Mining and tailor-made engineering of a novel keto reductase for asymmetric synthesis of structurally hindered γ- and δ-lactones

A novel carbonyl reductase from Hyphopichia burtoni (HbKR) was discovered by gene mining. HbKR is a NADPH-dependent dual function enzyme with reduction and oxidation activity belonging to SDR superfamily. HbKR strictly follows Prelog priority in the reduction of long-chain aliphatic keto acids/esters containing remote carbonyl groups, such as 4-oxodecanoic acid and 5-oxodecanoic acid, producing (S)-γ-decalactone and (S)-δ-decalactone in >99 % e.e. Tailor-made engineering of HbKR was conducted to improve its catalytic efficiency. Variant F207A/F86M was obtained with specific activity of 8.37 U/mg toward 5-oxodecanoic acid, which was 9.7-fold of its parent. Employing F207A/F86M, 100 mM 5-oxodecanoic acid could be reduced into optically pure (S)-δ-decalactone. Molecular docking analysis indicates that substitution of aromatic Phe with smaller residues renders sufficient space for accommodating substrates in a more stable conformation. This study offers an efficient biocatalyst for the biosynthesis of (S)-lactones, and provides guidance for engineering carbonyl reductases toward structurally hindered substrates.

Efficient biosynthesis of Vibegron intermediate using a novel carbonyl reductase based on molecular modification of hydrogen bonding network regulation

Vibegron is a novel, potent, highly selective β3-adrenergic receptor agonist for the treatment of overactive bladder with higher therapeutic capacity and lower side effects. Methyl(2S,3R)-2-((tert-butoxycarbonyl)amino)-3-hydroxy-3-phenylpropanoate ((2S,3R)-aminohydroxy ester) is a key chiral intermediate for the synthesis of Vibegron. A novel carbonyl reductase from Exiguobacterium sp. s126 (EaSDR6) was isolated using data mining technology from GenBank database with preferable catalytic activity. Hydrogen bond network regulation was performed using site-directed saturation mutagenesis and combination mutagenesis. The mutant EaSDR6A138L/S193A was obtained with the activity improvement by 4.58 folds compared with the wild type EaSDR6. The Km of EaSDR6A138L/S193A was decreased from 1.57 mM to 0.67 mM, kcat was increased by 2.17 folds, and the overall catalytic efficiency kcat/Km was increased by 5.07 folds. The organic-aqueous biphasic bioreaction system for the asymmetric synthesis of (2S,3R)-aminohydroxy ester was constructed for the first time. Under the substrate concentration of 150 g/L, the yield of (2S,3R)-aminohydroxy ester was > 99.99%, the e.e. was > 99.99%, and the spatiotemporal yield was 1.55 g/(L·h·g DCW) after 12 h reaction. While the substrate concentration was increased to 200 g/L and the reaction lasted for 36 h, the yield of (2S,3R)-aminohydroxy ester was > 99.99%, the e.e. was > 99.99% and the spatiotemporal yield was 1.05 g/(L·h·g DCW). The substrate concentration and spatiotemporal yield were higher than ever reported.

Synthesis, activity, metabolic stability and cell permeability of new cytosolic phospholipase A2α inhibitors with 1-indolyl-3-phenoxypropan-2-one structure

Cytosolic phospholipase A2α (cPLA2α), the key enzyme of the arachidonic acid cascade, is considered to be an interesting target for the development of new anti-inflammatory drugs. Potent inhibitors of the enzyme include indole-5-carboxylic acids with propan-2-one residues in position 1 of the indole. Previously, it was found that central pharmacophoric elements of these compounds are their ketone and carboxylic acid groups, which unfortunately are subject to pronounced metabolism by carbonyl reductases and glucuronosyltransferases, respectively. Here we show that the metabolic stability of these inhibitors can be improved by introducing alkyl substituents in the vicinity of the ketone group or by increasing their rigidity. Furthermore, permeability tests with Caco-2 cells revealed that the indole derivatives have only low permeability, which can be attributed to their affinity to efflux transporters. Among other things, the polar ketone group in the center of the molecules seems to be a decisive factor for their reverse transport. After its removal, the permeability increased significantly. The enhancement in metabolic stability and permeability achieved by the structural variations carried out was accompanied by a more or less pronounced decrease in the inhibitory potency of the compounds against cPLA2α.

The crystal structure of the S154Y mutant carbonyl reductase from Leifsonia xyli explains enhanced activity for 3,5-Bis(trifluoromethyl)acetophenone reduction

Carbonyl reductase from Leifsonia xyli (LXCAR, UniProtKB - T2FLN4) can stereoselectively catalyze the reduction of 3,5-bis(trifluoromethyl)acetophenone (BTAP) to its corresponding alcohol, (R)-[3,5-bis(trifluoromethyl)phenyl]ethanol ((R)-BTPE), which is a valuable chiral intermediate for the synthesis of antiemetic drugs, Aprepitant and Fosaprepitant. Moreover, this protein was found to have a broad spectrum of substrate specificity and can asymmetrically catalyze the reduction of a variety of ketones and keto esters. Even though molecular modelling of this protein was done by Wang et al. (2014), a crystal structure has not yet obtained. In this study, a single mutant, S154Y, which was shown to have higher catalytic activity toward BTAP than that of the wild type, was overexpressed in Escherichia coli BL21 (DE3), purified, and crystallized. The crystal structure of LXCAR-S154Y explains how the mutant enzyme can work with BTAP more efficiently than wild type carbonyl reductase. Furthermore, the structure explains why LXCAR-S154Y can use either NADH or NADPH efficiently as a cofactor, as well as elucidates a proton relay system present in the enzyme.

Induction of carbonyl reductase 1 (CR1) gene expression in Daphnia magna by TNT, but not its key metabolites 2-ADNT and 4-ADNT

2,4,6-trinitrotoluene (TNT) is a known source of reactive oxygen species (ROS), which cause oxidative stress in aquatic ecosystems. Carbonyl reductases (CRs) are one of several possible defense mechanisms induced against ROS products, especially those that result in the 'so-called' carbonyl stress. Daphnia magna, a freshwater organism living in stagnant freshwater bodies, expresses four copies of the CR gene (Dma_CR1, Dma_CR2, Dma_CR3 and Dma_CR4). In this study, induction of all four copies of Dma_CR by 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT), was investigated. Reverse transcription polymerase chain reaction (RT-PCR) analysis of treated daphnids revealed up-regulation of Dma_CR1 alone in response to TNT, but not 2-ADNT and 4-ADNT (which are key metabolites of TNT). This concentration- and time-dependent up-regulation in mRNA-expression was observed both in the presence and absence of light, in the same magnitude. Moreover, significant change in mRNA-expression could be observed 8 h after treatment with TNT. In the presence of TNT, the antioxidant N-acetylcysteine (NAc) could not reverse TNT-induced up-regulation of Dma_CR1 mRNA-expression. On the other hand, withdrawal of TNT from the culture medium caused a significant reduction in the TNT-induced mRNA-expression of Dma_CR1 within 24 h. These findings highlight the potential of Dma_CR1 as a biomarker for biomonitoring of TNT levels in freshwater bodies.

The explosive trinitrotoluene (TNT) induces gene expression of carbonyl reductase in the blue mussel (Mytilus spp.): a new promising biomarker for sea dumped war relicts?

Millions of tons of all kind of munitions, including mines, bombs and torpedoes have been dumped after World War II in the marine environment and do now pose a new threat to the seas worldwide. Beside the acute risk of unwanted detonation, there is a chronic risk of contamination, because the metal vessels corrode and the toxic and carcinogenic explosives (trinitrotoluene (TNT) and metabolites) leak into the environment. While the mechanism of toxicity and carcinogenicity of TNT and its derivatives occurs through its capability of inducing oxidative stress in the target biota, we had the idea if TNT can induce the gene expression of carbonyl reductase in blue mussels. Carbonyl reductases are members of the short-chain dehydrogenase/reductase (SDR) superfamily. They metabolize xenobiotics bearing carbonyl functions, but also endogenous signal molecules such as steroid hormones, prostaglandins, biogenic amines, as well as sugar and lipid peroxidation derived reactive carbonyls, the latter providing a defence mechanism against oxidative stress and reactive oxygen species (ROS). Here, we identified and cloned the gene coding for carbonyl reductase from the blue mussel Mytilus spp. by a bioinformatics approach. In both laboratory and field studies, we could show that TNT induces a strong and concentration-dependent induction of gene expression of carbonyl reductase in the blue mussel. Carbonyl reductase may thus serve as a biomarker for TNT exposure on a molecular level which is useful to detect TNT contaminations in the environment and to perform a risk assessment both for the ecosphere and the human seafood consumer.

Exposure to Spectracide® causes behavioral deficits in Drosophila melanogaster: Insights from locomotor analysis and molecular modeling

This study was focused on gaining insights into the mechanism by which the herbicide- Spectracide®, induces oxidative stress and alters behavior in Drosophila melanogaster. Exposure to Spectracide® (50%) significantly (p < 0.05) reduced the negative geotaxis response, jumping behavior and dampened locomotor activity rhythm in adult flies compared to non-exposed flies. Protein carbonyl levels indicative of oxidative damage increased significantly coupled with down-regulation of Sniffer gene expression encoding carbonyl reductase (CR) and its activity in Spectracide®-exposed flies. In silico modeling analysis revealed that the active ingredients of Spectracide® (atrazine, diquat dibromide, fluazifop-p-butyl, and dicamba) have significant binding affinity to the active site of CR enzyme, with atrazine having comparatively greater affinity. Our results suggest a mechanism by which ingredients in Spectracide® induce oxidative damage by competitive binding to the active site of a protective enzyme and impair its ability to prevent damage to proteins thereby leading to deficits in locomotor behavior in Drosophila.

Inhibition of Carbonyl Reductase 1 Enhances Metastasis of Head and Neck Squamous Cell Carcinoma through β-catenin-Mediated Epithelial-Mesenchymal Transition

Objective: Human carbonyl reductase 1 (CBR1) plays key roles in the regulation of oxidative stress and tumor progression. However, the detailed mechanism and clinical correlation between CBR1 and tumor progression in head and neck squamous cell carcinoma (HNSCC) is largely unexplored. This study will focus the effects of CBR1 on head and neck cancer progression and explore the possible mechanisms.

Materials and Methods:CBR1 mRNA expression was analyzed according to lymph node metastasis (LNM) status in patients with HNSCC from publicly available databases. CBR1 protein levels were measured and compared in HNSCC patient tissues, with or without metastasis, using immunohistochemistry (IHC). The invasive ability of HNSCC with modulated CBR1 expression was assayed using an invasion assay. Expression levels of EMT marker proteins were analyzed using immunoblotting.

Results: HNSCC patients with LNM showed lower expression of CBR1 than those without LNM. In addition, IHC in tissues indicated that patients with LNM had relatively lower levels of CBR1 in cancer tissue. Consistently, in vitro invasion assay, we found that CBR1 inhibition using specific short interfering RNA treatment resulted in two- to three-fold increased invasion ability of HNSCC cell lines. Also, we proved that depletion of CBR1 activated marker proteins participating in epithelial-mesenchymal transition (EMT) signaling. CBR1 inhibition increased levels of intracellular reactive oxygen species (ROS) in HNSCC cells leading to upregulation of β-catenin, one of main transcription factors that induce EMT-related genes.

Conclusion: Our findings suggested that CBR1 plays an important role in metastasis of HNSCC tumors via regulation of ROS-mediated β-catenin activity, and that CBR1 may be marker for progression of HNSCC to metastasis.

Asymmetric synthesis of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate using a self-sufficient biocatalyst based on carbonyl reductase and cofactor co-immobilization

tert-Butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate [(3R,5S)-CDHH] is the key chiral intermediate to synthesize the side chain of the lipid-lowering drug rosuvastatin. Carbonyl reductases showed excellent activity for the biosynthesis of (3R,5S)-CDHH. The requirement of cofactor NADH/NADPH leads to high cost for the industrial application of carbonyl reductases. In this study, a self-sufficient biocatalyst based on carbonyl reductase and NADP⁺ co-immobilization strategy was developed on an amino resin carrier LX-1000HAA (SCR-NADP⁺@LX-1000HAA). The self-sufficient biocatalyst achieved in situ cofactor regeneration and showed the activity recovery of 77.93% and the specific activity of 70.45 U/g. Asymmetric synthesis of (3R,5S)-CDHH using SCR-NADP⁺@LX-1000HAA showed high enantioselectivity (> 99% e.e.) and yield (98.54%). Batch reactions were performed for ten cycles without extra addition of NADP⁺, and the total yield of (3R,5S)-CDHH achieved at 10.56 g/g biocatalyst. The present work demonstrated the potential of the self-sufficient biocatalyst for the asymmetric biosynthesis of rosuvastatin intermediate.

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.

A novel carbonyl reductase with anti-Prelog stereospecificity for the production of t-butyl 6-cyano-(3R, 5R)-dihydroxyhexanoate

A novel gene (crc1) from Candida boidinii was cloned and then overexpressed in a recombinant strain BL21(DE3)/pET30a-crc1 of Escherichia coli. The resulting carbonyl reductase was prepared through fermentations using the recombinant strain. The purified enzyme showed an NADPH-dependent activity and specific activity was 4.65 U/mg using t-butyl 6-cyano-(5R)-hydroxy-3-oxohexanoate (ATS-6) as substrate. The enzyme was optimally active at 35 °C and pH 7, respectively. The apparent K _m and V _max of the enzyme for ATS-6 are 1.5 mM and 21.1 μmol/min mg, respectively, indicating excellent anti-Prelog stereospecificity. Under the optimum condition, t-butyl 6-cyano-(3R,5R)-dihydroxyhexanoate (ATS-7) was prepared with the enzyme with high d.e. value (99.9%) and good conversion (94%) in 4 h, indicating high stereoselectivity and conversion efficiency in biotransformation of ATS-6 to ATS-7.

Carbonyl reductase sniffer from the model organism daphnia: Cloning, substrate determination and inhibitory sensitivity

Carbonyl reductases (CRs) represent a fundamental enzymatic defense mechanism against oxidative stress. While commonly two carbonyl reductases (CBR1 and CBR3) are found in mammalian genomes, invertebrate model organisms like Drosophila melanogaster express no CR but a functional homolog to human CBR1, termed sniffer. The importance of sniffer could be demonstrated in D. melanogaster where it protected against age-dependent neurodegeneration. Interestingly, the microcrustacean Daphnia harbors four copies of the CR gene (CR1, CR2, CR3, CR4) in addition to one sniffer gene. Due to this unique equipment Daphnia is an ideal model organism to investigate the function of sniffer. Recombinant sniffer from D. magna und D. pules were produced in E. coli, purified by Ni-affinity chromatography and tested with a variety of aliphatic and aromatic diketones, reactive aldehydes and precursors of advanced glycation end products (AGE). The highest catalytic activities were determined for sniffer from D. pulex with the aromatic dicarbonyls 9,10-phenanthrenequinone (k_cat/K_m = 2.6 s^-1 x μM^-1) and isatin (k_cat/K_m = 1.5 s^-1 x μM^-1). While sniffer from D. magna displayed preference for the same two substances, the respective catalytic activities were noticeably lower. Kinetic constants with aliphatic diketones were generally lower than those with aromatic dicarbonyls for both sniffer enzymes. The best aliphatic diketone as substrate for sniffer from D. magna and D. pulex was hexane-3,4-dione with k_cat/K_m = 0.23 s^-1 μM^-1 and k_cat/K_m = 0.35 s^-1 μM^-1, respectively. Poor or no detectable activity of the two sniffer enzymes was seen with the aliphatic diketones 2,5-hexanedione and 3,5-heptanedione, the aldehydes butanal, hexanal, decanal, crotonaldehyde, acrolein, trans-2-hexenal, and the AGE precursors glyoxal, methylglyoxal, furfural and glyceraldehyde, indicating no physiological function in the metabolism of short-chain aldehydes. Substrate inhibition for both sniffer enzymes was observed with the quinone substrates 1,4-naphthoquinone and 2-methyl-1,4-benzoquinone. From a variety of pesticides endosulfan turned out as an effective inhibitor of the sniffer enzymes (Ki = 9.2 μM for sniffer from D. magna, Ki = 12.0 μM for sniffer from D. pulex). In conclusion, the present results on sniffer from the protein superfamily of the short-chain dehydrogenases/reductases (SDR) in Daphnia ssp. complement earlier studies on carbonyl reductases in the same species and indicate that Daphnia is an interesting model to study the overall response to carbonyl stress.

Synergistic anticancer activity of doxorubicin and piperlongumine on DU-145 prostate cancer cells - The involvement of carbonyl reductase 1 inhibition

One of the causes of therapeutic failure of chemotherapy is cancer cell resistance. In the case of anthracyclines, many resistance mechanisms have been described. One of them assumes the role of carbonyl reductase 1 (CBR1), a cytosolic enzyme that is responsible for the biotransformation process of anthracyclines to less active, undesirable metabolites. Therefore, CBR1 inhibitors are considered for use as a chemosensitizing agents. In the present study, piperlongumine (PL), a Piper longum L. alkaloid that has previously been described as a CBR1 inhibitor, was investigated for its chemosensitizing properties in co-treatment with doxorubicin (DOX). The biotransformation process of DOX in the presence of PL was tracked using human cytosol fraction and LC-MS, then a molecular modeling study was conducted to predict the interaction of PL with the active site of the CBR1. The biological interaction between DOX and PL was investigated using DU-145 prostate cancer cells. Cytotoxic and antiproliferative properties of DOX and PL were examined, and the type and potency of interaction was quantified by Combination Index. The mechanism of the cell death induced by the agents was investigated by flow cytometry and the anti-invasive properties of the drugs were determined by monitoring the movement of individual cells. PL showed dose-dependent inhibition of DOX metabolism in cytosol, which resulted in less doxorubicinol (DOXol) metabolite being formed. The possible mechanism of CBR1 inhibition was explained through molecular modeling studies by prediction of PL's binding mode in the active site of the enzyme's crystal structure-based model. DOX and PL showed a synergistic antiproliferative and proapoptotic effect on cancer cells. Significant anti-invasive properties of the combination of DOX and PL were found, but when the drugs were used separately they did not alter the cancer cells' motility. Cell motility inhibition was accompanied by significant changes in cytoskeleton architecture. DOX and PL used in co-treatment showed significant synergistic anticancer properties. Inhibition of DOX metabolism by PL was found to be a mechanism that was likely to be responsible for the observed interaction.

Enzymology of monoterpene functionalization in glandular trichomes

The plant kingdom supports an extraordinary chemical diversity, with terpenoids representing a particularly diversified class of secondary (or specialized) metabolites. Volatile and semi-volatile terpenoids in the C10-C20 range are often formed in specialized cell types and secretory structures. In the angiosperm lineage, glandular trichomes play an important role in enabling the biosynthesis and storage (or in some cases secretion) of functionalized terpenoids. The 'decoration' of a terpenoid scaffold with functional groups changes its physical and chemical properties, and can therefore affect the perception of a specific metabolite by other organisms. Because of the ecological implications (e.g. plant-herbivore interactions) and commercial relevance (e.g. volatiles used in the flavor and fragrance industries), terpenoid functionalization has been researched extensively. Recent successes in the cloning and functional evaluation of genes as well as the structural and biochemical characterization of enzyme catalysts have laid the foundation for an improved understanding of how pathways toward functionalized monoterpenes may have evolved. In this review, we will focus on an up-to-date account of functionalization reactions present in glandular trichomes.

Expression of engineered carbonyl reductase from Ogataea minuta in Rhodococcus opacus and its application to whole-cell bioconversion in anhydrous solvents

The carbonyl reductase from the methylotrophic yeast Ogataea minuta can catalyze the regio- and enantio-selective reduction of prochiral ketones to chiral alcohols, and is available for industrial manufacturing of statin drugs. We previously conducted a directed evolution experiment of the enzyme, and obtained a mutant (OCR_V166A) with improved tolerance to organic solvents. This expanded the applicability of the enzyme to the bioconversion of water-insoluble compounds (Honda et al., J. Biosci. Bioeng., 123, 673-678, 2017). In the present study, we expressed OCR_V166A in Rhodococcus opacus cells, which have a highly lipophilic surface structure and are dispersible in anhydrous organic solvents, and developed a whole-cell biocatalyst which can function in an organic-solvent-based reaction medium. The secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus (TeADH) was employed as an NADPH-regenerating enzyme and co-expressed with OCR_V166A in R. opacus. The whole-cell bioconversion of 2,2,2-trifluoroacetophenone to α-(trifluoromethyl)benzyl alcohol was performed in organic solvents, including isopropanol, isobutanol, and cyclohexanol, which served both as reaction media and as substrates for TeADH. The type of organic solvents markedly affected not only the product titer but also the enantio-purity of the product. When isobutanol was used as the reaction medium, the whole-cell biocatalyst showed higher stability than the isolated enzyme. Consequently, a high concentration (1 M) of the substrate was converted to the product with an overall conversion yield of 81% (mol/mol) in 24 h.

Attempt to simultaneously generate three chiral centers in 4-hydroxyisoleucine with microbial carbonyl reductases

A panel of microorganisms was screened for selective reduction ability towards a racemic mixture of prochiral 2-amino-3-methyl-4-ketopentanoate (rac-AMKP). Several of the microorganisms tested produced greater than 0.5mM 4-hydroxyisoleucine (HIL) from rac-AMKP, and the stereoselectivity of HIL formation was found to depend on the taxonomic category to which the microorganism belonged. The enzymes responsible for the AMKP-reducing activity, ApAR and FsAR, were identified from two of these microorganisms, Aureobasidium pullulans NBRC 4466 and Fusarium solani TG-2, respectively. Three AMKP reducing enzymes, ApAR, FsAR, and the previously reported BtHILDH, were reacted with rac-AMKP, and each enzyme selectively produced a specific composition of HIL stereoisomers. The enzymes appeared to have different characteristics in recognition of the stereostructure of the substrate AMKP and in control of the 4-hydroxyl group configuration in the HIL product.

Biosynthesis of tert-butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate by carbonyl reductase from Rhodosporidium toruloides in mono and biphasic media

tert-Butyl (3R,5S)-6-chloro-3,5-dihydroxyhexanoate ((3R,5S)-CDHH) is the key intermediate for synthesis of atorvastatin and rosuvastatin. Carbonyl reductase exhibits excellent activity toward tert-butyl (S)-6-chloro-5-hydroxy-3-oxohexanoate ((S)-CHOH) to synthesize (3R,5S)-CDHH. In this study, a whole cell biosynthesis reaction system to produce (3R,5S)-CDHH was constructed in organic solvents. A solution of 10% (v/v) Tween-80 was introduced to the reaction system as a co-solvent, which greatly enhanced biotransformation process, giving 98.9% yield, >99% ee and 1.8-fold higher space time yield in 5 h bioconversion of 1 M (S)-CHOH, compared with 98.7% yield and >99% ee in 9 h bioconversion of a purely aqueous reaction system. Moreover, a water-octanol biphasic reaction system was built and 20% of octanol was added as reservoir of substrate resulting in 98% yield, >99% ee and 4.08 mmol L^-1 h^-1 g^-1 (wet cell weight) space time yield. This study paved a way for the whole cell biosynthesis of (3R,5S)-CDHH in mono and biphasic media.

Efficient synthesis of a (S)-fluoxetine intermediate using carbonyl reductase coupled with glucose dehydrogenase

(S)-3-chloro-1-phenyl-1-propanol ((S)-CPPO) is an important chiral intermediate predominantly used in the synthesis of the chiral side chain of (S)-fluoxetine. In this study, carbonyl reductase (CBR) from Novosphingobium aromaticivorans was successfully expressed in recombinant E. coli. The enzymatic activity of the recombinant CBR was significantly increased to 1875 U/mL in the fed-batch fermentation in a 10 L fermenter and recombinant CBR was then purified and characterized. By regenerating NADH with glucose dehydrogenase, 100 g/L 3-chloro-1-phenyl-1-propanone (3-CPP) was successfully converted to (S)-CPPO with a conversion of 100% and ee value of 99.6% after 12 h at 30 °C in PBS buffer (pH 7.0), which are the highest reported to date for the bio-production of (S)-CPPO and presented great potential for green production of (S)-CPPO at industrial scale.

Characterization of two carbonyl reductases from Ogataea polymorpha NBRC 0799

The enzyme responsible for the enantioselective production of (S)-1,1,1-trifluoro-2-propanol ((S)-TFP) from 1,1,1-trifluoroacetone (TFA) has been identified in Ogataea polymorpha NBRC 0799. We purified two carbonyl reductases, OpCRD-A and OpCRD-B from this strain, and revealed their characteristics. Both enzymes were specific to NADH, but the following characteristics were different: The molecular mass of subunit OpCRD-A was 40 kDa and that of OpCRD-B was 43 kDa. Amino acid sequences of both enzymes were only 21% identical. OpCRD-B contained 4 mol of zinc per mole of enzyme, but OpCRD-A did not. The optimal pH, temperature, pH stability, thermostability, and inhibitor specificity were also remarkably different. With regard to substrate specificity, both enzymes exhibited high reductase activity toward a wide variety of ketones, aldehydes and fluoroketones, and dehydrogenase activity toward 2-propanol and 2-butanol. The reductase activity was much higher than the dehydrogenase activity at acidic pH. OpCRD-A enantioselectively produced (S)-TFP from TFA, but OpCRD-B preferentially produced (R)-TFP. Thus, we concluded that OpCRD-A plays the main role in the production of (S)-TFP by a reaction of O. polymorpha NBRC 0799 cells and that OpCRD-A has great potential for efficient production of (S)-TFP, as it is an S-specific enzyme and does not catalyze the dehydrogenation of (S)-TFP.

One pot simultaneous preparation of both enantiomer of β-amino alcohol and vicinal diol via cascade biocatalysis

OBJECTIVES

To investigate the efficiency of a new cascade biocatalysis system for the conversion of R, S-β-amino alcohols to enantiopure vicinal diol and β-amino alcohol.

RESULTS

An efficient cascade biocatalysis was achieved by combination of a transaminase, a carbonyl reductase and a cofactor regeneration system. An ee value of > 99% for 2-amino-2-phenylethanol and 1-phenyl-1, 2-ethanediol were simultaneously obtained with 50% conversion from R, S-2-amino-2-phenylethanol. The generality of the cascade biocatalysis was further demonstrated with the whole-cell approaches to convert 10-60 mM R, S-β-amino alcohol to (R)- and (S)-diol and (R)- and (S)-β-amino alcohol in 90-99% ee with 50-52% conversion. Preparative biotransformation was demonstrated at a 50 ml scale with mixed recombinant cells to give both (R)- and (S)-2-amino-2-phenylethanol and (R)- and (S)-1-phenyl-1, 2-ethanediol in > 99% ee and 40-42% isolated yield from racemic 2-amino-2-phenylethanol.

CONCLUSIONS

This cascade biocatalysis system provides a new practical method for the simultaneous synthesis of optically pure vicinal diol and an β-amino alcohol.

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

Asymmetric reduction of ketopantolactone using a strictly (R)-stereoselective carbonyl reductase through efficient NADPH regeneration and the substrate constant-feeding strategy

OBJECTIVES

To characterize a recombinant carbonyl reductase from Saccharomyces cerevisiae (SceCPR1) and explore its use in asymmetric synthesis of (R)-pantolactone [(R)-PL].

RESULTS

The NADPH-dependent SceCPR1 exhibited strict (R)-enantioselectivity and high activity in the asymmetric reduction of ketopantolactone (KPL) to (R)-PL. Escherichia coli, coexpressing SceCPR1 and glucose dehydrogenase from Exiguobacterium sibiricum (EsGDH), was constructed to fulfill efficient NADPH regeneration. During the whole-cell catalyzed asymmetric reduction of KPL, the spontaneous hydrolysis of KPL significantly affected the yield of (R)-PL, which was effectively alleviated by the employment of the substrate constant-feeding strategy. The established whole-cell bioreduction for 6 h afforded 458 mM (R)-PL with the enantiomeric excess value of >99.9% and the yield of 91.6%.

CONCLUSIONS

Escherichia coli coexpressing SceCPR1 and EsGDH efficiently catalyzed the asymmetric synthesis of (R)-PL through the substrate constant-feeding strategy.

Human carbonyl reductase 1 participating in intestinal first-pass drug metabolism is inhibited by fatty acids and acyl-CoAs

Human carbonyl reductase 1 (CBR1), a member of the short-chain dehydrogenase/reductase (SDR) superfamily, reduces a variety of carbonyl compounds including endogenous isatin, prostaglandin E₂ and 4-oxo-2-nonenal. It is also a major non-cytochrome P450 enzyme in the phase I metabolism of carbonyl-containing drugs, and is highly expressed in the intestine. In this study, we found that long-chain fatty acids and their CoA ester derivatives inhibit CBR1. Among saturated fatty acids, myristic, palmitic and stearic acids were inhibitory, and stearic acid was the most potent (IC₅₀ 9µM). Unsaturated fatty acids (oleic, elaidic, γ-linolenic and docosahexaenoic acids) and acyl-CoAs (palmitoyl-, stearoyl- and oleoyl-CoAs) were more potent inhibitors (IC₅₀ 1.0-2.5µM), and showed high inhibitory selectivity to CBR1 over its isozyme CBR3 and other SDR superfamily enzymes (DCXR and DHRS4) with CBR activity. The inhibition by these fatty acids and acyl-CoAs was competitive with respect to the substrate, showing the K_i values of 0.49-1.2µM. Site-directed mutagenesis of the substrate-binding residues of CBR1 suggested that the interactions between the fatty acyl chain and the enzyme's Met141 and Trp229 are important for the inhibitory selectivity. We also examined CBR1 inhibition by oleic acid in cellular levels: The fatty acid effectively inhibited CBR1-mediated 4-oxo-2-nonenal metabolism in colon cancer DLD1 cells and increased sensitivity to doxorubicin in the drug-resistant gastric cancer MKN45 cells that highly express CBR1. The results suggest a possible new food-drug interaction through inhibition of CBR1-mediated intestinal first-pass drug metabolism by dietary fatty acids.

Enzymatic synthesis of an ezetimibe intermediate using carbonyl reductase coupled with glucose dehydrogenase in an aqueous-organic solvent system

(4S)-3-[(5S)-5-(4-Fluorophenyl)-5-hydroxypentanoyl]-4-phenyl-1,3-oxazolidin-2-one ((S)-ET-5) is an important chiral intermediate in the synthesis of chiral side chain of ezetimibe. Recombinant Escherichia coli expressing carbonyl reductase (CBR) was successfully constructed in this study. The total E. coli biomass and the specific activity of recombinant CBR in 5L fermenter culture were 10.9gDCWL^-1 and 14900.3Ug^-1DCW, respectively. The dual-enzyme coupled biocatalytic process in an aqueous-organic biphasic solvent system was first constructed using p-xylene as the optimal organic phase under optimized reaction conditions, and 150gL^-1 (4S)-3-[5-(4-fluorophenyl)-1,5-dioxophentyl]-4-phenyl-1,3-oxazolidin-2-one (ET-4) was successfully converted to (S)-ET-5 with a conversion of 99.1% and diastereomeric excess of 99% after 24-h, which are the highest values reported to date for the production of (S)-ET-5.

Plant tissue cultures as sources of new ene- and ketoreductase activities

While many redox enzymes are nowadays available for synthetic applications, the toolbox of ene-reductases is still limited. Consequently, the screening for these enzymes from diverse sources in the search of new biocatalyst suitable for green chemistry approaches is needed. Among 13 plant tissue cultures, Medicago sativa and Tessaria absinthioides calli, as well as Capsicum annuum hairy roots, were selected due to their ability to hydrogenate the CC double bond of the model substrate 2-cyclohexene-1-one. The three axenic plant cultures showed more preference toward highly activated molecules such as nitrostyrene and maleimide rather than the classical substrates of the well-known Old Yellow Enzymes, resembling the skills of the NAD(P)H-dependent flavin-independent enzymes. When the three biocatalytic systems were applied in the reduction of chalcones, T. absinthioides showed high chemoselectivity toward the CC double bond whereas the other two demonstrated abilities to biohydrogenate the CC double bounds and the carbonyl groups in a sequential fashion.

Reductive metabolism of tiaprofenic acid by the human liver and recombinant carbonyl reducing enzymes

Tiaprofenic acid is a widely used anti-inflammatory drug; however, the reductive metabolism of tiaprofenic acid is not yet well understood. Here, we compared the reduction of tiaprofenic acid in microsomes and cytosol from the human liver. The microsomes exhibited lower K_m value toward tiaprofenic acid than the cytosol (K_m = 164 ± 18 μM vs. 569 ± 74 μM, respectively), whereas the cytosol showed higher specific activity during reduction than the microsomes (V_max = 728 ± 52 pmol mg of protein^-1 min^-1 vs. 285 ± 11 pmol mg of protein^-1 min^-1, respectively). Next, a panel of recombinant carbonyl reducing enzymes from AKR and SDR superfamilies has been studied to find the enzymes responsible for the cytosolic reduction of tiaprofenic acid. CBR1 was identified as the reductase of tiaprofenic acid with high specific activity (56,965 ± 6741 pmol mg of protein^-1 min^-1). Three other enzymes, AKR1A1, AKR1B10, and AKR1C4, were also able to reduce tiaprofenic acid, but with very low activity. Thus, CBR1 was shown to be a tiaprofenic acid reductase in vitro and was also suggested to be the principal tiaprofenic acid reductase in vivo.

Improvement of operational stability of Ogataea minuta carbonyl reductase for chiral alcohol production

Directed evolution of enantio-selective carbonyl reductase from Ogataea minuta was conducted to improve the operational stability of the enzyme. A mutant library was constructed by an error-prone PCR and screened using a newly developed colorimetric assay. The stability of a mutant with two amino acid substitutions was significantly higher than that of the wild type at 50°C in the presence of dimethyl sulfoxide. Site-directed mutagenesis analysis showed that the improved stability of the enzyme can be attributed to the amino acid substitution of V166A. The half-lives of the V166A mutant were 11- and 6.1-times longer than those of the wild type at 50°C in the presence and absence, respectively, of 20% (v/v) dimethyl sulfoxide. No significant differences in the substrate specificity and enantio-selectivity of the enzyme were observed. The mutant enzyme converted 60 mM 2,2,2-trifluoroacetophenone to (R)-(-)-α-(trifluoromethyl)benzyl alcohol in a molar yield of 71% whereas the conversion yield with an equivalent concentration of the wild-type enzyme was 27%.

Carbonyl reductase identification and development of whole-cell biotransformation for highly efficient synthesis of (R)-[3,5-bis(trifluoromethyl)phenyl] ethanol

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.

Results

A 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).

Conclusions

Recombinant 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 material

The online version of this article (doi:10.1186/s12934-016-0585-5) contains supplementary material, which is available to authorized users.

Single mutations of ketoreductase ChKRED20 enhance the bioreductive production of (1S)-2-chloro-1-(3, 4-difluorophenyl) ethanol

(1S)-2-chloro-1-(3, 4-difluorophenyl) ethanol ((S)-CFPL) is an intermediate for the drug ticagrelor, and is manufactured via chemical approaches. To develop a biocatalytic solution to (S)-CFPL, an inventory of ketoreductases from Chryseobacterium sp. CA49 were rescreened, and ChKRED20 was found to catalyze the reduction of the ketone precursor with excellent stereoselectivity (>99 % ee). After screening an error-prone PCR library of the wild-type ChKRED20, two mutants, each bearing a single amino acid substitution of H145L or L205M, were identified with significantly increased activity. Then, the two critical positions were each randomized by constructing saturation mutagenesis libraries, which delivered several mutants with further enhanced activity. Among them, the mutant L205A was the best performer with a specific activity of 178 μmol/min/mg, ten times of that of the wild-type. Its k _cat/K _m increased by 15 times and half-life at 50 °C increased by 70 %. The mutant catalyzed the complete conversion of 150 and 200 g/l substrate within 6 and 20 h, respectively, to yield enantiopure (S)-CFPL with an isolated yield of 95 %.

Stereoselective reduction of aromatic ketones by a new ketoreductase from Pichia glucozyma

A new NADPH-dependent benzil reductase (KRED1-Pglu) was identified from the genome of the non-conventional yeast Pichia glucozyma CBS 5766 and overexpressed in E. coli. The new protein was characterised and reaction parameters were optimised for the enantioselective reduction of benzil to (S)-benzoin. A thorough study of the substrate range of KRED1-Pglu was conducted; in contrast to most other known ketoreductases, KRED1-Pglu prefers space-demanding substrates, which are often converted with high stereoselectivity. A molecular modelling study was carried out for understanding the structural determinants involved in the stereorecognition experimentally observed and unpredictable on the basis of steric properties of the substrates. As a result, a new useful catalyst was identified, enabling the enantioselective preparation of different aromatic alcohols and hydroxyketones.

NADP(+)-dependent dehydrogenase activity of carbonyl reductase on glutathionylhydroxynonanal as a new pathway for hydroxynonenal detoxification

An NADP(+)-dependent dehydrogenase activity on 3-glutathionyl-4-hydroxynonanal (GSHNE) was purified to electrophoretic homogeneity from a line of human astrocytoma cells (ADF). Proteomic analysis identified this enzymatic activity as associated with carbonyl reductase 1 (EC 1.1.1.184). The enzyme is highly efficient at catalyzing the oxidation of GSHNE (KM 33 µM, kcat 405 min(-1)), as it is practically inactive toward trans-4-hydroxy-2-nonenal (HNE) and other HNE-adducted thiol-containing amino acid derivatives. Combined mass spectrometry and nuclear magnetic resonance spectroscopy analysis of the reaction products revealed that carbonyl reductase oxidizes the hydroxyl group of GSHNE in its hemiacetal form, with the formation of the corresponding 3-glutathionylnonanoic-δ-lactone. The relevance of this new reaction catalyzed by carbonyl reductase 1 is discussed in terms of HNE detoxification and the recovery of reducing power.

Cloning, expression, and characterization of an anti-Prelog stereospecific carbonyl reductase from Gluconobacter oxydans DSM2343

A new anti-Prelog stereospecific carbonyl reductase (GoKR) from Gluconobacter oxydans DSM2343 was cloned and identified in Escherichia coli. This GoKR formed a homo-tetramer with a subunit size of approximately 27.0kDa. GoKR exhibited full activity with NADPH but not with NADH as a cofactor. The optimal pH and temperature were 9.0 and 30°C, respectively. GoKR reduced various ketones, including aliphatic and aromatic ketones, α- and β-keto esters. Aromatic ketones were reduced to (R)-enantiomers, whereas keto esters were reduced to (S)-hydroxy esters with different enantioselectivities. The data indicate that GoKR does not obey Prelog's rule and exhibits anti-Prelog enantiopreference. Enzyme-substrate-cofactor docking analysis showed that hydride transfer occurred at the si faces of carbonyl group for ethyl 4-chloro-3-oxobutanoate (COBE), which was then selectively reduced to the chiral (S)-alcohol. Excellent enantioselectivities were obtained for reducing COBE and ethyl 2-oxo-4-phenylbutyrate into the corresponding (S)-type products. These products are important for synthesizing HMG-CoA reductase (statins) and angiotensin-converting enzyme inhibitors, respectively.

Metabolism of doxorubicin to the cardiotoxic metabolite doxorubicinol is increased in a mouse model of chronic glutathione deficiency: A potential role for carbonyl reductase 3

Doxorubicin is highly effective at inducing DNA double-strand breaks in rapidly dividing cells, which has led to it being a widely used cancer chemotherapeutic. However, clinical administration of doxorubicin is limited by off-target cardiotoxicity, which is thought to be mediated by doxorubicinol, the primary alcohol metabolite of doxorubicin. Carbonyl reductase 1 (CBR1), a well-characterized monomeric enzyme present at high basal levels in the liver, is known to exhibit activity toward doxorubicin. Little is known about a closely related enzyme, carbonyl reductase 3 (CBR3), which is present in the liver at low basal levels but is highly inducible by the transcription factor Nrf2. Genetic polymorphisms in CBR3, but not CBR1, are associated with differential cardiac outcomes in doxorubicin treated pediatric patients. Cbr3 mRNA and CBR3 protein are highly expressed in the livers of Gclm-/- mice (a mouse model of glutathione deficiency) relative to wild type mice. In the present study, we first investigated the ability of CBR3 to metabolize doxorubicin. Incubations of doxorubicin and purified recombinant murine CBR3 (mCBR3) were analyzed for doxorubicinol formation using HPLC, revealing for the first time that doxorubicin is a substrate of mCBR3. Moreover, hepatocytes from Gclm-/- mice produced more doxorubicinol than Gclm+/+ hepatocytes. In addition, differentiated rat myoblasts (C2C12 cells) co-cultured with primary Gclm-/- murine hepatocytes were more sensitive to doxorubicin-induced cytostasis/cytotoxicity than incubations with Gclm+/+ hepatocytes. Our results indicate a potentially important role for CBR3 in doxorubicin-induced cardiotoxicity. Because there is likely to be variability in hepatic CBR3 activity in humans (due to either genetic or epigenetic influences on its expression), these data also suggest that inhibition of CBR3 may provide protection from doxorubicinol cardiotoxicity.