pssA (PP_3664) encodes CDP-diacylglycerol--serine O-phosphatidyltransferase, the phosphatidylserine synthase that catalyzes the first of two consecutive reactions in the major bacterial phosphatidylethanolamine pathway. It transfers the phosphatidyl group of CDP-diacylglycerol to L-serine to form phosphatidylserine, which is then decarboxylated by Psd.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | TOO GENERAL | Summary: Generic catalytic activity is true but provides no information beyond the specific phosphatidyltransferase term. Reason: True, but entailed by GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity, accepted in this review. Supporting Evidence: file:PSEPK/pssA/pssA-uniprot.txt DR PIRSF; PIRSF000850; Phospholipase_D_PSS; 1. |
| GO:0003882 CDP-diacylglycerol-serine O-phosphatidyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Combined electronic annotation (EC mapping plus TreeGrafter placement at the PAINT phosphatidylserine-synthase node PTN001758495). Q88GQ4 carries the PssA-specific NCBIfam and PIRSF signatures, and its type-I ortholog in E. coli is the biochemically characterized phosphatidylserine synthase. Reason: This is the specific core molecular function of PssA. Supporting Evidence: file:PSEPK/pssA/pssA-uniprot.txt DR NCBIfam; NF006946; PRK09428.1; 1. file:PSEPK/pssA/pssA-uniprot.txt DR PIRSF; PIRSF000850; Phospholipase_D_PSS; 1. PMID:39693441 Type I PssA belongs to the phospholipase D (PLD) superfamily file:PSEPK/pssA/pssA-deep-research-openscientist.md The core function of PP_3664 is synthesis of phosphatidylserine as the obligatory precursor of phosphatidylethanolamine. |
| GO:0005737 cytoplasm | IEA GO_REF:0000117 | TOO GENERAL | Summary: PssA lacks transmembrane helices, but cytoplasm is redundant with the more specific cytosol annotation. Reason: True, but entailed by GO:0005829 cytosol, kept in this review; the active location is the cytoplasmic face of the inner membrane (GO:0005886). Supporting Evidence: PMID:39693441 A peripheral membrane protein PssA can associate with the cellular membrane in its active state or exist in the cytosol in an inactive form. |
| GO:0005829 cytosol | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: The soluble/peripheral phosphatidylserine synthase is assigned to the cytosol by TreeGrafter. Reason: Retain the soluble-state location, but do not use it as the core catalytic location because type-I PssA is active at the membrane surface. Supporting Evidence: PMID:39693441 the active state of PssA is associated with the inner membrane surface, contributing to PS synthesis, while the cytosolic form is inactive in this synthesis process |
| GO:0005886 plasma membrane | ISS PMID:39693441 Structural basis for membrane association and catalysis by p... | NEW | Summary: Type-I PssA carries out phosphatidylserine synthesis while peripherally associated with the cytoplasmic face of the inner membrane. Reason: The experimentally characterized E. coli type-I ortholog is active at the inner membrane surface, and Q88GQ4 has the same PLD-superfamily architecture. Supporting Evidence: PMID:39693441 the active state of PssA is associated with the inner membrane surface, contributing to PS synthesis, while the cytosolic form is inactive in this synthesis process |
| GO:0008444 CDP-diacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase activity | IEA GO_REF:0000002 | REMOVE | Summary: This is phosphatidylglycerophosphate synthase activity, using glycerol-3-phosphate rather than serine, and is a distinct enzyme reaction. Reason: PssA is assigned EC 2.7.8.8 and GO:0003882. GO:0008444 corresponds to the PgsA reaction and conflicts with the protein name and substrate specificity; the InterPro mapping has over-propagated a different phospholipid-synthase activity. Supporting Evidence: file:ECOLI/pssA/pssA-uniprot.txt Catalyzes the conversion of cytidine diphosphate diacylglycerol (CDP-DG) and L-serine into phosphatidylserine (PubMed:39693441, PubMed:8824831). file:PSEPK/pssA/pssA-notes.md PssA uses L-serine to form phosphatidylserine; GO:0008444 instead denotes transfer to glycerol-3-phosphate. |
| GO:0032049 cardiolipin biosynthetic process | IEA GO_REF:0000002 | REMOVE | Summary: Cardiolipin biosynthesis proceeds through phosphatidylglycerol and cardiolipin synthase, not through the PssA phosphatidylserine reaction. Reason: This process annotation is inherited from the same inappropriate phosphatidylglycerol/cardiolipin family mapping as GO:0008444. PssA instead supplies phosphatidylserine to Psd for phosphatidylethanolamine biosynthesis; in the E. coli type-I ortholog, loss of PssA raises rather than lowers phosphatidylglycerol and cardiolipin. Supporting Evidence: PMID:179992 while the combined levels of phosphatidylglycerol and cardiolipin rise from 34 to 68%. |
| GO:0006646 phosphatidylethanolamine biosynthetic process | IC file:PSEPK/pssA/pssA-notes.md | NEW | Summary: PssA supplies phosphatidylserine to the terminal Psd reaction in phosphatidylethanolamine biosynthesis. Reason: The accepted phosphatidylserine-synthase activity and consecutive PssA-Psd pathway support this missing process annotation. Supporting Evidence: file:PSEPK/pssA/pssA-notes.md PssA forms phosphatidylserine, which is the substrate for the consecutive Psd decarboxylation reaction. |
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