Biocatalytic modifications of pregnenolone by selected filamentous fungi

Bioactive compounds of Curvularia species as a source of various biological activities and biotechnological applications

Many filamentous fungi are known to produce several secondary metabolites or bioactive compounds during their growth and reproduction with sort of various biological activities. Genus Curvularia (Pleosporaceae) is a dematiaceous filamentous fungus that exhibits a facultative pathogenic and endophytic lifestyle. It contains ~213 species among which Curvularia lunata, C. geniculata, C. clavata, C. pallescens, and C. andropogonis are well-known. Among them, C. lunata is a major pathogenic species of various economical important crops especially cereals of tropical regions while other species like C. geniculata is of endophytic nature with numerous bioactive compounds. Curvularia species contain several diverse groups of secondary metabolites including alkaloids, terpenes, polyketides, and quinones. Which possess various biological activities including anti-cancer, anti-inflammatory, anti-microbial, anti-oxidant, and phytotoxicity. Several genes and gene factors are involved to carry and regulate the expression of these activities which are influenced by environmental signals. Some species of Curvularia also show negative impacts on humans and animals. Apart from their negative effects, there are some beneficial implications like production of enzymes of industrial value, bioherbicides, and source of nanoparticles is reported. Many researchers are working on these aspects all over the world but there is no review in literature which provides significant understanding about these all aspects. Thus, this review will provide significant information about secondary metabolic diversity, their biological activities and biotechnological implications of Curvularia species.

Hydroxylation of Progesterone and Its Derivatives by the Entomopathogenic Strain Isaria farinosa KCh KW1.1

Progesterone biotransformation is worth studying because of the high industrial value of its derivatives. This study investigated the catalytic ability of the entomopathogenic filamentous fungus strain Isaria farinosa KCh KW1.1 to transform progesterone derivatives: 11α-hydroxyprogesterone, 17α-hydroxyprogesterone, 16α,17α-epoxyprogesterone and pregnenolone. In the culture of Isaria farinosa KCh KW1.1, 11α-hydroxyprogesterone was effectively transformed into only one product: 6β,11α-dihydroxyprogesterone. Transformation of 17α-hydroxyprogesterone gave three hydroxy derivatives: 6β,17α-dihydroxyprogesterone, 12β,17α-dihydroxyprogesterone and 6β,12β,17α-trihydroxyprogesterone. Two products: 6β-hydroxy-16α,17α-epoxyprogesterone and 6β,11α-dihydroxy-16α,17α-epoxyprogesterone, were obtained from the 16α,17α-epoxyprogesterone transformation. We isolated two compounds from the biotransformation medium with pregnenolone: 11α-hydroxy-7-oxopregnenolone and 5α,6α-epoxy-3β,11α-dihydroxypregnan-7,20-dione. In this study, we observed only mono- and dihydroxy derivatives of the tested substrates, and the number of obtained products for each biotransformation did not exceed three.

Biotransformation of Androstenedione by Filamentous Fungi Isolated from Cultural Heritage Sites in the State Tretyakov Gallery

Simple Summary

Microorganisms are able to grow on substrates of the most diverse nature. One of the most practical habitats, in terms of cultural heritage conservation, is fine art objects such as tempera or oil paintings on canvas. Since tempera paints are produced on the basis of egg yolk, which is one of the richest sources of cholesterol in nature (up to 2% of dry weight), and in the process of aging of tempera materials, changes in cholesterol do not affect the core structure of the steroid nucleus, the group of fungi that we have isolated are tempera painting destructors is seen as a promising object for screening for their possible steroid-transforming activities. In this regard, the purpose of our work was to determine the ability to transform pharmaceutically significant steroids with dominant fungi-destructors of tempera paintings, previously isolated in the State Tretyakov Gallery. Consequently, we have demonstrated for the first time that fungi-destructors of tempera paintings have steroid-transforming activity and are promising microorganisms for screening for biotechnologically significant transformations of steroids with further industrial use.

Abstract

The transformation of steroids by microorganisms is widely used in medical biotechnology. A huge group of filamentous fungi is one of the most promising taxa for screening new biocatalytic reactions in order to obtain pharmaceutically significant steroids. In this work, we screened 10 filamentous fungi-destructors of egg tempera for the ability to biotransform androst-4-en-3,17-dione (AD) during cultivation in a liquid nutrient medium or in a buffer solution. These taxonomically unrelated strains, belonging to the classes Eurotiomycetes, Dothideomycetes and Sordariomycetes, are dominant representatives of the microbiome from halls where works of tempera painting are stored in the State Tretyakov Gallery (STG, Moscow, Russia). Since the binder of tempera paints, egg yolk, contains about 2% cholesterol, these degrading fungi appear to be a promising group for screening for steroid converting activity. It turned out that all the studied fungi-destructors are able to transform AD. Some strains showed transformation efficiency close to the industrial strain Curvularia lunata RNCIM F-981. In total, 33 steroids formed during the transformation of AD were characterized, for 19 of them the structure was established by gas chromatography/mass spectrometry analysis. In this work, we have shown for the first time that fungi-destructors of tempera paintings can efficiently transform steroids.

Engineering of a fungal steroid 11α-hydroxylase and construction of recombinant yeast for improved production of 11α-hydroxyprogesterone

Cytochrome P450 enzyme CYP68J5 from filamentous fungus Aspergillus ochraceus is industrially used for selective C11α-hydroxylation of canrenone and progesterone. To improve its selectivity of C11α-hydroxylation for relevant steroid substrates, a sequence-based targeted mutagenesis combined with saturation mutagenesis was conducted to search for variants with improved hydroxylation reaction specificity toward progesterone and D-ethylgonendione. Recombinant yeast expressing triple mutant V64F/E65G/N66T showed significantly increased C11α-hydroxylation selectivity (85 % VS WT 69.7 %). Saturation mutagenesis of V64, E65 and N66 resulted in the identification of single mutant V64K with greatly enhanced 11α-hydroxylation specificity toward progesterone (90.6 % VS WT 69.7 %). Furthermore, mutant N66D showed significant enhanced selectivity of C11α-hydroxylation toward D-ethylgonendione (70.8 % VS WT 58 %). Evaluation of recombinant yeast over-expressing V64K for progesterone transformation in 50 mL scale resulted in product 11α-OH progesterone concentrations of 432.5 mg/L, a 30.2 % increase compared with the CYP68J5 control. Our results also reveal that V64, E65 and N66 are key residues of CYP68J5 influencing its selectivity of C11α-hydroxylation, thus offering opportunities for further engineering of CYP68J5 for expanded industrial applications.

Hydroxylation of pregnenolone and dehydroepiandrosterone by zygomycete Backusella lamprospora VKM F-944: selective production of 7α-OH-DHEA

In this paper, we studied the transformation of two 3β-hydroxy-5-ene-steroids-pregnenolone and dehydroepiandrosterone (DHEA) by Backusella lamprospora VKM F- 944. The soil-dwelling zygomycete wild-type strain has been earlier selected during the screening and previously unexplored for this purpose. The fungus fully converted pregnenolone to form a mixture of axial 7α-hydroxy-pregnenolone and 7α,11α-dihydroxy-pregnenolone, while no metabolites with β-orientation of the hydroxyl group were detected. The pathway to 7α,11α-diOH-pregnenolone seems to include 7α-hydroxylation of 11α-hydroxylated derivative. The only product from DHEA was identified as 7α-hydroxy-DHEA. The structures of steroid metabolites were confirmed by HPLC, mass-spectrometry (MS), and ¹H and ¹³C NMR analyses. Under the optimized conditions, the yield of 7α-OH-DHEA reached 94% (w/w) or over 14 g/L in absolute terms, even at high concentration of the substrate (DHEA) (15 g/L). To our knowledge, it is the highest yield of the value-added 7α-OH-DHEA reported so far. The results contribute to the knowledge of the diversity of the wild-type fungal strains capable of effective steroid hydroxylation. They could be applied for the production of allylic steroid 7α-alcohols that are widely used in medicine. KEY POINTS: • Zygomycete Backusella lamprospora actively hydroxylates 3β-hydroxy-5-en-steroids. • Axial 7α-hydroxylation is the preferable reaction by the strain towards pregnenolone and DHEA. • The strain selectively produces 7α-OH-DHEA even at high substrate concentrations (up to 15 g/L).

Steroid modification by filamentous fungus Drechslera sp.: Focus on 7-hydroxylase and 17β-hydroxysteroid dehydrogenase activities

Fungal strain Drechslera sp. Ph F-34 was shown to modify 3-oxo- and 3-hydroxy steroids of androstane series to form the corresponding allylic 7-alcohols and 17β-reduced derivatives thus evidencing the presence of 7α-, 7β-hydroxylase and 17β-hydroxysteroid dehydrogenase (17β-HSD) activities. The growing mycelium predominantly hydroxylated androsta-1,4-diene-3,17-dione (ADD) at the 7β-position, while much lower 7α-hydroxylation was observed. Along with 7β-hydroxy-ADD and its corresponding 7α-isomer, their respective 17β-alcohols were produced. In this study, transformation of ADD, androst-4-en-17β-ol-3-one (testosterone, TS) and 3β-hydroxyandrost-5-en-17-one (dehydroepiandrosterone, DHEA) by resting mycelium of Drechslera sp. have been estimated in different conditions with regard to the inducibility and functionality of the 17β-HSD and 7-hydroxylase enzyme systems. Steroids of androstane, pregnane and cholane series were evaluated as inducers. The inhibitory analysis was provided using cycloheximide (CHX). Steroids were assayed using TLC and HPLC methods, and the structures were confirmed by mass-spectrometry, ¹H and ¹³C NMR spectroscopy data. 17β-HSD of the mycelium constitutively reduced 17-carbonyl group of ADD and DHEA to form the corresponding 17β-alcohols, namely, androsta-1,4-diene-17β-ol-3-one (1-dehydro-TS), and androst-5-ene-3β,17β-diol. Production of the 7α- and 7β-hydroxylated derivatives depended on the induction conditions. The inducer effect relied on the steroid structure and decreased in the order: DHEA > pregnenolone > lithocholic acid. β-Sitosterol did not induce hydroxylase activity in Drechslera sp. CHX fully inhibited the synthesis of 7-hydroxylase in Drechslera mycelium thus providing selective 17-keto reduction. Results contribute to the diversity of steroid modifying enzymes in fungi and can be used at the development of novel biocatalysts for production of valuable steroid 7(α/β)- and 17β-alcohols.

Improved 11α-hydroxycanrenone production by modification of cytochrome P450 monooxygenase gene in Aspergillus ochraceus

Eplerenone is a drug that protects the cardiovascular system. 11α-Hydroxycanrenone is a key intermediate in eplerenone synthesis. We found that although the cytochrome P450 (CYP) enzyme system in Aspergillus ochraceus strain MF018 could catalyse the conversion of canrenone to 11α-hydroxycanrenone, its biocatalytic efficiency is low. To improve the efficiency of 11α-hydroxycanrenone production, the CYP monooxygenase-coding gene of MF018 was predicted and cloned based on whole-genome sequencing results. A recombinant A. ochraceus strain MF010 with the high expression of CYP monooxygenase was then obtained through homologous recombination. The biocatalytic rate of this recombinant strain reached 93 % at 60 h without the addition of organic solvents or surfactants and was 17-18 % higher than that of the MF018 strain. Moreover, the biocatalytic time of the MF010 strain was reduced by more than 30 h compared with that of the MF018 strain. These results show that the recombinant A. ochraceus strain MF010 can overcome the limitation of substrate biocatalytic efficiency and thus holds a high poten tial for application in the industrial production of eplerenone.

New 6,19-oxidoandrostan derivatives obtained by biotransformation in environmental filamentous fungi cultures

Background

Steroid compounds with a 6,19-oxirane bridge possess interesting biological activities including anticonvulsant and analgesic properties, bacteriostatic activity against Gram-positive bacteria and selective anti-glucocorticoid action, while lacking mineralocorticoid and progestagen activity.

Results

The study aimed to obtain new derivatives of 3β-acetyloxy-5α-chloro-6,19-oxidoandrostan-17-one by microbial transformation. Twelve filamentous fungal strains were used as catalysts, including entomopathogenic strains with specific activity in the transformation of steroid compounds. All selected strains were characterised by high biotransformation capacity for steroid compounds. However, high substrate conversions were obtained in the cultures of 8 strains: Beauveria bassiana KCh BBT, Beauveria caledonica KCh J3.4, Penicillium commune KCh W7, Penicillium chrysogenum KCh S4, Mucor hiemalis KCh W2, Fusarium acuminatum KCh S1, Trichoderma atroviride KCh TRW and Isaria farinosa KCh KW1.1. Based on gas chromatography (GC) and nuclear magnetic resonance (NMR) analyses, it was found that almost all strains hydrolysed the ester bond of the acetyl group. The strain M. hiemalis KCh W2 reduced the carbonyl group additionally. From the P. commune KCh W7 and P. chrysogenum KCh S4 strain cultures a product of D-ring Baeyer–Villiger oxidation was isolated, whereas from the culture of B. bassiana KCh BBT a product of hydroxylation at the 11α position and oxidation of the D ring was obtained. Three 11α-hydroxy derivatives were obtained in the culture of I. farinosa KCh KW1.1: 3β,11α-dihydroxy-5α-chloro-6,19-oxidoandrostan-17-one, 3β,11α,19-trihydroxy-5α-chloro-6,19-oxidoandrostan-17-one and 3β,11α-dihydroxy-5α-chloro-6,19-oxidoandrostan-17,19-dione. They are a result of consecutive reactions of hydrolysis of the acetyl group at C-3, 11α- hydroxylation, then hydroxylation at C-19 and its further oxidation to lactone.

Conclusions

As a result of the biotransformations, seven steroid derivatives, not previously described in the literature, were obtained: 3β-hydroxy-5α-chloro-6,19-oxidoandrostan-17-one, 3β,17α-dihydroxy-5α-chloro-6,19-oxidoandrostane, 3β-hydroxy-5α-chloro-17α-oxa-D-homo-6,19-oxidoandrostan-17-one, 3β,11α-dihydroxy-5α-chloro-17α-oxa-D-homo-6,19-oxidoandrostan-17-one and the three above–mentioned 11α-hydroxy derivatives. This study will allow a better understanding and characterisation of the catalytic abilities of individual microorganisms, which is crucial for more accurate planning of experiments and achieving more predictable results.

Pregnenolone Overproduction in Yarrowia lipolytica by Integrative Components Pairing of the Cytochrome P450scc System

Microbial production of steroid drugs exhibits great potentials in much greener and more sustainable manners, in which engineering multiple cytochrome P450s is the prerequisite requirement. The pairing of multicomponents of P450 systems is a tremendous challenge. Herein, biosynthesis of pregnenolone (a common precursor of steroid drugs) in Yarrowia lipolytica was taken as a typical instance to explore the engineering strategy of the cytochrome P450 side-chain cleavage enzyme (P450scc) system. The mature forms of the components belonging to P450scc system, CYP11A1, adrenodoxin (Adx), and adrenodoxin reductase (AdR), were coexpressed in a former constructed campesterol producing strain. To maximize pregnenolone production, an integrative components pairing strategy was proposed for pairing the component sources and balancing the expression levels of CYP11A1, Adx, and AdR. Led by the above approaches, a 2344-fold improvement of pregnenolone titer was achieved at the shake flask level. Consequently, a highest reported pregnenolone titer of 78.0 mg/L in microbes was obtained in a 5 L bioreactor. Our study not only highlights the integrative components pairing of cytochrome P450scc as a general strategy for engineering other cytochrome P450s, but also provides a feasible and efficient platform of Y. lipolytica for other steroids production.