gpat3 (also called agpat9/agpat10) encodes glycerol-3-phosphate acyltransferase 3, a polytopic endoplasmic reticulum membrane enzyme of the GPAT3/GPAT4 (LPCAT1-like) branch of the PlsC acyltransferase family. The mammalian orthologue is the major N-ethylmaleimide-sensitive microsomal GPAT of adipose tissue: it acylates sn-glycerol 3-phosphate at the sn-1 position with long-chain acyl-CoAs to produce lysophosphatidic acid, the entry step of de novo triacylglycerol synthesis, and its overexpression raises triacylglycerol rather than phospholipid synthesis. Whether the same protein also acylates lysophosphatidic acid to phosphatidic acid (AGPAT activity) is contested between laboratories. The zebrafish enzyme has not been assayed directly; its function is inferred from strong conservation with the human protein.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003841 1-acylglycerol-3-phosphate O-acyltransferase activity | IEA GO_REF:0000120 | UNDECIDED | Summary: 1-acylglycerol-3-phosphate O-acyltransferase (EC 2.3.1.51): acylation of LPA at sn-2 to give phosphatidic acid. UniProt lists this second reaction by similarity to human Q53EU6. Reason: Rhea/EC mapping of the UniProt CATALYTIC ACTIVITY line. The primary literature on the human orthologue is in direct conflict: Sukumaran et al. report robust AGPAT (LPA acyltransferase) activity and no GPAT activity [PMID:19318427], whereas Cao et al. found no increase in product formation with LPA as acceptor and G3P-specific activity only [PMID:17170135]. No zebrafish enzymology exists; the activity is inferred from the human/mouse ortholog (UniProt evidence ECO:0000250|UniProtKB:Q53EU6). With two full-text primary papers disagreeing on whether the protein acylates LPA at all, and no zebrafish assay, the annotation cannot be adjudicated here; flagged UNDECIDED rather than accepted or removed, and not listed as a core function. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt Also converts LPA into 1,2-diacyl-sn-glycerol-3-phosphate (phosphatidic acid or PA) by incorporating an acyl moiety at the sn-2 position of the glycerol backbone. PMID:19318427 In vitro enzymatic activity using lysates of human embryonic kidney-293 cells infected with recombinant AGPAT10/GPAT3 adenovirus show that the protein has a robust AGPAT activity with an apparent V(max) of 2 nmol/min per mg protein, but lacks GPAT enzymatic activity. PMID:17170135 Importantly, acyltransferase activity conferred by GPAT3 overexpression is specific toward G3P, because no significant increase in product formation was observed when LPA, lysophosphatidylcholine, lysophosphatidylserine, lysophosphatidylglycerol, MAG, or DAG were presented as substrates file:DANRE/gpat3/gpat3-deep-research-falcon.md For zebrafish gpat3, these specificity statements should be treated as **inferred from orthology**, because zebrafish-specific enzymatic assays were not identified in the retrieved sources. |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Glycerol-3-phosphate O-acyltransferase (EC 2.3.1.15): acylation of sn-glycerol 3-phosphate at sn-1 to form lysophosphatidic acid, the first step of de novo glycerolipid synthesis. Reason: Rhea/EC mapping of the UniProt CATALYTIC ACTIVITY. The orthologous enzyme was identified as the ER (NEM-sensitive) GPAT: overexpression raises G3P-specific acyltransferase activity [PMID:17170135] and Gpat3-null mice lose 80% of white-adipose GPAT activity [PMID:24714397]. Sukumaran et al. could not detect GPAT activity in their lysate assay [PMID:19318427], but the knockout result settles the in vivo activity. No zebrafish enzymology exists; the activity is inferred from the human/mouse ortholog (UniProt evidence ECO:0000250|UniProtKB:Q53EU6). Accepted as the core activity of the zebrafish orthologue, which is 4-TM ER protein of the same PANTHER subfamily (PTHR23063:SF10). Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt by incorporating an acyl moiety at the sn-1 position of the glycerol backbone PMID:17170135 Ectopic expression of GPAT3 leads to a significant increase in N-ethylmaleimide-sensitive GPAT activity, whereas acyltransferase activity toward a variety of other lysophospholipids, as well as neutral lipid substrates, is not altered. PMID:24714397 Total GPAT activity in white adipose tissue of Gpat3(-/-) mice was reduced by 80%, suggesting that GPAT3 is the predominant GPAT in this tissue. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Endoplasmic reticulum membrane: gpat3 is a polytopic (four predicted transmembrane helices) ER membrane enzyme (UniProt SUBCELLULAR LOCATION, by similarity to human Q53EU6). Reason: UniProtKB-SubCell SL-0097 mapping. Both human characterisations place the tagged orthologue in the ER [PMID:17170135, PMID:19318427] and the enzyme accounts for the NEM-sensitive microsomal GPAT activity. Accepted as the core site of action; no zebrafish localisation data. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane PMID:17170135 GPAT3 is localized to the ER when overexpressed in COS-7 cells. PMID:19318427 When this AGPAT10/GPAT3 cDNA was expressed in Chinese Hamster ovary cells, the protein product localizes to the endoplasmic reticulum. |
| GO:0016746 acyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: Generic acyltransferase activity from the InterPro PlsC/acyltransferase domain signature (IPR002123). Reason: Correct but uninformative; the specific activity supported by the UniProt reaction and the human/mouse enzymology is glycerol-3-phosphate O-acyltransferase activity [PMID:17170135, PMID:24714397]. Modify to GO:0004366. Proposed replacements: glycerol-3-phosphate O-acyltransferase activity Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt by incorporating an acyl moiety at the sn-1 position of the glycerol backbone PMID:17170135 Ectopic expression of GPAT3 leads to a significant increase in N-ethylmaleimide-sensitive GPAT activity, whereas acyltransferase activity toward a variety of other lysophospholipids, as well as neutral lipid substrates, is not altered. |
| GO:0016024 CDP-diacylglycerol biosynthetic process | IEA GO_REF:0000041 | KEEP AS NON CORE | Summary: CDP-diacylglycerol biosynthetic process (UniPathway UPA00557): the LPA/PA produced by GPAT/AGPAT steps can be channelled to CDP-DAG by CDS enzymes. Reason: The GPAT step is formally the first step of the UniPathway CDP-DAG route, so the mapping is not wrong, but the only functional evidence for this enzyme points to triacylglycerol synthesis: overexpression raised TAG but not phospholipid formation [PMID:17170135]. Kept as non-core rather than accepted or removed. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt PATHWAY: Phospholipid metabolism; CDP-diacylglycerol biosynthesis PMID:17170135 Overexpression of GPAT3 in mammalian cells results in increased triacylglycerol, but not phospholipid, formation. |
| GO:0019432 triglyceride biosynthetic process | IEA GO_REF:0000041 | ACCEPT | Summary: Triglyceride biosynthetic process: GPAT catalyses the initial, rate-influencing step of de novo TAG synthesis (G3P to LPA). Reason: UniPathway UPA00282 mapping. The orthologue's overexpression increases triacylglycerol but not phospholipid formation, and GPAT3 siRNA removes most GPAT activity from adipocytes [PMID:17170135]; Gpat3-null mice lose 80% of adipose GPAT activity [PMID:24714397]. The enzyme performs a step of the pathway, so the participation test is met. Accepted as core, with the caveat that zebrafish-specific data are lacking. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt PATHWAY: Glycerolipid metabolism; triacylglycerol biosynthesis. PMID:17170135 Overexpression of GPAT3 in mammalian cells results in increased triacylglycerol, but not phospholipid, formation. PMID:17170135 A substantial loss of GPAT activity in 3T3-L1 adipocytes was achieved by reducing GPAT3 mRNA levels through GPAT3-specific siRNA knockdown. |
| GO:0003841 1-acylglycerol-3-phosphate O-acyltransferase activity | ISS GO_REF:0000024 | UNDECIDED | Summary: 1-acylglycerol-3-phosphate O-acyltransferase (EC 2.3.1.51): acylation of LPA at sn-2 to give phosphatidic acid. UniProt lists this second reaction by similarity to human Q53EU6. Reason: Manual transfer from human GPAT3 (Q53EU6). The primary literature on the human orthologue is in direct conflict: Sukumaran et al. report robust AGPAT (LPA acyltransferase) activity and no GPAT activity [PMID:19318427], whereas Cao et al. found no increase in product formation with LPA as acceptor and G3P-specific activity only [PMID:17170135]. No zebrafish enzymology exists; the activity is inferred from the human/mouse ortholog (UniProt evidence ECO:0000250|UniProtKB:Q53EU6). With two full-text primary papers disagreeing on whether the protein acylates LPA at all, and no zebrafish assay, the annotation cannot be adjudicated here; flagged UNDECIDED rather than accepted or removed, and not listed as a core function. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt Also converts LPA into 1,2-diacyl-sn-glycerol-3-phosphate (phosphatidic acid or PA) by incorporating an acyl moiety at the sn-2 position of the glycerol backbone. PMID:19318427 In vitro enzymatic activity using lysates of human embryonic kidney-293 cells infected with recombinant AGPAT10/GPAT3 adenovirus show that the protein has a robust AGPAT activity with an apparent V(max) of 2 nmol/min per mg protein, but lacks GPAT enzymatic activity. PMID:17170135 Importantly, acyltransferase activity conferred by GPAT3 overexpression is specific toward G3P, because no significant increase in product formation was observed when LPA, lysophosphatidylcholine, lysophosphatidylserine, lysophosphatidylglycerol, MAG, or DAG were presented as substrates file:DANRE/gpat3/gpat3-deep-research-falcon.md For zebrafish gpat3, these specificity statements should be treated as **inferred from orthology**, because zebrafish-specific enzymatic assays were not identified in the retrieved sources. |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | ISS GO_REF:0000024 | ACCEPT | Summary: Glycerol-3-phosphate O-acyltransferase (EC 2.3.1.15): acylation of sn-glycerol 3-phosphate at sn-1 to form lysophosphatidic acid, the first step of de novo glycerolipid synthesis. Reason: Manual transfer from human GPAT3 (Q53EU6). The orthologous enzyme was identified as the ER (NEM-sensitive) GPAT: overexpression raises G3P-specific acyltransferase activity [PMID:17170135] and Gpat3-null mice lose 80% of white-adipose GPAT activity [PMID:24714397]. Sukumaran et al. could not detect GPAT activity in their lysate assay [PMID:19318427], but the knockout result settles the in vivo activity. No zebrafish enzymology exists; the activity is inferred from the human/mouse ortholog (UniProt evidence ECO:0000250|UniProtKB:Q53EU6). Accepted as the core activity of the zebrafish orthologue, which is 4-TM ER protein of the same PANTHER subfamily (PTHR23063:SF10). Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt by incorporating an acyl moiety at the sn-1 position of the glycerol backbone PMID:17170135 Ectopic expression of GPAT3 leads to a significant increase in N-ethylmaleimide-sensitive GPAT activity, whereas acyltransferase activity toward a variety of other lysophospholipids, as well as neutral lipid substrates, is not altered. PMID:24714397 Total GPAT activity in white adipose tissue of Gpat3(-/-) mice was reduced by 80%, suggesting that GPAT3 is the predominant GPAT in this tissue. |
| GO:0005789 endoplasmic reticulum membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Endoplasmic reticulum membrane: gpat3 is a polytopic (four predicted transmembrane helices) ER membrane enzyme (UniProt SUBCELLULAR LOCATION, by similarity to human Q53EU6). Reason: Transfer from human GPAT3 (Q53EU6). Both human characterisations place the tagged orthologue in the ER [PMID:17170135, PMID:19318427] and the enzyme accounts for the NEM-sensitive microsomal GPAT activity. Accepted as the core site of action; no zebrafish localisation data. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane PMID:17170135 GPAT3 is localized to the ER when overexpressed in COS-7 cells. PMID:19318427 When this AGPAT10/GPAT3 cDNA was expressed in Chinese Hamster ovary cells, the protein product localizes to the endoplasmic reticulum. |
| GO:0005783 endoplasmic reticulum | ISS GO_REF:0000024 | ACCEPT | Summary: Endoplasmic reticulum (parent of ER membrane). Transfer from human GPAT3 (Q53EU6). Reason: human GPAT3 localises to the ER when expressed in COS-7 or CHO cells [PMID:17170135, PMID:19318427] and the UniProt location for the zebrafish protein is the ER membrane. Accepted, consistently with the more specific ER-membrane rows; the parent term is not an over-annotation. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane PMID:17170135 GPAT3 is localized to the ER when overexpressed in COS-7 cells. |
| GO:0019432 triglyceride biosynthetic process | ISS GO_REF:0000024 | ACCEPT | Summary: Triglyceride biosynthetic process: GPAT catalyses the initial, rate-influencing step of de novo TAG synthesis (G3P to LPA). Reason: Transfer from human GPAT3 (Q53EU6). The orthologue's overexpression increases triacylglycerol but not phospholipid formation, and GPAT3 siRNA removes most GPAT activity from adipocytes [PMID:17170135]; Gpat3-null mice lose 80% of adipose GPAT activity [PMID:24714397]. The enzyme performs a step of the pathway, so the participation test is met. Accepted as core, with the caveat that zebrafish-specific data are lacking. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt PATHWAY: Glycerolipid metabolism; triacylglycerol biosynthesis. PMID:17170135 Overexpression of GPAT3 in mammalian cells results in increased triacylglycerol, but not phospholipid, formation. PMID:17170135 A substantial loss of GPAT activity in 3T3-L1 adipocytes was achieved by reducing GPAT3 mRNA levels through GPAT3-specific siRNA knockdown. |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: Endoplasmic reticulum (parent of ER membrane). PAINT node PTN000551966 (is_active_in), seeded by human GPAT3/GPAT4, mouse, worm, fly-less plant and Dictyostelium members. Reason: The PAINT placement of ER activity at a deep node of the GPAT3/GPAT4 (LPCAT1-like) family is consistent with every characterised member being an ER acyltransferase; human GPAT3 localises to the ER when expressed in COS-7 or CHO cells [PMID:17170135, PMID:19318427] and the UniProt location for the zebrafish protein is the ER membrane. Accepted, consistently with the more specific ER-membrane rows; the parent term is not an over-annotation. Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane PMID:17170135 GPAT3 is localized to the ER when overexpressed in COS-7 cells. |
| GO:0016747 acyltransferase activity, transferring groups other than amino-acyl groups | IEA GO_REF:0000120 | MODIFY | Summary: Acyltransferase activity transferring non-amino-acyl groups, from ARBA rule ARBA00027717 and the LPCAT1-like family signature (IPR045252). Reason: Correct but a broad parent; the acyl-CoA:glycerol-3-phosphate acyltransferase activity is the demonstrated activity of the orthologue [PMID:17170135, PMID:24714397] and is captured by GO:0004366. Modify to the specific term (the AGPAT activity is left undecided, see GO:0003841 rows). Proposed replacements: glycerol-3-phosphate O-acyltransferase activity Supporting Evidence: file:DANRE/gpat3/gpat3-uniprot.txt by incorporating an acyl moiety at the sn-1 position of the glycerol backbone PMID:24714397 Total GPAT activity in white adipose tissue of Gpat3(-/-) mice was reduced by 80%, suggesting that GPAT3 is the predominant GPAT in this tissue. |
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Download this section (compressed HTML)Q: Does zebrafish Gpat3 have glycerol-3-phosphate acyltransferase activity, lysophosphatidate acyltransferase activity, or both, when expressed in a null background such as GPAT-deficient cells?
Q: Which tissues express gpat3 in zebrafish (adipose, intestine, yolk syncytial layer?), and does loss of gpat3 reduce microsomal GPAT activity or lipid droplet formation in larvae?
Experiment: Express V5-tagged zebrafish Gpat3 in HEK-293 or COS-7 cells and assay acyltransferase activity in parallel with G3P and LPA as acceptors using [14C]acyl-CoA, alongside human GPAT3 as control, to resolve the GPAT-versus-AGPAT discrepancy for the zebrafish orthologue.
Hypothesis: Zebrafish Gpat3 is an NEM-sensitive GPAT that produces LPA from G3P, with little or no LPA acyltransferase activity.
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