Tight binding of cytochrome b5 to cytochrome P450 17A1 is a critical feature of stimulation of C21 steroid lyase activity and androgen synthesis

Steroidogenic cytochrome P450 enzymes as drug target

Human cytochrome P450 (CYP) enzymes are composed of 57 individual enzymes that perform monooxygenase activities. They have diverse physiological roles in metabolizing xenobiotics and producing important endogenous compounds, such as steroid hormones and vitamins. At least seven CYP enzymes are involved in steroid biosynthesis. Steroidogenesis primarily occurs in the adrenal glands and gonads, connecting each reaction to substrates and products. Steroids are essential for maintaining life and significantly contribute to sexual differentiation and reproductive functions within the body. Disorders in steroid biosynthesis can frequently cause serious health problems and lead to the development of diseases, such as prostate cancer, breast cancer, and Cushing's syndrome. In this review, we provide current updated knowledge on the major CYP enzymes involved in the biosynthetic process of steroids, with respect to their enzymatic mechanisms and clinical implications for the development of new drug candidates.

Catalytic enhancements in cytochrome P450 2C19 by cytochrome b5

Human cytochrome P450 2C19 catalyzes P450 enzyme reactions of various substrates, including steroids and clinical drugs. Recombinant P450 2C19 enzyme with histidine tag was successfully expressed in Escherichia coli and purified using affinity column chromatography. Ultra-performance liquid chromatography-tandem mass (UPLC-MS/MS) spectrometry showed that the purified P450 2C19 enzyme catalyzed 5-hydroxylation reaction of omeprazole. The purified enzyme displayed typical type I binding spectra to progesterone with a Kd value of 4.5 ± 0.2 µM, indicating a tight substrate binding. P450 2C19 catalyzed the hydroxylation of progesterone to produce 21-hydroxy (OH) as a major and 17-OH product as a minor product. Steady-state kinetic analysis of progesterone 21-hydroxylation indicated that the addition of cytochrome b5 stimulated a five-times catalytic turnover number of P450 2C19 with a kcat value of 1.07 ± 0.08 min-1. The molecular docking model of progesterone in the active site of P450 2C19 displayed that the 21-carbon of progesterone was located close to the heme with a distance of 4.7 Å, suggesting 21-hydroxylation of progesterone is the optimal reaction of P450 2C19 enzyme for a productive orientation of the substrate. Our findings will help investigate the extent to which cytochrome b5 affects the metabolism of P450 2C19 to drugs and steroids.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00219-8.

Proteomics, modeling, and fluorescence assays delineate cytochrome b5 residues involved in binding and stimulation of cytochrome P450 17A1 17,20-lyase

Cytochrome b5 (b5) is known to stimulate some catalytic activities of cytochrome P450 (P450, CYP) enzymes, although mechanisms still need to be defined. The reactions most strongly enhanced by b5 are the 17,20-lyase reactions of P450 17A1 involved in steroid biosynthesis. We had previously used a fluorescently labeled human b5 variant (Alexa 488-T70C-b5) to characterize human P450 17A1-b5 interactions, but subsequent proteomic analyses indicated that lysines in b5 were also modified with Alexa 488 maleimide in addition to Cys-70, due to disulfide dimerization of the T70C mutant. A series of b5 variants were constructed with Cys replacements for the identified lysine residues and labeled with the dye. Fluorescence attenuation and the function of b5 in the steroid lyase reaction depended on the modified position. Apo-b5 (devoid of heme group) studies revealed the lack of involvement of the b5 heme in the fluorescence attenuation. A structural model of b5 with P450 17A1 was predicted using AlphaFold-Multimer algorithms/Rosetta docking, based upon the individual structures, which predicted several new contacts not previously reported, that is, interactions of b5 Glu-48:17A1 Arg-347, b5 Glu-49:17A1 Arg-449, b5 Asp-65:17A1 Arg-126, b5 Asp-65:17A1 Arg-125, and b5 Glu-61:17A1 Lys-91. Fluorescence polarization assays with two modified b5 variants yielded Kd values (for b5-P450 17A1) of 120 to 380 nM, the best estimate of binding affinity. We conclude that both monomeric and dimeric b5 can bind to P450 17A1 and stimulate activity. Results with the mutants indicate that several Lys residues in b5 are sensitive to the interaction with P450 17A1, including Lys-88 and Lys-91.

Ninety-eight semesters of cytochrome P450 enzymes and related topics-What have I taught and learned?

This Reflection article begins with my family background and traces my career through elementary and high school, followed by time at the University of Illinois, Vanderbilt University, the University of Michigan, and then for 98 semesters as a Vanderbilt University faculty member. My research career has dealt with aspects of cytochrome P450 enzymes, and the basic biochemistry has had applications in fields as diverse as drug metabolism, toxicology, medicinal chemistry, pharmacogenetics, biological engineering, and bioremediation. I am grateful for the opportunity to work with the Journal of Biological Chemistry not only as an author but also for 34 years as an Editorial Board Member, Associate Editor, Deputy Editor, and interim Editor-in-Chief. Thanks are extended to my family and my mentors, particularly Profs. Harry Broquist and Minor J. Coon, and the more than 170 people who have trained with me. I have never lost the enthusiasm for research that I learned in the summer of 1968 with Harry Broquist, and I have tried to instill this in the many trainees I have worked with. A sentence I use on closing slides is "It's not just a laboratory-it's a fraternity."

The steroid hormone ADIOL promotes learning by reducing neural kynurenic acid levels

Reductions in brain kynurenic acid levels, a neuroinhibitory metabolite, improve cognitive function in diverse organisms. Thus, modulation of kynurenic acid levels is thought to have therapeutic potential in a range of brain disorders. Here we report that the steroid 5-androstene 3β, 17β-diol (ADIOL) reduces kynurenic acid levels and promotes associative learning in Caenorhabditis elegans We identify the molecular mechanisms through which ADIOL links peripheral metabolic pathways to neural mechanisms of learning capacity. Moreover, we show that in aged animals, which normally experience rapid cognitive decline, ADIOL improves learning capacity. The molecular mechanisms that underlie the biosynthesis of ADIOL as well as those through which it promotes kynurenic acid reduction are conserved in mammals. Thus, rather than a minor intermediate in the production of sex steroids, ADIOL is an endogenous hormone that potently regulates learning capacity by causing reductions in neural kynurenic acid levels.

Peptide nanostructures-based delivery of DNA nanomaterial therapeutics for regulating gene expression

Self-assembled branched DNA (bDNA) nanomaterials have exhibited their functionality in various biomedical and diagnostic applications. However, the anionic cellular membrane has restricted the movement of bDNA nanostructures. Recently, amphiphilic peptides have been investigated as cationic delivery agents for nucleic acids. Herein, we demonstrate a strategy for delivering functional bDNA nanomaterials into mammalian cells using self-assembled linear peptides. In this study, antisense oligonucleotides of vascular endothelial growth factor (VEGF) were inserted in the overhangs of bDNAs. Novel linear peptides have been synthesized and the peptide-bound bDNA complex formation was examined using various biophysical experiments. Interestingly, the W4R4-bound bDNAs were found to be exceptionally stable against DNase I compared to other complexes. The delivery of fluorescent-labeled bDNAs into the mammalian cells confirmed the potential of peptide transporters. Furthermore, the functional efficacy of the peptide-bound bDNAs has been examined through RT-PCR and western blot analysis. The observed results revealed that W4R4 peptides exhibited excellent internalization of antisense bDNAs and significantly suppressed (3- to 4-fold) the transcripts and translated product of VEGF compared to the control. In summary, the results highlight the potential use of peptide-based nanocarrier for delivering bDNA nanostructures to regulate the gene expression in cell lines.

Non-steroidal CYP17A1 Inhibitors: Discovery and Assessment

CYP17A1 is an enzyme that plays a major role in steroidogenesis and is critically involved in the biosynthesis of steroid hormones. Therefore, it remains an attractive target in several serious hormone-dependent cancer diseases, such as prostate cancer and breast cancer. The medicinal chemistry community has been committed to the discovery and development of CYP17A1 inhibitors for many years, particularly for the treatment of castration-resistant prostate cancer. The current Perspective reflects upon the discovery and evaluation of non-steroidal CYP17A1 inhibitors from a medicinal chemistry angle. Emphasis is placed on the structural aspects of the target, key learnings from the presented chemotypes, and design guidelines for future inhibitors.

Steroid 17α-hydroxylase/17, 20-lyase (cytochrome P450 17A1)

Cytochrome P450 (P450) 17A1 plays a key role in steroidogenesis, in that this enzyme catalyzes the 17α-hydroxylation of both pregnenolone and progesterone, followed by a lyase reaction to cleave the C-20 land C-21 carbons from each steroid. The reactions are important in the production of both glucocorticoids and androgens. The enzyme is critical in humans but is also a drug target in treatment of prostate cancer. Detailed methods are described for the heterologous expression of human P450 17A1 in bacteria, purification of the recombinant enzyme, reconstitution of the enzyme system in the presence of cytochrome b5, and chromatographic procedures for sensitive analyses of reaction products. Historic assay approaches are reviewed. Some information is also provided about outstanding questions in the research field, including catalytic mechanisms and searches for selective inhibitors.

Hydroxylation and lyase reactions of steroids catalyzed by mouse cytochrome P450 17A1 (Cyp17a1)

Cytochrome P450 17A1 (CYP17A1) catalyzes 17α-hydroxylation and 17,20-lyase reactions with steroid hormones. Mice contain an orthologous Cyp17a1 enzyme in the genome, and its amino acid sequence has high similarity with human CYP17A1. We purified recombinant mouse Cyp17a1 and characterized its oxidation reactions with progesterone and pregnenolone. The open reading frame of the mouse Cyp17a1 gene was inserted and successfully expressed in Escherichia coli and then purified using Ni²⁺-nitrilotriacetic acid (NTA) affinity column chromatography. Purified mouse Cyp17a1 displayed typical Type I binding titration spectral changes upon the addition of progesterone, 17α-OH progesterone, pregnenolone, and 17α-OH pregnenolone, with similar binding affinities to those of human CYP17A1. Catalytic activities for 17α-hydroxylation and 17,20-lyase reactions were studied using ultra-performance liquid chromatography (UPLC)-mass spectrometry analysis. Mouse Cyp17a1 showed cytochrome b₅ stimulation in catalysis. In comparison to human enzyme, much higher specificity constants (k_cat/K_m) were observed with mouse Cyp17a1. In the reactions of Δ4-steroids (progesterone and 17α-OH progesterone), the specificity constants were 2100 times higher than the human enzyme. The addition of cytochrome b₅ produced significant stimulation of 17,20-lyase activities of mouse Cyp17a1. Two Arg mutants of mouse Cyp17a1 (R347H and R358Q) displayed a larger decrease in 17,20-lyase reaction (from 17α-OH pregnenolone to dehydroepiandrosterone, DHEA) than 17α-hydroxylation, indicating that -as in human CYP17A1-these basic residues in mouse Cyp17a1 are important in interacting with the cytochrome b₅ protein in the lyase reactions.

On 'Evidence for the participation of cytochrome b5 in hepatic microsomal mixed-function oxidation reactions' by Alfred Hildebrandt and Ronald W. Estabrook

This paper by Alfred G. Hildebrandt and Ronald W. Estabrook at the University of Texas (Southwestern) Medical School, led to the concept of cytochrome b₅ (b₅) as an auxiliary protein facilitating some cytochrome P450 (P450) reactions in the liver and other tissues. The gist of the paper is that DPNH (now known as NADH) enhanced rates of TPNH (now NADPH)-supported N-demethylation of O-ethylmorphine in rat liver microsomes. The conclusion was that b₅ was providing an electron to the ferrous-oxy form of P450 (Fe²⁺O₂), which was supported by some spectral observations on the oxidation state of b₅ in the microsomes in the steady state. This observation led to a flurry of activity, which is still in progress. This paper has been cited 678 times in Google (558 in Clarivate), and I have often cited it myself. A PubMed search for the terms P450 andb₅ yielded 2244 results.

Zuogui Wan improves spermatogenesis of GC1-spg cells through modulating AR-related pathways

Zuogui Wan (ZGW) is a common prescription medication used in traditional Chinese medicine (TCM) to significantly improve the sperm quality and treat male infertility. This study evaluated the repair effect of ZGW and Levocarnitine (LEV) on GC1-spg cell injury induced by Glucosides of Tripterygium WilforDII Hook (GTW). The results showed that the ultrastructure and apoptosis rate of GC1- spg cells in LEV and ZGW group were considerably better than GTW. The transcriptional and translational level of CYP1A1, CYP17A1, androgen receptor (AR), SRD5A2 and proliferating cell nuclear antigen (PCNA) in GC-1spg cells of the LEV group were considerably elevated than GTW group (p < 0.05 or 0.01). Furthermore, the transcriptional and translational levels of CYP19A1, CYP17A1, AR, SRD5A2 and PCNA in GC-1spg cells in ZGW group were found to be considerably elevated than the LEV group (p < 0.05 or 0.01). The findings indicate that ZGW and LEV could increase the expression of PCNA, CYP17A1, CYP19A1, SRD5A2 and AR at transcriptional and translational levels, inhibit GC-1spg cell apoptosis and promoting cell proliferation, and the effect of ZGW was found to be significantly better than that of LEV.

Insights into Interactions of Human Cytochrome P450 17A1: Review

Abstract:

Cytochrome P450s are a widespread and vast superfamily of hemeprotein monooxygenases that metabolize physiologically essential chemicals necessary for most species' survival, from protists to plants to humans. They catalyze the synthesis of steroid hormones, cholesterol, bile acids, and arachidonate metabolites and the degradation of endogenous compounds such as steroids, fatty acids, and other catabolizing compounds as an energy source and detoxifying xenobiotics such as drugs, procarcinogens, and carcinogens. The human CYP17A1 is one of the cytochrome P450 genes located at the 10q chromosome. The gene expression occurs in the adrenals and gonads, with minor amounts in the brain, placenta, and heart. This P450c17 cytochrome gene is a critical steroidogenesis regulator which performs two distinct activities: 17 alpha-hydroxylase activity (converting pregnenolone to 17-hydroxypregnenolone and progesterone to 17-hydroxyprogesterone, these precursors are further processed to provide glucocorticoids and sex hormones) and 17, 20-lyase activity (which converts 17-hydroxypregnenolone to DHEA). Dozens of mutations within CYP17A1 are found to cause 17-alpha-hydroxylase and 17, 20-lyase deficiency. This condition affects the function of certain hormone-producing glands, resulting in high blood pressure levels (hypertension), abnormal sexual development, and other deficiency diseases. This review highlights the changes in CYP17A1 associated with gene-gene interaction, drug-gene interaction, chemical-gene interaction, and its biochemical reactions; they have some insights to correlate with the fascinating functional characteristics of this human steroidogenic gene. The findings of our theoretical results will be helpful to further the design of specific inhibitors of CYP17A1.

Roles of cytochrome P450 enzymes in pharmacology and toxicology: Past, present, and future

The development of the cytochrome P450 (P450) field has been remarkable in the areas of pharmacology and toxicology, particularly in drug development. Today it is possible to use the knowledge base and relatively straightforward assays to make intelligent predictions about drug disposition prior to human dosing. Much is known about the structures, regulation, chemistry of catalysis, and the substrate and inhibitor specificity of human P450s. Many aspects of drug-drug interactions and side effects can be understood in terms of P450s. This knowledge has also been useful in pharmacy practice, as well as in the pharmaceutical industry and medical practice. However, there are still basic and practical questions to address regarding P450s and their roles in pharmacology and toxicology. Another aspect is the discovery of drugs that inhibit P450 to treat diseases.

Binding of cytochrome P450 27C1, a retinoid desaturase, to its accessory protein adrenodoxin

Of the 57 human cytochrome P450 (P450) enzymes, seven are mitochondrial: 11A1, 11B1, 11B2, 24A1, 27A1, 27B1, and 27C1. Mitochondrial P450s utilize an electron transport system with adrenodoxin (Adx) and NADPH-adrenodoxin reductase (AdR). AdR reduces Adx, which then transfers electrons to the P450. The interactions between proteins in the mitochondrial P450 system are largely driven by electrostatic interactions, though the specifics vary depending on the P450. Unlike other mitochondrial P450s, the interaction between P450 27C1, a retinoid 3,4-desaturase expressed in the skin, and Adx remains largely uncharacterized. In this work, we utilized an Alexa Fluor 488 C₅ maleimide-labeled Adx to measure binding affinities between Adx and P450 27C1 or AdR. Both proteins bound Adx tightly, with K_d values < 100 nM, and binding affinities decreased with increasing ionic strength, supporting the role of electrostatic interactions in mediating these interactions. Cross-linking mass spectrometry and computational modeling were performed to identify interactions between P450 27C1 and Adx. While the residues of Adx identified in interactions were consistent with studies of other mitochondrial P450s, the binding interface of P450 27C1 was quite large and supported multiple Adx binding positions, including ones outside of the canonical Adx binding site. Additionally, Adx did not appear to be an allosteric effector of P450 27C1 substrate binding, in contrast to some other mitochondrial P450s. Overall, we conclude that P450-Adx interactions are P450-specific.

Structure-Functional Analysis of Human Cytochrome P450 2C8 Using Directed Evolution

The human genome includes four cytochrome P450 2C subfamily enzymes, and CYP2C8 has generated research interest because it is subject to drug-drug interactions and various polymorphic outcomes. To address the structure-functional complexity of CYP2C8, its catalytic activity was studied using a directed evolution analysis. Consecutive rounds of random mutagenesis and screening using 6-methoxy-luciferin produced two mutants, which displayed highly increased luciferase activity. Wild-type and selected mutants were expressed on a large scale and purified. The expression levels of the D349Y and D349Y/V237A mutants were ~310 and 460 nmol per liter of culture, respectively. The steady-state kinetic analysis of paclitaxel 6α-hydroxylation showed that the mutants exhibited a 5-7-fold increase in k_cat values and a 3-5-fold increase in catalytic efficiencies (k_cat/K_M). In arachidonic acid epoxidation, two mutants exhibited a 30-150-fold increase in k_cat values and a 40-110-fold increase in catalytic efficiencies. The binding titration analyses of paclitaxel and arachidonic acid showed that the V237A mutation had a lower K_d value, indicating a tighter substrate-binding affinity. The structural analysis of CYP2C8 indicated that the D349Y mutation was close enough to the putative binding domain of the redox partner; the increase in catalytic activity could be partially attributed to the enhancement of the P450 coupling efficiency or electron transfer.

Cytochrome b 5 Binds Tightly to Several Human Cytochrome P450 Enzymes

Numerous studies have been reported in the past 50-plus years regarding the stimulatory role of cytochrome b ₅ (b ₅) in some, but not all, microsomal cytochrome P450 (P450) reactions with drugs and steroids. A missing element in most of these studies has been a sensitive and accurate measure of binding affinities of b ₅ with P450s. In the course of work with P450 17A1, we developed a fluorescent derivative of a human b ₅ site-directed mutant, Alexa 488-T70C-b ₅, that could be used in binding assays at sub-μM concentrations. Alexa 488-T70C-b ₅ bound to human P450s 1A2, 2B6, 2C8, 2C9, 2E1, 2S1, 4A11, 3A4, and 17A1, with estimated K _d values ranging from 2.5 to 61 nM. Only weak binding was detected with P450 2D6, and no fluorescence attenuation was observed with P450 2A6. All of the P450s that bound b ₅ have some reported activity stimulation except for P450 2S1. The affinity of P450 3A4 for b ₅ was decreased somewhat by the presence of a substrate or inhibitor. The fluorescence of a P450 3A4•Alexa 488-T70C-b ₅ complex was partially restored by titration with NADPH-P450 reductase (POR) (K _d,apparent 89 nM), suggesting the existence of a ternary P450 3A4-b ₅-POR complex, as observed previously with P450 17A1. Gel filtration evidence was also obtained for this ternary complex with P450 3A4. Overall, the results indicated that the affinity of b ₅ for many P450s is very high, and that ternary P450-b ₅-POR complexes are relevant in P450 3A4 reactions as opposed to a shuttle mechanism. SIGNIFICANCE STATEMENT: High-affinity binding of cytochrome b ₅ (b ₅) (K _d < 100 nM) was observed with many drug-metabolizing cytochrome P450 (P450) enzymes. There is some correlation of binding with reported stimulation, with several exceptions. Evidence is provided for a ternary P450 3A4-b ₅-NADPH-P450 reductase complex.

Stepwise binding of inhibitors to human cytochrome P450 17A1 and rapid kinetics of inhibition of androgen biosynthesis

Cytochrome P450 (P450) 17A1 catalyzes the 17α-hydroxylation of progesterone and pregnenolone as well as the subsequent lyase cleavage of both products to generate androgens. However, the selective inhibition of the lyase reactions, particularly with 17α-hydroxy pregnenolone, remains a challenge for the treatment of prostate cancer. Here, we considered the mechanisms of inhibition of drugs that have been developed to inhibit P450 17A1, including ketoconazole, seviteronel, orteronel, and abiraterone, the only approved inhibitor used for prostate cancer therapy, as well as clotrimazole, known to inhibit P450 17A1. All five compounds bound to P450 17A1 in a multistep process, as observed spectrally, over a period of 10 to 30 s. However, no lags were observed for the onset of inhibition in rapid-quench experiments with any of these five compounds. Furthermore, the addition of substrate to inhibitor–P450 17A1 complexes led to an immediate formation of product, without a lag that could be attributed to conformational changes. Although abiraterone has been previously described as showing slow-onset inhibition (t_1/2 = 30 min), we observed rapid and strong inhibition. These results are in contrast to inhibitors of P450 3A4, an enzyme with a larger active site in which complete inhibition is not observed with ketoconazole and clotrimazole until the changes are completed. Overall, our results indicate that both P450 17A1 reactions—17α-hydroxylation and lyase activity—are inhibited by the initial binding of any of these inhibitors, even though subsequent conformational changes occur.

Optimization of Multiparameters for Increased Yields of Cytochrome B5 in Bioreactors

The production of recombinant proteins is gaining increasing importance as the market requests high quality proteins for several applications. However, several process parameters affect both the growth of cells and product yields. This study uses high throughput systems and statistical methods to assess the influence of fermentation conditions in lab-scale bioreactors. Using this methodology, it was possible to find the best conditions to produce cytochrome b5 with recombinant cells of Escherichia coli. Using partial least squares, the height-to-diameter ratio of the bioreactor, aeration rate, and PID controller parameters were found to contribute significantly to the final biomass and cytochrome concentrations. Hence, we could use this information to fine-tune the process parameters, which increased cytochrome production and yield several-fold. Using aeration of 1 vvm, a bioreactor with a height-to-ratio of 2.4 and tuned PID parameters, a production of 72.72 mg/L of cytochrome b5 in the culture media, and a maximum of product to biomass yield of 24.97 mg/g could be achieved.