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

Solution structure of the glycosylated second type 2 module of fibronectin

Fibronectin is an extracellular matrix glycoprotein that plays a role in a number of physiological processes involving cell adhesion and migration. The modules of the fibronectin monomer are organized into proteolytically resistant domains that in isolation retain their affinity for various ligands. The tertiary structure of the glycosylated second type 2 module (2F2) from the gelatin-binding domain of fibronectin was determined by two-dimensional nuclear magnetic resonance spectroscopy and simulated annealing. The structure is well defined with an overall fold typical of F2 modules, showing two double-stranded antiparallel beta-sheets and a partially solvent-exposed hydrophobic cluster. An N-terminal beta-sheet, that was not present in previously determined F2 module structures, may be important for defining the relative orientation of adjacent F2 modules in fibronectin. This is the first three-dimensional structure of a glycosylated module of fibronectin, and provides insight into the possible role of the glycosylation in protein stability, protease resistance and modulation of collagen binding. Based on the structures of the isolated modules, models for the 1F22F2 pair were generated by randomly changing the orientation of the linker peptide between the modules. The models suggest that the two putative collagen binding sites in the pair form discrete binding sites, rather than combining to form a single binding site.

Characteristic hexasaccharide sequences in octasaccharides derived from shark cartilage chondroitin sulfate D with a neurite outgrowth promoting activity

A mouse brain chondroitin sulfate (CS) proteoglycan, DSD-1-PG, bears the DSD-1 epitope and has neurite outgrowth promoting properties. Shark cartilage CS-C inhibits the interactions between the DSD-1-specific monoclonal antibody 473HD and the CS chains of the DSD-1-PG, which is expressed on the mouse glial cells (Faissner, A., Clement, A., Lochter, A., Streit, A., Mandl, C., and Schachner, M. (1994) J. Cell Biol. 126, 783-799). On the other hand, several hexasaccharides isolated from commercial shark cartilage CS-D, which contains a higher proportion of characteristic D units (GlcUA(2-sulfate)beta1-3GalNAc(6-sulfate)) as compared with CS-C, has the A-D tetrasaccharide sequence composed of an A disaccharide unit (GlcUAbeta1-3GalNAc(4-sulfate)) and a D disaccharide unit (Nadanaka, S. and Sugahara, K. (1997) Glycobiology 7, 253-263). In this study, the biological activities and the structure of shark cartilage CS-D were investigated. CS-D inhibited the interactions between monoclonal antibody 473HD and DSD-1-PG and also promoted neurite outgrowth of embryonic day 18 hippocampal neurons. Eight octasaccharide fractions were isolated from CS-D after partial digestion with bacterial chondroitinase ABC by means of gel filtration chromatography and anion-exchange high performance liquid chromotography to investigate the frequency and the arrangement of the A-D tetrasaccharide unit in the polymer sequence. Structural analysis performed by a combination of enzymatic digestions with 500-MHz 1H NMR spectroscopy demonstrated that the isolated octasaccharides shared the common core structure DeltaHexAalpha1-3GalNAcbeta1-4(GlcUAbeta1-3GalNAc)3 with four, five, and six sulfate esters at various hydroxyl groups in different combinations. In the structure, DeltaHexA and GlcUA represent 4-deoxy-alpha-L-threo-hex-4-enepyranosyluronic acid and glucuronic acid, respectively. No D-D tetrasaccharide sequence was found, and discrete D disaccharide units were demonstrated exclusively as A-D tetrasaccharide units in either an A-D-A or an A-D-C hexasaccharide sequence in the five octasaccharides that represented about 5.0% (w/w) of the starting polysaccharides (C denotes the disaccharide GlcUAbeta1-3GalNAc(6-sulfate)). It remains to be determined whether such characteristic hexasaccharide sequences present in shark cartilage CS-D serve as functional domain structures recognized by some protein ligands.

Isomeric differentiation of asparagine-linked oligosaccharides by matrix-assisted laser desorption-ionization postsource decay time-of-flight mass spectrometry

Matrix-assisted laser desorption-ionization (MALDI)-postsource decay (PSD) was used to differentiate glycoprotein-released N-linked oligosaccharide isomers directly from aliquots of glycosidase digests and peak fractions collected from high-pH anion exchange chromatography (HPAEC) with minimal sample handling and material. With the implementation of instrumental tuning and acquisition controls, MALDI-PSD of NMR-characterized high-mannose, hybrid, and complex standards resulted in spectra with reproducible fragment ion peak intensity ratios which correlated well to the respective oligosaccharide branching patterns. A "knowledge-based" strategy was utilized to characterize unknown isomeric N-glycan structures in which specific fragment ion types and their distributions in the unknown PSD spectrum were compared to those in PSD spectra of standards possessing similar structural features. This PSD knowledge-based isomeric differentiation strategy was applied to distinguishing recombinant glycoprotein-derived Man7 D1 versus D2/D3 isomers directly from a PNGaseF digest aliquot of high-mannose N-glycans based on branching differences. A precursor ion selection device was employed to isolate the component of interest from the mass profile without additional chromatographic isolation steps. MALDI-MS signal-to-background was maximized for direct PSD with on-the-probe sample clean-up methods. The asialo complex N-glycan PSD knowledge base was used to differentiate HPAEC peak fractions containing the tri- and tri'-antennary branching isomers and two tetraantennary isomers with antennal versus core fucose locations. Although the particular asialo complex N-glycan isomers here were well separated by HPAEC, MALDI-MS alerted us to their presence using m/z-derived monosaccharide compositions and PSD fragmentation allowed us to differentiate these structures using the HPAEC elution positions as guides.

New conformational constraints in isotopically (13C) enriched oligosaccharides

Multidimensional heteronuclear NMR studies have been applied to the resonance assignment and conformational analysis of 13C-enriched Neu5Acalpha2-3Galbeta1-4Glc. It is demonstrated that three-dimensional ROESY-HSQC experiments provide through-space distance restraints which cannot be observed with conventional homonuclear 1H techniques due to resonance overlap. In particular, connectivities demonstrating the existence of the "anti" conformation about the Galbeta1-4Glc glycosidic linkage are unambiguously observed. It is shown that 13C isotopic enrichment of the trisaccharide at a level >95% enables straightforward measurement of trans-glycosidic 1H-13C and 13C-13C coupling constants and a Karplus-type relation is derived for the latter. In total 15 conformational restraints were obtained for the trisaccharide in aqueous solution, all of which were in excellent agreement with theoretical parameters computed from a 5 ns molecular dynamics simulation of the glycan.

A major common trisulfated hexasaccharide core sequence, hexuronic acid(2-sulfate)-glucosamine(N-sulfate)-iduronic acid-N-acetylglucosamine-glucuronic acid-glucosamine(N-sulfate), isolated from the low sulfated irregular region of porcine intestinal heparin

The major structure of the low sulfated irregular region of porcine intestinal heparin was investigated by characterizing the hexasaccharide fraction prepared by extensive digestion of the highly sulfated region with Flavobacterium heparinase and subsequent size fractionation by gel chromatography. Structures of a tetrasaccharide, a pentasaccharide, and eight hexasaccharide components in this fraction, which accounted for approximately 19% (w/w) of the starting heparin representing the major oligosaccharide fraction derived from the irregular region, were determined by chemical and enzymatic analyses as well as 1H NMR spectroscopy. Five compounds including one penta- and four hexasaccharides had hitherto unreported structures. The structure of the pentasaccharide with a glucuronic acid at the reducing terminus was assumed to be derived from the reducing terminus of a heparin glycosaminoglycan chain and may represent the reducing terminus exposed by a tissue endo-beta-glucuronidase involved in the intracellular post-synthetic fragmentation of macromolecular heparin. Eight out of the 10 isolated oligosaccharides shared the trisaccharide sequence, -4IdceA alpha 1-4GlcNAc alpha 1-4GlcA beta 1-, and its reverse sequence, -4GlcA beta 1-4GlcNAc alpha 1-4IdceA alpha 1-, was not found. The latter has not been reported to date for heparin/heparan sulfate, indicating the substrate specificity of the D-glucuronyl C-5 epimerase. Furthermore, seven hexasaccharides shared the common trisulfated hexasaccharide core sequence delta HexA(2-sulfate)alpha 1-4GlcN(N-sulfate)alpha 1-4IdceA alpha 1-4GlcNAc alpha 1-4GlcA beta 1-4GlcN(N-sulfate) which contained the above trisaccharide sequence (delta HexA, IdceA, GlcN, and GlcA represent 4-deoxy-alpha-L-threo-hex-4-enepyranosyluronic acid, L-iduronic acid, D-glucosamine, and D-glucuronic acid, respectively) and additional sulfate groups. The specificity of the heparinase used for preparation of the oligosaccharides indicates the occurrence of the common pentasulfated octasaccharide core sequence, -4GlcN(N-sulfate)alpha 1-4HexA(2-sulfate)1-4GlcN(N-sulfate) alpha 1-4IdceA alpha 1-4GlcNAc alpha 1-4GlcA beta 1-4 GlcN(N-sulfate)alpha 1-4HexA(2-sulfate)1-, where the central hexasaccharide is flanked by GlcN(N-sulfate) and HexA(2-sulfate) on the nonreducing and reducing sides, respectively. The revealed common sequence constituted a low sulfated trisaccharide representing the irregular region sandwiched by highly sulfated regions and should reflect the control mechanism of heparin biosynthesis.

Structural analysis of oligosaccharide-alditols released by reductive beta-elimination from oviducal mucins of Rana dalmatina

The O-linked oligosaccharides of the jelly coat surrounding the eggs of Rana dalmantina were released by alkaline borohydride treatment. Low-molecular-mass, monosialyl oligosaccharide-alditols were isolated by anion-exchange chromatography and fractionated by consecutive normal-phase high-performance liquid chromatography on a silica-based alkylamine column. The structures of the oligosaccharide-alditols were determined by 400-MHz 1H-NMR spectroscopy in combination with matrix assisted laser desorption ionization-time of flight analysis. The five structures were identified range in size from trisaccharides to hexasaccharides, possessing a core consisting of Gal(beta 1-3)GalNAc-ol (core type 1). Novel oligosaccharide-alditols are: [formula: see text] The carbohydrate chains isolated from Rana dalmatina are different from those found in other amphibian species, in which the presence of species-specific material has been characterized. Since the role of carbohydrates appears more and more apparent during the fertilization process, the biodiversity of the O-linked oligosaccharides could support such a biological role.

Sulfated lewis X determinants as a major structural motif in glycans from LS174T-HM7 human colon carcinoma mucin

This article describes oligosaccharide structures of mucin isolated from nude mouse xenograft tumors produced by LS174T-HM7 cells, a subline of the human colon carcinoma LS174T with higher metastatic tendency and higher mucin production. A striking feature of the oligosaccharides of the LS174T-HM7 xenograft tumor mucin was a predominance of sulfated Lewis X determinants: HSO3-Galbeta1-4(Fucalpha1-3)GlcNAc. In addition to one previously known saccharide with one sulfated Lewis X determinant, the HM7 xenograft tumor mucin contained multiple novel structures containing one, two, or three sulfated Lewis X determinants. This determinant, known to act as a selectin ligand, has been found previously in minor saccharide components of human milk as well as mucins, but never before as a predominant structure in one mucin source.

Enzyme-assisted synthesis of Asn-linked diantennary oligosaccharides occurring on glycodelin A

The preparation of a series of sialylated and fucosylated N,N'-diacetyllactosediamine-type diantennary glycopeptides is reported. By sequential enzymatic action of jack bean beta-galactosidase, snail beta 4-N-acetyl-galactosaminyltransferase, bovine colostrum alpha 6-sialyltransferase and human milk alpha 3-fucosyltransferase, a diantennary glycopeptide obtained from asialo fibrinogen was converted at a 5-mumol scale to a series of structures occurring on the glycoprotein glycodelin A, which potentially inhibit human sperm-egg binding.

Conformational stabilization of the altruronic acid residue in the O-specific polysaccharide of Shigella sonnei/Plesiomonas shigelloides

Complete assignments for the 1H- and the 13C-NMR spectra of the O-specific polysaccharide of S. sonnei/Plesiomonas shigelloides are reported. Evidence is presented that in this polysaccharide both pyranose residues exist preferentially in the 4C1 chair conformation and that the polysaccharide exists in the zwitterion form.

Primary structure of 21 novel monoantennary and diantennary N-linked carbohydrate chains from alphaD-hemocyanin of Helix pomatia

The primary structures of 21 novel monoantennary and diantennary N-glycans of the glycoprotein alphaD-hemocyanin (alphaD-Hc) of Helix pomatia have been determined. Outer oligosaccharide fragments (antennae) were released from the glycoprotein by Smith degradation of an alphaD-Hc pronase digest. The major antenna, obtained following HPLC fractionation on Lichrosorb-NH2, was characterized using 1H-NMR spectroscopy, fast-atom-bombardment mass spectrometry, and linkage analysis, and corresponds to a pentasaccharide fragment. The intact carbohydrate chains of alphaD-Hc were released with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase-F digestion, separated from the protein on Bio-Gel P-100, and subfractionated on Bio-Gel P-4. A portion of subfractions was reduced with sodium borodeuteride, and the non-reduced and reduced samples were further fractionated on CarboPac PA-1, Lichrosorb-NH2/Lichrosphere-NH2, and/or Lichrosphere-C18. Purified oligosaccharides and oligosaccharide-alditols were analyzed using 500/600-MHz 1H-NMR spectroscopy. In total, four novel types of antenna were identified, namely, [structures: see text] which are all attached to O-2 of alphaMan residues of the trimannosyl-N,N'-diacetylchitobiose core element, which is generally beta-1,2-xylosylated and alpha-1,6-fucosylated, Man(alpha1-6)[Man(alpha1-3)][+/-Xyl(beta1-2)]Man(beta1-4)GlcNAc(beta1-4) [+/-Fuc(alpha1-6)]GlcNAc.

Purification and characterization of UDP-N-acetylglucosamine: alpha1,3-D-mannoside beta1,4-N-acetylglucosaminyltransferase (N-acetylglucosaminyltransferase-IV) from bovine small intestine

A new beta1,4-N-acetylglucosaminyltransferase (GnT) which involves in branch formation of Asn-linked complex-type sugar chains has been purified 224,000-fold from bovine small intestine. This enzyme requires divalent cations, such as Mn2+, and catalyzes the transfer of GlcNAc from UDP-GlcNAc to biantennary oligosaccharide and produces triantennary oligosaccharide with the beta1-4-linked GlcNAc residue on the Manalpha1-3 arm. The purified enzyme shows a single band of Mr 58,000 and behaves as a monomer. The substrate specificity demonstrated that the beta1-2-linked GlcNAc residue on the Manalpha1-3 arm (GnT-I product) is essential for the enzyme activity. beta1-4-Galactosylaion to this essential beta1-2-linked GlcNAc residue or N-acetylglucosaminylation to the beta-linked Man residue (bisecting GlcNAc, GnT-III product) blocks the enzyme action, while beta1-6-N-acetylglucosaminylation to the Manalpha1-6 arm (GnT-V product) increases the transfer. Based on these findings, we conclude that the purified enzyme is UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,4-N-acetylglucosaminyltransferase IV (GnT-IV), that has been a missing link on biosynthesis of complex-type sugar chains.

Novel tetrasaccharides isolated from squid cartilage chondroitin sulfate E contain unusual sulfated disaccharide units GlcA(3-O-sulfate)beta1-3GalNAc(6-O-sulfate) or GlcA(3-O-sulfate)beta1-3GalNAc

We previously isolated novel tetrasaccharides containing 3-O-sulfated glucuronic acid from king crab cartilage chondroitin sulfate K and demonstrated that the disaccharide units containing 3-O-sulfated glucuronic acid were decomposed by chondroitinase ABC digestion (Sugahara, K., Tanaka, Y., Yamada, S., Seno, N., Kitagawa, H., Haslam, S. M., Morris, H. R., and Dell, A. (1996) J. Biol. Chem. 271, 26745-26754). The findings indicated the necessity to re-evaluate the disaccharide compositions of chondroitin sulfate preparations purified from other biological sources and analyzed using the above enzyme. In this study, to evaluate squid cartilage chondroitin sulfate E a series of even-numbered oligosaccharides were isolated after exhaustive digestion with sheep testicular hyaluronidase and subsequent fractionation by gel chromatography. The tetrasaccharide fraction was subfractionated by high performance liquid chromatography on an amine-bound silica column. Systematic structural analysis of five major fractions, h, l, m, n, and q, by fast atom bombardment mass spectrometry, enzymatic digestions in conjunction with capillary electrophoresis, and 500-MHz 1H NMR spectroscopy revealed one disulfated, three trisulfated, and one tetrasulfated tetrasaccharide structure: fraction h, GlcAbeta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S); fraction l, GlcA(3S)beta1-3GalNAc(6S)beta1-4GlcAbeta1-3GalNAc(4S); fraction m, GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S); fraction n, GlcAbeta1-3GalNAc(4S,6S)beta1-4GlcAbeta1-3GalNAc(4S); and fraction q, GlcA(3S)beta1-3GalNAc(4S,6S)beta1-4GlcAbeta1-3GalNAc(4S), where 3S, 4S, and 6S represent 3-O-, 4-O- and 6-O-sulfate, respectively. The structures found in fractions h and m as well as the unsaturated counterpart of that found in fraction n have been reported, whereas those in fractions l and q are novel in that they contained unusual disulfated and trisulfated disaccharide units where GlcA(3S) is directly linked to GalNAc(6S) and GalNAc(4S,6S), respectively. These novel tetrasaccharide sequences are distinct from those found in other chondroitin sulfate isoforms and may play key roles in the biological functions and activities of chondroitin sulfate E not only from squid cartilage but also from mammalian cells and tissues.

Structural determination of the O-linked sialyl oligosaccharides liberated from fetuin with endo-alpha-N-acetylgalactosaminidase-S by HPLC analysis and 600-MHz 1H-NMR spectroscopy

The endo-alpha-N-acetylgalactosaminidase from the culture medium of Streptomyces sp. OH-11242 (endo-GalNAc-ase-S) hydrolyzed the O-glycosidic linkage between GalNAc and Ser (Thr) in fetuin, liberating oligosaccharides. The O-linked oligosaccharides liberated from the fetuin with endo-GalNAc-ase-S were pyridylaminated following fractionation on a Bio-Gel P-4 column. The structure of the pyridylaminated O-linked oligosaccharides from fetuin has been determined by reverse-phase HPLC and 600-MHz 1H-NMR spectroscopy. The chemical shifts and the coupling constants of pyridylaminated (PA) NeuAc alpha2-3Gal beta1-3GalNAc were refined by computer simulation of the spectrum. The structures of NeuAc alpha2-3Gal beta1-3(NeuAc alpha2-6)GalNAc-PA and NeuAc alpha2-3Gal beta1-3(NeuAc alpha2-3Gal beta1-4GlcNAc beta1-6)GalNAc-PA were determined by their structural reporter groups.

NMR investigations of the role of the sugar moiety in glycosylated recombinant human granulocyte-colony-stimulating factor

Human granulocyte-colony-stimulating factor (G-CSF) is a hematopoietic growth factor that plays a major role in the stimulation of the proliferation and maturation of granulocyte neutrophil cells. With the recent increased understanding of its biological properties in vivo together with available preparations of recombinant human G-CSF, this growth factor has become an essential agent for clinical applications. The presence of an O-linked carbohydrate chain at position 133 greatly improves the physical stability of the protein. To clarify the molecular basis for the stabilisation effect of saccharide moieties on human G-CSF the whole glycoprotein expressed in CHO cells has been investigated by means of two 1H-NMR-spectroscopy and two 1H-detected-heteronuclear 1H-13C experiments at natural abundance, and compared with the non-glycosylated form. The present NMR study reports assignments of 1H and 13C resonances of the bound saccharidic chain NeuNAc(alpha2-3)Gal(beta1-3)[NeuNAc(alpha2-6)]GalNAc, where NeuNAc represents N-acetylneuraminic acid, and demonstrates the alpha-anomeric configuration of the N-acetylgalactosamine-threonine linkage. It also provides results suggesting that the carbohydrate moiety reduces the local mobility around the glycosylation site, which could be responsible for the stabilising effect observed on the glycoprotein.

Binding of the influenza A virus to cell-surface receptors: structures of five hemagglutinin-sialyloligosaccharide complexes determined by X-ray crystallography

The structures of five complexes of the X-31 influenza A (H3N2) virus hemagglutinin with sialyloligosaccharide receptor analogs have been determined from 2.5 to 2.8 A resolution by X-ray crystallography. There is well-defined electron density for three to five saccharides in all five complexes and a striking conformational difference between two linear pentasaccharides with the same composition but different linkage [alpha(2-->6) or alpha(2-->3)] at the terminal sialic acid. The bound position of the terminal sialic acid (NeuAc) is the same in all five complexes and is identical to that reported previously from the study of mono- and trisaccharides. The two oligosaccharides with NeuAc alpha(2-->6)Gal linkages and GlcNAc at the third position have a folded conformation with the GlcNAc doubled back to contact the sialic acid. The pentasaccharide with a terminal NeuAc alpha(2-->3)Gal linkage and GlcNAc at the third position has an extended (not folded) conformation and exits from the opposite side of the binding site than the alpha(2-->6)-linked molecule of the same composition. The difference between the conformation of the pentasaccharide with a 2,6 linkage and the trisaccharide 2,6-sialyllactose suggests that 2,6-sialyllactose is not, as previously believed, an appropriate analog of natural influenza A virus receptors. The oligosaccharides studied are NeuAc alpha(2-->3)Gal beta(1-->4)Glc, NeuAc alpha(2-->6)Gal beta(1-->4)Glc, NeuAc alpha(2-->3)Gal beta(1-->3)GlcNAc beta(1-->3)Gal beta(1-->4)Glc, NeuAc alpha(2-->6)Gal beta(1-->4)GlcNAc beta(1-->3)Gal beta(1-->4)Glc, and [NeuAc alpha(2-->6)Gal beta(1-->4)GlcNAc]2 beta(1-->3/6)Gal-beta-O-(CH2)5-COOCH3.

Structural characterization of N-linked oligosaccharides from cellobiohydrolase I secreted by the filamentous fungus Trichoderma reesei RUTC 30

We have characterized the primary structures of the predominant N-linked oligosaccharides on cellobiohydrolase I from the filamentous fungus Trichoderma reesei RUTC30. Different enzymatic and chromatographic techniques were used to analyze six oligosaccharides. The combined data showed that the fungal carbohydrates have a core structure that is identical to the mammalian N-linked core. In the bulk of the N-glycans, the alpha-1,3 arm is extended with two mannoses and a glucose, suggesting incomplete processing of the oligosaccharides in the endoplasmic reticulum. The alpha-1,6 arm shows a remarkable heterogeneity: in addition to alpha-1,2-Man and alpha-1,6-Man, the presence of a terminal mannose alpha-1,6-phosphodiester was observed. This latter substituent has not been characterized before on mannosidase-processed N-glycan and its function and synthesis pathway are entirely unknown. The predominant N-glycans on cellobiohydrolase I can be represented as follows: GlcMan8GlcNAc2, GlcMan7GlcNAc2, Man7GlcNAc2, ManPGlcMan7GlcNAc2, GlcMan5GlcNAc2 and Man5GlcNAc2.

Occurence of a sialylglycopeptide and free sialylglycans in hen's egg yolk

Free sialylglycans (FSGs) and a sialylglycopeptide (SGP) as components of hen's egg yolk were found and their chemical structures were determined. SGP and FSGs were isolated from fresh egg yolk by treatment with phenol, gel filtration and successive chromatographies on columns of anion- and cation-exchangers. They were localized in the yolk plasma. The glycan moiety of SGP, which was liberated by PNGase digestion, was studied for the chemical structure by HPLC mapping with p-aminobenzoic ethylester-derivatization, sugar composition analysis, 1H nuclear magnetic resonance and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and the glycomoiety was found to be an N-linked disialyl-biantennary glycan. The amino acid sequence of the peptide moiety of SGP was determined to consist of Lys-Val-Ala-Asn-Lys-Thr, the Asn of which is modified with the disialylglycan moiety. FSGs were determined to be two free disialyl-biantennary glycans whose reducing end was either Man beta1-4GlcNAc (FSG-I) or Man beta1-4GlcNAc beta1-4GlcNAc (FSG-II). Since the molar value of SGP present in one egg yolk (2.8 micromol) is comparable to those of well-known major yolk proteins, low density lipoprotein, lipovitellins and phosvitin, it can be considered that SGP is one of the major components in hen's egg yolk.

Molecular structure of the "low molecular weight antigen" of Toxoplasma gondii: a glucose alpha 1-4 N-acetylgalactosamine makes free glycosyl-phosphatidylinositols highly immunogenic

Toxoplasma gondii is a ubiquitous parasitic protozoan causing congenital infection and severe encephalitis in the course of the acquired immunodeficiency syndrome. Glycosyl-phosphatidylinositols of T. gondii have been shown to be identical with the low molecular weight antigen which elicits an early immunoglobulin M immune response in humans. A detailed study of the structures of these glycolipid antigens was performed. Radiolabelled glycolipids were extensively analysed by chemical and exoglycosidase treatments in combination with high pH anion-exchange chromatography, gel-filtration and lectin affinity chromatography. In addition, carbohydrate fragments prepared and purified from bulk preparations of unlabelled glycolipids by high performance liquid chromatography were subjected to two-dimensional 1H nuclear magnetic resonance spectroscopy, fast-atom bombardment-mass spectrometry, and methylation linkage analysis in order to elucidate the structure of T. gondii GPIs. The following structures were identified: (ethanolamine-PO4)-Man alpha 1-2Man alpha 1-6(GalNAc beta 1-4)Man alpha 1-4GlcN alpha-inositol-PO4-lipid and the novel structure (ethanolamine-PO4)-Man alpha 1-2Man alpha 1-6(Glc alpha 1-4GalNAc beta 1-4)Man alpha 1-4 GlcN alpha-inositol-PO4-lipid both with and without terminal ethanolamine phosphate. Evidence is provided, that only T. gondii GPIs bearing the unique glucose-N-acetylgalactosamine side branch are immunogenic in humans and that this structure is widely distributed among T. gondii isolates. Monoclonal antibodies have been characterized to recognize structures with different degrees of side-chain modification. We suggest that these reagents in combination with recently devised techniques for insertional mutagenesis in T. gondii should greatly facilitate the cloning of genes essential for GPI side-chain modification.

1H and 13C NMR analysis of the pentasaccharide Gal beta (1-->4)GlcNAc beta (1-->3)-[GlcNAc beta (1-->6)]Gal beta (1-->4)GlcNAc synthesized by the mid-chain beta-(1-->6)-D-N-acetylglucosaminyltransferase of rat serum

Chemical shifts and coupling constants of completely assigned 1H and 13C NMR spectra at 500 MHz, as well as ROESY and HMBC connectivities were used to establish the structure of the pentasaccharide Gal beta (1-->4)GlcNAc beta (1-->3)[GlcNAc beta (1-->6)]Gal beta (1-->4)GlcNAc, synthesized by the action of the mid-chain beta-(1-->6)-D-N-acetylglucosaminyltransferase of rat serum from UDP-GlcNAc and the linear tetrasaccharide Gal beta (1-->4)GlcNAc beta (1-->3)Gal beta (1-->4)GlcNAc.

Complete 1H and 13C resonance assignments of a 21-amino acid glycopeptide prepared from human serum transferrin

A 21-amino acid glycopeptide (Gp21) was isolated and purified in multi-milligram yields from commercially available human serum transferrin (HSTF) by a combination of tryptic digestion, Con A affinity chromatography, and reverse phase HPLC. The peptide chain of Gp21 contains a single N-glycosylation site to which a diantennary oligosaccharide is attached. The amino acid sequence and the glycan primary structure of Gp21 have been verified by peptide sequencing, electrospray mass spectrometry, and one-dimensional 1H NMR spectroscopy. Different glycoforms were found for the glycan of Gp21 derived from two different batches of commercial HSTF. These glycoforms differ from one another in the number of NeuAc residues (ranging from 0 to 2) and/or the number of Gal residues (ranging from 1 to 2). As for the monogalacto species, in the two-dimensional nuclear Overhauser effect (NOE) spectrum of Gp21, interglycosidic NOEs were observed between Man4 in the alpha (1-->3) branch and the terminal GlcNAc beta (1-->2) residue. No interglycosidic NOE was observed between Man4' in the alpha (1-->6) branch and the terminal GlcNAc residue. These observations indicate that the terminal GlcNAc residue in the minor glycoforms of Gp21 is exclusively located in the alpha (1-->3) branch of the Gp21 glycan. The occurrence of such a carbohydrate structure in HSTF has not been reported before. The 1H and 13C NMR spectra of Gp21 have been completely assigned by two-dimensional homonuclear and heteronuclear spectroscopy. The close similarity of the 1H and 13C chemical shift values for the Gp21 glycan with the respective values for the peptide-free diantennary oligosaccharide (Wieruszeski et al., Glycoconjugate J., 6 (1989) 183-194) indicates that the 1H and 13C chemical shifts of the diantennary oligosaccharide are not perturbed by the presence of the Gp21 peptide fragment. The complete 1H and 13C resonance assignments and the full characterization of the primary structure of Gp21 will permit us to study the conformation and dynamics of the N-linked diantennary oligosaccharides while covalently attached to a polypeptide fragment.

Exploring the substrate specificities of alpha-2,6- and alpha-2,3-sialyltransferases using synthetic acceptor analogues

The acceptor specificities of rat liver Gal(beta 1-4)GlcNAc alpha-2,6-sialyltransferase, recombinant full-length human liver Gal(beta 1-4)GlcNAc alpha-2,6-sialyltransferase, and a soluble form of recombinant rat liver Gal(beta 1-3/4)GlcNAc alpha-2,3-sialyltransferase were studied with a panel of analogues of the trisaccharide Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-O)(CH2)7CH3. These analogues contain structural variants of D-galactose, modified at either C3, C4 or C5 by deoxygenation, fluorination, O-methylation, epimerization, or by the introduction of an amino group. In addition, the enantiomer of D-galactose is included. The alpha-2,6-sialyltransferases tolerated most of the modifications at the galactose residue to some extent, whereas the alpha-2,3-sialyltransferase displayed a narrower specificity. Molecular dynamics simulations were performed in order to correlate enzymatic activity to three-dimensional structure. Ineffective acceptors for rat liver alpha-2,6-sialyltransferase were shown to be inhibitory towards the enzyme; likewise, the alpha-2,3-sialyltransferase was found to be inhibited by all non-substrates. Modified sialyloligosaccharides were obtained on a milligram scale by incubation of effective acceptors with one of each of the three enzymes, and characterized by 500-MHz 1H-NMR spectroscopy.

The structure of the keratan sulphate chains attached to fibromodulin isolated from articular cartilage

Fibromodulin has been isolated from bovine and equine articular cartilage and the attached keratan sulphate chains subjected to digestion by keratanase II. The oligosaccharides generated have been reduced and subsequently isolated by strong anion-exchange chromatography. Their structures have been determined by high-field 1H-NMR spectroscopy and high-pH anion-exchange chromatography. Both alpha(2-6)- and alpha(2-3)-linked N-acetylneuraminic acid have been found in the capping oligosaccharides, and, fucose which is alpha(1-3)-linked to N-acetylglucosamine has been found as a branch in both repeat region and capping oligosaccharides. These data demonstrate that there are fundamental differences between the structures present in the N-linked keratan sulphate chains attached to fibromodulin from articular cartilage and those from tracheal cartilage, which lack both alpha(2-6)-linked N-acetylneuraminic acid and alpha(1-3)-linked fucose. It has been confirmed that the keratan sulphate chains are short, being only eight or nine disaccharides in length. Very significant differences in the levels of galactose sulphation have been identified at the non-reducing end of the chain. The galactose residue adjacent to the non-reducing cap is sulphated in only 1-3% of chains, compared with a sulphation level of over 40% closer to the reducing end. This highlights the difference between the chain termini and the repeat region in terms of structure and points to the potential for functional importance. The repeat region and capping fragments of the N-linked keratan sulphates from bovine and equine articular cartilage fibromodulin have been found to have the following general structure: NeuAc-(alpha 2-3/6)Gal[6SO3-](beta 1-4)GlcNAc6SO3-(beta 1-3)Gal[6SO3-] (beta 1-4)¿[Fuc(alpha 1-3)]0-1GlcNAc6SO3-(beta 1-3)Gal-[6SO3-](beta 1-4)¿ 6-7GlcNAc6SO3-.

Primary structure of the N-linked carbohydrate chains of Calreticulin from spinach leaves

Calreticulin is a multifunctional Ca(2+)-binding protein of the endoplasmic reticulum of most eukaryotic cells. The 56 kDa Calreticulin glycoprotein isolated from spinach (Spinacia oleracea L.) leaves was N-deglycosylated by PNGase-F digestion. The carbohydrate moiety was isolated by gel permeation chromatography and purified by high-pH anion-exchange chromatography. The fractions were investigated by 500 MHz 1H-NMR spectroscopy, in combination with monosaccharide analysis and fast-atom bombardment-mass spectrometry. The following carbohydrate structure could be established as the major component (Man8GlcNAc2): (sequence see text) Heterogeneity was demonstrated by the presence of two minor components being Man7GlcNAc2 lacking a terminal residue (D1 or D3), compared to the major component. A cross-reactivity with an antibody against the endoplasmic reticulum retention signal HDEL was also found.

Glycopeptide mimics of mammalian Man9GlcNAc2. Ligand binding to mannan-binding proteins (MBPs)

A novel and simple approach for rational design of oligosaccharide mimics has been developed. Mammalian high-mannose triantennary structure Man9GlcNac2 has been subjected to molecular modelling using the NMR data available on structural fragments of the oligosaccharide. The analysis indicated four different low energy conformations, and the spatial arrangement of terminal disaccharides of the oligosaccharide antennae were stimulated with glycopeptides carrying disaccharides by applying weak constraints between the saccharide parts in MD-simulations on a large array of tri- to octaglycopeptides. The five glycopeptides exhibiting the best fit with the four minimum energy confirmations of the oligosaccharide were synthesized by solid phase glycopeptide assembly using glycosylated fluoren-9-ylmethyloxycarbonyl-amino acid-O-pentafluorophenyl esters as building blocks. The glycan was acyl protected alpha-D-Man-(1-->2)-alpha-D-Man and Ser, Thr and Hyp were the glycosylated amino acids. The deprotected and purified glycopeptides were subjected to NMR analysis for characterization, and in order to investigate the cis-trans isomerism of the carbimide bonds to Hyp. The glycopeptides were tested for their ability to inhibit binding of mannan-binding protein to mannan from Saccharomyces cerevisiae. They were found to be weak inhibitors showing no indication of multivalent interaction with the mannan-binding protein.

Novel sulfated oligosaccharides containing 3-O-sulfated glucuronic acid from king crab cartilage chondroitin sulfate K. Unexpected degradation by chondroitinase ABC

We prepared a series of oligosaccharides from king crab cartilage chondroitin sulfate K after exhaustive digestion with testicular hyaluronidase, and determined the structures of four tetrasaccharides and a pentasaccharide by fast atom bombardment mass spectrometry, high performance liquid chromatography analysis of chondroitinase AC-II digests, and 500-MHz 1H NMR spectroscopy. The tetrasaccharides shared the common core structure GlcAbeta1-3GalNAcbeta1-4GlcAbeta1-3GalNAc with various sulfation profiles. One structure was GlcAbeta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S), whereas three of them have the following hitherto unreported structures including a novel glucuronate 3-O-sulfate: GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcAbeta1-3GalNAc(4S), GlcAbeta1-3GalNAc(4S)beta1-4GlcA(3S)beta1-3GalNAc(4S), and GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcA(3S)beta1-3GalNAc(4S), where 3S or 4S represents 3-O- or 4-O-sulfate, respectively. The structure of the pentasaccharide was determined as GlcA(3S)beta1-3GalNAc(4S)beta1-4GlcA(3S)beta1- 3GalNAc(4S)beta1-4GlcA. Chondroitinase ABC digestion of the tetrasaccharides with GlcA(3S) at the internal position destroyed the disaccharide unit containing GlcA(3S) derived from the reducing side and resulted in only the disaccharide unit from the non-reducing side. In contrast, these tetrasaccharides remained totally resistant to chondroitinase AC-II. The results indicated that it is necessary to reevaluate the disaccharide composition of chondroitin sulfate poly- or oligosaccharides purified from various biological sources, since they were usually determined after chondroitinase ABC digestion. It is probable that the structures containing GlcA(3S) would not have been detected.

Multiple non-reducing chain termini isolated from bovine corneal keratan sulfates

Keratan sulfate-containing proteoglycans were isolated from bovine cornea (15-month-old to 3-year-old animals) and digested with the enzyme, keratanase II. The released oligosaccharides, which included non-reducing termini and repeat region oligosaccharides but not linkage regions, were reduced with alkaline borohydride and fractionated on a Spherisorb column. These oligosaccharides were examined by 600-MHz 1H NMR spectroscopy using one- and two-dimensional methods and, in addition to some oligosaccharide alditols previously recovered from skeletal keratan sulfate, the following new capping structures were identified: NeuAcalpha2-6Galbeta1-4GlcNAc(S)-ol, NeuAcalpha2-3Gal(S)beta1-4GlcNAc(S)beta1-3Galbeta1-4GlcNAc(S )-ol, NeuGcalpha2-6Galbeta1-4GlcNAc(S)beta1-3Galbeta1-4Gl cNA c(S)-ol, NeuGcalpha2-3Galbeta1-4GlcNAc(S)beta1-3Galbeta1-4Gl cNA c(S)-ol, NeuGcalpha2-3Gal(S)beta1-4GlcNAc(S)beta1-3Galbeta1-4GlcNAc(S )-ol, NeuGcalpha2-3Gal(S)beta1-4GlcNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)-o l, Galalpha1-3Galbeta1-4GlcNAc(S)beta1-3Galbeta1-4GlcNAc( S)-ol, Galalpha1-3Galbeta1-4GlcNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)- ol, GlcNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)-ol, and GalNAc(S)beta1-3Gal(S)beta1-4GlcNAc(S)-ol. These structures represent seven families of capping residues, whose relative molar proportions are given in parentheses: NeuAcalpha(2-3)- (12%), NeuAcalpha(2-6)- (41%), NeuGcalpha(2-3)- and NeuGcalpha(2-6)- families (12%), Galalpha(1-3)- (26%), GalNAc(S)beta(1-3)- (5%), and GlcNAc(S)beta(1-3)- (4%). It is not clear, at present, where each of these structures occurs on the bi-antennary N-linked corneal keratan sulfate chains, which themselves occur within three keratan sulfate proteoglycan species. However, examination of the relative proportions of the capping to the repeat structures and knowledge of the average molecular size suggests that the sum of these non-reducing termini represents the caps of two antennae.

Structure of the HNK-1 carbohydrate epitope on bovine peripheral myelin glycoprotein P0

The HNK-1 carbohydrate epitope, expressed by many neural recognition molecules, is involved in cell interactions that control cell type-specific neurite outgrowth and regeneration. It is also the target for autoimmune IgM antibodies in demyelinating neuropathies of the peripheral nervous system in humans. Despite its acknowledged importance in cell interactions, the HNK-1 carbohydrate structure, when expressed on glycoproteins, is still unknown. Here, we describe the structure of one of the predominant HNK-1-bearing glycans of bovine P0. The epitope consists of the sulfated trisaccharide SO4-3GlcAbeta1-3Galbeta1-4GlcNAc, attached to the alpha1-6 arm of a diantennary core with a bisecting N-acetylglucosamine. It is the first example of a terminal 3-sulfated glucuronic acid on an asparagine-linked carbohydrate. Because the similarity between the glycoprotein-derived structure and the glycosphingolipids carrying HNK-1 is restricted to the terminal sulfated trisaccharide, we conclude that this element is sufficient for HNK-1 immunoreactivity. Knowledge of the HNK-1 structure on proteins is an important prerequisite for the elucidation of its functional role in development and disease.

Structural comparison of a 15 residue peptide from the V3 loop of HIV-1IIIb and an O-glycosylated analogue

As part of a program to study the effect of glycosylation on the three-dimensional structures of HIV-1IIIB V3 peptide constructs, we have examined the solution structures of a 15 residue peptide (RIQRGPGRAFVTIGK, P18IIIB)- originally mapped as an epitope recognized by CD8+ Dd class I MHC-restricted murine cytotoxic T-lymphocytes (CTL), and an analogue (P18IIIB-g), O-glycosylated with an alpha-galactosamine on Thr-12, using NMR, circular dichroism and molecular modeling methods. Our studies show that the peptides sample mainly random conformations in aqueous solution near 25 degrees C and become more ordered by the addition of trifluoroethanol. Upon decreasing the temperature to 5 degrees C, a reverse turn is formed around the immunodominant tip (G5-R8). Glycosylation on T12 'tightens' the turn slightly as suggested by NOE and CD analysis. In addition, the sugar has a defined conformation with respect to the peptide backbone and influences the local peptide conformation. These data suggest that simple glycosylation may influence the conformational equilibrium of a V3 peptide which contains a domain critical for antibody recognition and virus neutralization. We also show that the ability of cytotoxic T-lymphocytes (CTL) to lyse tumor cells presenting P18IIIB was completely abrogated by threonine glycosylation.

Structural characterization of the N-linked carbohydrate chains of the zona pellucida glycoproteins from bovine ovarian and fertilized eggs

The N-linked oligosaccharides that were released by hydrazinolysis from glycoproteins of zonae pellucidae of bovine ovarian eggs, were composed of neutral (23%) and acidic (77%) carbohydrate chains; almost all the acidic chains were neutralized by sialidase digestion. Sugar mapping analysis of pyridylaminated N-linked chains by reverse-phase and normal-phase HPLC and 500-MHz 1H-NMR spectroscopy revealed that the major neutral chain is a high-mannose-type oligosaccharide and the acidic chains are di-, tri-, and tetra-antennary, fucosylated complex-type chains that have N-acetyllactosamine repeats in the non-reducing regions. The structures of the neutral chain and the core regions of the acidic chains of N-linked oligosaccharides from the zona proteins of fertilized eggs, which were obtained by the in vitro fertilization method, were essentially the same as those of the ovarian egg zonae. The amount, however, of the acidic chains decreased to 32 mol/100 mol in the fertilized egg zonae, which suggests that a sialidase released from the oocyte during fertilization operates on the zona glycoproteins.

Structural determination of symbiotic nodulation factors from the broad host-range Rhizobium species NGR234

Nod factors are secreted lipo-oligosaccharides produced by symbiotic nitrogen-fixing Rhizobium bacteria that induce nodule formation on the roots of host leguminous plants. Two biologically active fractions (NodNGRA and NodNGRB) were isolated by reversed-phase HPLC from the culture supernatant of a Nod factor overproducing strain of Rhizobium sp. NGR234. NodNGRA and NodNGRB are heterogeneous mixtures of N-acylated 2-O-methylfucosylated chitomers, in which the fucosyl residue may be either 3-sulfated (NodNGRA), or 4-O-acetylated or nonsubstituted (NodNGRB). Structurally analogous series of compounds occur with either N-vaccenic (C18:1) or N-palmitic (C16:0) substituents. The presence of 6-O-carbamoyl groups on the GlcNMe-Acyl residue occurs on some molecules, while others are di-O-carbamoylated. Detailed structural analysis of seventeen Nod factors are reported here.

Structural analysis of unsaturated hexasaccharides isolated from shark cartilage chondroitin sulfate D that are substrates for the exolytic action of chondroitin ABC lyase

The enzymatic action of highly purified chondroitin ABC lyase from Proteus vulgaris is dependent on the size of the substrate, and the enzyme does not cleave tetrasaccharides, irrespective of their sulfation profiles [Sugahara, K., Shigeno, K., Masuda, M., Fujii, N., Kurosaka, A. & Takeda, K. (1994) Carbohydr. Res. 255, 145-163]. To characterize the enzyme action in more detail, we isolated nine sulfated hexasaccharides from commercial shark cartilage chondroitin sulfate D, after partial digestion with highly purified chondroitin ABC lyase, by means of gel chromatography and HPLC on an amine-bound silica column. Structural analysis by 500-MHz H-NMR spectroscopy, and enzymatic digestion in conjunction with HPLC, demonstrated that these hexasaccharides, with the common core saccharide structure delta 4 HexA (alpha 1-3)GalNAc(beta 1-4)GlcA(beta 1-3)GalNAc(beta 1-4) GlcA(beta 1-3)GalNAc(where delta 4 HexA and GlcA represent 4-deoxy-alpha-L-threo-hex-4-enepyranosyluronic acid and glucuronic acid, respectively) bear three or four sulfate groups in different combinations. In the hexasaccharides, the D, disaccharide unit GlcA2-SO3 (beta 1-3) GalNAc4SO(3-) which is characteristic of chondroitin sulfate D, was arranged on the reducing side of the A disaccharide unit GlcA(beta 1-3)GalNAc4SO(3)-, and thus formed an A-D tetrasaccharide sequence GlcA(beta 1-3)GalNAc4SO(3)-(beta 1-4)GlcA2SO(3)-(beta 1-3) GalNAc6SO(3)-. Analysis of the degradation products of these hexasaccharides with highly purified chondroitin ABC lyase indicated that the enzyme preferentially acted on the unsaturated hexasaccharides in an exolytic fashion and removed an unsaturated disaccharide unit from the non-reducing termini, irrespective of the sulfation profiles of the hexasaccharides.

One-pot enzymatic synthesis of the Gal alpha 1-->3Gal beta 1-->4GlcNAc sequence with in situ UDP-Gal regeneration

The trisaccharide Gal alpha 1-->3Gal beta 1-->4GlcNAc beta 1-->O-(CH2)8COOCH3 was enzymatically synthesized, with in situ UDP-Gal regeneration. By combination in one pot of only four enzymes, namely, sucrose synthase, UDP-Glc 4'-epimerase, UDP-Gal:GlcNAc beta 4-galactosyltransferase and UDP-Gal:Gal beta 1-->4GlcNAc alpha 3-galactosyltransferase, Gal alpha 1-->3Gal beta 1-->4GlcNAc beta 1-->O-(CH2)8COOCH3 was formed in a 2.2 mumol ml-1 yield starting from the acceptor GlcNAc beta 1-->O-(CH2)8COOCH3. This is an efficient and convenient method for the synthesis of the Gal alpha 1-->3Gal beta 1-->4GlcNAc epitope which pays an important role in various biological and immunological processes.

Preparation of a series of sulfated tetrasaccharides from shark cartilage chondroitin sulfate D using testicular hyaluronidase and structure determination by 500 MHz 1H NMR spectroscopy

Six tetrasaccharide fractions were isolated from shark cartilage chondroitin sulfate D by gel filtration chromatography followed by HPLC on an amine-bound silica column after exhaustive digestion with testicular hyaluronidase. Their structures were determined unambiguously by one- and two-dimensional 500 MHz 1H NMR spectroscopy in conjunction with HPLC analysis of chondroitinase AC-II digests of the tetrasaccharides. One fraction was found to contain two tetrasaccharide components. All of the seven tetrasaccharides shared the common core structure GlcA beta 1-3GalNAc beta 1-4GLcA beta 1-3GalNAc with various sulfation profiles. Four were disulfated comprising of two monosulfated disaccharide units GLcA beta 1-3GalNAc(4-sulfate) and/or GlcA beta 1-3GalNAc(6-sulfate), whereas the other three were hitherto unreported trisulfated tetrasaccharides containing a disulfated disaccharide unit GlcA(2-sulfate)beta 1-3GalNAc(6-sulfate) and a monosulfated disaccharide unit GlcA beta 1-3GalNac(4- or 6-sulfate). These sulfated tetrasaccharides were demonstrated to serve as appropriate acceptor substrates for serum alpha-N-acetylgalactosaminyltransferase, indicating their usefulness as authentic oligosaccharide substrates or probes for the glycobiology of sulfated glycosaminoglycans.

Structural and conformational analysis of glycan moieties in situ on isotopically 13C, 15N-enriched recombinant human chorionic gonadotropin

The conformational properties in solution of the glycans on the alpha subunit of recombinant human chorionic gonadotropin are described, using high-resolution multinuclear NMR studies on uniformly 13C, 15N-enriched recombinant glycoprotein expressed in CHO cells. The glycan important for full biological activity of hCG, namely, that at Asn 52, appears to extend into solution both in the isolated alpha subunit and in complex with the beta subunit. The disposition of this glycan with respect to the protein backbone suggests that glycosylation maintains full biological activity of hCG either by interacting with a lectin-like region of the hCG receptor or by reducing the affinity of the hormone for the hCG receptor and preventing its down-regulation.

Occurrence and structural analysis of highly sulfated multiantennary N-linked glycan chains derived from a fertilization-associated carbohydrate-rich glycoprotein in unfertilized eggs of Tribolodon hakonensis

This study represents the first detailed investigation of the nature of highly sulfated (keratan-sulfate-like) complex-type asparagine-linked glycans having a tetraantennary core structure and shows the effectiveness of fast-atom-bombardment mass spectrometric (FAB-MS) methods incorporating derivatization and mild methanolysis for analyzing such complex types of sulfated glycans. The structure of the N-glycan chains was unambiguously established by a combination of compositional analysis, methylation analysis, mild methanolysis for desulfation, hydrazinolysis/nitrous acid deamination, enzymatic (endo-beta-galactosidase and peptide:N-glycosidase F) digestions, and instrumental analyses (1H-NMR spectroscopy and FAB-MS) which revealed the novel repeating sulfated carbohydrate sequences, +/- Gal beta 1-->4Gal beta 1[-->(HSO3-->6)GlcNAc beta 1-->3(+/- Gal beta 1-->4)Gal beta 1]n--> (see Structure I; p + q + r + s approximately 14). This sequence is unique in: (a) the skeletal structure is similar to that of keratan sulfate but is completely devoid of 6-O-sulfated Gal residues and (b) the presence of branched Gal residues in the sequence -->4GlcNAc beta 1-->3(Gal beta 1-->4)Gal beta 1-->. [formula: see text]

Structures of five sulfated hexasaccharides prepared from porcine intestinal heparin using bacterial heparinase. Structural variants with apparent biosynthetic precursor-product relationships for the antithrombin III-binding site

Porcine intestinal heparin was extensively digested with Flavobacterium heparinase and size-fractionated by gel chromatography. Subfractionation of the hexasaccharide fraction by anion exchange high pressure liquid chromatography yielded 10 fractions. Six contained oligosaccharides derived from the repeating disaccharide region, whereas four contained glycoserines from the glycosaminoglycan-protein linkage region. The latter structures were reported recently (Sugahara, K., Tsuda, H., Yoshida, K., Yamada, S., de Beer, T., and Vliegenthart, J.F.G. (1995) J. Biol. Chem. 270, 22914-22923). In this study, the structures of one tetra- and five hexasaccharides from the repeat region were determined by chemical and enzymatic analyses as well as 500-MHz 1H NMR spectroscopy. The tetrasaccharide has the hexasulfated structure typical of heparin. The five hexa- or heptasulfated hexasaccharides share the common core pentasulfated structure delta HexA(2S) alpha 1-4GlcN-(NS, 6S) alpha 1-4IdoA alpha/GlcA beta 1-4GlcN(6S) alpha 1-4GlcA beta 1-4GlcN (NS) with one or two additional sulfate groups (delta HexA, GlcN, IdoA, and GlcA represent 4-deoxy-alpha-L-threo-hex-4-enepyranosyluronic acid, D-glucosamine, L-iduronic acid, and D-glucuronic acid, whereas 2S, 6S and NS stand for 2-O-, 6-O-, and 2-N-sulfate, respectively). Three components have the following hitherto unreported structures: delta HexA(2S) alpha 1-4GlcN(NS, 6S) alpha 1-4GlcA beta 1-4GlcN(NS, 6S) alpha 1-4GlcA beta 1-4GlcN(NS,6S), delta HexA(2S) alpha 1-4GlcN(NS, 6S) alpha 1-4IdoA alpha 1-4GlcNAc(6S)-alpha 1-4GlcA beta 1-4GlcN(NS, 3S), and delta HexA(2S) alpha 1-4GlcN-(NS,6S) alpha 1-4IdoA (2S) alpha 1-4GlcNAc(6S) alpha 1-4GlcA beta 1-4GlcN(NS, 6S). Two of the five hexasaccharides are structural variants derived from the antithrombin III-binding sites containing 3-O-sulfated GlcN at the reducing termini with or without a 6-O-sulfate group on the reducing N,3-disulfated GlcN residue. Another contains the structure identical to that of the above heptasulfated antithrombin III-binding site fragment but lacks the 3-O-sulfate group and therefore is a pro-form for the binding site. Another has an extra sulfate group on the internal IdoA residue of this pro-form and therefore can be considered to have diverged from the binding site in the biosynthetic pathway. Thus, the isolated hexasacharides in this study include the three overlapping pairs of structural variants with an apparent biosynthetic precursor-product relationship, which may reflect biosynthetic regulatory mechanisms of the binding site.

The analysis of fluorophore-labeled carbohydrates by polyacrylamide gel electrophoresis

The glycans of glycoconjugates mediate numerous important biological processes. Their separation and structural determination present considerable difficulties because of the small quantities that are available from biological sources and the inherent difficulty of analyzing the wide variety of complex structures that exist. A method for the analysis of reducing saccharides by PAGE that uses specific fluorophore labeling and is simple, rapid, sensitive, and readily available to biological researchers, has been developed. This method is known acronimically either as PAGEFS (PAGE of Fluorophore-labeled Saccharides) or in one commercial format as FACE (Fluorophore-Assisted Carbohydrate Electrophoresis). In the PAGEFS method, saccharides having an aldehydic reducing end group are labeled quantitatively with a fluorophore and then separated with high resolution by PAGE. Two fluorophores, 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS) and 2-aminoacridone (AMAC), have been used to enable the separation of a variety of saccharide positional isomers, anomers, and epimers. Subpicomolar quantities of individual saccharides can be detected using a sensitive imaging system. Mixtures of oligosaccharides obtained by enzymatic cleavage from glycoproteins can be labeled and electrophoresed to yield an oligosaccharide profile of each protein. AMAC can be used to distinguish unequivocally between acidic and neutral oligosaccharides. Methods of obtaining saccharide sequence information from purified oligosaccharides have been developed using enzymatic degradation. Other applications and the potential of the system are described.

Identification of a GDP-Fuc:Gal beta 1-3GalNAc-R (Fuc to Gal) alpha 1-2 fucosyltransferase and a GDP-Fuc:Gal beta 1-4GlcNAc (Fuc to GlcNAc) alpha 1-3 fucosyltransferase in connective tissue of the snail Lymnaea stagnalis

Connective tissue of the freshwater pulmonate Lymnaea stagnalis was shown to contain fucosyltransferase activity capable of transferring fucose from GDP-Fuc in alpha 1 -2 linkage to terminal Gal of type 3 (Gal beta 1-3GalNAc) acceptors, and in alpha 1-3 linkage to GlcNAc ot type 2 (Gal beta 1-4GlcNAc) acceptors. The alpha 1-2 fucosyltransferase was active with Gal beta 1-3GalNAc beta 1-OCH2CH=CH2 (Km = 12mM, V(max) = 1.3 mUml-1) and Gal beta 1-3GalNAc (km =20 mM, V(max) = 2.1 mUml-1), whereas the alpha 1-3 fucosyltransferase was active with Gal beta 1-4GlcNAc (Km = 23 mM, V(max) = 1.1 mUml-1). The products formed from from Gal beta 1-3GalNAc beta 1-OCH2CH=CH2 and Gal beta 1-4GlcNAc were purified by high performance liquid chromatography, and identified by 500 MHz 1H-NMR spectroscopy and methylation analysis to be Fucalpha1-2Gal beta 1-3GalNAc beta 1-OCH2CH=CH2 and Gal beta 1-4(Fucalpha1-3)GlcNAc, respectively. Competition experiments suggest that the two fucosyltransferase activities are due to two distinct enzymes.

Isolation and structures of glycoprotein-derived free oligosaccharides from the unfertilized eggs of Scyliorhinus caniculus. Characterization of the sequences galactose(alpha 1-4)galactose(beta 1-3)-N-acetylglucosamine and N-acetylneuraminic acid(alpha 2-6)galactose(beta 1-3)-N-acetylglucosamine

As previously reported [Ishii, K., Iwasaki, M., Inoue, S., Kenny, P. T. M., Komura, H. & Inoue, Y. (1989) J. Biol. Chem. 264, 1623-1630; Inoue, S., Iwasaki, M., Ishii, K., Kitajima, K. & Inoue, Y. (1989) J. Biol. Chem. 264, 18520-185261, the unfertilized eggs of two different species of fresh-water fish, Plecoglossus altivelis and Tribodolon hakonensis, contain relatively large amounts of free sialooligosaccharides. These oligosaccharides were found to derive from glycophosphoproteins, owing to the activity of a peptide - N4-(N-acetyl-beta-D-glucosaminyl)asparagine amidase [Iwasaki, M., Seko, A., Kitajima, K., Inoue, Y. & Inoue, S. (1992) J. Biol. Chem. 267, 24287-24296; Seko, A., Kitajima, K., Inoue, Y. & Inoue, S. (1991) J. Biol. Chem. 266, 22110-22114]. Here we describe a new type of free oligosaccharides, isolated from unfertilized eggs of Scyliorhinus caniculus. From the structural analysis, based upon 1H-NMR spectroscopy, the following glycan units are proposed.[Formula: see text]

Preparative purification of tyrosinamide N-linked oligosaccharides

N-linked oligosaccharides from glycoproteins can be either analyzed on a sub-nanomole scale or preparatively purified on a multi-micromole scale. Each goal necessitates a unique analytical strategy often involving oligosaccharide derivatization to enhance separation and detection. Tyrosinamide-oligosaccharides were developed to facilitate the preparative purification of N-linked oligosaccharides. These have found many uses in oligosaccharide remodeling, in the preparation of neoglycoconjugates, in developing receptor probes, and even as analytical standards in chromatography. This review discusses progress in the preparation of tyrosinamide-oligosaccharides from different glycoproteins and their utility in glycobiology research.

LEC18, a dominant Chinese hamster ovary glycosylation mutant synthesizes N-linked carbohydrates with a novel core structure

The dominant Chinese hamster ovary cell glycosylation mutant, LEC18, was selected for resistance to pea lectin (Pisum sativum agglutinin (PSA)). Lectin binding studies show that LEC18 cells express altered cell surface carbohydrates with markedly reduced binding to 125I-PSA and increased binding to 125I-labeled Datura stramonium agglutinin (DSA) compared with parental cells. Desialylated [3H]Glc-labeled LEC18 cellular glycopeptides that did not bind to concanavalin A-Sepharose exhibited an increased proportion of species that were bound to DSA-agarose. Most of these glycopeptides bound to ricin-agarose and were unique to LEC18 cells. This fraction was purified from approximately 10(10) cells and shown by 1H NMR spectroscopy and methylation linkage analysis to contain novel N-linked structures. Digestion of these glycopeptides with mixtures of beta-D-galactosidases and N-acetyl-beta-D-glucosaminidases gave core glycopeptides that, in contrast to cores from parental cells, were mainly not bound to concanavalin A-Sepharose or to PSA-agarose. 1H NMR spectroscopy, matrix-assisted laser desorption ionization/time of flight mass spectrometry, electrospray mass spectrometry, and collision-activated dissociation mass spectrometry showed that the LEC18 core glycopeptides contained a new GlcNAc residue that substitutes the core GlcNAc residues. Methylation linkage analysis of the parent compound provided evidence that the GlcNAc is linked at O-6 to give the following novel, N-linked core structure. [formula: see text]

Structure of glycopeptides isolated from bovine milk component PP3

The heat-stable acid-soluble phosphoglycoprotein component PP3 was isolated from the bovine milk proteose peptone fraction by concanavalin A affinity chromatography. Glycopeptides were released by pronase digestion of the milk component PP3 and were subsequently separated by high-pH anion-exchange chromatography on CarboPac PA-1. The primary structures of the glycan and peptide moieties of eight N-glycopeptides have been established by combining methylation analysis, mass spectrometry, 400-MHz 1H-NMR spectroscopy, and peptide sequence analysis. All the analyzed fractions contained biantennary N-acetyllactosamine-type carbohydrate chains, some of them with a GalNAc(beta 1-4)GlcNAc or a NeuAc(alpha 2-6)GalNAc(beta 1-4)GlcNAc group. This particular sequence did or did not replace the Gal(beta 1-4)GlcNAc group usually found in most N-linked glycans. Moreover, the sialylated Gal and GalNAc residues were only found on the Man(alpha 1-3) antenna.

Enzymatic synthesis of a sialyl Lewis X dimer from egg yolk as an inhibitor of E-selectin

A dimeric sialyl Lewis X (SLex) glycopeptide was synthesized enzymatically in three steps from an N-linked oligosaccharide prepared from egg yolk. Treatment of delipidated hen egg yolk with the protease Orientase and neuraminidase gave a dimeric N-acetyllactosamine-containing oligosaccharide linked to asparagine. Addition of sialic acid and fucose catalyzed by alpha-2,3-sialyltransferase and alpha-1,3-fucosyltransferase provided the dimeric SLex, which was shown to be as active as monomeric SLex as an inhibitor of E-selectin with IC50 0.75 mM. The synthetic dimeric SLex of the mucin type (i.e. SLex linked to the 3- and 6-OH groups of Gal) is, however, about five times as active as the monomer. It is suggested that dimeric SLex glycopeptides of the mucin type would be effective ligands for E-selectin.

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

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

The uniform galactose 4-sulfate structure in the carbohydrate-protein linkage region of human urinary trypsin inhibitor

The carbohydrate-protein linkage region of a chondroitin 4-sulfate chain attached to urinary trypsin inhibitor (UTI) was isolated from human urine and characterized structurally. The chondroitin 4-sulfate chain was released from UTI by beta-elimination using alkaline NaBH4 then digested with chondroitinase ABC. These treatments resulted in only a single hexasaccharide alditol derived from the carbohydrate-protein linkage region. Chemical and enzymic analyses and 600-MHz 1H-NMR spectroscopy revealed that the hexasaccharide alditol had the following structure: delta HexA alpha 1-3GalNAc(4-sulfate) beta 1-4GlcA beta 1- 3Gal(4-sulfate) beta 1-3Gal beta 1-4Xyl-ol, where delta HexA, GlcA and Xyl-ol represent 4-deoxy-alpha-L-threo-hex-4-enepyranosyluronic acid, D-glucuronic acid and D-xylitol, respectively. This structure contained the novel 4-sulfated Gal residue, which was first demonstrated in one of the three linkage hexasaccharide-serines isolated from chondroitin 4-sulfate of rat chondrosarcoma [Sugahara, K., Yamashina, I., de Waard, P., Van Halbeek, H. & Vliegenhart, J. F. G. (1988) J. Biol. Chem. 263, 10168-10174]. This disulfated structure was recently identified as the sole structural component in the linkage hexasaccharide alditol fraction isolated from inter-alpha-trypsin inhibitor (ITI) in human plasma [Yamada, S., Oyama, M., Kinugasa, H., Nakagawa, T., Kawasaki, T., Nagasawa, S., Khoo, K.-H., Morris, H.R., Dell, A. & Sugahara, K. (1995) Glycobiology 5, 335-341]. The structural uniformity in the linkage hexasaccharide structure of ITI and UTI is in marked contrast to the heterogeneity demonstrated in the linkage hexasaccharides isolated from cartilaginous chondroitin sulfate whose linkage regions are sometimes but not always phosphorylated on the Xyl residue or sulfated on the Gal residue(s). The uniform structure containing the novel 4-sulfated Gal residue in the linkage region of UTI and ITI may imply its significance in the biosynthetic mechanism of chondroitin sulfate.