Purification and characterization of a recombinantCaulobacter crescentus epoxide hydrolase

Biosynthesis of chiral diols from alkenes using metabolically engineered type II methanotroph

Methanotrophs are environmentally friendly microorganisms capable of converting gas to liquid using methane monooxygenases (MMOs). In addition to methane-to-methanol conversion, MMOs catalyze the conversion of alkanes to alcohols and alkenes to epoxides. Herein, the efficacy of epoxidation by type I and II methanotrophs was investigated, and type II methanotrophs were observed to be more efficient in converting alkenes to epoxides. Subsequently, three (Epoxide hydrolase) EHs of different origins were overexpressed in the type II methanotroph Methylosinus trichosporium OB3b to produce 1,2-diols from epoxide. Methylosinus trichosporium OB3b expressing Caulobacter crescentus EH produced the highest amount of (R)-1,2-propanediol (251.5 mg/L) from 1-propene. These results demonstrate the possibility of using methanotrophs as a microbial platform for diol production and the development of a continuous bioreactor for industrial applications.

Production of (R)-styrene oxide by recombinant whole-cell biocatalyst in aqueous and biphasic system

The enantioselective resolution of racemic styrene oxide (rac-SO) to (R)-SO by whole cells of a recombinant Escherichia coli expressing epoxide hydrolase (EH) activity in aqueous and biphasic system were studied. Some parameters that may alter this bio-resolution, such as the concentration of recombinant cell, substrate and product were evaluated. The effect of the addition of different additives on the course of rac-SO biotransformation was also investigated. The results showed that the yield and the enantiomeric excess (ee) of (R)-SO were dependent on these variables. When the kinetic resolution was conducted with 350 mM of rac-SO, enantiopure (R)-SO with high (≥99%) ee was obtained with a yield of 38.2% yield at 12.2 h in the presence of 10% (v/v) Tween 80. An isooctane/aqueous system was developed to overcome the adverse factors in the aqueous phase, resulting in an improvement of yield from 38.2% to 42.9%. The results will provide a useful guidance for further application of this enzyme in the biocatalytic production of chiral synthons.

Cloning and characterization of an epoxide hydrolase from Cupriavidus metallidurans-CH34

A putative epoxide hydrolase-encoding gene was identified from the genome sequence of Cupriavidus metallidurans CH34. The gene was cloned and overexpressed in Escherichia coli with His(6)-tag at its N-terminus. The epoxide hydrolase (CMEH) was purified to near homogeneity and was found to be a homodimer, with subunit molecular weight of 36 kDa. The CMEH had broad substrate specificity as it could hydrolyze 13 epoxides, out of 15 substrates tested. CMEH had high specific activity with 1,2-epoxyoctane, 1,2-epoxyhexane, styrene oxide (SO) and was also found to be active with meso-epoxides. The enzyme had optimum pH and temperature of 7.5 and 37°C respectively, with racemic SO. Biotransformation of 80 mM SO with recombinant whole E. coli cells expressing CMEH led to 56% ee(P) of (R)-diol with 77.23% conversion in 30 min. The enzyme could hydrolyze (R)-SO, ∼2-fold faster than (S)-SO, though it accepted both (R)- and (S)-SO with similar affinity as K(m)(R) and K(m)(S) of CMEH were 2.05±0.42 and 2.11±0.16 mM, respectively. However, the k(cat)(R) and k(cat)(S) for the two enantiomers of SO were 4.80 and 3.34 s(-1), respectively. The wide substrate spectrum exhibited by CMEH combined with the fast conversion rate makes it a robust biocatalyst for industrial use. Regioselectivity studies with enantiopure (R)- and (S)-SO revealed that with slightly altered regioselectivity, CMEH has a high potential to synthesize an enantiopure (R)-PED, through an enantioconvergent hydrolytic process.

Molecular engineering of epoxide hydrolase and its application to asymmetric and enantioconvergent hydrolysis

Safety and regulatory issues favor increasing use of enantiopure compounds in pharmaceuticals. Enantiopure epoxides and diols are valuable intermediates in organic synthesis for the production of optically active pharmaceuticals. Enantiopure epoxide can be prepared using epoxide hydrolase (EH)-catalyzed asymmetric hydrolysis of its racemate. Enantioconvergent hydrolysis of racemic epoxides by EHs possessing complementary enantioselectivity and regioselectivity can lead to the formation of enantiopure vicinal diols with high yield. EHs are cofactor-independent and easy-to-use catalysts. EHs will attract much attention as commercial biocatalysts for the preparation of enantiopure epoxides and diols. In this paper, recent progress in molecular engineering of EHs is reviewed. Some examples and prospects of asymmetric and enantioconvergent hydrolysis reactions are discussed as supplements to molecular engineering to improve EH performance.