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A current challenge in synthetic organic chemistry is the development of methods that allow the regio- and stereoselective oxidative C–H activation of natural or synthetic compounds with formation of the corresponding alcohols. Cytochrome P450 enzymes enable C–H activation at non-activated positions, but the simultaneous control of both regio- and stereoselectivity is problematic. Here, we demonstrate that directed evolution using iterative saturation mutagenesis provides a means to solve synthetic problems of this kind. Using P450 BM3(F87A) as the starting enzyme and testosterone as the substrate, which results in a 1:1 mixture of the 2β- and 15β-alcohols, mutants were obtained that are 96–97% selective for either of the two regioisomers, each with complete diastereoselectivity. The mutants can be used for selective oxidative hydroxylation of other steroids without performing additional mutagenesis experiments. Molecular dynamics simulations and docking experiments shed light on the origin of regio- and stereoselectivity. Selective reaction of one C–H bond among many in complex organic molecules is a grand challenge for organic chemistry. Here, starting from an enzyme that oxidizes two positions in a steroid without bias, laboratory evolution is used to prepare mutants that can regio- and stereoselectively oxidize either position.

The three-dimensional structure of monomers and homodimers of CYP102A1/WT (wild-type) proteins and their A83F and A83I mutant forms was predicted using the AlphaFold2 (AF2) and AlphaFold Multimer (AFMultimer) programs, which were compared with the rate constants of hydroxylation reactions of these enzyme forms to determine the efficiency of intra- and interprotein electron transport in the CYP102A1 hydroxylase system. The electron transfer rate constants (ket), which determine the rate of indole hydroxylation by the CYP102A1 system, were calculated based on the distances (R) between donor-acceptor prosthetic groups (PG) FAD→FMN→HEME of these proteins using factor β, which describes an exponential decay from R the speed of electron transport (ET) according to the tunnelling mechanism. It was shown that the structure of monomers in the homodimer, calculated using the AlpfaFold Multimer program, is in good agreement with the experimental structures of globular domains (HEME-, FMN-, and FAD-domains) in CYP102A1/WT obtained by X-ray structural analysis, and the structure of isolated monomers predicted in AF2 does not coincide with the structure of monomers in the homodimer, although a high level of similarity in individual domains remains. The structures of monomers and homodimers of A83F and A83I mutants were also calculated, and their structures were compared with the wild-type protein. Significant differences in the structure of all isolated monomers with respect to the structures of monomers in homodimers were also found for them, and at the same time, insignificant differences were revealed for all homodimers. Comparative analysis for CYP102A1/WT between the calculated intra- and interprotein distances FAD→FMN→HEME and the rate constants of hydroxylation in these proteins showed that the distance between prosthetic groups both in the monomer and in the dimer allows the implementation of electron transfer between PGs, which is consistent with experimental literature data about kcat. For the mutant form of monomer A83I, an increase in the distance between PGs was obtained, which can restrict electron transportation compared to WT; however, for the dimer of this protein, a decrease in the distance between PGs was observed compared to the WT form, which can lead to an increase in the electron transfer rate constant and, accordingly, kcat. For the monomer and homodimer of the A83F mutant, the calculations showed an increase in the distance between the PGs compared to the WT form, which should have led to a decrease in the electron transfer rate, but at the same time, for the homodimer, the approach of the aromatic group F262 with heme can speed up transportation for this form and, accordingly, the rate of hydroxylation.

N -oxidation of N -heterocycles is essential in the synthesis of natural products but challenging due to low efficacy and poor regioselectivity. In this study, the N -oxidation selective potential of P450BM3 from Bacillus megaterium for N -heterocyclic compounds is investigated. Here, twelve amino acids located in the active center, including A74, L75, V78, A82, F87, I263, A264, A328, P329, A330, I401, and L437, are investigated by site-saturation mutation. As a result, F87, A264, L75, V78, A328, I401, and L437 are identified as hotspot residues. Subsequently, the combinatorial active-site saturation test/iterative saturation mutagenesis strategy is performed. Using quinoline as a model substrate, the mutant F87G/A264G/A328L exhibits N -oxidation selectivity of up to 99.0%, with a conversion rate of 99.3%. Molecular dynamics simulations uncover a “push-pull” molecular mechanism elucidating the pivotal role of steric factors in determining substrate recognition and N -oxidation selectivity. This study provides an efficient N -oxide synthesis method and insights into P450BM3’s molecular mechanisms. N -oxidation of N -heterocycles is essential in the synthesis of natural products and intermediates for pharmaceuticals and pesticides but challenging due to low efficacy and poor regioselectivity. Here, the authors employ structure-guided directed evolution of Bacillus megaterium P450BM3 to obtain variants with expanded N -oxidation selectivity for the synthesis of N -heterocyclic N -oxides.

Cytochromes P450 are a superfamily of heme-containing monooxygenases involved in a variety of oxidative metabolic reactions, primarily catalyzing the insertion of an oxygen atom into a C-H bond. CYP102 represents the first example of a bacterial P450 that can be classified as a type II (eukaryotic-like) P450 and functions as a catalytically self-sufficient enzyme. These unique features have made CYP102 an attractive system for studying P450 structure and function. However, an overall picture of the specific amino acid residues that are crucial to the functioning of CYP102 and the effect of mutations on the P450 structure and catalysis is yet to be reported. Such an approach will aid protein engineering approaches used to improve this enzyme. To address this research knowledge gap, we have investigated 105 CYP102 crystal structures in this study. We demonstrate that the CYP102 active site is highly dynamic and flexible. Amino acid residues that play critical roles in substrate binding, orientation, and anchoring were identified. Mutational studies highlighted the roles of amino acids and provided possible bioengineering improvement strategies for CYP102. Decoy molecules are a promising agent for deceiving CYP102 and permitting non-native substrates into the active site. Ru(II)-diimine photosensitizers and zinc/cobalt (III) sepulchrate (Co(III)Sep) could be used as alternative electron sources. The present study serves as a reference for understanding the structure–functional analysis of CYP102 family members precisely and of P450 enzymes in general. Significantly, this work contributes to the effort to develop an improved CYP102 enzyme, thereby advancing the field of P450 research and potentially leading to new industrial applications.

Cytochrome P450 (P450) enzymes are important in the metabolism of steroids, vitamins, carcinogens, drugs and other compounds. Two of the commonly used assays in this field are the measurements of total P450 and NADPH–P450 reductase in biological preparations. A detailed protocol is presented for the measurement of P450 by its spectral properties, along with a protocol for measuring NADPH–P450 reductase by its NADPH–cytochrome c reduction activity. Each assay can be completed in 5–10 min. Detailed explanations for the rationale of particular sequences in the protocols are provided, along with potential confounding problems.

We demonstrate a technique for mapping brain activity that combines molecular specificity and spatial coverage using a neurotransmitter sensor detectable by magnetic resonance imaging (MRI). This molecular functional MRI (fMRI) method yielded time-resolved volumetric measurements of dopamine release evoked by reward-related lateral hypothalamic brain stimulation of rats injected with the neurotransmitter sensor. Peak dopamine concentrations and release rates were observed in the anterior nucleus accumbens core. Substantial dopamine transients were also present in more caudal areas. Dopamine-release amplitudes correlated with the rostrocaudal stimulation coordinate, suggesting participation of hypothalamic circuitry in modulating dopamine responses. This work provides a foundation for development and application of quantitative molecular fMRI techniques targeted toward numerous components of neural physiology.

Withania somnifera (L.) Dunal, a highly reputed medicinal plant, synthesizes a large array of steroidal lactone triterpenoids called withanolides. Although its chemical profile and pharmacological activities have been studied extensively during the last two decades, limited attempts have been made to decipher the biosynthetic route and identification of key regulatory genes involved in withanolide biosynthesis. Cytochrome P450 reductase is the most imperative redox partner of multiple P450s involved in primary and secondary metabolite biosynthesis. We describe here the cloning and characterization of two paralogs of cytochrome P450 reductase from W. somnifera. The full length paralogs of WsCPR1 and WsCPR2 have open reading frames of 2058 and 2142 bp encoding 685 and 713 amino acid residues, respectively. Phylogenetic analysis demonstrated that grouping of dual CPRs was in accordance with class I and class II of eudicotyledon CPRs. The corresponding coding sequences were expressed in Escherichia coli as glutathione-S-transferase fusion proteins, purified and characterized. Recombinant proteins of both the paralogs were purified with their intact membrane anchor regions and it is hitherto unreported for other CPRs which have been purified from microsomal fraction. Southern blot analysis suggested that two divergent isoforms of CPR exist independently in Withania genome. Quantitative real-time PCR analysis indicated that both genes were widely expressed in leaves, stalks, roots, flowers and berries with higher expression level of WsCPR2 in comparison to WsCPR1. Similar to CPRs of other plant species, WsCPR1 was un-inducible while WsCPR2 transcript level increased in a time-dependent manner after elicitor treatments. High performance liquid chromatography of withanolides extracted from elicitor-treated samples showed a significant increase in two of the key withanolides, withanolide A and withaferin A, possibly indicating the role of WsCPR2 in withanolide biosynthesis. Present investigation so far is the only report of characterization of CPR paralogs from W. somnifera.

NADPH–cytochrome P450 reductase (CPR) is an essential redox partner for a wide range of metal-containing proteins, mediating the stepwise transfer of two electrons from nicotinamide adenine dinucleotide phosphate (NADPH) to the redox centers of its partner proteins. This Perspective summarizes recent advances in understanding the mechanisms underlying the CPR-mediated electron transfer (ET) cycle. Emphasis is placed on human and other mammalian CPRs, which provide critical insights into human biology and drug metabolism. Recent experimental and computational approaches that have deepened our mechanistic understanding of CPR function are highlighted. Selected studies are reviewed to illustrate progress in elucidating the interflavin ET within CPR, the interplay between its redox states and structural dynamics, and its protein–protein interactions with redox partners, along with the associated ET pathways. Finally, the remaining challenges and future research directions are outlined.

The monooxygenase activity of engineered CYP102A1 on α-terpineol was investigated. CYP102A1 M850 mutant (F11Y/R47L/D68G/F81I/F87V/E143G/L188Q/E267V/H408R) showed the highest catalytic activity toward α-terpineol among the engineered mutants produced by random mutagenesis. The major product (P1) of α-terpineol, p -menth-1-ene-3,8-diol, was characterized by high-performance liquid chromatography, gas-chromatography mass spectrometry, and nuclear magnetic resonance spectroscopy. Three minor products (P2–P4) of α-terpineol were considered as 6-hydroxy-α,α,4-trimethyl-3-cyclohexene-1-methanol (P2), trans -sobrerol (P3), and carvone hydrate (P4). Optimal conditions for product formation were determined as pH 7.0 and 30 °C. Production of p -menth-1-ene-3,8-diol was 0.87 mM at 1 h. Structure modeling using PyMOL and CAVER Web 1.2 server indicated that several mutations of CYP102A1 M850 were involved in access tunnels and active sites, resulting in increased activity toward α-terpineol. The major product, p -menth-1-ene-3,8-diol, of α-terpineol was produced by engineered CYP102A1 M850 via regioselective carbon hydroxylation. The engineered CYP102A1 could be a suitable biocatalyst for producing α-terpineol derivatives.

Expansion of the biosynthesis of plant specialized metabolites notably results from the massive recruitment of cytochrome P450s that catalyze multiple types of conversion of biosynthetic intermediates. For catalysis, P450s require a two-electron transfer catalyzed by shared cytochrome P450 oxidoreductases (CPRs), making these auxiliary proteins an essential component of specialized metabolism. CPR isoforms usually group into two distinct classes with different proposed roles, namely involvement in primary and basal specialized metabolisms for class I and inducible specialized metabolism for class II. By studying the role of CPRs in the biosynthesis of monoterpene indole alkaloids, we provide compelling evidence of an operational specialization of CPR isoforms in Catharanthus roseus (Madagascar periwinkle). Global analyses of gene expression correlation combined with transcript localization in specific leaf tissues and gene-silencing experiments of both classes of CPR all point to the strict requirement of class II CPRs for monoterpene indole alkaloid biosynthesis with a minimal or null role of class I. Direct assays of interaction and reduction of P450s in vitro, however, showed that both classes of CPR performed equally well. Such high specialization of class II CPRs in planta highlights the evolutionary strategy that ensures an efficient reduction of P450s in specialized metabolism.