Fungal unspecific peroxygenases (UPOs) are efficient biocatalysts that insert oxygen atoms into nonactivated C–H bonds with high selectivity. Many oxyfunctionalization reactions catalyzed by UPOs are favored in organic solvents, a milieu in which their enzymatic activity is drastically reduced. Using as departure point the UPO secretion mutant from Agrocybe aegerita (PaDa-I variant), in the current study we have improved its activity in organic solvents by directed evolution. Mutant libraries constructed by random mutagenesis and in vivo DNA shuffling were screened in the presence of increasing concentrations of organic solvents that differed both in regard to their chemical nature and polarity. In addition, a palette of neutral mutations generated by genetic drift that improved activity in organic solvents was evaluated by site directed recombination in vivo. The final UPO variant of this evolutionary campaign carried nine mutations that enhanced its activity in the presence of 30% acetonitrile (vol/vol) up to 23-fold over PaDa-I parental type, and it was also active and stable in aqueous acetone, methanol and dimethyl sulfoxide mixtures. These mutations, which are located at the surface of the protein and in the heme channel, seemingly helped to protect UPO from harmful effects of cosolvents by modifying interactions with surrounding residues and influencing critical loops.

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Propranolol is a widely used beta-blocker that is metabolized by human liver P450 monooxygenases into equipotent hydroxylated human drug metabolites (HDMs). It is paramount for the pharmaceutical industry to evaluate the toxicity and activity of these metabolites, but unfortunately, their synthesis has hitherto involved the use of severe conditions, with poor reaction yields and unwanted byproducts. Unspecific peroxygenases (UPOs) catalyze the selective oxyfunctionalization of C-H bonds, and they are of particular interest in synthetic organic chemistry. Here, we describe the engineering of UPO from Agrocybe aegerita for the efficient synthesis of 5′-hydroxypropranolol (5′-OHP). We employed a structure-guided evolution approach combined with computational analysis, with the aim of avoiding unwanted phenoxyl radical coupling without having to dope the reaction with radical scavengers. The evolved biocatalyst showed a catalytic efficiency enhanced by 2 orders of magnitude and 99% regioselectivity for the synthesis of 5′-OHP. When the UPO mutant was combined with an H₂O₂ in situ generation system using methanol as sacrificial electron donor, total turnover numbers of up to 264 000 were achieved, offering a cost-effective and readily scalable method to rapidly prepare 5′-OHP.

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Fungi produce heme-containing peroxidases and peroxygenases, flavin-containing oxidases and dehydrogenases, and different copper-containing oxidoreductases involved in the biodegradation of lignin and other recalcitrant compounds. Heme peroxidases comprise the classical ligninolytic peroxidases and the new dye-decolorizing peroxidases, while heme peroxygenases belong to a still largely unexplored superfamily of heme-thiolate proteins. Nevertheless, basidiomycete unspecific peroxygenases have the highest biotechnological interest due to their ability to catalyze a variety of regio- and stereo-selective monooxygenation reactions with H₂O₂ as the source of oxygen and final electron acceptor. Flavo-oxidases are involved in both lignin and cellulose decay generating H₂O₂ that activates peroxidases and generates hydroxyl radical. The group of copper oxidoreductases also includes other H₂O₂ generating enzymes - copper-radical oxidases - together with classical laccases that are the oxidoreductases with the largest number of reported applications to date. However, the recently described lytic polysaccharide monooxygenases have attracted the highest attention among copper oxidoreductases, since they are capable of oxidatively breaking down crystalline cellulose, the disintegration of which is still a major bottleneck in lignocellulose biorefineries, along with lignin degradation. Interestingly, some flavin-containing dehydrogenases also play a key role in cellulose breakdown by directly/indirectly “fueling” electrons for polysaccharide monooxygenase activation. Many of the above oxidoreductases have been engineered, combining rational and computational design with directed evolution, to attain the selectivity, catalytic efficiency and stability properties required for their industrial utilization. Indeed, using ad hoc software and current computational capabilities, it is now possible to predict substrate access to the active site in biophysical simulations, and electron transfer efficiency in biochemical simulations, reducing in orders of magnitude the time of experimental work in oxidoreductase screening and engineering. What has been set out above is illustrated by a series of remarkable oxyfunctionalization and oxidation reactions developed in the frame of an intersectorial and multidisciplinary European RTD project. The optimized reactions include enzymatic synthesis of 1-naphthol, 25-hydroxyvitamin D₃, drug metabolites, furandicarboxylic acid, indigo and other dyes, and conductive polyaniline, terminal oxygenation of alkanes, biomass delignification and lignin oxidation, among others. These successful case stories demonstrate the unexploited potential of oxidoreductases in medium and large-scale biotransformations.

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Peroxygenases catalyze a broad range of (stereo)selective oxyfunctionalization reactions. However, to access their full catalytic potential, peroxygenases need a balanced provision of hydrogen peroxide to achieve high catalytic activity while minimizing oxidative inactivation. Herein, we report an enzymatic cascade process that employs methanol as a sacrificial electron donor for the reductive activation of molecular oxygen. Full oxidation of methanol is achieved, generating three equivalents of hydrogen peroxide that can be used completely for the stereoselective hydroxylation of ethylbenzene as a model reaction. Overall we propose and demonstrate an atom‐efficient and easily applicable alternative to established hydrogen peroxide generation methods, which enables the efficient use of peroxygenases for oxyfunctionalization reactions. @en