Background: A NAD(P)H-dependent enoate reductase (OYE2p) from Saccharomyces cerevisiae YJM1341 was discovered by genome data mining for asymmetric reduction of (E/Z)-citral to (R)-citronellal with high enantioselectivity. Methods:This enzyme was heterologously expressed in E. coli and characterized for its biocatalytic properties. OYE2p was identified with reduction activities toward a diverse range of ɑ,β-unsaturated compounds bearing conjugated aldehyde, ketone, imide, carboxylic acid and ester.Results: OYE2p showed the highest specific activity at 40 °C and a pH optimum at 7.0-8.0. The stability of OYE2p was rather pH-independent, and the half-life time values of the enzyme at pH 6.0-8.0 were more than 257 h. With regard to the reduction of (E)-citral and (Z)-citral, OYE2p exhibited different selectivity patterns. (E)-citral was exclusively reduced to (R)-citronellal by OYE2p in ≥ 99% ee, which was independent on pH. OYE2p produced both enantiomers of citronellal from (Z)-citral, but showed (R)-citronellal formation tendency, and the ee value of (R)-citronellal was affected by pH in the reaction system. Accordingly, the ee values for (R)-citronellal formation increased with the increasing levels of E-isomer in the (E/Z)-citral mixture as well as the increase of pH. Under the reaction conditions (30 °C and pH 8.6), using purified OYE2p as catalyst, 200 mM (E/Z)-citral (an approximately 10:9 mixture of geometric E-isomer and Z-isomer) was efficiently converted to (R)-citronellal with 88.8% ee and 87.2% yield. Conclusion:All these positive features demonstrate high potential of OYE2p for practical synthesis of (R)-citronellal and in asymmetric reduction of activated alkenes.

MgER was characterized as a novel ene-reductase from yeast and showed great potential for the asymmetric reduction of activated C=C bonds of α,β-unsaturated compounds.

Objectives: 3,4-Dihydroxybutyric acid (3,4-DHBA) is a multi-functional C4 platform compound with wide applications in the synthesis of materials and pharmaceuticals. Currently, although the biosynthetic pathway for the production of 3,4-DHBA has been developed, low productivity still hampers its use on large scales. Here, a non-natural four-steps biosynthetic pathway was established in recombinant E. coli with a combinatorial strategy.Results: Firstly, several aldehyde dehydrogenases (ALDHs) were screened and characterized for catalyzing the dehydrogenation of 3,4-dihydroxybutanal (3,4-DHB) to 3,4-DHBA through in vitro enzyme assays. Secondly, a recombinant E. coli was successfully constructed to generate 3,4-DHBA from Dxylose by introducing the pathway containing BsGDH, YagF, PpMdlC and ALDH into E. coli with 3.04 g/L 3,4-DHBA obtained. Then, disruption of competing pathways by deleting xylA, ghrA, ghrB and adhP genes contributed to increase the accumulation of 3,4-DHBA by 87%. Final, fusion expression of PpMdlC and YagF resulted in an enhancement of 3,4-DHBA titer (7.71 g/L), as the highest titer reported so far. Conclusions: These results showed that deleting competing pathways and constructing fusion protein could signi cantly improve the 3,4-DHBA titer in engineered E. coli. This study E-C4-02 E. coli BL21(DE3) carrying pE01 and pA02 (pACYC184 harboring G. oxydans gox0499 and B. subtilis gdh) This study E-C4-03 E. coli BL21(DE3) carrying pE01 and pA03 (pACYC184 harboring G. oxydans gox1122 and B. subtilis gdh) This study E-01-C4 E. coli BL21(DE3) ΔxylA carrying pE01 and pA02 This study E-02-C4 E. coli BL21(DE3) ΔxylA ΔghrA carrying pE01 and pA02 This study E-03-C4 E. coli BL21(DE3) ΔxylA ΔghrA carrying pE01 and pA02 This study E-04-C4 E. coli BL21(DE3) ΔxylA ΔghrA ΔghrB carrying pE01 and pA02 This study E-05-C4 E. coli BL21(DE3) ΔxylA ΔghrA ΔghrB ΔadhP carrying pE01 and pA02 This study E-05-F4 E. coli BL21(DE3) ΔxylA ΔghrA ΔghrB ΔadhP carrying pE02 (pET28a harboring fusion gene of E. coli yagF and P. putida PpmdlC) and pA02 This study Construction of plasmids

Background(R)-[3,5-bis(trifluoromethyl)phenyl] ethanol [(R)-3,5-BTPE] is a valuable chiral intermediate for Aprepitant (Emend) and Fosaprepitant (Ivemend). Biocatalyzed asymmetric reduction is a preferred approach to synthesize highly optically active (R)-3,5-BTPE. However, the product concentration and productivity of reported (R)-3,5-BTPE synthetic processes remain unsatisfied.ResultsA NADPH-dependent carbonyl reductase from Lactobacillus kefir (LkCR) was discovered by genome mining for reduction of 3,5-bis(trifluoromethyl) acetophenone (3,5-BTAP) into (R)-3,5-BTPE with excellent enantioselectivity. In order to synthesize (R)-3,5-BTPE efficiently, LkCR was coexpressed with glucose dehydrogenase from Bacillus subtilis (BsGDH) for NADPH regeneration in Escherichia coli BL21 (DE3) cells, and the optimal recombinant strain produced 250.3 g/L (R)-3,5-BTPE with 99.9% ee but an unsatisfied productivity of 5.21 g/(L h). Then, four different linker peptides were used for the fusion expression of LkCR and BsGDH in E. coli to regulate catalytic efficiency of the enzymes and improved NADPH-recycling efficiency. Using the best strain (E. coli/pET-BsGDH-ER/K(10 nm)-LkCR), up to 297.3 g/L (R)-3,5-BTPE with enantiopurity >99.9% ee was produced via reduction of as much as 1.2 M of substrate with a 96.7% yield and productivity of 29.7 g/(L h).ConclusionsRecombinant E. coli/pET-BsGDH-ER/K(10 nm)-LkCR was developed for the bioreduction of 3,5-BTAP to (R)-3,5-BTPE, offered the best results in terms of high product concentration and productivity, demonstrating its great potential in industrial manufacturing of (R)-3,5-BTPE.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0585-5) contains supplementary material, which is available to authorized users.

Background: Photocontrol of protein activity has become a helpful strategy for regulating biological pathways. Herein, a method for the precise and reversible photocontrol of oxidase activity was developed by using the conformational change of the AsLOV2 domain. Results: The AsLOV2 domain was inserted into the nonconserved sites exposed on the surface of the AdhP protein, and the alov9 fusion was successfully screened for subsequent optical experiments under the assumption that neither of these actions affected the original activity of AdhP protein. The activity of alov9 was noticeably inhibited when the fusion was exposed to 470 nm blue light and recovered within 30 min. As a result, we could precisely and reversibly photocontrol alov9 activity through the optimization of several parameters, including cofactor concentration, light intensity, and illumination time. Conclusions: An efficient method was developed for the photoinhibition of enzymatic activity based on the insertion of the light-sensitive AsLOV2 domain, providing new ideas for photocontrolling metabolic pathways without carriers in the future.