Characterization of an excellent anti-Prelog short-chain dehydrogenase/reductase EbSDR8 from Empedobacter brevis ZJUY-1401

Enantiocomplementary Asymmetric Reduction of 2-Haloacetophenones Using TeSADH: Synthesis of Enantiopure 2-Halo-1-arylethanols

Enantiopure 2-halo-1-arylethanols are essential precursors for the synthesis of pharmaceuticals, agrochemicals, and fine chemicals. This study investigates the asymmetric reduction of 2-haloacetophenones and their substituted analogs to obtain their corresponding optically active 2-halo-1-arylethanols using secondary alcohol dehydrogenase from Thermoanaerobacter pseudethanolicus (TeSADH) mutants. Specifically, the ΔP84/A85G and P84S/A85G TeSADH mutants were evaluated for the asymmetric reduction of 2-haloacetophenones, generating their corresponding optically active halohydrins with high enantioselectivities. The asymmetric reduction of 2-haloacetophenones and their substituted analogs using the ΔP84/A85G TeSADH mutant yielded their corresponding (S)-2-halo-1-arylethanols with high enantiopurity in accordance with the anti-Prelog's rule. Conversely, the P84S/A85G TeSADH mutant produced (R)-alcohols when reducing 2-chloro-4'-chloroacetophenone, 2-chloro-4'-bromoacetophenone, and 2-bromo-4'-chloroacetophenone, while generating the (S)-configured halohydrin from 2-chloro-4'-fluoroacetophenone. Asymmetric reduction of the unsubstituted 2-bromoacetophenone, 2-chloroacetophenone, and 2,2,2-trifluoroacetophenone resulted in production of their (S)-halohydrins with the tested mutants, which reflects the importance of the nature of the substituent on the substrate's ring in controlling the stereopreference of these TeSADH-catalyzed reduction reactions. These findings contribute to the understanding and application of TeSADH in synthesizing optically active compounds and aid in the design of further mutants with the desired stereopreference.

Enhancing Acetophenone Tolerance of Anti-Prelog Short-Chain Dehydrogenase/Reductase EbSDR8 Using a Whole-Cell Catalyst by Directed Evolution

The short-chain dehydrogenase/reductase (SDR) from Empedobacter brevis ZJUY-1401 (EbSDR8, GenBank: ALZ42979.1) is a promising biocatalyst for the reduction of acetophenone to (R)-1-phenylethanol, but its industrial application is restricted by its insufficient tolerance to acetophenone. In this paper, we developed a chromogenic reaction-based high-throughput screening method and employed directed evolution to enhance the acetophenone tolerance of EbSDR8. The resulting variant, M190V, showed 74.8% improvement over the wild-type in specific activity when catalyzing the reduction of 200 mM acetophenone. Kinetic analysis revealed a 70% enhancement in its catalytic efficiency (kcat/Km). Molecular docking was conducted to reveal the possible mechanism behind the improved acetophenone tolerance, and the result implied that the M190V mutation is conducive to the binding and release of coenzyme. Aside from the improved catalytic performance when dealing with a high concentration of acetophenone, other features of M190V, such as a broad pH range (6.0 to 10.5), low optimal cosubstrate concentration (1% isopropanol), and a temperature optimum close to that of E. coli cells (35 °C), also contribute to its practical application as a whole-cell catalyst. In this study, we first designed a directed evolution means to engineer the enzyme and obtained the positive variant which has a high activity under high concentrations of acetophenone. After that, we optimized the catalytic performance of the variant to adapt to industrial applications.

Alcohol Dehydrogenases with anti-Prelog Stereopreference in Synthesis of Enantiopure Alcohols

Biocatalytic production of both enantiomers of optically active alcohols with high enantiopurities is of great interest in industry. Alcohol dehydrogenases (ADHs) represent an important class of enzymes that could be used as catalysts to produce optically active alcohols from their corresponding prochiral ketones. This review covers examples of the synthesis of optically active alcohols using ADHs that exhibit anti-Prelog stereopreference. Both wild-type and engineered ADHs that exhibit anti-Prelog stereopreference are highlighted.

Efficient biosynthesis of (2S, 3R)-4-methylsulfonylphenylserine by artificial self-assembly of enzyme complex combined with an intensified acetaldehyde elimination system

(2S, 3R)-4-methylsulfonylphenylserine [(2S, 3R)-MPS], a key chiral precursor for antibiotics florfenicol and thiamphenicol, could be asymmetrically synthesized by l-threonine transaldolase (LTTA) coupled with an acetaldehyde elimination system. The low efficiency of acetaldehyde elimination system blocked further accumulation of (2S, 3R)-MPS. To address this issue, strengthening acetaldehyde elimination system and enzyme self-assembly strategy were combined to accelerate biosynthesis of (2S, 3R)-MPS. The new multi-enzyme cascade with intensified acetaldehyde elimination system BL21 (PsLTTAD2/ScADH/BtGDH) could produce (2S, 3R)-MPS with a titer of 157.6 mM, 1.7-folds than that produced by the original system BL21 (PsLTTAD2/ApADH/CbFDH). Moreover, self-assembly of PsLTTAD2 and ScADH by respective fusion of SpyTag and SpyCatcher were carried out to develop a self-assembled multi-enzyme cascade BL21 (ST-PsLTTAD2/SC-ScADH/BtGDH). As a result, the yield of (2S, 3R)-MPS was up to 248.1 mM with 95% de. As far as we knew, that represented the highest yield of (2S, 3R)-MPS by enzymatic synthesis, and therefore was a promising and green route for industrial production of this valuable compound.

Rational design of the carbonyl reductase EbSDR8 for efficient biosynthesis of enantiopure (R)-3-chloro-1-phenyl-1-propanol

(R)-3-Chloro-1-phenyl-1-propanol ((R)-CPPO) is an important chiral intermediate for antidepressants. For its efficient biosynthesis, the carbonyl reductase EbSDR8 was engineered to asymmetrically reduce the unnatural substrate 3-chloro-1-phenyl-1-propanone (3-CPP) at high concentrations. Molecular docking and molecular dynamics simulations of the resulting mutants suggested enlarged substrate binding pocket and more reasonable interactions between the enzyme and the substrate or cofactor as the reasons for the enhanced catalytic activity and thus the remarkably improved conversion of high-concentration 3-CPP. Using the best mutant EbSDR8^{G94A/L153I/Y188A/Y202M} as the whole-cell biocatalyst, reduction of 3-CPP (1.0 M) was conducted using 100% isopropanol as both the solvent and co-substrate for NADH regeneration, delivering (R)-CPPO with ˃ 99% ee_p and 95.5% conversion. This result suggests EbSDR8^{G94A/L153I/Y188A/Y202M} as a potential biocatalyst for green production of (R)-CPPO at the industrial scale. KEY POINTS: • Rational design of EbSDR8 by modulating steric hindrance and molecular interactions; • Non-aqueous biocatalysis using isopropanol as both the solvent and co-substrate; • Whole-cell catalyzed production of 161 g/L enantiopure (R)-CPPO from 1.0 M of 3-CPP. Graphical Abstract.

Fine-tuning of the substrate binding mode to enhance the catalytic efficiency of an ortho-haloacetophenone-specific carbonyl reductase

Fine-tuning of the substrate binding mode was successfully applied for enhancing the catalytic efficiency of an ortho-haloacetophenone-specific carbonyl reductase.

Discovery of a novel ortho-haloacetophenones-specific carbonyl reductase from Bacillus aryabhattai and insight into the molecular basis for its catalytic performance

To exploit robust biocatalysts for chiral 1-(2-halophenyl)ethanols synthesis, an ortho-haloacetophenones-specific carbonyl reductase (BaSDR1) gene from Bacillus aryabhattai was cloned and expressed in Escherichia coli. The impressive properties regarding BaSDR1 application include preference for NADH as coenzyme, noticeable tolerance against high cosubstrate concentration, and remarkable catalytic performance over a broad pH range from 5.0 to 10.0. The optimal temperature was 35 °C, with a half-life of 3.1 h at 35 °C and 0.75 h at 45 °C, respectively. Notably, BaSDR1 displayed excellent catalytic performance toward various ortho-haloacetophenones, providing chiral 1-(2-halophenyl)ethanols with 99% ee for all the substrates tested. Most importantly, the docking results indicated that the enzyme-substrate interactions and the steric hindrance of halogen atoms act in a push-pull manner in regulating enzyme catalytic ability. These results provide valuable clues for the structure-function relationships of BaSDR1 and the role of halogen groups in catalytic performance, and offer important reference for protein engineering and mining of functional compounds.

Characterization of enzymes specifically producing chiral flavor compounds (R)- and (S)-1-phenylethanol from tea (Camellia sinensis) flowers

1-Phenylethanol is a chiral flavor compound that has enantiomers, (R)- and (S)-1-phenylethanol, with different flavor properties. Given that isolating these enantiomers from plants is low yielding and costly, enzymatic synthesis presents an alternative approach. However, the genes/enzymes that specifically produce (R)- and (S)-1-phenylethanol in plants are unknown. To identify these enzymes in tea (Camellia sinensis) flowers, 21 short chain dehydrogenase (SDR) genes were isolated from tea flowers, cloned, and functionally characterized. Several recombinant SDRs in Escherichia coli exhibited activity for converting acetophenone to (S)-1-phenylethanol (CsSPESs, >99.0%), while only one SDR produced (R)-1-phenylethanol (CsRPES, 98.6%). A pair of homologue enzymes (CsSPES and CsRPES) showed a strong preference for NADPH cofactor, with optimal enzymatic reaction conditions of 45-55 °C and pH 8.0. Identification of the tea flower-derived gene responsible for specific synthesis of (R)- and (S)-1-phenylethanolsuggests enzymatic synthesis of enantiopure 1-phenylethanol is possible using a plant-derived gene.

Enzymatic characterization of a recombinant carbonyl reductase from Acetobacter sp. CCTCC M209061

Background

Acetobacter sp. CCTCC M209061 could catalyze carbonyl compounds to chiral alcohols following anti-Prelog rule with excellent enantioselectivity. Therefore, the enzymatic characterization of carbonyl reductase (CR) from Acetobacter sp. CCTCC M209061 needs to be investigated.

Results

A CR from Acetobacter sp. CCTCC M209061 (AcCR) was cloned and expressed in E. coli. AcCR was purified and characterized, finding that AcCR as a dual coenzyme-dependent short-chain dehydrogenase/reductase (SDR) was more preferred to NADH for biocatalytic reactions. The AcCR was activated and stable when the temperature was under 35 °C and the pH range was from 6.0 to 8.0 for the reduction of 4′-chloroacetophenone with NADH as coenzyme, and the optimal temperature and pH were 45 °C and 8.5, respectively, for the oxidation reaction of isopropanol with NAD⁺. The enzyme showed moderate thermostability with half-lives of 25.75 h at 35 °C and 13.93 h at 45 °C, respectively. Moreover, the AcCR has broad substrate specificity to a range of ketones and ketoesters, and could catalyze to produce chiral alcohol with e.e. >99% for the majority of tested substrates following the anti-Prelog rule.

Conclusions

The recombinant AcCR exhibited excellent enantioselectivity, broad substrate spectrum, and highly stereoselective anti-Prelog reduction of prochiral ketones. These results suggest that AcCR is a powerful catalyst for the production of anti-Prelog alcohols.Graphical abstract

Structure-guided stereoselectivity inversion of a short-chain dehydrogenase/reductase towards halogenated acetophenones

The structure-guided rational design of an NADH-dependent short-chain dehydrogenase/reductase (SDR) reversed the stereoselectivity towards halogenated acetophenones from Prelog to anti-Prelog.