Production of highly phosphorylated glycopolymers by expression of R1 in Escherichia coli

The possible involvement of the starch bound R1 protein from potato (Solanum tuberosum L.) in the phosphorylation of starch was investigated by functional expression and characterisation of R1 in Escherichia coli. By expression of R1 in E. coli it is shown that it is possible to produce glycopolymers, e.g., glycogen, with an increased degree of phosphate substitution. The expression of R1 in E. coli resulted in a sixfold increase in glycogen bound phosphate and in an increased accumulation of glycogen leading to a glycogen excess (gex) phenotype. There was an overall shift in the unit-chain length of the isolated glycogen towards smaller degrees of polymerisation. The pleiotropic effects on the glycogen biosynthetic and amylolytic enzyme activities was investigated and showed an increase in ADPglucose pyrophosphorylase activity, as well as a decrease in exo-amylolytic activity. These results are discussed in relation to starch phosphorylation and a possible role of R1 in this respect.