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Ethyl ( S)-4-chloro-3-hydroxybutanoate ester (( S)-CHBE) is a precursor of enantiopure intermediates used for the production of chiral drugs, including the cholesterol-lowering 3-hydroxy-3-methyl-glutaryl CoA reductase inhibitors (statins). The asymmetric reduction of ethyl 4-chloro-3-oxobutanoate ester (COBE) to ( S)-CHBE by biocatalysis has several positive attributes, including low cost, mild reaction conditions, high yield, and a high level of enantioselectivity. During genome database mining of the yeast Pichia stipitis, our group found two novel carbonyl reductases (PsCRI and PsCRII) that have a promising future for the industrial production of ( S)-CHBE with >99% enantiomeric excess. This review covers the main process of biosynthesis of ( S)-CHBE: screening of microorganisms that catalyze the reduction of COBE to ( S)-CHBE (I); gene cloning, expression, and characterization of carbonyl reductases for the production of ( S)-CHBE in Escherichia coli (II); development of cofactor generation systems for regenerating cofactors (III); and biocatalysis of COBE to ( S)-CHBE by recombinant E. coli (IV). [ABSTRACT FROM AUTHOR]

cofactor regeneration system for enzymatic biosynthesis was constructed by coexpressing a carbonyl reductase from Pichia stipitis and a glucose dehydrogenase from Bacillus megaterium in Escherichia coli Rosetta (DE3) PlySs. Transformants containing the polycistronic plasmid pET-PII-SD2-AS1-B exhibited an activity of 13.5 U/mg protein with 4-chloro-3-oxobutanoate ethyl ester (COBE) as the substrate and an activity of 14.4 U/mg protein with glucose as the substrate; NAD(H) was the coenzyme in both cases. Asymmetric reduction of COBE to ( S)-4-chloro-3-hydroxybutanoate ethyl ester [( S)-CHBE] with more than 99% enantiomeric excess was demonstrated by transformants. Furthermore, the paper made a comparison of crude enzyme catalysis and whole-cell catalysis in an aqueous monophasic system and a water/organic solvent biphasic system. In the water/ n-butyl acetate system, the coexpression system produced 1,398 mM CHBE in the organic phase, which is the highest yield ever reported for CHBE production by NADH-dependent reductases from yeasts. In this case, the molar yield of CHBE was 90.7%, and the total turnover number, defined as moles ( S)-CHBE formed per mole NAD+, was 13,980. [ABSTRACT FROM AUTHOR]

To develop an economical industrial medium, untreated cane molasses (UCM) was tested as a carbon source for fermentation culturing of Escherichia coli. To test the industrial application of this medium, we chose a strain co-expressing a carbonyl reductase (PsCR) and a glucose dehydrogenase (BmGDH). Although corn steep liquor (CSL) could be used as an inexpensive nitrogen source to replace peptone, yeast extract could not be replaced in E. coli media. In a volume of 40 ml per 1-l flask, a cell concentration of optical density (OD600) 15.1 and enzyme activities of 6.51 U/ml PsCR and 3.32 U/ml BmGDH were obtained in an optimized medium containing 25.66 g/l yeast extract, 3.88 g/l UCM, and 7.1% ( v/ v) CSL. When 3.88 g/l UCM was added to the medium at 6 h in a fed-batch process, the E. coli concentration increased to OD600 of 24, and expression of both PsCR and BmGDH were twofold higher than that of a batch process. Recombinant cells from batch or fed-batch cultures were assayed for recombinant enzyme activity by testing the reduction of ethyl 4-chloro-3-oxobutanoate to ethyl ( S)-4-chloro-3-hydroxybutanoate (CHBE). Compared to cells from batch cultures, fed-batch cultured cells showed higher recombinant enzyme expression, producing 560 mM CHBE in the organic phase with a molar yield of 92% and an optical purity of the ( S)-isomer of >99% enantiomeric excess. [ABSTRACT FROM AUTHOR]

A whole cell biocatalytic process for uridine 5′-monophosphate (UMP) production from orotic acid by Saccharomyces cerevisiae was developed. The concentration of UMP was increased by 23% when 1 g l−1 sodium citrate was fed into the broth. Effects of citrate addition on UMP production were investigated. Glucose-6-phosphate pool was elevated by onefold, while FBP and pyruvate were decreased by 42% and 40%, respectively. Organic acid pools such as acetate and succinate were averagely decreased by 30% and 49%. The results demonstrated that manipulation of citrate levels could be used as a novel tool to regulate the metabolic fluxes distribution among glycolysis, pentose phosphate pathway, and TCA cycle. [ABSTRACT FROM AUTHOR]

Uridine diphosphate N-acetylglucosamine (UDPAG) can be produced by chemical, enzymatic, chemoenzymatic, and fermentative methods. In this study, we used whole-cell catalysis method to produce UDPAG for the first time by Saccharomyces cerevisiae. In order to increase the ATP utilization efficiency and UDPAG conversion yield, the response surface methodology was applied to optimize the whole-cell catalytic conditions for UDPAG production. Firstly, effects of uridine 5′-monophosphate (5′-UMP), glucosamine, vitamin B1, glycerol, magnesium chloride, potassium chloride, temperature, sodium dihydrogen phosphate, sodium acetate, fructose, and pH on UDPAG production were evaluated by a fractional factorial design. Results showed that UDPAG production was mainly affected by sodium dihydrogen phosphate, temperature, and vitamin B1. Then, the concentrations of sodium dihydrogen phosphate and vitamin B1 and temperature were further investigated with a central composite design and response surface analysis. The cultivation conditions to obtain the optimal UDPAG production were determined: sodium dihydrogen phosphate, 31.2 g/L; temperature, 29°C, and vitamin B1, 0.026 g/L. This optimization strategy led to an enhancement of UDPAG production from 2.51 to 4.25 g/L, yield from 44.6% to 75.6% based on the initial 5′-UMP concentration, and ATP utilization efficiency from 7.43% to 12.6%. [ABSTRACT FROM AUTHOR]