Further characterization of the structure of GM1b ganglioside from rat ascites hepatoma

The Structural Diversity of Natural Glycosphingolipids (GSLs)

Glycosphingolipids (GSLs) are a subclass of glycolipids made of a glycan and a ceramide that, in turn, is composed of a sphingoid base moiety and a fatty acyl group. GSLs represent the vast majority of glycolipids in eukaryotes, and as an essential component of the cell membrane, they play an important role in many biological and pathological processes. Therefore, they are useful targets for the development of novel diagnostic and therapeutic methods for human diseases. Since sphingosine was first described by J. L. Thudichum in 1884, several hundred GSL species, not including their diverse lipid forms that can further amplify the number of individual GSLs by many folds, have been isolated from natural sources and structurally characterized. This review tries to provide a comprehensive survey of the major GSL species, especially those with distinct glycan structures and modification patterns, and the ceramides with unique modifications of the lipid chains, that have been discovered to date. In particular, this review is focused on GSLs from eukaryotic species. This review has listed 251 GSL glycans with different linkages, 127 glycans with unique modifications, 46 sphingoids, and 43 fatty acyl groups. It should be helpful for scientists who are interested in GSLs, from isolation and structural analyses to chemical and enzymatic syntheses, as well as their biological studies and applications.

Gangliosides and Neuroblastomas

The focus of this review is the ganglio-series of glycosphingolipids found in neuroblastoma (NB) and the myriad of unanswered questions associated with their possible role(s) in this cancer. NB is one of the more common solid malignancies of children. Five-year survival for those diagnosed with low risk NB is 90-95%, while that for children with high-risk NB is around 40-50%. Much of the survival rate reflects age of diagnosis with children under a year having a much better prognosis than those over two. Identification of expression of GD2 on the surface of most NB cells led to studies of the effectiveness and subsequent approval of anti-GD2 antibodies as a treatment modality. Despite much success, a subset of patients, possibly those whose tumors fail to express concentrations of gangliosides such as GD1b and GT1b found in tumors from patients with a good prognosis, have tumors refractory to treatment. These observations support discussion of what is known about control of ganglioside synthesis, and their actual functions in NB, as well as their possible relationship to treatment response.

Glycosphingolipids of rat T cells. Predominance of asialo-GM1 and GD1c

Glycosphingolipids play an important role in the immune response, yet their compositions in T and B cells which mediate cellular and humoral immunity, respectively, have not been elucidated. In this study, characteristic features of glycosphingolipids in rat T lineage cells were revealed by comparing the gangliosides and neutral glycolipids of spleen T- and beta-cell-enriched fractions and thymocytes. In T cells, GD1c(NeuGc,NeuGc), a unique ganglioside synthesized through asialo-GM1 (GA1), was the predominant ganglioside as previously found in thymocytes [Nohara, K., Suzuki, M., Inagaki, F., & Kaya, K. (1991) J. Biochem. (Tokyo) 110, 274-278], and the amount was much higher than in thymocytes. In addition, three other GA1-derived gangliosides were detected in T cells and identified as GM1b(NeuAc), GM1b(NeuGc), and GD1 alpha(NeuAc,NeuAc). In contrast, GD1 alpha(NeuAc,NeuAc) was not discernible in thymocytes, although gangliosides corresponding to GM1b(NeuAc) and GM1b(NeuGc) were detected. The neutral glycolipids of T cells contained almost exclusively GA1, while thymocytes contained much lower amounts. The predominance of these GA1-derived gangliosides was confirmed as a singular feature of T lineage cells by comparison with gangliosides of spleen B-cell-enriched fractions which mainly consisted of gangliosides synthesized through GM3 and GM1. Furthermore, the unique structures, which contain the GM1 core and the extended modification of the lacto series, alpha Gal-LacNAc-GM1, alpha Gal-(LacNAc)2-GM1, and sialyl-LacNAc-GM1, were found in B-cell-enriched fractions. Unexpectedly, the neutral glycolipid composition of the thymocytes resembled that of the B-cell enriched fraction rather than that of the T cells.

In vitro synthesis of disialoganglioside (GD1 alpha) from asialo-GM1 using sialyltransferases in rat liver Golgi vesicles

Two gangliosides were efficiently synthesized from asialo-GM1 (Gal beta 1-3GalNAc beta 1-4Gal beta 1-4Glc beta 1-1 Cer) and cytidine 5'-phosphate-N-acetylneuraminic acid (CMP-NeuAc) by using sialyltransferases in rat liver Golgi vesicles in vitro. These gangliosides were rapidly purified by a combination of anion exchange and reverse-phase column chromatographies. The ganglioside structures were determined by TLC analysis, treatment with a sialidase from Salmonella typhimurium LT2, which specifically hydrolyzes alpha 2-3 N-acetylneuraminic acid (NeuAc alpha 2-3) linkages, TLC immunostaining, and 1H-NMR spectroscopy. One of the gangliosides was identified as GD1 alpha [Neu-Ac alpha 2-3Gal beta 1-3(NeuAc alpha 2-6)GalNAc beta 1-4Gal beta 1-4Glc beta 1-1 Cer]. The other ganglioside was determined to be GM1b (NeuAc alpha 2-3Gal beta 1-3GalNAc beta 1-4Gal beta 1-4Glc beta 1-1 Cer), which has been reported in a previous study [Pohlentz, G., Klein, D., Schmitz, D., Schwarzmann, G., Peter-Katalinic, J. & Sandhoff, K. (1988) Biol. Chem. Hoppe-Seyler 369, 55-63]. Finally, GM1b and GD1 alpha were obtained from asialo-GM1 as a starting material in 8.1% and 1.2% overall yields, respectively. This study also suggests that the novel synthetic pathway asialo-GM1-->GM1b-->GD1 alpha may exist in rat liver.

Regio- and stereo-selective synthesis of ganglioside GM1b and some positional analogs

Total syntheses of ganglioside GM1b (IV3NeuAcGgOse4Cer) and three of its positional analogs are described. Methyl O-(methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D- glycero-alpha-D-galacto-2-nonulopyranosylonate)- (2----3)-2,4,6-tri-O-benzoyl-1-thio-beta-D-galactopyranoside (7) and methyl O-(methyl 5- acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-D-glycero-alpha-D-galacto-2 -nonulopyranosylonate)-(2----6)-2,4-di-O-benzoyl-3-O-benzyl-1-thio - beta-D-galactopyranoside (8) were the key glycosyl donors, prepared according to our reported methods. Coupling of 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-alpha-D-galactopyranosyl bromide and 2-(trimethylsilyl)ethyl O-(2,3,6-tri-O-benzyl-beta-D- galactopyranosyl)-(1----4)-2,3,6-tri-O-benzyl-beta-D-glucopyranoside gave a trisaccharide, which after removal of O-acetyl and phthaloyl groups was converted separately, by benzylidenation and dibutyltin oxide-mediated selective benzylation, into two glycosyl acceptors. These were suitable respectively for C-3 and C-6 glycosylation reactions, promoted by dimethyl(methylthio)sulfonium triflate (DMTST), with the donors 7 and 8. The four possible coupling reactions gave the corresponding four pentasaccharide derivatives in high yields, and these were transformed into their respective alpha-trichloroacetimidates. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with the alpha-trichloroacetimidates gave the corresponding beta-glycosides, which on channeling through selective reduction of the azido group, coupling of the thus formed amino group with octadecanoic acid, O-deacetylation, and saponification of the methyl ester group, gave the title compounds.

Quantification of gangliotetraose gangliosides with cholera toxin

A procedure is described for assay of GM1 and other gangliotetraose-type gangliosides at the picomole level. The gangliosides are absorbed onto polystyrene microwells and treated with neuraminidase and then with cholera toxin B subunits conjugated to horseradish peroxidase. Color is developed and quantified spectrophotometrically. Omission of neuraminidase gives a measure of GM1 alone. Linearity was obtained between 0.5 and 3 pmol. This procedure was applied to ganglioside mixtures isolated fron neuro-2A neuroblastoma and PC12 pheochromocytoma cells. For the latter, an additional step involving reaction with fucosidase increased the yield of GM1 due to the presence of fucosylated gangliosides. Application of the same reagents as a TLC overlay procedure to the gangliosides from neuro-2A cells revealed the presence of GD1a, GD1b, and GT1b in addition to GM1, thus confirming the presence of a family of gangliotetraose gangliosides.

Human placenta gangliosides

Gangliosides extracted from human placenta were composed of four major components (G1-G4), which were purified by silica beads column chromatography. The structures of these gangliosides were analyzed by exoglycosidase treatments, 400 MHz proton magnetic resonance spectroscopy and gas chromatography-mass spectrometry and were concluded to be as follows: (Formula: see text). Gangliosides containing more than 10 sugar residues were observed in addition to the above four major components. But ganglio-series gangliosides were undetectable in the placenta.

Structure of a new disialoganglioside GD1c from spontaneous murine thymoma

A major mono- and a di-sialoganglioside were isolated and purified to homogeneity from a spontaneous thymoma that occurs in AKR mice. Compositional and methylation analyses and the use of exoglycosidases established the monosialoganglioside to be alpha Neu(2----3)beta Gal(1----3)beta GalNAc(1----4)beta Gal(1----4)Glc(1----4)Cer and the disialoganglioside to be alpha NeuAc(2----8)alpha NeuAc(2----3)beta Gal(1----3)beta GalNAc(1----4)beta Gal(1----4)Glc(1----1)Cer (GD1c). A possible pathway for the biosynthesis of this disialoganglioside is presented.

Effects of lectin activation on sialyltransferase activities in human lymphocytes

The effects of phytohemagglutinin (PHA) stimulation on the activities of sialyltransferase 1 (SAT-1), and sialyltransferase 3 (SAT-3), in human lymphocytes were investigated in vitro. For SAT-1 and SAT-3, respectively, the apparent Km values with variable CMP-NeuAc concentrations were 0.19 and 0.015 mM and with variable LacCer were 0.075 and 0.17 mM. Progressive increases in the activities of SAT-1 and SAT-3 were detected in lymphocytes stimulated with PHA, whereas no increase was observed in control lymphocytes incubated in culture medium alone. These increased activities occurred within 18-36 h of incubation and preceded optimum lymphocyte proliferation. Intact lymphocytes were needed for the lectin-stimulated increase of sialyltransferase activities because neither concanavalin A nor phytohemagglutinin added to the broken cell preparation modulated SAT-1 activity. The glycolipid products formed as a result of these enzymatic reactions in the presence of endogenous and exogenous acceptors were tentatively identified by thin-layer chromatography and autofluorography. The addition of exogenous LacCer to the SAT-1 assay resulted in the radiolabeling of a small amount of ganglioside GM1b (3.4%), but GM3 was the major labeled product (96%). When GgOse4Cer was added to the SAT-3 assay, 32% GM3 and 24.6% GM1b were detected while 44% consisted of glycolipids not labeled in assays performed without exogenous acceptors. Of the radioactivity transferred to endogenous acceptors, 81.3% was in GM3 and 14.6% in GM1b. These results demonstrate that the modulation of sialyltransferase activity occurs earlier than cellular activation.

Ganglioside GM1b as an influenza virus receptor

Receptor activity toward influenza virus A/Aichi/2/68 (H3N2) of a pair of gangliosides, GM1b (NeuAc alpha 2-3 Ga1 beta 1-3 GalNAc beta 1-4 Gal beta 1-4 GLc beta 1-1'-ceramide) and GM1a (Gal beta 1-3 GalNAc beta 1-4 (NeuAc alpha 2-3) Ga1 beta 1-4 Glc beta 1-1'-ceramide) is described. Receptor activity was monitored by an assay system including incorporation of gangliosides into chicken asialoerythrocytes which had lost the biological response for the virus, and subsequent estimation of recovery of virus-mediated haemagglutination and haemolysis. GM1a and GM1b were incorporated in similar amounts into chicken asialoerythrocytes. It was found that GM1b-erythrocytes revealed distinct recovery of influenza virus A/Aichi-mediated agglutination at 4 degrees C and subsequent haemolysis at 37 degrees C at pH 5.3. However, restoration of biological responsiveness of the erythrocytes to the virus by incorporation of GM1a was very low under the same conditions. The above results indicate that the haemagglutinin of the influenza virus A/Aichi/2/68 (H3N2) recognizes the saliosyl residue linked to nonreducing 'terminal' galactose rather than 'inner' galactose in the ganglio-tetraose core of gangliosides. GM1b could be one of the functional receptors to the influenza virus.