Dihydrolipoamide branched-chain transacylase E2 (DBT)

The Branched-chain alpha-keto acid dehydrogenase (BCKDH) complex E2 subunit, specifically its lipoyl domain, is a critical component of the mitochondrial multienzyme complex responsible for the oxidative decarboxylation of branched-chain alpha-keto acids (BCAAs) such as leucine, isoleucine, and valine (UniProt: P11182). The E2 subunit, known as dihydrolipoamide branched-chain transacylase, contains a lipoyl-bearing domain that facilitates the transfer of acyl groups to Coenzyme A during the catalytic cycle (PubMed: 15544939). Mutations in the DBT gene, which encodes this subunit, are a primary cause of Maple Syrup Urine Disease (MSUD), a condition where the inability to break down BCAAs leads to neurotoxic accumulation of ketoacids (NIH: GARD). Additionally, the lipoyl domain of BCKDH-E2 serves as a major autoantigen in Primary Biliary Cholangitis (PBC), where it is targeted by anti-mitochondrial antibodies (AMA) (PubMed: 16301011). While direct pharmacological targeting of the E2 subunit is limited, the complex's activity is therapeutically modulated by inhibiting BCKDH kinase with drugs like sodium phenylbutyrate to promote BCAA catabolism in metabolic disorders (PubMed: 21310481). This modulation is essential for managing patients with MSUD to prevent neurological damage and metabolic crises. The lipoyl domain's unique structure, involving a lipoylated lysine residue, is central to both its enzymatic function and its role as an immunodominant epitope.

Other names

BCKDH-E2Branched-chain alpha-keto acid dehydrogenase complex component E2BCOADC-E2Dihydrolipoyl transacylaseBranched-chain alpha-ketoacid dehydrogenase complex, E2 lipoyl domain

Activation of the BCKDH complex through the inhibition of BCKDH kinase, which reduces inhibitory phosphorylation of the E1 subunit, thereby increasing the flux of branched-chain amino acid catabolism; also acts as the primary immunodominant epitope for anti-mitochondrial antibodies in Primary Biliary Cholangitis.