E1 subunit of the branched-chain alpha-keto dehydrogenase complex that catalyzes both the decarboxylation of the alpha-ketoacid and the subsequent reductive acylation of the lipoyl moiety (another catalytic cofactor) that is covalently bound to E2 (PubMed:7883996). The branched-chain alpha-keto dehydrogenase complex catalyzes the overall conversion of alpha-keto acids to acyl-CoA and CO(2). It contains multiple copies of three enzymatic components: branched-chain alpha-keto acid decarboxylase (E1), lipoamide acyltransferase (E2) and lipoamide dehydrogenase (E3). (R)-N(6)-lipoyl-L-lysyl-[dihydrolipoyllysine-residue (2-methylpropanoyl)transferase] + 3-methyl-2-oxobutanoate + H(+) = (R)-N(6)-(S(8)-2-methylpropanoyldihydrolipoyl)-L-lysyl-[dihydrolipoyllysine-residue (2-methylpropanoyl)transferase] + CO2 Heterotetramer of alpha and beta chains. The disease is caused by variants affecting the gene represented in this entry. Bound potassium ions stabilize the protein structure. Belongs to the BCKDHA family. Truncated N-terminus.