Molecular mechanism for regulation of the human mitochondrial branched-chain alpha-ketoacid dehydrogenase complex by phosphorylation

Structure. 2004 Dec;12(12):2185-96. doi: 10.1016/j.str.2004.09.013.


The human mitochondrial branched-chain alpha-ketoacid dehydrogenase complex (BCKDC) is a 4 MDa macromolecular machine comprising three catalytic components (E1b, E2b, and E3), a kinase, and a phosphatase. The BCKDC overall activity is tightly regulated by phosphorylation in response to hormonal and dietary stimuli. We report that phosphorylation of Ser292-alpha in the E1b active site channel results in an order-to-disorder transition of the conserved phosphorylation loop carrying the phosphoryl serine. The conformational change is triggered by steric clashes of the phosphoryl group with invariant His291-alpha that serves as an indispensable anchor for the phosphorylation loop through bound thiamin diphosphate. Phosphorylation of Ser292-alpha does not severely impede the E1b-dependent decarboxylation of alpha-ketoacids. However, the disordered loop conformation prevents phosphorylated E1b from binding the E2b lipoyl-bearing domain, which effectively shuts off the E1b-catalyzed reductive acylation reaction and therefore completely inactivates BCKDC. This mechanism provides a paradigm for regulation of mitochondrial alpha-ketoacid dehydrogenase complexes by phosphorylation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) / metabolism*
  • Humans
  • Kinetics
  • Mitochondria / enzymology*
  • Mitochondria / metabolism
  • Phosphorylation
  • Protein Structure, Tertiary
  • Serine / metabolism
  • Time Factors


  • Serine
  • 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)

Associated data

  • PDB/1U5B
  • PDB/1X7W
  • PDB/1X7X
  • PDB/1X7Y
  • PDB/1X7Z
  • PDB/1X80