The immunochemistry of Shigella flexneri O-antigens. The biochemical basis of smooth to rough mutation

摘要

p1. Smooth to rough mutation has the same biochemical basis in iShigella/i as in iSalmonella/i. It is the result of enzyme defects blocking the incorporation of the O-specific side chains that characterize the smooth lipopolysaccharide with the consequent exposure of the underlying basal structures that determine ‘rough’-specificity. 2. The iShigella flexneri/i basal structure resembles its iSalmonella/i analogue in that it has the same qualitative sugar composition, and enzyme defects in its biosynthetic pathway give rise to ‘rough’-lipopolysaccharides that are indistinguishable from those of iSalmonella/i chemotypes Ra, Rb, Rc and Rd. However, the iSalmonella/i and iShigella/i basal structures are not identical as judged by quantitative analysis and the absence of serological cross-reaction. 3. The iSh. flexneri/i basal structure side chain has been isolated and characterized as an α-iN/i-acetylglucosaminyl-(1→4)-galactosyl-(1→3)-glucose sequence with α-glucosyl radicals substituted on the 3- and 4-positions of the galactose and glucose respectively. The different sugar types in this side chain are incorporated into the growing molecule in the same order as in iSalmonella/i, which explains why the enzyme defects associated with smooth to rough mutation produce the same series of R-chemotypes from both genera. The terminal α-glucosyl and α-iN/i-acetylglucosaminyl-(1→4)-galactosyl residues of the iSh. flexneri/i basal structure are sufficiently different from the terminal α-galactosyl and α-iN/i-acetylglucosaminylglucosyl residues of the iSalmonella/i analogue that they offer an explanation for the absence of serological cross-reaction between these two basal structures./p