Isolation and characterization of an altered cytochrome P-450 from a yeast mutant defective in lanosterol 14 alpha-demethylation

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.

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.

The 3-hydroxy group of lanosterol is essential for orienting the substrate site of cytochrome P-450(14DM) (lanosterol 14 alpha- demethylase)

Interaction of lanosterol, 3-epilanosterol, 3-oxolanosta-8,24-diene, 3-methylenelanost-8-ene and lanosterol acetate with cytochrome P-450(14DM) were studied. The cytochrome mediated the 14alpha-demethylation of 3-epilanosterol with nearly the same activity as lanosterol but could not mediate the 14alpha-demethylation of the 3-methylene derivative and the 3-acetate. The cytochrome catalyzed the 14alpha-demethylation of the 3-oxo derivative with low rate. Based on these and some additional observations the hydrogen bond formation between the 3-hydroxy group of lanosterol and the specific amino acid residue in the substrate site is assumed to be essential for orienting the substrate in the substrate site of the cytochrome.

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

We report the nucleotide sequence of the gene and flanking DNA for the cytochrome P450 lanosterol 14 alpha-demethylase (14DM) from the yeast Candida tropicalis ATCC750. An open reading frame (ORF) of 528 codons encoding a 60.9-kD protein is identified. This ORF includes a characteristic heme-binding domain, HR2, common to all P450 proteins. This protein and the 14DM from Saccharomyces cerevisiae share 66.5% identical and 23.1% conservatively replaced amino acids in a 516-amino-acid alignment, and thus are orthologous forms of the P450LIA1 gene. Conversely, C. tropicalis 14DM shares relatively little sequence similarity with P450alk, the predominant P450 protein present when this organism is grown on n-alkanes. Sequence information of these three yeast P450s will be useful for structure-function analyses in the future.

A single amino acid substitution converts cytochrome P450(14DM) to an inactive form, cytochrome P450SG1: complete primary structures deduced from cloned DNAS

Genes for lanosterol 14-demethylase, cytochrome P450(14DM), and a mutated inactive cytochrome P450SG1 were cloned from S. cerevisiae strains D587 and SG1, respectively. A single nucleotide change resulting in substitution of Asp for Gly-310 of cytochrome P450(14DM) was found to have occurred in cytochrome P450SG1. In this protein the 6th ligand to heme iron is a histidine residue instead of a water molecule, which may be the ligand for the active cytochrome P450(14DM). Molecular models of the active sites of the cytochrome P450(14DM) and cytochrome P450SG1 were built by computer modeling on the basis of the known structure of that of cytochrome P450CAM whose crystallographic data are available. The mechanisms which may cause a histidine residue to gain access to the heme iron are discussed.

Primary structure of the P450 lanosterol demethylase gene from Saccharomyces cerevisiae

We have sequenced the structural gene and flanking regions for lanosterol 14 alpha-demethylase (14DM) from Saccharomyces cerevisiae. An open reading frame of 530 codons encodes a 60.7-kDa protein. When this gene is disrupted by integrative transformation, the resulting strain requires ergosterol and, as expected, grows only in the absence of oxygen. The deduced amino acid sequence of 14DM includes a hydrophobic segment near the amino terminus which may be a transmembrane domain. The deduced sequence has been compared with those of eight other eukaryotic P450s, each from a different family within the P450 superfamily. These comparisons indicate that this yeast gene is the first member of a new P450 family, P450LI. The P450, designated P450LIA1, is more closely related to mammalian P450s than to the bacterial P450cam. In fact, both the yeast P450 and several mammalian P450s have equivalent alignment scores when each is compared with the bovine P450scc. Matrix comparisons of the amino acid sequence of this P450 with those of mammalian P450s reveal three conserved regions. The DNA region 5' to the structural 14DM gene includes poly(dA:dT) sequences and a repeating hexamer sequence.