Structure of the Hexose Region of Shigella sonnei Phase II Lipopolysaccharide with 3-Deoxy-d-manno-octulosonic Acid as Possible Immunodeterminant and Its Relation to Escherichia coli R1 Core

Comparative chemical analysis (methylation, gas chromatography/mass spectrometry, periodate oxidation, etc.) of the lipopolysaccharides and degraded polysaccharides derived from Shigella sonnei phase I, phase II and galactose-deficient R mutants revealed a structure as shown: (formula: see text) 3-Deoxy-D-manno-octulosonic acid (dOclA) as an immunodeterminant was observed in the passive hemolysis inhibition test by (a) selective inhibition of the phase II system by dOclA; (b) the kinetics of the change of serological activity during mild acid treatment: 1% acetic acid abolished serological activity; (c) a lack of activity in galactose-less R mutants and reactivity with Re mutants including Salmonella minnesota Re. An enhanced sensitivity of phase II lipopolysaccharide to galactose oxidase after prolonged treatment with 1% acetic acid suggests that dOclA is linked to C-6 of the terminal or subterminal galactose. dOclA as immunodeterminant could explain some different polysaccharide structures described for Escherichia coli R1 core.