title: Structural basis for the catalytic mechanism of a proficient enzyme: orotidine 5'-monophosphate decarboxylase.
abstract: Orotidine 5'-monophosphate decarboxylase (ODCase) catalyzes the decarboxylation of orotidine 5'-monophosphate, the last step in the de novo synthesis of uridine 5'-monophosphate. ODCase is a very proficient enzyme [Radzicka, A., and Wolfenden, R. (1995) Science 267, 90-93], enhancing the reaction rate by a factor of 10(17). This proficiency has been enigmatic, since it is achieved without metal ions or cofactors. Here we present a 2.5 A resolution structure of ODCase complexed with the inhibitor 1-(5'-phospho-beta-D-ribofuranosyl)barbituric acid. It shows a closely packed dimer composed of two alpha/beta-barrels with two shared active sites. The orientation of the orotate moiety of the substrate is unambiguously deduced from the structure, and previously proposed catalytic mechanisms involving protonation of O2 or O4 can be ruled out. The proximity of the OMP carboxylate group with Asp71 appears to be instrumental for the decarboxylation of OMP, either through charge repulsion or through the formation of a very short O.H.O hydrogen bond between the two carboxylate groups.
authors.affiliation: Centre for Crystallographic Studies, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Harris
authors.forename: J C
authors.initials: JC
authors.lastname: Navarro Poulsen
authors.forename: K F
authors.initials: KF
authors.lastname: Jensen
authors.forename: S
authors.initials: S
authors.lastname: Larsen
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009964:Orotidine-5'-Phosphate Decarboxylase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D014542:Uridine Monophosphate / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: C005417:orotidylic acid; C028372:1-(5'-phospho-beta-D-ribofuranosyl)barbituric acid; D014542:Uridine Monophosphate; D009964:Orotidine-5'-Phosphate Decarboxylase