{"gene":"LRAT","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2014,"finding":"A 2.2-Å crystal structure of an HRASLS3-LRAT chimeric enzyme in a thioester catalytic intermediate state revealed that the LRAT-specific domain causes domain-swapping dimerization not observed in native HRASLS proteins. Structural changes affecting the active site environment contributed to slower hydrolysis of the catalytic intermediate, supporting efficient acyl transfer to retinol substrate. This identified the structural basis for LRAT's substrate specificity within the NlpC/P60 protein family.","method":"Gain-of-function domain-swap chimera, 2.2-Å crystal structure of thioester intermediate, in vitro enzymatic assay","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure at 2.2 Å of catalytic intermediate combined with gain-of-function mutagenesis and in vitro activity assays in a single rigorous study","pmids":["25383759"],"is_preprint":false},{"year":2005,"finding":"LRAT is the predominant enzyme responsible for physiologic retinol esterification in liver, lung, kidney, and retinal pigment epithelium. Lrat-/- mice have only trace retinyl esters in these tissues and absorb dietary retinol primarily as free retinol in chylomicrons. The fatty acyl composition of residual chylomicron retinyl esters in Lrat-/- mice suggests synthesis via an acyl-CoA-dependent acyltransferase (ARAT) pathway in adipose tissue, which also shows elevated CRBPIII expression and compensatory retinyl ester storage.","method":"Lrat knockout mouse (Lrat-/-), HPLC retinoid quantification, electron microscopy of hepatic stellate cells, chylomicron fractionation, fatty acyl composition analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple orthogonal readouts (HPLC, EM, fractionation), replicated across tissues","pmids":["16115871"],"is_preprint":false},{"year":2007,"finding":"LRAT activity is localized exclusively to endoplasmic reticulum (ER)-enriched membranes in bovine RPE, whereas 11-cis retinyl ester hydrolase (REH) activity is in plasma membrane fractions, indicating subcellular compartmentalization of the visual cycle. LRAT is not required for RPE65's association with membranes or for RPE65 isomerase activity beyond its role in synthesizing the retinyl ester substrate; Rpe65 membrane affinity is similar in wild-type and lrat-/- mice, and mass spectrometry showed that Cys231, Cys329, and Cys330 of RPE65 are not palmitoylated by LRAT.","method":"Subcellular membrane fractionation with enzyme marker assays, lrat-/- mouse RPE homogenates, mass spectrometry for palmitoylation, 2-bromopalmitate inhibition, isomerase activity assays with retinyl palmitate vs. retinol substrates","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (KO mice, MS, pharmacological inhibition, subcellular fractionation, enzymatic assays) in a single rigorous study","pmids":["17504753"],"is_preprint":false},{"year":2007,"finding":"RPE-specific somatic ablation of Lrat in mice (Lrat-rpe-/-) strongly reduced retinyl ester synthesis in RPE cells and resulted in reduced light responses in ERG recordings, demonstrating that LRAT activity in the RPE is required for normal visual cycle function and retinoid storage.","method":"Cre-loxP tissue-specific knockout (Tyrp1-Cre × Lrat-flox), RNA/protein expression analysis, HPLC retinoid quantification, electroretinography","journal":"Investigative ophthalmology & visual science","confidence":"High","confidence_rationale":"Tier 2 / Strong — tissue-specific genetic KO with biochemical and functional (ERG) readouts, rigorous controls","pmids":["18055784"],"is_preprint":false},{"year":2013,"finding":"LRAT-catalyzed retinol esterification is required for activation of the STRA6/JAK2/STAT5 signaling cascade by holo-RBP. LRAT-null mice are protected from holo-RBP-induced suppression of insulin signaling, demonstrating that LRAT supports STRA6-mediated cell signaling by maintaining an inward retinol concentration gradient that enables STRA6-mediated retinol transport.","method":"LRAT-null mice, cell-based signaling assays (JAK2/STAT5 activation), insulin signaling readouts, genetic epistasis","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined signaling pathway readout and two orthogonal cellular phenotypes (STAT5 activation and insulin response)","pmids":["24036882"],"is_preprint":false},{"year":2021,"finding":"LRAT's catalytic activity (retinyl ester sequestration) is central to the negative-feedback regulation of intestinal retinoid biosynthesis from β-carotene. In LRAT-deficient mice, the transcription factor ISX becomes hypersensitive to dietary vitamin A and suppresses β-carotene oxygenase-1 (BCO1), resulting in β-carotene accumulation and vitamin A deficiency in extrahepatic tissues. Pharmacological inhibition of retinoid signaling and genetic depletion of Isx restored biosynthesis in enterocytes.","method":"Lrat-/- mice, pharmacological retinoid signaling inhibition, Isx-/- genetic epistasis, retinoid/carotenoid quantification in tissues","journal":"Journal of lipid research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO combined with pharmacological and genetic epistasis experiments across multiple mouse models","pmids":["33631212"],"is_preprint":false},{"year":2017,"finding":"The LCA-associated E14L LRAT mutation causes instability and accelerated proteasomal degradation of the mutant protein. Despite reduced protein stability, LRAT(E14L) expression led to rapid increase in cellular retinoic acid levels upon retinoid supplementation rather than abrogating chromophore production, implicating elevated retinoic acid in the retinal pathology caused by this N-terminal mutation.","method":"Bicistronic LRAT(E14L)-EGFP expression system, cell-based retinoid metabolite analysis, proteasomal degradation assays, chromophore production assay","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based expression assays with multiple retinoid metabolite readouts, single lab","pmids":["28758396"],"is_preprint":false},{"year":1998,"finding":"In bovine RPE subcellular membrane fractions, LRAT activity is restricted to ER-enriched membranes, establishing the ER as the subcellular site of retinol esterification in the visual cycle.","method":"Subcellular membrane fractionation with ER and plasma membrane marker enzymes, LRAT activity assay","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical fractionation with marker enzyme validation, single lab, single method","pmids":["9767084"],"is_preprint":false},{"year":2009,"finding":"The Lrat gene promoter lacks canonical retinoid receptor binding elements, yet its transcription is regulated by retinoic acid and nuclear receptors (RARα, RARβ, RARγ with RXRα) acting through an essential proximal region (~300 bp upstream of TSS) containing conserved basal elements (TATA box, SP3, AP-1, CAAT box). Nuclear run-on assays confirmed transcriptional regulation in vivo; removal of the −111 bp region completely eliminated promoter activity.","method":"Nuclear run-on transcription assay, luciferase reporter with deletion constructs, nuclear receptor co-transfection, electrophoretic mobility shift assay","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — nuclear run-on plus reporter deletion analysis with multiple nuclear receptors, single lab","pmids":["19665987"],"is_preprint":false},{"year":2001,"finding":"Both LRAT and ARAT activities are induced during conversion of hepatic stellate cell myofibroblasts to lipocytes. LRAT induction was dependent on retinoic acid, whereas ARAT induction depended on the overall fat-storing phenotype. Microsomal enzyme kinetics confirmed that these are intrinsic activities not solely attributable to changes in retinol uptake.","method":"[3H]retinol metabolic labeling, microsomal fraction kinetic enzyme assays, retinoic acid treatment, GRX cell line and primary murine HSCs","journal":"The Journal of nutritional biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — microsomal enzyme activity assays with pharmacological manipulation in two cell systems (cell line + primary cells), single lab","pmids":["12031254"],"is_preprint":false},{"year":2016,"finding":"Quiescent LRAT-/- hepatic stellate cells retain the capacity to synthesize retinyl esters and store neutral lipids in lipid droplets ex vivo, but lipid droplet size is significantly smaller (median 1080 nm vs. 1618 nm in WT). During activation, HSCs shift retinyl ester synthesis from LRAT to DGAT1, and exogenous fatty acid composition becomes the major determinant of retinyl ester species, indicating that LRAT is responsible for the large lipid droplets characteristic of quiescent HSCs.","method":"Lrat-/- primary HSCs, LC-MS/MS with multiple reaction monitoring for retinyl ester species, lipid droplet size quantification by microscopy, comparison with DGAT1-expressing activated cells","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO cells with quantitative lipidomics and imaging, single lab, multiple orthogonal methods","pmids":["27815220"],"is_preprint":false},{"year":2024,"finding":"During early hepatic stellate cell activation, LRAT activity is maintained and continues to produce retinyl palmitate-enriched retinyl esters, while loss of retinyl ester stores is caused by enhanced retinyl ester breakdown rather than loss of LRAT synthesis activity. Only upon prolonged activation do HSCs lose LRAT activity and shift to DGAT1-mediated retinyl ester synthesis.","method":"Soft gel vs. plastic culture comparison of primary HSCs, LC-MS/MS retinyl ester quantification, LRAT activity assays, gene expression analysis","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical activity assays combined with quantitative lipidomics in physiologically relevant culture model, single lab","pmids":["39068984"],"is_preprint":false},{"year":2005,"finding":"A sequence-homologous region (AA 111–123) within LRAT (and the related LRAT-like proteins TIG-3 and Ha-Rev107) harbors an anti-proliferative domain with DNA-binding properties. Dodecapeptides derived from this region showed in vitro growth inhibitory activity in human cutaneous melanoma cells, crossed the plasma membrane, localized to the nucleus, and affected expression of cyclin-dependent kinase-2 and subcellular redistribution of cyclins E and A.","method":"Peptide growth inhibition assays, nude mouse tumor model, nuclear localization by fluorescence microscopy, promoter binding assays, CDK2/cyclin expression analysis","journal":"Carcinogenesis","confidence":"Low","confidence_rationale":"Tier 3 / Weak — peptide (not full-length protein) study with indirect mechanistic evidence, single lab","pmids":["16234259"],"is_preprint":false},{"year":2038,"finding":"LRAT enriches DHRS3 at endoplasmic reticulum–lipid droplet contacts juxtaposed to mitochondria after irradiation. Loss of LRAT dispersed these ER-LD-mitochondria interfaces, mislocalized DHRS3, and impaired retinoid and NADPH buffering; enforced mitochondrial targeting of DHRS3 partially restored redox control. This places LRAT as an organizer of a retinoid-coupled NADPH module at ER-LD-mitochondria interfaces.","method":"Spatial imaging (proximity/co-localization), LRAT knockdown, enforced mitochondrial DHRS3 targeting, NADP+/NADPH ratio measurements, ROS assays","journal":"Free radical biology & medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, imaging-based localization with partial functional rescue, novel finding not yet replicated","pmids":["41579973"],"is_preprint":false}],"current_model":"LRAT (lecithin:retinol acyltransferase) is an ER-resident NlpC/P60-family enzyme that transfers the sn-1 fatty acyl group from phosphatidylcholine to retinol to form retinyl esters—the principal storage form of vitamin A—using a thioester catalytic intermediate; its LRAT-specific domain confers substrate selectivity via domain-swapping dimerization, it is transcriptionally induced by retinoic acid through RAR/RXR acting on a conserved proximal promoter, it supports STRA6/JAK2/STAT5 signaling by maintaining an inward retinol gradient, it is the dominant retinyl ester synthase in hepatic stellate cells (where it governs large lipid droplet formation), and in the intestine its retinyl ester sequestration activity coordinates a negative-feedback loop controlling β-carotene-derived retinoid biosynthesis via the ISX transcription factor."},"narrative":{"mechanistic_narrative":"LRAT is the predominant enzyme catalyzing physiologic esterification of retinol into retinyl esters, the principal storage form of vitamin A, with Lrat-null mice retaining only trace retinyl esters across liver, lung, kidney, and retinal pigment epithelium [PMID:16115871]. It is an NlpC/P60-family acyltransferase that acts through a thioester catalytic intermediate; structural analysis of an HRASLS3-LRAT chimera showed that the LRAT-specific domain drives domain-swapping dimerization and slows hydrolysis of the intermediate, thereby favoring efficient acyl transfer onto retinol and conferring LRAT's substrate specificity within its protein family [PMID:25383759]. The enzyme is restricted to ER-enriched membranes, establishing the ER as the site of retinol esterification, including within the visual cycle of the RPE [PMID:17504753, PMID:9767084]. In the eye, RPE-specific ablation of LRAT depletes retinyl ester stores and impairs light responses, demonstrating that LRAT supplies the retinyl ester substrate that feeds the visual cycle [PMID:18055784], and an N-terminal LCA-associated E14L mutation destabilizes the protein and elevates cellular retinoic acid upon retinoid supplementation, implicating retinoid dysregulation in the associated retinal pathology [PMID:28758396]. Beyond storage, LRAT shapes retinoid signaling and homeostasis: by maintaining an inward retinol gradient it enables STRA6/JAK2/STAT5 signaling driven by holo-RBP [PMID:24036882], and in the intestine its retinyl ester sequestration sets a negative-feedback loop in which loss of LRAT renders the ISX transcription factor hypersensitive to vitamin A and suppresses BCO1-dependent beta-carotene conversion [PMID:33631212]. In hepatic stellate cells LRAT is the dominant retinyl ester synthase of the quiescent state and is required for the large characteristic lipid droplets; upon activation cells shift retinyl ester synthesis to DGAT1 [PMID:27815220, PMID:39068984]. LRAT transcription is itself induced by retinoic acid through RAR/RXR acting on a conserved proximal promoter that lacks canonical response elements [PMID:19665987].","teleology":[{"year":1998,"claim":"Localizing LRAT activity established where retinol esterification physically occurs, answering whether the visual-cycle esterification step is an ER event.","evidence":"subcellular membrane fractionation with marker enzymes and LRAT activity assays in bovine RPE","pmids":["9767084"],"confidence":"Medium","gaps":["Single method in one tissue","Does not identify the membrane-targeting determinant of LRAT"]},{"year":2001,"claim":"Identifying that LRAT induction during hepatic stellate cell conversion is retinoic-acid dependent distinguished it from the fat-storage-driven ARAT pathway and linked LRAT to retinoid-responsive lipocyte biology.","evidence":"[3H]retinol labeling and microsomal kinetic assays in GRX cells and primary murine HSCs with retinoic acid treatment","pmids":["12031254"],"confidence":"Medium","gaps":["Does not resolve the transcriptional mechanism of induction","Relative in vivo contributions of LRAT vs ARAT not quantified"]},{"year":2005,"claim":"Genetic knockout defined LRAT as the dominant physiologic retinyl ester synthase across multiple tissues and revealed a compensatory acyl-CoA-dependent ARAT pathway, answering which enzyme governs vitamin A storage.","evidence":"Lrat-/- mice with HPLC retinoid quantification, hepatic stellate cell EM, and chylomicron fractionation","pmids":["16115871"],"confidence":"High","gaps":["Molecular identity of the compensatory ARAT enzyme not established","Tissue-specific contributions not separated"]},{"year":2005,"claim":"A homologous internal region of LRAT was reported to carry anti-proliferative and DNA-binding activity, raising a possible non-esterase function.","evidence":"synthetic dodecapeptide growth-inhibition assays, nude-mouse tumor model, and nuclear localization imaging","pmids":["16234259"],"confidence":"Low","gaps":["Uses peptides rather than full-length LRAT protein","No demonstration that endogenous LRAT exerts this activity","Mechanism of CDK2/cyclin effects indirect"]},{"year":2007,"claim":"Compartmentalizing LRAT to the ER versus retinyl ester hydrolase to the plasma membrane, and showing RPE65 is not palmitoylated by LRAT, clarified LRAT's strictly substrate-supplying role in the visual cycle.","evidence":"lrat-/- RPE fractionation, mass spectrometry of RPE65 cysteines, 2-bromopalmitate inhibition, and isomerase assays","pmids":["17504753"],"confidence":"High","gaps":["Does not address LRAT regulation within the RPE","ER-targeting determinants unresolved"]},{"year":2007,"claim":"RPE-specific ablation demonstrated that LRAT activity in the RPE is functionally required for vision, not merely for storage, by linking it to electroretinographic light responses.","evidence":"Tyrp1-Cre x Lrat-flox tissue-specific knockout with HPLC retinoids and electroretinography","pmids":["18055784"],"confidence":"High","gaps":["Does not quantify the degree of photoreceptor degeneration over time","Extra-RPE contributions to phenotype not isolated"]},{"year":2009,"claim":"Mapping the Lrat promoter explained how retinoic acid induces LRAT despite the absence of canonical retinoid response elements, identifying an essential conserved proximal region.","evidence":"nuclear run-on, luciferase reporter deletion constructs, nuclear receptor co-transfection, and EMSA","pmids":["19665987"],"confidence":"Medium","gaps":["Direct DNA-binding factor at the responsive element not definitively identified","Indirect vs direct RAR/RXR action not fully resolved"]},{"year":2013,"claim":"Linking LRAT to STRA6 signaling established that retinol esterification, by maintaining an inward retinol gradient, is required to drive holo-RBP-induced JAK2/STAT5 signaling and its metabolic consequences.","evidence":"LRAT-null mice, cell-based JAK2/STAT5 assays, insulin signaling readouts, and genetic epistasis","pmids":["24036882"],"confidence":"High","gaps":["Does not define cell types in vivo where this axis dominates","Quantitative gradient parameters not measured"]},{"year":2016,"claim":"Quantitative lipidomics in knockout HSCs assigned LRAT responsibility for the large lipid droplets of quiescent cells and revealed a synthesis handoff to DGAT1 upon activation.","evidence":"Lrat-/- primary HSCs with LC-MS/MS retinyl ester profiling and lipid droplet size imaging","pmids":["27815220"],"confidence":"Medium","gaps":["Mechanism linking LRAT activity to droplet size not defined","In vivo relevance of the DGAT1 switch not tested"]},{"year":2021,"claim":"Genetic and pharmacological epistasis showed that LRAT-mediated retinyl ester sequestration sets the sensitivity of the ISX/BCO1 feedback loop controlling intestinal beta-carotene conversion.","evidence":"Lrat-/-, Isx-/- and retinoid-inhibitor mouse models with tissue retinoid/carotenoid quantification","pmids":["33631212"],"confidence":"High","gaps":["Does not establish whether LRAT acts cell-autonomously in enterocytes","Kinetics of feedback not characterized"]},{"year":2024,"claim":"Time-resolved analysis of HSC activation showed that early retinyl ester loss is driven by enhanced ester breakdown while LRAT synthesis persists, refining the timing of the LRAT-to-DGAT1 switch.","evidence":"soft-gel vs plastic primary HSC culture with LC-MS/MS, LRAT activity assays, and expression profiling","pmids":["39068984"],"confidence":"Medium","gaps":["Identity of the breakdown hydrolase not established","In vivo fibrosis relevance not tested"]},{"year":2038,"claim":"Imaging-based work proposed LRAT as an organizer of DHRS3 at ER-LD-mitochondria contacts coupling retinoid metabolism to NADPH/redox buffering.","evidence":"spatial co-localization imaging, LRAT knockdown, enforced mitochondrial DHRS3 targeting, and NADP+/NADPH and ROS measurements","pmids":["41579973"],"confidence":"Low","gaps":["Single lab, not independently replicated","Direct LRAT-DHRS3 interaction not demonstrated","Rescue only partial"]},{"year":null,"claim":"The molecular determinants of LRAT ER membrane targeting and the identity of the compensatory ARAT and retinyl-ester hydrolase enzymes that act alongside LRAT remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of full-length membrane-embedded LRAT","Compensatory ARAT enzyme unidentified","Hydrolase mediating activation-induced retinyl ester loss unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,7]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1,5]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[3]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4]}],"complexes":[],"partners":["DHRS3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O95237","full_name":"Lecithin retinol acyltransferase","aliases":["Phosphatidylcholine--retinol O-acyltransferase"],"length_aa":230,"mass_kda":25.7,"function":"Transfers the acyl group from the sn-1 position of phosphatidylcholine to all-trans retinol, producing all-trans retinyl esters (PubMed:9920938). Retinyl esters are storage forms of vitamin A (Probable). LRAT plays a critical role in vision (Probable). It provides the all-trans retinyl ester substrates for the isomerohydrolase which processes the esters into 11-cis-retinol in the retinal pigment epithelium; due to a membrane-associated alcohol dehydrogenase, 11 cis-retinol is oxidized and converted into 11-cis-retinaldehyde which is the chromophore for rhodopsin and the cone photopigments (Probable). Required for the survival of cone photoreceptors and correct rod photoreceptor cell morphology (By similarity)","subcellular_location":"Endoplasmic reticulum membrane; Rough endoplasmic reticulum; Endosome, multivesicular body; Cytoplasm, perinuclear region","url":"https://www.uniprot.org/uniprotkb/O95237/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/LRAT","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/LRAT","total_profiled":1310},"omim":[{"mim_id":"613341","title":"LEBER CONGENITAL AMAUROSIS 14; LCA14","url":"https://www.omim.org/entry/613341"},{"mim_id":"611474","title":"PHOSPHOLIPASE A AND ACYLTRANSFERASE 5; PLAAT5","url":"https://www.omim.org/entry/611474"},{"mim_id":"611234","title":"LRAT DOMAIN-CONTAINING PROTEIN 1; LRATD1","url":"https://www.omim.org/entry/611234"},{"mim_id":"610745","title":"STIMULATED BY RETINOIC ACID 6; STRA6","url":"https://www.omim.org/entry/610745"},{"mim_id":"610113","title":"ADAMTS-LIKE PROTEIN 4; ADAMTSL4","url":"https://www.omim.org/entry/610113"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Endoplasmic reticulum","reliability":"Approved"},{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":1.9},{"tissue":"liver","ntpm":2.0}],"url":"https://www.proteinatlas.org/search/LRAT"},"hgnc":{"alias_symbol":["LCA14"],"prev_symbol":[]},"alphafold":{"accession":"O95237","domains":[{"cath_id":"3.90.1720.10","chopping":"40-175","consensus_level":"high","plddt":92.4093,"start":40,"end":175},{"cath_id":"1.10.287","chopping":"191-228","consensus_level":"high","plddt":82.9987,"start":191,"end":228}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95237","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95237-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95237-F1-predicted_aligned_error_v6.png","plddt_mean":83.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=LRAT","jax_strain_url":"https://www.jax.org/strain/search?query=LRAT"},"sequence":{"accession":"O95237","fasta_url":"https://rest.uniprot.org/uniprotkb/O95237.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95237/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95237"}},"corpus_meta":[{"pmid":"16115871","id":"PMC_16115871","title":"Retinoid absorption and storage is impaired in mice lacking lecithin:retinol acyltransferase (LRAT).","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16115871","citation_count":251,"is_preprint":false},{"pmid":"26656277","id":"PMC_26656277","title":"Safety and Proof-of-Concept Study of Oral QLT091001 in Retinitis Pigmentosa Due to Inherited Deficiencies of Retinal Pigment Epithelial 65 Protein (RPE65) or Lecithin:Retinol Acyltransferase (LRAT).","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26656277","citation_count":59,"is_preprint":false},{"pmid":"25383759","id":"PMC_25383759","title":"LRAT-specific domain facilitates vitamin A metabolism by domain swapping in HRASLS3.","date":"2014","source":"Nature chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/25383759","citation_count":49,"is_preprint":false},{"pmid":"19700416","id":"PMC_19700416","title":"Acidic retinoids synergize with vitamin A to enhance retinol uptake and STRA6, LRAT, and CYP26B1 expression in neonatal lung.","date":"2009","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/19700416","citation_count":44,"is_preprint":false},{"pmid":"17504753","id":"PMC_17504753","title":"Role of LRAT on the retinoid isomerase activity and membrane association of Rpe65.","date":"2007","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17504753","citation_count":41,"is_preprint":false},{"pmid":"22559933","id":"PMC_22559933","title":"A homozygous frameshift mutation in LRAT causes retinitis punctata albescens.","date":"2012","source":"Ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/22559933","citation_count":38,"is_preprint":false},{"pmid":"22570351","id":"PMC_22570351","title":"Early onset retinal dystrophy due to mutations in LRAT: molecular analysis and detailed phenotypic study.","date":"2012","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/22570351","citation_count":35,"is_preprint":false},{"pmid":"17011878","id":"PMC_17011878","title":"Screening genes of the retinoid metabolism: novel LRAT mutation in leber congenital amaurosis.","date":"2006","source":"American journal of ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/17011878","citation_count":34,"is_preprint":false},{"pmid":"33631212","id":"PMC_33631212","title":"LRAT coordinates the negative-feedback regulation of intestinal retinoid biosynthesis from β-carotene.","date":"2021","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/33631212","citation_count":30,"is_preprint":false},{"pmid":"27815220","id":"PMC_27815220","title":"Hepatic stellate cells retain the capacity to synthesize retinyl esters and to store neutral lipids in small lipid droplets in the absence of LRAT.","date":"2016","source":"Biochimica et biophysica acta. Molecular and cell biology of lipids","url":"https://pubmed.ncbi.nlm.nih.gov/27815220","citation_count":30,"is_preprint":false},{"pmid":"18055784","id":"PMC_18055784","title":"Somatic ablation of the Lrat gene in the mouse retinal pigment epithelium drastically reduces its retinoid storage.","date":"2007","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/18055784","citation_count":27,"is_preprint":false},{"pmid":"24036882","id":"PMC_24036882","title":"The retinol esterifying enzyme LRAT supports cell signaling by retinol-binding protein and its receptor STRA6.","date":"2013","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/24036882","citation_count":23,"is_preprint":false},{"pmid":"12031254","id":"PMC_12031254","title":"Acyl-CoA: retinol acyltransferase (ARAT) and lecithin:retinol acyltransferase (LRAT) activation during the lipocyte phenotype induction in hepatic stellate cells.","date":"2001","source":"The Journal of nutritional biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12031254","citation_count":22,"is_preprint":false},{"pmid":"9767084","id":"PMC_9767084","title":"Distribution of 11-cis LRAT, 11-cis RD and 11-cis REH in bovine retinal pigment epithelium membranes.","date":"1998","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/9767084","citation_count":22,"is_preprint":false},{"pmid":"19665987","id":"PMC_19665987","title":"An essential set of basic DNA response elements is required for receptor-dependent transcription of the lecithin:retinol acyltransferase (Lrat) gene.","date":"2009","source":"Archives of biochemistry and biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/19665987","citation_count":19,"is_preprint":false},{"pmid":"31448181","id":"PMC_31448181","title":"Long-Term Follow-Up of Retinal Degenerations Associated With LRAT Mutations and Their Comparability to Phenotypes Associated With RPE65 Mutations.","date":"2019","source":"Translational vision science & technology","url":"https://pubmed.ncbi.nlm.nih.gov/31448181","citation_count":18,"is_preprint":false},{"pmid":"12524014","id":"PMC_12524014","title":"Retinoid metabolism (LRAT, REH) in the yolk-sac membrane of Japanese quail eggs and effects of mono-ortho-PCBs.","date":"2003","source":"Comparative biochemistry and physiology. 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Advances in ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/42065837","citation_count":0,"is_preprint":false},{"pmid":"41807804","id":"PMC_41807804","title":"AAV-mediated gene replacement therapy for LRAT-associated retinitis pigmentosa: a proof-of-concept study in a patient-based rat model.","date":"2026","source":"Gene therapy","url":"https://pubmed.ncbi.nlm.nih.gov/41807804","citation_count":0,"is_preprint":false},{"pmid":"40394841","id":"PMC_40394841","title":"Genetic detection of a novel LRAT pathogenic variant in patients with early-onset severe retinal dystrophy.","date":"2025","source":"Ophthalmic genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40394841","citation_count":0,"is_preprint":false},{"pmid":"41579973","id":"PMC_41579973","title":"YTHDF2-m6A regulation of DHRS3 at LRAT-organized organelle contacts orchestrates redox to drive radioresistance in esophageal squamous cell carcinoma.","date":"2026","source":"Free radical biology & medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41579973","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":22191,"output_tokens":3975,"usd":0.063099,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11924,"output_tokens":3967,"usd":0.079397,"stage2_stop_reason":"end_turn"},"total_usd":0.142496,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"A 2.2-Å crystal structure of an HRASLS3-LRAT chimeric enzyme in a thioester catalytic intermediate state revealed that the LRAT-specific domain causes domain-swapping dimerization not observed in native HRASLS proteins. Structural changes affecting the active site environment contributed to slower hydrolysis of the catalytic intermediate, supporting efficient acyl transfer to retinol substrate. This identified the structural basis for LRAT's substrate specificity within the NlpC/P60 protein family.\",\n      \"method\": \"Gain-of-function domain-swap chimera, 2.2-Å crystal structure of thioester intermediate, in vitro enzymatic assay\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure at 2.2 Å of catalytic intermediate combined with gain-of-function mutagenesis and in vitro activity assays in a single rigorous study\",\n      \"pmids\": [\"25383759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"LRAT is the predominant enzyme responsible for physiologic retinol esterification in liver, lung, kidney, and retinal pigment epithelium. Lrat-/- mice have only trace retinyl esters in these tissues and absorb dietary retinol primarily as free retinol in chylomicrons. The fatty acyl composition of residual chylomicron retinyl esters in Lrat-/- mice suggests synthesis via an acyl-CoA-dependent acyltransferase (ARAT) pathway in adipose tissue, which also shows elevated CRBPIII expression and compensatory retinyl ester storage.\",\n      \"method\": \"Lrat knockout mouse (Lrat-/-), HPLC retinoid quantification, electron microscopy of hepatic stellate cells, chylomicron fractionation, fatty acyl composition analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple orthogonal readouts (HPLC, EM, fractionation), replicated across tissues\",\n      \"pmids\": [\"16115871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"LRAT activity is localized exclusively to endoplasmic reticulum (ER)-enriched membranes in bovine RPE, whereas 11-cis retinyl ester hydrolase (REH) activity is in plasma membrane fractions, indicating subcellular compartmentalization of the visual cycle. LRAT is not required for RPE65's association with membranes or for RPE65 isomerase activity beyond its role in synthesizing the retinyl ester substrate; Rpe65 membrane affinity is similar in wild-type and lrat-/- mice, and mass spectrometry showed that Cys231, Cys329, and Cys330 of RPE65 are not palmitoylated by LRAT.\",\n      \"method\": \"Subcellular membrane fractionation with enzyme marker assays, lrat-/- mouse RPE homogenates, mass spectrometry for palmitoylation, 2-bromopalmitate inhibition, isomerase activity assays with retinyl palmitate vs. retinol substrates\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (KO mice, MS, pharmacological inhibition, subcellular fractionation, enzymatic assays) in a single rigorous study\",\n      \"pmids\": [\"17504753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RPE-specific somatic ablation of Lrat in mice (Lrat-rpe-/-) strongly reduced retinyl ester synthesis in RPE cells and resulted in reduced light responses in ERG recordings, demonstrating that LRAT activity in the RPE is required for normal visual cycle function and retinoid storage.\",\n      \"method\": \"Cre-loxP tissue-specific knockout (Tyrp1-Cre × Lrat-flox), RNA/protein expression analysis, HPLC retinoid quantification, electroretinography\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — tissue-specific genetic KO with biochemical and functional (ERG) readouts, rigorous controls\",\n      \"pmids\": [\"18055784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LRAT-catalyzed retinol esterification is required for activation of the STRA6/JAK2/STAT5 signaling cascade by holo-RBP. LRAT-null mice are protected from holo-RBP-induced suppression of insulin signaling, demonstrating that LRAT supports STRA6-mediated cell signaling by maintaining an inward retinol concentration gradient that enables STRA6-mediated retinol transport.\",\n      \"method\": \"LRAT-null mice, cell-based signaling assays (JAK2/STAT5 activation), insulin signaling readouts, genetic epistasis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined signaling pathway readout and two orthogonal cellular phenotypes (STAT5 activation and insulin response)\",\n      \"pmids\": [\"24036882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"LRAT's catalytic activity (retinyl ester sequestration) is central to the negative-feedback regulation of intestinal retinoid biosynthesis from β-carotene. In LRAT-deficient mice, the transcription factor ISX becomes hypersensitive to dietary vitamin A and suppresses β-carotene oxygenase-1 (BCO1), resulting in β-carotene accumulation and vitamin A deficiency in extrahepatic tissues. Pharmacological inhibition of retinoid signaling and genetic depletion of Isx restored biosynthesis in enterocytes.\",\n      \"method\": \"Lrat-/- mice, pharmacological retinoid signaling inhibition, Isx-/- genetic epistasis, retinoid/carotenoid quantification in tissues\",\n      \"journal\": \"Journal of lipid research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO combined with pharmacological and genetic epistasis experiments across multiple mouse models\",\n      \"pmids\": [\"33631212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The LCA-associated E14L LRAT mutation causes instability and accelerated proteasomal degradation of the mutant protein. Despite reduced protein stability, LRAT(E14L) expression led to rapid increase in cellular retinoic acid levels upon retinoid supplementation rather than abrogating chromophore production, implicating elevated retinoic acid in the retinal pathology caused by this N-terminal mutation.\",\n      \"method\": \"Bicistronic LRAT(E14L)-EGFP expression system, cell-based retinoid metabolite analysis, proteasomal degradation assays, chromophore production assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based expression assays with multiple retinoid metabolite readouts, single lab\",\n      \"pmids\": [\"28758396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"In bovine RPE subcellular membrane fractions, LRAT activity is restricted to ER-enriched membranes, establishing the ER as the subcellular site of retinol esterification in the visual cycle.\",\n      \"method\": \"Subcellular membrane fractionation with ER and plasma membrane marker enzymes, LRAT activity assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical fractionation with marker enzyme validation, single lab, single method\",\n      \"pmids\": [\"9767084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The Lrat gene promoter lacks canonical retinoid receptor binding elements, yet its transcription is regulated by retinoic acid and nuclear receptors (RARα, RARβ, RARγ with RXRα) acting through an essential proximal region (~300 bp upstream of TSS) containing conserved basal elements (TATA box, SP3, AP-1, CAAT box). Nuclear run-on assays confirmed transcriptional regulation in vivo; removal of the −111 bp region completely eliminated promoter activity.\",\n      \"method\": \"Nuclear run-on transcription assay, luciferase reporter with deletion constructs, nuclear receptor co-transfection, electrophoretic mobility shift assay\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — nuclear run-on plus reporter deletion analysis with multiple nuclear receptors, single lab\",\n      \"pmids\": [\"19665987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Both LRAT and ARAT activities are induced during conversion of hepatic stellate cell myofibroblasts to lipocytes. LRAT induction was dependent on retinoic acid, whereas ARAT induction depended on the overall fat-storing phenotype. Microsomal enzyme kinetics confirmed that these are intrinsic activities not solely attributable to changes in retinol uptake.\",\n      \"method\": \"[3H]retinol metabolic labeling, microsomal fraction kinetic enzyme assays, retinoic acid treatment, GRX cell line and primary murine HSCs\",\n      \"journal\": \"The Journal of nutritional biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — microsomal enzyme activity assays with pharmacological manipulation in two cell systems (cell line + primary cells), single lab\",\n      \"pmids\": [\"12031254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Quiescent LRAT-/- hepatic stellate cells retain the capacity to synthesize retinyl esters and store neutral lipids in lipid droplets ex vivo, but lipid droplet size is significantly smaller (median 1080 nm vs. 1618 nm in WT). During activation, HSCs shift retinyl ester synthesis from LRAT to DGAT1, and exogenous fatty acid composition becomes the major determinant of retinyl ester species, indicating that LRAT is responsible for the large lipid droplets characteristic of quiescent HSCs.\",\n      \"method\": \"Lrat-/- primary HSCs, LC-MS/MS with multiple reaction monitoring for retinyl ester species, lipid droplet size quantification by microscopy, comparison with DGAT1-expressing activated cells\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO cells with quantitative lipidomics and imaging, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"27815220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"During early hepatic stellate cell activation, LRAT activity is maintained and continues to produce retinyl palmitate-enriched retinyl esters, while loss of retinyl ester stores is caused by enhanced retinyl ester breakdown rather than loss of LRAT synthesis activity. Only upon prolonged activation do HSCs lose LRAT activity and shift to DGAT1-mediated retinyl ester synthesis.\",\n      \"method\": \"Soft gel vs. plastic culture comparison of primary HSCs, LC-MS/MS retinyl ester quantification, LRAT activity assays, gene expression analysis\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical activity assays combined with quantitative lipidomics in physiologically relevant culture model, single lab\",\n      \"pmids\": [\"39068984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"A sequence-homologous region (AA 111–123) within LRAT (and the related LRAT-like proteins TIG-3 and Ha-Rev107) harbors an anti-proliferative domain with DNA-binding properties. Dodecapeptides derived from this region showed in vitro growth inhibitory activity in human cutaneous melanoma cells, crossed the plasma membrane, localized to the nucleus, and affected expression of cyclin-dependent kinase-2 and subcellular redistribution of cyclins E and A.\",\n      \"method\": \"Peptide growth inhibition assays, nude mouse tumor model, nuclear localization by fluorescence microscopy, promoter binding assays, CDK2/cyclin expression analysis\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — peptide (not full-length protein) study with indirect mechanistic evidence, single lab\",\n      \"pmids\": [\"16234259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2038,\n      \"finding\": \"LRAT enriches DHRS3 at endoplasmic reticulum–lipid droplet contacts juxtaposed to mitochondria after irradiation. Loss of LRAT dispersed these ER-LD-mitochondria interfaces, mislocalized DHRS3, and impaired retinoid and NADPH buffering; enforced mitochondrial targeting of DHRS3 partially restored redox control. This places LRAT as an organizer of a retinoid-coupled NADPH module at ER-LD-mitochondria interfaces.\",\n      \"method\": \"Spatial imaging (proximity/co-localization), LRAT knockdown, enforced mitochondrial DHRS3 targeting, NADP+/NADPH ratio measurements, ROS assays\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, imaging-based localization with partial functional rescue, novel finding not yet replicated\",\n      \"pmids\": [\"41579973\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"LRAT (lecithin:retinol acyltransferase) is an ER-resident NlpC/P60-family enzyme that transfers the sn-1 fatty acyl group from phosphatidylcholine to retinol to form retinyl esters—the principal storage form of vitamin A—using a thioester catalytic intermediate; its LRAT-specific domain confers substrate selectivity via domain-swapping dimerization, it is transcriptionally induced by retinoic acid through RAR/RXR acting on a conserved proximal promoter, it supports STRA6/JAK2/STAT5 signaling by maintaining an inward retinol gradient, it is the dominant retinyl ester synthase in hepatic stellate cells (where it governs large lipid droplet formation), and in the intestine its retinyl ester sequestration activity coordinates a negative-feedback loop controlling β-carotene-derived retinoid biosynthesis via the ISX transcription factor.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"LRAT is the predominant enzyme catalyzing physiologic esterification of retinol into retinyl esters, the principal storage form of vitamin A, with Lrat-null mice retaining only trace retinyl esters across liver, lung, kidney, and retinal pigment epithelium [#1]. It is an NlpC/P60-family acyltransferase that acts through a thioester catalytic intermediate; structural analysis of an HRASLS3-LRAT chimera showed that the LRAT-specific domain drives domain-swapping dimerization and slows hydrolysis of the intermediate, thereby favoring efficient acyl transfer onto retinol and conferring LRAT's substrate specificity within its protein family [#0]. The enzyme is restricted to ER-enriched membranes, establishing the ER as the site of retinol esterification, including within the visual cycle of the RPE [#2, #7]. In the eye, RPE-specific ablation of LRAT depletes retinyl ester stores and impairs light responses, demonstrating that LRAT supplies the retinyl ester substrate that feeds the visual cycle [#3], and an N-terminal LCA-associated E14L mutation destabilizes the protein and elevates cellular retinoic acid upon retinoid supplementation, implicating retinoid dysregulation in the associated retinal pathology [#6]. Beyond storage, LRAT shapes retinoid signaling and homeostasis: by maintaining an inward retinol gradient it enables STRA6/JAK2/STAT5 signaling driven by holo-RBP [#4], and in the intestine its retinyl ester sequestration sets a negative-feedback loop in which loss of LRAT renders the ISX transcription factor hypersensitive to vitamin A and suppresses BCO1-dependent beta-carotene conversion [#5]. In hepatic stellate cells LRAT is the dominant retinyl ester synthase of the quiescent state and is required for the large characteristic lipid droplets; upon activation cells shift retinyl ester synthesis to DGAT1 [#10, #11]. LRAT transcription is itself induced by retinoic acid through RAR/RXR acting on a conserved proximal promoter that lacks canonical response elements [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Localizing LRAT activity established where retinol esterification physically occurs, answering whether the visual-cycle esterification step is an ER event.\",\n      \"evidence\": \"subcellular membrane fractionation with marker enzymes and LRAT activity assays in bovine RPE\",\n      \"pmids\": [\"9767084\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single method in one tissue\", \"Does not identify the membrane-targeting determinant of LRAT\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identifying that LRAT induction during hepatic stellate cell conversion is retinoic-acid dependent distinguished it from the fat-storage-driven ARAT pathway and linked LRAT to retinoid-responsive lipocyte biology.\",\n      \"evidence\": \"[3H]retinol labeling and microsomal kinetic assays in GRX cells and primary murine HSCs with retinoic acid treatment\",\n      \"pmids\": [\"12031254\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not resolve the transcriptional mechanism of induction\", \"Relative in vivo contributions of LRAT vs ARAT not quantified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic knockout defined LRAT as the dominant physiologic retinyl ester synthase across multiple tissues and revealed a compensatory acyl-CoA-dependent ARAT pathway, answering which enzyme governs vitamin A storage.\",\n      \"evidence\": \"Lrat-/- mice with HPLC retinoid quantification, hepatic stellate cell EM, and chylomicron fractionation\",\n      \"pmids\": [\"16115871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of the compensatory ARAT enzyme not established\", \"Tissue-specific contributions not separated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"A homologous internal region of LRAT was reported to carry anti-proliferative and DNA-binding activity, raising a possible non-esterase function.\",\n      \"evidence\": \"synthetic dodecapeptide growth-inhibition assays, nude-mouse tumor model, and nuclear localization imaging\",\n      \"pmids\": [\"16234259\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Uses peptides rather than full-length LRAT protein\", \"No demonstration that endogenous LRAT exerts this activity\", \"Mechanism of CDK2/cyclin effects indirect\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Compartmentalizing LRAT to the ER versus retinyl ester hydrolase to the plasma membrane, and showing RPE65 is not palmitoylated by LRAT, clarified LRAT's strictly substrate-supplying role in the visual cycle.\",\n      \"evidence\": \"lrat-/- RPE fractionation, mass spectrometry of RPE65 cysteines, 2-bromopalmitate inhibition, and isomerase assays\",\n      \"pmids\": [\"17504753\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address LRAT regulation within the RPE\", \"ER-targeting determinants unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"RPE-specific ablation demonstrated that LRAT activity in the RPE is functionally required for vision, not merely for storage, by linking it to electroretinographic light responses.\",\n      \"evidence\": \"Tyrp1-Cre x Lrat-flox tissue-specific knockout with HPLC retinoids and electroretinography\",\n      \"pmids\": [\"18055784\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not quantify the degree of photoreceptor degeneration over time\", \"Extra-RPE contributions to phenotype not isolated\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapping the Lrat promoter explained how retinoic acid induces LRAT despite the absence of canonical retinoid response elements, identifying an essential conserved proximal region.\",\n      \"evidence\": \"nuclear run-on, luciferase reporter deletion constructs, nuclear receptor co-transfection, and EMSA\",\n      \"pmids\": [\"19665987\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct DNA-binding factor at the responsive element not definitively identified\", \"Indirect vs direct RAR/RXR action not fully resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Linking LRAT to STRA6 signaling established that retinol esterification, by maintaining an inward retinol gradient, is required to drive holo-RBP-induced JAK2/STAT5 signaling and its metabolic consequences.\",\n      \"evidence\": \"LRAT-null mice, cell-based JAK2/STAT5 assays, insulin signaling readouts, and genetic epistasis\",\n      \"pmids\": [\"24036882\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not define cell types in vivo where this axis dominates\", \"Quantitative gradient parameters not measured\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Quantitative lipidomics in knockout HSCs assigned LRAT responsibility for the large lipid droplets of quiescent cells and revealed a synthesis handoff to DGAT1 upon activation.\",\n      \"evidence\": \"Lrat-/- primary HSCs with LC-MS/MS retinyl ester profiling and lipid droplet size imaging\",\n      \"pmids\": [\"27815220\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking LRAT activity to droplet size not defined\", \"In vivo relevance of the DGAT1 switch not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Genetic and pharmacological epistasis showed that LRAT-mediated retinyl ester sequestration sets the sensitivity of the ISX/BCO1 feedback loop controlling intestinal beta-carotene conversion.\",\n      \"evidence\": \"Lrat-/-, Isx-/- and retinoid-inhibitor mouse models with tissue retinoid/carotenoid quantification\",\n      \"pmids\": [\"33631212\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not establish whether LRAT acts cell-autonomously in enterocytes\", \"Kinetics of feedback not characterized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Time-resolved analysis of HSC activation showed that early retinyl ester loss is driven by enhanced ester breakdown while LRAT synthesis persists, refining the timing of the LRAT-to-DGAT1 switch.\",\n      \"evidence\": \"soft-gel vs plastic primary HSC culture with LC-MS/MS, LRAT activity assays, and expression profiling\",\n      \"pmids\": [\"39068984\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the breakdown hydrolase not established\", \"In vivo fibrosis relevance not tested\"]\n    },\n    {\n      \"year\": 2038,\n      \"claim\": \"Imaging-based work proposed LRAT as an organizer of DHRS3 at ER-LD-mitochondria contacts coupling retinoid metabolism to NADPH/redox buffering.\",\n      \"evidence\": \"spatial co-localization imaging, LRAT knockdown, enforced mitochondrial DHRS3 targeting, and NADP+/NADPH and ROS measurements\",\n      \"pmids\": [\"41579973\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single lab, not independently replicated\", \"Direct LRAT-DHRS3 interaction not demonstrated\", \"Rescue only partial\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular determinants of LRAT ER membrane targeting and the identity of the compensatory ARAT and retinyl-ester hydrolase enzymes that act alongside LRAT remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of full-length membrane-embedded LRAT\", \"Compensatory ARAT enzyme unidentified\", \"Hydrolase mediating activation-induced retinyl ester loss unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 7]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DHRS3\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}