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Candida albicans has four ORFs for glutathione transferases (GSTs) of the GTT
classes, and another one coding for an Omega class member. Under laboratory
conditions, only GTT11 (GTT1/2 class) and GTO1 (Omega class) are expressed
significantly in exponentially growing cells, particularly when these are subjected
to diverse environmental stresses, including oxidative stress. They also become
transitorily upregulated at the early stationary phase. Accordingly, the levels of the
CaGto1 and CaGtt11 proteins increase after treatment with oxidants and upon
osmotic stress, in addition to the early stationary phase. GTT11 and GTO1
transcription shows a complex dependence on the Hog1 and Cap1 factors upon
different stresses. Purified CaGtt11 and CaGto1 proteins display enzyme activities
similar to the Saccharomyces cerevisiae homologues. Thus, CaGtt11 has activity
against standard GST substrates and is also active as peroxidase, while CaGto1
displays thiol oxidoreductase and dehydroascorbate reductase activities. Fluores-
cence microscopy and subfractionation studies indicate that CaGto1 is cytosolic,
while CaGtt11 is associated with a particulate fraction. Under ex vivo conditions, CaGto1 and CaGtt11 become transitorily upregulated inside macrophages and
neutrophils. Under these conditions, the promoter of GTT14 (GTT1/2 class) also
becomes activated. These observations point to the importance of C. albicans
GSTs in the defence against phagocytes. |
