Protein complex formation in methionine chain-elongation and leucine biosynthesis.

Affiliation

Chen LQ(1)(2), Chhajed S(2), Zhang T(2), Collins JM(2), Pang Q(2)(3), Song W(4), He Y(5)(6), Chen S(7).
Author information:
(1)State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, China.
(2)Department of Biology, Genetics Institute, Plant Molecular & Cellular Biology Program, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, USA.
(3)Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline-Alkali Vegetation Ecology Restoration in Oil Field, Northeast Forestry University, Harbin, Heilongjiang, China.
(4)Department of Plant Pathology, University of Florida, Gainesville, FL, USA.
(5)Department of Biology, Genetics Institute, Plant Molecular & Cellular Biology Program, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, USA. [Email]
(6)National Maize Improvement Center of China, Beijing Key Laboratory of Crop Genetic Improvement, China Agricultural University, Beijing, China. [Email]
(7)Department of Biology, Genetics Institute, Plant Molecular & Cellular Biology Program, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, USA. [Email]

Abstract

During the past two decades, glucosinolate (GLS) metabolic pathways have been under extensive studies because of the importance of the specialized metabolites in plant defense against herbivores and pathogens. The studies have led to a nearly complete characterization of biosynthetic genes in the reference plant Arabidopsis thaliana. Before methionine incorporation into the core structure of aliphatic GLS, it undergoes chain-elongation through an iterative three-step process recruited from leucine biosynthesis. Although enzymes catalyzing each step of the reaction have been characterized, the regulatory mode is largely unknown. In this study, using three independent approaches, yeast two-hybrid (Y2H), coimmunoprecipitation (Co-IP) and bimolecular fluorescence complementation (BiFC), we uncovered the presence of protein complexes consisting of isopropylmalate isomerase (IPMI) and isopropylmalate dehydrogenase (IPMDH). In addition, simultaneous decreases in both IPMI and IPMDH activities in a leuc:ipmdh1 double mutants resulted in aggregated changes of GLS profiles compared to either leuc or ipmdh1 single mutants. Although the biological importance of the formation of IPMI and IPMDH protein complexes has not been documented in any organisms, these complexes may represent a new regulatory mechanism of substrate channeling in GLS and/or leucine biosynthesis. Since genes encoding the two enzymes are widely distributed in eukaryotic and prokaryotic genomes, such complexes may have universal significance in the regulation of leucine biosynthesis.