title: Elucidation of stability determinants of cold-adapted monomeric isocitrate dehydrogenase from a psychrophilic bacterium, Colwellia maris, by construction of chimeric enzymes.
abstract: To elucidate determinants of differences in thermostability between mesophilic and psychrophilic monomeric isocitrate dehydrogenases (IDHs) from Azotobacter vinelandii (AvIDH) and Colwellia maris (CmIDH), respectively, chimeric enzymes derived from the two IDHs were constructed based on the recently resolved three-dimensional structure of AvIDH, and several characteristics of the two wild-type and six chimeric IDHs were examined. These characteristics were then compared with those of dimeric IDH from Escherichia coli (EcIDH). All recombinant enzymes with a (His)(6)-tag attached to the N-terminal were overexpressed in the E. coli cells and purified by Ni(2+)-affinity chromatography. The catalytic activity (k(cat)) and catalytic efficiency (k(cat)/K(m)) of the wild-type AvIDH and CmIDH were higher than those of EcIDH, implying that an improved catalytic rate more than compensates for the loss of a catalytic site in the former two IDHs due to monomerization. Analyses of the thermostability and kinetic parameters of the chimeric enzymes indicated that region 2, corresponding to domain II, and particularly region 3 located in the C-terminal part of domain I, are involved in the thermolability of CmIDH, and that the corresponding two regions of AvIDH are important for exhibiting higher catalytic activity and affinity for isocitrate than CmIDH. The relationships between the stability, catalytic activity and structural characteristics of AvIDH and CmIDH are discussed.
authors.affiliation: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Seiya
authors.initials: S
authors.lastname: Watanabe
authors.affiliation: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Yasutake
authors.affiliation: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Isao
authors.initials: I
authors.lastname: Tanaka
authors.affiliation: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Takada
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D016948:Azotobacter vinelandii / Q000201:enzymology / Q000235:genetics; D001483:Base Sequence; D003080:Cold Temperature; D004269:DNA, Bacterial / Q000235:genetics; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D020563:Gammaproteobacteria / Q000201:enzymology* / Q000235:genetics; D007521:Isocitrate Dehydrogenase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013696:Temperature; D014357:Trypsin
chemical_list: D004269:DNA, Bacterial; D011993:Recombinant Fusion Proteins; D007521:Isocitrate Dehydrogenase; D014357:Trypsin