ABSTRACT

Glycosylation of proteins was considered to be specic to eukaryotes around the mid-1990s. However, recent progress has revealed that glycoproteins are present in prokaryotes as well (Erickson and Herzberg 1993, Young et al. 2002), although bacterial sugar chains differ structurally from the eukaryotic counterparts (Wacker et al. 2002). Furthermore, evidence is provided that protein glycosylation pathways similar to those in eukaryotes exist in Gram-negative bacteria, and many bacterial glycosyltransferases have also been reported (Wacker et  al. 2002, Yamamoto 2006). In case of Gram-negative

14.1 Introduction ................................................................................................................................................................... 195 14.2 Sias: Structure and biological roles of sialylated sugar chains .............................................................................. 196

14.2.1 Structure of Sias ................................................................................................................................................ 196 14.2.2 Examples of the relationship between sugar chains and diseases ............................................................ 197

14.2.2.1 Inuenza .............................................................................................................................................. 197 14.2.2.2 Guillain-Barré syndrome ................................................................................................................. 197

14.3 Major methods for preparing sugar chains .............................................................................................................. 197 14.3.1 Chemical synthesis ........................................................................................................................................... 198 14.3.2 Enzymatic synthesis ......................................................................................................................................... 198 14.3.3 Fermentation method ....................................................................................................................................... 198

14.4 Sialyltransferases from marine environment ........................................................................................................... 199 14.4.1 Screening bacteria for sialyltransferases by measuring enzyme activity ................................................ 199 14.4.2 Screening bacteria for sialyltransferases by lectin staining ....................................................................... 200

14.5 Enzymatic characterization of marine bacterial sialyltransferases ....................................................................... 200 14.5.1 An α2,6-sialyltransferase produced by Photobacterium damselae JT0160 ............................................... 200 14.5.2 An α2,3-sialyltransferase produced by Photobacterium phosphoreum JT-ISH-467 ............................... 201

14.6 Sialyloligosaccharides as a drug candidate for disease .......................................................................................... 202 14.7 Summary ........................................................................................................................................................................ 202 References ................................................................................................................................................................................ 203

bacteria, it has been revealed that glycoconjugates, such as lipooligosaccharides (LOS), lipopolysaccharides, and glycoproteins, are present on their surface (Wakarchuk et al. 1998, Muldon et al. 2002). In particular, the sugar chain structures of glycoconjugates in human pathogens have well been studied. It has been demonstrated that some pathogenic bacteria have evolved to escape immune systems of hosts by mimicking surface sugar chains of the host cells, which are crucial for self/nonself recognition and that the glycoconjugates of the pathogens are involved in the virulence and adhesion to the host cells (Guerry et al. 2002).