title: Kinetic and crystallographic studies of glucopyranosylidene spirothiohydantoin binding to glycogen phosphorylase B.
abstract: Glucopyranosylidene spirothiohydantoin (TH) has been identified as a potential inhibitor of both muscle and liver glycogen phosphorylase b (GPb) and a (GPa) and shown to diminish liver GPa activity in vitro. Kinetic experiments reported here show that TH inhibits muscle GPb competitively with respect to both substrates phosphate (K(i)=2.3 microM) and glycogen (K(i)=2.8 microM). The structure of the GPb-TH complex has been determined at a resolution of 2.26 A and refined to a crystallographic R value of 0.193 (R(free)=0.211). The structure of GPb-TH complex reveals that the inhibitor can be accommodated in the catalytic site of T-state GPb with very little change of the tertiary structure, and provides a basis of understanding potency and specificity of the inhibitor. The glucopyranose moiety makes the standard hydrogen bonds and van der Waals contacts as observed in the glucose complex, while the rigid thiohydantoin group is in a favourable electrostatic environment and makes additional polar contacts to the protein.
authors.affiliation: Institute of Biological Research and Biotechnology, The National Hellenic Research Foundation, 48 Vas. Constantinou Avenue, Athens 11635, Greece. ngo@eie.gr
authors.forename: Nikos G
authors.initials: NG
authors.lastname: Oikonomakos
authors.forename: Vicky T
authors.initials: VT
authors.lastname: Skamnaki
authors.forename: Erzsébet
authors.initials: E
authors.lastname: Osz
authors.forename: László
authors.initials: L
authors.lastname: Szilágyi
authors.forename: László
authors.initials: L
authors.lastname: Somsák
authors.forename: Tibor
authors.initials: T
authors.lastname: Docsa
authors.forename: Béla
authors.initials: B
authors.lastname: Tóth
authors.forename: Pál
authors.initials: P
authors.lastname: Gergely
mesh_terms: D000818:Animals; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism*; D024982:Glycogen Phosphorylase, Muscle Form / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D009005:Monosaccharides / Q000737:chemistry* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology; D011487:Protein Conformation; D011817:Rabbits; D013141:Spiro Compounds / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D009005:Monosaccharides; D013141:Spiro Compounds; C452302:glucopyranosylidene spirothiohydantoin; D024982:Glycogen Phosphorylase, Muscle Form