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

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.

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.

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.

Microbial production and application of sophorolipids

Sophorolipids are surface-active compounds synthesized by a selected number of yeast species. They have been known for over 40 years, but because of growing environmental awareness, they recently regained attention as biosurfactants due to their biodegradability, low ecotoxicity, and production based on renewable resources. In this paper, an overview is given of the producing yeast strains and various aspects of fermentative sophorolipid production. Also, the biochemical pathways and regulatory mechanisms involved in sophorolipid biosynthesis are outlined. To conclude, a summary is given on possible applications of sophorolipids, either as native or modified molecules.

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.

Oxygen transfer rate and sophorose lipid production by Candida bombicola

Sophorose lipids (SLs) have applications as surfactants and are produced at high levels by several yeasts. We developed a fed-batch shake-flask method for the production of SLs by Candida bombicola ATCC 22214. Optimal aeration, expressed in terms of oxygen transfer rate, was between 50 and 80 mM O(2)/L h(-1) and resulted in maximum values for both volumetric product formation (1-1.5 g/L h(-1)) and SL yield (350 g/L). The lowest aeration levels resulted in the enrichment in saturated fatty acid SLs at the expense of unsaturated fatty acid SLs.

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.

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.