2-oxoisovalerate dehydrogenase subunit beta, mitochondrial (BCKDHB) (BCKDHB)

2-oxoisovalerate dehydrogenase subunit beta (BCKDHB) is a critical component of the mitochondrial branched-chain alpha-keto acid dehydrogenase (BCKD) complex (UniProt P21953). This multienzyme complex catalyzes the oxidative decarboxylation of branched-chain alpha-keto acids, which is the second and rate-limiting step in the catabolism of the essential branched-chain amino acids (BCAAs) leucine, isoleucine, and valine (MedlinePlus). BCKDHB specifically forms the beta subunit of the E1 decarboxylase component, which requires thiamine pyrophosphate as a cofactor (UniProt). Mutations in the BCKDHB gene lead to Maple Syrup Urine Disease (MSUD) Type 1B, a metabolic disorder characterized by the toxic accumulation of BCAAs and their keto acid derivatives, resulting in neurological impairment and a characteristic sweet odor in the urine (NIH). Therapeutic strategies include dietary restriction of BCAAs, high-dose thiamine supplementation for responsive variants, and the use of sodium phenylbutyrate to enhance residual enzyme activity by inhibiting the regulatory kinase BCKDK (PubMed). Recent advancements also explore gene therapy to restore functional enzyme levels in affected patients (ResearchGate).

Other names

Branched-chain alpha-keto acid dehydrogenase E1 component beta chainBCKDE1BBCKDH E1-betaOVD1BMSUD1BBranched chain keto acid dehydrogenase E1 subunit beta

Thiamine acts as a direct cofactor for the E1 subunit, while sodium phenylbutyrate indirectly activates the complex by inhibiting BCKDK, the kinase responsible for its inhibitory phosphorylation.