Cytosolic epoxide hydrolase

Meijer, Johan; DePierre, Joseph W.

doi:10.1016/0009-2797(88)90100-7

Cited by 99 publications

(27 citation statements)

References 188 publications

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“…Not only do the core domains of these enzymes have similar ␣/␤ structures, but the cap domains also have similar ␣ structures, although superimposition is reported to work less well for the cap domains of the ␣/␤ hydrolase superfamily than for the core domains (24,33,34). The active sites in FAc-DEX FA1 and haloalkane dehalogenases are small compared with those in epoxide hydrolases, possibly because epoxide hydrolases accept larger substrates than FAc-DEX FA1 and haloalkane dehalogenases (17,20,26,29,32,37).…”

Section: Resultsmentioning

confidence: 99%

X-Ray Crystallographic and Mutational Studies of Fluoroacetate Dehalogenase from Burkholderia sp. Strain FA1

et al. 2009

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Fluoroacetate dehalogenase catalyzes the hydrolytic defluorination of fluoroacetate to produce glycolate. The enzyme is unique in that it catalyzes the cleavage of a carbon-fluorine bond of an aliphatic compound: the bond energy of the carbon-fluorine bond is among the highest found in natural products. The enzyme also acts on chloroacetate, although much less efficiently. We here determined the X-ray crystal structure of the enzyme from Burkholderia sp. strain FA1 as the first experimentally determined three-dimensional structure of fluoroacetate dehalogenase. The enzyme belongs to the ␣/␤ hydrolase superfamily and exists as a homodimer. Each subunit consists of core and cap domains. The catalytic triad, Asp104-His271-Asp128, of which Asp104 serves as the catalytic nucleophile, was found in the core domain at the domain interface. The active site was composed of Phe34, Asp104, Arg105, Arg108, Asp128, His271, and Phe272 of the core domain and Tyr147, His149, Trp150, and Tyr212 of the cap domain. An electron density peak corresponding to a chloride ion was found in the vicinity of the N 1 atom of Trp150 and the N 2 atom of His149, suggesting that these are the halide ion acceptors. Site-directed replacement of each of the active-site residues, except for Trp150, by Ala caused the total loss of the activity toward fluoroacetate and chloroacetate, whereas the replacement of Trp150 caused the loss of the activity only toward fluoroacetate. An interaction between Trp150 and the fluorine atom is probably an absolute requirement for the reduction of the activation energy for the cleavage of the carbon-fluorine bond.Fluoroacetate is a naturally occurring organofluorine compound. An actinomycete, "Streptomyces cattleya" (30), and some plants in Australia and Africa (2) produce this highly toxic compound. Fluoroacetate has a carbon-fluorine bond, whose dissociation energy is among the highest found in nature (8). Despite this fact, fluoroacetate dehalogenases (FAcDEXs) from Burkholderia sp. strain FA1 (FAc-DEX FA1) (20) and Delftia acidovorans strain B (formerly Moraxella sp. strain B; FAc-DEX H1) (16) catalyze the hydrolytic defluorination of fluoroacetate to produce glycolate. These enzymes are unique in that they catalyze the cleavage of the carbon-fluorine bond, which is much stronger than other carbon-halogen bonds.FAc-DEXs show weak but significant sequence similarity to proteins that belong to the ␣/␤ hydrolase superfamily, such as epoxide hydrolases from Agrobacterium radiobacter AD1 (37) and humans and haloalkane dehalogenases from Sphingobium japonicum UT26 (formerly Sphingomonas paucimobilis UT26) (32) and Xanthobacter autotrophicus GJ10 (17). Although haloalkane dehalogenases of this superfamily catalyze the hydrolytic cleavage of carbon-halogen bonds, none of them catalyzes the cleavage of a carbon-fluorine bond. Dehalogenases that belong to other families, such as L-2-haloacid dehalogenase (22), DL-2-haloacid dehalogenase (28), and haloalcohol dehalogenase (42), also do not catalyze the cleavage of a carbon-...

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Section: Resultsmentioning

confidence: 99%

X-Ray Crystallographic and Mutational Studies of Fluoroacetate Dehalogenase from Burkholderia sp. Strain FA1

et al. 2009

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“…sEH in general catalyzes the hydrolysis of trans-substituted epoxides, as well as various aliphatic epoxides derived from fatty acid metabolism [33,52]. The prototypic substrate used to distinguish sEH activity from microsomal epoxide hydrolase activity is trans-stilbene oxide (Fig.…”

Section: Substrates and Inhibitorsmentioning

confidence: 99%

“…Soluble epoxide hydrolase (or cytosolic epoxide hydrolase) is a xenobiotic metabolizing enzyme that also participates in the metabolism of endogenously derived fatty acid epoxides [33]. The protein responsible for soluble epoxide hydrolase (sEH) activity has been purified and characterized [34][35][36][37].…”

Section: Introductionmentioning

confidence: 99%

Epoxide hydrolases: biochemistry and molecular biology

Fretland

Omiecinski

2000

Chemico-Biological Interactions

275

185

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Epoxides are organic three-membered oxygen compounds that arise from oxidative metabolism of endogenous, as well as xenobiotic compounds via chemical and enzymatic oxidation processes, including the cytochrome P450 monooxygenase system. The resultant epoxides are typically unstable in aqueous environments and chemically reactive. Biol. Chem. 260 (1985) 1630-1640). Therefore, it is of vital importance for the biological organism to regulate levels of these reactive species. The epoxide hydrolases (E.C. 3.3.2.3) belong to a sub-category of a broad group of hydrolytic enzymes that include esterases, proteases, dehalogenases, and lipases Beetham et al. (DNA Cell Biol. 14 (1995) 61 -71). In particular, the epoxide hydrolases are a class of proteins that catalyze the hydration of chemically reactive epoxides to their corresponding dihydrodiol products. Simple epoxides are hydrated to their corresponding vicinal dihydrodiols, and arene oxides to trans-dihydrodiols. In general, this hydration leads to more stable and less reactive intermediates, however exceptions do exist. In mammalian species, there are at least five epoxide hydrolase forms, microsomal cholesterol 5,6-oxide hydrolase, hepoxilin A 3 hydrolase, leukotriene A 4 hydrolase, soluble, and microsomal epoxide hydrolase. Each of these enzymes is distinct chemically and immunologically. Table 1 illustrates some general properties for each of these classes of hydrolases. Fig. 1 provides an overview of selected model substrates for each class of epoxide hydrolase.

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“…Most of our knowledge about cEH has been gained from studies on the purified enzymes from mouse and rabbit liver (12). These two species, together with the hamster, possess by far the highest TSO-hydrolyzing activity of all investigated species (165-335 nmole/min x g liver and 106-129 nmole/min x g liver compared to human and rat liver with 15-22 nmole/min x g and 10-15 nmole/min x g, respectively) (13).…”

Section: Introductionmentioning

confidence: 99%

Rat and human liver cytosolic epoxide hydrolases: evidence for multiple forms at level of protein and mRNA.

Thomas

Schladt

Doehmer

et al. 1990

Environ Health Perspect

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Two forms of human liver cytosolic epoxide hydrolase (cEH) with diagnostic substrate specificity for trans-stilbene oxide (cEHTso) and cis-stilbene oxide (cEHcso) have been identified, and cEHcso was purified to apparent homogeneity. The enzyme had a monomer molecular weight of 49 kDa and an isoelectric point of 9.2. Pure cEHcso hydrolyzed CSO at a rate of 145 nmole/min/mg. TSO was not metabolized at a detectable level, and like cEHTso, the enzyme was about three times more active at pH 7.4 than at pH 9.0. Unlike cEHrso, cEHcso was efficiently inhibited by 1 mM 1-trichloropropene oxide (90.5%) and 1 mM STO (92%). Similarly, liver cEH purified 541-fold from fenofibrate induced Fischer 344 rats was shown to be a native 120 kDa dimer of two 61 kDa subunits. The enzyme expressed maximum activity of 205 nmole/min/mg at pH 7.4 toward the diagnostic substrate TSO with an apparent Km of 1.7 ,M. In Western blots, polyclonal antibodies against rat liver cEH were shown to recognize a single 61 kDa protein band from liver cytosol of rat, mouse, guinea pig, Syrian hamster, and rabbit. This antibody precipitated neither human liver cEHTso or cEHcso. Antibodies against rat liver microsomal epoxide hydrolase reacted with cEHcso in the Western blot and on immunoprecipitation. Using antibodies against rat liver cEH, 24 positive clones were picked upon colony blot screening of a pEX 1IE. coli POP 2136 expression library. After Northern blotting against rat liver total RNA, clone 24 recognized a second mRNA-species besides the putative message for cEHTso, thus providing strong evidence for the multiplicity of rat liver cEH as well. The importance of these findings for the control of reactive metabolites ofvarious origins is discussed.

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Cytosolic epoxide hydrolase

Cited by 99 publications

References 188 publications

X-Ray Crystallographic and Mutational Studies of Fluoroacetate Dehalogenase from Burkholderia sp. Strain FA1

X-Ray Crystallographic and Mutational Studies of Fluoroacetate Dehalogenase from Burkholderia sp. Strain FA1

Epoxide hydrolases: biochemistry and molecular biology

Rat and human liver cytosolic epoxide hydrolases: evidence for multiple forms at level of protein and mRNA.

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