The complex allosteric and redox regulation of the fumarate hydratase and malate dehydratase reactions of Arabidopsis thaliana Fumarase 1 and 2 gives clues for understanding the massive accumulation of fumarate

• Published in: The FEBS journal 2018-06, Vol.285 (12), p.2205-2224
• Main Authors: Zubimendi, Juan P., Martinatto, Andrea, Valacco, Maria P., Moreno, Silvia, Andreo, Carlos S., Drincovich, María F., Tronconi, Marcos A.
• Format: Article
• Language: English
• Subjects: Accumulation; allosteric and redox regulation; Allosteric properties; Arabidopsis; Arabidopsis thaliana; Asparagine; Biological evolution; Coding; Dehydration; Disulfide bonds; enzyme kinetics; Enzymes; Fumarase; Fumarate hydratase; Genes; Glutamine; Krebs cycle; Malate; Mass spectrometry; Mass spectroscopy; Metabolism; Mitochondria; Modulators; Molecular chains; NADP; Oxidation; paralogous genes; pH effects; Phylogeny; Tricarboxylic acid cycle
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/febs.14483

Arabidopsis thaliana possesses two fumarase genes (FUM), AtFUM1 (At2g47510) encoding for the mitochondrial Krebs cycle‐associated enzyme and AtFUM2 (At5g50950) for the cytosolic isoform required for fumarate massive accumulation. Here, the comprehensive biochemical studies of AtFUM1 and AtFUM2 shows that they are active enzymes with similar kinetic parameters but differential regulation. For both enzymes, fumarate hydratase (FH) activity is favored over the malate dehydratase (MD) activity; however, MD is the most regulated activity with several allosteric activators. Oxalacetate, glutamine, and/or asparagine are modulators causing the MD reaction to become preferred over the FH reaction. Activity profiles as a function of pH suggest a suboptimal FUM activity in Arabidopsis cells; moreover, the direction of the FUM reaction is sensitive to pH changes. Under mild oxidation conditions, AtFUMs form high mass molecular aggregates, which present both FUM activities decreased to a different extent. The biochemical properties of oxidized AtFUMs (oxAtFUMs) were completely reversed by NADPH‐supplied Arabidopsis leaf extracts, suggesting that the AtFUMs redox regulation can be accomplished in vivo. Mass spectrometry analyses indicate the presence of an active site‐associated intermolecular disulfide bridge in oxAtFUMs. Finally, a phylogenetic approach points out that other plant species may also possess cytosolic FUM2 enzymes mainly encoded by paralogous genes, indicating that the evolutionary history of this trait has been drawn through a process of parallel evolution. Overall, according to our results, a multilevel regulatory pattern of FUM activities emerges, supporting the role of this enzyme as a carbon flow monitoring point through the organic acid metabolism in plants. Arabidopsis thaliana possesses two fumarase genes. AtFUM1 encodes the mitochondrial Krebs cycle‐associated enzyme, whereas AtFUM2 encodes the cytosolic isoform required for fumarate accumulation. Zubimendi et al. now provide detailed biochemical analysis of the two fumarase proteins, revealing that the enzymes have similar kinetic parameters but different mechanisms of regulation. Their results suggest that fumarase has an important role in monitoring and regulating carbon metabolism in plants.