Expression and characterization of a novel ω-transaminase from Burkholderia phytofirmans PsJN / 生物工程学报

Production of chiral amines and unnatural amino-acid using ω-transaminase can be achieved by kinetic resolution and asymmetric synthesis, thus ω-transaminase is of great importance in the synthesis of pharmaceutical intermediates. By genomic data mining, a putative ω-transaminase gene hbp was found in Burkholderia phytofirmans PsJN. The gene was cloned and over-expressed in Escherichia coli BL21 (DE3). The recombinant enzyme (HBP) was purified by Ni-NTA column and its catalytic properties and substrate profile were studied. HBP showed high relative activity (33.80 U/mg) and enantioselectivity toward β-phenylalanine (β-Phe). The optimal reaction temperature and pH were 40 ℃ and 8.0-8.5, respectively. We also established a simpler and more effective method to detect the deamination reaction of β-Phe by UV absorption method using microplate reader, and demonstrated the thermodynamic property of this reaction. The substrate profiling showed that HBP was specific to β-Phe and its derivatives as the amino donor. HBP catalyzed the resolution of rac-β-Phe and its derivatives, the products (R)-amino acids were obtained with about 50% conversions and 99% ee.

Expression and characterization of a novel halohydrin dehalogenase from Tistrella mobilis KA081020-065 / 生物工程学报

Halohydrin dehalogenase is of great significance for biodegradation of the chlorinated pollutants, and also serves as an important biocatalyst in the synthesis of chiral pharmaceutical intermediates. A putative halohydrin dehalogenase (HheTM) gene from Tistrella mobilis KA081020-065 was cloned and over-expressed in Escherichia coli BL21 (DE3). The recombinant enzyme was purified by Ni-NTA column and characterized. Gel filtration and SDS-PAGE analysis showed that the native form of HheTM was a tetramer. It exhibited the highest activity at 50 degrees C. The nature and pH of the buffer had a great effect on its activity. The enzyme maintained high stability under the alkaline conditions and below 30 degrees C. HheTM catalyzed the transformation of ethyl(S)-4-chloro-3-hydroxybutyrate in the presence of cyanide, to give ethyl (R)-4-cyano-3-hydroxybutyrate, a key intermediate for the synthesis of atorvastatin.

Effect of residue Y76 on co-enzyme specificity of meso-diaminopimelate dehydrogenase from Symbiobacterium thermophilum / 生物工程学报

In industrial application of NAD(P)H-dependent dehydrogenases, NAD(H) has the advantages over NADP(H) in higher stability, lower price and wider recycling system. Recently, a meso-2,6-diaminopimelate dehydrogenase from Symbiobacterium thermophilum (StDAPDH) has been found to be a useful biocatalyst for the production of D-amino acids, but it requires NADP(H) as co-enzyme. To switch the co-enzyme specificity from NADP(H) to NAD(H), we studied the effect of Y76 on the co-enzyme specificity of StDAPDH, because the crystal structural analysis indicated that residue Y76 is near the adenine ring. The mutation of Y76 exerted significant effect on the co-enzyme specificity. Furthermore, the double mutant R35S/R36V significantly lowered the specific activity toward NADP+, and the combination of R35S/R36V with some of the Y76 mutants resulted in mutant enzymes favorable NAD+ over NADP+. This study should provide useful guidance for the further development of highly active NAD(+)-dependent StDAPDH by enzyme engineering.

High throughput screening of active and stereoselective carbonyl reductases / 生物工程学报

In this study, a fast carbonyl reductases colorimetric screening method for discovering stereoselective carbonyl reductases was established by combining the reverse alcohol oxidation with the azoreductase-catalyzed reduction of azo dye. When azo dye (Orange I , 4-(4-hydroxy-1-naphthylazo) benzenesulfonic acid) and azoreductase (AzoB) were added into the reaction system of alcohol oxidation catalyzed by carbonyl reductase, the produced NAD(P)H served as electron donor for the azoreductase to reduce the azo dye, resulting the color fade. Hence, the carbonyl reductases can be screened by the obvious color change. When chiral alcohol was used as the substrate, the activity and stereoselectivity of carbonyl reductases can be screened at the same time.

Biocatalytic desymmetric hydrolysis of 3-(4-chlorophenyl)-glutaronitrile to the key precursor of optically pure baclofen / 生物工程学报

We produced (S)-4-cyano-3-(4-chlorophenyl)-butyrate by highly stereoselective biocatalyst in this study. A nitrilase-producing strain, named Gibberella intermedia WX12, was isolated by 3-(4-chlorophenyl)-glutaronitrile as substrate in the screening with phenol-sodium hypochlorite method. The fermentation conditions and catalytic properties of this strain were investigated. The preferred carbon and nitrogen sources for nitrilase production were lactose (30 g/L) and peptone (20 g/L). After being cultivated for 96 h, the cells were collected for use in biotransformation. The hydrolysis of 3-(4-chlorophenyl)-glutaronitrile was performed at 30 degrees C in phosphate buffer (pH 8.0, 50 mmol/L) for 24 h to give (S)-4-cyano-3-(4-chlorophenyl)-butyric acid with 90% yield and > 99% of ee, which can be used for the synthesis of (R)- and (S)-baclofen. The configuration of product was determined by chemically converting it to baclofen and comparison with the authentic sample by chiral HPLC analysis.

Cloning and characterization of a novel carbonyl reductase for asymmetric reduction of bulky diaryl ketones / 生物工程学报

Asymmetric reduction of bulky diaryl ketones is still one of the challenging tasks in biocatalysis. By genomic data mining, a putative carbonyl reductase gene pascr was found in Pichia pastoris GS115. pascr was cloned and over-expressed in Escherichia coli Rosseta2 (DE3). The recombinant enzyme was purified to homogeneity by Ni-NTA column and its catalytic properties were studied. PasCR strictly used NADPH as cofactor, gel filtration and SDS-PAGE analysis suggested that the native form of PasCR was a dimmer. PasCR exhibited the highest activity at 35 degrees C in phosphate buffer at pH 6.5. The enzyme catalyzed the reduction of some bulky diaryl ketones, such as 4-methylbenzophenone, 2-methylbenzophenone and 4-chlorobenzophenone, especially for 4-methylbenzophenone, the product S--alcohol was obtained with 85% ee.

Biochemical characterization and substrate profile of a highly enantioselective carbonyl reductase from Pichia pastoris / 生物工程学报

Carbonyl reductases catalyze carbonyl compounds to chiral alcohols that are important building blocks in fine chemical industry. To study carbonyl reductase from Pichia pastoris GS115 (ppcr), we discovered a new gene (ppcr) encoding an NADPH-dependent carbonyl reductase by genomic data mining. It was amplified by PCR from the genomic DNA, and expressed in Escherichia coli BL21 (DE3). The recombinant protein was purified to homogeneity. The optimum temperature was 37 degrees C and the optimum pH of PPCR was 6.0. PPCR was stable below 45 degrees C. The Km and k(cat) value of the enzyme for ethyl 3-methyl-2-oxobutanoate were 9.48 mmol/L and 0.12 s, respectively. The enzyme had broad substrate specificity and high enantioselectivity. It catalyzed the reduction of aldehydes, a-ketoesters, beta-ketoesters and aryl ketones to give the corresponding alcohols with >97% ee with only a few exceptions, showing its application potential in the synthesis of chiral alcohols.

Engineering the enantioselectivity of biocatalysts / 生物工程学报

Wild-type biocatalysts usually show high activity and selectivity towards their native substrates. Since non-native substrates are often used in synthetically useful biocatalytic transformations, it is necessary to engineer enzymes for improved activity, stability and selectivity (chemo-, regio- and stereoselectivity). Herein we give an overview of the recent advances in engineering the enantioselectivity of biocatalysts, with an aim to stimulate further development of this important field in China.