Oligosaccharide Alditols Research Articles

Monitoring of κ-carrageenan depolymerization by capillary electrophoresis and semisynthesis of oligosaccharide alditols

Different hydrolysis conditions to produce κ-carrageenan oligosaccharide alditols were studied and the depolymerization process monitored by capillary electrophoresis (CE). Semisynthesis, ion-exchange and exclusion chromatography were used to obtain and isolate sulfated di-, tetra- and hexasaccharide alditols, the last being fully characterized for the first time. Those derivatives were used as standards to validate a new quantitative CE analytical method which was used to compare two different partial hydrolysis methodologies: an acid hydrolysis followed by reduction and a one-pot reductive hydrolysis using 4-methylmorpholine borane. The resulting depolymerization profiles were quite different from each other. Optimal hydrolysis conditions to produce high yields of specific sulfated oligosaccharides as well as particular mixtures of oligosaccharide alditols were determined. Moreover, using the novel CE method, we were able to distinguish up to eight different oligosaccharides in the hydrolysate mixtures.

Identification of Sialylated Oligosaccharides Derived from Ovine and Caprine Caseinomacropeptide by Graphitized Carbon Liquid Chromatography–Electrospray Ionization Ion Trap Tandem Mass Spectrometry

Isolation and characterization of oligosaccharides from caseinomacropeptide (CMP) are important in understanding the biological and functional properties of CMP. However, it is difficult to achieve this goal, due to the high degree of isomerism present in these types of compounds. In this study, the sialylated oligosaccharides derived from ovine and caprine CMP were released as oligosaccharide alditols by reductive β-elimination and subsequently separated and characterized using graphite carbon column liquid chromatography–negative electrospray ionization ion trap tandem mass spectrometry (LC/ESI(−)-MSn). Although, the chromatographic resolution of isomeric oligosaccharides was not achieved perfectly, the characteristic tandem mass spectra of these compounds allowed differentiating and confirming unequivocally the structure of each one of the oligosaccharides. In CMP of both species, four trisaccharides and four tetrasaccharides were identified as O-glycans. Their chemical structures were identified to be Galβ1-3(NeuAcα2-6)GalNAcol, NeuAcα2-3Galβ1-3GalNAcol, Galβ1-3(NeuGcα2-6)GalNAcol, NeuGcα2-3Galβ1-3GalNAcol, NeuAcα2-3Galβ1-3(NeuGcα2-6)GalNAcol, NeuGcα2-3Galβ1-3(NeuAcα2-6)GalNAcol, NeuAcα2-3Galβ1-3(NeuAcα2-6)GalNAcol, and NeuGcα2-3Galβ1-3(NeuGcα2-6)GalNAcol. The LC/MSn methodology using an ion trap-type mass analyzer shown in this study is of general applicability for determination of short O-glycan oligosaccharides.

The monoclonal antibody HCM31 specifically recognises the Sda tetrasaccharide in goblet cell mucin

Rat small intestinal goblet cell mucins reacting with monoclonal antibody HCM31 increase significantly during regeneration from experimental mucosal damage and at the period of expulsion of parasitic nematode, Nippostrongylus brasiliensis (N.b). The reduction in reactivity of HCM31 with mucin upon neuraminidase treatment, suggested that HCM31 recognizes sialylated oligosaccharide on mucin. HCM31-reactive sialomucins are therefore considered to play an important role in the physiological and pathological changes in the gastrointestinal mucosa. To determine the epitope for HCM31, oligosaccharide–alditols reacted with HCM31 were obtained from the small intestinal mucins of N.b-infected rats and purified by ion-exchange chromatography followed by normal-phase HPLC. Two HCM31-reactive oligosaccharide-alditols were obtained. Analyses using tandem mass spectrometry and NMR spectroscopy showed that these oligosaccharides were core 4 mucin-type oligosaccharides having a common tetrasaccharide sequence, NeuAcα2-3(GalNAcβ1-4)Galβ1-4GlcNAcβ- (Sda blood group antigen). These structures were not found in the small intestinal mucin oligosaccharides from uninfected rats. This epitope specificity of HCM31 was also confirmed using previously established anti-GM2 and anti-Sda antibodies. Taken together, these results strongly suggest that HCM31 specifically recognizes mucin-type oligosaccharides with the Sda tetrasaccharide sequence. Immunohistochemical examination of human gastrointestinal tracts showed that HCM31 site-specifically stained the goblet cells in normal sigmoid colon and normal rectum, but the goblet cells stained with HCM31 were reduced in the corresponding cancer tissues. HCM31 seems to be useful for diagnosis of colonic cancer and for examining the function of secretory-type mucin with Sda antigen.

Structural characterization of complex O-linked glycans from insect-derived material

Although insects are among the most diverse groups of the animal kingdom and may be found in nearly all environments, one can observe an obvious lack of structural data on their glycosylation ability. Hymenoptera is the second largest of all insect orders with more than 110.000 identified species and includes the most famous examples of social insects’ species such as wasps, bees and ants. In this report, the structural variety of O-glycans has been studied in two Hymenoptera species. In a previous study, we showed that major O-glycans from common wasp ( Vespula germanica) salivary mucins correspond to T and Tn antigen, eventually substituted by phosphoethanolamine or phosphate groups. More detailed structural analysis performed by mass spectrometry revealed numerous minor O-glycan structures bearing Gal, GlcNAc, GalNAc and Fuc residues. Thus, in order to investigate glycosylation diversity in insects, we used common wasp nest ( V. germanica) and hornet nest ( Vespa cabro) as starting materials. These materials were submitted to reductive β-elimination and the released oligosaccharide–alditols further fractionated by multidimensional HPLC. Tandem mass spectrometry analyses combined with NMR data revealed the presence of various families of complex O-glycans differing accordingly to both core structures and external motifs. Glycans from wasp were characterized by the presence of core types 1 and 2, Lewis X and internal Gal-Gal motifs. We also observed unusual O-glycans containing a reducing GalNAc unit directly substituted by a fucose residue. In contrast, hornet O-glycans appeared as a rather homogeneous family of core 1 type O-glycans extended by galactose oligomers.

TLR4 Recognizes Pseudallescheria boydii Conidia and Purified Rhamnomannans

Pseudallescheria boydii (Scedosporium apiospermum) is a saprophytic fungus widespread in the environment, and has recently emerged as an agent of localized as well as disseminated infections, particularly mycetoma, in immunocompromised and immunocompetent hosts. We have previously shown that highly purified α-glucan from P. boydii activates macrophages through Toll-like receptor TLR2, however, the mechanism of P. boydii recognition by macrophage is largely unknown. In this work, we investigated the role of innate immune receptors in the recognition of P. boydii. Macrophages responded to P. boydii conidia and hyphae with secretion of proinflammatory cytokines. The activation of macrophages by P. boydii conidia required functional MyD88, TLR4, and CD14, whereas stimulation by hyphae was independent of TLR4 and TLR2 signaling. Removal of peptidorhamnomannans from P. boydii conidia abolished induction of cytokines by macrophages. A fraction highly enriched in rhamnomannans was obtained and characterized by NMR, high performance TLC, and GC-MS. Preparation of rhamnomannans derived from P. boydii triggered cytokine release by macrophages, as well as MAPKs phosphorylation and IκBα degradation. Cytokine release induced by P. boydii-derived rhamnomannans was dependent on TLR4 recognition and required the presence of non-reducing end units of rhamnose of the rhamnomannan, but not O-linked oligosaccharides from the peptidorhamnomannan. These results imply that TLR4 recognizes P. boydii conidia and this recognition is at least in part due to rhamnomannans expressed on the surface of P. boydii.

Selective Hydrolysis of the 3,6-Anhydrogalacotosidic Linkage in Red Algal Galactan: A Combination of Reductive Acid Hydrolysis and Anhydrous Mercaptolysis

Here we report a simple method for the structural analysis of red algal galactan containing 3,6-anhydrogalactose. Structural heterogeneity in the galactan was demonstrated by this method. For selective hydrolysis of 3,6-anhydrogalactosidic linkages in the galactan, conditions for reductive mild acid hydrolysis were examined by characterizing the resulting oligosaccharide alditols by anhydrous mercaptolysis. Residues other than alditols at the reducing ends, including labile 3,6-anhydrogalactose, were liberated quantitatively as diethyl dithioacetal derivatives, whereas alditols at the reducing ends were not derivatized and were liberated as alditols intact. The liberated sugars were then separated and measured quantitatively by gas-liquid chromatography. Heating of agarose in reductive hydrolysis with 0.3 M trifluoroacetic acid in the presence of an acid-stable reducing agent, 4-methyl morpholine borane, at 80 °C for 90 min and for 90 °C for 45 min was found to be optimum for the selective hydrolysis of 3,6-anhydrogalactosidic bonds, without detectable cleavage of other glycosidic bonds.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of oligosaccharides and oligosaccharide alditols obtained by hydrolysis of agaroses and carrageenans, two important types of red seaweed polysaccharides

MALDI-TOF mass spectrometry analyses of several oligosaccharides (aldoses) and oligosaccharide alditols derived from agaroses, kappa- and iota-carrageenans using different matrices (2,5-dihydroxybenzoic acid, nor-harmane, ferulic acid, and the ionic liquid matrices 2,5-dihydroxybenzoic acid–n-butylamine and ferulic acid–n-butylamine) were conducted. These carbohydrates were selected as model compounds to study the MALDI prompt and post-source decay (PSD) fragmentation processes of both families of oligosaccharides. Sulfated alditols showed in the negative-ion mode the molecular ion as [M−Na]− together with the species yielded by their prompt fragmentation (mainly desulfation) while the sulfated oligosaccharides (aldoses) showed mainly glycosidic prompt fragmentation (glycosidic C-cleavages and desulfation). Non-sulfated aldoses and alditols, which could only be analyzed in positive-ion mode ([M+Na]+), did not suffer any prompt fragmentation. The former yielded cross-ring fragmentation in the PSD mode. Best results were obtained by using 2,5-dihydroxybenzoic acid and/or nor-harmane as matrices for all the compounds studied.

The Identification and Location of Succinyl Residues and the Characterization of the Interior Arabinan Region Allow for a Model of the Complete Primary Structure of Mycobacterium tuberculosis Mycolyl Arabinogalactan

The complex cell wall of Mycobacterium tuberculosis is the hallmark of acid fast bacteria and is responsible for much of its physiological characteristics. Hence, much effort has been made to determine its primary structure. Such studies have been hampered by its extreme complexity. Also, its insolubility leads to difficulties determining the presence or absence of base labile groups. We have used an endogenous arabinase to solubilize the arabinan region of the cell wall and have shown using mass spectrometry and NMR that succinyl esters are present on O2 of the inner-branched 1,3,5-alpha-d-arabinofuranosyl residues. In addition, an inner arabinan region of 14 linear alpha-1,5 arabinofuranosyl residues has been identified. These and earlier results now allow the presentation of a model of the entire primary structure of the mycobacterial mycolyl arabinogalactan highlighted by three arabinan chains of 31 residues each.

Semisynthesis of Long-Chain Alkyl Ether Derivatives of Sulfated Oligosaccharides via Dibutylstannylene Acetal Intermediates

Long-chain alkyl ether derivatives of sulfated oligosaccharides were semisynthesized as follows: two naturally occurring red seaweed galactans (neutral agarose and kappa-carrageenan) were submitted to partial reductive hydrolysis to give neutral and sulfated oligosaccharide alditols. The neutral disaccharide alditol (1) and its trityl ether (5) were sulfated and/or alkylated through formation of their dibutylstannylene or (bis)dibutylstannylene acetals. In these reactions, the dibutylstannylene acetals of the terminal 1,2-diols in the alditol units were more reactive than those formed on the cis-diols of the galactopyranosidic units. This property allowed the regioselective monoalkylation of a neutral tetrasaccharide alditol (2), which contained eleven free hydroxyl groups, the highest selectivity ever observed with dibutylstannylene acetals. An alkylated/sulfated derivative (11) was also obtained through the regioselective alkylation of a naturally sulfated disaccharide alditol (10, a kappa-carrageenan derivative).

A Glycomics Platform for the Analysis of Permethylated Oligosaccharide Alditols

This communication reports the development of an LC/MS platform for the analysis of permethylated oligosaccharide alditols that, for the first time, demonstrates routine online oligosaccharide isomer separation of these compounds before introduction into the mass spectrometer. The method leverages a high-resolution liquid chromatography system with the superior fragmentation pattern characteristics of permethylated oligosaccharide alditols that are dissociated under low-energy collision conditions using quadrupole orthogonal time-of-flight (QoTOF) instrumentation and up to pseudo MS(3) mass spectrometry. Glycoforms, including isomers, are readily identified and their structures assigned. The isomer-specific spectra include highly informative cross-ring and elimination fragments, branch position specific signatures, and glycosidic bond fragments, thus facilitating linkage, branch, and sequence assignment. The method is sensitive and can be applied using as little as 40 fmol of derivatized oligosaccharide. Because permethylation renders oligosaccharides nearly chemically equivalent in the mass spectrometer, the method is semiquantitative and, in this regard, is comparable to methods reported using high field NMR and capillary electrophoresis. In this postgenomic age, the importance of glycosylation in biological processes has become clear. The nature of many of the important questions in glycomics is such that sample material is often extremely limited, thus necessitating the development of highly sensitive methods for rigorous structural assignment of the oligosaccharides in complex mixtures. The glycomics platform presented here fulfills these criteria and should lead to more facile glycomics analyses.

Structural analysis of a polysaccharide fromChlorella kessleri by means of gas chromatography—mass spectrometry of its saccharide alditols

Interpretation of gas chromatographic-mass spectrometric data of oligosaccharide alditols was used to determine their structures and to derive the structure of a water soluble polysaccharide isolated from Chlorella kessleri. 1H- and 13C-NMR was employed to assess the configuration of glycosidic bonds and individual monosaccharides were assigned to the L or D series by means of gas chromatography of the acetylated (S)-2-butyl glycosides.

Comparison of the methods for profiling glycoprotein glycans—HUPO Human Disease Glycomics/Proteome Initiative multi-institutional study

Mass spectrometry (MS) of glycoproteins is an emerging field in proteomics, poised to meet the technical demand for elucidation of the structural complexity and functions of the oligosaccharide components of molecules. Considering the divergence of the mass spectrometric methods employed for oligosaccharide analysis in recent publications, it is necessary to establish technical standards and demonstrate capabilities. In the present study of the Human Proteome Organisation (HUPO) Human Disease Glycomics/Proteome Initiative (HGPI), the same samples of transferrin and immunoglobulin-G were analyzed for N-linked oligosaccharides and their relative abundances in 20 laboratories, and the chromatographic and mass spectrometric analysis results were evaluated. In general, matrix-assisted laser desorption/ionization (MALDI) time-of-flight MS of permethylated oligosaccharide mixtures carried out in six laboratories yielded good quantitation, and the results can be correlated to those of chromatography of reductive amination derivatives. For underivatized oligosaccharide alditols, graphitized carbon-liquid chromatography (LC)/electrospray ionization (ESI) MS detecting deprotonated molecules in the negative ion mode provided acceptable quantitation. The variance of the results among these three methods was small. Detailed analyses of tryptic glycopeptides employing either nano LC/ESI MS/MS or MALDI MS demonstrated excellent capability to determine site-specific or subclass-specific glycan profiles in these samples. Taking into account the variety of MS technologies and options for distinct protocols used in this study, the results of this multi-institutional study indicate that MS-based analysis appears as the efficient method for identification and quantitation of oligosaccharides in glycomic studies and endorse the power of MS for glycopeptide characterization with high sensitivity in proteomic programs.

Positional isomers of sulfated oligosaccharides obtained from agarans and carrageenans: preparation and capillary electrophoresis separation

Partial reductive hydrolysis was used to produce oligosaccharide alditols from repetitive sulfated galactans obtained from four Rhodophyta species: κ-carrageenan (from Kappaphycus alvarezii), θ-carrageenan ( Gigartina skottsbergii—alkali-treated λ-carrageenan), agarose 6-sulfate ( Gracilaria domingensis), and pyruvylated agarose 2-sulfate ( Acanthophora spicifera—alkali-treated pyruvylated agaran sulfate). Each hydrolyzate was submitted to anion-exchange and gel-filtration chromatography, and the isolated oligosaccharide alditols were identified by 1D and 2D NMR spectroscopy and by ESI mass spectrometry. The positional isomers of the sulfated oligosaccharide alditols were then completely resolved by capillary electrophoresis in a borate buffer. Attempts to correlate the availability of the hydroxyl groups for borate complexation with the relative migration of the oligosaccharides are presented.

Structures of the glycopeptidolipid antigens from serovars in the Mycobacterium avium/Mycobacterium intracellulare/Mycobacterium scrofulaceum serocomplex.

The 'C-mycosidic' glycopeptidolipid typing antigens from all serovars in the Mycobacterium avium/M. intracellulare/M. scrofulaceum complex have been examined to varying extents. Detailed analysis of those from serovars 8, 9, 16 and 25 show that the antigens consist of short acetylated oligosaccharides linked to a common fattyacyl-peptidyl-O-(3,4-di-O-methylrhamnose) 'core'. The oligosaccharide units, in a form suitable for chemical studies, were liberated as oligosaccharide alditols on treatment of the glycopeptidolipids with alkaline borohydride solution. The alditol in the reduced oligosaccharides from all sources is 6-deoxytalitol. Moreover rhamnose is also always present, indicating that a 'basal' disaccharide, rhamnosyl-6-deoxytalosyl, is always linked to the allo-threonine in the acylpeptide. In addition the oligosaccharides from the glycopeptidolipids of each serovar are distinguished by their own individualistic sugars: 3-O-methylglucose in serovar 8; 2,3-di-O-methylfucose in serovar 9; 2-O-methylfucose in serovar 25; 4-O-methylrhamnose in the oligosaccharide from one of the two glycopeptidolipids in serovar 16 and apparently another rhamnosyl substituent in the other oligosaccharide. The glycopeptidolipid antigens in their structural principals, cellular location and physiological role bear a striking miniscule resemblance to cell wall components of other bacteria such as the O-antigenic and R-antigenic lipopolysaccharides.

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.

Heterogeneity in the biosynthesis of mucin O-glycans from Trypanosoma cruzi tulahuen strain with the expression of novel galactofuranosyl-containing oligosaccharides.

Sialoglycoprotein from Trypanosoma cruzi strains participates in important biological functions in which the O-linked glycans play a pivotal role, and their structural diversity may be related to the parasite's virulence pattern. To provide supporting evidence for this idea, we have determined the structure of novel linear and branched alpha-O-GlcNAc-linked oligosaccharides present on the mucins of the T. cruzi Tulahuen strain. The O-glycans were isolated as oligosaccharide alditols by reductive beta-elimination, purified, and characterized by nuclear magnetic resonance spectroscopy and methylation analysis. Two core families were synthesized by the parasite: the Galfbeta1-->4GlcNAc and Galpbeta1-->4GlcNAc. The Galfbeta1-->4GlcNAc core yields three series of O-chain structures. In the first, the Galf residue is nonsubstituted, while in the other series it is elongated by the activity of galactopyranosyl or galactofuranosyl transferases giving rise to Galp-beta-(1-->2)-Galf-beta-(1-->4) or Galf-beta-(1-->2)-Galf-beta-(1-->4) substructures not previously observed. The three series can arise by further galactopyranosylation of the GlcNAc O-6 arm. Sialylation was the only observed elaboration of the Galpbeta1-->4GlcNAc core family. Thus the determination of the structures of the O-glycans from T. cruzi Tulahuen mucins confirms the strain specificity of the glycosylation and predicts a relationship between it and parasite pathogenicity and the epidemiology of Chagas' disease.

Structural determination of neutral O-linked oligosaccharide alditols by negative ion LC-electrospray-MS n

Neutral O-linked oligosaccharides released from the salivary mucin MUC5B were separated and detected by negative ion LC-MS and LC-MS 2. The resolution of the chromatography and the information obtained from collision induced dissociation of detected [M − H] − ions were usually sufficient to identify the sequence of individual oligosaccharides, illustrated by the fact that 50 different oligosaccharides ranging from disaccharides to nonasaccharides could be assigned from the sample. Fragmentation was shown to yield mostly reducing end sequence fragments (Z i and Y i ), enabling primary sequence assignment. Specific fragmentation pathways or patterns were also detected giving specific linkage information. The reducing end core (Gal/GlcNAcβ1-3GalNAcol or Gal/GlcNAcβ1-3(GlcNAcβ1-6)GalNAcol) could be deduced from the pronounced glycosidic C-3 cleavage and A i type cleavages of the reducing end GalNAcol, together with the non reducing end fragment from the loss of a single substituted GalNAcol. Substitution patterns on GlcNAc residues were also found, indicative for C-4 substitution ( 0,2A i − H 2O cleavage) and disubstitution of C-3 and C-4 (Z i /Z i cleavages). This kind of fragmentation can be used for assigning the mode of chain elongation (Galβ1-3/4GlcNAcβ1-) and identification of Lewis type antigens like Lewis a/x and Lewis b/y on O-linked oligosaccharides. In essence, negative ion LC-MS 2 was able to generate extensive data for understanding the overall glycosylation pattern of a sample, especially when only a limited amount of material is available.

Diagnostic ions for the rapid analysis by nano-electrospray ionization quadrupole time-of-flight mass spectrometry of O-glycans from human mucins.

Nano-electrospray ionization quadrupole time-of-flight mass spectrometry (nanoESI-Q-TOFMS) was used for sensitive mapping and sequencing of underivatized oligosaccharide alditols obtained from human mucins. Using subnanomolar amounts of oligosaccharides previously analyzed by nuclear magnetic resonance (NMR), series of diagnostic ions relevant to the structural characterization of O-glycans were deduced. Determination of the core type as well as positions and partial linkages of fucose residues could be readily obtained from the dominant [M+Na](+) ions. Differentiation of isomeric structures and glycosidic linkages were defined by the characteristic cross-ring (0,2)A-type cleavages in the negative ion mode. Tandem (MS/MS) mass spectra of [M-H](-) ions from sialylated or sulfated O-glycans revealed information concerning the position and linkage of such residues. These fragmentation rules were further applied in the structural determination of glycans from human colonic mucins. All these findings indicated the efficiency of ESI-Q-TOFMS for the determination of oligosaccharide composition, sequence, partial linkage and substitution, providing a wealth of structural information with sensitivity sufficient for the analysis of quantities as obtained from natural sources.

Purification and further characterization of a glycoprotein from the skin mucus of Japanese eels

A glycoprotein (EGP) was purified from the skin mucus of Japanese eel Anguilla japonica. Apparent average molecular mass of the EGP was estimated to be 500 000. The EGP was found to contain 30·8% NeuAc, 26·4% GalNAc, 6·4% Gal, 0·4% NeuGc and 25·1% Thr‐rich protein. EGP was treated with alkaline borohydride for the release of carbohydrate chains (oligosaccharide alditols). Three carbohydrate chains were isolated from the released carbohydrate chains by Sephadex G‐25 (superfine) gel filtration and HPLC. Using 1H‐NMR spectroscopy, methylation analysis and glycosidase digestion, the structures of the three carbohydrate chains were determined to be NeuAcα2→6GalNAc‐ol, NeuAcα2→3GalNAc‐ol and NeuAcα2→6(GalNAcα1→3)GalNAc‐ol. An overall structure for the sialoglycoprotein from the skin mucus is proposed: the molecule is considered to consist of highly glycosylated 10 glycopeptide units (containing >40 carbohydrate chains) that are linked to the hydroxyl amino acids and spaced on average two amino acids apart.

Evidence of Regio-specific Glycosylation in Human Intestinal Mucins: PRESENCE OF AN ACIDIC GRADIENT ALONG THE INTESTINAL TRACT

Mucin glycans were isolated from different regions of the normal human intestine (ileum, cecum, transverse and sigmoid colon, and rectum) of two individuals with ALeb blood group. A systematic study of the monosaccharides and oligosaccharide alditols released by reductive beta-elimination from mucins was performed using gas chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and nuclear magnetic resonance spectroscopy techniques. Important variations were observed in the mucin-associated oligosaccharide content with an increasing gradient of sialic acid from the ileum to the colon associated with a reverse gradient of fucose. Moreover, a comparative study of the Sda/Cad and ABH blood group determinants along the gastrointestinal tract showed the same reverse distribution in the two kinds of antigens. In addition, besides their heterogeneity, sialic acids presented considerable variations in the degree of O-acetylation in relation to glycan sialylation level. These data are discussed in view of recent concepts suggesting that the oligosaccharide composition of the gut constitutes a varied ecosystem for microorganisms that are susceptible to adapt there and possess the specific adhesion system and specific enzymes able to provide a carbohydrate nutrient.