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.

Excreted/secreted glycoproteins of G. intestinalis play an essential role in the antibody response

In the present work, glycoproteins in the excretory/secretory products of G. intestinalis were identified and the reactivity in serum of immunized mice with these molecules was evaluated by western blotting before and after chemical treatment or enzymatic deglycosylation. Glycoproteins of 58 and 63 kDa were revealed in E/S products after periodic acid-Schiff (PAS) stain. Studies of carbohydrate specificity using digoxigenin-labeled lectins, revealed the presence of O-glycans and N-glycans. Chemical treatment of excretory/secretory products with sodium meta-periodate or enzymatic deglycosylation with N-glycosidase F reduced the reactivity in serum for proteins of 36, 58 and 63 kDa, respectively. These results show the presence of glycoproteins in E/S products of G. intestinalis and suggest that the antibody response is directed against glycoepitopes. The expression of carbohydrate moieties in the E/S-G. intestinalis may play an essential role in the antibody response and may be a target for serodiagnosis or immune intervention in human giardiasis.

Galactomannoproteins of Aspergillus fumigatus

Galactofuranose-containing molecules have been repeatedly shown to be important antigens among human fungal pathogens, including Aspergillus fumigatus. Immunogenic galactofuran determinants have been poorly characterized chemically, however. We reported here the characterization of two glycoproteins of A. fumigatus with an N-glycan containing galactofuranose. These proteins are a phospholipase C and a phytase. Chemical characterization of the N-glycan indicates that it is a mixture of Hex(5-13)HexNAc(2) oligosaccharides, the major molecular species corresponding to Hex(6-8)HexNAc(2). The N-glycan contained one galactofuranose unit that was in a terminal nonreducing position attached to the 2 position of Man. This single terminal nonreducing galactofuranose is essential for the immunoreactivity of the N-glycans assessed either with a monoclonal antibody that recognizes a tetra-beta-1,5-galactofuran chain of galactomannan or with Aspergillus-infected patient sera.

Two alpha(1-3) glucan synthases with different functions in Aspergillus fumigatus

Alpha(1-3) glucan is a main component of the Aspergillus fumigatus cell wall. In spite of its importance, synthesis of this amorphous polymer has not been investigated to date. Two genes in A. fumigatus, AGS1 and AGS2, are highly homologous to the AGS genes of Schizosaccharomyces pombe, which encode putative alpha(1-3) glucan synthases. The predicted Ags proteins of A. fumigatus have an estimated molecular mass of 270 kDa. AGS1 and AGS2 were disrupted in A. fumigatus. Both Deltaags mutants have similar altered hyphal morphologies and reduced conidiation levels. Only Deltaags1 presented a reduction in the alpha(1-3) glucan content of the cell wall. These results showed that Ags1p and Ags2p were functionally different. The cellular localization of the two proteins was in agreement with their different functions: Ags1p was localized at the periphery of the cell in connection with the cell wall, whereas Ags2p was intracellularly located. An original experimental model of invasive aspergillosis based on mixed infection and quantitative PCR was developed to analyze the virulence of A. fumigatus mutant and wild-type strains. Using this model, it was shown that the cell wall and morphogenesis defects of Deltaags1 and Deltaags2 were not associated with a reduction in virulence in either mutant. This result showed that a 50% reduction in the content of the cell wall alpha(1-3) glucan does not play a significant role in A. fumigatus pathogenicity.

FAB-MS characterization of sialyl Lewis x determinants on polylactosamine chains of human airway mucins secreted by patients suffering from cystic fibrosis or chronic bronchitis

Although a large body of structural data exists for bronchial mucins from cystic fibrosis (CF) and chronic bronchitis (CB) patients, little is known about terminal structures carried on poly-N-acetyllactosamine antennae. Such structures are of interest because they are potential ligands for bacterial adhesins and other lectins. In this study, we have used fast atom bombardment mass spectrometry (FAB-MS) to examine terminal sequences released by endo-beta-galactosidase from O-glycans obtained by reductive elimination of bronchial mucins purified from the sputum of 8 CF and 8 CB patients. Our data show that, although the polylactosamine antennae of CF and CB mucins have several terminal sequences in common, they differ significantly in their sialyl Lewis(x) (NeuAcalpha2-3Galbeta1-4[Fucalpha1-3]GlcNAcbeta1-) content. Thus all examined mucins from CF patients carry sialyl Lewis(x) on their polylactosamine antennae, whereas this type of epitope is present on only three out of the eight CB mucins examined, notably in the airways of one CB patient which were heavily infected by Pseudomonas aeruginosa as are the airways of all the CF patients. This suggests that, in airway mucins, the expression of sialyl Lewis(x) on polylactosamine antennae is probably more related to inflammation and infection than to a direct effect of the CF defect.

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

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

Phosphorylcholine-containing N-glycans of Trichinella spiralis: identification of multiantennary lacdiNAc structures

Although the presence of phosphorylcholine (PC) in Trichinella spiralis is well established, the precise structure of the PC-bearing molecules is not known. In this paper, we report structural studies of N-glycans released from T.spiralis affinity-purified antigens by peptide N-glycosidase F. Three classes of N-glycan structures were observed: high mannose type structures; those which had been fully trimmed to the trimannosyl core and were sub-stoichiometrically fucosylated; and those with a trimannosyl core, with and without core fucosylation, carrying between one and eight N-acetylhexosamine residues. Of the three classes of glycans, only the last was found to be substituted with detectable levels of phosphorylcholine.

Characterization of the N-linked oligosaccharides of megalin (gp330) from rat kidney

Megalin (gp 330) is a large cell surface receptor expressed on the apical surfaces of epithelial tissues, that mediates the binding and internalization of a number of structurally and functionally distinct ligands. In this paper we report the first detailed structural characterization of megalin-derived oligosaccharides. Using strategies based on mass spectrometric analysis, we have defined the structures of the N-glycans of megalin. The results reveal that megalin glycoprotein is heterogeneously glycosylated. The major N-glycans identified belong to the following two classes: high mannose structures and complex type structures, with complex structures being more abundant than high mannose structures. The major nonreducing epitopes in the complex-type glycans are: GlcNAc, Galbeta1-4GlcNAc (LacNAc), NeuAcalpha2-6Galbeta1-4GlcNAc (sialylated LacNAc), GalNAcbeta1-4[NeuAcalpha2-3]Galbeta1-4GlcNAc (Sd(a)) and Galalpha1-3Galbeta1-4GlcNAc. Most complex structures are characterized by the presence of (alpha1,6)-core fucosylation and the presence of a bisecting GlcNAc residue.

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 three sulfated oligosaccharides isolated from human milk

The structures of two sulfated octasaccharides and one sulfated nonasaccharide isolated from human milk have been investigated. Using 13C and 1H NMR spectroscopy and ESMS, the following structures 1-3 were established: [formula: see text].

Structural analysis of O-linked oligosaccharide-alditols by electrospray-tandem mass spectrometry after mild periodate oxidation and derivatization with 2-aminopyridine

O-linked oligosaccharide-alditols were analyzed by a combination of high-performance liquid chromatography (HPLC) and electrospray-tandem mass spectrometry (ESI-MS/MS). First, oligosaccharide-alditols were treated with sodium meta-periodate under conditions where core N-acetylgalactosaminitol is specifically degraded. The resulting fragments were labeled with 2-aminopyridine and purified on a reversed-phase column. Pyridylamino oligosaccharides yielded protonated molecular ions in positive-ion ES-MS and gave Y-series sequence ions, arising from glycosidic cleavages, by ESI-tandem mass spectrometry. Information on sugar sequence and branching of oligosaccharides linked at C6 and C3 to the N-acetylgalactosaminitol can be obtained. A systematic study of various oligosaccharide-alditols demonstrated that this approach constitutes a powerful tool for the structural characterization of O-glycans available only in limited quantities.

Structural analysis of oligosaccharide-alditols released by reductive beta-elimination from the jelly coats of the anuran Bufo arenarum

Amphibian egg jelly coats are formed by components secreted along the oviduct. These secretion products overlay the oocytes as they are transported toward the cloaca. Mucin type glycoproteins are the major constituents of the egg jelly coats. In this study, the O-linked carbohydrate chains of the jelly coat surrounding the eggs of Bufo arenarum were released by alkaline borohydride treatment. Fractionation of the mixture of O-linked oligosaccharide-alditols was achieved by a combination of chromatographic techniques comprising gel-permeation chromatography, ion-exchange chromatography and high-performance liquid chromatography using an amino-bonded silica column, afforded 11 fractions. The primary structures of these O-glycans were determined by one-dimensional and two-dimensional 1H-NMR spectroscopy in conjunction with matrix-assisted laser-desorption-ionization--time-of-flight mass spectrometry. 11 oligosaccharide structures, possessing a core consisting of Galbeta1-->3GalNAc-ol with or without branching through a GlcNAc residue linked beta1-->6 to the GalNAc residue (core type 2 or core type 1, respectively) are described. These oligosaccharide-alditols with these types of cores have been identified previously in mammalian mucins or in oviducal amphibian jellies. These glycans contain blood group determinants such as H, A or Cad antigens.

Isolation of the O-glycosidically linked oligosaccharides obtained by alkaline borohydride degradation from oviducal mucins of the toad Bufo bufo

A combination of normal-phase high-performance liquid chromatography (HPLC) on amino-bonded silica and reversed-phase HPLC on octadecylsilica has been used to separate the reduced oligosaccharides produced by alkaline borohydride degradation of oviducal mucins obtained from the jelly coat of Bufo bufo. The former technique provides suitable separation on the basis of molecular size, while the latter method offers selectivity for stereoisomers. Thirty-four compounds, ranging in size from a trisaccharide to a dodecaoligosaccharide, have been isolated preparatively using a Supelcosyl LC-NH2 normal-phase column eluted with aqueous acetonitrile and a Zorbax ODS reversed-phase column eluted with water.

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

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

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.

Structural analysis of hexa to dodecaoligosaccharide-alditols released by reductive beta-elimination from oviducal mucins of Bufo bufo

Hexa to dodecasaccharide-alditols of the jelly coat surrounding the eggs of the toad Bufo bufo were studied by methylation analysis, MALDI-TOF mass spectrometry, and H-NMR spectroscopy. These highly species-specific carbohydrate chains exhibit new structural features, such as the elongation of the blood group A determinant with an external alpha-1,3-linked galactose unit, or ramification belonging from a fucosylated galactose. The most representative oligosaccharide-alditol of the series was defined as following: [structure in text]. Since the jellies surrounding amphibian eggs are involved in egg-sperm interactions, these structural investigations can provide biochemical support for exploring the fertilization process.

Structural analysis of oligosaccharide-alditols released by reductive beta-elimination from oviducal mucins of Bufo bufo: characterization of the carbohydrate sequence Gal(alpha1-3)GalNAc(alpha1-3)[Fuc(alpha1-2)]Gal

Several tri- to hexasaccharide-alditols of the jelly coat surrounding the eggs of Bufo bufo were studied by methylation analysis, MALDI-TOF mass spectrometry, and 1H-NMR spectroscopy. As observed for six other amphibian species, these carbohydrate chains are highly species-specific. The main characteristics of the species Bufo bufo consists in the presence of the new carbohydrate sequence Gal(alpha1-3)GalNAc(alpha1-3)[Fuc(alpha1-2)]Gal, in which a blood group A determinant is substituted with an external alpha1-3 linked galactose unit. Since the role of carbohydrates appears more and more apparent during the fertilization processes, the species-specificity of these carbohydrate moieties should be relevant to the species-specific gamete recognition which characterizes most amphibians.

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.

Chondroitin sulphate covalently cross-links the three polypeptide chains of inter-alpha-trypsin inhibitor

Inter-alpha-trypsin inhibitor (ITI) is a tight complex of three different proteins: bikunin and two heavy chains H1 and H2. In order to demonstrate that the three chains are covalently linked by a chondroitin sulphate chain as previously proposed [Enghild, J. J., Salvesen, G., Hefta, S. A., Thogersen, I. B., Rutherford, S. and Pizzo, S. V. (1991) J. Biol. Chem. 266, 747-751], ITI was extensively digested with thermolysin and the glycosaminoglycan-containing fragment was isolated from the digest by ion-exchange chromatography. Its peptide structural determination and mass spectrometry analysis both provide evidence that the different peptide chains constituting ITI are associated by the new cross-link described as the protein-glycosaminoglycan-protein cross-link.