Domains involved in allosteric regulation of ADP-glucose pyrophosphorylase

FIGUEROA CM; DEMONTE AM; BALLICORA MA; PREISS J; IGLESIAS AA

Pinamar

Congreso; X Congreso de la PABMB, XLI Reunión Anual de la SAIB y XX Reunión Anual de la SAN; 2005

SAIB

Previous studies in ADPGlcPPase from bacteria evidenced a region critical for activation in the N-term domain. Sequence alignment of ADPGlcPPases from different organisms showed that conserved residues located in loops positioned between regulator- and substrate-binding sites play a role in allosteric activation. Sitedirected mutants in these domains of the Escherichia coli and Agrobacterium tumefaciens enzymes were insensitive to allosteric effectors, fructose-1,6-bisP and fructose-6P, respectively. Interestingly, the A. tumefaciens mutants were still activated by pyruvate. To evaluate if this mechanism depends on the type of regulatory metabolite, two equivalent residues in the enzyme from Anabaena sp. PCC 7120 (activated by 3P-glycerate) were mutated. Mutants Q58A and W96A of the cyanobacteria enzyme were characterized. Results revealed that, while substrate kinetics were similar to those of the wild type, the mutant enzymes were unable to be activated by 3P-glycerate. Apparently, the activation of cyanobacterial ADPGlcPPase by this metabolite is similar to that exerted by hexose-P in other bacterial enzymes but different to the activation by pyruvate.