Oxygen activation by cytochrome P450 monooxygenase

The presence of substrate warrants oxygen access tunnels toward the catalytic site of lipoxygenases

Ferroptosis is a regulated form of cell death driven by lipid peroxidation, with 15-lipoxygenase (15LOX) enzyme playing a critical role in catalyzing the oxygenation of polyunsaturated fatty acid-containing phospholipids, such as 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphoethanolamine (SAPE), to initiate this process. The molecular oxygen required for this catalytic reaction is subject to continuous competition among various oxygen-consuming enzymes, which influences the efficiency of lipid peroxidation. In this study, we utilized structure-based modeling and all-atom molecular dynamics simulations to explore the oxygen diffusion pathways in 15LOX-1 under varying oxygen concentrations and in the presence of key components, including a substrate, binding partner PE-binding protein 1 (PEBP1), and the membrane environment. Extensive computational experiments were performed on various system configurations, examining the role of substrate binding, membrane presence, and PEBP1 association in oxygen acquisition. Our computational results indicate that the substrate binding induces a conformational change in 15LOX-1, facilitating the simultaneous recruitment of one or two O2 molecules, which drive peroxidation, leading predominantly to monohydroperoxide products and, less frequently, to dihydroperoxide products. A similar trend was observed in our redox lipidomics analysis. Moreover, we noticed that the presence of the membrane significantly reduces irrelevant oxygen binding spots, directing oxygen molecules toward a primary tunnel essential for the catalytic activity. We identified two primary oxygen tunnels with sequentially and structurally conserved regions across the lipoxygenase family. These findings provide novel insights into the regulation of oxygen acquisition mechanism for LOX members, shedding light on the molecular basis of ferroptosis signaling.

Protein Engineering for Enhancing Electron Transfer in P450-Mediated Catalysis

Cytochrome P450 enzymes (P450s) are versatile biocatalysts with applications spanning pharmaceutical development and natural product biosynthesis. A critical bottleneck in P450-mediated reactions is the electron transfer process, which often limits catalytic efficiency and promotes uncoupling events leading to reactive oxygen species (ROS) formation. This review comprehensively examines recent protein engineering strategies aimed at enhancing electron transfer efficiency in P450 systems. We explore the design and application of different fusion constructs, which improve proximity between the P450 enzyme and its redox partners (RPs), as well as scaffold-mediated protein assembly, enabling precise spatial organization of P450s and RPs. Furthermore, we discuss targeted modifications at the P450-RP interaction interface and optimization of electron transfer pathways through site-directed mutagenesis and directed evolution. These strategies enhance catalytic activity, improve coupling efficiency, and reduce ROS formation. Finally, we address the remaining challenges in understanding and engineering P450 electron transfer, and discuss the future directions, emphasizing the need for advanced computational modeling, structural characterization, and integration of synthetic and systems biology approaches.

Exploring the selectivity of cytochrome P450 for enhanced novel anticancer agent synthesis

Cytochrome P450 monooxygenases are an extensive and unique class of enzymes, which can regio- and stereo-selectively functionalise hydrocarbons by way of oxidation reactions. These enzymes are naturally occurring but have also been extensively applied in a synthesis context, where they are used as efficient biocatalysts. Recently, a biosynthetic pathway where a cytochrome P450 monooxygenase catalyses a critical step of the pathway was uncovered, leading to the production of a number of products that display high antitumour potency. In this work, we use computational techniques to gain insight into the factors that determine the relative yields of the different products. We use conformational search algorithms to understand the substrate stereochemistry. On a machine-learned 3D protein structure, we use molecular docking to obtain a library of favourable poses for substrate-protein interaction. With molecular dynamics, we investigate the most favourable poses for reactivity on a molecular level, allowing us to investigate which protein-substrate interactions favour a given product and thus gain insight into the product selectivity.

Leveraging ligand-based proton and electron transfer for aerobic reactivity and catalysis

While O2 is an abundant, benign, and thermodynamically potent oxidant, it is also kinetically inert. This frequently limits its use in synthetic transformations. Correspondingly, direct aerobic reactivity with O2 often requires comparatively harsh or forcing conditions to overcome this kinetic barrier. Forcing conditions limit product selectivity and can lead to over oxidation. Alternatively, O2 can be activated by a catalyst to facilitate oxidative reactivity, and there are a variety of sophisticated examples where transition metal catalysts facilitate aerobic reactivity. Many efforts have focused on using metal-ligand cooperativity to facilitate the movement of protons and electrons for O2 activation. This approach is inspired by enzyme active sites, which frequently use the secondary sphere to facilitate both the activation of O2 and the oxidation of substrates. However, there has only recently been a focus on harnessing metal-ligand cooperativity for aerobic reactivity and, especially, catalysis. This perspective will discuss recent efforts to channel metal-ligand cooperativity for the activation of O2, the generation and stabilization of reactive metal-oxygen intermediates, and oxidative reactivity and catalysis. While significant progress has been made in this area, there are still challenges to overcome and opportunities for the development of efficient catalysts which leverage this biomimetic strategy.

Superoxide to Peroxide Interconversion in Ni-TMC Complexes: The Significance of Structure and Spin States

A deeper comprehension of the characteristics of metal-superoxide and metal-peroxide chemical species is imperative, considering their pivotal functions in oxygen transport, enzymatic activation, and catalytic oxygenations. O2 activation is mediated by the interconversion of superoxide and peroxide species. Even though there are multiple studies on metal-superoxide and -peroxide intermediates, robust examples of their interconversion processes are scarce synthetically. For example, Ni-superoxide/peroxide complexes have been characterized with N-Tetramethylated Cyclam (TMC) ligands with different ring sizes, i.e., Nickel(II)-superoxide complex is characterized with 14-TMC while Nickel(III)-peroxide complex with 12-TMC. Later, both complexes were obtained with 13-TMC ligand by employing different bases; interestingly, no evidence of interconversion between them was identified. What are the factors influencing these processes and why is this preference? We attempt a computational analysis of this issue and provide arguments based on our conclusions. 2-dimensional potential energy scan is performed on the 12-TMC, 13-TMC, and 14-TMC systems to identify the reaction path connecting superoxide and peroxide species. Analyses indicate that structure and spin states play a significant role in determining the probability of interconversion. The superoxide-peroxide interconversion process appears to be bound by their propensity for distinct structural features and spin states.

Dimer Stabilization by SpyTag/SpyCatcher Coupling of the Reductase Domains of a Chimeric P450 BM3 Monooxygenase from Bacillus spp. Improves its Stability, Activity, and Purification

The vast majority of known enzymes exist as oligomers, which often gives them high catalytic performance but at the same time imposes constraints on structural conformations and environmental conditions. An example of an enzyme with a complex architecture is the P450 BM3 monooxygenase CYP102A1 from Bacillus megaterium. Only active as a dimer, it is highly sensitive to dilution or common immobilization techniques. In this study, we engineered a thermostable P450BM3 chimera consisting of the heme domain of a CYP102A1 variant and the reductase domain of the homologous CYP102A3. The dimerization of the hybrid was even weaker compared to the corresponding CYP102A1 variant. To create a stable dimer, we covalently coupled the C-termini of two monomers of the chimera via SpyTag003/SpyCatcher003 interaction. As a result, purification, thermostability, pH stability, and catalytic activity were improved. Via a bioorthogonal two-step affinity purification, we obtained high purity (94 %) of the dimer-stabilized variant being robust against heme depletion. Long-term stability was increased with a half-life of over 2 months at 20 °C and 80-90 % residual activity after 2 months at 5 °C. Most catalytic features were retained with even an enhancement of the overall activity by ~2-fold compared to the P450BM3 chimera without SpyTag003/SpyCatcher003.

Deciphering the Role of Fatty Acid-Metabolizing CYP4F11 in Lung Cancer and Its Potential As a Drug Target

Lung cancer is the leading cause of cancer deaths worldwide. We found that the cytochrome P450 isoform CYP4F11 is significantly overexpressed in patients with lung squamous cell carcinoma. CYP4F11 is a fatty acid ω-hydroxylase and catalyzes the production of the lipid mediator 20-hydroxyeicosatetraenoic acid (20-HETE) from arachidonic acid. 20-HETE promotes cell proliferation and migration in cancer. Inhibition of 20-HETE-generating cytochrome P450 enzymes has been implicated as novel cancer therapy for more than a decade. However, the exact role of CYP4F11 and its potential as drug target for lung cancer therapy has not been established yet. Thus, we performed a transient knockdown of CYP4F11 in the lung cancer cell line NCI-H460. Knockdown of CYP4F11 significantly inhibits lung cancer cell proliferation and migration while the 20-HETE production is significantly reduced. For biochemical characterization of CYP4F11-inhibitor interactions, we generated recombinant human CYP4F11. Spectroscopic ligand binding assays were conducted to evaluate CYP4F11 binding to the unselective CYP4A/F inhibitor HET0016. HET0016 shows high affinity to recombinant CYP4F11 and inhibits CYP4F11-mediated 20-HETE production in vitro with a nanomolar IC 50 Cross evaluation of HET0016 in NCI-H460 cells shows that lung cancer cell proliferation is significantly reduced together with 20-HETE production. However, HET0016 also displays antiproliferative effects that are not 20-HETE mediated. Future studies aim to establish the role of CYP4F11 in lung cancer and the underlying mechanism and investigate the potential of CYP4F11 as a therapeutic target for lung cancer. SIGNIFICANCE STATEMENT: Lung cancer is a deadly cancer with limited treatment options. Cytochrome P450 4F11 (CYP4F11) is significantly upregulated in lung squamous cell carcinoma. Knockdown of CYP4F11 in a lung cancer cell line significantly attenuates cell proliferation and migration with reduced production of the lipid mediator 20-hydroxyeicosatetraenoic acid (20-HETE). Studies with the unselective inhibitor HET0016 show a high inhibitory potency of CYP4F11-mediated 20-HETE production using recombinant enzyme. Overall, our studies demonstrate the potential of targeting CYP4F11 for new transformative lung cancer treatment.

Theoretical study of the formation of metal-oxo species of the first transition series with the ligand 14-TMC: driving factors of the "Oxo Wall"

Terminal metal-oxo species of the early transition metal series are well known, whereas those for the late transition series are rare, and this is related to the "Oxo Wall". Here, we have undertaken a theoretical study on the formation of metal-oxo species from the metal hydroperoxo species of the 3d series (Cr, Mn, Fe, Co, Ni, and Cu) with the ligand 14-TMC (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) via O⋯O bond cleavage. DFT calculations reveal that the barrier for O⋯O bond cleavage is higher with the late transition metals (Co, Ni, and Cu) than the early transition metals (Cr, Mn, and Fe), and the formed late metal-oxo species are also thermodynamically less stable. The higher barrier may be due to electronic repulsion because of the pairing of d electrons. In the late transition metal series, the electron goes into an antibonding orbital, which decreases the bond order and hence decreases the possibility of metal-oxo formation. Computed structural parameters and spin densities suggest that valence tautomerism occurs in the late transition metal-oxo species which remain as a metal-oxyl. Our findings support the concept of the "Oxo Wall".

The Role of the Redox Non-Innocent Hydroxyl Ligand in the Activation of O2 Performed by [Ni(H)(OH)]. Chemistry 2023;29:e202203128. [PMID: 36447369 DOI: 10.1002/chem.202203128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The cationic complex [Ni(H)(OH)]⁺ was previously found to activate dioxygen and methane in gas phase under single collision conditions. These remarkable reactivities were thought to originate from a non-classical electronic structure, where the Ni-center adopts a Ni(II), instead of the classically expected Ni(III) oxidation state by formally accepting an electron from the hydroxo ligand, which formally becomes a hydroxyl radical in the process. Such radicaloid oxygen moieties are envisioned to easily react with otherwise inert substrates, mimicking familiar reactivities of free radicals. In this study, the reductive activation of dioxygen by [Ni(H)(OH)]⁺ to afford the hydroperoxo species was investigated using coupled cluster, multireference ab initio and density functional theory calculations. Orbital and wave function analyses indicate that O₂ binding tranforms the aforementioned non-classical electronic structure to a classical Ni(III)-hydroxyl system, before O₂ reduction takes place. Remarkably, we found no evidence for a direct involvement of the radicaloid hydroxyl in the reaction with O₂ , as is often assumed. The function of the redox non-innocent character of the activator complex is to protect the reactive electronic structure until the complex engages O₂ , upon which a dramatic electronic reorganization releases internal energy and drives the chemical reaction to completion.

Melatonin Activation by Cytochrome P450 Isozymes: How Does CYP1A2 Compare to CYP1A1?

Cytochrome P450 enzymes are versatile enzymes found in most biosystems that catalyze mono-oxygenation reactions as a means of biosynthesis and biodegradation steps. In the liver, they metabolize xenobiotics, but there are a range of isozymes with differences in three-dimensional structure and protein chain. Consequently, the various P450 isozymes react with substrates differently and give varying product distributions. To understand how melatonin is activated by the P450s in the liver, we did a thorough molecular dynamics and quantum mechanics study on cytochrome P450 1A2 activation of melatonin forming 6-hydroxymelatonin and N-acetylserotonin products through aromatic hydroxylation and O-demethylation pathways, respectively. We started from crystal structure coordinates and docked substrate into the model, and obtained ten strong binding conformations with the substrate in the active site. Subsequently, for each of the ten substrate orientations, long (up to 1 μs) molecular dynamics simulations were run. We then analyzed the orientations of the substrate with respect to the heme for all snapshots. Interestingly, the shortest distance does not correspond to the group that is expected to be activated. However, the substrate positioning gives insight into the protein residues it interacts with. Thereafter, quantum chemical cluster models were created and the substrate hydroxylation pathways calculated with density functional theory. These relative barrier heights confirm the experimental product distributions and highlight why certain products are obtained. We make a detailed comparison with previous results on CYP1A1 and identify their reactivity differences with melatonin.

Evidence of Sulfur Non-Innocence in [CoII (dithiacyclam)]2+ -Mediated Catalytic Oxygen Reduction Reactions

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]²⁺ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S₂ N₂ -cyclam)]²⁺ (2; S₂ N₂ -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the Co^II centers in 1 and 2 point to the involvement of sulfur in the O₂ reduction process as the key for the improved catalytic ORR capabilities of 2.

Biotransformation of phenytoin in the electrochemically-driven CYP2C19 system

The possibility of the detection of atypical kinetic profiles of drug biotransformation using electrochemical systems based on immobilized cytochromes P450 with phenytoin hydroxylation by cytochrome P450 2C19 (CYP2C19) as an example was evaluated for the first time. For this purpose, we developed an electrochemical system, where one of the electrodes was modified by didodecyldimethylammonium bromide (DDAB) and was used as an electron donor for reduction of heme iron ion of the immobilized CYP2C19 and initiation of the catalytic reaction, while the second electrode was not modified and served for an electrochemical quantitation of 4-hydroxyphenytoin, which is a metabolite of antiepileptic drug phenytoin, by its oxidation peak. It was revealed that the dependence of the rate of 4-hydroxyphenytoin formation on phenytoin concentration is described by the equation for two enzymes or two binding sites indicating the existing of high- and low-affinity forms of the enzyme. The atypical kinetics and the kinetic parameters of CYP2C19-mediated phenytoin hydroxylation in the electrochemical system correlate to the same characteristics obtained by other authors in an alternative enzymatic system. Our results demonstrate the possibility of electrochemical systems based on cytochromes P450 to be applied for the detection of atypical kinetic profiles of drug metabolism.

Effect of Fe3+ on Na,K-ATPase: Unexpected activation of ATP hydrolysis

Iron is a key element in cell function; however, its excess in iron overload conditions can be harmful through the generation of reactive oxygen species (ROS) and cell oxidative stress. Activity of Na,K-ATPase has been shown to be implicated in cellular iron uptake and iron modulates the Na,K-ATPase function from different tissues. In this study, we determined the effect of iron overload on Na,K-ATPase activity and established the role that isoforms and conformational states of this enzyme has on this effect. Total blood and membrane preparations from erythrocytes (ghost cells), as well as pig kidney and rat brain cortex, and enterocytes cells (Caco-2) were used. In E1-related subconformations, an enzyme activation effect by iron was observed, and in the E2-related subconformations enzyme inhibition was observed. The enzyme's kinetic parameters were significantly changed only in the Na⁺ curve in ghost cells. In contrast to Na,K-ATPase α2 and α3 isoforms, activation was not observed for the α1 isoform. In Caco-2 cells, which only contain Na,K-ATPase α1 isoform, the FeCl₃ increased the intracellular storage of iron, catalase activity, the production of H₂O₂ and the expression levels of the α1 isoform. In contrast, iron did not affect lipid peroxidation, GSH content, superoxide dismutase and Na,K-ATPase activities. These results suggest that iron itself modulates Na,K-ATPase and that one or more E1-related subconformations seems to be determinant for the sensitivity of iron modulation through a mechanism in which the involvement of the Na, K-ATPase α3 isoform needs to be further investigated.

Atractylenolide-I covalently binds to CYP11B2, selectively inhibits aldosterone synthesis, and improves hyperaldosteronism

Hyperaldosteronism is a common disease that is closely related to endocrine hypertension and other cardiovascular diseases. Cytochrome P450 11B2 (CYP11B2), an important enzyme in aldosterone (ALD) synthesis, is a promising target for the treatment of hyperaldosteronism. However, selective inhibitors targeting CYP11B2 are still lacking due to the high similarity with CYP11B1. In this study, atractylenolide-I (AT-I) was found to significantly reduce the production of ALD but had no effect on cortisol synthesis, which is catalyzed by CYP11B1. Chemical biology studies revealed that due to the presence of Ala320, AT-I is selectively bound to the catalytic pocket of CYP11B2, and the C8/C9 double bond of AT-I can be epoxidized, which then undergoes nucleophilic addition with the sulfhydryl group of Cys450 in CYP11B2. The covalent binding of AT-I disrupts the interaction between heme and CYP11B2 and inactivates CYP11B2, leading to the suppression of ALD synthesis; AT-I shows a significant therapeutic effect for improving hyperaldosteronism.

Functional Interaction between Cytochrome P450 and UDP-Glucuronosyltransferase on the Endoplasmic Reticulum Membrane: One of Post-translational Factors Which Possibly Contributes to Their Inter-Individual Differences

Cytochrome P450 (P450) and uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) catalyze oxidation and glucuronidation in drug metabolism, respectively. It is believed that P450 and UGT work separately because they perform distinct reactions and exhibit opposite membrane topologies on the endoplasmic reticulum (ER). However, given that some chemicals are sequentially metabolized by P450 and UGT, it is reasonable to consider that the enzymes may interact and work cooperatively. Previous research by our team detected protein-protein interactions between P450 and UGT by analyzing solubilized rat liver microsomes with P450-immobilized affinity column chromatography. Although P450 and UGT have been known to form homo- and hetero-oligomers, this is the first report indicating a P450-UGT association. Based on our previous study, we focused on the P450-UGT interaction and reported lines of evidence that the P450-UGT association is a functional protein-protein interaction that can alter the enzymatic capabilities, including enhancement or suppression of the activities of P450 and UGT, helping UGT to acquire novel regioselectivity, and inhibiting substrate binding to P450. Biochemical and molecular bioscientific approaches suggested that P450 and UGT interact with each other at their internal hydrophobic domains in the ER membrane. Furthermore, several in vivo studies have reported the presence of a functional P450-UGT association under physiological conditions. The P450-UGT interaction is expected to function as a novel post-translational factor for inter-individual differences in the drug-metabolizing enzymes.

Tylosin toxicity in the alga Raphidocelis subcapitata revealed by integrated analyses of transcriptome and metabolome: Photosynthesis and DNA replication-coupled repair

Tylosin (TYN) is widely used in veterinary prophylactic as a macrolide and frequently detected in the surface water. Previous studies showed that exposure to TYN caused suppression of chlorophyll biosynthesis and inhibition of photosynthesis at the physiological level, associated with reduced growth performances in algae, but the molecular mechanisms remain unknown, especially at environmental exposure levels. The present study elucidated the underlying molecular mechanism(s) of TYN toxicity in a model green alga Raphidocelis subcapitata using approaches of transcriptomics and metabolomics. Following a 7-day exposure, algal growth performances were reduced by 26.3% and 58.3% in the 3 (an environmentally realistic level) and 400 μg L^-1 TYN treatment group, respectively. A total of 577 (99) and 5438 (180) differentially expressed genes (differentially accumulated metabolites) were identified in algae treated with 3 and 400 μg L^-1 TYN, respectively. Signaling pathways including photosynthesis - antenna protein, porphyrin and chlorophyll metabolism, carbon fixation in photosynthetic organisms, and DNA replication were altered in the 400 μg L^-1 TYN treatment, while photosynthesis and DNA replication were the shared pathways in both TYN treatments. The metabolomic data further suggest that molecular pathways related to photosynthesis, DNA replication-coupled repair and energy metabolism were impaired. Photosynthesis was identified as the most sensitive target of TYN toxicity in R. subcapitata, in contrast to protein synthesis inhibition caused by TYN in bacteria. This study provides novel mechanistic information of TYN toxicity in R. subcapitata.

Aldosterone Synthase Structure With Cushing Disease Drug LCI699 Highlights Avenues for Selective CYP11B Drug Design

[Figure: see text].

Single gold nanoparticle-driven heme cofactor nanozyme as an unprecedented oxidase mimetic

The catalytic diversity of heme enzymes is a perpetuating pursuit for biomimetic chemistry, but heme nanozymes exhibit catalytic activity only reminiscent of peroxidases. Miraculously, the oxidase-like catalytic function of a heme cofactor is elicited with the help of gold nanoparticles (AuNPs) by maintaining heme with a low-valence state (ferrous) in a confined configuration.

An electron transfer competent structural ensemble of membrane-bound cytochrome P450 1A1 and cytochrome P450 oxidoreductase

Cytochrome P450 (CYP) heme monooxygenases require two electrons for their catalytic cycle. For mammalian microsomal CYPs, key enzymes for xenobiotic metabolism and steroidogenesis and important drug targets and biocatalysts, the electrons are transferred by NADPH-cytochrome P450 oxidoreductase (CPR). No structure of a mammalian CYP-CPR complex has been solved experimentally, hindering understanding of the determinants of electron transfer (ET), which is often rate-limiting for CYP reactions. Here, we investigated the interactions between membrane-bound CYP 1A1, an antitumor drug target, and CPR by a multiresolution computational approach. We find that upon binding to CPR, the CYP 1A1 catalytic domain becomes less embedded in the membrane and reorients, indicating that CPR may affect ligand passage to the CYP active site. Despite the constraints imposed by membrane binding, we identify several arrangements of CPR around CYP 1A1 that are compatible with ET. In the complexes, the interactions of the CPR FMN domain with the proximal side of CYP 1A1 are supplemented by more transient interactions of the CPR NADP domain with the distal side of CYP 1A1. Computed ET rates and pathways agree well with available experimental data and suggest why the CYP-CPR ET rates are low compared to those of soluble bacterial CYPs.

DFT Case Study of the Mechanism of a Metal-Free Oxygen Atom Insertion into a p-Quinone Methide C(sp3)-C(sp2) Bond

The site-selective introduction of an oxygen atom into an organic molecule, without the assistance of metals, is a useful transformation, though understanding the mechanistic underpinning of such a process is oftentimes a challenging task. In exploring this chemical space and in building upon experimental precedents, we have utilized computational tools to delineate the mechanistic details of site-selective oxygen atom insertion into a p-quinone methide C(sp³)-C(sp²) bond. To this end, several different reaction pathways for oxygen atom insertion were explored-each encompassing a unique element qualifying the respective pathway as being more or less feasible. The findings of these investigations revealed several features that were vital to this reactivity, including the formation of a dimeric intermediate, interconversion between ground- and excited-state species, and strain. Notably, the latter finding adds to the portfolio of strain-release-driven reactions that have emerged as popular methods to achieve otherwise difficult chemical transformations.

Structure and Function of the Cytochrome P450 Monooxygenase Cinnamate 4-hydroxylase from Sorghum bicolor

Cinnamate 4-hydroxylase (C4H; CYP73A) is a cytochrome P450 monooxygenase associated externally with the endoplasmic reticulum of plant cells. The enzyme uses NADPH-cytochrome P450 reductase as a donor of electrons and hydroxylates cinnamic acid to form 4-coumaric acid in phenylpropanoid metabolism. In order to better understand the structure and function of this unique class of plant P450 enzymes, we have characterized the enzyme C4H1 from lignifying tissues of sorghum (Sorghum bicolor), encoded by Sobic.002G126600 Here we report the 1.7 Å resolution crystal structure of CYP73A33. The obtained structural information, along with the results of the steady-state kinetic analysis and the absorption spectroscopy titration, displays a high degree of similarity of the structural and functional features of C4H to those of other P450 proteins. Our data also suggest the presence of a putative allosteric substrate-binding site in a hydrophobic pocket on the enzyme surface. In addition, comparing the newly resolved structure with those of well-investigated cytochromes P450 from mammals and bacteria enabled us to identify those residues of critical functional importance and revealed a unique sequence signature that is potentially responsible for substrate specificity and catalytic selectivity of C4H.

How a cofactor-free protein environment lowers the barrier to O2 reactivity

Molecular oxygen (O₂)-utilizing enzymes are among the most important in biology. The abundance of O₂, its thermodynamic power, and the benign nature of its end products have raised interest in oxidases and oxygenases for biotechnological applications. Although most O₂-dependent enzymes have an absolute requirement for an O₂-activating cofactor, several classes of oxidases and oxygenases accelerate direct reactions between substrate and O₂ using only the protein environment. Nogalamycin monooxygenase (NMO) from Streptomyces nogalater is a cofactor-independent enzyme that catalyzes rate-limiting electron transfer between its substrate and O₂ Here, using enzyme-kinetic, cyclic voltammetry, and mutagenesis methods, we demonstrate that NMO initially activates the substrate, lowering its pK_a by 1.0 unit (ΔG* = 1.4 kcal mol^-1). We found that the one-electron reduction potential, measured for the deprotonated substrate both inside and outside the protein environment, increases by 85 mV inside NMO, corresponding to a ΔΔG ⁰' of 2.0 kcal mol^-1 (0.087 eV) and that the activation barrier, ΔG ^‡, is lowered by 4.8 kcal mol^-1 (0.21 eV). Applying the Marcus model, we observed that this suggests a sizable decrease of 28 kcal mol^-1 (1.4 eV) in the reorganization energy (λ), which constitutes the major portion of the protein environment's effect in lowering the reaction barrier. A similar role for the protein has been proposed in several cofactor-dependent systems and may reflect a broader trend in O₂-utilizing proteins. In summary, NMO's protein environment facilitates direct electron transfer, and NMO accelerates rate-limiting electron transfer by strongly lowering the reorganization energy.

Insight into conformationally-dependent binding of 1-n-alkyl-3-methylimidazolium cations to porphyrin molecules using quantum mechanical calculations

The first step in the biodegradation of imidazolium-based ionic liquids involves the insertion of the –OH group into the alkyl side chain, and it is believed to be triggered by cytochrome P450. In this work, we investigate the effect of conformations on binding energies of ionic liquid cations to the catalytic center of P450.

Ligand Access Channels in Cytochrome P450 Enzymes: A Review

Quantitative structure-activity relationships may bring invaluable information on structural elements of both enzymes and substrates that, together, govern substrate specificity. Buried active sites in cytochrome P450 enzymes are connected to the solvent by a network of channels exiting at the distal surface of the protein. This review presents different in silico tools that were developed to uncover such channels in P450 crystal structures. It also lists some of the experimental evidence that actually suggest that these predicted channels might indeed play a critical role in modulating P450 functions. Amino acid residues at the entrance of the channels may participate to a first global ligand recognition of ligands by P450 enzymes before they reach the buried active site. Moreover, different P450 enzymes show different networks of predicted channels. The plasticity of P450 structures is also important to take into account when looking at how channels might play their role.

Biochemical and structural characterization of CYP109A2, a vitamin D3 25-hydroxylase from Bacillus megaterium

Cytochrome P450 enzymes are increasingly investigated due to their potential application as biocatalysts with high regio- and/or stereo-selectivity and under mild conditions. Vitamin D₃ (VD₃ ) metabolites are of pharmaceutical importance and are applied for the treatment of VD₃ deficiency and other disorders. However, the chemical synthesis of VD₃ derivatives shows low specificity and low yields. In this study, cytochrome P450 CYP109A2 from Bacillus megaterium DSM319 was expressed, purified, and shown to oxidize VD₃ with high regio-selectivity. The in vitro conversion, using cytochrome P450 reductase (BmCPR) and ferredoxin (Fdx2) from the same strain, showed typical Michaelis-Menten reaction kinetics. A whole-cell system in B. megaterium overexpressing CYP109A2 reached 76 ± 5% conversion after 24 h and allowed to identify the main product by NMR analysis as 25-hydroxylated VD₃ . Product yield amounted to 54.9 mg·L^-1 ·day^-1 , rendering the established whole-cell system as a highly promising biocatalytic route for the production of this valuable metabolite. The crystal structure of substrate-free CYP109A2 was determined at 2.7 Å resolution, displaying an open conformation. Structural analysis predicts that CYP109A2 uses a highly similar set of residues for VD₃ binding as the related VD₃ hydroxylases CYP109E1 from B. megaterium and CYP107BR1 (Vdh) from Pseudonocardia autotrophica. However, the folds and sequences of the BC loops in these three P450s are highly divergent, leading to differences in the shape and apolar/polar surface distribution of their active site pockets, which may account for the observed differences in substrate specificity and the regio-selectivity of VD₃ hydroxylation.

DATABASE

The atomic coordinates and structure factors have been deposited in the Protein Data Bank with accession code 5OFQ (substrate-free CYP109A2).

ENZYMES

Cytochrome P450 monooxygenase CYP109A2, EC 1.14.14.1, UniProt ID: D5DF88, Ferredoxin, UniProt ID: D5DFQ0, cytochrome P450 reductase, EC 1.8.1.2, UniProt ID: D5DGX1.

ROS Signaling in the Pathogenesis of Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS)

The generation of reactive oxygen species (ROS) plays an important role for the maintenance of cellular processes and functions in the body. However, the excessive generation of oxygen radicals under pathological conditions such as acute lung injury (ALI) and its most severe form acute respiratory distress syndrome (ARDS) leads to increased endothelial permeability. Within this hallmark of ALI and ARDS, vascular microvessels lose their junctional integrity and show increased myosin contractions that promote the migration of polymorphonuclear leukocytes (PMNs) and the transition of solutes and fluids in the alveolar lumen. These processes all have a redox component, and this chapter focuses on the role played by ROS during the development of ALI/ARDS. We discuss the origins of ROS within the cell, cellular defense mechanisms against oxidative damage, the role of ROS in the development of endothelial permeability, and potential therapies targeted at oxidative stress.

Functioning of drug-metabolizing microsomal cytochrome P450s: In silico probing of proteins suggests that the distal heme 'active site' pocket plays a relatively 'passive role' in some enzyme-substrate interactions

PURPOSE

The currently held mechanistic understanding of microsomal cytochrome P450s (CYPs) seeks that diverse drug molecules bind within the deep-seated distal heme pocket and subsequently react at the heme centre. To explain a bevy of experimental observations and meta-analyses, we indulge a hypothesis that involves a "diffusible radical mediated" mechanism. This new hypothesis posits that many substrates could also bind at alternate loci on/within the enzyme and be reacted without the pertinent moiety accessing a bonding proximity to the purported catalytic Fe-O enzyme intermediate.

METHODS

Through blind and heme-distal pocket centered dockings of various substrates and non-substrates (drug molecules of diverse sizes, classes, topographies etc.) of microsomal CYPs, we explored the possibility of access of substrates via the distal channels, its binding energies, docking orientations, distance of reactive moieties (or molecule per se) to/from the heme centre, etc. We investigated specific cases like- (a) large drug molecules as substrates, (b) classical marker drug substrates, (c) class of drugs as substrates (Sartans, Statins etc.), (d) substrate preferences between related and unrelated CYPs, (e) man-made site-directed mutants' and naturally occurring mutants' reactivity and metabolic disposition, (f) drug-drug interactions, (g) overall affinities of drug substrate versus oxidized product, (h) meta-analysis of in silico versus experimental binding constants and reaction/residence times etc.

RESULTS

It was found that heme-centered dockings of the substrate/modulator drug molecules with the available CYP crystal structures gave poor docking geometries and distances from Fe-heme centre. In conjunction with several other arguments, the findings discount the relevance of erstwhile hypothesis in many CYP systems. Consequently, the newly proposed hypothesis is deemed a viable alternate, as it satisfies Occam's razor.

CONCLUSIONS

The new proposal affords expanded scope for explaining the mechanism, kinetics and overall phenomenology of CYP mediated drug metabolism. It is now understood that the heme-iron and the hydrophobic distal pocket of CYPs serve primarily to stabilize the reactive intermediate (diffusible radical) and the surface or crypts of the apoprotein bind to the xenobiotic substrate (and in some cases, the heme distal pocket could also serve the latter function). Thus, CYPs enhance reaction rates and selectivity/specificity via a hitherto unrecognized modality.

Structural basis of steroid binding and oxidation by the cytochrome P450 CYP109E1 from Bacillus megaterium

Cytochrome P450 monooxygenases (P450s) are attractive enzymes for the pharmaceutical industry, in particular, for applications in steroidal drug synthesis. Here, we report a comprehensive functional and structural characterization of CYP109E1, a novel steroid‐converting cytochrome P450 enzyme identified from the genome of Bacillus megaterium DSM319. In vitro and whole‐cell in vivo turnover experiments, combined with binding assays, revealed that CYP109E1 is able to hydroxylate testosterone at position 16β. Related steroids with bulky substituents at carbon C17, like corticosterone, bind to the enzyme without being converted. High‐resolution X‐ray structures were solved of a steroid‐free form of CYP109E1 and of complexes with testosterone and corticosterone. The structural analysis revealed a highly dynamic active site at the distal side of the heme, which is wide open in the absence of steroids, can bind four ordered corticosterone molecules simultaneously, and undergoes substantial narrowing upon binding of single steroid molecules. In the crystal structures, the single bound steroids adopt unproductive binding modes coordinating the heme‐iron with their C3‐keto oxygen. Molecular dynamics (MD) simulations suggest that the steroids may also bind in ~180° reversed orientations with the C16 carbon and C17‐substituents pointing toward the heme, leading to productive binding of testosterone explaining the observed regio‐ and stereoselectivity. The X‐ray structures and MD simulations further identify several residues with important roles in steroid binding and conversion, which could be confirmed by site‐directed mutagenesis. Taken together, our results provide unique insights into the CYP109E1 activity, substrate specificity, and regio/stereoselectivity.

Database

The atomic coordinates and structure factors have been deposited in the Protein Data Bank with accession codes 5L90 (steroid‐free CYP109E1), 5L91 (CYP109E1‐COR4), 5L94 (CYP109E1‐TES), and 5L92 (CYP109E1‐COR).

Enzymes

Cytochrome P450 monooxygenase CYP109E1, EC 1.14.14.1, UniProt ID: D5DKI8, Adrenodoxin reductase EC 1.18.1.6.

Analysis of the complex formation, interaction and electron transfer pathway between the "open" conformation of NADPH-cytochrome P450 reductase and aromatase

The complex structure of human aromatase (CYP19) and the open form of ΔTGEE mutant NADPH-cytochrome P450 reductase (mCPR) was constructed using template-based protein alignment method. Dynamic simulation of formed complex was performed on NAMD 2.9, in which CHARMm all 27_prot_lipid_na force field and an explicit TIP3P water solvent model were applied. The result showed mCPR in its open conformation could steadily combine with aromatase from the proximal face. Data analysis indicates hydrogen bonds and four salt bridges on the binding surface enhance the interaction between the two protein molecules. Amino acid, Lys108 plays a key role in aromatase activity through the formation of a salt bridge with Asp147 and two hydrogen bonds with Asp147 and Gln150 in mCPR. The optimal pathway for the first electron transfer from CPR to aromatase was revealed and calculated using HARLEM software. The rates for solvent mediated and non-solvent mediated electron transfer from FMNH2 to heme were determined as 1.04×10(6)s(-)(1) and 4.86×10(5)s(-)(1) respectively, which indicates the solvent water can facilitate the electron transfer from FMNH2 to heme. This study presents a novel strategy for the study of the protein-protein interactions based on the template-based protein alignment, which may help new aromtase development targeting the electron transfer between mCPR and aromatase.

Mechanistic elucidation of C-H oxidation by electron rich non-heme iron(IV)-oxo at room temperature

Non-heme iron(IV)-oxo species form iron(III) intermediates during hydrogen atom abstraction (HAA) from the C-H bond. While synthesizing a room temperature stable, electron rich, non-heme iron(IV)-oxo compound, we obtained iron(III)-hydroxide, iron(III)-alkoxide and hydroxylated-substrate-bound iron(II) as the detectable intermediates. The present study revealed that a radical rebound pathway was operative for benzylic C-H oxidation of ethylbenzene and cumene. A dissociative pathway for cyclohexane oxidation was established based on UV-vis and radical trap experiments. Interestingly, experimental evidence including O-18 labeling and mechanistic study suggested an electron transfer mechanism to be operative during C-H oxidation of alcohols (e.g. benzyl alcohol and cyclobutanol). The present report, therefore, unveils non-heme iron(IV)-oxo promoted substrate-dependent C-H oxidation pathways which are of synthetic as well as biological significance.

Interactions between CYP3A4 and Dietary Polyphenols

The human cytochrome P450 enzymes (P450s) catalyze oxidative reactions of a broad spectrum of substrates and play a critical role in the metabolism of xenobiotics, such as drugs and dietary compounds. CYP3A4 is known to be the main enzyme involved in the metabolism of drugs and most other xenobiotics. Dietary compounds, of which polyphenolics are the most studied, have been shown to interact with CYP3A4 and alter its expression and activity. Traditionally, the liver was considered the prime site of CYP3A-mediated first-pass metabolic extraction, but in vitro and in vivo studies now suggest that the small intestine can be of equal or even greater importance for the metabolism of polyphenolics and drugs. Recent studies have pointed to the role of gut microbiota in the metabolic fate of polyphenolics in human, suggesting their involvement in the complex interactions between dietary polyphenols and CYP3A4. Last but not least, all the above suggests that coadministration of drugs and foods that are rich in polyphenols is expected to stimulate undesirable clinical consequences. This review focuses on interactions between dietary polyphenols and CYP3A4 as they relate to structural considerations, food-drug interactions, and potential negative consequences of interactions between CYP3A4 and polyphenols.

Evaluation of Tetrahydropalmatine Enantiomers on the Activity of Five Cytochrome P450 Isozymes in Rats Using a Liquid Chromatography / Mass Spectrometric Method and a Cocktail Approach

The aim was to evaluate the effects of tetrahydropalmatine (THP) enantiomers on the activity of five cytochrome P450 (CYP450) isozymes in vivo. A liquid chromatography / mass spectrometric (LC-MS) method was developed for simultaneous determination of five specific probe substrates including metoprolol (2D6), caffeine (1A2), dapsone (3A4), chlorzoxazone (2E1), and tolbutamide (2C9) in rat plasma. Analytes were separated with the mobile phase consisting of 0.1% acetic acid aqueous solution and acetonitrile in a gradient elution. The mass spectrometric detection via selected ion monitoring (SIM) was operated in both positive ion mode (for metoprolol m/z 268, caffeine m/z 195, and dapsone m/z 249) and negative ion mode (for chlorzoxazone m/z 168 and tolbutamide m/z 269) in the same run. Linear correlation was obtained (r(2)  > 0.99) over the concentration range of 0.050-25.0 µg/mL for caffeine and dapsone, 0.025-10.0 µg/mL for metoprolol, 0.050-50.0 µg/mL for chlorzoxazone, and 0.25-100.0 µg/mL for tolbutamide. Intra- and interday precision were less than 12.09%. The matrix effect ranged from 87.50% to 109.25% and the absolute recoveries were greater than 70%. The method was successfully applied to evaluate the effect of THP enantiomers on the activity of CYP450 isozymes by a cocktail approach. The pharmacokinetic results of five probe drugs indicated that there were stereoselective differences between the two THP enantiomers, i.e., d-THP had the potential to inhibit the activities of CYP2D6 and CYP1A2 isozymes, while l-THP inhibited CYP1A2 isozyme and induced CYP3A4 and CYP2C9 isozymes.

Oxidation of methane by an N-bridged high-valent diiron–oxo species: electronic structure implications on the reactivity

Methane activation by dinuclear high-valent iron–oxo species: do we need two metals to activate such inert bonds? Our theoretical study using DFT methods where electronic structure details and mechanistic aspects are established answers this intriguing question.

Human recombinant cytochrome P450 enzymes display distinct hydrogen peroxide generating activities during substrate independent NADPH oxidase reactions

Microsomal enzymes generate H2O2 in the presence of NADPH. In this reaction, referred to as "oxidase" activity, H2O2 is generated directly or indirectly via the formation of superoxide anion. In the presence of redox active transition metals, H2O2 can form highly toxic hydroxyl radicals and, depending on the "oxidase" activity of individual cytochrome P450 isoenzymes, this can compromise cellular functioning and contribute to tissue injury. In the present studies, we compared the initial rates of H2O2 generating activity of microsomal preparations containing various human recombinant cytochromes P450s. In the absence of cytochrome P450s the human recombinant NADPH cytochrome P450 reductase (CPR) generated low, but detectable amounts of H2O2 (∼0.04 nmol H2O2/min/100 units of reductase). Significantly greater activity was detected in preparations containing individual cytochrome P450s coexpressed with CPR (from 6.0 nmol H2O2/min/nmol P450 to 0.2 nmol/min/nmol P450); CYP1A1 was the most active, followed by CYP2D6, CYP3A4, CYP2E1, CYP4A11, CYP1A2, and CYP2C subfamily enzymes. H2O2 generating activity of the cytochrome P450s was independent of the ratio of CYP/CPR. Thus, similar H2O2 generating activity was noted with the same cytochrome P450s (CYP3A4, CYP2E1, and CYP2C9) expressed at or near the ratio of CYP/CPR in human liver microsomes (5-7), and when CPR was present in excess (CYP/CPR = 0.2-0.3). Because CYP3A4/5/7 represent up to 40% of total cytochrome P450 in the liver, these data indicate that these enzymes are the major source of H2O2 in human liver microsomes.

Electron paramagnetic resonance and electron-nuclear double resonance studies of the reactions of cryogenerated hydroperoxoferric-hemoprotein intermediates

The fleeting ferric peroxo and hydroperoxo intermediates of dioxygen activation by hemoproteins can be readily trapped and characterized during cryoradiolytic reduction of ferrous hemoprotein–O₂ complexes at 77 K. Previous cryoannealing studies suggested that the relaxation of cryogenerated hydroperoxoferric intermediates of myoglobin (Mb), hemoglobin, and horseradish peroxidase (HRP), either trapped directly at 77 K or generated by cryoannealing of a trapped peroxo-ferric state, proceeds through dissociation of bound H₂O₂ and formation of the ferric heme without formation of the ferryl porphyrin π-cation radical intermediate, compound I (Cpd I). Herein we have reinvestigated the mechanism of decays of the cryogenerated hydroperoxyferric intermediates of α- and β-chains of human hemoglobin, HRP, and chloroperoxidase (CPO). The latter two proteins are well-known to form spectroscopically detectable quasistable Cpds I. Peroxoferric intermediates are trapped during 77 K cryoreduction of oxy Mb, α-chains, and β-chains of human hemoglobin and CPO. They convert into hydroperoxoferric intermediates during annealing at temperatures above 160 K. The hydroperoxoferric intermediate of HRP is trapped directly at 77 K. All studied hydroperoxoferric intermediates decay with measurable rates at temperatures above 170 K with appreciable solvent kinetic isotope effects. The hydroperoxoferric intermediate of β-chains converts to the S = 3/2 Cpd I, which in turn decays to an electron paramagnetic resonance (EPR)-silent product at temperature above 220 K. For all the other hemoproteins studied, cryoannealing of the hydroperoxo intermediate directly yields an EPR-silent majority product. In each case, a second follow-up 77 K γ-irradiation of the annealed samples yields low-spin EPR signals characteristic of cryoreduced ferrylheme (compound II, Cpd II). This indicates that in general the hydroperoxoferric intermediates relax to Cpd I during cryoanealing at low temperatures, but when this state is not captured by reaction with a bound substrate, it is reduced to Cpd II by redox-active products of radiolysis.

Anchoring a plant cytochrome P450 via PsaM to the thylakoids in Synechococcus sp. PCC 7002: evidence for light-driven biosynthesis

Plants produce an immense variety of specialized metabolites, many of which are of high value as their bioactive properties make them useful as for instance pharmaceuticals. The compounds are often produced at low levels in the plant, and due to their complex structures, chemical synthesis may not be feasible. Here, we take advantage of the reducing equivalents generated in photosynthesis in developing an approach for producing plant bioactive natural compounds in a photosynthetic microorganism by functionally coupling a biosynthetic enzyme to photosystem I. This enables driving of the enzymatic reactions with electrons extracted from the photosynthetic electron transport chain. As a proof of concept, we have genetically fused the soluble catalytic domain of the cytochrome P450 CYP79A1, originating from the endoplasmic reticulum membranes of Sorghum bicolor, to a photosystem I subunit in the cyanobacterium Synechococcus sp. PCC 7002, thereby targeting it to the thylakoids. The engineered enzyme showed light-driven activity both in vivo and in vitro, demonstrating the possibility to achieve light-driven biosynthesis of high-value plant specialized metabolites in cyanobacteria.

Redirecting photosynthetic electron flow into light-driven synthesis of alternative products including high-value bioactive natural compounds

Photosynthesis in plants, green algae, and cyanobacteria converts solar energy into chemical energy in the form of ATP and NADPH, both of which are used in primary metabolism. However, often more reducing power is generated by the photosystems than what is needed for primary metabolism. In this review, we discuss the development in the research field, focusing on how the photosystems can be used as synthetic biology building blocks to channel excess reducing power into light-driven production of alternative products. Plants synthesize a large number of high-value bioactive natural compounds. Some of the key enzymes catalyzing their biosynthesis are the cytochrome P450s situated in the endoplasmic reticulum. However, bioactive compounds are often synthesized in low quantities in the plants and are difficult to produce by chemical synthesis due to their often complex structures. Through a synthetic biology approach, enzymes with a requirement for reducing equivalents as cofactors, such as the cytochrome P450s, can be coupled directly to the photosynthetic energy output to obtain environmentally friendly production of complex chemical compounds. By relocating cytochrome P450s to the chloroplasts, reducing power can be diverted toward the reactions catalyzed by the cytochrome P450s. This provides a sustainable production method for high-value compounds that potentially can solve the problem of NADPH regeneration, which currently limits the biotechnological uses of cytochrome P450s. We describe the approaches that have been taken to couple enzymes to photosynthesis in vivo and to photosystem I in vitro and the challenges associated with this approach to develop new green production platforms.

7,8- and 5,8-Linoleate diol synthases support the heterolytic scission of oxygen-oxygen bonds by different amide residues

Linoleate diol synthases (LDS) are fungal dioxygenase-cytochrome P450 fusion enzymes. They oxidize 18:2n-6 sequentially to 8R-hydroperoxylinoleic acid (8R-HPODE) and 7S,8S- or 5S,8R-dihydroxylinoleic acids (DiHODE) by intramolecular oxygen transfer. The P450 domains contain a conserved sequence, Ala-Asn-Gln-Xaa-Gln, presumably located in the I-helices. The Asn938Leu replacement of 7,8-LDS of Gaeumannomyces graminis virtually abolished and the Asn938Asp and Asn938Gln replacements reduced the hydroperoxide isomerase activity. Gln941Leu and Gln941Glu substitutions had little effects. Replacements of the homologous Asn(887) and Gln(890) residues of 5,8-LDS of Aspergillus fumigatus yielded the opposite results. Asn887Leu and Asn887Gln of 5,8-LDS retained 5,8-DiHODE as the main metabolite with an increased formation of 6,8- and 8,11-DiHODE, whereas Gln890Leu almost abolished the 5,8-LDS activity. Replacement of Gln(890) with Glu also retained 5,8-DiHODE as the main product, but shifted oxygenation from C-5 to C-7 and C-11 and to formation of epoxyalcohols by homolytic scission of 8R-HPODE. P450 hydroxylases usually contain an "acid-alcohol" pair in the I-helices for the heterolytic scission of O2 and formation of compound I (Por(+) Fe(IV)=O) and water. The function of the acid-alcohol pair appears to be replaced by two different amide residues, Asn(938) of 7,8-LDS and Gln(890) of 5,8-LDS, for heterolysis of 8R-HPODE to generate compound I.

Redirecting photosynthetic reducing power toward bioactive natural product synthesis

In addition to the products of photosynthesis, the chloroplast provides the energy and carbon building blocks required for synthesis of a wealth of bioactive natural products of which many have potential uses as pharmaceuticals. In the course of plant evolution, energy generation and biosynthetic capacities have been compartmentalized. Chloroplast photosynthesis provides ATP and NADPH as well as carbon sources for primary metabolism. Cytochrome P450 monooxygenases (P450s) in the endoplasmic reticulum (ER) synthesize a wide spectrum of bioactive natural products, powered by single electron transfers from NADPH. P450s are present in low amounts, and the reactions proceed relatively slowly due to limiting concentrations of NADPH. Here we demonstrate that it is possible to break the evolutionary compartmentalization of energy generation and P450-catalyzed biosynthesis, by relocating an entire P450-dependent pathway to the chloroplast and driving the pathway by direct use of the reducing power generated by photosystem I in a light-dependent manner. The study demonstrates the potential of transferring pathways for structurally complex high-value natural products to the chloroplast and directly tapping into the reducing power generated by photosynthesis to drive the P450s using water as the primary electron donor.

Hydrogen peroxide and ecdysone in the cryoprotective dehydration strategy of Megaphorura arctica (Onychiuridae: Collembola)

The Arctic springtail, Megaphorura arctica, survives sub-zero temperatures in a dehydrated state via trehalose-dependent cryoprotective dehydration. Regulation of trehalose biosynthesis is complex; based in part on studies in yeast and fungi, its connection with oxidative stress caused by exposure of cells to oxidants, such as hydrogen peroxide (H₂O₂), or dehydration, is well documented. In this respect, we measured the amount of H₂O₂ and antioxidant enzyme activities (superoxide dismutases: copper, zinc--CuZnSOD and manganese containing--MnSOD, and catalase--CAT), as the regulatory components determining H₂O₂ concentrations, in Arctic springtails incubated at 5 °C (control) versus -2 °C (threshold temperature for trehalose biosynthesis). Because ecdysone also stimulates trehalose production in insects and regulates the expression of genes involved in redox homeostasis and antioxidant protection in Drosophila, we measured the levels of the active physiological form of ecdysone--20-hydroxyecdysone (20-HE). Significantly elevated H₂O₂ and 20-HE levels were observed in M. arctica incubated at -2 °C, supporting a link between ecdysone, H₂O₂, and trehalose levels during cryoprotective dehydration. CAT activity was found to be significantly lower in M. arctica incubated at -2 °C versus 5 °C, suggesting reduced H₂O₂ breakdown. Furthermore, measurement of the free radical composition in Arctic springtails incubated at 5 °C (controls) versus -2 °C by Electron Paramagnetic Resonance spectroscopy revealed melanin-derived free radicals at -2 °C, perhaps an additional source of H₂O₂. Our results suggest that H₂O₂ and ecdysone play important roles in the cryoprotective dehydration process in M. arctica, linked with the regulation of trehalose biosynthesis.

Genetic polymorphisms of the CYP3A4, CYP3A5, CYP3A7 and CYP1A2 among the Jordanian population

Cytochromes P450 (CYP450) plays an extremely vital role in oxidation, reduction, and peroxidation of numerous endogenous and exogenous compounds, like drugs and procarcinogens. Mainly, expression occurs in the liver, in varying polymorphic forms. Therefore, proposed as biomarkers of susceptibility to carcinogenicity and toxicity. The objective of this study was to find the allelic frequencies of CYP3A5*2,*3,*4,*5,*6,*7, CYP3A4*1B, CYP3A7*1C and CYP1A2*1C, *1D, *1E, *1F enzymes in Jordanians, and to compare them with other ethnic groups. We used polymerase chain reaction-restriction fragment length (PCR-RFLP) to genotype alleles, and we calculated frequencies using Hardy Weinberg's equation (HWE). Allelic frequencies results were: CYP3A5*2 (0.2%), CYP3A5*3 (86.6%), CYP3A5*6 (1.7%), CYP*3A5*4,*5*7 not detected, CYP3A4*1B (11.7%), CYP3A7*1C (1.7%). Finally 6.5%, 18.2%, 6.0%, 67.3% were the results of CYP1A2*1C, 1D, 1E and 1F, respectively. In conclusion, genotyping method and results of this study can be adopted or used in pharmacotherapy, toxicity and carcinogenic studies in Jordan.