Identification and characterization of additional members of the cytochrome P450 multigene family CYP52 of Candida tropicalis

Mid-Long Chain Dicarboxylic Acid Production via Systems Metabolic Engineering: Progress and Prospects

Mid-to-long-chain dicarboxylic acids (DCAi, i ≥ 6) are organic compounds in which two carboxylic acid functional groups are present at the terminal position of the carbon chain. These acids find important applications as structural components and intermediates across various industrial sectors, including organic compound synthesis, food production, pharmaceutical development, and agricultural manufacturing. However, conventional petroleum-based DCA production methods cause environmental pollution, making sustainable development challenging. Hence, the demand for eco-friendly processes and renewable raw materials for DCA production is rising. Owing to advances in systems metabolic engineering, new tools from systems biology, synthetic biology, and evolutionary engineering can now be used for the sustainable production of energy-dense biofuels. Here, we explore systems metabolic engineering strategies for DCA synthesis in various chassis via the conversion of different raw materials into mid-to-long-chain DCAs. Subsequently, we discuss the future challenges in this field and propose synthetic biology approaches for the efficient production and successful commercialization of these acids.

Utilization of n-alkane and roles of lipid transfer proteins in Yarrowia lipolytica

Yarrowia lipolytica, a dimorphic yeast belonging to the Ascomycota, has potent abilities to utilize hydrophobic compounds, such as n-alkanes and fatty acids, as carbon and energy sources. Yarrowia lipolytica can synthesize and accumulate large amounts of lipids, making it a promising host to produce various lipids and convert n-alkanes to useful compounds. For advanced use of Y. lipolytica in these applications, it is necessary to understand the metabolism of these hydrophobic compounds in this yeast and the underlying molecular mechanisms. In this review, current knowledge on the n-alkane metabolism and how this is regulated in Y. lipolytica is summarized. Furthermore, recent studies revealed that lipid transfer proteins are involved in the utilization of n-alkanes and the regulation of cell morphology in response to n-alkanes. This review discusses the roles of membrane lipids in these processes in Y. lipolytica.

Development of mazF-based markerless genome editing system and metabolic pathway engineering in Candida tropicalis for producing long-chain dicarboxylic acids

Candida tropicalis can grow with alkanes or plant oils as the sole carbon source, and its industrial application thus has great potential. However, the choice of a suitable genetic operating system can effectively increase the speed of metabolic engineering. MazF functions as an mRNA interferase that preferentially cleaves single-stranded mRNAs at ACA sequences to inhibit protein synthesis, leading to cell growth arrest. Here, we constructed a suicide plasmid named pPICPJ-mazF that uses the mazF gene of Escherichia coli as a counterselectable marker for the markerless editing of C. tropicalis genes to increase the rate of conversion of oils into long-chain dicarboxylic acids. To reduce the β-oxidation of fatty acids, the carnitine acetyltransferase gene (CART) was deleted using the gene editing system, and the yield of long-chain acids from the strain was increased to 8.27 g/L. By two homologous single exchanges, the promoters of both the cytochrome P450 gene and the NADPH–cytochrome P450 reductase gene were subsequently replaced by the constitutively expressed promoter pGAP, and the production of long-chain dicarboxylic acids by the generated strain (C. tropicalis PJPP1702) reached 11.39 g/L. The results of fed-batch fermentation showed that the yield of long-chain acids from the strain was further increased to 32.84 g/L, which was 11.4 times higher than that from the original strain. The results also showed that the pPICPJ-mazF-based markerless editing system may be more suited for completing the genetic editing of C. tropicalis.

Fungal Cytochrome P450s and the P450 Complement (CYPome) of Fusarium graminearum

Cytochrome P450s (CYPs), heme-containing monooxygenases, play important roles in a wide variety of metabolic processes important for development as well as biotic/trophic interactions in most living organisms. Functions of some CYP enzymes are similar across organisms, but some are organism-specific; they are involved in the biosynthesis of structural components, signaling networks, secondary metabolisms, and xenobiotic/drug detoxification. Fungi possess more diverse CYP families than plants, animals, or bacteria. Various fungal CYPs are involved in not only ergosterol synthesis and virulence but also in the production of a wide array of secondary metabolites, which exert toxic effects on humans and other animals. Although few studies have investigated the functions of fungal CYPs, a recent systematic functional analysis of CYP genes in the plant pathogen Fusarium graminearum identified several novel CYPs specifically involved in virulence, asexual and sexual development, and degradation of xenobiotics. This review provides fundamental information on fungal CYPs and a new platform for further metabolomic and biochemical studies of CYPs in toxigenic fungi.

Genomic Understanding of an Infectious Brain Disease from the Desert

Rhinocladiella mackenziei accounts for the majority of fungal brain infections in the Middle East, and is restricted to the arid climate zone between Saudi Arabia and Pakistan. Neurotropic dissemination caused by this fungus has been reported in immunocompromised, but also immunocompetent individuals. If untreated, the infection is fatal. Outside of humans, the environmental niche of R. mackenziei is unknown, and the fungus has been only cultured from brain biopsies. In this paper, we describe the whole-genome resequencing of two R. mackenziei strains from patients in Saudi Arabia and Qatar. We assessed intraspecies variation and genetic signatures to uncover the genomic basis of the pathogenesis, and potential niche adaptations. We found that the duplicated genes (paralogs) are more susceptible to accumulating significant mutations. Comparative genomics with other filamentous ascomycetes revealed a diverse arsenal of genes likely engaged in pathogenicity, such as the degradation of aromatic compounds and iron acquisition. In addition, intracellular accumulation of trehalose and choline suggests possible adaptations to the conditions of an arid climate region. Specifically, protein family contractions were found, including short-chain dehydrogenase/reductase SDR, the cytochrome P450 (CYP) (E-class), and the G-protein β WD-40 repeat. Gene composition and metabolic potential indicate extremotolerance and hydrocarbon assimilation, suggesting a possible environmental habitat of oil-polluted desert soil.

Effects of glucose concentration on 1,18-cis-octadec-9-enedioic acid biotransformation efficiency and lipid body formation in Candida tropicalis

The unsaturated long-chain α,ω-dicarboxylic acid 1,18-cis-octadec-9-enedioic acid (cis-ODA) is a versatile precursor of various valuable compounds, such as polymers, and can be obtained from renewable resources. This makes cis-ODA highly attractive for the chemical industry where there is a growing interest in sustainable processes. However, chemical synthesis of the cis isomers is currently not feasible. In contrast, biotechnological production allows for highly specific and selective reactions. Therefore, we developed an efficient production strategy for cis-ODA using Candida tropicalis as a whole-cell biocatalyst for the biotransformation of oleic acid, which naturally occurs in various fats and oils. Applying a bench-top system comprising eight parallel bioreactors, the production process was characterised and optimised for high productivity. Glucose feed rate was identified as the most crucial process parameter influencing product yield, with high rates inducing oleic acid incorporation into triacylglycerols and storage in lipid bodies. Conversely, application of medium-chain length fatty acid as a substrate did not show any occurrence of lipid bodies. Applying the lowest possible molar ratio of glucose to oleic acid (1.5) resulted in marginal lipid body formation, but led to a peak volumetric productivity of 0.56 g/L/h and a final titre of approximately 45 g/L with a corresponding yield of 70%.

Biotechnological production of bio-based long-chain dicarboxylic acids with oleogenious yeasts

Long-chain α,ω-dicarboxylic acids (DCAs) are versatile chemical intermediates of industrial importance used as building blocks for the production of polymers, lubricants, or adhesives. The majority of industrial long-chain DCAs is produced from petro-chemical resources. An alternative is their biotechnological production from renewable materials like plant oil fatty acids by microbial fermentation using oleogenious yeasts. Oleogenious yeasts are natural long-chain DCA producers, which have to be genetically engineered for high-yield DCA production. Although, some commercialized fermentation processes using engineered yeasts are reported, bio-based long-chain DCAs are still far from being a mass product. Further progress in bioprocess engineering and rational strain design is necessary to advance their further commercialization. The present article reviews the basic strategies, as well as novel approaches in the strain design of oleogenious yeasts, such as the combination of traditional metabolic engineering with system biology strategies for high-yield long-chain DCA production. Therefore a detailed overview of the involved metabolic processes for the biochemical long-chain DCA synthesis is given.

Functional roles and substrate specificities of twelve cytochromes P450 belonging to CYP52 family in n-alkane assimilating yeast Yarrowia lipolytica

Yarrowia lipolytica possesses twelve ALK genes, which encode cytochromes P450 in the CYP52 family. In this study, using a Y. lipolytica strain from which all twelve ALK genes had been deleted, strains individually expressing each of the ALK genes were constructed and their roles and substrate specificities were determined by observing their growth on n-alkanes and analyzing fatty acid metabolism. The results suggested that the twelve Alk proteins can be categorized into four groups based on their substrate specificity: Alk1p, Alk2p, Alk9p, and Alk10p, which have significant activities to hydroxylate n-alkanes; Alk4p, Alk5p, and Alk7p, which have significant activities to hydroxylate the ω-terminal end of dodecanoic acid; Alk3p and Alk6p, which have significant activities to hydroxylate both n-alkanes and dodecanoic acid; and Alk8p, Alk11p, and Alk12p, which showed faint or no activities to oxidize these substrates. The involvement of Alk proteins in the oxidation of fatty alcohols and fatty aldehydes was also analyzed by measuring viability of the mutant deleted for twelve ALK genes in medium containing dodecanol and by observing growth on dodecanal of a mutant strain, in which twelve ALK genes were deleted along with four fatty aldehyde dehydrogenase genes. It was suggested that ALK gene(s) is/are involved in the detoxification of dodecanol and the assimilation of dodecanal. These results imply that genes encoding CYP52-family P450s have undergone multiplication and diversification in Y. lipolytica for assimilation of various hydrophobic compounds.

Production of Long-Chain α,ω-Dicarboxylic Acids by Engineered Escherichia coli from Renewable Fatty Acids and Plant Oils

Long-chain α,ω-dicarboxylic acids (LDCAs, ≥ C12) are widely used as a raw material for preparing various commodities and polymers. In this study, a CYP450-monooxygenase-mediated ω-oxidation pathway system with high ω-regioselectivity was heterologously expressed in Escherichia coli to produce DCAs from fatty acids. The resulting engineered E. coli produced a maximum of 41 mg/L of C12 DCA and 163 mg/L of C14 DCA from fatty acids (1 g/L), following 20 h of whole cell biotransformation. Addition of a heme precursor and the hydroxyl radical scavenger, thiourea, increased product concentration (159 mg/L of C12 DCA and 410 mg/L of C14 DCA) in a shorter culture duration than that of the corresponding controls. DCAs of various chain lengths were synthesized from coconut oil hydrolysate using the engineered E. coli. This novel synthetic biocatalytic system could be applied to produce high value DCAs in a cost-effective manner from renewable plant oils.

Fatty aldehyde dehydrogenase multigene family involved in the assimilation of n-alkanes in Yarrowia lipolytica

In the n-alkane assimilating yeast Yarrowia lipolytica, n-alkanes are oxidized to fatty acids via fatty alcohols and fatty aldehydes, after which they are utilized as carbon sources. Here, we show that four genes (HFD1-HFD4) encoding fatty aldehyde dehydrogenases (FALDHs) are involved in the metabolism of n-alkanes in Y. lipolytica. A mutant, in which all of four HFD genes are deleted (Δhfd1-4 strain), could not grow on n-alkanes of 12-18 carbons; however, the expression of one of those HFD genes restored its growth on n-alkanes. Production of Hfd2Ap or Hfd2Bp, translation products of transcript variants generated from HFD2 by the absence or presence of splicing, also supported the growth of the Δhfd1-4 strain on n-alkanes. The FALDH activity in the extract of the wild-type strain was increased when cells were incubated in the presence of n-decane, whereas this elevation in FALDH activity by n-decane was not observed in Δhfd1-4 strain extract. Substantial FALDH activities were detected in the extracts of Escherichia coli cells expressing the HFD genes. Fluorescent microscopic observation suggests that Hfd3p and Hfd2Bp are localized predominantly in the peroxisome, whereas Hfd1p and Hfd2Ap are localized in both the endoplasmic reticulum and the peroxisome. These results suggest that the HFD multigene family is responsible for the oxidation of fatty aldehydes to fatty acids in the metabolism of n-alkanes, and raise the possibility that Hfd proteins have diversified by gene multiplication and RNA splicing to efficiently assimilate or detoxify fatty aldehydes in Y. lipolytica.

Expression and characterization of CYP52 genes involved in the biosynthesis of sophorolipid and alkane metabolism from Starmerella bombicola

Three cytochrome P450 monooxygenase CYP52 gene family members were isolated from the sophorolipid-producing yeast Starmerella bombicola (former Candida bombicola), namely, CYP52E3, CYP52M1, and CYP52N1, and their open reading frames were cloned into the pYES2 vector for expression in Saccharomyces cerevisiae. The functions of the recombinant proteins were analyzed with a variety of alkane and fatty acid substrates using microsome proteins or a whole-cell system. CYP52M1 was found to oxidize C16 to C20 fatty acids preferentially. It converted oleic acid (C18:1) more efficiently than stearic acid (C18:0) and linoleic acid (C18:2) and much more effectively than α-linolenic acid (C18:3). No products were detected when C10 to C12 fatty acids were used as the substrates. Moreover, CYP52M1 hydroxylated fatty acids at their ω- and ω-1 positions. CYP52N1 oxidized C14 to C20 saturated and unsaturated fatty acids and preferentially oxidized palmitic acid, oleic acid, and linoleic acid. It only catalyzed ω-hydroxylation of fatty acids. Minor ω-hydroxylation activity against myristic acid, palmitic acid, palmitoleic acid, and oleic acid was shown for CYP52E3. Furthermore, the three P450s were coassayed with glucosyltransferase UGTA1. UGTA1 glycosylated all hydroxyl fatty acids generated by CYP52E3, CYP52M1, and CYP52N1. The transformation efficiency of fatty acids into glucolipids by CYP52M1/UGTA1 was much higher than those by CYP52N1/UGTA1 and CYP52E3/UGTA1. Taken together, CYP52M1 is demonstrated to be involved in the biosynthesis of sophorolipid, whereas CYP52E3 and CYP52N1 might be involved in alkane metabolism in S. bombicola but downstream of the initial oxidation steps.

Construction and characterization of a Yarrowia lipolytica mutant lacking genes encoding cytochromes P450 subfamily 52

The initial hydroxylation of n-alkane is catalyzed by cytochrome P450ALK of the CYP52 family in the n-alkane-assimilating yeast Yarrowia lipolytica. A mutant with a deletion of all 12 genes, ALK1 to ALK12, which are deduced to encode cytochromes P450 of the CYP52 family in Y. lipolytica, was successfully constructed. This deletion mutant, Δalk1-12, completely lost the ability to grow on n-alkanes of 10-16 carbons. In contrast, Δalk1-12 grew on the metabolite of n-dodecane, i.e., n-dodecanol, n-dodecanal, or n-dodecanoic acid, as well as the wild-type strain. In addition, production of n-dodecanoic acid was not observed when Δalk1-12 was incubated in the presence of n-dodecane. These results indicate the essential roles of P450ALKs in the oxidation of n-alkane. Δalk1-12 will be valuable as a host strain to express an individual ALK gene to elucidate the molecular function and substrate specificity of each P450ALK. Transcriptional activation of the ALK1 promoter by n-alkanes was observed in Δalk1-12 as in the wild-type strain, implying that n-alkanes per se, but not their metabolites, trigger n-alkane-induced transcriptional activation in Y. lipolytica.

Molecular characterization and expression analysis of a suite of cytochrome P450 enzymes implicated in insect hydrocarbon degradation in the entomopathogenic fungus Beauveria bassiana

The insect epicuticle or waxy layer comprises a heterogeneous mixture of lipids that include abundant levels of long-chain alkanes, alkenes, wax esters and fatty acids. This structure represents the first barrier against microbial attack and for broad-host-range insect pathogens, such as Beauveria bassiana, it is the initial interface mediating the host–pathogen interaction, since these organisms do not require any specialized mode of entry and infect target hosts via the cuticle. B. bassiana is able to grow on straight chain alkanes up to n-C33 as a sole source of carbon and energy. The cDNA and genomic sequences, including putative regulatory elements, for eight cytochrome P450 enzymes, postulated to be involved in alkane and insect epicuticle degradation, were isolated and characterized. Expression studies using a range of alkanes as well as an insect-derived epicuticular extract from the blood-sucking bug Triatomas infestans revealed a differential expression pattern for the P450 genes examined, and suggest that B. bassiana contains a series of hydrocarbon-assimilating enzymes with overlapping specificity in order to target the surface lipids of insect hosts. Phylogenetic analysis of the translated ORFs of the sequences revealed that the enzyme which displayed the highest levels of induction on both alkanes and the insect epicuticular extract represents the founding member of a new cytochrome P450 family, with three of the other sequences assigned as the first members of new P450 subfamilies. The remaining four proteins clustered with known P450 families whose members include alkane monooxygenases.

Cytochrome P450 enzymes in the fungal kingdom

Cytochrome P450 monooxygenases of fungi are involved in many essential cellular processes and play diverse roles. The enzymes catalyze the conversion of hydrophobic intermediates of primary and secondary metabolic pathways, detoxify natural and environmental pollutants and allow fungi to grow under different conditions. Fungal genome sequencing projects have enabled the annotation of several thousand novel cytochromes P450, many of which constitute new families. This review presents the characteristics of fungal cytochrome P450 systems and updates information on the functions of characterized fungal P450 monooxygenases as well as outlines the currently used strategies for determining the function of the many putative P450 enzymes.

Yas3p, an Opi1 family transcription factor, regulates cytochrome P450 expression in response to n-alkanes in Yarrowia lipolytica

In the alkane-assimilating yeast Yarrowia lipolytica, the expression of ALK1, a gene encoding cytochrome P450 that catalyzes the first step of n-alkane oxidation, is induced by n-alkanes. We previously demonstrated that two basic helix-loop-helix proteins, Yas1p and Yas2p, activate the transcription of ALK1 in an alkane-dependent manner by forming a heterocomplex and binding to alkane-responsive element 1 (ARE1), a cis-acting element in the ALK1 promoter. Here we identified an Opi1 family transcription factor, Yas3p, involved in the alkane-dependent transcription regulation of ALK genes. Deletion of YAS3 caused a significant increase in ALK1 mRNA in cells grown on glucose, glycerol, and n-alkanes. The YAS3 deletion also resulted in a marked elevation of reporter gene expression driven by an ARE1-containing promoter on glycerol and n-decane. Bacterially expressed Yas3p bound specifically to Yas2p, but not to Yas1p, in vitro. In addition, although green fluorescent protein-tagged Yas3p was localized in the nucleus in glucose-containing medium, it changed its localization to an endoplasmic reticulum-like compartment upon transfer to medium containing n-decane. These findings suggest that Yas3p functions as a master regulator of transcriptional response, which changes its localization between the nucleus and endoplasmic reticulum membrane in response to different carbon sources. Furthermore, quantitative real time PCR analysis of 12 ALK genes in YAS1, YAS2, and YAS3 deletion mutants suggested that Yas3p is involved in the transcriptional repression of a variety of ALK genes, including ALK1. In contrast, YAS3 deletion did not affect the mRNA level of an INO1 ortholog in Y. lipolytica, indicating functional diversity of Opi1 family transcription factors.

Basic helix-loop-helix transcription factor heterocomplex of Yas1p and Yas2p regulates cytochrome P450 expression in response to alkanes in the yeast Yarrowia lipolytica

The expression of the ALK1 gene, which encodes cytochrome P450, catalyzing the first step of alkane oxidation in the alkane-assimilating yeast Yarrowia lipolytica, is highly regulated and can be induced by alkanes. Previously, we identified a cis-acting element (alkane-responsive element 1 [ARE1]) in the ALK1 promoter. We showed that a basic helix-loop-helix (bHLH) protein, Yas1p, binds to ARE1 in vivo and mediates alkane-dependent transcription induction. Yas1p, however, does not bind to ARE1 by itself in vitro, suggesting that Yas1p requires another bHLH protein partner for its DNA binding, as many bHLH transcription factors function by forming heterodimers. To identify such a binding partner of Yas1p, here we screened open reading frames encoding proteins with the bHLH motif from the Y. lipolytica genome database and identified the YAS2 gene. The deletion of the YAS2 gene abolished the alkane-responsive induction of ALK1 transcription and the growth of the yeast on alkanes. We revealed that Yas2p has transactivation activity. Furthermore, Yas1p and Yas2p formed a protein complex that was required for the binding of these proteins to ARE1. These findings allow us to postulate a model in which bHLH transcription factors Yas1p and Yas2p form a heterocomplex and mediate the transcription induction in response to alkanes.

n-Alkane and clofibrate, a peroxisome proliferator, activate transcription of ALK2 gene encoding cytochrome P450alk2 through distinct cis-acting promoter elements in Candida maltosa

The ALK2 gene, encoding one of the n-alkane-hydroxylating cytochromes P450 in Candida maltosa, is induced by n-alkanes and a peroxisome proliferator, clofibrate. Deletion analysis of this gene's promoter revealed two cis-acting elements-an n-alkane-responsive element (ARE2) and a clofibrate-responsive element (CRE2)-that partly overlap in sequence but have distinct functions. ARE2-mediated activation responded to n-alkanes but not to clofibrate and was repressed by glucose. CRE2-mediated activation responded to polyunsaturated fatty acids and steroid hormones as well as to peroxisome proliferators but not to n-alkanes, and it was not repressed by glucose. Both elements mediated activation by oleic acid. Mutational analysis demonstrated that three CCG sequences in CRE2 were critical to the activation by clofibrate as well as to the in vitro binding of a specific protein to this element. These findings suggest that ALK2 is induced by peroxisome proliferators and steroid hormones through a specific CRE2-mediated regulatory mechanism.

Cloning and heterologous expression of the NADPH cytochrome P450 oxidoreductase genes from an industrial dicarboxylic acid-producingCandida tropicalis

NADPH cytochrome P450 oxidoreductase (CPR) catalyses the transfer of electrons during P450-mediated oxidation, which plays an important role in the omega-oxidation pathway of Candida tropicalis. Two putative allelic genes, CPR-a and CPR-b, were cloned from the long chain dicarboxylic acid-producing Candida tropicalis 1230, using cassette PCR methods. Both the identified open reading frames predict the gene products of 679 amino acid residues. The deduced amino acid sequences of CPR-a and CPR-b are highly homologous to CPR genes from C. tropicalis ATCC 750 and Candida maltosa. Both genes were individually expressed in a cpr mutant of Saccharomyces cerevisiae with high CPR activities, in which only a small distinction was observed between recombinant CPR-a and CPR-b. Both CPR-a and CPR-b contain one CTG codon, which codes for serine (amino acid 50) in C. tropicalis rather than universal leucine. A mutated cDNA of CPR-a with a TCG codon instead of CTG codon was constructed and expressed, resulting in little increase in CPR activity. This indicates that the alteration of Ser-50 has little effect on functional expression of CPR. Furthermore, high ketoconazole sensitivity for the cpr mutant was complemented by heterologous expression of the cloned CPR-a or CPR-b.

A Basic Helix-Loop-Helix Transcription Factor Essential for Cytochrome P450 Induction in Response to Alkanes in Yeast Yarrowia lipolytica

When the alkane-assimilating yeast Yarrowia lipolytica is cultivated on n-alkanes, it changes cellular metabolism for adaptation by inducing cytochrome p450 and other genes. From a comparative analysis of promoters of alkane-inducible genes, we identified a cis-acting element, ARE1 (alkane responsive element 1), which provides transcription induction in response to n-alkanes. In a genetic selection for mutants that were defective in ARE1-mediated transcription induction in the presence of n-alkanes, we found that the YAS1 (yeast alkane signaling) gene is essential for alkane response. The YAS1 gene encodes a basic helix-loop-helix (bHLH) family protein. Loss of Yas1p causes defects in n-alkane-dependent transcription induction of the p450 gene and growth on n-alkanes. Yas1p localizes to nuclei and binds to promoters containing ARE1. Yas1p also binds to its own promoter, and the expression of YAS1 is induced by n-alkanes. These features suggest that Yas1p is a novel transcription factor mediating alkane signaling and that it provides an autoregulatory loop.

Identification and characterization of the CYP52 family of Candida tropicalis ATCC 20336, important for the conversion of fatty acids and alkanes to alpha,omega-dicarboxylic acids

Candida tropicalis ATCC 20336 excretes alpha,omega-dicarboxylic acids as a by-product when cultured on n-alkanes or fatty acids as the carbon source. Previously, a beta-oxidation-blocked derivative of ATCC 20336 was constructed which showed a dramatic increase in the production of dicarboxylic acids. This paper describes the next steps in strain improvement, which were directed toward the isolation and characterization of genes encoding the omega-hydroxylase enzymes catalyzing the first step in the omega-oxidation pathway. Cytochrome P450 monooxygenase (CYP) and the accompanying NADPH cytochrome P450 reductase (NCP) constitute the hydroxylase complex responsible for the first and rate-limiting step of omega-oxidation of n-alkanes and fatty acids. 10 members of the alkane-inducible P450 gene family (CYP52) of C. tropicalis ATCC20336 as well as the accompanying NCP were cloned and sequenced. The 10 CYP genes represent four unique genes with their putative alleles and two unique genes for which no allelic variant was identified. Of the 10 genes, CYP52A13 and CYP52A14 showed the highest levels of mRNA induction, as determined by quantitative competitive reverse transcription-PCR during fermentation with pure oleic fatty acid (27-fold increase), pure octadecane (32-fold increase), and a mixed fatty acid feed, Emersol 267 (54-fold increase). The allelic pair CYP52A17 and CYP52A18 was also induced under all three conditions but to a lesser extent. Moderate induction of CYP52A12 was observed. These results identify the CYP52 and NCP genes as being involved in alpha,omega-dicarboxylic acid production by C. tropicalis and provide the foundation for biocatalyst improvement.

Multidrug Resistance in Yeast Candida

The opportunistic human pathogens Candida albicans and other non-albicans species have acquired considerable significance in the recent past due to the enhanced susceptibility of immunocompromised patients. These pathogenic species of Candida derive their importance not only from the severity of their infections but also from their ability to develop resistance against antifungals. Widespread and prolonged use of azoles has led to the rapid development of the phenomenon of multidrug resistance (MDR), which poses a major hurdle in antifungal therapy. Various mechanisms that contribute to the development of MDR have been implicated in Candida as well as in other human fungal pathogens, and some of these include overexpression of or mutations in the target enzyme of azoles, lanosterol 14 alpha-demethylase, and transcriptional activation of genes encoding drug efflux pump proteins belonging to ATP-binding cassette (ABC) as well as to major facilitator superfamilies (MFS) of transporters. The ABC transporters, CDR1, CDR2, and an MFS pump CaMDR1, play a key role in azole resistance as deduced from their high level of expression found in several azole-resistant clinical isolates.

Development of a plant viral-vector-based gene expression assay for the screening of yeast cytochrome p450 monooxygenases

Development of a gene discovery tool for heterologously expressed cytochrome P450 monooxygenases has been inherently difficult. The activity assays are labor-intensive and not amenable to parallel screening. Additionally, biochemical confirmation requires coexpression of a homologous P450 reductase or complementary heterologous activity. Plant virus gene expression systems have been utilized for a diverse group of organisms. In this study we describe a method using an RNA vector expression system to phenotypically screen for cytochrome P450-dependent fatty acid omega-hydroxylase activity. Yarrowia lipolytica CYP52 gene family members involved in n-alkane assimilation were amplified from genomic DNA, cloned into a plant virus gene expression vector, and used as a model system for determining heterologous expression. Plants infected with virus vectors expressing the yeast CYP52 genes (YlALK1-YlALK7) showed a distinct necrotic lesion phenotype on inoculated plant leaves. No phenotype was detected on negative control constructs. YlALK3-, YlALK5-, and YlALK7-inoculated plants all catalyzed the terminal hydroxylation of lauric acid as confirmed using thin-layer and gas chromatography/mass spectrometry methods. The plant-based cytochrome P450 phenotypic screen was tested on an n-alkane-induced Yarrowia lipolytica plant virus expression library. A subset of 1,025 random library clones, including YlALK1-YlALK7 constructs, were tested on plants. All YlALK gene constructs scored positive in the randomized screen. Following nucleotide sequencing of the clones that scored positive using a phenotypic screen, approximately 5% were deemed appropriate for further biochemical analysis. This report illustrates the utility of a plant-based system for expression of heterologous cytochrome P450 monooxygenases and for the assignment of gene function.

Drug resistance in yeasts--an emerging scenario

In view of the increasing threat posed by fungal infections in immunocompromised patients and due to the non-availability of effective treatments, it has become imperative to find novel antifungals and vigorously search for new drug targets. Fungal pathogens acquire resistance to drugs (antifungals), a well-established phenomenon termed multidrug resistance (MDR), which hampers effective treatment strategies. The MDR phenomenon is spread throughout the evolutionary scale. Accordingly, a host of responsible genes have been identified in the genetically tractable budding yeast Saccharomyces cerevisiae, as well as in a pathogenic yeast Candida albicans. Studies so far suggest that, while antifungal resistance is the culmination of multiple factors, there may be a unifying mechanism of drug resistance in these pathogens. ABC (ATP binding cassette) and MFS (major facilitator superfamily) drug transporters belonging to two different superfamilies, are the most prominent contributors to MDR in yeasts. Considering the abundance of the drug transporters and their wider specificity, it is believed that these drug transporters may not exclusively export drugs in fungi. It has become apparent that the drug transporters of the ABC superfamily of S. cerevisiae and C. albicans are multifunctional proteins, which mediate important physiological functions. This review summarizes current research on the molecular mechanisms underlying drug resistance, the emerging regulatory circuits of MDR genes, and the physiological relevance of drug transporters.

Peroxisome deficiency represses the expression of n-alkane-inducible YlALK1 encoding cytochrome P450ALK1 in Yarrowia lipolytica

Among the eight genes (YlALK1-YlALK8) encoding P450 cytochromes of the CYP52 family of the n-alkane-assimilating yeast Yarrowia lipolytica, Y1ALK1 is most highly induced by n-alkanes with short hydrocarbon chains, such as n-decane, and involved in the initial hydroxylation of n-alkane. To determine the factors regulating YlALK1 expression, we isolated an n-decane assimilation-deficient mutant, B0-6-1, whose YlALK1 expression level was lower than that of the wild-type. By complementation of the mutation of B0-6-1, we cloned a gene having an open reading frame of 1062 bp. The putative gene product is a protein of 354 amino acids and has significant homology to Pex10ps of other organisms. We named this gene YlPEX10. YlPex10p has a C(3)HC(4) ring finger motif common among Pex10ps in its C-terminal region. This motif was also essential for the function of YlPex10p. Both B0-6-1 and a null mutant of YlPEX10 failed to form peroxisome and showed low-level transcription of YlALK1 after the change of carbon source to n-decane. Furthermore, YlPEX5 and YlPEX6 disruptants also showed low-level transcription of YlALK1 like the YlPEX10 disruptant and B0-6-1 mutant. We propose that in this organism peroxisome deficiency represses the expression of n-alkane-inducible YlALK1 encoding cytochrome P450ALK1.

YlALK1 encoding the cytochrome P450ALK1 in Yarrowia lipolytica is transcriptionally induced by n-alkane through two distinct cis-elements on its promoter

The YlALK1 gene, which encodes cytochrome P450ALK1, plays a primary role in the assimilation of n-decane by yeast Yarrowia lipolytica and is inducible by n-decane at the transcriptional level. Deletion analysis of the YlALK1 promoter revealed that a 95-bp region on the YlALK1 promoter (from the position -400 to -304 upstream of the ATG codon) is essential for the induction by n-decane and we named this region ARR1 (alkane-responsive region). ARR1 was found to be made up of two different elements, ARE1 (alkane-responsive element 1; from -394 to -371) and ARE2 (from -325 to -305). By electrophoretic mobility shift assay, we found that the respective elements gave specific shift bands with the extracts from Y. lipolytica cells grown on n-alkane, but not much evidently from the cells grown on glycerol or glucose. This suggests that proteins that specifically bind to these elements are present and their binding or synthesis is dependent on n-alkane.

CaALK8, an alkane assimilating cytochrome P450, confers multidrug resistance when expressed in a hypersensitive strain of Candida albicans

We report the isolation of a novel C. albicans gene designated CaALK8, by its ability to complement drug hypersensitivity of a pdr5 (ABC: ATP-binding cassette drug extrusion pump) null mutant of S. cerevisiae (JG436). CaALK8 in JG436 conferred resistance to drugs such as cycloheximide (CYH), fluconazole (FCZ), O-phenanthroline (PHE) and 4-nitroquinoline oxide (NQO). The gene was so designated because its sequence was identical to a partial sequence entry named as ALK8 in the Candida database (http://alces.med.umn.edu/candida.html). CaALK8 encodes for a putative 515 amino acid protein highly homologous to alkane-inducible cytochromes P450 (CYP52 gene family) of C. maltosa and C. tropicalis. The ability of CaALK8 to confer drug resistance was also established by its expression in another drug-hypersensitive strain of S. cerevisiae (AD 1234568), which was deleted in seven ABC efflux pumps. The homozygous disruption of CaALK8 in a wild-type C. albicans strain (CAI4) did not result in altered drug susceptibilities. The overexpression of CaALK8 in CAI4 resulted in only FCZ resistance. However, a distinct MDR phenotype was evident when CaALK8 was overexpressed in a drug-hypersensitive C. albicans strain disrupted in both CDR1 and CDR2 (ABC drug extrusion pumps of C. albicans). Alk8p, similar to other Alk proteins from C. maltosa and C. tropicalis, could hydroxylate alkanes and fatty acids. In this study we demonstrate that several drugs could compete with the hydroxylation activity by directly interacting with CaAlk8p. Taken together, our results suggest that a member of the CYP52 gene family could mediate MDR in C. albicans, although it does not seem to be involved in the development of azole resistance in clinical isolates. The nucleotide sequence reported in this paper has been submitted to GenBank under Accession No. Y14766.

The cytochrome P450ALK multigene family of an n-alkane-assimilating yeast, Yarrowia lipolytica: cloning and characterization of genes coding for new CYP52 family members

Genes encoding cytochromes P450 of the CYP52 family in the n-alkane-assimilating yeast Yarrowia lipolytica have been cloned and analyzed. Degenerate PCR primers which were designed for the conserved amino acid sequences of cytochromes P450ALK of Candida species were used for amplification and isolation of genes encoding P450ALK from a genomic DNA library of Y. lipolytica CX161-1B. Seven new genes (YlALK2-YlALK8) were isolated. Five of the seven YlALK genes were induced by n-alkane under the culture conditions used in this study, whereas their expression was strictly repressed by glycerol but not by glucose, similar to the case of YlALK1, reported previously. Disruption of YlALK2, YlALK3, YlALK4 or YlALK6 did not change the growth of Y. lipolytica on medium containing n-alkanes of various chain lengths. A mutant with disruptions in both YlALK1 and YlALK2 did not grow well on n-hexadecane, whereas one with disruptions in both YlALK1 and YlALK3, which has the same phenotype as the YlALK1 singly disrupted mutant, grew well on n-hexadecane. These results suggest that the presence of multiple P450ALK species is a rather common phenomenon among the n-alkane-assimilating yeasts and that in the n-alkane assimilation of Y. lipolytica, YlALK1 functions to assimilate n-decane and longer molecules, whereas YlALK2 is involved in the assimilation of molecules longer than n-dodecane; other YlALKs are not significantly involved in the assimilation of C10-C16 n-alkanes.

Molecular modelling of lanosterol 14 alpha-demethylase (CYP51) from Saccharomyces cerevisiae via homology with CYP102, a unique bacterial cytochrome P450 isoform: quantitative structure-activity relationships (QSARs) within two related series of antifungal azole derivatives

The construction of a three-dimensional molecular model of the fungal form of cytochrome P450 (CYP51) from Saccharomyces cerevisiae, based on homology with the haemoprotein domain of CYP102 from Bacillus megaterium (a unique bacterial P450 of known crystal structure) is described. It is found that the endogenous substrate, lanosterol, can readily occupy the putative active site of the CYP51 model such that the known mono-oxygenation reaction, leading to C14-demethylation of lanosterol, is the preferred route of metabolism for this particular substrate. Key amino acid contacts within the CYP51 active site appear to orientate lanosterol for oxidative attack at the C14-methyl group, and the position of the substrate relative to the haem moiety is consistent with the phenyl-iron complexation studies reported by Tuck et al. [J. Biol. Chem., 267, 13175-13179 (1992)]. Typical azole inhibitors, such as ketoconazole, are able to fit the putative active site of CYP51 by a combination of haem ligation, hydrogen bonding, pi-pi stacking and hydrophobic interactions within the enzyme's haem environment. The mode of action of azole antifungals, as described by the modelling studies, is supported by quantitative structure-activity relationship (QSAR) analyses on two groups of structurally related fungal inhibitors. Moreover, the results of molecular electrostatic isopotential (EIP) energy calculations are compatible with the proposed mode of binding between azole antifungal agents and the putative active site of CYP51, although membrane interactions may also have a role in the antifungal activity of azole derivatives.

Multiple p450alk (cytochrome P450 alkane hydroxylase) genes from the halotolerant yeast Debaryomyces hansenii

The halotolerant alkane-assimilating yeast Debaryomyces hansenii was examined for P450 alkane hydroxylase genes known to be required for alkane assimilation in Candida. Four distinct P450alk gene segments and an allelic segment were isolated using PCR based on degenerate primers derived from the CYP52 family of alkane-inducible P450 genes. A screen of a genomic library (15-20kb inserts) constructed for this study, using a probe based on the PCR-isolated segments, yielded seven clones. This has led to the isolation and sequence of two full-length genes DH-ALK1 and DH-ALK2. These genes, each with an ORF of 1557 bp (519 aa), contained no apparent introns and showed 64% nucleotide sequence homology (61% based on the deduced amino acid sequences). The deduced proteins had predicted molecular weights of 59,254Da (DH-ALK1) and 59,614Da (DH-ALK2) and have been designated CYP52A12 and CYP52A13 by the P450 Nomenclature Committee. Phylogenetic analysis based on Neighbor Joining Tree showed that DH-ALK1 and DH-ALK2 constitute new genes located on two distinct branches and are most related to the gene CYP52A3 (60% deduced aa homology) and are least related to the gene CYP52C2 (41% deduced aa homology), both of C. maltosa. The isolated genes will provide tools to better understand the diversity of the P450alk family in eukaryotic microorganisms adapted to varied environmental conditions.

Oxygenation cascade in conversion of n-alkanes to alpha,omega-dioic acids catalyzed by cytochrome P450 52A3

Purified recombinant cytochrome P450 52A3 and the corresponding NADPH-cytochrome P450 reductase from the alkane-assimilating yeast Candida maltosa were reconstituted into an active alkane monooxygenase system. Besides the primary product, 1-hexadecanol, the conversion of hexadecane yielded up to five additional metabolites, which were identified by gas chromatography-electron impact mass spectrometry as hexadecanal, hexadecanoic acid, 1, 16-hexadecanediol, 16-hydroxyhexadecanoic acid, and 1, 16-hexadecanedioic acid. As shown by substrate binding studies, the final product 1,16-hexadecanedioic acid acts as a competitive inhibitor of n-alkane binding and may be important for the metabolic regulation of the P450 activity. Kinetic studies of the individual sequential reactions revealed high Vmax values for the conversion of hexadecane, 1-hexadecanol, and hexadecanal (27, 23, and 69 min-1, respectively), whereas the oxidation of hexadecanoic acid, 1, 16-hexadecanediol, and 16-hydroxyhexadecanoic acid occurred at significantly lower rates (9, 9, and 5 min-1, respectively). 1-Hexadecanol was found to be the main branch point between mono- and diterminal oxidation. Taken together with data on the incorporation of 18O2-derived oxygen into the hexadecane oxidation products, the present study demonstrates that a single P450 form is able to efficiently catalyze a cascade of sequential mono- and diterminal monooxygenation reactions from n-alkanes to alpha, omega-dioic acids with high regioselectivity.

Cloning and characterization of an n-alkane-inducible cytochrome P450 gene essential for n-decane assimilation by Yarrowia lipolytica

A gene encoding cytochrome P450 involved in n-alkane utilization was cloned from an n-alkane assimilating yeast, Yarrowia lipolytica CX161-1B. The RT-PCR was performed on the mRNA prepared from the cells grown on n-alkane as a template using degenerated PCR primers designed for the conserved amino acid sequences of the CYP52 family. The RT-PCR amplified fragment was then used as a probe to isolate genes coding for P450 of the CYP52 family from the genomic DNA library of the strain CX161-1B. The nucleotide sequence of one of the positive clones was determined. An open reading frame which had the same nucleotide sequence as the RT-PCR-amplified fragment was identified. It was of 523 amino acid residues, 60.2 kDa in molecular mass, and had 30-45% sequence identity with the other members of the CYP52 family of Candida species so far analysed. The expression of the P450 gene that was named as YlALK1 was induced by n-tetradecane and repressed by glycerol. A YlALK1 gene disruptant did not grow well on n-decane, but grew on longer-chain n-alkanes such as hexadecane as a sole carbon source. Introduction of YlALK1 on a plasmid to the disruptant restored the decane assimilation. These results suggest that the YlALK1 gene product is the major P450A1k to metabolize short-chain n-alkanes such as decane and dodecane in Y. lipolytica.

Relation between evolutionary distance and enzymatic properties among the members of the CYP52A subfamily of Candida maltosa

The CYP52A subfamily of the alkane-assimilating yeast Candida maltosa consists of six structurally related isoforms. Four of them (CYP52A3, 4, 5, and 9) are strongly induced by alkanes and play an important role for the conversion of various alkanes and fatty acids. Taking advantage of a homologous overexpression system, we found in the present study that both of the two other CYP52A forms, CYP52A10 and CYP52A11, represent specialists for the hydroxylation of lauric acid suggesting their preference for short-chain fatty acids. At the same time, they hydroxylated palmitic acid only moderately and failed to convert hexadecane. Based on the now completed knowledge about the principal substrate specificities of all members of the CYP52A subfamily of C. maltosa, it became apparent that evolutionarily more distantly related P450 forms developed either to alkane or to fatty acid hydroxylases, whereas P450 forms which retained the ability to convert both types of substrates were also found to be evolutionarily related to both alkane and fatty acid hydroxylases.

Isozyme function of n-alkane-inducible cytochromes P450 in Candida maltosa revealed by sequential gene disruption

An n-alkane-assimilating yeast Candida maltosa contains multiple n-alkane-inducible forms of cytochromes P450 (P450alk), which can be assumed to catalyze terminal hydroxylation of n-alkanes in the assimilation pathway. Eight structurally related P450alk genes have been identified. In the present study, the function of four major isoforms of P450alk (encoded by ALK1, ALK2, ALK3, and ALK5 genes) was investigated by sequential gene disruption. Auxotrophic markers used for the selection of disrupted strains were regenerated repeatedly through either mitotic recombination between heterozygous alleles of the diploid genome or directed deletion of the marker gene, to allow sequential gene disruptions within a single strain. The strain depleted of all four isoforms could not utilize n-alkanes for growth, providing direct evidence that P450alk is essential for n-alkane assimilation. Growth properties of a series of intermediate disrupted strains, plasmid-based complementation, and enzyme assays after heterologous expression of single isoforms revealed (i) that each of the four individual isoforms is alone sufficient to allow growth on long chain n-alkane; (ii) that the ALK1-encoding isoform is the most versatile and efficient P450alk form, considering both its enzymatic activity and its ability to confer growth on n-alkanes of different chain length; and (iii) that the ALK5-encoding isoform exhibits a rather narrow substrate specificity and thus cannot support the utilization of short chain n-alkanes.

Amino acid substitutions in the cytochrome P-450 lanosterol 14alpha-demethylase (CYP51A1) from azole-resistant Candida albicans clinical isolates contribute to resistance to azole antifungal agents

The cytochrome P-450 lanosterol 14alpha-demethylase (CYP51A1) of yeasts is involved in an important step in the biosynthesis of ergosterol. Since CYP51A1 is the target of azole antifungal agents, this enzyme is potentially prone to alterations leading to resistance to these agents. Among them, a decrease in the affinity of CYP51A1 for these agents is possible. We showed in a group of Candida albicans isolates from AIDS patients that multidrug efflux transporters were playing an important role in the resistance of C. albicans to azole antifungal agents, but without excluding the involvement of other factors (D. Sanglard, K. Kuchler, F. Ischer, J.-L. Pagani, M. Monod, and J. Bille, Antimicrob. Agents Chemother. 39:2378-2386, 1995). We therefore analyzed in closer detail changes in the affinity of CYP51A1 for azole antifungal agents. A strategy consisting of functional expression in Saccharomyces cerevisiae of the C. albicans CYP51A1 genes of sequential clinical isolates from patients was designed. This selection, which was coupled with a test of susceptibility to the azole derivatives fluconazole, ketoconazole, and itraconazole, enabled the detection of mutations in different cloned CYP51A1 genes, whose products are potentially affected in their affinity for azole derivatives. This selection enabled the detection of five different mutations in the cloned CYP51A1 genes which correlated with the occurrence of azole resistance in clinical C. albicans isolates. These mutations were as follows: replacement of the glycine at position 129 with alanine (G129A), Y132H, S405F, G464S, and R467K. While the S405F mutation was found as a single amino acid substitution in a CYP51A1 gene from an azole-resistant yeast, other mutations were found simultaneously in individual CYP51A1 genes, i.e., R467K with G464S, S405F with Y132H, G129A with G464S, and R467K with G464S and Y132H. Site-directed mutagenesis of a wild-type CYP51A1 gene was performed to estimate the effect of each of these mutations on resistance to azole derivatives. Each single mutation, with the exception of G129A, had a measurable effect on the affinity of the target enzyme for specific azole derivatives. We speculate that these specific mutations could combine with the effect of multidrug efflux transporters in the clinical isolates and contribute to different patterns and stepwise increases in resistance to azole derivatives.

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.

Conserved promoter elements in the CYP6B gene family suggest common ancestry for cytochrome P450 monooxygenases mediating furanocoumarin detoxification

Despite the fact that Papilio glaucus and Papilio polyxenes share no single hostplant species, both species feed to varying extents on hostplants that contain furanocoumarins. P. glaucus contains two nearly identical genes, CYP6B4v2 and CYP6B5v1, and P. polyxenes contains two related genes, CYP6B1v3 and CYP6B3v2. Except for CYP6B3v2, the substrate specificity of which has not yet been defined, each of the encoded cytochrome P450 monooxygenases (P450s) metabolizes an array of linear furanocoumarins. All four genes are transcriptionally induced in larvae by exposure to the furanocoumarin xanthotoxin; several are also induced by other furanocoumarins. Comparisons of the organizational structures of these genes indicate that all have the same intron/exon arrangement. Sequences in the promoter regions of the P. glaucus CYP6B4v2/CYP6B5v1 genes and the P. polyxenes CYP6B3v2 gene are similar but not identical to the -146 to -97 region of CYP6B1v3 gene, which contains a xanthotoxin-responsive element (XRE-xan) important for basal and xanthotoxin-inducible transcription of CYP6B1v3. Complements of the xenobiotic-responsive element (XRE-AhR) in the dioxin-inducible human and rat CYP1A1 genes also exist in all four promoters, suggesting that these genes may be regulated by dioxin. Antioxidant-responsive elements (AREs) in mouse and rat glutathione S-transferase genes and the Barbie box element (Bar) in the bacterial CYP102 gene exist in the CYP6B1v3, CYP6B4v2, and CYP6B5v1 promoters. Similarities in the protein sequences, intron positions, and xanthotoxin- and xenobiotic-responsive promoter elements indicate that these insect CYP6B genes are derived from a common ancestral gene. Evolutionary comparisons between these P450 genes are the first available for a group of insect genes transcriptionally regulated by hostplant allelochemicals and provide insights into the process by which insects evolve specialized feeding habits.

Cytochromes P450 of the sophorose lipid-producing yeast Candida apicola: heterogeneity and polymerase chain reaction-mediated cloning of two genes

Candida apicola belongs to a group of yeasts producing high amounts of surface-active extracellular glycolipids consisting of sophorose and long-chain-omega- and (omega-1)-hydroxy fatty acids. The involvement of cytochrome P450 in the synthesis of sophorose lipid by the hydroxylation of long-chain fatty acids was suggested from a simultaneous increase of cellular P450 content. Hydroxylation studies indicated the existence of multiple P450 forms capable of hydroxylating not only long-chain fatty acids, but also n-alkanes. In this report, two different P450 DNA fragments amplified in a polymerase chain reaction with heterologous primers and chromosomal DNA of Candida apicola were used as homologous probes for the isolation of full-length clones from a genomic library. The open reading frames of both genes encode proteins of 519 amino acids with calculated molecular weights of 58,656 and 58,631, respectively, that contain N-terminal membrane anchor sequences and hallmark residues, in common with other eukaryotic P450s. The deduced amino acid sequences of the C. apicola P450 genes are 84.4% identical. They share 34.5 to 44.1% identity with the proteins of the yeast family CYP52 and about 25% identity with fatty acid hydroxylases of higher eukaryotes (family CYP4A) and of Bacillus megaterium (CYP102). Southern hybridization experiments revealed the existence of further P450-related genes in C. apicola. According to the P450 nomenclature system, the cloned genes were named CYP52E1 and CYP52E2, establishing a new subfamily in yeast family CYP52.

Localization of lipase genes on Candida rugosa chromosomes

In the yeast Candida rugosa the lipase isozymes are encoded by a family of genes, five of which have been cloned and sequenced in our laboratory. In this paper we report on the identification and preliminary characterization of two new related sequences, thus extending this multigene family to seven members. The total DNA content of Candida cells was estimated by laser flow-cytometry at about 20 Mb. Eight chromosomes with sizes ranging between 100 kb and 2.1 Mb, as determined by comparison with S. cerevisiae chromosomal bands, were resolved by pulsed-field gel electrophoresis. The lipase-encoding genes were localized on chromosome I, therefore suggesting that they have originated through multiple duplication events of an ancestral gene.

In vivo reconstitution of highly active Candida maltosa cytochrome P450 monooxygenase systems in inducible membranes of Saccharomyces cerevisiae

To establish a system for functional characterization of individual Candida maltosa cytochrome P450 monooxygenases, the NADPH-cytochrome P450 reductase from this yeast species was co-expressed in Saccharomyces cerevisiae with each of the following cytochrome P450 forms; P450Cm1 (CYP52 A3), P450Cm2 (CYP52 A4), and P450AlK2A (CYP52 A5). For this purpose, a multicopy plasmid was constructed that contained two independent expression units controlled by the galactose-inducible GAL10 promoter. As shown by spectral and immunological methods, large amounts of the desired monooxygenase components could be simultaneously produced in the respective S. cerevisiae transformants. It was important, however, to adjust semi-anaerobic cultivation conditions during induction by galactose to minimize a mutual impairment of cytochrome P450 and NADPH-cytochrome P450 reductase formation. Compared to the specific cellular content of the host-own enzyme, a 75- to 100-fold overproduction of the reductase component was obtained resulting in P450/reductase molar ratios of about 1:3 in the microsomal fractions prepared from the co-expression strains. At the same time, the rates of cytochrome P450-dependent lauric acid hydroxylation increased more than 10-fold, showing a proper reconstitution of the C. maltosa monooxygenase systems in S. cerevisiae. Using intact cells, an efficient biotransformation of lauric acid to omega-hydroxylauric acid and dodecanedioic acid was found. S. cerevisiae cells coexpressing cytochrome P450 and NADPH-cytochrome P450 reductase were characterized by a marked proliferation of the endoplasmic reticulum. Immunoelectron microscopy revealed a colocalization of the monooxygenase components produced to these newly formed membrane structures.

CYP52 (cytochrome P450alk) multigene family in Candida maltosa: identification and characterization of eight members

Previously, we characterized three genes and presented evidence for an n-alkane-inducible cytochrome P450 (P450alk) multigene family in an n-alkane-assimilating and diploid-type yeast, Candida maltosa. In the present report, we isolated and characterized additional members of this gene family, including a total of thirteen P450alk-related sequences (eight genes and five of their alleles). Two sets, each consisting of two genes, were tandemly arranged in the genome. A gene replacement experiment showed that at least one gene had only a single allele in the genome. The determined nucleotide and the deduced amino acid sequences indicated that all had a characteristic constituent for P450s and exhibited amino acid identities from 94% to 37% to each other. Six genes showed relatively higher similarities to each other than to the other two genes and were thus classified into a subfamily. All the members of this subfamily were assigned to the same single chromosome, showing a good correlation between sequence similarity and chromosomal linkage. Although all the genes except for one were induced by n-alkane, their inducibilities by some other aliphatic carbon sources showed variabilities.

A deviation from the universal genetic code in Candida maltosa and consequences for heterologous expression of cytochromes P450 52A4 and 52A5 in Saccharomyces cerevisiae

We demonstrate that serine instead of leucine is specified by the CUG codon in the yeast Candida maltosa. Evidence for this deviation from the universal genetic code was obtained by means of in vitro translation experiments. Depending on the cell-free system used, either serine, in the C. maltosa system, or leucine, in the control with the conventional wheat germ system, was found to be incorporated into the translation products of artificial CUG-containing mRNAs. Moreover, we were able to transfer the non-universal decoding of CUG to the wheat germ system by adding a tRNA fraction isolated from C. maltosa. This finding indicates the presence in C. maltosa of an unusual serine tRNA that recognizes CUG. As a consequence of the altered genetic code, expression in Saccharomyces cerevisiae of C. maltosa cytochrome P450 genes required an exchange of their CTG triplets by TCT encoding serine in order to produce the authentic proteins. In contrast, heterologous expression of the original C. maltosa genes resulted in the formation of still active but unstable enzymes probably subject to selective proteolysis in the host cells.