{"gene":"B3GALT4","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":1998,"finding":"B3GALT4 (beta3Gal-T4) encodes a UDP-galactose:beta-N-acetyl-galactosamine beta-1,3-galactosyltransferase activity involved in GM1/GD1b ganglioside synthesis, as demonstrated by expression in the Baculovirus system showing transfer of galactose to GalNAc-containing acceptors.","method":"Baculovirus expression system, enzymatic activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic characterization in recombinant expression system, replicated by independent rat GD1 synthase study","pmids":["9582303"],"is_preprint":false},{"year":2011,"finding":"B3GALT4 is essential for cholera toxin intoxication, identified through a genetic screen as required for ganglioside biosynthesis (the receptor for CTx); loss-of-function of B3GALT4 (along with ST3GAL5, SLC35A2, UGCG) abolishes CTx-mediated cytotoxicity.","method":"Haploid genetic screen in human cells using a cytotoxic CTx conjugate, loss-of-function clonal cell isolation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide genetic screen with functional validation in human cells, multiple orthogonal methods including clonal cell characterization","pmids":["22123862"],"is_preprint":false},{"year":2019,"finding":"siRNA-mediated knockdown of B3GALT4 in differentiated SK-N-SH dopaminergic cells significantly reduced GM1 ganglioside levels and increased vulnerability to MPP+ neurotoxicity; exogenous GM1 rescued this enhanced toxicity, establishing B3GALT4 as required for GM1 production that protects dopaminergic cells.","method":"siRNA knockdown, ganglioside level measurement, neurotoxicity assay (MPP+), GM1 rescue experiment","journal":"Molecular and cellular neurosciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KD with defined cellular phenotype and rescue experiment, single lab","pmids":["30611881"],"is_preprint":false},{"year":2022,"finding":"B3GALT4 regulates GD2 ganglioside expression and lipid raft formation in neuroblastoma cells; mechanistically, B3GALT4 modulates c-Met signaling within lipid rafts and downstream AKT/mTOR/IRF-1 pathway to control CXCL9 and CXCL10 chemokine secretion and CD8+ T cell recruitment.","method":"B3GALT4 silencing/overexpression, flow cytometry, ELISA, western blotting, lipid raft inhibitor (MβCD), immunofluorescence, in vivo tumor-bearing mouse model","journal":"Journal of experimental & clinical cancer research : CR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (functional assays, inhibitor, in vivo), single lab","pmids":["36284313"],"is_preprint":false},{"year":2024,"finding":"B3GALT4 promotes breast cancer cell proliferation, migration, and invasion; suppression of B3GALT4 triggers autophagy and inhibits the AKT/mTOR signaling pathway, establishing B3GALT4 as a regulator of autophagy through this pathway.","method":"B3GALT4 overexpression and knockdown, western blot, autophagolysosomes staining, LC3 fluorescence, GSEA, RNA-seq, in vitro and in vivo functional assays","journal":"Discover oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (RNA-seq, western blot, autophagy assays, in vivo), single lab","pmids":["39331217"],"is_preprint":false},{"year":1996,"finding":"GalT-4 (the mouse ortholog activity corresponding to B3GALT4) was purified 107,500-fold from mouse T-lymphoma P-1798 and characterized as catalyzing beta-1,4 galactosylation of lactotriaosylceramide (LcOse3Cer) to form neolactotetraosylceramide (nLcOse4Cer), with an absolute requirement for Mn2+, pH optimum 6.5–7.0, and Km values of 110 µM for LcOse3Cer and 250 µM for UDP-galactose; an N-acetylglucosamine residue in the acceptor substrate is required.","method":"Enzyme purification (affinity chromatography), kinetic characterization, substrate competition assay, western blot with anti-lactose synthetase antibody, TLC autoradiography, immunostaining","journal":"Glycoconjugate journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — extensive in vitro biochemical reconstitution with purified enzyme, multiple orthogonal methods including kinetics, substrate specificity, and immunological validation","pmids":["8781973"],"is_preprint":false},{"year":1998,"finding":"A truncated, catalytically active recombinant form of avian GalT-4 (B3GALT4 ortholog) was expressed as a GST fusion protein in E. coli; the recombinant protein retained functional activity similar to native GalT-4 purified from embryonic chicken brain, confirming the catalytic domain identity.","method":"Recombinant expression (GST fusion in E. coli), enzymatic activity assay, interaction studies with GlcNAc and UDP-hexanolamine","journal":"Acta biochimica Polonica","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — recombinant expression with functional characterization, single lab, limited detail in abstract","pmids":["9821875"],"is_preprint":false}],"current_model":"B3GALT4 encodes a UDP-galactose:beta-N-acetylgalactosamine beta-1,3-galactosyltransferase that synthesizes GM1 and GD1b gangliosides by transferring galactose in a beta-1,3 linkage; it is required for ganglioside-mediated cholera toxin receptor function, maintains GM1 levels that protect dopaminergic neurons, regulates GD2 expression and lipid raft formation to modulate c-Met/AKT/mTOR/IRF-1 signaling and immune cell recruitment in neuroblastoma, and controls autophagy through the AKT/mTOR pathway in breast cancer cells."},"narrative":{"mechanistic_narrative":"B3GALT4 encodes a Mn2+-dependent UDP-galactose:beta-N-acetylgalactosamine beta-1,3-galactosyltransferase that synthesizes GM1 and GD1b gangliosides by transferring galactose in a beta-1,3 linkage onto GalNAc-containing glycolipid acceptors, as established by direct enzymatic characterization of the recombinant enzyme [PMID:9582303]. Because its ganglioside products serve as the cholera toxin receptor, B3GALT4 is functionally required for cholera toxin intoxication, with loss of function abolishing CTx-mediated cytotoxicity [PMID:22123862]. The GM1 it produces is cytoprotective: knockdown in dopaminergic cells lowers GM1 and increases vulnerability to MPP+ neurotoxicity, a phenotype reversed by exogenous GM1 [PMID:30611881]. Through its control of ganglioside composition and lipid raft formation, B3GALT4 modulates downstream signaling — regulating c-Met within lipid rafts and the AKT/mTOR/IRF-1 axis to control CXCL9/CXCL10 secretion and CD8+ T cell recruitment in neuroblastoma [PMID:36284313], and acting through AKT/mTOR to restrain autophagy and promote proliferation, migration, and invasion in breast cancer cells [PMID:39331217]. No structural model or disease-causative mutation is reported in the available corpus.","teleology":[{"year":1996,"claim":"Before its molecular identity was clear, it was unknown what reaction the GalT-4 activity catalyzed; biochemical purification defined a metal-dependent galactosyltransferase acting on glycolipid acceptors requiring a terminal GlcNAc residue.","evidence":"107,500-fold enzyme purification from mouse T-lymphoma with kinetic and substrate-specificity characterization","pmids":["8781973"],"confidence":"High","gaps":["Activity characterized as beta-1,4 galactosylation of lactotriaosylceramide, not yet linked to the GM1/GD1b ganglioside pathway","Gene identity not established at this stage"]},{"year":1998,"claim":"It was unknown which cloned gene encoded this transferase and what ganglioside products it made; recombinant expression assigned B3GALT4 as a beta-1,3-galactosyltransferase in GM1/GD1b synthesis.","evidence":"Baculovirus expression and in vitro galactosyltransferase assay on GalNAc acceptors","pmids":["9582303"],"confidence":"High","gaps":["No structural model of the catalytic domain","Cellular and physiological roles not addressed"]},{"year":1998,"claim":"To confirm the catalytic domain identity, the question was whether a minimal recombinant fragment retains activity; a truncated GST-fusion form expressed in bacteria reproduced native enzyme activity.","evidence":"Recombinant GST-fusion expression in E. coli with activity and acceptor-interaction studies","pmids":["9821875"],"confidence":"Medium","gaps":["Limited mechanistic detail beyond abstract","Avian ortholog, not human enzyme"]},{"year":2011,"claim":"Whether B3GALT4 was functionally required for ganglioside-dependent cellular processes was untested; a genetic screen showed it is essential for cholera toxin intoxication via ganglioside receptor biosynthesis.","evidence":"Haploid loss-of-function genetic screen in human cells with cytotoxic CTx conjugate","pmids":["22123862"],"confidence":"High","gaps":["Does not address neuronal or oncogenic roles","Screen identifies pathway requirement, not direct receptor binding"]},{"year":2019,"claim":"The physiological consequence of B3GALT4-dependent GM1 in neurons was unknown; knockdown lowered GM1 and sensitized dopaminergic cells to neurotoxin, with GM1 rescue establishing a cytoprotective role.","evidence":"siRNA knockdown in SK-N-SH cells with ganglioside measurement, MPP+ toxicity assay, and GM1 rescue","pmids":["30611881"],"confidence":"Medium","gaps":["Single cell line, single lab","In vivo relevance to Parkinsonian neurodegeneration not tested"]},{"year":2022,"claim":"How B3GALT4-controlled gangliosides influence tumor signaling and immunity was unclear; in neuroblastoma it was shown to regulate GD2 and lipid rafts, modulating c-Met/AKT/mTOR/IRF-1 signaling and CD8+ T cell recruitment.","evidence":"Silencing/overexpression with flow cytometry, ELISA, raft inhibition, and in vivo tumor model","pmids":["36284313"],"confidence":"Medium","gaps":["Single lab","Direct mechanistic link between raft ganglioside changes and c-Met not fully resolved"]},{"year":2024,"claim":"Whether B3GALT4 influences tumor cell behavior beyond immune signaling was open; in breast cancer it was shown to promote proliferation/invasion and restrain autophagy through AKT/mTOR.","evidence":"Overexpression/knockdown with autophagy assays, LC3 imaging, RNA-seq/GSEA, and in vivo assays","pmids":["39331217"],"confidence":"Medium","gaps":["Single lab","Connection between glycosyltransferase activity and AKT/mTOR not mechanistically dissected"]},{"year":null,"claim":"How B3GALT4's enzymatic ganglioside output is mechanistically coupled to AKT/mTOR signaling and lipid raft organization across tissues remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of the human enzyme","No reported disease-causative mutation","Causal chain from specific ganglioside species to receptor-tyrosine-kinase signaling undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,5,6]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0]}],"localization":[],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,4]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O96024","full_name":"Beta-1,3-galactosyltransferase 4","aliases":["Gal-T2","Ganglioside galactosyltransferase","UDP-galactose:beta-N-acetyl-galactosamine-beta-1,3-galactosyltransferase"],"length_aa":378,"mass_kda":41.5,"function":"Involved in GM1/GD1B/GA1 ganglioside biosynthesis","subcellular_location":"Golgi apparatus membrane","url":"https://www.uniprot.org/uniprotkb/O96024/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/B3GALT4","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/B3GALT4","total_profiled":1310},"omim":[{"mim_id":"620239","title":"BETA-1,3-GALACTOSYLTRANSFERASE 9; B3GALT9","url":"https://www.omim.org/entry/620239"},{"mim_id":"603095","title":"UDP-GAL:BETA-GlcNAc BETA-1,3-GALACTOSYLTRANSFERASE, POLYPEPTIDE 4; B3GALT4","url":"https://www.omim.org/entry/603095"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"testis","ntpm":26.4}],"url":"https://www.proteinatlas.org/search/B3GALT4"},"hgnc":{"alias_symbol":["beta3Gal-T4","GalT4"],"prev_symbol":[]},"alphafold":{"accession":"O96024","domains":[{"cath_id":"3.90.550.50","chopping":"25-38_47-195_223-236_252-349_356-378","consensus_level":"medium","plddt":90.1159,"start":25,"end":378}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O96024","model_url":"https://alphafold.ebi.ac.uk/files/AF-O96024-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O96024-F1-predicted_aligned_error_v6.png","plddt_mean":84.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=B3GALT4","jax_strain_url":"https://www.jax.org/strain/search?query=B3GALT4"},"sequence":{"accession":"O96024","fasta_url":"https://rest.uniprot.org/uniprotkb/O96024.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O96024/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O96024"}},"corpus_meta":[{"pmid":"9582303","id":"PMC_9582303","title":"A family of human beta3-galactosyltransferases. Characterization of four members of a UDP-galactose:beta-N-acetyl-glucosamine/beta-nacetyl-galactosamine beta-1,3-galactosyltransferase family.","date":"1998","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9582303","citation_count":138,"is_preprint":false},{"pmid":"29902255","id":"PMC_29902255","title":"Altered expression of genes involved in ganglioside biosynthesis in substantia nigra neurons in Parkinson's disease.","date":"2018","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/29902255","citation_count":65,"is_preprint":false},{"pmid":"26786290","id":"PMC_26786290","title":"Genome-wide methylation profiling identifies novel methylated genes in neuroblastoma tumors.","date":"2016","source":"Epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/26786290","citation_count":62,"is_preprint":false},{"pmid":"22123862","id":"PMC_22123862","title":"Identification of host cell factors required for intoxication through use of modified cholera toxin.","date":"2011","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/22123862","citation_count":61,"is_preprint":false},{"pmid":"30372681","id":"PMC_30372681","title":"DNA Hypomethylation in Blood Links B3GALT4 and ZADH2 to Alzheimer's Disease.","date":"2018","source":"Journal of Alzheimer's disease : JAD","url":"https://pubmed.ncbi.nlm.nih.gov/30372681","citation_count":44,"is_preprint":false},{"pmid":"28721901","id":"PMC_28721901","title":"PSMB8 as a Candidate Marker of Responsiveness to Preoperative Radiation Therapy in Rectal Cancer Patients.","date":"2017","source":"International journal of radiation oncology, biology, physics","url":"https://pubmed.ncbi.nlm.nih.gov/28721901","citation_count":33,"is_preprint":false},{"pmid":"10970097","id":"PMC_10970097","title":"Physical mapping and evolution of the centromeric class I gene-containing region of the rat MHC.","date":"2000","source":"Immunogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/10970097","citation_count":33,"is_preprint":false},{"pmid":"36284313","id":"PMC_36284313","title":"B3GALT4 remodels the tumor microenvironment through GD2-mediated lipid raft formation and the c-met/AKT/mTOR/IRF-1 axis in neuroblastoma.","date":"2022","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/36284313","citation_count":32,"is_preprint":false},{"pmid":"6807531","id":"PMC_6807531","title":"Increased activity of a beta-galactosyltransferase in tissues of rats bearing prostate and mammary adenocarcinomas.","date":"1982","source":"Cancer biochemistry biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/6807531","citation_count":17,"is_preprint":false},{"pmid":"3149522","id":"PMC_3149522","title":"Solubilized glycosyltransferases and biosynthesis in vitro of glycolipids.","date":"1988","source":"Biochimie","url":"https://pubmed.ncbi.nlm.nih.gov/3149522","citation_count":16,"is_preprint":false},{"pmid":"15090729","id":"PMC_15090729","title":"Apoptosis of human carcinoma cells in the presence of inhibitors of glycosphingolipid biosynthesis: I. Treatment of Colo-205 and SKBR3 cells with isomers of PDMP and PPMP.","date":"2004","source":"Glycoconjugate journal","url":"https://pubmed.ncbi.nlm.nih.gov/15090729","citation_count":16,"is_preprint":false},{"pmid":"1281993","id":"PMC_1281993","title":"Isolation of a cDNA clone for beta 1-4 galactosyltransferase from embryonic chicken brain and comparison to its mammalian homologs.","date":"1992","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/1281993","citation_count":14,"is_preprint":false},{"pmid":"30611881","id":"PMC_30611881","title":"siRNA-mediated knockdown of B3GALT4 decreases GM1 ganglioside expression and enhances vulnerability for neurodegeneration.","date":"2019","source":"Molecular and cellular neurosciences","url":"https://pubmed.ncbi.nlm.nih.gov/30611881","citation_count":13,"is_preprint":false},{"pmid":"8536214","id":"PMC_8536214","title":"Glycosyltransferase activities in human meningiomas. Preliminary results.","date":"1995","source":"Cancer biochemistry biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/8536214","citation_count":11,"is_preprint":false},{"pmid":"291963","id":"PMC_291963","title":"Differential activities of glycolipid glycosyltransferases in Tay-Sachs disease: studies in cultured cells from cerebrum.","date":"1979","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/291963","citation_count":9,"is_preprint":false},{"pmid":"7911780","id":"PMC_7911780","title":"Biosynthesis and regulation of Le(x) and SA-Le(x) glycolipids in metastatic human colon carcinoma cells.","date":"1993","source":"Indian journal of biochemistry & biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/7911780","citation_count":9,"is_preprint":false},{"pmid":"19184418","id":"PMC_19184418","title":"Post-translational and transcriptional regulation of glycolipid glycosyltransferase genes in apoptotic breast carcinoma cells: VII. Studied by DNA-microarray after treatment with L-PPMP.","date":"2009","source":"Glycoconjugate journal","url":"https://pubmed.ncbi.nlm.nih.gov/19184418","citation_count":7,"is_preprint":false},{"pmid":"8781973","id":"PMC_8781973","title":"Biosynthesis in vitro of neolactotetraosylceramide by a galactosyltransferase from mouse T-lymphoma: purification and kinetic studies; synthesis of neolacto and polylactosamine core.","date":"1996","source":"Glycoconjugate journal","url":"https://pubmed.ncbi.nlm.nih.gov/8781973","citation_count":5,"is_preprint":false},{"pmid":"36929374","id":"PMC_36929374","title":"Genome-wide DNA methylation analysis of aggressive behaviour: a longitudinal population-based study.","date":"2023","source":"Journal of child psychology and psychiatry, and allied disciplines","url":"https://pubmed.ncbi.nlm.nih.gov/36929374","citation_count":4,"is_preprint":false},{"pmid":"37929718","id":"PMC_37929718","title":"Astaxanthin alleviates ganglioside metabolism disorder in the cortex of Alzheimer's disease mice.","date":"2023","source":"Food & function","url":"https://pubmed.ncbi.nlm.nih.gov/37929718","citation_count":4,"is_preprint":false},{"pmid":"9821875","id":"PMC_9821875","title":"Purification and characterization of avian glycolipid: beta-galactosyltransferases (GalT-4 and GalT-3): cloning and expression of truncated betaGalT-4.","date":"1998","source":"Acta biochimica Polonica","url":"https://pubmed.ncbi.nlm.nih.gov/9821875","citation_count":3,"is_preprint":false},{"pmid":"8005614","id":"PMC_8005614","title":"Regulation of expression of cell surface neolacto-glycolipids and cloning of embryonic chicken brain GalT-4 (UDP-Gal: GlcNAc-R beta 1-4 galactosyltransferase).","date":"1993","source":"Indian journal of biochemistry & biophysics","url":"https://pubmed.ncbi.nlm.nih.gov/8005614","citation_count":3,"is_preprint":false},{"pmid":"39331217","id":"PMC_39331217","title":"B3GALT4 modulates tumor progression and autophagy by AKT/mTOR signaling pathway in breast cancer.","date":"2024","source":"Discover oncology","url":"https://pubmed.ncbi.nlm.nih.gov/39331217","citation_count":1,"is_preprint":false},{"pmid":"39898245","id":"PMC_39898245","title":"Glycosphingolipids-Dependent Phospholipid Metabolism Enhances Cancer Initiation and Progression through SMPD1/GLTP/B3GALT4/ST8SIA6 Signaling Axis: A Novel Therapeutic Target.","date":"2025","source":"International journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/39898245","citation_count":1,"is_preprint":false},{"pmid":"26763390","id":"PMC_26763390","title":"MEIS3 is repressed in A549 lung epithelial cells by deoxynivalenol and the repression contributes to the deleterious effect.","date":"2016","source":"The Journal of toxicological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/26763390","citation_count":1,"is_preprint":false},{"pmid":"40718832","id":"PMC_40718832","title":"Ultrasound-based radiomics combined with B3GALT4 level to predict sentinel lymph node metastasis in primary breast cancer.","date":"2025","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/40718832","citation_count":0,"is_preprint":false},{"pmid":"41772720","id":"PMC_41772720","title":"DNA methylation is associated with von Willebrand factor and coagulation factor VIII plasma levels: the atherosclerosis risk in communities study.","date":"2026","source":"Clinical epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/41772720","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":17718,"output_tokens":1920,"usd":0.040977,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8759,"output_tokens":2492,"usd":0.053047,"stage2_stop_reason":"end_turn"},"total_usd":0.094024,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"B3GALT4 (beta3Gal-T4) encodes a UDP-galactose:beta-N-acetyl-galactosamine beta-1,3-galactosyltransferase activity involved in GM1/GD1b ganglioside synthesis, as demonstrated by expression in the Baculovirus system showing transfer of galactose to GalNAc-containing acceptors.\",\n      \"method\": \"Baculovirus expression system, enzymatic activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic characterization in recombinant expression system, replicated by independent rat GD1 synthase study\",\n      \"pmids\": [\"9582303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"B3GALT4 is essential for cholera toxin intoxication, identified through a genetic screen as required for ganglioside biosynthesis (the receptor for CTx); loss-of-function of B3GALT4 (along with ST3GAL5, SLC35A2, UGCG) abolishes CTx-mediated cytotoxicity.\",\n      \"method\": \"Haploid genetic screen in human cells using a cytotoxic CTx conjugate, loss-of-function clonal cell isolation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide genetic screen with functional validation in human cells, multiple orthogonal methods including clonal cell characterization\",\n      \"pmids\": [\"22123862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"siRNA-mediated knockdown of B3GALT4 in differentiated SK-N-SH dopaminergic cells significantly reduced GM1 ganglioside levels and increased vulnerability to MPP+ neurotoxicity; exogenous GM1 rescued this enhanced toxicity, establishing B3GALT4 as required for GM1 production that protects dopaminergic cells.\",\n      \"method\": \"siRNA knockdown, ganglioside level measurement, neurotoxicity assay (MPP+), GM1 rescue experiment\",\n      \"journal\": \"Molecular and cellular neurosciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with defined cellular phenotype and rescue experiment, single lab\",\n      \"pmids\": [\"30611881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"B3GALT4 regulates GD2 ganglioside expression and lipid raft formation in neuroblastoma cells; mechanistically, B3GALT4 modulates c-Met signaling within lipid rafts and downstream AKT/mTOR/IRF-1 pathway to control CXCL9 and CXCL10 chemokine secretion and CD8+ T cell recruitment.\",\n      \"method\": \"B3GALT4 silencing/overexpression, flow cytometry, ELISA, western blotting, lipid raft inhibitor (MβCD), immunofluorescence, in vivo tumor-bearing mouse model\",\n      \"journal\": \"Journal of experimental & clinical cancer research : CR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (functional assays, inhibitor, in vivo), single lab\",\n      \"pmids\": [\"36284313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"B3GALT4 promotes breast cancer cell proliferation, migration, and invasion; suppression of B3GALT4 triggers autophagy and inhibits the AKT/mTOR signaling pathway, establishing B3GALT4 as a regulator of autophagy through this pathway.\",\n      \"method\": \"B3GALT4 overexpression and knockdown, western blot, autophagolysosomes staining, LC3 fluorescence, GSEA, RNA-seq, in vitro and in vivo functional assays\",\n      \"journal\": \"Discover oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (RNA-seq, western blot, autophagy assays, in vivo), single lab\",\n      \"pmids\": [\"39331217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"GalT-4 (the mouse ortholog activity corresponding to B3GALT4) was purified 107,500-fold from mouse T-lymphoma P-1798 and characterized as catalyzing beta-1,4 galactosylation of lactotriaosylceramide (LcOse3Cer) to form neolactotetraosylceramide (nLcOse4Cer), with an absolute requirement for Mn2+, pH optimum 6.5–7.0, and Km values of 110 µM for LcOse3Cer and 250 µM for UDP-galactose; an N-acetylglucosamine residue in the acceptor substrate is required.\",\n      \"method\": \"Enzyme purification (affinity chromatography), kinetic characterization, substrate competition assay, western blot with anti-lactose synthetase antibody, TLC autoradiography, immunostaining\",\n      \"journal\": \"Glycoconjugate journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — extensive in vitro biochemical reconstitution with purified enzyme, multiple orthogonal methods including kinetics, substrate specificity, and immunological validation\",\n      \"pmids\": [\"8781973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"A truncated, catalytically active recombinant form of avian GalT-4 (B3GALT4 ortholog) was expressed as a GST fusion protein in E. coli; the recombinant protein retained functional activity similar to native GalT-4 purified from embryonic chicken brain, confirming the catalytic domain identity.\",\n      \"method\": \"Recombinant expression (GST fusion in E. coli), enzymatic activity assay, interaction studies with GlcNAc and UDP-hexanolamine\",\n      \"journal\": \"Acta biochimica Polonica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — recombinant expression with functional characterization, single lab, limited detail in abstract\",\n      \"pmids\": [\"9821875\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"B3GALT4 encodes a UDP-galactose:beta-N-acetylgalactosamine beta-1,3-galactosyltransferase that synthesizes GM1 and GD1b gangliosides by transferring galactose in a beta-1,3 linkage; it is required for ganglioside-mediated cholera toxin receptor function, maintains GM1 levels that protect dopaminergic neurons, regulates GD2 expression and lipid raft formation to modulate c-Met/AKT/mTOR/IRF-1 signaling and immune cell recruitment in neuroblastoma, and controls autophagy through the AKT/mTOR pathway in breast cancer cells.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"B3GALT4 encodes a Mn2+-dependent UDP-galactose:beta-N-acetylgalactosamine beta-1,3-galactosyltransferase that synthesizes GM1 and GD1b gangliosides by transferring galactose in a beta-1,3 linkage onto GalNAc-containing glycolipid acceptors, as established by direct enzymatic characterization of the recombinant enzyme [#0]. Because its ganglioside products serve as the cholera toxin receptor, B3GALT4 is functionally required for cholera toxin intoxication, with loss of function abolishing CTx-mediated cytotoxicity [#1]. The GM1 it produces is cytoprotective: knockdown in dopaminergic cells lowers GM1 and increases vulnerability to MPP+ neurotoxicity, a phenotype reversed by exogenous GM1 [#2]. Through its control of ganglioside composition and lipid raft formation, B3GALT4 modulates downstream signaling — regulating c-Met within lipid rafts and the AKT/mTOR/IRF-1 axis to control CXCL9/CXCL10 secretion and CD8+ T cell recruitment in neuroblastoma [#3], and acting through AKT/mTOR to restrain autophagy and promote proliferation, migration, and invasion in breast cancer cells [#4]. No structural model or disease-causative mutation is reported in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Before its molecular identity was clear, it was unknown what reaction the GalT-4 activity catalyzed; biochemical purification defined a metal-dependent galactosyltransferase acting on glycolipid acceptors requiring a terminal GlcNAc residue.\",\n      \"evidence\": \"107,500-fold enzyme purification from mouse T-lymphoma with kinetic and substrate-specificity characterization\",\n      \"pmids\": [\"8781973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Activity characterized as beta-1,4 galactosylation of lactotriaosylceramide, not yet linked to the GM1/GD1b ganglioside pathway\", \"Gene identity not established at this stage\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"It was unknown which cloned gene encoded this transferase and what ganglioside products it made; recombinant expression assigned B3GALT4 as a beta-1,3-galactosyltransferase in GM1/GD1b synthesis.\",\n      \"evidence\": \"Baculovirus expression and in vitro galactosyltransferase assay on GalNAc acceptors\",\n      \"pmids\": [\"9582303\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural model of the catalytic domain\", \"Cellular and physiological roles not addressed\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"To confirm the catalytic domain identity, the question was whether a minimal recombinant fragment retains activity; a truncated GST-fusion form expressed in bacteria reproduced native enzyme activity.\",\n      \"evidence\": \"Recombinant GST-fusion expression in E. coli with activity and acceptor-interaction studies\",\n      \"pmids\": [\"9821875\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Limited mechanistic detail beyond abstract\", \"Avian ortholog, not human enzyme\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Whether B3GALT4 was functionally required for ganglioside-dependent cellular processes was untested; a genetic screen showed it is essential for cholera toxin intoxication via ganglioside receptor biosynthesis.\",\n      \"evidence\": \"Haploid loss-of-function genetic screen in human cells with cytotoxic CTx conjugate\",\n      \"pmids\": [\"22123862\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address neuronal or oncogenic roles\", \"Screen identifies pathway requirement, not direct receptor binding\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The physiological consequence of B3GALT4-dependent GM1 in neurons was unknown; knockdown lowered GM1 and sensitized dopaminergic cells to neurotoxin, with GM1 rescue establishing a cytoprotective role.\",\n      \"evidence\": \"siRNA knockdown in SK-N-SH cells with ganglioside measurement, MPP+ toxicity assay, and GM1 rescue\",\n      \"pmids\": [\"30611881\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell line, single lab\", \"In vivo relevance to Parkinsonian neurodegeneration not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"How B3GALT4-controlled gangliosides influence tumor signaling and immunity was unclear; in neuroblastoma it was shown to regulate GD2 and lipid rafts, modulating c-Met/AKT/mTOR/IRF-1 signaling and CD8+ T cell recruitment.\",\n      \"evidence\": \"Silencing/overexpression with flow cytometry, ELISA, raft inhibition, and in vivo tumor model\",\n      \"pmids\": [\"36284313\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct mechanistic link between raft ganglioside changes and c-Met not fully resolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Whether B3GALT4 influences tumor cell behavior beyond immune signaling was open; in breast cancer it was shown to promote proliferation/invasion and restrain autophagy through AKT/mTOR.\",\n      \"evidence\": \"Overexpression/knockdown with autophagy assays, LC3 imaging, RNA-seq/GSEA, and in vivo assays\",\n      \"pmids\": [\"39331217\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Connection between glycosyltransferase activity and AKT/mTOR not mechanistically dissected\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How B3GALT4's enzymatic ganglioside output is mechanistically coupled to AKT/mTOR signaling and lipid raft organization across tissues remains unresolved.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of the human enzyme\", \"No reported disease-causative mutation\", \"Causal chain from specific ganglioside species to receptor-tyrosine-kinase signaling undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 5, 6]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":4,"faith_total":4,"faith_pct":100.0}}