Candida albicans estrogen-binding protein gene encodes an oxidoreductase that is inhibited by estradiol.

Department of Medicine, Stanford University School of Medicine, CA 94305.

Candida albicans, the most common fungal pathogen of humans, possesses an estrogen-binding protein (EBP) that binds mammalian estrogens with high affinity. We report here the cloning and complete nucleotide sequence of a gene encoding a C. albicans EBP. Amino acid sequences obtained from cyanogen bromide fragments of purified EBP were used to design oligonucleotide primers for PCR. An 800-bp product was amplified and used to screen a C. albicans genomic library. A clone was isolated containing an insert with an open reading frame of 1221 nt capable of encoding a protein with 407 amino acids and having a calculated molecular mass of 46,073 Da, the estimated size of EBP. The cloned gene, expressed in Escherichia coli as a lacZ fusion protein, demonstrated high-affinity binding for estradiol and a competition profile comparable to C. albicans wild-type EBP. Northern blots of C. albicans RNA revealed a single transcript of approximately 1600 nt, whereas Southern blots identified three hybridizing fragments. Computer searches of data bases showed that EBP shares a 46% amino acid identity with the old yellow enzyme, an oxidoreductase from Saccharomyces cerevisiae, but was unrelated to the human estrogen receptor as previously speculated. In addition, a 51-amino acid region of EBP is highly conserved among a group of flavoproteins including old yellow enzyme. Expressed EBP was shown to exhibit oxidoreductase activity that could be inhibited by 17 beta-estradiol in vitro. In conclusion, the EBP from C. albicans has no evident homology to the mammalian steroid receptor superfamily but appears to be a member of a recently identified family of flavoproteins.

PMID: 8302868 [PubMed - indexed for MEDLINE]

PMCID: PMC521425