Glutathione reductase (Pgr1, EC 1.8.1.7) of Schizosaccharomyces pombe, a class-I pyridine nucleotide-disulfide oxidoreductase that, as an FAD-containing homodimer, uses NADPH to reduce glutathione disulfide (GSSG) to two molecules of reduced glutathione (GSH), maintaining a high GSH:GSSG ratio. Unlike its budding-yeast ortholog GLR1, pgr1 is essential: deletion spores are inviable and depletion causes G1 arrest under aerobic conditions. S. pombe uses a single translation start, and the single protein form is found both in the cytosol and in an organellar (most likely mitochondrial) fraction. Depletion raises the GSSG/GSH ratio, lowers respiration, inactivates oxidation-labile Fe-S enzymes (mitochondrial aconitase, cytosolic sulfite reductase) and causes iron accumulation; overexpression of the mitochondrial thioredoxin Trx2 suppresses lethality, indicating that the essential role is protection of Fe-S enzymes. pgr1 transcription is induced by oxidants and other stresses through the AP-1-like factor Pap1.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004362 glutathione-disulfide reductase (NADPH) activity | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER PTN002448883 IBA (donors include human GSR, S. cerevisiae GLR1 and Pgr1 itself). Pgr1 has all conserved glutathione reductase features and measurable GR activity, so inheritance of the activity is correct. Supporting Evidence: PMID:9287302 The level of transcript as well as the GR enzyme activity increased more than 11-fold when the cloned pgr1(+) gene was expressed on a multicopy plasmid. |
| GO:0004362 glutathione-disulfide reductase (NADPH) activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA from InterPro IPR006322 (glutathione reductase, eukaryote/bacterial), RHEA:11740 and EC 1.8.1.7; this is the correct specific activity for Pgr1. Supporting Evidence: PMID:9287302 The level of transcript as well as the GR enzyme activity increased more than 11-fold when the cloned pgr1(+) gene was expressed on a multicopy plasmid. |
| GO:0004362 glutathione-disulfide reductase (NADPH) activity | IMP PMID:9287302 Isolation, expression, and regulation of the pgr1(+) gene en... | ACCEPT | Summary: Lee et al. cloned pgr1+; multicopy expression raised GR enzyme activity about 11-fold and loss of pgr1 is lethal. Direct S. pombe evidence for GR activity. Supporting Evidence: PMID:9287302 The level of transcript as well as the GR enzyme activity increased more than 11-fold when the cloned pgr1(+) gene was expressed on a multicopy plasmid. PMID:9287302 These results indicate that GR activity, which efficiently reduces GSSG, is essentially required for the growth of S. pombe, unlike in Saccharomyces cerevisiae or Escherichia coli. |
| GO:0005737 cytoplasm | EXP PMID:16950927 Glutathione reductase and a mitochondrial thioredoxin play o... | ACCEPT | Summary: Song et al. fractionated cells expressing chromosomally integrated Pgr1-Myc and found it in the cytosolic fraction (plus an organellar fraction). Cytoplasm is correct, cytosol is more precise and is separately annotated. Supporting Evidence: PMID:16950927 revealed that GR resides not only in the cytosol but also in the organelle fraction |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping (Cytoplasm, from PMID:16950927); correct though less precise than the cytosol IDA. Supporting Evidence: file:SCHPO/pgr1/pgr1-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16950927}. |
| GO:0005739 mitochondrion | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: ORFeome-wide YFP localization (Matsuyama et al.) recorded Pgr1 in mitochondria, independently corroborating the organellar fractionation of Song et al. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein PMID:16950927 GR is distributed in organelles, most likely in mitochondria, as well as in the cytosol |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA for mitochondrion; GR is dual cytosolic/mitochondrial across eukaryotes (GLR1, GSR). Consistent with S. pombe fractionation and the Trx2 suppression data. Supporting Evidence: PMID:16950927 GR is distributed in organelles, most likely in mitochondria, as well as in the cytosol |
| GO:0005739 mitochondrion | IDA PMID:16950927 Glutathione reductase and a mitochondrial thioredoxin play o... | ACCEPT | Summary: Pgr1-Myc was found in a crude organellar fraction separated from cytosol (Sod2 marker), which the authors interpret as most likely mitochondrial; the essential function is suppressed only by mitochondrially targeted thioredoxin. The fraction was not strictly mitochondrial, but with the HDA and functional data the annotation is well supported. Supporting Evidence: PMID:16950927 GR is distributed in organelles, most likely in mitochondria, as well as in the cytosol PMID:16950927 revealed that GR resides not only in the cytosol but also in the organelle fraction |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell mapping (Mitochondrion, from PMID:16950927); consistent with the IDA. Supporting Evidence: PMID:16950927 GR is distributed in organelles, most likely in mitochondria, as well as in the cytosol |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA for cytosol; matches the cytosolic fraction observed for Pgr1-Myc. Supporting Evidence: PMID:16950927 revealed that GR resides not only in the cytosol but also in the organelle fraction |
| GO:0005829 cytosol | IDA PMID:16950927 Glutathione reductase and a mitochondrial thioredoxin play o... | ACCEPT | Summary: Direct fractionation evidence that Pgr1 is in the cytosol (G6PD marker), where it maintains the reduced GSH pool. Supporting Evidence: PMID:16950927 revealed that GR resides not only in the cytosol but also in the organelle fraction |
| GO:0006749 glutathione metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA; regenerating GSH from GSSG is part of glutathione metabolism. Supporting Evidence: PMID:9287302 These results indicate that GR activity, which efficiently reduces GSSG, is essentially required for the growth of S. pombe, unlike in Saccharomyces cerevisiae or Escherichia coli. |
| GO:0006749 glutathione metabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO from IPR006322 (glutathione reductase); correct for Pgr1. Supporting Evidence: PMID:9287302 These results indicate that GR activity, which efficiently reduces GSSG, is essentially required for the growth of S. pombe, unlike in Saccharomyces cerevisiae or Escherichia coli. |
| GO:0006749 glutathione metabolic process | IMP PMID:9287302 Isolation, expression, and regulation of the pgr1(+) gene en... | ACCEPT | Summary: pgr1 repression/disruption data (Lee et al.) tie Pgr1 to maintenance of reduced glutathione. Supporting Evidence: PMID:9287302 These results indicate that GR activity, which efficiently reduces GSSG, is essentially required for the growth of S. pombe, unlike in Saccharomyces cerevisiae or Escherichia coli. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: Generic oxidoreductase activity from InterPro FAD/NAD(P)-binding domain entries; true but uninformative compared with GO:0004362. Supporting Evidence: PMID:9287302 The level of transcript as well as the GR enzyme activity increased more than 11-fold when the cloned pgr1(+) gene was expressed on a multicopy plasmid. |
| GO:0016668 oxidoreductase activity, acting on a sulfur group of donors, NAD(P) as acceptor | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro2GO from IPR012999 (pyridine nucleotide-disulfide oxidoreductase class I active site); a correct parent of glutathione-disulfide reductase activity, less specific. Supporting Evidence: PMID:9287302 The level of transcript as well as the GR enzyme activity increased more than 11-fold when the cloned pgr1(+) gene was expressed on a multicopy plasmid. |
| GO:0034599 cellular response to oxidative stress | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: PANTHER IBA for cellular response to oxidative stress. In S. pombe pgr1 is Pap1-induced by oxidants and its overexpression protects against menadione, so a role in the oxidative stress response is reasonable, but it is a downstream consequence of keeping GSH reduced. Supporting Evidence: PMID:9287302 The level of pgr1(+) transcripts increased by treatment with oxidants such as menadione, cumene hydroperoxide, and diamide. |
| GO:0045454 cell redox homeostasis | IBA GO_REF:0000033 | ACCEPT | Summary: PANTHER IBA; maintaining the GSH:GSSG ratio is the core physiological role of glutathione reductase. Supporting Evidence: PMID:16950927 Trx2 did not reverse the high ratio of oxidized glutathione to GSH |
| GO:0045454 cell redox homeostasis | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO from IPR046952 (GSHR/TRXR-like); correct for Pgr1. Supporting Evidence: PMID:16950927 Trx2 did not reverse the high ratio of oxidized glutathione to GSH |
| GO:0045454 cell redox homeostasis | IMP PMID:16950927 Glutathione reductase and a mitochondrial thioredoxin play o... | ACCEPT | Summary: GR depletion raised the GSSG/GSH ratio and inactivated oxidation-labile Fe-S enzymes in mitochondria and cytosol, direct evidence that Pgr1 maintains cellular thiol-redox state. Supporting Evidence: PMID:16950927 Trx2 did not reverse the high ratio of oxidized glutathione to GSH PMID:16950927 These results indicate that the essentiality of GR in the aerobic growth of S. pombe is derived from its role in maintaining oxidation-labile Fe-S enzymes and iron homeostasis. |
| GO:0050660 flavin adenine dinucleotide binding | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: FAD is the prosthetic group of glutathione reductase (inferred from GLR1). A cofactor-binding descriptor rather than the enzyme function. Supporting Evidence: file:SCHPO/pgr1/pgr1-uniprot.txt Note=Binds 1 FAD per subunit. |
| GO:0050660 flavin adenine dinucleotide binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO for FAD binding; correct cofactor descriptor. Supporting Evidence: file:SCHPO/pgr1/pgr1-uniprot.txt Note=Binds 1 FAD per subunit. |
| GO:0050661 NADP binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: InterPro2GO for NADP binding; NADPH is the electron donor of GR. Correct, non-core. Supporting Evidence: file:SCHPO/pgr1/pgr1-uniprot.txt Reaction=2 glutathione + NADP(+) = glutathione disulfide + NADPH + |
| GO:0070301 cellular response to hydrogen peroxide | IMP NOT PMID:9287302 Isolation, expression, and regulation of the pgr1(+) gene en... | ACCEPT | Summary: NOT annotation from Lee et al.: pgr1 overexpression conferred resistance to menadione but not to H2O2. Because pgr1 is essential, this rests only on an overexpression phenotype and does not show that Pgr1 has no role in the H2O2 response; it does faithfully record what the paper reports, so it is retained as curated. Supporting Evidence: PMID:9287302 This overexpression conferred on S. pombe cells more resistance against menadione, a redox cycling agent, but not against H2O2. |
| GO:0098869 cellular oxidant detoxification | IC PMID:9287302 Isolation, expression, and regulation of the pgr1(+) gene en... | KEEP AS NON CORE | Summary: Curator inference from GR activity (with GO:0004362). GR supplies GSH for peroxide/xenobiotic detoxification and overexpression protects against menadione, but Pgr1 does not itself act on oxidants. Acceptable as non-core. Supporting Evidence: PMID:9287302 The level of transcript as well as the GR enzyme activity increased more than 11-fold when the cloned pgr1(+) gene was expressed on a multicopy plasmid. |
Loading supporting content…
Download this section (compressed HTML)Q: How does the single Pgr1 translation product reach mitochondria without a predictable targeting sequence, and is it in the matrix?
Q: Why is glutathione reductase essential in S. pombe but dispensable in S. cerevisiae: does S. pombe lack a thioredoxin-based backup for GSSG reduction in mitochondria?
Experiment: Protease-protection and submitochondrial fractionation of purified mitochondria from a strain expressing endogenous Pgr1-tag, with matrix and IMS markers.
Hypothesis: Pgr1 is imported into the mitochondrial matrix.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)