Expression, characterization, and improvement of a newly cloned halohydrin dehalogenase from Agrobacterium tumefaciens and its application in production of epichlorohydrin

Enhanced catalytic efficiency and thermostability of glucose isomerase from Thermoanaerobacter ethanolicus via site-directed mutagenesis

Glucose isomerase (GI) is a key enzyme in the preparation of high fructose corn syrup (HFCS). In this study, a mutant TEGI-M-L38 M/V137 L (TEGI-M2) of glucose isomerase (TEGI-M) originated from Thermoanaerobacter ethanalicus CCSD1 was obtained by site-directed mutagenesis. The TEGI-M2 showed an optimal activity at 85 ℃ and pH 6.5 with the divalent cations Co²⁺ and Mg²⁺. The structural differences between TEGI-M and TEGI-M2 were investigated based on the homology modeling and molecular docking, to elucidate the mechanism of improvement in the enzymatic properties. Compared with the original enzyme, the TEGI-M2 showed a 2.0-fold increased enzyme activity and a decreased K_m from 234.2 mM to 85.9 mM. Finally, the application of mutant TEGI-M2 in HFCS one-step biosynthesis was attempted, resulting in a d-fructose yield of 67.3 %, which was 14.3 % higher than that of TEGI-M. This improved catalytic performance of TEGI-M2 was of great importance for the industrial preparation of d-fructose in one-step process.

Molecular modification of a halohydrin dehalogenase for kinetic regulation to synthesize optically pure (S)-epichlorohydrin

Asymmetric synthesis of chiral epichlorohydrin (ECH) from 1,3-dichloro-2-propanol (1,3-DCP) using halohydrin dehalogenases (HHDHs) is of great value due to the 100% theoretical yield and high enantioselectivity. The vital problem in the asymmetric synthesis is to prepare optically pure ECH. In this study, key amino acid residues located at halide ion channels of HheC (P175S/W249P) (HheC_PS) were modified to regulate the kinetic parameters. HheC_PS I81W, F86N and V94R were constructed with the corresponding halide ion channels destroyed. The catalytically efficiencies (k_cat/K_m) of the three mutants exhibited 0.38-, 0.23- and 0.23-fold decrease toward (S)-ECH and the reverse reaction was significantly inhibited. As the results, (S)-ECH was synthesized with >99% enantiomeric excess (e.e.) and 63.42%, 67.08% and 57.01% yields, respectively, under 20 mM 1,3-DCP as substrate. To our knowledge, this is the first investigation of the molecule kinetic modification of HHDHs and also the first report for the biosynthesis of optically pure (S)-ECH from 1,3-DCP using HHDHs.

Biosynthesis of chiral epichlorohydrin using an immobilized halohydrin dehalogenase in aqueous and non-aqueous phase

Asymmetric synthesis of chiral epichlorohydrin (ECH) from 1,3-dichloro-2-propanol (1,3-DCP) using halohydrin dehalogenase (HHDH) is of great value due to the 100% theoretical yield and high enantioselectivity. In this study, HheC (P175S/W249P) was immobilized on an A502Ps resin and used for the preparation of (S)-ECH. In aqueous system, the immobilized HheC catalyzed the biosynthesis of (S)-ECH with 83.78% yield and 92.53% enantiomeric excess (ee) at 1,3-DCP concentration of 20 mM. The non-aqueous system was further developed using water saturated ethyl acetate as solvent and reaction phase. The non-aqueous bioconversion system showed higher enantioselectivity (>98% ee) toward (S)-ECH production with modest conversion (52.34%) compared with ever reported aqueous reactions. Batch reactions were performed in a packed-bed bioreactor for 45 batches in aqueous phase and 24 batches in non-aqueous phase. The present work demonstrated the potential of immobilized HheC (P175S/W249P) in aqueous and non-aqueous phase biosynthesis of chiral ECH.

Recent advances on halohydrin dehalogenases-from enzyme identification to novel biocatalytic applications

Halohydrin dehalogenases are industrially relevant enzymes that catalyze the reversible dehalogenation of vicinal haloalcohols with formation of the corresponding epoxides. In the reverse reaction, also other negatively charged nucleophiles such as azide, cyanide, or nitrite are accepted besides halides to open the epoxide ring. Thus, novel C-N, C-C, or C-O bonds can be formed by halohydrin dehalogenases, which makes them attractive biocatalysts for the production of various β-substituted alcohols. Despite the fact that only five individual halohydrin dehalogenase enzyme sequences have been known until recently enabling their heterologous production, a large number of different biocatalytic applications have been reported using these enzymes. The recent characterization of specific sequence motifs has facilitated the identification of novel halohydrin dehalogenase sequences available in public databases and has largely increased the number of recombinantly available enzymes. These will help to extend the biocatalytic repertoire of this enzyme family and to foster novel biotechnological applications and developments in the future. This review gives a general overview on the halohydrin dehalogenase enzyme family and their biochemical properties and further focuses on recent developments in halohydrin dehalogenase biocatalysis and protein engineering.

Enzymatic approaches to the preparation of chiral epichlorohydrin

Enantiomerically pure epichlorohydrin is a key chiral synthon in the preparation of 4-chloro-3-hydroxybutyrate, pheromones,l-carnitine, and β-adrenergic blockers.