Activity of human dihydrolipoamide dehydrogenase is largely reduced by mutation at isoleucine-51 to alanine.
Dihydrolipoamide dehydrogenase (E3) belongs to the pyridine nucleotide-disulfide oxidoreductase family including glutathione reductase and thioredoxin reductase. It catalyzes the reoxidation of dihydrolipoyl moiety of the acyltransferase components of three alpha-keto acid dehydrogenase complexes and of the hydrogen-carrier protein of the glycine cleavage system. Isoleucine-51 of human E3, located near the active disulfide center Cys residues, is highly conserved in most E3s from several sources. To examine the importance of this highly conserved Ile-51 in human E3 function, it was substituted with Ala using site-directed mutagenesis. The mutant was expressed in Escherichia coli and highly purified using an affinity column. Its E3 activity was decreased about 100-fold, indicating that the conservation of the Ile-51 residue in human E3 was very important to the efficient catalytic function of the enzyme. Its altered spectroscopic properties implied that conformational changes could occur in the mutant.
Department of Chemistry, College of Natural Science, Daegu University, Kyoungsan 712-714, Korea. hjkim@daegu.ac.kr
Hakjung
H
Kim
D000409:Alanine / Q000235:genetics*; D019943:Amino Acid Substitution; D002384:Catalysis; D008058:Dihydrolipoamide Dehydrogenase / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000235:genetics / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007532:Isoleucine / Q000235:genetics*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011487:Protein Conformation
D007532:Isoleucine; D008058:Dihydrolipoamide Dehydrogenase; D000409:Alanine