title: Hydrophobic interaction at the subunit interface contributes to the thermostability of 3-isopropylmalate dehydrogenase from an extreme thermophile, Thermus thermophilus.
abstract: We cloned and sequenced the leuB gene encoding 3-isopropylmalate dehydrogenase from Escherichia coli K-12 (JM103). Errors (33 residues) were found and corrected in the sequence previously reported for the leuB gene of Thermus thermophilus. The three-dimensional structure of the thermophile enzyme and the amino acid sequence comparison suggested that a part of the high stability of the T. thermophilus enzyme is conferred by increased hydrophobic interaction at the subunit-subunit interface. Two residues at the interface of the T. thermophilus enzyme, Leu246 and Val249, are substituted with less hydrophobic residues, Glu and Met, respectively, in the E. coli enzyme, whereas other residues in this region are highly conserved. The mutated T. thermophilus enzyme [L246E, V249M]IPMDH had reduced stability to heat. Two residues of the E. coli dehydrogenase, Glu256 and Met259, were replaced with the corresponding residues from the thermophile sequence. The resulted mutant enzyme was more resistant to heat than the wild-type enzyme.
authors.affiliation: Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kirino
authors.forename: M
authors.initials: M
authors.lastname: Aoki
authors.forename: M
authors.initials: M
authors.lastname: Aoshima
authors.forename: Y
authors.initials: Y
authors.lastname: Hayashi
authors.forename: M
authors.initials: M
authors.lastname: Ohba
authors.forename: A
authors.initials: A
authors.lastname: Yamagishi
authors.forename: T
authors.initials: T
authors.lastname: Wakagi
authors.forename: T
authors.initials: T
authors.lastname: Oshima
mesh_terms: D050539:3-Isopropylmalate Dehydrogenase; D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000235:genetics; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005798:Genes, Bacterial; D006358:Hot Temperature; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D016963:Thermus thermophilus / Q000201:enzymology* / Q000235:genetics
chemical_list: D017931:DNA Primers; D004269:DNA, Bacterial; D000429:Alcohol Oxidoreductases; D050539:3-Isopropylmalate Dehydrogenase