Lipopolysaccharides chemical properties

KDO has chemical properties similar to those of neuraminic acid as it has a carboxylate group, a 3-deoxy group, and a similar biosynthesis (see Chapter 10). The monosaccharide composition, sequence, and linkages, along with the position of attachment of phosphate and ethanolamine pyrophosphate substituted onto the heptose residues of the core polysaccharide have been determined [53-58] and are shown in Fig. 9.16C. The fatty acids in the lipopolysaccharide participate in the formation of a lipid bilayer for the outer membrane. The carbohydrate is hydrophilic and is located on the outer faces of the lipid bilayer membrane. The O-antigen polysaccharides and other capsular polysaccharides are attached to position-4 of the next to last monosaccharide residue, a-D-glucopyranose of the core polysaccharide. 

In the last decades, structural details of lipopolysaccharides derived from selected bacterial serotypes have been elucidated, and it became possible to ascribe distinct biological properties to distinct domains of the macromolecule. As a consequence, a number of organic chemists have undertaken the chemical synthesis of biologically relevant partial structures of lipopolysaccharide. 

Aside from the expression of histidine mutations that are easily detected, other properties have been built into the Salmonella strains by mutation to increase their sensitivity. The strains cure defective in DNA excision repair (uvrB). In this case, the increased sensitivity probably is due to the failure to remove some DNA adducts that could lead to mutation. The strains also possess a mutation (rfa) that removes part of the lipopolysaccharide barrier of the bacterial cell wall and thereby makes the cells more permeable to some chemicals. Finally, Salmonella strains TA98 and TA100 contain the R-factor plasmid pkMIOl,277 which increases sensitivity probably by increasing the activity of an error-prone DNA-repair system. 

Amano, K.I., Williams, J.C., Dasch, G.A. Structural properties of lipopolysaccharides from Rickettsia typhi and Rickettsia prowazekii and their chemical similarity to the lipopolysac-charide from Proteus vulgaris 0X19 used in the Weil-Felix test. Infect Immun 66 (1998) 923-926. 

E.T. Westphal, O. Chemical, physicochemical and biological properties of bacterial lipopolysaccharides. In Biomedi- 47. cal Applications of the Horseshoe Crab (Limulidae) ... 

Purified endotoxin consists only of lipopolysaccharide. This itself has three distinct chemical regions an inner core called lipid A. an intermediate polysaccharide layer, and an outer polysaccharide side chain. Lipid A, a highly substituted disaccharide of gluct amiiie, is responsible for pyrogenicity and other immunological and biological properties associated with endotoxin. 

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