Biosynthesis of Lipid-linked Oligosaccharides in Rhizobium-leguminosarum

As a first step in the study of the biosynthesis of Rhizobium leguminosarum 8401 exopolysaccharides (EPS) the formation of lipid-linked derivatives that could act as intermediate carriers has been investigated. UDP-GlcA and UDP-Glc, either [C-14]labeled or not, were used as sugar precursors and EDTA-treated calls as enzyme system. This preparation contains also endogenous donors and lipidic acceptors.Seven lipid-linked sugars were isolated and partially characterized in chloroform/methanol/water (1:2:0.3) extracts, as judged by paper chromatography and electrophoresis, DEAE-cellulose ion exchange chromatography and gel filtration. The structure proposed for the repeat unit of the EPS under study is(Lamb et al., 1982, Mol. Gen. Genet. 186, 449-452):[GRAPHICS]The results obtained suggest that the octasaccharide repeat unit (compound A) with one (compound B) or two (compound C) ketal pyruvate residues are assembled on a lipid acceptor. In addition, a lipid-linked tri-saccharide GlcA-->(beta)4GlcA-->(beta)4Glc (compound D-1) and its acetylated derivative (compoundD(2)) were also detected. A sixth compound, containing only glucose-linked lipid, could be the first step in. the assembly of the repeat unit. All these compounds are assumed to be intermediates in the biosynthesis of the 8401 EPS. The seventh lipid-linked compound contained only GlcA. These studies anal characterizations have been performed in comparison. to a Rhizobium leguminosarum bv. trifolii NA-30 system that produces similar lipid-linked derivatives, anal an EPS with the same structure (J. C. Bossio et al., 1986, Biochem. Biophys. Res. Commun. 134, 205-211).