Sialic acids functions

In addition to binding to sialic acid residues of the carbohydrate side chains of cellular proteins that the virus exploits as receptors, hemagglutinin has a second function in the infection of host cells. Viruses, bound to the plasma membrane via their membrane receptors, are taken into the cells by endocytosis. Proton pumps in the membrane of endocytic vesicles that now contain the bound viruses cause an accumulation of protons and a consequent lowering of the pH inside the vesicles. The acidic pH (below pH 6) allows hemagglutinin to fulfill its second role, namely, to act as a membrane fusogen by inducing the fusion of the viral envelope membrane with the membrane of the endosome. This expels the viral RNA into the cytoplasm, where it can begin to replicate. 

Pyruvate-dependent lyases serve catabolic functions in vivo in the degradation of sialic acids and KDO (2-keto-3-deoxy-manno-octosonate), and in that of 2-keto-3-deoxy aldonic acid intermediates from hexose or pentose catabolism. 

Corfleld AP, Schauer R (1982) Metabolism of sialic acids. In Schauer R (ed) Sialic acids - Chemistry, metabolism and function. Springer, Wien, pp 195-261 Corfleld AP, Higa H, Paulson JC, Schauer R (1983) The specificity of viral and bacterial sial-idases for alpha(2-3)- and alpha(2-6)-linked sialic acids in glycoproteins. Biochim Biophys Acta 744 121-126... 

Rye CS, Withers SG (2000) Glycosidase mechanisms, CurrOpin Chem Biol 4 573-580 Saito M, Yu RK (1995) Biochemistry and function of sialidases. In Rosenberg A (ed) Biology of the sialic acids. Plenum, NY, pp 261-313... 

Accordingly, they generally contain either N- or O-hnked oligosaccharide chains, or both (Chapter 47). Albumin is the major exception it does not contain sugar residues. The ohgosaccharide chains have various functions (Table 47-2). Removal of terminal sialic acid... 

In 1991, Li and Chan reported the use of indium to mediate Barbier-Grignard-type reactions in water (Eq. 8.49).108 When the allylation was mediated by indium in water, the reaction went smoothly at room temperature without any promoter, whereas the use of zinc and tin usually requires acid catalysis, heat, or sonication. The mildness of the reaction conditions makes it possible to use the indium method to allylate a methyl ketone in the presence of an acid-sensitive acetal functional group (Eq. 8.50). Furthermore, the coupling of ethyl 2-(bromomethyl)acrylate with carbonyl compounds proceeds equally well under the same reaction conditions, giving ready access to various hydroxyl acids including, for example, sialic acids. 

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