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4-Phenyl-N-(β-D-glucopyranosyl)-1H-1,2,3-triazole-1-acetamide (glucosyltriazolylacetamide) has been studied in kinetic and crystallographic experiments with glycogen phosphorylase b (GPb), in an effort to utilize its potential as a lead for the design of potent antihyperglycaemic agents. Docking and molecular dynamics (MD) calculations have been used to monitor more closely the binding modes in operation and compare the results with experiment. Kinetic experiments in the direction of glycogen synthesis showed that glucosyltriazolylacetamide is a better inhibitor (Ki = 0.18 mM) than the parent compound α-D-glucose (Ki = 1.7 mM) or β-D-glucose (Ki = 7.4 mM) but less potent inhibitor than the lead compound N-acetyl-β-D-glucopyranosylamine (Ki = 32 μM). To elucidate the molecular basis underlying the inhibition of the newly identified compound, we determined the structure of GPb in complex with glucosyltriazolylacetamide at 100 K to 1.88 Å resolution, and the structure of the compound in the free form. Glucosyltriazolylacetamide is accommodated in the catalytic site of the enzyme and the glucopyranose interacts in a manner similar to that observed in the GPb-α-D-glucose complex, while the substituent group in the β-posi tion of the C1 atom makes additional hydrogen bonding and van der Waals interactions to the protein. A bifurcated donor type hydrogen bonding involving O3H, N3, and N4 is seen as an important structural motif strengthening the binding of glucosyltriazolylacetamide with GP which necessitated change in the torsion about C8-N2 bond by about 62° going from its free to the complex form with GPb. On binding to GP, glucosyltriazolylacetamide induces significant conformational changes in the vicinity of this site. Specifically, the 280s loop (residues 282-288) shifts 0.7 to 3.1 Å (CA atoms) to accommodate glucosyltriazolylacetamide. These conformational changes do not lead to increased contacts between the inhibitor and the protein that would improve ligand binding compared with the lead compound. In the molecular modeling calculations, the GOLD docking runs with and without the crystallographic ordered cavity waters using the GoldScore scoring function, and without cavity waters using the ChemScore scoring function successfully reproduced the crystallographic binding conformation. However, the GLIDE docking calculations both with (GLIDE XP) and without (GLIDE SP and XP) the cavity water molecules were, impressively, further able to accurately reproduce the finer details of the GPb-glucosyltriazolylacetamide complex structure. The importance of cavity waters in flexible receptor MD calculations compared to "rigid" (docking) is analyzed and highlighted, while in the MD itself very little conformational flexibility of the glucosyltriazolylacetamide ligand was observed over the time scale of the simulations. © 2007 Wiley-Liss, Inc. 71 3 1307 1323 Cited By :27

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Human coilin interacting nuclear ATPase protein (hCINAP) directly interacts with coilin, a marker protein of Cajal Bodies (CBs), nuclear organelles involved in the maturation of small nuclear ribonucleoproteins UsnRNPs and snoRNPs. hCINAP has previously been designated as an adenylate kinase (AK6), but is very atypical as it exhibits unusually broad substrate specificity, structural features characteristic of ATPase/GTPase proteins (Walker motifs A and B) and also intrinsic ATPase activity. Despite its intriguing structure, unique properties and cellular localization, the enzymatic mechanism and biological function of hCINAP have remained poorly characterized. Here, we offer the first high-resolution structure of hCINAP in complex with the substrate ADP (and dADP), the structure of hCINAP with a sulfate ion bound at the AMP binding site, and the structure of the ternary complex hCINAP-Mg(2+) ADP-Pi. Induced fit docking calculations are used to predict the structure of the hCINAP-Mg(2+) ATP-AMP ternary complex. Structural analysis suggested a functional role for His79 in the Walker B motif. Kinetic analysis of mutant hCINAP-H79G indicates that His79 affects both AK and ATPase catalytic efficiency and induces homodimer formation. Finally, we show that in vivo expression of hCINAP-H79G in human cells is toxic and drastically deregulates the number and appearance of CBs in the cell nucleus. Our findings suggest that hCINAP may not simply regulate nucleotide homeostasis, but may have broader functionality, including control of CB assembly and disassembly in the nucleus of human cells.

With an aim toward glycogenolysis control in Type 2 diabetes, we have investigated via kinetic experiments and computation the potential of indirubin (IC 50 > 50 μM), indirubin-3'-oxime (IC 50 = 144 nM), KT5720 (K i = 18.4 nM) and staurosporine (K i = 0.37 nM) as phosphorylase kinase (PhKγtrnc) ATP-binding site inhibitors, with the latter two revealed as potent inhibitors in the low nM range. Because of lack of structural information, we have exploited information from homologous kinase complexes to direct in silico calculations (docking, molecular dynamics, and MM-GBSA) to predict the binding characteristics of the four ligands. All inhibitors are predicted to bind in the same active site area as the ATP adenine ring, with binding dominated by hinge region hydrogen bonds to Asp104:O and Met106:O (all four ligands) and also Met106:NH (for the indirubins). The PhKγtrnc-staurosporine complex has the greatest number of receptor-ligand hydrogen bonds, while for the indirubin-3'-oxime and KT5720 complexes there is an important network of interchanging water molecules bridging inhibitor-enzyme contacts. The MM-GBSA results revealed the source of staurosporine's low nM potency to be favorable electrostatic interactions, while KT5720 has strong van der Waals contributions. KT5720 interacts with the greatest number of protein residues either by direct or 1-water bridged hydrogen bond interactions, and the potential for more selective PhK inhibition based on a KT5720 analogue has been established. Including receptor flexibility in Schrödinger induced-fit docking calculations in most cases correctly predicted the binding modes as compared with the molecular dynamics structures the algorithm was less effective when there were key structural waters bridging receptor-ligand contacts. © 2010 Wiley-Liss, Inc. 79 3 703 719 Tradenames: kt 5720 Cited By :37