Publications

• Oxetane Substrates of Human Microsomal Epoxide Hydrolase.

  Toselli F., Fredenwall M., Svensson P., Li X.Q., Johansson A., Weidolf L., Hayes M.A.

  Oxetanyl building blocks are increasingly used in drug discovery because of the improved drug-like properties they confer on drug candidates, yet little is currently known about their biotransformation. A series of oxetane-containing analogs was studied and we provide the first direct evidence of ... >> More

  Oxetanyl building blocks are increasingly used in drug discovery because of the improved drug-like properties they confer on drug candidates, yet little is currently known about their biotransformation. A series of oxetane-containing analogs was studied and we provide the first direct evidence of oxetane hydrolysis by human recombinant microsomal epoxide hydrolase (mEH). Incubations with human liver fractions and hepatocytes were performed with and without inhibitors of cytochrome P450 (P450), mEH and soluble epoxide hydrolase (sEH). Reaction dependence on NADPH was investigated in subcellular fractions. A full kinetic characterization of oxetane hydrolysis is presented, in both human liver microsomes and human recombinant mEH. In human liver fractions and hepatocytes, hydrolysis by mEH was the only oxetane ring-opening metabolic route, with no contribution from sEH or from cytochrome P450-catalyzed oxidation. Minimally altering the structural elements in the immediate vicinity of the oxetane can greatly modulate the efficiency of hydrolytic ring cleavage. In particular, higher p<i>K</i>_a in the vicinity of the oxetane and an increased distance between the oxetane ring and the benzylic nitrogen improve reaction rate, which is further enhanced by the presence of methyl groups near or on the oxetane. This work defines oxetanes as the first nonepoxide class of substrates for human mEH, which was previously known to catalyze the hydrolytic ring opening of electrophilic and potentially toxic epoxide-containing drugs, drug metabolites, and exogenous organochemicals. These findings will be of value for the development of biologically active oxetanes and may be exploited for the biocatalytic generation of enantiomerically pure oxetanes and diols. << Less

  Drug Metab Dispos 45:966-973(2017) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Catalytic triad of microsomal epoxide hydrolase: replacement of Glu404 with Asp leads to a strongly increased turnover rate.

  Arand M., Mueller F., Mecky A., Hinz W., Urban P., Pompon D., Kellner R., Oesch F.

  Microsomal epoxide hydrolase (mEH) belongs to the superfamily of alpha/beta-hydrolase fold enzymes. A catalytic triad in the active centre of the enzyme hydrolyses the substrate molecules in a two-step reaction via the intermediate formation of an enzyme-substrate ester. Here we show that the mEH ... >> More

  Microsomal epoxide hydrolase (mEH) belongs to the superfamily of alpha/beta-hydrolase fold enzymes. A catalytic triad in the active centre of the enzyme hydrolyses the substrate molecules in a two-step reaction via the intermediate formation of an enzyme-substrate ester. Here we show that the mEH catalytic triad is composed of Asp226, Glu404 and His431. Replacing either of these residues with non-functional amino acids results in a complete loss of activity of the enzyme recombinantly expressed in Saccharomyces cerevisiae. For Glu404 and His431 mutants, their structural integrity was demonstrated by their retained ability to form the substrate ester intermediate, indicating that the lack of enzymic activity is due to an indispensable function of either residue in the hydrolytic step of the enzymic reaction. The role of Asp226 as the catalytic nucleophile driving the formation of the ester intermediate was substantiated by the isolation of a peptide fraction carrying the 14C-labelled substrate after cleavage of the ester intermediate with cyanogen bromide. Sequence analysis revealed that one of the two peptides within this sample harboured Asp226. Surprisingly, the replacement of Glu404 with Asp greatly increased the Vmax of the enzyme with styrene 7,8-oxide (23-fold) and 9, 10-epoxystearic acid (39-fold). The increase in Vmax was paralleled by an increase in Km with both substrates, in line with a selective enhancement of the second, rate-limiting step of the enzymic reaction. Owing to its enhanced catalytic properties, the Glu404-->Asp mutant might represent a versatile tool for the enantioselective bio-organic synthesis of chiral fine chemicals. The question of why all native mEHs analysed so far have a Glu in place of the acidic charge relay residue is discussed. << Less

  Biochem. J. 337:37-43(1999) [PubMed] [EuropePMC]

• Cloning, partial purification and in vivo developmental profile of expression of the juvenile hormone epoxide hydrolase of Ctenocephalides felis.

  Keiser K.C.L., Brandt K.S., Silver G.M., Wisnewski N.

  cDNAs encoding two different epoxide hydrolases (nCfEH1 and nCfEH2) were cloned from a cDNA library prepared from the wandering larval stage of the cat flea, Ctenocephalides felis. Predicted translations of the open reading frames indicated the clones encoded proteins of 464 (CfEH1) and 465 (CfEH2 ... >> More

  cDNAs encoding two different epoxide hydrolases (nCfEH1 and nCfEH2) were cloned from a cDNA library prepared from the wandering larval stage of the cat flea, Ctenocephalides felis. Predicted translations of the open reading frames indicated the clones encoded proteins of 464 (CfEH1) and 465 (CfEH2) amino acids. These proteins have a predicted molecular weight of 53 kDa and a putative 22 amino acid N-terminal hydrophobic membrane anchor. The amino acid sequences are 77% identical, and both are homologous to previously isolated epoxide hydrolases from Manduca sexta, Trichoplusia ni, and Rattus norvegicus. Purification of native juvenile hormone epoxide hydrolase (JHEH) from unfed adult cat fleas generated a partially pure protein that hydrolyzed juvenile hormone III to juvenile hormone III-diol. The amino terminal sequence of this;50-kDa protein is identical to the deduced amino terminus of the protein encoded by the nCfEH1 clone. Affinity-purified rabbit polyclonal antibodies raised against Escherichia coli-expressed HisCfEH1 recognized a approximately 50-kDa protein present in the partially purified fraction containing JHEH activity. Immunohistochemistry experiments using the same affinity-purified rabbit polyclonal antibodies localized the epoxide hydrolase in developing oocytes, fat body, and midgut epithelium of the adult flea. The presence of JHEH in various flea life stages and tissues was assessed by Northern blot and enzymatic activity assays. JHEH mRNA expression remained relatively constant throughout the different flea larval stages and was slightly elevated in the unfed adult flea. JHEH enzymatic activity was highest in the late larval, pupal, and adult stages. In all stages and tissues examined, JHEH activity was significantly lower than juvenile hormone esterase (JHE) activity, the other enzyme responsible for JH catalysis. << Less

  Arch. Insect Biochem. Physiol. 50:191-206(2002) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.