Oxidative Diversification of Steroids by Nature-Inspired Scanning Glycine Mutagenesis of P450BM3 (CYP102A1)

Biosynthesis of eriodictyol in citrus waster by endowing P450BM3 activity of naringenin hydroxylation

The flavonoid naringenin is abundantly present in pomelo peels, and the unprocessed naringenin in wastes is not friendly for the environment once discarded directly. Fortunately, the hydroxylated product of eriodictyol from naringenin exhibits remarkable antioxidant and anticancer properties. The P450s was suggested promising for the bioconversion of the flavonoids, but less naturally existed P450s show hydroxylation activity to C3' of the naringenin. By well analyzing the catalytic mechanism and the conformations of the naringenin in P450, we proposed that the intermediate Cmpd I ((porphyrin)Fe = O) is more reasonable as key conformation for the hydrolyzation, and the distance between C3'/C5' of naringenin to the O atom of CmpdI determines the hydroxylating activity for the naringenin. Thus, the "flying kite model" that gradually drags the C-H bond of the substrate to the O atom of CmpdI was put forward for rational design. With ab initio design, we successfully endowed the self-sufficient P450-BM3 hydroxylic activity to naringenin and obtained mutant M5-5, with kcat, Km, and kcat/Km values of 230.45 min-1, 310.48 µM, and 0.742 min-1 µM-1, respectively. Furthermore, the mutant M4186 was screened with kcat/Km of 4.28-fold highly improved than the reported M13. The M4186 also exhibited 62.57% yield of eriodictyol, more suitable for the industrial application. This study provided a theoretical guide for the rational design of P450s to the nonnative compounds. KEY POINTS: •The compound I is proposed as the starting point for the rational design of the P450BM3 •"Flying kite model" is proposed based on the distance between O of Cmpd I and C3'/C5' of naringenin •Mutant M15-5 with 1.6-fold of activity than M13 was obtained by ab initio modification.

Recent developments in the enzymatic modifications of steroid scaffolds

Steroids are an important family of bioactive compounds. Steroid drugs are renowned for their multifaceted pharmacological activities and are the second-largest category in the global pharmaceutical market. Recent developments in biocatalysis and biosynthesis have led to the increased use of enzymes to enhance the selectivity, efficiency, and sustainability for diverse modifications of steroids. This review discusses the advancements achieved over the past five years in the enzymatic modifications of steroid scaffolds, focusing on enzymatic hydroxylation, reduction, dehydrogenation, cascade reactions, and other modifications for future research on the synthesis of novel steroid compounds and related drugs, and new therapeutic possibilities.

Choose Your Own Adventure: A Comprehensive Database of Reactions Catalyzed by Cytochrome P450 BM3 Variants

Cytochrome P450 BM3 monooxygenase is the topic of extensive research as many researchers have evolved this enzyme to generate a variety of products. However, the abundance of information on increasingly diversified variants of P450 BM3 that catalyze a broad array of chemistry is not in a format that enables easy extraction and interpretation. We present a database that categorizes variants by their catalyzed reactions and includes details about substrates to provide reaction context. This database of >1500 P450 BM3 variants is downloadable and machine-readable and includes instructions to maximize ease of gathering information. The database allows rapid identification of commonly reported substitutions, aiding researchers who are unfamiliar with the enzyme in identifying starting points for enzyme engineering. For those actively engaged in engineering P450 BM3, the database, along with this review, provides a powerful and user-friendly platform to understand, predict, and identify the attributes of P450 BM3 variants, encouraging the further engineering of this enzyme.

Selective P450BM3 Hydroxylation of Cyclobutylamine and Bicyclo[1.1.1]pentylamine Derivatives: Underpinning Synthetic Chemistry for Drug Discovery

Achieving single-step syntheses of a set of related compounds divergently and selectively from a common starting material affords substantial efficiency gains when compared with preparing those same compounds by multiple individual syntheses. In order for this approach to be realized, complementary reagent systems must be available; here, a panel of engineered P450BM3 enzymes is shown to fulfill this remit in the selective C-H hydroxylation of cyclobutylamine derivatives at chemically unactivated sites. The oxidations can proceed with high regioselectivity and stereoselectivity, producing valuable bifunctional intermediates for synthesis and applications in fragment-based drug discovery. The process also applies to bicyclo[1.1.1]pentyl (BCP) amine derivatives to achieve the first direct enantioselective functionalization of the bridging methylenes and open a short and efficient route to chiral BCP bioisosteres for medicinal chemistry. The combination of substrate, enzyme, and reaction engineering provides a powerful general platform for small-molecule elaboration and diversification.

A Compound I Mimic Reveals the Transient Active Species of a Cytochrome P450 Enzyme: Insight into the Stereoselectivity of P450-Catalysed Oxidations

Catching the structure of cytochrome P450 enzymes in flagrante is crucial for the development of P450 biocatalysts, as most structures collected are found trapped in a precatalytic conformation. At the heart of P450 catalysis lies Cpd I, a short-lived, highly reactive intermediate, whose recalcitrant nature has thwarted most attempts at capturing catalytically relevant poses of P450s. We report the crystal structure of P450BM3 mimicking the state in the precise moment preceding epoxidation, which is in perfect agreement with the experimentally observed stereoselectivity. This structure was attained by incorporation of the stable Cpd I mimic oxomolybdenum mesoporphyrin IX into P450BM3 in the presence of styrene. The orientation of styrene to the Mo-oxo species in the crystal structures sheds light onto the dynamics involved in the rotation of styrene to present its vinyl group to Cpd I. This method serves as a powerful tool for predicting and modelling the stereoselectivity of P450 reactions.

Efficient heterologous expression of cytochrome P450 enzymes in microorganisms for the biosynthesis of natural products

Natural products, a chemically and structurally diverse class of molecules, possess a wide spectrum of biological activities, have been used therapeutically for millennia, and have provided many lead compounds for the development of synthetic drugs. Cytochrome P450 enzymes (P450s, CYP) are widespread in nature and are involved in the biosynthesis of many natural products. P450s are heme-containing enzymes that use molecular oxygen and the hydride donor NAD(P)H (coupled via enzymic redox partners) to catalyze the insertion of oxygen into C-H bonds in a regio- and stereo-selective manner, effecting hydroxylation and several other reactions. With the rapid development of systems biology, numerous novel P450s have been identified for the biosynthesis of natural products, but there are still several challenges to the efficient heterologous expression of active P450s. This review covers recent developments in P450 research and development, including the properties and functions of P450s, discovery and mining of novel P450s, modification and screening of P450 mutants, improved heterologous expression of P450s in microbial hosts, efficient whole-cell transformation with P450s, and current applications of P450s for the biosynthesis of natural products. This resource provides a solid foundation for the application of highly active and stable P450s in microbial cell factories to biosynthesize natural products.

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.

H2O2-Driven Hydroxylation of Steroids Catalyzed by Cytochrome P450 CYP105D18: Exploration of the Substrate Access Channel

CYP105D18 supports H2O2 as an oxygen surrogate for catalysis well and shows high H2O2 resistance capacity. We report the hydroxylation of different steroids using H2O2 as a cosubstrate. Testosterone was regiospecifically hydroxylated to 2β-hydroxytestosterone. Based on the experimental data and molecular docking, we predicted that hydroxylation of methyl testosterone and nandrolone would occur at position 2 in the A-ring, while hydroxylation of androstenedione and adrenosterone was predicted to occur in the B-ring. Further, structure-guided rational design of the substrate access channel was performed with the mutagenesis of residues S63, R82, and F184. Among the mutants, S63A showed a marked decrease in product formation, while F184A showed a significant increase in product formation in testosterone, nandrolone, methyl testosterone, androstenedione, and adrenosterone. The catalytic efficiency (kcat/Km) toward testosterone was increased 1.36-fold in the F184A mutant over that in the wild-type enzyme. These findings might facilitate the potential use of CYP105D18 and further engineering to establish the basis of biotechnological applications. IMPORTANCE The structural modification of steroids is a challenging chemical reaction. Modifying the core ring and the side chain improves the biological activity of steroids. In particular, bacterial cytochrome P450s are used as promiscuous enzymes for the activation of nonreactive carbons of steroids. In the present work, we reported the H2O2-mediated hydroxylation of steroids by CYP105D18, which also overcomes the use of expensive cofactors. Further, exploring the substrate access channel and modifying the bulky amino acid F184A increase substrate conversion while modifying the substrate recognizing amino acid S63 markedly decreases product formation. Exploring the substrate access channel and the rational design of CYP105D18 can improve the substrate conversion, which facilitates the engineering of P450s for industrial application.

Oxidization of benzo[a]pyrene by CYP102 in a novel PAHs-degrader Pontibacillus sp. HN14 with potential application in high salinity environment

Benzo [a]pyrene (BaP) is a type of high-molecular-weight polycyclic aromatic hydrocarbons (PAHs) with potent carcinogenicity; however, there are limited studies on its degradation mechanism. Here, a strain of Pontibacillus sp. HN14 with BaP degradation ability was isolated from mangrove sediments in Dongzhai Port, Hainan Province. Our study showed that biodegradation efficiencies reached 42.15% after Pontibacillus sp. HN14 was cultured with 20 mg L^-1 BaP as the sole carbon source for 25 days and still had degradability of BaP at a 25% high salinity level. Moreover, 9,10-dihydrobenzo [a]pyrene-7(8H)-one, an intermediate metabolite, was detected during BaP degradation in the HN14 strain. Genome analysis identified a gene encoding the CYP102(HN14) enzyme. The results showed that the E. coli strain with CYP102(HN14) overexpression could transfer BaP to 9,10-dihydrobenzo [a]pyrene-7(8H)-one with a conversion rate of 43.5%, indicating that CYP102(HN14) played an essential role in BaP degradation in Pontibacillus sp. HN14. Thus, our results provide a novel BaP biodegradation molecule, which could be used in BaP bioremediation in high salinity conditions. This study is the first to show that CYP102(HN14) had the BaP oxidization ability in bacteria. CYP102(HN14) could be essential in removing PAHs in saline-alkali soil and other high salt environments through enzyme immobilization.

Oxygenating Biocatalysts for Hydroxyl Functionalisation in Drug Discovery and Development

C-H oxyfunctionalisation remains a distinct challenge for synthetic organic chemists. Oxygenases and peroxygenases (grouped here as "oxygenating biocatalysts") catalyse the oxidation of a substrate with molecular oxygen or hydrogen peroxide as oxidant. The application of oxygenating biocatalysts in organic synthesis has dramatically increased over the last decade, producing complex compounds with potential uses in the pharmaceutical industry. This review will focus on hydroxyl functionalisation using oxygenating biocatalysts as a tool for drug discovery and development. Established oxygenating biocatalysts, such as cytochrome P450s and flavin-dependent monooxygenases, have widely been adopted for this purpose, but can suffer from low activity, instability or limited substrate scope. Therefore, emerging oxygenating biocatalysts which offer an alternative will also be covered, as well as considering the ways in which these hydroxylation biotransformations can be applied in drug discovery and development, such as late-stage functionalisation (LSF) and in biocatalytic cascades.

Biotransformation Enables Innovations Toward Green Synthesis of Steroidal Pharmaceuticals

Steroids have been widely used in birth-control, prevention, and treatment of various diseases, representing the largest sector after antibiotics in the global pharmaceutical market. The steroidal active pharmaceutical ingredients (APIs) have been produced via partial synthetic processes first mainly from sapogenins, which was converted into 16-dehydropregnenolone by the famous "Marker Degradation". Traditional mutation and screening, and process engineering have resulted in the industrial production of 4-androstene-3,17-dione (AD), androst-1,4-diene-3,17-dione (ADD), 9α-hydroxy-androsta-4-ene-3,17-dione (9α-OH-AD), and so on, which serve as the key intermediates for the synthesis of steroidal APIs. Recently, genetic and metabolic engineering have generated highly efficient microbial strains for the production of these precursors, leading to the replacement of sapogenins with phytosterols as the starting materials. Further advances in synthetic biology hold promise in the design and construction of microbial cell factories for the industrial production of steroidal intermediates and/or APIs from simple carbon sources such as glucose. Integration of biotransformation into the synthesis of steroidal APIs can greatly reduce the number of reaction steps, achieve lower waste discharge and higher production efficiency, thus enabling a greener steroidal pharmaceutical industry.

Latent Functions and Applications of Cytochrome P450 Monooxygenases from Thamnidium elegans: A Novel Biocatalyst for 14α-Hydroxylation of Testosterone

Cytochrome P450 monooxygenases (P450s) are ubiquitous enzymes with high availability and diversity in nature. Fungi provide a diverse and complex array of P450s, and these enzymes play essential roles in various secondary metabolic processes. Besides the physiological impacts of P450s on fungal life, their versatile functions are attractive for use in advanced applications of the biotechnology sector. Herein, we report gene identification and functional characterization of P450s from the zygomycetous fungus Thamnidium elegans (TeCYPs). We identified 48 TeCYP genes, including two putative pseudogenes, from the whole-genome sequence of T. elegans. Furthermore, we constructed a functional library of TeCYPs and heterologously expressed 46 TeCYPs in Saccharomyces cerevisiae. Recombinants of S. cerevisiae were then used as whole-cell biocatalysts for bioconversion of various compounds. Catalytic potentials of various TeCYPs were demonstrated through a functionomic survey to convert a series of compounds, including steroidal substrates. Notably, CYP5312A4 was found to be highly active against testosterone. Based on nuclear magnetic resonance analysis, enzymatic conversion of testosterone to 14α-hydroxytestosterone by CYP5312A4 was demonstrated. This is the first report to identify a novel fungal P450 that catalyzes the 14α-hydroxylation of testosterone. In addition, we explored the latent potentials of TeCYPs using various substrates. This study provides a platform to further study the potential use of TeCYPs as catalysts in pharmaceutical and agricultural industries and biotechnology.

Remote B-Ring Oxidation of Sclareol with an Engineered P450 Facilitates Divergent Access to Complex Terpenoids

Though chiral pool synthesis is widely accepted as a powerful strategy in complex molecule synthesis, the effectiveness of the approach is intimately linked to the range of available chiral building blocks and the functional groups they possess. To date, there is still a pressing need for new remote functionalization methods that would allow the installation of useful chemical handles on these building blocks to enable a broader spectrum of synthetic manipulations. Herein, we report the engineering of a P450_BM3 variant for the regioselective C-H oxidation of sclareol at C6. The synthetic utility of the resulting product was demonstrated in a formal synthesis of ansellone B, the first total synthesis of the 2,3-seco-labdane excolide B, and a model study toward (+)-pallavicinin.

Recent Advances in Biocatalysis for Drug Synthesis

Biocatalysis is constantly providing novel options for the synthesis of active pharmaceutical ingredients (APIs). In addition to drug development and manufacturing, biocatalysis also plays a role in drug discovery and can support many active ingredient syntheses at an early stage to build up entire scaffolds in a targeted and preparative manner. Recent progress in recruiting new enzymes by genome mining and screening or adapting their substrate, as well as product scope, by protein engineering has made biocatalysts a competitive tool applied in academic and industrial spheres. This is especially true for the advances in the field of nonribosomal peptide synthesis and enzyme cascades that are expanding the capabilities for the discovery and synthesis of new bioactive compounds via biotransformation. Here we highlight some of the most recent developments to add to the portfolio of biocatalysis with special relevance for the synthesis and late-stage functionalization of APIs, in order to bypass pure chemical processes.

One-pot biosynthesis of 7β-hydroxyandrost-4-ene-3,17-dione from phytosterols by cofactor regeneration system in engineered mycolicibacterium neoaurum

Background

7β-hydroxylated steroids (7β-OHSt) possess significant activities in anti-inflammatory and neuroprotection, and some of them have been widely used in clinics. However, the production of 7β-OHSt is still a challenge due to the lack of cheap 7β-hydroxy precursor and the difficulty in regio- and stereo-selectively hydroxylation at the inert C7 site of steroids in industry. The conversion of phytosterols by Mycolicibacterium species to the commercial precursor, androst-4-ene-3,17-dione (AD), is one of the basic ways to produce different steroids. This study presents a way to produce a basic 7β-hydroxy precursor, 7β-hydroxyandrost-4-ene-3,17-dione (7β-OH-AD) in Mycolicibacterium, for 7β-OHSt synthesis.

Results

A mutant of P450-BM3, mP450-BM3, was mutated and engineered into an AD producing strain for the efficient production of 7β-OH-AD. The enzyme activity of mP450-BM3 was then increased by 1.38 times through protein engineering and the yield of 7β-OH-AD was increased from 34.24 mg L^− 1 to 66.25 mg L^− 1. To further enhance the performance of 7β-OH-AD producing strain, the regeneration of nicotinamide adenine dinucleotide phosphate (NADPH) for the activity of mP450-BM3-0 was optimized by introducing an NAD kinase (NADK) and a glucose-6-phosphate dehydrogenase (G6PDH). Finally, the engineered strain could produce 164.52 mg L^− 1 7β-OH-AD in the cofactor recycling and regeneration system.

Conclusions

This was the first report on the one-pot biosynthesis of 7β-OH-AD from the conversion of cheap phytosterols by an engineered microorganism, and the yield was significantly increased through the mutation of mP450-BM3 combined with overexpression of NADK and G6PDH. The present strategy may be developed as a basic industrial pathway for the commercial production of high value products from cheap raw materials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01786-5.

Influence of tissue and geographic locality on culturable endophytic bacteria of Atractylodes macrocephala

The endophytic bacterial community and their diversity are closely related to the host's growth and development. This paper explores the culturable endophytic bacteria in the stems, leaves, roots and rhizomes of Atractylodes macrocephala (AM) of four localities (Yuqian, Wenxian, Pan'an and Pingjiang) and the potential correlation between the bacteria and plant bioactive compounds. A total of 118 endophytic bacteria belonging to 3 phyla, 5 classes, 11 orders, 26 families and 48 genera were isolated and identified from the four AM tissues. Among them, Bacillus was the dominant genus. In AM, the tissue type and locality influenced the endophytic bacterial community. Approximately 29.7 and 28.8% of the endophytic bacteria exhibited tissue specificity and geographic specificity, respectively. Furthermore, high-performance liquid chromatography revealed that the sesquiterpenoid (atractylenolide I, atractylenolide Ⅱ and atractylon) content was more in the rhizomes of Wenxian than in those of Pingjiang, Yuqian and Pan'an. The multiple linear regression was used to screen the bacterial strains related to the bioactive compounds of AM. The relative frequency of Microbacterium positively correlated with atractylenolide I and atractylon content in AM but negatively correlated with atractylenolide Ⅱ content. The study also provides a theoretical framework for future research on endophytic bacteria as alternative sources of secondary plant metabolites.

A Promiscuous Bacterial P450: The Unparalleled Diversity of BM3 in Pharmaceutical Metabolism

CYP102A1 (BM3) is a catalytically self-sufficient flavocytochrome fusion protein isolated from Bacillus megaterium, which displays similar metabolic capabilities to many drug-metabolizing human P450 isoforms. BM3's high catalytic efficiency, ease of production and malleable active site makes the enzyme a desirable tool in the production of small molecule metabolites, especially for compounds that exhibit drug-like chemical properties. The engineering of select key residues within the BM3 active site vastly expands the catalytic repertoire, generating variants which can perform a range of modifications. This provides an attractive alternative route to the production of valuable compounds that are often laborious to synthesize via traditional organic means. Extensive studies have been conducted with the aim of engineering BM3 to expand metabolite production towards a comprehensive range of drug-like compounds, with many key examples found both in the literature and in the wider industrial bioproduction setting of desirable oxy-metabolite production by both wild-type BM3 and related variants. This review covers the past and current research on the engineering of BM3 to produce drug metabolites and highlights its crucial role in the future of biosynthetic pharmaceutical production.

Engineered and Artificial Metalloenzymes for Selective C-H Functionalization

The direct functionalization of C-H bonds constitutes a powerful strategy to construct and diversify organic molecules. However, controlling the chemo- and site-selectivity of this transformation in particularly complex molecular settings represents a significant challenge. Metalloenzymes are ideal platforms for achieving catalyst-controlled selective C-H bond functionalization as their reactivities can be tuned by protein engineering and/or redesign of their cofactor environment. In this review, we highlight recent progress in the development of engineered and artificial metalloenzymes for C-H functionalization, with a focus on biocatalytic strategies for selective C-H oxyfunctionalization and halogenation as well as C-H amination and C-H carbene insertion via abiological nitrene and carbene transfer chemistries. Engineered heme- and non-heme iron dependent enzymes have emerged as promising scaffolds for executing these transformations with high chemo-, regio- and stereocontrol as well as tunable selectivity. These emerging systems and methodologies have expanded the toolbox of sustainable strategies for organic synthesis and created new opportunities for the generation of chiral building blocks, the late-stage C-H functionalization of complex molecules, and the total synthesis of natural products.

Hemoprotein Catalyzed Oxygenations: P450s, UPOs, and Progress toward Scalable Reactions

The selective oxygenation of nonactivated carbon atoms is an ongoing synthetic challenge, and biocatalysts, particularly hemoprotein oxygenases, continue to be investigated for their potential, given both their sustainable chemistry credentials and also their superior selectivity. However, issues of stability, activity, and complex reaction requirements often render these biocatalytic oxygenations problematic with respect to scalable industrial processes. A continuing focus on Cytochromes P450 (P450s), which require a reduced nicotinamide cofactor and redox protein partners for electron transport, has now led to better catalysts and processes with a greater understanding of process requirements and limitations for both in vitro and whole-cell systems. However, the discovery and development of unspecific peroxygenases (UPOs) has also recently provided valuable complementary technology to P450-catalyzed reactions. UPOs need only hydrogen peroxide to effect oxygenations but are hampered by their sensitivity to peroxide and also by limited selectivity. In this Perspective, we survey recent developments in the engineering of proteins, cells, and processes for oxygenations by these two groups of hemoproteins and evaluate their potential and relative merits for scalable reactions.

Recent trends in biocatalysis

Biocatalysis has undergone revolutionary progress in the past century. Benefited by the integration of multidisciplinary technologies, natural enzymatic reactions are constantly being explored. Protein engineering gives birth to robust biocatalysts that are widely used in industrial production. These research achievements have gradually constructed a network containing natural enzymatic synthesis pathways and artificially designed enzymatic cascades. Nowadays, the development of artificial intelligence, automation, and ultra-high-throughput technology provides infinite possibilities for the discovery of novel enzymes, enzymatic mechanisms and enzymatic cascades, and gradually complements the lack of remaining key steps in the pathway design of enzymatic total synthesis. Therefore, the research of biocatalysis is gradually moving towards the era of novel technology integration, intelligent manufacturing and enzymatic total synthesis.

Synthetic utility of oxygenases in site-selective terpenoid functionalization

Terpenoids are one of the largest classes of natural products whose members possess a wide variety of biological activities. With several exceptions, scalable production of complex terpenoids with either purely biological or chemical methods still remains a major challenge. However, recent efforts to combine the two approaches in chemoenzymatic synthesis hold tremendous promise to address this challenge. Central to this paradigm is the development of useful biocatalytic methods, such as regioselective C–H oxidation, for terpene modifications. This review highlights recent applications of biocatalytic hydroxylation for site-selective modification of terpenoids.

Conformational Motion of Ferredoxin Enables Efficient Electron Transfer to Heme in the Full-Length P450TT

Cytochrome P450 monooxygenases (P450s) are versatile biocatalysts used in natural products biosynthesis, xenobiotic metabolisms, and biotechnologies. In P450s, the electrons required for O₂ activation are supplied by NAD(P)H through stepwise electron transfers (ETs) mediated by redox partners. While much is known about the machinery of the catalytic cycle of P450s, the mechanisms of long-range ET are largely unknown. Very recently, the first crystal structure of full-length P450_TT was solved. This enables us to decipher the interdomain ET mechanism between the [2Fe-2S]-containing ferredoxin and the heme, by use of molecular dynamics simulations. In contrast to the "distal" conformation characterized in the crystal structure where the [2Fe-2S] cluster is ∼28 Å away from heme-Fe, our simulations demonstrated a "proximal" conformation of [2Fe-2S] that is ∼17 Å [and 13.7 Å edge-to-edge] away from heme-Fe, which may enable the interdomain ET. Key residues involved in ET pathways and interdomain complexation were identified, some of which have already been verified by recent mutation studies. The conformational transit of ferredoxin between "distal" and "proximal" was found to be controlled mostly by the long-range electrostatic interactions between the ferredoxin domain and the other two domains. Furthermore, our simulations show that the full-length P450_TT utilizes a flexible ET pathway that resembles either P450_Scc or P450_cam. Thus, this study provides a uniform picture of the ET process between reductase domains and heme domain.

CYP154C5 Regioselectivity in Steroid Hydroxylation Explored by Substrate Modifications and Protein Engineering*

CYP154C5 from Nocardia farcinica is a P450 monooxygenase able to hydroxylate a range of steroids with high regio- and stereoselectivity at the 16α-position. Using protein engineering and substrate modifications based on the crystal structure of CYP154C5, an altered regioselectivity of the enzyme in steroid hydroxylation had been achieved. Thus, conversion of progesterone by mutant CYP154C5 F92A resulted in formation of the corresponding 21-hydroxylated product 11-deoxycorticosterone in addition to 16α-hydroxylation. Using MD simulation, this altered regioselectivity appeared to result from an alternative binding mode of the steroid in the active site of mutant F92A. MD simulation further suggested that the entrance of water to the active site caused higher uncoupling in this mutant. Moreover, exclusive 15α-hydroxylation was observed for wild-type CYP154C5 in the conversion of 5α-androstan-3-one, lacking an oxy-functional group at C17. Overall, our data give valuable insight into the structure-function relationship of this cytochrome P450 monooxygenase for steroid hydroxylation.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as patulignan A from Melicope patulinervia.