The unique nucleotide specificity of the sucrose synthase from Thermosynechococcus elongatus

Sucrose synthase catalyzes the reversible conversion of sucrose and UDP into fructose and UDP-glucose. In filamentous cyanobacteria, the sucrose cleavage direction plays a key physiological function in carbon metabolism, nitrogen fixation, and stress tolerance. In unicellular strains, the function of sucrose synthase has not been elucidated. We report a detailed biochemical characterization of sucrose synthase from Thermosynechococcus elongatus after the gene was artificially synthesized for optimal expression in Escherichia coli. The homogeneous recombinant sucrose synthase was highly specific for ADP as substrate, constituting the first one with this unique characteristic, and strongly suggesting an interaction between sucrose and glycogen metabolism.

► Artificial gene synthesis with optimized codons for expression of sucrose synthase. ► The enzyme was specific for ADP/ADP-Glc rather than UDP/UDP-Glc. ► Activity of the recombinant enzyme was higher at temperatures of 60–70 °C. ► Homology modeling showed striking differences in ADP and UDP binding. ► Results suggest a strong interaction between sucrose and glycogen metabolisms.