CHO1 (PSS1) encodes phosphatidylserine synthase (CDP-diacylglycerol--serine O-phosphatidyltransferase, EC 2.7.8.8) of Saccharomyces cerevisiae, a multi-pass membrane enzyme of the CDP-alcohol phosphatidyltransferase family. Using Mn2+ or Mg2+, it transfers the phosphatidyl group of CDP-diacylglycerol to L-serine, producing phosphatidylserine (PS) and CMP. Cho1 is the only source of PS in yeast; PS is decarboxylated to phosphatidylethanolamine by Psd1/Psd2 and then methylated to phosphatidylcholine, so Cho1 initiates the de novo (CDP-DAG) route to PE and PC. cho1 null mutants lack PS and require ethanolamine or choline (Kennedy pathway) for growth, and show mitochondrial and sporulation defects. Cho1 resides in the ER membrane, with activity also reported in mitochondria-associated membrane/outer mitochondrial membrane fractions. Its expression is repressed by inositol and choline through the Ino2/Ino4-Opi1 circuit. PS made by Cho1 is required for autophagosome biogenesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | EXP PMID:6274497 Solubilization of microsomal-associated phosphatidylserine s... | ACCEPT | Summary: PS synthase activity was solubilised from yeast microsomes and characterised kinetically (Mn2+-dependent, Km values for CDP-DAG and serine). Direct biochemical evidence for the core activity. Supporting Evidence: PMID:6274497 were solubilized from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | IDA PMID:6088519 Phosphatidylserine synthesis in Saccharomyces cerevisiae. Pu... | ACCEPT | Summary: PS synthase was purified from microsomes of wild type and a CHO1-overexpressing strain; the CHO1 plasmid increased enzyme 6-7-fold, linking the purified activity to the CHO1 gene. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae PMID:6088519 contains a hybrid plasmid bearing the structural gene for phosphatidylserine synthase and overproduces the enzyme 6-7 fold |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: ARBA/RHEA:16913/EC 2.7.8.8 mapping. Correct. Supporting Evidence: file:yeast/CHO1/CHO1-uniprot.txt FUNCTION: Catalyzes the synthesis of phosphatidylserine (PtdSer). |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | IMP PMID:6988386 Yeast mutants auxotrophic for choline or ethanolamine. | ACCEPT | Summary: cho1 mutants lack PS under all growth conditions, consistent with loss of the PS synthase activity. Accept (IMP supports the activity together with the biochemical data). Supporting Evidence: PMID:6988386 The lipid composition suggests that cho1 mutants do not synthesize phosphatidylserine under any growth conditions. |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PHOS-PWY, superpathway of phosphatidic acid and phospholipid biosynthesis) assigning EC 2.7.8.8 (CDP-DAG + L-serine -> PS + CMP) to Cho1. Correct reaction assignment. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PHOSLIPSYN2-PWY-1, phospholipid biosynthesis) assigning EC 2.7.8.8 (CDP-DAG + L-serine -> PS + CMP) to Cho1. Correct reaction assignment. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PWY-5669, phosphatidylethanolamine biosynthesis I) assigning EC 2.7.8.8 (CDP-DAG + L-serine -> PS + CMP) to Cho1. Correct reaction assignment. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PWY3O-2, superpathway of phospholipid biosynthesis) assigning EC 2.7.8.8 (CDP-DAG + L-serine -> PS + CMP) to Cho1. Correct reaction assignment. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0005737 cytoplasm | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA annotation to cytoplasm. Technically true (ER is within the cytoplasm) but much less informative than ER membrane. Supporting Evidence: file:yeast/CHO1/CHO1-uniprot.txt SUBCELLULAR LOCATION: Microsome membrane {ECO:0000269|PubMed:6274497}; |
| GO:0005741 mitochondrial outer membrane | IDA PMID:3005242 Subcellular and submitochondrial localization of phospholipi... | KEEP AS NON CORE | Summary: Kuchler et al. (1986) found PS synthase activity in outer mitochondrial membrane fractions, exposed to the cytosol. Later work attributes much of this to mitochondria-associated ER membranes (MAM) co-purifying with mitochondria; Cho1 is primarily an ER enzyme. Experimental curator call retained but non-core. Reason: Experimental fractionation evidence; principal location is ER/MAM. Supporting Evidence: PMID:3005242 Glycerolphosphate acyltransferase, phosphatidylinositol synthase, and phosphatidylserine synthase were exposed at the cytosolic surface of the outer mitochondrial membrane. |
| GO:0005741 mitochondrial outer membrane | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt subcellular location (mitochondrion outer membrane, SL-0172) derived from Kuchler et al. 1986. Retained as secondary location. Reason: Secondary location relative to ER. Supporting Evidence: PMID:3005242 Glycerolphosphate acyltransferase, phosphatidylinositol synthase, and phosphatidylserine synthase were exposed at the cytosolic surface of the outer mitochondrial membrane. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular location (ER membrane, SL-0097). Consistent with microsomal purification of the enzyme; this is the main site of PS synthesis. Supporting Evidence: file:yeast/CHO1/CHO1-uniprot.txt SUBCELLULAR LOCATION: Microsome membrane {ECO:0000269|PubMed:6274497}; PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0005829 cytosol | RCA GO_REF:0000123 | MODIFY | Summary: YeastPathways RCA (PHOS-PWY) places the PS synthase reaction in the cytosol by pathway default. Cho1 is a multi-pass ER (microsomal) membrane enzyme acting on membrane CDP-DAG; its activity is not cytosolic. Reason: Wrong compartment from pathway default. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0005829 cytosol | RCA GO_REF:0000123 | MODIFY | Summary: YeastPathways RCA (PHOSLIPSYN2-PWY-1) places the PS synthase reaction in the cytosol by pathway default. Cho1 is a multi-pass ER (microsomal) membrane enzyme acting on membrane CDP-DAG; its activity is not cytosolic. Reason: Wrong compartment from pathway default. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0005829 cytosol | RCA GO_REF:0000123 | MODIFY | Summary: YeastPathways RCA (PWY-5669) places the PS synthase reaction in the cytosol by pathway default. Cho1 is a multi-pass ER (microsomal) membrane enzyme acting on membrane CDP-DAG; its activity is not cytosolic. Reason: Wrong compartment from pathway default. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0005829 cytosol | RCA GO_REF:0000123 | MODIFY | Summary: YeastPathways RCA (PWY3O-2) places the PS synthase reaction in the cytosol by pathway default. Cho1 is a multi-pass ER (microsomal) membrane enzyme acting on membrane CDP-DAG; its activity is not cytosolic. Reason: Wrong compartment from pathway default. Proposed replacements: endoplasmic reticulum membrane Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0006646 phosphatidylethanolamine biosynthetic process | IEA GO_REF:0000041 | KEEP AS NON CORE | Summary: UniPathway UPA00558 (PE from CDP-DAG, step 1/2) mapping. Cho1 performs the first step of the de novo PE route (PS is then decarboxylated by Psd1/Psd2); cho1 mutants need ethanolamine/choline to make PE/PC. Valid pathway membership, but the reaction Cho1 catalyses is PS synthesis. Reason: Pathway-level parent; the specific step is PS biosynthesis. Supporting Evidence: PMID:6988386 If phosphatidylethanolamine or phosphatidylcholine, which are usually derived from phosphatidylserine, were synthesized from exogenous ethanolamine or choline, the mutants grew and divided relatively normally. |
| GO:0006646 phosphatidylethanolamine biosynthetic process | RCA GO_REF:0000123 | KEEP AS NON CORE | Summary: YeastPathways RCA (PWY-5669, PE biosynthesis I). Same reasoning: Cho1 makes the PS that Psd1/2 convert to PE. Reason: Pathway-level parent; core step is PS biosynthesis. Supporting Evidence: PMID:6988386 If phosphatidylethanolamine or phosphatidylcholine, which are usually derived from phosphatidylserine, were synthesized from exogenous ethanolamine or choline, the mutants grew and divided relatively normally. |
| GO:0006659 phosphatidylserine biosynthetic process | IDA PMID:6088519 Phosphatidylserine synthesis in Saccharomyces cerevisiae. Pu... | ACCEPT | Summary: Purified Cho1 synthesises PS from CDP-DAG and serine. Core process. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0006659 phosphatidylserine biosynthetic process | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA annotation to PS biosynthetic process; correct. Supporting Evidence: file:yeast/CHO1/CHO1-uniprot.txt FUNCTION: Catalyzes the synthesis of phosphatidylserine (PtdSer). |
| GO:0006659 phosphatidylserine biosynthetic process | IMP PMID:3031455 The membrane-associated enzyme phosphatidylserine synthase i... | ACCEPT | Summary: CHO1 subclone complemented the PS synthesis defect and ethanolamine/choline auxotrophy of cho1 mutants; disruption abolished PSS activity. Supporting Evidence: PMID:3031455 Disruption of the CHO1 gene resulted in the simultaneous disappearance of 1.2-kb RNA and PSS activity. PMID:3031455 a 2.8-kb subclone was shown to complement the ethanolamine-choline auxotrophy and to repair the defect in the synthesis of phosphatidylserine |
| GO:0006659 phosphatidylserine biosynthetic process | IMP PMID:6988386 Yeast mutants auxotrophic for choline or ethanolamine. | ACCEPT | Summary: cho1 mutants do not synthesise PS under any growth condition; Cho1 is the sole PS synthase. Supporting Evidence: PMID:6988386 The lipid composition suggests that cho1 mutants do not synthesize phosphatidylserine under any growth conditions. |
| GO:0008654 phospholipid biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IPR000462 (CDP-alcohol phosphatidyltransferase) mapping to phospholipid biosynthetic process. Correct general process. Supporting Evidence: file:yeast/CHO1/CHO1-uniprot.txt FUNCTION: Catalyzes the synthesis of phosphatidylserine (PtdSer). |
| GO:0008654 phospholipid biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PHOS-PWY) to phospholipid biosynthetic process. Correct general process. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0008654 phospholipid biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PHOSLIPSYN2-PWY-1) to phospholipid biosynthetic process. Correct general process. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0008654 phospholipid biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: YeastPathways RCA (PWY3O-2) to phospholipid biosynthetic process. Correct general process. Supporting Evidence: PMID:6088519 Membrane-associated phosphatidylserine synthase (CDP-diacylglycerol:L-serine O-phosphatidyltransferase, EC 2.7.8.8) was purified from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0016020 membrane | IDA PMID:6274497 Solubilization of microsomal-associated phosphatidylserine s... | TOO GENERAL | Summary: Membrane localisation inferred from the need for detergent solubilisation of PS synthase from microsomes. Correct but general. Supporting Evidence: PMID:6274497 were solubilized from the microsomal fraction of Saccharomyces cerevisiae |
| GO:0016020 membrane | IEA GO_REF:0000002 | TOO GENERAL | Summary: InterPro-based membrane annotation; correct but general. Supporting Evidence: file:yeast/CHO1/CHO1-uniprot.txt SUBCELLULAR LOCATION: Microsome membrane {ECO:0000269|PubMed:6274497}; |
| GO:0016239 positive regulation of macroautophagy | IMP PMID:41176028 Regulation of macroautophagy and microautophagic lipophagy b... | KEEP AS NON CORE | Summary: cho1 deletion abolished autophagosome formation and macroautophagic flux (GFP-Atg8 processing). The effect is attributed to loss of PS, a lipid needed for autophagosome biogenesis; Cho1 acts by supplying PS rather than as a regulator of autophagy. Retained as non-core, as an IMP whose full text is not available here. Reason: Indirect consequence of PS supply; not a regulatory function of Cho1. Supporting Evidence: PMID:41176028 autophagosomes were absent in the cytosol, and macroautophagic bodies were not observed in the vacuoles of the starved cho1∆ mutant |
| GO:0016780 phosphotransferase activity, for other substituted phosphate groups | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IPR000462 mapping to phosphotransferase activity, for other substituted phosphate groups. Correct parent of PS synthase activity. Supporting Evidence: file:yeast/CHO1/CHO1-uniprot.txt FUNCTION: Catalyzes the synthesis of phosphatidylserine (PtdSer). |
| GO:0140505 regulation of microlipophagy | IMP PMID:41176028 Regulation of macroautophagy and microautophagic lipophagy b... | UNDECIDED | Summary: Annotated as acts_upstream_of_or_within_positive_effect regulation of microlipophagy. The abstract reports that cho1 deletion (in the presence of ethanolamine) increased microautophagic uptake of lipid droplets, i.e. loss of Cho1 enhances microlipophagy, so the direction implied by 'positive effect' is unclear from the abstract alone. Full text not available; neither accept nor reject. Supporting Evidence: PMID:41176028 numerous microautophagic vesicles containing lipid droplets were observed in the vacuoles of cho1∆ mutants starved in the presence of Etn |
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Download this section (compressed HTML)Q: Is the PS synthase activity found in mitochondrial fractions entirely due to MAM-resident Cho1, or does a pool reside in the outer mitochondrial membrane proper?
Q: Does Cho1 deficiency affect autophagy only through PS depletion, or also through altered PE/ethanolamine partitioning between Kennedy and CDP-DAG routes?
Experiment: Rescue of cho1 autophagy defects by catalytically dead Cho1 versus exogenous lyso-PS supplementation, to test whether the autophagy phenotype is purely PS-dependent.
Phosphatidylserine synthase; functions in phospholipid biosynthesis; transcriptionally repressed by myo-inositol and choline
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