Abstract
The membrane-derived oligosaccharides of Escherichia coli constitute a closely related family of oligosaccharides containing approximately 9 glucose units variously substituted with sn-glycero-1-phosphate and phosphoethanolamine residues derived from the head groups of membrane phospholipids, and also with succinate in O-ester linkage (Kennedy, E.P., Rumley, M.K., Schulman, H., and van Golder, L.M.G. (1976) J. Biol. Chem. 251, 4208-4213). Studies with mutant strains defective in the synthesis of various nucleoside diphosphate sugars have now revealed that UDP-glucose is an essential intermediate in the biosynthesis of these oligosaccharides. Mutants unable to synthesize UDP-glucose do not contain significant amounts of the membrane-derived oligosaccharides. In contrast, a strain unable to synthesize ADP-glucose, the glucosyl donor for glycogen synthesis in E. coli, contained normal amounts of the membrane-derived oligosaccharides, although with a somewhat different pattern of distribution of the various subspecies. In confirmation of these genetic studies, pulse-label isotope tracer studies have been carried out with glucose of high specific activity, under conditions in which UDP-glucose comprises a large fraction of the total radioactivity in the low molecular weight pool. Subsequent "chase" experiments clearly revealed the conversion of UDP-glucose to the higher molecular weight membrane-derived oligosaccharides.
Highlights
Studies with mutant strains defective in the synthesis of various nucleoside diphosphate sugars have revealed that UDP-glucose is an essential intermediate in the biosynthesis of these oligosaccharides
In the synthesis of polysaccharides localized in the membrane or in extracellular compartments, biosynthesis often proceeds with transfer of glycosyl units from the nucleoside diphosphate sugar to a lipid intermediate, from which in turn they are transferred to the growing polysaccharide chain
Synthesis of Membrane-derived Oligosaccharides in Mutant Strains of Escherichia coli - Previous work has established that the membrane-derived oligosaccharides comprise virtually all of the anthrone-reactive material extracted from cells with 50% ethanol, and of intermediate molecular weight, migrating near the void volume during chromatography on Sephadex G-25 [1, 14]
Summary
Studies with mutant strains defective in the synthesis of various nucleoside diphosphate sugars have revealed that UDP-glucose is an essential intermediate in the biosynthesis of these oligosaccharides. A strain unable to synthesize ADP-glucose, the glucosyl donor for glycogen synthesis in E. coli, contained normal amounts of the membrane-derived oligosaccharides, with a somewhat different pattern of distribution of the various subspecies. In confirmation of these genetic studies, pulse-label isotope tracer studies have been carried out with glucose of high specific activity, under conditions in which UDP-glucase comprises a large fraction of the total radioactivity in the low molecular weight pool. Scheme 1, based on reviews of Ginsburg [3] and Nikaido These include three forms of activated glucose: TDP-glucose, ADP-glucose, and UDP-glucose.
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