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
- PubMed: 12902323
- DOI: 10.1074/jbc.M306204200
- Primary Citation of Related Structures:
1OLU, 1OLS, 1OLX
- PubMed Abstract:
- Roles of Active Site and Novel K+ Ion-Binding Site Residues in Human Mitochondrial Branched-Chain Alpha-Ketoacid Decarboxylase/Dehydrogenase
Wynn, R.M., Ho, R., Chuang, J.L., Chuang, D.T.
(2001) J Biol Chem 274: 4168
- Crystal Structure of Human Branched-Chain Alpha-Ketoacid Dehydrogenase and the Molecular Basis of Multienzyme Complex Deficiency in Maple Syrup Urine Disease
Aevarsson, A., Chuang, J.L., Wynn, R.M., Turley, S., Chuang, D.T., Hol, W.G.J.
(2000) Structure 8: 277
We report here that alterations of either His291-alpha or His146-beta' in the active site of human branched-chain alpha-ketoacid dehydrogenase (E1b) impede both the decarboxylation and the reductive acylation reactions catalyzed by E1b as well as the ...
We report here that alterations of either His291-alpha or His146-beta' in the active site of human branched-chain alpha-ketoacid dehydrogenase (E1b) impede both the decarboxylation and the reductive acylation reactions catalyzed by E1b as well as the binding of cofactor thiamin diphosphate (ThDP). In a refined human E1b active-site structure, His291-alpha, which aligns with His407 in Escherichia coli pyruvate dehydrogenase and His263 in yeast transketolase, is on a largely ordered phosphorylation loop. The imidazole ring of His291-alpha in E1b coordinates to the terminal phosphate oxygen atoms of bound ThDP. The N3 atom of wild-type His146-beta', which can be protonated, binds a water molecule and points toward the aminopyrimidine ring of ThDP. Remarkably, the H291A-alpha mutation results in a complete order-to-disorder transition of the loop region, which precludes the binding of the substrate lipoyl-bearing domain to E1b. The H146A-beta' mutation, on the other hand, does not alter the loop structure, but nullifies the reductive acylation activity of E1b. Our results suggest that: 1) His291-alpha plays a structural rather than a catalytic role in the binding of cofactor ThDP and the lipoyl-bearing domain to E1b, and 2) His146-beta' is an essential catalytic residue, probably functioning as a proton donor in the reductive acylation of lipoamide on the lipoyl-bearing domain.
Departments of Biochemistry and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9038, USA.