Improved Production of (R)-1-phenyl-1,2-ethanediol by a Codon-optimized R-specific Carbonyl Reductase from Candida parapsilosis in Escherichia coli

Half-Preparative Scale Synthesis of (S)-1-Phenylethane-1,2-Diol as a Result of 2-Phenylethanol Hydroxylation with Aspergillus niger (IAFB 2301) Assistance

Aspergillus niger (IAFB 2301) was employed for bioconversions of 2-phenylethanol as an immobilized or free mycelium and also as a spore suspension. Experiments were conducted on laboratory and half-preparative scale (bioreactor New Brunswick Scientific, BioFlo Model C32). Thus, A. niger applied as free mycelium, depending on the outcome, supported formation of the mixture of 4-hydroxyphenylacetic acid and hydroxytyrosol (final concentration of 13.8 mg/L and 3.7% efficiency) or 4-hydroxyphenylacetic acid, as single product (final concentration of 140 mg/L and 18% efficiency). In case of scaling experiments conducted with flow and batch reactors, accordingly, the following results were achieved: 1. mixture of antioxidants 4-hydroxyphenylacetic acid and hydroxytyrosol formed with final concentration of 76 mg/L and 10% efficiency (simplified flow system and immobilized mycelium); 2. (S)-1-phenylethane-1,2-diol synthesized with a final concentration of 447 mg/L and 65% (1.3 L batch reactor).

In situ expression of (R)-carbonyl reductase rebalancing an asymmetric pathway improves stereoconversion efficiency of racemic mixture to (S)-phenyl-1,2-ethanediol in Candida parapsilosis CCTCC M203011

Background

Candida parapsilosis (R)-carbonyl reductase (RCR) and (S)-carbonyl reductase (SCR) are involved in the stereoconversion of racemic (R,S)-1-phenyl-1,2-ethanediol (PED) to its (S)-isomer. RCR catalyzes (R)-PED to 2-hydroxyacetophenone (2-HAP), and SCR catalyzes 2-HAP to (S)-PED. However, the stereoconversion efficiency of racemic mixture to (S)-PED is not high because of an activity imbalance between RCR and SCR, with RCR performing at a lower rate than SCR. To realize the efficient preparation of racemic mixture to (S)-PED, an in situ expression of RCR and a two-stage control strategy were introduced to rebalance the RCR- and SCR-mediated pathways.

Results

An in situ expression plasmid pCP was designed and RCR was successfully expressed in C. parapsilosis. With respect to wild-type, recombinant C. parapsilosis/pCP-RCR exhibited over four-fold higher activity for catalyzing racemic (R,S)-PED to 2-HAP, while maintained the activity for catalyzing 2-HAP to (S)-PED. The ratio of k_cat/K_M for SCR catalyzing (R)-PED and RCR catalyzing 2-HAP was about 1.0, showing the good balance between the functions of SCR and RCR. Based on pH and temperature preferences of RCR and SCR, a two-stage control strategy was devised, where pH and temperature were initially set at 5.0 and 30 °C for RCR rapidly catalyzing racemic PED to 2-HAP, and then adjusted to 4.5 and 35 °C for SCR transforming 2-HAP to (S)-PED. Using these strategies, the recombinant C. parapsilosis/pCP-RCR catalyzed racemic PED to its (S)-isomer with an optical purity of 98.8 % and a yield of 48.4 %. Most notably, the biotransformation duration was reduced from 48 to 13 h.

Conclusions

We established an in situ expression system for RCR in C. parapsilosis to rebalance the functions between RCR and SCR. Then we designed a two-stage control strategy based on pH and temperature preferences of RCR and SCR, better rebalancing RCR and SCR-mediated chiral biosynthesis pathways. This work demonstrates a method to improve chiral biosyntheses via in situ expression of rate-limiting enzyme and a multi-stage control strategy to rebalance asymmetric pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0539-y) contains supplementary material, which is available to authorized users.

Optimized expression of (S)-carbonyl reductase in Pichia pastoris for efficient production of (S)-1-phenyl-1, 2-ethanediol

The recombinant (S)-carbonyl reductase (SCR) in Escherichia coli catalyzed the reduction of 2-hydroxyacetophenone to (S)-1-phenyl-1,2-ethanediol (PED) with low efficiency. In this work, its 6× histidine fusion gene his6 -scr was cloned in Pichia pastoris under the control of the AOX1 methanol inducible promoter. The heterologous protein SCR was expressed through a Mut(s) phenotype. Under the optimal conditions: pH 7.0, initial OD600 2.5, methanol daily addition concentration 1.0% and induction duration 4-5 days, the recombinant protein SCR was produced at the highest level. The enzyme activity in the cell-free exacts of P. pastoris was 0.38, which was over twofold than that of the recombinant E. coli-SCR. The enzyme was purified to homogeneity with a specific activity of 3.41 U mg(-1) , and it catalyzed the biotransformation of (S)-PED with a high optical purity of 96.9% in a high yield of 89.7% at optimum pH of 7.0. The developed effective system of P. pastoris-SCR will facilitate the preparation of pure chiral alcohol in industry.