title: Structural elucidation of chalcone reductase and implications for deoxychalcone biosynthesis.
abstract: 4,2',4',6'-Tetrahydroxychalcone (chalcone) and 4,2',4'-trihydroxychalcone (deoxychalcone) serve as precursors of ecologically important flavonoids and isoflavonoids. Deoxychalcone formation depends on chalcone synthase and chalcone reductase; however, the identity of the chalcone reductase substrate out of the possible substrates formed during the multistep reaction catalyzed by chalcone synthase remains experimentally elusive. We report here the three-dimensional structure of alfalfa chalcone reductase bound to the NADP+ cofactor and propose the identity and binding mode of its substrate, namely the non-aromatized coumaryl-trione intermediate of the chalcone synthase-catalyzed cyclization of the fully extended coumaryl-tetraketide thioester intermediate. In the absence of a ternary complex, the quality of the refined NADP+-bound chalcone reductase structure serves as a template for computer-assisted docking to evaluate the likelihood of possible substrates. Interestingly, chalcone reductase adopts the three-dimensional structure of the aldo/keto reductase superfamily. The aldo/keto reductase fold is structurally distinct from all known ketoreductases of fatty acid biosynthesis, which instead belong to the short-chain dehydrogenase/reductase superfamily. The results presented here provide structural support for convergent functional evolution of these two ketoreductases that share similar roles in the biosynthesis of fatty acids/polyketides. In addition, the chalcone reductase structure represents the first protein structure of a member of the aldo/ketoreductase 4 family. Therefore, the chalcone reductase structure serves as a template for the homology modeling of other aldo/keto-reductase 4 family members, including the reductase involved in morphine biosynthesis, namely codeinone reductase.
authors.affiliation: Jack Skirball Chemical Biology and Proteomics Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037, USA
authors.forename: Erin K
authors.initials: EK
authors.lastname: Bomati
authors.forename: Michael B
authors.initials: MB
authors.lastname: Austin
authors.forename: Marianne E
authors.initials: ME
authors.lastname: Bowman
authors.forename: Richard A
authors.initials: RA
authors.lastname: Dixon
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Noel
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry*; D001665:Binding Sites; D002599:Chalcone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D047188:Chalcones; D002850:Chromatography, Gel; D018360:Crystallography, X-Ray; D004952:Esters / Q000378:metabolism; D019143:Evolution, Molecular; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism; D000455:Medicago sativa / Q000201:enzymology; D008956:Models, Chemical; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D064430:NAD (+) and NADP (+) Dependent Alcohol Oxidoreductases; D009249:NADP / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity
chemical_list: D047188:Chalcones; D004952:Esters; D005227:Fatty Acids; D009249:NADP; D002599:Chalcone; C040920:isoliquiritigenin; D000429:Alcohol Oxidoreductases; D064430:NAD (+) and NADP (+) Dependent Alcohol Oxidoreductases; C093070:chalcone reductase; C096678:codeinone reductase (NADPH)