title: Kinetic and crystallographic studies on 2-(beta-D-glucopyranosyl)-5-methyl-1, 3, 4-oxadiazole, -benzothiazole, and -benzimidazole, inhibitors of muscle glycogen phosphorylase b. Evidence for a new binding site.
abstract: In an attempt to identify leads that would enable the design of inhibitors with enhanced affinity for glycogen phosphorylase (GP), that might control hyperglycaemia in type 2 diabetes, three new analogs of beta-D-glucopyranose, 2-(beta-D-glucopyranosyl)-5-methyl-1, 3, 4-oxadiazole, -benzothiazole, and -benzimidazole were assessed for their potency to inhibit GPb activity. The compounds showed competitive inhibition (with respect to substrate Glc-1-P) with K(i) values of 145.2 (+/-11.6), 76 (+/-4.8), and 8.6 (+/-0.7) muM, respectively. In order to establish the mechanism of this inhibition, crystallographic studies were carried out and the structures of GPb in complex with the three analogs were determined at high resolution (GPb-methyl-oxadiazole complex, 1.92 A; GPb-benzothiazole, 2.10 A; GPb-benzimidazole, 1.93 A). The complex structures revealed that the inhibitors can be accommodated in the catalytic site of T-state GPb with very little change of the tertiary structure, and provide a rationalization for understanding variations in potency of the inhibitors. In addition, benzimidazole bound at the new allosteric inhibitor or indole binding site, located at the subunit interface, in the region of the central cavity, and also at a novel binding site, located at the protein surface, far removed (approximately 32 A) from the other binding sites, that is mostly dominated by the nonpolar groups of Phe202, Tyr203, Val221, and Phe252.
authors.affiliation: Institute of Organic and Pharmaceutical Chemistry, The National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, 116 35 Athens, Greece.
authors.forename: Evangelia D
authors.initials: ED
authors.lastname: Chrysina
authors.forename: Magda N
authors.initials: MN
authors.lastname: Kosmopoulou
authors.forename: Constantinos
authors.initials: C
authors.lastname: Tiraidis
authors.forename: Rozina
authors.initials: R
authors.lastname: Kardakaris
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bischler
authors.forename: Demetres D
authors.initials: DD
authors.lastname: Leonidas
authors.forename: Zsuzsa
authors.initials: Z
authors.lastname: Hadady
authors.forename: Laszlo
authors.initials: L
authors.lastname: Somsak
authors.forename: Tibor
authors.initials: T
authors.lastname: Docsa
authors.forename: Pal
authors.initials: P
authors.lastname: Gergely
authors.forename: Nikos G
authors.initials: NG
authors.lastname: Oikonomakos
mesh_terms: D001562:Benzimidazoles / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism; D005960:Glucosides / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D010069:Oxadiazoles / Q000737:chemistry* / Q000378:metabolism; D010763:Phosphorylase b / Q000737:chemistry* / Q000378:metabolism; D013844:Thiazoles / Q000737:chemistry* / Q000378:metabolism
chemical_list: C502367:2-glucopyranosyl-5-methyl-1,3,4-oxadiazole; C502368:2-glucopyranosyl-5-methylbenzimidazole; C502369:2-glucopyranosyl-5-methylbenzothiazole; D001562:Benzimidazoles; D004791:Enzyme Inhibitors; D005960:Glucosides; D010069:Oxadiazoles; D013844:Thiazoles; D010763:Phosphorylase b
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