Characterization of the Saccharomyces cerevisiae ERG26 gene encoding the C-3 sterol dehydrogenase (C-4 decarboxylase) involved in sterol biosynthesis
AUTOR(ES)
Gachotte, D.
FONTE
The National Academy of Sciences
RESUMO
All but two genes involved in the ergosterol biosynthetic pathway in Saccharomyces cerevisiae have been cloned, and their corresponding mutants have been described. The remaining genes encode the C-3 sterol dehydrogenase (C-4 decarboxylase) and the 3-keto sterol reductase and in concert with the C-4 sterol methyloxidase (ERG25) catalyze the sequential removal of the two methyl groups at the sterol C-4 position. The protein sequence of the Nocardia sp NAD(P)-dependent cholesterol dehydrogenase responsible for the conversion of cholesterol to its 3-keto derivative shows 30% similarity to a 329-aa Saccharomyces ORF, YGL001c, suggesting a possible role of YGL001c in sterol decarboxylation. The disruption of the YGL001c ORF was made in a diploid strain, and the segregants were plated onto sterol supplemented media under anaerobic growth conditions. Segregants containing the YGL001c disruption were not viable after transfer to fresh, sterol-supplemented media. However, one segregant was able to grow, and genetic analysis indicated that it contained a hem3 mutation. The YGL001c (ERG26) disruption also was viable in a hem 1Δ strain grown in the presence of ergosterol. Introduction of the erg26 mutation into an erg1 (squalene epoxidase) strain also was viable in ergosterol-supplemented media. We demonstrated that erg26 mutants grown on various sterol and heme-supplemented media accumulate nonesterified carboxylic acid sterols such as 4β,14α-dimethyl-4α-carboxy-cholesta-8,24-dien-3β-ol and 4β-methyl-4α-carboxy-cholesta-8,24-dien-3β-ol, the predicted substrates for the C-3 sterol dehydrogenase. Accumulation of these sterol molecules in a heme-competent erg26 strain results in an accumulation of toxic-oxygenated sterol intermediates that prevent growth, even in the presence of exogenously added sterol.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=24900Documentos Relacionados
- Characterization of the Saccharomyces cerevisiae ERG27 gene encoding the 3-keto reductase involved in C-4 sterol demethylation
- Cloning and characterization of ERG25, the Saccharomyces cerevisiae gene encoding C-4 sterol methyl oxidase.
- Molecular cloning, characterization, and overexpression of ERG7, the Saccharomyces cerevisiae gene encoding lanosterol synthase.
- Regulation of partitioned sterol biosynthesis in Saccharomyces cerevisiae.
- Identification of the Gene Encoding Sulfopyruvate Decarboxylase, an Enzyme Involved in Biosynthesis of Coenzyme M