Glycosyltransferases In Nature Structure Of The Bacterial Lipopolysaccharides

Bacterial cells express an enormous variety of polysaccharide structures. Usually found protruding from the outer membrane, these entities include exopolysaccharide (EPS), lipopolysaccharide (LPS), and lipo-oligosaccharide (LOS). EPS can be found in both gram-positive and gram-negative cells and is made of repeating polysaccha-ride units. Membrane-attached EPS forms the cell capsule. However, it can also be released into the surrounding medium as slime. LPS is composed of lipid A, core polysaccharide, and O-antigen, whereas LOS is a variation of LPS that lacks the repeating units of the O-antigen. In some gram-negative cells (e.g., E. coli and Salmonella typhimurium), the outer leaflet of the outer membrane can be composed almost exclusively of lipid A molecules. Lipid A in E. coli [22,23], Salmonella typhimurium [24,25], and Neisseria meningitidis [26] consists of two ^,1-6-linked 2,3-diacylglucosamine units. The fatty acid chains attached to the 2- and 3-positions are generally 2-6 carbons shorter than their counterparts in glycerophospholipids. In addition, the 2,3-diacyl chains contain an R-3-hydroxyl substituent. The R3-hy-droxyls of the nonreducing sugar are esterified with laurate and myristate fatty acids. The structure is phosphorylated at the 1- and 4'-positions. The core polysaccharide is attached at the 6'-position of lipid A. The inner core consists of a KDO (3-deoxy-d-manno-octulosonic acid) region and a heptose (Hep) region (Fig. 2). The number of residues varies between species.

Figure 2 Schematic representation of the LOS structure of N. meningitidis and N. gonorrhoeae. Variations in the largest a chain are responsible for most of the immunogenic properties of the LOS. Abbreviations: KDO, 3-deoxy-D-manno-2-octulosonic acid; Hep, L-glycero-D-manno-heptose; Glc, glucose; GlcNAc, N-acetylglucosamine; PEA, phosphoethanolamine. Note: Cu indicates an additional 11 carbon atoms, not the total chain length.

Figure 2 Schematic representation of the LOS structure of N. meningitidis and N. gonorrhoeae. Variations in the largest a chain are responsible for most of the immunogenic properties of the LOS. Abbreviations: KDO, 3-deoxy-D-manno-2-octulosonic acid; Hep, L-glycero-D-manno-heptose; Glc, glucose; GlcNAc, N-acetylglucosamine; PEA, phosphoethanolamine. Note: Cu indicates an additional 11 carbon atoms, not the total chain length.

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