title: Squalene epoxidase encoded by ERG1 affects morphogenesis and drug susceptibilities of Candida albicans.
abstract: 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.
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India. rp47@mail.jnu.ac.in
authors.forename: Ritu
authors.initials: R
authors.lastname: Pasrija
authors.forename: Shankarling
authors.initials: S
authors.lastname: Krishnamurthy
authors.forename: Tulika
authors.initials: T
authors.lastname: Prasad
authors.forename: Joachim F
authors.initials: JF
authors.lastname: Ernst
authors.forename: Rajendra
authors.initials: R
authors.lastname: Prasad
mesh_terms: 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
chemical_list: C094693:CDR1 protein, Candida albicans; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D010105:Oxygenases; D050603:Squalene Monooxygenase; D004875:Ergosterol