Structure and mechanism of isopropylmalate dehydrogenase from Arabidopsis thaliana: Insights on leucine and aliphatic glucosinolate biosynthesis

Soon Goo Lee, Ronald Nwumeh, Joseph M. Jez

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Isopropylmalate dehydrogenase (IPMDH) and 3-(2′-methylthio)ethylmalate dehydrogenase catalyze the oxidative decarboxylation of different β-hydroxyacids in the leucine- and methionine-derived glucosinolate biosynthesis pathways, respectively, in plants. Evolution of the glucosinolate biosynthetic enzyme from IPMDH results from a single amino acid substitution that alters substrate specificity. Here, we present the x-ray crystal structures of Arabidopsis thaliana IPMDH2 (AtIPMDH2) in complex with either isopropylmalate and Mg2+ or NAD+. These structures reveal conformational changes that occur upon ligand binding and provide insight on the active site of the enzyme. The x-ray structures and kinetic analysis of site-directed mutants are consistent with a chemical mechanism in which Lys-232 activates a water molecule for catalysis. Structural analysis of the AtIPMDH2 K232M mutant and isothermal titration calorimetry supports a key role of Lys-232 in the reaction mechanism. This study suggests that IPMDH-like enzymes in both leucine and glucosinolate biosynthesis pathways use a common mechanism and that members of the β-hydroxyacid reductive decarboxylase family employ different active site features for similar reactions.

Original languageEnglish
Pages (from-to)13421-13430
Number of pages10
JournalJournal of Biological Chemistry
Volume291
Issue number26
DOIs
StatePublished - Jun 24 2016

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