Structure elucidation and gene cluster annotation of the O-antigen of Escherichia coli O39; application of anhydrous trifluoroacetic acid for selective cleavage of glycosidic linkages

Abstract

O-Polysaccharide (O-antigen) accompanied by a minor mannan was isolated from the lipopolysaccharide of Escherichia coli O39 and studied by component analyses, methylation, Smith degradation, mass spectrometry, and 1D and 2D NMR spectroscopy. In addition, a new approach, solvolysis with anhydrous trifluoroacetic acid, was applied to cleave selectively the rhamnosidic linkage. The following structure of the O-polysaccharide was established: [Display omitted] where d-Qui4N(R3Hb) indicates 4,6-dideoxy-4-[(R)-3-hydroxybutanoylamino]-d-glucose. The O-antigen gene cluster of E. coli O39 has been sequenced. The gene functions were tentatively assigned by a comparison with sequences in the available databases and found to be in agreement with the O-polysaccharide structure.