Shigella Lipopolysaccharide: Structure, Genetics, and Vaccine Development

Abstract

Lipopolysaccharide (LPS) is a compound macromolecule anchored in the outer leaflet of the outer membrane of Gram-negative bacteria (Fig. 1) and extending out from the cell into the external medium (for detailed reviews see Jann and Jann 1984; MaKELa and Stocker 1984). It is a major structural component of the cell surface, and it has been calculated that there are about 2.5 × 106 molecules per cell in Salmonella typhimurium, occupying some 45% of the surface of the outer membrane (Inouye 1979). Each LPS molecule is composed of three distinct structural segments, namely the innermost hydrophobic lipid A moiety, which constitutes the main lipid component of the outer leaflet of the asymmetrical outer membrane; the outermost O-specific polysaccharide (also called the O-antigen or somatic antigen), which consists of a short orlong linear polymer of an oligosaccharide repeat unit; and the core oligosaccharide, which links the O-antigen to the lipid A. LPS molecules interact structurally and functionally with a number of other cell surface components, including several outer membrane proteins (LUGTENBREG and van Alphen 1983; Nikaido and Vaara 1985).