Co-expression of the recombined alcohol dehydrogenase and glucose dehydrogenase and cross-linked enzyme aggregates stabilization

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.

An improved whole‐cell biotransformation system for ( S )‐equol production

(S)‐equol, the most active metabolite of the soybean isoflavones in vivo, has exhibited various biological activities and clinical benefits. Existing studies on the heterologous biosynthesis of (S)‐equol via the engineered E. coli constructed have been significantly progressed. In the present study, the engineered E. coli was further improved to be more suitable for (S)‐equol production. The four enzymes involved in the biosynthesis of (S)‐equol and another GDH for NADPH regeneration were combined to construct the recombinant E. coli BL21(DE3). The optimal conditions for (S)‐equol production were explored, respectively. The yield of equol reached 98.05% with 1 mM substrate daidzein and 4% (wt/vol) glucose. Even when the substrate concentration increased to 1.5 mM, (S)‐equol could maintain a high yield of 90.25%. Based on the 100 ml one‐pot reaction system, (S)‐equol was produced with 223.6 mg/L in 1.5 h. The study presented a more suitable engineered E. coli for the production of (S)‐equol.

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.

Multicatalytic Hybrid Materials for Biocatalytic and Chemoenzymatic Cascades—Strategies for Multicatalyst (Enzyme) Co-Immobilization

During recent decades, the use of enzymes or chemoenzymatic cascades for organic chemistry has gained much importance in fundamental and industrial research. Moreover, several enzymatic and chemoenzymatic reactions have also served in green and sustainable manufacturing processes especially in fine chemicals, pharmaceutical, and flavor/fragrance industries. Unfortunately, only a few processes have been applied at industrial scale because of the low stabilities of enzymes along with the problematic processes of their recovery and reuse. Immobilization and co-immobilization offer an ideal solution to these problems. This review gives an overview of all the pathways for enzyme immobilization and their use in integrated enzymatic and chemoenzymatic processes in cascade or in a one-pot concomitant execution. We place emphasis on the factors that must be considered to understand the process of immobilization. A better understanding of this fundamental process is an essential tool not only in the choice of the best route of immobilization but also in the understanding of their catalytic activity.

Cross-linked α-galactosidase aggregates: optimization, characterization and application in the hydrolysis of raffinose-type oligosaccharides in soymilk

BACKGROUND

Cross-linked enzyme aggregates (CLEAs) of α-galactosidase, partially purified from maize (Zea mays) flour, were prepared. The impact of various parameters on enzyme activity was examined to optimize the immobilization procedure. Biochemical characterization of the free and immobilized enzyme was carried out. Stability (thermal, pH, storage and operational stability) and reusability tests were performed. The potential use of the free enzyme and the CLEAs in hydrolysis processes of raffinose-type oligosaccharides present in soymilk was investigated.

RESULTS

α-galactosidase CLEAs were prepared with 47% activity recovery under optimum conditions [1:5 (v/v) enzyme solution:saturated ammonium sulfate solution ratio; 7.5 mg protein and 0.1% (v/v) glutaraldehyde, 6 h, 4 °C, 150 rpm]. α-galactosidase CLEAs exhibited increased stability in comparison to the free enzyme. The CLEAs and the free enzyme showed a maximum activity at 40°C and their optimal pH values were5.5 and 6.0, respectively. Kinetic constants (K_M , V_max and k_cat ) were calculated for the free enzyme and the CLEAs in the presence of p-nitrophenyl-α-d-galactopyranoside, stachyose, melibiose and raffinose. The effect of various chemicals and sugars on enzyme activity showed that both enzyme forms were significantly inhibited by HgCl₂ and galactose. The CLEAs hydrolyzed 85% of raffinose and 96% of stachyose.

CONCLUSION

The α-galactosidase CLEAs, with their satisfactory enzymatic characteristics, have much potential for use in the food and feed industry. © 2019 Society of Chemical Industry.

Coenzyme Binding Site Analysis of an Isopropanol Dehydrogenase with Wide Substrate Spectrum and Excellent Organic Solvent Tolerance

NAD(P)H-dependent enzymes are ideal biocatalysts for the industrial production of chiral compounds, such as chiral alcohols, chiral amino acids, and chiral amines; however, efficient strategies for the regeneration of coenzyme are expected as costly of the coenzymes. Herein, a solvent-tolerant isopropanol dehydrogenase (IDH) showing lower similarity (37%) with other proteins was obtained and characterized. The enzyme exhibits high catalysis ability of its substrates methanol, ethanol, ethylene glycol, glycerol, isopropanol, n-butanol, isobutanol, and acetone. And it has good adaptability in organic solvents (isopropanol, acetonitrile, acetone, and acetophenone). Interaction force and the corresponding amino acid residues between IDH and NAD⁺ or NADP⁺ were parsed by docking. The wide substrate spectrum, excellent organic solvent tolerance, and good biocatalytic activity make the excavated enzyme a promising biocatalyst for the production of chiral compounds industrially and the construction of coenzyme regeneration systems in aqueous organic phase or organic phase.

Biotransformation of a crizotinib intermediate using a mutant alcohol dehydrogenase of Lactobacillus kefir coupled with glucose dehydrogenase

(S)-1-(2, 6-dichloro-3-fluorophenyl) ethanol, the key chiral intermediate of crizotinib, was prepared from 1-(2, 6-dichloro-3-fluorophenyl) ethanone using the alcohol dehydrogenases from Lactobacillus kefir (ADH-LK) with a tetrad mutant (ADH-LKM, F147L/Y190P/V196L/A202W), coupled with glucose dehydrogenase (GDH). In the present study, ADH-LKM and GDH were successfully heterologous expressed in recombinant Escherichia coli. During the regeneration of NADPH with GDH, 150 g/L substrate was totally transformed into target chiral alcohol with an enantiomeric excess value of 99.9% after 12 h at 30 °C (pH 7.0). Our study demonstrates the potential for industrial green production of the key chiral intermediate of crizotinib.

CLEAs, Combi-CLEAs and ‘Smart’ Magnetic CLEAs: Biocatalysis in a Bio-Based Economy

Biocatalysis has emerged in the last decade as a pre-eminent technology for enabling the envisaged transition to a more sustainable bio-based economy. For industrial viability it is essential that enzymes can be readily recovered and recycled by immobilization as solid, recyclable catalysts. One method to achieve this is via carrier-free immobilization as cross-linked enzyme aggregates (CLEAs). This methodology proved to be very effective with a broad selection of enzymes, in particular carbohydrate-converting enzymes. Methods for optimizing CLEA preparations by, for example, adding proteic feeders to promote cross-linking, and strategies for making the pores accessible for macromolecular substrates are critically reviewed and compared. Co-immobilization of two or more enzymes in combi-CLEAs enables the cost-effective use of multiple enzymes in biocatalytic cascade processes and the use of “smart” magnetic CLEAs to separate the immobilized enzyme from other solids has raised the CLEA technology to a new level of industrial and environmental relevance. Magnetic-CLEAs of polysaccharide-converting enzymes, for example, are eminently suitable for use in the conversion of first and second generation biomass.

Combined Cross-Linked Enzyme Aggregates as Biocatalysts

Enzymes are efficient biocatalysts providing an important tool in many industrial biocatalytic processes. Currently, the immobilized enzymes prepared by the cross-linked enzyme aggregates (CLEAs) have drawn much attention due to their simple preparation and high catalytic efficiency. Combined cross-linked enzyme aggregates (combi-CLEAs) including multiple enzymes have significant advantages for practical applications. In this review, the conditions or factors for the preparation of combi-CLEAs such as the proportion of enzymes, the type of cross-linker, and coupling temperature were discussed based on the reaction mechanism. The recent applications of combi-CLEAs were also reviewed.

Highly Efficient Deracemization of Racemic 2-Hydroxy Acids in a Three-Enzyme Co-Expression System Using a Novel Ketoacid Reductase

Enantiopure 2-hydroxy acids (2-HAs) are important intermediates for the synthesis of pharmaceuticals and fine chemicals. Deracemization of racemic 2-HAs into the corresponding single enantiomers represents an economical and highly efficient approach for synthesizing chiral 2-HAs in industry. In this work, a novel ketoacid reductase from Leuconostoc lactis (LlKAR) with higher activity and substrate tolerance towards aromatic α-ketoacids was discovered by genome mining, and then its enzymatic properties were characterized. Accordingly, an engineered Escherichia coli (HADH-LlKAR-GDH) co-expressing 2-hydroxyacid dehydrogenase, LlKAR, and glucose dehydrogenase was constructed for efficient deracemization of racemic 2-HAs. Most of the racemic 2-HAs were deracemized to their (R)-isomers at high yields and enantiomeric purity. In the case of racemic 2-chloromandelic acid, as much as 300 mM of substrate was completely transformed into the optically pure (R)-2-chloromandelic acid (> 99% enantiomeric excess) with a high productivity of 83.8 g L^-1 day^-1 without addition of exogenous cofactor, which make this novel whole-cell biocatalyst more promising and competitive in practical application.

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.

Designing cross-linked xylanase aggregates for bioconversion of agroindustrial waste biomass towards potential production of nutraceuticals

Immobilized biocatalysts design has the potential to efficiently produce valuable bioproducts from lignocellulosic biomass. Among them, the carrier-free immobilization through the cross-linked enzyme aggregates technology is a simple and low-cost alternative. A two steps statistical approach was utilized to evaluate the synthesis of a cross-linked enzyme aggregate from a xylanolytic preparation, which was produced by Cohnella sp. AR92 grown in a peptone-based culture medium. The resulting immobilized biocatalyst, Xyl-CLEA, was significate more stable (25 to 45%) towards temperatures up to 50°C with respect to the free enzyme, and retained over 50% of its initial activity after 5 consecutive cycles of reuse. By means of infrared spectroscopy and electron microscopy, the Xyl-CLEA showed architectural features described as signature of type I and type II of protein aggregates. These, were the result of the simultaneous aggregation of a multiplicity of proteins from the crude enzymatic extract. The enzymatic activity was assessed using alkali pretreated sugar cane bagasse as substrate. Whereas the free enzymatic preparation released xylose as the main product, the immobilized xylanase produced xylooligosaccharides, thus showing that the immobilization procedure modified the potential application of the extracellular xylanase from Conhella sp. AR92.