Role of a sugar-lipid intermediate in colanic acid synthesis by Escherichia coli

Abstract

Membrane fractions from a lon strain of E. coli but not a wild-type strain catalyze the incorporation of fucose from GDP-fucose into a lipid and into polymeric material. Both incorporation reactions specifically require only UDP-glucose. The sugar lipid was an intermediate in the synthesis of the polymer which was related to colanic acid. The sugar lipid had the structure (fucose3, glucose2)-glucose P[phosphate]-P-lipid. Its behavior on TLC and column chromatography, the rates of its hydrolysis in acid and base, and the response of its synthesis to inhibitors are all identical to the other sugar-lipid intermediates which contain sugars attached to the C55-polyisoprenol, undecaprenol, by a pyrophosphate linkage. The membrane fractions from both the lon strain and the wild-type strain also catalyzed the incorporation of glucose from UDP-glucose or galactose from UDP-galactose into a lipid fraction which contained the free sugar attached by a monophosphate linkage to an undecaprenol-like lipid. This lipid was isolated and its NMR spectra was identical to undecaprenol. The membrane fractions from both strains also incorporated glucose from UDP-glucose into glycogen and into a polymer that behaved like E. coli lipopolysaccharide. Conditions were found where the incorporation of glucose could be directed specifically into each compound by adding the appropriate inhibitors.