Stereo- and regioselective hydroxylation of alpha-ionone by Streptomyces strains

The effect of β-ionone on bacterial cells: the use of specific lux-biosensors

The diversity of the biological activity of volatile organic compounds (VOCs), including unsaturated ketone β-ionone, promising pharmacological, biotechnological, and agricultural agent, has aroused considerable interest. However, the functional role and mechanisms of action of VOCs remain insufficiently studied. In this work, the response of bacterial cells to the action of β-ionone was studied using specific bioluminescent lux-biosensors containing stress-sensitive promoters. We determined that in Escherichia coli cells, β-ionone induces oxidative stress (PkatG and Pdps promoters) through a specific response mediated by the OxyR/OxyS regulon, but not SoxR/SoxS (PsoxS promoter). It has been shown that β-ionone at high concentrations (50 μM and above) causes a weak induction of the expression from the PibpA promoter and slightly induces the PcolD promoter in the E. coli biosensors; the observed effect is enhanced in the ΔoxyR mutants. This indicates the presence of some damage to proteins and DNA. β-Ionone was found to inhibit the bichaperone-dependent DnaKJE-ClpB refolding of heat-inactivated bacterial luciferase in E. coli wild-type and ΔibpB mutant strains. In the cells of the Gram-positive bacterium Bacillus subtilis 168 pNK-MrgA β-ionone does not cause oxidative stress. Thus, in this work, the specificity of bacterial cell stress responses to the action of β-ionone was shown.

Selective Oxygenation of Ionones and Damascones by Fungal Peroxygenases

Apocarotenoids are among the most highly valued fragrance constituents, being also appreciated as synthetic building blocks. This work shows the ability of unspecific peroxygenases (UPOs, EC1.11.2.1) from several fungi, some of them being described recently, to catalyze the oxyfunctionalization of α- and β-ionones and α- and β-damascones. Enzymatic reactions yielded oxygenated products such as hydroxy, oxo, carboxy, and epoxy derivatives that are interesting compounds for the flavor and fragrance and pharmaceutical industries. Although variable regioselectivity was observed depending on the substrate and enzyme, oxygenation was preferentially produced at the allylic position in the ring, being especially evident in the reaction with α-ionone, forming 3-hydroxy-α-ionone and/or 3-oxo-α-ionone. Noteworthy were the reactions with damascones, in the course of which some UPOs oxygenated the terminal position of the side chain, forming oxygenated derivatives (i.e., the corresponding alcohol, aldehyde, and carboxylic acid) at C-10, which were predominant in the Agrocybe aegerita UPO reactions, and first reported here.

Allelopathic Potency and an Active Substance from Anredera cordifolia (Tenore) Steenis

Anredera cordifolia (Tenore) Steenis is widely planted as an ornamental and medicinal plant in Indonesia. On the other hand, in some other countries this plant is classified as a noxious weed. As a harmful weed, A. cordifolia is reported to have the ability to smother all native vegetation, collapse canopies of tall trees, cultivate as a ground cover and disrupt native seedling development. There is no available information about the involvement of any allelochemicals from A. cordifolia related to these issues. The present study evaluated the allelopathic effect by isolating and identifying the allelopathic substance from A. cordifolia leaf extract. The allelopathic potency of A. cordifolia was determined by a series of bioassays of shoot and root growth on some selected test plants. Separation and purification of the active substances was achieved through several chromatography processes. Finally, the substances with allelopathic activity were identified through high-resolution electrospray ionization mass spectrometry (HRESIMS) analysis and determined by the specific rotation of compound, proton and carbon NMR spectroscopies. The results show that A. cordifolia possesses allelopathic properties which affect other plant species. The isolated compound from the plant material, 3-hydroxy-alpha-ionone, may contribute to the allelopathic effects of A. cordifolia.

Fungi-Mediated Biotransformation of the Isomeric Forms of the Apocarotenoids Ionone, Damascone and Theaspirane

In this work, we describe a study on the biotransformation of seven natural occurring apocarotenoids by means of eleven selected fungal species. The substrates, namely ionone (α-, β- and γ-isomers), 3,4-dehydroionone, damascone (α- and β-isomers) and theaspirane are relevant flavour and fragrances components. We found that most of the investigated biotransformation reactions afforded oxidized products such as hydroxy- keto- or epoxy-derivatives. On the contrary, the reduction of the keto groups or the reduction of the double bond functional groups were observed only for few substrates, where the reduced products are however formed in minor amount. When starting apocarotenoids are isomers of the same chemical compound (e.g., ionone isomers) their biotransformation can give products very different from each other, depending both on the starting substrate and on the fungal species used. Since the majority of the starting apocarotenoids are often available in natural form and the described products are natural compounds, identified in flavours or fragrances, our biotransformation procedures can be regarded as prospective processes for the preparation of high value olfactory active compounds.

Shedding light on Aspergillus niger volatile exometabolome

An in-depth exploration of the headspace content of Aspergillus niger cultures was performed upon different growth conditions, using a methodology based on advanced multidimensional gas chromatography. This volatile fraction comprises 428 putatively identified compounds distributed over several chemical families, being the major ones hydrocarbons, alcohols, esters, ketones and aldehydes. These metabolites may be related with different metabolic pathways, such as amino acid metabolism, biosynthesis and metabolism of fatty acids, degradation of aromatic compounds, mono and sesquiterpenoid synthesis and carotenoid cleavage. The A. niger molecular biomarkers pattern was established, comprising the 44 metabolites present in all studied conditions. This pattern was successfully used to distinguish A. niger from other fungi (Candida albicans and Penicillium chrysogenum) with 3 days of growth by using Partial Least Squares-Discriminant Analysis (PLS-DA). In addition, PLS-DA-Variable Importance in Projection was applied to highlight the metabolites playing major roles in fungi distinction; decreasing the initial dataset to only 16 metabolites. The data pre-processing time was substantially reduced, and an improvement of quality-of-fit value was achieved. This study goes a step further on A. niger metabolome construction and A. niger future detection may be proposed based on this molecular biomarkers pattern.

Selective oxidation of carotenoid-derived aroma compounds by CYP260B1 and CYP267B1 from Sorangium cellulosum So ce56

Due to their bioactive properties as well as their application as precursors in chemical synthesis, hydroxylated isoprenoids and norisoprenoids are very valuable compounds. The efficient hydroxylation of such compounds remains a challenge in organic chemistry caused by the formation of a variety of side products and lack of overall regio- and stereoselectivity. In contrast, cytochromes P450 are known for their selective oxidation under mild conditions. Here, we demonstrate for the first time the ability of myxobacterial CYP260B1 and CYP267B1 from Sorangium cellulosum So ce56 to oxidize such carotenoid-derived aroma compounds. A focused library of 14 substrates such as ionones, damascones, as well as some of their isomers and derivatives was screened in vitro. Both P450s were capable of an efficient oxidation of all tested compounds. CYP260B1-dependent conversions mainly formed multiple products, whereas conversions by CYP267B1 resulted predominantly in a single product. To identify the main products by NMR spectroscopy, an Escherichia coli-based whole-cell system was used. CYP267B1 showed a hydroxylase activity towards the formation of allylic alcohols. Likewise, CYP260B1 performed the allylic hydroxylation of β-damascone [(E)-1-(2,6,6-trimethylcyclohex-1-enyl)but-2-en-1-one] and δ-damascone [(E)-1-(2,6,6-trimethylcyclohex-3-enyl)but-2-en-1-one]. Moreover, CYP260B1 showed an epoxidase activity towards β-ionone [(E)-4-(2,6,6-trimethylcyclohex-1-enyl)but-3-en-2-one] as well as the methyl-substituted α-ionone derivatives raldeine [(E)-1-(2,6,6-trimethylcyclohex-2-enyl)pent-1-en-3-one] and isoraldeine [(E)-3-methyl-4-(2,6,6-trimethylcyclohex-2-enyl)but-3-en-2-one]. In addition, to known products, also novel products such as 2-OH-δ-damascone [(E)-1-(5-hydroxy-2,6,6-trimethylcyclohex-3-enyl)but-2-en-1-one], 3-OH-allyl-α-ionone [(E)-1-(4-hydroxy-2,6,6-trimethylcyclohex-2-enyl)hepta-1,6-dien-3-one], and 4-OH-allyl-β-ionone [(E)-1-(3-hydroxy-2,6,6-trimethylcyclohex-1-enyl)hepta-1,6-dien-3-one] were identified during our studies.

The crystal structure of the versatile cytochrome P450 enzyme CYP109B1 from Bacillus subtilis

The crystal structure of the versatile CYP109B1 enzyme from Bacillus subtilis has been solved at 1.8 Å resolution. This is the first structure of an enzyme from this CYP family, whose members are prevalent across diverse species of bacteria. In the crystal structure the enzyme has an open conformation with an access channel leading from the heme to the surface. The substrate-free structure reveals the location of the key residues in the active site that are responsible for binding the substrate in the correct orientation for regioselective oxidation. Importantly, there are significant differences among these residues in members of the CYP109 and closely related CYP106 families and these likely account for the variations in substrate binding and oxidation profiles observed with these enzymes. A whole-cell oxidation biosystem was developed, which contains CYP109B1 and a phthalate family oxygenase reductase (PFOR), from Pseudomonas putida KT24440, as the electron transfer partner. This electron transfer system is able to support CYP109B1 activity resulting in the regioselective hydroxylation of both α- and β-ionone in vivo and in vitro. The PFOR is therefore a versatile electron transfer partner that is able to support the activity of CYP enzymes from other bacterium. The crystal structure of CYP109B1 has a positively charged proximal face and this explains why it can interact with PFOR and adrenodoxin which are predominantly negatively charged around their [2Fe-2S] clusters.

Terpene hydroxylation with microbial cytochrome P450 monooxygenases

Terpenoids comprise a highly diverse group of natural products. In addition to their basic carbon skeleton, they differ from one another in their functional groups. Functional groups attached to the carbon skeleton are the basis of the terpenoids' diverse properties. Further modifications of terpene olefins include the introduction of acyl-, aryl-, or sugar moieties and usually start with oxidations catalyzed by cytochrome P450 monooxygenases (P450s, CYPs). P450s are ubiquitously distributed throughout nature, involved in essential biological pathways such as terpenoid biosynthesis as well as the tailoring of terpenoids and other natural products. Their ability to introduce oxygen into nonactivated C-H bonds is unique and makes P450s very attractive for applications in biotechnology. Especially in the field of terpene oxidation, biotransformation methods emerge as an attractive alternative to classical chemical synthesis. For this reason, microbial P450s depict a highly interesting target for protein engineering approaches in order to increase selectivity and activity, respectively. Microbial P450s have been described to convert industrial and pharmaceutically interesting terpenoids such as ionones, limone, valencene, resin acids, and triterpenes (including steroids) as well as vitamin D3. Highly selective and active mutants have been evolved by applying classical site-directed mutagenesis as well as directed evolution of proteins. As P450s usually depend on electron transfer proteins, mutagenesis has also been applied to improve the interactions between P450s and their respective redox partners. This chapter provides an overview of terpenoid hydroxylation reactions catalyzed by bacterial P450s and highlights the achievements made by protein engineering to establish productive hydroxylation processes.

The efficient and selective biocatalytic oxidation of norisoprenoid and aromatic substrates by CYP101B1 from Novosphingobium aromaticivorans DSM12444

CYP101B1 fromNovosphingobium aromaticivoransoxidises ionone derivatives and phenylcyclohexane with high activity and regioselectivity.

Environmental and seasonal influences on red raspberry flavour volatiles and identification of quantitative trait loci (QTL) and candidate genes

Raspberry volatiles are important for perceptions of sensory quality, mould resistance and some have nutraceutical activities. Twelve raspberry character volatiles were quantified, 11 of them in fruit from two seasons, from plants from the Glen Moy × Latham mapping population growing in both open field and under cover (polytunnels). Effects of season and environment were examined for their impact on the content of α-ionone, α-ionol, β-ionone, β-damascenone, linalool, geraniol, benzyl alcohol, (Z)-3-hexenol, acetoin, acetic and hexanoic acids, whilst raspberry ketone was measured in one season. A significant variation was observed in fruit volatiles in all progeny between seasons and method of cultivation. Quantitative trait loci were determined and mapped to six of the seven linkage groups, as were candidate genes in the volatiles pathways.

Free energy calculations give insight into the stereoselective hydroxylation of α-ionones by engineered cytochrome P450 BM3 mutants

Previously, stereoselective hydroxylation of α-ionone by Cytochrome P450 BM3 mutants M01 A82W and M11 L437N was observed. While both mutants hydroxylate α-ionone in a regioselective manner at the C3 position, M01 A82W catalyzes formation of trans-3-OH-α-ionone products whereas M11 L437N exhibits opposite stereoselectivity, producing trans-(3S,6S)-OH-α-ionone and cis-(3S,6R)-OH-α-ionone. Here, we explore the stereoselective C3 hydroxylation of α-ionone by Cytochrome P450 BM3 mutants M01 A82W and M11 L437N using molecular dynamics-based free energy calculations to study the interaction between the enzyme and both the substrates and the products. The one-step perturbation approach is applied using an optimized reference state for substrates and products. While the free energy differences between the substrates free in solution amount to ~0 kJ mol(-1), the differences in mutant M01 A82W agree with the experimentally obtained dissociation constants K(d). Moreover, a correlation with experimentally observed trends in product formation is found in both mutants. The trans isomers show the most favorable relative binding free energy in the range of all four possible hydroxylated diastereomers for mutant M01 A82W, while the trans product from (6S)-α-ionone and the cis product from (6R)-α-ionone show highest affinity for mutant M11 L437N. Marcus theory is subsequently used to relate the thermodynamic stability to transition state energies and rates of formation.

Regioselective hydroxylation of norisoprenoids by CYP109D1 from Sorangium cellulosum So ce56

Sesquiterpenes are particularly interesting as flavorings and fragrances or as pharmaceuticals. Regio- or stereoselective functionalizations of terpenes are one of the main goals of synthetic organic chemistry, which are possible through radical reactions but are not selective enough to introduce the desired chiral alcohol function into those compounds. Cytochrome P450 monooxygenases are versatile biocatalysts and are capable of performing selective oxidations of organic molecules. We were able to demonstrate that CYP109D1 from Sorangium cellulosum So ce56 functions as a biocatalyst for the highly regioselective hydroxylation of norisoprenoids, alpha- and beta-ionone, which are important aroma compounds of floral scents. The substrates alpha- and beta-ionone were regioselectively hydroxylated to 3-hydroxy-alpha-ionone and 4-hydroxy-beta-ionone, respectively, which was confirmed by (1)H NMR and (13)C NMR. The results of docking alpha- and beta-ionone into a homology model of CYP109D1 gave a rational explanation for the regio-selectivity of the hydroxylation. Kinetic studies revealed that alpha- and beta-ionone can be hydroxylated with nearly identical V (max) and K (m) values. This is the first comprehensive investigation of the regioselective hydroxylation of norisoprenoids by CYP109D1.

Microbial Production of C13-Norisoprenoids and Other Aroma Compounds via Carotenoid Cleavage

Carotenoids are important precursors of a variety of compounds: the C(20)-retinoids, the C(15)-phytohormones, and the C(9)- to C(13)-aromas. Among the last type, C(13)-carotenoid-derived compounds (norterpenoids/norisoprenoids) such as ionones and damascones, constitute an essential aroma note in tea, grapes, roses, tobacco, and wine. Extraction of carotenoid-derived aroma compounds from plant sources is not economically realistic or considerably expensive. The biotechnological production of aroma compounds represents a feasible alternative and offers the production of enantiomerically pure molecules which can be labeled as "natural." To date, research in the production of ionones or the C(10)-compound, safranal, has mainly been focused on plant dioxygenases that cleave carotenoids in the positions between carbons 9 and 10 (9'-10') or 7 and 8 (7'-8'), respectively. Although relatively little is known about the microbial conversion of carotenoids into compounds with aroma due to the well known advantages of manipulating microorganisms, the aim of this work is to review the current state of the research in microbial production of norisoprenoids and other aroma compounds derived from carotenoid cleavage.

A novel ketone derivative of artemisinin biotransformed by Streptomyces griseus ATCC 13273

A novel ketone derivative of artemisinin, artemisitone-9, was produced by the biotransformation of cultured Streptomyces griseus ATCC 13273. The structure of the ketone product was fully elucidated by various spectroscopic techniques, and the mechanism of generating such novel metabolite is also discussed.

Generation of aroma compounds from Ditaxis heterantha by Saccharomyces cerevisiae

Ditaxis heterantha, a plant of the Euphorbiaceae family, is growing wild in the semiarid regions of Mexico. The seed endosperm contains yellow pigments (carotenoids). By high-pressure liquid chromatography the total pigment (TP) was separated into seven fractions: two of them, heterathin (F4) and ditaxin (F5), characterized as apocarotenoids, represent 80% of TP. Both molecules have double bonds, which seem to be the target for degradation and aroma formation. In this work, TP, F4, and F5 were supplied to nine cultures able to degrade lutein. From these strains, only one (identified as Saccharomyces cerevisiae) was able to produce aromas from either TP or F4. Using TP as substrate, the produced aromas were 4-oxo-isophorone (1), isophorone (2), cinnamic aldehyde (6), 3-hydroxy-beta-cyclocitral (7), safranal (8), geranyl (9), 3-oxo-alpha-ionone (10), 3-oxo-alpha-ionol (11), 3-oxo-7,8-dihydro-alpha-ionone (12), and eugenol (13). Of these aromas, only seven were produced from F4: (1), (2), (7), (8), (10), (11), and (12). In both cases, safranal was the main degradation product (30%). The enzymatic activity responsible for this effect was found in the cytosolic fraction and detected only when S. cerevisiae was grown in the presence of TP or F4.

Biotransformation of β-ionone by engineered cytochrome P450 BM-3

Wild-type cytochrome P450 monooxygenase from Bacillus megaterium (P450 BM-3) has a low hydroxylation activity for beta-ionone (<1 min(-1)). Substitution of phenylalanine by valine at position 87 led to a more than 100-fold increase in beta-ionone hydroxylation activity (115 min(-1)). Enzyme activity could be further increased by both site-directed and random mutagenesis. The mutant R47L Y51F F87V, designed by site-directed mutagenesis, and the mutant A74E F87V P386S, obtained after two rounds of error-prone polymerase chain reaction, exhibited an increase in activity of up to 300-fold compared to the wild-type enzyme. The triple mutant R47 LY51F F87V exhibited moderate enantioselectivity, forming (R)-4-hydroxy-beta-ionone with an optical purity of 39%. All mutants regioselectively converted beta-ionone into 4-hydroxy-beta-ionone. The regioselectivity is determined amongst others by the absolute configuration of the substrate.

Antifungal compounds from the root and root exudate of Zea mays

A maize plant (Zea mays) planted in a test tube was found to inhibit the growth of the soil-borne plant pathogen, Fusarium oxysporum f. sp. melongenae. The antifungal compounds, 6-methoxybenzoxazolinone and 6,7-dimethoxybenzoxazolinone, were isolated from an ethanol extract of Zea mays roots, and (6R)-7,8-dihydro-3-oxo-alpha-ionone and (6R,9R)-7,8-dihydro-3-oxo-alpha-ionol were isolated from the root exudate.

Efficient terpene hydroxylation catalysts based upon P450 enzymes derived from Actinomycetes

The hydroxylation of alpha-ionone 1 and beta-ionone 2 to their corresponding mono-hydroxylated derivatives has been examined using a recombinant E. coli whole cell system, in which cytochromes P450 SU1 and SU2, and P450 SOY were over-expressed with their cognate ferrodoxins. Both substrates are hydroxylated with a high degree of regioselectivity and for alpha-ionone 1 the reaction is highly diastereoselective yielding the anti-isomer.

Biotransformation of alpha-isomethylionone to 1-(2,6,6-trimethyl-2-cyclohexen-1-yl)propan-2-one

The main biodegradation product of (+/-)-alpha-isomethylionone (2) with standard activated sludge was characterized as (+/-)-1-(2,6,6-trimethyl-2-cyclohexen-1-yl)propan-2-one (1) by its analysis and synthesis. Both enantiomers (1a and 1b) of 1 were synthesized by starting from (R)- and (S)-2,4,4-trimethyl-2-cyclohexen-1-ol (3a and 3b), respectively.