Hydrazinolysis of asparagine-linked sugar chains to produce free oligosaccharides

Investigation of two glycosylated forms of bile-salt-dependent lipase in human pancreatic juice

Pure human pancreatic bile-salt-dependent lipase, devoid of its oncofetal glycoform [Mas, E., Abouakil, N., Roudani, S., Miralles, F., Guy-Crotte., O., Figarella, C., Escribano, M. J. & Lombardo, D. (1993) Biochem. J. 289, 609-615], was analyzed on immobilized concanavalin A (ConA). Two variants were separated: an unabsorbed ConA-unreactive fraction; and an absorbed ConA-reactive fraction. Carbohydrate compositions of ConA-reactive and ConA-unreactive fractions were not significantly different, and analysis of 3H-labelled oligosaccharides liberated from these fractions on the ConA-Sepharose column indicated that the fractionation of the bile-salt-dependent lipase on this column depends upon oligosaccharide structures. The activity of the ConA-reactive fraction was however much lower, independent of the substrate (4-nitrophenyl hexanoate or cholesteryl esters), than that of the ConA-unreactive fraction. Therefore, catalytic constants for the hydrolysis of 4-nitrophenyl hexanoate were determined; both fractions had quite similar Km, while the kcat for the ConA-unreactive fraction was 3-4-fold higher than that of the ConA-reactive fraction. ConA-reactive and ConA-unreactive fractions were shown to have slightly different molecular masses and different amino acid compositions. Cleavage patterns after cyanogen bromide treatment of the ConA-reactive and ConA-unreactive fractions suggested that the ConA-reactive (high Mr form) and ConA-unreactive (low Mr form) forms could be different isoforms of the bile-salt-dependent lipase secreted by the human pancreas.

Farmer's lung: patients' IgG2 antibodies specifically recognize Saccharopolyspora rectivirgula proteins and carbohydrate structures

Farmer's lung is a frequent form of extrinsic allergic alveolitis. In Europe and Northern America the main source of the antigenic components that induce farmer's lung is the bacterium Saccharopolyspora rectivirgula (Micropolyspora faeni). It remains unclear, however, which S. rectivirgula components are responsible for the disease. We approached these problems by investigating the serologic reaction of patients with farmer's lung and demonstrated specific binding of patients' IgG2 to S. rectivirgula antigens. No such antibodies were found in exposed, unaffected subjects. Thus IgG2 antibodies reacting with S. rectivirgula antigens are useful for the serologic diagnosis of patients with farmer's lung and for the isolation of disease-causing antigens. After separation of S. rectivirgula extract on concanavalin A-Sepharose (Pharmacia, Uppsala, Sweden), we found that approximately one third of the patients' IgG2 reactivity occurred with nonglycosylated proteins. Among these, we characterized two major acidic proteins with molecular weights of 12 and 30 kd, respectively, and with identical N-terminal sequences. Approximately two thirds of the patients' IgG2 reactivity was observed against concanavalin A-binding glycoproteins that contained mainly glucose, mannose, and galactose residues. Deglycosylation of the concanavalin A-bound fraction indicated that most of the IgG2 reactivity occurred with the carbohydrate components.

Characterisation of the tumour-associated carbohydrate epitope recognised by monoclonal antibody 4D3

The tumour-associated epitope recognised by monoclonal antibody (MAb) 4D3 is expressed on a high m.w. mucin glycoprotein preparation known as small intestinal mucin antigen (SIMA). This epitope is detected in tissue from a high proportion of patients with colorectal cancer, and elevated levels occur in serum from a significant number of such patients, highlighting the potential clinical utility of MAb 4D3. In the present study, insight into the composition and structure of the carbohydrate epitope recognised by MAb 4D3 was gained following characterisation of 2 glycopeptides that co-purified with SIMA. Sequence analysis of 1 of these glycopeptides revealed that it was identical to the glycoprotein alpha-1-anti-chymotrypsin. This glycoprotein was subsequently deglycosylated to yield 5 forms corresponding to alpha-1-anti-chymotrypsin substituted with 4, 3, 2, 1 or no branched glycans. MAb 4D3 was reactive with each of the glycosylated forms, including the form carrying only 1 branched glycan, but did not react with fully deglycosylated alpha-1-anti-chymotrypsin. MAb 4D3 also reacted to different extents with ovine, bovine or porcine submaxillary mucins, each of which has a different amount of the O-linked sialylated disaccharide known as sialosyl Tn. Of these mucins, MAb 4D3 was most reactive with ovine submaxillary mucin, in which almost all of the carbohydrate chains are sialosyl Tn. Reactivity of MAb 4D3 towards isolated glycans, sialosyl Tn and related structures led to the conclusion that the preferred MAb 4D3 epitope involves the sialylated N-acetyl galactosamine disaccharide as well as an additional monosaccharide present on a neighbouring carbohydrate chain. Although the preferred epitope recognised by MAb 4D3 involves this sialylated disaccharide, the specificity of MAb 4D3 was different from that of other MAbs with a reported specificity for sialosyl Tn.

Comparative study of the sugar chains of alkaline phosphatases purified from rat liver and rat AH-130 hepatoma cells. Occurrence of fucosylated high-mannose-type and hybrid-type sugar chains

The N-linked sugar chains of alkaline phosphatases, purified from rat AH-130 hepatoma and from normal rat liver, were released quantitatively as oligosaccharides by hydrazinolysis and were labeled by reduction with NaB3H4. A comparative study of their structures revealed that following structural differences are induced by hepatocyte carcinogenesis: complex-type tetraantennary sugar chains and hybrid-type sugar chains appear; outer-chain moieties of the sugar chains of the hepatoma enzyme contain exclusively the Gal(Beta 1-4)GlcNAc groups (type 2 chains) but those of the normal enzyme contain other Gal(Beta 1-)GlcNAc groups and type 2 chains; and novel fucosylated high-mannose-type sugar chains are found in the oligosaccharides of the hepatoma enzyme.

Fingerprinting of glycans as their 2-aminoacridone derivatives by capillary electrophoresis and laser-induced fluorescence

Capillary electrophoresis and laser-induced fluorescence detection have been used to fingerprint the 2-aminoacridone derivatives of complex glycans released from bovine fetuin and human IgG monoclonal antibodies. The utility of this method in distinguishing between N- and O-linked oligosaccharides and in determining the presence of sialic acid residues in glycan mixtures at an early stage of analysis has been demonstrated.

Fractionation of glycoprotein-derived oligosaccharides by affinity chromatography using immobilized lectin columns

Lectin affinity column chromatography is becoming a method of choice for the fractionation and purification of oligosaccharides, especially N-linked oligosaccharides. Using lectin affinity, it is easy to separate structural isomers and to isolate oligosaccharides based on specific features. Further, serial lectin column chromatography, when various lectin columns are used at the same time, can afford a very sensitive method for the fractionation and characterization of extremely small amounts of oligosaccharides. Thus, when used in conjunction with other separation techniques, lectin affinity chromatography can help to purify rapidly oligosaccharides and provide substantial information about their structural features.

Molecular cloning of NIPP-1, a nuclear inhibitor of protein phosphatase-1, reveals homology with polypeptides involved in RNA processing

NIPP-1 was originally isolated as a potent and specific nuclear inhibitory polypeptide (16-18 kDa) of protein phosphatase-1. We report here the cDNA cloning of NIPP-1 from bovine thymus and show that the native polypeptide consists of 351 residues and has a calculated mass of 38.5 kDa. The bacterially expressed central third of NIPP-1 completely inhibited the type-1 catalytic subunit, but displayed a reduced inhibitory potency after phosphorylation by protein kinase A and casein kinase 2. Translation of NIPP-1 mRNA in reticulocyte lysates resulted in the accumulation of both intact NIPP-1 and a smaller polypeptide generated by alternative initiation at the codon corresponding to Met143. A data base search showed that the COOH terminus of NIPP-1 is nearly identical to the human ard-1 protein (13 kDa), which has been implicated in RNA processing (Wang, M., and Cohen, S. N. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 10591-10595). Comparison of the cDNAs encoding ard-1 and NIPP-1 suggests that their mRNAs are generated by alternative splicing of the same pre-mRNA. Western blotting with antibodies against the COOH terminus of NIPP-1, however, showed a single polypeptide of 47 kDa, which was enriched in the nucleus. Northern analysis revealed a single transcript of 2.2 kilobases in bovine thymus and of 2.4 kilobases in various human tissues.

Unusual anionic N-linked oligosaccharides from bovine lung

We previously described a diverse family of sulfated anionic N-linked oligosaccharides released by peptide: N-glycosidase F (PNGaseF) from calf pulmonary artery endothelial (CPAE) cells (Roux, L., Holoyda, S., Sundblad, G., Freeze, H.H., and Varki, A. (1988) J. Biol. Chem. 263, 8879-8889). Since a major fraction of the intact lung consists of endothelial cells, we reasoned that bovine lung might be a rich source of similar molecules. Total N-linked oligosaccharides from bovine lung acetone powder were released by PNGaseF, labeled by [3H]NaBH4 reduction, and the anionic fractions were studied with a variety of techniques. The sugar chains with lesser negative charge (designated Class I) share several properties of conventional multiantennary complex-type chains. However, unlike the case with CPAE cells, sialic acids account only for a minority of the anionic properties and only a small proportion carry sulfate esters. A variety of different treatments indicate that most of the unexplained negative charge is due to multiple carboxylic acid groups. Resistance to beta-glucuronidase and alpha-iduronidase suggests that these may be previously undescribed modifications of mammalian oligosaccharides. The most highly charged N-linked chains (designated Class II) are more similar in general structure to the corresponding ones from CPAE cells, although relatively more abundant. Their high charge is primarily due to chondroitin sulfate, heparin/heparan sulfate, or keratan sulfate glycosaminoglycan chains. Sequential digestion studies suggest that a significant proportion of these molecules have more than one type of glycosaminoglycan chain associated with them. Compositional analysis indicates the presence of xylose residues in Class II, but not Class I molecules. However, unlike the case with conventional glycosaminoglycans, these residues are not at the reducing terminus. Most previously reported structures of complex-type N-linked oligosaccharides are derived from the glycoproteins of blood cells, plasma, or the secretions of cultured mammalian cells. This library of N-linked oligosaccharides from an intact mammalian organ (lung) contains a high proportion of novel anionic sugar chains whose structures are different from conventional complex-type sialylated chains and only partially related to those from CPAE cells. Further exploration of the N-linked chains of intact mammalian tissues seems warranted.

Role of terminal galactose residues in N-linked sugar chains of sheep erythrocyte membrane glycoproteins in rosette formation with T lymphocytes

In this study, we found that rosette formation of T lymphoblastic Molt-3 cells with sheep erythrocytes is inhibited by addition of membrane glycoproteins which were solubilized from sheep erythrocyte ghosts by the lithium diiodosalicylate extraction methods. Their rosetting inhibitory activity was markedly reduced by digestion with N-glycanase, but not with O-glycanase. The inhibitory activity was also reduced by beta-galactosidase digestion, while it was enhanced by desialylation. These observations indicate that nonreducing terminal galactose residues of N-linked sugar chains included in membrane glycoproteins on sheep erythrocytes are important for rosette formation with T lymphocytes.

Structural study of the glycosylated and unglycosylated forms of a genetic variant of human serum albumin (63 Asp-->Asn)

A genetic variant of human serum albumin (alloalbumin) exhibited atypical electrophoretic mobility and chromatographic behavior apparently because of the effect of a point substitution on the molecular conformation. Three forms of albumin were isolated by DEAE HPLC chromatography: normal albumin, and two variant forms V1 and V2. The point substitution (Asp-63-->Asn) generated a canonical tripeptide acceptor sequence for glycosylation with an N-linked oligosaccharide (Asn-Lys-Ser). Neuraminidase digestion followed by electrophoresis showed that the V2 variant form was glycosylated and the V1 form was not. Time-of-flight mass spectrometry yielded a molecular weight of about 2000 for the carbohydrate. Structural analysis of the carbohydrate was done by chromatographic comparison of the pyridylaminated derivatives with standards and was confirmed by proton NMR of the three pronase glycopeptides and of the pyridylaminated oligosaccharide. The oligosaccharide had a complex biantennary structure with two sialic acid residues. In normal albumin Asp-63 is exposed and is adjacent to the first disulfide bond, Cys-62-->Cys-53. The apparent effect on molecular conformation resulting in incomplete glycosylation and atypical electrophoretic mobility suggests that glycosylation may interfere with disulfide bond formation at this site.

Effects of N-3554S, a polyprenyl phosphate, on B16-F10 mouse melanoma cells

N-3554S, an optically active S-isomer of alpha-dihydrodecaprenyl phosphate, reduced the tumorigenicity of cultured B16-F10 mouse melanoma cells probably by affecting protein N-glycosylation. Accordingly, membrane glycoprotein samples were prepared from the melanoma cells cultured with or without N-3554S, and amounts and structures of N-linked sugar chains were determined. Analyses of the N-linked oligosaccharides released by hydrazinolysis from these samples and reduced with NaB3H4 revealed that the N-3554S-treated cells contain 1.5-1.8 times as much oligosaccharides as the control cells, and the relative amounts of high-mannose-type and bi-, tri- and tetra-antennary complex-type sugar chains are almost the same between two samples. Western blot analysis, however, showed that binding of L-PHA, which binds to oligosaccharides with the GlcNAc beta 1-->6(GlcNAc beta 1-->2)Man structure, is significantly reduced in 90 K, 96 K, 140 K, 155 K and 180 K glycoproteins in N-3554S-treated cells. Immunoblot analysis showed that the 140 K glycoprotein could be a fibronectin receptor. It was also shown that N-3554S treatment enhances the adhesiveness of the cells to fibronectin. These results indicate that N-3554S affects N-glycosylation of membrane glycoproteins and alters the cell surface properties of B16-F10 cells.

Dolichol is not a necessary moiety for lipid-linked oligosaccharide substrates of the mannosyltransferases involved in in vitro N-linked-oligosaccharide assembly

Dolichol is utilized in vivo as an unusually large anchor on which the precursor for N-linked oligosaccharides is assembled by a series of glycosyltransferases. The role of dolichol in enzyme substrate recognition is investigated. Thus the biosynthetic intermediate NN'-diacetylchitobiose was chemically linked to either dolichol or the much shorter fully saturated tetraisoprenoid phytanol. Both lipids were used as substrates by a recombinant, soluble beta-1,4-mannosyltransferase. beta-[3H]Mannosylated lipids from this reaction were then used as substrates for the subsequent mannosyltransferases from yeast or rat liver microsomes. It was found that both the dolichyl- and phytanyl-linked substrates were easily mannosylated to form Man5GlcNAc2, with some further mannosylation to Man7GlcNAc2 and Man9GlcNAc2 at low concentrations of lipid-linked substrate. It is concluded that dolichol is not necessary in vitro as part of the substrate for the mannosyltransferases in the biosynthetic pathway for N-glycosylation.

Structural differences between complex-type Asn-linked glycan chains of glycoproteins in rat hepatocytes and Zajdela hepatoma cells

Using serial lectin-affinity chromatography, glycosidase digestion, and NMR and methylation analysis, the structures of complex N-linked glycan chains (M(r) range 2000-3500) of rat hepatocytes and poorly differentiated chemically transformed Zajdela ascites hepatoma cells were determined and compared. The results revealed considerable differences between the two cell types: (i) hepatoma cells only expressed tri- and/or tetra-antennary complex N-linked glycan chains, whereas hepatocytes displayed large amounts of bi-antennary N-linked structures and smaller amounts of tri-/tetra-antennary structures; (ii) 20% of the glycan chains in hepatoma cells contained a bisecting GlcNAc residue which was beta (1,4)-linked to the beta-mannosyl residue of the core and was not detected in the hepatocytes; (iii) hepatoma cells expressed a high proportion of the fucosylated or not GlNAc beta (1,6) Man alpha 1-->branch, whereas hepatocytes only contained a little of this branch; (iv) hepatoma cells, but not hepatocytes, exhibited a repeating (Gal beta(1,4) GlcNAc beta (1,3)) sequence characteristic of poly-N-acetyllactosaminoglycans. These glycans were capped by both alpha-galactosyl and sialyl residues; (v) The alpha (2,3)/alpha (2,6)-linkage ratio of sialic acid was significantly higher in hepatoma cells (4/1 vs. 2/1 in hepatocytes); (vi) Only hepatocytes expressed an unusual structure in which a sialyl residue was alpha (2,6)-linked to a GlcNAc residue located within a NeuAc alpha (2,3) Gal beta (1,3) GlcNAc branch which was beta (1,4)-linked to Man alpha 1,3-->. The differences between these complex N-linked glycan chains in hepatocytes and hepatoma cells seem to be both quantitative and qualitative, since some glycan structures were only present in one cell type.

Carbohydrate heterogeneity of human myeloma proteins of the IgA1 and IgA2 subclasses

Comparative studies of the N-linked carbohydrate chains of human myeloma proteins of the IgA1 and IgA2 subclasses were performed. The N-linked carbohydrate chains were released by hydrazinolysis from the polypeptide backbone, converted to radioactive oligosaccharides by sodium borotritide reduction after N-acetylation and separated into one neutral and two acidic fractions by paper electrophoresis. The acidic oligosaccharides were completely converted to neutral oligosaccharides by sialidase treatment, indicating that they were sialyl derivatives. The neutral and sialidase-treated acidic oligosaccharides were further fractionated by Bio-Gel P-4 column chromatography. Structural studies of each oligosaccharide by sequential exoglycosidase digestion and methylation analysis revealed that human myeloma IgA proteins contained significant amounts of biantennary complex-type carbohydrate chains in addition to a small amount of the high mannose-type. The results indicated that the oligosaccharide structures of human IgA1 and IgA2 display a high degree of heterogeneity not only in the number of carbohydrate chains, but also in their composition.

Synthesis of neoglycopeptides and analyses of their biodistribution in vivo to identify tissue specific uptake and novel putative membrane lectins

Complex type N-linked oligosaccharides derived from fetuin, fibrinogen and thyroglobulin were coupled to acetyltyrosine affording a series of neoglycopeptides with retention of terminal structures and the beta-anomeric configuration of their reducing end N-acetylglycosamine residue. The neoglycopeptides thus synthesized could be labelled to high specific activities with 125I in the aromatic side chain of tyrosine. Analysis of the fate of these neoglycopeptides in conjunction with inhibition with asialofetuin and oligosaccharides of defined structure in mice in vivo revealed the uptake of galactosylated biantennary compound by kidneys, in addition to the known itinerary of triantennary galactosylated complex oligosaccharide from fetuin to liver and the galactosylated biantennary chain with fucosylation in the core to bone marrows. On the other hand, the agalacto, aglucosamino biantennary chains with and without fucosylation in the core region are taken up by submaxillary glands while the conserved trimannosyl core with fucose is primarily concentrated in stomach tissue. These studies thus define new routes for the uptake of complex N-linked glycans and also subserve to identify lectins presumably involved in their recognition.

Structural analysis of N-linked oligosaccharides of equine chorionic gonadotropin and lutropin beta-subunits

Equine chorionic gonadotropin (eCG) and lutropin (eLH) are composed of alpha- and beta-subunits with an identical amino acid sequence but show different biological activities. To elucidate the molecular difference between these gonadotropins, the structure of the N-linked oligosaccharides of each beta-subunit was determined. N-linked sugar chains, liberated as tritum-labeled oligosaccharides by hydrazinolysis followed by N-acetylation and reduction with NaB3H4, were neutralized by sialidase digestion and/or methanolytic desulfation. Neutralized oligosaccharides were fractionated by sequential chromatography on serial lectin affinity columns and on a Bio-Gel P-4 column. Each oligosaccharide structure was determined by sequential exoglycosidase digestion in conjunction with elution profiles on lectin columns and methylation analysis. Each beta-subunit contained a single N-glycosylation site, but a high degree of microheterogeneity was observed in the structure of its N-linked oligosaccharides. eCG beta contained mono-, bi-, tri-, and tetraantennary complex-type oligosaccharides in a ratio of 3:63:13:1. eCG beta oligosaccharides contained about 16% of the bisecting GlcNAc and about 20% of poly-N-acetyllactosamine structures. Elongation of N-acetyllactosamine units showed a preference to the Man alpha 1-->6 side rather than the Man alpha 1-->3 side. Triantennary chains had only a C-2, 4-branched structure. eLH beta contained only mono- and biantennary complex-type and hybrid-type oligosaccharides in a ratio of approximately 18:67:10. eLH beta also contained bisected structures in about 18%. Oligosaccharides derived from the sulfated fraction of eLH beta contained GalNAc residues at nonreducing termini. Oligosaccharides from the sialylated/sulfated fraction of eLH beta contained both Gal and GalNAc residues at nonreducing termini, and those GalNAc residues were preferentially distributed to the Man alpha 1-->3 side of the trimannosyl core. These results clearly indicate that eCG beta and eLH beta possess structurally distinct N-linked oligosaccharides in addition to different charge groups even though they have a protein moiety identical to each other. Our results suggest that the biological activity of these hormones might be modulated by its terminal charge groups and stem structures of carbohydrate moiety synthesized in different organs.

The carbohydrate structure of the asparagine-linked oligosaccharides of rat plasma thiostatin

The complete carbohydrate structure of the asparagine-linked oligosaccharides of rat plasma thiostatin was elucidated through chemical and enzymatic methods including gas chromatography-mass spectrometry (GC-MS) and lectin affinity chromatography. Pronase digestion of thiostatin yielded a major glycopeptide fraction with asparagine the most abundant amino acid present. Based on one mole of aspartic acid, the following molar ratios obtained for the four major amino acids: aspartic acid (1.0), threonine (0.53), glycine (0.48) and serine (0.30). Neutral sugar analysis yielded a 3:2 molar ratio for mannose to galactose based on an assigned value to mannose of 3. On this basis, the fraction also contained 3 residues of sialic acid and, on average, 0 to 1 residue of fucose. GC-MS of partially methylated alditol acetates from the glycopeptide fraction identified the presence of biantennary and triantennary structure. Analyses of the neutral sugar and amino-acid composition, together with methylation data, support a biantennary N-linked structure for this major glycopeptide fraction and a triantennary N-linked structure as a lesser component. Sequencing of the desialyated 14C-labelled glycopeptide fraction by sequential exoglycosidase digestion and lectin affinity chromatography uncovered the following saccharide order: terminal galactose, N-acetylglucosamine and pentasaccharide inner core. This sequence is consistent with the N-linked glycan structures demonstrated by methylation and compositional analyses.

Relation of N-glycosylation of apolipoprotein B-100 to cellular metabolism of low density lipoprotein

We studied the functional role of N-linked sugar chains of apolipoprotein (apo) B-100 of low density lipoprotein (LDL) in cholesterol metabolism. The N-linked sugar chains of apo B-100 of LDL obtained from four homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits were liberated by hydrazinolysis, followed by NaB3H4 reduction and were fractionated by paper electrophoresis and column chromatography. They consisted of one neutral (N) and two acidic (A1, A2) fractions. The ratio of apo B-100 acidic fractions (A1+A2) varied among 4 WHHL rabbits. Serial measurements of serum cholesterol levels showed that they decreased with aging in each of 4 WHHL rabbits. We investigated the relation of the ratio of acidic sugar chains of apo B-100 to the serum cholesterol levels. Reciprocals of the serum cholesterol levels were significantly correlated with the ratio of acidic sugar chains of apo B-100 (r = 0.901, P < 0.001). To elucidate the role of N-linked sugar chains of apo B-100, we investigated cellular uptake of LDL in normal rabbit skin fibroblasts. The amounts of association, degradation and cholesteryl esterification of LDL with a lower ratio of acidic sugar chains at 37 degrees C were greater than those of LDL with a higher ratio of acidic sugar chains. These results suggest that N-glycosylation of apo B-100 may be related with serum cholesterol levels and N-linked sugar chains of apo B-100 may play an important role in cellular metabolism of LDL.

Structural analysis of the N-glycans from human immunoglobulin A1: comparison of normal human serum immunoglobulin A1 with that isolated from patients with rheumatoid arthritis

The primary structures of the N-linked oligosaccharides from normal human serum IgA1 were determined by a combination of sequential exoglycosidase digestion, Bio-Gel P-4 chromatography, anion-exchange chromatography and one-dimensional n.m.r. spectroscopy. Three major N-linked disialylated biantennary-complex-type structures were found (55%). The remaining N-linked oligosaccharides consisted of at least nine further structures, some of which (7%) were of the triantennary type and included disialylated triantennary oligosaccharides with outer-arm fucose substitution [Fuc alpha 1-3(4)]. Compared with IgG, the N-glycan structures on IgA are more completely processed: the outer arms have a higher proportion of galactose and sialic acid, and only trace levels of incompletely galactosylated oligosaccharides, commonly found on IgG, were detected. Analysis of the sialylated O-glycans revealed that 64% were [NeuAc2 alpha 3(6)]2Gal beta 3GalNAc and 9% were [NeuAc2 alpha 3(6)]-Gal beta 4GlcNAc beta 6[NeuAc2 alpha 3(6)Gal beta 3]GalNAc, and 27% were monosialylated. The N-linked glycosylation of both serum IgA1 and IgG isolated from a group of six normal individuals was compared with that from ten patients with rheumatoid arthritis (RA). In contrast with the hypogalactosylation found in IgG from diseased sera, there was no evidence of an equivalent decrease in the galactosylation of the IgA1 oligosaccharides. In addition, the N-glycosylation of IgA1 was remarkably consistent within the group of normal individuals. These data suggest that incomplete galactosylation of N-linked glycans and its augmentation in RA does not extend to IgA1 and that the RA-associated galactosyltransferase deficiency may be restricted to cells producing gamma-chain.

The elimination of O-linked glycans from glycoproteins under non-reducing conditions

A simple procedure is described for the elimination of O-linked glycans from bovine submaxillary mucin under non-reducing conditions, using triethylamine in aqueous hydrazine. The glycans were isolated as the hydrazones, which were converted to the reducing glycans by exchange with acetone in neutral aqueous solution. The glycan alditols obtained after reduction corresponded to those obtained by the reductive beta-elimination of O-glycans.

Tools to cleave glycoproteins

There are a variety of enzymes available that are able to cleave glycoproteins, including enzymes that are specific for carbohydrate-carbohydrate linkages, carbohydrate-protein bonds and the peptide backbone. Such enzymes are useful for determining the sites of glycosylation within proteins, and for releasing glycan structures for subsequent carbohydrate analysis. One protease has been identified as being specific for O-sialoglycoproteins and can be used to identify such molecules and their epitope regions. The lack of cytotoxicity and the narrow specificity of this enzyme provides an improved method for the immunomagnetic selection of human bone-marrow stem-cells.

Biotinylated diaminopyridine: an approach to tagging oligosaccharides and exploring their biology

Fluorescent tagging of free oligosaccharides by reductive amination permits sensitive detection and fractionation of these molecules. To expand the scope of this approach, we have synthesized a fluorescent reagent, 2-amino-(6-amidobiotinyl)pyridine. This reagent can tag oligosaccharides under nondegradative conditions with high efficiency. The resulting adducts show excellent fractionation by reverse-phase HPLC with sensitive detection in the low picomole range. When combined with sequential exoglycosidase digestion, stepwise sequencing of the sugar chains is possible. The biotinyl group can also be used to recover the sugar chain from reaction mixtures. The high-affinity interaction of the biotinyl group with multivalent avidin or streptavidin can be used to create the functional equivalent of neoglycoproteins carrying multiple copies of oligosaccharides of defined structure. These complexes allow the production of IgG antibodies directed against the oligosaccharide chain. They can also harness the power of (strept)avidin-biotin technology for the detection and isolation of oligosaccharide-specific receptors from native sources of recombinant libraries.

Comparative studies of asparagine-linked sugar chains of immunoglobulin G from eleven mammalian species

1. Asparagine-linked sugar chains released by hydrazinolysis from IgGs of porcine, equine, bovine, goat, ovine, canine, rabbit, guinea-pig and rat were comparatively analyzed by microsequencing and lectin affinity chromatography. 2. Sugar chains of all IgGs basically consisted of biantennary complex-type oligosaccharides containing 0-2 sialic acid residue(s). More than 70% of the oligosaccharides were neutral, except for guinea-pig IgG, and fucosylated trimannosyl core structures were dominant except for rabbit IgG. Bisecting N-acetylglucosamine residue was absent in porcine and equine IgGs. 3. A large quantity of galactose-less oligosaccharides were present in IgGs of porcine, equine, canine and rat.

Structural characterization of the N-linked carbohydrate chains from mouse zona pellucida glycoproteins ZP2 and ZP3

N-linked oligosaccharides of mouse zona pellucida glycoproteins ZP2 and ZP3 were prepared as pyridylaminated derivatives. Anion-exchange HPLC revealed that 95% or more of them are acidic. About 80% of these acidic chains were neutralized by digestion with Arthrobacter ureafaciens sialidase and a small amount of sulfate was found in the residual acidic chains. The neutralized fractions (SN fractions) from ZP2 and ZP3 were similarly fractionated by size-fractionation HPLC into many peaks having different numbers of LacNAc in the non-reducing regions. The SN fractions from ZP2 were cleaved by endo-beta-galactosidase into the core and non-reducing regions. The tri- and tetra-antennary complex-type chains with a Fuc residue were predominant in the core region. On the other hand, four kinds of fragment containing the LacNAc sequence were obtained from the non-reducing region. Sialic acids were shown to be linked to the core fragments, as well as the non-reducing fragments. The N-linked oligosaccharides of ZP3 were suggested to have essentially the same structures as those of ZP2.

A change in soybean agglutinin binding patterns of bovine milk fat globule membrane glycoproteins during early lactation

Milk fat globule membrane (MFGM) glycoproteins were prepared from bovine milk at different stages of early lactation. Western blot analyses using several lectins revealed that reactivity of MFGM glycoproteins, especially 47K and 80K bands, to soybean agglutinin (SBA) remarkably increased during the lactation, while no change was observed for Ricinus communis agglutinin-I (RCA-I) binding. Sialidase treatment of MFGM glycoproteins revealed that the number of SBA-positive bands and the amount of SBA-positive oligosaccharides in these bands are increased during the lactation. Since SBA binds N-acetylgalactosamine terminated oligosaccharides, the results indicated that N-acetylgalactosaminylation of bovine MFGM glycoproteins is stimulated during the lactation.

The structure of N-linked oligosaccharides of human pancreatic bile-salt-dependent lipase

This study describes the structure of the N-linked oligosaccharide chains of bile-salt-dependent lipase isolated from the pancreatic juice of a normal donor. After hydrazinolysis, neutral sugar chains were separated from acidic chains by paper electrophoresis and were fractionated using serial column chromatography with immobilized lectins and Bio-Gel P-4 filtration. Structural analysis was performed by means of sequential glycosidase digestion and revealed that the neutral sugar chains are mainly of the biantennary complex type. Fucose residues were identified for some trimannosyl core structures and were alpha(1-6) or alpha(1-2) linked to the innermost GlcNAc residue and a terminal Gal residue, respectively. Sialyl residues were also involved in the oligosaccharide structures. Most of these structures have no linear N-acetyllactosamine repeats. Evidence from several approaches suggests that the sugar chains of the human pancreatic bile-salt-dependent lipase possess a blood-group-related antigenic determinant.

Characterization of the oligosaccharide structures on bee venom phospholipase A2

The N-linked oligosaccharide structures on bee venom phospholipase A2 were investigated. The oligosaccharides on purified phospholipase A2 were released by hydrazinolysis and labeled in vitro by reduction with NaB3H4. Following purification, the labeled oligosaccharides were characterized by size exclusion chromatography in combination with digestion with specific glycosidases. Linkage positions were determined by methylation analysis. Four types of structures were identified on the molecule, all of which were of truncated high-mannose type and none of which contained any alpha-(1-->2)-linked mannose residues. The majority of the structures were Man3 oligosaccharides with (43%) or without (38%) a fucose residue linked alpha-(1-->6) to the reducing N-acetylglucosamine. The remaining 19% of the oligosaccharides on the molecule were identified as a Man5 oligosaccharide without core fucose (9.6%) and a core-fucosylated Man4 structure (9.2%).

Selective identification and differentiation of N- and O-linked oligosaccharides in glycoproteins by liquid chromatography-mass spectrometry

A mass spectrometry method has been developed for selective detection of glycopeptides at the low (< or = 25) picomole level during chromatography of glycoprotein digests and for differentiation of O-linked from N-linked oligosaccharides. The technique involves observation of diagnostic sugar oxonium-ion fragments, particularly the HexNAc+ fragment at m/z 204, from collisionally excited glycopeptides. Collision-induced fragmentation can be accomplished in either of two regions of a triple quadrupole mass spectrometer equipped with an atmospheric pressure, electrospray (ES) ionization source. If collisions before the first quadrupole are chosen, it is possible to enhance formation of carbohydrate-related fragment ions without distorting the distribution of peptide and glycopeptide signals by increasing the collisional excitation potential only during that portion of each scan in which the low mass carbohydrate-related ions are being detected. This procedure, requiring only a single quadrupole instrument, identifies putative glycopeptide-containing fractions in the chromatogram but suffers from a lack of specificity in the case of co-eluting peptides. Increased specificity is obtained by selectively detecting only those parent ions that fragment in Q2, the second collision region of the triple quadrupole, to produce an ion at m/z 204 (HexNAc+). Only (M + H)+ ions of glycopeptides are observed in these liquid chromatography-electrospray tandem mass spectrometry (LC-ESMS/MS) "parent-scan" spectra. N-linked carbohydrates are differentiated from O-linked by LC-ESMS/MS analysis of the digested glycoprotein prior to and after selective removal of N-linked carbohydrates by peptide N:glycosidase F. These methods, which constitute the first liquid chromatography-mass spectrometry (LC-MS)-based strategies for selective identification of glycopeptides in complex mixtures, facilitate location and preparative fractionation of glycopeptides for further structural characterization. In addition, these techniques may be used to assess the compositional heterogeneity at specific attachment sites, and to define the sequence context of the attachment site in proteins of known sequence. The strategy is demonstrated for bovine fetuin, a 42-kDa glycoprotein containing three N-linked, and at least three O-linked carbohydrates. Over 90% of the fetuin protein sequence was also corroborated by these LC-ESMS studies.

Use of hydrazine to release in intact and unreduced form both N- and O-linked oligosaccharides from glycoproteins

The use of hydrazine to release unreduced N- and O-linked oligosaccharides from glycoproteins has been investigated using several "standard" glycoproteins of previously defined glycosylation. It is shown that hydrazinolysis can be used to release intact N- and O-linked oligosaccharides in an unreduced form. The release of O-linked oligosaccharides occurs with a lower temperature dependence than the release of N-linked oligosaccharides, and the kinetic parameters governing release of oligosaccharides from these standard glycoproteins have been determined. These parameters allow a definition of reaction conditions under which anhydrous hydrazinolysis can be used to selectively release O-linked oligosaccharides (60 degrees C, 5 h) or release both N- and O-linked oligosaccharides (95 degrees C, 4 h) in high yield (> 85%) from all glycoproteins investigated (n = 11). Under these reaction conditions, the recovered N- and O-linked oligosaccharides are structurally intact (as judged by 600-MHz 1H-NMR, laser-desorption mass spectrometry, HPAEC-PAD, gel filtration, and glycosidase digestion), with the possible exception of certain N- and O-acyl substituents of sialic acid. This use of mild hydrazinolysis therefore allows both the simultaneous and sequential chemical release from glycoproteins of O- and N-linked oligosaccharides in their intact unreduced form.

Altered glycosylation of beta 1 integrins associated with reduced adhesiveness to fibronectin and laminin

The carbohydrate structures of the beta 1 integrins obtained from a mouse metastatic melanoma B16 F1 and its weakly metastatic wheat-germ agglutinin-resistant mutant Wa4-b1 were studied comparatively. The results indicated that the integrins from both cells contain high mannose-type and bi-, tri- and tetra-antennary complex-type sugar chains. No significant difference was found in the outer chain branching between both integrins, but sialylation of the sugar chains of the mutant's integrin was markedly decreased and almost all the outer chain moieties of tri- and tetra-antennary oligosaccharides of the mutant's integrin were fucosylated, resulting in the formation of X-antigenic determinants, Gal beta 1-->4 (Fuc alpha 1-->3) GlcNAc. In contrast, the integrin from parental cell contained no X-antigenic determinant. These structural differences found in the integrin are thought to account for the reduction in the metastatic potential of the mutant which also shows reduced adhesion to fibronectin and laminin as compared with the parental cell.

Localization and characterization of the carbohydrate-binding site of the porcine lymphocyte mannan-binding protein

Mannan-binding proteins found in the liver and serum of several vertebrate species are supposed to play an important role in the intracellular transport of glycoproteins, as well as in several protective reactions including complement activation and elimination of various pathogens. To study these protective functions at molecular level it is necessary to understand the fine oligosaccharide specificity and mutual relation among various forms of these soluble lectins. We have isolated mannan-binding protein as peripheral membrane proteins of porcine lymphocytes. This lectin was purified to homogeneity and shown to possess many properties in common with the well studied rat liver proteins (mol. mass, subunit composition and general organization of the molecule). Binding studies performed with three series of defined oligosaccharides (high mannose, hybrid type, and complex) on native lectin molecules as well as isolated carbohydrate-binding domains revealed distinctive features of this mannan-binding protein, including its impaired ability to bind the oligosaccharide ligand after reduction and decyclization at core N-acetyl-D-glucosamine 1.

Use of large-scale hydrazinolysis in the preparation of N-linked oligosaccharide libraries: application to brain tissue

In this report, we describe the preparation of a library of N-linked glycans from whole murine brain obtained by the large-scale hydrazinolysis of an acetone powder of the tissue followed by chromatographic procedures. 84% of the characterized oligosaccharides were found to be anionic, the remainder neutral. The anionic species were successively neutralized by neuraminidase (29%), aq. hydrofluoric acid (30%), and methanolysis (26%), indicating that approximately equal portions were sensitive to desialylation, dephosphorylation and desulfation, respectively. The presence of the sulfated fraction was confirmed by direct 35SO4 metabolic labelling. A residual partially characterized fraction was found to be anionic through possession of carboxylic acid groups, unrelated to sialic acid. The purified oligosaccharides, in the absence of their original protein conjugates, were shown to retain those immunological characteristics essential for recognition by a specific monoclonal antibody, LS (412), that is known to recognize a carbohydrate epitope present on a number of neural adhesion molecules and functional in neural cell adhesion. These properties confirm the viability of scaling up the size of the hydrazinolysis procedure and adapting it to whole tissue for the production of glycan libraries and for the probing of structures of interest.

Structure of the acidic N-linked carbohydrate chains of the 55-kDa glycoprotein family (PZP3) from porcine zona pellucida

N-linked carbohydrate chains of the major 55-kDa family, PZP3, of porcine zona pellucida glycoproteins are composed of neutral (28%) and acidic (72%) complex-type chains. The structures of the main components of the neutral chain have been established [Noguchi, S., Hatanaka, Y., Tobita, T. & Nakano, M. (1992) Eur. J. Biochem. 204, 1089-1100]. Here we report the structures of the acidic chains. Only two kinds of acidic fragments were released from PZP3 by endo-beta-galactosidase digestion following beta-elimination of O-linked chains. 500-MHz one-dimensional and two-dimensional 1H-NMR spectroscopy revealed their structures to be Sia alpha(2-3)Gal beta(1-4) [HSO3-6]GlcNAc beta(1-3)Gal and HSO3-6GlcNAc beta(1-3)Gal, showing that the sulfate-containing acidic chains are constructed with non-branched N-acetyllactosamine repeats which have sialic acid(s) at the non-reducing end(s) and sulfate at the C-6 position of GlcNAc residues. The acidic N-linked chains obtained from PZP3 by hydrazinolysis were separated into diantennary chains (34%) and tri- and tetra-antennary chains (66%) by concanavalin-A--agarose gel chromatography. The diantennary chains and their sialidase digests were fractionated by DEAE-HPLC. From the analyses of the endo-beta-galactosidase digests of each fraction, structures of the diantennary acidic chains were determined. They are classified into four groups. The first group is the sialylated chains without the sulfated N-acetyllactosamine repeating unit. The other three groups have the chains of various lengths differing in the number of monosulfated N-acetyllactosamine unit. These chains are extended from the Man alpha(1-3) branch of the trimannosyl core in the second group, from the Man alpha(1-6) branch in the third group, and from both branches in the fourth group. The structural features of the tri- and tetra-antennary acidic chains are also presented.

Molecular structures of glycoprotein hormones and functions of their carbohydrate components

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The mapping by high-pH anion-exchange chromatography with pulsed amperometric detection and capillary electrophoresis of the carbohydrate moieties of human plasma alpha 1-acid glycoprotein

The reducing oligosaccharides released from alpha 1-acid glycoprotein (AGP) by conventional hydrazinolysis have been analyzed by two different mapping techniques, using high-pH anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) and capillary electrophoresis (CE) with uv detection at 190 nm. The CE measurements proved about 4000 times more sensitive than the measurements by HPAE-PAD. The N-glycan pool was fractionated by Mono Q anion-exchange chromatography, and individual fractions so obtained were desialylated using Vibrio cholerae neuraminidase. The resulting asialo-N-glycans were further analyzed by HPAE-PAD, revealing 2 major, 4 intermediate, and 4 small peaks and at least 3 spikes, which counted for at least 13 different asialo-N-glycans. The carbohydrate structures were tentatively assigned by comparison of the Mono Q-separated N-glycans with the known AGP carbohydrate structures and known structures contained in a mapping database that allows structural assignment of N-glycans by mere comparison of retention times. In addition to the hitherto known AGP carbohydrate structures, we have tentatively identified a number of sulfated N-glycans that are currently being analyzed in more detail. We have also compared the glycan pools recovered from AGP using hydrazinolysis and glycopeptidase F (PNGase F). Approximately 40 distinct peaks could be detected in the hydrazinolysis-derived N-glycan pool by either technique (HPAE-PAD and CE), while about 30 distinct peaks were detected in the N-glycan pool derived by PNGase F digestion of the tryptic AGP digest of the same batch of AGP. These differences were attributed to an increased desialylation (approximately 3 mol%) during hydrazinolysis, based on the detection by HPAE-PAD and CE of free sialic acid and monosialylated oligosaccharides in the glycan pool derived by conventional hydrazinolysis. The integrity of the N-glycans' chitobiose core was examined by 500-MHz 1H NMR spectoscopy. The hydrazinolysis procedure could be optimized such that the hydrazinolysis-derived N-glycan pool was chromatographically essentially identical to the PNGase F-derived N-glycan pool. Hydrazinolysis proved best, with practically no loss of N-acetlylneuraminic acid and the closest resemblance to the PNGase F-derived N-glycan pool, using an automated apparatus. Notably, it was recognized that, in our hands, PNGase F digestion in the presence of sodium dodecyl sulfate resulted in partial desialylation of the liberated N-glycans.

Structures and functions of the sugar chains of glycoproteins

Most proteins within living organisms contain sugar chains. Recent advancements in cell biology have revealed that many of these sugar chains play important roles as signals for cell-surface recognition phenomena in multi-cellular organisms. In order to elucidate the biological information included in the sugar chains and link them with biology, a novel scientific field called 'glycobiology' has been established. This review will give an outline of the analytical techniques for the structural study of the sugar chains of glycoproteins, the structural characteristics of the sugar chains and the biosynthetic mechanism to produce such characteristics. Based on this knowledge, functional aspects of the sugar chains of glycohormones and of those in the immune system will be described to help others understand this new scientific field.

Altered glycosylation of membrane glycoproteins associated with human mammary carcinoma

N-Linked sugar chains of normal mammary gland, mammary carcinomas (primary lesion), and axillary lymph node metastases of mammary carcinomas were released from their membrane preparations by hydrazinolysis and their structures were analyzed. Fractionation using a Datura stramonium agglutinin (DSA)-Sepharose column revealed that the metastasized carcinomas contain more than twice as much DSA-binding oligosaccharides as the normal gland, and the primary carcinomas contain an intermediate amount. These oligosaccharides were elucidated to have tri- and tetraantennary structures containing the GlcNAc beta 1-->6(GlcNAc beta 1-->2)Man group with and without N-acetyllactosamine repeating units. Lectin blot analysis of membrane glycoproteins and histochemical staining of tissues using biotinylated DSA indicated that these glycosylation changes predominantly occur in a limited number of glycoproteins with apparent molecular weights of 90, 160, and 210 kilodaltons, and mammary carcinomas are distinguishable from normal gland by their intense intracytoplasmic staining.

Formation of homogeneous carbohydrate-lectin cross-linked precipitates from mixtures of D-galactose/N-acetyl-D-galactosamine-specific lectins and multiantennary galactosyl carbohydrates

Quantitative precipitation studies have shown that the Man/Glc-specific lectin concanavalin A (ConA) forms homogeneous (homopolymeric) cross-linked precipitates with individual asparagine-linked oligomannose and bisected hybrid-type glycopeptides in the presence of binary mixtures of the carbohydrates [Bhattacharyya, L., Khan, M. I. & Brewer, C. F. (1988) Biochemistry 27, 8762-8767]. The results indicate that the ConA-glycopeptide precipitates are highly organized cross-linked lattices that are unique for each carbohydrate. Using similar techniques, the present study shows that the Gal-specific lectins from Erythrina indica and Ricinus communis (agglutinin I) form homogeneous cross-linked complexes with individual carbohydrates in binary mixtures of triantennary and tetraantennary complex-type oligosaccharides with terminal Gal residues. Conversely, binary mixtures of Gal/GalNAc-specific lectins from E. indica, Erythrina cristagalli, Erythrina flabelliformis, R. communis, soybean (Glycine max), and Wistaria floribunda (tetramer) in the presence of a naturally occurring or synthetic branched-chain oligosaccharide with terminal GalNAc or Gal residues provide evidence for the formation of separate cross-linked lattices between each lectin and the carbohydrate. The present results therefore demonstrate the formation of homogeneous lectin-carbohydrate cross-linked lattices in (a) a mixture of branched-chain complex-type oligosaccharides in the presence of a specific Gal/GalNAc-binding lectin, and (b) a mixture of lectins with similar physicochemical and carbohydrate binding properties in the presence of an oligosaccharide. These findings show that lectin-carbohydrate cross-linking interactions provide a high degree of specificity which may be relevant to their biological functions as receptors.

High-performance anion-exchange chromatography coupled with mass spectrometry for the determination of carbohydrates

Methodology has been developed to couple high-performance anion-exchange chromatography (HPAE) with mass spectrometry utilizing the ion spray liquid chromatography/mass spectrometry (LC/MS) interface. Anion micro-membrane suppression (AMMS) has been used to remove the high concentrations of NaOH and NaOAc (10-400 mM total [Na+]) necessary for the separation of mixtures of monosaccharides and oligosaccharides. Post-suppressor addition of CH3CN/H2O solutions containing NH4OAc or LiOAc provided low-nanomole detection of the monosaccharides by selected ion monitoring of the cationized adducts. Maltooligosaccharide mixtures (three to seven residues) were separated and detected by the HPAE/AMMS LC/MS system in the full-scan mode. Low declustering potentials (35 V) in the LC/MS API source afforded intact singly and doubly charge ammoniated and diammoniated adducts of the sugars. Higher declustering potentials (65 V) produced abundant fragmentation of the ammoniated adducts. The corresponding lithiated and dilithiated species produced intact molecule ion species at higher declustering potentials. The endo H-released oligomannose species from RNase B were determined by the HPAE/AMMS LC/MS system as ammoniated adducts and resulting fragment ions with a high declustering potential (95 V) in the full-scan mode.