PlsC (formerly YhdO) catalyses the second acylation of membrane phospholipid synthesis in Bacillus subtilis, transferring a fatty acyl group from acyl-ACP to the sn-2 position of 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid) to give phosphatidic acid, the precursor of phosphatidylethanolamine, phosphatidylglycerol and cardiolipin. It is a peripheral enzyme of the cytoplasmic membrane, concentrated with the other lipid synthases in the septal membrane, and it carries the HXXXXD acyltransferase motif of the PlsC/AGPAT family. It is the only PlsC/AGPAT-family protein encoded in the genome and is indispensable, since when it is inactivated its substrate accumulates and phospholipid synthesis stops. Unlike eukaryotic AGPATs it uses acyl-ACP rather than acyl-CoA as the acyl donor. In a coupled in vitro system the enzyme acylates both the (R)- and the (S)-enantiomer of lysophosphatidic acid, with more of the (R) product formed.
Definition: Catalysis of the reaction: a fatty acyl-[ACP] + a 1-acyl-sn-glycero-3-phosphate = a 1,2-diacyl-sn-glycero-3-phosphate + holo-[ACP].
Justification: GO:0003841, the term used for every bacterial PlsC, is defined with acyl-CoA as donor, yet B. subtilis PlsC uses acyl-ACP and not acyl-CoA, and its UniProt catalytic activity is written with fatty acyl-[ACP] (Rhea:42296; it has no official EC number, only EC 2.3.1.n4). Both parents of GO:0003841, lysophosphatidic acid acyltransferase activity and lysophospholipid acyltransferase activity, are also written with acyl-CoA, so the whole sub-branch assumes the eukaryotic donor. GO already makes exactly this donor distinction one step earlier in the same pathway, between GO:0004366 acyl-CoA glycerol-3-phosphate O-acyltransferase activity and GO:0043772 acyl-phosphate glycerol-3-phosphate acyltransferase activity, so the proposal follows an established pattern rather than introducing one. The existing annotations are left in place because the term name is donor-neutral and the assignment is right about the reaction; the request is for a term that also matches the donor, as part of a broader question for GO about donor- and stereo-specific terms in this pathway.
Parent term: acyltransferase activity, transferring groups other than amino-acyl groups
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003841 1-acylglycerol-3-phosphate O-acyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: The ancestral LPAAT activity of PTHR10434, inherited and experimentally confirmed in B. subtilis. Reason: The node placement is the thing to test, not the donor list, and it holds. PTN000046632 is seeded by plant, mouse, yeast and human AGPATs together with E. coli PlsC (P26647), so this is not a eukaryote-only node but an ancestral LPAAT assertion spanning bacteria and eukaryotes, which is where this activity belongs. B. subtilis PlsC lies inside that clade, has the family HXXXXD motif, and its own genetics confirm the inherited reaction, since a plsC temperature-sensitive strain accumulates 1-acyl-G3P and makes no phospholipid. The committed PAINT slice and the repository family review record this node's assertion as sound. One caveat, recorded but not acted on, is that the term's definition names acyl-CoA as donor while B. subtilis PlsC uses only acyl-ACP; see proposed_new_terms and suggested_questions. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000046632 SUPPORTS TRANSFER The cached PAINT IBD at this node carries GO:0003841 and its seeds include E. coli PlsC alongside the eukaryotic AGPATs, so the curator placed the activity at a node ancestral to both domains rather than transferring a eukaryote-specific function. The B. subtilis member's own loss-of-function phenotype corroborates inheritance. Supporting Evidence: PMID:17645809 At the restrictive temperature, however, 1-acyl-G3P accumulation was observed, and phospholipid synthesis did not take place (Figure 3B). file:interpro/panther/PTHR10434/PTHR10434-paint.tsv PTHR10434 PTN000046632 GO:0003841 F IBD false file:BACSU/plsC/plsC-uniprot.txt The HXXXXD motif is essential for acyltransferase activity |
| GO:0003841 1-acylglycerol-3-phosphate O-acyltransferase activity | IEA GO_REF:0000002 | ACCEPT | Summary: Same activity assignment from the AGP acyltransferase signature; correct, and consistent with the IBA row. Reason: IPR004552 is the bacterial 1-acyl-G3P acyltransferase family, and this protein's reaction, the acylation of lysophosphatidic acid to phosphatidic acid, is established for B. subtilis itself by substrate accumulation on loss of function and by membrane assays of donor specificity. The acyl-CoA wording of the term definition is noted on the IBA row. Supporting Evidence: PMID:17557823 whereas PlsC used only acyl-ACP as an acyl donor file:BACSU/plsC/plsC-uniprot.txt Converts lysophosphatidic acid (LPA) into phosphatidic acid PMID:42286214 Subsequently, 1-acyl-sn-glycerol-3-phosphate acyltransferase PlsC, belonging to the lysophosphatidic acid acyltransferases (LPAAT) family, catalyzes the attachment of a second activated fatty acid to the sn-2 position of the glycerol-phosphate backbone |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoplasmic membrane location; supported by GFP localization of the enzyme to the septal membrane. Reason: PlsC acts on membrane-embedded lysophosphatidic acid and its activity is a property of the B. subtilis membrane fraction. GFP-fusion imaging places 1-acyl-glycerol-3-phosphate acyltransferase in the septal membrane of this monoderm bacterium, whose only membrane is the plasma membrane, so the electronic assignment is right and now has direct backing. Supporting Evidence: PMID:15743965 The majority of the lipid synthases were also localized in the septal membranes; this includes 1-acyl-glycerol-3-phosphate acyltransferase file:BACSU/plsC/plsC-uniprot.txt Note=Localized in the septal membrane. |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: Correct but less precise than the plasma membrane term the gene already carries. Reason: Generic membrane is not a root organelle term, so the refinement rule applies. The bacterium has one membrane, the plasma membrane, and the enzyme is imaged there, so GO:0005886, a descendant that the gene already carries, is the supported granularity. Proposed replacements: plasma membrane Supporting Evidence: PMID:15743965 The majority of the lipid synthases were also localized in the septal membranes; this includes 1-acyl-glycerol-3-phosphate acyltransferase |
| GO:0006644 phospholipid metabolic process | IEA GO_REF:0000041 | MODIFY | Summary: True but uninformative; the specific step is known and already annotated. Reason: PlsC catalyses the final step of phosphatidic acid synthesis, and the gene already carries GO:0006654 phosphatidic acid biosynthetic process, a descendant of this term, by IBA. The claim is correct, so this is a refinement rather than a correction, and it keeps this row consistent with the accepted GO:0006654 row. Proposed replacements: phosphatidic acid biosynthetic process Supporting Evidence: PMID:17645809 This is consistent with the known 1-acyl-G3P acyltransferase activity of PlsC. |
| GO:0006654 phosphatidic acid biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: The core process; PlsC performs the acylation that produces phosphatidic acid. Reason: This is participation in the strict sense, because the gene product itself catalyses a step of the process. The B. subtilis genetics show it directly, as blocking PlsC leaves its substrate 1-acyl-G3P accumulating and no phospholipid made. The node is the same ancestral LPAAT node, seeded here too by E. coli PlsC as well as mammalian AGPATs, so the process assertion sits at a node that includes bacteria. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000046632 SUPPORTS TRANSFER The committed PAINT slice carries GO:0006654 at this node with E. coli PlsC among the seeds, and the B. subtilis member's depletion phenotype shows the same step is performed here. Supporting Evidence: PMID:17557823 Phospholipid synthesis ceased following PlsC depletion file:interpro/panther/PTHR10434/PTHR10434-paint.tsv PTHR10434 PTN000046632 GO:0006654 P IBD false |
| GO:0008654 phospholipid biosynthetic process | IEA GO_REF:0000002 | MODIFY | Summary: Correct, but the characterized step warrants the phosphatidic acid term. Reason: All phospholipid synthesis in B. subtilis requires PlsC, so the term is true, but the reaction it catalyses is the second acylation that yields phosphatidic acid, which the gene already carries as GO:0006654. Consistent with the other refinements in this review. Proposed replacements: phosphatidic acid biosynthetic process Supporting Evidence: PMID:17645809 At the restrictive temperature, however, 1-acyl-G3P accumulation was observed, and phospholipid synthesis did not take place (Figure 3B). |
| GO:0016746 acyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: True but entailed by the specific acyltransferase term asserted elsewhere in this review. Reason: IPR002123 is the broad phospholipid/glycerol acyltransferase signature, so the electronic mapping stops at the class. The specific reaction is known for this protein and is already annotated, so the supported granularity is GO:0003841, a descendant that the gene carries by IBA and IEA. Proposed replacements: 1-acylglycerol-3-phosphate O-acyltransferase activity Supporting Evidence: PMID:17557823 whereas PlsC used only acyl-ACP as an acyl donor file:BACSU/plsC/plsC-uniprot.txt Converts lysophosphatidic acid (LPA) into phosphatidic acid |
| GO:0032153 cell division site | IDA PMID:15743965 Phosphatidylethanolamine domains and localization of phospho... | NEW | Summary: Proposed new annotation; the enzyme concentrates in the septal membrane at the division site. Reason: GFP-fusion imaging of the B. subtilis lipid synthases placed 1-acyl-glycerol-3-phosphate acyltransferase in the septal membranes, alongside the phosphatidylserine, cardiolipin and phosphatidylglycerophosphate synthases, in the same study that showed the septal membrane is enriched in phosphatidylethanolamine. This is a direct observation on the B. subtilis enzyme and is absent from GOA, which holds only the whole-membrane location. It is a location claim, not a claim that PlsC participates in cell division. Supporting Evidence: PMID:15743965 The majority of the lipid synthases were also localized in the septal membranes; this includes 1-acyl-glycerol-3-phosphate acyltransferase file:BACSU/plsC/plsC-uniprot.txt Note=Localized in the septal membrane. |
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Download this section (compressed HTML)Q: Should GO's lysophosphatidic acid acyltransferase sub-branch be rewritten to be donor-neutral, or given acyl-ACP children, given that every bacterial PlsC uses acyl-ACP while GO:0003841 and both its parents are defined with acyl-CoA?
Suggested experts: GO molecular function curators, lipid metabolism curators
Q: Does GO want stereochemistry-aware terms for the bacterial acyltransferase steps, so that acylation of (S)-lysophosphatidic acid can be distinguished from the canonical (R) reaction, or should stereochemistry be left to the reaction cross-reference?
Suggested experts: GO Consortium biocurators, Rhea and ChEBI curators
Q: Is the septal-membrane concentration of the lipid synthases, including PlsC, best captured as a cell division site location, or does it need a bacterial septal membrane term?
Suggested experts: GO cellular component curators, bacterial cell biologists
Experiment: Synthesise both lysophosphatidic acid enantiomers chemically, reconstitute purified PlsC into liposomes containing each at equal known concentration, and measure steady-state kinetics with acyl-ACP as donor, so that the enzyme's preference is separated from substrate supply in the published coupled assay.
Hypothesis: PlsC acylates (S)-lysophosphatidic acid at a rate sufficient to account for the heterochiral phospholipid of B. subtilis.
Type: enzyme kinetics on reconstituted protein with defined substrates
Experiment: Compare initial rates of purified PlsC with fatty acyl-ACP and with acyl-CoA over a donor concentration range, and test whether acyl-CoA inhibits the acyl-ACP-dependent reaction, as is the case for PlsY.
Hypothesis: The acyl donor of B. subtilis PlsC is strictly acyl-ACP, as required for the proposed donor-specific GO term.
Type: donor specificity assay
Experiment: Image a functional PlsC fluorescent fusion in dividing and sporulating cells together with a division-site marker such as FtsZ or DivIVA, and ask whether phosphatidic acid synthesis, measured by pulse labelling of isolated septal and lateral membrane fractions, follows the protein.
Hypothesis: PlsC function is localised to the division septum, where phosphatidic acid is made.
Type: fluorescence co-localization with metabolic labelling
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: Whether PlsC acylates (S)-lysophosphatidic acid, the glycerol 1-phosphate-backbone intermediate, at a physiologically meaningful rate is unknown, so it is unknown whether the heterochiral phospholipid of B. subtilis is completed by PlsC.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: What is established is that in a coupled liposome system containing PlsY, B. subtilis PlsC converts both enantiomers of lysophosphatidic acid into phosphatidic acid, with significantly more of the (R) product. What is not established is any rate on a defined (S) substrate, because (S)-lysophosphatidic acid is not commercially available and had to be generated in situ, so its lower concentration and the enzyme's preference are confounded, as the authors state. No kinetic constants exist for either enantiomer.
Significance: PlsC is the only PlsC/AGPAT-family enzyme in B. subtilis, so if heterochiral phospholipid is made at all, PlsC must act on the (S) intermediate; that inference is what currently stands in for a measurement. The result decides whether a stereo-alternative molecular function should be annotated to the bacterial LPAAT step, for which GO has no term, the paired request being the glycerol 1-phosphate term proposed in the plsY review.
What would resolve it: Assay reconstituted PlsC on chemically synthesised (R)- and (S)-lysophosphatidic acid supplied at equal, known concentrations, uncoupled from PlsY, and determine kinetic constants for both; then test in vivo whether (S)-backbone phosphatidic acid and phosphatidylglycerol depend on PlsC levels.
Provenance (the field's own admissions):
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