PDBsum entry 1a80

Oxidoreductase

PDB id

1a80

Contents

			Protein chain

					277 a.a.

			Ligands

					NDP

			Waters ×105

References listed in PDB file

Key reference

Title

Crystal structure of 2,5-Diketo-D-Gluconic acid reductase a complexed with NADPH at 2.1-A resolution.

Authors

S.Khurana, D.B.Powers, S.Anderson, M.Blaber.

Ref.

Proc Natl Acad Sci U S A, 1998, 95, 6768-6773. [DOI no: 10.1073/pnas.95.12.6768]

PubMed id

9618487

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.



	Figure 1. Fig. 1. Structures of 2,5-diketo-D-gluconate (2,5-DKG), 2-keto-L-gulonate (2-KLG), and L-ascorbate (vitamin C). The uppermost carbon is C1.		Figure 4. Fig. 4. Noncovalent interactions between the NADPH cofactor and 2,5-DKGR A. In addition to hydrogen bonding and electrostatic interactions, the side chain of Trp-187 is involved in an aromatic stacking interaction with the nicotinamide ring of the NADPH cofactor.