title: Role of catalytic residues in enzymatic mechanisms of homologous ketosteroid isomerases.
abstract: Ketosteroid isomerase (KSI) is one of the most proficient enzymes catalyzing an allylic isomerization reaction at a diffusion-controlled rate. In this study of KSI, we have detailed the structures of its active site, the role of various catalytic residues, and have explained the origin of the its fast reactivity by carrying out a detailed investigation of the enzymatic reaction mechanism. This investigation included the X-ray determination of 15 crystal structures of two homologous enzymes in free and complexed states (with inhibitors) and extensive ab initio calculations of the interactions between the active sites and the reaction intermediates. The catalytic residues, through short strong hydrogen bonds, play the role of charge buffer to stabilize the negative charge built up on the intermediates in the course of the reaction. The hydrogen bond distances in the intermediate analogues are found to be about 0.2 A shorter in the product analogues both experimentally and theoretically.
authors.affiliation: National Creative Research Initiative Center for Superfunctional Materials, Pohang University of Science and Technology, San 31, Hyojadong, Nam.
authors.forename: K S
authors.initials: KS
authors.lastname: Oh
authors.forename: S S
authors.initials: SS
authors.lastname: Cha
authors.forename: D H
authors.initials: DH
authors.lastname: Kim
authors.forename: H S
authors.initials: HS
authors.lastname: Cho
authors.forename: N C
authors.initials: NC
authors.lastname: Ha
authors.forename: G
authors.initials: G
authors.lastname: Choi
authors.forename: J Y
authors.initials: JY
authors.lastname: Lee
authors.forename: P
authors.initials: P
authors.lastname: Tarakeshwar
authors.forename: H S
authors.initials: HS
authors.lastname: Son
authors.forename: K Y
authors.initials: KY
authors.lastname: Choi
authors.forename: B H
authors.initials: BH
authors.lastname: Oh
authors.forename: K S
authors.initials: KS
authors.lastname: Kim
mesh_terms: D001224:Aspartic Acid; D001665:Binding Sites; D002384:Catalysis; D020134:Catalytic Domain; D020604:Comamonas testosteroni / Q000201:enzymology; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D016958:Pseudomonas putida / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D013251:Steroid Isomerases / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry
chemical_list: D001224:Aspartic Acid; D014443:Tyrosine; D013251:Steroid Isomerases; C022660:steroid delta-isomerase