Squalene epoxidase encoded by ERG1 affects morphogenesis and drug susceptibilities of Candida albicans.
OBJECTIVE
Functional characterization of the erg1 mutant of ergosterol biosynthesis of Candida albicans.


METHODS
We disrupted the ERG1 gene of C. albicans, which encodes squalene epoxidase (EC 1.14.99.7). Since the disruption of both alleles of ERG1 was lethal, the second allele of a heterozygous disruptant was placed under the control of a regulable promoter, MET3p, which is repressed by methionine and cysteine.


RESULTS
The reverse-phase HPLC analysis of sterol, extracted from the conditional mutant strain, showed a total lack of ergosterol and instead accumulation of squalene. This imbalance in sterol composition led to defects in growth and increased susceptibilities to drugs including fluconazole, ketoconazole, cycloheximide, nystatin, amphotericin B and terbinafine. Reduced drug efflux activity of the erg1 mutant was associated with poor surface localization of Cdr1p, suggesting that enhanced passive diffusion and reduced efflux mediated by the ABC (ATP binding cassette) transporter Cdr1p increases drug susceptibility. Additionally, conditional erg1 mutant strains were unable to form hyphae in various media.


CONCLUSIONS
Taken together, our results demonstrate that the absence of ergosterol, which is one of the constituents of membrane microdomains (rafts), has a direct effect on drug susceptibility and morphogenesis of C. albicans.
Pasrija
Ritu
R
School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India. rp47@mail.jnu.ac.in
Krishnamurthy
Shankarling
S
Prasad
Tulika
T
Ernst
Joachim F
JF
Prasad
Rajendra
R
D002176:Candida albicans / Q000187:drug effects* / Q000254:growth & development*; D004058:Diffusion; D004875:Ergosterol / Q000096:biosynthesis; D005656:Fungal Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D009024:Morphogenesis; D009154:Mutation; D010105:Oxygenases / Q000235:genetics / Q000502:physiology*; D050603:Squalene Monooxygenase
C094693:CDR1 protein, Candida albicans; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D010105:Oxygenases; D050603:Squalene Monooxygenase; D004875:Ergosterol