The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The requested identity is coherent and unambiguous: human GPAM (HGNC:24865; UniProt Q9HCL2; synonyms GPAT1, KIAA1560) encodes mitochondrial glycerol-3-phosphate acyltransferase 1, EC 2.3.1.15. It is an integral outer mitochondrial membrane enzyme of the GPAT/DHAPAT, PlsB-like glycerolipid acyltransferase family. Its primary function is to transfer a long-chain fatty acyl group—preferentially a saturated chain, especially palmitoyl—from acyl-CoA to the sn-1 position of glycerol-3-phosphate, generating lysophosphatidic acid (LPA). This is the first committed and commonly rate-limiting reaction of de novo glycerolipid synthesis. No evidence reviewed here concerned a different gene sharing the GPAM symbol. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24, yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 4-7, zhang2024gpat1activityand pages 1-2)
| Feature | Validated annotation | Strongest evidence or qualification |
|---|---|---|
| Identity | Human GPAM; UniProt Q9HCL2; also called GPAT1 or mitochondrial glycerol-3-phosphate acyltransferase 1 | The accession and organism derive from the specified UniProt record. Literature independently identifies GPAT1 as a mitochondrial GPAT distinct from GPAT2, GPAT3, and GPAT4. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24) |
| Catalytic reaction | sn-Glycerol-3-phosphate + long-chain fatty acyl-CoA → 1-acyl-sn-glycerol-3-phosphate (LPA) + CoA; EC 2.3.1.15 | Acylation occurs at the sn-1 position and constitutes the first committed, commonly rate-limiting step of de novo glycerolipid synthesis. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 4-7, zhang2024gpat1activityand pages 1-2) |
| Family and catalytic architecture | Member of the GPAT/DHAPAT, PlsB-like glycerolipid acyltransferase family, consistent with the supplied InterPro domains; the conserved HXXXXD motif participates in catalysis | The family and domains are human database annotations. Motif functions are mechanistic inferences supported by biochemical and comparative analyses of GPAT-family enzymes. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 4-7) |
| Cellular location and topology | Integral outer mitochondrial membrane protein with two transmembrane helices, cytosolic N- and C-termini, an intermembrane-space loop, and a cytosol-facing active site | This topology gives the catalytic site access to cytosolic glycerol-3-phosphate and acyl-CoA. Detailed topology comes mainly from mammalian models rather than a high-resolution human GPAM structure. (nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24, daniel2015physiologicalconsequencesof pages 25-29) |
| Acyl-donor specificity | Accepts long-chain acyl-CoAs but favors saturated substrates, especially palmitoyl-CoA (16:0-CoA); activity with 16:0-CoA is approximately 2–3-fold higher than with 18:0- or 18:1-CoA | The preference is established mainly through mammalian and rodent enzyme assays and is consistent with enrichment of saturated downstream lipid species. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, daniel2015physiologicalconsequencesof pages 25-29) |
| Biochemical discriminator | GPAT1 activity is resistant to N-ethylmaleimide (NEM) | This distinguishes GPAT1 from mitochondrial GPAT2 and ER-localized GPAT3 and GPAT4, which are NEM-sensitive. NEM-resistant GPAT activity is commonly used as an operational measure of GPAT1. (zhang2024gpat1activityand pages 1-2, zhang2024gpat1activityand pages 3-5) |
| Pathway role | GPAM-generated LPA is converted successively to phosphatidic acid (PA) and diacylglycerol (DAG), then routed into triacylglycerol (TAG) or glycerophospholipid synthesis | GPAM influences glycerolipid flux and the fatty-acyl composition of downstream LPA, PA, DAG, TAG, and membrane phospholipids. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, heras2026targetingthemitochondrial pages 24-28) |
| Metabolic partitioning | In hepatocytes, GPAT1 channels newly synthesized fatty acids into TAG and away from mitochondrial beta-oxidation | Mouse Gpat1-null hepatocytes oxidized approximately 2-fold more exogenous fatty acid; knockout liver contained 3-fold more long-chain acylcarnitines after fasting and 3.5-fold more after fasting and refeeding. These are rodent mechanistic data, not human effect estimates. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9) |
| Regulation | Lipogenic conditions induce GPAT1 through SREBP1c and ChREBP; insulin- and LXR-associated signaling promote expression or activity, whereas glucagon, cAMP, and AMPK oppose it | This model integrates promoter, nutritional, and rodent or cell evidence. Transcriptional regulation is better established than some proposed acute phosphorylation mechanisms. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, nagle2007glycerol3phosphateacyltransferaseisoforms pages 30-35, zhang2024gpat1activityand pages 8-9) |
| 2024 mechanistic findings | In primary mouse hepatocytes, 25 mM glucose raised GPAT1 mRNA 5.7-fold, total GPAT activity 1.9-fold, and NEM-resistant activity 1.8-fold; GPAT1 overexpression raised NEM-resistant activity 4.0-fold and di-16:0 PA approximately 4.4-fold, or 5.3-fold with 200 μM palmitate | High glucose reduced insulin suppression of glucose production from 58.1% to 31.3%, while added palmitate abolished suppression. High glucose inhibited insulin-stimulated Akt Ser473 phosphorylation by 51%, increasing to 98% with palmitate. These cultured-mouse-hepatocyte results support a GPAT1–di-16:0-PA–mTORC2/Akt mechanism but are not human clinical evidence. (zhang2024gpat1activityand pages 6-8, zhang2024gpat1activityand pages 8-9, zhang2024gpat1activityand pages 5-6, zhang2024gpat1activityand pages 3-5) |
Table: Core annotation of human GPAM/Q9HCL2 with supporting biochemical and mechanistic evidence. Human annotations are distinguished from findings in rodent and cultured-cell systems.
The literature’s biochemical description matches the supplied UniProt annotation: mitochondrial GPAT1 is encoded by GPAM, acts as an acyl-CoA:glycerol-3-phosphate acyltransferase, resides in the mitochondrial outer membrane, favors palmitoyl-CoA, and is resistant to N-ethylmaleimide (NEM). These combined features distinguish it from every other mammalian GPAT isoform. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24, zhang2024gpat1activityand pages 1-2)
The supplied InterPro assignments—GPAT/DHAPAT, GPAT/DHAPAT_C, GPAT/DHAPAT_LPLAT, GPAT_PlsB, and phospholipid/glycerol acyltransferase—are therefore consistent with the established enzymology and evolutionary family. No contradictory family or organism assignment was found.
sn-Glycerol-3-phosphate + long-chain fatty acyl-CoA → 1-acyl-sn-glycerol-3-phosphate (LPA) + CoA
GPAM acylates the glycerol backbone at sn-1. The product is therefore 1-acyl-LPA rather than phosphatidic acid or triacylglycerol itself. LPA is subsequently acylated by AGPAT enzymes to phosphatidic acid (PA), dephosphorylated by lipins/phosphatidate phosphatases to diacylglycerol (DAG), and either acylated by DGAT to triacylglycerol (TAG) or routed into glycerophospholipid synthesis. (heras2026targetingthemitochondrial pages 24-28, nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24, yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 4-7, zhang2024gpat1activityand pages 1-2)
The reaction is considered the first committed—and often rate-limiting—step in de novo glycerolipid synthesis because it commits glycerol-3-phosphate and activated fatty acid to an LPA-centered biosynthetic pathway. Nevertheless, “rate-limiting” is physiological and context-dependent rather than an invariant property in every tissue. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, zhang2024gpat1activityand pages 1-2)
GPAT1 uses multiple long-chain acyl-CoAs but favors saturated acyl donors, particularly palmitoyl-CoA (16:0-CoA). Mammalian assays report approximately two- to threefold greater activity with 16:0-CoA than with stearoyl- or oleoyl-CoA. This preference helps explain the enrichment of saturated species such as di-16:0 PA downstream when GPAT1 activity and palmitate availability are high. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, daniel2015physiologicalconsequencesof pages 25-29, zhang2024gpat1activityand pages 6-8)
NEM resistance is a useful operational biochemical marker. In membrane preparations, 1 mM NEM inhibits GPAT2–4 but not GPAT1; consequently, activity remaining after NEM treatment is commonly interpreted as GPAT1 activity. The 2024 assay directly measured incorporation of radiolabeled glycerol-3-phosphate into 16:0-LPA using 82.5 μM palmitoyl-CoA. (zhang2024gpat1activityand pages 1-2, zhang2024gpat1activityand pages 3-5)
GPAM belongs to the GPAT/DHAPAT class of membrane-associated glycerolipid acyltransferases. The conserved HXXXXD motif is central to catalysis: histidine is proposed to act as a general base, activating the glycerol-3-phosphate hydroxyl, while aspartate contributes to charge relay. Conserved motifs II and III are implicated in glycerol-3-phosphate recognition, and motif IV may contribute to acyl-CoA binding. These assignments derive mainly from comparative sequence analysis and family-wide mutagenesis rather than an atomic-resolution structure of full-length human Q9HCL2. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 4-7)
Topology studies support two transmembrane segments, with both termini and the catalytic site exposed to the cytosol and the connecting loop facing the mitochondrial intermembrane space. This arrangement is chemically sensible because both glycerol-3-phosphate and long-chain acyl-CoA are supplied from the cytosolic side. The resulting LPA must subsequently reach downstream enzymes, many of which reside in the ER; liver fatty-acid-binding protein can mediate mitochondrial-to-ER LPA transfer in vitro, although the complete trafficking mechanism in intact human cells remains incompletely resolved. (nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24, daniel2015physiologicalconsequencesof pages 25-29)
The functional site is the cytosolic face of the mitochondrial outer membrane, not the matrix or inner membrane. GPAT1 and mitochondrial CPT1 therefore occupy a strategically important interface where long-chain acyl-CoAs can be partitioned between esterification and mitochondrial β-oxidation. (nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24, nagle2007glycerol3phosphateacyltransferaseisoforms pages 30-35)
GPAT1 is especially important in lipogenic tissues. Older mammalian estimates attribute approximately 40–50% of total hepatic GPAT activity to GPAT1, compared with roughly 10–20% in most other tissues. Expression and activity are high in liver and adipose tissue, with additional expression in muscle, kidney, brain, and epidermal cells. These percentages are biochemical estimates from mammalian tissues rather than modern quantitative human proteomic fractions. (daniel2015physiologicalconsequencesof pages 25-29, nagle2007glycerol3phosphateacyltransferaseisoforms pages 24-25)
GPAM supplies LPA for synthesis of PA, DAG, TAG, and membrane glycerophospholipids. Because GPAT1 favors palmitoyl-CoA, it influences not only pathway flux but also downstream lipid molecular species. In GPAT1-overexpressing CHO cells, DAG and TAG labeling rose approximately twofold, TAG mass rose two- to threefold, and phospholipid labeling fell by about 30%, illustrating that increased GPAT1 can redistribute glycerolipid intermediates toward storage lipid under suitable substrate conditions. (nagle2007glycerol3phosphateacyltransferaseisoforms pages 24-25)
GPAT1 channels newly synthesized fatty acids—particularly de novo synthesized palmitate—toward esterification and away from oxidation. In mouse Gpat1-null hepatocytes, oxidation of exogenous fatty acid was approximately twofold higher; long-chain hepatic acylcarnitines were approximately threefold higher after fasting and 3.5-fold higher after fasting/high-sucrose refeeding. These experiments demonstrate metabolic partitioning, although they should not be interpreted as human effect sizes. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9)
AMPK reinforces the opposite metabolic state: it inhibits GPAT1 while lowering malonyl-CoA through ACC inhibition, relieving CPT1 restraint and favoring β-oxidation. Thus, GPAM is best understood as a mitochondrial-surface branch-point enzyme coupling nutritional state to the choice between lipid storage/membrane synthesis and fatty-acid catabolism. (nagle2007glycerol3phosphateacyltransferaseisoforms pages 30-35)
GPAT1-generated products are not merely biosynthetic intermediates. LPA, PA, and DAG can participate in signaling. Evidence also associates GPAT1-dependent LPA with mitochondrial fusion, although this remains less comprehensively defined than its glycerolipid-synthetic function. Overexpressing GPAT1 in CHO cells increased LPA, PPARγ activity, and expression of the PPARγ target CD36. These results indicate potential intracellular signaling functions but do not establish a universal GPAM–PPARγ pathway in human tissues. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, heras2026targetingthemitochondrial pages 24-28)
GPAM is strongly nutritionally regulated:
Acute regulation by phosphorylation has been proposed. Insulin may increase activity, AMPK may inhibit it, and CK2 treatment of isolated rat mitochondria increased activity approximately twofold. The transcriptional response to carbohydrate is better established than the physiological importance and exact sites of every proposed phosphorylation event. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, nagle2007glycerol3phosphateacyltransferaseisoforms pages 30-35)
Zhang and colleagues, published online 13 February 2024 in The Journal of Nutrition, tested GPAT1 directly in primary hepatocytes from male C57BL/6J mice. Cells were exposed to 5.5 or 25 mM glucose, adenovirally overexpressed GPAT1 or GPAT3, and in some conditions received 200 μM palmitate or linoleate. This is a mechanistically precise study, but it is an ex vivo mouse experiment—not a human clinical study. DOI/URL: https://doi.org/10.1016/j.tjnut.2024.02.004. (zhang2024gpat1activityand pages 1-2, zhang2024gpat1activityand pages 2-3, zhang2024gpat1activityand pages 3-5)
Key quantitative observations were:
The authors’ mechanistic interpretation is that carbohydrate-responsive induction of GPAT1, together with abundant palmitate, increases di-16:0 PA. This lipid species disrupts mTOR–rictor/mTORC2 assembly, reduces Akt activation, and weakens insulin suppression of hepatic glucose production. This is strong pathway-level evidence but remains a model requiring confirmation in human liver in vivo. (zhang2024gpat1activityand pages 2-3, zhang2024gpat1activityand pages 8-9)
GPAM is biologically plausible in metabolic dysfunction-associated steatotic liver disease because it promotes hepatic glycerolipid synthesis and determines whether newly synthesized saturated fatty acids enter TAG or oxidation. Human genetics and recent functional-genomic studies have nominated GPAM as a regulator of hepatocyte lipid accumulation, but the evidence retrieved here did not provide sufficiently detailed human effect estimates to report responsibly. The strongest causal mechanistic evidence remains cellular and rodent work.
Importantly, TAG storage and insulin resistance are not identical phenotypes. GPAT1 deficiency can reduce hepatic steatosis without necessarily restoring insulin sensitivity in every mouse model, and different GPAT isoforms generate spatially distinct lipid pools. Expert interpretation therefore emphasizes compartmentalized LPA/PA/DAG signaling, rather than assuming total hepatic TAG alone drives insulin resistance. (daniel2015physiologicalconsequencesof pages 25-29, nagle2007glycerol3phosphateacyltransferaseisoforms pages 24-25, nagle2007glycerol3phosphateacyltransferaseisoforms pages 30-35)
GPAM is being investigated as a metabolic target for reducing hepatic lipid synthesis, saturated PA signaling, and possibly tumor-associated lipid metabolism. Current practical implementations are preclinical: genetic knockdown/knockout, adenoviral manipulation, NEM-resistant activity assays, lipidomics, and experimental GPAT inhibitors. No approved GPAM-selective medicine, validated companion diagnostic, or established GPAM-directed clinical treatment was identified in the reviewed evidence. Broad GPAT inhibition also presents a selectivity problem because GPAT1–4 occupy different organelles and produce functionally distinct lipid pools.
A rational translational strategy would require GPAT1-selective compounds, confirmation of target engagement through NEM-resistant activity or isotope tracing, and lipidomic monitoring of LPA/PA species—especially di-16:0 PA—rather than relying solely on total TAG. Potential liabilities include altered membrane-phospholipid composition, excessive fatty-acid oxidation, mitochondrial effects, and tissue-specific responses.
High-confidence annotation: identity as human mitochondrial GPAT1; EC 2.3.1.15 reaction; outer-mitochondrial-membrane localization; NEM resistance; preference for saturated acyl-CoA/palmitoyl-CoA; role in initiating LPA-dependent glycerolipid synthesis. (yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 7-9, nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24, yamashita2014glycerophosphateacylglycerophosphateacyltransferases pages 4-7, zhang2024gpat1activityand pages 1-2)
Strong mechanistic but largely nonhuman evidence: metabolic competition with β-oxidation; carbohydrate/SREBP1c/ChREBP regulation; saturated PA–mTORC2–Akt signaling; effects on hepatic glucose production. (nagle2007glycerol3phosphateacyltransferaseisoforms pages 30-35, zhang2024gpat1activityand pages 6-8, zhang2024gpat1activityand pages 8-9, zhang2024gpat1activityand pages 5-6)
Still incomplete: an experimentally resolved full-length human GPAM structure; exact human tissue-specific flux contribution; mechanisms transferring mitochondrial LPA to ER pathways; consequences of common human GPAM variants; and clinical safety or efficacy of selective GPAM inhibition.
Overall, the most defensible functional annotation is that GPAM/GPAT1 is a cytosol-facing mitochondrial outer-membrane gatekeeper that preferentially commits newly synthesized saturated fatty acyl-CoA—especially palmitoyl-CoA—to LPA and downstream glycerolipid synthesis, thereby influencing both lipid storage and lipid-mediated signaling at the interface with fatty-acid oxidation.
References
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(nagle2007glycerol3phosphateacyltransferaseisoforms pages 21-24): CA Nagle. Glycerol-3-phosphate acyltransferase isoforms: hepatic triacylglycerol synthesis and the development of insulin resistance. Unknown journal, 2007.
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(zhang2024gpat1activityand pages 1-2): Chongben Zhang, Mathew Steadman, Hudson P Santos, Saame R Shaikh, and Rose Mary Xavier. Gpat1 activity and abundant palmitic acid impair insulin suppression of hepatic glucose production in primary mouse hepatocytes. Apr 2024. URL: https://doi.org/10.1016/j.tjnut.2024.02.004, doi:10.1016/j.tjnut.2024.02.004. This article has 5 citations.
(daniel2015physiologicalconsequencesof pages 25-29): Physiological Consequences of Compartmentalized Glycerolipid Synthesis This article has 0 citations and is from a peer-reviewed journal.
(zhang2024gpat1activityand pages 3-5): Chongben Zhang, Mathew Steadman, Hudson P Santos, Saame R Shaikh, and Rose Mary Xavier. Gpat1 activity and abundant palmitic acid impair insulin suppression of hepatic glucose production in primary mouse hepatocytes. Apr 2024. URL: https://doi.org/10.1016/j.tjnut.2024.02.004, doi:10.1016/j.tjnut.2024.02.004. This article has 5 citations.
(heras2026targetingthemitochondrial pages 24-28): M Alvarez de las Heras. Targeting the mitochondrial lysophosphatidic acid-producing enzyme glycerol-3-phosphate acyltransferase 1 in ovarian cancer using a stable knockdown …. Unknown journal, 2026.
(nagle2007glycerol3phosphateacyltransferaseisoforms pages 30-35): CA Nagle. Glycerol-3-phosphate acyltransferase isoforms: hepatic triacylglycerol synthesis and the development of insulin resistance. Unknown journal, 2007.
(zhang2024gpat1activityand pages 8-9): Chongben Zhang, Mathew Steadman, Hudson P Santos, Saame R Shaikh, and Rose Mary Xavier. Gpat1 activity and abundant palmitic acid impair insulin suppression of hepatic glucose production in primary mouse hepatocytes. Apr 2024. URL: https://doi.org/10.1016/j.tjnut.2024.02.004, doi:10.1016/j.tjnut.2024.02.004. This article has 5 citations.
(zhang2024gpat1activityand pages 6-8): Chongben Zhang, Mathew Steadman, Hudson P Santos, Saame R Shaikh, and Rose Mary Xavier. Gpat1 activity and abundant palmitic acid impair insulin suppression of hepatic glucose production in primary mouse hepatocytes. Apr 2024. URL: https://doi.org/10.1016/j.tjnut.2024.02.004, doi:10.1016/j.tjnut.2024.02.004. This article has 5 citations.
(zhang2024gpat1activityand pages 5-6): Chongben Zhang, Mathew Steadman, Hudson P Santos, Saame R Shaikh, and Rose Mary Xavier. Gpat1 activity and abundant palmitic acid impair insulin suppression of hepatic glucose production in primary mouse hepatocytes. Apr 2024. URL: https://doi.org/10.1016/j.tjnut.2024.02.004, doi:10.1016/j.tjnut.2024.02.004. This article has 5 citations.
(nagle2007glycerol3phosphateacyltransferaseisoforms pages 24-25): CA Nagle. Glycerol-3-phosphate acyltransferase isoforms: hepatic triacylglycerol synthesis and the development of insulin resistance. Unknown journal, 2007.
(zhang2024gpat1activityand pages 2-3): Chongben Zhang, Mathew Steadman, Hudson P Santos, Saame R Shaikh, and Rose Mary Xavier. Gpat1 activity and abundant palmitic acid impair insulin suppression of hepatic glucose production in primary mouse hepatocytes. Apr 2024. URL: https://doi.org/10.1016/j.tjnut.2024.02.004, doi:10.1016/j.tjnut.2024.02.004. This article has 5 citations.