3ebo
Glycogen Phosphorylase b/Chrysin complex
Structural highlights
FunctionPYGM_RABIT Phosphorylase is an important allosteric enzyme in carbohydrate metabolism. Enzymes from different sources differ in their regulatory mechanisms and in their natural substrates. However, all known phosphorylases share catalytic and structural properties. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedFlavonoids have been discovered as novel inhibitors of glycogen phosphorylase (GP), a target to control hyperglycemia in type 2 diabetes. To elucidate the mechanism of inhibition, we have determined the crystal structure of the GPb-chrysin complex at 1.9A resolution. Chrysin is accommodated at the inhibitor site intercalating between the aromatic side chains of Phe285 and Tyr613 through pi-stacking interactions. Chrysin binds to GPb approximately 15 times weaker (K(i)=19.01muM) than flavopiridol (K(i)=1.24muM), exclusively at the inhibitor site, and both inhibitors display similar behavior with respect to AMP. To identify the source of flavopiridols' stronger affinity, molecular docking with Glide and postdocking binding free energy calculations using QM/MM-PBSA have been performed and compared. Whereas docking failed to correctly rank inhibitor binding conformations, the QM/MM-PBSA method employing M06-2X/6-31+G(*) to model the pi-stacking interactions correctly reproduced the experimental results. Flavopiridols' greater binding affinity is sourced to favorable interactions of the cationic 4-hydroxypiperidin-1-yl substituent with GPb, with desolvation effects limited by the substituent conformation adopted in the crystallographic complex. Further successful predictions using QM/MM-PBSA for the flavonoid quercetagetin (which binds at the allosteric site) leads us to propose the methodology as a useful and inexpensive tool to predict flavonoid binding. Sourcing the affinity of flavonoids for the glycogen phosphorylase inhibitor site via crystallography, kinetics and QM/MM-PBSA binding studies: Comparison of chrysin and flavopiridol.,Tsitsanou KE, Hayes JM, Keramioti M, Mamais M, Oikonomakos NG, Kato A, Leonidas DD, Zographos SE Food Chem Toxicol. 2012 Dec 29. pii: S0278-6915(12)00903-9. doi:, 10.1016/j.fct.2012.12.030. PMID:23279842[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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