car2 (SPBC21C3.08c) encodes the only ornithine aminotransferase (OAT, EC 2.6.1.13) of fission yeast, a pyridoxal-phosphate-dependent class-III aminotransferase orthologous to S. cerevisiae CAR2. It transfers the delta-amino group of L-ornithine (produced by the arginases car1 and aru1) to 2-oxoglutarate, forming L-glutamate and L-glutamate 5-semialdehyde, which cyclises to 1-pyrroline-5-carboxylate (P5C), the second step of arginine catabolism. Unlike the mitochondrial animal and plant enzymes, car2 is cytoplasmic. Deletion of car2 strongly reduces the conversion of arginine into proline, glutamate, glutamine and lysine that occurs in wild-type cells.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004587 L-ornithine transaminase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for L-ornithine transaminase activity at node PTN000241224 (sources include S. cerevisiae CAR2, human OAT, Arabidopsis deltaOAT). Reason: Correct inherited activity; car2 is the sole OAT and its deletion blocks the arginase-OAT route. Supporting Evidence: file:SCHPO/car2/car2-uniprot.txt Reaction=a 2-oxocarboxylate + L-ornithine = L-glutamate 5-semialdehyde PMID:20460254 In a car2Ξ single deletion strain, arginine conversion was similarly prevented |
| GO:0004587 L-ornithine transaminase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined IEA from InterPro IPR010164 (ornithine aminotransferase), Rhea 13877 and EC 2.6.1.13. Reason: Correct activity. Supporting Evidence: file:SCHPO/car2/car2-uniprot.txt Reaction=a 2-oxocarboxylate + L-ornithine = L-glutamate 5-semialdehyde |
| GO:0005634 nucleus | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt SubCell mapping (SL-0191 Nucleus) from the ORFeome observation. Reason: High-throughput observation without functional context; the enzyme acts in the cytosol. Supporting Evidence: file:SCHPO/car2/car2-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16823372}. Nucleus |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | MODIFY | Summary: UniProt SubCell mapping (SL-0086 Cytoplasm) from the ORFeome observation. Reason: Cytoplasm is correct but broader than the supported cytosolic enzyme location already represented in this review. Refine to cytosol; this does not deny separate context-specific nuclear observations. Proposed replacements: cytosol Supporting Evidence: file:SCHPO/car2/car2-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16823372}. Nucleus |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | UNDECIDED | Summary: The inherited mitochondrial assignment differs from the curated cytosolic/nuclear localization, but exclusive absence from mitochondria has not been established here. Reason: The PAINT node PTN000241155 places mitochondrial location ancestrally. The current target has cytosolic HDA and curated nuclear/cytoplasmic observations, which support that enzyme pool but do not alone exclude dual localization. The source images/fractionation needed to resolve mitochondrial residence were not accessible; an unverified absence of a classical targeting peptide is insufficient to overturn the ancestral assignment. The cytosolic catalytic core remains supported. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN000241155 UNRESOLVED This node propagates mitochondrial location. The target has curated cytosolic/nuclear observations, but neither dual localization nor target-specific loss of mitochondrial targeting was resolved from accessible evidence. No failure is inferred from the descendant species list. Supporting Evidence: file:SCHPO/car2/car2-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16823372}. Nucleus PMID:16823372 we determined the localization of 4,431 proteins |
| GO:0005829 cytosol | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: ORFeome-wide YFP screen places car2 in the cytosol. Reason: Matches the cytosolic location of fungal OAT and the PomBase GO-CAM. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins file:SCHPO/car2/car2-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16823372}. Nucleus |
| GO:0006527 L-arginine catabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for L-arginine catabolic process at node PTN000241155 (sources include S. cerevisiae CAR2, Arabidopsis deltaOAT and car2 itself). Reason: Correct core process; car2 appears among its own sources because of its IMP annotation. Supporting Evidence: PMID:20460254 In a car2Ξ single deletion strain, arginine conversion was similarly prevented |
| GO:0006527 L-arginine catabolic process | IMP PMID:20460254 A genetic engineering solution to the "arginine conversion p... | ACCEPT | Summary: PomBase IMP from Bicho et al. 2010: car2 deletion prevents conversion of labelled arginine into other amino acids. Reason: Direct genetic evidence that car2 performs the ornithine transamination step of arginine catabolism. Supporting Evidence: PMID:20460254 In a car2Ξ single deletion strain, arginine conversion was similarly prevented PMID:20460254 We focused our attention on the arginases Car1 (30) and Aru1 and on ornithine transaminase Car2. |
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO from IPR005814 (class-III aminotransferase) to pyridoxal phosphate binding. Reason: PLP is the catalytic cofactor of OAT; consistent with the yeast CAR2 review. Supporting Evidence: file:SCHPO/car2/car2-uniprot.txt Name=pyridoxal 5'-phosphate; Xref=ChEBI:CHEBI:597326; |
| GO:0055129 L-proline biosynthetic process | IEA GO_REF:0000041 | KEEP AS NON CORE | Summary: UniPathway UPA00098 (L-proline biosynthesis; L-glutamate 5-semialdehyde from L-ornithine) mapping. Reason: car2 does catalyse a step of arginine-to-proline conversion, and in S. pombe this route labels all detectable proline when arginine is supplied, so the term is not wrong. De novo proline synthesis from glutamate (pro2, pro1, pro3) does not need car2, and the physiological role is arginine catabolism (same treatment as the yeast CAR2 review). Supporting Evidence: file:SCHPO/car2/car2-uniprot.txt PATHWAY: Amino-acid biosynthesis; L-proline biosynthesis; L-glutamate PMID:20460254 Further analysis revealed incorporation of label in all detectable proline as well as in 25β30% of glutamate, glutamine, and lysine |
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Download this section (compressed HTML)Q: Does arginine-derived P5C made by cytosolic car2 in S. pombe reach glutamate only via pro3 and mitochondrial put1/put2 (the budding-yeast proline shuttle), or can it be oxidised directly?
Experiment: Trace 13C-arginine into proline and glutamate in car2, pro3 (if viable with proline), put1 and put2 deletions to define the route of P5C disposal in fission yeast.
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