Caa1 is the cytosolic PLP-dependent aspartate aminotransferase of Schizosaccharomyces pombe. It reversibly interconverts L-aspartate plus 2-oxoglutarate with oxaloacetate plus L-glutamate. Native caa1 deletion causes aspartate auxotrophy, and a catalytic-site mutant compromises growth and TORC1 activation in the studied nutrient conditions. These effects require catalytic competence but do not establish direct TOR binding or a dedicated sensor mechanism. Caa1 does not replace mitochondrial Maa1 in the tested ammonium-assimilation rescue experiment; its malate-aspartate-shuttle assignment remains a comparative inference.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004069 L-aspartate:2-oxoglutarate transaminase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for AspAT activity from the cytosolic-isozyme clade (SGD AAT2, MGI Got1, FB Got1). caa1 is in PTHR11879:SF55 with the fungal cytosolic enzymes and conserves the class-I aminotransferase fold; the S. pombe genetics place it as the main aspartate-forming enzyme. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; PMID:39502420 The cytoplasmic Caa1 has a major role for this reaction in PMID:9288922 We demonstrate that the gene AAT2 codes for the cytosolic and peroxisomal AAT activities. |
| GO:0004069 L-aspartate:2-oxoglutarate transaminase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Rhea/EC mapping (RHEA:21824, EC 2.6.1.1) from the UniProt catalytic-activity annotation; correct specific MF for caa1. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
| GO:0004069 L-aspartate:2-oxoglutarate transaminase activity | ISS GO_REF:0000024 | ACCEPT | Summary: Manual PomBase ISS from chicken mitochondrial AspAT (P00508). The transaminase chemistry is shared by the cytosolic and mitochondrial isozymes, so the MF transfer is valid even though the donor is the other isozyme. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
| GO:0004069 L-aspartate:2-oxoglutarate transaminase activity | ISS GO_REF:0000024 | ACCEPT | Summary: Manual PomBase ISS from the S. cerevisiae cytosolic ortholog Aat2 (P23542), the direct counterpart of caa1. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; PMID:9288922 We demonstrate that the gene AAT2 codes for the cytosolic and peroxisomal AAT activities. |
| GO:0005737 cytoplasm | EXP PMID:16823372 ORFeome cloning and global analysis of protein localization ... | MODIFY | Summary: The cytoplasmic annotation is correct; cytosol is the supported location of the represented soluble enzyme. Reason: Refine the broad cytoplasm term to cytosol, already supported for this gene. Conditional filament assembly or additional organelles are assessed separately. Proposed replacements: cytosol Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16823372}. PMID:16823372 we determined the localization of 4,431 proteins |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | MODIFY | Summary: The cytoplasmic annotation is correct; cytosol is the supported location of the represented soluble enzyme. Reason: Refine the broad cytoplasm term to cytosol, already supported for this gene. Conditional filament assembly or additional organelles are assessed separately. Proposed replacements: cytosol Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16823372}. |
| GO:0005829 cytosol | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: HDA cytosol from the ORFeome localisation screen; the cytosol is where caa1 carries out transamination. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins PMID:39502420 The cytoplasmic Caa1 has a major role for this reaction in |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA placing the cytosolic AspAT clade in the cytosol (SGD AAT2, MGI Got1); agrees with the S. pombe GFP data. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000269|PubMed:16823372}. |
| GO:0006103 2-oxoglutarate metabolic process | ISS GO_REF:0000024 | ACCEPT | Summary: The aminotransferase directly consumes or produces 2-oxoglutarate in its core reaction. Reason: This is participation in 2-oxoglutarate metabolism through the enzyme chemistry, not an indirect phenotype; the broad process is appropriate because the physiological direction is context dependent. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
| GO:0006520 amino acid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: The enzyme directly catalyzes amino-acid metabolism; the established reaction-specific process is more informative. Reason: Retain the biological claim and refine to the supported biosynthetic or catabolic processes already represented in this review. Proposed replacements: L-aspartate biosynthetic process Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
| GO:0006531 aspartate metabolic process | ISS GO_REF:0000024 | MODIFY | Summary: Aspartate metabolism is correct, with more specific supported directional processes. Reason: Refine the broad process using the native biosynthetic role or the supported inherited catabolic direction; reversibility does not imply equal net flux in all conditions. Proposed replacements: L-aspartate biosynthetic process Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
| GO:0006532 L-aspartate biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Native caa1 deletion causes aspartate auxotrophy, independently supporting the inherited aspartate-biosynthetic role. Reason: PMID:31641022 directly tests the target and its catalytic-site mutant; this is stronger than analogy to budding yeast and is consistent with the PAINT assertion. Supporting Evidence: PMID:39502420 The cytoplasmic Caa1 has a major role for this reaction in PMID:33397945 suggesting that Aat2p is the major enzyme for aspartate synthesis under nitrogen starvation PMID:31641022 Deletion of the entire ORF of caa1 + from the genome by replacing it with KanMX (Ξ caa1 ) resulted in cells that showed the expected slow growth, aspartate auxotrophy, and rapamycin sensitivity |
| GO:0006536 glutamate metabolic process | ISS GO_REF:0000024 | ACCEPT | Summary: Glutamate is directly consumed or produced by the core transamination reaction. Reason: The enzyme performs glutamate metabolism; a generic co-substrate designation does not make this chemistry non-core. A single universal net direction is not inferred. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
| GO:0008483 transaminase activity | IEA GO_REF:0000002 | MODIFY | Summary: The broad molecular-function annotation is true; the characterized or conserved L-aspartate:2-oxoglutarate transaminase activity is the informative activity. Reason: Refine to L-aspartate:2-oxoglutarate transaminase activity, already supported elsewhere in this review. This is term specificity, not a rejection of the original evidence. Proposed replacements: L-aspartate:2-oxoglutarate transaminase activity Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
| GO:0030170 pyridoxal phosphate binding | IEA GO_REF:0000002 | ACCEPT | Summary: Pyridoxal phosphate binding is integral to the aminotransferase catalytic mechanism. Reason: The cofactor-binding property is core to this enzyme, not peripheral merely because it is not an independent reaction. Direct target biochemical evidence, where available, and conserved PLP-dependent architecture support the claim. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Name=pyridoxal 5'-phosphate; Xref=ChEBI:CHEBI:597326; |
| GO:0043490 malate-aspartate shuttle | IC GO_REF:0000111 | KEEP AS NON CORE | Summary: PomBase IC (GO_REF:0000111, with GO:0004069) from the GO-CAM malate-aspartate shuttle model (gomodel:67c10cc400005826), where caa1 is the cytosolic AspAT of the shuttle. Cytosolic AspAT is a canonical shuttle component in animals, and S. pombe has the mitochondrial carriers (odc1) and isozymes needed; but no fission-yeast experiment shows that caa1 operates a malate-aspartate shuttle, and the only S. pombe genetic data place caa1 in aspartate synthesis. Kept as a plausible but non-core role. Reason: Inferred by pathway analogy; aspartate synthesis is the supported core role. Supporting Evidence: PMID:39502420 The cytoplasmic Caa1 has a major role for this reaction in |
| GO:0043490 malate-aspartate shuttle | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: ARBA (ARBA00043538) machine-learning rule for malate-aspartate shuttle, applied to both S. pombe AspAT isozymes. Same considerations as the IC row: plausible, not demonstrated in S. pombe. Reason: Family-level rule; shuttle role not tested in S. pombe. Supporting Evidence: file:SCHPO/caa1/caa1-uniprot.txt Reaction=L-aspartate + 2-oxoglutarate = oxaloacetate + L-glutamate; |
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Download this section (compressed HTML)Q: Does caa1 participate in a malate-aspartate NADH shuttle in S. pombe, as asserted by the PomBase GO-CAM, or is its cytosolic role restricted to aspartate synthesis?
Q: Is a caa1 deletion an aspartate auxotroph, as predicted if it is the major aspartate-forming enzyme?
Experiment: Measure aspartate auxotrophy and 13C-label incorporation into aspartate in caa1-deleted, maa1-deleted and double mutants on ammonium medium.
Type: genetic interaction and metabolic labelling
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