title: Crystal structure of 2,5-diketo-D-gluconic acid reductase A complexed with NADPH at 2.1-A resolution.
abstract: The three-dimensional structure of Corynebacterium 2, 5-diketo-D-gluconic acid reductase A (2,5-DKGR A; EC 1.1.1.-), in complex with cofactor NADPH, has been solved by using x-ray crystallographic data to 2.1-A resolution. This enzyme catalyzes stereospecific reduction of 2,5-diketo-D-gluconate (2,5-DKG) to 2-keto-L-gulonate. Thus the three-dimensional structure has now been solved for a prokaryotic example of the aldo-keto reductase superfamily. The details of the binding of the NADPH cofactor help to explain why 2,5-DKGR exhibits lower binding affinity for cofactor than the related human aldose reductase does. Furthermore, changes in the local loop structure near the cofactor suggest that 2,5-DKGR will not exhibit the biphasic cofactor binding characteristics observed in aldose reductase. Although the crystal structure does not include substrate, the two ordered water molecules present within the substrate-binding pocket are postulated to provide positional landmarks for the substrate 5-keto and 4-hydroxyl groups. The structural basis for several previously described active-site mutants of 2,5-DKGR A is also proposed. Recent research efforts have described a novel approach to the synthesis of L-ascorbate (vitamin C) by using a genetically engineered microorganism that is capable of synthesizing 2,5-DKG from glucose and subsequently is transformed with the gene for 2,5-DKGR. These modifications create a microorganism capable of direct production of 2-keto-L-gulonate from D-glucose, and the gulonate can subsequently be converted into vitamin C. In economic terms, vitamin C is the single most important specialty chemical manufactured in the world. Understanding the structural determinants of specificity, catalysis, and stability for 2,5-DKGR A is of substantial commercial interest.
authors.affiliation: Institute of Molecular Biophysics and Department of Chemistry, Florida State University, Tallahassee, FL 32306-3015, USA.
authors.forename: S
authors.initials: S
authors.lastname: Khurana
authors.forename: D B
authors.initials: DB
authors.lastname: Powers
authors.forename: S
authors.initials: S
authors.lastname: Anderson
authors.forename: M
authors.initials: M
authors.lastname: Blaber
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D003352:Corynebacterium / Q000201:enzymology*; D018360:Crystallography, X-Ray; D006801:Humans; D008969:Molecular Sequence Data; D009249:NADP / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013401:Sugar Alcohol Dehydrogenases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D009249:NADP; D013401:Sugar Alcohol Dehydrogenases; C053163:2,5-diketo-D-gluconate 5-reductase