Variable domain-linked oligosaccharides of a human monoclonal IgG: structure and influence on antigen binding.
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The variable-domain-attached oligosaccharide side chains of a human IgG produced by a human-human-mouse heterohybridoma were analysed. In addition to the conserved N-glycosylation site at Asn-297, an N-glycosylation consensus sequence (Asn-Asn-Ser) is located at position 75 in the variable region of its heavy chain. The antibody was cleaved into its antigen-binding (Fab) and crystallizing fragments. The oligosaccharides of the Fab fragment were released by digestion with various endo- and exoglycosidases and analysed by anion-exchange chromatography and fluorophore-assisted carbohydrate electrophoresis. The predominant components were disialyl- bi-antennary and tetra-sialyl tetra-antennary complex carbohydrates. Of note is the presence in this human IgG of oligosaccharides containing N-glycolylneuraminic acid and N-acetylneuraminic acid in the ratio of 94:6. Furthermore, we determined N-acetylgalactosamine in the Fab fragment of this antibody, suggesting the presence of O-linked carbohydrates. A three-dimensional structure of the glycosylated variable (Fv) fragment was suggested using computer-assisted modelling. In addition, the influence of the Fv-associated oligosaccharides of the CBGA1 antibody on antigen binding was tested in several ELISA systems. Deglycosylation resulted in a decreased antigen-binding activity. (+info)
Structural characterization of the N-linked oligosaccharides in bile salt-stimulated lipase originated from human breast milk.
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The detailed structures of N- glycans derived from bile salt-stimulated lipase (BSSL) found in human milk were determined by combining exoglycosidase digestion with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The N- glycan structures were conclusively determined in terms of complexity and degree of fucosylation. Ion-exchange chromatography with pulsed amperometric detection, together with mass-spectral analysis of the esterified N- glycans, indicated the presence of monosialylated structures. The molecular mass profile of esterified N- glycans present in BSSL further permitted the more detailed studies through collision-induced dissociation (CID) and sequential exoglycosidase cleavages. The N- glycan structures were elucidated to be complex/dibranched, fucosylated/complex/dibranched, monosialylated/complex/dibranched, and monosialylated/fucosylated/dibranched entities. (+info)
Gas-liquid chromatography of the heptafluorobutyrate derivatives of the O-methyl-glycosides on capillary columns: a method for the quantitative determination of the monosaccharide composition of glycoproteins and glycolipids.
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We have developed a method involving the formation of hepta-fluorobutyrate derivatives of O-methyl-glycosides liberated from glycoproteins and glycolipids following methanolysis. The stable derivatives of the most common monosaccharides of these glycoconjugates (Ara, Rha, Xyl, Fuc, Gal, Man, Glc, GlcNAc, GalNAc, Neu5Ac, KDN) can be separated and quantitatively and reproducibly determined with a high degree of sensitivity level (down to 25 pmol) in the presence of lysine as an internal standard. The GlcNAc residue bound to Asn in N-glycans is quantitatively recovered as two peaks. The latter were easily distinguished from the other GlcNAc residues of N-glycans, thus allowing a considerable improvement of the data on structure of N-glycans obtained from a single carbohydrate analysis. The most common contaminants present in buffers commonly used for the isolation of soluble or membrane-bound glycoproteins (SDS, Triton X-100, DOC, TRIS, glycine, and polyacrylamide or salts, as well as monosaccharide constituents of proteoglycans or degradation products of nucleic acids) do not interfere with these determinations. A carbohydrate analysis of glycoproteins isolated from a SDS/PAGE gel or from PDVF membranes can be performed on microgram amounts without significant interferences. Since fatty acid methyl esters and sphingosine derivatives are separated from the monosaccharide peaks, the complete composition of gangliosides can be achieved in a single step starting from less than 1 microg of the initial compound purified by preparative Silicagel TLC. Using electron impact ionization mass spectrometry, reporter ions for the different classes of O-methyl-glycosides (pentoses, deoxy-hexoses, hexoses, hexosamines, uronic acids, sialic acid, and KDN) allow the identification of these compounds in very complex mixtures. The mass of each compound can be determined in the chemical ionization mode and detection of positive or negative ions. This method presents a considerable improvement compared to those using TMS derivatives. Indeed the heptafluorobutyrate derivatives are stable, and acylation of amino groups is complete. Moreover, there is no interference with contaminants and the separation between fatty acid methyl-esters and O-methyl glycosides is achieved. (+info)
An improved method for the structural profiling of keratan sulfates: analysis of keratan sulfates from brain and ovarian tumors.
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A previously developed method for the structural fingerprinting of keratan sulfates (Brown et al., Glycobiology, 5, 311-317, 1995) has been adapted for use with oligosaccharides fluorescently labeled with 2-aminobenzoic acid following keratanase II digestion. The oligosaccharides are separated by high-pH anion-exchange chromatography on a Dionex AS4A-SC column. This methodology permits quantitative analysis of labeled oligosaccharides which can be detected at the sub-nanogram ( approximately 100 fmol) level. Satisfactory calibration of this method can be achieved using commercial keratan sulfate standards. Keratan sulfates from porcine brain phosphocan and human ovarian tumors have been examined using this methodology, and their structural features are discussed. (+info)
The sialylation of bronchial mucins secreted by patients suffering from cystic fibrosis or from chronic bronchitis is related to the severity of airway infection.
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Bronchial mucins were purified from the sputum of 14 patients suffering from cystic fibrosis and 24 patients suffering from chronic bronchitis, using two CsBr density-gradient centrifugations. The presence of DNA in each secretion was used as an index to estimate the severity of infection and allowed to subdivide the mucins into four groups corresponding to infected or noninfected patients with cystic fibrosis, and to infected or noninfected patients with chronic bronchitis. All infected patients suffering from cystic fibrosis were colonized by Pseudomonas aeruginosa. As already observed, the mucins from the patients with cystic fibrosis had a higher sulfate content than the mucins from the patients with chronic bronchitis. However, there was a striking increase in the sialic acid content of the mucins secreted by severely infected patients as compared to noninfected patients. Thirty-six bronchial mucins out of 38 contained the sialyl-Lewis x epitope which was even expressed by subjects phenotyped as Lewis negative, indicating that at least one alpha1,3 fucosyltransferase different from the Lewis enzyme was involved in the biosynthesis of this epitope. Finally, the sialyl-Lewis x determinant was also overexpressed in the mucins from severely infected patients. Altogether these differences in the glycosylation process of mucins from infected and noninfected patients suggest that bacterial infection influences the expression of sialyltransferases and alpha1,3 fucosyltransferases in the human bronchial mucosa. (+info)
Inhibition of L-selectin-mediated leukocyte rolling by synthetic glycoprotein mimics.
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Synthetic carbohydrate and glycoprotein mimics displaying sulfated saccharide residues have been assayed for their L-selectin inhibitory properties under static and flow conditions. Polymers displaying the L-selectin recognition epitopes 3',6-disulfo Lewis x(Glc) (3-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)-6-O-SO3-Glcbeta+ ++-OR) and 3',6'-disulfo Lewis x(Glc) (3, 6-di-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)Glcbeta-OR) both inhibit L-selectin binding to heparin under static, cell-free binding conditions with similar efficacies. Under conditions of shear flow, however, only the polymer displaying 3',6-disulfo Lewis x(Glc) inhibits the rolling of L-selectin-transfected cells on the glycoprotein ligand GlyCAM-1. Although it has been shown to more effective than sialyl Lewis x at blocking the L-selectin-GlyCAM-1 interaction in static binding studies, the corresponding monomer had no effect in the dynamic assay. These data indicate that multivalent ligands are far more effective inhibitors of L-selectin-mediated rolling than their monovalent counterparts and that the inhibitory activities are dependent on the specific sulfation pattern of the recognition epitope. Importantly, our results indicate the L-selectin specificity for one ligand over another found in static, cell-free binding assays is not necessarily retained under the conditions of shear flow. The results suggest that monovalent or polyvalent carbohydrate or glycoprotein mimetics that inhibit selectin binding in static assays may not block the more physiologically relevant process of selectin-mediated rolling. (+info)
Novel proteoglycan linkage tetrasaccharides of human urinary soluble thrombomodulin, SO4-3GlcAbeta1-3Galbeta1-3(+/-Siaalpha2-6)Galbeta1-4Xyl.
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O-linked sugar chains with xylose as a reducing end linked to human urinary soluble thrombomodulin were studied. Sugar chains were liberated by hydrazinolysis followed by N-acetylation and tagged with 2-aminopyridine. Two fractions containing pyridylaminated Xyl as a reducing end were collected. Their structures were determined by partial acid hydrolysis, two-dimensional sugar mapping combined with exoglycosidase digestions, methylation analysis, mass spectrometry, and NMR as SO4-3GlcAbeta1-3Galbeta1-3(+/-Siaalpha2-6)Galbeta1+ ++-4Xyl. These sugar chains could bind to an HNK-1 monoclonal antibody. This is believed to be the first example of a proteoglycan linkage tetrasaccharide with glucuronic acid 3-sulfate and sialic acid. (+info)
The role of homophilic binding in anti-tumor antibody R24 recognition of molecular surfaces. Demonstration of an intermolecular beta-sheet interaction between vh domains.
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The murine antibody R24 and mouse-human Fv-IgG1(kappa) chimeric antibody chR24 are specific for the cell-surface tumor antigen disialoganglioside GD3. X-ray diffraction and surface plasmon resonance experiments have been employed to study the mechanism of "homophilic binding," in which molecules of R24 recognize and bind to other molecules of R24 though their heavy chain variable domains. R24 exhibits strong binding to liposomes containing disialoganglioside GD3; however, the kinetics are unusual in that saturation of binding is not observed. The binding of chR24 to GD3-bearing liposomes is significantly weaker, suggesting that cooperative interactions involving antibody constant regions contribute to R24 binding of membrane-bound GD3. The crystal structures of the Fabs from R24 and chR24 reveal the mechanism for homophilic binding and confirm that the homophilic and antigen-binding idiotopes are distinct. The homophilic binding idiotope is formed largely by an anti-parallel beta-sheet dimerization between the H2 complementarity determining region (CDR) loops of two Fabs, while the antigen-binding idiotope is a pocket formed by the three CDR loops on the heavy chain. The formation of homophilic dimers requires the presence of a canonical conformation for the H2 CDR in conjunction with participation of side chains. The relative positions of the homophilic and antigen-binding sites allows for a lattice of GD3-specific antibodies to be constructed, which is stabilized by the presence of the cell membrane. This model provides for the selective recognition by R24 of cells that overexpress GD3 on the cell surface. (+info)