Serum-stimulated cell cycle entry promotes ncOGT synthesis required for cyclin D expression

Nuclear and cytoplasmic O-GlcNAc transferase (OGT) is a unique and universally expressed enzyme catalyzing O-GlcNAcylation of thousands of proteins. Although OGT interferes with many crucial intracellular processes, including cell cycle, only few studies have focused on elucidating the precise role of the glycosyltransferase during cell cycle entry. We first demonstrated that starved MCF7 cells reincubated with serum quickly induced a significant OGT increase concomitantly to activation of PI3K and MAPK pathways. Co-immunoprecipitation experiments performed upon serum stimulation showed a progressive interaction between OGT and β-catenin, a major factor in the regulation of cell cycle. OGT expression was also observed in starved HeLa cells reincubated with serum. In these cells, the O-GlcNAcylation status of the β-catenin-2XFLAG was increased following stimulation. Moreover, β-catenin-2XFLAG was heavily O-GlcNAcylated in exponentially proliferating HeLa cells when compared to confluent cells. Furthermore, blocking OGT activity using the potent inhibitor Ac-5SGlcNAc prevented serum-stimulated cyclin D1 synthesis and slightly delayed cell proliferation. At last, interfering with OGT expression (siOGT) blocked cyclin D1 expression and decreased PI3K and MAPK activation. Together, our data indicate that expression and catalytic activity of OGT are necessary and essential for G0/G1 transition.

Lysosomal dysfunction causes neurodegeneration in mucolipidosis II 'knock-in' mice

Mucolipidosis II is a neurometabolic lysosomal trafficking disorder of infancy caused by loss of mannose 6-phosphate targeting signals on lysosomal proteins, leading to lysosomal dysfunction and accumulation of non-degraded material. However, the identity of storage material and mechanisms of neurodegeneration in mucolipidosis II are unknown. We have generated 'knock-in' mice with a common mucolipidosis II patient mutation that show growth retardation, progressive brain atrophy, skeletal abnormalities, elevated lysosomal enzyme activities in serum, lysosomal storage in fibroblasts and brain and premature death, closely mimicking the mucolipidosis II disease in humans. The examination of affected mouse brains at different ages by immunohistochemistry, ultrastructural analysis, immunoblotting and mass spectrometric analyses of glycans and anionic lipids revealed that the expression and proteolytic processing of distinct lysosomal proteins such as α-l-fucosidase, β-hexosaminidase, α-mannosidase or Niemann-Pick C2 protein are more significantly impacted by the loss of mannose 6-phosphate residues than enzymes reaching lysosomes independently of this targeting mechanism. As a consequence, fucosylated N-glycans, GM2 and GM3 gangliosides, cholesterol and bis(monoacylglycero)phosphate accumulate progressively in the brain of mucolipidosis II mice. Prominent astrogliosis and the accumulation of organelles and storage material in focally swollen axons were observed in the cerebellum and were accompanied by a loss of Purkinje cells. Moreover, an increased neuronal level of the microtubule-associated protein 1 light chain 3 and the formation of p62-positive neuronal aggregates indicate an impairment of constitutive autophagy in the mucolipidosis II brain. Our findings demonstrate the essential role of mannose 6-phosphate for selected lysosomal proteins to maintain the capability for degradation of sequestered components in lysosomes and autophagolysosomes and prevent neurodegeneration. These lysosomal proteins might be a potential target for a valid therapeutic approach for mucolipidosis II disease.

DMBT1 expression and glycosylation during the adenoma-carcinoma sequence in colorectal cancer

The gene DMBT1 (deleted in malignant brain tumour-1) has been proposed to play a role in brain and epithelial cancer, but shows unusual features for a classical tumour-suppressor gene. On the one hand, DMBT1 has been linked to mucosal protection, whereas, on the other, it potentially plays a role in epithelial differentiation. Thus its function in a particular tissue is of mechanistic importance for its role in cancer. Because the former function requires secretion to the lumen and the latter function may depend on its presence in the extracellular matrix, we decided to investigate DMBT1 expression, location and its mode of secretion during malignant transformation in colorectal cancer. Using human colorectal PC/AA cell lines and tissue sections from individual patients, we have examined the expression of DMBT1 and its glycosylation in the adenoma-carcinoma sequence leading to the adenocarcinoma phenotype.

Association of ATP synthase alpha-chain with neurofibrillary degeneration in Alzheimer's disease

Amyloid deposits and neurofibrillary tangles (NFT) are the two hallmarks that characterize Alzheimer's disease (AD). In order to find the molecular partners of these degenerating processes, we have developed antibodies against insoluble AD brain lesions. One clone, named AD46, detects only NFT. Biochemical and histochemistry analyses demonstrate that the labeled protein accumulating in the cytosol of Alzheimer degenerating neurons is the alpha-chain of the ATP synthase. The cytosolic accumulation of the alpha-chain of ATP synthase is observed even at early stages of neurofibrillary degenerating process. It is specifically observed in degenerating neurons, either alone or tightly associated with aggregates of tau proteins, suggesting that it is a new molecular event related to neurodegeneration. Overall, our results strongly suggest the implication of the alpha-chain of ATP synthase in neurofibrillary degeneration of AD that is illustrated by the cytosolic accumulation of this mitochondrial protein, which belongs to the mitochondrial respiratory system. This regulatory subunit of the respiratory complex V of mitochondria is thus a potential target for therapeutic and diagnostic strategies.

The effects of ethanol on the glycosylation of human transferrin

Appearance of a hyposialylated transferrin fraction in the plasma during chronic alcohol exposure is a well-known phenomenon, and it represents the best available marker of chronic alcohol consumption. The mechanisms of its appearance are still not well understood and are extremely complex, involving biosynthesis and catabolism alterations, although the only structural abnormality described corresponds to the loss of an entire glycan chain. We analyzed and compared the oligosaccharides present on the different isoforms of purified transferrin isolated from control and patients with severe alcohol abuse by fluorescent carbohydrate electrophoresis and matrix-assisted laser desorption ionization mass spectrometry. Our data indicate that the major modification observed is the loss of an entire oligosaccharide chain; we also demonstrate that there is a modification of terminal sialylation. Carbohydrate-deficient transferrin (CDT) is the result of multiple alterations of glycosylation. These results give a partial explanation to the poor sensitivity of the measurement of CDT and its controversial use as a marker of chronic alcohol consumption.

The SPASIBA force field as an essential tool for studying the structure and dynamics of saccharides

The SPASIBA force field has been applied to the determination of the structure and dynamical properties of various disaccharides. It has been shown that the experimental properties (structure, dipole moment, conformational relative energies) are satisfactorily predicted. The anomeric and exo-anomeric effects are confidently reproduced without specific terms for the alpha and beta anomers and the type of glycosidic linkages.

Paracellular transport of avidin saturated or not with biotinylated cobalamin through Caco-2 cell epithelium monolayer

BACKGROUND

The cationic charge of molecules may promote their uptake across epithelia, which are rich in brush border anionic sites. The transport of unsaturated avidin and avidin saturated with a biotinylated compound was investigated across Caco-2 adenocarcinoma cell with fetal enterocyte phenotype.

METHODS

The unsaturated avidin and avidin saturated with either biotin or a biotinyl-cobalamin conjugate (biotinyl-Cbl) were iodinated to follow their transport through the cell monolayer. Their apparent permeability coefficient (Papp) and transepithelial pathway were determined and compared to those for control radiolabeled markers [3H]-mannitol, [125I]-beta-lactoglobulin and [57Co]-cobalamin/intrinsic factor (Cbl/IF).

RESULTS

The Papp of [125I]-avidin estimated at 2.8 x 10(-7) +/- 0.08 cm/s was close to that for mannitol that uses paracellular pathway. The binding of biotin or biotin conjugate to avidin enhanced its tetrameric conformation. The Papp for [125I]-avidin/biotin and [125I]- avidin/biotinyl-Cbl were respectively increased by 2-fold, compared to that for [125I]-avidin and 4-fold, compared to that for [125I]-beta-lactoglobulin and [54Co]-Cbl/IF. The protein was not accumulated in the cell and was found in intact form in the basolateral side, after its transport across the monolayer. Chloroquine (0.66 micromol/ml) did not significantly decrease the Papp for [125I]-avidin/biotinyl-Cbl. Conversely it decreased by 80% the Papp for Cbl/IF, that uses transepithelial pathway.

CONCLUSIONS

Avidin (either saturated or not with biotin and biotinyl-Cbl) was able to cross the monolayer of Caco-2 cell line through a paracellular pathway. This study pointed out the interest for using this protein as a shuttle for increasing the transport rate of biotinylated compounds through fetal epithelial barriers.

Identification of substituted sites on MUC5AC mucin motif peptides after enzymatic O-glycosylation combining beta-elimination and fixed-charge derivatization

A strategy for determination of O-glycosylation site(s) in glycopeptides has been developed using model compounds obtained by enzymatic glycosylation (by human GaNTase-T2 isoform) on peptides derived from the human MUC5AC mucin tandem repeat motif. The beta-elimination-addition reaction (using dimethylamine and concomitantly ethanethiol) on the formerly glycosylated sites through a Michael-type condensation produced efficient deglycosylation with appropriate chemical modification. After N-terminal derivatization by a phosphonium group, peptide sequencing was then carried out by nanospray tandem mass spectrometry experiments. The highly predictable fragmentation pathways of these fixed-charge phosphonium derivatives enable straightforward recognition of glycosylation site(s) based on the mass increment of +44 Da for originally glycosylated threonine compared to the mass of fragments containing nonglycosylated residues.

Identification of N-acetyl-d-glucosamine-specific lectins from rat liver cytosolic and nuclear compartments as heat-shock proteins

Cytosolic and nuclear O-linked N-acetylglucosaminylation has been proposed to be involved in the nuclear transport of cytosolic proteins. We have isolated nuclear and cytosolic N-acetyl-d-glucosamine (GlcNAc)-specific lectins from adult rat liver by affinity chromatography on immobilized GlcNAc and identified these lectins, by a proteomic approach, as belonging to the heat-shock protein (HSP)-70 family (one of them being heat-shock cognate 70 stress protein). Two-dimensional electrophoresis indicated that the HSP-70 fraction contained three equally abundant proteins with molecular masses of 70, 65 and 55 kDa. The p70 and p65 proteins are phosphorylated and are themselves O-linked GlcNAc (O-GlcNAc)-modified. The HSP-70 associated into high molecular mass complexes that dissociated in the presence of reductive and chaotropic agents. The lectin(s) present in this complex was (were) able to recognize cytosolic and nuclear ligands, which have been isolated using wheat germ agglutinin affinity chromatography. These ligands are O-GlcNAc glycosylated as demonstrated by [(3)H]galactose incorporation and analysis of the products released by reductive beta-elimination. The isolated lectins specifically recognized ligands present in both the cytosol and the nucleus of human resting lymphocytes. These results demonstrated the existence of endogenous GlcNAc-specific lectins, identified as HSP-70 proteins, which could act as a shuttle for the nucleo-cytoplasmic transport of O-GlcNAc glycoproteins between the cytosol and the nucleus.

Sd(a)-antigen-like structures carried on core 3 are prominent features of glycans from the mucin of normal human descending colon

This paper describes structural characterization by NMR, MS and degradative studies of mucin glycans from normal human descending colon obtained freshly at autopsy. The saccharides were mainly based on core 3 (GlcNAcbeta1-3GalNAc). Among the terminal saccharide determinants Sd(a)/Cad-antigen-like structures were prominent, and Lewis x, sialyl Lewis x and sulphated Lewis x were found as minor components, whereas blood group H and A antigenic determinants were absent. The saccharides were markedly different from those of mucins from colon cancers or colon cancer cell lines analysed so far, in which cores 1 and 2 are prominent features, and in which various other terminal determinants have been found, but not Sd(a)/Cad.

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.

Ancestral exonic organization of FUT8, the gene encoding the alpha6-fucosyltransferase, reveals successive peptide domains which suggest a particular three-dimensional core structure for the alpha6-fucosyltransferase family

Based on PCR strategies and expression studies, we define the genomic organization of the FUT8b gene. This gene encodes the only known mammalian enzyme transferring fucose in an alpha1-->6 linkage on the asparagine-branched GlcNAc residue of the chitobiose unit of complex N:-glycans. The intron/exon organization of the bovine coding sequence determines five successive functional domains. The first exon encodes a domain homologous to cytoskeleton proteins, the second presents a proline-rich region including a motif XPXPPYXP similar to the peptide ligand of the SH3-domain proteins, the third encodes a gyrase-like domain (an enzyme which can bind nucleotides), and the fourth encodes a peptide sequence homologous to the catalytic domain of proteins transferring sugars. Finally, the last exon encodes a domain homologous to the SH3 conserved motif of the SH2-SH3 protein family. This organization suggests that intramolecular interactions might give a tulip-shaped scaffolding, including the catalytic pocket of the enzyme in the Golgi lumen. Deduced from the published sequence of chromosome 14 (AL109847), the human gene organization of FUT8 seems to be similar to that of bovine FUT8b, although the exon partition is more pronounced (bovine exons 1 and 2 correspond to human exons 1-6). The mosaicism and phylogenetic positions of the alpha6-fucosyltransferase genes are compared with those of other fucosyltransferase genes.

Analysis of 8-aminonaphthalene-1,3,6-trisulfonic acid labelled N-glycans by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Fluorophore-assisted carbohydrate electrophoresis (FACE) is a fast and efficient analytical method which is now widely used in glycobiology for the separation and quantification of free or glycoprotein-released oligosaccharides. However, since identification by FACE of N-glycan structures is only based on their electrophoretic mobility after labelling with 8-aminonaphthalene-1,3, 6-trisulfonic acid (ANTS), co-migration of derived glycans on gel could occur which may result in erroneous structural assignments. As a consequence, a protocol was developed for the fast and efficient matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometric analysis of ANTS-labelled N-glycans. N-Glycans were isolated from plant and mammalian glycoproteins, reductively aminated with the charged fluorophore 8-aminonaphthalene-1, 3, 6-trisulfonic acid (ANTS) and separated using high resolution polyacrylamide gel electrophoresis. The ANTS-labelled glycans were eluted from FACE gel slices and then analysed by MALDI-TOF mass spectrometry in negative ion mode. Using 3-aminoquinoline containing 2.5 mM citrate NH(4)(+) as matrix, neutral N-linked N-glycans, as well as labelled sialylated oligosaccharides, were found to be easily detected in the 2-10 picomole range giving rise to ¿M - H(-) ions.

Effect of okadaic acid on O-linked N-acetylglucosamine levels in a neuroblastoma cell line

O-Linked N-Acetylglucosamine (O-GlcNAc) is a major form of post-translational modification found in nuclear and cytoplasmic proteins. Several authors have advanced the hypothesis according to which phosphorylation and O-GlcNAc glycosylation are reciprocally related to one another [1,2]. In order to test this hypothesis we have investigated the effect of a broad spectrum phosphatase inhibitor, okadaic acid (OA), generally used to induce protein hyperphosphorylation, on the GlcNAc content of cellular glycoproteins. We demonstrate that in neuronal cells lines OA decreases the level of O-GlcNAc in both nuclear and cytoplasmic proteins with a greater effect in the nuclear fraction. This phenomenon was demonstrated by the use of three different procedures for the detection of O-GlcNAc in conjunction with a systematic treatment with PNGase F. O-Linked GlcNAc was characterized using respectively lectin staining with WGA, galactosyltransferase labeling and metabolic labeling of cultured cells with [3H]glucosamine. Although the effects on individual proteins varied, a less pronounced effect was observed on HeLa or COS cell total homogenates. When Kelly cells were treated with OA, the major observation was a decrease in O-GlcNAc content of nuclear proteins. The measurement of the UDP-GlcNAc level clearly demonstrates that the decrease on the O-GlcNAc level in the neuroblastoma cell line after treatment with okadaic acid is not a consequence of the modification of the UDP-GlcNAc pool.

Glycoprotein lysosomal storage disorders: alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency

Glycoproteinoses belong to the lysosomal storage disorders group. The common feature of these diseases is the deficiency of a lysosomal protein that is part of glycan catabolism. Most of the lysosomal enzymes involved in the hydrolysis of glycoprotein carbohydrate chains are exo-glycosidases, which stepwise remove terminal monosaccharides. Thus, the deficiency of a single enzyme causes the blockage of the entire pathway and induces a storage of incompletely degraded substances inside the lysosome. Different mutations may be observed in a single disease and in all cases account for the nonexpression of lysosomal glycosidase activity. Different clinical phenotypes generally characterize a specific disorder, which rather must be described as a continuum in severity, suggesting that other biochemical or environmental factors influence the course of the disease. This review provides details on clinical features, genotype-phenotype correlations, enzymology and biochemical storage of four human glycoprotein lysosomal storage disorders, respectively alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency. Moreover, several animal disorders of glycoprotein metabolism have been found and constitute valuable models for the understanding of their human counterparts.

Phosphorylation and O-glycosylation sites of human chromogranin A (CGA79-439) from urine of patients with carcinoid tumors

Because of their water-soluble properties, chromogranins (CGs) and chromogranin-derived fragments are released together with catecholamines from adrenal chromaffin cells during stress situations and can be detected in the blood by radiochemical and enzyme assays. It is well known that chromogranins can serve as immunocytochemical markers for neuroendocrine tissues and as a diagnostic tool for neuroendocrine tumors. In 1993, large CGA-derived fragments have been shown to be excreted into the urine in patients with carcinoid tumors and the present study deals with the characterization of the post-translational modifications (phosphorylation and O-glycosylation) located along the largest natural CGA-derived fragment CGA79-439. Using mild proteolysis of peptidic material, high performance liquid chromatography, sequencing, and mass spectrometry analysis, six post-translational modifications were detected along the C-terminal CGA-derived fragment CGA79-439. Three O-linked glycosylation sites were located in the core of the protein on Thr163, Thr165, and Thr233, consisting in di-, tri-, and tetrasaccharides. Three phosphorylation sites were located in the middle and C-terminal domain, on serine residues Ser200, Ser252, and Ser315. These modified sites were compared with sequences of others species and discussed in relation with the post-translational modifications that we have reported previously for bovine CGA.

Human preformed IgG combining with membrane-bound porcine serotransferrin lyse porcine endothelial cells through antibody-dependent cellular cytotoxicity

Preformed antibodies are involved in xenograft rejection. The purpose of this work was to characterize porcine xenoantigens recognized by human preformed IgG (hpIgG), and to investigate the role of hpIgG in xenogeneic rejection. IgG eluted from porcine livers perfused with human plasma, human sera and total human IgG were immunoblotted on porcine aortic endothelial cell extracts. The amino acid sequence of a 76-kDa antigen constantly revealed was 100% homologous with porcine serotransferrin (psTf). hpIgG from human sera, human IgG1 and IgG2 and F(ab')2gamma specifically bound to psTf. Neutralization by psTf abolished that binding. Although alpha1,3-linked galactose residues (Gal(alpha)1,3Gal) is the dominant epitope recognized by preformed antibodies in the swine-to-human combination, the analysis of carbohydrate composition of psTf showed that the molecule was devoid of Gal(alpha)1,3Gal moieties and that preformed anti-psTf IgG bound to epitopes localized on the peptide core of the molecule. Purified human anti-psTf IgG antibodies were able to bind to psTf linked to its receptor on porcine endothelial cells, and to kill those cells through antibody-dependent cellular cytotoxicity.

Identification of urinary oligosaccharides by matrix-assisted laser desorption ionization time-of-flight mass spectrometry

A new method of urinary oligosaccharides identification by matrix-assisted laser desorption time-of-flight mass spectrometry is presented. The method involves three steps: coupling of the urinary oligosaccharides with 8-aminonaphthalene-1,3,6-trisulfonic acid; fast purification over a porous graphite carbon extraction column; and mass spectrometric analysis. Identification of urinary oligosaccharides is based on the patterns and values of the pseudomolecular ions observed. We report here the patterns in urines from patients with Pompe disease, alpha and beta mannosidoses, galacto-sialidosis, and GM1 gangliosidosis. The protocols described here allowed facile and sensitive identification of the pathognomonic oligosacchariduria present in lysosomal diseases and can be extended to any pathological oligosacchariduria.

Differential binding of lectins IL-2 and CSL to candida albicans and cancer cells

The demonstration that interleukin 2 (IL-2) is a lectin specific for oligomannosides allows to understand a new function for this cytokine: as a bifunctional molecule when bound to its receptor ss, IL-2 associates the latter which the CD3/TCR complex, interacting with oligosaccharides of CD3 through its carbohydrate-recognition domain (Zanetta et al. , 1996, Biochem. J., 318, 49-53). This induces the tyrosine phosphorylation of the IL-2R beta by ++p56(lck) , the first step of the IL-2-dependent signaling. Since this specific association is disrupted in vitro by oligomannosides with five and six mannose residues, we made the hypothesis that pathogenic cells or microorganisms could bind IL-2, consequently disturbing the IL-2-dependent response. This study shows that the pathogenic yeast Candida albicans (in contrast with nonpathogenic yeasts) binds high amounts of IL-2 as did cancer cells. In contrast with cancer cells, yeasts do not bind the Man6GlcNAc2-specific lectin CSL, an endogenous "amplifier of activation signals" (Zanetta et al. , 1995, Biochem. J., 311, 629-636).

N-glycans harboring the Lewis a epitope are expressed at the surface of plant cells

In plants, N-linked glycans are processed in the Golgi apparatus to complex-type N-glycans of limited size containing a beta(1,2)-xylose and/or an alpha(1,3)-fucose residue. Larger mono- and bi-antennary N-linked complex glycans have not often been described. This study has re-examined the structure of such plant N-linked glycans, and, through both immunological and structural data, it is shown that the antennae are composed of Lewis a (Le(a)) antigens, comprising the carbohydrate sequence Gal beta 1-3[Fuc alpha 1-4]GlcNAc. Furthermore, a fucosyltransferase activity involved in the biosynthesis of this antigen was detected in sycamore cells. This is the first characterization in plants of a Lewis antigen that is usually found on cell-surface glycoconjugates in mammals and involved in recognition and adhesion processes. Le(a)-containing N-linked glycans are widely distributed in plants and highly expressed at the cell surface, which may suggest a putative function in cell/cell communication.

The oncofetal J28 epitope involves fucosylated O-linked oligosaccharide structures of the fetoacinar pancreatic protein

The fetoacinar pancreatic protein (FAP), characterized by the mAb J28, is an oncofetal form of bile salt dependent lipase (BSDL), the expression of which is related to pancreatic differentiation and neoplastic processes. Because the J28 epitope, recognized by mAb J28, is suggested to be dependent upon carbohydrates, we have attempted to gain information about the structure of this epitope. Indeed, treatment of FAP with sodium periodate abolished the reactivity of the protein to mAb J28, which demonstrates the implication of oligosaccharides in the structure of the J28 epitope. FAP offers both O-linked and N-linked carbohydrate structures, of which, as we have determined, one is involved. Peptides obtained after cyanogen bromide cleavage were desialylated then separated by affinity chromatography on an immobilized peanut agglutinin agarose column. The peptide retained on this column carried out the reactivity with the mAb J28. Although some differences in amino acid analysis were observed, the N-terminal sequence of this peptide correlates with that of the C-terminal part of the enzyme. Carbohydrate analysis of the peptide bearing the J28 epitope revealed fucose, galactose, N-acetylgalactosamine, N-acetylglucosamine, and N-acetylneuraminic acid. The competition observed between mAb J28 and Ulex europaeus I lectin for binding to the J28 epitope suggested that fucose residue alpha (1-2) linked to a galactose residue was implicated in the structure of the J28 epitope. Alternatively, the loss of the mAb J28 reactivity upon treatment of FAP either with bovine kidney or bovine epididymis fucosidase was observed indicating that fucose residues linked at the alpha (1-2) and alpha (1-6) positions may be involved in the establishment of the structure of the J28 epitope. These observations suggest that mAb J28 recognized a particular fucosylated O-linked oligosaccharide structure located at the mucin-like extended C-terminal part of FAP.

Lectin activities of cytokines and growth factors: function and implications for pathology

The discovery that certain cytokines have carbohydrate-binding (lectin) properties opens new concepts in the understanding of their mechanism of action. The carbohydrate-recognition domain, which is localized opposite to the receptor-binding domain, makes these molecules bi-functional. The expression of the biological activity of the cytokine relies on its carbohydrate-binding activity which allows the association of the cytokine receptor with molecular complexes comprising the specific kinase involved in receptor phosphorylation and in specific signal transduction. It is expected that blood accumulation of free or membrane-bound glucan ligands of cytokines may dramatically perturb their endogenous function inducing specific immunodeficiencies.

Interleukin 2 is a lectin that associates its receptor with the T-cell receptor complex

To determine the nature of the mechanism by which the binding of interleukin-2 (IL-2) to its receptor (IL-2R beta) induces IL-2R beta phosphorylation by the tyrosine kinase p56lck associated with the T-cell receptor (TCR) complex, we investigated the possibility that this mechanism was due to the putative lectin activity of IL-2 ([Sherblom, Sathyamoorthy, Decker and Muchmore (1989) J. Immunol. 143, 939-944]. Here we demonstrate that IL-2 is a calcium-independent lectin specific for oligomannosidic N-glycans with five and six mannose residues. This lectin activity is preserved after binding of IL-2 to IL-2R beta. IL-2 behaves as a bifunctional molecule that associates IL-2R beta with specific glycoprotein ligands of the TCR complex including a glycosylated form of CD3.

Oligomannosides or oligosaccharide-lipids as potential substrates for rat liver cytosolic alpha-D-mannosidase

We have previously reported the substrate specificity of the cytosolic alpha-D-mannosidase purified from rat liver using Man9GlcNAc, i.e. Man alpha 1-2Man alpha 1-3(Man alpha 1-2Man alpha 1-6)Man alpha 1-6(Man alpha 1-2Man alpha 1-2Man alpha 1-3) Man beta 1-4G1cNAc, as substrate [Grard, Saint-Pol, Haeuw, Alonso, Wieruszeski, Strecker and Michalski (1994) Eur. J. Biochem. 223, 99-106]. Man9 G1cNAc is hydrolysed giving Man5GlcNAc, i.e. Man alpha 1-2 Man alpha 1-2Man alpha 1-3(Man alpha 1-6)Man beta 1-4GlcNAc, possessing the same structure as the oligosaccharide of the dolichol pathway formed in the cytosolic compartment during the biosynthesis of N-glycosylprotein glycans. We study here the activity of the purified cytosolic alpha-D-mannosidase towards the oligosaccharide-diphosphodolichol intermediates formed during the biosynthesis of N-glycans, and also towards soluble oligosaccharides released from the endoplasmic reticulum which are glucosylated or not and possessing at their reducing end either a single N-acetylglucosamine residue or a di-N-acetylchitobiose sequence. We demonstrate that (1) dolichol pyrophosphate oligosaccharide substrates are poorly hydrolysed by the cytosolic alpha-D-mannosidase; (2) oligosaccharides with a terminal reducing di-N-acetylchitobiose sequence are not hydrolysed at all; (3) soluble oligosaccharides bearing a single reducing N-acetylglucosamine are the real substrates for the enzyme. These results suggest a role for alpha-D-mannosidase in the catabolism of glycans released from the endoplasmic reticulum rather than in the regulation of the biosynthesis of asparagine-linked oligosaccharides.

Purification by cobalamin-Sepharose affinity chromatography and intrinsic factor-binding activity of an extramembrane proteolytic product from pig ileal mucosa

We have purified a cobalamin-binding protein obtained by papain digestion of pig intestine by cobalamin-AH-Sepharose affinity chromatography, with a purification factor of 17,300, a yield of 63% and a cobalamin-binding activity of 11,260 pmol/mg of protein. The protein contained 3.8% carbohydrate and was O- and N-glycosylated. Its molecular mass was 69 kDa on SDS/PAGE and its isoelectric point was 5.1. It had a binding activity for both [57Co]cobalamin and [57Co]cobalamin-intrinsic factor in native PAGE autoradiography and it inhibited the binding of intrinsic factor to the intact intestinal receptor with an IC50 of 49.31 nmol/l in a radioisotope assay. In conclusion, the purified protein shared a binding activity for both cobalamin and intrinsic factor-cobalamin complexes and could correspond to the extracellular domain of the ileal intrinsic factor receptor.

Structure of the phosphopeptidomannans from flocculent and non-flocculent yeast Kluyveromyces lactis

After extraction from whole cells, and purification by gel filtration, the chemical composition and molecular mass estimation of the cell-wall phosphopeptidomannan (PPM) showed no significant difference respectively between flocculent, weakly, very weakly and non-flocculent Kluyveromyces lactis yeast strains. However, when PPMs were tested as ligands of a lectin, extracted from the flocculent strain, the PPM isolated from the flocculent and weakly flocculent strain were recognized to a higher degree than those isolated from the non and very weakly flocculent strains. Acetolysis of PPM extracted from the four strains produced five oligosaccharide fractions corresponding to mono-, di-, tri-, penta-and hexa-saccharides. The flocculent strain was characterised by a high content of di-and penta-saccharides. The 1H NMR analysis of the oligosaccharides demonstrated that the flocculent strain contained equivalent levels of the two mannobioses: Man(alpha 1-->2)Man and Man(alpha 1-->3)Man and of the two mannotrioses Man(alpha 1-->2)Man(alpha 1-->2)Man and Man(alpha 1-->3)Man(alpha 1-->2)Man. In contrast, the non-flocculent and the very weakly flocculent strains contained a single type of mannobiose Man(alpha 1-->2)Man and one type of mannotriose Man(alpha 1-->2)Man(alpha 1-->2)Man.

Catabolism of glycan moieties of lipid intermediates leads to a single Man5GlcNAc oligosaccharide isomer: a study with permeabilized CHO cells

This paper presents kinetic and structural analyses of oligosaccharide material released during glycosylation in permeabilized Chinese hamster ovary cells incubated with sugar nucleotides. Permeabilized cells released 30 times more oligosaccharide material than metabolically labelled cells, normalized to the amount of labelled glycoprotein acceptor, making this an amenable system for study. Fifteen to forty per cent of the oligosaccharide material released by permeabilized cells was oligosaccharide-phosphate, depending on the nature and amount of the oligosaccharide-lipids synthesized. The oligosaccharide-phosphates released were recovered in the cytosol, and were exclusively Man2Glc-NAc2P and Man5GlcNAc2P, released from oligosaccharide-lipids thought to be facing the cytosol. In contrast, the structures found as neutral oligosaccharide material were similar to those attached to newly synthesized glycoproteins, indicating that the oligosaccharides were subjected to the same processing enzymes whether or not they were protein bound. Importantly, the kinetics of the transfer to protein and the release of free neutral oligosaccharide were parallel, suggesting that the same enzyme was responsible for both processes. Structural analyses demonstrated that the same Man5GlcNAc2 structure was transferred to protein and released as free oligosaccharide. Neutral oligosaccharides were found in both the cytosol and the pellet; however, oligosaccharides with one GlcNAc residue at the reducing end (OS-Gn1) were found exclusively in the supernate. The major neutral oligosaccharide produced after 2 h of metabolic labelling was Man5GlcNAc and it was found in the cytosol.

First evidence of human meconium glycoasparagines

During a systematic study of carbohydrate material present in human meconium, in addition to the previously described mucins, glycolipids and free oligosaccharides, we have now characterized a significant quantity of free glycoasparagines. These glycoasparagines have been isolated from human meconium by a combination of ion-exchange, concanavalin A (ConA)-affinity and high-performance liquid (HPLC) chromatographies. Their structures have been established by 400 MHz 1H-NMR spectroscopy. These compounds are related to N-acetyllactosaminic type structures and are based on the common core: [formula: see text] These glycoasparagines are probably derived from both protease and partial exoglycosidase hydrolysis of fetal gastrointestinal N-glycosyl proteins. Their structures are discussed in the context of the known catabolic pathways of N-glycans.

Soluble forms of alpha-D-mannosidases from rat liver. Separation and characterization of two enzymic forms with different substrate specificities

We have previously reported the substrate specificity of the rat liver cytosolic alpha-D-mannosidase [Haeuw, J. F., Strecker, G., Wieruszeski, J. M., Montreuil, J. & Michalski, J.-C. (1991) Eur. J. Biochem. 202, 1257-1268]. Here, we report the characterization and the purification of this alpha-D-mannosidase and the presence of two soluble forms of alpha-D-mannosidases from rat liver. The cytosolic alpha-D-mannosidase was purified nearly 660-fold with 2.66% recovery to a state approaching homogeneity using: (a) (NH4)2SO4 precipitation; (b) concanavalin-A-Sepharose chromatography; (c) affinity chromatography on a cobalt-chelating Sepharose column; (d) ion-exchange (DEAE-trisacryl M) column chromatography; (e) molecular-size chromatography (Sephacryl S 200). The enzyme was eluted from the final column at an apparent molecular mass of 113 kDa. SDS/PAGE analysis yielded a major protein band at 108 kDa. Moreover, the purification allowed to distinguish two mannosidase activities with different kinetic properties. The first cytosolic activity retained on the cobalt-chelating column was optimally active at neutral pH, was activated by Co2+, was strongly inhibited by swainsonine (Ki = 3.7 microM) but not by deoxymannojirimycin and was active with p-nitrophenyl alpha-D-mannoside (Km = 0.072 mM). Man9GlcNAc was hydrolysed by the purified enzyme down to a Man5GlcNAc structure, i.e. Man(alpha 1-2)Man(alpha 1-2)Man(alpha 1-3)[Man(alpha 1-6)]Man(beta 1-4) GlcNA c, which represents the Man5 oligosaccharide chain of the dolichol pathway formed in the cytosolic compartment during the biosynthesis of N-glycosylprotein glycans. The second activity not retained on the cobalt-chelating column was optimally active at neutral pH, was inhibited by swainsonine (Ki = 28.4 microM) but not by deoxymannojirimycin and was active with p-nitrophenyl alpha-D-mannoside (Km = 0.633 mM). Man9GlcNAc was broken by this enzymic activity down to Man8GlcNAc and Man7GlcNAc structures. Similitaries with endoplasmic reticulum alpha-D-mannosidase exist and this enzyme could be the cytosolic form of the endoplasmic reticulum alpha-D-mannosidase.

Expression of beta 1-6-branched N-linked oligosaccharides is associated with activation in human T4 and T8 cell populations

Activation of human T lymphocytes by phorbol 12-myristate 13-acetate and leukoagglutinin from Phaseolus vulgaris (L-PHA) results in important changes in N-glycosylation. The most important event is the increase, in both T4 and T8 cells (especially the latter), of L-PHA+ structures characterized by beta 1-6-branching of complex-type oligosaccharides. Moreover, the existence of a CD4-mediated increase of these beta 1-6-branched structures on positively selected T4 cells, as compared with the negatively selected ones, suggests that the presence of these structures, not detectable on T8 resting cells, could be related to stimulation events triggered by both selection methods. This beta 1-6-branching on N-glycans, strongly associated with a metastatic phenotype in human and rodent tumors, is exhibited by numerous glycoproteins on stimulated cells, as shown by blot analysis.

The core-specific lysosomal alpha(1-6)-mannosidase activity depends on aspartamidohydrolase activity

The substrate specificity of the core-specific rat liver lysosomal alpha(1-6)-mannosidase was investigated using mannosylated oligosaccharides and glycoasparagines. Hydrolysis of Man(alpha 1-6) linkage hydrolysis was demonstrated to follow the action of endoglycosidases, namely aspartyl-N-acetyl-beta-D-glucosaminidase and endo-N-acetyl-beta-D-glucosaminidase. The results are discussed with respect to the nature of the carbohydrate materials stored in the tissues and excreted in the urine from patients suffering from aspartylglucosaminuria and fucosidosis.

Primary structure of human milk octa-, dodeca- and tridecasaccharides determined by a combination of 1H-NMR spectroscopy and fast-atom-bombardment mass spectrometry. Evidence for a new core structure, the para-lacto-N-octaose

Two octasaccharides, two dodecasaccharides and a tridecasaccharide have been isolated from human milk by a combination of paper chromatography, high-performance liquid chromatography and high-performance anion-exchange chromatography. Their structural analysis investigated by 400-MHz 1H- and 13C-NMR spectroscopy and by mass spectrometry led to the following structures. [formula: see text] The two octasaccharides have been previously characterized in human milk; the complete assignment of the 1H and 13C spectra is reported here. One of the dodecasaccharides is a tetrafucosyl derivative with a new core: typeI-(beta 1-3)-typeII-(beta 1-3)-typeII-(beta 1-3)-Gal((beta 1-4)Glc, where typeI = Gal(beta 1-3)GlcNAc and typeII = Gal(beta 1-4)GlcNAc. These oligosaccharides display simultaneously Lewis(b) and Lewis(x) determinants or Lewis(a), Lewis(b) and Lewis(x) determinants.

Complete 1H- and 13C-resonance assignments for D-mannooligosaccharides of the beta-D-(1-->2)-linked series released from the phosphopeptidomannan of Candida albicans VW.32 (serotype A)

D-Mannooligosaccharides (dp 1 to > 17) were released by mild acid hydrolysis from the phosphopeptidomannan of a Candida albicans strain of A serotype (VW.32). Among these, mannooligosaccharides ranging from bi- to hepta-ose, which were obtained in appreciable amounts, were structurally investigated and found to belong to the beta-D-(1-->2)-linked series. The occurrence of such compounds has already been reported in other Candida albicans strains. The complete 1H- and 13C-resonance assignments for manno-tri- to manno-hepta-ose are reported and general rules applicable for the 1NMR spectrum analysis of linear mannooligosaccharide of the general structure, beta-D-Man p-(1-->2)-[beta-D-Man p-(1-->2)]n-beta-D-Man p are proposed.

1H-and 13C-n.m.r. spectroscopy of 2-oxo-3-deoxy-D-glycero-D- galactononulosonic acid-containing oligosaccharide-alditols bearing Lewis X, Lewis Y and A-Lewis Y determinants isolated from the jelly coat of Pleurodeles waltl eggs

Three acidic oligosaccharide-alditols carrying Lewis X, Lewis Y and A-Lewis Y determinants were isolated from the jelly coat of Pleurodeles waltl eggs. These compounds possess the following structures. Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3[2-oxo-3-deoxy-D- glycero-D-galactononulosonic acid (KDN)alpha 2-6] GalNAc-ol; Fuc alpha 1-2Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(KDN alpha 2-6) GalNAc-ol and Fuc alpha 1-2(GalNAc alpha 1-3)Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3(KDN alpha 2-6)GalNAc-ol. The complete 1H-n.m.r.-spectrum assignment for the three compounds and the 13C-n.m.r. analysis of the A-Lewis Y determinant-containing heptasaccharide are reported.

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

Six major neutral and acidic oligosaccharide-alditols were prepared from the jelly coat of Mexican axolotl eggs. These compounds were demonstrated to contain 3-deoxy-D-glycero-D-galacto-nonulosonic acid (dNloA) and L-fucose (Fuc). The structures of the six major oligosaccharides were established as follows: [sequence: see text]

Evaluation of an enzyme immunoassay using neoglycolipids constructed from Candida albicans oligomannosides to define the specificity of anti-mannan antibodies

In order to study the respective roles of oligomannoside sequences in the antigenicity of Candida albicans phosphopeptidomannan, a method was developed for constructing neoglycolipids from oligomannosides released by depolymerisation of this molecule. Oligomannosides released by acetolysis were converted to neoglycolipids by coupling them to 4-hexadecylaniline in an equimolar reaction checked by thin layer chromatography. When coated onto microEIA plates, the neoglycolipids exhibited strong reactions which were dose dependent and were saturable with concanavalin A. Reactivity of neoglycolipids with immunoglobulins were then tested with a panel of monoclonal and polyclonal antibodies reacting with epitopes present in the original phosphopeptidomannan. One of two IgM monoclonal antibodies and two of five monospecific rabbit polyclonal IgG reacted strongly with neoglycolipids therefore providing evidence of the presence of structures mimicking epitopes within the pool of neoglycolipids. When 38 sera from 18 hospital inpatients with various levels of antibodies to Candida albicans were tested, a correlation was observed between the EIA to detect neoglycolipids and the EIA to detect phosphopeptidomannan. Successive sera from all patients showing seroconversion in the immunofluorescence assay had increased EIA signals for neoglycolipids.

Characterization of Le(x), Le(y) and A Le(y) antigen determinants in KDN-containing O-linked glycan chains from Pleurodeles waltlii jelly coat eggs

Novel acidic oligosaccharides were isolated in large amounts by reductive alkaline treatment of the jelly coat of Pleurodeles waltlii (Michah) eggs. The oligosaccharides were found to contain the newly described KDN as acidic monosaccharide and possess either the Le(x), Le(y) and A Le(y) antigenic determinants. Occurrence of Le(x) and Le(y) determinants previously recognized as tumor-associated antigen (TAA) demonstrates that mucins of lower animals may represent a rich and easily available source for preparing TAA. Moreover, it reinforces the hypothesis according to which TAA are evolution markers.

Comparative study of asparagine-linked glycans of plasma T-kininogen in normal rats and during acute inflammation

Rat T-kininogen has been separated into two molecular variants by affinity chromatography on concanavalin A (ConA): a ConA-reactive (ConA+) and a ConA-non-reactive (ConA-) fraction, from which carbohydrate chains were quantitatively released by hydrazinolysis. On the basis of high-resolution 400 MHz 1H-n.m.r. spectroscopy of the re-N-acetylated hydrazinolysates, the carbohydrate structures of the two ConA molecular variants of rat T-kininogen were established. The ConA-non-reactive species contains a single type of carbohydrate chain with the following structure: [formula: see text] The ConA-reactive fraction contains the same structure and the following additional one: [formula: see text] The relative abundance of the two molecular forms is profoundly affected during inflammation (ratio ConA+/ConA-: 44% in normal and 95% in inflamed T-kininogen), but no structural modification of the carbohydrate chains was observed.

Primary structure of four human milk octa-, nona-, and undeca-saccharides established by 1H- and 13C-nuclear magnetic resonance spectroscopy

The structures of two octasaccharides, one nonasaccharide, and one undecasaccharide, isolated from human milk, have been investigated by 1H- and 13C-nuclear magnetic resonance spectroscopy. The structures of these oligosaccharides are: beta-D-Galp-(1----4)-[alpha-L-Fucp- (1----3)]-beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-[alpha-L-Fucp+ ++- (1----3)]-beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-D-Glc; beta-D-GALp-(1----3)-[alpha-L-Fucp-(1----4)]-beta-D-GlcpNAc-(1---- 3)-beta-D - Galp-(1----4)-[alpha-L-Fucp-(1----3)]-beta-D-GlcpNAc-(1----3)-beta -D-Galp- (1----4)-D-Glc; beta-D-Galp-(1----4)-[alpha-L-Fucp-(1----3)]-beta-D-GlcpNAc-(1---- 6)-(alpha - L-Fucp-(1----2)-beta-D-Gal-(1----3)-[alpha-L-Fucp-(1----4)]- beta-D-GlcpNAc- (1----3))-beta-D-Galp-(1----4)-D-Glc; and alpha-L-Fucp-(1----2)-beta-D-Galp-(1----3)-beta-D-GlcpNAc-(1----3) -beta-D- Galp-(1----4)-[alpha-L-Fucp-(1----3)]-beta-D-GlcpNAc-(1----6)-[alp ha-L- Fucp-(1----2)-beta-D-Galp-(1----3)-beta-D-GlcpNAc-(1----3)]-beta-D -Galp- (1----4)-D-Glc. The two octasaccharides have been previously isolated from human milk as a mixture, and in a pure form from new-born feces, but the n.m.r. data were not provided. These two octasaccharides display the di-Lewis X and the composite Lewis A-Lewis X antigenic determinant, previously described as neo-antigens of adenocarcinoma cell lines.

1H and 13C-NMR assignments for sialylated oligosaccharide-alditols related to mucins. Study of thirteen components from hen ovomucin and swallow nest mucin

Four hundred MHz 1H-NMR and 100 MHz 13C-NMR spectra of thirteen sialylated oligosaccharide-alditols isolated from hen ovomucin and swallow nests (Collocalia mucin) were studied. The resonance assignments were determined by combining multiple-relayed coherence-transfer chemical-shift-correlated spectroscopy (multiple-Relay-Cosy) and 1H/13C chemical-shift-correlated 2-D experiments.

1H-NMR spectroscopy of manno-oligosaccharides of the beta-1,2-linked series released from the phosphopeptidomannan of Candida albicans VW-32 (serotype A)

Manno-oligosaccharides (DP 2 to greater than 15) were released by mild acid hydrolysis from the phosphopeptidomannan of a Candida albicans strain of A serotype (VW-32). Manno-oligosaccharides ranging from biose to heptaose were obtained in appreciable amount. Structural investigation of these oligosaccharides showed them to be of the beta-1,2-linked series. The occurrence of such compounds has already been reported in other strains of Candida albicans. We here report the assignment of the structural reporter groups of each of them, and general rules applicable for the 1H-NMR spectrum analysis of linear manno-oligosaccharide of general structure: Man(beta 1-2) [Man(beta 1-2)]nMan

Substrate specificity of rat liver cytosolic alpha-D-mannosidase. Novel degradative pathway for oligomannosidic type glycans

The substrate specificity of rat liver cytosolic neutral alpha-D-mannosidase was investigated by in vitro incubation with a crude cytosolic fraction of oligomannosyl oligosaccharides Man9GlcNAc, Man7GlcNAc, Man5GlcNAc I and II isomers and Man4GlcNAc having the following structures: Man9GlcNAc, Man(alpha 1-2)Man(alpha 1-3)[Man(alpha 1-2)Man(alpha 1-6)]Man(alpha 1-6) [Man(alpha 1-2)Man(alpha 1-3)]Man(beta 1-4)GlcNAc; Man5GlcNAc I, Man(alpha 1-3)[Man(alpha 1-6)]-Man(alpha 1-6)Man(alpha 1-3)] Man(beta 1-4)GlcNAc; Man5GlcNAc II, Man(alpha 1-2)Man(alpha 1-2)Man(alpha 1-3) [Man(alpha 1-6)]Man(beta 1-4)GlcNAc; Man4GlcNAc, Man(alpha 1-2)Man(alpha 1-2)Man(alpha 1-3)Man(beta 1-4)GlcNAc. The different oligosaccharide isomers resulting from alpha-D-mannosidase hydrolysis were analyzed by 1H-NMR spectroscopy after HPLC separation. The cytosolic alpha-D-mannosidase activity is able to hydrolyse all types of alpha-mannosidic linkages found in the glycans of the oligomannosidic type, i.e. alpha-1,2, alpha-1,3 and alpha-1,6. Nevertheless the enzyme is highly active on branched Man9GlcNAc or Man5GlcNAc I oligosaccharides and rather inactive towards the linear Man4GlcNAc oligosaccharide. Structural analysis of the reaction products of the soluble alpha-D-mannosidase acting on Man5-GlcNAc I and Man9GlcNAc gives Man3GlcNAc, Man(alpha 1-6)[Man(alpha 1-3)]Man(beta 1-4)GlcNAc, and Man5GlcNAc II oligosaccharides, respectively. This Man5GlcNAc II, Man(alpha 1-2)Man(alpha 1-3)[Man(alpha 1-6)]Man(beta 1-4)GlcNAc, represents the 'construction' Man5 oligosaccharide chain of the dolichol pathway formed in the cytosolic compartment during the biosynthesis of N-glycosylprotein glycans. The cytosolic alpha-D-mannosidase is activated by Co2+, insensitive to 1-deoxymannojirimycin but strongly inhibited by swainsonine in the presence of Co2+ ions. The enzyme shows a highly specific action different from that previously described for the lysosomal alpha-D-mannosidases [Michalski, J.C., Haeuw, J.F., Wieruszeski, J.M., Montreuil, J. and Strecker, G. (1990) Eur. J. Biochem. 189, 369-379]. A possible complementarity between cytosolic and lysosomal alpha-D-mannosidase activities in the catabolism of N-glycosylprotein is proposed.

Cytosolic glycosidases: do they exist?

The substrate specificity of the alpha-D-mannosidases of rat liver lysosome and cytosol was examined using oligosaccharides of the oligomannosidic type. The hydrolysis products were characterized by 400 MHz 1H-NMR spectroscopy. Both catabolic pathways occur in ordered ways, but are quite different. In fact, the lysosomal pathway is a two-step process: the first step involves a Zn(2+)-independent alpha-1,2-mannosidase activity, whereas the second involves a Zn(2+)-dependent alpha-1,3- and alpha-1,6-mannosidase activity. The final product is the disaccharide Man(beta 1-4)GlcNAc. In contrast, the cytosolic pathway leads, in one step, to a unique hexasaccharide (Man5GlcNAc) which has the same structure as the polyprenolic intermediate synthesized on the cytosolic face of the rough endoplasmic reticulum during the biosynthesis of N-glycosylprotein glycans: Man(alpha 1-2)-Man(alpha 1-2)Man(alpha 1-3)[Man(alpha 1-6)] Man(beta 1-4)GlcNAc(beta 1-4)-GlcNAc(alpha)P-P-Dol. In addition, the enzymatic parameters of lysosome, endoplasmic reticulum and cytosol alpha-D-mannosidases are quite different. These results lead to the conclusion that the cytosol contains specific alpha-D-mannosidases which do not originate from lysosomes nor from endoplasmic reticulum. The discovery of cytosolic endo-N-acetyl-beta-D-glucosaminidase active on 'immature complex glycans' (glycopeptides of the oligomannosidic type and of the desialylated N-acetyllactosaminic type) as well as on the glycosyl-dolichol pyrophosphate intermediates allows us to hypothesize that these enzymes belong to a control system of N-glycosylprotein biosynthesis, their role being to destroy unfinished glycans. The fate of the formed oligosaccharide structures is discussed: are they destroyed by cytosolic or lysosomal exoglycosidases, or do they carry an 'oligosaccharin-like activity'?

Characterization and 400-MHz 1H-NMR analysis of urinary fucosyl glycoasparagines in fucosidosis

Fucosyl glycoasparagines accumulating in the urine of a patient with fucosidosis were isolated using reverse-phase HPLC. Structural analysis of 25 glycoasparagines was carried out by combination of methylation and 400-MHz 1H-NMR spectroscopy analyses. The compounds represent different steps in the incomplete catabolism of N-glycosidically linked glycans, as the result of an alpha-L-fucosidase deficiency. All of the glycoasparagines possess a fucose residue alpha-1,6-linked to the GlcNAc 1 residue attached to asparagine. Fucose residues on the peripheral branches were linked either alpha-1,3 to GlcNAc residues (X determinant) or alpha-1,2 to galactose residues (H determinant). The present study allows precise assignments of the NMR parameters for most of the fucosyl linkages occurring in N-glycosidically linked glycans of the N-acetyllactosamine type.

Primary structure of a trisialylated oligosaccharide from human milk

A novel oligosaccharide has been isolated from human milk and identified as a trisialylated derivative of lacto-N-hexaose. This compound was purified by combining ion-exchange chromatography, preparative paper chromatography and high performance liquid chromatography. Structural analyses by methylation, fast atom bombardment-mass spectrometry and proton nuclear magnetic resonance spectroscopy are consistent with the following structure: formula: see text.

Characterization of a novel type of chain-terminator Gal beta 1-6Gal beta 1-4)GlcNAc in an oligosaccharide related to N-glycosylated protein glycans isolated from GM1 the urine of patients with gangliosidosis

Two new oligosaccharides were isolated from the urine of a patient with GM1 gangliosidosis. Final purification of the oligosaccharides was accomplished by capillary supercritical fluid chromatography. Structural analysis was by chemical analysis, chemical-ionization mass spectrometry and 400-MHz 1H-NMR spectroscopy, leading to two primary structures. The first is derived from a classical triantennary N-acetyllactosamine-type glycan: Gal beta 1-4GlcNAc beta 1-4(Gal beta 1-4GlcNAc beta 1-2)Man alpha 1-3Man beta 1-4GlcNAc. The second is unusual with a terminal disaccharide Gal beta 1-6Gal, which had not yet been described for glycans of the N-acetyllactosamine type: Gal beta 1-6Gal beta 1-4GlcNAc beta 1-2Man alpha 1-6Man beta 1-4GlcNAc.

Structure determination of the glycans of human-serum alpha 1-antichymotrypsin using 1H-NMR spectroscopy and deglycosylation by N-glycanase

alpha 1-Antichymotrypsin purified from normal human serum was separated by affinity chromatography into th ree microheterogeneous forms on a concanavalin-A-Sepharose column: a pass-through (peak 1), a retarded (peak 2) and a bound form (peaks 3 + 4). For each form the asparagine-linked carbohydrate chains were liberated as oligosaccharides by hydrazinolysis, submitted to reduction with NaBH4 after re-N-acetylation and further separated by affinity chromatography on a concanavalin-A-Sepharose column. The complete primary structure of the glycans was determined by high-resolution 1H-NMR spectroscopy. The results indicated the presence of disialyl diantennary and of trisialyl triantennary type glycanic structures, the latter being accompanied by traces of disialylated triantennary oligosaccharide. The N-glycanase was used for the deglycosylation of the unfractionated alpha 1-antichymotrypsin; the successive removal of the N-linked complex-type oligosaccharide side chains of alpha 1-antichymotrypsin was studied in the presence of detergents. From these experiments it is concluded that alpha 1-antichymotrypsin carries four oligosaccharide side chains. Moreover our results show that the peak 1 contains four triantennary glycans, the peak 2 three triantennary and one diantennary glycans while the bound peaks 3 + 4 possess, on average, about one triantennary and three diantennary glycans per molecule. Since we showed that the peak 4 contains mostly diantennary glycans, it can be deduced that in peak 3 there are molecules carrying two triantennary and two diantennary glycans and others carrying one triantennary and three diantennary glycans.