New Insights on Steroid Biotechnology

Evaluating the Potential of Microdroplet Flow in Two-Phase Biocatalysis: A Systematic Study

Two-phase biocatalysis in batch reactions often suffers from inefficient mass transfer, inconsistent reaction conditions, and enzyme inactivation issues. Microfluidics offer uniform and controlled environments ensuring better reproducibility and enable efficient, parallel processing of many small-scale reactions, making biocatalysis more scalable. In particular, the use of microfluidic droplets can increase the interfacial area between the two phases and can therefore also increase reaction rates. For these reasons, slug flow has been extensively used in two-phase biocatalysis in recent years. However, microdroplet flow has been largely neglected for this application despite its great potential. In this work, we performed biphasic biocatalysis in microfluidic droplets, both in microdroplets and slugs, as well as in batch, and systematically investigated the effect of various reaction parameters on the outcome of the reaction. We show that microdroplet flow outperforms the more commonly used batch and slug flow configurations for most reaction conditions by providing shorter substrate diffusion paths and larger interfacial area for the reaction. The potential trade-off between maximized mass transfer and possibly higher enzyme inactivation rates in small droplets with large surface-to-volume ratios was also investigated for the first time, and a pipeline was established to allow evaluation in other reactions. Finally, the effect of surfactant necessary for microdroplet stabilization was also investigated in all reaction setups for the first time, and it was shown that a properly selected surfactant can have a positive effect at low concentrations by creating more stable emulsions and smaller droplets, thus increasing the interfacial area between the two phases.

Improvement of 9α-hydroxyandrost-4-ene-3,17-dione production in Mycolicibacterium neoaurum by regulation of cell wall formation and transcriptional regulator PadR

The biotransformation of phytosterol into high value steroid intermediates such as 9α-hydroxyandrost-4-ene-3,17-dione (9-OHAD) in Mycolicibacterium is the cornerstone of the steroid pharmaceuticals. However, the limited permeability of the dense mycobacterial cell wall severely hinders the efficient transportation of phytosterol and their bioconversion to 9-OHAD. In this study, we disrupted the genetic pathways involved in trehalose biosynthesis, trehalose recycle and by-product formation, leading to alterations in cell wall formation, cell permeability and 9-OHAD productivity. This manipulation led to an increase of 63.7% in the yield of 9-OHAD, reaching 10.8 g/L at a phytosterol concentration of 20 g/L in shake flask. The enhancement of cell permeability and 9-OHAD production were achieved through the deletion of genes TreS, TreY, OtsA, LpqY, and SugC, as well as the inactivation of regulator PadR. Notably, it was found that the increase in TMM content of cell wall components via TLC analysis directly affected the distribution of 9-OHAD within and outside the cell, ultimately leading to an increase in extracellular production of 9-OHAD from 12% to 32.1%. Therefore, this study provides with an effective strategy for enhancing 9-OHAD production by increasing cell permeability while minimizing by-product 4-AD formation.

Potent Anti-Cancer Activity of 1-Dehydrodiosgenone from the Product of Microbial Transformation of Steroid Saponins

Steroids are extensively used in the pharmaceutical industry as industrial raw materials for the production of anti-inflammatory and anti-tumor drugs. Microbial transformation, an environmentally friendly method, displays the potential for preparing steroids on an industrial scale. In this study, four steroids, including Diosgenin, Smilagenone, Yamogenin, and 1-Dehydrodiosgenone, were isolated and identified from the solid-state fermentation (SSF) product of a novel Fusarium oxysporum strain, and their anti-tumor activities were investigated. The cytotoxicity assay showed that 1-Dehydrodiosgenone had significant inhibitory effects on three tumor cell lines, Hala, A549, and Mad-MB468 cells, with IC50s of 6.59 μM, 5.43 μM, and 4.81 μM, respectively. 1-Dehydrodiosgenone significantly induced apoptosis and necrosis of Hala, A549, and Mad-MB468 cells by upregulating the expressions of cleaved caspase-3, cleaved PARP, Bax, and Bad. Moreover, no significant organ damage was observed in mice based on safety tests. Therefore, 1-Dehydrodiosgenone is expected to be developed as a safe and broad-spectrum anti-cancer agent.

Increased thermal stability and catalytic efficiency of 3-ketosteroid Δ1-dehydrogenase5 from Arthrobacter simplex significantly reduces enzyme dosage in prednisone acetate biosynthesis

The 3-ketosteroid-Δ1-dehydrogenase5 (KsdD5) from Arthrobacter simplex converts cortisone acetate to prednisone acetate, an important step in steroid catabolism. To achieve sustainable and efficient enzyme production, we employed computer-aided screening, structural analysis, and combinatorial experiments to identify engineered KsdD5 variants (M1 and M3) with dual advantages of stability and active sites. M1 had a 8.2-fold longer half-life (19.6 h at 30 °C) than KsdD5-WT, an 11.8 °C higher half-inactivation temperature (T5015min), and a 10.6 °C higher melting temperature (Tm). M3 had 3.82-fold higher catalytic activity than WT, a 3.9-fold longer half-life at 30 °C, and higher T5015min and Tm by 14 °C and 6.9 °C, respectively. Furthermore, kinetic and microscale thermophoresis analyses revealed M3 exhibited higher catalytic efficiency due to its larger enzymatic channel. Molecular dynamics simulations showed M1 promoted tighter secondary structure packing, reduced residue flexibility, and increased hydrogen bond formation, ensuring enzyme stability and activity at elevated temperatures. Under industrial conditions, M1 converted >96 % cortisone acetate within 12 h at 30 °C with a 60 g·L-1 substrate dosage and 6 g·L-1 cell mass, whereas the M3 conversion rate was 95 %. This study demonstrates a robust strategy for developing efficient enzyme mutants, facilitating sustainable industrial production of prednisone acetate with a minimal enzyme dosage.

Boldenone and Testosterone Production from Phytosterol via One-Pot Cascade Biotransformations

Testosterone (TS) and its 1(2)-dehydrogenated derivative boldenone (BD) are widely used in medicine, veterinary science and as precursors in organic synthesis of many therapeutic steroids. Green production of these compounds is possible from androstenedione (AD) enzymatically, or from phytosterol (PS) using fermentation stages. In this study, the ascomycete Curvularia sp. VKM F-3040 was shown to convert androstadienedione (ADD, 4 and 10 g/L) to yield 97% and 78% (mol/mol) of BD, respectively. Based on its high 17β-hydroxysteroid dehydrogenase (17β-HSD) activity, a novel cascade biotransformation of PS was developed for production of TS and BD. At the first stage, the strains of Mycolicibacterium neoaurum VKM Ac-1815D or M. neoaurum VKM Ac-1816D converted PS (5 or 10 g/L) into AD or ADD (each in a concentration of 2.5 or 5 g/L), respectively. At the second stage, mycelium of the fungus under the revealed optimal conditions reduced AD or ADD with more than 90% efficiency to form TS or BD, respectively. Based on transcriptome analysis, six candidate genes that might encode 17β-HSDs in the Curvularia sp. genome were revealed. Along with 17β-HSDs, the fungus possessed inducible P450cur 7-monooxygenase, which led to the accumulation of 7α-hydroxytestosterone (7α-OH-TS) as a major product from AD (up to 83% within 24 h after mycelium addition at the second stage of cascade biotransformation). The presence of protein synthesis inhibitor cycloheximide (CHX) prevented 7α/β-hydroxylation due to inhibition of de novo synthesis of the enzyme in the fungal cells. The results demonstrate the high biotechnological potential of the Curvularia sp. strain and open up prospects for the synthesis of valuable 17β-reduced and 7-hydroxylated steroids by cascade biotransformations.

Oestrogen Detoxification Ability of White Rot Fungus Trametes hirsuta LE-BIN 072: Exoproteome and Transformation Product Profiling

White rot fungi, especially representatives of the genus Trametes spp. (Polyporaceae), are effective destructors of various xenobiotics, including oestrogens (phenol-like steroids), which are now widespread in the environment and pose a serious threat to the health of humans, animals and aquatic organisms. In this work, the ability of the white rot fungus Trametes hirsuta LE-BIN 072 to transform oestrone (E1) and 17β-oestradiol (E2), the main endocrine disruptors, was shown. More than 90% of the initial E1 and E2 were removed by the fungus during the first 24 h of transformation. The transformation process proceeded predominantly in the direction of the initial substrates' detoxification, with the radical oxidative coupling of E1 and E2 as well as their metabolites and the formation of less toxic dimers in various combinations. A number of minor metabolites, in particular, less toxic estriol (E3), were identified by HPLC-MS. The formation of E1 from E2 and vice versa were shown. The exoproteome of the white rot fungus during the transformation of oestrogens was studied in detail for the first time. The contribution of ligninolytic peroxidases (MnP5, MnP7 and VP2) to the process of the extracellular detoxification of oestrogens and their possible metabolites is highlighted. Thus, the studied strain appears to be a promising mycodetoxicant of phenol-like steroids in aquatic environments.

Unveiling the Longevity Potential of Natural Phytochemicals: A Comprehensive Review of Active Ingredients in Dietary Plants and Herbs

Ancient humans used dietary plants and herbs to treat disease and to pursue eternal life. Today, phytochemicals in dietary plants and herbs have been shown to be the active ingredients, some of which have antiaging and longevity-promoting effects. Here, we summarize 210 antiaging phytochemicals in dietary plants and herbs, systematically classify them into 8 groups. We found that all groups of phytochemicals can be categorized into six areas that regulate organism longevity: ROS levels, nutrient sensing network, mitochondria, autophagy, gut microbiota, and lipid metabolism. We review the role of these processes in aging and the molecular mechanism of the health benefits through phytochemical-mediated regulation. Among these, how phytochemicals promote longevity through the gut microbiota and lipid metabolism is rarely highlighted in the field. Our understanding of the mechanisms of phytochemicals based on the above six aspects may provide a theoretical basis for the further development of antiaging drugs and new insights into the promotion of human longevity.

Modification of B-Nor Steroids Mediated by Filamentous Fungus Fusarium culmorum: Focus on 15α-Hydroxylase Activity

The metabolic activities of microorganisms to modify the chemical structures of organic compounds are an effective tool for the production of high-value steroidal drugs or active pharmaceutical ingredients (APIs). The integration of biotransformation into the synthesis of APIs can greatly reduce the number of reaction steps and achieve higher process efficiency, thus enabling their greener production. The current research efforts are focused on either the optimization of existing processes or identification of new potentially useful bioconversions. This study aimed to assess the catalytic abilities of the filamentous fungus Fusarium culmorum AM 282 to transform B-nor analogues (5(6→7)abeo compounds) of steroid hormones: androstenedione (AD), dehydroepiandrosterone (DHEA) and its acetate. Our previous studies have demonstrated that this strain is an active hydroxylating catalyst for many steroidal compounds with diverse structures. The results presented in this work showed that the hydroxylation of B-nor steroids occurred with the regio- and stereoselectivity typical of this strain in relation to the corresponding natural hormones of the standard 6:6 A/B series. After the transformations of B-nor-DHEA and its acetate, 15α-hydroxy-B-nor-DHEA was obtained as the sole product of the reaction, while the transformation of the AD analogue resulted in a mixture of its 15α- and 6α-hydroxy derivatives. A detailed analysis of the transformation course indicated that all the obtained hydroxy derivatives could be the result of the activity of the same enzyme. The presented results may provide a basis for research aimed at understanding the molecular nature of cytochrome P-450 monooxygenase from F. culmorum AM 282 with its ability for 15α-hydroxylation of steroidal compounds. An analysis of the pharmacokinetic and pharmacodynamic properties of the obtained metabolites with cheminformatics tools suggests their potential biological activity.

Improving the bioconversion of phytosterols to 9α-hydroxy-4-androstene-3,17-dione by disruption of acyltransferase SucT and TmaT associated with the mycobacterial cell wall synthesis

The bioconversion of low value-added phytosterols into high value-added 9α-hydroxy-4-androstene-3,17-dione (9-OHAD) in Mycolicibacterium neoaurum is a representative step in the steroid pharmaceutical industry. However, the complex mycobacterial cell walls with extremely low permeability and flowability greatly decrease the overall conversion efficiency. Herein, we preliminarily identified two key acyltransferases encoded by Mn_TmaT and Mn_SucT required for the proper synthesis of cell wall in mycobacteria and achieved a significant increase in cell permeability by disrupting them without affecting the cell wall structural stability. At length, the destruction of Mn_TmaT and Mn_SucT alone increased the conversion rate of 9-OHAD from 45.3% (6.67 ± 0.39 g/L) to 62.4% (9.19 ± 0.58 g/L) and 67.9% (10.02 ± 0.62 g/L) while the continuous destruction of Mn_TmaT and Mn_SucT did not further improve the conversion efficiency of 9-OHAD. Notably, it was investigated that the continuous destruction of Mn_TmaT and Mn_SucT led to alterations in both the covalent and non-covalent binding layers of the cell wall, resulting in excessive changes in cell morphology and structure, which ultimately decreased 9-OHAD production. Therefore, this study deciphered a pivotal biosynthetic path of cell wall and provided an efficient and feasible construction strategy of 9-OHAD synthesis in mycobacteria.

Current advances in phytosterol free forms and esters: Classification, biosynthesis, chemistry, and detection

Phytosterols are plant sterols that are important secondary plant metabolites with significant pharmacological properties. Their presence in the plant kingdom concerns many unrelated botanical families such as oleageneous plants and cereals. The structures of phytosterols evoke those of cholesterol. These molecules are composed of a sterane ring, also known as perhydrocyclopentanophenanthrene, along with a methyl or ethyl group at C-24 in their side chains, a hydroxyl group at C-3 on ring A, and one or two double bonds in the B ring. Phytosterols display different oxidation degrees at the sterane ring and at the side chain as well as varying numbers of carbons with complex stereochemistries. Fats and water solubilities of phytosterols have been achieved by physical, chemical and enzymatic esterifications to favor their bioavailability and to improve the sensory quality of food, and the efficiency of pharmaceutic and cosmetic products. This review aims to provide comprehensive information starting from the definition and structural classification of phytosterols, and exposes an update of their biogenic relationships. Next, the synthesis of phytosterol esters and their applications as well as their effective roles as hormone precursors are discussed. Finally, a concise exploration of the latest advancements in phytosterol / oxyphytosterols analysis techniques is provided, with a particular focus on modern hyphenated techniques.

Holistic transcriptional responses of Cordyceps militaris to different culture temperatures

Cordyceps militaris is a medicinal entomopathogenic fungus containing valuable biometabolites for pharmaceutical applications. Its genetic inheritance and environmental factors play a crucial role in the production of biomass enriched with cordycepin. While temperature is a crucial controlled parameter for fungal cultivation, its impacts on growth and metabolite biosynthesis remains poorly characterized. This study aimed to investigate the metabolic responses and cordycepin production of C. militaris strain TBRC6039 under various temperature conditions through transcriptome analysis. Among 9599 expressed genes, 576 genes were significantly differentially expressed at culture temperatures of 15 and 25 °C. The changes in the transcriptional responses induced by these temperatures were found in several metabolisms involved in nutrient assimilation and energy source, including amino acids metabolism (e.g., glycine, serine and threonine metabolism) and lipid metabolism (e.g., biosynthesis of unsaturated fatty acids and steroid biosynthesis). At the lower temperature (15 °C), the biosynthetic pathways of lipids, specifically ergosterol and squalene, were the target for maintaining membrane function by transcriptional upregulation. Our study revealed the responsive mechanisms of C. militaris in acclimatization to temperature conditions that provide an insight on physiological manipulation for the production of metabolites by C. militaris.

Shy is a proteobacterial steroid hydratase which catalyzes steroid side chain degradation without requiring a catalytically inert partner domain

Shy (side chain hydratase) and Sal (side chain aldolase), are involved in successive reactions in the pathway of bile acid side chain catabolism in Proteobacteria. Untagged Shy copurified with His-tagged Sal indicating that the two enzymes form a complex. Shy contains a MaoC and a DUF35 domain. When coexpressed with Sal, the DUF35 domain but not the MaoC domain of Shy was observed to copurify with Sal, indicating Sal interacts with Shy through its DUF35 domain. The MaoC domain of Shy (ShyMaoC) remained catalytically viable and could hydrate cholyl-enoyl-CoA with similar catalytic efficiency as in the Shy-Sal complex. Sal expressed with the DUF35 domain of Shy (Sal-ShyDUF35) was similarly competent for the retro-aldol cleavage of cholyl-3-OH-CoA. ShyMaoC showed a preference for C5 side chain bile acid substrates, exhibiting low activity toward C3 side chain substrates. The ShyMaoC structure was determined by X-ray crystallography, showing a hot dog fold with a short central helix surrounded by a twisted antiparallel β-sheet. Modeling and mutagenesis studies suggest that the bile acid substrate occupies the large open cleft formed by the truncated central helix and repositioning of the active site housing. ShyMaoC therefore contains two substrate binding sites per homodimer, making it distinct from previously characterized MaoC steroid hydratases that are (pseudo) heterodimers with one substrate binding site per dimer. The characterization of Shy provides insight into how MaoC family hydratases have adapted to accommodate large polycyclic substrates that can facilitate future engineering of these enzymes to produce novel steroid pharmaceuticals.

Improving the production of 22-hydroxy-23,24-bisnorchol-4-ene-3-one in Mycolicibacterium smegmatis

The 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) is a C22 steroid synthon of pharmaceutical interest that can be produced as a lateral end-product of the catabolism of natural sterols (e.g., cholesterol or phytosterols). This work studies the role of an aldehyde dehydrogenase coded by the MSMEG_6563 gene of Mycolicibacterium smegmatis, named msRed, in 4-HBC production. This gene is located contiguously to the MSMEG_6561 encoding the aldolase msSal which catalyses the retroaldol elimination of acetyl-CoA of the metabolite intermediate 22-hydroxy-3-oxo-cholest-4-ene-24-carboxyl-CoA to deliver 3-oxo-4-pregnene-20-carboxyl aldehyde (3-OPA). We have demonstrated that msRed reduces 3-OPA to 4-HBC. Moreover, the role of msOpccR reductase encoded by MSMEG_1623 was also explored confirming that it also performs the reduction of 3-OPA into 4-HBC, but less efficiently than msRed. To obtain a M. smegmatis 4-HBC producer strain we deleted MSMEG_5903 (hsd4A) gene in strain MS6039-5941 (ΔkshB1, ΔkstD1) that produces 4-androstene-3,17-dione (AD) from natural sterols (cholesterol or phytosterols). The triple MS6039-5941-5903 mutant was able to produce 9 g/L of 4-HBC from 14 g/L of phytosterols in 2 L bioreactor, showing a productivity of 0.140 g/L h-1. To improve the metabolic flux of sterols towards the production of 4-HBC we have cloned and overexpressed the msSal and msRed enzymes in the MS6039-5941-5903 mutant rendering a production titter of 12.7 g/L with a productivity of 0.185 g/L h-1, and demonstrating that the new recombinant strain has a great potential for its industrial application.

Design, synthesis and molecular modeling of novel D-ring substituted steroidal 4,5-dihydropyrazole thiazolinone derivatives as anti-inflammatory agents by inhibition of COX-2/iNOS production and down-regulation of NF-κB/MAPKs in LPS-induced RAW264.7 macrophage cells

It has been reported that 4,5-dihydropyrazole and thiazole derivatives have many biological functions, especially in the aspect of anti-inflammation. According to the strategy of pharmacophore combination, we introduced thiazolinone and dihydropyrazole moiety into steroid skeleton to design and synthesize a novel series of D-ring substituted steroidal 4,5-dihydropyrazole thiazolinone derivatives, and assessed their in vitro anti-inflammatory profiles against Lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 macrophage cells. The anti-inflammatory activities assay demonstrated that compound 12e was considered as the most effective anti-inflammatory drug, which suppressed the expression of pro-inflammatory mediators including nitric oxide (NO), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), it also dose-dependently inhibited the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-induced RAW 264.7 macrophage cells. Furthermore, the results of the Western blot analysis showed a correlation between the inhibition of the Nuclear factor-kappa B (NF-κB) and Mitogen-activated protein kinases (MAPKs) signaling pathways and the suppressive effects of compound 12e on pro-inflammatory cytokines. Molecular docking studies of compound 12e into the COX-2 protein receptor (PDB ID: 5IKQ) active site was performed to rationalize their COX-2 inhibitory potency. The results were found to be in line with the biological findings as they exerted more favorable interactions compared to that of dexamethasone (DXM), explaining their remarkable COX-2 inhibitory activity. The findings revealed that these candidates could be identified as potent anti-inflammatory agents, compound 12e could be a promising drug for the treatment of inflammatory diseases.

Cytochrome P450 Mining for Bufadienolide Diversification

Bufadienolides are a class of steroids with a distinctive α-pyrone ring at C17, mostly produced by toads and consisting of over 100 orthologues. They exhibit potent cardiotonic and antitumor activities and are active ingredients of the traditional Chinese medicine Chansu and Cinobufacini. Direct extraction from toads is costly, and chemical synthesis is difficult, limiting the accessibility of active bufadienolides with diverse modifications and trace content. In this work, based on the transcriptome and genome analyses, using a yeast-based screening platform, we obtained eight cytochrome P450 (CYP) enzymes from toads, which catalyze the hydroxylation of bufalin and resibufogenin at different sites. Moreover, a reported fungal CYP enzyme Sth10 was found functioning in the modification of bufalin and resibufogenin at multiple sites. A total of 15 bufadienolides were produced and structurally identified, of which six were first discovered. All of the compounds were effective in inhibiting the proliferation of tumor cells, especially 19-hydroxy-bufalin (2) and 1β-hydroxy-bufalin (3), which were generated from bufalin hydroxylation catalyzed by CYP46A35. The catalytic efficiency of CYP46A35 was improved about six times and its substrate diversity was expanded to progesterone and testosterone, the common precursors for steroid drugs, achieving their efficient and site-specific hydroxylation. These findings elucidate the key modification process in the synthesis of bufadienolides by toads and provide an effective way for the synthesis of unavailable bufadienolides with site-specific modification and active potentials.

Efficient Production of 9,22-Dihydroxy-23,24-bisnorchol-4-ene-3-one from Phytosterols by Modifying Multiple Genes in Mycobacterium fortuitum

C19 steroids and C22 steroids are vital intermediates for the synthesis of steroid drugs. Compared with C19 steroids, C22 steroids are more suitable for synthesizing progesterone and adrenocortical hormones, albeit less developed. 9,22-dihydroxy-23,24-bisnorchol-4-ene-3-one(9-OHBA), due to its substituents at positions C-9 and C-22, is a beneficial and innovative steroid derivative for synthesizing corticosteroids. We focused on the C22 pathway in Mycobacterium fortuitum ATCC 35855, aiming to develop a productive strain that produces 9-OHBA. We used a mutant strain, MFΔkstD, that knocked out kstds from Mycobacterium fortuitum ATCC 35855 named MFKD in this study as the original strain. Hsd4A and FadA5 are key enzymes in controlling the C19 metabolic pathway of steroids in Mycobacterium fortuitum ATCC 35855. After knocking out hsd4A, MFKDΔhsd4A accumulated 81.47% 9-OHBA compared with 4.13% 9-OHBA in the strain MFKD. The double mutant MFKDΔhsd4AΔfadA5 further improved the selectivity of 9-OHBA to 95.13%, and 9α-hydroxy-4-androstenedione (9-OHAD) decreased to 0.90% from 4.19%. In the end, we obtained 6.81 g/L 9-OHBA from 10 g/L phytosterols with a molar yield of 80.33%, which showed the best performance compared with formerly reported strains.

Combining Metabolic Engineering and Lipid Droplet Assembly to Achieve Campesterol Overproduction in Saccharomyces cerevisiae

Campesterol is a kind of important functional food additive. Therefore, stable and efficient campesterol biosynthesis is significant. Herein, we first knocked out the sterol 22-desaturase gene in Saccharomyces cerevisiae and expressed sterol Δ7-reductase from Pangasianodon hypophthalmus, obtaining a strain that produced 6.6 mg/L campesterol. Then, the modular expression of campesterol synthesis enzymes was performed, and a campesterol titer of 88.3 mg/L was achieved. Because campesterol is a lipid-soluble macromolecule, we promoted lipid droplet formation by exploring regulatory factors, and campesterol production was improved to 169.20 mg/L. Next, triacylglycerol lipase was used to achieve compartment campesterol synthesis. After enhancing the expression of sterol Δ7-reductase and screening cations, the campesterol titer reached 438.28 mg/L in a shake flask and 1.44 g/L in a 5 L bioreactor, which represents the highest campesterol titer reported to date. Metabolic regulation combined with lipid droplet engineering may be useful for the synthesis of other steroids as well.

Bioassay-guided isolation of anti-leukemic steroids from Aglaia abbreviata by inducing apoptosis

The strategy of bioactivity-guided isolation is widely used to obtain active compounds as quickly as possible. Thus, the inhibitory effects on human erythroleukemia cells (HEL) were applied to guide the isolation of the anti-leukemic compounds from Aglaia abbreviata. As a result, 19 compounds (16 steroids, two phenol derivatives, and a rare C12 chain nor-sesquiterpenoid), including 13 new compounds, were isolated and identified based on spectroscopic data analysis, single-crystal X-ray diffraction data, and electronic circular dichroism (ECD) calculations. Among them, 9 steroids exhibited good selective anti-leukemic activity against HEL and K562 (human chronic myeloid leukemia cells) cells with IC50 values between 2.29 ± 0.18 μM and 19.58 ± 0.13 μM. Notably, all the active compounds had relatively lower toxicity on the normal human liver cell line (HL-7702). Furthermore, five compounds (1, 4, 8, 10, and 19) displayed good anti-inflammatory effects, with IC50 values between 7.15 ± 0.16 and 27.1 ± 0.37 μM. An α,β-unsaturated ketone or a 5,6Δ double bond was crucial for improving anti-leukemic effect from the structure-activity relationship analysis. The compound with the most potential, 14 was selected for the preliminary mechanistic study. Compound 14 can induce apoptosis and cause cell cycle arrest. The expression of the marker proteins, such as PARP and caspase 3, were notably effected by this compound, thus inducing apoptosis. In conclusion, our investigation implied that compound 14 may serve as a potential anti-leukemia agent.

Immobilization of rough morphotype Mycolicibacterium neoaurum R for androstadienedione production

OBJECTIVES

Enhance the androstadienedione (Androst-1,4-diene-3,17-dione, ADD) production of rough morphotype Mycolicibacterium neoaurum R by repeated-batch fermentation of immobilized cells.

RESULTS

M. neoaurum R was a rough colony morphotype variant, obtained from the routine plating of smooth M. neoaurum strain CICC 21097. M. neoaurum R showed rougher cell surface and aggregated in broth. The ADD production of M. neoaurum R was notably lower than that of M. neoaurum CICC 21097 during the free cell fermentation, but the yield gap could be erased after proper cell immobilization. Subsequently, repeated-batch fermentation of immobilized M. neoaurum R was performed to shorten the production cycle and enhance the bio-production efficiency of ADD. Through the optimization of the immobilization carriers and the co-solvents for phytosterols, the ADD productivity of M. neoaurum R immobilized by semi-expanded perlite reached 0.075 g/L/h during the repeated-batch fermentation for 40 days.

CONCLUSIONS

The ADD production of the rough-type M. neoaurum R was notably enhanced by the immobilization onto semi-expanded perlite. Moreover, the ADD batch yields of M. neoaurum R immobilized by semi-expanded perlite were maintained at high levels during the repeated-batch fermentation.

Microbial metabolism of diosgenin by a novel isolated Mycolicibacterium sp. HK-90: A promising biosynthetic platform to produce 19-carbon and 21-carbon steroids

Green manufacture of steroid precursors from diosgenin by microbial replacing multistep chemical synthesis has been elusive. It is currently limited by the lack of strain and degradation mechanisms. Here, we demonstrated the feasibility of this process using a novel strain Mycolicibacterium sp. HK-90 with efficiency in diosgenin degradation. Diosgenin degradation by strain HK-90 involves the selective removal of 5,6-spiroketal structure, followed by the oxygenolytic cleavage of steroid nuclei. Bioinformatic analyses revealed the presence of two complete steroid catabolic gene clusters, SCG-1 and SCG-2, in the genome of strain HK-90. SCG-1 cluster was found to be involved in classic phytosterols or cholesterol catabolic pathway through the deletion of key kstD1 gene, which promoted the mutant m-∆kstD1 converting phytosterols to intermediate 9α-hydroxyandrostenedione (9-OHAD). Most impressively, global transcriptomics and characterization of key genes suggested SCG-2 as a potential gene cluster encoding diosgenin degradation. The gene inactivation of kstD2 in SCG-2 resulted in the conversion of diosgenin to 9-OHAD and 9,16-dihydroxy-pregn-4-ene-3,20-dione (9,16-(OH)2 -PG) in mutant m-ΔkstD2. Moreover, the engineered strain mHust-ΔkstD1,2,3 with a triple deletion of kstDs was constructed, which can stably accumulate 9-OHAD by metabolizing phytosterols, and accumulate 9-OHAD and 9,16-(OH)2 -PG from diosgenin. Diosgenin catabolism in strain mHust-ΔkstD1,2,3 was revealed as a progression through diosgenone, 9,16-(OH)2 -PG, and 9-OHAD to 9α-hydroxytestosterone (9-OHTS). So far, this work is the first report on genetically engineered strain metabolizing diosgenin to produce 21-carbon and 19-carbon steroids. This study presents a promising biosynthetic platform for the green production of steroid precursors, and provide insights into the complex biochemical mechanism of diosgenin catabolism.

Actinobacteria as Microbial Cell Factories and Biocatalysts in The Synthesis of Chiral Intermediates and Bioactive Molecules; Insights and Applications

Actinobacteria are one of the most intriguing bacterial phyla in terms of chemical diversity and bioactivities of their reported biomolecules and natural products, including various types of chiral molecules. Actinobacterial genera such as Detzia, Mycobacterium, and Streptomyces are among the microbial sources targeted for selective reactions such as asymmetric biocatalysis catalyzed by whole cells or enzymes induced in their cell niche. Remarkably, stereoselective reactions catalyzed by actinobacterial whole cells or their enzymes include stereoselective oxidation, stereoselective reduction, kinetic resolution, asymmetric hydrolysis, and selective transamination, among others. Species of actinobacteria function with high chemo-, regio-, and enantio-selectivity under benign conditions, which could help current industrial processing. Numerous selective enzymes were either isolated from actinobacteria or expressed from actinobacteria in other microbes and hence exploited in the production of pure organic compounds difficult to obtain chemically. In addition, different species of actinobacteria, especially Streptomyces species, function as natural producers of chiral molecules of therapeutic importance. Herein, we discuss some of the most outstanding contributions of actinobacteria to asymmetric biocatalysis, which are important in the organic and/or pharmaceutical industries. In addition, we highlight the role of actinobacteria as microbial cell factories for chiral natural products with insights into their various biological potentialities.

Efficiency aspects of regioselective testosterone hydroxylation with highly active CYP450-based whole-cell biocatalysts

Steroid hydroxylations belong to the industrially most relevant reactions catalysed by cytochrome P450 monooxygenases (CYP450s) due to the pharmacological relevance of hydroxylated derivatives. The implementation of respective bioprocesses at an industrial scale still suffers from several limitations commonly found in CYP450 catalysis, that is low turnover rates, enzyme instability, inhibition and toxicity related to the substrate(s) and/or product(s). Recently, we achieved a new level of steroid hydroxylation rates by introducing highly active testosterone-hydroxylating CYP450 BM3 variants together with the hydrophobic outer membrane protein AlkL into Escherichia coli-based whole-cell biocatalysts. However, the activity tended to decrease, which possibly impedes overall productivities and final product titres. In this study, a considerable instability was confirmed and subject to a systematic investigation regarding possible causes. In-depth evaluation of whole-cell biocatalyst kinetics and stability revealed a limitation in substrate availability due to poor testosterone solubility as well as inhibition by the main product 15β-hydroxytestosterone. Instability of CYP450 BM3 variants was disclosed as another critical factor, which is of general significance for CYP450-based biocatalysis. Presented results reveal biocatalyst, reaction and process engineering strategies auguring well for industrial implementation of the developed steroid hydroxylation platform.

Identification of the aldolase responsible for the production of 22-hydroxy-23,24-bisnorchol-4-ene-3-one from natural sterols in Mycolicibacterium smegmatis

Mycobacterial mutants blocked in ring degradation constructed to achieve C19 synthons production, also accumulate by-products such as C22 intermediates throughout an alternative pathway reducing the production yields and complicating the downstream purification processing of final products. In this work, we have identified the MSMEG_6561 gene, encoding an aldolase responsible for the transformation of 22-hydroxy-3-oxo-cholest-4-ene-24-carboxyl-CoA (22-OH-BCN-CoA) into the 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) precursor (20S)-3-oxopregn-4-ene-20-carboxaldehyde (3-OPA). The deletion of this gene increases the production yield of the C-19 steroidal synthon 4-androstene-3,17-dione (AD) from natural sterols, avoiding the production of 4-HBC as by-product and the drawbacks in the AD purification. The molar yield of AD production using the MS6039-5941-6561 triple mutant strain was checked in flasks and bioreactor improving very significantly compared with the previously described MS6039-5941 strain.

Approaches Towards Better Immunosuppressive Agents

Several classes of compounds are applied in clinics due to their immunosuppressive properties in transplantology and the treatment of autoimmune diseases. Derivatives of mycophenolic acid, corticosteroids and chemotherapeutics bearing heterocyclic moieties like methotrexate, azathioprine, mizoribine, and ruxolitinib are active substances with investigated mechanisms of action. However, improved synthetic approaches of known drugs and novel derivatives are still being reported to attempt better accessibility and therapeutic properties. In this review article, we present the synthesis of the designed chemical structures based on recent literature reports concerning novel compounds as promising immunosuppressive drugs. Moreover, some of the discussed derivers revealed also other types of activities with prospective medicinal potential.

Phytosterol conversion into C9 non-hydroxylated derivatives through gene regulation in Mycobacterium fortuitum

Androst-4-ene-3,17-dione (AD) and 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) are important drug intermediates that can be biosynthesized from phytosterols. However, the C9 hydroxylation of steroids via 3-ketosteroid 9α-hydroxylase (KSH) limits AD and 4-HBC accumulation. Five active KshAs, the oxidation component of KSH, were identified in Mycobacterium fortuitum ATCC 35855 for the first time. The deletion of kshAs indicated that the five KshA genes were jointly responsible for C9 hydroxylation during phytosterol biotransformation. MFKDΔkshA, the five KshAs deficient strain, blocked C9 hydroxylation and produced 5.37 g/L AD and 0.55 g/L 4-HBC. The dual function reductase Opccr knockout and 17β-hydroxysteroid dehydrogenase Hsd4A enhancement reduced 4-HBC content from 8.75 to 1.72% and increased AD content from 84.13 to 91.34%, with 8.24 g/L AD being accumulated from 15 g/L phytosterol. In contrast, hsd4A and thioesterase fadA5 knockout resulted in the accumulation of 5.36 g/L 4-HBC from 10 g/L phytosterol. We constructed efficient AD (MFKDΔkshAΔopccr_hsd4A) and 4-HBC (MFKDΔkshAΔhsd4AΔfadA5) producers and provided insights for further metabolic engineering of the M. fortuitum ATCC 35855 strain for steroid productions. KEY POINTS: • Five active KshAs were first identified in M. fortuitum ATCC 35855. • Deactivation of all five KshAs blocks the steroid C9 hydroxylation reaction. • AD or 4-HBC production was improved by Hsd4A, FadA5, and Opccr modification.

Synthesis of Metabolites and Metabolite-like Compounds Using Biocatalytic Systems

Methodologies for the synthesis and purification of metabolites, which have been developed following their discovery, analysis, and structural identification, have been involved in numerous life science milestones. The renewed focus on the small molecule domain of biological cells has also created an increasing awareness of the rising gap between the metabolites identified and the metabolites which have been prepared as pure compounds. The design and engineering of resource-efficient and straightforward synthetic methodologies for the production of the diverse and numerous metabolites and metabolite-like compounds have attracted much interest. The variety of metabolic pathways in biological cells provides a wonderful blueprint for designing simplified and resource-efficient synthetic routes to desired metabolites. Therefore, biocatalytic systems have become key enabling tools for the synthesis of an increasing number of metabolites, which can then be utilized as standards, enzyme substrates, inhibitors, or other products, or for the discovery of novel biological functions.

Advances and Challenges in Plant Sterol Research: Fundamentals, Analysis, Applications and Production

Plant sterols (PS) are cholesterol-like terpenoids widely spread in the kingdom Plantae. Being the target of extensive research for more than a century, PS have topped with evidence of having beneficial effects in healthy subjects and applications in food, cosmetic and pharmaceutical industries. However, many gaps in several fields of PS's research still hinder their widespread practical applications. In fact, many of the mechanisms associated with PS supplementation and their health benefits are still not fully elucidated. Furthermore, compared to cholesterol data, many complex PS chemical structures still need to be fully characterized, especially in oxidized PS. On the other hand, PS molecules have also been the focus of structural modifications for applications in diverse areas, including not only the above-mentioned but also in e.g., drug delivery systems or alternative matrixes for functional foods and fats. All the identified drawbacks are also superimposed by the need of new PS sources and technologies for their isolation and purification, taking into account increased environmental and sustainability concerns. Accordingly, current and future trends in PS research warrant discussion.

Research progress in steroidal saponins from the genus Polygonatum: Chemical components, biosynthetic pathways and pharmacological effects

The genus Polygonatum Mill. belongs to the Liliaceae family, which is widely distributed all over the world. Modern studies have found that Polygonatum plants are very rich in chemical compounds such as saponins, polysaccharides and flavonoids. Steroidal saponins are the most commonly studied saponins in the genus Polygonatum and a total of 156 compounds have been isolated from 10 species of the genus. These molecules possess antitumor, immunoregulatory, anti-inflammatory, antibacterial, antiviral, hypoglycemic, lipid-lowering and anti-osteoporotic activities. In this review, we summarize recent advances in studies of the chemical constituents of steroidal saponins from Polygonatum, including their structural characteristics, possible biosynthetic pathways and pharmacological effects. Then, the relationship between the structure and some physiological activities is considered. This review aims to provide reference for further exploitation and utilization of the genus Polygonatum.

Expression of Synthetic cyp102A1-LG23 Gene and Functional Analysis of Recombinant Cytochrome P450 BM3-LG23 in the Actinobacterium Mycolicibacterium smegmatis

Cytochrome CYP102A1 (P450 BM3) of Priestia megaterium (bas. Bacillus megaterium) has several unique functional features and thus provides an ideal object for directed evolution and other synthetic applications. Previously, the CYP102A1-LG23 mutant with 14 mutations in the heme part was obtained that hydroxylates several androstanes at C7β with the formation of products with the anti-inflammatory and neuroprotective activities. In this study, synthetic cyp102A1-LG23 gene encoding the P450 BM3 mutant was expressed as a component of either monocistronic operon or bicistronic operon containing the gdh (glucose dehydrogenase, GDH) or zwf2 (glucose 6-phosphate dehydrogenase, G6PD) gene in Mycolicibacterium smegmatis BD cells. The recombinant bacteria were able hydroxylate androst-4-ene-3,17-dione (AD) into 7β-OH-AD. Their biocatalytic activity was increased twice by increasing the solubility of CYP102A1-LG23 protein in the cells and supplementing the cells with the additional cofactor regeneration system by introducing GDH and G6PD. The maximum 7β-OH-AD yield (37.68 mol%) was achieved by co-expression of cyp102A1-LG23 and gdh genes in M. smegmatis. These results demonstrate the possibility of using synthetic genes to obtain recombinant enzymes and expand our understanding of the processes involved in steroid hydroxylation by bacterial cytochromes. The data obtained can be used to develop new approaches for microbiological production of 7β-hydroxylated steroids in genetically modified Mycolicibacterium species.

Driving the conversion of phytosterol to 9α-hydroxy-4-androstene-3,17-dione in Mycolicibacterium neoaurum by engineering the supply and regeneration of flavin adenine dinucleotide

BACKGROUND

The conversion of phytosterols to steroid synthons by engineered Mycolicibacteria comprises one of the core steps in the commercial production of steroid hormones. This is a complex oxidative catabolic process, and taking the production of androstenones as example, it requires about 10 equivalent flavin adenine dinucleotide (FAD). As the high demand for FAD, the insufficient supply of FAD may be a common issue limiting the conversion process.

RESULTS

We substantiated, using the production of 9α-hydroxy-4-androstene-3,17-dione (9-OHAD) as a model, that increasing intracellular FAD supply could effectively increase the conversion of phytosterols into 9-OHAD. Overexpressing ribB and ribC, two key genes involving in FAD synthesis, could significantly enhance the amount of intracellular FAD by 167.4% and the production of 9-OHAD by 25.6%. Subsequently, styrene monooxygenase NfStyA2B from Nocardia farcinica was employed to promote the cyclic regeneration of FAD by coupling the oxidation of nicotinamide adenine dinucleotide (NADH) to NAD+, and the production of 9-OHAD was further enhanced by 9.4%. However, the viable cell numbers decreased by 20.1%, which was attributed to sharply increased levels of H2O2 because of the regeneration of FAD from FADH2. Thus, we tried to resolve the conflict between FAD regeneration and cell growth by the overexpression of catalase and promotor replacement. Finally, a robust strain NF-P2 was obtained, which could produce 9.02 g/L 9-OHAD after adding 15 g/L phytosterols with productivity of 0.075 g/(L h), which was 66.7% higher than that produced by the original strain.

CONCLUSIONS

This study highlighted that the cofactor engineering, including the supply and recycling of FAD and NAD+ in Mycolicibacterium, should be adopted as a parallel strategy with pathway engineering to improve the productivity of the industrial strains in the conversion of phytosterols into steroid synthons.

Whole-Genome Analysis of Mycobacterium neoaurum DSM 1381 and the Validation of Two Key Enzymes Affecting C22 Steroid Intermediates in Sterol Metabolism

Mycobacterium neoaurum DSM 1381 originated from Mycobacterium neoaurum ATCC 25790 by mutagenesis screening is a strain of degrading phytosterols and accumulating important C22 steroid intermediates, including 22-hydroxy-23, 24-bisnorchola-4-en-3-one (4-HP) and 22-hydroxy-23, 24-bisnorchola-1,4-dien-3-one (HPD). However, the metabolic mechanism of these C22 products in M. neoaurum DSM 1381 remains unknown. Therefore, the whole-genome sequencing and comparative genomics analysis of M. neoaurum DSM 1381 and its parent strain M. neoaurum ATCC 25790 were performed to figure out the mechanism. As a result, 28 nonsynonymous single nucleotide variants (SNVs), 17 coding region Indels, and eight non-coding region Indels were found between the genomes of the two strains. When the wild-type 3-ketosteroid-9α-hydroxylase subunit A1 (KshA1) and β-hydroxyacyl-CoA dehydrogenase (Hsd4A) were overexpressed in M. neoaurum DSM 1381, the steroids were transformed into the 4-androstene-3, 17- dione (AD) and 1,4-androstadiene-3,17-dione (ADD) instead of C22 intermediates. This result indicated that 173N of KshA1 and 171K of Hsd4A are indispensable to maintaining their activity, respectively. Amino acid sequence alignment analysis show that both N173D in KshA1 and K171E in Hsd4A are conservative sites. The 3D models of these two enzymes were predicted by SWISS-MODEL and AlphaFold2 to understand the inactivation of the two key enzymes. These results indicate that K171E in Hsd4A may destroy the inaction between the NAD+ with the NH3+ and N173D in KshA1 and may disrupt the binding of the catalytic domain to the substrate. A C22 steroid intermediates-accumulating mechanism in M. neoaurum DSM 1381 is proposed, in which the K171E in Hsd4A leads to the enzyme's inactivation, which intercepts the C19 sub-pathways and accelerates the C22 sub-pathways, and the N173D in KshA1 leads to the enzyme's inactivation, which blocks the degradation of C22 intermediates. In conclusion, this study explained the reasons for the accumulation of C22 intermediates in M. neoaurum DSM 1381 by exploring the inactivation mechanism of the two key enzymes.

Improving the production of 9α-hydroxy-4-androstene-3,17-dione from phytosterols by 3-ketosteroid-Δ1-dehydrogenase deletions and multiple genetic modifications in Mycobacterium fortuitum

BACKGROUND

9α-hydroxyandrost-4-ene-3,17-dione (9-OHAD) is a significant intermediate for the synthesis of glucocorticoid drugs. However, in the process of phytosterol biotransformation to manufacture 9-OHAD, product degradation, and by-products restrict 9-OHAD output. In this study, to construct a stable and high-yield 9-OHAD producer, we investigated a combined strategy of blocking Δ¹‑dehydrogenation and regulating metabolic flux.

RESULTS

Five 3-Ketosteroid-Δ¹-dehydrogenases (KstD) were identified in Mycobacterium fortuitum ATCC 35855. KstD2 showed the highest catalytic activity on 3-ketosteroids, followed by KstD3, KstD1, KstD4, and KstD5, respectively. In particular, KstD2 had a much higher catalytic activity for C9 hydroxylated steroids than for C9 non-hydroxylated steroids, whereas KstD3 showed the opposite characteristics. The deletion of kstDs indicated that KstD2 and KstD3 were the main causes of 9-OHAD degradation. Compared with the wild type M. fortuitum ATCC 35855, MFΔkstD, the five kstDs deficient strain, realized stable accumulation of 9-OHAD, and its yield increased by 42.57%. The knockout of opccr or the overexpression of hsd4A alone could not reduce the metabolic flux of the C22 pathway, while the overexpression of hsd4A based on the knockout of opccr in MFΔkstD could remarkably reduce the contents of 9,21 ‑dihydroxy‑20‑methyl‑pregna‑4‑en‑3‑one (9-OHHP) by-products. The inactivation of FadE28-29 leads to a large accumulation of incomplete side-chain degradation products. Therefore, hsd4A and fadE28-29 were co-expressed in MFΔkstDΔopccr successfully eliminating the two by-products. Compared with MFΔkstD, the purity of 9-OHAD improved from 80.24 to 90.14%. Ultimately, 9‑OHAD production reached 12.21 g/L (83.74% molar yield) and the productivity of 9-OHAD was 0.0927 g/L/h from 20 g/L phytosterol.

CONCLUSIONS

KstD2 and KstD3 are the main dehydrogenases that lead to 9-OHAD degradation. Hsd4A and Opccr are key enzymes regulating the metabolic flux of the C19- and C22-pathways. Overexpression of fadE28-29 can reduce the accumulation of incomplete degradation products of the side chains. According to the above findings, the MF-FA5020 transformant was successfully constructed to rapidly and stably accumulate 9-OHAD from phytosterols. These results contribute to the understanding of the diversity and complexity of steroid catabolism regulation in actinobacteria and provide a theoretical basis for further optimizing industrial microbial catalysts.

New Insights into the Modification of the Non-Core Metabolic Pathway of Steroids in Mycolicibacterium and the Application of Fermentation Biotechnology in C-19 Steroid Production

Androsta-4-ene-3,17-dione (AD), androsta-1,4-diene-3,17-dione (ADD), and 9α-hydroxy-4-androstene-3,17-dione (9-OHAD), which belong to C-19 steroids, are critical steroid-based drug intermediates. The biotransformation of phytosterols into C-19 steroids by Mycolicibacterium cell factories is the core step in the synthesis of steroid-based drugs. The production performance of engineered mycolicibacterial strains has been effectively enhanced by sterol core metabolic modification. In recent years, research on the non-core metabolic pathway of steroids (NCMS) in mycolicibacterial strains has made significant progress. This review discusses the molecular mechanisms and metabolic modifications of NCMS for accelerating sterol uptake, regulating coenzyme I balance, promoting propionyl-CoA metabolism, reducing reactive oxygen species, and regulating energy metabolism. In addition, the recent applications of biotechnology in steroid intermediate production are summarized and compared, and the future development trend of NCMS research is discussed. This review provides powerful theoretical support for metabolic regulation in the biotransformation of phytosterols.

Alcohols as Efficient Intermolecular Initiators for a Highly Stereoselective Polyene Cyclisation Cascade

The use of benzylic and allylic alcohols in HFIP solvent together with Ti(Oi Pr)4 has been shown to trigger a highly stereoselective polyene cyclisation cascade. Three new carbon-carbon bonds are made during the process and complete stereocontrol of up to five new stereogenic centers is observed. The reaction is efficient, has high functional group tolerance and is atom-economic generating water as a stoichiometric by-product. A new polyene substrate-class is employed, and subsequent mechanistic studies indicate a stereoconvergent mechanism. The products of this reaction can be used to synthesize steroid-analogues in a single step.

Production of 21-hydroxy-20-methyl-pregna-1,4-dien-3-one by modifying multiple genes in Mycolicibacterium

C22 steroid drug intermediates are suitable for corticosteroids synthesis, and the production of C22 steroids is unsatisfactory due to the intricate steroid metabolism. Among the C22 steroids, 21-hydroxy-20-methyl-pregna-1,4-dien-3-one (1,4-HP) could be used for Δ¹-steroid drug synthesis, such as prednisolone. Nevertheless, the production of 1,4-HP remains unsatisfactory. In this study, an ideal 1,4-HP producing strain was constructed. By the knockout of 3-ketosteroid-9-hydroxylase (KshA) genes and 17β-hydroxysteroid dehydrogenase (Hsd4A) gene, the steroid nucleus degradation and the accumulation of C19 steroids in Mycolicibacterium neoaurum were blocked. The mutant strain could transform phytosterols into 1,4-HP as the main product and 21-hydroxy-20-methyl-pregna-4-ene-3-one as a by-product. Subsequently, the purity of 1,4-HP improved to 95.2% by the enhancement of 3-ketosteroid-Δ¹-dehydrogenase (KSTD) activity, and the production of 1,4-HP was improved by overexpressing NADH oxidase (NOX) and catalase (KATE) genes. Consequently, the yield of 1,4-HP achieved 10.5 g/L. The molar yield and the purity of 1,4-HP were optimal so far, and the production of 1,4-HP provides a new intermediate for the pharmaceutical steroid industry. KEY POINTS: • A third 3-ketosteroid-9-hydroxylase was identified in Mycolicibacterium neoaurum. • An 1,4-HP producer was constructed by KshA and Hsd4A deficiency. • The production of 1,4-HP was improved by KSTD, NOX, and KATE overexpression.

Bioconversion of 4-hydroxyestradiol by extradiol ring-cleavage dioxygenases from Novosphingobium sp. PP1Y

Livestock breeding activities and pharmaceutical wastes lead to considerable accumulation of steroid hormones and estrogens in wastewaters. Here estrogens act as pro-cancerogenic agents and endocrine disruptors interfering with the sexual development of aquatic animals and having toxic effects in humans. Environmental bacteria play a vital role in estrogens degradation. Their wide reservoir of enzymes, such as ring cleavage dioxygenases (RCDs), can degrade the steroid nucleus, catalyzing the meta-cleavage of A, B or D steroid rings. In this work, 4 extra-diol ring cleavage dioxygenases (ERCDs), PP28735, PP26077, PP00124 and PP00193, were isolated from the marine sphingomonad Novosphingobium sp. PP1Y and characterized. Enzymes kinetic parameters were determined on different synthetic catecholic substrates. Then, the bioconversion of catechol estrogens was evaluated. PP00124 showed to be an efficient catalyst for the degradation of 4-hydroxyestradiol (4-OHE2), a carcinogenic hydroxylated derivate of E2. 4-OHE2 complete cleavage was obtained using PP00124 both in soluble form and in whole recombinant E. coli cells. LC-MS/MS analyses confirmed the generation of a semialdehyde product, through A-ring meta cleavage. To the best of our knowledge, PP00124 is the first characterized enzyme able to directly degrade 4-OHE2 via meta cleavage. Moreover, the complete 4-OHE2 biodegradation using recombinant whole cells highlighted advantages for bioremediation purposes.

Loop pathways are responsible for tuning the accumulation of C19- and C22-sterol intermediates in the mycobacterial phytosterol degradation pathway

4-Androstene-3,17-dione (4-AD) and 22-hydroxy-23,24-bisnorchol-4-ene-3-one (BA) are the most important and representative C19- and C22-steroidal materials. The optimalization of sterol production with mycobacterial phytosterol conversion has been investigated for decades. One of the major challenges is that current industrial mycobacterial strains accumulate unignorable impurities analogous to desired sterol intermediates, significantly hampering product extractions and refinements. Previously, we identified Mycobacterium neoaurum HGMS2 as an efficient 4-AD-producing strain (Wang et al. in Microb Cell Fact. 19:187, 2020). Recently, we have genetically modified the HGMS2 strain to remove its major impurities including ADD and 9OH-AD (Li et al. in Microb Cell Fact. 20:158, 2021). Unexpectedly, the modified mutants started to significantly accumulate BA compared with the HGMS2 strain. In this work, while we attempted to block BA occurrence during 4-AD accumulation in HGMS2 mutants, we identified a few loop pathways that regulated metabolic flux switching between 4-AD and BA accumulations and found that both the 4-AD and BA pathways shared a 9,10-secosteroidial route. One of the key enzymes in the loop pathways was Hsd4A1, which played an important role in determining 4-AD accumulation. The inactivation of the hsd4A1 gene significantly blocked the 4-AD metabolic pathway so that the phytosterol degradation pathway flowed to the BA metabolic pathway, suggesting that the BA metabolic pathway is a complementary pathway to the 4-AD pathway. Thus, knocking out the hsd4A1 gene essentially made the HGMS2 mutant (HGMS2^Δhsd4A1) start to efficiently accumulate BA. After further knocking out the endogenous kstd and ksh genes, an HGMS2^Δhsd4A1 mutant, HGMS2^{Δhsd4A1/Δkstd1}, enhanced the phytosterol conversion rate to BA in 1.2-fold compared with the HGMS2^Δhsd4A1 mutant in pilot-scale fermentation. The final BA yield increased to 38.3 g/L starting with 80 g/L of phytosterols. Furthermore, we knocked in exogenous active kstd or ksh genes to HGMS2^{Δhsd4A1/Δ kstd1} to construct DBA- and 9OH-BA-producing strains. The resultant DBA- and 9OH-BA-producing strains, HGMS2^{Δhsd4A1/kstd2} and HGMS2^{Δkstd1/Δhsd4A1/kshA1B1}, efficiently converted phytosterols to DBA- and 9OH-BA with the rates of 42.5% and 40.3%, respectively, and their final yields reached 34.2 and 37.3 g/L, respectively, starting with 80 g/L phytosterols. Overall, our study not only provides efficient strains for the industrial production of BA, DBA and 9OH-BA but also provides insights into the metabolic engineering of the HGMS2 strain to produce other important steroidal compounds.

Biocatalysis of Steroids by Mycobacterium sp. in Aqueous and Organic Media

Mycobacterium sp. can convert steroids such as β-sitosterol, campesterol, and cholesterol, by selective side-chain cleavage and oxidation of the C3 hydroxyl group to a ketone, into key intermediates that can be easily functionalized to yield commercially interesting pharmaceutical products. In aqueous systems, the biocatalysis is limited by the low solubility of the steroids in water. Several strategies have been introduced to tackle this limitation, e.g., formation of cyclodextrin-steroid complexes and generation of aqueous microdispersions with steroid particle size in the range of hundreds of nanometers. Still, the introduction of an organic phase acting as a substrate and/or product reservoir is a well-established and relatively easy to implement strategy to overcome the sparing water solubility of steroid molecules. However, the organic phase has to be carefully chosen to prevent tampering with the activity/viability of microbial cells.In this chapter, we describe the methodology for the biocatalysis of β-sitosterol to 4-androstene-3,17-dione (AD) and 1,4-androstadiene-3,17-dione (ADD), both in aqueous and organic:aqueous systems. In the latter case, both traditional organic solvents and green solvents are proposed.

Targeted Mutagenesis of Mycobacterium Strains by Homologous Recombination

Targeted mutagenesis by homologous recombination (TMHR) is an efficient allelic exchange mutagenesis for bacterial genome engineering in synthetic biology. Unlike other allelic exchange methods, TMHR does not require a heterologous recombinase to insert or excise a selectable marker from the genome. In contrast, positive and negative selection is achieved solely by suicide vector-encoded functional and host cell proteins. Here we describe a concise protocol to knock out and knock in a 3-ketosteroid-1,2-dehydrogenase gene (kstd) in Mycobacterium neoaurum HGMS2 using TMHR approach. The homology arms flanking the kstd gene are amplified by PCR in vitro and then subcloned into a common homologous recombination vector. The vector is then electroporated into the HGMS2 competent cells. The replacement of the kstd gene by homologous recombination produces antibiotic-resistant single-crossover recombination via the first allelic exchange. Double-crossover markerless mutants are directly separated using sucrose-mediated counterselection. These two steps can generate seamless mutations down to a single DNA base pair. The whole process takes less than 2 weeks.

Current Trends and Perspectives in Microbial Bioconversions of Steroids

The microbiological transformation of sterols is currently the technological basis for the industrial production of valuable steroid precursors, the so-called synthons, from which a wide range of steroid and indane isoprenoids are obtained by combined chemical and enzymatic routes. These compounds include value-added corticoids, neurosteroids, sex hormones, bile acids, and other terpenoid lipids required by the medicine, pharmaceutical, food, veterinary, and agricultural industries.Progress in understanding the molecular mechanisms of microbial degradation of steroids, and the development and implementation of genetic technologies, opened a new era in steroid biotechnology. Metabolic engineering of microbial producers makes it possible not only to improve the biocatalytic properties of industrial strains by enhancing their target activity and/or suppressing undesirable activities in order to avoid the formation of by-products or degradation of the steroid core, but also to redirect metabolic fluxes in cells towards accumulation of new metabolites that may be useful for practical applications. Along with whole-cell catalysis, the interest of researchers is growing in enzymatic methods that make it possible to carry out selective structural modifications of steroids, such as the introduction of double bonds, the oxidation of steroidal alcohols, or the reduction of steroid carbonyl groups. A promising area of research is strain engineering based on the heterologous expression of foreign steroidogenesis systems (bacterial, fungal, or mammalian) that ensure selective formation of demanded hydroxylated steroids.Here, current trends and progress in microbial steroid biotechnology over the past few years are briefly reviewed, with a particular focus on the application of metabolic engineering and synthetic biology techniques to improve existing and create new whole-cell microbial biocatalysts.

Bidimensional Analyses of the Intra- and Extracellular Proteomes of Steroid Producer Mycobacteria

The importance of the pathogenic mycobacteria has mainly focused the omic analyses on different aspects of their clinical significance. However, those industrially relevant mycobacteria have received less attention, even though the steroid market sales in 2021 were estimated in $56.45 billion.The extracellular proteome, due to its relevance in the sterol processing and uptake, and the intracellular proteome, because of its role in steroids bioconversion, are the core of the present chapter. Both, monodimensional gels, as preparatory analysis, and bidimensional gels as proteome analysis are described. As a proof of concept, the protein extraction methods for both sub-proteomes of Mycobacterium are described. Thus, procedures and relevant key points of these proteome analyses are fully detailed.

Isolation of Environmental Bacteria Able to Degrade Sterols and/or Bile Acids: Determination of Cholesterol Oxidase and Several Hydroxysteroid Dehydrogenase Activities in Rhodococcus, Gordonia, and Pseudomonas putida

Interest about the isolation and characterization of steroid-catabolizing bacteria has increased over time due to the massive release of these recalcitrant compounds and their deleterious effects or their biotransformation derivatives as endocrine disruptors for wildlife, as well as their potential use in biotechnological approaches for the synthesis of pharmacological compounds. Thus, in this chapter, an isolation protocol to select environmental bacteria able to degrade sterols, bile acids, and androgens is shown. Moreover, procedures for the determination of cholesterol oxidase or different hydroxysteroid dehydrogenase activities in Pseudomonas putida DOC21, Rhodococcus sp. HE24.12, Gordonia sp. HE24.4J and Gordonia sp. HE24.3 are also detailed.

Obtaining of 24-Norchol-4-ene-3,22-dione from Phytosterol with Mutants of Mycolicibacterium neoaurum

Engineered mutants of Mycolicibacterium spp. are known producers of valuable steroid synthons with C19 or C22 skeleton. Here we describe a method for site-directed mutagenesis of Mycolicibacterium neoaurum strains, bioconversion from phytosterol, and selective purification of C23 steroid 24-norchol-4-ene-3,22-dione (24-NCED) and C22 steroid 20-hydroxymethylpregn-4-ene-3-one (20-HMP). The yields of crystalline products with 95% purity by the method here described are 2.74 ± 0.085 g for 24-NCED and 1.42 ± 0.085 g for 20-HMP from 10 g/L phytosterol. 20-HMP is recognized as the key precursor in chemical syntheses of pharmaceutical corticosteroids and 24-NCED is a promising synthon for the synthesis of valuable steroids and own potent biological activity.

Production of 11α-Hydroxysteroid Derivatives by Corynebacterium glutamicum Expressing the Rhizopus oryzae Hydroxylating System

Hydroxylation of steroids has acquired special relevance for the pharmaceutical industry. Particularly, the 11α-hydroxylation of steroids is a process of biotechnological importance currently carried out at industrial scale for the production of contraceptive drugs and glucocorticoids. This process is performed by several fungal species including Rhizopus nigricans, Aspergillus ochraceus, Aspergillus niger, and Rhizopus oryzae that are used to produce by biotransformation hydroxylated steroids for pharmaceutical purposes (Wang et al., J Steroid Biochem Mol Biol 171:254-261, 2017). However, the development of more efficient biotransformation processes is essential since the steroidal derivatives obtained by the in vivo hydroxylation are often a mixture of hydroxylated compounds in different positions of the steroid molecule. This phenomenon is due to the large number of different CYPs contained in the fungal strains.The genes responsible for the 11α-hydroxylase activity in R. oryzae consisting in the cytochrome CYP509C12 and its redox partner, the reductase RoCPR1, have been chemically synthetized forming a synthetic operon named FUN optimized to be expressed in bacteria. To express this operon, we have selected the strain Corynebacterium glutamicum R31 that is a robust and GRAS bacterial strain widely used for industrial purposes. The synthetic operon has been cloned in the pECXK-99E vector, yielding pXKFUN plasmid, and transformed C. glutamicum R31 to generate C. glutamicum R31 (pXKFUN) strain. This strain is not a steroid degrader and can efficiently transport C19 and C21 steroids across the cytoplasmic membrane (García-Fernandez et al. Catalysts 316:1-12, 2017). C. glutamicum can be used as a clean host for steroid biotransformation, because it does not introduce additional undesired side reactions on the steroids, thus reducing the contamination of the final products (Felpeto-Santero et al., Microbiol Biotechnol 12:856-868, 2019). Here we show a proof of concept that C. glutamicum can be used as a suitable chassis to perform steroid biotransformation expressing eukaryotic cytochromes. The protocol below provides detailed information on steroid 11α-hydroxylations by Corynebacterium recombinant strain.

Scale-Up of Phytosterols Bioconversion into Androstenedione

Phytosterols, coming as a by-product of vegetable oils or wood pulp, contain the cyclopentanoperhydrophenanthrene nucleus and can be bioconverted into steroid intermediates by removing the C17 side chain. This chapter shows the scale-up, from flask to bioreactor, of phytosterols bioconversion into 4-androstene-3,17-dione (androstenedione; AD) using Mycolicibacterium neoaurum B-3805. Due to the fact that phytosterols and AD are nearly insoluble in water, two-phase systems and the use of chemically modified cyclodextrins have been described as methods to solve it. Here, we use a water-oil two-phase system that allows the bioconversion of up to 20 g/L of phytosterols into AD in 5 L and 20 L bioreactors.

Correlation Relationship between Phase Inversion of Pickering Emulsions and Biocatalytic Activity of Microbial Transformation of Phytosterols

Microbial transformation of hydrophobic phytosterols into the pharmaceutical steroid precursors AD (androst-4-ene-3, 17-dione) and ADD (androst-4-diene-3, 17-dione) in a water–plant oil two-phase system by Mycolicibacterium neoaurum is a paradigm of interfacial biocatalysis in Pickering emulsions stabilized by bacterial cells. In the present work, phase inversion of Pickering emulsions—i.e., Pickering emulsions turning from water-in-oil (W/O) emulsions into oil-in-water (O/W) ones—was observed during microbial transformation in the presence of high concentrations of crystal phytosterols. It was found that there is a correlation relationship between the phase behaviors of Pickering emulsions and the biocatalytic activity of utilizing M. neoaurum as a whole-cell catalyst. Efficient microbial transformation under the high crystal phytosterol loadings was achieved due to the formation of O/W emulsions where interfacial biocatalysis took place. Under the optimal conditions (volume ratio of soybean oil to water: 15:35 mL, phytosterols concentration in the soybean oil: 80 g/L, glucose as co-substrate in the aqueous culture medium: 10 g/L), the concentrations of AD and ADD reached 4.8 g/L based on the whole broth (16 g/L based on the oil phase) after microbial transformation for 9 days.

Biological activity of new bioactive steroids deriving from biotransformation of cortisone

Cortisone is a metabolite belonging to the corticosteroid class that is used pharmaceutically directly as a drug or prodrug. In addition to its large consumption, its use is linked to several side effects, so pharmaceutical research aims to develop effective drugs with low or no side effects, alternative compounds to cortisone are part of an active investment in ongoing research on drug discovery. Since biotransformation can be considered a source of new molecules with potential therapeutic use, the present work focuses on a preliminary in vitro study aimed at evaluating the mutagenic, anti-inflammatory, antioxidant and neuroprotective activity of SCA and SCB molecules obtained from the biotransformation of cortisone using Rh. Rhodnii strain DSM 43960. The results obtained are very encouraging due to the safety of biotransformed compounds with reference to genotoxicity checked by Ames test, to the very high antioxidant capacity and to the anti-inflammatory activity. In fact, thecompounds inhibited both the TNFα-stimulated expression and secretion of NFkB target cytokines, and COX activity, and can activate the glucocorticoid receptor. Finally SCA and SCB exhibited neuroprotective properties.

Concise synthesis of E/F ring spiroethers from tigogenin. Carbaanalogs of steroidal sapogenins and their biological activity

A four-step synthesis of five- and six-membered E/F ring spiroethers from tigogenin has been developed. An efficient strategy that features bis-Grignard reaction of dinorcholanic lactone with appropriate bis(bromomagnesio)alkanes followed by acid-mediated spirocyclization was employed to construct a new class of steroid compounds having E and F ring junction as an oxa-carbacyclic system. The synthesized carbaanalogs interact with liposomes and albumin, and also exhibit antibacterial and antifungal activity, demonstrating their pharmacological potential.