Gpat2 encodes glycerol-3-phosphate acyltransferase 2, mitochondrial (GPAT2), an ~89 kDa integral protein of the mitochondrial outer membrane with two transmembrane segments and cytosol-facing N- and C-terminal regions, including the catalytic acyltransferase (HXXXXD) domain. It belongs to the GPAT/DHAPAT family and is the paralog of GPAT1 (Gpam). GPAT2 is an N-ethylmaleimide-sensitive glycerol-3-phosphate acyltransferase that transfers an acyl group from acyl-CoA to the sn-1 position of sn-glycerol 3-phosphate to form lysophosphatidic acid, the first step of de novo glycerolipid synthesis; unlike GPAT1 it prefers arachidonoyl-CoA, and its overexpression channels arachidonate into triacylglycerol and increases phosphatidic acid production (an additional 1-acylglycerol-3-phosphate acyltransferase activity has been reported in membranes of overexpressing cells). Gpat2 is expressed mainly in the testis, transiently in pachytene spermatocytes, under control of promoter methylation and retinoic acid. Separately from its catalytic activity, GPAT2 binds the PIWI protein MILI (PIWIL2) and is required for primary piRNA biogenesis in male germ cells; catalytically dead HXXXXD mutants still support piRNA production, suggesting a scaffolding role on the mitochondrial surface. Loss of GPAT2 in mice impairs piRNA production, derepresses IAP and LINE-1 retrotransposons in fetal testis, and causes germ cell apoptosis and defective spermatogenesis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003841 1-acylglycerol-3-phosphate O-acyltransferase activity | IDA PMID:22905194 Glycerol-3-phosphate acyltransferase-2 is expressed in sperm... | KEEP AS NON CORE | Summary: AGPAT activity was increased in total membranes of CHO-K1 cells overexpressing mouse GPAT2, most strongly with arachidonoyl-CoA. Reason: The paper shows increased AGPAT activity and PA formation in crude membranes of overexpressing cells. The authors themselves present this as possibly a second activity of GPAT2 and could not separate a direct activity from an indirect effect on endogenous AGPATs; no purified-protein assay exists. The activity is plausible and is recorded by UniProt, but it is secondary to the established GPAT (sn-1 acylation) activity, so it is retained as non-core. Supporting Evidence: PMID:22905194 GPAT2 overexpression increased AGPAT activity ∼50% with oleoyl-CoA and 2- fold when arachidonoyl-CoA was used as substrate, confirming the preference of GPAT2 for this fatty acid. PMID:22905194 These findings suggest that the increase in PA may be due to an AGPAT activity for this heterologously-expressed protein, but we cannot exclude the possibility that the protein has dual enzymatic activities. |
| GO:0003841 1-acylglycerol-3-phosphate O-acyltransferase activity | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Electronic mapping from UniProt's curated AGPAT catalytic-activity lines, which themselves rest on PMID:22905194. Reason: Same claim as the IDA row from PMID:22905194; the underlying evidence comes from membranes of overexpressing cells and the authors left open whether the activity is intrinsic. Kept, as non-core, consistent with that row. Supporting Evidence: PMID:22905194 GPAT2 overexpression significantly increased both GPAT and AGPAT activities only when arachidonoyl-CoA was used as a substrate |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | EXP PMID:22905194 Glycerol-3-phosphate acyltransferase-2 is expressed in sperm... | ACCEPT | Summary: GPAT activity of overexpressed mouse GPAT2 measured with radiolabelled glycerol-3-phosphate and a panel of acyl-CoAs; activity was specific for arachidonoyl-CoA. Reason: Direct enzyme assay of the mouse protein expressed in two cell lines, with acyl-CoA specificity. This is the core catalytic activity of the gene product. Supporting Evidence: PMID:22905194 GPAT2 overexpression significantly increased GPAT activity only when arachidonoyl-CoA was used as a substrate. PMID:22905194 we have identified mitochondrial GPAT2 as an acyltransferase that prefers arachidonoyl-CoA. |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBD at the eumetazoan GPAT1/GPAT2 node PTN000970957; mouse Gpat2 itself is one of the experimental donors. Reason: Gpat2 sits in PANTHER subfamily PTHR12563:SF15 below PTN000970957, and the activity is experimentally established for this very protein, so the phylogenetic inference is sound. The target appearing among the donors reflects its own experimental grounding. Supporting Evidence: PMID:17689486 When Cos-7 cells were transiently transfected with GPAT2, NEM-sensitive GPAT activity increased 30%. |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | IDA PMID:14724270 Identification of a new glycerol-3-phosphate acyltransferase... | ACCEPT | Summary: Lewin et al. detected a novel NEM-sensitive GPAT activity (named mtGPAT2) in liver mitochondria of GPAT1-null mice, before the Gpat2 gene was cloned. Reason: The activity measured is a native mitochondrial NEM-sensitive GPAT activity, and later cloning work showed Gpat2 encodes a mitochondrial NEM-sensitive GPAT. The abstract alone does not identify the activity with the Gpat2 gene product, but MGI curators read the full paper and the claim (GPAT activity) is independently established for this protein, so the annotation is kept rather than second-guessed. Supporting Evidence: PMID:14724270 We conclude that a novel GPAT (mtGPAT2) with antigenic epitopes similar to those of mtGPAT is detectable in mitochondria from the livers of mtGPAT(-/-) mice. |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | IDA PMID:17689486 Cloning and functional characterization of a novel mitochond... | ACCEPT | Summary: Cloned mouse GPAT2 increased NEM-sensitive GPAT activity when expressed in Cos-7 cells. Reason: Direct assay of the cloned mouse protein; core activity. Supporting Evidence: PMID:17689486 When Cos-7 cells were transiently transfected with GPAT2, NEM-sensitive GPAT activity increased 30%. PMID:17013544 xGPAT1 was distributed in the membrane fraction and showed GPAT activity when epitope-tagged xGPAT1 was expressed in Chinese hamster ovary (CHO)-K1 cells. |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic mapping from UniProt's curated GPAT reaction (RHEA:15325, RHEA:37463). Reason: Consistent with the experimental rows; the UniProt reaction is curated from PMID:22905194. Supporting Evidence: PMID:22905194 GPAT2 overexpression significantly increased GPAT activity only when arachidonoyl-CoA was used as a substrate. |
| GO:0004366 glycerol-3-phosphate O-acyltransferase activity | ISO GO_REF:0000119 | ACCEPT | Summary: Automated mouse-human ortholog transfer from human GPAT2 (Q6NUI2). Reason: The term is correct for mouse GPAT2 on its own experimental evidence. Note that human GPAT2 annotations are themselves ISS transfers from this mouse protein, so this row adds no independent support; it is accepted for consistency with the experimental rows for the same term. Supporting Evidence: PMID:17689486 When Cos-7 cells were transiently transfected with GPAT2, NEM-sensitive GPAT activity increased 30%. |
| GO:0005515 protein binding | IPI PMID:23611983 GPAT2, a mitochondrial outer membrane protein, in piRNA biog... | REMOVE | Summary: GPAT2 co-immunoprecipitates with MILI (PIWIL2, Q8CDG1) in germline stem cells, testis and transfected HEK293T cells. Reason: Bare protein binding is uninformative. The MILI interaction is real and well supported (co-IP plus mass spectrometry, confirmed in testis), and is captured in core_functions under the piRNA role; but no informative molecular-function term fits, because the mechanism of GPAT2 action in piRNA biogenesis is unknown (a scaffold role is only proposed). Removal does not mean the interaction is false. Supporting Evidence: PMID:23611983 Binding of MILI to GPAT2 was confirmed by coimmunoprecipitation analysis of testis samples |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBD for mitochondrion at PTN000970957. Reason: Correct but general. The protein is an integral outer-membrane protein (topology study, and repeatedly described as such), and the gene already carries mitochondrial outer membrane (GO:0005741, a part_of descendant), which is the precise location. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000970957 SUPPORTS TRANSFER Gpat2 (PTHR12563:SF15) descends from this GPAT1/GPAT2 node and has its own experimental evidence; the node-level term is correct but more general than the gene-specific evidence supports. Proposed replacements: mitochondrial outer membrane Supporting Evidence: PMID:22285183 These results suggest that the GPAT2 protein has two transmembrane segments and that the N-terminal and C-terminal regions of this protein face the cytoplasm. PMID:23611983 glycerol-3-phosphate acyltransferase 2 (GPAT2), a mitochondrial outer membrane protein |
| GO:0005739 mitochondrion | IDA PMID:14724270 Identification of a new glycerol-3-phosphate acyltransferase... | MODIFY | Summary: NEM-sensitive GPAT activity and an immunoreactive protein were detected in liver mitochondrial fractions of GPAT1-null mice. Reason: Mitochondrial location is correct; the more precise supported location is the mitochondrial outer membrane (GO:0005741), which the gene already carries. Proposed replacements: mitochondrial outer membrane Supporting Evidence: PMID:14724270 we detected a novel NEM-sensitive GPAT activity in mitochondrial fractions and an anti-mtGPAT immunoreactive protein in liver mitochondria, but not in microsomes. PMID:22285183 These results suggest that the GPAT2 protein has two transmembrane segments and that the N-terminal and C-terminal regions of this protein face the cytoplasm. |
| GO:0005739 mitochondrion | IDA PMID:17689486 Cloning and functional characterization of a novel mitochond... | MODIFY | Summary: Confocal microscopy of transfected Cos-7 cells showed mitochondrial location. Reason: Correct but general; refine to mitochondrial outer membrane (GO:0005741), already on the gene and supported by the topology study. Proposed replacements: mitochondrial outer membrane Supporting Evidence: PMID:17689486 Confocal microscopy confirmed a mitochondrial location. PMID:22285183 These results suggest that the GPAT2 protein has two transmembrane segments and that the N-terminal and C-terminal regions of this protein face the cytoplasm. |
| GO:0005741 mitochondrial outer membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (Mitochondrion outer membrane), curated from PMID:17013544, PMID:17689486 and PMID:22285183. Reason: Precise, experimentally supported location of the protein and of its catalytic domain (cytosolic face of the outer membrane). Supporting Evidence: PMID:22285183 These results suggest that the GPAT2 protein has two transmembrane segments and that the N-terminal and C-terminal regions of this protein face the cytoplasm. file:mouse/Gpat2/Gpat2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion outer membrane |
| GO:0005741 mitochondrial outer membrane | ISO GO_REF:0000096 | ACCEPT | Summary: Automated mouse-rat ortholog transfer from rat Gpat2. Reason: Correct; directly supported for the mouse protein as well. Supporting Evidence: PMID:22285183 These results suggest that the GPAT2 protein has two transmembrane segments and that the N-terminal and C-terminal regions of this protein face the cytoplasm. |
| GO:0005741 mitochondrial outer membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Curator sequence-similarity transfer from rat GPAT2 (D3ZI76). Reason: Correct; consistent with mouse topology data. Supporting Evidence: PMID:23611983 glycerol-3-phosphate acyltransferase 2 (GPAT2), a mitochondrial outer membrane protein |
| GO:0006072 glycerol-3-phosphate metabolic process | IDA PMID:14724270 Identification of a new glycerol-3-phosphate acyltransferase... | KEEP AS NON CORE | Summary: Reflects the GPAT reaction, which consumes sn-glycerol 3-phosphate. Reason: GPAT2 acylates glycerol-3-phosphate, so it formally participates in glycerol-3-phosphate metabolism. The biologically informative process is the glycerolipid synthesis it initiates (phosphatidic acid and triacylglycerol biosynthesis, captured elsewhere); GO:0006072 is not an ancestor of those, so this is kept as a correct but peripheral substrate-centred description. Supporting Evidence: PMID:14724270 Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the initial and rate-limiting step of glycerolipid synthesis. |
| GO:0006072 glycerol-3-phosphate metabolic process | IDA PMID:17689486 Cloning and functional characterization of a novel mitochond... | KEEP AS NON CORE | Summary: As above; reflects consumption of glycerol-3-phosphate by the GPAT reaction. Reason: Consistent with the PMID:14724270 row for the same term. Supporting Evidence: PMID:17689486 Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the initial and rate-limiting step in glycerolipid synthesis. |
| GO:0006629 lipid metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the GPAT/DHAPAT family signature. Reason: Correct but very general. The gene's supported processes are phosphatidic acid biosynthesis (GO:0006654) and triglyceride biosynthesis (GO:0019432), both descendants of lipid metabolic process and both already on the gene. Proposed replacements: phosphatidic acid biosynthetic process triglyceride biosynthetic process Supporting Evidence: PMID:22905194 With arachidonoyl-CoA, GPAT2 overexpression increased the synthesis of PA, whereas the synthesis of LPA was not affected. PMID:17689486 increased incorporation of [(14)C]oleate into TAG 84% |
| GO:0006650 glycerophospholipid metabolic process | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBD at PTN000970957 for glycerophospholipid metabolism. Reason: The clade-level inference is sound (GPATs make lysophosphatidic acid, the first glycerophospholipid intermediate), but the term is general. The specific supported process for GPAT2 is phosphatidic acid biosynthesis (GO:0006654, an is_a descendant already on the gene). Note that in transfected cells GPAT2 directed fatty acid toward TAG and away from bulk phospholipid, so a broader phospholipid-synthesis role is not supported. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000970957 SUPPORTS TRANSFER Gpat2 (PTHR12563:SF15) descends from this GPAT1/GPAT2 node and has its own experimental evidence; the node-level term is correct but more general than the gene-specific evidence supports. Proposed replacements: phosphatidic acid biosynthetic process Supporting Evidence: PMID:22905194 With arachidonoyl-CoA, GPAT2 overexpression increased the synthesis of PA, whereas the synthesis of LPA was not affected. |
| GO:0006654 phosphatidic acid biosynthetic process | IMP PMID:22905194 Glycerol-3-phosphate acyltransferase-2 is expressed in sperm... | ACCEPT | Summary: GPAT2 overexpression increased PA synthesis from glycerol-3-phosphate and arachidonoyl-CoA. Reason: GPAT2 catalyses the first acylation (to LPA) and possibly the second (to PA), so it performs steps of PA biosynthesis. The evidence is from overexpression rather than loss of function, but the process assignment follows directly from the measured activity. Supporting Evidence: PMID:22905194 With arachidonoyl-CoA, GPAT2 overexpression increased the synthesis of PA, whereas the synthesis of LPA was not affected. |
| GO:0016024 CDP-diacylglycerol biosynthetic process | IEA GO_REF:0000041 | KEEP AS NON CORE | Summary: UniPathway mapping (CDP-diacylglycerol from sn-glycerol 3-phosphate, step 1/3). Reason: The GPAT reaction is formally step 1 of the UniPathway route to CDP-diacylglycerol, so the annotation is not wrong. However there is no evidence that GPAT2-derived PA feeds CDP-diacylglycerol synthesis specifically; in overexpressing cells GPAT2 channelled fatty acid into TAG and reduced incorporation into phospholipids. Kept as non-core. Supporting Evidence: file:mouse/Gpat2/Gpat2-uniprot.txt PATHWAY: Phospholipid metabolism; CDP-diacylglycerol biosynthesis; CDP- PMID:17689486 In contrast, incorporation into phospholipid species was lower than in control cells. |
| GO:0016746 acyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the phospholipid/glycerol acyltransferase domain. Reason: Correct but general; the specific activity, glycerol-3-phosphate O-acyltransferase activity (GO:0004366, an is_a descendant), is experimentally established and already on the gene. Proposed replacements: glycerol-3-phosphate O-acyltransferase activity Supporting Evidence: PMID:22905194 GPAT2 overexpression significantly increased GPAT activity only when arachidonoyl-CoA was used as a substrate. |
| GO:0016747 acyltransferase activity, transferring groups other than amino-acyl groups | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the GPAT/DHAPAT family signature. Reason: Correct but general; refine to glycerol-3-phosphate O-acyltransferase activity (GO:0004366, an is_a descendant), which is experimentally established and already on the gene. Proposed replacements: glycerol-3-phosphate O-acyltransferase activity Supporting Evidence: PMID:17689486 When Cos-7 cells were transiently transfected with GPAT2, NEM-sensitive GPAT activity increased 30%. |
| GO:0019432 triglyceride biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBD at PTN000970957 for triglyceride biosynthesis; mouse Gpat2 is a donor. Reason: GPAT2 catalyses the first step of de novo TAG synthesis and its expression increases TAG synthesis and arachidonate-rich TAG in cells, consistent with the clade-level inference. Supporting Evidence: PMID:22905194 Consistently, arachidonic acid was present in the TAG fraction of cells that overexpressed GPAT2, but not in control cells, corroborating GPAT2's role in synthesizing TAG that is rich in arachidonic acid. |
| GO:0019432 triglyceride biosynthetic process | IDA PMID:17689486 Cloning and functional characterization of a novel mitochond... | ACCEPT | Summary: GPAT2 expression in Cos-7 cells increased [14C]oleate incorporation into TAG. Reason: Supports GPAT2's role in initiating TAG synthesis; consistent with the IBA row. Supporting Evidence: PMID:17689486 increased incorporation of [(14)C]oleate into TAG 84% |
| GO:0034587 piRNA processing | IMP PMID:23611983 GPAT2, a mitochondrial outer membrane protein, in piRNA biog... | MODIFY | Summary: GPAT2 knockdown in MILI-rescued germline stem cells severely impaired piRNA production; small-RNA profiles resembled MILI-null cells, indicating a defect in primary processing. Reason: Correct, and the paper specifically localises the defect to the primary piRNA processing pathway, so the precise term is primary piRNA processing (GO:0140990, is_a GO:0034587, checked via OLS). GPAT2 is not merely a substrate or upstream requirement here; it binds MILI, a core primary-processing component, and the requirement is independent of its acyltransferase activity (HXXXXD mutants rescue), consistent with a proposed structural/scaffold contribution on the mitochondrial outer membrane. The in vivo knockout (PMID:30951587) confirms defective piRNA production. The exact mechanism remains unknown. This role is GPAT2-specific and was not propagated by PAINT to the GPAT1/GPAT2 node. Proposed replacements: primary piRNA processing Supporting Evidence: PMID:23611983 These data clearly show that GPAT2 plays a critical role in primary processing during piRNA production. PMID:23611983 These data suggest that the acyltransferase activity of GPAT2 is dispensable for the biogenesis of piRNA. PMID:30951587 The deficient mice showed defective piRNA production and subsequent de-silencing of IAP and Line-1 retrotransposons in fetal testes. |
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Download this section (compressed HTML)Q: Is the AGPAT (LPA to PA) activity seen in membranes of GPAT2-overexpressing cells intrinsic to GPAT2, or due to induced or co-operating endogenous AGPATs?
Q: What molecular activity does GPAT2 contribute to primary piRNA processing independently of catalysis? Does it act as an adaptor that recruits MILI or other machinery to the mitochondrial outer membrane?
Q: Human GPAT2 annotations are ISS transfers from mouse; should ortholog transfers of the piRNA role be limited to the GPAT2 subfamily (PTHR12563:SF15) and not extended to GPAT1?
Experiment: Assay purified or reconstituted recombinant GPAT2 for GPAT and AGPAT activity with defined acyl-CoAs (including arachidonoyl-CoA) to determine kinetics and whether it has dual activity.
Type: in vitro enzyme assay
Experiment: Map the MILI-binding region of GPAT2 by deletion/point mutants and test which mutants fail to rescue piRNA production in Gpat2-knockdown germline stem cells, to separate a scaffold role from catalysis.
Type: mutagenesis and rescue
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Download this section (compressed HTML)Loading supporting content…
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