Contains thiamine diphosphate. It acts not only on 3-methyl-2-oxobutanaoate, but also on 4-methyl-2-oxopentanoate and (S)-3-methyl-2-oxopentanoate, so that it acts on the 2-oxo acids that derive from the action of transaminases on valine, leucine and isoleucine. It is a component of the multienzyme 3-methyl-2-oxobutanoate dehydrogenase complex in which multiple copies of it are bound to a core of molecules of EC 188.8.131.52, dihydrolipoyllysine-residue (2-methylpropanoyl)transferase, which also binds multiple copies of EC 184.108.40.206, dihydrolipoyl dehydrogenase. It does not act on free lipoamide or lipoyllysine, but only on the lipoyllysine residue in EC 220.127.116.11.
scaffold of the human branched-chain alpha-ketoacid dehydrogenase complex, contains the lipoyl-bearing domain (hbLBD), the subunit-binding domain (hbSBD) and the inner core domain that are linked to carry out E2 functions in substrate channeling and recognition