STRUCTURE OF ISOCITRATE DEHYDROGENASE WITH ALPHA-KETOGLUTARATE AT 2.7 ANGSTROMS RESOLUTION: CONFORMATIONAL CHANGES INDUCED BY DECARBOXYLATION OF ISOCITRATE
The structure of the isocitrate dehydrogenase (IDH) complex with bound alpha-ketoglutarate, Ca2+, and NADPH was solved at 2.7-A resolution. The alpha-ketoglutarate binds in the active site at the same position and orientation as isocitrate, with a difference between the two bound molecules of about 0 ...
The structure of the isocitrate dehydrogenase (IDH) complex with bound alpha-ketoglutarate, Ca2+, and NADPH was solved at 2.7-A resolution. The alpha-ketoglutarate binds in the active site at the same position and orientation as isocitrate, with a difference between the two bound molecules of about 0.8 A. The Ca2+ metal is coordinated by alpha-ketoglutarate, three conserved aspartate residues, and a pair of water molecules. The largest motion in the active site relative to the isocitrate enzyme complex is observed for tyrosine 160, which originally forms a hydrogen bond to the labile carboxyl group of isocitrate and moves to form a new hydrogen bond to Asp 307 in the complex with alpha-ketoglutarate. This triggers a number of significant movements among several short loops and adjoining secondary structural elements in the enzyme, most of which participate in dimer stabilization and formation of the active-site cleft. These rearrangements are similar to the ligand-binding-induced movements observed in globins and insulin and serve as a model for an enzymatic mechanism which involves local shifts of secondary structural elements during turnover, rather than large-scale domain closures or loop transitions induced by substrate binding such as those observed in hexokinase or triosephosphate isomerase.
Related Citations:
The Structure of Isocitrate Dehydrogenase with Isocitrate, Nadp, and Calcium at 2.5 Angstroms Resolution: A Pseudo-Michaelis Ternary Complex Stoddard, B.L., Dean, A., Koshland Junior, D.E. (1993) Biochemistry 32: 9310
Organizational Affiliation:
Department of Molecular and Cellular Biology, University of California, Berkeley 94720.
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