of the three mammalian proteins differ from that of the plant lectin concanavalin A, which showed preferential binding to the high-mannose type, weak binding to biantennary complex type and no binding to the fuco-oligosaccharide and simple oligosaccharide probes. As a group, the three mammalian proteins resemble bovine serum conglutinin and behave as lectins with rather broad sugar specificities directed at certain non-reducing terminal N-acetylglucosamine, mannose, glucose and fucose residues, but with subtle differences in fine specificities. These results illustrate the potential of neoglycolipids in studies of oligosaccharide recognition by natural and recombinant proteins of diverse biological systems.

High molecular weight glycoproteins of human B and T lymphocytes known as leucocyte common antigen or T200 have been shown to carry O- and N-glycosidically linked, sialylated, carbohydrate chains. The O-linked chains are polydisperse and those of B rather than T cell type are highly susceptible to degradation by endo-beta-galactosidase. These differences among lymphocytes that are functionally distinct raise the possibility that the oligosaccharides may contribute to the functions of these differentiation molecules as well as to their electrophoretic diversity.

The antigens expressed on the carbohydrate chains of the receptor for epidermal growth factor of A431 cells were studied by immunoblotting with monoclonal antibodies. Blood group A and the Type 1 based blood group ALeb and Lea antigens were detected as well as antigens associated with unsubstituted, monofucosylated and difucosylated Type 2 blood group chains. The Lea and the difucosylated Type 2 antigen activities were abolished by treating the blotted receptor with endo-beta-galactosidase, indicating that they are expressed on backbone structures of poly-lacto/neolacto type. (The term 'poly-lacto/neolacto' is used here to describe oligosaccharide backbone structures consisting of repeating Type 1, Gal beta 1-3GlcNAc (lacto) or Type 2, Gal beta 1-4GlcNAc (neolacto) sequences.) The glycosidic linkage of oligosaccharides to protein was investigated using Pronase digests of the receptor biosynthetically labelled with [3H]glucosamine or [3H]fucose. The oligosaccharides were alkali-resistant, consistent with N- rather than O-glycosidically linked chains. A proportion of [3H]fucose-labelled glycopeptides was susceptible to endo-beta-galactosidase, confirming the immunoblotting experiment using antibodies against the Lea and the difucosylated Type 2 antigenic determinants. Oligosaccharides were released from the [3H]fucose- and [3H]-glucosamine-labelled glycopeptides by hydrazinolysis. Chromatography of the oligosaccharides on Bio-Gel P6 and Concanavalin A columns indicated a spectrum of oligosaccharides which include those of high mannose type labelled with [3H]glucosamine, and a mixture of oligosaccharides labelled with [3H]fucose and [3H]glucosamine of bi- and multiantennary complex types of which a subpopulation is susceptible to digestion with endo-beta-galactosidase.

This report describes the preparation of a library of oligosaccharide probes (neoglycolipids) from N-glycosylated proteins, characterization of the probes by liquid secondary ion mass spectrometry, and investigation of their reactions with 125I-labeled bovine serum conglutinin by chromatogram binding assays. The results, together with additional binding studies using neoglycolipids derived from purified complex type bi-, tri-, and tetraantennary oligosaccharides from urine, or their glycosidase-treated products, have shown that the combining specificity of conglutinin includes structures not only on high mannose-type oligosaccharides but also on hybrid- and complex-type chains. With high mannose-type oligosaccharides there is increased reactivity from the Man5 to the Man8 structures, indicating a preference for the terminal Man alpha 1-2 sequence. With complex- and hybrid-type oligosaccharides, the requirements for binding are the presence of nonreducing terminal N-acetylglucosamine or mannose residues, but the presence of a bisecting N-acetylglucosamine residue may inhibit binding. From these results it is deduced that the reactivity of conglutinin with the complement glycopeptide iC3b rather than the intact glycoprotein C3 is due to the oligosaccharide accessibility rendered by proteolysis in the complement cascade.

A series of oligosaccharides derived from glycoproteins or from human milk were coupled to lipid and used as probes of the binding specificities of Escherichia coli isolated from patients with urinary tract infections. Selective binding to the glycoprotein oligosaccharide probes rich in mannose residues (high-mannose type) was demonstrated with fimbriated E coli that give mannose-inhibitable haemagglutination. This observation is in accordance with predictions from inhibition studies. Binding studies with the human milk oligosaccharide probes, which resemble structures found on host-cell membranes, revealed adhesive specificity unrelated to the presence of fimbriae. This new type of host oligosaccharide receptor is affected by the presence of the blood group genetic markers. It involves the disaccharide sequence linked to the membrane-associated lipid moiety of host-cell glycolipids, and may have a role in initiation of infection on damaged epithelial cell membranes.