title: Molecular mechanism for regulation of the human mitochondrial branched-chain alpha-ketoacid dehydrogenase complex by phosphorylation.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
authors.forename: R Max
authors.initials: RM
authors.lastname: Wynn
authors.forename: Masato
authors.initials: M
authors.lastname: Kato
authors.forename: Mischa
authors.initials: M
authors.lastname: Machius
authors.forename: Jacinta L
authors.initials: JL
authors.lastname: Chuang
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Diana R
authors.initials: DR
authors.lastname: Tomchick
authors.forename: David T
authors.initials: DT
authors.lastname: Chuang
mesh_terms: 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
chemical_list: D012694:Serine; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)