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Publication Abstract from PubMed

NADP(+) dependent isocitrate dehydrogenase (IDH; EC 1.1.1.42) belongs to a large family of alpha-hydroxyacid oxidative beta-decarboxylases that catalyze similar three-step reactions, with dehydrogenation to an oxaloacid intermediate preceding beta-decarboxylation to an enol intermediate followed by tautomerization to the final alpha-ketone product. A comprehensive view of the induced fit needed for catalysis is revealed on comparing the first "fully closed" crystal structures of a pseudo-Michaelis complex of wild-type Escherichia coli IDH (EcoIDH) and the "fully closed" reaction product complex of the K100M mutant with previously obtained "quasi-closed" and "open" conformations. Conserved catalytic residues, binding the nicotinamide ring of NADP(+) and the metal-bound substrate, move as rigid bodies during domain closure by a hinge motion that spans the central beta-sheet in each monomer. Interactions established between Thr105 and Ser113, which flank the "phosphorylation loop", and the nicotinamide mononucleotide moiety of NADP(+) establish productive coenzyme binding. Electrostatic interactions of a Lys100-Leu103-Asn115-Glu336 tetrad play a pivotal role in assembling a catalytically competent active site. As predicted, Lys230* is positioned to deprotonate/reprotonate the alpha-hydroxyl in both reaction steps and Tyr160 moves into position to protonate C3 following beta-decarboxylation. A proton relay from the catalytic triad Tyr160-Asp307-Lys230* connects the alpha-hydroxyl of isocitrate to the bulk solvent to complete the picture of the catalytic mechanism.

Induced fit and the catalytic mechanism of isocitrate dehydrogenase.,Goncalves S, Miller SP, Carrondo MA, Dean AM, Matias PM Biochemistry. 2012 Sep 11;51(36):7098-115. Epub 2012 Aug 27. PMID:22891681^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.