Hydrazinolysis of asparagine-linked sugar chains to produce free oligosaccharides

Sulfated N-linked carbohydrate chains in porcine thyroglobulin

N-linked carbohydrate chains of porcine thyroglobulin were released by the hydrazinolysis procedure. The resulting mixture of oligosaccharide-alditols was fractionated by high-voltage paper electrophoresis, the acidic fractions were further separated by high-performance liquid chromatography on Lichrosorb-NH2, and analyzed by 500-MHz 1H-NMR spectroscopy and, partially, by permethylation analysis. Of the acidic oligosaccharide-alditols, the following sulfated carbohydrate chains could be identified: NeuAc alpha 2----6Gal beta 1----4GlcNAc beta 1----2Man alpha 1----3[(SO3Na----3)Gal beta 1----4GlcNAc beta1----2-Mana alpha 1----6]Man beta 1----4GlcNAc beta 1----4[Fuc alpha 1----6]GlcNAc-ol and NeuAc alpha 2----6Gal beta 1----4(SO3Na----)0-1 GlcNAc beta 1----2-Man alpha 1----3[NeuAc alpha 2----6Gal beta 1----4(SO3Na----6)1-0GlcNAc beta 1----2Man alpha 1----6]Man beta 1----4GlcNAc beta 1----4[Fuc alpha 1----6]GlcNAc- ol. The sulfated structural elements for porcine thyroglobulin form novel details of N-linked carbohydrate chains. They contribute to the fine structure of these oligosaccharides and are another type of expression of microheterogeneity.

Improved procedure for the construction of neoglycolipids having antigenic and lectin-binding activities, from reducing oligosaccharides

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

Chromatography of carbohydrates

The coupling of high-performance anion-exchange chromatography with pulsed amperometric detection provides a much needed analytical tool for the analysis of the carbohydrates of glycoconjugates.

Parasite glycoconjugates: towards the exploitation of their structure

The parasitic protozoa express many unusual complex carbohydrates at the cell surface in the form of glycoproteins and glycophospholipids. In several cases, such molecules have been shown to be involved in parasite survival, infectivity and host-cell recognition. The carbohydrate chains of these glycoconjugates are often highly immunogenic, and can in some cases elicit protective immunity. The immunogenicity of some parasite glycans is a function of their unusual chemical structure as compared with mammalian glycans. This suggests differences in the glycosylation pathways between host and parasite due to their evolutionary distance. This article describes how a combination of biophysical and biochemical techniques can be used to determine the primary and three-dimensional structures of parasite carbohydrate and how this information might be exploited towards the development of new selective chemotherapeutic agents and synthetic vaccines.

Carbohydrate structures of the human-immunodeficiency-virus (HIV) recombinant envelope glycoprotein gp120 produced in Chinese-hamster ovary cells

The present paper describes the structures of the N-linked oligosaccharides of the human-immunodeficiency-virus (HIV) envelope glycoprotein gp120 (cloned from the HTLV-III B isolate and expressed as a secreted fusion protein after transfection of Chinese-hamster ovary cells), which is known to bind with high affinity to human T4-lymphocytes. Oligosaccharides were released from peptide by hydrazinolysis, fractionated by paper electrophoresis, high-performance lectin-affinity chromatography and Bio-Gel P-4 column chromatography, and their structures determined by sequential exoglycosidase digestions in conjunction with methylation analysis. The glycoprotein was found to be unique in its diversity of oligosaccharide structures. These include high-mannose type and hybrid type, as well as four categories of complex-type chains: mono-, bi-, tri- and tetra-antennary, with or without N-acetyl-lactosamine repeats, and with or without a core-region fucose residue. Among the sialidase-treated oligosaccharides, no less than 29 structures were identified as follows: (formula; see text) where G is galactose, GN is N-acetylglucosamine, M is mannose, F is fucose, and '+/- ' means that residues are present in a proportion of chains. The actual number of oligosaccharide structures is much greater, since before desialylation there was evidence that, among the hybrid and complex-type chains, all but 6% contained sialic acid at the C-3 position of terminal galactose residues, and partially sialylated forms of the bi- and multi-antennary chains were present. Detailed evidence for the proposed oligosaccharide sequences will be published as a supplementary paper [T. Mizuochi, M. W. Spellman, M. Larkin, J. Solomon, L. J. Basa & T. Feizi (1988) Biomed. Chromatogr., in the press].

Comparative studies of the sugar chains of aminopeptidase N and dipeptidylpeptidase IV purified from rat kidney brush-border membrane

Asparagine-linked sugar chains of rat kidney aminopeptidase N and dipeptidylpeptidase IV were investigated comparatively. Oligosaccharides released from the two enzymes by hydrazinolysis were fractionated by paper electrophoresis, serial chromatographies on columns of immobilized Aleuria aurantia lectin, concanavalin A, phytohemagglutinin E4, and Datura stramonium agglutinin, and Bio-Gel P-4 (less than 400 mesh) column chromatography. Structures of oligosaccharides in each fraction were assumed by their effective molecular sizes and behaviors on the four lectin columns and then confirmed by sequential exoglycosidase digestion and methylation analysis. The sugar chains of aminopeptidase N and dipeptidylpeptidase IV are almost the same as those of rat kidney gamma-glutamyltranspeptidase reported previously [Yamashita, K., Hitoi, A., Matsuda, Y., Tsuji, A., Katunuma, N., & Kobata, A. (1983) J. Biol. Chem. 258, 1098-1107]. They are a mixture of 5 high mannose type sugar chains and 32 (for aminopeptidase N) or 26 (for dipeptidylpeptidase IV) mono-, bi-, tri-, and tetraantennary complex type sugar chains. The unique feature of the complex-type sugar chains of both enzymes is that they all contain the bisecting N-acetylglucosamine residue and are incompletely galactosylated in their outer-chain moieties.

Comparative structural study of N-linked oligosaccharides of urinary and recombinant erythropoietins

The structures of the N-linked oligosaccharides of the urinary erythropoietin (u-EPO) purified from urine of aplastic anemic patients were analyzed and compared with those for recombinant erythropoietin (r-EPO) prepared with baby hamster kidney (BHK) cells. Asparagine-linked neutral oligosaccharides were released from each EPO protein by N-oligosaccharide glycopeptidase (almond) digestion. The reducing ends of the oligosaccharide chains thus obtained were aminated with a fluorescent reagent, 2-aminopyridine, and the mixture of pyridylamino derivatives of the oligosaccharides was separated by high-performance liquid chromatography (HPLC) on an ODS silica column. More than 8 and 13 kinds of oligosaccharide fractions for u-EPO and r-EPO (BHK), respectively, were completely separated by the one-step HPLC procedure. The structure of each oligosaccharide thus isolated was analyzed by a combination of sequential exoglycosidase digestion and another kind of HPLC with an amide-silica column. Furthermore, high-resolution proton nuclear magnetic resonance (1H NMR) spectroscopy and methylation analyses were carried out in the case of r-EPO (BHK).(ABSTRACT TRUNCATED AT 250 WORDS)

Separation of positional isomers of oligosaccharides and glycopeptides by high-performance anion-exchange chromatography with pulsed amperometric detection

High-performance anion-exchange (HPAE) chromatography under alkaline conditions (pH congruent to 13) has been found to efficiently separate neutral oligosaccharides (triose to undecaose) according to molecular size, sugar composition, and linkage of monosaccharide units. The method was able to resolve 1----3, 1----4, and 1----6 positional isomers of neutral oligosaccharides, which are defined as having the same number, type, sequence, and anomeric configurations of monosaccharides but differing in the linkage position of a single sugar. From correlating structural features of different oligosaccharides and retention times, we deduced that at least two factors are operative to determine the superior resolution of oligosaccharides by this type of chromatography: (i) the relative acidities of the hydroxyl groups and (ii) the accessibility of oxyanions of the oligosaccharides to the functional groups of the stationary phase. Splitting of peaks attributable to mutarotation was not observed. Reducing oligosaccharides were much more retained than their reduced counterparts. Linkage of Fuc(alpha 1-3) to GlcNAc of oligosaccharides markedly decreased retention times. Positional isomers of two branched monosaccharides, which differed by 1----6 and 1----4 linkages, were widely separated. The separation of 1----3 and 1----4 positional isomers of both tetrasaccharides and glycopeptides containing undecasaccharides demonstrated the significant improvement in resolution of HPAE compared to previous chromatographic methods by either reverse-phase or amine-bonded stationary phases. Picomole quantities of underivatized oligosaccharides have been detected by triple-pulse amperometric detection, which produced similar responses for a wide range of structures. Quantification of two triantennary glycopeptides from bovine fetuin by using either detector response or 1H NMR was comparable. The N-glycanase-catalyzed release of two 1----4 and 1----3 positional isomers of an undecasaccharide from a tryptic glycopeptide of bovine fetuin could be observed and quantified by direct injection of the enzyme mixture into the chromatograph.

Structures, function, and transformational changes of the sugar chains of glycohormones

Human chorionic gonadotropin (hCG), human luteinizing hormone, human thyroid-stimulating hormone, and human follicle-stimulating hormone are closely related family of proteins which share a common alpha-subunit. However, their sugar moieties are quite different. hCG contains five acidic asparagine-linked sugar chains. These five sugar chains are derived by sialylation from three neutral oligosaccharides: two biantennary (N-1 and N-2) and one monoantennary (N-3) complex-type oligosaccharides. Although hCG purified from the urine of pregnant women is more enriched in sialylated sugar chains than that purified from placenta, the molar ratio of N-1, N-2, and N-3 of these two hCGs are the same (1:2:1). Comparative study of the sugar moieties of the alpha- and beta-subunits of hCG revealed that alpha contains 1 mol each of N-2 and N-3, while beta contains 1 mol each of N-1 and N-2. This specific distribution of oligosaccharides at the four asparagine loci of the hCG molecule is now helping us to consider the functional role of the sugar moiety of glycohormones. hCG is produced not only by the trophoblast but also by various trophoblastic diseases. The hCGs purified from the urine of patients with hydatidiform mole contain the same oligosaccharides as normal hCG. However, those from the urine of choriocarcinoma patients contain five additional neutral oligosaccharides. In contrast, hCGs from invasive-mole patients contain three of the five oligosaccharides, specifically found in choriocarcinoma hCGs. The malignant transformational change of the sugar moiety of hCG can be explained by an increase of a fucosyltransferase, which forms the Fuc alpha 1----6GlcNAc group and by ectopic expression and subsequent modification of N-acetylglucosaminyltransferase IV. The appearance of tumor-specific sugar chains of hCG has been used to develop a new diagnostic method for invasive mole and choriocarcinoma.

Identification of a tetrasialylated monofucosylated tetraantennary N-linked carbohydrate chain in human platelet glycocalicin

Glycocalicin (140 kDa), the main constituent of the glycoprotein Ib alpha-chain (150 kDa) of the human platelet membrane, contains 4 putative N-glycosylation sites. For the structural analysis of the N-glycosidic carbohydrate chains of glycocalicin, the glycoprotein has been subjected to the hydrazinolysis procedure. The acidic carbohydrate chains obtained were fractionated by ion-exchange chromatography on DEAE-Sephadex A-25, and subsequently analyzed by sugar analysis, anion-exchange chromatography on Mono Q HR 5/5 and 500 MHz 1H-NMR spectroscopy. A novel tetrasialylated monofucosylated tetraantennary chain was identified in the glycoprotein. It could also be deduced that in all structures the alpha 2----6-linked NeuAc is attached exclusively at the Gal beta 1----2Man alpha 1----3 antenna, whereas the other antennae can be terminated with alpha 2----3-linked NeuAc. As minor constituents sialylated N-linked carbohydrate chains with a terminal Fuc alpha 1----2Gal beta 1----sequence were detected.

Separation of sialyl-oligosaccharides by medium pressure anion-exchange chromatography on Mono Q

On columns prepacked with the recently introduced anion-exchange material, Mono Q (Pharmacia), sialyl-oligosaccharides could be fractionated excellently according to the sialic acid content. With u.v. absorption at 214 nm as the detection method, analytical runs of carbohydrate material on the microgram scale, were possible. The value of the method for preparative purposes was demonstrated for sialic acid-containing carbohydrates obtained from human serotransferrin by hydrazinolysis.

Characterization of N-linked gluco-oligomannose type of carbohydrate chains of glycoproteins from the ovary of the starfish Asterias rubens (L.)

Glycoproteins were isolated from the ovary of the starfish Asterias rubens (L.). After delipidation, sugar analysis revealed the presence of mannose, glucose and N-acetylglucosamine in a molar ratio of 9.0:1.3:2.3. Subsequently, hydrazinolysis, re-N-acetylation, reduction and high-voltage paper electrophoresis were carried out, resulting in a mixture of neutral oligosaccharide alditols which was fractionated on Bio-Gel P-4. The alditols, investigated by 500-MHz 1H-NMR spectroscopy, turned out to be of the oligomannose type or of the gluco-oligomannose type containing 9 mannose and 1-3 glucose residues. The most abundant compounds were established to be: (Formula: see text) and (Formula: see text).

Oligosaccharides of arterial basement membrane-like material studied on rabbit aortic myomedial cells in culture

Oligosaccharides from myomedial basement membrane-like material were characterized in respect of size, attachment to protein and charge heterogeneity after metabolic labelling with [3H] glucosamine. Arterial basement membrane-like material was isolated from cultures of aortic myomedial cells by a sonication-differential centrifugation technique. Glycopeptides were then obtained by proteinase digestion and Sephadex G-50 chromatography. Alkaline borohydride treatment of the glycopeptides followed by Sephadex G-25 chromatography revealed that 10-14% of the oligosaccharides were released by a beta-eliminative reaction. The molecular weight of the alkali labile carbohydrate units was estimated to be approximately 750. Alkali stable oligosaccharides were released from the glycopeptides by hydrazinolysis. The liberated oligosaccharides were retarded by Sephadex G-50 chromatography corresponding to a molecular weight of 2700 using unit B thyroglobulin oligosaccharides as standard. The chromatographic pattern obtained by anion exchange chromatography of the glycopeptides after neuraminidase treatment showed that a major part of the glycopeptides contain one or more sialic acid residues, but also other negatively charged groups--possibly phosphomannosyl residues were present as suggested by [32PO4(3-)] labelling and concanavalin-A-Sepharose chromatography. Concanavalin-A-Sepharose chromatography combined with alpha- mannosidase treatment and gel filtration suggested that a minor part of the glycopeptides were of high-mannose- type.

MS and NMR analysis of the cross-reacting determinant glycan from Trypanosoma brucei brucei MITat 1.6 variant specific glycoprotein

The cross-reacting determinant glycan from Trypanosoma brucei brucei MITat 1.6 is known to contain galactose, mannose and non-acetylated glucosamine. The structural elucidation of this oligosaccharide has been impeded by an unusual non-glycosidic linkage to the peptide chain and a glycosidic linkage to inositol phosphate on either side of the oligosaccharide. Using two different approaches for the isolation of the glycan, namely hydrolysis to give the oligosaccharide directly or pronase digestion to yield the glycan-containing C-terminal glycophosphopeptide, the structure of this glycan was elucidated by mass spectrometry and 1H-NMR spectroscopy. There was evidence of heterogeneity in the glycan residue.

The beta 1----2-D-xylose and alpha 1----3-L-fucose substituted N-linked oligosaccharides from Erythrina cristagalli lectin. Isolation, characterisation and comparison with other legume lectins

The carbohydrate moieties of Erythrina cristagalli lectin were released as oligosaccharides by hydrazinolysis, followed by N-acetylation and reduction with NaB3H4. Fractionation of the tritium-labelled oligosaccharide mixture by Bio-Gel P-4 column chromatography and high-voltage borate electrophoresis revealed that it is composed of five neutral oligosaccharides. Structural studies by sequential exoglycosidase digestion in combination with methylation analysis and two-dimensional 1H-NMR showed that the major component was the fucose-containing heptasaccharide Man alpha 3(Man alpha 6)(Xyl beta 2)Man beta 4GlcNAc beta 4(Fuc alpha 3)GlcNAcol. This is the first report of such a structure in plant lectins. Small amounts of the corresponding afucosyl hexasaccharide were also identified, as well as three other minor components. The structure of the heptasaccharide shows the twin characteristics of a newly established family of N-linked glycans, found to date only in plants. The characteristics are substitution of the common pentasaccharide core [Man alpha 3(Man alpha 6)Man beta 4GlcNAc beta 4GlcNAc] by a D-xylose residue linked beta 1----2 to the beta-mannosyl residue and an L-fucose residue linked alpha 1----3 to the reducing terminal N-acetylglucosamine residue. The oligosaccharide heterogeneity pattern for Erythrina cristagalli lectin was also found for the lectins from four other Erythrina species and the lectins of two other legumes, Sophora japonica and Lonchocarpus capassa.

Primary structure of O- and N-glycosylic carbohydrate chains derived from murine submandibular mucin (MSM)

The carbohydrate moiety of mouse submandibular mucin (MSM) contains mainly D-mannose and 2-acetamido-2-deoxy-D-glucose together with sialic acid, D-galactose, and 2-acetamido-2-deoxy-D-galactose. O-Glycosylically bound saccharides, obtained by treatment of MSM with alkaline borohydride, were shown by methylation analysis to have the structure: alpha-NeuAc-(2----3)-beta-Gal-(1----3)-GalNAc-ol. N-Glycosylically bound saccharides obtained from MSM by hydrazinolysis, and analysed by 500-MHz 1H-n.m.r. spectroscopy, were shown to have the following comprehensive structures. (Formula: see text).

Receptors for fucose-binding proteins of Lotus tetragonolobus isolated from mouse embryonal carcinoma cells. Structural characteristics of the poly(N-acetyllactosamine)-type glycan

Receptors for fucose-binding proteins of Lotus tetragonolobus were isolated from N4-1 and F9 embryonal carcinoma cells. They were glycoproteins, whose major components had apparent relative molecular masses of more than 100,000. Carbohydrates released from the receptors of N4-1 cells by hydrazinolysis were separated into three fractions by gel filtration. Binding activity to the lectin was detected in the high-molecular-mass fraction. The composition of the large glycan was characteristic of the poly (N-acetyllactosamine)-type, and glucosamine was identified as the sugar involved in the protein-carbohydrate linkage. The glycan has one fucosyl residue per four N-acetyllactosamine units. Most of the fucose was linked to the C-3 hydroxyl group of N-acetylglucosamine. No Fuc alpha 1----2Gal or Fuc alpha 1----4GlcNAc linkage was detected. The glycan had a relative molecular mass of 9000 or more and the poly(N-acetyllactosamine) units were branched. N-Acetylgalactosamine residues were detected in non-reducing ends of at least a part of the glycan. Therefore, the glycan has a more complex structure than the related one from human granulocytes, although both of them have Fuc alpha 1----3GlcNAc termini.

Neoglycolipid micro-immunoassays applied to the oligosaccharides of human milk galactosyltransferase detect blood-group related antigens on both O- and N-linked chains

Reduced O-linked chains and reducing N-linked chains were obtained from human milk galactosyltransferase by degradation with alkaline borohydride and hydrazinolysis, and then purified by ion-exchange chromatography. The reactivities of the conjugates of the oligosaccharides with L-alpha-phosphatidyl ethanolamine dipalmitoyl (PPEADP) towards monoclonal anti-Lea and anti-SSEA-1 were then determined, either by antibody-binding assays after absorbing the neoglycolipids onto plastic wells, or by inhibition assays after incorporating the neoglycolipids into liposomes and testing them as inhibitors of antibody binding. The oligosaccharides were also immunostained with monoclonal anti-Lea after h.p.t.l.c. and coupling to PPEADP. Antigenic activities were detected in the O-linked chains by all three assay systems, whereas, for the less abundant N-linked chains, reactivities were detected by the inhibition assays only. The results provide evidence for the expression of Lea and SSEA-1 antigen activities on both the O- and N-linked chains of this enzyme glycoprotein.

Synthesis of beta-glucans in Prototheca zopfii. Isolation and characterization of the glycoprotein primer

When Prototheca zopfii cells were pulse-labeled with 14C-containing amino acids and homogenized, 14C-labeled membranes were obtained. In vitro incubations with the previously labeled membranes and UDP-[3H]Glc produced a trichloroacetic-acid-insoluble fraction having both isotopes. A double-labeled glucoprotein was isolated and characterized. It has a relative molecular mass of 28,000-30,000 and a carbohydrate content of 10%. The oligosaccharide chain is linked to the protein through an O-glycosidic bond between hydroxyproline and glucose. The oligosaccharide has a polymerization degree ranging over 10-20 hexose units. Glucose is the only monosaccharide found; most of the glucose residues are beta-1,4-linked (90%) but some are beta-1,3-linked (10%).

Determination of the structure of the carbohydrate chains of acid alpha-glucosidase from human placenta

Acid alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) from human placenta (70 and 76 kDa) was found to contain 4 N-glycosidic carbohydrate chains per molecule. Sugar analysis of purified enzyme revealed the presence of mannose, N-acetylglucosamine and fucose at a molar ratio of 5.0:2.0:0.6. In addition, trace amounts of galactose and N-acetylneuraminic acid were detected. The sugar chains were liberated from the polypeptides by the hydrazinolysis procedure and subsequently fractionated by gel filtration and HPLC. Purified compounds were investigated by 500-MHz 1H-NMR spectroscopy. Oligomannoside-type chains of intermediate size, e.g., Man5GlcNAcGlcNAc-ol and Man7GlcNAcGlcNAc-ol, and N-type chains of smaller size e.g., Man2-3GlcNAc[Fuc]0-1GlcNAc-ol, were demonstrated to be present at a ratio of 2:3. In addition, a small amount of sialylated N-acetyllactosamine-type chains has been found. The possible biosynthetic route of the fucose-containing small-size chains is discussed.

Primary structure of a low-molecular-mass N-linked oligosaccharide from hemocyanin of Lymnaea stagnalis. 3-O-methyl-D-mannose as a constituent of the xylose-containing core structure in an animal glycoprotein

Hemocyanin from the freshwater snail Lymnaea stagnalis is a high-molecular-mass copper-containing oxygen-transport protein, which occurs freely dissolved in the hemolymph. It is a glycoprotein containing fucose, xylose, 3-O-methylmannose, 3-O-methylgalactose, mannose, galactose, N-acetylgalactosamine and N-acetylglucosamine residues as sugar constituents. The N-glycosidic carbohydrate chains of this glycoprotein were released by hydrazinolysis of a pronase digest and subsequently fractionated as oligosaccharide-alditols on Bio-Gel P-4 followed by Lichrosorb-NH2. Investigation with 500-MHz 1H-NMR spectroscopy, in conjunction with sugar and methylation analysis revealed the lowest-molecular-mass glycan chain to have the structure: (Formula: see text).

Primary structure of the neutral carbohydrate chains of hemocyanin from Panulirus interruptus

The N-glycosidic carbohydrate chains of Panulirus interruptus hemocyanin, consisting of only mannose and N-acetylglucosamine residues, were liberated by hydrazinolysis of a pronase digest of the purified glycoprotein. The carbohydrate chains were fractionated by high-voltage paper electrophoresis, yielding mainly neutral oligosaccharide-alditols. These were further separated by high-performance liquid chromatography and characterized by 500-MHz 1H-NMR spectroscopy as (formula; see text).

Isolation and characterization of a wheat germ agglutinin-binding glycoprotein from B16 mouse melanoma cells

Cells of B16 mouse melanoma grown in serum-free medium in the presence of [3H]glucosamine secreted or shed labeled glycoproteins. A wheat germ agglutinin-binding glycoprotein was isolated that accounted for 37% of the total [3H]glucosamine incorporated; it had a molecular weight of approximately 50,000 and was absent in less-tumorgenic wheat germ agglutinin (isolectin I)-resistant variants of the cells. The glycoprotein contained approximately 25% of serine and threonine plus equimolar amounts of glucosamine and galactosamine, indicating both N- and O-linked oligosaccharide chains. Neuraminidase treatment released approximately 60% of the glycoprotein's 3H radioactivity as N-acetylneuraminic acid. The sialoglycoprotein did not, but the desialylated species did, bind (97%) to ricin-Sepharose, suggesting the presence of terminal sialic acid and penultimate galactose residues in most of the saccharide units. Alkaline borohydride released 61% of the glycoprotein's radioactivity as oligosaccharide alcohols that were mainly tetrasaccharides (75%) with some branched trisaccharides (10%) from the O-linked structures. Hydrazinolysis and analysis of the alkaline borohydride-resistant portion of the glycoprotein indicated the presence of mainly triantennary, complex-type structures (N-linked) containing three sialic acids residues plus L-fucose. Serial lectin-affinity chromatography of the hydrazine-released saccharides with concanavalin A-agarose, pea lectin-agarose, L-PHA-agarose, and E-PHA-agarose, indicated the absence of high-mannose or hybrid-type structures and further confirmed the presence of triantennary, complex-type units.

Purification of oligosaccharides having a free reducing-end from glycopeptide sources

A hydrazinolysis-N-reacetylation procedure, modified by the inclusion of a mild acid-hydrolysis step after N-acetylation, was used to prepare, in overall yields of 60-70%, pure oligosaccharides containing a reducing D-GlcNAc residue from glycopeptide sources. Three types of asparagine-linked glycopeptides were treated: a high-mannose type, a complex-type not containing sialic acid, and a complex-type containing sialic acid, linked both alpha-(2----3) and alpha-(2----6) to beta-D-Galp residues. After the hydrazinolysis-N-reacetylation procedure, there was often contamination of the reducing oligosaccharides with glycopeptide that remained intact through the procedure, as well as minor oligosaccharide products, altered in the nature of the residue at the reducing end. Oligosaccharides having a reducing D-GlcNAc residue were purified by standard liquid chromatography and high-pressure liquid chromatography (l.c.) 360-MHz 1H-n.m.r. was valuable in establishing common structural reporter signals which enabled major products to be identified at stages during the production of free reducing oligosaccharides, and their purity to be assessed.

Structures of the asparagine-linked sugar chains of laminin

This investigation describes the isolation and characterization of oligosaccharides of the basement membrane glycoprotein, laminin. Pronase-released glycopeptides of isolated laminin, from a mouse Engelbreth-Holm-Swarm tumor, were fractionated using a combination of gel permeation chromatography and Con A-Sepharose affinity chromatography. The glycopeptides were analyzed for sugar linkage patterns by methylation analysis. Glycopeptides and hydrazine-released oligosaccharides were further analyzed using endo-beta-galactosidase, endo-beta-N-acetylglucosaminidase H and specific exoglycosidases in conjunction with calibrated gel permeation chromatography. Based on these experiments, murine tumor laminin was shown to contain asparagine-linked oligosaccharides with the following structures: bi-, tri- and tetraantennary complex-type oligosaccharides; polylactosaminyl side chains containing Gal(beta 1----4)GlcNAc(beta 1----3) repeating units attached to the trimannose core portion of the bi-, tri- and tetraantennary complex-type oligosaccharides; unusual complex-type oligosaccharides terminated at the nonreducing end with sialic acid, alpha-galactose, beta-galactose and beta-N-acetylglucosamine; alpha-galactosyl residues linked to N-acetyllactosamine sequences; high-mannose-type oligosaccharides. These results, in conjunction with analytical data, indicate that most of the carbohydrate of this laminin is N-linked to asparagine and that there are about 43 such N-linked oligosaccharides per laminin molecule.

Structure identification of the complex-type, asparagine-linked sugar chains of beta-D-galactosyl-transferase purified from human milk

The asparagine-linked sugar chains of human milk galactosyltransferase were quantitatively released as oligosaccharides from the polypeptide backbone by hydrazinolysis. They were converted into radioactive oligosaccharides by sodium borotritiate reduction after N-acetylation, and fractionated by paper electrophoresis and by Bio-Gel P-4 column chromatography after sialidase treatment. Structural studies of each oligosaccharides by sequential exoglycosidase digestion and methylation analysis indicated that the galactosyltransferase contains bi, tri-, and probably tetra-antennary, complex-type oligosaccharides having alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-beta-D- GlcpNac-(1----4)-alpha-L-[Fucp-(1----6)]-D-GlcNAc as their common core. Variation is produced by the different locations and numbers of the five different outer chains: beta-D-Galp-(1----4)-D-GlcNAc, alpha-L-Fucp-(1----3)-[beta-D-Galp-(1----4)]-D-GlcNAc, alpha-NeuAc-(2----6)-beta-D-Galp-(1----4)-D-GlcNAc, alpha-L-Fucp-(1----3)-[beta-D-Galp-(1----4)]-beta-D-GlcpNAc-(1---- 3)-beta- D-Galp-(1----4)-[alpha-L-Fucp-(1----3)]-D-GlcNAc, and alpha-NeuAc-(2----6)-beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-beta-D - Galp-(1----4)-[alpha-L-Fucp-(1----3)]-beta-D-GlcNAc.

Identification of a alpha-NeuAc-(2----3)-beta-D-galactopyranosyl N-acetyl-beta-D-galactosaminyltransferase in human kidney

Microsomal preparations from human kidney were found to contain enzymic activity capable to transfer N-acetylgalactosamine from UDP-N-acetylgalactosamine to native bovine fetuin. The acceptor structures on the fetuin molecules were identified as N- as well as O-linked glycans with a markedly higher incorporation into the N-linked carbohydrate chains. Analysis of the alkali-labile transferase products by thin-layer chromatography indicated that the enzyme is able to synthesize structures having mobilities identical with those found on glycophorin from Cad erythrocytes. Mild acid treatment and enzymic hydrolysis with N-acetylhexosaminidase from jack beans of the N-linked transferase products suggested that beta-D-GalpNAc-(1----4)-[alpha-NeuAc-(2----3)]-beta-D-Galp-(1----s tructures were formed by the enzymic reaction on both N- and O-linked acceptors. The enzyme might, therefore, be involved in the biosynthesis of Sda (and Cad) antigenic structures. By use of various oligosaccharides, glycopeptides, and glycolipids having well characterized carbohydrate sequences, the acceptor-substrate specificity of the N-acetylgalactosaminyltransferase was determined. The enzyme generally recognized alpha-NeuAc-(2----3)-beta-D-Gal groups as acceptors, but in a certain conformation. Thus, tri- and tetra-saccharide alditols, native human glycophorin A, and GM3 were not acceptor substrates although they carry the potential disaccharide acceptor unit. When these structures were presented as sialyl-(2----3)-lactose or as a tryptic peptide from glycophorin A, they were shown to be rather good acceptor substrates for the N-acetyl-beta-D-galactosaminyltransferase from human kidney.

A brain sialyltransferase having a narrow specificity for O-glycosyl-linked oligosaccharide chains

The existence of a brain sialyltransferase catalyzing the specific transfer of NeuAc on native fetuin was demonstrated. This enzyme was not able to sialylate either asialofetuin or desialylated and nondesialylated orosomucoid, transferrin, and bovine submaxillary mucin. It required the presence of Mn2+ for optimal activity. Moreover, in fetuin, this activity was closely related to the proportion of NeuAc residues, but in liver tissue sialylation occurred only onto asialofetuin. In native fetuin, sialylation took place on O-glycan chains to give an O-disialyltetrasaccharidic structure. The Gal----GalNAc----protein was not an acceptor, but alpha-NeuAc-(2----3)-Gal----GalNAc----protein was, suggesting a specific transfer alpha-(2----6) to the GalNAc residue.

Structural studies of the carbohydrate chains of human gamma-interferon

Human gamma-interferon (IFN-gamma) was prepared biotechnologically using Chinese hamster ovary cells. These cells were shown to be able to produce glycosylated IFN-gamma. Sugar analysis revealed the presence of Man, Gal, GlcNAc, NeuAc and Fuc residues in a molar ratio of 3.8:2.0:3.5:0.6:0.4 suggesting the occurrence of N-glycosidically linked N-acetyllactosamine type of carbohydrate chains. For structure determination of these chains, the glycoprotein was subjected to the hydrazinolysis procedure, yielding oligosaccharide-alditols. The latter compounds were analysed by 500-MHz 1H-NMR spectroscopy. The carbohydrate material was found to consist of biantennary structures, exhibiting microheterogeneity as to the terminal sialic acids and the core Fuc residue: (Formula: see text). As similar carbohydrates are present on several human secreted proteins, this glycosyl group is not expected to be immunogenic in man. It remains to be established to what extent the carbohydrate chains of this biotechnologically produced IFN-gamma are identical to those of naturally occurring human IFN-gamma.

Hydrazinolysis-N-reacetylation of glycopeptides and glycoproteins. Model studies using 2-acetamido-1-N-(L-aspart-4-oyl)-2-deoxy-beta-D-glucopyranosy lamine

2-Acetamido-1-N-(L-aspart-4-oyl)-2-deoxy-beta-D-glucopyranosyla mine (1) was used as a model glycopeptide to study the hydrazinolysis-N-reacetylation procedure. The major, initial product was the beta-acetohydrazide derivative of 2-acetamido-2-deoxy-D-glucose (2) which gave 2-acetamido-2-deoxy-D-glucose (5) after exposure to acidic conditions. Very mild conditions of hydrolysis of 2 gave a 75-80% overall yield of 5 from 1 after the hydrazinolysis-N-reacetylation procedure. Several other minor compounds were detected which were not converted into 5 upon mild acid hydrolysis, indicating that 20-25% of product cannot be recovered as 5 at the reducing end of oligosaccharides.