Recombinant Production of Human Microsomal Cytochrome P450 2D6 in the Methylotrophic Yeast Pichia pastoris

Pharmaceutical removal from wastewater by introducing cytochrome P450s into microalgae

Pharmaceuticals are of increasing environmental concern as they emerge and accumulate in surface- and groundwater systems around the world, endangering the overall health of aquatic ecosystems. Municipal wastewater discharge is a significant vector for pharmaceuticals and their metabolites to enter surface waters as humans incompletely absorb prescription drugs and excrete up to 50% into wastewater, which are subsequently incompletely removed during wastewater treatment. Microalgae present a promising target for improving wastewater treatment due to their ability to remove some pollutants efficiently. However, their inherent metabolic pathways limit their capacity to degrade more recalcitrant organic compounds such as pharmaceuticals. The human liver employs enzymes to break down and absorb drugs, and these enzymes are extensively researched during drug development, meaning the cytochrome P450 enzymes responsible for metabolizing each approved drug are well studied. Thus, unlocking or increasing cytochrome P450 expression in endogenous wastewater microalgae could be a cost-effective strategy to reduce pharmaceutical loads in effluents. Here, we discuss the challenges and opportunities associated with introducing cytochrome P450 enzymes into microalgae. We anticipate that cytochrome P450-engineered microalgae can serve as a new drug removal method and a sustainable solution that can upgrade wastewater treatment facilities to function as "mega livers".

Metabolic Engineering of Saccharomyces cerevisiae for Heterologous Carnosic Acid Production

Carnosic acid (CA), a phenolic tricyclic diterpene, has many biological effects, including anti-inflammatory, anticancer, antiobesity, and antidiabetic activities. In this study, an efficient biosynthetic pathway was constructed to produce CA in Saccharomyces cerevisiae. First, the CA precursor miltiradiene was synthesized, after which the CA production strain was constructed by integrating the genes encoding cytochrome P450 enzymes (P450s) and cytochrome P450 reductase (CPR) SmCPR. The CA titer was further increased by the coexpression of CYP76AH1 and SmCPR ∼t28SpCytb5 fusion proteins and the overexpression of different catalases to detoxify the hydrogen peroxide (H₂O₂). Finally, engineering of the endoplasmic reticulum and cofactor supply increased the CA titer to 24.65 mg/L in shake flasks and 75.18 mg/L in 5 L fed-batch fermentation. This study demonstrates that the ability of engineered yeast cells to synthesize CA can be improved through metabolic engineering and synthetic biology strategies, providing a theoretical basis for microbial synthesis of other diterpenoids.

Functional expression of eukaryotic cytochrome P450s in yeast

Cytochrome P450 enzymes (P450s) are a superfamily of heme-thiolate proteins widely existing in various organisms. Due to their key roles in secondary metabolism, degradation of xenobiotics, and carcinogenesis, there is a great demand to heterologously express and obtain a sufficient amount of active eukaryotic P450s. However, most eukaryotic P450s are endoplasmic reticulum-localized membrane proteins, which is the biggest challenge for functional expression to high levels. Furthermore, the functions of P450s require the cooperation of cytochrome P450 reductases for electron transfer. Great efforts have been devoted to the heterologous expression of eukaryotic P450s, and yeasts, particularly Saccharomyces cerevisiae are frequently considered as the first expression systems to be tested for this challenging purpose. This review discusses the strategies for improving the expression and activity of eukaryotic P450s in yeasts, followed by examples of P450s involved in biosynthetic pathway engineering.

Optimization of the process parameters for reduction of gossypol levels in cottonseed meal by functional recombinant NADPH-cytochrome P450 reductase and cytochrome P450 CYP9A12 of Helicoverpa armigera

Gossypol is a toxic polyphenolic product that is derived from cotton plants. The toxicity of gossypol has limited the utilization of cottonseed meal (CSM) in the feed industry. The gene, Helicoverpa armigera CYP9A12, is a gossypol-inducible cytochrome P450 gene. The objective of our study was to obtain the functional recombinant H. armigera CYP9A12 enzyme in Pichia pastoris and to verify whether this candidate enzyme could decrease gossypol in vitro. Free and total gossypol contents were detected in the enzyme solution and in CSM. The H. armigera CYP9A12 enzyme degraded free concentration of gossypol. After optimization of the single-test and response surface method, free gossypol content could be decreased to 40.91 mg/kg in CSM by the H. armigera CYP9A12 enzyme when the initial temperature was 35 °C, the enzymatic hydrolysis time lasted 2.5 h, the enzyme addition was 2.5 mL, and the substrate moisture was 39%.

Biosynthesis of Long-Chain ω-Hydroxy Fatty Acids by Engineered Saccharomyces cerevisiae

Long-chain hydroxy fatty acids (HFAs) are rare in nature but have many promising industrial applications. In this study, we developed a biosynthesis method to produce long-chain ω-hydroxy fatty acids. Through disruption of the acyl-CoA synthetases FAA1 and FAA4 and the fatty acyl-CoA oxidase POX1, a Saccharomyces cerevisiae strain was engineered to accumulate free fatty acids (FFAs). Subsequently, the cytochrome P450 monooxygenase CYP52M1 from Starmerella bombicola was introduced to convert FFAs to HFAs, leading to the production of C16 and C18 HFAs at the ω or ω-1 positions. Next, CYP52M1 was reconstituted with the homologous reductase S. bombicola CPR and the heterologous reductase Arabidopsis thaliana cytochrome P450 reductase. The results showed that the CYP52M1-AtCPR1 system significantly increased the hydroxylation in FFA. Moreover, a self-sufficient P450 enzyme system was constructed to achieve higher transformation efficiency. Finally, fed-batch fermentation yielded as much as 347 ± 9.2 mg/L ω-HFAs.

Fungal Lanosterol 14α-demethylase: A target for next-generation antifungal design

The cytochrome P450 enzyme lanosterol 14α-demethylase (LDM) is the target of the azole antifungals used widely in medicine and agriculture as prophylaxis or treatments of infections or diseases caused by fungal pathogens. These drugs and agrochemicals contain an imidazole, triazole or tetrazole substituent, with one of the nitrogens in the azole ring coordinating as the sixth axial ligand to the LDM heme iron. Structural studies show that this membrane bound enzyme contains a relatively rigid ligand binding pocket comprised of a deeply buried heme-containing active site together with a substrate entry channel and putative product exit channel that reach to the membrane. Within the ligand binding pocket the azole antifungals have additional affinity determining interactions with hydrophobic side-chains, the polypeptide backbone and via water-mediated hydrogen bond networks. This review will describe the tools that can be used to identify and characterise the next generation of antifungals targeting LDM, with the goal of obtaining highly potent broad-spectrum fungicides that will be able to avoid target and drug efflux mediated antifungal resistance.

Effect of a functional recombinant cytochrome P450 enzyme of Helicoverpa armigera on gossypol metabolism co-expressed with NADPH-cytochrome P450 reductase in Pichia pastoris

Gossypol is a polyphonic toxic compound that is present in cotton plants. The P450 cytochromes CYP6AE14 and CYP9A12 of Helicoverpa armigera are highly induced by gossypol and have been reported to be possibly involved in gossypol degradation. To determine whether the candidate H. armigera CYP6AE14 and CYP9A12 enzymes could metabolize gossypol in vitro, functional recombinant H. armigera CYP6AE14 and CPR (CYP9A12 and CPR) enzymes were successfully expressed in Pichia pastoris (P. pastoris). UPLC-QTOF/MS demonstrated the following results: (1) Free gossypol was spontaneously degraded to the gossypol metabolites G1 (m/z 265) and G2 (m/z 293) without the addition of any enzyme. (2) Free gossypol was observed following the addition of the endogenous or recombinant H. armigera P450 cytochrome CYP6AE14/CYP9A12 enzyme: in the first pathway, free gossypol was dehydroxylated and decarboxylated to G3 (m/z 453), and in the second pathway, the aldehyde group of gossypol and its metabolite were covalently bound with the amine products to form G4 (m/z 437) and G5 (m/z 783). (3) In addition to the gossypol binding pathways, the recombinant H. armigera CPR and CYP9A12 enzymes was found that could further decarboxylate the gossypol intermediate demethylated reduction of gossypolonic acid (m/z 294) and demethylated gossic acid (m/z 265) to G0 (m/z 209) and G0' (m/z 249) respectively.

Heterologous Co-expression of CYP6B7 and NADPH-Dependent Cytochrome P450 Reductase From Helicoverpa armigera (Lepidoptera: Noctuidae) in Pichia pastoris

As important metabolic enzymes, the function of cytochrome P450 monooxygenases (CYPs) has been demonstrated repeatedly through various means, including heterologous expression systems. Unfortunately, most model systems typically lack expression of a conspecific NADPH-dependent cytochrome P450 reductase (CPR), which is the electron transfer partner of CYPs. As a result, the activities of heterologously expressed insect CYPs may not accurately reflect detoxification activities in vivo. Previously, CYP6B7 from Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) (HaCYP6B7) has been expressed in the Pichia pastoris GS115 strain and shown to detoxify bifenthrin, fenvalerate and chlorpyrifos. However, it remains to be determined if co-expression of HaCYP6B7 with HaCPR will enhance the detoxification ability of the expression system. In the present study, HaCYP6B7 and HaCPR genes were co-expressed in P. pastoris using a reconstituted expression vector, pPICZA-HaCYP6B7-HaCPR. Protein expression was confirmed by Western blot, and the detoxification activities of microsomal fractions to p-nitroanisole O-demethylation (PNOD), 7-ethoxycoumarin O-deethylation (ECOD), fenvalerate and chlorpyrifos were measured. Co-expression of HaCYP6B7 with HaCPR resulted in PNOD and ECOD activities of 1.90 nmol/min/mg·protein and 12.39 pmol/min/mg·protein, which were 1.6- and 1.5-fold of that catalyzed by HaCYP6B7 expressed alone, respectively. Furthermore, microsomes of pPICZA-HaCYP6B7-HaCPR-GS115 had higher detoxification activity than that of pPICZA-HaCYP6B7-GS115 to fenvalerate, but not chlorpyrifos. The results indicated that co-expression of HaCYP6B7 with conspecific CPR could enhance the detoxification activities to some substrates comparing with expression of HaCYP6B7 alone.

The NDE1 genomic locus can affect treatment of psychiatric illness through gene expression changes related to microRNA-484

Genetic studies of familial schizophrenia in Finland have observed significant associations with a group of biologically related genes, DISC1, NDE1, NDEL1, PDE4B and PDE4D, the ‘DISC1 network’. Here, we use gene expression and psychoactive medication use data to study their biological consequences and potential treatment implications. Gene expression levels were determined in 64 individuals from 18 families, while prescription medication information has been collected over a 10-year period for 931 affected individuals. We demonstrate that the NDE1 SNP rs2242549 associates with significant changes in gene expression for 2908 probes (2542 genes), of which 794 probes (719 genes) were replicable. A significant number of the genes altered were predicted targets of microRNA-484 (p = 3.0 × 10⁻⁸), located on a non-coding exon of NDE1. Variants within the NDE1 locus also displayed significant genotype by gender interaction to early cessation of psychoactive medications metabolized by CYP2C19. Furthermore, we demonstrate that miR-484 can affect the expression of CYP2C19 in a cell culture system. Thus, variation at the NDE1 locus may alter risk of mental illness, in part through modification of miR-484, and such modification alters treatment response to specific psychoactive medications, leading to the potential for use of this locus in targeting treatment.

Recombinant production of eukaryotic cytochrome P450s in microbial cell factories

Cytochrome P450s (P450s) comprise one of the largest known protein families. They occur in every kingdom of life and catalyze essential reactions, such as carbon source assimilation, synthesis of hormones and secondary metabolites, or degradation of xenobiotics. Due to their outstanding ability of specifically hydroxylating complex hydrocarbons, there is a great demand to use these enzymes for biocatalysis, including applications at an industrial scale. Thus, the recombinant production of these enzymes is intensively investigated. However, especially eukaryotic P450s are difficult to produce. Challenges are faced due to complex cofactor requirements and the availability of a redox-partner (cytochrome P450 reductase, CPR) can be a key element to get active P450s. Additionally, most eukaryotic P450s are membrane bound which complicates the recombinant production. This review describes current strategies for expression of P450s in the microbial cell factories Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris.

Heterologous expression of Helicoverpa armigera cytochrome P450 CYP6B7 in Pichia pastoris and interactions of CYP6B7 with insecticides

BACKGROUND

Previous studies indicated that constitutive over-expression of cytochrome P450 CYP6B7 was involved in fenvalerate resistance in Helicoverpa armigera. In this study, the CYP6B7 gene from H. armigera (namely HaCYP6B7), was heterologously expressed in Pichia pastoris GS115. A vector pPICZA-HaCYP6B7 was constructed and transformed into P. pastoris GS115, the transformant of pPICZA-HaCYP6B7-GS115 was then cultured and induced by 1% (v/v) methanol and the heterologous expression of HaCYP6B7 protein in P. pastoris was confirmed by SDS-PAGE and western blot.

RESULTS

Microsomes containing the expressed HaCYP6B7 showed activities against model substrate p-nitroanisole and 7-ethoxycoumarin, with p-nitroanisole O-demethylation (PNOD) and 7-ethoxycoumarin O-deethylation (ECOD) activities of 15.66- and 4.75-fold of the control, respectively. Moreover, it showed degradation activities against the insecticides bifenthrin, fenvalerate and chlorpyrifos, with clearance activities of 6.88-, 1.49- and 2.27-fold of the control, respectively. The interactions of HaCYP6B7 with insecticides were further confirmed by molecular docking in silico with binding scores of 5.450, 5.295 and 2.197 between putative HaCYP6B7 protein and bifenthrin, fenvalerate and chlorpyrifos, respectively.

CONCLUSION

The results of present study provided more direct and important evidence on the role of HaCYP6B7 conferring pyrethroid resistance in H. armigera. © 2017 Society of Chemical Industry.

Procarcinogens - Determination and Evaluation by Yeast-Based Biosensor Transformed with Plasmids Incorporating RAD54 Reporter Construct and Cytochrome P450 Genes

In Vietnam, a great number of toxic substances, including carcinogens and procarcinogens, from industrial and agricultural activities, food production, and healthcare services are daily released into the environment. In the present study, we report the development of novel yeast-based biosensor systems to determine both genotoxic carcinogens and procarcinogens by cotransformation with two plasmids. One plasmid is carrying human CPR and CYP (CYP3A4, CYP2B6, or CYP2D6) genes, while the other contains the RAD54-GFP reporter construct. The three resulting coexpression systems bearing both CPR-CYP and RAD54-GFP expression cassettes were designated as CYP3A4/CYP2B6/CYP2D6 + RAD54 systems, respectively and used to detect and evaluate the genotoxic potential of carcinogens and procarcinogens by selective activation and induction of both CPR-CYP and RAD54-GFP expression cassettes in response to DNA damage. Procarcinogens were shown to be predominantly, moderately or not bioactivated by one of the CYP enzymes and thus selectively detected by the specific coexpression system. Aflatoxin B₁ and benzo(a)pyrene were predominantly detected by the CYP3A4 + RAD54 system, while N-nitrosodimethylamine only moderately activated the CYP2B6 + RAD54 reporter system and none of them was identified by the CYP2D6 + RAD54 system. In contrast, the genotoxic carcinogen, methyl methanesulfonate, was detected by all systems.

Our yeast-reporter system can be performed in 384-well microplates to provide efficient genotoxicity testing to identify various carcinogenic compounds and reduce chemical consumption to about 53% as compared with existing 96-well genotoxicity bioassays. In association with a liquid handling robot, this platform enables rapid, cost-effective, and high-throughput screening of numerous analytes in a fully automated and continuous manner without the need for user interaction.

RNAi down-regulation of cinnamate-4-hydroxylase increases artemisinin biosynthesis in Artemisia annua

Cinnamate-4-hydroxylase (C4H) converts trans-cinnamic acid (CA) to p-coumaric acid (COA) in the phenylpropanoid/lignin biosynthesis pathway. Earlier we reported increased expression of AaCYP71AV1 (an important gene of artemisinin biosynthesis pathway) caused by CA treatment in Artemisia annua. Hence, AaC4H gene was identified, cloned, characterized and silenced in A. annua with the assumption that the elevated internal CA due to knock down may increase the artemisinin yield. Accumulation of trans-cinnamic acid in the plant due to AaC4H knockdown was accompanied with the reduction of p-coumaric acid, total phenolics, anthocyanin, cinnamate-4-hydroxylase (C4H) and phenylalanine ammonia lyase (PAL) activities but increase in salicylic acid (SA) and artemisinin. Interestingly, feeding trans-cinnamic acid to the RNAi line increased the level of artemisinin along with benzoic (BA) and SA with no effect on the downstream metabolites p-coumaric acid, coniferylaldehyde and sinapaldehyde, whereas p-coumaric acid feeding increased the content of downstream coniferylaldehyde and sinapaldehyde with no effect on BA, SA, trans-cinnamic acid or artemisinin. SA is reported earlier to be inducing the artemisinin yield. This report demonstrates the link between the phenylpropanoid/lignin pathway with artemisinin pathway through SA, triggered by accumulation of trans-cinnamic acid because of the blockage at C4H.

Fungal cytochrome P450 monooxygenases of Fusarium oxysporum for the synthesis of ω-hydroxy fatty acids in engineered Saccharomyces cerevisiae

Background

Omega hydroxy fatty acids (ω-OHFAs) are multifunctional compounds that act as the basis for the production of various industrial products with broad commercial and pharmaceutical implications. However, the terminal oxygenation of saturated or unsaturated fatty acids for the synthesis of ω-OHFAs is intricate to accomplish through chemocatalysis, due to the selectivity and controlled reactivity in C-H oxygenation reactions. Cytochrome P450, the ubiquitous enzyme is capable of catalyzing the selective terminal omega hydroxylation naturally in biological kingdom.

Results

To gain a deep insight on the biochemical role of fungal P450s towards the production of omega hydroxy fatty acids, two cytochrome P450 monooxygenases from Fusarium oxysporum (FoCYP), FoCYP539A7 and FoCYP655C2; were identified, cloned, and heterologously expressed in Saccharomyces cerevisiae. For the efficient production of ω-OHFAs, the S. cerevisiae was engineered to disrupt the acyl-CoA oxidase enzyme and the β-oxidation pathway inactivated (ΔPox1) S. cerevisiae mutant was generated. To elucidate the significance of the interaction of redox mechanism, FoCYPs were reconstituted with the heterologous and homologous reductase systems - S. cerevisiae CPR (ScCPR) and F. oxysporum CPR (FoCPR). To further improve the yield, the effect of pH was analyzed and the homologous FoCYP-FoCPR system efficiently hydroxylated caprylic acid, capric acid and lauric acid into their respective ω-hydroxy fatty acids with 56%, 79% and 67% conversion. Furthermore, based on computational simulations, we identified the key residues (Asn106 of FoCYP539A7 and Arg235 of FoCYP655C2) responsible for the recognition of fatty acids and demonstrated the structural insights of the active site of FoCYPs.

Conclusion

Fungal CYP monooxygenases, FoCYP539A7 and FoCYP655C2 with its homologous redox partner, FoCPR constitutes a promising catalyst due to its high regio- and stereo-selectivity in the hydroxylation of fatty acids and in the substantial production of industrially valuable ω-hydroxy fatty acids.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0228-2) contains supplementary material, which is available to authorized users.

Genotoxicity of Chemical Compounds Identification and Assessment by Yeast Cells Transformed With GFP Reporter Constructs Regulated by the PLM2 or DIN7 Promoter

Yeast cells transformed with high-copy number plasmids comprising a green fluorescent protein (GFP)-encoding gene optimized for yeast under the control of the new DIN7 or PLM2 and the established RNR2 and RAD54 promoters were used to assess the genotoxic potential of chemical compounds. The activity of potential DNA-damaging agents was investigated by genotoxicity assays and by OxoPlate assay in the presence of various test compounds. The fluorescence signal generated by GFP in response to DNA damage was related to the different concentrations of analytes and the analyte-dependent GFP synthesis. The use of distinct DNA damage-inducible promoters presents alternative genotoxicity testing strategies by selective induction of promoters in response to DNA damage. The new DIN7 and PLM2 systems show higher sensitivity than the RNR2 and RAD54 systems in detecting 4-nitroquinoline- N-oxide and actinomycin D. Both DIN7 and PLM2 systems are able to detect camptothecin while RNR2 and RAD54 systems are not. Automated laboratory systems with assay performance on 384-well microplates provide for cost-effective high-throughput screening of DNA-damaging agents, reducing compound consumption to about 53% as compared with existing eukaryotic genotoxicity bioassays.

Comparative functional characterization of a novel benzoate hydroxylase cytochrome P450 of Fusarium oxysporum

FoCYP53A19, a novel cytochrome P450 capable of performing benzoate hydroxylation, was identified and characterized from the ascomycete Fusarium oxysporum f.sp. lycopersici. Comparative functional analysis of FoCYP53A19 with the heterologous and homologous cytochrome P450 reductases (CPR) such as Saccharomyces cerevisiae (ScCPR), Candida albicans (CaCPR) and F. oxysporum (FoCPR) revealed novel catalytic properties. The catalytic efficiency and substrate specificity of FoCYP53A19 were significantly influenced and altered by the source of the reductase employed. The yeast reconstitution system of FoCYP53A19 with ScCPR performed the hydroxylation of benzoic acid (BA) and demethylation of 3-methoxybenzoic acid (3-MBA); but when reconstituted with CaCPR, FoCYP53A19 performed only the essential hydroxylation of fungal benzoate catabolism. Remarkably, FoCYP53A19 with its homologous reductase FoCPR, not only demonstrated the improved conversion rates of BA and 3-MBA, but also exhibited activity toward the hydroxylation of 3-hydroxybenzoic acid. The electron transfer compatibility and the coupling efficiency between the homologous FoCYP-FoCPR system are significant and it favored enhanced monooxygenase activity with broader substrate specificity.

Cloning and Expression in Pichia pastoris of a New Cytochrome P450 Gene from a Dandruff-causing Malassezia globosa

The Malassezia fungi are responsible for various human skin disorders including dandruff and seborrheic dermatitis. Of the Malassezia fungi, Malassezia globosa (M. globosa) is one of the most common in human scalp. The completed genome sequence of M. globosa contains four putative cytochrome P450 genes. To determine the roles of Malassezia P450 enzymes in the biosynthesis of ergosterol, we isolated MGL3996 gene from M. globosa chromosomal DNA by PCR. The MGL3996 gene encodes an enzyme of 616 amino acids, which shows strong similarity with known CYP52s of other species. MGL3996 gene was cloned and expressed in Pichia pastoris (P. pastoris) heterologous yeast expression system. Using the yeast microsomes expressing MGL3996 protein, a typical P450 CO-difference spectrum was shown with absorption maximum at 448 nm. SDS-PAGE analysis revealed a protein band of apparent molecular weight 69 kDa and Western blot with anti-histidine tag antibody showed that MGL3996 was successfully expressed in P. pastoris. Cloning and expression of a new P450 gene is an important step to study the P450 monooxygenase system of M. globosa and to understand the role of P450 enzymes in pathophysiology of dandruff.

Double site saturation mutagenesis of the human cytochrome P450 2D6 results in regioselective steroid hydroxylation

The human cytochrome P450 2D6 (CYP2D6) is one of the major human drug metabolizing enzymes and acts preferably on substrates containing a basic nitrogen atom. Testosterone - just as other steroids - is an atypical substrate and only poorly metabolized by CYP2D6. The present study intended to investigate the influence of the two active site residues 216 and 483 on the capability of CYP2D6 to hydroxylate steroids such as for example testosterone. All 400 possible combinatorial mutations at these two positions have been generated and expressed individually in Pichia pastoris. Employing whole-cell biotransformations coupled with HPLC-MS analysis the testosterone hydroxylase activity and regioselectivity of every single CYP2D6 variant was determined. Covering the whole sequence space, CYP2D6 variants with improved activity and so far unknown regio-preference in testosterone hydroxylation were identified. Most intriguingly and in contrast to previous literature reports about mutein F483I, the mutation F483G led to preferred hydroxylation at the 2β-position, while the slow formation of 6β-hydroxytestosterone, the main product of wild-type CYP2D6, was further reduced. Two point mutations have already been sufficient to convert CYP2D6 into a steroid hydroxylase with the highest ever reported testosterone hydroxylation rate for this enzyme, which is of the same order of magnitude as for the conversion of the standard substrate bufuralol by wild-type CYP2D6. Furthermore, this study is also an example for efficient human CYP engineering in P. pastoris for biocatalytic applications and to study so far unknown pharmacokinetic effects of individual and combined mutations in these key enzymes of the human drug metabolism.

Steroid biotransformations in biphasic systems with Yarrowia lipolytica expressing human liver cytochrome P450 genes

BACKGROUND

Yarrowia lipolytica efficiently metabolizes and assimilates hydrophobic compounds such as n-alkanes and fatty acids. Efficient substrate uptake is enabled by naturally secreted emulsifiers and a modified cell surface hydrophobicity and protrusions formed by this yeast. We were examining the potential of recombinant Y. lipolytica as a biocatalyst for the oxidation of hardly soluble hydrophobic steroids. Furthermore, two-liquid biphasic culture systems were evaluated to increase substrate availability. While cells, together with water soluble nutrients, are maintained in the aqueous phase, substrates and most of the products are contained in a second water-immiscible organic solvent phase.

RESULTS

For the first time we have co-expressed the human cytochromes P450 2D6 and 3A4 genes in Y. lipolytica together with human cytochrome P450 reductase (hCPR) or Y. lipolytica cytochrome P450 reductase (YlCPR). These whole-cell biocatalysts were used for the conversion of poorly soluble steroids in biphasic systems.Employing a biphasic system with the organic solvent and Y. lipolytica carbon source ethyl oleate for the whole-cell bioconversion of progesterone, the initial specific hydroxylation rate in a 1.5 L stirred tank bioreactor was further increased 2-fold. Furthermore, the product formation was significantly prolonged as compared to the aqueous system. Co-expression of the human CPR gene led to a 4-10-fold higher specific activity, compared to the co-overexpression of the native Y. lipolytica CPR gene. Multicopy transformants showed a 50-70-fold increase of activity as compared to single copy strains.

CONCLUSIONS

Alkane-assimilating yeast Y. lipolytica, coupled with the described expression strategies, demonstrated its high potential for biotransformations of hydrophobic substrates in two-liquid biphasic systems. Especially organic solvents which can be efficiently taken up and/or metabolized by the cell might enable more efficient bioconversion as compared to aqueous systems and even enable simple, continuous or at least high yield long time processes.

Expression of CYP107Z13 in Streptomyces lividans TK54 catalyzes the oxidation of avermectin to 4″-oxo-avermectin

Streptomyces ahygroscopicus ZB01 has strong catalytic activity for the regiospecific oxidation of 4″-OH of avermectin to form 4″-oxo-avermectin. A cytochrome P450 gene from S. ahygroscopicus ZB01, cyp107z13, was cloned into pKC1139 to generate pKCZ1 and was transformed into Streptomyces lividans TK54, which does not have the ability to catalyze the conversion of avermectin. CYP107Z13, under the control of an ermE* promoter, was actively expressed in the TK54 recombinant strain as determined by a reduced CO difference spectrum analysis of the crude protein. Analysis of whole-cell biocatalytic activity by high-performance liquid chromatography revealed the recombinant to be able to oxidize avermectin regiospecifically to 4″-oxo-avermectin and CYP107Z13 to be a regioselective oxidase of avermectin. In addition, the whole-cell reaction conditions of the recombinant were optimized. Growth on medium ISP-2 at pH 6 was more conducive for the expression of CYP107Z13 than on medium PYG1 or at pH 7, and active cells of the recombinant strain had higher biocatalytic activity than resting cells.

Biotechnological synthesis of drug metabolites using human cytochrome P450 isozymes heterologously expressed in fission yeast

Cytochrome P450 mono-oxygenases (CYPs) are the major enzymes involved in the metabolism of drugs and poisons in humans. The variation of their activity - due to genetic polymorphisms or enzyme inhibition/induction - potentially increases the risk of side effects or toxicity. Studies on CYP-dependent metabolism are important in drug-development or toxicity studies. Reference standards of drug metabolites required for such studies, especially in the context of metabolites in safety testing (MIST), are often not commercially available and their classical chemical synthesis can be cumbersome. Recently, a biotechnological approach using human CYP isozymes heterologously expressed in fission yeast was developed for the synthesis of drug metabolites. Among other aspects, this approach has the distinct advantages that the reactions run under mild conditions and that only the final product must be isolated and characterized. This review overviews the first practical applications of this new approach and discusses the selection of substrates, metabolites and fission yeast strains as well as important aspects of incubation, product isolation and clean-up.

Functional expression and characterisation of human cytochrome P45017α in Pichia pastoris

Human cytochrome P45017alpha (CYP17), present in mammalian adrenal and gonadal tissues, catalyses both steroid 17-hydroxylation and C17,20 lyase reactions, producing intermediates for the glucocorticoid and androgenic pathways, respectively. The characterisation of this complex enzyme was initially hampered due to low level in vivo expression of CYP17. Heterologous expression systems have contributed greatly to our current knowledge of CYP17's dual catalytic activity. However, due to the hydrophobic nature of this membrane-bound protein, primarily truncated and modified forms of CYP17 are currently being expressed heterologously. Although the N-terminally modified enzyme has been well characterised, protein structure and function studies still necessitate the expression of unmodified, wild-type CYP17. We report here the expression of a catalytically active, unmodified human CYP17 in the industrial methylotrophic yeast, Pichia pastoris. A typical P450 carbon monoxide difference spectrum, with an absorption maximum at 448nm and a substrate-induced type I spectrum were recorded using a detergent-solubilised cellular fraction containing CYP17. The expressed enzyme catalysed the conversion of progesterone to 17-hydroxyprogesterone as well as 16-hydroxyprogesterone, a product unique to human and chimpanzee CYP17. This is the first report showing the heterologous expression of a fully functional human steroidogenic cytochrome P450 enzyme in P. pastoris.

Recent advances in oxygenase-catalyzed biotransformations

Oxygenases continue to be widely studied for selective biooxidation of organic compounds. Protein engineering has resulted in heme and flavin monooxygenases with widely altered substrate specificities, and attempts have been reported to scale-up reactions catalyzed by these enzymes. Cofactor regeneration is still a key issue in these developments. Protein engineering contributed to understanding of structure versus function in dioxygenases.