Indirubin-3-Aminooxy-Acetate Inhibits Glycogen Phosphorylase by Binding at the Inhibitor and the Allosteric Site. Broad Specificities of the Two Sites
Magda N. Kosmopoulou,
Demetres D. Leonidas,
Evangelia D. Chrysina,
Nikos G. Oikonomakos.
The binding of the indirubin analogue indirubin-3-aminooxy-acetate (E243) to glycogen phosphorylase (GP) has been studied by kinetic and crystallographic experiments. E243 was shown to be a competitive inhibitor of GPb with respect to both Glc-1-P and AMP (Ki values of 21 ± 7 μM and 16 ± 3 μM, respectively). The crystal structure of the GPb-E243 complex determined at 1.9 Å resolution showed one ligand molecule bound at the inhibitor site, mainly by intercalating between the two aromatic side chains of Phe285 and Tyr613. In addition, two E243 molecules, Mol 1 and Mol 2, were bound at the allosteric activator AMP binding site and a new sub-site in the vicinity of the allosteric site, respectively, with their indole-aminooxyacetate rings inclined approximately 40°. The binding mode of E243 to GPb inhibitor and allosteric site is different from those of flavopiridol, AMP, Glc-6-P, W1807, and a potent phenoxy-phthalate compound, previously described, illustrating how the enzyme can accommodate a number of diverse chemical entities.
Keywords: type diabetes, glycogen phosphorylase, indirubin-aminooxy-acetate, inhibition, x-ray crystallography
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