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.
Primary Citation of Related Structures: 1OLS, 1OLU, 1OLX
PubMed Abstract:
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) ...
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.
Related Citations:
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. (2003) 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
Organizational Affiliation:
Departments of Biochemistry and Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9038, USA.
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