Biosynthesis of polysaccharides in Acetobacter xylinum. Sequential synthesis of a heptasaccharide diphosphate prenol

The sequential synthesis in vitro of a heptasaccharide diphosphate prenol, containing glucose, mannose, glucuronic acid and rhamnose in the ratio 4:1:1:1 is described. The enzyme preparation consisted of EDTA-treated Acetobacter xylinum cells and UDP-glucose, GDP-mannose, UDP-glucuronic acid and TDP-rhamnose were employed as sugar donors. The compounds soluble in chloroform/methanol/water (1:2:0.3) formed from incubations carried out under different conditions in the presence of a variety of combinations of the donors labeled with 14C, 3H or 32P were analysed by DEAE-cellulose column chromatography, gel filtration, partial acid hydrolysis, acetolysis, periodate oxidation, etc. The following structure is proposed for the most complex compound characterized: rhamnosyl-(1 leads to 6)-beta-glucosyl-(1 leads to 6)-alpha-glucosyl-(1 leads to 4)-beta-glucuronyl-(1 leads to 6)-beta-mannosyl-(1 leads to 3)-beta-glucosyl-(1 leads to 4)-alpha-glucosyl diphosphate prenol. The smaller oligosaccharide diphosphate prenols formed as intermediate steps are also characterized in this or in previous work [Garcia, R. C., Recondo, E. and Dankert, M. A. (1974) Eur. J. Biochem. 43, 93-105; Couso, R. O., Ielpi, L., and Dankert, M. A. (1980) Arch. Biochem. Biophys. 204, 434-443]. The role of these compounds in the biosynthesis of a complex exopolysaccharide that this microorganism forms in addition to cellulose is discussed.