Molecular mechanism for regulation of the human mitochondrial branched-chain alpha-ketoacid dehydrogenase complex by phosphorylation.
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.
Wynn
R Max
RM
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Kato
Masato
M
Machius
Mischa
M
Chuang
Jacinta L
JL
Li
Jun
J
Tomchick
Diana R
DR
Chuang
David T
DT
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D012694:Serine / Q000378:metabolism; D013997:Time Factors
D012694:Serine; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)