Ceramide Glycanase Research Articles

Synthesis of bi-fluorescence-labeled lactoside: A substrate for continual assay of ceramide glycanase

A bi-fluorescence labeled derivative suitable for analysis of ceramide glycanase activity was constructed from 4-pentenyl lactoside. Selective modification of the galactosyl residue was attained by formation of 4′,6′-naphthylmethylidene derivative, which was followed by regioselective reductive ring opening. The aglycon was extended by Michael addition of 2-aminoethanetiol, and dansylated at the terminal amino group. Excitation of the naphthyl group results in emission from the dansyl group, while the emission from the naphthyl group is quenched by the dansyl group. Upon digestion with ceramide glycanase, the energy transfer is severed and a decrease in the dansyl emission concommitant with an increase in the naphthyl emission was observed. This substrate was successfully used to analyze ceramide glycanase activity.

Polysialic acid engineering: synthesis of polysialylated neoglycosphingolipids by using the polysialyltransferase from neuroinvasive Escherichia coli K1.

The CMP-sialic acid:poly alpha 2,8sialosyl sialyltransferase (polyST) in neurotropic Escherichia coli K1 inner membranes catalyzes synthesis of the alpha 2,8-linked polysialic acid capsule. The capsule is a neurovirulent determinant associated with neonatal meningitis in humans. A functionally similar polyST in human neuroblastomas polysialylates neural cell adhesion molecules. While bacteria do not synthesize glycosphingolipids (GSLs), we report here that the E. coli K1 polyST can selectively polysialylate several structurally related GSLs, when added as exogenous sialyl acceptors. A structural feature common to the preferred sialyl acceptors (GD3 > GT1a > GQ1b = GT1b > GD2 = GD1b = GD1a > GM1) was the disialyl glycotope, Sia alpha 2,8Sia, alpha 2,3-linked to galactose (Sia is sialic acid). A linear tetrasaccharide with a terminal Sia residue (e.g., GD3) was the minimum length oligosaccharide recognized by the polyST. Endo-N-acylneuraminidase was used to confirm the alpha 2,8-specific polysialylation of GSL. Ceramide glycanase was used to release the polysialyllactose chains from the ceramide moiety. Size analysis of these chains showed that 60-80 Sia residues were transferred to the disialyllactose moiety of GD3. The significance of these findings is two-fold. (i) The E. coli K1 polyST can be used as a synthetic reagent to enzymatically engineer the glycosyl moiety of GSL, thus creating oligo- or polysialylated GSLs. Such "designer" GSLs may have potentially important biological and pharmacological properties. (ii) The use of GSLs as exogenous sialyl acceptors increases the sensitivity of detecting polyST activity. The practical advantage of this finding is that polyST activity can be identified and studied in those eukaryotic cells that express low levels of this developmentally regulated enzyme and/or its acceptor.

Analysis of Glycosphingolipids by Fluorophore-Assisted Carbohydrate Electrophoresis Using Ceramide Glycanase from Mercenaria mercenaria

Polyacrylamide gel electrophoresis of fluorophore-labeled saccharides is a simple and sensitive separation method for glycan analysis. This method requires an aldehydic reducing carbon on the saccharide in order to react with the amine group of the fluorophore (8-aminonaphthalene-1,3,6-trisulfonic acid or 2-aminoacridone). We have used exoglycosidase-free ceramide glycanase from hard-shelled clam to expose the reducing terminal of the glycan in glycosphingolipid by cleaving the linkage between the glycan and the ceramide. The released glycan was used for fluorophore-assisted carbohydrate electrophoresis, in order to qualitatively determine its monosaccharide composition, chain length, and glycosidic linkages using linkage-specific glycosidases, including a β1-3,4 galactosidase from clam.

Assay for evaluation of rotavirus-cell interactions: identification of an enterocyte ganglioside fraction that mediates group A porcine rotavirus recognition.

A virus-host cell-binding assay was developed and used to investigate specific binding between group A porcine rotavirus and MA-104 cells or porcine enterocytes. A variety of glycoconjugates and cellular components were screened for their ability to block rotavirus binding to cells. During these experiments a crude ganglioside mixture was observed to specifically block rotavirus binding. On the basis of these results, enterocytes were harvested from susceptible piglets and a polar lipid fraction was isolated by solvent extraction and partitioning. Throughout subsequent purification of this fraction by Sephadex partition, ion-exchange, silicic acid, and thin-layer chromatography, blocking activity behaved as a monosialoganglioside (GMX) that displayed a thin-layer chromatographic mobility between those of GM2 and GM3. The blocking activity of GMX was inhibited by treatment with neuraminidase and ceramide glycanase but not by treatment with protease or heat (100 degrees C). Further purification of GMX by high-pressure liquid chromatography resulted in the resolution of two monosialogangliosides, GMX and a band which comigrated with GM1 on thin-layer chromatography. These data suggest that a cell surface monosialoganglioside or family of monosialogangliosides may function as an in vivo relevant receptor for group A porcine rotavirus and that sialic acid is a required epitope for virus-binding activity.

Cell surface ligands for rotavirus: Mouse intestinal glycolipids and synthetic carbohydrate analogs

Rotaviral binding to receptors on epithelial cells in the small intestine is thought to be a key event in the infection process and may be carbohydrate-mediated. Strain SA11 of rotavirus bound in vitro both to glycolipids isolated from mouse small intestine and to authentic glycolipids using thin layer chromatography overlay and microtiter well adsorption assays. Neutral mouse intestinal glycolipids which bound rotavirus were GA1 (Galβ1 → 3GaINAcβ1 → 4Galβ1 4GIcβ1 → 1-ceramide) and pentaosylceramides with terminal N-acetylgalactosamine, while acidic lipids which bound rotavirus included cholesterol 3-sulfate and two compounds termed bands 80 and 81. Digestion with ceramide glycanase suggested that bands 80 and 81 have lactosyl ceramide cores and an unidentified acidic moiety(s). No sialic-acid-containing glycolipids tested were active in viral binding. Band 81, which may have a ganglio core, bound rotavirus with greatest avidity, followed by GA1. Of authentic glycolipids assayed, only GA1 and GA2 (GaINAcβ1 → 4Galβ1 → 4GIcβ1 → 1-ceramide) displayed rotaviral binding. A phosphatidylethanolamide dipalmitoyl-containing neoglycolipid analog of GA2 bound rotavirus with avidity similar to native GA2. Substitution of β1 → 4-linked GIcNAc or β1 → 3-linked GaINAc for terminal GaINAc of GA2 neoglycolipid supported rotaviral binding, while other substitutions abrogated it. These findings suggest that a carbohydrate epitope similar to that of GA2 is sufficient for in vitro rotaviral binding, although binding may be enhanced by galactose and/or an acidic moiety in a secondary epitope.

Ceramide glycanase from the earthworm, Lumbricus terrestris.

Ceramide glycanase (CGase) is an enzyme that cleaves the linkage between the sugar chain and the ceramide. To make this enzyme readily available, we have developed a simple method for preparing it from the earthworm, Lumbricus terrestris. The method involves Bio-Gel A-0.5m, octyl-Sepharose and p-aminophenylthiogalactoside-agarose column chromatography. By gel filtration, the molecular mass of earthworm CGase was found to be 43.7 kDa. With ganglioside GM1 as substrate, the optimal pH of this enzyme was found to be between pH 3.5 and 4.0. Earthworm CGase hydrolyses glycolipids only in the presence of a detergent. Among various bile salts tested, sodium cholate was found to be the most effective in stimulating the hydrolysis of GM1 by this enzyme. Earthworm CGase released intact glycan chains from various glycosphingolipids in which the glycan chain is linked to the ceramide through a beta-glucosyl linkage. It also detached glycan chains from lactosyldialkylglycerol and alkyl-beta-lactosides.

Polyglycosylceramides with branched N-acetyllactosamine sequences are synthesized by the human pancreatic carcinoma cell line PANC-1.

We have metabolically labeled the human pancreatic tumor cell line PANC-1 with high specific activity tritiated sugar precursors to study the expression of glycosphingolipids by this cell type. We have used a combination of detergent solubilization, exhaustive protease digestion, ceramide glycanase digestion, and reverse-phase chromatography to isolate glycosphingolipid-derived oligosaccharides specifically labeled in their component sugars. A significant proportion of the oligosaccharides derived from polar glycosphingolipids were of high molecular mass (greater than 2000 Da). The results of compositional studies, lectin affinity chromatography, and methylation analysis suggested that this high molecular weight fraction consists of lactosaminoglycan type oligosaccharides derived from polyglycosylceramides. There are on average three beta 1-6 linked N-acetyllactosamine branches attached to the polylactosamine backbone in this type of glycosphingolipid-derived oligosaccharide. The majority of the oligosaccharides also contain 1-2 mol of sialic acid that are linked alpha 2-3 to penultimate galactose. The results indicate that PANC-1 cells, like human colorectal tumor cells, express highly extended neolacto type glycosphingolipids. However, the lactosaminoglycan sequences are highly branched, unlike those associated with colorectal tumor cells.

The human blood fluke Schistosoma mansoni synthesizes a novel type of glycosphingolipid.

Previous studies have shown that the glycoprotein oligosaccharides synthesized by adult Schistosoma mansoni, the organism responsible for human schistosomiasis, are unusual in that they contain terminal beta-GalNAc residues and lack sialic acid. These observations and other studies indicating that schistosome glycoproteins and glycolipids are antigenic in infected animals led us to investigate the structures of the glycosphingolipids synthesized by these organisms and to determine whether they are structurally related to those synthesized by their vertebrate hosts. For our studies, adult schistosomes were metabolically radiolabeled with either [3H]galactose or [3H]glucosamine, and the newly synthesized glycosphingolipids were isolated and characterized. The major glycosphingolipids synthesized by adult schistosomes were found to be galactosylceramide and glucosylceramide. The adult worms synthesized no lactosylceramide (Gal beta 1-4Glc-ceramide), a common constituent of vertebrate cells; however, another disaccharide-containing glycosphingolipid cleavable by ceramide glycanase was found. The results of compositional and methylation analyses and exoglycosidase treatments demonstrated that this ceramide-disaccharide has the structure GalNAc beta 1-4Glc-ceramide. We also found that extracts of adult schistosomes are unable to transfer Gal from UDP-Gal to glucosylceramide, whereas extracts of Chinese hamster ovary cells, as a control, are able to do so, confirming that schistosomes are unable to synthesize lactosylceramide. Low levels of higher molecular weight glycosphingolipids were also found to be synthesized by adult schistosomes, and although their levels were too small to allow definitive characterization, compositional analyses indicated that they also contained GalNAc. We have tentatively designated the new disaccharide structure GalNAc beta 1, 4Glc- the "schistocore", which may represent a new type of glycosphingolipid core series.

Synthesis of neoglycoconjugates using oligosaccharide transferring activity of ceramide glycanase

Ceramide glycanase (CGase) isolated from the leech Macrobdella decora was found to transfer the oligosaccharide en bloc from various glycosphingolipids to suitable acceptors. For example, CGase transferred the intact II3NeuAcGgOse4 from GM1 to 4-phenyl-1-butanol, 1,8-octanediol and various 1-alkanols having a chain length of six or more carbons. Among various 1-alkanols, 1-octanol was found to be the best acceptor. In an incubation mixture of 50 microliters containing 30 nmol of GM1, 50 micrograms of sodium cholate, 20 microliters of 1-octanol, and 0.1 unit of CGase, the ratio between hydrolysis and transglycosylation was approximately 3:1. Negative fast atom bombardment-mass spectral analysis of the enzymatically synthesized octyl-II3NeuAcGgOse4 showed a mass ion at m/z 1109.7 for the parent ion, consistent with its expected mass. NMR analysis of the enzymatically synthesized octyl-II3NeuAcGgOse4 showed that the Glc residue is linked to the octanol through a beta-linkage. Vicinal coupling constants of the ring protons of the sugar residues indicate that their pyranose ring geometries are not affected by the transferase activity. CGase also transferred the oligosaccharide from GM1 to CF3CO-NH(CH2)5CH2OH, (CH3)3CO-CO-NH(CH2)5CH2OH, (HOCH2)3C-NHCO-(CH2)4-COOMe, CH2 = CH-(CH2)7CH2OH and 1,2:3,4-di-O-isopropylidene-D-galactopyranose. The oligosaccharide transferring reaction carried out by CGase should become useful for the synthesis of neoglycoconjugates to study the biological functions expressed by glycan chains in glycosphingolipids.

Direct evidence that ganglioside is an integral component of the thyrotropin receptor.

Gangliosides were extracted from purified human and porcine thyrotropin (TSH) receptors (TSH-R) and were detected by probing with an 125I-labeled sialic acid-specific lectin, Limax flavus agglutinin. Gangliosides copurified with human and porcine TSH-R migrated between monosialoganglioside GM1 and disialoganglioside GD1a. Ceramide glycanase digestion of the purified human TSH-R-associated glycolipid confirmed its ganglioside nature. It was resistant to Vibrio cholerae sialidase, which digests all gangliosides except GM1, but was sensitive to Arthrobacter ureafaciens sialidase, which digests all gangliosides including GM1. These findings indicate that the human TSH-R contains ganglioside that belongs to the galactosyl(beta 1----3)-N-acetylgalactosaminyl (beta 1----4)-[N-acetylneuraminyl(alpha 2----3)]galactosyl(beta 1----4) glucosyl(beta 1----1)ceramide (GM1) family. Its intimate association with receptor protein implies a key role for ganglioside in the structure and function of the TSH-R.

Transient expression of type 2 chain in A-active hexaglycosylceramide of rat small intestine at weaning time. Demonstration by affinity chromatography and ceramide glycanase hydrolysis of A-active glycosphingolipids followed by gas chromatography and mass spectrometry of permethylated hexasaccharides

The small intestine of 15- to 23-day-old rats was cut into four segments from the duodenum to the ileum. Neutral glycosphingolipids were purified from each segment and submitted to thin-layer chromatography and immunostaining with the A005 monoclonal anti-A antibody. This antibody detected an hexaglycosyleeramide located mainly in the duodenum during the postnatal development. In order to characterize hexaglycosylceramides, blood group A-active glycolipids were purified by affinity chromatography on immobilized Helix pomatia lectin in organic solvent. Hexaglycosylceramides (A-6) were subsequently isolated by preparative thin-layer chromatography and hydrolyzed with ceramide glycanase. The free hexasaccharides were permethylated and analyzed by gas chromatography. Two peaks were detected in varying ratios during development, corresponding to type 1 and type 2 chain A hexasaccharides. Gas chromatography clearly demonstrated that type 2 A-6 occurred in the duodenum of developing rats, and that a shift from type 2 to type 1 A-6 occurred with growing age. The change from type 2 to type 1 chain was also assessed by methylation analysis, and by the variation of the characteristic fragmentations of type 1 and type 2 chain hexasaccharides upon mass spectometry of the permethylated A-6 oligosaccharides from the duodenum of 19-day-old and adult rats.

Characterization of glycosphingolipid mixtures with up to ten sugars by gas chromatography and gas chromatography-mass spectrometry as permethylated oligosaccharides and ceramides released by ceramide glycanase.

A novel, effective method for structural characterization of glycosphingolipids has been devised. It employs ceramide glycanase to release intact oligosaccharides followed by analysis using high-mass gas chromatography-mass spectrometry. The oligosaccharides and ceramides released by the glycanase were permethylated and analyzed. The capillary gas chromatography gave excellent resolution and separated, for example, two isomeric 10-sugar oligosaccharides with a molecular mass of 2150 daltons differing only by a Gal1-3GlcNAc and a Gal1-4GlcNAc linkage. The oligosaccharides released from sialic acid containing glycosphingolipids (gangliosides) were also analyzed for monosialo compounds. This analytical approach is simple, is quick, and can readily allow quantitation of individual glycosphingolipids.

Isolation and Characterization of Ceramide Glycanase from the Leech, Macrobdella decora

We have devised a simple method for achieving 890-fold purification of ceramide glycanase with 17% recovery from a North American leech, Macrobdella decora. The method includes water extraction, ammonium sulfate fractionation, and chromatography on octyl-Sepharose, Matrex gel blue A, and Bio-Gel A-0.5m columns. The final preparation showed one major protein band at 54 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By using Bio-Gel A-0.5m filtration, the native enzyme was found to have a molecular mass of 330 kDa. With GM1 as substrate, the optimum pH of this enzyme was determined to be 5.0; the enzyme was stable between pH 4.5 and 8.5. Zn2+ at 5 mM and Cu2+, Ag+, and Hg2+ at 1 mM strongly inhibited the hydrolysis of GM1 by ceramide glycanase. The ceramide glycanase released the intact glycan chain from various glycosphingolipids in which the glycan chain is linked to the ceramide through a beta-glucosyl linkage. This enzyme also cleaved lyso-glycosphingolipids such as lyso-GM1 and lyso-LacCer and synthetic alkyl beta-lactosides. Among seven alkyl beta-lactosides tested, the enzyme only hydrolyzed the ones with an alkyl chain length of four or more carbons. The enzyme also hydrolyzed 2-(octadecylthio)ethyl O-beta-lactoside and 2-(2-carbomethoxyethylthio)ethyl O-beta-lactoside. p-Nitrophenyl, benzyl, and phytyl beta-lactosides, on the other hand, were not hydrolyzed. These results suggest that the enzyme can recognize the hydrophobic portion of glycolipid substrates. The fact that 2-(2-carbomethoxyethylthio)ethyl O-beta-N-acetyllactosaminide and DiGalCer were refractory to the enzyme indicated that in the substrate the first sugar attached to the hydrophobic chain cannot be N-acetylglucosamine and galactose. Furthermore, dodecyl maltoside, Gal alpha 1----6Glc beta Cer, and the LacCer in which the --CH2OH of the galactose was converted into --CHO were also resistant to the enzyme, and Man beta 1----4 Glc beta Cer was hydrolyzed at a much slower rate than LacCer. These results indicate that the nature and the linkage of the sugar attached to the glucose have a profound effect on the action of this enzyme. The hydrolysis of glycosphingolipids by ceramide glycanase is stimulated by bile salts. Among various bile salts tested, sodium cholate at a concentration of 1 microgram/microliter was found to be most effective in stimulating the hydrolysis of various glycosphingolipids with the exception of LacCer. For LacCer, sodium taurodeoxycholate at a concentration of 2-3 micrograms/microliters was most effective. Tween 20, Nonidet P-40, and Triton X-100 did not stimulate the hydrolysis of GM1.(ABSTRACT TRUNCATED AT 400 WORDS)