Mutagenesis of an amino acid residue in the activator-binding site of cyanobacterial ADP-glucose pyrophosphorylase causes alteration in activator specificity.

The specificity for activator of ADP-glucose pyrophosphorylase is closely related to the corresponding major carbon-assimilation pathway. The enzyme from Escherichia coli is mainly activated by fructose-1,6-P2, while the cyanobacterial, algal, and higher-plant enzymes are activated by 3-P-glycerate. Previous results have shown that Lys39 of the E. coli enzyme is involved in the binding of fructose-1,6-P2 while for the Anabaena enzyme, lysine residues 382 and 419 have been shown to be involved in the binding of 3-phosphoglycerate. This report shows that if Lys419 of the Anabaena enzyme is changed to glutamine, activation of the cyanobacterial enzyme by fructose-1,6-P2 becomes more effective than that of 3-P-glycerate at lower concentrations. Kinetic studies show that fructose-1,6-P2 competitively inhibits 3-P-glycerate activation of the Anabaena wild-type enzyme, suggesting that these two compounds bind to the same site. Thus a change of one amino acid at the activator binding domain can affect the specificity of activation of the Anabaena ADP-glucose pyrophosphorylase.