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4) Symposium Posters | Main^

P6. X-ray structure of apo-2,5-di-keto-D-gluconic acid reductase A.

45th Biophysical Society Meeting, Feb. 17-21, 2001, Boston, MA.
Gulsah Sanli, Thayumanasamy Somasundaram, and Michael Blaber.
Department of Chemistry, 104 Institute of Molecular Biophysics, Florida State Univ., Tallahassee, FL 32306, USA

A 1.9 A resolution x-ray structure of recombinant Corynebacterium 2,5-diketo-D- gluconic acid reductase A (2,5-DKGR A) was determined by molecular replacement using the complex structure of the same enzyme with NADPH cofactor as the search model. This enzyme catalyzes the NADPH-dependent stereo-specific reduction of 2,5- diketo-D-gluconate (2,5-DKG) to 2-keto-L-gulonate, a precursor in the industrial production of vitamin C. 2,5-DKGR A belongs to the aldo-keto reductase superfamily and shares the common TIM barrel fold. The superimposed structures of apoenzyme and NADPH:enzyme complex reveal significant conformational changes around the cofactor binding region formed by residues 22-28, 46-52 and 107-114. All of the active site residues are displaced in their positions by 1.03-6.46 A. Residues important for catalysis or cofactor binding, such as His-108, Trp-109, Arg-238, Ser-233, have poorly defined density in the apo form and appear to be somewhat disordered. Additionally, the last 15 residues at the C-terminal, which form one side of the substrate binding pocket, have no defined electron density in the apo-form. The results show that besides providing a hydride ion for catalytic reduction, the binding of NADPH cofactor to 2,5-DKGR A appears to order the structure to a catalyticaly competent conformation.

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