Engineering a Bacillus subtilis esterase for selective hydrolysis of d, l-menthyl acetate in an organic solvent-free system†

Abridgement of Microbial Esterases and Their Eminent Industrial Endeavors

Esterases are hydrolases that contribute to the hydrolysis of ester bonds into both water-soluble acyl esters and emulsified glycerol-esters containing short-chain acyl groups. They have garnered significant attention from biotechnologists and organic chemists due to their immense commercial value. Esterases, with their diverse and significant properties, have become highly sought after for various industrial applications. Synthesized ubiquitously by a wide range of living organisms, including animals, plants, and microorganisms, these enzymes have found microbial esterases to be the preferred choice in industrial settings. The cost-effective production of microbial esterases ensures higher yields, unaffected by seasonal variations. Their applications span diverse sectors, such as food manufacturing, leather tanneries, paper and pulp production, textiles, detergents, cosmetics, pharmaceuticals, biodiesel synthesis, bioremediation, and waste treatment. As the global trend shifts toward eco-friendly and sustainable practices, industrial processes are evolving with reduced waste generation, lower energy consumption, and the utilization of biocatalysts derived from renewable and unconventional raw materials. This review explores the background, structural characteristics, thermostability, and multifaceted roles of bacterial esterases in crucial industries, aiming to optimize and analyze their properties for continued successful utilization in diverse industrial processes. Additionally, recent advancements in esterase research are overviewed, showcasing novel techniques, innovations, and promising areas for further exploration.

Enhancing the Enantioselectivity and Catalytic Efficiency of Esterase from Bacillus subtilis for Kinetic Resolution of l-Menthol through Semirational Design

Enzymatic kinetic resolution is a promising way to produce l-menthol. However, the properties of the reported biocatalysts are still unsatisfactory and far from being ready for industrial application. Herein, a para-nitrobenzylesterase (pnbA) gene from Bacillus subtilis was cloned and expressed to produce l-menthol from d,l-menthyl acetate. The highest enantiomeric excess (ee) value of the product generated by pnbA was only approximately 80%, with a high conversion rate (47.8%) of d,l-menthyl acetate with the help of a cosolvent, indicating high catalytic activity but low enantioselectivity (E = 19.95). To enhance the enantioselectivity and catalytic efficiency of pnbA to d,l-menthyl acetate in an organic solvent-free system, site-directed mutagenesis was performed based on the results of molecular docking. The F314E/F315T mutant showed the best catalytic properties (E = 36.25) for d,l-menthyl acetate, with 92.11% ee and 30.58% conversion of d,l-menthyl acetate. To further improve the properties of pnbA, additional mutants were constructed based on the structure-guided triple-code saturation mutagenesis strategy. Finally, four mutants were screened for the best enantioselectivity (ee > 99%, E > 300) and catalytic efficiency at a high substrate concentration (200 g/L) without a cosolvent. This work provides several generally applicable biocatalysts for the industrial production of l-menthol.

Efficient enzymatic synthesis of chiral 2,3-dihydro-1,4-benzodioxane motif using engineered Candida antarctica lipase B

Chiral motifs of 2,3-dihydro-1,4 benzodioxane are extensively utilized in diverse medicinal substances and bioactive natural compounds, exhibiting significant biological activities. Notable examples of such therapeutic agents include prosympal, dibozane, piperoxan, and doxazosin. In this work, using 1,4-benzodioxane-2-carboxylic acid methyl ester as the substrate, after screening 38 CALB covariant residues, we found that mutants A225F and A225F/T103A can catalyze the kinetic resolution of the substrate. The effect of temperature, cosolvent, and cosolvent concentration on kinetic resolution was investigated, revealing that the best results were achieved at 30 °C with 20% n-butanol as a cosolvent, resulting in an optimal resolution (e.e._s 97%, E = 278) at 50 mM substrate concentration. Structure analysis showed that mutation sites 225 and 103 are not among the sites that interact directly with the substrate, which means that covariant amino acids that interact remotely with the substrate also regulate enzyme catalysis. This research may provide us with a new strategy for enzyme evolution.