High-Resolution, 1H-Nuclear Magnetic Resonance Spectroscopy as a Tool in the Structural Analysis of Carbohydrates Related to Glycoproteins

Structures of N-glycans of a ricin-resistant mutant of baby hamster kidney cells. Synthesis of high-mannose and hybrid N-glycans

The asparagine-linked glycopeptides (N-glycans) of a ricin-resistant mutant of baby hamster kidney (BHK) cells, RicR21, have been isolated and fractionated from a Pronase digest of disrupted cells by concanavalin A (Con A)-Sepharose chromatography, ion-exchange chromatography, and lentil lectin chromatography. The structures of all the major N-glycans have been determined by 500-MHz H NMR spectroscopy. RicR21 synthesizes only hybrid and high-mannose N-glycans. All the hybrid structures contain only three mannose residues. The major hybrid glycopeptide has the following structure: (Formula: see text). There is also about 15% of the nonfucosylated species present. Only a small amount (less than or equal to 5%) of the asialo hybrid is produced. Branched hybrid N-glycans are also present in RicR21 cells, containing two complex antenna linked beta 1----2 and beta 1----4 to the Man alpha 1----3 arm; about 70% of this species is core fucosylated. Man6GlcNAc2 glycopeptide is the most abundant (about 70%) of the high-mannose N-glycans. These studies account for the very poor ricin binding property of this mutant, as the sialic acid residues of the major hybrid N-glycan are exclusively linked alpha 2----3 to galactose and ricin is unable to bind to alpha 2----3-substituted galactosyl residues [Baenziger, J. U., & Fiete, D. (1979) J. Biol. Chem. 254, 9795-9799].

Structure determination of oligosaccharides isolated from Cad erythrocyte membranes by permethylation analysis and 500-MHz 1H-NMR spectroscopy

Alkaline borohydride reductive cleavage (beta-elimination) of glycophorin A isolated from one individual of the rare blood group Cad, resulted in the release of six acidic oligosaccharide-alditols which were separated by high-performance liquid chromatography (HPLC) on an alkyl amine silicagel column. The structure of four of them has been determined by the application of methanolysis, methylation analysis and 1H-NMR spectroscopy at 500 MHz. The structures and relative amounts were as follows: oligosaccharide 1: NeuAc(alpha 2-3)Gal(beta 1-3)GalNAc-ol (3.5%); oligosaccharide 3: GalNAc(beta 1-4)[NeuAc(alpha 2-3)]Gal(beta 1-3)GalNAc-ol (10.5%); oligosaccharide 5: NeuAc(alpha 2-3)Gal(beta 1-3)[NeuAc(alpha 2-6)]GalNAc-ol (10.4%); oligosaccharide 6: GalNAc(beta 1-4)[NeuAc(alpha 2-3)]Gal(beta 1-3)[NeuAc(alpha 2-6)]GalNAc-ol (71.2%). The two other oligosaccharides (2 and 4) were obtained in very low amount. The major pentasaccharide (oligosaccharide 6) carries the blood group Cad determinant and is a potent inhibitor of human anti-Sda antibody.

Structural analysis of the carbohydrate moieties of human Tamm-Horsfall glycoprotein

Glycopeptides present in a pronase digest of human Tamm-Horsfall glycoprotein were fractionated by chromatography on DEAE-Sephadex A25 in 0.1M acetic acid. The separated glycopeptides were characterised by 500-MHz 1H-n.m.r. spectroscopy, in conjunction with sugar and amino acid analysis, and they were shown to be of the N-glycosylic, N-acetyllactosamine type. Each fraction consisted mainly of a tetra-antennary entity having various degrees of complexity, with lesser amounts of the triantennary structure, and even smaller amounts of the diantennary type. There was extensive heterogeneity in non-reducing terminal groups in each of the glycopeptides, whereas the peptide portions were similar. The extent to which any one of the galactose residues in the N-acetyllactosamine units was substituted, and the type of substitution, differed. The substituents were alpha-NeuAc-(2----6), alpha-NeuAc-(2----3), and alpha-NeuAc-(2----3)[beta-GalNAc-(1----4)]. The carbohydrate moieties of the glycoprotein were heterogeneous also because of an uneven distribution of the fucose residues, which were attached to GlcNAc residues, both that linked to asparagine and one or more of those present in the N-acetyllactosamine units. The alpha-NeuAc-(2----3)[beta-GalNAc-(1----4)]-beta-Gal-(1---- sequence forms, at least in part, the Sda immunodeterminant. The pKa of the carboxyl group of the sialic acid residue in this entity is lower than that for molecules lacking Gal-NAc in this position. Thus, the difference in the number of Sda determinants carried by the glycopeptides enabled the latter to be fractionated on DEAE-Sephadex.

Major oligosaccharides in the glycoprotein of Friend murine leukemia virus: structure elucidation by one- and two-dimensional proton nuclear magnetic resonance and methylation analysis

The highly microheterogeneous, N-glycosidically linked oligosaccharides in the glycoproteins of Friend murine leukemia virus (as produced by Eveline cells) were liberated with endo-beta-N-acetylglucosaminidase H and by alkaline hydrolysis. They were fractionated (as desialylated oligosaccharitols) by gel filtration and by concanavalin A affinity chromatography, and the major fractions were analyzed by methylation-gas chromatography-mass spectrometry, by digestion with exoglycosidases, and, especially, by one- and two-dimensional proton nuclear magnetic resonance spectroscopy. Guidelines for qualitative and quantitative analysis of complex oligosaccharide mixtures by NMR were worked out and the results compared with those obtained by methylation analysis. It was found that these major fractions consist of bi-, tri-, and tetraantennary oligosaccharitols of the "complex" type (comprising a minority of species with N-acetyllactosamine repeating units), which are, in part, substituted by nonreducing terminal Gal alpha (1----3) and/or bisecting GlcNAc beta (1----4) residues.

Further characterization, by a combined high-performance liquid chromatography/1H-NMR approach, of the heterogeneity displayed by the neutral carbohydrate chains of human bronchial mucins

From bronchial mucins of cystic fibrosis patients with blood group O, the carbohydrate chains were released in the form of oligosaccharide-alditols by alkaline borohydride treatment. Application of high-performance liquid chromatography directly on the pool of neutral oligosaccharides afforded 23 fractions. Twenty oligosaccharide structures were characterized by employing 500-MHz 1H-NMR spectroscopy in conjunction with sugar analysis. Thirteen among these had been revealed before to occur in human bronchial mucins [Van Halbeek, H., Dorland, L., Vliegenthart, J. F. G., Hull, W. E., Lamblin, G., Lhermitte, M., Boersma, A., and Roussel, P. (1982) Eur. J. Biochem. 127, 7-20], when paper-chromatographic fractionation of this pool of neutral oligosaccharides was employed. High-performance liquid chromatography enabled to obtain another seven pentasaccharide and hexasaccharide alditols; the largest-size representatives are: (Formula see text). Thereby, this approach afforded deeper insight into the structural heterogeneity displayed by the carbohydrate chains of bronchial mucins.

The identification of terminal alpha (1----3)-linked galactose in N-acetyllactosamine type of glycopeptides by means of 500-MHz 1H-NMR spectroscopy

500-MHz 1H-NMR spectroscopy was employed to study two N-acetyllactosamine-type glycopeptide fractions which were derived from a bovine thyroglobulin preparation (Cummings, R.D., and Kornfeld, S. (1982) J. Biol. Chem. 257, 11230-11234). By this method, their branches were found to be terminated either by NeuAc in alpha (2----6)-linkage or by Gal in alpha (1----3)-linkage. For the first time, the Gal alpha (1----3) Gal beta (1----4) GlcNAc beta (1----.) sequence is characterized by 1H-NMR to occur in N-glycosidic carbohydrate chains of glycoproteins. Moreover, this approach made possible the branch localization of such a unit. Microheterogeneity with respect to the presence of alpha-linked Gal or NeuAc in terminal position of a certain branch in one of the preparations, could be adequately assessed in terms of structures by 1H-NMR.

Primary structure of the major glycans of the N-acetyllactosamine type derived from the human immunoglobulins M from two patients with Waldenström's macroglobulinemia

The carbohydrate chains of the pathological human immunoglobulins M from two patients with Waldenström's macroglobulinemia were released by hydrazinolysis. The N-acetyllactosamine-type glycans were obtained by affinity chromatography on concanavalin A and fractionated by high-voltage paper electrophoresis. The primary structure of the major compounds was elucidated on the basis of carbohydrate analysis, methylation analysis, including mass-spectrometry, and 500 MHz 1H-NMR spectroscopy. For both patients, this appeared to be a monosialyl monofucosyl biantennary structure; the compounds differed by the presence of an intersecting N-acetylglucosamine residue.

Structure elucidation by one- and two-dimensional 360- and 500-MHz 1H NMR of the oligosaccharide units of two glycoproteins isolated from alveoli of patients with alveolar proteinosis

The structure of the oligosaccharide units of the glycoproteins of Mr 36,000 and 62,000 isolated from alveoli of patients with alveolar proteinosis have been determined by one- and two-dimensional 1H NMR spectroscopy at 500 and 360 MHz. Bi-, tri-, and tetraantennary glycans of N-acetyllactosaminic type have been found in high percentage. They are 1----6 monofucosylated and fully sialylated, the ratio NeuAc(2----3)/NeuAc X (2----6) increasing with increasing degree of branching.

Structural studies on the O-linked carbohydrate chains of human platelet glycocalicin

Glycocalicin (140 kDa), constituting the main part of glycoprotein Ib (160 kDa), was released from the human platelet membrane by the action of a Ca2+-dependent protease, present in the platelet cytoplasm and liberated during sonication of the platelet suspension. After activation of the protease by Ca2+, the sonicated platelet suspension was subjected to differential centrifugation. The supernatant was applied to a column of wheat germ agglutinin linked to Sepharose 4B; glycocalicin was eluted from the column with 2.5% (w/v) N-acetylglucosamine. Glycocalicin was found to contain 40% carbohydrate by weight, representing N- as well as O-glycosidically linked carbohydrate chains. The O-glycosidic chains were split off by alkaline cleavage in the presence of 3H-labelled NaBH4. The liberated 3H-labelled oligosaccharide-alditols were fractionated on a DEAE-Sephadex A-25 column. The structures of the oligosaccharide-alditols were investigated by 500-MHz 1H-NMR spectroscopy. The major compound was identified as NeuAc alpha(2----3)Ga1 beta(1----3)[NeuAc alpha(2----3)Ga1 beta(1----4)GlcNAc beta(1----6)]GalNAc-ol. Two minor compounds were found to be NeuAc alpha(2----3)Gal beta(1----3)[NeuAc alpha(2----6)]GalNAc-ol and NeuAc alpha(2----3)Gal beta(1----3)GalNAc-ol.

The structure of sialyl-glycopeptides of the O-glycosidic type, isolated from sialidosis (mucolipidosis I) urine

Sialyl-glycopeptides containing an O-glycosidically linked tetrasaccharide chain were obtained from the urine of a patient suffering from mucolipidosis I. Isolation of these compounds was achieved by gel filtration, ion-exchange chromatography and preparative paper chromatography. Their structures were determined by a combination of carbohydrate and amino acid analysis, dansylation, periodate oxidation, methylation studies, enzymatic hydrolysis and 1H-NMR spectroscopy, to be as follows: (formula; see text) wherein R = peptide linked through -Thr-, -Ser-Thr- or -Thr-Ser-. The finding of these glycopeptides in urine shows that mucolipidosis I is characterized by a general "glycoprotein-specific" sialidase deficiency. The possibility of the existence of a human endo-alpha-N-acetylgalactosaminidase is discussed.

Primary structure of N-glycosidically linked asialoglycans of secretory immunoglobulins A from human milk

The asialoglycopeptides obtained from secretory immunoglobulins A from human milk have been separated by gel filtration and affinity chromatography on Concanavalin A-Sepharose and Lens culinaris agglutinin-Sepharose columns. Their structures have been determined by sugar analysis, methylation studies including mass spectrometry and 500-MHz 1H-NMR spectroscopy. The glycans are of the biantennary N-acetyllactosamine type differing in their degree of extension by fucosyl-N-acetyllactosamine residues. The overall structures of the glycopeptides are as follows: (Formula: see text) Most of the asialoglycopeptide structures possess an intersecting GlcNAc residue; they are suggested to be located on the alpha chain of the secretory immunoglobulins A of human milk. The non-intersected structures probably occur on the secretory piece. The methodology applied to the structural analysis adequately coped with the extremely high degree of heterogeneity shown by the structures.

Terminal alpha (1 leads to 4)-linked N-acetylglucosamine: a characteristic constituent of duodenal-gland mucous glycoproteins in rat and pig. A high-resolution 1H-NMR study

The structure of the carbohydrate chains of mucous glycoproteins from the gastro-intestinal tract was examined for species- and tissue-specificity. To this purpose, oligosaccharides were released from purified glycoprotein preparations of rat and pig gastric, duodenal-gland and small-intestinal mucus, by alkaline borohydride reductive cleavage. Based on the results of 500-MHz 1H-NMR spectroscopy and of sugar analysis of the total oligosaccharide fractions, terminal GlcNAc, alpha (1 leads to 4)-linked to galactose, appears to be a characteristic constituent of duodenal-gland oligosaccharides. Similarly, NeuAc in alpha (2 leads to 3)-linkage to galactose turns out to be a typical constituent of small-intestinal mucous glycoproteins. In general, glycoproteins from gastric mucus possess larger and more-branched carbohydrate chains than those from duodenal-gland and small-intestinal mucus. Comparing rat and pig, oligosaccharide structures for corresponding tissues are less complex for the former. After fractionation, the rat duodenal-gland oligosaccharides could be characterized by application of 1H-NMR spectroscopy as being branched tetra- up to hexa-saccharide chains, all sharing the italicized trisaccharide element. The chains exhibit microheterogeneity as to the termination by fucose in alpha (1 leads to 2)- or by GlcNAc in alpha (1 leads to 4)-linkage to galactose. The following structures can be proposed for the most abundant rat duodenal-gland oligosaccharides: (table; see text).

Characterization of the neutral glycopeptides containing the structure alpha-L-fucopyranosyl-(1 leads to 3)-2-acetamido-2-deoxy-D-glucose from human neuroblastoma cells

Human tumor cells of neurectoderm origin contain a high proportion of alpha-L-fucosyl linkages were determined by high-resolution, 500-MHz, 1H-n.m.r. spectroscopy which gave signals characteristic for alpha-L-Fucp-(1 leads to 3)-D-GlcNAc residues these L-fucosyl residues. This was shown by use of a specific alpha-L-fucosidase from almond emulsin and a broad-spectrum alpha-L-fucosidase from rat testes. The exact alpha-L-fucosyl linkages were determined by high-resolution, 500-MHz, 1H-n.m.r. spectroscopy which gave signals characteristic for alpha-L-Fucp-(1 leads to 3)-D-GlcNAc residues linked to branches and for alpha-L-Fucp-(1 leads to 6)-D-GlcNAc residues linked to the core. More than 95% of the asparagine-linked GlcNAc residues were substituted with (1 leads to 6)-alpha-L-fucosyl groups. Further definition of the range of neutral glycopeptides was obtained with immobilized lectins. Binding to E-PHA-agarose suggested the presence of a beta-D-mannopyranosyl residue substituted at O-4 by a 2-acetamido-2-deoxy-D-glucopyranosyl group. alpha-L-Fucp-(1 leads to 3)-GlcNAc interfered with this binding since removal of alpha-L-fucosyl groups by almond emulsin alpha-L-fucosidase increased the binding by 100%. These studies demonstrate the ability of a combination of high-resolution 1H-n.m.r., enzyme degradation, and lectin-binding affinities to delineate structural elements of small amounts of oligosaccharide residues.