title: The crystal structures of mutated 3-isopropylmalate dehydrogenase from Thermus thermophilus HB8 and their relationship to the thermostability of the enzyme.
abstract: The structures of two mutant forms (G240A and L246E/V249M) of 3-isopropylmalate dehydrogenase from Thermus thermophilus HB8 were studied by X-ray crystallography. In the case of G240A, the replacement of glycine by alanine at residue 240 was expected to decrease the thermostability as a result of abnormal contacts between the methyl group of alanine and the peptide chain. However, the normal van der Waals' contacts were achieved owing to a shift in a bundle of beta-strands that yielded a vacant space for the alanine residue. The extended hydrogen bonds within the beta-sheet are the major reason for the decreased thermostability of G240A. The mutations in L246E/V249M are located in an alpha-helix region which is involved in subunit-subunit contact via hydrophobic interaction. Loosening of the subunit-subunit contact owing to ionic repulsion was the major cause of the lower heat stability of L246E/V249M.
authors.affiliation: Department of Life Science, Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama.
authors.forename: H
authors.initials: H
authors.lastname: Moriyama
authors.forename: K
authors.initials: K
authors.lastname: Onodera
authors.forename: M
authors.initials: M
authors.lastname: Sakurai
authors.forename: N
authors.initials: N
authors.lastname: Tanaka
authors.forename: H
authors.initials: H
authors.lastname: Kirino-Kagawa
authors.forename: T
authors.initials: T
authors.lastname: Oshima
authors.forename: Y
authors.initials: Y
authors.lastname: Katsube
mesh_terms: D050539:3-Isopropylmalate Dehydrogenase; D000429:Alcohol Oxidoreductases / Q000096:biosynthesis / Q000737:chemistry*; D000595:Amino Acid Sequence; D001120:Arginine; D001483:Base Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D017931:DNA Primers; D004795:Enzyme Stability; D006358:Hot Temperature; D006860:Hydrogen Bonding; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D013816:Thermodynamics; D016963:Thermus thermophilus / Q000201:enzymology*
chemical_list: D017931:DNA Primers; D046911:Macromolecular Substances; D011994:Recombinant Proteins; D001120:Arginine; D000429:Alcohol Oxidoreductases; D050539:3-Isopropylmalate Dehydrogenase