OPEN ACCESS ARTICLE

This Article Free via Open Access: OA OA Full Text Full Text (PDF) Supplmental Data OA All Versions of this Article: 143/2/970    most recent pp.106.085555v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via ISI Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by de Kraker, J.-W. Articles by Gershenzon, J. Search for Related Content PubMed PubMed Citation Articles by de Kraker, J.-W. Articles by Gershenzon, J. Agricola Articles by de Kraker, J.-W. Articles by Gershenzon, J.

BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Two Arabidopsis Genes (IPMS1 and IPMS2) Encode Isopropylmalate Synthase, the Branchpoint Step in the Biosynthesis of Leucine^1,[W],[OA]

Max Planck Institute for Chemical Ecology, Beutenberg Campus, D–07745 Jena, Germany

Heterologous expression of the Arabidopsis (Arabidopsis thaliana) IPMS1 (At1g18500) and IPMS2 (At1g74040) cDNAs in Escherichia coli yields isopropylmalate synthases (IPMSs; EC 2.3.3.13). These enzymes catalyze the first dedicated step in leucine (Leu) biosynthesis, an aldol-type condensation of acetyl-coenzyme A (CoA) and 2-oxoisovalerate yielding isopropylmalate. Most biochemical properties of IPMS1 and IPMS2 are similar: broad pH optimum around pH 8.5, Mg²⁺ as cofactor, feedback inhibition by Leu, K_m for 2-oxoisovalerate of approximately 300 µM, and a V_max of approximately 2 x 10³ µmol min^–1 g^–1. However, IPMS1 and IPMS2 differ in their K_m for acetyl-CoA (45 µM and 16 µM, respectively) and apparent quaternary structure (dimer and tetramer, respectively). A knockout insertion mutant for IPMS1 showed an increase in valine content but no changes in Leu content; two insertion mutants for IPMS2 did not show any changes in soluble amino acid content. Apparently, in planta each gene can adequately compensate for the absence of the other, consistent with available microarray and reverse transcription-polymerase chain reaction data that show that both genes are expressed in all organs at all developmental stages. Both encoded proteins accept 2-oxo acid substrates in vitro ranging in length from glyoxylate to 2-oxohexanoate, and catalyze at a low rate the condensation of acetyl-CoA and 4-methylthio-2-oxobutyrate, i.e. a reaction involved in glucosinolate chain elongation normally catalyzed by methylthioalkylmalate synthases. The evolutionary relationship between IPMS and methylthioalkylmalate synthase enzymes is discussed in view of their amino acid sequence identity (60%) and overlap in substrate specificity.

² Present address: Department of Horticulture, Virginia Tech, Blacksburg, VA 24061.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jonathan Gershenzon (gershenzon{at}ice.mpg.de).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.085555

^* Corresponding author; e-mail gershenzon{at}ice.mpg.de; fax 49–3641–57–1302.

Received June 21, 2006; accepted December 7, 2006; published December 22, 2006.

This article has been cited by other articles:

				S. P. Slocombe, I. Schauvinhold, R. P. McQuinn, K. Besser, N. A. Welsby, A. Harper, N. Aziz, Y. Li, T. R. Larson, J. Giovannoni, et al. Transcriptomic and Reverse Genetic Analysesof Branched-Chain Fatty Acid and Acyl Sugar Production in Solanum pennellii and Nicotiana benthamiana Plant Physiology, December 1, 2008; 148(4): 1830 - 1846. [Abstract] [Full Text] [PDF]

				T. Knill, J. Schuster, M. Reichelt, J. Gershenzon, and S. Binder Arabidopsis Branched-Chain Aminotransferase 3 Functions in Both Amino Acid and Glucosinolate Biosynthesis Plant Physiology, March 1, 2008; 146(3): 1028 - 1039. [Abstract] [Full Text] [PDF]