E1 component of the 2-oxoglutarate dehydrogenase (OGDH) complex which catalyzes the decarboxylation of 2-oxoglutarate, the first step in the conversion of 2-oxoglutarate to succinyl-CoA and CO(2). (R)-N(6)-lipoyl-L-lysyl-[dihydrolipoyllysine-residue succinyltransferase] + 2-oxoglutarate + H(+) = (R)-N(6)-(S(8)-succinyldihydrolipoyl)-L-lysyl-[dihydrolipoyllysine-residue succinyltransferase] + CO2 Homodimer. Part of the 2-oxoglutarate dehydrogenase (OGDH) complex composed of E1 (2-oxoglutarate dehydrogenase), E2 (dihydrolipoamide succinyltransferase) and E3 (dihydrolipoamide dehydrogenase); the complex contains multiple copies of the three enzymatic components (E1, E2 and E3). Belongs to the alpha-ketoglutarate dehydrogenase family.