Understanding the molecular basis for controlled H 2 O 2 activation is of fundamental importance for peroxide-driven catalysis by metalloenzymes. In addition to O 2 activation in the presence of stoichiometric reductants, an increasing number of metalloenzymes are found to activate the H 2 O 2 cosubstrate for oxidative transformations in the absence of stoichiometric reductants. Herein, we characterized the X-ray structure of the P450BM3 F87A mutant in complex with the dual-functional small molecule (DFSM) N-(ω-imidazolyl)-hexanoyl-Lphenylalanine (Im-C6-Phe), which enables an efficient peroxygenase activity for P450BM3. Our computational investigations show that the H 2 O 2 activations by P450BM3 are highly dependent on the substrate and the DFSM. In the absence of both the substrate and the DFSM, H 2 O 2 activation via the O−O homolysis mechanism is significantly inhibited by the H-bonding network from the proximal H of H 2 O 2 . However, the presence of the substrate expels the solvation waters and disrupts the H-bonding network from the proximal H of H 2 O 2 , thus remarkably favoring homolytic O−O cleavage toward Cpd I formation. However, the presence of the DFSM forms a proton channel between the imidazolyl group of the DFSM and the proximal H of H 2 O 2 , thus enabling a heterolytic O−O cleavage and Cpd I formation that is greatly favored over the homolysis mechanism. Meanwhile, our simulations demonstrate that the H-bonding network from the distal H of H 2 O 2 is the key to control of the H 2 O 2 activation in the homolytic route. These findings are in line with all available experimental data and highlight the key roles of H-bonding networks in dictating H 2 O 2 activations.

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Given prominent physicochemical similarities between H2O2 and water, we report a new strategy for promoting the peroxygenase activity of P450 enzymes by engineering their water tunnels to facilitate H2O2 access to the heme center buried therein. Specifically, the H2O2-driven activities of two native NADH-dependent P450 enzymes (CYP199A4 and CYP153A M.aq ) increase significantly (by >183-fold and >15-fold, respectively). Additionally, the amount of H2O2 required for an artificial P450 peroxygenase facilitated by a dual-functional small molecule to obtain the desired product is reduced by 95%–97.5% (with ∼95% coupling efficiency). Structural analysis suggests that mutating the residue at the bottleneck of the water tunnel may open a second pathway for H2O2 to flow to the heme center (in addition to the natural substrate tunnel). This study highlights a promising, generalizable strategy whereby P450 monooxygenases can be modified to adopt peroxygenase activity through H2O2 tunnel engineering, thus broadening the application scope of P450s in synthetic chemistry and synthetic biology.

It is a great challenge to optionally access diverse hydroxylation products from a given substrate bearing multiple reaction sites of sp 3 and sp 2 CÀ 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.

o-Succinylbenzoyl-CoA (OSB-CoA) synthetase, or MenE, catalyzes an essential step in vitamin K biosynthesis and is a valuable drug target. Like many other adenylating enzymes, it changes its structure to accommodate substrate binding, catalysis, and product release along the path of a domain alternation catalytic mechanism. We have determined the crystal structure of its complex with the adenylation product, o-succinylbenzoyl-adenosine monophosphate (OSB-AMP), and captured a new postadenylation state. This structure presents unique features such as a strained conformation for the bound adenylate intermediate to indicate that it represents the enzyme state after completion of the adenylation reaction but before release of the C domain in its transition to the thioesterification conformation. By comparison to the ATP-bound preadenylation conformation, structural changes are identified in both the reactants and the active site to allow inference about how these changes accommodate and facilitate the adenylation reaction and to directly support an in-line backside attack nucleophilic substitution mechanism for the first half-reaction. Mutational analysis suggests that the conserved His196 plays an important role in desolvation of the active site rather than stabilizing the transition state of the adenylation reaction. In addition, comparison of the new structure with a previously determined OSB-AMP-bound structure of the same enzyme allows us to propose a release mechanism of the C domain in its alteration to form the thioesterification conformation. These findings allow us to better understand the domain alternation catalytic mechanism of MenE as well as many other adenylating enzymes.

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.

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.

Herein, we describe an environmentally benign enzymatic approach for the preparation of indigoid from indole derivatives. A series of beneficial P450BM3 mutants were obtained using a stepwise approach involving site‐directed, random, and combinatory hot‐site mutations. Using H2O2 as the terminal oxidant and N‐(ω‐imidazolyl)‐hexanoyl‐L‐phenylalanine as a co‐catalyst, the quadruple‐mutant F87G/T268V/F77I/E140D efficiently catalyzed the 3‐hydroxylation of indole and subsequent autooxidation to indigo with higher efficiency than the flavin‐containing monooxygenase, PTDH‐mFMO, which was the best oxidizing enzyme for indigo synthesis reported to date. Following this procedure, 12 indigoid compounds were prepared using indole derivatives with various substituents as starting materials with moderate to high isolated yields (31.3–79.5 %). The catalytic efficiencies (kcat/Km) of the beneficial mutants for typical indole substrates ranged from 182–2849 mM−1 ⋅ min−1, almost 2‐ to 712‐fold higher than those of the reported P450 enzymes. This study provides a new enzymatic approach for the biosynthesis of indigoid dyes from indole derivatives.