Abstract:
In yeast, the cytoplasmic thioredoxin system is composed of NADPH, thioredoxin reductase-1 (TRR1) and 2 thioredoxin
genes (TRX1, TRX2). In this study, using yeast knockout mutants for TRR1, TRX1 and TRX2 genes, the role of the thioredoxin
system in methionine sulfoxide reduction was investigated. Cells lacking both TRX1 and TRX2 genes simultaneously were not able
to reduce methionine sulfoxides to methionine; however, mutants missing the TRR1 gene were able to reduce methionine sulfoxides
to methionine, which showed that electrons could be transferred from NADPH to thioredoxins in the absence of TRR1. Similar
results were observed for 3-phosphoadenosine 5-phosphosulfate reduction in the inorganic sulfate assimilation pathway. Results
from both assays suggested that yeast cells have additional cytoplasmic thioredoxin reductase activity that could compensate for
methionine sulfoxide reduction and sulfate assimilation in the absence of TRR1. This report also constitutes the first evidence that
thioredoxins are the in vivo electron donors for methionine sulfoxide reductases in yeast.
