Novel chiral tool, (R)-2-octanol dehydrogenase, from Pichia finlandica: purification, gene cloning, and application for optically active α-haloalcohols

A secretion-based dual fluorescence assay for high-throughput screening of alcohol dehydrogenases

Alcohol dehydrogenases (ADHs) play key roles in the production of various chemical precursors that are essential in pharmaceutical and fine chemical industries. To achieve a practical application of ADHs in industrial processes, tailoring enzyme properties through rational design or directed evolution is often required. Here, we developed a secretion-based dual fluorescence assay (SDFA) for high-throughput screening of ADHs. In SDFA, an ADH of interest is fused to a mutated superfolder green fluorescent protein (MsfGFP), which could result in the secretion of the fusion protein to culture broth. After a simple centrifugation step to remove the cells, the supernatant can be directly used to measure the activity of ADH based on a red fluorescence signal, whose increase is coupled to the formation of NADH (a redox cofactor of ADHs) in the reaction. SDFA allows easy quantification of ADH concentration based on the green fluorescence signal of MsfGFP. This feature is useful in determining specific activity and may improve screening accuracy. Out of five ADHs we have tested with SDFA, four ADHs can be secreted and characterized. We successfully screened a combinatorial library of an ADH from Pichia finlandica and identified a variant with a 197-fold higher k_cat /k_m value toward (S)-2-octanol compared to its wild type.

Enantioconvergent Biocatalytic Redox Isomerization

Alcohol dehydrogenases can act as powerful catalysts in the preparation of optically pure γ-hydroxy-δ-lactones by means of an enantioconvergent dynamic redox isomerization of readily available Achmatowicz-type pyranones. Imitating the traditionally metal-mediated "borrowing hydrogen" approach to shuffle hydrides across molecular architectures and interconvert functional groups, this chemoinspired and purely biocatalytic interpretation effectively expands the enzymatic toolbox and provides new opportunities in the assembly of multienzyme cascades and tailor-made cellular factories.

Enzymatic cascades for the stereo-complementary epimerisation of in situ generated epoxy alcohols

The synthesis of optically pure secondary epoxy alcohols from racemic allylic alcohols using a single whole-cell biocatalyst of recombinant Escherichia coli coexpressing three oxidoreductases is described. The cascade involves the concurrent action of a styrene monooxygenase that catalyzes the formation of the chiral epoxy group, and two alcohol dehydrogenases that fulfil the epimerisation of the hydroxy group. Two sets of alcohol dehydrogenases were each applied to couple with styrene monooxygenase in order to realize the epimerisation in a stereo-complementary manner. Excellent enantio- and diastereo-selectivities were achieved for most of the 12 substrates.

Combination of deep eutectic solvent and ionic liquid to improve biocatalytic reduction of 2-octanone with Acetobacter pasteurianus GIM1.158 cell

The efficient anti-Prelog asymmetric reduction of 2-octanone with Acetobacter pasteurianus GIM1.158 cells was successfully performed in a biphasic system consisting of deep eutectic solvent (DES) and water-immiscible ionic liquid (IL). Various DESs exerted different effects on the synthesis of (R)-2-octanol. Choline chloride/ethylene glycol (ChCl/EG) exhibited good biocompatibility and could moderately increase the cell membrane permeability thus leading to the better results. Adding ChCl/EG increased the optimal substrate concentration from 40 mM to 60 mM and the product e.e. kept above 99.9%. To further improve the reaction efficiency, water-immiscible ILs were introduced to the reaction system and an enhanced substrate concentration (1.5 M) was observed with C₄MIM·PF₆. Additionally, the cells manifested good operational stability in the reaction system. Thus, the efficient biocatalytic process with ChCl/EG and C₄MIM·PF₆ was promising for efficient synthesis of (R)-2-octanol.