Branched-Chain Amino Acid Metabolism inArabidopsis thaliana

Abstract

Valine, leucine and isoleucine form the small group of branched-chain amino acids (BCAAs) classified by their small branched hydrocarbon residues. Unlike animals, plants are able to de novo synthesize these amino acids from pyruvate, 2-oxobutanoate and acetyl-CoA. In plants, biosynthesis follows the typical reaction pathways established for the formation of these amino acids in microorganisms. Val and Ile are synthesized in two parallel pathways using a single set of enzymes. The pathway to Leu branches of from the final intermediate of Val biosynthesis. The formation of this amino acid requires a three-step pathway generating a 2-oxoacid elongated by a methylene group. In Arabidopsis thaliana and other Brassicaceae, a homologous three-step pathway is also involved in Met chain elongation required for the biosynthesis of aliphatic glucosinolates, an important class of specialized metabolites in Brassicaceae. This is a prime example for the evolutionary relationship of pathways from primary and specialized metabolism. Similar to animals, plants also have the ability to degrade BCAAs. The importance of BCAA turnover has long been unclear, but now it seems apparent that the breakdown process might by relevant under certain environmental conditions. In this review, I summarize the current knowledge about BCAA metabolism, its regulation and its particular features in Arabidopsis thaliana.

Methylcrotonyl-CoA Carboxylase Regulates Triacylglycerol Accumulation in the Model Diatom Phaeodactylum tricornutum

“…The entire degradation pathway is illustrated in Figure 4A. The different BCAAs, Leu, Val, and Ile, are degraded by the same BCAT and BCKDH enzymes, which catalyze the first two steps in the pathway (Binder, 2010). BCAT also catalyzes the synthesis of the BCAAs dependent on its localization (Campbell et al, 2001).…”

“…MCC is a mitochondria-localized carboxylase involved in Leu catabolism and catalyzes the ATP-dependent carboxylation of 3-methylcrotonyl-CoA to form 3-methylglutaconyl-CoA, which is ultimately converted into acetoacetate and acetyl CoA (Binder, 2010). It is a heteromeric enzyme composed of two subunits: a biotinylated subunit and a nonbiotinylated subunit (Binder, 2010).…”

“…It is a heteromeric enzyme composed of two subunits: a biotinylated subunit and a nonbiotinylated subunit (Binder, 2010). Two putative genes, Protein IDs 843 (MCC1) and 19329 (MCC2), encoding MCC a-and b-subunits, respectively, have been annotated in the genome of P. tricornutum.…”

Biochemistry of apple aroma: A review

“…First, the α-keto acid is irreversibly converted to a branched-chain acyl-CoA (2-methyl butanoil-CoA, 4-methyl butyl-CoA and 2-methyl propyl-CoA from Ile, Leu and Val, respectively) (141,149) by the action of branched-chain α-keto acid dehydrogenase (BCKDH), which substitutes a CO 2 from the 2-oxo acid for the CoA cofactor with NAD + reduction (140). Then, the acyl-CoA can be converted to a fatt y acid by phosphate acetyltransferase (PAT) (18,140).…”

Analysis of Loss-of-Function Mutants in Aspartate Kinase and Homoserine Dehydrogenase Genes Points to Complexity in the Regulation of Aspartate-Derived Amino Acid Contents

“…His biosynthesis uses Gln and Glu as substrates (Stepansky and Leustek, 2006); free His had a very strong positive correlation with free Gln (r = 0.9028, P = 0.0003) and a moderate positive correlation with free Glu (r = 0.6327, P = 0.0497). Leu can be synthesized from the transamination between Glu and 4-methyl-2-oxopentanoate (Binder, 2010); free Leu had a moderate positive correlation with free Glu (r = 0.5385, P = 0.1083). It is not uncommon that perturbation in the biosynthesis of Asp-derived amino acids results in changes in other amino acids.…”