Properties of carbohydrate-free recombinant glycogenin expressed in an Escherichia coli mutant lacking UDP-glucose pyrophosphorylase activity

AbstractGlycogenin, the self-glucosylating primer for glycogen synthesis is expressed in wild-type E. coli as a recombinant protein in an already partly glucosylated form owing to the presence of its substrate UDP-glucose. By using an E. coli mutant strain lacking in UDP-glucose pyrophosphorylase activity, we have succeeded in expressing carbohydrate-free glycogenin (apo-glycogenin) in good yield. When provided with UDPxy-lose, it autocatalytically adds 1 xylose residue. With UDP-glucose, an average of 8 glucose residues are added. However release of the self-synthesized maltosaccharide chains with isoamylase reveals them to be a mixture. Chains as long as 11 glucose residues (maltoundecaose) are present. The ability of recombinant apo-glycogenin to self-glucosylate is further proof that a separate enzyme is not needed for the addition of the first glucose residue to Tyr-194 of the protein