A novel carbonyl reductase from Pichia stipitis for the production of ethyl (S)-4-chloro-3-hydroxybutanoate

Two-Step Epimerization of Deoxynivalenol by Quinone-Dependent Dehydrogenase and Candida parapsilosis ACCC 20221

Deoxynivalenol (DON), one of the main mycotoxins with enteric toxicity, genetic toxicity, and immunotoxicity, and is widely found in corn, barley, wheat, and rye. In order to achieve effective detoxification of DON, the least toxic 3-epi-DON (1/357th of the toxicity of DON) was chosen as the target for degradation. Quinone-dependent dehydrogenase (QDDH) reported from Devosia train D6-9 detoxifies DON by converting C3-OH to a ketone group with toxicity of less than 1/10 that of DON. In this study, the recombinant plasmid pPIC9K-QDDH was constructed and successfully expressed in Pichia pastoris GS115. Within 12 h, recombinant QDDH converted 78.46% of the 20 μg/mL DON to 3-keto-DON. Candida parapsilosis ACCC 20221 was screened for its activity in reducing 86.59% of 3-keto-DON within 48 h; its main products were identified as 3-epi-DON and DON. In addition, a two-step method was performed for epimerizing DON: 12 h catalysis by recombinant QDDH and 6 h transformation of the C. parapsilosis ACCC 20221 cell catalyst. The production rates of 3-keto-DON and 3-epi-DON were 51.59% and 32.57%, respectively, after manipulation. Through this study, effective detoxification of 84.16% of DON was achieved, with the products being mainly 3-keto-DON and 3-epi-DON.

Stairway to Stereoisomers: Engineering Short- and Medium-Chain Ketoreductases To Produce Chiral Alcohols

The short- and medium-chain dehydrogenase/reductase superfamilies are responsible for most chiral alcohol production in laboratories and industries. In nature, they participate in diverse roles such as detoxification, housekeeping, secondary metabolite production, and catalysis of several chemicals with commercial and environmental significance. As a result, they are used in industries to create biopolymers, active pharmaceutical intermediates (APIs), and are also used as components of modular enzymes like polyketide synthases for fabricating bioactive molecules. Consequently, random, semi-rational and rational engineering have helped transform these enzymes into product-oriented efficient catalysts. The rise of newer synthetic chemicals and their enantiopure counterparts has proved challenging, and engineering them has been the subject of numerous studies. However, they are frequently limited to the synthesis of a single chiral alcohol. The study attempts to defragment and describe hotspots of engineering short- and medium-chain dehydrogenases/reductases for the production of chiral synthons.

Biocatalyzed Synthesis of Statins: A Sustainable Strategy for the Preparation of Valuable Drugs

Statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, are the largest selling class of drugs prescribed for the pharmacological treatment of hypercholesterolemia and dyslipidaemia. Statins also possess other therapeutic effects, called pleiotropic, because the blockade of the conversion of HMG-CoA to (R)-mevalonate produces a concomitant inhibition of the biosynthesis of numerous isoprenoid metabolites (e.g., geranylgeranyl pyrophosphate (GGPP) or farnesyl pyrophosphate (FPP)). Thus, the prenylation of several cell signalling proteins (small GTPase family members: Ras, Rac, and Rho) is hampered, so that these molecular switches, controlling multiple pathways and cell functions (maintenance of cell shape, motility, factor secretion, differentiation, and proliferation) are regulated, leading to beneficial effects in cardiovascular health, regulation of the immune system, anti-inflammatory and immunosuppressive properties, prevention and treatment of sepsis, treatment of autoimmune diseases, osteoporosis, kidney and neurological disorders, or even in cancer therapy. Thus, there is a growing interest in developing more sustainable protocols for preparation of statins, and the introduction of biocatalyzed steps into the synthetic pathways is highly advantageous—synthetic routes are conducted under mild reaction conditions, at ambient temperature, and can use water as a reaction medium in many cases. Furthermore, their high selectivity avoids the need for functional group activation and protection/deprotection steps usually required in traditional organic synthesis. Therefore, biocatalysis provides shorter processes, produces less waste, and reduces manufacturing costs and environmental impact. In this review, we will comment on the pleiotropic effects of statins and will illustrate some biotransformations nowadays implemented for statin synthesis.

A Comparative Study on Asymmetric Reduction of Ketones Using the Growing and Resting Cells of Marine-Derived Fungi

Whole-cell biocatalysts offer a highly enantioselective, minimally polluting route to optically active alcohols. Currently, most of the whole-cell catalytic performance involves resting cells rather than growing cell biotransformation, which is one-step process that benefits from the simultaneous growth and biotransformation, eliminating the need for catalysts preparation. In this paper, asymmetric reduction of 14 aromatic ketones to the corresponding enantiomerically pure alcohols was successfully conducted using the growing and resting cells of marine-derived fungi under optimized conditions. Good yields and excellent enantioselectivities were achieved with both methods. Although substrate inhibition might be a limiting factor for growing cell biotransformation, the selected strain can still completely convert 10-mM substrates into the desired products. The resting cell biotransformation showed a capacity to be recycled nine times without a significant decrease in the activity. This is the first study to perform asymmetric reduction of ketones by one-step growing cell biotransformation.

A carbonyl reductase from Candida parapsilosis ATCC 7330: substrate selectivity and enantiospecificity

A purified carbonyl reductase (SRED) asymmetrically reduces ketones and α-ketoesters to (S)-alcohols with a potential application in the synthesis of industrially important chiral molecules.

Biochemical characterisation of a NADPH-dependent carbonyl reductase from Neurospora crassa reducing α- and β-keto esters

A gene encoding an NADPH-dependent carbonyl reductase from Neurospora crassa (nccr) was cloned and heterologously expressed in Escherichia coli. The enzyme (NcCR) was purified and biochemically characterised. NcCR exhibited a restricted substrate spectrum towards various ketones, and the highest activity (468U/mg) was observed with dihydroxyacetone. However, NcCR proved to be very selective in the reduction of different α- and β-keto esters. Several compounds were converted to the corresponding hydroxy ester in high enantiomeric excess (ee) at high conversion rates. The enantioselectivity of NcCR for the reduction of ethyl 4-chloro-3-oxobutanoate showed a strong dependence on temperature. This effect was studied in detail, revealing that the ee could be substantially increased by decreasing the temperature from 40 °C (78.8%) to -3 °C (98.0%). When the experimental conditions were optimised to improve the optical purity of the product, (S)-4-chloro-3-hydroxybutanoate (ee 98.0%) was successfully produced on a 300 mg (1.8 mmol) scale using NcCR at -3 °C.

Purification and characterization of a novel NADH-dependent carbonyl reductase from Pichia stipitis involved in biosynthesis of optically pure ethyl (S)-4-chloro-3-hydroxybutanoate

A novel NADH-dependent dehydrogenases/reductases (SDRs) superfamily reductase (PsCRII) was isolated from Pichia stipitis. It produced ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE] in greater than 99% enantiomeric excess. This enzyme was purified to homogeneity by ammonium sulfate precipitation followed by Q-Sepharose chromatography. Compared to similar known reductases producing (S)-CHBE, PsCR II was more suitable for production since the purified PsCRII preferred the inexpensive cofactor NADH to NADPH as the electron donor. Furthermore, the Km of PsCRII for ethyl 4-chloro-3-oxobutanoate (COBE) was 3.3 mM, and the corresponding Vmax was 224 μmol/mg protein/min. The catalytic efficiency is the highest value ever reported for NADH-dependent reductases from yeasts that produce CHBE with high enantioselectivity. In addition, this enzyme exhibited broad substrate specificity for several β-keto esters using NADH as the coenzyme. The properties of PsCRII with those of other carbonyl reductases from yeasts were also compared in this study.

Biosynthesis of (S)-4-chloro-3-hydroxybutanoate ethyl using Escherichia coli co-expressing a novel NADH-dependent carbonyl reductase and a glucose dehydrogenase

A novel NADH-dependent carbonyl reductase (PsCR II) gene with an open reading frame of 855bp encoding 285 amino acids was cloned from Pichia stipitis. Analysis of the amino acid sequence of PsCR II revealed less than 55% identity to known reductases that produce (S)-4-chloro-3-hydroxybutanoates ethyl [(S)-CHBE]. When NADH was provided as an electron donor, Escherichia coli with pET-22b-PsCRII exhibited an activity of 15U/mg protein using 4-chloro-3-oxobutanoate ethyl (COBE) as a substrate. This activity was the highest ever reported for reductases, with the exception of PsCR I, which in our previous analysis required NADPH for catalysis. Biocatalysis of COBE to (S)-CHBE was investigated using E. coli with a polycistronic plasmid pET-BP II co-expressing PsCR II and a glucose dehydrogenase in a water/butyl acetate system for 24h. The transformants gave a molar yield of 91%, and an optical purity of the (S)-isomer of higher than 99% enantiomeric excess.

Construction and co-expression of a polycistronic plasmid encoding carbonyl reductase and glucose dehydrogenase for production of ethyl (S)-4-chloro-3-hydroxybutanoate

Biocatalysis of ethyl 4-chloro-3-oxobutanoate (COBE) to ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE] was carried out using Escherichia coli co-expressing a carbonyl reductase gene from Pichia stipitis and a glucose dehydrogenase gene from Bacillus megaterium. An efficient polycistronic plasmid with a high-level of enzyme co-expression was constructed by changing the order of the genes, altering the Shine-Dalgarno (SD) regions, and aligned spacing (AS) between the SD sequence and the translation initiation codon. The optimal SD sequence was 5-TAAGGAGG-3, and the optimal AS distance was eight nucleotides. Asymmetric reduction of COBE to (S)-CHBE with more than 99% enantiomeric excess was demonstrated by transformants, using a water/ethyl caprylate system. The recombinant cells produced 1260 mM product in the organic phase, and the total turnover number, defined as moles (S)-CHBE formed per mole NADP(+), was 12,600, which was more than 10-fold higher than in aqueous systems.

A new member of the short-chain dehydrogenases/reductases superfamily: purification, characterization and substrate specificity of a recombinant carbonyl reductase from Pichia stipitis

A novel short-chain dehydrogenases/reductases superfamily (SDRs) reductase (PsCR) from Pichia stipitis that produced ethyl (S)-4-chloro-3-hydroxybutanoate with greater than 99% enantiomeric excess, was purified to homogeneity using fractional ammonium sulfate precipitation followed by DEAE-Sepharose chromatography. The enzyme purified from recombinant Escherichia coli had a molecular mass of about 35 kDa on SDS-PAGE and only required NADPH as an electron donor. The K(m) value of PsCR for ethyl 4-chloro-3-oxobutanoate was 4.9 mg/mL and the corresponding V(max) was 337 micromol/mg protein/min. The catalytic efficiency value was the highest ever reported for reductases from yeasts. Moreover, PsCR exhibited a medium-range substrate spectrum toward various keto and aldehyde compounds, i.e., ethyl-3-oxobutanoate with a chlorine substitution at the 2 or 4-position, or alpha,beta-diketones. In addition, the activity of the enzyme was strongly inhibited by SDS and beta-mercaptoethanol, but not by ethylene diamine tetra acetic acid.