Egghead and brainiac are essential for glycosphingolipid biosynthesis in vivo

The Drosophila genes, brainiac and egghead, encode glycosyltransferases predicted to act sequentially in early steps of glycosphingolipid biosynthesis, and both genes are required for development in Drosophila. egghead encodes a beta4-mannosyltransferase, and brainiac encodes a beta3-N-acetylglucosaminyltransferase predicted by in vitro analysis to control synthesis of the glycosphingolipid core structure, GlcNAcbeta1-3Manbeta1-4Glcbeta1-Cer, found widely in invertebrates but not vertebrates. In this report we present direct in vivo evidence for this hypothesis. egghead and brainiac mutants lack elongated glycosphingolipids and exhibit accumulation of the truncated precursor glycosphingolipids. Furthermore, we demonstrate that despite fundamental differences in the core structure of mammalian and Drosophila glycosphingolipids, the Drosophila egghead mutant can be rescued by introduction of the mammalian lactosylceramide glycosphingolipid biosynthetic pathway (Galbeta1-4Glcbeta1-Cer) using a human beta4-galactosyltransferase (beta4Gal-T6) transgene. Conversely, introduction of egghead in vertebrate cells (Chinese hamster ovary) resulted in near complete blockage of biosynthesis of glycosphingolipids and accumulation of Manbeta1-4Glcbeta1-Cer. The study demonstrates that glycosphingolipids are essential for development of complex organisms and suggests that the function of the Drosophila glycosphingolipids in development does not depend on the core structure.     

Novel Leb-like Helicobacter pylori-binding glycosphingolipid created by the expression of human alpha-1,3/4-fucosyltransferase in FVB/N mouse stomach

The "Le(b) mouse" was established as a model for investigations of the molecular events following Le(b)-mediated adhesion of Helicobacter pylori to the gastric epithelium. By the expression of a human alpha-1,3/4-fucosyltransferase in the gastric pit cell lineage of FVB/N transgenic mice, a production of Le(b) glycoproteins in gastric pit and surface mucous cells was obtained in this "Le(b) mouse," as demonstrated by binding of monoclonal anti-Le(b) antibodies. To explore the effects of the human alpha-1,3/4-fucosyltransferase on glycosphingolipid structures, neutral glycosphingolipids were isolated from stomachs of transgenic alpha-1,3/4-fucosyltransferase-expressing mice. A glycosphingolipid recognized by BabA-expressing H. pylori was isolated and characterized by mass spectrometry and proton NMR as Fuc alpha 2Gal beta 3(Fuc alpha 4)GalNAc beta 4 Gal beta 4 Glc beta 1Cer, i.e., a novel Le(b)-like glycosphingolipid on a ganglio core. In addition, two other novel glycosphingolipids were isolated from the mouse stomach epithelium that were found to be nonbinding with regard to H. pylori. The first was a pentaglycosylceramide, GalNAc beta 3 Gal alpha 3(Fuc alpha 2)Gal beta 4 Glc beta 1Cer, in which the isoglobotetrasaccharide has been combined with Fuc alpha 2 to yield an isoglobotetraosylceramide with an internal blood group B determinant. The second one was an elongated fucosyl-gangliotetraosylceramide, GalNAc beta 3(Fuc alpha 2)Gal beta 3GalNAc beta 4Gal beta 4 Glc beta 1Cer.     

The blood group B type-4 heptaglycosylceramide is a minor blood group B structure in human B kidneys in contrast to the corresponding A type-4 compound in A kidneys. Structural and in vitro biosynthetic studies.

Blood group A glycolipid antigens have been found based upon at least four different core saccharides (types 1 to 4). The biological significance of this structural polymorphism is not known, although the successful outcome of transplantations of blood group A2 kidneys to blood group O individuals have been partly explained by the low expression of A type-3 and -4 chain glycolipid antigens in A2 kidneys. If graft rejection due to ABO incompatibility is, in any way, correlated to the expression of type-3 and -4 chain blood group glycolipids, it is of interest to identify possible blood group B structures based on these core saccharides. In a non-acid glycosphingolipid fraction isolated from human blood group B kidneys, mass spectrometry, high-temperature gas chromatography-mass spectrometry and probing of thin-layer chromatograms with Gal alpha 1-4Gal-specific Escherichia coli and monoclonal anti-B antibodies provided evidence for minute amounts of a Gal alpha 1-3(Fuc alpha 1-2)Gal beta-HexNAc-Gal alpha 1-4Gal beta-Hex-Ceramide structure consistent with a B type-4 chain heptaglycosylceramide. In contrast, blood group A kidneys have the corresponding A type-4 chain heptaglycosylceramide as the predominant blood group A glycolipid. No, or very low activity of the blood group B gene enzyme on the type-4 chain blood group H hexaglycosylceramide precursor was found by biosynthetic experiments in vitro, which might explain the low expression of type-4 chain blood group B heptaglycosylceramides in human blood group B kidneys.     

The blood group B type-4 heptaglycosylceramide is a minor blood group B structure in human B kidneys in contrast to the corresponding A type-4 compound in A kidneys. Structural and in vitro biosynthetic studies

Blood group A glycolipid antigens have been found based upon at least four different core saccharides (types 1 to 4). The biological significance of this structural polymorphism is not known, although the successful outcome of transplantations of blood group A₂ kidneys to blood group O individuals have been partly explained by the low expression of A type-3 and -4 chain glycolipid antigens in A₂ kidneys. If graft rejection due to ABO incompatibility is, in any way, correlated to the expression of type-3 and -4 chain blood group glycolipids, it is of interest to identify possible blood group B structures based on these core saccharides. In a non-acid glycosphingolipid fraction isolated from human blood group B kidneys, mass spectrometry, high-temperature gas chromatography-mass spectrometry and probing of thin-layer chromatograms with Galα1–4Gal-specific Escherichia coli and monoclonal anti-B antibodies provided evidence for minute amounts of Gaα1–3(Fucα1–2)Galβ-HexNac-Galα1–4Galβ-Hex-Ceramide structure consistent with a B type-4 chain heptaglycosylceramide. In contrast, blood group A kidneys have the corresponding A type-4 chain heptaglycosylceramide as the predominant glood group A glycolipid. No, or very low activity of the blood group B gene enzyme on the type-4 chain blood group H hexaglycosylceramide precursor was found by biosynthetic experiments in vitro, which migh explain the low expression of type-4 chain blood group heptaglycosylceramides in human blood group B kidneys.     

Studies on Galalpha3-binding proteins: comparison of the glycosphingolipid binding specificities of Marasmius oreades lectin and Euonymus europaeus lectin

The carbohydrate binding preferences of the Galalpha3Galbeta4 GlcNAc-binding lectins from Marasmius oreades and Euonymus europaeus were examined by binding to glycosphingolipids on thin-layer chromatograms and in microtiter wells. The M. oreades lectin bound to Galalpha3-terminated glycosphingolipids with a preference for type 2 chains. The B6 type 2 glycosphingolipid (Galalpha3[Fucalpha2]Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer) was preferred over the B5 glycosphingolipid (Galalpha3Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer), suggesting that the alpha2-linked Fuc is accommodated in the carbohydrate binding site, providing additional interactions. The lectin from E. europaeus had broader binding specificity. The B6 type 2 glycosphingolipid was the best ligand also for this lectin, but binding to the B6 type 1 glycosphingolipid (Galalpha3[Fucalpha2]Galbeta3GlcNAcbeta3Galbeta4Glcbeta1Cer) was also obtained. Furthermore, the H5 type 2 glycosphingolipid (Fucalpha2Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer), devoid of a terminal alpha3-linked Gal, was preferred over the the B5 glycosphingolipid, demonstrating a significant contribution to the binding affinity by the alpha2-linked Fuc. The more tolerant nature of the lectin from E. europaeus was also demonstrated by the binding of this lectin, but not the M. oreades lectin, to the x2 glycosphingolipid (GalNAcbeta3Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer) and GlcNAcbeta3Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer. The A6 type 2 glycosphingolipid (GalNAcalpha3[Fucalpha2]Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer) and GalNAcalpha3Galbeta4GlcNAcbeta3Galbeta4Glcbeta1-Cer were not recognized by the lectins despite the interaction with B6 type 2 glycosphingolipid and the B5 glycosphingolipid. These observations are explained by the absolute requirement of a free hydroxyl in the 2-position of Galalpha3 and that the E. europaea lectin can accommodate a GlcNAc acetamido moiety close to this position by reorienting the terminal sugar, whereas the M. oreades lectin cannot.     

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.     

Chromogenic labeling of monosaccharides using 4'-N,N-dimethylamino-4-aminoazobenzene

Twenty-three monosaccharides, e.g., D- or L-pentoses, D- or L-hexoses, heptose, 2- or 6-deoxyhexoses, 2-deoxy-2-aminohexoses, hexuronic acids, and N-acetylmuramic acid, were coupled to the azo dye 4'-N,N-dimethylamino-4-aminoazobenzene by reductive amination using sodium cyanoborohydride as reducing agent and in the presence of pentaerythritol. The structure of the colored glycamines was established by mass spectrometry. The average yield of the reaction was more than 80%. The sugar derivatives were separated either by silica-gel thin-layer chromatography or by high-performance liquid chromatography. Spectrophotometric quantitation was performed in the visible range at the picomole level. The method was applied to the determination of the sugar composition of the glycosphingolipid globotetraosyl ceramide and the human milk oligosaccharide lacto-N-fucopentaose I.     

Isolation and characterization of four major neutral glycosphingolipids from the liver of the English sole (Parophrys vetulus). Presence of a novel branched lacto-ganglio-iso-globo hybrid structure

We have previously reported on carbohydrate structures of the major acidic glycosphingolipids from the liver of the English sole, Parophrys vetulus (Ostrander, G. K., Levery, S. B., Hakomori, S., and Holmes, E. H. (1988) J. Biol. Chem. 263, 3103-3110). We have now isolated four major neutral glycosphingolipids from English sole liver. They have been characterized by 1H nuclear magnetic resonance spectroscopy, methylation analysis, and by fast atom bombardment-mass spectrometry. In addition to neutral glycosphingolipids with known structures (CMH, lactosylceramide, and Gg3), a major polar neutral glycosphingolipid was isolated and characterized as having the following novel structure: (formula; see text) The compound represents a novel hybrid of neolacto-, ganglio-, and iso-globo-series glycosphingolipid structures, a combination not previously encountered. Furthermore, the linkage Fuc alpha 1----3GalNac has not been previously reported for a glycosphingolipid. The relationship of these structural elements to known glycoconjugates is discussed.     

Role of multiple drug resistance protein 1 in neutral but not acidic glycosphingolipid biosynthesis

Transfection studies have implicated the multiple drug resistance pump, MDR1, as a glucosyl ceramide translocase within the Golgi complex (Lala, P., Ito, S., and Lingwood, C. A. (2000) J. Biol. Chem. 275, 6246-6251). We now show that MDR1 inhibitors, cyclosporin A or ketoconazole, inhibit neutral glycosphingolipid biosynthesis in 11 of 12 cell lines tested. The exception, HeLa cells, do not express MDR1. Microsomal lactosyl ceramide and globotriaosyl ceramide synthesis from endogenous or exogenously added liposomal glucosyl ceramide was inhibited by cyclosporin A, consistent with a direct role for MDR1/glucosyl ceramide translocase activity in their synthesis. In contrast, cellular ganglioside synthesis in the same cells, was unaffected by MDR1 inhibition, suggesting neutral and acid glycosphingolipids are synthesized from distinct precursor glycosphingolipid pools. Metabolic labeling in wild type and knock-out (MDR1a, 1b, MRP1) mouse fibroblasts showed the same loss of neutral glycosphingolipid (glucosyl ceramide, lactosyl ceramide) but not ganglioside (GM3) synthesis, confirming the proposed role for MDR1 translocase activity. Cryo-immunoelectron microscopy showed MDR1 was predominantly intracellular, largely in rab6-containing Golgi vesicles and Golgi cisternae, the site of glycosphingolipid synthesis. These studies identify MDR1 as the major glucosyl ceramide flippase required for neutral glycosphingolipid anabolism and demonstrate a previously unappreciated dichotomy between neutral and acid glycosphingolipid synthesis.     

A novel difucosylated neutral glycosphingolipid from the eggs of the sea urchin, Hemicentrotus pulcherrimus: I. Purification and structural determination of the glycolipid.

A novel fucose-containing neutral glycosphingolipid (GL-5) was purified from the eggs of the sea urchin, Hemicentrotus pulcherrimus. The chemical structure was determined to be Fuc alpha 1-3GalNAc beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-4Glc beta 1-1Cer by methylation analysis, partial acid hydrolysis, fast atom bombardment mass spectrometry, and proton nuclear magnetic resonance spectroscopy. The unique characteristics of GL-5 are that: the reducing terminal disaccharide portion is not Gal beta 1-4Glc but GlcNAc beta 1-4Glc; it includes a GalNAc beta 1-4GlcNAc sequence and a Fuc-GalNAc linkage; the defucosylated core is a novel trisaccharide chain; and the sugar structure is one of the smallest ever characterized for a difucosylated glycolipid. The major fatty acids were 22:1 and 22h:1, and about 30% of the total acids was 2-hydroxylated. All the long-chain bases were phytosphingosines, of which about 90% was n-t18:0. The similarity of the ceramide moiety to that of glucosylceramide from the same eggs [Kubo, H. et al. (1992) J. Biochem. 111, 726-731] suggests a close biosynthetic relationship between GL-5 and the glucosylceramide.     

Characterization of a major neutral glycolipid in PC12 cells as III3Gal alpha-globotriaosylceramide by the method for determining glycosphingolipid saccharide sequence with endoglycoceramidase

Neutral glycolipids in PC12 cells were examined. A major neutral glycosphingolipid, isolated from a chloroform/methanol extract of the cells, was found to contain only galactose and glucose at a ratio of 3:1 and identified as ceramide tetrahexoside by fast atom bombardment (FAB) mass spectrometry. Its saccharide sequence was determined by a new method developed here using endoglycoceramidase (Ito, M., and Yamagata, T. (1986) J. Biol. Chem. 261, 14278-14282). The glycosphingolipid was digested with endoglycoceramidase to produce oligosaccharide which was subsequently pyridylaminated. The fluorescence-labeled oligosaccharide was digested with a series of specific exoglycosidases and fractionated by high performance liquid chromatography. The 2-aminopyridyl oligosaccharide was hydrolyzed by alpha-galactosidase to give a 2-aminopyridyl oligosaccharide which was identified as 2-aminopyridyl lactose by high performance liquid chromatography, indicating the glycolipid structure to be Gal alpha Gal alpha Gal beta GlcCer. Ceramide trihexoside obtained by limited digestion of the intact glycolipid was clearly identical with ceramide trihexoside obtained from human erythrocytes, according to NMR spectroscopy and methylation analysis. From these and other data on the intact glycolipid, obtained by methylation analysis and NMR spectroscopy, its structure was confirmed as Gal alpha 1-3Gal alpha 1-4Gal beta 1-4Glc beta 1-1Cer, III3-Gal alpha-globotriaosylceramide. This is the first report indicating the presence of this glycosphingolipid in PC12 cells.     

Glycosphingolipid expression in pig aorta: identification of possible target antigens for human natural antibodies

Total non-acid glycosphingolipids were isolated from the aortas of more than 80 pigs. The glycolipids were separated by HPLC, analysed by thin- layer chromatography, and tested for reactivity with monoclonal anti- blood group antibodies. The fractions were structurally characterized by NMR spectroscopy and mass spectrometry. Reactivity with both anti- blood group A and H antibodies was seen. The major glycosphingolipid constituents were globotri- and globotetraosylceramides and blood group H pentaglycosylceramides based on type 1 and type 2 core saccharide chains. Globopentaosylceramides, blood group H hexaglycosylceramides based on type 4 chain, and blood group A hexaglycosylceramides based on type 1 core chain were also present. Two structures, that may be important targets for human antibodies initiating hyperacute rejection following pig to human xenotransplantation, were present as minor constituents compared to the blood group components. These were Galalpha1,3neolactotetraosylceramide and a Galalpha1, 3Lexstructure. A Leb/Y hexaglycosylceramide was also present.      

Structure elucidation of sphingolipids from the mycopathogen Sporothrix schenckii: identification of novel glycosylinositol phosphorylceramides with core manalpha1-->6Ins linkage

Acidic glycosphingolipid components were extracted from the mycelium form of the thermally dimorphic mycopathogen Sporothrix schenckii. Two fractions from the mycelium form (Ss-M1 and Ss-M2), having the highest Rf values on HPTLC analysis, were isolated and their structures elucidated by 1- and 2-D 13C- and 1H-nuclear magnetic resonance spectroscopy, and electrospray ionization mass spectrometry with lithium adduction of molecular ions. The structures of Ss-M1 and Ss-M2 were determined to be Manalpha1-->Ins1-P-1Cer and Manalpha1--> 3Manalpha1-->Ins1-P-1Cer, respectively (where Ins = myo-inositol, P = phosphodiester). The Manalpha1-->6Ins motif is found normally in diacylglycerol-based glycophosphatidylinositols of Mycobacteria, but this is the first unambiguous identification of the same linkage making up the core structure of fungal glycosylinositol phosphorylceramides (GIPCs). These results are discussed in relation to the structures of GIPCs of other mycopathogens, including Histoplasma capsulatum and Paracoccidioides brasiliensis.     

Regulation of the expression of Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipids in kidney

Previous studies (Galili, U., Clark, M. R., Shohet, S. B., Buehler, J., and Macher, B. A. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 1369-1373; Galili, U., Shohet, S. B., Korbrin, E., Stults, C. L. M., and Macher, B. A. (1988) J. Biol. Chem. 263, 17755-17762) have established that there is a unique evolutionary distribution of glycoconjugates carrying the Gal alpha 1-3Gal beta 1-4GlcNAc epitope. These glycoconjugates are expressed by cells from New World monkeys and non-primate mammals, but not by cells from humans, Old World monkeys, or apes. The lack of expression of this epitope in the latter species appears to result from the suppression of gene expression for the enzyme UDP-galactose:nLc4Cer alpha 1-3-galactosyltransferase (alpha 1-3GalT) (Joziasse, D. H., Shaper, J. H., Van den Eijnden, D. H., Van Tunen, A. J., and Shaper, N. L. (1989) J. Biol. Chem. 264, 14290-14297). Although many non-primate species are known to express this carbohydrate epitope, the nature (i.e. glycoprotein or glycosphingolipid) of the glycoconjugate carrying this epitope is only known for a few tissues in a few animal species. Furthermore, it is not known whether all animal species express this epitope in the same tissues. We have investigated these questions by analyzing the glycosphingolipids in kidney from several non-primate animal species. Immunostained thin layer chromatograms of glycosphingolipids from sheep, pig, rabbit, cow, and rat kidney with the Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipid-specific monoclonal antibody, Gal-13, demonstrated that kidney from all of these species except rat contained Gal alpha 1-3Gal beta 1-4GlcNAc neutral glycosphingolipids. A lack of expression of Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipids in rat may be due to the lack of expression of the enzyme (alpha 1-3GalT) which catalyzes the formation of the Gal alpha 1-3Gal nonreducing terminal sequence of these compounds or to the lack of expression of glycosyltransferases which are necessary for the synthesis of the neolacto core structure of these compounds. These possibilities were evaluated in two ways. First, the three enzymes (UDP-N-acetylglucosamine:LacCer beta 1-3-N-acetyl-glucosaminyltransferase, UDP-galactose:Lc3Cer beta 1-4-galactosyltransferase, and alpha 1-3GalT) involved in the synthesis of the Gal alpha 1-3Gal beta 1-4GlcNAc glycosphingolipids were assayed using an enzyme-linked immunosorbent assay-based assay system and carbohydrate sequence-specific monoclonal antibodies. Second, TLC immunostaining was done to determine if the glycosphingolipid precursors (i.e. Lc3Cer and nLc4Cer) are expressed in rat kidney. Interestingly, rat kidney had a relatively high level of alpha 1-3GalT activity compared with the other animals tested.(ABSTRACT TRUNCATED AT 400 WORDS)     

ON THE STRUCTURE OF A NEW, FUCOSE CONTAINING GANGLIOSIDE FROM PIG CEREBELLUM

A new ganglioside, provisionally named GLIVa, was isolated in pure form from pig cerebellum. Ganglioside GLIVa is a disialoganglioside containing fucose. Its basic neutral glycosphingolipid core is the gangliotetraose ceramide: Gal, β 1 → 3 GalNAc, β 1 → 4 Gal, β 1 → 4 Glc, β 1 → Cer. Fucose is α-glycosidically linked to the 2-position of external galactose and one N-acetylneuraminic acid is linked to the other one by an α, 2 → 8 linkage. Thus the total structure of ganglioside GLIVa is the following: Fuc, α 1 → 2 Gal, β 1 → 3 GalNAc, β 1 → 4 (NeuAc, α 2 48 NeuAc, α 2 → 3) Gal, β 1 → 4 Glc, β 1 → Ceramide. According to the IUPAC-IUB Commission on Biochemical Nomenclature is indicated as II³α(NeuAc)₂ IV²αFuc-GgOse₄Cer.     

Elevated endosomal cholesterol levels in Niemann-Pick cells inhibit rab4 and perturb membrane recycling

In normal human skin fibroblasts (HSFs), fluorescent glycosphingolipid analogues are endocytosed and sorted into two pools, one that is recycled to the plasma membrane and one that is transported to the Golgi complex. Here, we investigated glycosphingolipid recycling in Niemann-Pick type A and C lipid storage disease fibroblasts (NPFs). Cells were incubated with a fluorescent analogue of lactosylceramide (LacCer) at 16 degrees C to label early endosomes (EEs), shifted to 37 degrees C, and lipid recycling was quantified. Using dominant negative rabs, we showed that, in normal HSFs, LacCer recycling was rapid (t1/2 approximately 8 min) and mainly rab4-dependent. In NPFs, LacCer recycling was delayed (t1/2 approximately 30-40 min), and rab4-dependent recycling was absent, whereas rab11-dependent recycling predominated. Transferrin recycling via the rab4 pathway was similarly perturbed in NPFs. Compared with normal HSFs, EEs in NPFs showed high cholesterol levels and an altered organization of rab4. In vitro extraction of rab4 (but not rab11) with GDP dissociation inhibitor was severely attenuated in NPF endosomal fractions. This impairment was reversed with cholesterol depletion of isolated endosomes or with high-salt treatment of endosomes. These data suggest that abnormal membrane recycling in NPFs results from specific inhibition of rab4 function by excess cholesterol in EEs.     

A novel plasmal conjugate to glycerol and psychosine ("glyceroplasmalopsychosine"): isolation and characterization from bovine brain white matter

A novel plasmal conjugate of glycosphingolipid having cationic lipid properties was isolated from the white matter of bovine brain. Linkage analysis of galactosyl residue by methylation, liquid secondary ion, and electrospray ionization mass spectrometry of intact and methylated derivatives, and by (1)H- and (13)C-NMR spectroscopy, identified the structure unambiguously as an O-acetal conjugate of plasmal to the primary hydroxyl group of glycerol and to the 6-hydroxyl group of galactosyl residue of beta-galactosyl 1-->1 sphingosine (psychosine). This novel compound is hereby termed "glyceroplasmalopsychosine"; its structure is shown below (see text).     

Carbohydrate recognition by enterohemorrhagic Escherichia coli: characterization of a novel glycosphingolipid from cat small intestine

A key virulence trait of pathogenic bacteria is the ability to bind to receptors on mucosal cells. Here the potential glycosphingolipid receptors of enterohemorrhagic Escherichia coli were examined by binding of 35S-labeled bacteria to glycosphingolipids on thin-layer chromatograms. Thereby a selective interaction with two nonacid glycosphingolipids of cat small intestinal epithelium was found. The binding-active glycosphingolipids were isolated and, on the basis of mass spectrometry, proton NMR spectroscopy, and degradation studies, identified as Galalpha3Galbeta4Glcbeta1Cer (isoglobotriaosylceramide) and Galalpha3Galalpha3Galbeta4Glcbeta1Cer. The latter glycosphingolipid has not been described before. The interaction was not based on terminal Galalpha3 because the bacteria did not recognize the structurally related glycosphingolipids Galalpha3Galalpha4Galbeta4Glcbeta1Cer and Galalpha3Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer (B5 glycosphingolipid). However, further binding assays using reference glycosphingolipids showed that the enterohemorrhagic E. coli also bound to lactosylceramide with phytosphingosine and/or hydroxy fatty acids, suggesting that the minimal structural element recognized is a correctly presented lactosyl unit. Further binding of neolactotetraosylceramide, lactotetraosylceramide, the Le(a)-5 glycosphingolipid, as well as a weak binding to gangliotriaosylceramide and gangliotetraosylceramide, was found in analogy with binding patterns that previously have been described for other bacteria classified as lactosylceramide-binding.     

Ceramide as a TLR4 agonist; a putative signalling intermediate between sphingolipid receptors for microbial ligands and TLR4

Mucosal Toll-like receptors (TLRs) respond to pathogens, but remain inert to the indigenous flora, suggesting that the TLRs can receive pathogen-specific signals. For example, TLR4 signalling is activated in CD14-negative epithelial cells by P-fimbriated, uropathogenic Escherichia coli, but not by lipopolysaccharide. The fimbriae use glycosphingolipids as recognition receptors and there is release of ceramide, which is the membrane-anchoring domain of the receptors. In this study, ceramide was identified as a TLR4 agonist and as a putative signalling intermediate between the glycosphingolipid recognition receptors and TLR4. Exogenous ceramide activated a TLR4-dependent epithelial cell response, as shown by exposing stably transfected TLR4-positive or -negative human embryonal kidney cells to C2 and C6 ceramide. A similar, TLR4-dependent response occurred after deliberate release of endogenous long-chained ceramide with sphingomyelinase. Microbial ligands with glycosphingolipid specificity (P fimbriae or the B subunit of Shiga toxin) were shown to increase the levels of ceramide and to trigger a TLR4-dependent response in epithelial cells. The results show that ceramide activates TLR4 signalling and suggest that this mechanism might allow pathogens to elicit mucosal TLR4 responses by perturbing sphingolipid receptors for virulence ligands like P fimbriae.     

Isolation and characterization of a novel uronic acid-containing acidic glycosphingolipid from the ascidian Halocynthia roretzi

A novel uronic acid-containing glycosphingolipid (UGL-1) was isolated from the ascidian Halocynthia roretzi. UGL-1 was prepared from chloroform-methanol extracts and purified by the use of successive column chromatography on DEAE-Sephadex, Florisil, and Iatrobeads. Chemical structural analysis was performed using methylation analysis, gas chromatography, gas chromatography-mass spectrometry, matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry, and 1H-NMR spectra. The chemical structure of UGL-1 was determined to be a glucuronic acid-containing glycosphingolipid, Galbeta1-4(Fucalpha1-3)GlcAbeta1-1Cer. The ceramide component was composed of C16:0 and C18:0 acids and C16-, C17-, and C18-phytosphingosines as major components.