Direct conversion of sulfatides into cerebrosides

Targeted release and fractionation reveal glucuronylated and sulphated N- and O-glycans in larvae of dipteran insects

Mosquitoes are important vectors of parasitic and viral diseases with Anopheles gambiae transmitting malaria and Aedes aegypti spreading yellow and Dengue fevers. Using two different approaches (solid-phase extraction and reversed-phase or hydrophilic interaction HPLC fractionation followed by MALDI-TOF MS or permethylation followed by NSI-MS), we examined the N-glycans of both A. gambiae and A. aegypti larvae and demonstrate the presence of a range of paucimannosidic glycans as well as bi- and tri-antennary glycans, some of which are modified with fucose or with sulphate or glucuronic acid residues; the latter anionic modifications were also found on N-glycans of larvae from another dipteran species (Drosophila melanogaster). The sulphate groups are attached primarily to core α-mannose residues (especially the α1,6-linked mannose), whereas the glucuronic acid residues are linked to non-reducing β1,3-galactose. Also, O-glycans were found to possess glucuronic acid and sulphate as well as phosphoethanolamine modifications. The presence of sulphated and glucuronylated N-glycans is a novel feature in dipteran glycomes; these structures have the potential to act as additional anionic glycan ligands involved in parasite interactions with the vector host.

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 (Gal beta 1----3GalNAc beta 1---4Glc beta 1----4Glc beta 1----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 (GalNAc beta 1----4Gal beta 1----4Glc beta 1----1-ceramide) displayed rotaviral binding. A phosphatidylethanolamide dipalmitoyl-containing neoglycolipid analog of GA2 bound rotavirus with avidity similar to native GA2. Substitution of beta 1----4-linked GlcNAc or beta 1----3-linked GalNAc for terminal GalNAc 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.

Evidence that secondary rat Schwann cells in culture maintain their differentiated phenotype

Schwann cells, on receiving the correct signal, will encircle an axon and wrap it with a myelin sheath. To begin examining some of the mechanisms underlying the process of myelination in vitro, we isolated Schwann cells from the sciatic nerves of neonatal rats and generated large cell populations with cholera toxin. The immunological and biochemical properties of these secondary Schwann cells were characterized after five to seven passages in the absence of axonal contact. These cells continued to express antigens found in both myelinating (P0 and 2',3'-cyclic nucleotide phosphohydrolase) and nonmyelinating cells in vivo (A5E3 and glial fibrillary acidic protein) in addition to the markers common to both types of cells (Ran-1, 217c, S-100, and laminin). Biochemical analyses showed that these cells synthesize the very-long-chain fatty acids (22-26 carbon atoms) found in myelin membranes. Moreover, the enzymes required for the synthesis of myelin glycolipids (including sphingosine acyltransferase, UDP-galactose:ceramide galactosyltransferase, and cerebroside sulfotransferase) were still active, and metabolic labeling studies showed that galactocerebroside and sulfatide were synthesized even though the galactocerebroside pool was insufficient to be detected by immunostaining. Secondary Schwann cells also synthesized four species of myelin basic protein and the major structural glycoprotein in myelin, P0. The pathway necessary for glycosylation of P0 protein remained active, and an analysis of the oligosaccharide chain revealed that approximately 70% was processed to a complex form. In summary, we found that secondary Schwann cells still express most of the immunological markers of differentiated cells and continue to synthesize low levels of myelin components. Therefore, Schwann cells do not dedifferentiate in culture, as previously believed.

Synthesis and transport of cerebrosides and sulfatides in rat brain during development

Synthesis and transport of nonhydroxy fatty acid (NFA)- and hydroxy fatty acid (HFA)-containing ceramides, cerebrosides, and sulfatides were studied in vivo in rat brain during development. After an intracerebral injection of [3H]serine, incorporation into these lipids of microsomal and myelin membranes was analyzed after HPLC. Distribution of amounts and incorporation of radioactivity were also determined in individual molecular species of these lipids. The results showed that HFA-ceramides and long-chain NFA-ceramides have small pool sizes and rapid turnover rates in the microsomal membranes and are preferentially utilized for the synthesis of long-chain (greater than or equal to 20:0) HFA- and NFA-galactocerebrosides of both microsomal and myelin membranes. Glucocerebrosides are not expressed in myelin and their synthesis in microsomal membranes is predominant before the onset of myelination. With development, synthesis and accumulation of HFA-cerebrosides increase over NFA-cerebrosides in both microsomal and myelin membranes. In myelin, incorporation of radioactivity into HFA-cerebrosides is even higher than that expected by transport alone from microsomal membranes and it is possible that part of the HFA-cerebrosides in myelin could be due to de novo synthesis by myelin itself. The amount of NFA- and HFA-sulfatides is about equal, both in myelin and microsomal membranes, and this relative proportion does not change with development. Similar relative rates of incorporation of radioactivity into sulfatides of microsomal and myelin membranes are consistent with the notion that both NFA and HFA sulfatides are synthesized in the microsomal (Golgi) membranes and are transported to myelin.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfatide-binding proteins

Sulfatides (galactosyl ceramide-I3-sulfate) and other sulfated glycolipids are found in many tissues. The cell adhesion proteins laminin, thrombospondin, and von Willebrand factor bind specifically to sulfated glycolipids. Methods for characterizing the specificity of these interactions using surface-adsorbed glycolipids are reviewed. The three proteins do not bind to other anionic lipids, including gangliosides, phospholipids, or cholesterol 3-sulfate. Binding to sulfatides is saturable and of relatively high affinity. Relative binding avidity depends on the oligosaccharide structure of the glycolipids. Binding to sulfatides in erythrocyte membranes can account for the hemagglutinating activities of the three proteins and may play a role in the interactions of these proteins with other cell types.

Structure and immunological localization of spleen sulfolipid

By using chemical and immunological techniques, the structure of the spleen sulfolipid was confirmed as being a sulfogalactosylceramide. This lipid was localized in the spleen granulocytes (polymorphonuclear leukocytes).

Sulpholipid formation in rat submandibular gland

The sulphotransferase activity of rat submandibular gland differs markedly from that of testis, kidney and brain. The addition of lipid acceptors and Mn2+ (or Mg2+), which have been shown to enhance sulpholipid formation from adenosine 3'-phosphate 5'-sulphatophosphate in other tissues, has either no effect or inhibits the transfer process.

A comparative study of the glycolipids of human, bird and fish testes and of human sperm

The glycolipids of human testis and sperm have been compared. Both adult testis and the sperm exhibited remarkably complex, but generally similar, patterns of glycolipids. In particular, both contained appreciable amounts of the sulfogalactosylmonoalkylmonoacylglycerol, recently shown to be the principal glycolipid of the testis and sperm of a number of animals. In contrast, immature (prebuteral) human testis did not contain this compound. To extend knowledge on the possible distribution of sulfogalactosylmonoalkylmonoacylglycerol in the testes of other chordates, we have also analysed the glycolipids of the testes of a number of birds and fish. None of the testes from these species contained the above compound. Instead, sulfogalactosylceramide was found to be a major glycolipid of the testis of mature fowl, duck and skate-fish and sulfogalactosylglucosylceramide of the testis of mature salmon and trout. Immature duck testis contained only a trace of sulfogalactosylceramide. These studies reveal intriguing differences between the sulfatides of various chordates, lend support to the concept that sulfatides increase markedly in testis at a specific stage of spermatogenesis and suggest an important role for sulfatides in testicular and spermatozoal function.