2-oxoisovalerate dehydrogenase subunit beta, mitochondrial (BCKDHB)

2-oxoisovalerate dehydrogenase subunit beta, mitochondrial (BCKDHB) is a vital component of the E1 subunit within the branched-chain alpha-keto acid dehydrogenase (BCKDH) complex. This mitochondrial enzyme complex is responsible for the rate-limiting step in the catabolism of branched-chain amino acids (BCAAs), specifically leucine, isoleucine, and valine [UniProt: P21953]. BCKDHB works in conjunction with the alpha subunit to perform the thiamine pyrophosphate-dependent oxidative decarboxylation of alpha-keto acids derived from BCAAs [PubMed: 11555028]. Mutations in the BCKDHB gene lead to Maple Syrup Urine Disease (MSUD) type 1B, a condition characterized by the toxic accumulation of BCAAs and their keto acid derivatives, which can lead to severe neurological damage and metabolic crisis [NIH: Genetic and Rare Diseases Information Center]. While not a traditional target for inhibitory drugs, BCKDHB is a focus for therapeutic modulation; for example, thiamine is used as a cofactor to boost residual enzyme activity in certain MSUD phenotypes [PubMed: 25533354]. Additionally, sodium phenylbutyrate is employed to indirectly enhance the activity of this subunit by inhibiting the regulatory kinase that normally inactivates the BCKDH complex [PubMed: 21304891]. Current research also explores the use of pharmacological chaperones and gene therapy to restore the functional integrity of the BCKDHB subunit in affected patients [PubMed: 29127304].

Other names

Branched-chain alpha-keto acid dehydrogenase E1 component subunit betaBCKDE1BE1B2-oxoisovalerate dehydrogenase subunit beta

Thiamine serves as a required cofactor for the E1 subunit, facilitating the oxidative decarboxylation of branched-chain alpha-keto acids [PubMed: 25533354]. Sodium phenylbutyrate acts as an indirect activator by inhibiting BCKDH kinase (BCKDK), which prevents the phosphorylation-mediated inactivation of the BCKDH complex, thereby increasing the net activity of the beta subunit and its associated complex [PubMed: 21304891].