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The glutathione system of Aspergillus nidulans involves a fungus-specific glutathione S-transferase.

ABSTRACT: The tripeptide glutathione is involved in cellular defense mechanisms for xenobiotics and reactive oxygen species. This study investigated glutathione-dependent mechanisms in the model organism Aspergillus nidulans. A recombinant dimeric protein of A. nidulans glutathione reductase (GR) contained FAD and reduced oxidized glutathione (GSSG) using NADPH as an electron donor. A deletion strain of the GR gene (glrA) accumulated less intracellular reduced glutathione (GSH), indicating that the fungal GR contributes to GSSG reduction in vivo. Growth of the deletion strain of glrA was temperature-sensitive, and this phenotype was suppressed by adding GSH to the medium. The strain subsequently accumulated more intracellular superoxide, and cell-free respiration activity was partly defective. Growth of the strain decreased in the presence of oxidants, which induced glrA expression 1.5-6-fold. These results indicated that the fungal glutathione system functions as an antioxidant mechanism in A. nidulans. Our findings further revealed an initial proteomic differential display on GR-depleted and wild type strains. Up-regulation of thioredoxin reductase, peroxiredoxins, catalases, and cytochrome c peroxidase in the glrA-deletion strain revealed interplay between the glutathione system and both the thioredoxin system and hydrogen peroxide defense mechanisms. We also identified a hypothetical, up-regulated protein in the GR-depleted strains as glutathione S-transferase, which is unique among Ascomycetes fungi.

SUBMITTER: Sato I

PROVIDER: S-EPMC2658098 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Glutathione (GSH) is an abundant tripeptide that plays a crucial role in shielding cellular macromolecules from various reactive oxygen and nitrogen species in fungi. Understanding GSH metabolism is of vital importance for deciphering redox regulation in these microorganisms. In the present study, to better understand the GSH metabolism in filamentous fungi, we investigated functions of the dugB and dugC genes in the model fungus Aspergillus nidulans These genes are orthologues of dug2 and dug3, which are involved in cytosolic GSH degradation in Saccharomyces cerevisiae The deletion of dugB, dugC, or both resulted in a moderate increase in the GSH content in mycelia grown on glucose, reduced conidium production, and disturbed sexual development. In agreement with these observations, transcriptome data showed that genes encoding mitogen-activated protein (MAP) kinase pathway elements (e.g., steC, sskB, hogA, and mkkA) or regulatory proteins of conidiogenesis and sexual differentiation (e.g., flbA, flbC, flbE, nosA, rosA, nsdC, and nsdD) were downregulated in the ΔdugB ΔdugC mutant. Deletion of dugB and/or dugC slowed the depletion of GSH pools during carbon starvation. It also reduced accumulation of reactive oxygen species and decreased autolytic cell wall degradation and enzyme secretion but increased sterigmatocystin formation. Transcriptome data demonstrated that enzyme secretions-in contrast to mycotoxin production-were controlled at the posttranscriptional level. We suggest that GSH connects starvation and redox regulation to each other: cells utilize GSH as a stored carbon source during starvation. The reduction of GSH content alters the redox state, activating regulatory pathways responsible for carbon starvation stress responses.IMPORTANCE Glutathione (GSH) is a widely distributed tripeptide in both eukaryotes and prokaryotes. Owing to its very low redox potential, antioxidative character, and high intracellular concentration, GSH profoundly shapes the redox status of cells. Our observations suggest that GSH metabolism and/or the redox status of cells plays a determinative role in several important aspects of fungal life, including oxidative stress defense, protein secretion, and secondary metabolite production (including mycotoxin formation), as well as sexual and asexual differentiations. We demonstrated that even a slightly elevated GSH level can substantially disturb the homeostasis of fungi. This information could be important for development of new GSH-producing strains or for any biotechnologically relevant processes where the GSH content, antioxidant capacity, or oxidative stress tolerance of a fungal strain is manipulated.

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The glutathione system of Aspergillus nidulans involves a fungus-specific glutathione S-transferase.

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