Production of Propene from n-Butanol: A Three-Step Cascade Utilizing the Cytochrome P450 Fatty Acid Decarboxylase OleTJE

Microbial P450 repertoire (P450ome) and its application feasibility in pharmaceutical industry, chemical industry, and environmental protection

Cytochrome P450s (CYPs) are heme-thiolated enzymes that catalyze the oxidation of C-H bonds in a regio- and stereo-selective manner. CYPs are widely present in the biological world. With the completion of more biological genome sequencing, the number and types of P450 enzymes have increased rapidly. P450 in microorganisms is easy to clone and express, rich in catalytic types, and strong in substrate adaptability, which has good application potential. Although the number of P450 enzymes found in microorganisms is huge, the function of most of the microorganism P450s has not been studied, and it contains a large number of excellent biocatalysts to be developed. This review is based on the P450 groups in microorganisms. First, it reviews the distribution of P450 groups in different microbial species, and then studies the application of microbial P450 enzymes in the pharmaceutical industry, chemical industry and environmental pollutant treatment in recent years. And focused on the application fields of P450 enzymes of different families to guide the selection of suitable P450s from the huge P450 library. In view of the current shortcomings of microbial P450 in the application process, the final solution is the most likely to assist the application of P450 enzymes in large-scale, that is, whole cell transformation combined with engineering, fusion P450 combined with immobilization technology.

P450 fatty acid decarboxylase

P450 fatty acid decarboxylases are able to utilize hydrogen peroxide as the sole cofactor to decarboxylate free fatty acids to produce α-olefins with abundant applications as drop-in biofuels and important chemical precursors. In this chapter, we review diverse approaches for discovery, characterization, engineering, and applications of P450 fatty acid decarboxylases. Information gained from structural data has been advancing our understandings of the unique mechanisms underlying alkene production, and providing important insights for exploring new activities. To build an efficient olefin-producing system, various engineering strategies have been proposed and applied to this unusual P450 catalytic system. Furthermore, we highlight a select number of applied examples of P450 fatty acid decarboxylases in enzyme cascades and metabolic engineering.

CYP108N12 initiates p-cymene biodegradation in Rhodococcus globerulus

Rhodococcus globerulus (R. globerulus) isolated from soil beneath Eucalyptus sp. was found to live on the monoterpenes 1,8-cineole, p-cymene and (R)- and (S)-limonene as sole sources of carbon and energy. Previous metabolic studies revealed that R. globerulus is capable of living on 1,8-cineole, the main monoterpene component of eucalyptus essential oil through the activity of cytochrome P450_cin (CYP176A1) [1]. Genomic sequencing of R. globerulus revealed a novel putative cytochrome P450 (CYP108N12) that shares 48% sequence identity with CYP108A1 (P450_terp) from Pseudomonas sp., an α-terpineol hydroxylase. Given the sequence similarity between CYP108N12 and P450_terp, it was hypothesised that CYP108N12 may be responsible for initiating the biodegradation of a monoterpene structurally similar to α-terpineol such as (R)-limonene, (S)-limonene or p-cymene. Encoded within the operon containing CYP108N12 were two putative bacterial P450 redox partners and putative alcohol and aldehyde dehydrogenases, suggesting a complete catalytic system for activating these monoterpenes. Binding studies revealed that p-cymene and (R)- and (S)-limonene all bound tightly to CYP108N12 but α-terpineol did not. A catalytically active system was reconstituted using the non-native redox partner putidaredoxin and putidaredoxin reductase that act with CYP101A1 (P450_cam) from Pseudomonas. This reconstituted system catalysed the hydroxylation of p-cymene to 4-isopropylbenzyl alcohol, and (R)- and (S)-limonene to (R)- and (S)-perillyl alcohol, respectively. R. globerulus was successfully grown on solely p-cymene, (R)-limonene or (S)-limonene. CYP108N12 was detected when R. globerulus was grown on p-cymene, but not either limonene enantiomer. The native function of CYP108N12 is therefore proposed to be initiation of p-cymene biodegradation by methyl oxidation and is a potentially attractive biocatalyst capable of specific benzylic and allylic hydroxylation.

Product Distributions of Cytochrome P450 OleTJE with Phenyl-Substituted Fatty Acids: A Computational Study

There are two types of cytochrome P450 enzymes in nature, namely, the monooxygenases and the peroxygenases. Both enzyme classes participate in substrate biodegradation or biosynthesis reactions in nature, but the P450 monooxygenases use dioxygen, while the peroxygenases take H₂O₂ in their catalytic cycle instead. By contrast to the P450 monooxygenases, the P450 peroxygenases do not require an external redox partner to deliver electrons during the catalytic cycle, and also no external proton source is needed. Therefore, they are fully self-sufficient, which affords them opportunities in biotechnological applications. One specific P450 peroxygenase, namely, P450 OleT_JE, reacts with long-chain linear fatty acids through oxidative decarboxylation to form hydrocarbons and, as such, has been implicated as a suitable source for the biosynthesis of biofuels. Unfortunately, the reactions were shown to produce a considerable amount of side products originating from C^α and C^β hydroxylation and desaturation. These product distributions were found to be strongly dependent on whether the substrate had substituents on the C^α and/or C^β atoms. To understand the bifurcation pathways of substrate activation by P450 OleT_JE leading to decarboxylation, C^α hydroxylation, C^β hydroxylation and C^α–C^β desaturation, we performed a computational study using 3-phenylpropionate and 2-phenylbutyrate as substrates. We set up large cluster models containing the heme, the substrate and the key features of the substrate binding pocket and calculated (using density functional theory) the pathways leading to the four possible products. This work predicts that the two substrates will react with different reaction rates due to accessibility differences of the substrates to the active oxidant, and, as a consequence, these two substrates will also generate different products. This work explains how the substrate binding pocket of P450 OleT_JE guides a reaction to a chemoselectivity.

Computational Enzyme Engineering Pipelines for Optimized Production of Renewable Chemicals

To enable a sustainable supply of chemicals, novel biotechnological solutions are required that replace the reliance on fossil resources. One potential solution is to utilize tailored biosynthetic modules for the metabolic conversion of CO₂ or organic waste to chemicals and fuel by microorganisms. Currently, it is challenging to commercialize biotechnological processes for renewable chemical biomanufacturing because of a lack of highly active and specific biocatalysts. As experimental methods to engineer biocatalysts are time- and cost-intensive, it is important to establish efficient and reliable computational tools that can speed up the identification or optimization of selective, highly active, and stable enzyme variants for utilization in the biotechnological industry. Here, we review and suggest combinations of effective state-of-the-art software and online tools available for computational enzyme engineering pipelines to optimize metabolic pathways for the biosynthesis of renewable chemicals. Using examples relevant for biotechnology, we explain the underlying principles of enzyme engineering and design and illuminate future directions for automated optimization of biocatalysts for the assembly of synthetic metabolic pathways.

Tunnel engineering for modulating the substrate preference in cytochrome P450BsβHI

An active site is normally located inside enzymes, hence substrates should go through a tunnel to access the active site. Tunnel engineering is a powerful strategy for refining the catalytic properties of enzymes. Here, P450BsβHI (Q85H/V170I) derived from hydroxylase P450Bsβ from Bacillus subtilis was chosen as the study model, which is reported as a potential decarboxylase. However, this enzyme showed low decarboxylase activity towards long-chain fatty acids. Here, a tunnel engineering campaign was performed for modulating the substrate preference and improving the decarboxylation activity of P450BsβHI. The finally obtained BsβHI-F79A variant had a 15.2-fold improved conversion for palmitic acid; BsβHI-F173V variant had a 3.9-fold improved conversion for pentadecanoic acid. The study demonstrates how the substrate preference can be modulated by tunnel engineering strategy.

Production of Propene from n-Butanol: A Three-Step Cascade Utilizing the Cytochrome P450 Fatty Acid Decarboxylase OleTJE

Propene is one of the most important starting materials in the chemical industry. Herein, we report an enzymatic cascade reaction for the biocatalytic production of propene starting from n-butanol, thus offering a biobased production from glucose. In order to create an efficient system, we faced the issue of an optimal cofactor supply for the fatty acid decarboxylase OleTJE , which is said to be driven by either NAD(P)H or H2 O2 . In the first system, we used an alcohol and aldehyde dehydrogenase coupled to OleTJE by the electron-transfer complex putidaredoxin reductase/putidaredoxin, allowing regeneration of the NAD+ cofactor. With the second system, we intended full oxidation of n-butanol to butyric acid, generating one equivalent of H2 O2 that can be used for the oxidative decarboxylation. As the optimal substrate is a long-chain fatty acid, we also tried to create an improved variant for the decarboxylation of butyric acid by using rational protein design. Within a mutational study with 57 designed mutants, we generated the mutant OleTV292I , which showed a 2.4-fold improvement in propene production in our H2 O2 -driven cascade system and reached total turnover numbers >1000.