Thiol-Independent Action of Mitochondrial Thioredoxin To Support the Urea Cycle of Arginine Biosynthesis in Schizosaccharomyces pombe

School of Biological Sciences, Seoul National University, 56-1 Shillim-dong, Kwanak-gu, Seoul 151-742, Korea.
Eukaryotic Cell (Impact Factor: 3.18). 11/2008; 7(12):2160-7. DOI: 10.1128/EC.00106-08
Source: PubMed


Thioredoxins usually perform a role as a thiol-disulfide oxidoreductase using their active-site cysteines. The fission yeast
Schizosaccharomyces pombe contains two thioredoxins: Trx1 for general stress protection and Trx2 for mitochondrial functions. The Δtrx2 mutant grows as well as the wild type on complex media containing glucose. However, on nonfermentable carbon source such
as glycerol, the mutant did not grow, indicating a defect in mitochondrial function. The mutant also exhibited auxotrophy
for arginine and cysteine on minimal medium. In order to find the reason for the unexpected arginine auxotrophy, we searched
for multicopy suppressors and found that the arg3+ gene encoding ornithine carbamoyltransferase (OCTase) in the urea cycle of the arginine biosynthetic pathway rescued the
arginine auxotrophy. The levels of arg3+ transcript, Arg3 protein, and OCTase activity were all decreased in Δtrx2. Through immunocoprecipitation, we observed a direct interaction between Trx2 and Arg3 in cell extracts. The mutant forms
of Trx2 lacking either one or both of the active site cysteines through substitution to serines also rescued the arginine
auxotrophy and restored the decreased OCTase activity. They also rescued the growth defect of Δtrx2 on glycerol medium. This contrasts with the thiol-dependent action of overproduced Trx2 in complementing glutathione reductase.
Therefore, Trx2 serves multiple functions in mitochondria, protecting mitochondrial components against thiol-oxidative damage
as a thiol-disulfide oxidoreductase, and supporting urea cycle and respiration in mitochondria in a manner independent of
active site thiols.

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    • "The free radical scavenger thioredoxin is conserved from prokaryote to eukaryote and plays a role in maintaining the cellular redox environment [15]. There are two thioredoxins, cytosolic thioredoxin Trx1 and mitochondrial thioredoxin Trx2 in S. pombe [16]. We looked at H2O2 sensitivity of Δtrx1 and Δtrx2 cells. "
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    ABSTRACT: Glucose is one of the most important sources of cellular nutrition and glucose deprivation induces various cellular responses. In Schizosaccharomyces pombe, zinc finger protein Rst2 is activated upon glucose deprivation, and regulates gene expression via the STREP (stress response element of Schizosaccharomyces pombe) motif. However, the activation mechanism of Rst2 is not fully understood. We monitored Rst2 transcriptional activity in living cells using a Renilla luciferase reporter system. Hydrogen peroxide (H2O2) enhanced Rst2 transcriptional activity upon glucose deprivation and free radical scavenger inhibited Rst2 transcriptional activity upon glucose deprivation. In addition, deletion of the trx2 (+) gene encoding mitochondrial thioredoxin enhanced Rst2 transcriptional activity. Notably, nitric oxide (NO) generators enhanced Rst2 transcriptional activity upon glucose deprivation as well as under glucose-rich conditions. Furthermore, NO specific scavenger inhibited Rst2 transcriptional activity upon glucose deprivation. Altogether, our data suggest that NO and reactive oxygen species may be involved in the activation of transcription factor Rst2.
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