The ancestral activation promiscuity of ADP-glucose pyrophosphorylase from oxygenic photosynthetic organisms

KUHN ML; FIGUEROA CM; IGLESIAS AA; BALLICORA MA

Minneapolis

Congreso; Plant Biology 2011; 2011

American Society of Plant Biologists

ADP-glucose pyrophosphorylase (ADPGlcPPase) catalyzes the first committed step in the synthesis of glycogen and starch in bacteria and plants, respectively. In oxygenic photosynthetic organisms, ADPGlcPPase is mainly regulated by 3PGA (activator) and Pi (inhibitor). In this work, we analyzed the activation promiscuity of ADPGlcPPases from Anabaena, Ostreococcus tauri (OtaS/OtaL) and potato tuber (StuS/StuL) by determining the Activation/A0.5 ratios for 3PGA, Fru1,6bisP, Fru6P and Glc6P. As expected, 3PGA ratios for the Anabaena, OtaS/OtaL and StuS/StuL enzymes (73.3, 60.7 and 1259, respectively) where significantly higher than those calculated for other activators. Conversely, the OtaS homotetramer showed a ratio for Fru-1,6-bisP (8.5) similar to that for 3PGA (8.9). To further explore the role of OtaS and OtaL on determining the specificity of the heterotetramer, we alternatively knocked the activity of both subunits by constructing the mutants OtaSD149A/OtaL and OtaS/OtaLD171A. Interestingly, both mutants presented higher ratios for 3PGA than for Fru1,6bisP (2527 and 153 compared with 0.61 and 3.9, respectively). Our results suggest that promiscuity toward different activators was already present in the common ancestor. Though, after gene duplication, both subunits adopted different activation properties: OtaS lost specificity for 3PGA and gained specificity for Fru-1,6-bisP, whereas the opposite occurred in OtaL. However, when both subunits are co-expressed, the resulting heterotetramer (i.e. the wild type enzyme) recovers the specificity for 3PGA. This could constitute an efficient evolutionary mechanism to differentially accommodate ADPGlcPPase regulation to the metabolic scenario operating in different organisms.