Gas-Liquid Chromatography and Mass Spectrometry of Sialic Acids. In: Schauer R, editor. Sialic Acids. Vienna: Springer; 1982. pp. 95-125. [DOI: 10.1007/978-3-7091-8680-0_6]

Systematic Optimisation of Microtiter Plate Lectin Assay to Improve Sialic Acid Linkage Detection

AIMS

We aimed to develop a high-throughput lectin assay with minimized background signals to investigate the interactions of lectins and sialic acid glycans, focusing on prostate-specific antigen (PSA).

BACKGROUND

High background signals resulting from nonspecific binding are a significant concern for microtiter plate-based enzyme-linked lectin sorbent assays (ELLSAs), as they can mask specific binding signals and cause false-positive results.

METHODS

In this study, we constructed an ELLSA based on different washing step parameters, including the number of washing cycles, NaCl and Tween-20 concentrations, and the type of blocking agent and evaluated the effects on both specific and nonspecific binding signals. Furthermore, we performed a PSA binding assay using the optimized ELLSA.

RESULTS

The optimal washing parameters based on the highest specific binding signal proposed four cycles of washing steps using a washing buffer containing a high salt concentration (0.5 M NaCl) and mild detergent (0.05% Tween-20). The utilization of the optimized washing parameters in this assay was shown to be sufficient to obtain the optimal binding signals without the use of any blocking agent. Binding assays performed using the optimized ELLSA revealed that the glycan of the PSA sample used in this study mainly consists of terminal α2,6-linked sialic acid, as strongly recognized by Sambucus nigra agglutinin (SNA) with a KD value of 12.38 nM.

CONCLUSION

The ELLSA reported in this study provides a simple yet sensitive assay for sialic acid linkage recognition.

Serum sialylation changes in cancer

Cancer is a major cause of death in both developing and developed countries. Early detection and efficient therapy can greatly enhance survival. Aberrant glycosylation has been recognized to be one of the hallmarks of cancer as glycans participate in many cancer-associated events. Cancer-associated glycosylation changes often involve sialic acids which play important roles in cell-cell interaction, recognition and immunological response. This review aims at giving a comprehensive overview of the literature on changes of sialylation in serum of cancer patients. Furthermore, the methods available to measure serum and plasma sialic acids as well as possible underlying biochemical mechanisms involved in the serum sialylation changes are surveyed. In general, total serum sialylation levels appear to be increased with various malignancies and show a potential for clinical applications, especially for disease monitoring and prognosis. In addition to overall sialic acid levels and the amount of sialic acid per total protein, glycoprofiling of specific cancer-associated glycoproteins, acute phase proteins and immunoglobulins in serum as well as the measurements of sialylation-related enzymes such as sialidases and sialyltransferases have been reported for early detection of cancer, assessing cancer progression and improving prognosis of cancer patients. Moreover, sialic-acid containing glycan antigens such as CA19-9, sialyl Lewis X and sialyl Tn on serum proteins have also displayed their value in cancer diagnosis and management whereby increased levels of these factors positively correlated with metastasis or poor prognosis.

Strategies for analysis of glycoprotein glycosylation

Glycoproteins are known to exhibit multiple biological functions. In order to assign distinct functional properties to defined structural features, detailed information on the respective carbohydrate moieties is required. Chemical and biochemical analyses, however, are often impeded by the small amounts of sample available and the vast structural heterogeneity of these glycans, thus necessitating highly sensitive and efficient methods for detection, separation and structural investigation. The aim of this article is to briefly review suitable strategies for characterization of glycosylation at the levels of intact proteins, glycopeptides and free oligosaccharides. Furthermore, methods commonly used for isolation, fractionation and carbohydrate structure analysis of liberated glycoprotein glycans are discussed in the context of potential applications in glycoproteomics.

O-acetylation and de-O-acetylation of sialic acids in human colorectal carcinoma

A decrease in the level of O-acetylated sialic acids observed in colorectal carcinoma may lead to an increase in the expression of sialyl Lewis(X), a tumor-associated antigen, which is related to progression of colorectal cancer to metastasis. The underlying mechanism for this reduction is, however, not fully understood. Two enzymes are thought to be primarily responsible for the turnover of O-acetyl ester groups on sialic acids; sialate-O-acetyltransferase (OAT) and sialate-O-acetylesterase (OAE). We have previously reported the characterization of OAT activity from normal colon mucosa, which efficiently O-acetylates CMP-Neu5Ac exclusively in the Golgi apparatus prior to the action of sialyltransferase. In this report we describe the identification of a lysosomal and a cytosolic OAE activity in human colonic mucosa that specifically hydrolyses 9-O-acetyl groups on sialic acid. Utilizing matched resection margin and cancer tissue from colorectal carcinoma patients we provide strong evidence suggesting that the level of O-acetylated sialic acids present in normal and diseased human colon may be dependent on the relative activities of OAT to lysosomal OAE. Furthermore, we show that the level of free cytosolic Neu5,9Ac2 in human colon is regulated by the relative activity of the cytosolic OAE.

In vitro synthesis and properties of pectin/Acetobacter xylinus cellulose composites

Pectin and cellulose are major components of most primary cell walls, yet little is known about the way in which they interact either during assembly or in subsequent functional performance of the wall. As a mimic of cell wall assembly, we studied the formation of molecular composites formed by deposition of cellulose from Acetobacter xylinus into pectin/calcium systems, and the molecular, architectural and mechanical properties of the composites obtained. The formation of interpenetrating cellulose/pectin composite networks (as envisaged in current models for primary cell walls) required a pre-existing, but not too strong, pectin network. For pectin either in solution or strongly networked, phase separation from cellulose occurred, providing two physical models for the formation of middle lamellae. Composite networks showed no evidence of direct molecular interaction between the components, but pectin networks became more aggregated following deposition of cellulose into them. The shear strength under small deformation conditions for cellulose/pectin composites was very similar to that of cellulose alone. In contrast, under uniaxial tension, extensibility was greatly increased and stiffness decreased. These major changes were due to the effect of pectin on cellulose network architecture at deposition, as they were maintained upon removal of the pectin component. These results show that the presence and physical state of pectin at the time of cellulose deposition in muro may be a significant determinant of subsequent extensibility without compromising strength.

A novel disorder of N-glycosylation due to phosphomannose isomerase deficiency

Three siblings suffered from an unusual disorder of cyclic vomiting and congenital hepatic fibrosis. Serum transferrin isoelectric focusing showed increased asialo- and disialotransferrin isoforms as seen in the carbohydrate-deficient glycoprotein (CDG) syndrome type I. Phosphomannomutase, which is deficient in most patients with type I CDG syndrome, was found to be normal in all three patients. Structural analysis of serum transferrin revealed nonglycosylated, hypoglycosylated, and normoglycosylated transferrin molecules. These findings suggested a defect in the early glycosylation pathway. Phosphomannose isomerase was found to be deficient and the defect was present in leucocytes, fibroblasts, and liver tissue. Phosphomannose isomerase deficiency appears to be a novel glycosylation disorder, which is biochemically indistinguishable from CDG syndrome type I. However, the clinical presentation is entirely different.

1H- and 13C-NMR characterization of the digalactosylmannopentaose liberated from legume seed galactomannan by beta-mannanase action

Incubation of Locust bean gum with an Aspergillus niger beta-D-mannanase released a wide variety of galactomannan oligomers. A single heptasaccharide, digalactosylmannopentaose, was obtained from fractionation of the mixture by size exclusion chromatography. The purity and chemical composition of the sample was demonstrated using mass spectrometry, high performance anion-exchange chromatography and monosaccharide composition analysis. The primary structure of this heptasaccharide was unambiguously identified using 2D 1H and 13C homonuclear and heteronuclear NMR. A complete assignment of the 1H and 13C signals of this oligomer was achieved, producing an NMR dataset that will be of importance in the primary structure elucidation of larger and more complex galactomannan oligomers.

Occurrence of N-acetyl- and N-O-diacetyl-neuraminic acid derivatives in wild and mutant Crithidia fasciculata

The cell-surface expression of sialic acids in wild-type Crithidia fasciculata and three drug-resistant mutants (FU(R)11, TR3, and TFRR1) was analyzed using fluorescein-labeled Limulus polyphemus agglutinin (LPA) binding, glycosidase of known sugar specificity, and thin-layer chromatography (TLC). Gas-liquid chromatography-mass spectrometry (GC-MS) analysis using both electron-impact (EI-MS) and chemical ionization (CI-MS) by isobutane with selected ion monitoring (SIM) was also used. The surface location of sialic acid was inferred from LPA binding to whole cells abrogated by previous treatment with neuraminidase. An exception occurred with the TFRR1 strain, which after incubation with neuraminidase showed increased reactivity with the fluorescent lectin. Both N-acetyl- and N-O-diacetyl-neuraminic acids were identified in the flagellates by TLC, with a clear predominance being noted for the former derivative. However, the content of N-O-diacetyl-neuraminic acid was preferentially found in the TFRR1 strain. The GC-MS analysis of the acidic component of the TFRR1 mutant strain confirmed the occurrence of N-acetyl-neuraminic acid (Neu5Ac) by the presence of the diagnostic ions (m/z values: 684 and 594 for CI-MS and 478, 298, and 317 for EI-MS) and also by comparison with the standard Neu5Ac retention time. GC-MS analysis also showed fragments (m/z values: 654 and 564 for CI-MS and 594, 478, 298, and 317 for EI-MS) expected for the 7-O- and 9-O-acetyl-N-acetyl-neuraminic acids (Neu5,7Ac2 and Neu 5,9Ac2, respectively).

Primary structure of the major glycan from human seminal transferrin

Human seminal transferrin (HSmT) is an iron-containing glycoprotein whose structural properties have not been adequately investigated. The carbohydrate content of the purified glycoprotein amount to 6.1%, and monosaccharide analysis revealed the major oligosaccharide moiety to be of the N-glycoside type. The carbohydrate chains were released from the iron-free form by digestion with peptide N-glycosidase F (PNGase F) in the presence of detergents such as SDS and beta-octylglucoside. After ethanol precipitation and fractionation on Bio-Gel P-6 and Bio-Gel P-2, the oligosaccharide was further purified on Mono-Q and desalted on Bio-Gel P-2. By 600-MHz 1H-NMR spectroscopy, the primary structure of the major N-linked oligosaccharide component was established to be: [formula: see text]

Primary structure of hemocyanin subunit c from Panulirus interruptus

The amino acid sequence of the hemocyanin subunit c from the spiny lobster, Panulirus interruptus, has been determined. The elucidation was mainly based on three digests, with CNBr, trypsin and endoproteinase Glu-C, respectively. Additional evidence was obtained by sequencing of peptides from an endoproteinase Lys-C digest. Subunit c is a polypeptide with 661 amino acid residues and with a carbohydrate group attached to residue 476 in the third domain. No heterogeneity was observed. The degree of identity with subunit a is 59%. Some differences with subunit a are an N-terminal extension of six residues, a one-residue C-terminal extension, and a three-residue deletion. Furthermore, carbohydrate attachment is in a different position, as are most half-cystine residues. Limited trypsinolysis resulted in cleavage at the same site as in subunits a and b.

Structural analysis of a novel sialic-acid-containing trisaccharide from Rhodobacter capsulatus 37b4 lipopolysaccharide

Sialic-acid-containing lipopolysaccharides from Rhodobacter capsulatus 37b4 (S-form lipopolysaccharide), KB-1 (R-type lipopolysaccharide) and Sp 18 (deep R-type lipopolysaccharide) were investigated for the linkage and substitution of sialic acids. Methylation analysis and behaviour towards acid and enzymic hydrolysis indicated a non-reducing terminal location of sialic acids in the R-type lipopolysaccharide of strain Sp 18, whereas an internal, chain-linked location of sialic acids was found in the lipopolysaccharides of strains 37b4 and KB-1. For these latter strains, methylation analysis revealed a substitution of sialic acids by other sugars at position 7 for strain 37b4 and positions 4 and 7 for strain KB-1. In accordance with the chain-linked position of sialic acids, mild hydrolysis of R. capsulatus 37b4 lipopolysaccharide with acetic acid released a trisaccharide with sialic acid at the reducing terminus. Structural investigation of this trisaccharide by methylation analysis, 1H- and 13C-NMR spectroscopy revealed the presence of the disaccharide Gal1-6Glc at the non-reducing end, probably with an alpha-anomeric configuration of the galactose residue, i.e. melibiose, beta-glycosidically linked to position 7 of sialic acid. Therefore the structure Gal alpha 1-6Glc beta 1-7Neu5Ac is proposed for this core oligosaccharide from R. capsulatus 37b4 lipopolysaccharide.

1H-N.m.r. study of enzymically generated wheat-endosperm arabinoxylan oligosaccharides: structures of hepta- to tetradeca-saccharides containing two or three branched xylose residues

The structures of hepta- to tetradeca-saccharides, generated by digestion of wheat-endosperm arabinoxylan with endo-(1----4)-beta-D-xylanase, and isolated by gel-permeation chromatography on Bio-Gel P-6 and high-performance anion-exchange chromatography with pulsed amperometric detection (h.p.a.e.-p.a.d.), were elucidated using monosaccharide and methylation analysis, f.a.b.-m.s., and 1H-n.m.r. spectroscopy. The structures identified had two branching elements, ----4)[alpha-L-Araf-(1----3)]-beta-D-Xylp-(1---- and/or ----4) [alpha-L-Araf-(1----2)][alpha-L-Araf-(1----3)]-beta-D-Xyl p-(1----, directly connected to each other in all four possible combinations. The h.p.a.e.-p.a.d. elution pattern showed that these combinations are not present in equal amounts. Also, compounds containing two 2,3-branched beta-D-Xylp residues separated by one or two unbranched beta-D-Xylp residues were found, and the presence of a tetradecasaccharide containing three 2,3-branched beta-D-Xylp residues was established.

Characterisation by 1H-n.m.r. spectroscopy of oligosaccharides, derived from arabinoxylans of white endosperm of wheat, that contain the elements ----4)[alpha-L-Araf-(1----3)]-beta-D-Xylp-(1---- or ----4)[alpha- L-Araf-(1----2)][alpha-L-Araf-(1----3)]-beta-D-Xylp-(1----

The structure of penta- to hepta-saccharides, generated by digestion of purified wheat-endosperm arabinoxylan with endo-(1----4)-beta-D-xylanase and isolated by gel-permeation chromatography on Bio-Gel P-6 followed by high-performance anion-exchange chromatography with pulsed amperometric detection, was established using monosaccharide and methylation analysis, f.a.b.-m.s., and 1H-n.m.r. spectroscopy. The oligosaccharides had a core of (1----4)-linked beta-D-xylopyranosyl residues 3- or 2,3-substituted with single alpha-L-arabinofuranosyl groups, and gave 1H-n.m.r. spectra typical for each type.

A comparative study of sialyloligosaccharides isolated from sialidosis and galactosialidosis urine

Sialic acid-containing carbohydrates were isolated from sialidosis urine by a combination of gel-filtration on Bio-Gel P-6 and medium-pressure anion-exchange chromatography on Mono Q. The Mono Q fractions were subjected to 500-MHz 1H-NMR spectroscopy, sugar analysis and analytical HPLC on Lichrosorb-NH2. These methods indicated the presence of various N-acetyllactosamine type sialyloligosaccharides differing from each other in branching pattern and sialic acid linkage types. Among the structures were fully and partially sialylated mono-, di-, tri- and tetra-antennary compounds. A comparison with the results from galactosialidosis urine indicated that essentially the same carbohydrates were present in both urines, but that the relative amounts of the various sialyloligosaccharides differ to some extent. Sialidosis urinary oligosaccharides contained relatively more alpha 2-6 linked sialic acid than oligosaccharides from galactosialidosis urine. It could be concluded that the additional beta-galactosidase deficiency in galactosialidosis did not influence the nature of the excreted material and that the sialidase deficiency determined completely the defective catabolism of glycoproteins in both sialidosis and galactosialidosis.

Conformational studies on the N-linked carbohydrate chain of bromelain

1H- and 13C-NMR assignments for the carbohydrate part of the glycopeptide alpha-D-Man-(1----6)-[beta-D-Xyl-(1----2)]-beta-D-Man-(1----4)-beta-D- GlcNAc-(1----4)-[alpha-L-Fuc-(1----3)]-beta-D-GlcNAc-(1----N)-Asn approximately, derived from the proteolytic enzyme bromelain (EC 3.4.22.4), have been obtained using homo- and heteronuclear correlation spectroscopy, two-dimensional homonuclear Hartmann-Hahn and nuclear Overhauser enhancement experiments. A conformational model for the carbohydrate chain, deduced from the NMR data and consistent with hard-sphere exo-anomeric calculations shows that the rotamer population about the C-5--C-6 bond of beta-Man is restricted to the P omega = 180 rotamer, mainly.

Structure determination of the major N- and O-linked carbohydrate chains of the beta subunit from equine chorionic gonadotropin

The carbohydrate moieties of equine chorionic gonadotropin alpha and beta subunits were released from the protein backbones by successive treatments with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F and alkaline borohydride and then fractionated by FPLC and HPLC. The major N- and O-linked glycans of the beta subunit were characterized by 500-MHz 1H-NMR spectroscopy, showing a remarkable structural heterogeneity for the N-glycosidically linked chains, comprising mono-, di-, tri- and tri'-antennary N-acetyllactosamine type of glycans, being partly alpha 1-6 fucosylated at the Asn-bound GlcNAc residue and having alpha 2-6 and alpha 2-3 linked N-acetyl- and N-acetyl-4-O-acetylneuraminic acid residues as sialic acid constituents. Significant differences in this respect were detected for the partially characterized glycans of the alpha subunit. The major part of the O-linked carbohydrate chains, occurring solely in the beta subunit, is formed by tri-, tetra-, penta- and hexa-saccharides. There are indications for the presence of oligo(N-acetyllactosamine) units in both the N- and O-linked glycans of the beta subunit.

Accumulation of mannosyl-beta(1----4)-N-acetylglucosamine in fibroblasts and leukocytes of patients with a deficiency of beta-mannosidase

Cultured fibroblasts from two brothers with beta-mannosidosis were shown to accumulate the disaccharide mannosyl-beta(1----4)-N-acetylglucosamine in amounts of 52 and 68 nmol/mg protein. Structural identification of the Man beta(1----4)GlcNAc, isolated by HPLC, was performed by 500-MHz 1H-NMR spectroscopy and sugar composition analysis. Control fibroblasts did not contain a detectable amount of Man beta(1----4)GlcNAc. The disaccharide was also present in leukocytes from these patients, but not in controls, as could be demonstrated by thin-layer chromatography and sugar composition analysis. However, the amounts in leukocytes (5 and 6 nmol/mg protein) were much smaller than those in fibroblasts.

Structure and properties of a Cephalosporium acremonium alpha-galactosidase

The amino acid and sugar composition of the enzyme protein, the effect of urea, sodium dodecyl sulphate and Concanavalin A on the purified alpha-galactosidase (EC 3.2.1.22) from the mold Cephalosporium acremonium has been studied. The results obtained by gas liquid chromatography indicated the presence of N-acetylglucosamine, mannose, galactose and N-acetylneuramic acid in the molar proportions 2:7:3:11. The presence of two types of Asn-linked oligosaccharide structures in the enzyme molecule is assumed. The alpha-galactosidase liberates alpha(1-3), alpha(1-4) and alpha(1-6)-linked D-galactose units from various synthetic and natural substrates which have been tested. The effects of pH, substrate concentration and temperature on the catalytic activity of the enzyme are described. The purified alpha-galactosidase also exhibited a lectin activity with an affinity towards glucose, and to some extent mannose.

Isolation and structural studies of phosphate-containing oligosaccharides from alkaline and acid hydrolysates of Streptococcus pneumoniae type 6B capsular polysaccharide

The capsular polysaccharide of Streptococcus pneumoniae serotype 6B [----2)-alpha-D-Galp-(1----3)-alpha-D-Glcp-(1----3)-alpha-L-Rhap-( 1----4)- D-RibOH-(5-P----]n was depolymerised under alkaline (NaOH) and acidic (HF) conditions. The former treatment yielded, as the major component, alpha-2-P-Galp-(1----3)-alpha-Glcp-(1----3)-alpha-Rhap-(1----4)-5- P-RibOH. The latter treatment at -16 degrees gave alpha-Galp-(1----3)-alpha-Glcp-(1----3)-alpha-Rhap-(1----4)-Rib OH-(5-P----2)- alpha-Galp-(1----3)-alpha-Glcp-(1----3)-alpha-Rhap-(1----4)-Rib OH and at 4 degrees gave alpha-Galp-(1----3)-alpha-Glcp-(1----3)-alpha-Rhap-(1----4)-Rib OH. These oligosaccharides were characterised by sugar analysis, f.a.b.-m.s., and 1H- and 13C-n.m.r. spectroscopy.

G.L.C.-M.S. of N-(1-deoxyalditol-1-yl)octadecylamine derivatives in the analysis of methanolysates of neoglycolipids obtained by reductive amination

Hydrophobic conjugates of a series of aldoses have been prepared by reductive amination with octadecylamine and sodium cyanoborohydride, as model compounds for the analysis of reductively aminated oligosaccharides derived from capsular polysaccharides of Streptococcus pneumoniae. In the context of the methanolysis procedure for sugar analysis, g.l.c. and g.l.c.-m.s. (e.i.-mode) studies were carried out on the N-(1-deoxyalditol-1-yl)octadecylamine derivatives obtained after treatment with methanolic HCl, and subsequent N-acetylation and trimethylsilylation.

Analysis of N-acetyl-4-O-acetylneuraminic-acid-containing N-linked carbohydrate chains released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Application to the structure determination of the carbohydrate chains of equine fibrinogen

The carbohydrate chains of equine fibrinogen were enzymatically released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. The oligosaccharides obtained were fractionated by a combination of FPLC and HPLC and analyzed by 500-MHz 1H-NMR spectroscopy. Four monosialo and four disialo diantennary N-acetyllactosamine type of carbohydrate chains occur: (formula; see text)

A detailed study of the periodate oxidation of sialic acids in glycoproteins

Periodate oxidation of terminal N-acetyl- and N-glycoloylneuraminic acid residues in the mucins from edible bird nest substance and pig submandibular gland, respectively, can be carried out under conditions which exclusively give rise to the formation of the C-7 analogues of these sialic acids. In contrast, the C-8 compounds can be obtained in a maximum yield of about 40%. Under identical conditions, N-glycoloylneuraminic acid is oxidized about 1.5 times faster than the N-acetylated derivative. After release of the sialic acids by acid hydrolysis, the characterization of the oxidation products was carried out by TLC, by GLC and GLC-MS of the corresponding pertrimethylsilyl derivatives, and by 500-MHz 1H-NMR spectroscopy. In addition, molar response factors for GLC analysis and extinction coefficients in the orcinol/Fe3+/HCl assay were determined.

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.

Phosphoenolpyruvate-dependent flavinylation of 6-hydroxy-D-nicotine oxidase

The reaction leading to the flavinylation of apo-6-hydroxy-D-nicotine oxidase was investigated in cell-free extracts of Eschericia coli carrying the 6-hydroxy-D-nicotine oxidase (6-HDNO) gene on the expression plasmid pDB222. It was demonstrated that the reaction required phosphoenolpyruvate (P-pyruvate) in addition to FAD. When [32P]P-pyruvate or [14C]P-pyruvate were used in the reaction with apo-6-HDNO, no phosphorylated or pyruvylated apo-protein could be detected, however. In order to drive the reaction to completion, FAD and P-pyruvate had to be present simultaneously in the reaction mixture. When apo-6-HDNO, highly purified by affinity chromatography, was used in the reaction with P-pyruvate and FAD, no additional protein fraction was required. A possible reaction scheme for the formation of holoenzyme from 6-HDNO is discussed.

A comparative study of the accumulated sialic acid-containing oligosaccharides from cultured human galactosialidosis and sialidosis fibroblasts

Sialic acid-containing storage material was isolated from cultured human galactosialidosis fibroblasts, by a combination of gel filtration and anion-exchange chromatography on Mono Q. The obtained sialyloligosaccharides were analyzed by 500-MHz 1H-NMR spectroscopy in combination with sugar analysis and analytical HPLC. The storage material consisted of a series of completely sialylated N-acetyl-lactosamine type of structures having Man beta 1-4GlcNAc at the reducing terminus in common, similar to those recently reported for human sialidosis fibroblasts. Comparison of the storage material from both sources revealed only differences in their relative amounts. In control fibroblasts these compounds could not be detected. The nature of the accumulated compounds is in accordance with the alpha-neuraminidase deficiency in both genetic diseases. The additional deficiency of beta-galactosidase in case of galactosialidosis is not reflected in the storage material.

Structural analysis of O-glycosidic type of sialyloligosaccharide-alditols derived from urinary glycopeptides of a sialidosis patient

Sialidosis urine was fractionated by gel filtration on Bio-Gel P-6. All pooled fractions containing carbohydrates showed the presence of small amounts of GalNAc in non-reducing position, besides free N-acetyllactosamine type of oligosaccharides as major constituents. The fractions were subjected to reductive alkaline borohydride degradation, after which the major part of GalNAc was recovered as N-acetyl-D-galactosaminitol (GalNAc-ol). The GalNAc-ol-containing material was separated from the N-glycosidic oligosaccharides by a second gel-filtration step on AcA 202. Subsequently, the O-glycosidic sialyloligosaccharide-alditols were subfractionated by anion-exchange chromatography on Mono Q. Structural analysis by 500-MHz 1H-NMR spectroscopy revealed two major components in all fractions, namely: NeuAc alpha 2-3Gal beta 1-3GalNAc-ol and NeuAc alpha 2-3Gal beta 1-3[NeuAc alpha 2-6]GalNAc-ol. Furthermore, NeuAc alpha 2-3Gal beta 1-3[NeuAc alpha 2-3Gal beta 1-4GlcNAc beta 1-6]GalNAc-ol was found as a minor component in some of the fractions. The presence of these carbohydrate chains in Bio-Gel fractions differing in molecular mass suggested that they are derived from glycopeptides which are heterogeneous in their peptide part.

Isolation and structural characterization of sialic acid-containing storage material from mucolipidosis I (sialidosis) fibroblasts

Sialic acid-containing storage material was isolated from cultured human mucolipidosis I (sialidosis) fibroblasts by gel permeation chromatography on Bio-Gel P-6 followed by medium-pressure anion-exchange chromatography on Mono Q. The structure determination of the isolated sialyloligosaccharides was carried out by 500-MHz 1H-NMR spectroscopy in conjunction with sugar analysis and analytical HPLC. The storage material showed completely sialylated mono-, di- and triantennary N-glycosidic N-acetyllactosamine oligosaccharides having the Man beta 1----4GlcNAc sequence at the reducing end in common. Heterogeneity occurred with respect to the linkages between terminal sialic acid and the penultimate galactose residues (alpha 2----3/alpha 2----6). It turned out that all the identified carbohydrate chains are consistent with the neuraminidase deficiency.

The N- and O-linked carbohydrate chains of human, bovine and porcine plasminogen. Species specificity in relation to sialylation and fucosylation patterns

The structures of the N- and O-glycans of human, bovine and porcine plasminogen were determined by 500-MHz 1H-NMR spectroscopy. The N-glycans of all three species proved to be of the N-acetyllactosamine type differing from one another with respect to the sialylation and fucosylation patterns. In the N-glycan of human plasminogen the two antennae are sialylated with N-acetylneuraminic acid (NeuAc), whereas in the bovine counterpart both branches carry significant amounts of N-glycolylneuraminic acid (NeuGc). In porcine plasminogen the sialic acid is mainly NeuAc; the Man alpha 1----6 branch, however, is only partially sialylated. In addition, the porcine N-glycan is fucosylated to about 80% in alpha 1----6 linkage to the GlcNAc-1 residue. The O-glycans of the three species possess an identical Gal beta 1----3GalNAc core which is alpha 2----3 sialylated with NeuAc at Gal. The disialylated form, which is also present in all three species, has an additional NeuAc residue in alpha 2----6 linkage to GalNAc. Mono- and disialylated forms occur in different molar ratios in the different plasminogens: 80:20 in human, 70:30 in bovine and 50:50 in porcine. This study on the carbohydrate moiety of these three plasminogens reveals species specificity in terms of various types of microheterogeneities.

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.

Primary structure determination of seven novel N-linked carbohydrate chains derived from hemocyanin of Lymnaea stagnalis. 3-O-methyl-D-galactose and N-acetyl-D-galactosamine as constituents of xylose-containing N-linked oligosaccharides in an animal glycoprotein

Hemocyanin from the freshwater snail Lymnaea stagnalis is a high-molecular-mass copper-containing glyco-protein which functions as oxygen carrier in the hemolymph. To release the carbohydrate chains, the protein was digested by pronase followed by hydrazinolysis and reduction. The oligosaccharide-alditols were purified by gel permeation chromatography on Bio-Gel P-4, followed by HPLC on a Lichrosorb-NH2 column. Using 500-MHz 1H-NMR spectroscopy, in conjunction with sugar, methylation and deamination analysis, the following seven novel primary oligosaccharide structures could be unravelled. (Formula: see text).

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).

The glycoprotein Ib complex of human blood platelets

Human glycoprotein Ib (GPIb) is a major integral membrane protein on human blood platelets responsible for the initial attachment of platelets to the exposed vascular subendothelium. In this report we describe an isolation method for a 'GPIb complex' as well as for its individual components. A three-step procedure involving Triton X-114 phase-partition, affinity chromatography on wheat germ agglutinin and ion-exchange chromatography on DEAE-Sephacel yielded milligram quantities of purified GPIb complex. The single components of the complex were further purified by gel filtration on AcA34 in 0.1% sodium dodecyl sulfate. As well as GPIb, the complex contains GP17, actin-binding protein, actin and a series of unidentified proteins with different molecular masses. In contrast to GPIb alpha, which is very rich in O-linked oligosaccharides, sugar analysis revealed that GPIb beta and GP17 seem to have only N-linked chains of the lactosamine type. The C-terminal alpha-chain remnant, which probably spans the plasma membrane, was identified and isolated for the first time. Western blotting with polyclonal rabbit anti-GPIb antibodies and silver-staining of one- or two-dimensional dodecyl sulfate/polyacrylamide gels revealed that it has an apparent molecular mass of 20 kDa and is linked to GPIb beta by a disulfide bridge close to the membrane. The thrombin-binding site on GPIb is located near the N-terminus on a 40-kDa fragment of GPIb alpha. A disulfide bridge in the N-terminal region is not essential for thrombin binding to GPIb.

Migration of O-acetyl groups in N,O-acetylneuraminic acids

Highly purified N-acetyl-4-O-acetylneuraminic acid (Neu4,5Ac2), N-acetyl-7-O-acetylneuraminic acid (Neu5,7Ac2) and N-acetyl-7,9-di-O-acetylneuraminic acid (Neu5,7,9Ac3) were used to study spontaneous migrations of acetyl groups between hydroxyl groups. The techniques applied involved thin-layer chromatography, gas-liquid chromatography/mass spectrometry, high-performance liquid chromatography and 360-MHz 1H-NMR spectroscopy. It was found that at pH values at which no significant de-O-acetylation is observed: (a) Neu5,7Ac2 can easily be transformed into Neu5,9Ac2, (b) Neu5,7,9Ac3 yields an equilibrium of Neu5,7,9Ac3 and Neu5,8,9Ac3 in a molar ratio of approximately 1:1, and (c) Neu4,5Ac2 does not give rise to O-acetyl migrations. The importance of these findings is discussed in terms of the biosynthesis of O-acetylated sialic acids.

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).