title: Identification of the rate-limiting step of the peroxygenase reactions catalyzed by the thermophilic cytochrome P450 from Sulfolobus tokodaii strain 7.
abstract: Cytochrome P450 from the thermoacidophilic crenarchaeon Sulfolobus tokodaii strain 7 (P450st) is a thermophilic cytochrome P450 that shows high tolerance of harsh conditions and is capable of catalyzing some peroxygenase reactions. Here, we investigated the pH dependence of the peroxygenase reactions catalyzed by wild-type P450st and a mutant in which the residues located close to the proximal heme ligand are mutated. Both hydrogen peroxide-driven ethylbenzene hydroxylation and styrene epoxidation by wild-type P450st were found to be activated in weak acidic and weak basic solutions. Under these conditions, the Michaelis constant for hydrogen peroxide (KmH2O2 ) was decreased. The turnover rate (kcat ) of ethylbenzene hydroxylation was increased and followed an S-shaped curve, with an increase in the pH value. The apparent acid dissociation constant (pKa (app) ) of the kcat was 7.0, which suggests that the rate-limiting step of this reaction is deprotonation of the Fe(III) -H2 O2 complex. By introducing a double mutation around the proximal heme ligand, the peroxygenase activity was increased over a wide pH range, and was dramatically increased at pH 5. The spectroscopic properties of this F310A/A320Q mutant indicated that the Lewis acidity of the heme was increased by this mutation. Kinetic investigations showed that the increase in the Lewis acidity of the heme facilitates the reaction rate of the rate-limiting step of peroxygenase reactions and decreases the KmH2O2 value. Differences in the pH dependence of the kcat value between wild-type P450st and the mutant suggest that the rate-limiting step switches to protonation of the ferric-hydroperoxo species (compound 0) under alkaline conditions.
authors.affiliation: Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Japan.
authors.forename: Shohei
authors.initials: S
authors.lastname: Hayakawa
authors.affiliation: Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Japan.|Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health and Science University, Beaverton, OR, USA.
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Matsumura
authors.affiliation: Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Japan.
authors.forename: Nobuhumi
authors.initials: N
authors.lastname: Nakamura
authors.affiliation: Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Yohda
authors.affiliation: Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohno
mesh_terms: D019943:Amino Acid Substitution; D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001555:Benzene Derivatives / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006900:Hydroxylation; D007700:Kinetics; D058116:Lewis Acids / Q000737:chemistry; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016944:Sulfolobus / Q000235:genetics / Q000378:metabolism*
chemical_list: D019843:Archaeal Proteins; D001555:Benzene Derivatives; D058116:Lewis Acids; D011994:Recombinant Proteins; D006418:Heme; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C022333:peroxygenase; C004912:ethylbenzene
keywords: cytochrome P450; pH dependence; peroxygenase reaction; rate-limiting step; site-directed mutagenesis