Dual-Functional Small Molecules for Generating an Efficient Cytochrome P450BM3 Peroxygenase

Al2O3-Stabilized Pt Nanozymes: Peroxidase Mimetics and Application in Glucose Detection

As promising alternatives for natural enzymes, much attention has been paid to nanozymes. And our recent study showed that the medium acid sites on the support are the active sites for the adsorption and oxidation of the substrate. Thus, in this work, due to the abundance of medium acid sites, Al2O3 was chosen as the support to prepare Pt/Al2O3 nanozymes. Through the Pt/Al2O3 samples, we further proved that the distribution of the Pt clusters and the amount of the medium acid sites can significantly influence the peroxidase-like activity. Then the Pt/Al2O3 sample was used for the detection of glucose. And as low as 0.96 μM glucose could be detected with a linear range from 5-60 μM via our method. This work showed the great potential applications of the easily prepared Pt/Al2O3 samples in varieties of simple, robust, and easy-to-make analytical approaches in the future.

Recent Progress on Peroxidase Modification and Application

Peroxdiase is one of the member of oxireductase super family, which has a broad substrate range and a variety of reaction types, including hydroxylation, epoxidation or halogenation of unactivated C-H bonds, and aromatic group or biophenol compounds. Here, we summarized the recently discovered enzymes with peroxidation activity, and focused on the special structures, sites, and corresponding strategies that can change the peroxidase catalytic activity, stability, and substrate range. The comparison of the structural differences between these natural enzymes and the mimic enzymes of binding nanomaterials and polymer materials is helpful to expand the application of peroxidase in industry. In addition, we also reviewed the catalytic application of peroxidase in the synthesis of important organic molecules and the degradation of pollutants.

Engineering Cytochrome P450BM3 Enzymes for Direct Nitration of Unsaturated Hydrocarbons

Applications of the peroxidase activity of cytochrome P450 enzymes in synthetic chemistry remain largely unexplored. We present herein a protein engineering strategy to increase cytochrome P450BM3 peroxidase activity for the direct nitration of aromatic compounds and terminal aryl-substituted olefins in the presence of a dual-functional small molecule (DFSM). Site-directed mutations of key active-site residues allowed the efficient regulation of steric effects to limit substrate access and, thus, a significant decrease in monooxygenation activity and increase in peroxidase activity. Nitration of several phenol and aniline compounds also yielded ortho- and para-nitration products with moderate-to-high total turnover numbers. Besides direct aromatic nitration by P450 variants using nitrite as a nitrating agent, we also demonstrated the use of the DFSM-facilitated P450 peroxidase system for the nitration of the vinyl group of styrene and its derivatives.

Efficient Production of Epoxy-Norbornane from Norbornene by an Engineered P450 Peroxygenase

Epoxy-norbornane (EPO-NBE) is a crucial building block for the synthesis of various biologically active heterocyclic systems. To develop an efficient protocol for producing EPO-NBE using norbornene (NBE) as a substrate, cytochrome P450 enzyme from Pseudomonas putida (CYP238A1) was examined and its crystal structure (PDB code: 7X53) was resolved. Molecular mechanism analysis showed a high energy barrier related to iron-alkoxy radical complex formation. Therefore, a protein engineering strategy was developed and an optimal CYP238A1^NPV variant containing a local hydrophobic "fence" at the active site was obtained, which increased the H₂ O₂ -dependent epoxidation activity by 7.5-fold compared with that of CYP238A1^WT . Among the "fence", Glu255 participates in an efficient proton transfer system. Whole-cell transformation using CYP238A1^NPV achieved an EPO-NBE yield of 77.6 g ⋅ L^-1 in a 30-L reactor with 66.3 % conversion. These results demonstrate the potential of this system for industrial production of EPO-NBE and provides a new biocatalytic platform for epoxidation chemistry.

Regiodivergent and Enantioselective Hydroxylation of C-H bonds by Synergistic Use of Protein Engineering and Exogenous Dual-Functional Small Molecules

It is a great challenge to optionally access diverse hydroxylation products from a given substrate bearing multiple reaction sites of sp³ and sp² C-H bonds. Herein, we report the highly selective divergent hydroxylation of alkylbenzenes by an engineered P450 peroxygenase driven by a dual-functional small molecule (DFSM). Using combinations of various P450BM3 variants with DFSMs enabled access to more than half of all possible hydroxylated products from each substrate with excellent regioselectivity (up to >99 %), enantioselectivity (up to >99 % ee), and high total turnover numbers (up to 80963). Crystal structure analysis, molecular dynamic simulations, and theoretical calculations revealed that synergistic effects between exogenous DFSMs and the protein environment controlled regio- and enantioselectivity. This work has implications for exogenous-molecule-modulated enzymatic regiodivergent and enantioselective hydroxylation with potential applications in synthetic chemistry.

Investigating the Active Oxidants Involved in Cytochrome P450 Catalyzed Sulfoxidation Reactions

Cytochrome P450 (CYP) heme-thiolate monooxygenases catalyze the hydroxylation of the C-H bonds of organic molecules. This reaction is initiated by a ferryl-oxo heme radical cation (Cpd I). These enzymes can also catalyze sulfoxidation reactions and the ferric-hydroperoxy complex (Cpd 0) and the Fe(III)-H₂ O₂ complex have been proposed as alternative oxidants for this transformation. To investigate this, the oxidation of 4-alkylthiobenzoic acids and 4-methoxybenzoic acid by the CYP199A4 enzyme from Rhodopseudomonas palustris HaA2 was compared using both monooxygenase and peroxygenase pathways. By examining mutants at the mechanistically important, conserved acid alcohol-pair (D251N, T252A and T252E) the relative amounts of the reactive intermediates that would form in these reactions were disturbed. Substrate binding and X-ray crystal structures helped to understand changes in the activity and enabled an attempt to evaluate whether multiple oxidants can participate in these reactions. In peroxygenase reactions the T252E mutant had higher activity towards sulfoxidation than O-demethylation but in the monooxygenase reactions with the WT enzyme the activity of both reactions was similar. The peroxygenase activity of the T252A mutant was greater for sulfoxidation reactions than the WT enzyme, which is the reverse of the activity changes observed for O-demethylation. The monooxygenase activity and coupling efficiency of sulfoxidation and oxidative demethylation were reduced by similar degrees with the T252A mutant. These observations infer that while Cpd I is required for O-dealkylation, another oxidant may contribute to sulfoxidation. Based on the activity of the CYP199A4 mutants it is proposed that this is the Fe(III)-H₂ O₂ complex which would be more abundant in the peroxide-driven reactions.

Co-Crystal Structure-Guided Optimization of Dual-Functional Small Molecules for Improving the Peroxygenase Activity of Cytochrome P450BM3

We recently developed an artificial P450–H₂O₂ system assisted by dual-functional small molecules (DFSMs) to modify the P450BM3 monooxygenase into its peroxygenase mode, which could be widely used for the oxidation of non-native substrates. Aiming to further improve the DFSM-facilitated P450–H₂O₂ system, a series of novel DFSMs having various unnatural amino acid groups was designed and synthesized, based on the co-crystal structure of P450BM3 and a typical DFSM, N-(ω-imidazolyl)-hexanoyl-L-phenylalanine, in this study. The size and hydrophobicity of the amino acid residue in the DFSM drastically affected the catalytic activity (up to 5-fold), stereoselectivity, and regioselectivity of the epoxidation and hydroxylation reactions. Docking simulations illustrated that the differential catalytic ability among the DFSMs is closely related to the binding affinity and the distance between the catalytic group and heme iron. This study not only enriches the DFSM toolbox to provide more options for utilizing the peroxide-shunt pathway of cytochrome P450BM3, but also sheds light on the great potential of the DFSM-driven P450 peroxygenase system in catalytic applications based on DFSM tunability.

Valorization of Small Alkanes by Biocatalytic Oxyfunctionalization

The oxidation of alkanes into valuable chemical products is a vital reaction in organic synthesis. This reaction, however, is challenging, owing to the inertness of C-H bonds. Transition metal catalysts for C-H functionalization are frequently explored. Despite chemical alternatives, nature has also evolved powerful oxidative enzymes (e. g., methane monooxygenases, cytochrome P450 oxygenases, peroxygenases) that are capable of transforming C-H bonds under very mild conditions, with only the use of molecular oxygen or hydrogen peroxide as electron acceptors. Although progress in alkane oxidation has been reviewed extensively, little attention has been paid to small alkane oxidation. The latter holds great potential for the manufacture of chemicals. This Minireview provides a concise overview of the most relevant enzyme classes capable of small alkanes (C_<6 ) oxyfunctionalization, describes the essentials of the catalytic mechanisms, and critically outlines the current state-of-the-art in preparative applications.

Harnessing P450 Enzyme for Biotechnology and Synthetic Biology

Cytochrome P450 enzymes (P450s, CYPs) catalyze the oxidative transformation of a wide range of organic substrates. Their functions are crucial to xenobiotic metabolism and steroid transformation in humans and other organisms. The enzymes are promising for synthetic biology applications but limited by several drawbacks including low turnover rates, poor stability, the dependance of expensive cofactors and redox partners, and the narrow substrate scope. To conquer these obstacles, emerging strategies including substrate engineering, usage of decoy and decoy-based small molecules auxiliaries, designing of artificial enzyme cascades and the incorporation of materials have been explored based on the unique properties of P450s. These strategies can be applied to a wide range of P450s and can be combined with protein engineering to improve the enzymatic activities. This minireview will focus on some recent developments of these strategies which have been used to leverage P450 catalysis. Remaining challenges and future opportunities will also be discussed.

Solar-Powered Whole-Cell P450 Catalytic Platform for C-Hydroxylation Reactions

Photobiocatalysis is a green platform for driving redox enzymatic reactions using solar energy, not needing high-cost cofactors and redox partners. Here, a visible light-driven whole-cell platform for human cytochrome P450 (CYP) photobiocatalysis was developed using natural flavins as a photosensitizer. Photoexcited flavins mediate NADPH/reductase-free, light-driven biocatalysis by human CYP2E1 both in vitro and in the whole-cell systems. In vitro tests demonstrated that the photobiocatalytic activity of CYP2E1 is dependent on the substrate type, the presence of catalase, and the acid type used as a sacificial electron donor. A protective effect of catalase was found against the inactivation of CYP2E1 heme by H₂ O₂ and the direct transfer of photo-induced electrons to the heme iron not by peroxide shunt. Furthermore, the P450 photobiocatalysis in whole cells containing human CYPs 1A1, 1A2, 1B1, and 3A4 demonstrated the general applicability of the solar-powered, flavin-mediated P450 photobiocatalytic system.

Using Small Molecules to Enhance P450 OleT Enzyme Activity in Situ

Cytochrome P450 OleT is a fatty acid decarboxylase that catalyzes the production of olefins with biofuel and synthetic applications. However, the relatively sluggish catalytic efficiency of the enzyme limits its applications. Here, we report the application of a novel class of benzene containing small molecules to improve the OleT activity. The UV-Vis spectroscopy study and molecular docking results confirmed the high proximity of the small molecules to the heme group of OleT. Up to 6-fold increase of product yield has been achieved in the small molecule-modulated enzymatic reactions. Our work thus sheds the light to the application of small molecules to increase the OleT catalytic efficiency, which could be potentially used for future olefin productions.

Enhanced Activity and Substrate Specificity by Site-Directed Mutagenesis for the P450 119 Peroxygenase Catalyzed Sulfoxidation of Thioanisole

P450 119 peroxygenase was found to catalyze the sulfoxidation of thioanisole and the sulfonation of sulfoxide in the presence of tert-butyl hydroperoxide (TBHP) for the first time with turnover rates of 1549 min^-1 and 196 min^-1 respectively. Several mutants were designed to improve the peroxygenation activity and thioanisole specificity by site-directed mutagenesis. The F153G/T213G mutant gave an increase of sulfoxide yield and a decrease of sulfone yield. Moreover the S148P/I161T/K199E/T214V mutant and the K199E mutant with acidic Glu residue contributed to improving the product ratio of sulfoxide to sulfone. Addition of short-alkyl-chain organic acids to the P450 119 peroxygenase-catalyzed sulfur oxidation of thioanisole was investigated. Octanoic acid was found to induce a preferred sulfoxidation of thioanisole catalyzed by the F153G/T213G mutant to give approximately 2.4-fold increase in turnover rate with a k _cat value of 3687 min^-1 relative to that of the wild-type, and by the F153G mutant to give the R-sulfoxide up to 30 % ee. The experimental control and the proposed mechanism for the P450 119 peroxygenase-catalyzed sulfoxidation of thioanisole in the presence of octanoic acid suggested that octanoic acid could partially occupy the substrate pocket; meanwhile the F153G mutation could enhance the substrate specificity, which could lead to efficiently regulate the spatial orientation of thioanisole and facilitate the formation of Compound I. This is the most effective catalytic system for the P450 119 peroxygenase-catalyzed sulfoxidation of thioanisole.

Strategies for Substrate-Regulated P450 Catalysis: From Substrate Engineering to Co-catalysis

Cytochrome P450 enzymes (P450s) catalyze the monooxygenation of various organic substrates. These enzymes are fascinating and promising biocatalysts for synthetic applications. Despite the impressive abilities of P450s in the oxidation of C-H bonds, their practical applications are restricted by intrinsic drawbacks, such as poor stability, low turnover rates, the need for expensive cofactors (e.g., NAD(P)H), and the narrow scope of useful non-native substrates. These issues may be overcome through the general strategy of protein engineering, which focuses on the improvement of the catalysts themselves. Alternatively, several emerging strategies have been developed that regulate the P450 catalytic process from the viewpoint of the substrate. These strategies include substrate engineering, decoy molecule, and dual-functional small-molecule co-catalysis. Substrate engineering focuses on improving the substrate acceptance and reaction selectivity by means of an anchoring group. The latter two strategies utilize co-substrate-like small molecules that either are proposed to reform the active site, thereby switching the substrate specificity, or directly participate in the catalytic process, thereby creating new catalytic peroxygenation capabilities towards non-native substrates. For at least 10 years, these approaches have played unique roles in solving the problems highlighted above, either alone or in conjunction with protein engineering. Herein, we review three strategies for substrate regulation in the P450-catalyzed oxidation of non-native substrates. Furthermore, we address remaining challenges and potential solutions associated with these approaches.

Effects of Alternative Redox Partners and Oxidizing Agents on CYP154C8 Catalytic Activity and Product Distribution

CYP154C8 catalyzes the hydroxylation of diverse steroids, as has previously been demonstrated, by using an NADH-dependent system including putidaredoxin and putidaredoxin reductase as redox partner proteins carrying electrons from NADH. In other reactions, CYP154C8 reconstituted with spinach ferredoxin and NADPH-dependent ferredoxin reductase displayed catalytic activity different from that of the NADH-dependent system. The NADPH-dependent system showed multistep oxidation of progesterone and other substrates including androstenedione, testosterone, and nandrolone. (Diacetoxyiodo)benzene was employed to generate compound I (FeO³⁺ ), actively supporting the redox reactions catalyzed by CYP154C8. In addition to 16α-hydroxylation, progesterone and 11-oxoprogesterone also underwent hydroxylation at the 6β-position in reactions supported by (diacetoxyiodo)benzene. CYP154C8 was active in the presence of high concentrations (>10 mm) of H₂ O₂ , with optimum conversion surprisingly being achieved at ≈75 mm H₂ O₂ . More importantly, H₂ O₂ tolerance by CYP154C8 was evident in the very low heme oxidation rate constant (K) even at high concentrations of H₂ O₂ . Our results demonstrate that alternative redox partners and oxidizing agents influence the catalytic efficiency and product distribution of a cytochrome P450 enzyme. More importantly, these choices affected the type and selectivity of reaction catalyzed by the P450 enzyme.

Coexpression of 5-Aminolevulinic Acid Synthase Gene Facilitates Heterologous Production of Thermostable Cytochrome P450, CYP119, in Holo Form in Escherichia coli

Cytochrome P450 enzymes are heme-containing monooxygenases that exhibit potential as biocatalysts for practical applications. The Escherichia coli expression system is frequently used for biocatalyst production; however, heterologous production of hemeproteins in their holo form is difficult due to insufficient heme synthesis by the host. In this study, 5-aminolevulinic acid synthase (ALAS) from Rhodobacter capsulatus is used to accelerate intracellular heme biosynthesis in E. coli; this demonstrates that coexpression of the ALAS gene (ALAS) improves the heterologous production of cytochrome P450, CYP119, from Sulfolobus acidocaldarius. Coexpression of ALAS increased the amount of heterologous CYP119 isolated and the ratio of its holo form. The ratio of holo-CYP119 resulting from the coexpression of ALAS in E. coli was 99 %, whereas that from cells expressing CYP119 exclusively was 66 %. Coexpression of ALAS is a promising alternative for the efficient heterologous production of hemeproteins by using E. coli.