Primary structure of the cytochrome P450 lanosterol 14 alpha-demethylase gene from Candida tropicalis

Identification of two different 14-alpha sterol demethylase-related genes (cyp51A and cyp51B) in Aspergillus fumigatus and other Aspergillus species

Two cyp51-related genes (cyp51A and cyp51B) encoding 14-alpha sterol demethylase-like enzymes were identified in the opportunistic human pathogen Aspergillus fumigatus. PCR amplification using degenerate oligonucleotides based on conserved areas of cytochrome P450 demethylases of other filamentous fungi and yeasts allowed the cloning and sequencing of two different homologue genes in A. fumigatus. Southern analysis confirmed that both genes hybridized to distinct genomic loci and that both are represented as single copies in the genome. Comparison of the deduced Cyp51A and Cyp51B proteins with the CYP51 proteins from Penicillium italicum, Aspergillus nidulans, Erysiphe graminis, Uncinula necator, Botrytis cinerea, Ustilago maydis, Cryptococcus neoformans, Candida albicans, Saccharomyces cerevisiae, Candida tropicalis, and Candida glabrata showed that the percentages of identity of the amino acid sequences (range, 40 to 70%) were high enough to consider Cyp51A and Cyp51B to be members of the fungal CYP51 family. Fragments from both genes were also cloned from other Aspergillus spp. (A. flavus, A. nidulans, and A. terreus). Phylogenetic analysis showed that, at least in the most pathogenic species of Aspergillus, there are two fungal CYP51 proteins. This is the first report of the existence of two homologue genes coding for 14-alpha sterol demethylase in the fungal kingdom. This finding could provide insights into the azole resistance mechanisms operating in fungi. The primers used here may be useful molecular tools for facilitating the cloning of novel 14-alpha sterol demethylase genes in other filamentous fungi.

Characterization of the mouse lanosterol 14alpha-demethylase (CYP51), a new member of the evolutionarily most conserved cytochrome P450 family

Genes encoding sterol 14alpha-demethylases in eukaryotes and in Mycobacterium belong to the CYP51 family which is evolutionary the most conserved gene family within the cytochrome P450 superfamily. We have characterized a new member of this family, the mouse lanosterol 14alpha-demethylase, with the aim to study the in vivo role of this gene in spermatogenesis in mammals. The amino acid sequence of mouse Cyp51 is 96% identical to rat and 91% to human. Comparison of all known CYP51 proteins by the neighbor-joining method suggests that fungal and animal CYP51 genes arose from a common ancestral gene (98.3% probability) and interestingly, that plant and bacterial CYP51 genes share a common progenitor (88.8% probability). This suggests that the first CYP51 gene may have arisen in eukaryotes and has been transferred horizontally from plants to Mycobacterium. The mouse CYP51 gene is approximately 17-kb long and contains 10 exons. Transcription starts at several locations within the CpG island, which is characteristic for the TATA-less housekeeping genes. The mouse 5'-untranslated region (800 bp) contains putative cAMP-responsive elements (CRE), sterol regulatory elements (SRE) and GC-boxes at positions similar to human and rat, suggesting an evolutionary conserved mechanism of CYP51 transcriptional regulation in mammals. The mouse Cyp51 gene resides on chromosome 5, region A2, close to the centromere. No signals outside this region were detected as well as no evidence of processed pseudogenes using long PCR was found. This indicates that the mouse genome most likely lacks CYP51 processed pseudogenes.

Multiple amino acid substitutions in lanosterol 14alpha-demethylase contribute to azole resistance in Candida albicans

Lanosterol 14alpha-demethylase (14DM) is the target of the azole antifungals, and alteration of the 14DM sequence leading to a decreased affinity of the enzyme for azoles is one of several potential mechanisms for resistance to these drugs in Candida albicans. In order to identify such alterations the authors investigated a collection of 19 C. albicans clinical isolates demonstrating either frank resistance (MICs > or = 32 microg ml(-1)) or dose-dependent resistance (MICs 8-16 microg ml(-1)) to fluconazole. In cell-free extracts from four isolates, including the Darlington strain ATCC 64124, sensitivity of sterol biosynthesis to inhibition by fluconazole was greatly reduced, suggesting that alterations in the activity or affinity of the 14DM could contribute to resistance. Cloning and sequencing of the 14DM gene from these isolates revealed 12 different alterations (two to four per isolate) leading to changes in the deduced amino acid sequence. Five of these mutations have not previously been reported. To demonstrate that these alterations could affect fungal susceptibility to azoles, the 14DM genes from one sensitive and three resistant C. albicans strains were tagged at the carboxyl terminus with a c-myc epitope and expressed in Saccharomyces cerevisiae under control of the endogenous promoter. Transformants receiving 14DM genes from resistant strains had fluconazole MICs up to 32-fold higher than those of transformants receiving 14DM from a sensitive strain, although Western blot analysis indicated that the level of expressed 14DM was similar in all transformants. Amino acid substitutions in the 14DM gene from the Darlington strain also conferred a strong cross-resistance to ketoconazole. In conclusion, multiple genetic alterations in C. albicans 14DM, including several not previously reported, can affect the affinity of the enzyme for azoles and contribute to resistance of clinical isolates.

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.

Optimized expression and catalytic properties of a wheat obtusifoliol 14alpha-demethylase (CYP51) expressed in yeast. Complementation of erg11Delta yeast mutants by plant CYP51

CYP51s form the only family of P450 proteins conserved in evolution from prokaryotes to fungi, plants and mammals. In all eukaryotes, CYP51s catalyse 14alpha-demethylation of sterols. We have recently isolated two CYP51 cDNAs from sorghum [Bak, S., Kahn, R.A., Olsen, C. E. & Halkier, B.A. (1997) Plant J. 11, 191-201] and wheat [Cabello-Hurtado, F., Zimmerlin, A., Rahier, A., Taton, M., DeRose, R., Nedelkina, S., Batard, Y., Durst, F., Pallett, K.E. & Werck-Reichhart, D. (1997) Biophys. Biochem. Res. Commun. 230, 381-385]. Wheat and sorghum CYP51 proteins show a high identity (92%) compared with their identity with their fungal and mammalian orthologues (32-39%). Data obtained with plant microsomes have previously suggested that differences in primary sequences reflect differences in sterol pathways and CYP51 substrate specificities between animals, fungi and plants. To investigate more thoroughly the properties of the plant CYP51, the wheat enzyme was expressed in yeast strains overexpressing different P450 reductases as a fusion with either yeast or plant (sorghum) membrane targeting sequences. The endogenous sterol demethylase gene (ERG11) was then disrupted. A sorghum-wheat fusion protein expressed with the Arabidopsis thaliana reductase ATR1 showed the highest level of expression and activity. The expression induced a marked proliferation of microsomal membranes so as to obtain 70 nmol P450.(L culture)-1, with CYP51 representing 1.5% of microsomal protein. Without disruption of the ERG11 gene, the expression level was fivefold reduced. CYP51 from wheat complemented the ERG11 disruption, as the modified yeasts did not need supplementation with exogenous ergosterol and grew normally under aerobic conditions. The fusion plant enzyme catalysed 14alpha-demethylation of obtusifoliol very actively (Km,app = 197 microm, kcat = 1.2 min-1) and with very strict substrate specificity. No metabolism of lanosterol and eburicol, the substrates of the fungal and mammalian CYP51s, nor metabolism of herbicides and fatty acids was detected in the recombinant yeast microsomes. Surprisingly lanosterol (Ks = 2.2 microM) and eburicol (Ks = 2.5 microm) were found to bind the active site of the plant enzyme with affinities higher than that for obtusifoliol (Ks = 289 microM), giving typical type-I spectra. The amplitudes of these spectra, however, suggested that lanosterol and eburicol were less favourably positioned to be metabolized than obtusifoliol. The recombinant enzyme was also used to test the relative binding constants of two azole compounds, LAB170250F and gamma-ketotriazole, which were previously reported to be potent inhibitors of the plant enzyme. The Ks of plant CYP51 for LAB170250F (0.29 microM) and gamma-ketotriazole (0.40 microM) calculated from the type-II sp2 nitrogen-binding spectra were in better agreement with their reported effects as plant CYP51 inhibitors than values previously determined with plant microsomes. This optimized expression system thus provides an excellent tool for detailed enzymological and mechanistic studies, and for improving the selectivity of inhibitory molecules.

Purification and characterization of cytosolic cytochrome P450 forms from yeasts belonging to the genus Trichosporon

The yeast Trichosporon spec. SBUG 752 isolated from soil produced cytochrome P450 during the stationary phase of growth on glucose. After cell disruption and ultracentrifugation, large amounts of P450 (250 pmol/mg protein) were found in the cytosolic fraction. In contrast, no P450 was detectable in the microsomes. Similar results were also obtained from some other yeast species of the genus Trichosporon. After purification to electrophoretic homogeneity, the P450 from Trichosporon spec. SBUG 752 migrated in SDS-PAGE with an apparent Mr of 43,000. Final purification by isoelectric focusing yielded two different isoenzymes in their spectrally active state-P450TS1 and P450TS2-having pI values of 5.9 and 6.2, respectively. Partial N-terminal amino acid sequencing revealed a high degree of sequence homology between P450TS1 and P450TS2 and their close relationship to the soluble P450 forms of the CYP55 family which are known to act as nitric oxide reductases in some filamentous fungi. The P450TS1 from Trichosporon spec. SBUG 752 catalyzed nitric oxide reduction under anaerobic conditions in an NADH- and NADPH-dependent manner-an activity not yet described for yeasts. These results demonstrate the existence of soluble P450 forms in yeasts exhibiting functional and structural characteristics similar to those of the P450 forms of the CYP55 family.

Cloning and sequence analysis of the eburicol 14alpha-demethylase gene of the obligate biotrophic grape powdery mildew fungus

In order to obtain molecular data concerning field resistance of Uncinula necator, the causal agent of grape powdery mildew, to sterol demethylation inhibitors, a major group of fungicides, the gene encoding the target of these compounds (eburicol 14alpha-demethylase) was cloned and sequenced from this obligately biotrophic phytopathogenic fungus. This single-copy gene encodes a 524 amino acid protein which displays high similarity to other known sterol 14alpha-demethylases (CYP51s). The coding sequence is interrupted by two short introns at positions identical to introns in Penicillium italicum CYP51, which is the only other known CYP51 gene in which introns have been identified. Intron excision was verified by cDNA sequencing.

A mutation in the 14 alpha-demethylase gene of Uncinula necator that correlates with resistance to a sterol biosynthesis inhibitor

We investigated the molecular basis of resistance of the obligate biotrophic grape powdery mildew fungus Uncinula necator to sterol demethylation-inhibiting fungicides (DMIs). The sensitivity of 91 single-spore field isolates of U. necator to triadimenol was assessed by using a leaf disc assay. Resistance factors (RF) ranged from 1.8 to 26.0. The gene encoding the target of DMIs (eburicol 14 alpha-demethylase) from five sensitive and seven resistant isolates was cloned and sequenced. A single mutation, leading to the substitution of a phenylalanine residue for a tyrosine residue at position 136, was found in all isolates exhibiting an RF higher than 5. No mutation was found in sensitive or weakly resistant (RF, < 5) isolates. An allele-specific PCR assay was developed to detect the mutation. Among the 91 isolates tested, only isolates with RF higher than 5 carried the mutation. Three of the 19 resistant isolates and all sensitive and weakly resistant isolates did not possess the mutation. The mutation at codon 136 is thus clearly associated with high levels of resistance to triadimenol.

Molecular mechanisms of azole resistance in fungi

This paper reviews the current status of our understanding of azole antifungal resistance mechanisms at the molecular level and explores their implications. Extensive biochemical studies have highlighted a significant diversity in mechanisms conferring resistance to azoles, which include alterations in sterol biosynthesis, target site, uptake and efflux. In stark contrast, few examples document the molecular basis of azole resistance. Those that do refer almost exclusively to mechanisms in laboratory mutants, with the exception of the role of multi-drug resistance proteins in clinical isolates of Candida albicans. It is clear that the technologies required to examine and define azole resistance mechanisms at the molecular level exist, but research appears distinctly lacking in this most important area.

Identification of various medically important Candida species in clinical specimens by PCR-restriction enzyme analysis

A single primer pair amplifying a cytochrome P-450 lanosterol-14 alpha-demethylase (L1A1) gene fragment that encodes a highly conserved region was used to detect yeast DNA in clinical specimens. Positive PCR products were obtained from genomic DNAs of Candida albicans, C. parapsilosis, C. tropicalis, C. guilliermondii, C. krusei, C. (Torulopsis) glabrata, and C. kefyr. No human, bacterial, or parasitic DNA was amplified. The sensitivity was evaluated for C. albicans genomic DNA by using various DNA concentrations (200 pg to 2 fg). The amplified DNAs of Candida species with unknown P-450 L1A1 gene sequences were subcloned and sequenced. Identification at the species level was achieved by digestion of the PCR products with different restriction enzymes. A specific restriction enzyme analysis pattern was determined for each species investigated. Subsequently, we used PCR to detect specific yeast DNA directly with clinical specimens such as blood and bronchoalveolar lavage specimens. After appropriate treatment, the specimens were processed by PCR and the results were compared with those obtained by traditional diagnostic procedures such as cultures and serology. Although preliminary, the PCR results seem to correlate well, at least for blood, with those of antigen detection assays and traditional blood cultures, with a better and earlier detection of candidemia.

Cloning and functional expression in yeast of a cDNA coding for an obtusifoliol 14alpha-demethylase (CYP51) in wheat

Screening of a wheat cDNA library with an heterologous CYP81B1 probe from Helianthus tuberosus led to the isolation of a partial cDNA coding a protein with all the characteristics of a typical P450 with high homology (32-39% identity) to the fungal and mammalian CYP51s. Extensive screening of several wheat cDNA libraries isolated a longer cDNA (W516) coding a peptide of 453 amino acids. Alignment of W516 with other P450 sequences revealed that it was missing a segment corresponding to the N-terminal membrane anchor of the protein. The corresponding segment from the yeast lanosterol 14alpha-demethylase was linked to the partial wheat cDNA and the chimera expressed in Saccharomyces cerevisiae. Compared to microsomes from control yeasts, membranes of yeast expressing the chimera catalysed 14alpha-demethylation of obtusifoliol with an increased efficiency relative to lanosterol demethylase activity. W516 is thus a plant member of the most ancient and conserved P450 family, CYP51.

Isolation and reconstitution of the heme-thiolate protein obtusifoliol 14alpha-demethylase from Sorghum bicolor (L.) Moench

The heme-thiolate (cytochrome P450) enzyme which catalyzes the 14alpha-demethylation of obtusifoliol has been isolated from microsomes prepared from etiolated seedlings of Sorghum bicolor (L.) Moench. The obtusifoliol 14alpha-demethylase is a key enzyme in plant sterol biosynthesis and a target for the design of phyla-specific sterol 14alpha-demethylase inhibitors. Microsomal cytochrome P450s were solubilized by using the detergents Renex 690 and reduced Triton X-100, and the obtusifoliol 14alpha-demethylase was isolated by DEAE ion exchange and dye affinity column chromatography. The isolated enzyme has an absorption spectrum characteristic for low spin cytochrome P450s and produces a Type I binding spectrum with obtusifoliol as substrate. Binding spectra were not obtained with lanosterol, campesterol, sitosterol, or stigmasterol. Obtusifoliol 14alpha-demethylase has an apparent molecular mass of 53 kDa and is estimated to constitute approximately 20% of the total cytochrome P450 content of the microsomal membranes and about 0.2% of the total microsomal protein. Gas chromatography-mass spectrometry analysis of reconstitution experiments with dilauroylphosphatidylcholine micelles containing isolated obtusifoliol 14alpha-demethylase and sorghum NADPHcytochrome P450 oxidoreductase demonstrated the conversion of obtusifoliol (4alpha,14alpha-dimethyl-5alpha-ergosta-8, 24(28)-dien-3beta-ol) to 4alpha-methyl-5alpha-ergosta-8,14, 24(28)-trien3beta-ol, the 14alpha-demethylated product of obtusifoliol with a double bond introduced at the Delta14 position. The N-terminal amino acid sequence of the protein is MDLADIPQ/KQQRLMAGXALVV. Five internal sequences were obtained after endoproteinase Lys-C and Glu-C digestion. The fragment AAGAFSYISFGGGRH aligns with the unique heme binding domain of mammalian and yeast sterol 14alpha-demethylases which belong to the CYP51 family. Therefore it is conceivable that the obtusifoliol 14alpha-demethylase from plants also belongs to the CYP51 family, the only P450 family so far known to be conserved across the phyla.

Mechanisms of fungicide resistance in phytopathogenic fungi

The disciplines traditionally used to investigate the mode of action of fungicides have been biochemistry and physiology. Over the past decade, classical and molecular genetics have been brought to bear on this problem with increasing success. Recently, genetic studies of fungicide resistance have led to advances in our understanding of the site of action of chemicals active against plant pathogens and, in some cases, to an appreciation of additional mechanisms of resistance to fungicide action.

Isolation of an Ustilago maydis ERG11 gene and its expression in a mutant deficient in sterol 14 alpha-demethylase activity

A gene (ERG11) encoding cytochrome P450 sterol 14 alpha-demethylase (P450(14DM)) was isolated from the maize pathogen, Ustilago maydis, by amplifying part of the coding region of the gene using PCR and by employing the amplified DNA fragment as a hybridization probe to recover the complete gene from an U. maydis lambda EMBL3 genomic library. The deduced amino acid sequence of the U. maydis gene showed homology to P450(14DM)s from other organisms and contained specific motifs which were hallmarks of P450s. Expression of the gene in an U. maydis mutant (A20) deficient in P450(14DM) led to only a partial restoration of P450(14DM) activity. Accumulation of ergosta-7,22-dienol and ergost-7-enol in A20 transformants containing the ERG11 gene implied that an additional mutation affecting sterol delta 5,6-desaturase activity accompanied the P450(14DM) lesion.

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.

Cloning and functional expression of the cDNA encoding rat lanosterol 14-alpha demethylase

Lanosterol 14 alpha-demethylase (LDM) is a cytochrome P-450 enzyme in the biosynthetic pathway of cholesterol. As such, it represents a target for cholesterol-lowering drugs. Rat LDM (rLDM) has been purified from the livers of rats treated with cholestyramine. The purified protein was used to generate tryptic fragments which were then sequenced. The amino acid (aa) sequences were used to design oligodeoxyribonucleotide primers and a DNA fragment was generated by RT-PCR to probe a phagemid library. A clone encoding rLDM was isolated from the livers of cholestyramine-treated rats. The clone contains an open reading frame encoding a polypeptide of 486 aa and a predicted molecular mass of 55 045 Da. The deduced aa sequence shows a high degree of identity to the yeast LDM sequences, as well as sequences which match typical P-450 sequence motifs. When produced in a baculovirus/insect cell culture system, LDM activity was detected and inhibited by the specific inhibitor azalanstat with an IC50 value of less than 2 nM. The isolation of this full-length coding sequence should facilitate research into understanding the direct and indirect effects of LDM in the regulation of cholesterol biosynthesis and the search for cholesterol-lowering drugs.

Modeling cytochrome P450 14 alpha demethylase (Candida albicans) from P450cam

The tertiary structure of cytochrome P450 14 alpha demethylase--Candida albicans (P450 CA) is modeled on the basis of sequence alignment with two closely related proteins and the crystallographic structure of Pseudomonas putida P450cam. The secondary structure prediction system used combines the information from several algorithms and trains the data to offer an optimized prediction of the known P450cam. The trained algorithm was then used to predict the secondary structure of the other P450 sequences. The prediction of the surface coil regions was aided by an alignment between P450 CA and the homologous sequences P450 14 alpha demethylase--Saccharomyces cerevisiae (66 SD) and P450 14 alpha demethylase--Candida tropicalis (72 SD). The prediction and alignment information was combined to establish an alignment between P450 CA and P450cam, and to assign full secondary structure to the target protein. This secondary structure was folded from the template of P450cam and the predicted structure was relaxed by molecular dynamics. Model checking highlighted minor adjustments in the alignment, correctly orienting hydrophobic and hydrophilic side chains. The model offers explanations for several known experimental results and suggests further investigations that may prove fruitful in understanding the structure and mechanisms of the P450 family (Porter, T.D. and Coon, M.J. Minireview cytochrome P450. J. Biol. Chem. 1991, 266, 13469-13472. Waterman, M.R. Cytochrome P450 cellular distribution and structural considerations. Current Opinion in Structural Biology 1992, 2, 384-387. Aoyama, Y., Yoshida, Y., Sonohdo, Y. and Sato, Y. Structural analysis of the interaction between the side-chain of substrates and the active site of lanosterol 14 alpha demethylase (P450 14DM) of yeast. Biochim. Biophys. Acta 1992, 1122, 251-255.).

Rapid detection and identification of Candida albicans and Torulopsis (Candida) glabrata in clinical specimens by species-specific nested PCR amplification of a cytochrome P-450 lanosterol-alpha-demethylase (L1A1) gene fragment

PCR of a Candida albicans cytochrome P-450 lanosterol-alpha-demethylase (P450-L1A1) gene segment is a rapid and sensitive method of detection in clinical specimens. This enzyme is a target for azole antifungal action. In order to directly detect and identify the clinically most important species of Candida, we cloned and sequenced 1.3-kbp fragments of the cytochrome P450-L1A1 genes from Torulopsis (Candida) glabrata and from Candida krusei. These segments were compared with the published sequences from C. albicans and Candida tropicalis. Amplimers for gene sequences highly conserved throughout the fungal kingdom were first used; positive PCR results were obtained for C. albicans, T. glabrata, C. krusei, Candida parapsilosis, C. tropicalis, Cryptococcus neoformans, and Trichosporon beigelii DNA extracts. Primers were then selected for a highly variable region of the gene, allowing the species-specific detection from purified DNA of C. albicans, T. glabrata, C. krusei, and C. tropicalis. The assay sensitivity as tested for C. albicans in seeded clinical specimens such as blood, peritoneal fluid, or urine was 10 to 20 cells per 0.1 ml. Compared with results obtained by culture, the sensitivity, specificity, and efficiency of the species-specific nested PCR tested with 80 clinical specimens were 71, 95, and 83% for C. albicans and 100, 97, and 98% for T. glabrata, respectively.

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature

We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.

Cytochrome P450 lanosterol 14α-demethylase (CYP51): insights from molecular genetic analysis of the ERG11 gene in Saccharomyces cerevisiae

Eukaryotes characteristically express a cytochrome P450-catalyzed sterol 14α-methyl demethylase as an essential step in the production of membrane sterols. Lanosterol 14α-demethylase of Saccharomyces cerevisiae is the best characterized representative of these enzymes among fungi and provides a model system for the molecular genetic analysis of the reaction. The gene for this P450 and the gene for the S. cerevisiae NADPH-cytochrome P450 reductase have been examined by mutational inactivation and for their regulation of expression. Our results have contributed to a better understanding of sterol biosynthesis in relation to mechanisms of resistance to fungicidal demethylase inhibitors, and promote the rationale for using S. cerevisiae in the further characterization of structure function relationships among sterol 14α-demethylases.

Plant sterol biosynthesis: novel potent and selective inhibitors of cytochrome P450-dependent obtusifoliol 14 alpha-methyl demethylase

The R-(-) isomer of methyl 1-(2,2-dimethylindan-1-yl)imidazole-5-carboxylate (CGA 214372; 2) strongly inhibited P450-dependent obtusifoliol 14 alpha-demethylase (P450OBT.14DM) (I50 = 8 x 10(-9) M, I50/Km = 5 x 10(-5) in a maize (Zea mays) microsomal preparation. Kinetic studies indicated uncompetitive inhibition with respect to obtusifoliol. The corresponding S-(+) isomer was a 20-fold weaker inhibitor for P450OBT.14DM. The molecular features of a variety of analogues of 2 were related to their potency as inhibitors of P450OBT.14DM in vitro, allowing delineation of the key structural requirements governing inhibition of the demethylase. CGA 214372 proved to have a high degree of selectivity for P450OBT.14DM. This allowed easy distinction of this activity from other P450-dependent activities present in the maize microsomal preparation and gave strong evidence that P450OBT.14DM is a herbicidal target. Microsomal maize P450OBT.14DM and yeast P450LAN.14DM, the only known examples of P450-dependent enzymes carrying out an identical metabolic function in different eukaryotes, showed distinct inhibition patterns with CGA 214372 and ketoconazole, a substituted imidazole anti-mycotic.

Non-sterol structural probes of the lanosterol 14 alpha-demethylase from Saccharomyces cerevisiae

A number of non-sterol iron-liganding molecules were used to probe the active site of the lanosterol 14 alpha-demethylase from Saccharomyces cerevisiae. Simple bi- and tricyclic aromatic amines were found to exhibit Type II binding spectra with the demethylase. Stereochemical and positional effects appear to play critical roles in the binding of these compounds to the demethylase. These compounds have been used to generate additional active-site structural information on this enzyme, currently a target for the development of new antifungal agents.

Comparative study on cytochrome P-450 of yeasts using specific antibodies to cytochromes P-450alk and P-450(14DM)

The occurrence of cytochrome P-450(14DM) (lanosterol 14 alpha-demethylase) and cytochrome P-450alk (long-chain alkane terminal hydroxylase) in various yeast strains was determined with immunological procedures. Cytochrome P-450(14DM), which is constitutive or housekeeping enzyme playing an essential role in ergosterol biogenesis, was found in all yeast strains so far tested. Cytochromes P-450(14DM) from different species of yeast were immunologically different, although they may have had a few common antigenic sites. In contrast, cytochrome P-450alk was detected only in the alkane-assimilating yeasts.

Biochemical approaches to selective antifungal activity. Focus on azole antifungals

Azole antifungals (e.g. the imidazoles: miconazole, clotrimazole, bifonazole, imazalil, ketoconazole, and the triazoles: diniconazole, triadimenol, propiconazole, fluconazole and itraconazole) inhibit in fungal cells the 14 alpha-demethylation of lanosterol or 24-methylenedihydrolanosterol. The consequent inhibition of ergosterol synthesis originates from binding of the unsubstituted nitrogen (N-3 or N-4) of their imidazole or triazole moiety to the heme iron and from binding of their N-1 substituent to the apoprotein of a cytochrome P-450 (P-450(14)DM) of the endoplasmic reticulum. Great differences in both potency and selectivity are found between the different azole antifungals. For example, after 16h of growth of Candida albicans in medium supplemented with [14C]-acetate and increasing concentrations of itraconazole, 100% inhibition of ergosterol synthesis is achieved at 3 x 10(-8) M. Complete inhibition of this synthesis by fluconazole is obtained at 10(-5) M only. The agrochemical imidazole derivative, imazalil, shows high selectivity, it has almost 80 and 98 times more affinity for the Candida P-450(s) than for those of the piglet testes microsomes and bovine adrenal mitochondria, respectively. However, the topically active imidazole antifungal, bifonazole, has the highest affinity for P-450(s) of the testicular microsomes. The triazole antifungal itraconazole inhibits at 10(-5) M the P-450-dependent aromatase by 17.9, whereas 50% inhibition of this enzyme is obtained at about 7.5 x 10(-6)M of the bistriazole derivative fluconazole. The overall results show that both the affinity for the fungal P-450(14)DM and the selectivity are determined by the nitrogen heterocycle and the hydrophobic N-1 substituent of the azole antifungals. The latter has certainly a greater impact. The presence of a triazole and a long hypdrophobic nonligating portion form the basis for itraconazole's potency and selectivity.

Disruption of the Saccharomyces cerevisiae gene for NADPH-cytochrome P450 reductase causes increased sensitivity to ketoconazole

Strains of Saccharomyces cerevisiae deleted in the NADPH-cytochrome P450 reductase gene by transplacement are 200-fold more sensitive to ketoconazole, an inhibitor of the cytochrome P450 lanosterol 14 alpha-demethylase. Resistance is restored through complementation by the plasmid-borne wild type gene from either S. cerevisiae or Candida tropicalis. Neither Southern hybridization nor Western immunoblot techniques provided evidence for a second NADPH-cytochrome P450 reductase gene, suggesting that an alternate pathway may provide for the functions of this reductase in S. cerevisiae.

The P450 superfamily: updated listing of all genes and recommended nomenclature for the chromosomal loci

In this update we provide a list of the 71 P450 genes and the four P450 pseudogenes that have been characterized as of September 30, 1988. The chromosomal locations of many of these genes are also summarized. A modest revision of the initially proposed nomenclature of the P450 superfamily (Nebert et al., DNA 6, 1-11, 1987) is described specifically for the human and mouse chromosomal loci. The motivation for this revision is to conform to the rules of nomenclature for human and mouse genes. Recommendations for the naming of chromosomal loci include the root symbol "CYP" for human ("Cyp" for mouse), denoting "cytochrome P450." We recommend that this root also be used for other organisms. For a chromosomal locus, the root symbol is followed by an Arabic numeral designating the P450 family, a letter indicating the subfamily, and an Arabic numeral representing the individual gene within the family or subfamily. Numbers of the individual genes usually will be assigned in the order the genes are identified. This system is consistent with our earlier proposed nomenclature for P450 families and gene products from all eukaryotes and prokaryotes.