Characterization of a robust glucose 1-dehydrogenase, SyGDH, and its application in NADPH regeneration for the asymmetric reduction of haloketone by a carbonyl reductase in organic solvent/buffer system

Cascade reactions with two non-physiological partners for NAD(P)H regeneration via renewable hydrogen

An attractive application of hydrogenases, combined with the availability of cheap and renewable hydrogen (i.e., from solar and wind powered electrolysis or from recycled wastes), is the production of high-value electron-rich intermediates such as reduced nicotinamide adenine dinucleotides. Here, the capability of a very robust and oxygen-resilient [FeFe]-hydrogenase (CbA5H) from Clostridium beijerinckii SM10, previously identified in our group, combined with a reductase (BMR) from Bacillus megaterium (now reclassified as Priestia megaterium) was tested. The system shows a good stability and it was demonstrated to reach up to 28 ± 2 nmol NADPH regenerated s-1 mg of hydrogenase-1 (i.e., 1.68 ± 0.12 U mg-1, TOF: 126 ± 9 min-1) and 0.46 ± 0.04 nmol NADH regenerated s-1 mg of hydrogenase-1 (i.e., 0.028 ± 0.002 U mg-1, TOF: 2.1 ± 0.2 min-1), meaning up to 74 mg of NADPH and 1.23 mg of NADH produced per hour by a system involving 1 mg of CbA5H. The TOF is comparable with similar systems based on hydrogen as regenerating molecule for NADPH, but the system is first of its kind as for the [FeFe]-hydrogenase and the non-physiological partners used. As a proof of concept a cascade reaction involving CbA5H, BMR and a mutant BVMO from Acinetobacter radioresistens able to oxidize indole is presented. The data show how the cascade can be exploited for indigo production and multiple reaction cycles can be sustained using the regenerated NADPH.

Characterization and Application of a Novel Glucose Dehydrogenase with Excellent Organic Solvent Tolerance for Cofactor Regeneration in Carbonyl Reduction

An efficient cofactor regeneration system has been developed to provide a hydride source for the preparation of optically pure alcohols by carbonyl reductase-catalyzed asymmetric reduction. This system employed a novel glucose dehydrogenase (BcGDH90) from Bacillus cereus HBL-AI. The gene encoding BcGDH90 was found through the genome-wide functional annotation. Homology-built model study revealed that BcGDH90 was a homo-tetramer, and each subunit was composed of βD-αE-αF-αG-βG motif, which was responsible for substrate binding and tetramer formation. The gene of BcGDH90 was cloned and expressed in Escherichia coli. The recombinant BcGDH90 exhibited maximum activity of 45.3 U/mg at pH 9.0 and 40 °C. BcGDH90 showed high stability in a wide pH range of 4.0-10.0 and was stable after the incubation at 55 °C for 5 h. BcGDH90 was not a metal ion-dependent enzyme, but Zn2+ could seriously inhibit its activity. BcGDH90 displayed excellent tolerance to 90% of acetone, methanol, ethanol, n-propanol, and isopropanol. Furthermore, BcGDH90 was applied to regenerate NADPH for the asymmetric biosynthesis of (S)-(+)-1-phenyl-1,2-ethanediol ((S)-PED) from hydroxyacetophenone (2-HAP) with high concentration, which increased the final efficiency by 59.4%. These results suggest that BcGDH90 is potentially useful for coenzyme regeneration in the biological reduction.

Controllably crosslinked dual enzymes enabled by genetic-encoded non-standard amino acid for efficiently enantioselective hydrogenation

In traditional method for preparing crosslinked enzymes aggregates using glutaraldehyde, random linkage is inevitable, which often destroys the enzyme active sites and severely decreases the activity. To address this issue, using genetic encode expanding, nonstandard amino acids (NSAAs) were inserted into enzyme proteins at the preselected sites for crosslinking. When aldehyde ketone reductase (AKR), alcohol dehydrogenase (ADH) and glucose dehydrogenase (GDH) were utilized as model enzymes, their mutants containing p-azido-L-phenylalanine were bio-orthogonally crosslinked with diyne to form crosslinked dual enzymes (CLDEs) acting as a cascade biological oxidation and reduction system. Then, the resultant self-purified CLDEs were characterized using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM), etc. In the asymmetric synthesis of (S)-1-(2,6-dichloro-3-fluorophenyl) ethanol using CLDEs, high product yield (76.08%), ee value (99.99%) and reuse stability were achieved. The yield and ee value were 12.05 times and 1.39 times higher than those using traditional crosslinked enzyme aggregates, respectively. Thus, controllable insertion NSAAs in number and location can engender reasonable linkage and metal-free self-purification for target enzyme proteins. This facile and sustainable method could be further expanded to other dual and multienzyme systems for cascade biocatalysis.

Enantioselective Biosynthesis of L-Phenyllactic Acid From Phenylpyruvic Acid In Vitro by L-Lactate Dehydrogenase Coupling With Glucose Dehydrogenase

As a valuable versatile building block, L-phenyllactic acid (L-PLA) has numerous applications in the fields of agriculture, pharmaceuticals, and biodegradable plastics. However, both normally chemically synthesized and naturally occurring PLA are racemic, and the production titer of L-PLA is not satisfactory. To improve L-PLA production and reduce the high cost of NADH, an in vitro coenzyme regeneration system of NADH was achieved using the glucose dehydrogenase variant LsGDHD255C and introduced into the L-PLA production process. Here an NADH-dependent L-lactate dehydrogenase-encoding variant gene (L-Lcldh1Q88A/I229A) was expressed in Pichia pastoris GS115. The specific activity of L-LcLDH1Q88A/I229A (Pp) was as high as 447.6 U/mg at the optimum temperature and pH of 40°C and 5.0, which was 38.26-fold higher than that of wild-type L-LcLDH1 (Pp). The catalytic efficiency (kcat/Km) of L-LcLDH1Q88A/I229A (Pp) was 94.3 mM−1 s−1, which was 67.4- and 25.5-fold higher than that of L-LcLDH1(Pp) and L-LcLDH1Q88A/I229A (Ec) expressed in Escherichia coli, respectively. Optimum reactions of L-PLA production by dual-enzyme catalysis were at 40°C and pH 5.0 with 10.0 U/ml L-LcLDH1Q88A/I229A (Pp) and 4.0 U/ml LsGDHD255C. Using 0.1 mM NAD+, 400 mM (65.66 g/L) phenylpyruvic acid was completely hydrolyzed by fed-batch process within 6 h, affording L-PLA with 90.0% yield and over 99.9% eep. This work would be a promising technical strategy for the preparation of L-PLA at an industrial scale.

Efficiently Enantioselective Hydrogenation Photosynthesis of (R)-1-[3,5-Bis(trifluoromethyl)phenyl] ethanol over a CLEs-TiO2 Bioinorganic Hybrid Materials

Engineering of biological pathways with man-made materials provides inspiring blueprints for sustainable drug production. (R)-1-[3,5-Bis(trifluoromethyl)phenyl]ethanol [(R)-3,5-BTPE], as an important artificial chiral intermediate for complicated pharmaceutical drugs and biologically active molecules, is often synthesized through a hydrogenation reaction of 3,5-bis(trifluoromethyl)acetophenone (3,5-BTAP), in which enantioselectivity and sufficient active hydrogen are the key to restricting the reaction. In this work, a biohybrid photocatalytic hydrogenation system based on an artificial cross-linked enzymes (CLEs)-TiO₂-Cp*Rh(bpy) photoenzyme is developed through a bottom-up engineering strategy. Here, TiO₂ nanotubes in the presence of Cp*Rh(bpy) are used to transform NADP⁺ to NADPH during the formation of chiral alcohol intermediates from the catalytic reduction of a ketone substrate by alcohol dehydrogenase CLEs. Hydrogen and electrons, provided by water and photocatalytic systems, respectively, are transferred to reduce NADP⁺ to NADPH via [Cp*Rh(bpy)(H₂O)]²⁺. With the resulting NADPH, [(R)-3,5-BTPE] is synthesized using our efficient CLEs obtained from the cell lysate by nonstandard amino acid modification. Through this biohybrid photocatalytic system, the photoenzyme-catalyzed combined reductive synthesis of [(R)-3,5-BTPE] has a yield of 41.2% after reaction for 24 h and a very high enantiomeric excess value (>99.99%). In the case of reuse, this biohybrid system retained nearly 95% of its initial catalytic activity for synthesizing the above chiral alcohol. The excellent reusability of the CLEs and TiO₂ nanotubes hybrid catalytic materials highlights the environmental friendliness of (R)-3,5-BTPE production.

Efficient Biosynthesis of Raspberry Ketone by Engineered Escherichia coli Coexpressing Zingerone Synthase and Glucose Dehydrogenase

Raspberry ketone (RK), the main aroma compound of raspberry fruit, has applications in cosmetics, food industry, and pharmaceutics. In this study, we biosynthesized RK via the catalytic reduction of 4-hydroxybenzylidenacetone using a whole-cell biocatalyst. Reductase RiRZS1 from Rubus idaeus and glucose dehydrogenase SyGDH from Thermoplasma acidophilum were expressed in Escherichia coli to regenerate NADPH for the whole-cell catalytic reaction. Following the optimization of balancing the coexpression of two enzymes in pRSFDuet-1, we obtained 9.89 g/L RK with a conversion rate of 98% and a space-time yield of 4.94 g/(L·h). The optimum conditions are 40 °C, pH 5.5, and a molar ratio of substrate to auxiliary substrate of 1:2.5. Our study findings provide a promising method of biosynthesizing RK.