A novel branched-chain amino acid metabolon. Protein-protein interactions in a supramolecular complex.

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Islam MM, Wallin R, Wynn RM, Conway M, Fujii H, Mobley JA, Chuang DT, Hutson SM

A novel branched-chain amino acid metabolon. Protein-protein interactions in a supramolecular complex.

J Biol Chem. 2007 Apr 20;282(16):11893-903. Epub 2007 Feb 21.

PubMed ID

17314104 [ View in PubMed

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Abstract

The catabolic pathways of branched-chain amino acids have two common steps. The first step is deamination catalyzed by the vitamin B(6)-dependent branched-chain aminotransferase isozymes (BCATs) to produce branched-chain alpha-keto acids (BCKAs). The second step is oxidative decarboxylation of the BCKAs mediated by the branched-chain alpha-keto acid dehydrogenase enzyme complex (BCKD complex). The BCKD complex is organized around a cubic core consisting of 24 lipoate-bearing dihydrolipoyl transacylase (E2) subunits, associated with the branched-chain alpha-keto acid decarboxylase/dehydrogenase (E1), dihydrolipoamide dehydrogenase (E3), BCKD kinase, and BCKD phosphatase. In this study, we provide evidence that human mitochondrial BCAT (hBCATm) associates with the E1 decarboxylase component of the rat or human BCKD complex with a K(D) of 2.8 microM. NADH dissociates the complex. The E2 and E3 components do not interact with hBCATm. In the presence of hBCATm, k(cat) values for E1-catalyzed decarboxylation of the BCKAs are enhanced 12-fold. Mutations of hBCATm proteins in the catalytically important CXXC center or E1 proteins in the phosphorylation loop residues prevent complex formation, indicating that these regions are important for the interaction between hBCATm and E1. Our results provide evidence for substrate channeling between hBCATm and BCKD complex and formation of a metabolic unit (termed branched-chain amino acid metabolon) that can be influenced by the redox state in mitochondria.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
NADH	Dihydrolipoyl dehydrogenase, mitochondrial	Protein	Humans	Unknown	Not Available	Details