• DOI:10.1021/BI00099A026
• Corpus ID: 31702744

Catalytic mechanism of NADP(+)-dependent isocitrate dehydrogenase: implications from the structures of magnesium-isocitrate and NADP+ complexes.

@article{Hurley1991CatalyticMO,
  title={Catalytic mechanism of NADP(+)-dependent isocitrate dehydrogenase: implications from the structures of magnesium-isocitrate and NADP+ complexes.},
  author={James H. Hurley and Antony M Dean and Daniel E. Koshland and Robert M. Stroud},
  journal={Biochemistry},
  year={1991},
  volume={30 35},
  pages={
          8671-8
        }
}

• J. Hurley, A. Dean, +1 author R. Stroud
• Published 3 September 1991
• Chemistry, Biology
• Biochemistry

The structures of NADP+ and magnesium isocitrate bound to the NADP(+)-dependent isocitrate dehydrogenase of Escherichia coli have been determined and refined at 2.5-A resolution. NADP+ is bound by the large domain of isocitrate dehydrogenase, a structure that has little similarity to the supersecondary structure of the nucleotide-binding domain of the lactate dehydrogenase-like family of nucleotide-binding proteins. The coenzyme-binding site confirms the fundamentally different evolution of the isocitrate dehydrogenase-like and the lactate dehydrogenase-like classes of nucleotide-binding proteins. In the magnesium-isocitrate complex, magnesium is coordinated to the alpha-carboxylate and alpha-hydroxyl oxygen of isocitrate in a manner suitable for stabilization of a negative charge on the hydroxyl oxygen during both the dehydrogenation and decarboxylation steps of the conversion of isocitrate to alpha-ketoglutarate. The metal ion is also coordinated by aspartate side chains 283' (of the second subunit of the dimer) and 307 and two water molecules in a roughly octahedral arrangement. On the basis of the geometry of the active site, the base functioning in the dehydrogenation step is most likely aspartate 283'. E. coli isocitrate dehydrogenase transfers a hydride stereospecifically to the A-side of NADP+, and models for a reactive ternary complex consistent with this stereospecificity are discussed.