Engineering a Highly Regioselective Fungal Peroxygenase for the Synthesis of Hydroxy Fatty Acids.

The hydroxylation of fatty acids is an appealing reaction in synthetic chemistry, although the lack of selective catalysts hampers its industrial implementation. In this study, we have engineered a highly regioselective fungal peroxygenase for the ω-1 hydroxylation of fatty acids with quenched stepwise over-oxidation. One single mutation near the Phe catalytic tripod narrowed the heme cavity, promoting a dramatic shift toward subterminal hydroxylation with a drop in the over-oxidation activity. While crystallographic soaking experiments and molecular dynamic simulations shed light on this unique oxidation pattern, the selective biocatalyst was produced by Pichia pastoris at 0.4 g L-1 in a fed-batch bioreactor and used in the preparative synthesis of 1.4 g of (ω-1)-hydroxytetradecanoic acid with 95 % regioselectivity and 83 % ee for the S enantiomer.

Adaptation of Listeria monocytogenes to perturbation of c-di-AMP metabolism underpins its role in osmoadaptation and identifies a fosfomycin uptake system.

The human pathogen Listeria monocytogenes synthesizes and degrades c-di-AMP using the diadenylate cyclase CdaA and the phosphodiesterases PdeA and PgpH respectively. c-di-AMP is essential because it prevents the uncontrolled uptake of osmolytes. Here, we studied the phenotypes of cdaA, pdeA, pgpH and pdeA pgpH mutants with defects in c-di-AMP metabolism and characterized suppressor mutants restoring their growth defects. The characterization of the pdeA pgpH mutant revealed that the bacteria show growth defects in defined medium, a phenotype that is invariably suppressed by mutations in cdaA. The previously reported growth defect of the cdaA mutant in rich medium is suppressed by mutations that osmotically stabilize the c-di-AMP-free strain. We also found that the cdaA mutant has an increased sensitivity against isoleucine. The isoleucine-dependent growth inhibition of the cdaA mutant is suppressed by codY mutations that likely reduce the DNA-binding activity of encoded CodY variants. Moreover, the characterization of the cdaA suppressor mutants revealed that the Opp oligopeptide transport system is involved in the uptake of the antibiotic fosfomycin. In conclusion, the suppressor analysis corroborates a key function of c-di-AMP in controlling osmolyte homeostasis in L. monocytogenes.

Singlet-Oxygen Generation by Peroxidases and Peroxygenases for Chemoenzymatic Synthesis.

Singlet oxygen is a reactive oxygen species undesired in living cells but a rare and valuable reagent in chemical synthesis. We present a fluorescence spectroscopic analysis of the singlet-oxygen formation activity of commercial peroxidases and novel peroxygenases. Singlet-oxygen sensor green (SOSG) is used as fluorogenic singlet oxygen trap. Establishing a kinetic model for the reaction cascade to the fluorescent SOSG endoperoxide permits a kinetic analysis of enzymatic singlet-oxygen formation. All peroxidases and peroxygenases show singlet-oxygen formation. No singlet oxygen activity could be found for any catalase under investigation. Substrate inhibition is observed for all reactive enzymes. The commercial dye-decolorizing peroxidase industrially used for dairy bleaching shows the highest singlet-oxygen activity and the lowest inhibition. This enzyme was immobilized on a textile carrier and successfully applied for a chemical synthesis. Here, ascaridole was synthesized via enzymatically produced singlet oxygen.

Functional Expression of Two Unusual Acidic Peroxygenases from Candolleomyces aberdarensis in Yeasts by Adopting Evolved Secretion Mutations.

Fungal unspecific peroxygenases (UPOs) are emergent biocatalysts that perform highly selective C-H oxyfunctionalizations of organic compounds, yet their heterologous production at high levels is required for their practical use in synthetic chemistry. Here, we achieved functional expression of two new unusual acidic peroxygenases from Candolleomyces (Psathyrella) aberdarensis (PabUPO) in yeasts and their production at a large scale in a bioreactor. Our strategy was based on adopting secretion mutations from an Agrocybe aegerita UPO mutant, the PaDa-I variant, designed by directed evolution for functional expression in yeast, which belongs to the same phylogenetic family as PabUPOs, long-type UPOs, and shares 65% sequence identity. After replacing the native signal peptides with the evolved leader sequence from PaDa-I, we constructed and screened site-directed recombination mutant libraries, yielding two recombinant PabUPOs with expression levels of 5.4 and 14.1 mg/liter in Saccharomyces cerevisiae. These variants were subsequently transferred to Pichia pastoris for overproduction in a fed-batch bioreactor, boosting expression levels up to 290 mg/liter, with the highest volumetric activity achieved to date for a recombinant peroxygenase (60,000 U/liter, with veratryl alcohol as the substrate). With a broad pH activity profile, ranging from pH 2.0 to 9.0, these highly secreted, active, and stable peroxygenases are promising tools for future engineering endeavors as well as for their direct application in different industrial and environmental settings. IMPORTANCE In this work, we incorporated several secretion mutations from an evolved fungal peroxygenase to enhance the production of active and stable forms of two unusual acidic peroxygenases. The tandem-yeast expression system based on S. cerevisiae for directed evolution and P. pastoris for overproduction on an ∼300-mg/liter scale is a versatile tool to generate UPO variants. By employing this approach, we foresee that acidic UPO variants will be more readily engineered in the near future and adapted to practical enzyme cascade reactions that can be performed over a broad pH range to oxyfunctionalize a variety of organic compounds.

A Peroxygenase from Chaetomium globosum Catalyzes the Selective Oxygenation of Testosterone.

Unspecific peroxygenases (UPO, EC 1.11.2.1) secreted by fungi open an efficient way to selectively oxyfunctionalize diverse organic substrates, including less-activated hydrocarbons, by transferring peroxide-borne oxygen. We investigated a cell-free approach to incorporate epoxy and hydroxyl functionalities directly into the bulky molecule testosterone by a novel unspecific peroxygenase (UPO) that is produced by the ascomycetous fungus Chaetomium globosum in a complex medium rich in carbon and nitrogen. Purification by fast protein liquid chromatography revealed two enzyme fractions with the same molecular mass (36 kDa) and with specific activity of 4.4 to 12 U mg-1 . Although the well-known UPOs of Agrocybe aegerita (AaeUPO) and Marasmius rotula (MroUPO) failed to convert testosterone in a comparative study, the UPO of C. globosum (CglUPO) accepted testosterone as substrate and converted it with total turnover number (TTN) of up to 7000 into two oxygenated products: the 4,5-epoxide of testosterone in ß-configuration and 16α-hydroxytestosterone. The reaction performed on a 100 mg scale resulted in the formation of about 90 % of the epoxide and 10 % of the hydroxylation product, both of which could be isolated with purities above 96 %. Thus, CglUPO is a promising biocatalyst for the oxyfunctionalization of bulky steroids and it will be a useful tool for the synthesis of pharmaceutically relevant steroidal molecules.

Fatty Acid Chain Shortening by a Fungal Peroxygenase.

A recently discovered peroxygenase from the fungus Marasmius rotula (MroUPO) is able to catalyze the progressive one-carbon shortening of medium and long-chain mono- and dicarboxylic acids by itself alone, in the presence of H2 O2 . The mechanism, analyzed using H218 O2 , starts with an α-oxidation catalyzed by MroUPO generating an α-hydroxy acid, which is further oxidized by the enzyme to a reactive α-keto intermediate whose decarboxylation yields the one-carbon shorter fatty acid. Compared with the previously characterized peroxygenase of Agrocybe aegerita, a wider heme access channel, enabling fatty acid positioning with the carboxylic end near the heme cofactor (as seen in one of the crystal structures available) could be at the origin of the unique ability of MroUPO shortening carboxylic acid chains.

Primary-like human hepatocytes genetically engineered to obtain proliferation competence display hepatic differentiation characteristics in monolayer and organotypical spheroid cultures.

Primary human hepatocytes are in great demand during drug development and in hepatology. However, both scarcity of tissue supply and donor variability of primary cells create a need for the development of alternative hepatocyte systems. By using a lentivirus vector system to transfer coding sequences of Upcyte® proliferation genes, we generated non-transformed stable hepatocyte cultures from human liver tissue samples. Here, we show data on newly generated proliferation-competent HepaFH3 cells investigated as conventional two-dimensional monolayer and as organotypical three-dimensional (3D) spheroid culture. In monolayer culture, HepaFH3 cells show typical cobblestone-like hepatocyte morphology and anchorage-dependent growth for at least 20 passages. Immunofluorescence staining revealed that characteristic hepatocyte marker proteins cytokeratin 8, human serum albumin, and cytochrome P450 (CYP) 3A4 were expressed. Quantitative real-time PCR analyses showed that expression levels of analyzed phase I CYP enzymes were at similar levels compared to those of cultured primary human hepatocytes and considerably higher than in the liver carcinoma cell line HepG2. Additionally, transcripts for phase II liver enzymes and transporter proteins OATP-C, MRP2, Oct1, and BSEP were present in HepaFH3. The cells produced urea and converted model compounds such as testosterone, diclofenac, and 7-OH-coumarin into phases I and II metabolites. Interestingly, phases I and II enzymes were expressed at about the same levels in convenient monolayer cultures and complex 3D spheroids. In conclusion, HepaFH3 cells and related primary-like hepatocyte lines seem to be promising tools for in vitro research of liver functions and as test system in drug development and toxicology analysis.

Back to "once a caesarean: always a caesarean"? A trend analysis in Switzerland.

PURPOSE: Caesarean sections (CS) have significantly increased worldwide and a previous CS is nowadays an important and increasingly reported indication to perform a repeat CS. There is a paucity of information in Switzerland on the incidence of repeat CS after previous CS and relationship between the rates of vaginal birth after CS (VBAC). The aim of this study was to analyse the actual trend in VBAC in Switzerland. METHODS: We performed a retrospective cohort study to analyse the proportion of VBAC among all pregnant women with previous sections which give birth during two time periods (group 1:1998/1999 vs. group 2:2004/2005) in our tertiary care referral hospital and in the annual statistics of Swiss Women's Hospitals (ASF-Statistics). In addition, the proportion of induction of labour after a previous caesarean and its success was analysed. RESULTS: In both cohorts studied, we found a significant decrease of vaginal births (p < 0.05) and a significant increase of primary elective repeat caesarean section (p < 0.05) from the first to the second time period, while there was a decrease of secondary repeat caesarean sections. The prevalence of labour induction did not decrease. CONCLUSION: Our study shows that vaginal birth after a prior caesarean section has decreased over time in Switzerland. There was no significant change in labour induction during the study period. While this trend might reflect an increasing demand for safety in pregnancy and childbirth, it concomitantly increases maternal risks of further pregnancies, and women need to be appropriately informed about long-term risks.

From Alkanes to Carboxylic Acids: Terminal Oxygenation by a Fungal Peroxygenase.

A new heme-thiolate peroxidase catalyzes the hydroxylation of n-alkanes at the terminal position-a challenging reaction in organic chemistry-with H2 O2 as the only cosubstrate. Besides the primary product, 1-dodecanol, the conversion of dodecane yielded dodecanoic, 12-hydroxydodecanoic, and 1,12-dodecanedioic acids, as identified by GC-MS. Dodecanal could be detected only in trace amounts, and 1,12-dodecanediol was not observed, thus suggesting that dodecanoic acid is the branch point between mono- and diterminal hydroxylation. Simultaneously, oxygenation was observed at other hydrocarbon chain positions (preferentially C2 and C11). Similar results were observed in reactions of tetradecane. The pattern of products formed, together with data on the incorporation of (18) O from the cosubstrate H2 (18) O2 , demonstrate that the enzyme acts as a peroxygenase that is able to catalyze a cascade of mono- and diterminal oxidation reactions of long-chain n-alkanes to give carboxylic acids.

Steroid hydroxylation by basidiomycete peroxygenases: a combined experimental and computational study.

The goal of this study is the selective oxyfunctionalization of steroids under mild and environmentally friendly conditions using fungal enzymes. With this purpose, peroxygenases from three basidiomycete species were tested for the hydroxylation of a variety of steroidal compounds, using H2O2 as the only cosubstrate. Two of them are wild-type enzymes from Agrocybe aegerita and Marasmius rotula, and the third one is a recombinant enzyme from Coprinopsis cinerea. The enzymatic reactions on free and esterified sterols, steroid hydrocarbons, and ketones were monitored by gas chromatography, and the products were identified by mass spectrometry. Hydroxylation at the side chain over the steroidal rings was preferred, with the 25-hydroxyderivatives predominating. Interestingly, antiviral and other biological activities of 25-hydroxycholesterol have been reported recently (M. Blanc et al., Immunity 38:106-118, 2013, http://dx.doi.org/10.1016/j.immuni.2012.11.004). However, hydroxylation in the ring moiety and terminal hydroxylation at the side chain also was observed in some steroids, the former favored by the absence of oxygenated groups at C-3 and by the presence of conjugated double bonds in the rings. To understand the yield and selectivity differences between the different steroids, a computational study was performed using Protein Energy Landscape Exploration (PELE) software for dynamic ligand diffusion. These simulations showed that the active-site geometry and hydrophobicity favors the entrance of the steroid side chain, while the entrance of the ring is energetically penalized. Also, a direct correlation between the conversion rate and the side chain entrance ratio could be established that explains the various reaction yields observed.

One-pot synthesis of human metabolites of SAR548304 by fungal peroxygenases.

Unspecific peroxygenases (UPOs, EC 1.11.2.1) have proved to be stable oxygen-transferring biocatalysts for H2O2-dependent transformation of pharmaceuticals. We have applied UPOs in a drug development program and consider the enzymatic approach in parallel to a conventional chemical synthesis of the human metabolites of the bile acid reabsorption inhibitor SAR548304. Chemical preparation of N,N-di-desmethyl metabolite was realized by a seven-step synthesis starting from a late precursor of SAR548304 and included among others palladium catalysis and laborious chromatographic purification with an overall yield of 27%. The enzymatic approach revealed that the UPO of Marasmius rotula is particularly suitable for selective N-dealkylation of the drug and enabled us to prepare both human metabolites via one-pot conversion with an overall yield of 66% N,N-di-desmethyl metabolite and 49% of N-mono-desmethylated compound in two separated kinetic-controlled reactions.

Structural basis of substrate conversion in a new aromatic peroxygenase: cytochrome P450 functionality with benefits.

Aromatic peroxygenases (APOs) represent a unique oxidoreductase sub-subclass of heme proteins with peroxygenase and peroxidase activity and were thus recently assigned a distinct EC classification (EC 1.11.2.1). They catalyze, inter alia, oxyfunctionalization reactions of aromatic and aliphatic hydrocarbons with remarkable regio- and stereoselectivities. When compared with cytochrome P450, APOs appear to be the choice enzymes for oxyfunctionalizations in organic synthesis due to their independence from a cellular environment and their greater chemical versatility. Here, the first two crystal structures of a heavily glycosylated fungal aromatic peroxygenase (AaeAPO) are described. They reveal different pH-dependent ligand binding modes. We model the fitting of various substrates in AaeAPO, illustrating the way the enzyme oxygenates polycyclic aromatic hydrocarbons. Spatial restrictions by a phenylalanine pentad in the active-site environment govern substrate specificity in AaeAPO.

Preparation of labeled human drug metabolites and drug-drug interaction-probes with fungal peroxygenases.

Enzymatic conversion of a drug can be an efficient alternative for the preparation of a complex metabolite compared with a multi-step chemical synthesis approach. Limitations exist for chemical methods for direct oxygen incorporation into organic molecules often suffering from low yields and unspecific oxidation and also for alternative whole-cell biotransformation processes, which require specific fermentation know-how. Stable oxygen-transferring biocatalysts such as unspecific peroxygenases (UPOs) could be an alternative for the synthesis of human drug metabolites and related stable isotope-labeled analogues. This work shows that UPOs can be used in combination with hydrogen/deuterium exchange for an efficient one-step process for the preparation of 4'-OH-diclofenac-d6. The scope of the reaction was investigated by screening of different peroxygenase subtypes for the transformation of selected deuterium-labeled substrates such as phenacetin-d3 or lidocaine-d3. Experiments with diclofenac-d7 revealed that the deuterium-labeling does not affect the kinetic parameters. By using the latter substrate and H2 (18) O2 as cosubstrate, it was possible to prepare a doubly isotope-labeled metabolite (4'-(18) OH-diclofenac-d6). UPOs offer certain practical advantages compared with P450 enzyme systems in terms of stability and ease of handling. Given these advantages, future work will expand the existing 'monooxygenation toolbox' of different fungal peroxygenases that mimic P450 in vitro reactions.

A spectrophotometric assay for the detection of fungal peroxygenases.

Rapid and simple spectrophotometric methods are required for the unambiguous detection of recently discovered fungal peroxygenases in vivo and in vitro. This paper describes a peroxygenase-specific assay using 5-nitro-1,3-benzodioxole as substrate. The product, 4-nitrocatechol, produces a yellow color at pH 7, which can be followed over time at 425 nm (ε(425)=9,700 M(-1) cm(-1)), and a red color when adjusted to pH >12, which can be measured in form of an end-point determination at 514 nm (ε(514)=11,400 M(-1) cm(-1)). The assay is suitable for detecting peroxygenase activities in complex growth media and environmental samples as well as for high-throughput screenings.

The aromatic peroxygenase from Marasmius rutola--a new enzyme for biosensor applications.

The aromatic peroxygenase (APO; EC 1.11.2.1) from the agraric basidomycete Marasmius rotula (MroAPO) immobilized at the chitosan-capped gold-nanoparticle-modified glassy carbon electrode displayed a pair of redox peaks with a midpoint potential of -278.5 mV vs. AgCl/AgCl (1 M KCl) for the Fe(2+)/Fe(3+) redox couple of the heme-thiolate-containing protein. MroAPO oxidizes aromatic substrates such as aniline, p-aminophenol, hydroquinone, resorcinol, catechol, and paracetamol by means of hydrogen peroxide. The substrate spectrum overlaps with those of cytochrome P450s and plant peroxidases which are relevant in environmental analysis and drug monitoring. In M. rotula peroxygenase-based enzyme electrodes, the signal is generated by the reduction of electrode-active reaction products (e.g., p-benzoquinone and p-quinoneimine) with electro-enzymatic recycling of the analyte. In these enzyme electrodes, the signal reflects the conversion of all substrates thus representing an overall parameter in complex media. The performance of these sensors and their further development are discussed.

Peroxide-Mediated Oxygenation of Organic Compounds by Fungal Peroxygenases.

Unspecific peroxygenases (UPOs), whose sequences can be found in the genomes of thousands of filamentous fungi, many yeasts and certain fungus-like protists, are fascinating biocatalysts that transfer peroxide-borne oxygen (from H2O2 or R-OOH) with high efficiency to a wide range of organic substrates, including less or unactivated carbons and heteroatoms. A twice-proline-flanked cysteine (PCP motif) typically ligates the heme that forms the heart of the active site of UPOs and enables various types of relevant oxygenation reactions (hydroxylation, epoxidation, subsequent dealkylations, deacylation, or aromatization) together with less specific one-electron oxidations (e.g., phenoxy radical formation). In consequence, the substrate portfolio of a UPO enzyme always combines prototypical monooxygenase and peroxidase activities. Here, we briefly review nearly 20 years of peroxygenase research, considering basic mechanistic, molecular, phylogenetic, and biotechnological aspects.

Novel Unspecific Peroxygenase from Truncatella angustata Catalyzes the Synthesis of Bioactive Lipid Mediators.

Lipid mediators, such as epoxidized or hydroxylated eicosanoids (EETs, HETEs) of arachidonic acid (AA), are important signaling molecules and play diverse roles at different physiological and pathophysiological levels. The EETs and HETEs formed by the cytochrome P450 enzymes are still not fully explored, but show interesting anti-inflammatory properties, which make them attractive as potential therapeutic target or even as therapeutic agents. Conventional methods of chemical synthesis require several steps and complex separation techniques and lead only to low yields. Using the newly discovered unspecific peroxygenase TanUPO from the ascomycetous fungus Truncatella angustata, 90% regioselective conversion of AA to 14,15-EET could be achieved. Selective conversion of AA to 18-HETE, 19-HETE as well as to 11,12-EET and 14,15-EET was also demonstrated with known peroxygenases, i.e., AaeUPO, CraUPO, MroUPO, MweUPO and CglUPO. The metabolites were confirmed by HPLC-ELSD, MS1 and MS2 spectrometry as well as by comparing their analytical data with authentic standards. Protein structure simulations of TanUPO provided insights into its substrate access channel and give an explanation for the selective oxyfunctionalization of AA. The present study expands the scope of UPOs as they can now be used for selective syntheses of AA metabolites that serve as reference material for diagnostics, for structure-function elucidation as well as for therapeutic and pharmacological purposes.

Draft Genome Sequence of Truncatella angustata (Anamorph) S358.

The ascomycete Truncatella angustata has a worldwide distribution. Commonly, it is associated with plants as an endophyte, pathogen, or saprotroph. The genome assembly comprises 44.9 Mbp, a G+C content of 49.2%, and 12,353 predicted genes, among them 12 unspecific peroxygenases (EC 1.11.2.1).

Enzymatic Epoxidation of Long-Chain Terminal Alkenes by Fungal Peroxygenases.

Terminal alkenes are among the most attractive starting materials for the synthesis of epoxides, which are essential and versatile intermediate building blocks for the pharmaceutical, flavoring, and polymer industries. Previous research on alkene epoxidation has focused on the use of several oxidizing agents and/or different enzymes, including cytochrome P450 monooxygenases, as well as microbial whole-cell catalysts that have several drawbacks. Alternatively, we explored the ability of unspecific peroxygenases (UPOs) to selectively epoxidize terminal alkenes. UPOs are attractive biocatalysts because they are robust extracellular enzymes and only require H2O2 as cosubstrate. Here, we show how several UPOs, such as those from Cyclocybe (Agrocybe) aegerita (AaeUPO), Marasmius rotula (MroUPO), Coprinopsis cinerea (rCciUPO), Humicola insolens (rHinUPO), and Daldinia caldariorum (rDcaUPO), are able to catalyze the epoxidation of long-chain terminal alkenes (from C12:1 to C20:1) after an initial optimization of several reaction parameters (cosolvent, cosubstrate, and pH). In addition to terminal epoxides, alkenols and other hydroxylated derivatives of the alkenes were formed. Although all UPOs were able to convert and epoxidize the alkenes, notable differences were observed between them, with rCciUPO being responsible for the highest substrate turnover and MroUPO being the most selective with respect to terminal epoxidation. The potential of peroxygenases for epoxidizing long-chain terminal alkenes represents an interesting and green alternative to the existing synthesis technologies.

Cell-Free Protein Synthesis with Fungal Lysates for the Rapid Production of Unspecific Peroxygenases.

Unspecific peroxygenases (UPOs, EC 1.11.2.1) are fungal biocatalysts that have attracted considerable interest for application in chemical syntheses due to their ability to selectively incorporate peroxide-oxygen into non-activated hydrocarbons. However, the number of available and characterized UPOs is limited, as it is difficult to produce these enzymes in homologous or hetero-logous expression systems. In the present study, we introduce a third approach for the expression of UPOs: cell-free protein synthesis using lysates from filamentous fungi. Biomass of Neurospora crassa and Aspergillus niger, respectively, was lysed by French press and tested for translational activity with a luciferase reporter enzyme. The upo1 gene from Cyclocybe (Agrocybe) aegerita (encoding the main peroxygenase, AaeUPO) was cell-free expressed with both lysates, reaching activities of up to 105 U L-1 within 24 h (measured with veratryl alcohol as substrate). The cell-free expressed enzyme (cfAaeUPO) was successfully tested in a substrate screening that included prototypical UPO substrates, as well as several pharmaceuticals. The determined activities and catalytic performance were comparable to that of the wild-type enzyme (wtAaeUPO). The results presented here suggest that cell-free expression could become a valuable tool to gain easier access to the immense pool of putative UPO genes and to expand the spectrum of these sought-after biocatalysts.