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 ...
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.
Related Citations:
Crosstalk between thiamin diphosphate binding and phosphorylation loop conformation in human branched-chain A-ketoacid decarboxylase/dehydrogenase Li, J., Wynn, R.M., Machius, M., Chuang, J.L., KARTHIKEYAN, S., Tomchick, D.R., Chuang, D.T. (2004) J Biol Chem 279: 32968
Roles of His291-alpha and His146-beta in the reductive acylation reaction catalyzed by human branched-chain alpha-ketoacid dehydrogenase: refined phosphorylation loop structure in the active site Wynn, R.M., Machius, M., Chuang, J.L., Li, J., Tomchick, D.R., Chuang, D.T. (2003) J Biol Chem 278: 43402
Organizational Affiliation:
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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