Role of glutathione in the oxidative stress response in the fungal pathogen Candida glabrata

Abstract

Candida glabrata, an opportunistic fungal pathogen, accounts for 18-26 % of all Candida systemic infections in the US. C. glabrata has a robust oxidative stress response (OSR) and in this work we characterized the role of glutathione (GSH), an essential tripeptide-like thiol-containing molecule required to keep the redox homeostasis and in the detoxification of metal ions. GSH is synthesized from glutamate, cysteine, and glycine by the sequential action of Gsh1 (γ-glutamyl-cysteine synthetase) and Gsh2 (glutathione synthetase) enzymes. We first screened for suppressor mutations that would allow growth in the absence of GSH1 (gsh1∆ background) and found a single point mutation in PRO2 (pro2-4), a gene that encodes a γ-glutamyl phosphate reductase and catalyzes the second step in the biosynthesis of proline. We demonstrate that GSH is important in the OSR since the gsh1∆ pro2-4 and gsh2∆ mutant strains are more sensitive to oxidative stress generated by H2O2 and menadione. GSH is also required for Cadmium tolerance. In the absence of Gsh1 and Gsh2, cells show decreased viability in stationary phase. Furthermore, C. glabrata does not contain Saccharomyces cerevisiae high affinity GSH transporter ortholog, ScOpt1/Hgt1, however, our genetic and biochemical experiments show that the gsh1∆ pro2-4 and gsh2∆ mutant strains are able to incorporate GSH from the medium. Finally, GSH and thioredoxin, which is a second redox system in the cell, are not essential for the catalase-independent adaptation response to H2O2.

Candida glabrata: A Lot More Than Meets the Eye

“…C. glabrata is highly tolerant to oxidative, cell wall, osmotic and endoplasmic reticulum (ER) stress [79]. The environmental stress response in C. glabrata is governed by two transcriptional regulators CgMsn2 and CgMsn4 [38], while the oxidative stress response is regulated by the sole catalase CgCta1 [80], two superoxide dismutases CgSod1 and CgSod2 [81], and glutathione biosynthetic enzymes CgGsh1 and CgGsh2 [82,83]. CgCTA1 expression is regulated by several stress response transcriptional regulators including CgYap1, CgMsn2, CgMsn4 and CgSkn7 [80,84,85,86].…”

Gln3 is a main regulator of nitrogen assimilation in Candida glabrata

“…We generated fusion PCR products for gene disruption using the URA3 gene to construct the knockout mutant strains as the selection marker, as previously described (Guti errez-Escobedo et al, 2013). All primers used in this study are listed in Table S2.…”

A new regulator in the crossroads of oxidative stress resistance and virulence in Candida glabrata: The transcription factor CgTog1

“…It is striking that a determinant of OSR presents such a regulatory portrait, even during H 2 O 2 stress. These observations appear to be consistent with studies in S. cerevisiae that show respiration disruption is correlated with H 2 O 2 sensitivity [ 36 , 37 ], while reduced cofactors (e.g., NADPH) are especially relevant in oxidative stress conditions, as NADPH is a final electron donor in glutathione and thioredoxin systems [ 38 ]. This data is further corroborated by other C. glabrata studies reporting mitochondrial processes and activity of dehydrogenases as crucial under oxidative stress [ 13 ].…”