Primary structure of seven sulfated oligosaccharide-alditols released by reductive beta-elimination from oviducal mucins of Rana temporaria. Characterization of the sequence HSO3 (3) GlcA (beta1--3)Gal

Glucuronylated core 1 glycans are required for precise localization of neuromuscular junctions and normal formation of basement membranes on Drosophila muscles

T antigen (Galβ1-3GalNAcα1-Ser/Thr) is an evolutionary-conserved mucin-type core 1 glycan structure in animals synthesized by core 1 β1,3-galactosyltransferase 1 (C1GalT1). Previous studies showed that T antigen produced by Drosophila C1GalT1 (dC1GalT1) was expressed in various tissues and dC1GalT1 loss in larvae led to various defects, including decreased number of circulating hemocytes, hyper-differentiation of hematopoietic stem cells in lymph glands, malformation of the central nervous system, mislocalization of neuromuscular junction (NMJ) boutons, and ultrastructural abnormalities in NMJs and muscle cells. Although glucuronylated T antigen (GlcAβ1-3Galβ1-3GalNAcα1-Ser/Thr) has been identified in Drosophila, the physiological function of this structure has not yet been clarified. In this study, for the first time, we unraveled biological roles of glucuronylated T antigen. Our data show that in Drosophila, glucuronylation of T antigen is predominantly carried out by Drosophila β1,3-glucuronyltransferase-P (dGlcAT-P). We created dGlcAT-P null mutants and found that mutant larvae showed lower expression of glucuronylated T antigen on the muscles and at NMJs. Furthermore, mislocalization of NMJ boutons and a partial loss of the basement membrane components collagen IV (Col IV) and nidogen (Ndg) at the muscle 6/7 boundary were observed. Those two phenotypes were correlated and identical to previously described phenotypes in dC1GalT1 mutant larvae. In addition, dGlcAT-P null mutants exhibited fewer NMJ branches on muscles 6/7. Moreover, ultrastructural analysis revealed that basement membranes that lacked Col IV and Ndg were significantly deformed. We also found that the loss of dGlcAT-P expression caused ultrastructural defects in NMJ boutons. Finally, we showed a genetic interaction between dGlcAT-P and dC1GalT1. Therefore, these results demonstrate that glucuronylated core 1 glycans synthesized by dGlcAT-P are key modulators of NMJ bouton localization, basement membrane formation, and NMJ arborization on larval muscles.

Enhancing structural characterisation of glucuronidated O-linked glycans using negative mode ion trap higher energy collision-induced dissociation mass spectrometry

RATIONALE

High protein production and secretion with eukaryotic glycosylation machinery make T. reesei RUT-C30 a suitable expression host for recombinant proteins. The N-glycosylation of secreted proteins of RUT-C30 is known to vary depending on culture nutrients but O-glycosylation has been less extensively studied.

METHODS

O-Glycans and glycopeptides from secreted proteins were separated by porous graphitised carbon and C-18 liquid chromatography, respectively. O-Glycans were analysed in negative ion mode by electrospray ionisation linear ion trap mass spectrometry and glycopeptides in positive ion mode by electrospray ionisation hybrid quadrupole-orbitrap mass spectrometry. Tandem mass spectrometry was used on O-glycans and glycopeptides including ion trap higher energy collision-induced dissociation (tHCD) to detect glycan fragments not detectable with standard ion trap fragmentation. tHCD allowed targeted MS³ experiments to be performed on structures containing hexuronic acid, which was not possible with ion trap CID, validating this novel O-glycan composition. Positive mode C18-LC/ESI-MS/MS was used to identify and characterise glycopeptides found to be modified with this class of O-glycans, identifying cellobiohydrolase I as a carrier of these novel O-glycans.

RESULTS

Negative mode ion trap higher energy collision-induced dissociation allowed detection and targeted MS³ experiments to be performed on the hexuronic acid substituent of O-glycan structures, which was not possible with ion trap CID, validating the novel O-glycan composition to include hexuronic acid. Using glycopeptide analysis, this novel O-glycan composition was found to be present on the catalytic domain of cellobiohydrolase I, the most abundant secreted protein by T. reesei.

CONCLUSIONS

These are the first reported O-glycans to contain acidic sugars in fungi and they could have significant implications for cellobiohydrolase I structure and activity as well as the activity of recombinant proteins expressed in this host system. Copyright © 2017 John Wiley & Sons, Ltd.

Glucuronic acid can extend O-linked core 1 glycans, but it contributes only weakly to the negative surface charge of Drosophila melanogaster Schneider-2 cells

Previous studies of the mucin-type O-glycome of the fruit fly Drosophila melanogaster have revealed a restricted pattern of neutral core-type glycans corresponding to the Tn-(GalNAcalpha) and the T-antigen (Galbeta1-3GalNAcalpha). In particular, no extension of the core 1 glycan with acidic sugars, like sialic acid, was detected. Here we report on the identification of an acidic O-linked trisaccharide expressed on secreted endogenous and recombinant glycoproteins of the embryonal hemocyte-like Drosophila Schneider-2 (S2) cell line. The glycan is composed of glucuronic acid, galactose and N-acetylgalactosamine and its structure was determined as GlcA1-3Gal1-3GalNAc. The O-linked trisaccharide resembles the peripheral structures of acidic D. melanogaster glycosphingolipids. Glucuronic acid may substitute for sialic acid in this organism, however its expression on the S2 cell surface may only marginally contribute to the negative surface charge as revealed by free-flow cell electrophoresis prior to and after beta-glucuronidase treatment of the cells.

Fragmentations of isomeric sulfated monosaccharides using electrospray ion trap mass spectrometry

Electrospray ionization combined with ion trap mass spectrometry (ESI-ITMS) is a powerful tool for structural analysis of complex carbohydrates. Although its application to sulfated glycans has been limited so far, it should provide critical information, such as sulfate positions, on their structures. In this work, MS(n) spectra of nine monosulfated monosaccharides, consisting of five hexoses and four N-acetylhexosamines, were measured in negative ion mode to find basic fragmentation rules for sulfated sugars. Two pairs of positional isomers with respect to sulfation, i.e., Gal4S and Gal6S, and GalNAc4S and GalNAc6S, showed characteristic fragmentation patterns in MS(3), and could be discriminated from one another by the appearance of particular diagnostic fragment ions that characterize individual isomers. It was also demonstrated that, even if a mixture of these positional isomers was analyzed, the proportion of each species could be estimated through analysis of the abundance ratios of the diagnostic ions. However, 3-O-sulfated saccharides (Glc3S and GlcNAc3S) gave a single abundant diagnostic ion in MS(2) corresponding to the hydrogensulfate ion, [OSO(3)H](-), and this characteristic clearly differentiated them from their positional isomers. In contrast, 6-O-sulfated diastereomers consisting of two groups, Glc6S, Man6S, Gal6S, and GlcNAc6S, GalNAc6S, could not be discriminated by the types of fragment ions; however, the abundance ratios of particular fragment ions differed significantly between Glc(NAc)6S and Gal(NAc)6S. Since ESI-ITMS yielded large quantities of useful information on structures of monosulfated hexoses and N-acetylhexosamines in an extremely simple and reproducible manner, establishment of a comprehensive strategy based on ESI-ITMS(n) appears to be a promising technique for structural elucidation of sulfated complex carbohydrates.

Structural analysis of the oligosaccharide alditols released from the jelly coat of Rana dalmatina eggs by reductive beta-elimination

A combination of ion-exchange chromatography and high performance liquid chromatography (HPLC) has been used to separate the reduced oligosaccharides produced by alkaline borohydride degradation of oviducal mucins obtained from the jelly coat of Rana dalmatina. The primary structures of 26 O-glycans were determined by one-dimensional and two-dimensional 1H and 1H13C NMR spectroscopy. As observed for 20 other amphibian species, these carbohydrate chains are highly species-specific. The main typical feature of the species R. dalmatina consists in the presence of the backbone Gal(beta1-3)[Gal(beta1-4)]Gal(beta1-3)GalNAc-ol, previously observed among Ranidae, such as R. temporaria and R. ridibunda. Nevertheless, the nature of carbohydrates present at the periphery of the glycans perfectly differentiates the three species.

Function and molecular modeling of the interaction between human interleukin 6 and its HNK-1 oligosaccharide ligands

Interleukin 6 (IL-6) is endowed with a lectin activity for oligosaccharide ligands possessing the HNK-1 epitope (3-sulfated glucuronic acid) found on some mammalian glycoprotein N-glycans (Cebo, C., Dambrouck, T., Maes, E., Laden, C., Strecker, G., Michalski, J. C., and Zanetta, J. P. (2001) J. Biol. Chem. 276, 5685-5691). Using high affinity oligosaccharide ligands, it is demonstrated that this lectin activity is responsible for the early dephosphorylation of tyrosine residues found on specific proteins induced by interleukin 6 in human resting lymphocytes. The gp130 glycoprotein, the signal-transducing molecule of the IL-6 pathway, is itself a molecule possessing the HNK-1 epitope. This indicates that IL-6 is a bi-functional molecule able to extracellularly associate its alpha-receptor with the gp130 surface complex. Computational modeling indicates that the lower energy conformers of the high affinity ligands of IL-6 have a common structure. Docking experiments of these conformers suggest that the carbohydrate recognition domain of IL-6 is localized in the domain previously identified as site 3 of IL-6 (Somers, W., Stahl, M., and Seehra, J. S. (1997) EMBO J. 16, 989-997), already known to be involved in interactions with gp130.

Species-specificity of amphibia carbohydrate chains: the Bufo viridis case study

The jelly coat surrounding the eggs of amphibia is composed of oviducal mucins and plays an important role in the fertilization process. From a structural and chemical point of view, these jellies are very different from one species to another. Bufo viridis is the 13th amphibia species studied in term of carbohydrate structural analysis. The oligosaccharides have been released from the oviducal mucins by reductive beta elimination, purified by various chromatography procedures and analyzed by (1)H and (13)C 1D-2D NMR spectroscopy. Among the 15 compounds, ten have novel structures, although they possess some well-known structural patterns as blood group epitopes (Le(x), Le(y)) or other sequences already observed in other amphibia species. These results reinforce our hypothesis about the strict species-specificity of these carbohydrate chains. It must be noted that such species-specificity does not depend on one particular monosaccharide but it is rather due to a set of particular tri- or tetrasaccharide sequences. Hence, B. viridis species could be characterized by the simultaneous presence of a 2,3,6-trisubstituted galactosyl residue, the GlcNAc(beta 1-3)[Fuc(alpha 1-4)]GlcNAc beta sequence and the Le(x), Le(y) or Cad determinants. The anionic charge of the oligosaccharides is carried only by sialic acid alpha-(2-->6)-linked to GalNAc-ol residue as in Bufo bufo or in Bufo arenarum.

Diversity of O-linked glycosylation patterns between species. Characterization of 25 carbohydrate chains from oviducal mucins of Rana ridibunda

Amphibia egg jelly coats are formed by components secreted along the oviduct. These secretion products overlay the oocytes as they pass along the different oviducal portions. Mucin type glycoproteins are the major constituents of the egg jelly coats. In this study, the O-linked carbohydrate chains of the jelly coats surrounding the eggs of Rana ridibunda were released by alkaline borohydride treatment. Fractionation of the mixture of O-linked oligosaccharide-alditols was achieved by a combination of chromatographic techniques including gel-permeation chromatography, ion-exchange chromatography and high-performance liquid chromatography using an amino-bonded silica column. The primary structures of these O-glycans were determined by one-dimensional and two-dimensional 1H-NMR spectroscopy and matrix-assisted laser-desorption-ionization-time-of flight mass spectrometry. 25 oligosaccharide structures, possessing a core consisting of Gal(beta1-3)GalNAc-ol with or without branching through a GlcNAc residue linked (beta1-6) to the GalNAc residue (core type 2 or core type 1, respectively) are described. The most representative antennae are: HSO3(6)[Fuc(alpha1-3)]GlcNAc; Gal(beta1-2)Gal; Gal(beta1-2)Gal(alpha1-3)[Fuc(alpha1-2)]Gal; GlcA(beta1-3)-Gal(beta1-3)[Fuc(alpha1-2)]Gal; GalNAc(alpha1-4)Gal(beta1-4)Gal; Gal(beta1-3)GalNAc(alpha1-4)Gal(beta1-4)Gal and GlcA(beta1-3)Gal(beta1-3)GalNAc. These results confirm the species-specific O-glycosylation of Amphibia oviducal mucins. The significance of this observation should be linked to a symbiotic role of carbohydrates involved in host-parasite interactions.

Recombinant human interleukins IL-1alpha, IL-1beta, IL-4, IL-6, and IL-7 show different and specific calcium-independent carbohydrate-binding properties

A method was developed for the determination of putative lectin activities of cytokines. It involved the immunoblotting measurement of the quantity of these cytokines unbound to a series of different immobilized glycoconjugates and displacement of the bound cytokines with oligosaccharides of known structures. This method allows demonstrating that the following interleukins specifically recognize different oligosaccharide structures in a calcium-independent mechanism: interleukin-1alpha binds to the biantennary disialylated N-glycan completed with two Neu5Acalpha2-3 residues; interleukin-1beta to a GM4 sialylated glycolipid Neu5Acalpha2-3Galbeta1-Cer having very long and unusual long-chain bases; interleukin-4 to the 1,7 intramolecular lactone of N-acetyl-neuraminic acid; interleukin-6 to compounds having N-linked and O-linked HNK-1-like epitopes; and interleukin-7 to the sialyl-Tn antigen. Because the glycan ligands are rare structures in human circulating cells, it is suggested that such activities could be essential for providing specific signaling systems to cells having both the receptors and the oligosaccharide ligands of the interleukin at their cell surface.

Acquisition of species-specific O-linked carbohydrate chains from oviducal mucins in Rana arvalis. A case study

The extracellular matrix surrounding amphibian eggs is composed of mucin-type glycoproteins, highly O-glycosylated and plays an important role in the fertilization process. Oligosaccharide-alditols were released from the oviducal mucins of the anuran Rana arvalis by alkali-borohydride treatment in reduced conditions. Neutral and acidic oligosaccharides were fractionated by ion-exchange chromatographies and purified by HPLC. Each compound was identified by matrix assisted laser desorption ionization-time of flight (MALDI-TOF) spectrometry, NMR spectroscopy, electrospray ionization-tandem mass spectroscopy (ESI-MS/MS) and permethylation analyses. This paper reports on the structures of 19 oligosaccharide-alditols, 12 of which have novel structures. These structures range in size from disaccharide to octasaccharide. Some of them are acidic, containing either a glucuronic acid or, more frequently, a sulfate group, located either at the 6 position of GlcNAc or the 3 or 4 positions of Gal. This latter sulfation is novel and has only been characterized in the species R. arvalis. This structural analysis led to the establishment of several novel carbohydrate structures, demonstrating the structural diversity and species-specificity of amphibian glycoconjugates.

Structural analysis of 13 neutral oligosaccharide-alditols released by reductive beta-elimination from oviducal mucins of Rana temporaria

Amphibian eggs are always surrounded by an extracellular matrix, named the jelly coat. This is mainly composed of a highly O-glycosylated, mucin-type glycoprotein. This work has consisted of isolating O-linked neutral oligosaccharides from oviducal mucin of Rana temporaria, with a view to determining their primary structure. Hence, these carbohydrate chains have been released by alkaline borohydride treatment leading to stable glycans. The oligosaccharide-alditols have been purified by ion-exchange chromatography and separated by HPLC. The primary structure of 13 of these carbohydrate chains have been obtained by 1D/2D 1H-NMR spectroscopy and methylation analyses, in combination with MALDI-TOF mass spectroscopy. The results confirm what has been observed for six other amphibians about the species-specificity of the carbohydrate moieties and their likely involvement in the species-specific gamete recognition.

Structural analysis of 20 oligosaccharide-alditols released from the jelly coat of Rana palustris eggs by reductive beta-elimination characterization of the polymerized sequence [Gal(beta1, 3)GalNAc(alpha1-4)]n

The eggs of amphibians are surrounded by three to eight layers of jelly coats. This extracellular matrix is mainly composed of hydrated mucin-type glycoproteins. These highly glycosylated molecules are synthesized by oviduct and play an important role in the fertilization process. Recent structural analyses have shown the strict species-specificity of the O-linked oligosaccharides which constitute 60-70% of these oviducal mucins. Consequently, these carbohydrate chains represent new phenotypic markers, and from a biological point of view, can influence parasite tropism or can be involved in species-specific interaction of gametes. The primary structure of 20 oligosaccharide-alditols, released by alkali/borohydride treatment from the mucin of Rana palustris egg jelly coats, was established by 1H and 13C-NMR analysis. Thirteen of these components possess new structures and the polymerization of the sequence Gal(beta1-3)GalNAc(alpha1-4) characterizes the species-specificity of R. palustris.

Novel proteoglycan linkage tetrasaccharides of human urinary soluble thrombomodulin, SO4-3GlcAbeta1-3Galbeta1-3(+/-Siaalpha2-6)Galbeta1-4Xyl

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.

Inhibition of L- and P-selectin by a rationally synthesized novel core 2-like branched structure containing GalNAc-Lewisx and Neu5Acalpha2-3Galbeta1-3GalNAc sequences

The selectins interact in important normal and pathological situations with certain sialylated, fucosylated glycoconjugate ligands containing sialyl Lewisx(Neu5Acalpha2-3Galbeta1-4(Fucalpha1-3)GlcN Ac). Much effort has gone into the synthesis of sialylated and sulfated Lewisxanalogs as competitive ligands for the selectins. Since the natural selectin ligands GlyCAM-1 and PSGL-1 carry sialyl Lewisxas part of a branched Core 2 O-linked structure, we recently synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(SE-3Galbeta1++ +-3)GalNAc1alphaOMe and found it to be a moderately superior ligand for L and P-selectin (Koenig et al. , Glycobiology 7, 79-93, 1997). Other studies have shown that sulfate esters can replace sialic acid in some selectin ligands (Yeun et al. , Biochemistry, 31, 9126-9131, 1992; Imai et al. , Nature, 361, 555, 1993). Based upon these observations, we hypothesized that Neu5Acalpha2-3Galbeta1-3GalNAc might have the capability of interacting with L- and P-selectin. To examine this hypothesis, we synthesized Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Neu5Acalpha2++ +-3Galbeta1-3)-GalNAc alpha1-OB, which was found to be 2- to 3-fold better than sialyl Lexfor P and L selectin, respectively. We also report the synthesis of an unusual structure GalNAcbeta1-4(Fucalpha1- 3)GlcNAcbeta1-OMe (GalNAc-Lewisx-O-methyl glycoside), which also proved to be a better inhibitor of L- and P-selectin than sialyl Lewisx-OMe. Combining this with our knowledge of Core 2 branched structures, we have synthesized a molecule that is 5- to 6-fold better at inhibiting L- and P-selectin than sialyl Lewisx-OMe, By contrast to unbranched structures, substitution of a sulfate ester group for a sialic acid residue in such a molecule resulted in a considerable loss of inhibition ability. Thus, the combination of a sialic acid residue on the primary (beta1-3) arm, and a modified Lexunit on the branched (beta1-6) arm on an O-linked Core 2 structure generated a monovalent synthetic oliogosaccharide inhibitor superior to SLexfor both L- and P-selectin.

Structural analysis of a new series of oligosaccharide-alditols released by reductive beta-elimination from oviducal mucins of Rana utricularia

Egg jelly coats from Rana utricularia are formed by components secreted along the oviduct. These secretion products overlay the oocytes as they pass along the different oviducal portions. In this study, carbohydrate chains of the jelly coat surrounding the eggs of R. utricularia were released by alkali/borohydride treatment. Fractionation of O-linked oligosaccharide-alditols was achieved by a combination of chromatographic techniques comprising anion-exchange chromatography, gel-permeation chromatography and HPLC on a silica column bonded with aminopropyl groups. Structural characterization was performed by one- and two-dimensional 1H-NMR spectroscopy in combination with matrix-assisted laser-desorption ionization-time of flight MS and methylation analysis. Ten oligosaccharide structures possessing a core consisting of Galbeta(1-->3)GalNAc-ol with or without branching through a GlcNAc residue linked beta(1-->6) to the GalNAc residue (core type 2 or core type 1 respectively) are described. The most representative carbohydrate sequences are: GlcNAc(beta1-3)[Fuc(alpha1-4)]GlcNAc, GalNAc(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)GlcNAc(beta1-3)GlcNAc and Gal(beta1-3)GlcNAc(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)GlcNAc. The carbohydrate chains isolated from R. utricularia are quite different from those found in other amphibian species, in which the presence of species-specific material has been characterized. Since the jellies surrounding amphibian eggs are involved in egg-sperm interactions, these structural investigations can provide biochemical support for investigation of the fertilization process.