Since the past decades, the plant stilbenoid resveratrol has gained significant attention of the general public as well as the research community due to its versatile medicinal properties. Apart from resveratrol, there is also an increasing interest in other plant stilbenoids because of their different potential biological activities. In order to meet the increasing demand for stilbenoids, alternative and sustainable approaches for their production are needed. We identified the cytochrome P450 monooxygenase 154E1 from Thermobifida fusca YX (CYP154E1) which enables the synthesis of (E)‐4,4′‐dihydroxystilbene via direct double hydroxylation of (E)‐stilbene. The construction of a triple mutant led to a more than six‐fold increased catalytic efficiency compared to the wild type enzyme. CYP154E1 and variants thereof accepted not only (E)‐stilbene but also possessed remarkable activity towards ortho‐ and meta‐substituted hydroxystilbenes leading to resveratrol, (E)‐2,4′‐dihydroxystilbene, (E)‐2,4′,5‐trihydroxystilbene and (E)‐3,4′‐dihydroxystilbene. The combination of protein engineering and the use of methyl‐β‐cyclodextrin as substrate solubilizing agent resulted in product titers of up to 4.2 g L−1 and enzyme total turnover numbers (TTN) of up to 20,000.magnified image

Most bacterial cytochrome P450 monooxygenases (P450s or CYPs) require two redox partner proteins for activity. To reduce complexity of the redox chain, the Bacillus subtilis flavodoxin YkuN (Y) was fused to the Escherichia coli flavodoxin reductase Fpr (R), and activity was tuned by placing flexible (GGGGS)n or rigid ([E/L]PPPP)n linkers (n = 1–5) in between. P-linker constructs typically outperformed their G-linker counterparts, with superior performance of YR-P5, which carries linker ([E/L]PPPP)5. Molecular dynamics simulations demonstrated that ([E/L]PPPP)n linkers are intrinsically rigid, whereas (GGGGS)n linkers are highly flexible and biochemical experiments suggest a higher degree of separation between the fusion partners in case of long rigid P-linkers. The catalytic properties of the individual redox partners were best preserved in the YR-P5 construct. In comparison to the separate redox partners, YR-P5 exhibited attenuated rates of NADPH oxidation and heme iron (III) reduction, while coupling efficiency was improved (28% vs. 49% coupling with B. subtilis CYP109B1, and 44% vs. 50% with Thermobifida fusca CYP154E1). In addition, YR-P5 supported monooxygenase activity of the CYP106A2 from Bacillus megaterium and bovine CYP21A2. The versatile YR-P5 may serve as a non-physiological electron transfer system for exploitation of the catalytic potential of other P450s.

Recently, the anesthetic (S)-ketamine has been approved as a rapid-acting and long-lasting antidepressant. Its metabolite, (2S,6S)-hydroxynorketamine, has been found to have a similar antidepressant effect but with less undesirable side effects, which make this compound an interesting target for synthesis. Using the first-sphere mutagenesis of the cytochrome P450 154E1 from Thermobifida fusca YX, we constructed a triple mutant that enables the effective production of (2S,6S)-hydroxynorketamine from (S)-ketamine. This engineered P450 monooxygenase catalyzes the consecutive oxidative N-demethylation and highly regio- and stereoselective C6-hydroxylation reactions leading directly to the desired product with 85% product selectivity. The integration of this selective monooxygenase into an Escherichia coli whole-cell biocatalyst allowed the production of (2S,6S)-hydroxynorketamine at a semipreparative scale. The metabolite was purified and its structure was confirmed by NMR spectroscopy.

Previous studies on cytochrome P450 monooxygenases (CYP) from family 154 reported their substrate promiscuity and high activity. Hence, herein, the uncharacterized family member CYP154F1 is described. Screening of more than 100 organic compounds revealed that CYP154F1 preferably accepts small linear molecules with a carbon chain length of 8-10 atoms. In contrast to thoroughly characterized CYP154E1, CYP154F1 has a much narrower substrate spectrum and lower activity. A structural alignment of homology models of CYP154F1 and CYP154E1 revealed few differences in the active sites of both family members. By gradual mutagenesis of the CYP154F1 active site towards those of CYP154E1, a key residue accounting for the different activities of both enzymes was identified at position 234. Substitution of T234 for large hydrophobic amino acids led to up to tenfold higher conversion rates of small substrates, such as geraniol. Replacement of T234 by small hydrophobic amino acids, valine or alanine, resulted in mutants with extended substrate spectra. These mutants are able to convert some of the larger substrates of CYP154E1, such as (E)-stilbene and (+)-nootkatone.

A new catalyst system for the enantioselective bromineinduced semipinacol rearrangement of cyclic allylic alcohols is described. Using the commercially available (DHQD) 2 Pyr catalyst the products containing an all-carbon quaternary chiral centre can be obtained in good yield and high enantioselectivity.