Selectivity for Allosteric Effectors of Bacterial ADP-Glucose Pyrophosphorylase: Structural and Functional Studies

The biosynthesis of the intracellular polysaccharide in bacteria and plants, glycogen and starch, respectively, controlled by the key regulatory step that catalyzed by ADP-Glucose Pyrophosphorylase (ADP-Glc PPase). ADP-Glc PPase is an allosteric enzyme regulated by metabolites produced of the principle carbon assimilation pathway in each organism. Agrobacterium tumefaciens enzyme activated by fructose 6-phosphate (Fru6P) and pyruvate, whereas Escherichia coli enzyme activated by fructose 1,6-bisphosphate (FBP), and both enzymes inhibited by AMP. Here, we targeted the allosteric regulation of the A. tumefaciens enzyme, examined some residues that may impact the regulation mechanism (Ser72, His71, Arg75, Ser351, Ser334, Arg368, Asn350, and Asp291), and locate the binding site for the Fru6P and AMP. in addition, studies on the enzyme-ligand interaction and how does the evolution of the enzyme alter the specificity toward different modulators in A. tumefaciens and E. coli. Our results identified the allosteric binding site and determined the residues involved in the interaction with the ligands. Other efficient effectors of the enzyme have been found and solved crystal structures with some of these effectors. Moreover, a second inhibitor binding site has been found for the A. tumefaciens ADP-Glc PPase enzyme and a high sensitivity to another inhibitor (GMP) has been reported. Ser72, His71, and Arg75 are involved in the Fru6P and AMP binding site, and Ser351, Ser334, Arg368, Asn350, and Asp291 bond to the inhibitor in the second binding site