Glycosphingolipids carbohydrates

Chemistry of Glycosphingolipids-Carbohydrate Molecules of Biological Significance. Vankar, Y. D. Schmidt. R. R. Chem. Soc. Rev. 2000, 29, 201-216,... 

Vankar, YD and Schmidt, RR (2000) Chemistry of glycosphingolipids - carbohydrate molecules of biological significance. Chem Soc Rev, 29, 201-216. 

Sialic acid units are grafted onto neutral glycosphingolipid carbohydrates to produce gan-gliosides. The donor is an achvated nucleotide sugar (CMP-sialic acid) that is transferred to an oligosaccharide chain by a sialyltransferase. Conversely, sialic acids can be removed from... 

Yu Z W, Calvert T L and Leckband D 1998 Molecular forces between membranes displaying neutral glycosphingolipids evidence for carbohydrate attraction Biochemistry 37 1540-50... 

Three types of carbohydrate sample have been reported to give data above mass 4000, namely, permethylated polysaccharides, permethylated glycosphingolipids, and naturally acylated forms of a mycobacterial O-methyl-D-glucose polysaccharide. All are hydrophobic, and desorption is probably facilitated by their inability to form strongly hydrogen-bonded aggregates, either with themselves or with the matrix. 

M. J. Hemaiz, J. M. de la Fuente, A. G. Barrientos, and S. Penades, A model system mimicking glycosphingolipid clusters to quantify carbohydrate selfinteractions by surface plasmon resonance, Angew. Chem. Int. Ed., 40 (2001) 2258-2261. 

Teneberg, S., Angstrom, J., and Ljungh, A. (2004). Carbohydrate recognition by enterohemorrhagic Escherichia coli Characterization of a novel glycosphingolipid from cat small intestine. Glycobiology 14, 187-196. 

Due to the biological roles of glycolipids, many papers have been devoted to their syntheses over the last ten years. The coupling of a fully protected carbohydrate donor to a lipid acceptor requires efficient and highly stereoselective glycosylation methods because lipid derivatives often have low reactivity. A few examples of glycosphingolipids syntheses will be discussed below as well as multistep preparations of other amphiphilic carbohydrates designed as biochemical mimetics, surfactants or liquid crystals. 

Measurements of the quantities of glycolipids inserted into the membrane have also been reported by a technique based on the use of C-labeled lipid anchors. In this method, the carbohydrate (a-o-Man) was covalently coupled to the anchor at the surface of a pre-formed vesicle. Indeed, the liposome structure was shown to remain intact in the treatment. Nevertheless, the measurement of the incorporated mannose was performed after separation of bound and unbound material by centrifugation. The yields of coupling were shown to increase with the increase of the initial mannose/ C-anchor ratio, but non covalent insertions were displayed at high initial mannose concentrations. Therefore, the aforementioned method was not as accurate as could have been expected for the use of radioactive materials [142]. Radiolabeled phospholipids were also used for such determinations thus the amounts of glycosphingolipids incorporated into liposomes were quantified by the use of H-phospholipids whereas the amounts of glycolipids were determined by a sphingosine assay [143]. 

An article by Li and Li (Tnlane University, LA) on the biosynthesis and catabolism of glycosphingolipids serves to extend that by Kiss (Vol. 24), which dealt mainly with the chemistry of these compounds. Schwarz and Datema (Giessen) provide a detailed account of the lipid pathway of protein glyeosylation and of its inhibitors, and then discuss the biological significance of protein-bound carbohydrates, thereby... 

Sulfation of the carbohydrate chain occurs after the monosaccharide to be sulfated has been incorporated into the growing carbohydrate j chain. The source of the sulfate is 3 -phosphoadenosyl-5 -phospho-sulfate (PAPS, a molecule of AMP with a sulfate group attached to the 5-phosphate). Sulfotransferases cause the sulfation of the carbohydrate chain at specific sites. [Note An example of the synthesis of a sulfated glycosaminoglycan, chondroitin sulfate, is shown in Figure 14.11.] PAPS is also the sulfur donor in glycosphingolipid synthesis. [Note A defect in the sulfation process results in one of several autosomal recessive disorders that affect the proper development and maintenance of the skeletal system. This illustrates Ihe importance of the sulfation step.]... 

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