Structure function analysis of ADP-dependent cyanobacterial phosphofructokinase reveals new phylogenetic grouping in the PFK-A family.

Depending on the light conditions, photosynthetic organisms switch between carbohydrate synthesis or breakdown, for which the reversibility of carbohydrate metabolism, including glycolysis, is essential. Kinetic regulation of phosphofructokinase (PFK), a key-control point in glycolysis, was studied in the cyanobacterium Synechocystis sp. PCC 6803. The two PFK iso-enzymes (PFK- A1, PFK-A2), were found to use ADP instead of ATP, and have similar kinetic characteristics, but differ in their allosteric regulation. PFK-A1 is inhibited by 3-phosphoglycerate, a product of the Calvin-Benson-Bassham cycle, while PFK-A2 is inhibited by ATP, which is provided by photosynthesis. This regulation enables cyanobacteria to switch PFK off in light, and on in darkness. ADP dependence has not been reported before for the PFK-A enzyme family and was thought to be restricted to the PFK-B ribokinase superfamily. Phosphate donor specificity within the PFK-A family could be related to specific binding motifs in ATP-, ADP-, and PPi-dependent PFK-As. Phylogenetic analysis revealed a distribution of ADP-PFK-As in cyanobacteria and in a few alphaproteobacteria, which was confirmed in enzymatic studies.