Primary structure of 12 neutral oligosaccharide-alditols released from the jelly coats of the anuran Xenopus laevis by reductive beta-elimination

Diversity of sialic acids and sialoglycoproteins in gametes and at fertilization

Sialic acids are a family of 9-carbon monosaccharides with particular physicochemical properties. They modulate the biological functions of the molecules that carry them and are involved in several steps of the reproductive process. Sialoglycoproteins participate in the balance between species recognition and specificity, and the mechanisms of these aspects remain an issue in gametes formation and binding in metazoan reproduction. Sialoglycoproteins form a specific coat at the gametes surface and specific polysialylated chains are present on marine species oocytes. Spermatozoa are submitted to critical sialic acid changes in the female reproductive tract facilitating their migration, their survival through the modulation of the female innate immune response, and the final oocyte-binding event. To decipher the role of sialic acids in gametes and at fertilization, the dynamical changes of enzymes involved in their synthesis and removal have to be further considered.

Biochemical and ligand binding properties of recombinant Xenopus laevis cortical granule lectin-1

Intelectins are putative innate immune lectins that are found throughout chordates. The first intelectin reported was Xenopus laevis cortical granule lectin-1 (XCGL-1 or XL-35). XCGL-1 is critical in fertilization membrane development in Xenopus. Here, we explored the biochemical properties of XCGL-1. The cysteines responsible for forming intermolecular disulfide bonds were identified. XCGL-1 adopted a four-lobed structure as observed by electron microscopy. The full-length XCGL-1 and the carbohydrate recognition domain (CRD) bind galactose-containing carbohydrates at nanomolar to micromolar affinities. Molecular modeling suggested that galactoside ligands coordinated the binding site calcium ion and interacted with residues around the groove made available by the non-conserved substitution compared to human intelectin-1. Folding conditions for production of recombinant XCGL-1 CRD were also investigated. Our results not only provide new biochemical insights into the function of XCGL-1, but may also provide foundation for further applications of XCGL-1 as glycobiology tools.

Saccharide binding by intelectins

This communication probes ligand binding by human Intelectin-1 with several saccharides. Human Intelectin-1 was previously reported to bind to microbial glycans via ribofuranoside or galactofuranoside residues, whereas subsequently, a crystal structure of ligand bound hITLN1 indicated that hITLN1 does not bind to ribofuranoside but distinguishes between microbial and human glycans through a glycan motif - a terminal, acyclic 1,2-diol, which is present on galactofuranose and other microbial saccharides. Here, we demonstrate that besides glycerol and glycerol derivatives (which have an acyclic 1,2-diol), and 2-deoxy-d-galactose, d-ribose and 2-deoxy-d-ribose, which have been previously reported as human Intelectin-1 ligands, 2-C-hydroxymethyl-d-ribose, d-talose, d-idose, d-altrose and sorbitol also elute human Intelectin-1 from Sepharose CL-6B. Interestingly, Sepharose, 2-deoxy-d-galactose (in its pyranose form), 2-C-hydroxymethyl-d-ribose, d-ribose and 2-deoxy d-ribose lack a terminal, acyclic 1,2-diol. We discuss the implications of these observations and rationalize the discrepancies in the apparent affinity of saccharide ligands for hITLN1 with different assay formats. We also report the distinct saccharide binding profiles of the hITLN1 homologues, HaloITLN and XL35ITLN, and demonstrate that hITLN1 binding to a saccharide ligand may modulate binding to its protein ligand, lactoferrin and vice versa.

The laminated layer: Recent advances and insights into Echinococcus biology and evolution

The laminated layer is the unique mucin-based extracellular matrix that protects Echinococcus larvae, and thus to an important extent, shapes host-parasite relationships in the larval echinococcoses. In 2011, we published twin reviews summarizing what was known about this structure. Since then, important advances have been made. Complete genomes and some RNAseq data are now available for E. multilocularis and E. granulosus, leading to the inference that the E. multilocularis LL is probably formed by a single type of mucin backbone, while a second apomucin subfamily additionally contributes to the E. granulosus LL. Previously suspected differences between E. granulosus and E. multilocularis in mucin glycan size have been confirmed and pinned down to the virtual absence of Galβ1-3 chains in E. multilocularis. The LL carbohydrates from both species have been found to interact selectively with the Kupffer cell receptor expressed in rodent liver macrophages, highlighting the ancestral adaptations to rodents as intermediate hosts and to the liver as infection site. Finally, LL particles have been shown to possess carbohydrate-independent mechanisms profoundly conditioning non-liver-specific dendritic cells and macrophages. These advances are discussed in an integrated way, and in the context of the newly determined phylogeny of Echinococcus and its taenid relatives.

Atlantic Salmon Carries a Range of Novel O-Glycan Structures Differentially Localized on Skin and Intestinal Mucins

Aquaculture is a growing industry, increasing the need for understanding host-pathogen interactions in fish. The skin and mucosal surfaces, covered by a mucus layer composed of mucins, is the first point of contact between fish and pathogens. Highly O-glycosylated mucins have been shown to be an important part of the defense against pathogens, and pathogens bind to host surfaces using lectin-like adhesins. However, knowledge of piscine O-glycosylation is very limited. We characterized mucin O-glycosylation of five freshwater acclimated Atlantic salmon, using mass spectrometry. Of the 109 O-glycans found, most were sialylated and differed in distribution among skin, pyloric ceca, and proximal and distal intestine. Skin O-glycans were shorter (2-6 residues) and less diverse (33 structures) than intestinal O-glycans (2-13 residues, 93 structures). Skin mucins carried O-glycan cores 1, 2, 3, and 5 and three types of sialic acids (Neu5Ac, Neu5Gc, and Kdn) and had sialyl-Tn as the predominant structure. Intestinal mucins carried only cores 1, 2, and 5, Neu5Ac was the only sialic acid present, and sialylated core 5 was the most dominant structure. This structural characterization can be used for identifying structures of putative importance in host-pathogen interactions for further testing in biological assays and disease intervention therapies.

O-Glycosylation of snails

The glycosylation abilities of snails deserve attention, because snail species serve as intermediate hosts in the developmental cycles of some human and cattle parasites. In analogy to many other host-pathogen relations, the glycosylation of snail proteins may likewise contribute to these host-parasite interactions. Here we present an overview on the O-glycan structures of 8 different snails (land and water snails, with or without shell): Arion lusitanicus, Achatina fulica, Biomphalaria glabrata, Cepaea hortensis, Clea helena, Helix pomatia, Limax maximus and Planorbarius corneus. The O-glycans were released from the purified snail proteins by β-elimination. Further analysis was carried out by liquid chromatography coupled to electrospray ionization mass spectrometry and – for the main structures – by gas chromatography/mass spectrometry. Snail O-glycans are built from the four monosaccharide constituents: N-acetylgalactosamine, galactose, mannose and fucose. An additional modification is a methylation of the hexoses. The common trisaccharide core structure was determined in Arion lusitanicus to be N-acetylgalactosamine linked to the protein elongated by two 4-O-methylated galactose residues. Further elongations by methylated and unmethylated galactose and mannose residues and/or fucose are present. The typical snail O-glycan structures are different to those so far described. Similar to snail N-glycan structures they display methylated hexose residues.

Structure determination by MALDI-IRMPD mass spectrometry and exoglycosidase digestions of O-linked oligosaccharides from Xenopus borealis egg jelly

Differences in the fertilization behavior of Xenopus borealis from X. laevis and X. tropicalis suggest differences in the glycosylation of the egg jellies. To test this assumption, O-linked glycans were chemically released from the egg jelly coat glycoproteins of X. borealis. Over 50 major neutral glycans were observed, and no anionic glycans were detected from the released O-glycan pool. Preliminary structures of ∼30 neutral oligosaccharides were determined using matrix-assisted laser desorption/ionization (MALDI) infrared multiphoton dissociation tandem mass spectrometry (MS). The mass fingerprint of a group of peaks for the core-2 structure of O-glycans was conserved in the tandem mass spectra and was instrumental in rapid and efficient structure determination. Among the 29 O-glycans, 22 glycans contain the typical core-2 structure, 3 glycans have the core-1 structure and 2 glycans contained a previously unobserved core structure with hexose at the reducing end. There were seven pairs of structural isomers observed in the major O-linked oligosaccharides. To further elucidate the structures of a dozen O-linked glycans, specific and targeted exoglycosidase digestions were carried out and the products were monitored with MALDI-MS. Reported here are the elucidated structures of O-linked oligosaccharides from glycoproteins of X. borealis egg jelly coats. The structural differences in O-glycans from jelly coats of X. borealis and its close relatives may provide a better understanding of the structure-function relationships and the role of glycans in the fertilization process within Xenopodinae.

Collision-induced dissociation tandem mass spectrometry for structural elucidation of glycans

The complexity of glycans poses a major challenge for structure elucidation. Tandem mass spectrometry is currently an efficient and powerful technique for the structural characterization of glycans. Collision-induced dissociation (CID) is most commonly used, and involves first isolating the glycan ions of interest, translationally exciting them, and then striking them with inert target gas to fragment the precursor ions. The structural information of the glycan can be obtained from the fragment ions of the tandem MS spectra. In this chapter, sustained off-resonance irradiation-collision-induced dissociation (SORI-CID) implemented with matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI FT ICR MS) is demonstrated to be a useful analysis tool for structural elucidation of mucin-type O-glycans released from mucin glycoproteins. The mechanisms by which the glycans undergo fragmentations in the tandem mass analysis are also discussed.

Okra pectin contains an unusual substitution of its rhamnosyl residues with acetyl and alpha-linked galactosyl groups

The okra plant, Abelmoschus esculentus (L.) Moench, a native plant from Africa, is now cultivated in many other areas such as Asia, Africa, Middle East, and the southern states of the USA. Okra pods are used as vegetables and as traditional medicines. Sequential extraction showed that the Hot Buffer Soluble Solids (HBSS) extract of okra consists of highly branched rhamnogalacturonan (RG) I containing high levels of acetyl groups and short galactose side chains. In contrast, the CHelating agent Soluble Solids (CHSS) extract contained pectin with less RG I regions and slightly longer galactose side chains. Both pectic populations were incubated with homogeneous and well characterized rhamnogalacturonan hydrolase (RGH), endo-polygalacturonase (PG), and endo-galactanase (endo-Gal), monitoring both high and low molecular weight fragments. RGH is able to degrade saponified HBSS and, to some extent, also non-saponified HBSS, while PG and endo-Gal are hardly able to degrade either HBSS or saponified HBSS. In contrast, PG is successful in degrading CHSS, while RGH and endo-Gal are hardly able to degrade the CHSS structure. These results point to a much higher homogalacturonan (HG) ratio for CHSS when compared to HBSS. In addition, the CHSS contained slightly longer galactan side chains within its RG I region than HBSS. Matrix-assisted laser desorption ionization-time of flight mass spectrometry indicated the presence of acetylated RG oligomers in the HBSS and CHSS enzyme digests and electron spray ionization-ion trap-mass spectrum showed that not only galacturonosyl residues but also rhamnosyl residues in RG I oligomers were O-acetylated. NMR spectroscopy showed that all rhamnose residues in a 20kDa HBSS population were O-acetylated at position O-3. Surprisingly, the NMR data also showed that terminal alpha-linked galactosyl groups were present as neutral side chain substituents. Taken together, these results demonstrate that okra contained RG I structures which have not been reported before for pectic RG I.

Long-term evolution of the CAZY glycosyltransferase 6 (ABO) gene family from fishes to mammals—a birth-and-death evolution model

Functional glycosyltransferase 6 (GT6) family members catalyze the transfer of galactose or N-acetylgalactosamine in alpha1,3 linkage to various substrates and synthesize structures related to the A and B histo-blood group antigens, the Forssman antigen, alphaGal epitope, and iGb3 glycolipid. In rat, mouse, dog, and cow genomes, we have identified three new mammalian genes (GT6m5, GT6m6, and GT6m7) encoding putative proteins belonging to the GT6 family. Among these, GT6m6 protein does not display major alterations of the GT6 motifs involved in binding of the divalent cation and the substrate. Based on protein sequence comparison, gene structure, and synteny, GT6 homologous sequences were also identified in bird, fish, and amphibian genomes. Strikingly, the number and type of GT6 genes varied widely from species to species, even within phylogenetically related groups. In human, except ABO functional alleles, all other GT6 genes are either absent or nonfunctional. Human, mouse, and cow have only one ABO gene, whereas rat and dog have several. In the chicken, the Forssman synthase-like is the single GT6 family member. Five Forssman synthase-like genes were found in zebrafish, but are absent from three other fishes (fugu, puffer fish, and medaka). Two iGb3 synthase-like genes were found in medaka, which are absent from zebrafish. Fugu, puffer fish, and medaka have an additional GT6 gene that we termed GT6m8, which is absent from all other species analyzed here. These observations indicate that individual GT6 genes have expanded and contracted by recurrent duplications and deletions during vertebrate evolution, following a birth-and-death evolution type.

Infrared multiphoton dissociation of O-linked mucin-type oligosaccharides

Oligosaccharides are known to play important roles in many biological processes. In the study of oligosaccharides, collision-induced dissociation (CID) is the most common dissociation method to elucidate the sequence and connectivity. However, a disadvantage of CID is the decrease in both the degree and efficiency of dissociation with increasing mass. In the present study, we have successfully performed infrared multiphoton dissociation (IRMPD) on 39 O-linked mucin-type oligosaccharide alditols (both neutral and anionic). CID and IRMPD spectra of several oligosaccharides were also compared. They yielded nearly identical fragment ions corresponding to the lowest energy fragmentation pathways. The characteristic fragmentations of structural motifs, which can provide the linkage information, were similarly presented in both CID and IRMPD spectra. Multistage of CID (MS(3) or MS(4)) is commonly needed to completely sequence the oligosaccharides, while IRMPD of the same compounds yielded the fragment ions corresponding to the loss of the first residue to the last residue during a single-stage tandem MS (MS(2)). Finally, it is shown that the fragmentation efficiency of IRMPD increases with the increasing size of oligosaccharides.

Profiling the morphological distribution of O-linked oligosaccharides

The morphological distribution of oligosaccharides is determined in the egg jelly surrounding Xenopus laevis eggs. This biological system is used to illustrate a method for readily identifying and quantifying oligosaccharides in specific tissues. The extracellular matrix surrounding X. laevis eggs consists of a vitelline envelope and a jelly coat. The jelly coat contains three morphologically distinct layers designated J1, J2, and J3 from the innermost to the outermost and is composed of 9-11 distinct glycoproteins. Each jelly layer is known to have specific functions in the fertilization of the egg. We developed a rapid method to separate and identify the oligosaccharides from X. laevis egg jelly layers. Identification was based on the retention times in high-performance liquid chromatography (porous graphitized carbon column), exact masses, and tandem mass spectrometry. Over 40 neutral and 30 sulfated oligosaccharides were observed in the three jelly layers. Neutral oligosaccharide structures from different jelly layers were both unique and overlapping, while sulfated oligosaccharides were detected only in layers J1 and J2. Neutral oligosaccharides unique to jelly layer J3 and the combined layers J1+J2 had similar core structures and similar residues. However, differences between these two sets of unique oligosaccharides were also observed and were primarily due to the branching carbohydrate moieties rather than the core structures.

Application of Fourier transform ion cyclotron resonance mass spectrometry to oligosaccharides

The application of Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) to the structural elucidation of oligosaccharides is described. This review covers the analyses of oligosaccharides in the context of the unique features of FTICR MS and the improvements in instrumentation that make it possible to study this class of compounds. It consists of work performed initially to understand the fundamental aspects of oligosaccharide ionization and unimolecular fragmentation. More recent investigation includes the application of the technique to samples of direct biological origin. Chemical and enzymatic degradation methods in conjunction with mass spectrometry (MS) and the use front-end methods with FTICR MS are also discussed. The current applications including the characterization of bacterial lipooligosaccharides and phosporylated carbohydrates are described.

Strategy for Profiling and Structure Elucidation of Mucin-Type Oligosaccharides by Mass Spectrometry

A strategy combining accurate mass determination, tandem mass spectrometry, structure homology, and exoglycosidases is described that allows the structural characterization of mucin-type O-linked oligosaccharides. The method is used to profile with quantitation the O-linked oligosaccharide (both neutral and anionic) components of the only diploid Xenopus frog, Xenopus tropicalis. Collision-induced dissociation was used to determine connectivity, to identify previously characterized oligosaccharides, and to determine the presence of structural motifs in unknown oligosaccharides. Exoglycosidase digestion was used to identify the individual residues along with the linkages. The enzymes were also used to cleave larger oligosaccharides to smaller units that are similar to previously elucidated components. By using CID, isomeric structures were compared to determine whether they were identical. In this way, the exoglycosidases were more effectively used, and their use was minimized. A total of 35 oligosaccharides including neutral, sialylated, and sulfated were characterized in this way. The relative abundances of all components were also determined based on HPLC.

High-avidity, low-affinity multivalent interactions and the block to polyspermy in Xenopus laevis

The interaction of the lectin XL35 with the jelly coat protein (JCP) surrounding oocytes in Xenopus laevis is essential for the block to polyspermy. The molecular details of this event are poorly understood, and the present study has been undertaken with a view to delineating the mechanism of formation of the fertilization envelope. A range of JCP-derived oligosaccharides were synthesized, and all were installed with an artificial aminopropyl arm. This arm allowed the preparation of monovalent derivatives by acetylation of the amino group or the synthesis of polyvalent compounds by attachment to an activated polyacrylamide polymer. A number of analytical techniques, including enzyme-linked lectin assays and surface plasmon resonance, have been developed and utilized to study the interactions of the mono- and polyvalent compounds with XL35. The results reveal that the lectin XL35 has remarkably broad specificity for galactose-containing saccharides and the affinities are only slightly modulated by secondary features, such as anomeric configuration of the terminal sugar or the identity and linkage pattern of branching sugars. Broad specificity was also observed when the saccharides were presented in a polyvalent fashion. The glycopolymers displayed 10-20-fold increases in valency-corrected affinities compared to the corresponding monovalent counterparts. Although the synthetic polymers are not as potent as the JCP, the kinetics of their interactions mirror closely those of the native ligand, and in each case extremely long-lived interactions were observed. The results of this study indicate that, in X. laevis, the true biological function of multivalency is not to create an extremely tightly binding complex between XL35 and its natural ligand but, instead, to create a very stable protective layer that will not dissociate and is yet flexible enough to encapsulate the developing embryo. It is postulated that, even if these partners are unable to attain true equilibrium on the time scale of the biological event, their mode of interaction would, nevertheless, be expected to guarantee an insurmountable physical block to polyspermy. This study has also highlighted that multivalent interactions require a very long time to achieve equilibrium, and this feature may well be the origin of several of the ambiguities reported in the literature when multivalent ligands have been evaluated.

Species specificity of O-linked carbohydrate chains of the oviducal mucins in amphibians: structural analysis of neutral oligosaccharide alditols released by reductive beta-elimination from the egg-jelly coats of Rana clamitans

The extracellular matrix (the so-called jelly coat) surrounding amphibian eggs mainly comprises highly O-glycosylated proteins. These oviducal mucins have an important role in the fertilization process, and their carbohydrate chains are remarkably species-specific. Alkaline reductive treatment of the jelly-coat material of the frog Rana clamitans led to the release of oligosaccharide alditols. The neutral oligosaccharide alditols were fractionated and purified by successive chromatographic techniques. The structures of 27 of them, ranging from three to sixteen monosaccharides, were established by a combination of NMR spectroscopy, methylation analyses and matrix-assisted laser-desorption ionization-time of flight MS. Typically, some of the neutral compounds appeared to possess the core structure: Gal(beta1-3)[GlcNAc(beta1-6)]Gal(beta1-3)[GlcNAc(beta1-6)]GalNAc-ol (where GalNAc-ol represents N-acetylgalactosaminitol). Moreover, a novel type of chain termination, characterized by an unusual sequence [Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-3/4)] was observed. Indeed, the most complex representative structure of this series was found to be: Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-3)[Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-4)GlcNAc(beta1-6)]Gal(beta1-3)[Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-4)GlcNAc(beta1-6)]GalNAc-ol.

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.

Targeted use of exoglycosidase digestion for the structural elucidation of neutral O-linked oligosaccharides

Exoglycosidase digestion in combination with the catalog-library approach (CLA) is used with matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) to obtain the complete structure of oligosaccharides. The CLA is a collision-induced dissociation (CID)-based method used to determine the structure of O-linked neutral oligosaccharides. It provides both linkage and stereochemical information. Exoglycosidases are used to confirm independently the validity of the CLA. In some cases, the CLA provides structural information on all but a single residue. Exoglycosidase is used to refine these structures. In this way, exoglycosidase use is targeted employing only a small number of enzymes. Exoglycosidase arrays, which have been used with N-linked oligosaccharides, is avoided despite the larger variations in structures of O-linked species.

Identification and structural elucidation of lectin-binding oligosaccharides by bioaffinity matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

Cortical granule lectin (CGL) is released by the egg of the South African toad Xenopus laevis upon fertilization. The lectin binds to oligosaccharides in the extracellular matrix of the egg to form a physical block to prevent additional sperm penetration or polyspermy. To identify the oligosaccharides that bind to CGL, the lectin was immobilized on the surface of a matrix-assisted laser desorption/ionization probe. This bioaffinity probe was used to determine oligosaccharides that bind preferentially to CGL. Structural analyses based on collision-induced dissociation was used to determine that oligosaccharides with the sulfate esters at the nonreducing ends preferentially bind to the lectin.

Profiling with structural elucidation of the neutral and anionic O-linked oligosaccharides in the egg jelly coat of Xenopus laevis by Fourier transform mass spectrometry

A strategic method with high speed and sensitivity is outlined for the analysis of mucin-type oligosaccharide from the jelly coat of Xenopus laevis. The method relies primarily on mass spectrometric techniques, in this case matrix-assisted laser desorption/ionization Fourier-transform mass spectrometry (MALDI-FTMS) and collision-induced dissociation (CID). Separation with isolation of the oligosaccharides was streamlined to couple well with mass spectrometry allowing the rapid determination of all detectable components from both neutral and anionic species. Partial structures of anionic components, composed primarily of sulfate esters, were obtained with CID. For neutral species, a method that allowed the complete structural determination using mass spectrometry was used. The method builds on the structure of small number of known compounds to determine unknown structures from the same biological source. In this example, a small number of oligosaccharides, elucidated previously by NMR, were used to develop a set of substructural motifs that were characterized by CID. The presence of the motifs in the CID spectra were then used to determine the structures of unknown compounds that were in abundances too small for NMR analysis.

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.

Catalog-library approach for the rapid and sensitive structural elucidation of oligosaccharides

We obtained the nearly complete structural elucidation of oligosaccharide components, including sequence, linkage, and even stereochemistry in the picomolar levels. The "catalog-library" approach is used for elucidating the structures of minor components in a mixture of oligosaccharides. Oligosaccharides released from a family of glycoproteins are often composed of a small finite set of monosaccharides. In this regard, the numerous oligosaccharide species are analogous to the products found in syntheses involving combinatorial libraries. The great structural diversity in the library is the result of the nearly infinite combinations in which even a small number of monosaccharides can be arranged. Fortunately, structural similarities exist between different oligosaccharides, as specific substructural motifs are preserved among different compounds. We propose that a catalog of substructural motifs can be identified and characterized by collision-induced dissociation mass spectrometry. The catalog is constructed from a set of known compounds that have been fully structurally elucidated by, for example, nuclear magnetic resonance. The catalog consists of the characteristic fragmentation patterns belonging to a set of specific substructural motifs. Collision-induced dissociation is used to determine the presence of these motifs and reconstruct the structures of less abundant components.

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.

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

The mucins isolated from Rana temporaria egg jelly coats were found to be composed of Gal, Fuc, GlcNac, GalNAc and GlcA acid. The primary structure of seven sulfated oligosaccharide-alditols was obtained by 1D/2D NMR analyses (1H-13C). The results show the presence of the sulfate monosaccharides. HSO3(3)Gal, HSO(6)GlcNAc and HSO3(3)GlcA. The sequence HSO3(3)GlcA (beta1-3)Gal, which constitutes the major determinant of the HNK-1 oncofoetal epitope, was characterized.

Characterization of neutral oligosaccharide-alditols from Xenopus laevis egg jelly coats by matrix-assisted laser desorption Fourier transform mass spectrometry

Neutral oligosaccharides were released by alkaline sodium borohydride reduction of the jelly coating from the South African clawed toad, Xenopus laevis. The oligosaccharides were isolated by HPLC and analyzed by matrix-assisted laser desorption ionization (MALDI)-Fourier transform mass spectrometry (FTMS). The mass spectrometry analysis allowed confirmation of 12 structures first proposed by Strecker et al. using nuclear magnetic resonance. In addition, seven new oligosaccharides with weak abundances were found and characterized by mass spectrometry. A method for discriminating metastable fragments from quasimolecular ions is described. It involves doping the sample with cesium chloride. Cesium-coordinated oligosaccharides do not fragment as readily as those coordinated to sodium. Tandem MS experiments are performed on an unknown oligosaccharide illustrating the potential of MALDI-collision-induced dissociation-FTMS.

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

The O-linked oligosaccharides of the jelly coat surrounding the eggs of Rana utricularia were analysed by 1H-NMR spectroscopy. Comparison of their structures with those characterized from seven other amphibians confirms that the carbohydrate chains of the jelly coat mucins are markers of the species. The new sequence GlcNAc(beta1-3)GlcNAc(beta1-6)[Gal(beta1-3)]GalNAc-ol is characteristic of Rana utricularia. The presence of blood group A determinants constitutes the main feature of this mucin.

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

The carbohydrate chains of the mucins which constitute the jelly coat surrounding the eggs of Rana temporaria were released by alkaline borohydride treatment. Neutral and acidic oligosaccharide-alditols were purified by ion-exchange chromatography and HPLC. From the structural analysis, based upon 1H and 13C-NMR spectroscopy in combination with MALDI-TOF, the following glycan units are proposed.

O-linked protein glycosylation structure and function

There has been a recent resurgence of interest in the post-translational modification of serine and threonine hydroxyl groups by glycosylation, because the resulting O-linked oligosaccharide chains tend to be clustered over short stretches of peptide and hence they can present multivalent carbohydrate antigenic or functional determinants for antibody recognition, mammalian cell adhesion and microorganism binding. Co-operativity can greatly increase the affinity of interactions with antibodies or carbohydrate binding proteins. Thus, in addition to their known importance in bearing tumour associated antigens in the gastrointestinal and respiratory tracts, glycoproteins with O-linked chains have been implicated as ligands or co-receptors for selectins (mammalian carbohydrate binding proteins). Microorganisms may have adopted similar mechanisms for interactions with mammalian cells in infection, by having relatively low affinity ligands (adhesins) for carbohydrate binding, which may bind with higher affinity due to the multivalency of the host ligand and which are complemented by other virulence factors such as interactions with integrin-type molecules. In addition to specific adhesion signals from O-linked carbohydrate chains, multivalent O-glycosylation is involved in determining protein conformation and forming conjugate oligosaccharide-protein antigenic, and possible functional determinants.

A unique multifucosylated -3GalNAc beta 1-->4GlcNAc beta 1-->3Gal alpha 1- motif constitutes the repeating unit of the complex O-glycans derived from the cercarial glycocalyx of Schistosoma mansoni

The entire surface of the cercarial stage of the human blood fluke Schistosoma mansoni is covered by a 1-microns thick, highly immunogenic, fucose-rich glycocalyx (GCX). Using strategies based on enzymatic, chemical, and mass spectrometric analysis, we have defined the structures of the major glycans released by reductive elimination from GCX. They comprise a heterogeneous population of multifocosylated complex oligosaccharides with the following nonreducing terminal sequences: [formula: see text] Our structural data suggest that these tri- to pentafucosylated epitopes are carried on type 1, R-->Gal beta-1-->3GalNAc, and type 2, R-->Gal beta 1-->3(R-->GlcNAc beta-1-->6)GalNAc, core structures via repeat units of (3GalNAc beta 1-->4(Fuc alpha 1-->2Fuc alpha 1-->2Fuc alpha 1-->3)GlcNAc beta-1-->3Gal alpha-->)n, where n is mainly 0 and 1, and all sugars are in the pyranose form. The proposed structure represents the first instance where an alpha-galactosylated beta-GalNAc(1-->4)-beta-GlcNAc sequence occurs as a repeating unit in a glycoprotein. It is also unique in being substituted with oligofucosyl appendages. The unusual oligosaccharide structures described here, particularly the potentially immunodominant oligofucosyl moieties, are most likely responsible for the known potency of GCX in modulating various immune responses including complement activation, B cell mitogenesis, and delayed type hypersensitivity in schistosomiasis.

Structure of four acidic oligosaccharides from the jelly coat surrounding the eggs of Xenopus laevis

Novel acidic oligosaccharides were released by reductive beta-elimination from the jelly coat eggs of the Anuran Xenopus laevis. According to the structural analysis of these oligosaccharide-alditols, the following structures are proposed: [sequence: see text] where Kdn, 3-deoxy-D-glycero-D-galactononulosonic acid. These results confirm the species specificity of the glycanic structures present in the secretion of amphibian oviducts, and may form the basis of a specific egg-sperm recognition process.

Primary structure of acidic oligosaccharide-alditols derived from the jelly coat of Ambystoma tigrinum. Occurrence of oligosaccharides with fucosyl(alpha 1-5)[fucosyl(alpha 1-4)]-3-deoxy-D-glycero-D-galacto- nonulosonic acid and fucosyl (alpha 1-2) galactosyl (alpha 1-3)-N- acetylgalactosamine sequences

Eleven O-glycosidic carbohydrate units derived from the jelly coat of Ambystoma tigrinum were analyzed by 1H-NMR spectroscopy. As previously shown for four other amphibian species, the glycans display a remarkable species specificity. As a characteristic feature, 3-deoxy-D-glycero-D-galacto-nonulosonic acid (Kdn) was found difucosylated at C4 and C5, and alpha-Gal attached to C3 of GalNAc-ol. The most representative carbohydrate units are: [formula: see text]