Lipid Salmonella core

Figure 3.23 A Provisional Scheme for the Biosynthesis of the Lipid A-core Region of Salmonella...

Figure 3.25 Biosynthesis of the 0-side Chain Polysaccharide in Salmonella anatum. At the inner face of the cytoplasmic membrane the nucleotide sugars are transferred in sequence to the C55 polyisoprenoid phosphate carrier lipid ( ). Following the transfer of the mannosylrhamnosyl-galactose trisaccharide-carrier lipid to the outer face of the membrane the trisaccharides polymerise forming the lipid-linked 0-antigen polymer, the polysaccharide portion of which is then passed to the lipid A core (A C). The liberated carrier lipid is then dephosphorylated and returned to the cytoplasmic face of the membrane.

In a very elegant study, Droge and coworkers26 investigated the structures of the LPS from four Salmonella minnesota R-mutants designated mR595, mR3, mR7, and mR5. These mutants synthesize LPS that contains only lipid A and the inner core oligosaccharides,... 

FIGURE 7-32 Bacterial lipopolysaccharides. (a) Schematic diagram of the lipopolysaccharide of the outer membrane of Salmonella ty-phimurium. Kdo is 3-deoxy-o-manno-octulosonic acid, previously called ketodeoxyoctonic acid Hep is L-glycero-D-mannoheptose AbeOAc is abequose (a 3,6-dideoxyhexose) acetylated on one of its hydroxyls. There are six fatty acids in the lipid A portion of the molecule. Different bacterial species have subtly different lipopolysaccharide structures, but they have in common a lipid region (lipid A), a core oligosaccharide, and an "O-specific" chain, which is the prin-... 

Figure 1 represents the general structure of Salmonella lipopolysaccharides. They contain an external polysaccharide, the O-antigenic chain, and an innermost component, termed lipid A. O-chain and lipid A are linked to each other by an oligosaccharide referred to as the core. O-Specific Chains. As indicated in Figure 1, O chains are in general made up of repeating units of di-, tri-, or higher oligosaccharides. In rare cases the O-chain is a homopolysaccharide. The structure of the O-chain is unique to each bacterial serotype great diversity is encountered in the structures of O-chains.

Figure 2. Specific immunoabsorbents for Salmonella O and R form antibodies. Key PS, O-specific polysaccharide, core, core fragment and GlcNHr glucosamine and fatty acids. Specific immunoabsorbents for lipid A antibodies have also been prepared (C. Galanos and D. Nerkar, unpublished results Luderitz et a ., 1982).

Following the identification of KDO as a constituent of LPS, studies by Osborn and her group ( 5) have revealed that, in LPS, KDO (or the KDO region ) is located at the reducing end of the polysaccharide chain, linking the core segment to lipid A. Later, the application of differential color reactions based on thiobarbituric acid (TBA tests) (6, 7) has led to the view that KDO is present, in LPS from Salmonella or E. coli, in the form of a branched trisaccharide (Fig. 1). In this model, a branchpoint KDO residue (KDO I), ketosidically-linked to the second glucosaminyl residue of lipid A, is substituted in position 4 or 5 by a... 

Figure 1. A schematic diagram illustrating a basic lipopolysaccharide molecule from Salmonella typhimurium with the polysaccharide and lipid regions. Also shown are core polysaccharide mutants (Ra through Re).

Lipopolysaccharides are considered to be composed of three segments, lipid A, the core polysaccharide and the antigenic side chains. The core polysaccharide, in turn, has an inner region (which is linked to lipid A) called the backbone sequence and an outer core to which the antigen chains are attached. The lipopolysaccharides of Salmonella typhimurium are the best known and they will be used here as examples. 

In Salmonella spp. the core region of lipopolysaccharide has quite a complex structure and forms a well-defined domain this is not so in some other genera, where the core is either considerably simpler, or effectively absent, so that the polysaccharide antigen is attached more or less directly to lipid A. 

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