title: Activation of aldo-keto reductase family member 1B14 (AKR1B14) by bile acids: Activation mechanism and bile acid-binding site.
abstract: Aldo-keto reductase (AKR) 1B14, a rat ortholog of mouse androgen-dependent vas deferens protein (AKR1B7), is involved in the synthesis of prostaglandin F(2α) and detoxification of 4-oxononenal formed by lipid peroxidation. The NADPH-linked reductase activity of AKR1B14 was activated by various bile acids. Although the activation was increased by decreasing pH from 9.0 to 6.0, the concentrations giving maximum stimulation (2- to 18-fold) were 0.2-6.0 μM for bile acids at pH 7.4. Kinetic analyses of the activation by glycochenodeoxycholic acid in the forward and reverse reactions, together with fluorescence changes and protection against 4-oxononenal-induced inactivation by bile acid, indicate that the bile acid binds to the enzyme and its coenzyme binary complex as a non-essential activator. The bile acid binding to AKR1B14 mainly accelerates the NADP(+) dissociation, the rate-limited step of the enzyme reaction. AKR1B7 was also activated by bile acids, but the activation was low and independent of pH. The mutagenesis of His269 and Leu267 of AKR1B14 into the corresponding residues (Arg and Pro, respectively) of AKR1B7 resulted in low and pH-independent activation by bile acids. The results, together with the docking of the bile acid in the recently determined crystal structure of AKR1B14, identify the bile acid-binding site of which His269 plays a key role in significant activation through its electrostatic interaction with the carboxyl group of bile acid, facilitating the release of NADP(+).
authors.affiliation: Laboratory of Biochemistry, Gifu Pharmaceutical University, 1-25-4 Daigaku-Nishi, Gifu 501-1196, Japan. sendo@gifu-pu.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Endo
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsunaga
authors.forename: Anna
authors.initials: A
authors.lastname: Fujita
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Kuragano
authors.forename: Midori
authors.initials: M
authors.lastname: Soda
authors.forename: Krithika
authors.initials: K
authors.lastname: Sundaram
authors.forename: Urmi
authors.initials: U
authors.lastname: Dhagat
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tajima
authors.forename: Ossama
authors.initials: O
authors.lastname: El-Kabbani
authors.forename: Akira
authors.initials: A
authors.lastname: Hara
mesh_terms: D000449:Aldehyde Reductase / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001647:Bile Acids and Salts / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002417:Cattle; D002478:Cells, Cultured; D004789:Enzyme Activation; D006639:Histidine / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007930:Leucine / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009249:NADP / Q000737:chemistry / Q000378:metabolism; D051381:Rats
chemical_list: D001647:Bile Acids and Salts; D006639:Histidine; D009249:NADP; C558977:Akr1b7 protein, rat; D000449:Aldehyde Reductase; D007930:Leucine