Cholesterol ester oxidation by mycobacterial cytochrome P450

The oxidation of steroid derivatives by the CYP125A6 and CYP125A7 enzymes from Mycobacterium marinum

The members of the bacterial cytochrome P450 (CYP) monooxygenase family CYP125, catalyze the oxidation of steroid derivatives including cholesterol and phytosterols, as the initial activating step in their catabolism. However, several bacterial species contain multiple genes encoding CYP125 enzymes and other CYP enzymes which catalyze cholesterol/cholest-4-en-3-one hydroxylation. An important question is why these bacterium have more than one enzyme with overlapping substrate ranges capable of catalyzing the terminal oxidation of the alkyl chain of these sterols. To further understand the role of these enzymes we investigated CYP125A6 and CYP125A7 from Mycobacterium marinum with various cholesterol analogues. These have modifications on the A and B rings of the steroid and we assessed the substrate binding and catalytic activity of these with each enzyme. CYP125A7 gave similar results to those reported for the CYP125A1 enzyme from M. tuberculosis. Differences in the substrate binding and catalytic activity with the cholesterol analogues were observed with CYP125A6. For example, while cholesteryl sulfate could bind to both enzymes it was only oxidized by CYP125A6 and not by CYP125A7. CYP125A6 generated higher levels of metabolites with the majority of C-3 and C-7 substituted cholesterol analogues such 7-ketocholesterol. However, 5α-cholestan-3β-ol was only oxidized by CYP125A7 enzyme. The cholest-4-en-3-one and 7-ketocholesterol-bound forms of the CYP125A6 and CYP125A7 enzymes were modelled using AlphaFold. The structural models highlighted differences in the binding modes of the steroid derivatives within the same enzyme. Significant changes in the binding mode of the steroids between these CYP125 enzymes and other bacterial cholesterol oxidizing enzymes, CYP142A3 and CYP124A1, were also seen. Despite this, all these models predicted the selectivity for terminal methyl hydroxylation, in agreement with the experimental data.

Structure Based Discovery of Inhibitors of CYP125 and CYP142 from Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) was responsible for approximately 1.6 million deaths in 2021. With the emergence of extensive drug resistance, novel therapeutic agents are urgently needed, and continued drug discovery efforts required. Host-derived lipids such as cholesterol not only support Mtb growth, but are also suspected to function in immunomodulation, with links to persistence and immune evasion. Mtb cytochrome P450 (CYP) enzymes facilitate key steps in lipid catabolism and thus present potential targets for inhibition. Here we present a series of compounds based on an ethyl 5-(pyridin-4-yl)-1H-indole-2-carboxylate pharmacophore which bind strongly to both Mtb cholesterol oxidases CYP125 and CYP142. Using a structure-guided approach, combined with biophysical characterization, compounds with micromolar range in-cell activity against clinically relevant drug-resistant isolates were obtained. These will incite further development of much-needed additional treatment options and provide routes to probe the role of CYP125 and CYP142 in Mtb pathogenesis.

The oxidation of cholesterol derivatives by the CYP124 and CYP142 enzymes from Mycobacterium marinum

The CYP124 and CYP142 families of bacterial cytochrome P450 monooxygenases (CYPs), catalyze the oxidation of methyl branched lipids, including cholesterol, as one of the initial activating steps in their catabolism. Both enzymes are reported to supplement the CYP125 family of P450 enzymes. These CYP125 enzymes are found in the same bacteria, and are the primary cholesterol/cholest-4-en-3-one metabolizing enzymes. To further understand the role of the CYP124 and CYP142 cytochrome P450s we investigated the Mycobacterium marinum enzymes, MmarCYP124A1 and CYP142A3, with various cholesterol analogues with modifications on the A and B rings of the steroid. We assessed the substrate binding and catalytic activity of each enzyme. Neither enzyme could bind or oxidize cholesteryl acetate or 3,5-cholestadiene, which have modifications at the C3 hydroxyl moiety of cholesterol. The CYP142 enzyme was better able to accommodate and oxidize cholesterol analogues which have changes on the A/B rings including cholesterol-5α,6α-epoxide and diastereomers of 5-cholestan-3-ol. The CYP124 enzyme was more tolerant of changes at C7 of the cholesterol B ring, e.g., 7-ketocholesterol than in the A ring. The selectivity for oxidation at the ω-carbon of a branched chain was observed in all steroids that were oxidized. The 7-ketocholesterol-bound MmarCYP124A1 enzyme from M. marinum, was structurally characterized by X-ray crystallography to 1.81Å resolution. The 7-ketocholesterol-bound X-ray crystal structure of the MmarCYP124A1 enzyme revealed that the substrate binding mode of this cholesterol derivative was altered compared to those observed with other non-steroidal ligands. The structure provided an explanation for the selectivity of the enzyme for terminal methyl hydroxylation.

The catalytic activity and structure of the lipid metabolizing CYP124 cytochrome P450 enzyme from Mycobacterium marinum

The CYP124 family of cytochrome P450 enzymes, as exemplified by CYP124A1 from Mycobacterium tuberculosis, is involved in the metabolism of methyl branched lipids and cholesterol derivatives. The equivalent enzyme from Mycobacterium marinum was investigated to compare the degree of functional conservation between members of this CYP family from closely related bacteria. We compared substrate binding of each CYP124 enzyme using UV-vis spectroscopy and the catalytic oxidation of methyl branched lipids, terpenes and cholesterol derivatives was investigated. The CYP124 enzyme from M. tuberculosis displayed a larger shift to the ferric high-spin state on binding cholesterol derivatives compared to the equivalent enzyme from M. marinum. The biggest difference was observed with cholesteryl sulfate which induced distinct UV-vis spectra in each CYP124 enzyme. The selectivity for oxidation at the ω-carbon of a branched chain was maintained for all substrates, except cholesteryl sulfate which was not oxidized by either enzyme. The CYP124A1 enzyme from M. marinum, in combination with farnesol and farnesyl acetate, was structurally characterized by X-ray crystallography. These ligand-bound structures of the CYP124 enzyme revealed that the polar component of the substrates bound in a different manner to that of phytanic acid in the structure of CYP124A1 from M. tuberculosis. However, closer to the heme the structures were similar providing an explanation for the high selectivity of the enzyme for terminal methyl C-H bond oxidation. The work here demonstrates that there were differences in the biochemistry of the CYP124 enzymes from these closely related bacteria.

The Structures of the Steroid Binding CYP142 Cytochrome P450 Enzymes from Mycobacterium ulcerans and Mycobacterium marinum

The steroid binding CYP142 cytochrome P450 enzymes of Mycobacterium species are involved in the metabolism of cholesterol and its derivatives. The equivalent enzyme from Mycobacterium ulcerans was studied to compare the degree of functional conservation between members of this CYP family. We compared substrate binding of the CYP142A3 enzymes of M. ulcerans and M. marinum and CYP142A1 from M. tuberculosis using UV-vis spectroscopy. The catalytic oxidation of cholesterol derivatives by all three enzymes was undertaken. Both CYP142A3 enzymes were structurally characterized by X-ray crystallography. The amino acid sequences of the CYP142A3 enzymes are more similar to CYP142A1 from M. tuberculosis than CYP142A2 from Mycolicibacterium smegmatis. Both CYP142A3 enzymes have substrate binding properties, which are more resemblant to CYP142A1 than CYP142A2. The cholest-4-en-3-one-bound X-ray crystal structure of both CYP142A3 enzymes were determined at a resolution of <1.8 Å, revealing the substrate binding mode at a high level of detail. The structures of the cholest-4-en-3-one binding CYP142 enzymes from M. ulcerans and M. marinum demonstrate how the steroid binds in the active site of these enzymes. They provide an explanation for the high selectivity of the enzyme for terminal methyl C-H bond oxidation to form 26-hydroxy derivatives. These enzymes in pathogenic Mycobacterium species are candidates for inhibition. The work here demonstrates that similar drug molecules could target these CYP142 enzymes from different species in order to combat Buruli ulcer or tuberculosis.

Roles of cysteine in the structure and metabolic function of Mycobacterium tuberculosis CYP142A1

CYP142A1 is a cytochrome P450 (CYP) enzyme expressed in Mycobacterium tuberculosis (Mtb), which supports the growth of Mtb H37Rv relying on cholesterol, in the absence of CYP125A1. Since cysteine residues usually play a fundamental role in maintaining the structure and function of CYP enzymes, in this study, we aimed to determine the potential biochemical functions of six cysteine residues except for the heme-binding cysteine in the amino acid sequence of recombinant Mtb CYP142A1 by replacing each one using site-directed mutagenesis. Recombinant CYP142A1 mutants were heterologously expressed, purified, and analyzed using ESI-MS, far-UV CD spectroscopy, UV-vis spectrophotometric titration, and metabolic function assays. Substitution of the cysteine residues caused various effects on the structure and function of CYP142A1. Separate substitution of the six cysteine residues resulted in numerous changes in the secondary structure, expression level, substrate-binding ability, inhibitor-binding ability, thermal stability and oxidation efficiency of the enzyme. These results contribute to our understanding of the biochemical roles of cysteine residues in the structure and function of Mtb CYP enzymes, especially their effects on the structure and function of CYP142A1.

Substitution of the six cysteine residues resulted in changes in Mtb CYP142A1 structure, binding ability, thermal stability and oxidation efficiency.

Mycolicibacterium cell factory for the production of steroid-based drug intermediates

Steroid-based drugs have been developed as the second largest medical category in pharmaceutics. The well-established route of steroid industry includes two steps: the conversion of natural products with a steroid framework to steroid-based drug intermediates and the synthesis of varied steroid-based drugs from steroid-based drug intermediates. The biosynthesis of steroid-based drug intermediates from phytosterols by Mycolicibacterium cell factories bypasses the potential undersupply of diosgenin in the traditional steroid chemical industry. Moreover, the biosynthesis route shows advantages on multiple steroid-based drug intermediate products, more ecofriendly processes, and consecutive reactions carried out in one operation step and in one pot. Androsta-4-ene-3,17-dione (AD), androsta-1,4-diene-3,17-dione (ADD) and 9-hydroxyandrostra-4-ene-3,17-dione (9-OH-AD) are the representative steroid-based drug intermediates synthesized by mycolicibacteria. Other steroid metabolites of mycolicibacteria, like 4-androstene-17β-ol-3-one (TS), 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC), 22-hydroxy-23,24-bisnorchol-1,4-diene-3-one (1,4-HBC), 9,22-dihydroxy-23,24-bisnorchol-4-ene-3-one (9-OH-HBC), 3aα-H-4α-(3'-propionic acid)-7aβ-methylhexahydro-1,5-indanedione (HIP) and 3aα-H-4α-(3'-propionic acid)-5α-hydroxy-7aβ-methylhexahydro-1-indanone-δ-lactone (HIL), also show values as steroid-based drug intermediates. To improve the bio-production efficiency of the steroid-based drug intermediates, mycolicibacterial strains and biotransformation processes have been continuously studied in the past decades. Many mycolicibacteria that accumulate steroid drug intermediates have been isolated, and subsequently optimized by conventional mutagenesis and genetic engineering. Especially, with the clarification of the mycolicibacterial steroid metabolic pathway and the developments on gene editing technologies, rational design is becoming an important measure for the construction and optimization of engineered mycolicibacteria strains that produce steroid-based drug intermediates. Hence, by reviewing researches in the past two decades, this article updates the overall process of steroid metabolism in mycolicibacteria and provides comprehensive schemes for the rational construction of mycolicibacterial strains that accumulate steroid-based drug intermediates. In addition, the special strategies for the bioconversion of highly hydrophobic steroid in aqueous media are discussed as well.

Structural Perspectives of the CYP3A Family and Their Small Molecule Modulators in Drug Metabolism

Cytochrome P450 enzymes function to catalyze a wide range of reactions, many of which are critically important for drug response. Members of the human cytochrome P450 3A (CYP3A) family are particularly important in drug clearance, and they collectively metabolize more than half of all currently prescribed medications. The ability of these enzymes to bind a large and structurally diverse set of compounds increases the chances of their modulating or facilitating drug metabolism in unfavorable ways. Emerging evidence suggests that individual enzymes in the CYP3A family play discrete and important roles in catalysis and disease progression. Here we review the similarities and differences among CYP3A enzymes with regard to substrate recognition, metabolism, modulation by small molecules, and biological consequence, highlighting some of those with clinical significance. We also present structural perspectives to further characterize the basis of these comparisons.

Steroids as Environmental Compounds Recalcitrant to Degradation: Genetic Mechanisms of Bacterial Biodegradation Pathways

Steroids are perhydro-1,2-cyclopentanophenanthrene derivatives that are almost exclusively synthesised by eukaryotic organisms. Since the start of the Anthropocene, the presence of these molecules, as well as related synthetic compounds (ethinylestradiol, dexamethasone, and others), has increased in different habitats due to farm and municipal effluents and discharge from the pharmaceutical industry. In addition, the highly hydrophobic nature of these molecules, as well as the absence of functional groups, makes them highly resistant to biodegradation. However, some environmental bacteria are able to modify or mineralise these compounds. Although steroid-metabolising bacteria have been isolated since the beginning of the 20th century, the genetics and catabolic pathways used have only been characterised in model organisms in the last few decades. Here, the metabolic alternatives used by different bacteria to metabolise steroids (e.g., cholesterol, bile acids, testosterone, and other steroid hormones), as well as the organisation and conservation of the genes involved, are reviewed.

Cytochrome P450 research and The Journal of Biological Chemistry

In honor of the 100th birthday of Dr. Herbert Tabor, JBC's Editor-in-Chief for 40 years, I will review here JBC's extensive coverage of the field of cytochrome P450 (P450) research. Research on the reactions catalyzed by these enzymes was published in JBC before it was even realized that they were P450s, i.e. they have a "pigment" with an absorption maximum at 450 nm. After the P450 pigment discovery, reported in JBC in 1962, the journal proceeded to publish the methods for measuring P450 activities and many seminal findings. Since then, the P450 field has grown extensively, with significant progress in characterizing these enzymes, including structural features, catalytic mechanisms, regulation, and many other aspects of P450 biochemistry. JBC has been the most influential journal in the P450 field. As with many other research areas, Dr. Tabor deserves a great deal of the credit for significantly advancing this burgeoning and important topic of research.

Cholesterol and fatty acids grease the wheels of Mycobacterium tuberculosis pathogenesis

Tuberculosis is a distinctive disease in which the causative agent, Mycobacterium tuberculosis, can persist in humans for decades by avoiding clearance from host immunity. During infection, M. tuberculosis maintains viability by extracting and utilizing essential nutrients from the host, and this is a prerequisite for all of the pathogenic activities that are deployed by the bacterium. In particular, M. tuberculosis preferentially acquires and metabolizes host-derived lipids (fatty acids and cholesterol), and the bacterium utilizes these substrates to cause and maintain disease. In this review, we discuss our current understanding of lipid utilization by M. tuberculosis, and we describe how these pathways promote pathogenesis to fuel metabolic processes in the bacillus. Finally, we highlight weaknesses in these pathways that potentially can be targeted for drug discovery.

Structural and functional characterisation of the cytochrome P450 enzyme CYP268A2 from Mycobacterium marinum

Members of the cytochrome P450 monooxygenase family CYP268 are found across a broad range of Mycobacterium species including the pathogens Mycobacterium avium, M. colombiense, M. kansasii, and M. marinum. CYP268A2, from M. marinum, which is the first member of this family to be studied, was purified and characterised. CYP268A2 was found to bind a variety of substrates with high affinity, including branched and straight chain fatty acids (C10–C12), acetate esters, and aromatic compounds. The enzyme was also found to bind phenylimidazole inhibitors but not larger azoles, such as ketoconazole. The monooxygenase activity of CYP268A2 was efficiently reconstituted using heterologous electron transfer partner proteins. CYP268A2 hydroxylated geranyl acetate and trans-pseudoionone at a terminal methyl group to yield (2E,6E)-8-hydroxy-3,7-dimethylocta-2,6-dien-1-yl acetate and (3E,5E,9E)-11-hydroxy-6,10-dimethylundeca-3,5,9-trien-2-one, respectively. The X-ray crystal structure of CYP268A2 was solved to a resolution of 2.0 Å with trans-pseudoionone bound in the active site. The overall structure was similar to that of the related phytanic acid monooxygenase CYP124A1 enzyme from Mycobacterium tuberculosis, which shares 41% sequence identity. The active site is predominantly hydrophobic, but includes the Ser99 and Gln209 residues which form hydrogen bonds with the terminal carbonyl group of the pseudoionone. The structure provided an explanation on why CYP268A2 shows a preference for shorter substrates over the longer chain fatty acids which bind to CYP124A1 and the selective nature of the catalysed monooxygenase activity.

Potential drug targets in the Mycobacterium tuberculosis cytochrome P450 system

The Mycobacterium tuberculosis genome encodes twenty cytochrome P450 enzymes, most or all of which appear to have specific physiological functions rather than being devoted to the removal of xenobiotics. However, in many cases their specific functions remain obscure. Considerable spectroscopic, biophysical, crystallographic, and catalytic information is available on nine of these cytochrome P450 enzymes, although gaps exist in our knowledge of even these enzymes. The available evidence indicates that at least three of the better-characterized enzymes are promising targets for antituberculosis drug discovery. This review summarizes the information on the nine relatively well-characterized cytochrome P450 enzymes, with a particular emphasis on CYP121, CYP125, and CYP142 from Mycobacterium tuberculosis and Mycobacterium smegmatis.

Microbial Offense vs Host Defense: Who Controls the TB Granuloma?

The granuloma is the hallmark of tuberculosis and simultaneously signifies acquisition of an infection and induction of a host immune response. But who benefits more from the development of the granuloma, the host or the pathogen? Is microbe or man dictating disease course and progression? Mycobacterial diseases affect humans and animals alike, and the concepts presented in this review reflect host-pathogen interactions that influence not only mycobacterial granulomas in humans and animals but also other infectious granulomatous diseases that are encountered in veterinary medicine. Current dogma supports that an organized granuloma is a mark of an adequate and “restrictive” host immune response. However, the formation of a granuloma also provides a niche for the maturation, growth, and persistence of numerous infectious agents, and these pathogens devote some portion of their genetic machinery to ensuring these structures’ form. An understanding of pathogens’ contributions to granuloma formation can aid the development of host-directed therapies and other antimicrobial and antiparasitic therapies that can tip this balance in favor of a restrictive host response and elimination—not just containment—of the infectious organism. This review discusses animal models that have aided our understanding of pathogens’ contribution to the host response and how mycobacterial virulence genes direct host pathology in ways that may aid disease transmission and/or persistence in the form of latent infection.

The Minimal Unit of Infection: Mycobacterium tuberculosis in the Macrophage

The interaction between Mycobacterium tuberculosis and its host cell is highly complex and extremely intimate. Were it not for the disease, one might regard this interaction at the cellular level as an almost symbiotic one. The metabolic activity and physiology of both cells are shaped by this coexistence. We believe that where this appreciation has greatest significance is in the field of drug discovery. Evolution rewards efficiency, and recent data from many groups discussed in this review indicate that M. tuberculosis has evolved to utilize the environmental cues within its host to control large genetic programs or regulons. But these regulons may represent chinks in the bacterium's armor because they include off-target effects, such as the constraint of the metabolic plasticity of M. tuberculosis. A prime example is how the presence of cholesterol within the host cell appears to limit the ability of M. tuberculosis to fully utilize or assimilate other carbon sources. And that is the reason for the title of this review. We believe firmly that, to understand the physiology of M. tuberculosis and to identify new drug targets, it is imperative that the bacterium be interrogated within the context of its host cell. The constraints induced by the environmental cues present within the host cell need to be preserved and exploited. The M. tuberculosis-infected macrophage truly is the "minimal unit of infection."

Triphenyltin degradation and proteomic response by an engineered Escherichia coli expressing cytochrome P450 enzyme

Although triphenyltin (TPT) degradation pathway has been determined, information about the enzyme and protein networks involved was severely limited. To this end, a cytochrome P450 hydroxylase (CYP450) gene from Bacillus thuringiensis was cloned and expressed in Escherichia coli BL21 (DE3), namely E. coli pET32a-CYP450, whose dosage at 1gL^-1 could degrade 54.6% TPT at 1mgL^-1 within 6 d through attacking the carbon-tin bonds of TPT by CYP450. Sequence analysis verified that the CYP450 gene had a 1214bp open reading frame, encoding a protein with 404 amino acids. Proteomic analysis determined that 60 proteins were significantly differentially regulated expression in E. coli pET32a-CYP450 after TPT degradation. The up-regulated proteins enriched in a network related to transport, cell division, biosynthesis of amino acids and secondary metabolites, and microbial metabolism in diverse environments. The current findings demonstrated for the first time that P450 received electrons transferring from NADH could effectively cleave carbon-metal bonds.

Role Identification and Application of SigD in the Transformation of Soybean Phytosterol to 9α-Hydroxy-4-androstene-3,17-dione in Mycobacterium neoaurum

9α-Hydroxy-4-androstene-3,17-dione (9-OHAD) is a valuable steroid pharmaceutical intermediate which can be produced by the conversion of soybean phytosterols in mycobacteria. However, the unsatisfactory productivity and conversion efficiency of engineered mycobacterial strains hinder their industrial applications. Here, a sigma factor D (sigD) was investigated due to its dramatic downregulation during the conversion of phytosterols to 9-OHAD. It was determined as a negative regulator in the metabolism of phytosterols, and the deletion of sigD in a 9-OHAD-producing strain significantly enhanced the titer of 9-OHAD by 18.9%. Furthermore, a high yielding strain was constructed by the combined modifications of sigD and choM2, a key gene in the phytosterol metabolism pathway. After the modifications, the productivity of 9-OHAD reached 0.071 g/L/h (10.27 g/L from 20 g/L phytosterol), which was 22.5% higher than the original productivity of 0.058 g/L/h (8.37 g/L from 20 g/L phytosterol) in the industrial resting cell biotransformation system.

Drug targeting of heme proteins in Mycobacterium tuberculosis

TB, caused by the human pathogen Mycobacterium tuberculosis (Mtb), causes more deaths than any other infectious disease. Iron is crucial for Mtb to infect the host and to sustain infection, with Mtb encoding large numbers of iron-binding proteins. Many of these are hemoproteins with key roles, including defense against oxidative stress, cellular signaling and regulation, host cholesterol metabolism, and respiratory processes. Various heme enzymes in Mtb are validated drug targets and/or products of genes essential for bacterial viability or survival in the host. Here, we review the structure, function, and druggability of key Mtb heme enzymes and strategies used for their inhibition.

Molecular evolutionary dynamics of cytochrome P450 monooxygenases across kingdoms: Special focus on mycobacterial P450s

Since the initial identification of cytochrome P450 monooxygenases (CYPs/P450s), great progress has been made in understanding their structure-function relationship, diversity and application in producing compounds beneficial to humans. However, the molecular evolution of P450s in terms of their dynamics both at protein and DNA levels and functional conservation across kingdoms still needs investigation. In this study, we analyzed 17 598 P450s belonging to 113 P450 families (bacteria -42; fungi -19; plant -28; animal -22; plant and animal -1 and common P450 family -1) and found highly conserved and rapidly evolving P450 families. Results suggested that bacterial P450s, particularly P450s belonging to mycobacteria, are highly conserved both at protein and DNA levels. Mycobacteria possess the highest P450 diversity percentage compared to other microbes and have a high coverage of P450s (≥1%) in their genomes, as found in fungi and plants. Phylogenetic and functional analyses revealed the functional conservation of P450s despite belonging to different biological kingdoms, suggesting the adherence of P450s to their innate function such as their involvement in either generation or oxidation of steroids and structurally related molecules, fatty acids and terpenoids. This study's results offer new understanding of the dynamic structural nature of P450s.

Recent Structural Insights into Cytochrome P450 Function

Cytochrome P450 (P450) enzymes are important in the metabolism of drugs, steroids, fat-soluble vitamins, carcinogens, pesticides, and many other types of chemicals. Their catalytic activities are important issues in areas such as drug-drug interactions and endocrine function. During the past 30 years, structures of P450s have been very helpful in understanding function, particularly the mammalian P450 structures available in the past 15 years. We review recent activity in this area, focusing on the past 2 years (2014-2015). Structural work with microbial P450s includes studies related to the biosynthesis of natural products and the use of parasitic and fungal P450 structures as targets for drug discovery. Studies on mammalian P450s include the utilization of information about 'drug-metabolizing' P450s to improve drug development and also to understand the molecular bases of endocrine dysfunction.

Structural characterization of CYP144A1 - a cytochrome P450 enzyme expressed from alternative transcripts in Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) causes the disease tuberculosis (TB). The virulent Mtb H37Rv strain encodes 20 cytochrome P450 (CYP) enzymes, many of which are implicated in Mtb survival and pathogenicity in the human host. Bioinformatics analysis revealed that CYP144A1 is retained exclusively within the Mycobacterium genus, particularly in species causing human and animal disease. Transcriptomic annotation revealed two possible CYP144A1 start codons, leading to expression of (i) a “full-length” 434 amino acid version (CYP144A1-FLV) and (ii) a “truncated” 404 amino acid version (CYP144A1-TRV). Computational analysis predicted that the extended N-terminal region of CYP144A1-FLV is largely unstructured. CYP144A1 FLV and TRV forms were purified in heme-bound states. Mass spectrometry confirmed production of intact, His₆-tagged forms of CYP144A1-FLV and -TRV, with EPR demonstrating cysteine thiolate coordination of heme iron in both cases. Hydrodynamic analysis indicated that both CYP144A1 forms are monomeric. CYP144A1-TRV was crystallized and the first structure of a CYP144 family P450 protein determined. CYP144A1-TRV has an open structure primed for substrate binding, with a large active site cavity. Our data provide the first evidence that Mtb produces two different forms of CYP144A1 from alternative transcripts, with CYP144A1-TRV generated from a leaderless transcript lacking a 5′-untranslated region and Shine-Dalgarno ribosome binding site.

The Role of fadD19 and echA19 in Sterol Side Chain Degradation by Mycobacterium smegmatis

Mycobacteria are able to degrade natural sterols and use them as a source of carbon and energy. Several genes which play an important role in cholesterol ring degradation have been described in Mycobacterium smegmatis. However, there are limited data describing the molecular mechanism of the aliphatic side chain degradation by Mycobacterium spp. In this paper, we analyzed the role of the echA19 and fadD19 genes in the degradation process of the side chain of cholesterol and β-sitosterol. We demonstrated that the M. smegmatis fadD19 and echA19 genes are not essential for viability. FadD19 is required in the initial step of the biodegradation of C-24 branched sterol side chains in Mycobacterium smegmatis mc²155, but not those carrying a straight chain like cholesterol. Additionally, we have shown that echA19 is not essential in the degradation of either substrate. This is the first report, to our knowledge, on the molecular characterization of the genes playing an essential role in C-24 branched side chain sterol degradation in M. smegmatis mc²155.

Incorporation of fluorophore-cholesterol conjugates into liposomal and mycobacterial membranes

Fluorescently-labeled steroids that emit intense blue light in nonpolar solvent (λem (CH2Cl2)≈440nm, ΦF=0.70) were prepared by treating cholesteryl chloroformate with 4-amino-1,8-naphthalimides. The lipid portion of the conjugates embeds into liposomal membrane bilayers in minutes, leaving the fluorophore exposed to the external aqueous environment. This causes a 40-nm red-shift in λem and significant quenching. DFT optimizations predict the conjugates to be about 30Å long when fully extended, but rotation about the linker group can bring the compounds into an 'L'-shape. Such a conformation would allow the cholesteryl anchor to remain parallel to the acyl chains of a membrane while the fluorescent group resides in the interfacial region, instead of extending beyond it. When incubated with Mycobacterium smegmatis mc2 155, a bacterial species known to use natural cholesterol, the labeled steroids support growth and can be found localized in the membrane fraction of the cells using HPLC. These findings demonstrate stable integration of fluorescent cholesterols into bacterial membranes in vivo, indicating that these compounds may be useful for evaluating cholesterol uptake in prokaryotic organisms.

Cytochrome P450 125A4, the Third Cholesterol C-26 Hydroxylase from Mycobacterium smegmatis

Mycobacterium tuberculosis (Mtb) and Mycobacterium smegmatis (Msmeg) can grow on cholesterol as the sole carbon source. In Mtb the utilization of cholesterol can be initiated by CYP125A1 or CYP142A1 and in Msmeg by the orthologous CYP125A3 and CYP142A2. Double knockout of the two enzymes in Mtb prevents its growth on cholesterol, but the double knockout of Msmeg is still able to grow, albeit at a slower rate. We report here that Msmeg has a third enzyme, CYP125A4, that also oxidizes cholesterol, although it has a much higher activity for the oxidation of 7α-hydroxycholesterol. The ability of Msmeg CYP125A4 (and Mtb CYP125A1) to oxidize 7α-hydroxycholesterol is due, at least in part, to the presence of a smaller amino acid side chain facing C-7 of the sterol substrate than in CYP125A3. The ability to oxidize 7-substituted steroids broadens the range of sterol carbon sources for growth, but even more importantly in Mtb, additional biological effects are possible due to the potent immunomodulatory activity of 7α,26-dihydroxycholesterol.

α-Methyl Acyl CoA Racemase Provides Mycobacterium tuberculosis Catabolic Access to Cholesterol Esters

Metabolism of cholesterol by Mycobacterium tuberculosis (Mtb) contributes to its pathogenesis. We show that ChsE4-ChsE5 (Rv3504/Rv3505) specifically catalyzes dehydrogenation of the (25S)-3-oxo-cholest-4-en-26-oyl-CoA diastereomer in cholesterol side chain β-oxidation. Thus, a dichotomy between the supply of both 25R and 25S metabolic precursors by upstream cytochrome P450s and the substrate stereospecificity of ChsE4-ChsE5 exists. We reconcile the dilemma of 25R metabolite production by demonstrating that mycobacterial MCR (Rv1143) can efficiently epimerize C25 diastereomers of 3-oxo-cholest-4-en-26-oyl-CoA. Our data suggest that cholesterol and cholesterol ester precursors can converge into a single catabolic pathway, thus widening the metabolic niche in which Mtb survives.