Cloning and characterization of the NADPH cytochrome P450 oxidoreductase gene from the filamentous fungus Aspergillus niger

A bacterial-like Pictet-Spenglerase drives the evolution of fungi to produce β-carboline glycosides together with separate genes

Diverse β-carboline (βC) alkaloids are produced by microbes, plants, and animals with myriad bioactivities and drug potentials. However, the biosynthetic mechanism of βCs remains largely elusive, especially regarding the hydroxyl and glucosyl modifications of βCs. Here, we report the presence of the bacterial-like Pictet-Spenglerase gene Fcs1 in the entomopathogenic Beauveria fungi that can catalyze the biosynthesis of the βC skeleton. The overexpression of Fcs1 in Beauveria bassiana led to the identification of six βC methyl glycosides, termed bassicarbosides (BCSs) A-F. We verified that the cytochrome P450 (CYP) genes adjacent to Fcs1 cannot oxidize βCs. Alternatively, the separated CYP684B2 family gene Fcs2 was identified to catalyze βC hydroxylation together with its cofactor gene Fcs3. The functional homologue of Fcs2 is only present in the Fcs1-containing fungi and highly similar to the Fcs1-connected yet nonfunctional CYP. Both evolved quicker than those from fungi without Fcs1 homologues. Finally, the paired methyl/glucosyl transferase genes were verified to mediate the production of BCSs from hydroxy-βCs. All these functionally verified genes are located on different chromosomes of Beauveria, which is in contrast to the typical content-clustered feature of fungal biosynthetic gene clusters (BGCs). We also found that the production of BCSs selectively contributed to fungal infection of different insect species. Our findings shed light on the biosynthetic mechanism of βC glycosides, including the identification of a βC hydroxylase. The results of this study also propose an evolving process of fungal BGC formation following the horizontal transfer of a bacterial gene to fungi.

Heterologous production of ascofuranone and ilicicolin A in Aspergillus sojae

Ascofuranone and its precursor, ilicicolin A, are secondary metabolites with various pharmacological activities that are produced by Acremonium egyptiacum. In particular, ascofuranone strongly inhibits trypanosome alternative oxidase and represents a potential drug candidate against African trypanosomiasis. However, difficulties associated with industrial production of ascofuranone by A. egyptiacum, specifically the co-production of ascochlorin, which inhibits mammalian respiratory chain complex III at low concentrations, has precluded its widespread application. Therefore, in this study, ascofuranone biosynthetic genes (ascA-E and H-J) were heterologously expressed in Aspergillus sojae, which produced very low-levels of endogenous secondary metabolites under conventional culture conditions. As a result, although we obtained transformants producing both ilicicolin A and ascofuranone, they were produced only when an adequate concentration of chloride ions was added to the medium. In addition, we succeeded in increasing the production of ilicicolin A, by enhancing the expression of the rate-determining enzyme AscD, using a multi-copy integration system. The heterologous expression approach described here afforded the production of both ascofuranone and ilicicolin A, allowing for their development as therapeutics.

The P450 oxidoreductase, RedA, controls development beyond the mound stage in Dictyostelium discoideum

BACKGROUND

NADPH-cytochrome-P450 oxidoreductase (CPR) is a ubiquitous enzyme that belongs to a family of diflavin oxidoreductases and is required for activity of the microsomal cytochrome-P450 monooxygenase system. CPR gene-disruption experiments have demonstrated that absence of this enzyme causes developmental defects both in mouse and insect.

RESULTS

Annotation of the sequenced genome of D. discoideum revealed the presence of three genes (redA, redB and redC) that encode putative members of the diflavin oxidoreductase protein family. redA transcripts are present during growth and early development but then decline, reaching undetectable levels after the mound stage. redB transcripts are present in the same levels during growth and development while redC expression was detected only in vegetative growing cells. We isolated a mutant strain of Dictyostelium discoideum following restriction enzyme-mediated integration (REMI) mutagenesis in which redA was disrupted. This mutant develops only to the mound stage and accumulates a bright yellow pigment. The mound-arrest phenotype is cell-autonomous suggesting that the defect occurs within the cells rather than in intercellular signaling.

CONCLUSION

The developmental arrest due to disruption of redA implicates CPR in the metabolism of compounds that control cell differentiation.

The weak-acid preservative sorbic acid is decarboxylated and detoxified by a phenylacrylic acid decarboxylase, PadA1, in the spoilage mold Aspergillus niger

Resistance to sorbic and cinnamic acids is mediated by a phenylacrylic acid decarboxylase (PadA1) in Aspergillus niger. A. niger DeltapadA1 mutants are unable to decarboxylate sorbic and cinnamic acids, and the MIC of sorbic acid required to inhibit spore germination was reduced by approximately 50% in DeltapadA1 mutants.

The expression of cytochrome P-450 and cytochrome P-450 reductase genes in the simultaneous transformation of corticosteroids and phenanthrene byCunninghamella elegans

The expression of cytochrome P-450 and cytochrome P-450 reductase (CPR) genes in the conterminous biotransformation of corticosteroids and PAHs was studied in Cunninghamella elegans 1785/21Gp. We had previously used this strain as a microbial eucaryotic model for studying the relationship between mammalian steroid hydroxylation and the metabolization of PAHs. We reported that cytochrome P-450 reductase is involved in the biotransformaton of cortexolone and phenanthrene. RT-PCR and Northern blotting analyses indicated that the cytochrome P-450 and CPR genes appear to be inducible by both steroids and PAHs. The expression of the cytochrome P-450 gene was increased ninefold and the expression of the CPR gene increased 6.4-fold in cultures with cortexolone and/or phenanthrene in comparison with controls. We conclude that the increase in cytochrome P-450 gene expression was accompanied by an increase in cytochrome P-450 enzymatic activity levels.

Gibberellin biosynthesis in fungi: genes, enzymes, evolution, and impact on biotechnology

Gibberellins (GAs) constitute a large family of tetracyclic diterpenoid carboxylic acids, some members of which function as growth hormones in higher plants. As well as being phytohormones, GAs are also present in some fungi and bacteria. In recent years, GA biosynthetic genes from Fusarium fujikuroi and Arabidopsis thaliana have been cloned and well characterised. Although higher plants and the fungus both produce structurally identical GAs, there are important differences indicating that GA biosynthetic pathways have evolved independently in higher plants and fungi. The fact that horizontal gene transfer of GA genes from the plant to the fungus can be excluded, and that GA genes are obviously missing in closely related Fusarium species, raises the question of the origin of fungal GA biosynthetic genes. Besides characterisation of F. fujikuroi GA pathway genes, much progress has been made in the molecular analysis of regulatory mechanisms, especially the nitrogen metabolite repression controlling fungal GA biosynthesis. Basic research in this field has been shown to have an impact on biotechnology. Cloning of genes, construction of knock-out mutants, gene amplification, and regulation studies at the molecular level are powerful tools for improvement of production strains. Besides increased yields of the final product, GA3, it is now possible to produce intermediates of the GA biosynthetic pathway, such as ent-kaurene, ent-kaurenoic acid, and GA14, in high amounts using different knock-out mutants. This review concentrates mainly on the fungal biosynthetic pathway, the genes and enzymes involved, the regulation network, the biotechnological relevance of recent studies, and on evolutionary aspects of GA biosynthetic genes.

The P450 monooxygenase BcABA1 is essential for abscisic acid biosynthesis in Botrytis cinerea

The phytopathogenic ascomycete Botrytis cinerea is known to produce abscisic acid (ABA), which is thought to be involved in host-pathogen interaction. Biochemical analyses had previously shown that, in contrast to higher plants, the fungal ABA biosynthesis probably does not proceed via carotenoids but involves direct cyclization of farnesyl diphosphate and subsequent oxidation steps. We present here evidence that this "direct" pathway is indeed the only one used by an ABA-overproducing strain of B. cinerea. Targeted inactivation of the gene bccpr1 encoding a cytochrome P450 oxidoreductase reduced the ABA production significantly, proving the involvement of P450 monooxygenases in the pathway. Expression analysis of 28 different putative P450 monooxygenase genes revealed two that were induced under ABA biosynthesis conditions. Targeted inactivation showed that one of these, bcaba1, is essential for ABA biosynthesis: DeltaBcaba1 mutants contained no residual ABA. Thus, bcaba1 represents the first identified fungal ABA biosynthetic gene.

The NADPH-cytochrome P450 reductase gene from Gibberella fujikuroi is essential for gibberellin biosynthesis

The fungus Gibberella fujikuroi is used for the commercial production of gibberellins (GAs), which it produces in very large quantities. Four of the seven GA biosynthetic genes in this species encode cytochrome P450 monooxygenases, which function in association with NADPH-cytochrome P450 reductases (CPRs) that mediate the transfer of electrons from NADPH to the P450 monooxygenases. Only one cpr gene (cpr-Gf) was found in G. fujikuroi and cloned by a PCR approach. The encoded protein contains the conserved CPR functional domains, including the FAD, FMN, and NADPH binding motifs. cpr-Gf disruption mutants were viable but showed a reduced growth rate. Furthermore, disruption resulted in total loss of GA(3), GA(4), and GA(7) production, but low levels of non-hydroxylated C(20)-GAs (GA(15) and GA(24)) were still detected. In addition, the knock-out mutants were much more sensitive to benzoate than the wild type due to loss of activity of another P450 monooxygenase, the detoxifying enzyme, benzoate p-hydroxylase. The UV-induced mutant of G. fujikuroi, SG138, which was shown to be blocked at most of the GA biosynthetic steps catalyzed by P450 monooxygenases, displayed the same phenotype. Sequence analysis of the mutant cpr allele in SG138 revealed a nonsense mutation at amino acid position 627. The mutant was complemented with the cpr-Gf and the Aspergillus niger cprA genes, both genes fully restoring the ability to produce GAs. Northern blot analysis revealed co-regulated expression of the cpr-Gf gene and the GA biosynthetic genes P450-1, P450-2, P450-4 under GA production conditions (nitrogen starvation). In addition, expression of cpr-Gf is induced by benzoate. These results indicate that CPR-Gf is the main but not the only electron donor for several P450 monooxygenases from primary and secondary metabolism.

Catalytic and immunochemical properties of NADPH-cytochrome P450 reductase from fungus Rhizopus nigricans

Flavoprotein NADPH-cytochrome P450 reductase (CPR, EC 1.6.2.4) from filamentous fungus Rhizopus nigricans is a membrane bound enzyme which is involved in the reduction of cytochrome P450 during the hydroxylation of progesterone at 11alpha position. After purification of the enzyme from induced mycelia three forms of fungal CPR were detected on SDS-PAGE: a predominant form with an apparent molecular mass of 78kDa and two truncated forms. N-terminal sequences of all three forms were determined as well as some internal sequences of 78kDa form. Dose-dependent immunoinhibition of NADPH-cytochrome c reductase and progesterone 11alpha-hydroxylase activities was observed with mouse anti-CPR antisera. No cross-reactions were obtained on Western blots between mouse anti-CPR antisera and protein preparations from noninduced mycelia and microsomal fraction from fungus Pleurotus osteatus, plant Ginkgo biloba or chicken liver. The kinetic mechanism of CPR was proposed on the basis of model reaction with cytochrome c(3+). Results obtained at high ionic strength suggest a nonclassical two-site ping pong mechanism and at low ionic strength a sequential mechanism of bisubstrate reaction.

The genes gmdA, encoding an amidase, and bzuA, encoding a cytochrome P450, are required for benzamide utilization in Aspergillus nidulans

Two unlinked loci, gmdA and bzuA, have previously been identified as being required for the utilization of benzamide as the sole nitrogen source by Aspergillus nidulans. We have cloned each of these genes via direct complementation. The gmdA gene encodes a predicted product belonging to the amidase signature sequence family that displays similarity to AmdS from A. nidulans. However, identity is significantly higher to the amdS gene from Aspergillus niger. The bzuA gene encodes a protein belonging to the cytochrome P450 superfamily and is orthologous to the benzoate para-hydroxylase-encoding gene bphA of A. niger. The bzuA1 mutation prevents the use of benzoate as a carbon source and intracellular accumulation of benzoate results in growth inhibition on benzamide. Northern blot analysis has shown that gmdA expression is subject solely to AreA-dependent nitrogen metabolite repression while bzuA is strongly benzoate inducible and subject to CreA-mediated carbon catabolite repression and a probable inactivation of benzoate induction by glucose. Fluorescence microscopy of a fusion of the N-terminal end of BzuA to green fluorescent protein revealed that this protein localizes to the endoplasmic reticulum.

Purification and characterization of benzoate-para-hydroxylase, a cytochrome P450 (CYP53A1), from Aspergillus niger

Benzoate-para-hydroxylase (CYP51A or BpH) and NADPH:cytochrome P450 reductase from the filamentous fungus Aspergillus niger were purified to apparent homogeneity, using an overproducing A. niger strain. This is the first membrane-bound fungal cytochrome P450 to be isolated and characterized. Combining BpH with NADPH:cytochrome P450 oxidoreductase in the presence of the phospholipid dilauryl phosphatidylcholine restored the BpH activity, although to only a minor extent. Spectral analysis of BpH showed characteristic spectra for a cytochrome P450. Substrate binding studies with purified BpH as a function of temperature and as a function of pH were performed. Temperature-dependent studies, at pH 8.0, showed that the simplified spin equilibrium model originally proposed for camphor binding to cytochrome P450cam (M. T. Fisher and S. G. Sligar, 1987, Biochemistry 26, 4797-4803) also applies to the benzoate-BpH system. Two equilibrium constants were determined, K(1) for substrate binding without a spin change and K(2) for the spin change of the benzoate-BpH complex. pH-dependent binding studies showed that both K(1) and K(2) increase with pH, indicative of a higher affinity. As K(1) decreases more strongly with pH than K(2), we suggest that benzoate first binds to a binding site on the outside of the protein in a pH-dependent way, followed by transfer to the inside of the protein causing a spin change at the heme iron. The strong pH dependence of K(1) could be the result of the need to break salt bridges at the binding site on the outside of the protein. pH-dependent kinetic studies with microsomes showed that the apparent K(M) values followed the trend observed for benzoate binding to purified BpH, while k(cat) values were virtually constant between pH 6.6 and 8.0 and decreased above pH 8, probably due to loss of productive interaction between BpH and NADPH:cytochrome P450 oxidoreductase. Research into the substrate specificity of BpH showed that BpH can only use benzoic acid and some of its derivatives. Monosubstitution on the phenyl ring is allowed but only at certain positions with specific, not too large groups. Substitution always leads to a lower affinity of the substrate. With one exception, all substrates were converted to their 4-hydroxy derivative. The exception, 3-methoxybenzoate, was demethylated to yield 3-hydroxybenzoate only. The restricted number of substrates and the specificity in catalysis suggest that BpH is not a general-purpose hydroxylase but that its role is confined to benzoate hydroxylation in the beta-ketoadipate pathway of A. niger.

Identification and characterization of a family of secretion-related small GTPase-encoding genes from the filamentous fungus Aspergillus niger: a putative SEC4 homologue is not essential for growth

DNA fragments containing genetic information for five secretion-related small GTPases of Aspergillus niger (srgA-E) were isolated and identified as members of different Rab/Ypt subfamilies. This isolation and the search for similar sequences in fungal genomic and EST databases showed that, in contrast to Saccharomyces cerevisiae, filamentous fungi also possess homologues of mammalian Rab2 GTPases. Multiple transcripts with unusually long 5' and 3' untranslated regions were found for all srg genes. Their level of expression was independent of the type of carbon source used for growth. Although the transcripts of srgA and srgB were abundant to the same extent throughout the cultivation, that of the other genes peaked during the early growth phase and then declined. Two genes, srgA and srgB, were characterized further. The protein encoded by srgA exhibited relatively low identity (58%) to its closest S. cerevisiae homologue SEC4, whereas the protein encoded by srgB showed 73% identity with S. cerevisiae YPT1. In contrast to other SEC4 homologues, srgA was unable to complement an S. cerevisiae sec4 mutant, and its disruption was not lethal in A. niger. SrgA mutants displayed a twofold increase in their hyphal diameter, unusual apical branching and strongly reduced protein secretion during growth on glucose.

Cloning and characterization of the cytochrome P450 oxidoreductase gene from the zygomycete fungus Cunninghamella

The filamentous fungus Cunninghamella utilizes cytochrome P450 system(s) in the metabolism of a broad range of polyaromatic and aliphatic pollutants and a variety of drugs, but prior attempts at isolation of P450 system components of this fungus have been generally unsuccessful. We report upon the cytochrome P450 oxidoreductase (CPR) gene from two widely studied species, C. elegans and C. echinulata. The C. elegans CPR gene was obtained by screening a genomic library using as probe a PCR amplicon obtained with degenerate primers based on known CPRs. The 2420 bp coding region contained two apparent introns (149 bp and 138 bp). Northern blot analysis showed that the CPR gene is transcriptionally expressed in C. elegans and appears to be inducible by an alkane substrate, n-tetradecane. Phylogenetic comparison of the deduced C. elegans CPR (710 aa) suggested that it is more closely related to animal CPRs (41-42%) than to yeast (38-41%) and plant (35-36%) forms. A 2074 bp sequence containing most of the CPR gene homolog from C. echinulata was also isolated.

Cytochrome P450 enzyme systems in fungi

The involvement of cytochrome P450 enzymes in many complex fungal bioconversion processes has been characterized in recent years. Accordingly, there is now considerable scientific interest in fungal cytochrome P450 enzyme systems. In contrast to S. cerevisiae, where surprisingly few P450 genes have been identified, biochemical data suggest that many fungi possess numerous P450 genes. This review summarizes the current information pertaining to these fungal cytochrome P450 systems, with emphasis on the molecular genetics. The use of molecular techniques to improve cytochrome P450 activities in fungi is also discussed.

Enzymatic Mechanisms Involved in Phenanthrene Degradation by the White Rot Fungus Pleurotus ostreatus

The enzymatic mechanisms involved in the degradation of phenanthrene by the white rot fungus Pleurotus ostreatus were examined. Phase I metabolism (cytochrome P-450 monooxygenase and epoxide hydrolase) and phase II conjugation (glutathione S-transferase, aryl sulfotransferase, UDP-glucuronosyltransferase, and UDP-glucosyltransferase) enzyme activities were determined for mycelial extracts of P. ostreatus. Cytochrome P-450 was detected in both cytosolic and microsomal fractions at 0.16 and 0.38 nmol min(sup-1) mg of protein(sup1), respectively. Both fractions oxidized [9,10-(sup14)C]phenanthrene to phenanthrene trans-9,10-dihydrodiol. The cytochrome P-450 inhibitors 1-aminobenzotriazole (0.1 mM), SKF-525A (proadifen, 0.1 mM), and carbon monoxide inhibited the cytosolic and microsomal P-450s differently. Cytosolic and microsomal epoxide hydrolase activities, with phenanthrene 9,10-oxide as the substrate, were similar, with specific activities of 0.50 and 0.41 nmol min(sup-1) mg of protein(sup-1), respectively. The epoxide hydrolase inhibitor cyclohexene oxide (5 mM) significantly inhibited the formation of phenanthrene trans-9,10-dihydrodiol in both fractions. The phase II enzyme 1-chloro-2,4-dinitrobenzene glutathione S-transferase was detected in the cytosolic fraction (4.16 nmol min(sup-1) mg of protein(sup-1)), whereas aryl adenosine-3(prm1)-phosphate-5(prm1)-phosphosulfate sulfotransferase (aryl PAPS sulfotransferase) UDP-glucuronosyltransferase, and UDP-glucosyltransferase had microsomal activities of 2.14, 4.25, and 4.21 nmol min(sup-1) mg of protein(sup-1), respectively, with low activity in the cytosolic fraction. However, when P. ostreatus culture broth incubated with phenanthrene was screened for phase II metabolites, no sulfate, glutathione, glucoside, or glucuronide conjugates of phenanthrene metabolites were detected. These experiments indicate the involvement of cytochrome P-450 monooxygenase and epoxide hydrolase in the initial phase I oxidation of phenanthrene to form phenanthrene trans-9,10-dihydrodiol. Laccase and manganese-independent peroxidase were not involved in the initial oxidation of phenanthrene. Although P. ostreatus had phase II xenobiotic metabolizing enzymes, conjugation reactions were not important for the elimination of hydroxylated phenanthrene.

An improved colony-PCR method for filamentous fungi for amplification of PCR-fragments of several kilobases

A method was developed to perform PCR directly on mycelial pellets or colonies treated with NOVOzym 234. The method allows rapid screening of large numbers of transformants of both sporulating and non-sporulating fungi for the presence of (co)transforming plasmid copies or for specific genetic modifications such as gene disruption and site specific integration. PCR fragments of at least 3.2 kb can be obtained. Using this method the identification of specific disruption mutants from Aspergillus niger and Beauveria bassiana was carried out.

Optimization of the benzoate-inducible benzoate p-hydroxylase cytochrome P450 enzyme system in Aspergillus niger

Introduction in the fungus Aspergillus niger of multiple copies of the A. niger bphA gene, encoding the cytochrome P450 enzyme benzoate p-hydroxylase, did not result in increased activities of this enzyme [Gorcom RFM van, et al. Mol Gen Genet (1990) 223: 192-197] probably because of low expression levels of the gene encoding the second component of the microsomal cytochrome P450 enzyme system, cytochrome P450 reductase. For improvement of this and other cytochrome-P450-dependent reactions, A. niger strains were constructed in which the copy number of the A. niger cprA gene (encoding cytochrome-P450 reductase) or the copy numbers of both cprA and the cytochrome-P450-encoding gene were increased. Expression of both genes was controlled by their own transcription control regions. Benzoate p-hydroxylase activity of different transformants was determined in microsomal fractions using a newly developed indirect in vitro assay. In transformants containing multiple copies of both genes, benzoate p-hydroxylase activity was significantly higher than in the wild-type strain or in transformants in which the copy number of only one of the genes was increased. These results clearly indicate the importance of co-expression of cytochrome-P450 reductase for achieving maximal cytochrome P450 activities in cytochrome-P450-overproducing filamentous fungi.

Increased resistance to 14 alpha-demethylase inhibitors (DMIs) in Aspergillus niger by coexpression of the Penicillium italicum eburicol 14 alpha-demethylase (cyp51) and the A. niger cytochrome P450 reductase (cprA) genes

In this paper we describe the effects of over-expression of the Penicillium italicum gene encoding eburicol 14 alpha-demethylase (cyp51), in Aspergillus niger strains with one or multiple copies of the gene encoding cytochrome P450 reductase (cprA), on the eburicol 14 alpha-demethylase activity. Eburicol 14 alpha-demethylase activity was determined by measuring the resistance of transformants against some eburicol 14 alpha-demethylase inhibitors (DMIs). DMIs are widely used as fungicides in crop protection and human and veterinarian health care. DMI resistance in a transformant overexpressing both CPR and CYP51 was increased 5-30-fold compared to DMI resistance in the wild type strain, depending on the test compound used. Resistance in this strain was approximately 2-5-fold increased compared to DMI resistance in a transformant that was overexpressing the cyp51 gene but had only the wild type copy of the cprA gene and approximately 3-12-fold increased compared to a strain overexpressing the cprA gene (and having only the wild type copy of the cyp51 gene). These results show the importance of CPR overexpression for increasing cytochrome P450 activities in filamentous fungi.

Isolation and molecular characterisation of the gene encoding eburicol 14 alpha-demethylase (cYP51) from Penicillium italicum

The CYP51 gene encoding eburicol 14 alpha-demethylase (P450(14DM)) was cloned from a genomic library of the filamentous fungal plant pathogen Penicillium italicum, by heterologous hybridisation with the corresponding gene encoding lanosterol 14 alpha-demethylase from the yeast Candida tropicalis. The nucleotide sequence of a 1739-bp genomic fragment and the corresponding cDNA clone comprises an open reading frame (ORF) of 1545 bp, encoding a protein of 515 amino acids with a predicted molecular mass of 57.3 kDa. The ORF is interrupted by three introns of 60, 72 and 62 bp. The C-terminal part of the protein includes a characteristic haem-binding domain, HR2, common to all P450 genes. The deduced P. italicum P450(14DM) protein and the P450(14DM) proteins from Candida albicans, C. tropicalis and Saccharomyces cerevisiae share 47.2, 47.0 and 45.8% amino acid sequence identity. Therefore, the cloned gene is classified as a member of the CYP51 family. Multiple copies of a genomic DNA fragment of Pl italicum containing the cloned P450 gene were introduced into Aspergillus niger by transformation. Transformants were significantly less sensitive to fungicides which inhibit P450(14DM) activity, indicating that the cloned gene encodes a functional eburicol 14 alpha-demethylase.