Sialyltransferases glycolipid specific

More recently, studies on Campylobacter jejuni have demonstrated how specific bacterial carbohydrate antigens can mimic the fine structure of human cell surface glycolipid structures and elicit autoimmune reactivity. Yuki et al.61 first identified that the lipooligosaccharide (LOS) of C. jejuni mimicked human G(M)1 ganglioside and subsequently extended these studies to demonstrate that specific single amino acid variants of the C. jejuni Cst-II sialyltransferase protein are responsible for the synthesis of LOS variants that in turn, mimic different... 

The substrate requirements, linkage specificity, and kinetic mechanism of an q -2,3-sialyltransferase have been compared with an a-2,6-sialyltransferase from porcine submaxillary mucin.The former enzyme will specifically modify glycoproteins and glycolipids which contain 2-acetamido-2-deoxy-3-O S-D-galactosyl-D-galactose sequences. The only acceptor substrates reported for the a-2,6-sialyltransferase are those glycoproteins containing the structure (58). ... 

Sialyltransferases. In eukaryotic cells, addition of terminal sialic acid to glycoconjugates is carried out by specific enzymes called sialyltransferases (STs). STs catalyze the transfer of a sialic acid from the activated nucleotide sugar donor CMP-N-acelylneuraminic acid (CMP-NeuSAc) to the terminal nonreducing position of oligosaccharide chains either of glycoproteins or glycolipids. 

At present little detailed evidence is available for sialyltransferases specifically involved in membrane glycoprotein biosynthesis. It is probable that the membrane-bound sialyltransferase specificities described for glycoproteins (sections III. 3 and III.4) and glycolipids (section III. 5) will be similar, as the structures of membrane complex carbohydrates show the same features found in soluble molecules (e.g. Kobata 1979, Rauvala and Finne 1979, Montreuil 1980). Much indirect evidence has come from cell culture studies, frequently in studies on normal and transformed or malignant cells (Hughes 1976, Harmon 1978, Kottgen et al. 1979). 

The specific induction of de novo synthesis of sialyltransferase for glycolipid substrates by fatty acids has been studied in detail, and a hormonal regulation discussed by Fishman et al. (1976). Morphological changes in HeLa cells could be associated with the specific induction of LacCer sialyltransferase (IPNeu5AcLacCer formation), which was blocked by protein synthesis inhibitors. 

Glycolipids are potential receptors also for influenza viruses (Suzuki et al., 1986 Herrler and Klenk, 1987). As discussed above, glycoproteins may function as alternative receptors. Cells that are resistant to infection by influenza C virus because of a lack of receptors, have been shown to become susceptible to infection if they are resialylated with 9-0-acetylated sialic acid (Szepanski et al., 1992). As the a2,6-sialyltransferase used attaches sialic acid specifically to oligosaccharides present on glycoproteins, the virus obviously used glycoprotein receptors to infect these cells. The same approach has been applied to influenza A virus. In this case, cells were pretreated with sialidase to inactivate endoge-... 

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