Neoglycolipids: probes of oligosaccharide structure, antigenicity, and function

10E4 antigen of Scrapie lesions contains an unusual nonsulfated heparan motif

The carbohydrate antigen on heparan sulfate recognized by monoclonal antibody 10E4 is uniquely codistributed with the abnormal prion protein, PrP(Sc), even in the earliest detectable brain lesions of scrapie-infected mice. Determining the chemical structure of 10E4 antigen is, therefore, an important aspect of structure elucidation of scrapie lesions, and a prerequisite for designing experiments to understand its role in scrapie pathogenesis. Toward this aim, we have examined preparations of heparan sulfate, with differing sulfate contents, for binding by 10E4 antibody. The highest antigenicity was observed in a preparation (HS-1) with the lowest sulfate content. HS-1 was partially depolymerized with heparin lyase III, and oligosaccharide fragments examined for 10E4 antigen expression by the neoglycolipid technology. An antigen-positive and two antigen-negative tetrasaccharides were isolated and examined by electrospray mass spectrometry. The antigen-positive tetrasaccharide sequence on heparan sulfate was thus deduced to contain a unique unsulfated motif that includes an N-unsubstituted glucosamine in the sequence, UA-GlcN-UA-GlcNAc. Antibody binding experiments with neoglycolipids prepared from a series of heparin/heparan sulfate disaccharides, and the trisaccharide derived from the antigen-positive tetrasaccharide after removal of the terminal hexuronic acid, show that both the penultimate glucosamine and the outer nonsulfated hexuronic acid are important for 10E4 antigenicity.

Expression of glycoconjugates bearing the Lewis X epitope during neural differentiation of P19 EC cells

The Lewis X (Le(x)) bearing glycolipids were noticeably increased in amounts during the course of neural differentiation of P19 EC cells induced by retinoic acid (RA, all-trans form). Applying neoglycolipid technology and in situ TLC-LSIMS, the oligosaccharide chains of these scarce Le(x) bearing glycolipids were partially characterized after released by endoglycoceramidase and subsequent conversion into neoglycolipids. In order to understand the enzymatic basis for the expression of Le(x) bearing glycolipids, we measured glycolipid, glycoprotein and oligosaccharide fucosyltransferase (Fuc-T) activities using appropriate substrates in P19 EC cells with or without RA treatment. All three Fuc-Ts were increased after RA treatment and the highest activity was in the differentiated neural cells. We then investigated the two possible Fuc-T genes that might be responsible for these changes using RT-PCR analysis. Mouse Fuc-TIX (mFuc-TIX) transcript was detected in all cell types but it was only strongly expressed in RA-induced aggregates and neural cells. In the case of mouse Fuc-TIV (mFuc-TIV) gene, its transcript was only detectable in RA-induced aggregates and not found in either undifferentiated or RA-induced neural cells. These results strongly support that RA induces only a transient expression of the mFuc-TIV gene in cell aggregates but a more persistent expression of the mFuc-TIX gene at the transcription level throughout neural cell differentiation. The mFuc-TIX gene is probably the main cause for the increased expression of Le(x) glycoconjugates during neural differentiation of P19 EC cells.

‘Glyco-Epitope’ Assignments for the Selectins: Advances Enabled By the Neoglycolipid (Ngl) Technology in Conjunction with Synthetic Carbohydrate Chemistry’

The neoglycolipid (NGL) technology involving the preparation of lipid-linked oligosaccharide probes for binding experiments with carbohydrate-recognizing proteins, and their analysis by mass spectrometry, is a unique and powerful means of discovering oligosaccharide ligands for carbohydrate-binding proteins, and assigning details of their specificities. The key feature is that it enables the pinpointing and sequence determination of bioactive oligosaccharides within highly heterogeneous mixtures derived from natural glycoconjugates. A new generation of NGLs incorporating a fluorescent label now establishes the principles for a streamlined technology whereby oligosaccharide populations are carried through ligand detection and isolation steps, and sequence determination. Advances in selectin research made through applications of the NGL technology include (i) demonstration of the importance of density of selectin expression, and of oligosaccharide ligands, in the magnitude and the specificity of the binding signals; (ii) demonstration of the efficacy of lipid-linked oligosaccharides in supporting selectin-mediated cell interactions; (iii) the discovery of 3-sulphated Le(a)/Le(x) as selectin ligands; (iv) the isolation and sequencing of carbohydrate ligands for E-selectin on murine myeloid cells and kidney; (v) the finding that sulphation at position 6 of the penultimate N-acetylglucosamine confers superior L-selectin binding signals not only to 3-sialyl-Le(x) but also to 3'-sulpho-Le(x); and (vi) the finding that sialic acid de-N-acetylation, or further modification with formation of an intra-molecular amide bond in the carboxyl group, enhances or virtually abolishes, respectively, the potency of the 6'-sulfo-sialyl-Le(X) ligand. Working with biotinylated forms of the oligosaccharide ligands, we have observed that their presentation on a streptavidin matrix influences differentially the efficacy of interactions of the L- and P-selectins (but not E-selectin) with the sialylated and sulphated ligands.

The synthesis of biotinylated carbohydrates as probes for carbohydrate-recognizing proteins

The intimate involvement of carbohydrate-protein interactions in a number of important biological processes has prompted several research efforts towards developing new methods of investigating these glycobiological interactions. Biotinylated oligosaccharides are emerging as a new and powerful tool in this area of research, primarily due to their high affinity towards streptavidin and their ease of immobilization on matrices. Here we describe a novel synthetic approach towards biotinylated saccharides which incorporate a UV absorbing group into the final compounds. The synthetic strategy described is applicable to a variety of saccharides, with examples of biotinylated mono-, di-, and trisaccharides being prepared with overall high efficiency.

Progress in deciphering the information content of the 'glycome'--a crescendo in the closing years of the millennium

The closing years of the second millennium have been uplifting for carbohydrate biology. Optimism that oligosaccharide sequences are bearers of crucial biological information has been borne out by the constellation of efforts of carbohydrate chemists, biochemists, immunochemists, and cell- and molecular biologists. The direct involvement of specific oligosaccharide sequences in protein targeting and folding, and in mechanisms of infection, inflammation and immunity is now unquestioned. With the emergence of families of proteins with carbohydrate-binding activities, assignments of information content for defined oligosaccharide sequences will become more common, but the pinpointing and elucidation of the bioactive domains on oligosaccharides will continue to pose challenges even to the most experienced carbohydrate biologists. The neoglycolipid technology incorporates some of the key requirements for this challenge: namely the resolution of complex glycan mixtures, and ligand binding coupled with sequence determination by mass spectrometry.

The cysteine-rich domain of the macrophage mannose receptor is a multispecific lectin that recognizes chondroitin sulfates A and B and sulfated oligosaccharides of blood group Lewis(a) and Lewis(x) types in addition to the sulfated N-glycans of lutropin

The mannose receptor (MR) is an endocytic protein on macrophages and dendritic cells, as well as on hepatic endothelial, kidney mesangial, tracheal smooth muscle, and retinal pigment epithelial cells. The extracellular portion contains two types of carbohydrate-recognition domain (CRD): eight membrane-proximal C-type CRDs and a membrane-distal cysteine-rich domain (Cys-MR). The former bind mannose-, N-acetylglucosamine-, and fucose-terminating oligosaccharides, and may be important in innate immunity towards microbial pathogens, and in antigen trapping for processing and presentation in adaptive immunity. Cys-MR binds to the sulfated carbohydrate chains of pituitary hormones and may have a role in hormonal clearance. A second feature of Cys-MR is binding to macrophages in marginal zones of the spleen, and to B cell areas in germinal centers which may help direct MR-bearing cells toward germinal centers during the immune response. Here we describe two novel classes of carbohydrate ligand for Cys-MR: chondroitin-4 sulfate chains of the type found on proteoglycans produced by cells of the immune system, and sulfated blood group chains. We further demonstrate that Cys-MR interacts with cells in the spleen via the binding site for sulfated carbohydrates. Our data suggest that the three classes of sulfated carbohydrate ligands may variously regulate the trafficking and function of MR-bearing cells.

Fluorescent neoglycolipids. Improved probes for oligosaccharide ligand discovery

A second generation of lipid-linked oligosaccharide probes, fluorescent neoglycolipids, has been designed and synthesized for ligand discovery within highly complex mixtures of oligosaccharides. The aminolipid 1,2-dihexadecyl-sn-glycero-3-phosphoethanolamine (DHPE), which has been used extensively to generate neoglycolipids for biological and structural studies, has been modified to incorporate a fluorescent label, anthracene. This new lipid reagent, N-aminoacetyl-N-(9-anthracenylmethyl)-1, 2-dihexadecyl-sn-glycero-3-phosphoethanolamine (ADHP), synthesized from anthracenaldehyde and DHPE gives an intense fluorescence under UV light. Fluorescent neoglycolipids derived from a variety of neutral and acidic oligosaccharides by conjugation to ADHP, by reductive amination, can be detected and quantified by spectrophotometry and scanning densitometry, and resolved by TLC and HPLC with subpicomole detection. Antigenicities of the ADHP-neoglycolipids are well retained, and picomole levels can be detected using monoclonal carbohydrate sequence-specific antibodies. Among O-glycans from an ovarian cystadenoma mucin, isomeric oligosaccharide sequences, sialyl-Lea- and sialyl-Lex-active, could be resolved by HPLC as fluorescent neoglycolipids, and sequenced by liquid secondary-ion mass spectrometry. Thus the neoglycolipid technology now uniquely combines high sensitivity of immuno-detection with a comparable sensitivity of chemical detection. Principles are thus established for a streamlined technology whereby an oligosaccharide population is carried through ligand detection and ligand isolation steps, and sequence determination by mass spectrometry, enzymatic sequencing and other state-of-the-art technologies for carbohydrate analysis.

Neoglycolipids derived from phosphatidylethanolamine serve as probes in cell culture studies on glycolipid metabolism

The neoglycolipid (NeoGL) N-acetyl-1-deoxy-1-phosphatidylethanolamino lacto-N-tetraositol [Lc4Ose-PtdEtn(NAc)] and the radioactivly labeled analog [Lc4Ose-PtdEtn(N[14C]Ac)] were synthesized by coupling the corresponding oligosaccharide to phosphatidylethanolamine (dihexadecyl) via reductive amination and subsequent N-acetylation with unlabeled and [14C]acetic acid anhydride, respectively. Lc4Ose-PtdEtn(N[14C]Ac) was then incubated with homogenates of rat small intestine epithelial cells (IEC-6) at pH 4. The reaction products were shown to be the degradation products formed by glycosidases by fast atom bombardment mass spectrometry (FAB MS). On the other hand, incubation of Lc4Ose-PtdEtn(NAc) with IEC-6 cell homogenates in sialyltransferase assays yielded the corresponding sialylated product. When Lc4Ose-PtdEtn(N[14C]Ac) was fed to IEC-6 cells as BSA complex, up to 5% of the NeoGL administered were taken up by the cells. After extraction of the NeoGL and separation by thin layer chromatography (TLC) the catabolic products Lc3Ose-PtdEtn(N[14C]Ac), Lac-PtdEtn(N[14C]Ac), and Glc-PtdEtn(N[14C]Ac), as well as the main anabolic product NeuGc-Lc4Ose-PtdEtn(N[14C]Ac) could be identified by FAB MS. These results demonstrate that PtdEtn-derived NeoGL can be used as probes for studies on the metabolism of specific oligosaccharide structures in cell culture.

Immunochemical characterisation of Schistosoma mansoni glycolipid antigens

The aim of this study was to investigate the occurrence, distribution and immunochemical properties of antibody-defined carbohydrate epitopes in neutral glycolipid fractions of Schistosoma mansoni eggs, cercariae and adults. The amount of extractable, antigenic, neutral glycolipids was lowest in adult worms, increasing consecutively in cercariae and eggs. The immunoreactivity of the glycolipids resided in the carbohydrate moiety in that it was periodate-sensitive. Serological reactivity, and monosaccharide component analysis, anomeric configuration and methylation-linkage analyses indicated that there were two dominant epitopes, which could be partially defined immunologically. The first epitope was detected on egg, cercarial and adult glycolipids. It was strongly recognised by mouse chronic infection sera and rabbit hyperimmune sera raised against specific egg antigens, and was defined by the monoclonal antibody M2D3H (Bickle QD, Andrews BJ. Characterisation of Schistosoma mansoni monoclonal antibodies which block in-vitro killing: failure to demonstrate blockage of immunity in vivo. Parasite Immunol 1988;10:151-168). M2D3H appeared to have the same epitope specificity as monoclonal antibody 128C3/3 (Weiss J, Magnani JL, Strand M. Identification of Schistosoma mansoni glycolipids that share immunogenic carbohydrate epitopes with glycoproteins. J Immunol. 1986;136:4275-82). The internal epitope was defined structurally by the presence of fucose 3-linked to 3,4-disubstituted N-acetylglucosamine, which was itself partially substituted by a second fucose residue, to yield the determinant -4[Fucalpha1,2Fucalpha3]GlcNAcbeta1-. The second epitope was defined by the anti-LewisX monoclonal antibody 4D1 and was found primarily on cercarial glycolipids. It was chemically characterised as the LewisX epitope of Galbeta1,4[Fucalpha1,3]GlcNAcbeta1- in a terminal position. The removal of fucose greatly diminished the binding of the anti-LewisX and M2D3H monoclonal antibodies, as well as the polyclonal chronic infection sera, to glycolipids of all three life-cycle stages and thus revealed the epitopic importance of fucose.

High prevalence of 2-mono- and 2,6-di-substituted manol-terminating sequences among O-glycans released from brain glycopeptides by reductive alkaline hydrolysis

Di- to heptasaccharides isolated from total nondialyzable brain glycopeptides after release by alkaline borohydride treatment have been subjected to mass spectrometric and nuclear magnetic resonance spectroscopic analyses supplemented by TLC-MS analyses of derived neoglycolipids. A family of Manol-terminating oligosaccharides has been revealed which includes novel sequences with a 2, 6-disubstituted Manol: In contrast to the Manol-terminating HNK-1 antigen-positive chains described previously that occur as a minor population [Yuen, C.-T., Chai, W., Loveless, R.W., Lawson, A.M., Margolis, R.U. & Feizi, T. (1997) J. Biol. Chem. 272, 8924-8931], the above oligosaccharides are abundant. The ratio of these compounds to the classical N-acetylgalactosaminitol-terminating oligosaccharides is about 1 : 3. Thus, there appears to be in higher eukaryotes a major alternative pathway related to the yeast-type protein O-mannosylation, the enzymatic basis and functional importance of which now require investigation.

Influence of oligosaccharide presentation on the interactions of carbohydrate sequence-specific antibodies and the selectins. Observations with biotinylated oligosaccharides

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.

L-selectin interactions with novel mono- and multisulfated Lewisx sequences in comparison with the potent ligand 3'-sulfated Lewisa

The cell adhesion molecule L-selectin binds to 3'-sialyl-Lewis (Le)x and -Lea and to 3'-sulfo-Lex and -Lea sequences. The binding to 3'-sialyl-Lex is strongly affected by the presence of 6-O-sulfate as found on oligosaccharides of the counter receptor, GlyCAM-1; 6-O-sulfate on the N-acetylglucosamine (6-sulfation) enhances, whereas 6-O-sulfate on the galactose (6'-sulfation) virtually abolishes binding. To extend knowledge on the specificity of L-selectin, we have investigated interactions with novel sulfo-oligosaccharides based on the Lex pentasaccharide sequence. We observe that, also with 3'-sulfo-Lex, the 6-sulfation enhances and 6'-sulfation suppresses L-selectin binding. The 6'-sulfation without 3'-sialyl or 3'-sulfate gives no binding signal with L-selectin. Where the 6-sulfo,3'-sialyl-Lex is on an extended di-N-acetyllactosamine backbone, additional 6-O-sulfates on the inner galactose and inner N-acetylglucosamine do not influence the binding. Although binding to the 6,3'-sulfo-Lex and 6-sulfo, 3'-sialyl-Lex sequences is comparable, the former is a more effective inhibitor of L-selectin binding. This difference is most apparent when L-selectin is in paucivalent form (predominantly di- and tetramer) rather than multivalent. Indeed, as inhibitors of the paucivalent L-selectin, the 3'-sulfo-Lex series are more potent than the corresponding 3'-sialyl-Lex series. Thus, for synthetic strategies to design therapeutic oligosaccharide analogs as antagonists of L-selectin binding, those based on the simpler 3'-sulfo-Lex (and also the 3'-sulfo-Lea) would seem most appropriate.

Core-branching pattern and sequence analysis of mannitol-terminating oligosaccharides by neoglycolipid technology

The occurrence of mannitol-terminating oligosaccharides (2-substituted or 2,6-disubstituted) among the O-glycans released by alkaline borohydride treatment from glycoproteins of the nervous system has prompted the development of a microscale method to analyze the core-branching pattern and sequence by the neoglycolipid (NGL) technology, analogous to a method previously described for GalNAcol-terminating oligosaccharides (M. S. Stoll, E. F. Hounsell, A. M. Lawson, W. Chai, and T. Feizi, Eur. J. Biochem. 189, 499-507, 1990). The approach involves the selective cleavage at the core mannitol by mild periodate treatment and analysis of the reaction products as NGLs by in situ TLC/liquid secondary ion mass spectrometry. Oxidation conditions have been optimized using as reference compounds 2-, 3-, 4-, or 6-monosubstituted mannobi-itols, 3,6-disubstituted mannitol-terminating pentasaccharides, and 2-mono- and 2,6-disubstituted mannitol-terminating neutral and sialylated oligosaccharides isolated from brain glycopeptides. When a 2:1 molar ratio of periodate to alditol is used, the core mannitol is cleaved at the C3-C4 threo-diol bond and in the absence of a threo-diol cleavage occurs to a lesser extent at erythro-diols. Saccharide ring diols are not cleaved under these conditions, and it is also shown that the side chain of sialic acid on the oligosaccharide is largely unaffected. Substituents at 2- and 6-positions of the core mannitol can be identified, and the method is applicable to neutral and sialylated oligosaccharide alditols. Typically, the starting material is 5 nmol of oligosaccharide and 0.5-1 nmol of derivatives is applied for analysis. By this strategy, the core-branching pattern and position of sialic acid of two branched monosialylated mannitol-terminating oligosaccharide isomers have been determined.

Monoclonal antibody 91.9H raised against sulfated mucins is specific for the 3'-sulfated Lewisa tetrasaccharide sequence

The IgG1hybridoma antibody, 91.9H, was originally raised against sulfated mucins isolated from normal human colonic mucosa. Previous studies have shown that the 91.9H antigen is expressed on normal colonic epithelial cells and the sulfomucins that they produce, but not in the normal small intestine and stomach. Tissue-specific changes occur in 91.9H antigen expression in disease: the antigen diminishes in colonic carcinomas, whereas in regions of gastric mucosa showing intestinal metaplasia and in gastric carcinomas, the antigen is expressed as a "neo-antigen." This report is concerned with elucidation, by the neoglycolipid technology, of the determinant recognized by antibody 91.9H using sulfated and sialyl oligosaccharides of Lewisa(Lea) and Lextypes, and analogs that lack sulfate, sialic acid, or fucose. Binding experiments with the lipid-linked oligosaccharides immobilized on chromatograms or on microwells, and inhibition of binding experiments with free oligosaccharides based on di-, tri- and tetrasaccharide backbones, show that the 91.9H antigenic determinant is based on a trisaccharide backbone, and consists of the 3'-sulfated Leatetrasaccharide sequence, which is a potent ligand for the E- and L-selectins. The antibody gives a relatively low signal with the 3'-sulfated non-fucosylated backbone, and has no detectable cross-reaction with the 3'-sulfated Lexisomer, nor with sialyl-Leaand -Lexanalogues. Antibody 91.9H is a valuable addition, therefore, to the repertoire of reagents for mapping details of the distribution, and determining the relative importance of sulfated and sialyl oligosaccharides as ligands for the selectins, in normal and pathological epithelia and endothelia.

Identification of oligo-N-glycolylneuraminic acid residues in mammal-derived glycoproteins by a newly developed immunochemical reagent and biochemical methods

The occurrence of the alpha2-->8-linked oligomeric form of N-glycolylneuraminic acid (oligo-Neu5Gc) residues in mammalian glycoproteins was unequivocally demonstrated using a newly developed anti-oligo/poly-Neu5Gc monoclonal antibody as well as by chemical and biochemical methods. First, the antibody, designated mAb.2-4B, which specifically recognized oligo/poly-Neu5Gc with a degree of polymerization of >2, was developed by establishing a hybridoma cell line from P3U1 myeloma cells fused with splenocytes from an MRL autoimmune mouse immunized with dipalmitoylphosphatidylethanolamine-conjugated oligo/poly-Neu5Gc. Second, oligo-Neu5Gc was shown to occur in glycoproteins derived from pig spleen by Western blot analysis using mAb.2-4B, which was also confirmed by fluorometric high performance liquid chromatographic analysis of the product of periodate oxidation/reduction/acid hydrolysis of the purified glycopeptide fractions and by TLC and 600-MHz 1H NMR spectroscopic analysis of their mild acid hydrolysates. Finally, the ubiquitous occurrence of oligo-Neu5Gc chains as glycoproteinaceous components in Wistar rat tissue was immunochemically indicated. This is the first example demonstrating the diversity in oligo/poly-Sia structure in mammalian glycoproteins, where only poly-N-acetylneuraminic acid is known to occur. Such diversity in oligo/poly-Sia structure also implicates a diverged array of biological functions of this glycan unit in glycoproteins.

Engineering proteins that bind to cell surface carbohydrates

Carbohydrate residues covalently linked to plasma membrane proteins and lipids often provide specific markers at the cell surface. Traditionally such carbohydrate structures have been identified using antibodies and lectins. However problems of affinity and lack of specificity have restricted their usefulness. Protein engineering offers a way round these difficulties. In the case of some specialised cell surface carbohydrate structures, such as polysialic acid, enzymes may be useful analytical tools. Endosialidases specific for polysialic acid have recently been cloned and sequenced.

Identification of phosphatidylinositol mannoside as a mycobacterial adhesin mediating both direct and opsonic binding to nonphagocytic mammalian cells

The molecular basis for the binding of Mycobacterium tuberculosis to nonphagocytic cells, which are readily infected in vitro, and the in vivo significance of this interaction are incompletely understood. Of six cell types tested, we found that only two, Chinese hamster ovary (CHO) fibroblasts and primary porcine aortic endothelial cells, were able to bind M. tuberculosis H37Rv efficiently in vitro. Binding to both CHO and endothelial cells was markedly (three- to fivefold) enhanced by 10 to 20% human or bovine serum, suggesting that the bacteria were coated by a serum opsonin. Preincubation with individual candidate opsonins revealed that recombinant human mannose-binding protein (rMBP), fibronectin, and transferrin were each able to enhance binding threefold. Preincubation of bacteria in serum depleted of mannan-binding lectins or in genetic MBP-deficient serum resulted in enhancements that were only approximately 60 and 58%, respectively, of that produced by preincubation in control serum. In contrast, serum depleted of fibronectin or transferrin retained its opsonizing capacity, suggesting that the latter two are not significant opsonins in whole serum. Binding of M. tuberculosis and Mycobacterium smegmatis to both CHO and endothelial cells in the presence or absence of serum was blocked (60 to 70%) by a monoclonal antibody, MAb 1D1, selected for recognition of intact bacilli. The 1D1 antigen was purified from mycobacterial cell walls and chemically identified as a polar phosphatidylinositol mannoside (PIM). Latex beads coated with purified 1D1 antigen bound to CHO cells, which was enhanced threefold by serum and abolished by periodate treatment, suggesting a requirement for the PIM mannoses in opsonic adhesion. This was likely mediated, at least in part, by serum MBP, as rMBP bound strongly to 1D1 antigen in both thin-layer chromatography overlay and plate binding assays, the latter in a mannan-inhibitable manner. This is the first demonstration that mycobacterial PIMs can function as adhesins for binding to nonphagocytic cells, both directly and after opsonization with serum proteins, including MBP.

Unusual lactam formation occurring in the synthesis of a biotinylated T-antigen-serine derivative

Synthesis of the biotinylated T-antigens, linked to a serine by an alpha (7 alpha) or a beta (7 beta) 2-acetamido-2-deoxy-D-galactoside bond, is described. These derivatives were needed for the detection of a specific endogenous lectin at the surface and/or on the migration pathway of melanoma cells. In the course of the synthesis, an unusual lactam formation was observed with the beta anomer of the azido-disaccharide 5 beta.

Brain contains HNK-1 immunoreactive O-glycans of the sulfoglucuronyl lactosamine series that terminate in 2-linked or 2,6-linked hexose (mannose)

The monoclonal antibody HNK-1 originally raised to an antigenic marker of natural killer cells also binds to selected regions in nervous tissue. The antigen is a carbohydrate that has attracted much interest as its expression is developmentally regulated in nervous tissue, and it is found, and proposed to be a ligand, on several of the adhesive glycoproteins of the nervous system. It is also expressed on glycolipids and proteoglycans, and is the target of monoclonal auto-antibodies that give rise to a demyelinating disease. The epitope, as characterized on glycolipids isolated from the nervous system, is expressed on 3-sulfated glucuronic acid joined by beta1-3-linkage to a neolacto backbone. Here we exploit the neoglycolipid technology, in conjunction with immunodetection and in situ liquid secondary ion mass spectrometry, to characterize HNK-1-positive oligosaccharide chains derived by reductive alkaline release from total brain glycopeptides. The immunoreactive oligosaccharides detected are tetra- to octasaccharides that are very minor components among a heterogeneous population, each representing less than 0.1% of the starting material. Their peripheral and backbone sequences resemble those of the HNK-1-positive glycolipids. An unexpected finding is that they terminate not with N-acetylgalactosaminitol but with hexitol (2-substituted and 2,6-disubstituted). In a tetrasaccharide investigated in the greatest detail, the hexitol is identified as 2-substituted mannitol.

Blood group B glycosphingolipids in alpha-galactosidase deficiency (Fabry disease): influence of secretor status

Defect in degradation of blood group B-immunoactive glycosphingolipids in Fabry disease (deficiency of lysosomal alpha-galactosidase EC 3.2.1.22) has been studied using highly sensitive and specific TLC-immunostaining analysis of urinary sediments and tonsillar tissues of blood group B patients and healthy controls, secretors and nonsecretors. The B glycolipid antigens with hexasaccharide chains were consistently found increased (25- to 100-fold) in the urinary sediments of three Fabry patients, blood group B or AB secretors. Conversely, they were absent in the urinary sediment of one blood group B nonsecretor patient. In normal secretors, B glycosphingolipids were present only in traces. Moreover, significant increase in B glycolipid antigens (8-fold) was found in the tonsillar tissue of a Fabry patient blood group B secretor. We conclude that the secretor status is responsible for increased concentration of blood group B glycosphingolipids in both urinary cells and tonsils in alpha-galactosidase deficiency. The quantity of stored B-immunoactive glycosphingolipids, however, is much lower than that of the mainly accumulated glycosphingolipid Gb(3)Cer. The results clearly indicate that active or silent Se gene, which controls synthesis of B-antigen precursors, is responsible for notable difference in B-glycosphingolipids expression in Fabry patients - secretors and nonsecretors. Whether this novel aspect may be of prognostic significance, remains to be established.

Synthesis of alpha- and beta-biotinylated T-antigen

The T-antigen [beta-D-Gal-(1-->3)-D-Ga1NAc] has been linked to biotin through a C6 spacer arm for the detection of a specific 'T-antigen-lectin' complex at the surface and/or on the migration pathway of melanoma cells. When 4,6-di-O-acetyl-2-azido-2-deoxy-3-O-(2,3,4, 6-tetra-O-acetyl-beta-D-galactopyranosyl)-alpha- or -beta-D-galactopyranosyl halides were treated with N-benzyloxycarbonyl or N-fluorenylmethoxycarbonyl protected aminohexanols (used as the spacer arm), unusual stereoselectivities were observed for the synthesis of the alpha and beta anomers. The synthesis of the alpha anomer could only be achieved, in reasonable yields, with the Schiff base of aminohexanol.

Carbohydrate recognition by Mycoplasma pneumoniae and pathologic consequences

Mycoplasma pneumoniae infection in the human is often followed by a transient autoimmune hemolytic disorder characterized by high titer autoantibodies to a carbohydrate antigen, the I antigen. Because the major host cell receptor for the Mycoplasma is the sialylated form of this antigen, it is likely that the immunologic disorder is initiated by the microbe-saccharide interaction. Here we review briefly knowledge on the autoantibodies and the structures and distribution of the saccharide antigens and receptors. We discuss possible mechanisms for the triggering of autoantibody production and consider ways in which perturbation of various glycoprotein carriers of the carbohydrate ligands may elicit a variety of pathobiologic responses. We conclude by highlighting ideas on further molecular dissections of the elements of the microbe-host interaction.

Carbohydrate-carbohydrate interactions in adhesion

Cell-cell interactions play an important role in the development, maintenance, and pathogenesis of tissues. They are highly dynamic processes which include migration, recognition, signaling, adhesion, and finally attachment. Cells on their pathway to a final location have to pass and interact with their substratum formed of matrix and cell layers. Testing and recognition are important keys for the proper result of tissue formation. They can, however, also lead to diseases when they are misused in pathological situations, by microorganisms or malignant cells, for instance. Carbohydrates, which are the most prominent surface-exposed structures, must play an important role as recognition molecules in such processes. The rich variability of carbohydrate sequences which cell surfaces can present to lectins, adhesion molecules, and other ligands creates a refined pattern of potential attachment sites. The subtle control of the surface presentation density can provide variations in attachment strength. Not only the carbohydrate sequences but also the fact that carbohydrates can be branched while proteins cannot and that the oligosaccharide chains can be attached to the protein backbone in different densities and patterns will create yet more interaction possibilities. Maximal use of the combinatorial richness of carbohydrate molecules would be made when carbohydrate sequences could interact with other carbohydrate sequences. Such interactions have only very rarely been considered for biochemically and biologically relevant situations since they are difficult to measure. A few are known and will be summarized here with the hope that this wealth of possible chemical interactions may be considered more and more by surface cell biochemists when analyzing fine tuning in cellular interactions.

High-resolution thin-layer chromatography of gangliosides

In this review an updated overview of current improvements on thin-layer chromatography (TLC) of gangliosides over the past decade is provided. Basic general techniques and special advice is given for successful separation of glycosphingolipids. New approaches concerning continuous and multiple development, and several preparative TLC methods are also included. Emphasis is placed on TLC immunostaining and related techniques, i.e. practical applications of carbohydrate-specific antibodies, toxins and bacteria, viruses, lectins and eukaryotic cells. Thus, this review on ganglioside TLC summarizes its power as an analytical tool for a wide range of purposes.

Characterization of the antigenic specificity of four different anti-(alpha 2-->8-linked polysialic acid) antibodies using lipid-conjugated oligo/polysialic acids

A rapid, sensitive, and facile method for screening and characterizing anti-polysialic acid (polySia) antibodies using lipid-conjugated oligo/polysialic acids (oligo/polySia) was developed, which is based on an enzyme-linked immunosorbent assay. Homooligo/polymers of alpha 2-->8-linked N-acetylneuraminic acid (Neu5Ac), N-glycoly-neuraminic acid, and 2-keto-3-deoxy-D-galacto-nononic acid (KDN) were conjugated with phosphatidylethanolamine dipalmitoyl (PE) by reductive amination to prepare neo-oligo/polysialoglycolipids (oligo/polySia-PE). Using this method, the anti-polySia equine antibody, H.46, bound to (-->8Neu5Ac alpha 2-->)n-PE, where n = 9 or more residues, a result in confirmation of previous binding studies using radiolabeled oligo/polyNeu5Ac. The antigenic specificity and sensitivity of two monoclonal anti-poly/oligoNeu5Ac antibodies (mAb.12E3 and mAb.5A5) and one anti-oligoKDN antibody (mAb.kdn8kdn), were also determined. mAb.12E3 could detect as little as 25 pg/well of oligo/polyNeu5Ac-PE, while 0.4 ng/well of oligo/polyNeu5Ac-PE to be detected. mAb.kdn8kdn detected as little as 12 ng/well of oligoKDN-PE. Using a series of oligo/polySia-PE with defined degrees of polymerization (DP), the minimum chain length for immunoreactivity of the anti-polySia antibodies was determined to be: DP 5 for mAb.12E3; DP 3 for mAb.5A5; DP 2 for mAb.kdn8kdn; and DP 8 for H.46. Thus, mAb.12E3 and mAb.5A5 recognize shorter oligomers of Neu5Ac than H.46, a finding that is of practical value for identifying shorter oligoSia chains in glycoconjugates. Because mAb.12E3 and mAb.5A5 also recognize extended polySia chains, these antibodies cannot be used, however, to differentiate between short and long chains of polySia when both are expressed on the same molecule.

TLC-LSIMS of neoglycolipids of glycosaminoglycan disaccharides and of oxymercuration cleavage products of heparin fragments that contain unsaturated uronic acid

Heparin and chondroitin sulfate disaccharides have been investigated by high-performance (HP) TLC and liquid secondary-ion mass spectrometry (LSIMS) after conversion to neoglycolipid derivatives by reductive-amination with an aminolipid (dihexadecyl phosphatidylethanolamine, DHPE). Mobility on HPTLC was largely determined by the number of sulfate groups present, but was also influenced by the position of sulfate, monosaccharide composition and linkage. The mass spectra acquired directly from the TLC plate provided quasimolecular and fragment ions from which composition, including sulfate content, and sequence information was obtained at high sensitivity. Lipid DHPE conjugation and TLC-LSIMS were performed to analyse products of the oxymercuration reaction used to cleave unsaturated uronic acid (delta UA) residues from glycosaminoglycan (GAG) fragments produced by enzymatic degradation with glycan lyases. Previously the identification of the product from delta UA and the integrity of the remaining structures from oligosaccharides larger than disaccharide have not been made. Multiple and characteristic products of the cleaved delta UA were detected and these can be used for identification of terminal delta UA and its sulfate content. It was established with several disaccharides and a tetrasaccharide that glycosidic linkages and O- and N-sulfate groups are preserved in the remaining structures after removal of delta UA. These results indicate that the oxymercuration reaction will be applicable to generating series of GAG fragments containing unmodified sequences for biological activity studies.

Natural killer cell receptors

In the past year, significant strides have been made in understanding natural killing, the process whereby natural killer cells lyse target cells. Recognition of susceptible targets and activation now appear to be mediated by a natural killer cell receptor that binds carbohydrate determinants on target cells and initiates target lysis. Conversely, receptors have been identified that bind MHC class I molecules on targets that inhibit natural killer cell activation. These findings provide the basis for understanding the molecular processes in the initial steps of natural killing.

Oligosaccharide ligands for NKR-P1 protein activate NK cells and cytotoxicity

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.

The adhesive specificity of the soluble human lectin, IgE-binding protein, toward lipid-linked oligosaccharides. Presence of the blood group A, B, B-like, and H monosaccharides confers a binding activity to tetrasaccharide (lacto-N-tetraose and lacto-N-neotetraose) backbones

The immunoglobulin E-binding protein, epsilon BP (also known as CBP35, Mac-2, L-34, and L-29), is a beta-galactoside-binding protein of approximately 30 kDa and a member of the animal lectin family termed S-type or S-Lac. Multiple biological activities have been attributed to this lectin such as mediation of IgE binding to the surface of Langerhans cells and activation of mast cells through binding to the high affinity IgE receptor. In order to better understand the cell-binding activity and the proposed role for epsilon BP as a biological response modifier, we have studied the specificity of binding of the radioiodinated epsilon BP to a series of lipid-linked, structurally defined oligosaccharide sequences of the lacto/neolacto family. The results show that the minimum lipid-linked oligosaccharides that can support epsilon BP binding are pentasaccharides of the lacto/neolacto series and that the lectin binds more strongly to oligosaccharides of this family that bear the blood group A, B, or B-like determinants than to those bearing blood group H. This preferential binding of epsilon BP is also manifest with whole cells, as erythrocytes of blood groups A and B are more strongly bound by epsilon BP than those of blood group O. Blood group Le(a) and Le(x) sequences are not bound by the lectin.(ABSTRACT TRUNCATED AT 250 WORDS)