Evaluation of P450 monooxygenase activity in lyophilized recombinant E. coli cells compared to resting cells

A tailored cytochrome P450 monooxygenase from Gordonia rubripertincta CWB2 for selective aliphatic monooxygenation

Cytochrome P450 monooxygenases are recognized as versatile biocatalysts due to their broad reaction capabilities. One important reaction is the hydroxylation of non-activated C-H bonds. The subfamily CYP153A is known for terminal hydroxylation reactions, giving access to functionalized aliphatics. Whilst fatty derivatives may be converted by numerous enzyme classes, midchain aliphatics are seldomly accepted, a prime property of CYP153As. We report here on a new CYP153A member from the genome of the mesophilic actinobacterium Gordonia rubripertincta CWB2 as an efficient biocatalyst. The gene was overexpressed in Escherichia coli and fused with a surrogate electron transport system from Acinetobacter sp. OC4. This chimeric self-sufficient whole-cell system could perform hydroxylation and epoxidation reactions: conversions of C6-C14 alkanes, alkenes, alcohols and of cyclic compounds were observed, yielding production rates of, e.g., 2.69 mM h-1 for 1-hexanol and 4.97 mM h-1 for 1,2-epoxyhexane. Optimizing the linker compositions between the protein units led to significantly altered activity. Balancing linker length and flexibility with glycine-rich and helix-forming linker units increased 1-hexanol production activity to 350 % compared to the initial linker setup with entirely helical linkers. The study shows that strategic coupling of efficient electron supply and a selective enzyme enables previously challenging monooxygenation reactions of midchain aliphatics.

Production of 17α-hydroxyprogesterone using an engineered biocatalyst with efficient electron transfer and improved 5-aminolevulinic acid synthesis coupled with a P450 hydroxylase

17α-Hydroxyprogesterone (17α-OH-PROG) is an important intermediate with a wide range of applications in the pharmaceutical industry. Strategies based on efficient electron transfer and cofactor regeneration were used for the production of 17α-OH-PROG. Here, CYP260A1, Fpr and Adx were expressed using a double plasmid system, resulting in higher biotransformation efficiency. Further optimization of reaction conditions and addition of polymyxin B increased the production of 17α-OH-PROG from 12.52 mg/L to 102.37 mg/L after 12 h of biotransformation. To avoid the addition of external 5-aminolevulinic acid (ALA) as a heme precursor for the P450 enzyme, a modified C5 pathway was introduced into the engineered strain, further reducing the overall process cost. The resulting whole-cell biocatalyst achieved the highest biotransformation yield of 17α-OH-PROG reported to date, offering a promising strategy for commercial application of P450 enzymes in industrial production of hydroxylated intermediates.

The thin line between monooxygenases and peroxygenases. P450s, UPOs, MMOs, and LPMOs: A brick to bridge fields of expertise

Many scientific fields, although driven by similar purposes and dealing with similar technologies, often appear so isolated and far from each other that even the vocabularies to describe the very same phenomenon might differ. Concerning the vast field of biocatalysis, a special role is played by those redox enzymes that employ oxygen-based chemistry to unlock transformations otherwise possible only with metal-based catalysts. As such, greener chemical synthesis methods and environmentally-driven biotechnological approaches were enabled over the last decades by the use of several enzymes and ultimately resulted in the first industrial applications. Among what can be called today the environmental biorefinery sector, biomass transformation, greenhouse gas reduction, bio-gas/fuels production, bioremediation, as well as bulk or fine chemicals and even pharmaceuticals manufacturing are all examples of fields in which successful prototypes have been demonstrated employing redox enzymes. In this review we decided to focus on the most prominent enzymes (MMOs, LPMO, P450 and UPO) capable of overcoming the ∼100 kcal mol-1 barrier of inactivated CH bonds for the oxyfunctionalization of organic compounds. Harnessing the enormous potential that lies within these enzymes is of extreme value to develop sustainable industrial schemes and it is still deeply coveted by many within the aforementioned fields of application. Hence, the ambitious scope of this account is to bridge the current cutting-edge knowledge gathered upon each enzyme. By creating a broad comparison, scientists belonging to the different fields may find inspiration and might overcome obstacles already solved by the others. This work is organised in three major parts: a first section will be serving as an introduction to each one of the enzymes regarding their structural and activity diversity, whereas a second one will be encompassing the mechanistic aspects of their catalysis. In this regard, the machineries that lead to analogous catalytic outcomes are depicted, highlighting the major differences and similarities. Finally, a third section will be focusing on the elements that allow the oxyfunctionalization chemistry to occur by delivering redox equivalents to the enzyme by the action of diverse redox partners. Redox partners are often overlooked in comparison to the catalytic counterparts, yet they represent fundamental elements to better understand and further develop practical applications based on mono- and peroxygenases.

Bacterial cytochrome P450 enzymes: Semi-rational design and screening of mutant libraries in recombinant Escherichia coli cells

Bacterial cytochromes P450 (P450s) have been recognized as attractive targets for biocatalysis and protein engineering. They are soluble cytosolic enzymes that demonstrate higher stability and activity than their membrane-associated eukaryotic counterparts. Many bacterial P450s possess broad substrate spectra and can be produced in well-known expression hosts like Escherichia coli at high levels, which enables quick and convenient mutant libraries construction. However, the majority of bacterial P450s interacts with two auxiliary redox partner proteins, which significantly increase screening efforts. We have established recombinant E. coli cells for screening of P450 variants that rely on two separate redox partners. In this chapter, a case study on construction of a selective P450 to synthesize a precursor of several chemotherapeutics, (-)-podophyllotoxin, is described. The procedure includes co-expression of P450 and redox partner genes in E. coli with subsequent whole-cell conversion of the substrate (-)-deoxypodophyllotoxin in 96-deep-well plates. By omitting the chromatographic separation while measuring mass-to-charge ratios specific for the substrate and product via MS in so-called multiple injections in a single experimental run (MISER) LC/MS, the analysis time could be drastically reduced to roughly 1 min per sample. Screening results were verified by using isolated P450 variants and purified redox partners.

Biocatalytic characterization of an alcohol dehydrogenase variant deduced from Lactobacillus kefir in asymmetric hydrogen transfer

Hydrogen transfer biocatalysts to prepare optically pure alcohols are in need, especially when it comes to sterically demanding ketones, whereof the bioreduced products are either essential precursors of pharmaceutically relevant compounds or constitute APIs themselves. In this study, we report on the biocatalytic potential of an anti-Prelog (R)-specific Lactobacillus kefir ADH variant (Lk-ADH-E145F-F147L-Y190C, named Lk-ADH Prince) employed as E. coli/ADH whole-cell biocatalyst and its characterization for stereoselective reduction of prochiral carbonyl substrates. Key enzymatic reaction parameters, including the reaction medium, evaluation of cofactor-dependency, organic co-solvent tolerance, and substrate loading, were determined employing the drug pentoxifylline as a model prochiral ketone. Furthermore, to tap the substrate scope of Lk-ADH Prince in hydrogen transfer reactions, a broad range of 34 carbonylic derivatives was screened. Our data demonstrate that E. coli/Lk-ADH Prince exhibits activity toward a variety of structurally different ketones, furnishing optically active alcohol products at the high conversion of 65-99.9% and in moderate-to-high isolated yields (38-91%) with excellent anti-Prelog (R)-stereoselectivity (up to >99% ee) at substrate concentrations up to 100 mM.

Unique alcohol dehydrogenases involved in algal sugar utilization by marine bacteria

Marine algae produce complex polysaccharides, which can be degraded by marine heterotrophic bacteria utilizing carbohydrate-active enzymes. The red algal polysaccharide porphyran contains the methoxy sugar 6-O-methyl-D-galactose (G6Me). In the degradation of porphyran, oxidative demethylation of this monosaccharide towards D-galactose and formaldehyde occurs, which is catalyzed by a cytochrome P450 monooxygenase and its redox partners. In direct proximity to the genes encoding for the key enzymes of this oxidative demethylation, genes encoding for zinc-dependent alcohol dehydrogenases (ADHs) were identified, which seem to be conserved in porphyran utilizing marine Flavobacteriia. Considering the fact that dehydrogenases could play an auxiliary role in carbohydrate degradation, we aimed to elucidate the physiological role of these marine ADHs. Although our results reveal that the ADHs are not involved in formaldehyde detoxification, a knockout of the ADH gene causes a dramatic growth defect of Zobellia galactanivorans with G6Me as a substrate. This indicates that the ADH is required for G6Me utilization. Complete biochemical characterizations of the ADHs from Formosa agariphila KMM 3901T (FoADH) and Z. galactanivorans DsijT (ZoADH) were performed, and the substrate screening revealed that these enzymes preferentially convert aromatic aldehydes. Additionally, we elucidated the crystal structures of FoADH and ZoADH in complex with NAD+ and showed that the strict substrate specificity of these new auxiliary enzymes is based on a narrow active site. KEY POINTS: • Knockout of the ADH-encoding gene revealed its role in 6-O-methyl-D-galactose utilization, suggesting a new auxiliary activity in marine carbohydrate degradation. • Complete enzyme characterization indicated no function in a subsequent reaction of the oxidative demethylation, such as formaldehyde detoxification. • These marine ADHs preferentially convert aromatic compounds, and their strict substrate specificity is based on a narrow active site.