Isolation, characterization, and regulation of the Candida albicans ERG27 gene encoding the sterol 3-keto reductase.

The Candida albicans ERG27 gene which encodes the 3-keto reductase enzyme required for sterol C-4 demethylation was isolated and found to encode a 349 amino acid protein that is 60% identical at the amino acid level to the Saccharomyces cerevisiae Erg27p. A C. albicans erg27 null was created in a strain containing an integrated ERG27 rescue cassette under the control of the pMAL2 inducible promoter. The C. albicans erg27 strain was able to grow only in the presence of maltose indicating that the ERG27 gene is essential. The C. albicans erg27 null showed complete loss of both 3-keto reductase and oxidosqualene cyclase (Erg7p) activities compromising all sterol synthesis. These results suggest that Erg27p inhibitors might be effective antifungals. To explore ERG27 regulation, an erg11 null strain was generated. C. albicans erg6 and erg24 mutants were also employed along with the inhibitors, itraconazole and zaragozic acid A, to characterize ERG27 expression using Northern analysis. Expression was increased two- to fourfold in erg11, erg6 and erg24 backgrounds. However, itraconazole which targets Erg11p (lanosterol demethylase) increased ERG27 expression 10-fold and zaragozic acid A which targets the Erg9p (squalene synthase) increased ERG27 expression fivefold. The azole and erg11 results support other observations that azoles may affect non-sterol targets.