Affiliation:
1. Centre for Cytochrome P450 Biodiversity, Institute of Life Science, College of Medicine, Swansea University, Swansea, Wales, United Kingdom
2. Center for Chemical Biology, Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
Abstract
ABSTRACT
A candidate CYP51 gene encoding sterol 14α-demethylase from the fish oomycete pathogen
Saprolegnia parasitica
(SpCYP51) was identified based on conserved CYP51 residues among CYPs in the genome. It was heterologously expressed in
Escherichia coli
, purified, and characterized. Lanosterol, eburicol, and obtusifoliol bound to purified SpCYP51 with similar binding affinities (
K
s
, 3 to 5 μM). Eight pharmaceutical and six agricultural azole antifungal agents bound tightly to SpCYP51, with posaconazole displaying the highest apparent affinity (
K
d
, ≤3 nM) and prothioconazole-desthio the lowest (
K
d
, ∼51 nM). The efficaciousness of azole antifungals as SpCYP51 inhibitors was confirmed by 50% inhibitory concentrations (IC
50
s) of 0.17 to 2.27 μM using CYP51 reconstitution assays. However, most azole antifungal agents were less effective at inhibiting
S. parasitica
,
Saprolegnia diclina
, and
Saprolegnia ferax
growth. Epoxiconazole, fluconazole, itraconazole, and posaconazole failed to inhibit
Saprolegnia
growth (MIC
100
, >256 μg ml
−1
). The remaining azoles inhibited
Saprolegnia
growth only at elevated concentrations (MIC
100
[the lowest antifungal concentration at which growth remained completely inhibited after 72 h at 20°C], 16 to 64 μg ml
−1
) with the exception of clotrimazole, which was as potent as malachite green (MIC
100
, ∼1 μg ml
−1
). Sterol profiles of azole-treated
Saprolegnia
species confirmed that endogenous CYP51 enzymes were being inhibited with the accumulation of lanosterol in the sterol fraction. The effectiveness of clotrimazole against SpCYP51 activity (IC
50
, ∼1 μM) and the concentration inhibiting the growth of
Saprolegnia
species
in vitro
(MIC
100
, ∼1 to 2 μg ml
−1
) suggest that clotrimazole could be used against
Saprolegnia
infections, including as a preventative measure by pretreatment of fish eggs, and for freshwater-farmed fish as well as in leisure activities.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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