title: L-Threonine dehydrogenase from the hyperthermophilic archaeon Pyrococcus horikoshii OT3: gene cloning and enzymatic characterization.
abstract: A gene encoding the L-threonine dehydrogenase homologue has been identified in a hyperthermophlic archaeon Pyrococcus horikoshii OT3 via genome sequencing. The gene was cloned and expressed in Escherichia coli. The purified enzyme from the recombinant E. coli was extremely thermostable; the activity was not lost after incubation at 100 degrees C for 20 min. The enzyme (molecular mass: 192 kDa) is composed of a tetrameric structure with a type of subunit (41 kDa). The enzyme is specific for NAD and utilizes L-threonine, L-serine and DL-threo-3-phenylserine as the substrate. The enzyme required divalent cations such as Zn(2+), Mn(2+) and Co(2+) for the activity, and contained one zinc ion/subunit. The K(m) values for L-threonine and NAD at 50 degrees C were 0.20 mM and 0.024 mM, respectively. Kinetic analyses indicated that the L-threonine oxidation reaction proceeds via a random mechanism with regard to the binding of L-threonine and NAD. The enzyme showed pro-R stereospecificity for hydrogen transfer at the C4 position of the nicotinamide moiety of NADH. This is the first description of the characteristics of an L-threonine dehydrogenase from the archaea domain.
authors.affiliation: Department of Biological Science and Technology, Faculty of Engineering, The University of Tokushima, 2-1 Minamijosanjimacho, Tokushima, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shimizu
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Sakuraba
authors.forename: Ryushi
authors.initials: R
authors.lastname: Kawakami
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Goda
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kawarabayasi
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Ohshima
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D003001:Cloning, Molecular; D006859:Hydrogen / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009249:NADP / Q000378:metabolism; D043902:Pyrococcus horikoshii / Q000201:enzymology* / Q000235:genetics*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D012694:Serine; D009249:NADP; D006859:Hydrogen; D000429:Alcohol Oxidoreductases; C023159:L-threonine 3-dehydrogenase