Hydrazinolysis of asparagine-linked sugar chains to produce free oligosaccharides

Calcium ion-independent recognition of sialyl and nonsialyl N-acetyllactosamine and Le(x) structures by boar sperm

Recognition of defined carbohydrate structures by boar sperm was studied on the basis of oligosaccharide structures of porcine zona pellucida glycoproteins so far elucidated. Boar sperm abundantly adhered to fetuin-Sepharose beads, moderately to asialofetuin-Sepharose beads, but not at all to galactosidase (beta1-4-linkage-specific)-digested asialofetuin-Sepharose beads. The sperm also adhered to Le(x) oligosaccharide probe-coupled avidin-Sepharose beads. These adhesive activities were retained in the medium containing EDTA instead of calcium ion but abolished after induction of acrosome reaction by preincubation of sperm with calcium ionophore. Inhibition study of sperm adhesion to the beads by soluble ligands demonstrated that boar sperm express at least two kinds of carbohydrate recognition molecules, one recognizing both sialyl and nonsialyl N-acetyllactosamines but not the Le(x) structure and the other recognizing the Le(x) structure but not N-acetyllactosamines. Sperm binding to the zona pellucida on fixed porcine oocytes was inhibited by N-glycans of fetuin and their asialo form but not by the asialo, agalacto-N-glycans. Finally, dextran-based multivalent oligosaccharide polymers were prepared and their inhibitory activities in sperm-oocyte binding were examined. The result indicated that the polymer composed of fetuin N-glycans, its asialo-N-glycans, or lacto-N-fucopentaose III causes a remarkable inhibition at the oligosaccharide-based concentration of 50 microM. Thus, boar sperm are suggested to express multiple carbohydrate recognition molecules which may be involved in the sperm-egg interaction.

Microscale synthesis of dextran-based multivalent N-linked oligosaccharide probes

We developed a convenient method for the synthesis of dextran-based multivalent probes containing N-linked oligosaccharides which is efficient even in a small scale. Oligosaccharides were derivatized with succinic dihydrazide and dimethylamine borane under a mild acidic condition. The derivatized oligosaccharides were then conjugated in a good yield to periodate-oxidized dextran (500 kDa). Thus, the conjugates containing 120 to 140 oligosaccharide chains per dextran molecule were successfully synthesized. Their practical advantage was shown by the example that the asialofetuin oligosaccharide-dextran conjugate has much higher affinity to Ricinus communis agglutinin (RCA-I) than asialofetuin oligosaccharide itself or asialofetuin. The conjugates were further labeled with fluorescent reagent or biotinylation reagent containing a hydrazino group by the use of the unreacted aldehyde groups of the oxidized dextran, yielding probes with similar densities of fluorophores or biotin groups. Direct binding of the biotinylated asialofetuin oligosaccharide-dextran probe to RCA-I coated on the titer plate at a concentration of 50 ng/50 microl was easily detected using 50 fmol (as oligosaccharides) of the probe. The method for the synthesis of dextran-based oligosaccharide probes will facilitate the investigation of carbohydrate-mediated molecular interactions based on the native oligosaccharide structures.

Normal levels of serum glycoproteins maintained in beta-1, 4-galactosyltransferase I-knockout mice

The galactose-mediated clearance of serum glycoproteins from the circulation was evaluated using beta-1,4-galactosyltransferase (beta-1,4-GalT) I-knockout mice. Partial structural study of the oligosaccharides released from mouse serum glycoproteins revealed that 77.4% of the oligosaccharides from beta-1,4-GalT I(+/+) mouse contain galactose, while 7.7% of those from beta-1,4-GalT I(-/-) mouse were galactosylated. Under the conditions, no significant change in serum protein concentrations was observed between the normal and mutant mice. The results indicate that the hepatic asialoglycoprotein receptor-mediated system is not functioning in the clearance of endogenous serum glycoproteins.

Intracellular lectins associated with N-linked glycoprotein traffic

The vectorial intracellular transport of N-glycan-linked glycoproteins is indispensable for biological functions. In order to sort these glycoproteins to the correct destination, animal intracellular lectins play important roles as sorting receptors. The roles of such lectins in the biosynthetic pathway from the endoplasmic reticulum (ER) to the cell surface are addressed in this review. Calnexin and calreticulin function via specific carbohydrates in quality control of newly synthesized glycoproteins in the ER, and ERGIC-53 seems to function in the transport of glycoproteins from ER to the Golgi complex. In addition to the well-understood role of mannose 6-phosphate receptor in lysosomal protein sorting, the vesicular integral protein of 36 kDa (VIP36) functions as a sorting receptor by recognizing high-mannose type glycans containing alpha1-->2Man residues for transport from Golgi to the cell surface in polarized epithelial cells.

Asn-linked sugar chain structures of recombinant human thrombopoietin produced in Chinese hamster ovary cells

Human thrombopoietin (TPO) that regulates the numbers of megakaryocytes and platelets is a heavily N- and O-glycosylated glycoprotein hormone with partial homology to human erythropoietin (EPO). We prepared recombinant human TPO produced in Chinese hamster ovary (CHO) cells and analyzed the sugar chain structures quantitatively using 2-aminobenzamide labeling, sequential glycosidase digestion and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS). We found bi-, tri- and tetraantennary complex-type sugar chains with one or two N-acetyllactosamine repeats, which are common to recombinant human EPO produced in CHO cells. On the other hand, there were triantennary sugar chains with one or two N-acetyllactosamine repeats that were specific to the recombinant human TPO, and their distributions of branch structures were also different. These results suggested that proximal protein structure should determine the branch structure of Asn-linked sugar chains in addition to the glycosyltransferases subset.

Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates

This review describes the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to carbohydrate analysis and covers the period 1991-1998. The technique is particularly valuable for carbohydrates because it enables underivatised, as well as derivatised compounds to be examined. The various MALDI matrices that have been used for carbohydrate analysis are described, and the use of derivatization for improving mass spectral detection limits is also discussed. Methods for sample preparation and for extracting carbohydrates from biological media prior to mass spectrometric analysis are compared with emphasis on highly sensitive mass spectrometric methods. Quantitative aspects of MALDI are covered with respect to the relationship between signal strength and both mass and compound structure. The value of mass measurements by MALDI to provide a carbohydrate composition is stressed, together with the ability of the technique to provide fragmentation spectra. The use of in-source and post-source decay and collision-induced fragmentation in this context is described with emphasis on ions that provide information on the linkage and branching patterns of carbohydrates. The use of MALDI mass spectrometry, linked with exoglycosidase sequencing, is described for N-linked glycans derived from glycoproteins, and methods for the analysis of O-linked glycans are also covered. The review ends with a description of various applications of the technique to carbohydrates found as constituents of glycoproteins, bacterial glycolipids, sphingolipids, and glycolipid anchors.

Study of the sugar chains of recombinant human amyloid precursor protein produced by Chinese hamster ovary cells

The N- and O-glycans of recombinant amyloid precursor protein (APP), purified from Chinese hamster ovary cells transfected with the human 695-amino acid form of APP, were separately released by hydrazinolysis under different conditions. The reducing ends of the released N- and O-glycans were reduced with NaB3H4 and derivatized with 2-aminobenzamide (2AB), respectively. After acidic N-glycans were obtained by anion-exchange column chromatography, these were converted to neutral oligosaccharides by sialidase digestion, demonstrating that their acidic nature was entirely due to sialylation. The sialidase-treated N-glycans were then fractionated by lectin column chromatography and their structures were determined by linkage-specific sequential exoglycosidase digestion. These results demonstrated that recombinant APP has bi- and triantennary complex type N-glycans with fucosylated and nonfucosylated trimannosyl cores. In a similar fashion, the 2AB-labeled O-glycans derived from APP were determined to be mono- and disialylated core type 1 structures. Taken together, these results indicate that recombinant APP has sialylated bi- and triantennary N-glycans with fucosylated and nonfucosylated cores and sialylated O-glycans with core type 1 structures.

Structure, pathology and function of the N-linked sugar chains of human chorionic gonadotropin

Human chorionic gonadotropin (hCG) contains five acidic N-linked sugar chains, which are derived from three neutral oligosaccharides by sialylation. Each of the two subunits (hCGalpha and hCGbeta) of hCG contain two glycosylated Asn residues. Glycopeptides, each containing a single glycosylated Asn, were obtained by digestion of hCGalpha with trypsin, and of hCGbeta with chymotrypsin and lysyl endopeptidase. Comparative study of the sugar chains of the four glycopeptides revealed the occurrence of site-directed glycosylation. Studies of the sugar chains of hCGs, purified from urine of patients with various trophoblastic diseases, revealed that choriocarcinoma hCGs contain sialylated or non-sialylated forms of eight neutral oligosaccharides. In contrast, hCGs from invasive mole patients contain sialyl derivatives of five neutral oligosaccharides. The structural characteristics of the five neutral oligosaccharides, detected in choriocarcinoma hCGs but not in normal placental hCGs, indicate that N-acetylglucosaminyltransferase IV (GnT-IV) is abnormally expressed in the malignant cells. This supposition was confirmed by molecular biological study of GnT-IV in placenta and choriocarcinoma cell lines. The appearance of tumor-specific sugar chains in hCG has been used to develop a diagnostic method of searching for malignant trophoblastic diseases. In addition, a summary of the current knowledge concerning the functional role of N-linked sugar chains in the expression of the hormonal activity of hCG has been presented.

Growth of Viridans streptococci on human serum alpha1-acid glycoprotein

Viridans streptococci have emerged as major opportunistic pathogens. We suggest that for these bacteria to proliferate in vivo and cause disease, they must utilize host tissue components. We have therefore examined the ability of all recognized species of viridans streptococci to liberate and utilize the constituent sugars of the glycans of the extensively sialylated human serum alpha1-acid glycoprotein (AGP) as the sole source of carbohydrate to support in vitro growth. Analysis of residual glycans following bacterial growth was performed by high-pH anion exchange chromatography with pulsed amperometric detection and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Only those species which produced sialidase-namely, Streptococcus oralis, S. intermedius, and S. defectivus--grew on AGP. The extent of degradation of glycans was dependent on the particular glycosidases produced by the bacteria. S. defectivus produced only a sialidase which released the terminal N-acetylneuraminic acid residues of the glycans, and the liberated sugar was utilized. S. intermedius also produced beta-galactosidase and beta-N-acetylglucosaminidase, which removed galactose and N-acetylglucosamine from desialylated glycans, all of which again were utilized by the organism. S. oralis produced beta-galactosidase, beta-N-acetylglucosaminidase, and alpha-fucosidase and novel alpha- and beta-mannosidases which were apparent only from the analysis of the residual sugars of AGP. S. oralis cleaved all the sugars from AGP except for 22% of the N-acetylglucosamine. The residual N-acetylglucosamine residues remaining were those linked to the asparagine of the peptide backbone. All the monosaccharides released by S. oralis from AGP, with the exception of fucose, were utilized. Sialidase production may be a key factor for growth of these species of viridans streptococci on glycoproteins in vivo, since they are commonly associated with extra-oral diseases, with S. oralis emerging as an important pathogen.

Impaired galactosylation of core 2 O-glycans in erythrocytes of beta1,4-galactosyltransferase knockout mice

O- and N-glycans included in erythrocyte membrane glycoproteins from beta1,4-galactosyltransferase I (GalT-I) knockout mice were analyzed to examine how this enzyme deficiency affects glycosylation of proteins in erythroid cells. The results indicated that greater than 80% of core 2 O-glycans from GalT-I-/- mice are not galactosylated by beta1,4 linkage, resulting in the expression of Neu5Acalpha2 --> 3Galbeta1 --> 3(GlcNAcbeta1 --> 6)GalNAc, while core 2 O-glycans from GalT-I+/+ mice are fully galactosylated and occur as Neu5Acalpha2 --> 3Galbeta1 --> 3(Neu5Acalpha2 --> 3Galbeta1 --> 4GlcNAcbeta1 --> 6)GalNAc. On the other hand, beta1, 4-galactosylation of N-glycans of the mutant was approximately 60% that of the wild type. Thus, it is suggested that GalT-I is predominantly responsible for beta1,4-galactosylation of the core 2 O-glycan branch in erythroid cells.

Phosphoglycosylation of a secreted acid phosphatase from Leishmania donovani

The secreted acid phosphatase (SAcP) of L.donovani is a heterogeneous glycoprotein that displays a wide array of N- and O-linked glycosylations. The O-linked sugars are of particular interest due to their similarity to the phosphoglycan structures of the major lipophosphoglycan surface antigen and released phosphoglycan (Turco et al., 1987; Greis et al., 1992). This study describes a structural analysis of the SAcP O-linked glycosylations using mass spectroscopy, amino acid sequencing, and enzymatic carbohydrate sequencing. Analysis of glycan chain lengths and peptide glycosylation site distribution was performed, revealing that the average O-linked structure was approximately 32 repeat units in length. Amino acid sequence analysis of glycosylated peptides showed that phosphoglycosylations did not occur randomly but were localized to specific serine residues within an array of degenerate serine/threonine-rich repeat sequences localized in the C-terminus. No evidence was obtained for modification of threonine residues. The observed pattern suggested that a consensus sequence may exist for localization of phosphoglycan structures.

Behaviour of dehydroalanine derivatives under hydrazinolysis conditions. Possible relevance to glycoprotein hydrazinolysis

Reactions that are relevant to the cleavage, by hydrazinolysis, of O-linked oligosaccharides from glycoproteins were studied using dehydroalanine derivatives as models of the intermediates formed from O-glycosylated serine residues. Conjugate addition of hydrazine followed by cyclisation to form pyrazolidinones, if occurring during glycoprotein hydrazinolysis, could reduce the yield of released oligosaccharide. However, N-acetyldehydroalanine amide derivatives, which modelled the dehydroalanine derivatives believed to be intermediates in the hydrazinolysis of glycoproteins containing O-linked oligosaccharides, underwent conjugate addition but no cyclisation.

Detection of novel carbohydrate binding activity of interleukin-1

Tamm-Horsfall glycoprotein (THGP) and the oligosaccharide fraction liberated from THGP by hydrazinolysis inhibited tetanus toxoid-induced T cell proliferation. Intact THGP showed approximately 100-fold more inhibitory activity than the free oligosaccharides. After fractionating the oligosaccharides by anion-exchange column chromatography, the inhibitory activity could be detected in a sialidase-resistant acidic oligosaccharide fraction (fraction AR). The inhibitory activity of fraction AR was not observed when the fraction was added to the T cell culture medium 24 h after the addition of tetanus toxoid. Increased concentration of interleukin (IL) 1beta and decreased concentration of IL-2 were observed in the T cell culture medium after the addition of fraction AR. The oligosaccharides in fraction AR also inhibited the growth of an IL-1-dependent cell line, D10-G4. These results strongly suggested that the oligosaccharides in fraction AR bind to IL-1beta and suppress its cytokine activity. IL-1beta actually bound to the fraction AR immobilized on an amino-bonded thin layer plate. Fractionation of the oligosaccharides indicated that only oligosaccharides containing an N-acetylgalactosamine residue and a sulfate residue bound specifically to IL-1beta. Removal of either the sulfate residue or the N-acetylgalactosamine residue from the oligosaccharides abolished both the proliferation-inhibition and IL-1beta binding activities. Since IL-1beta did not bind to thyroid-stimulating hormone, which has the sulfate group at C-4 of the N-acetylgalactosamine residue in its N-linked sugar chains, the binding of IL-1beta toward oligosaccharides in fraction AR was considered to be highly specific.

Developmental changes in Asn-linked neutral oligosaccharides in murine cerebrum

The changes in Asn-linked oligosaccharide composition in the murine cerebrum during development have been examined by high-performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS). The oligosaccharides, obtained from murine cerebrum in several developmental stages, were separated by HPLC on anion-exchange and reverse-phase columns. We found that two Asn-linked oligosaccharides, designated oligosaccharide I and oligosaccharide II, had their expression changed during postnatal development. Whereas oligosaccharide I was reduced during brain development, oligosaccharide II was increased. The structures of oligosaccharides I and II were analyzed by ESI-MS and sequential exoglycosidase digestions. Judging from the molecular and fragment ions in each oligosaccharide, the oligosaccharide I was composed of 5Hex+2HexNAc+ABOE (MW 1467.2) and the oligosaccharide II was 3Hex+4HexNAc+DoHex+ABOE (MW 1695.2). The results of sequential exoglycosidase digestion indicated that the oligosaccharide I was an oligomannose type saccharide and the oligosaccharide II was a biantennary complex type saccharide including fucose. The proposed structures are shown below. These results offer an important clue to the role of Asn-linked oligosaccharides associated with development of the central nervous system.

Effect of 1-phenyl-3-methyl-5-pyrazolone labeling on the fragmentation behavior of asialo and sialylated N-linked glycans under electrospray ionization conditions

The advantages of labeling free N-linked oligosaccharides with 1-phenyl-3-methyl-5-pyrazolone (PMP), for high performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (ESI-MS) are discussed. The study focuses on some asialo and sialylated sugars, and compares the HPLC and ESI-MS behaviors of the PMP-labeled substances vs. the native compounds. It is pointed out that native free N-linked carbohydrates have very low affinities for the C18 reversed phases commonly used in HPLC. Native asialo oligosaccharides yield good ESI-MS sensitivity, although they are very susceptible to in-source collision-induced dissociation (CID), and the fragments are produced from any of the branches of the molecules, i.e. do not give specific structural information. Native N-linked standards bearing one sialic acid residue yield a 10-fold loss of ESI-MS sensitivity vs. asialo compounds, and native sugars with two sialic acid moieties were not detectable. The PMP labeling of asialo and sialylated sugars yielded higher affinities for HPLC C18 columns and, even at the early stages of method development, it was possible to separate three PMP-labeled standards to a useful extent. In ESI-MS, PMP-asialo sugars did not yield a significant increase in sensitivity vs. the native species; however, fragmentation produced by in-source CID was more directed as all predominant fragment ions contained the bis-PMP label. This feature is particularly useful when structural determination of an unknown sugar is required. PMP-sialylated sugars gave rise to very clean and informative ESI mass spectra. The monosialo sugar yielded a 100-fold sensitivity improvement vs. its native analog and, in the case of the disialylated compound, a 100% improvement was obtained in the positive mode. Most fragment ions were informative and contained the reducing end on the molecules, thus facilitating spectral interpretation. The combination of PMP derivatization with on-line HPLC/ESI-MS is a promising method for the analysis of asialo and sialylated carbohydrate mixtures.

Characterization of fibroblast growth factor-6 expressed by Chinese hamster ovary cells as a glycosylated mitogen for human vascular endothelial cells

The gene for fibroblast growth factor (FGF)-6/hst-2 was originally identified by its close homology with the FGF-4/hst-1 gene. Aside from its ability to transform cultured fibroblasts, the characteristics of FGF-6 protein have only been studied using a simple preparation from E. coli. In the present study, we expressed FGF-6 cDNA in CHO cells and characterized the resultant protein. We found that CHO cells secreted several forms of the FGF-6 polypeptide, and that there were multiple N-terminal modifications. The longest form (18-kDa) contained the sequence, SerProAlaGlyAlaArg, as its N-terminus, which was consistent with the signal peptide cleavage site predicted from its primary structure. The core polypeptide was primarily modified by heterogeneous N-glycans that were sialylated to a small degree; among them, biantennary structures were found to predominate. Moreover, possible O-glycosylation was also detected. N-glycosylated FGF-6 potently induced DNA synthesis and proliferation of human vascular endothelial cells, whereas in the absence of N-glycosylation, FGF-6 mitogenicity was substantially diminished. The results clearly indicate that FGF-6 expressed by mammalian cells is a glycosylated mitogen for vascular endothelial cells and further suggests that N-glycosylation plays a key role in determining the mitogenicity of FGF-6.

Preparative purification of a high-mannose type N-glycan from soy bean agglutinin by hydrazinolysis and tyrosinamide derivatization

The N-linked oligosaccharide from soy bean agglutinin (Man9) was isolated on a preparative scale following derivatization with Boc-tyrosine. The procedure utilized preparative hydrazinolysis to release the oligosaccharide and yielded multi-micromol quantities of Boc-tyrosine-Man9 which was characterized by 1H NMR and ES-MS.

Identification and characterization of N-acetylglucosamine-6-O-sulfate-specific beta1,4-galactosyltransferase in human colorectal mucosa

6-Sulfo-sialyl Lewis X structure is attributable to recognition between lymphocytes and high endothelial venules. However, the biosynthetic pathway still remains unclear. We found that a beta-galactosyltransferase (betaGalT) in human colorectal mucosa preferentially acts on GlcNAc-6-O-sulfate (6S-GN). 6S-GN:beta4GalT was partially purified by UDP-hexanolamine-Sepharose and asialo-agalacto-ovomucin-Sepharose chromatographies. The optimum pH of this enzyme was found to be 6.5-7.5 and the Michaelis constants for 6S-GN and UDP-Gal were 0.43 mM and 16 microM, respectively. The enzymatic activity was dependent on divalent cations and the substrate specificity was not affected by alpha-lactalbumin. This is the first demonstration of the occurrence of 6S-GN:beta4GalT.

Increased sialylation of oligosaccharides on IgG paraproteins--a potential new tumour marker in multiple myeloma

AIMS

To investigate whether changes in carbohydrate structure of IgG are related to malignancy and stage of disease in myeloma and monoclonal gammopathy of uncertain significance (MGUS).

METHODS

61 patients were studied at diagnosis: 14 with MGUS, nine with stage I multiple myeloma, 11 with stage II, 21 with stage III, and five with solitary plasmacytoma. IgG was extracted from serum by protein G affinity chromatography. Oligosaccharides were cleaved from the protein backbone enzymatically by N-glycosidase F. Oligosaccharide analysis was performed by high pressure anion exchange chromatography with pulsed electrochemical detection (HPAE-PED).

RESULTS

Up to 15 oligosaccharide peaks were identified in three major fractions: neutral, monosialylated, and disialylated. Patients with myeloma showed an increase in the proportion of sialylated oligosaccharides in comparison with patients with MGUS. The ratio of neutral to sialylated oligosaccharides (N:S) was reduced at all stages of myeloma compared with MGUS: MGUS, 11.35; myeloma stage I, 7.6 (p = 0.047); stage II, 5.20 (p = 0.035); stage III, 3.60 (p = 0.0002); plasmacytoma, 7.5 (p = 0.046). The N:S ratio was independent of paraprotein concentration (r = 0.05).

CONCLUSIONS

The ratio of neutral to sialylated oligosaccharides may act as a new marker of malignancy in IgG paraproteinaemia and warrants further investigation.

Analysis of 2-aminobenzamide-labeled oligosaccharides by high-pH anion-exchange chromatography with fluorometric detection

To establish high-pH anion-exchange chromatography with fluorometric detection (HPAEC-FD) for the sensitive oligosaccharide analysis, the system for HPAEC with pulsed amperometric detection (PAD) was modified by placing the anion micromembrane suppressor between PAD and fluoromonitor to neutralize the alkaline eluate and connecting the flow path. N-Linked oligosaccharides were released from various glycoproteins by hydrazinolysis followed by labeling with 2-aminobenzamide, and their asialooligosaccharides were analyzed by HPAEC-FD using an isocratic elution with 0.3 M NaOH solution. The results indicated that the new system using FD offers fine separation of oligosaccharides at the subpicomole level. Coinjection of reduced dextran oligomers as internal standards which are detected by PAD permits us to express elution positions of the fluorescent oligosaccharides as glucose units, resulting in a much more reliable analysis. The system was also effectively used for structural analysis of oligosaccharides by sequential glycosidase digestion. Thus, HPAEC-FD promises to be an alternative tool for the sensitive analysis of oligosaccharides.

Direct action of a protein-bound polysaccharide, PSK, on transforming growth factor-beta

We investigated the action of a protein-bound polysaccharide, PSK, on transforming growth factor-beta (TGF-beta). (1) In in vitro-mixed culture of peripheral blood mononuclear cells (PBMC) from healthy human and mitomycin C-treated human colon cancer cells, PSK or polyclonal antibody to TGF-beta significantly enhanced incorporation of 3H-thymidine into PBMC, and apparently decreased TGF-beta1 levels of acid-treated culture supernatant. (2) PSK or the antibody interfered with the quantitation by enzyme immunoassay of TGF-beta1 in acid-treated supernatant of the mixed culture. (3) PSK was suggested to form a complex with 125I-human recombinant TGF-beta1 standard, when changes in molecular weight of radioactivities were assessed by gel filtration. Recombinant human TGF-beta1 inhibited growth of mink lung epithelial cell line Mv1Lu and promoted collagen synthesis in rat kidney fibroblast cell line NRK49F, but the complex did not have such activities. (4) In addition to TGF-beta1, PSK bound with TGF-beta2 and platelet-derived growth factor; however, PSK did not bind with 22 other species of cytokines and growth factors. (5) Protein moiety of PSK is suggested to play an important role in the expression of the activity. These results suggest that PSK modulates the biological activity of TGF-beta1 by binding to its active form.

Evidence for mannosidase activities in Streptococcus oralis when grown on glycoproteins as carbohydrate source

Streptococcus oralis when cultured using ribonuclease B as the sole source of carbohydrate, selectively uses the sugars of the Man5 glycoform as shown by HPAEC and MALDI-TOF mass spectrometric analyses. The organism is able to do this by producing novel alpha-(1-->3), alpha-(1-->6) and beta-(1-->4) mannosidase activities and these act in a concerted manner in what appears as a single-step process. The selective utilisation of Man5 is explained by the absence of an alpha-(1-->2) mannosidase which is required to initiate breakdown of the glycan chains present in the other glycoforms which are components of the glycoprotein.

The DSD-1 carbohydrate epitope depends on sulfation, correlates with chondroitin sulfate D motifs, and is sufficient to promote neurite outgrowth

The neural chondroitin sulfate (CS) proteoglycan (PG) DSD-1-PG was originally identified with the monoclonal antibody (mAb) 473HD. It promotes neurite outgrowth of hippocampal neurons when coated as a substrate in the presence of polycations. This effect is inhibited by mAb 473HD that specifically recognizes the DSD-1 epitope. The DSD-1 epitope is also detectable in CS-C and CS-D preparations from shark cartilage but not in other chondroitin sulfates that are structurally related and differ in their sulfation patterns. Non-sulfated DSD-1-PG and chemically desulfated CS-D were not recognized by mAb 473HD, suggesting that the DSD-1 epitope depends on sulfation. It was possible to enrich DSD-1 epitope-bearing carbohydrates and D disaccharide units from CS-C and CS-D preparations on a mAb 473HD affinity matrix. This indicates that the DSD-1 epitope represents a distinct glycosaminoglycan structure containing D units. The analysis of glycosaminoglycan digestion products by high pressure liquid chromatography revealed that DSD-1-PG preparations contain a unique D disaccharide unit as well as an A, a C, and a non-sulfated disaccharide unit. In neurite outgrowth assays with hippocampal neurons, substrate-bound CS-D promoted neurite outgrowth, whereas CS-A, CS-B, or CS-C did not. This effect of CS-D was inhibited by mAb 473HD. DSD-1 epitope-enriched fractions obtained from CS-D and CS-C promoted neurite outgrowth, whereas CS-C had no such effect prior to enrichment on the mAb 473HD matrix. Based on these findings we conclude that the DSD-1 epitope by itself is sufficient to promote neurite outgrowth and that this activity is possibly associated with D motifs.

Evidence for a site-specific fucosylation of N-linked oligosaccharide of immunoglobulin A1 from normal human serum

Glycopeptides containing the N-linked oligosaccharide from human serum IgA1 were analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS). Two glycopeptides, GP1 and GP2, prepared from the endoproteinase Asp-N digest of the IgA1 heavy chain, were derived from the CH2 domain (N-glycan site at Asn263) and the tailpiece portion (N-glycan site at Asn459), respectively. The structure of the attached sugar chain was deduced from the mass number of the glycopeptide and confirmed by a two-dimensional mapping technique for a pyridylaminated oligosaccharide. GP1 was composed of two major components having a fully galactosylated bianntena sugar chain with or without a bisecting N-acetylglucosamine (GlcNAc) residue. On the other hand, the GP2 fraction corresponded to the glycopeptides having a fully galactosylated and fucosylated bianntena sugar chain partly bearing a bisecting GlcNAc residue. Thus, the site-specific fucosylation of the N-linked oligosaccharide on the tailpiece of the alpha1 chain became evident for normal human serum IgA1.

Structural determination of N-linked carbohydrates by matrix-assisted laser desorption/ionization-mass spectrometry following enzymatic release within sodium dodecyl sulphate-polyacrylamide electrophoresis gels: application to species-specific glycosylation of alpha1-acid glycoprotein

This paper describes a sensitive method for analysis of N-linked carbohydrates released enzymatically from within the gel following separation of glycoproteins (50-100 pmols) by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The separated bands containing the glycoproteins were cut from the gel, destained, reduced and alkylated. N-linked glycans were then released by in-gel incubation with peptide N-glycosidase-F (PNGase-F) and extracted with water and acetonitrile. Sialic acid-containing glycans were converted into methyl esters by reaction with methyl iodide, salts and reagents were removed by passage through a mixed-bed column of ion-exchange resins and the glycans were examined by matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry. Structural determination of the released glycans was performed by exoglycosidase digestion. Following glycan release and extraction, the protein could be digested within the gel with trypsin, and the masses of the tryptic peptides could be compared with those generated from a sequence database for protein identification. The method is applied to the analysis of N-linked glycans from alpha1-acid glycoprotein from man, cow, sheep and dog. Major species-specific differences in glycosylation were found. Thus, although all four species used N-acetyl-neuraminic acid, only cow and sheep additionally used N-glycolyl-neuraminic acid. Biantennary glycans were the predominant carbohydrates in cow, sheep and dog but man produced more triantennary glycans and a substantial amount of tetraantennary sugars. Fucosylation was only found in glycans from man and cow and both cow and sheep glycans were found to have beta1-3- and well as beta1-4-linked galactose residues in the antennae.

Dissolved oxygen concentration in serum-free continuous culture affects N-linked glycosylation of a monoclonal antibody

The murine B-lymphocyte hybridoma, CC9C10, was grown at steady state in serum-free continuous culture at dissolved oxygen (DO) concentrations of 10, 50, and 100% of air saturation. The secreted mAb, an IgG1, was purified and subjected to both enzymatic deglycosylation using PNGase F and chemical deglycosylation by hydrazinolysis. Both methods resulted in complete removal of N-linked oligosaccharide chains. Isolated N-glycan pools were analyzed by fluorophore-assisted carbohydrate electrophoresis (FACE) and high pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The FACE profiles and corresponding HPAEC-PAD chromatograms of N-linked oligosaccharides obtained by PNGase F digestion and hydrazinolysis provided complementary and corroborating information. The predominant N-linked structures were core-fucosylated asialo biantennary chains with varying galactosylation. There were also minor amounts of monosialylated, and trace amounts of afucosyl, oligosaccharides. A definite shift towards decreased galactosylation of glycan chains was observed as DO concentration in continuous culture was reduced. The vast majority of N-linked glycosylation occurred on the heavy chain. There was no evidence for N-linked glycosylation of the light chain or for O-linked glycosylation of the mAb.

Paradoxical behavior of asymmetric IgG antibodies

Changes in the quantity and quality of antibodies occur in the course of an immune response. This review describes the physicochemical and biological properties of asymmetric antibodies as well as their functions, beneficial or harmful to the host, according to the nature of the antigen and the particular situation in which they act. Asymmetric antibodies have two paratopes, one of high affinity, with K0 similar to that of symmetric antibodies, and the other one with an affinity for the antigen 100 times lower. Functional univalence is due to steric hindrance present in one of the paratopes by the carbohydrate moiety attached to the Fd fragment of the Fab region, so these antibodies are unable to form large antibody-antigen complexes and cannot trigger reactions, such as complement fixation, phagocytic activity and antigen clearance. When asymmetric IgG antibodies are specific for self-antigens, they prove beneficial for the host by exerting regulatory functions. In allergic manifestations, in autoimmune diseases and especially during pregnancy, despite the fact that the antigens responsible for the process are foreign to the host, they also perform beneficial activity. During pregnancy, the placenta secretes molecules or factors that regulate the synthesis of these antibodies, thus favoring fetal protection.

Occurrence of reducing terminal N-acetylglucosamine 3-sulfate and fucosylated outer chains in acidic N-glycans of porcine zona pellucida glycoproteins

Structures of acidic N-glycans released from porcine zona pellucida glycoproteins by hydrazinolysis were studied. The results indicated that the acidic glycans are of mono- to tetraantennary complex-type with and without N-acetyllactosamine repeating units. Sulfated residues are not only located at the C-6 position of GlcNAc included in the N-acetyllactosamine repeating units, but also at the C-6 position of GlcNAc in the non-repeated antennae and at the C-3 position of reducing terminal GlcNAc residue. Analysis of the oligosaccharide fragments released by endo-beta-galactosidase digestion and by hydrazine/nitrous acid treatment also revealed that various sulfated and non-sulfated forms of fucosylated structures such as Fucalpha1 --> 2Galbeta1 --> 4(+/-SO3- --> 6)GlcNAc (type 2H), Galbeta1 --> 4(Fucalpha1 --> 3)(+/-SO3- --> 6)GlcNAc(Lex) and Fucalpha1 --> 3 or 4(+/-SO3- --> 6)GlcNAc, are expressed in the repeated outer chain moieties.

Distribution of glycoproteins with beta-N-acetylgalactosaminylated N-linked sugar chains among bovine tissues

Only a small number of glycoproteins has been reported to contain N-linked sugar chains with GalNAcbeta1-->4GlcNAc structure. Our previous studies showed that most glycoproteins from bovine milk fat globule membranes contain beta-N-acetylgalactosaminylated N-linked sugar chains [Sato et al., J. Biochem. 114 (1993) 890-900]. In order to study how widely this glycosylation occurs, lectin blot analysis of membrane glycoproteins from 12 bovine tissues was performed using Wistaria floribunda agglutinin (WFA), which interacts with oligosaccharides terminating with N-acetylgalactosamine. The WFA-positive bands were detected in samples from most tissues except for intestine although the number and reactivity of bands to lectin varied among the tissues. Upon pretreatment of blotted filters with Bacillus beta-N-acetylgalactosaminidase or N-glycanase, no lectin binding was observed. WFA-agarose column chromatography of oligosaccharides released by hydrazinolysis from membrane glycoproteins of bovine tissues except for intestine revealed that a few to 18% of the released oligosaccharides bind and are eluted from the column with 100 mM N-acetylgalactosamine. These results indicate that many glycoproteins from a variety of bovine tissues contain N-linked sugar chains with GalNAcbeta1-->4GlcNAc structure, suggesting a wider occurrence of this glycosylation in bovine tissues.

Structural analysis and molecular model of a self-incompatibility RNase from wild tomato

Self-incompatibility RNases (S-RNases) are an allelic series of style glycoproteins associated with rejection of self-pollen in solanaceous plants. The nucleotide sequences of S-RNase alleles from several genera have been determined, but the structure of the gene products has only been described for those from Nicotiana alata. We report on the N-glycan structures and the disulfide bonding of the S3-RNase from wild tomato (Lycopersicon peruvianum) and use this and other information to construct a model of this molecule. The S3-RNase has a single N-glycosylation site (Asn-28) to which one of three N-glycans is attached. S3-RNase has seven Cys residues; six are involved in disulfide linkages (Cys-16-Cys-21, Cys-46-Cys-91, and Cys-166-Cys-177), and one has a free thiol group (Cys-150). The disulfide-bonding pattern is consistent with that observed in RNase Rh, a related RNase for which radiographic-crystallographic information is available. A molecular model of the S3-RNase shows that four of the most variable regions of the S-RNases are clustered on one surface of the molecule. This is discussed in the context of recent experiments that set out to determine the regions of the S-RNase important for recognition during the self-incompatibility response.

Structural study of N-linked sugar chains of sheep erythrocyte membrane glycoproteins

Our previous study showed that non-reducing terminal galactose residues of N-linked sugar chains present in sheep erythrocyte membrane glycoproteins are important for rosette formation with T lymphoblastic cells [Ogasawara et al. (1995) Immunol Lett 48: 35-38]. As a first step to elucidate the significant structures of sugar chains involved in rosette formation, we analysed N-linked sugar chains released from the membrane glycoproteins by hydrazinolysis. The oligosaccharides were labeled with NaB3H4 and fractionated using columns of Aleuria aurantia lectin-Sepharose, MonoQ and Bio-Gel P-4. Structural analyses of oligosaccharides by sequential exoglycosidase digestion in combination with methylation analysis revealed that the membrane glycoproteins contain bi- (19%), tri- (33%), and tetraantennary (44%) complex-type oligosaccharides and that the oligosaccharides having exposed galactose residues amount to 40% of the total.

Asparagine-linked carbohydrate chains of inducible rat parotid proline-rich glycoprotein contain terminal beta-linked N-acetylgalactosamine

Rats treated with daily injection of DL-isoproterenol for 10 consecutive days (25 mg kg(-1) body weight) showed marked induction of a proline-rich glycoprotein (GPRP) of 220 kDa. Proteinase K digestion of GPRP produced a homogeneous glycopeptide with an average chemical composition as follows (residues per mol): Pro4, Glx3, Asx2, Gly1, His1, Thr1, Arg1, GlcNAc5, GalNac1, Man3, Gal2-3, and Fuc1. The structural analysis of the asparagine-linked carbohydrate unit was performed by methylation, periodate oxidation and enzymatic degradation. Methylation studies indicated that the three mannosyl residues were substituted at 1,2-, 1,2,4-, and 1,3,6-positions. Fucose, N-acetylgalactosamine, 1.5 residues of galactose and 0.35 residues of N-acetylglucosamine were terminally located and one galactose residue was 1,4-substituted. Approximately four of the 5 N-acetylglucosamine residues were substituted at 1,4-position and approximately 1 residue of N-acetylglucosamine was substituted at 1,4,6-positions. Periodate oxidation studies and exoglycosidase results were consistent with the methylation data. Based on the results of Smith degradation, methylation and sequential exoglycosidase digestions a triantennary oligosaccharide structure having terminal N-acetylgalactosamine in one of the branches is proposed for the major Asn-linked carbohydrate moiety of GPRP.

Analysis of O-linked oligosaccharide alditols by high-pH anion-exchange chromatography with pulsed amperometric detection

To apply high-pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) to the accurate and sensitive analysis of O-linked oligosaccharide alditol, removal of glycopeptides and peptides from oligosaccharide samples obtained by beta-elimination was first investigated. The results obtained by using fetuin as a model glycoprotein indicated that (glyco)peptides derivatized by fluorescamine are easily removed from the beta-eliminated oligosaccharide sample by means of a Sep-Pak C18 cartridge due to their increased hydrophobicity. This clean-up procedure was also effectively applied to the beta-eliminated oligosaccharide sample obtained from delipidated sheep erythrocyte ghosts. Furthermore, structural analysis of the oligosaccharide alditols by HPAEC-PAD was successfully performed in combination with partial and complete desialylation, composition analysis, periodate oxidation, and glycosidase digestion and revealed that sheep erythrocyte membrane glycoproteins contain Gal beta 1-->3Gal-NAc and Gal beta 1-->4GlcNAc beta 1-->3Gal beta 1-->3GalNac, to which one or two residues of Neu5Ac and Neu5Gc are attached in different combinations.

CBP70, a glycosylated nuclear lectin

Some years ago, a lectin designated CBP70 that recognized glucose (Glc) but had a stronger affinity for N-acetylglucosamine (GlcNAc), was first isolated from HL60 cell nuclei. Recently, a cytoplasmic form of this lectin was described, and one 82 kDa nuclear ligand was characterized for the nuclear CBP70. In the present study, the use of Pronase digestion and the trifluoromethanesulphonic acid (TFMS) procedure strongly suggest that the nuclear and the cytoplasmic CBP70 have a same 23 kDa polypeptide backbone and, consequently, could be the same protein. In order to know the protein better and to obtain the best recombinant possible in the future, the post-translational modification of the nuclear and cytoplasmic CBP70 was analyzed in terms of glycosylation. Severals lines of evidence indicate that both forms of CBP70 are N- and O-glycosylated. Surprisingly, this glycosylation pattern differs between the two forms, as revealed by beta-elimination, hydrazinolysis, peptide-N-glycosydase F (PNGase F), and TFMS reactions. The two preparations were analyzed by affinity chromatography on immobilized lectins [Ricinus communis-l agglutinin (RCA-I), Arachis hypogaea agglutinin (PNA), Galanthus nivalis agglutinin (GNA), and wheat germ agglutinin (WGA)] and by lectin-blotting analysis Sambucus nigra agglutinin (SNA), Maackia amurensis agglutinin (MAA), Lotus tetragonolobus (Lotus), succinylated-WGA, and Psathyrella velutina agglutinin (PVA)]. Both forms of CBP70 have the following sugar moities: terminal beta Gal residues, Gal beta 1-3 GalNAc, Man alpha 1-3 Man, sialic acid alpha 2-6 linked to Gal or GalNAc; and sialic acid alpha 2-3 linked to Gal. However, only nuclear CBP70 have terminal GlcNAc and alpha-L-fucose residues. All these data are consistent with the fact that different glycosylation pattern found for each form of CBP70 might act as a complementary signal for cellular targeting.

Expression and characterization of a lactosaminoglycan-carrying glycoprotein of Zajdela hepatoma cell surface--structural analysis of the carbohydrate moiety

In poorly differentiated hepatoma cells, a glycoprotein carrying lactosaminoglycans is identified, and the structure of its glycan moiety is proposed. After membrane solubilization, protein fractionation by gel filtration, and electroelution, this glycoprotein (GPIII) was identified by its affinity for Datura stramonium lectin and its content in large glycopeptides. As shown by PAGE, GPIII has an apparent molecular mass of 100 kDa and is highly glycosylated (36%). It appears as an integral membrane glycoprotein. It is absent from normal hepatocytes, in that no heavy glycopeptides could be detected that bound to Datura lectin or to specific antiserum. The glycan moiety of GPIII has been analyzed according to carbohydrate composition, glycosidase treatment, affinity chromatography on immobilized pokeweed, Datura and Griffonia lectins, and by NMR and methylation analyses. The glycan is a N-linked tetraantennary lactosaminoglycan of 6.6 kDa, containing Gal, GlcNAc, Man, and NeuNAc in a 16:14:3:4 molar ratio, with an average of three repeating units/branch. Its beta-Gal residues are in the penultimate position and are linked in beta1-4 at least in four structural elements (three peripheral and one internal). It contains a very branched structure with Gal alpha1-3Gal beta1-4GlcNAc side chains linked in the C6 position to an inner Gal residue in a main branch. Alpha-Gal and NeuNAc residues [mainly NeuNAc alpha(2-3) linkage] are expressed as the nonreducing terminal groups. A possible structural model is proposed for this heterogeneous lactosaminoglycan, although no definitive structure can be established. That this lactosaminoglycan-carrying glycoprotein GPIII is not expressed in hepatocytes suggests its expression to be linked to the undifferentiated and/or malignant state of this hepatoma.

Sequencing of N-linked oligosaccharides directly from protein gels: in-gel deglycosylation followed by matrix-assisted laser desorption/ionization mass spectrometry and normal-phase high-performance liquid chromatography

A generally applicable, rapid, and sensitive method for profiling and sequencing of glycoprotein-associated N-linked oligosaccharides from protein gels was developed. The method employed sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for protein separation and purification and in-gel deglycosylation using PNGase F for glycan release. Profiles of the neutral glycans from bovine ribonuclease B, chicken ovalbumin, and human immunoglobulin G (IgG), as well as sialic acid-containing sugars (following esterification of the acidic groups) of bovine fetuin and bovine alpha1-acid glycoprotein, were obtained by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and by normal-phase high-performance liquid chromatography following fluorescent labeling. Oligosaccharides were sequenced using specific exoglycosidases, and digestion products were analyzed by MALDI MS. Between 50 and 100 pmol (1.5 to 15 microg) of glycoprotein applied to the gel was sufficient to characterize its oligosaccharide contents. The identity of all glycoproteins investigated could be confirmed after deglycosylation by in-gel trypsin treatment followed by MALDI MS mass mapping and matching the measured molecular weights to a sequence database. The technique was used for the characterization of the glycan moieties of human immunodeficiency virus recombinant gp120 (Chinese hamster ovary cells) and to monitor changes in the glycosylation of this glycoprotein when produced in the presence of a glucosidase I inhibitor. Furthermore, since heavy and light chains of IgG became separated by SDS-PAGE, it could be established that most glycans were associated with the heavy chains.

Generation and characterization of mouse monoclonal antibodies specific for N-linked neutral oligosaccharides of glycoproteins

We generated four monoclonal antibodies (MAbs) specific for asparagine-linked neutral oligosaccharides of glycoproteins by immunizing mice with neoglycolipids, which were derived from glycoproteins by conjugation to phosphatidylethanolamine dipalmitoyl. The binding specificity of these MAbs was determined by an enzyme-linked immunosorbent assay and immunostaining on thin-layer chromatography. The four MAbs designated OMB3, OMB4, OMR5, and OMR6 reacted strongly with the neoglycolipids, Gal beta1-4GlcNAc beta1-2Man alpha1-6(Gal beta1-4GlcNAc beta1-2Man alpha1-3)Man beta1-4GlcNAc-PD, GlcNAc beta1-2Man alpha1-6(GlcNAc beta1-2Man alpha1-3)(GlcNAc beta1-4)Man beta1-4GlcNAc beta1-4GlcNAc-PD, Man alpha1-6Man beta1-4GlcNAc beta1-4(Fuc alpha1-6)GlcNAc-PD, and Man alpha1-3Man beta1-4GlcNAc-PD, respectively, that were used as immunogens. All of these MAbs exhibited a high binding specificity. The epitopes of the MAbs OMB3 and OMB4 were suggested to be nonreducing terminal trisaccharides, Gal beta1-4GlcNAc beta1-2Man-, and nonreducing beta-GlcNAc residues, respectively. MAbs OMR5 and OMR6 showed a highly restricted binding specificity, reacting only with the immunizing neoglycolipids. Subsequently, MAbs OMB3 and OMB4 were shown to react strongly with asialo-alpha1-acid-glycoprotein and asialo-agalacto-alpha1-acid-glycoprotein, respectively, by Western blotting. Furthermore, it was shown that these MAbs reacted specifically with the epitope on Chinese hamster ovary cells by an immunofluorescence technique. MAb OMB4 was also shown to detect the accumulated oligosaccharides with nonreducing terminal beta-GlcNAc residues as granular inclusions in the cultured fibroblasts from a classical Sandhoff disease patient.

Identification of sulfated oligosialic acid units in the O-linked glycan of the sea urchin egg receptor for sperm

The Strongylocentrotus purpuratus sea urchin egg receptor for sperm is a cell surface glycoprotein with a molecular mass of 350 kDa. Recent studies indicate that the sulfated O-linked glycans isolated from the receptor bind to acrosome-reacted sperm. The purified receptor was analyzed with respect to amino acid and carbohydrate content and shown to be composed of 70% carbohydrate by weight. Compositional analysis indicated that both N- and O-linked oligosaccharide chains were present. After peptide:N-glycanase treatment of the receptor to remove most of the N-linked glycan chains, the majority of the sialic acid residues remained associated with the receptor and were shown by several types of experiments to be composed of sulfated oligosialic acid units attached to the O-linked glycan chains of the receptor. Chemical and physical studies on oligosialic chains discovered earlier in the Pronase-generated glycopeptide fraction isolated from the egg cell surface complex of another species of sea urchin, Hemicentrotus pulcherrimus, established that these molecules had the structure: (SO(4)-)-9Neu5Gc alpha2(-->5-O(glycolyl)Neu5Gc alpha2-->)n. Based on comparative and analytical studies, it was concluded that this sulfated oligosaccharide is a component of a GalNAc-containing chain that is O-linked to the polypeptide chain of the sea urchin egg receptor for sperm. Using a competitive inhibition of fertilization bioassay it was shown that the sulfated oligosialic acid chains derived from the S. purpuratus egg cell surface complex inhibited fertilization; the nonsulfated form of this oligosialic chain had little inhibitory activity.

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

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

Species-specific beta-N-acetylgalactosaminylation of serum IgG proteins

Lectin blot analysis of bovine, goat, human, rabbit and mouse serum immunoglobulin G (IgG) samples revealed that Wisteria floribunda agglutinin (WFA) binds to the heavy chains of bovine, goat and human serum IgG proteins but not those of the rabbit and mouse proteins. WFA-positive light chain bands were also detected in bovine, goat and human serum IgG samples only after the filters were treated with Arthrobacter ureafaciens sialidase. The WFA-binding to these IgG proteins was abolished by treatment of the filter with sialidase and then beta-N-acetylhexosaminidase or N-glycanase prior to incubation with the lectin. WFA-agarose column chromatography of the oligosaccharides released by hydrazinolysis from the IgG samples followed by reduction with NaB3H4 revealed that 0.15, 0.09 and 0.07% of the total oligosaccharides from bovine, goat and human serum IgG samples bind to the column, respectively. Partial characterization of WFA-positive bovine IgG oligosaccharides by Bio-Gel P-4 column chromatography suggested that the major oligosaccharide is of non-fucosylated biantennary complex-type. These results indicate that beta-N-acetylgalactosaminylation occurs to N-linked sugar chains of heavy and light chains of IgG proteins in a species-specific manner.