{"gene":"MGAT3","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":1993,"finding":"Human GnT-III (MGAT3) encodes a 531-amino acid type II transmembrane protein that catalyzes the addition of N-acetylglucosamine in β1,4 linkage to the β-linked mannose of the trimannosyl core of N-linked sugar chains, producing a bisecting GlcNAc residue. The amino-terminal transmembrane domain and catalytic domain are conserved between human and rat. The gene maps to chromosome 22q13.1.","method":"cDNA cloning, open reading frame analysis, chromosomal mapping by fluorescence in situ hybridization (FISH)","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct sequencing and functional characterization of human cDNA, replicated across species; foundational cloning paper","pmids":["8370666"],"is_preprint":false},{"year":1995,"finding":"The mouse Mgat3 gene encodes GlcNAc-TIII and is expressed as a single-copy gene at high levels in kidney and brain. A sense-orientation ORF transfected into CHO cells confers GlcNAc-TIII enzymatic activity, demonstrating the ORF encodes the catalytic enzyme. Mouse Mgat3 maps to chromosome 15.","method":"Genomic cloning, mammalian expression transfection, enzymatic activity assay, Southern blot, FISH mapping","journal":"Gene","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct enzymatic activity confirmed by transfection with sense/antisense control, consistent with human gene characterization","pmids":["7590346"],"is_preprint":false},{"year":1997,"finding":"Mgat3-deficient mice generated by Cre/loxP-mediated gene deletion lack GlcNAc-TIII activity and are deficient in E4-PHA-visualized GlcNAc-bisected N-linked oligosaccharides, yet are viable, fertile, and show no overt developmental, hematological, or organ morphology defects. This establishes that bisecting GlcNAc is dispensable for normal murine development and homeostasis.","method":"Gene targeting (Cre/loxP), enzymatic activity assay, lectin blotting, flow cytometry, histology","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with multiple orthogonal readouts; definitive loss-of-function study","pmids":["9061364"],"is_preprint":false},{"year":2002,"finding":"Active-site mutagenesis of rat GnT-III identified two conserved aspartate residues (Asp321 and Asp323) as absolutely required for catalytic activity based on sequence homology with snail β1,4GlcNAc transferase and β1,4Gal transferase-1. Overexpression of the catalytically inactive Asp323-substituted mutant suppressed endogenous GnT-III activity (dominant negative effect) and specifically blocked formation of bisected N-glycans without reducing endogenous GnT-III expression levels.","method":"Sequence homology analysis, site-directed mutagenesis, enzymatic activity assay, overexpression in Huh6 cells, N-glycan structural analysis","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis with in vitro activity assay and structural glycan analysis in a single rigorous study","pmids":["11784313"],"is_preprint":false},{"year":1995,"finding":"GnT-III activity is elevated in CML blast crisis and multiple myeloma cells. Immunoprecipitation and lectin blot analysis showed that elevated GnT-III in KU812 (CML) cells results in increased bisecting GlcNAc on CD45, a major leukocyte surface glycoprotein, as its substrate.","method":"Enzymatic activity assay (HPLC), immunoprecipitation, Western/lectin blot with E4-PHA","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — immunoprecipitation plus lectin blot confirms CD45 as substrate; single lab, two orthogonal methods","pmids":["7829256"],"is_preprint":false},{"year":2002,"finding":"In GnT-III transgenic mice with DEN-induced hepatic tumors, glycomic analysis (2D gel electrophoresis, lectin blot, sequencing, immunoprecipitation) identified haptoglobin as a target glycoprotein modified by GnT-III-mediated bisecting GlcNAc addition, and GnT-III overexpression dramatically suppressed hepatic tumor incidence.","method":"Transgenic mouse model, 2D gel electrophoresis, lectin blot, sequence analysis, immunoprecipitation with E4-PHA lectin blot","journal":"Free radical research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — glycomic approach with immunoprecipitation validation identifies haptoglobin as substrate; single lab study","pmids":["12420740"],"is_preprint":false},{"year":2012,"finding":"During epithelial-mesenchymal transition (EMT), Mgat3 promoter methylation causes dramatic reduction in Mgat3 expression and loss of GnT-III-mediated bisecting GlcNAc modification on E-cadherin; this is reversed during mesenchymal-epithelial transition (MET) by promoter demethylation. This identifies epigenetic regulation of Mgat3 as a mechanism controlling E-cadherin glycosylation during EMT/MET.","method":"Bisulfite sequencing, qPCR, Western blot, lectin blot, glycan analysis during TGF-β-induced EMT/MET in cell lines","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter methylation analysis linked to enzymatic product on defined substrate; single lab, multiple methods","pmids":["22427986"],"is_preprint":false},{"year":2012,"finding":"All-trans-retinoic acid (ATRA) upregulates GnT-III expression via the ERK signaling pathway, causing bisecting GlcNAc modification of ICAM-1 N-glycans (shown by reduced ICAM-1 molecular mass reversible by PNGase F and by GnT-III siRNA knockdown). This GnT-III-dependent ICAM-1 glycan remodeling inhibits cell adhesion and trans-endothelial migration.","method":"siRNA knockdown, qPCR, gel mobility shift assay, PNGase F treatment, cell adhesion assay, trans-endothelial migration assay, ERK inhibitor treatment","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function (siRNA) links GnT-III to specific ICAM-1 glycan change and defined cellular phenotype; single lab, multiple methods","pmids":["23300837"],"is_preprint":false},{"year":2014,"finding":"In Fut8-deficient mouse embryonic fibroblasts (MEFs), loss of core fucose leads to upregulation of GnT-III expression via activation of Wnt/β-catenin signaling. A Wnt signaling inhibitor abrogates GnT-III upregulation. As a result, bisecting GlcNAc on β1-integrin and N-cadherin is increased; IgG1 glycan analysis by mass spectrometry confirms increased bisecting GlcNAc in Fut8-/- mouse serum in vivo.","method":"Mouse embryonic fibroblasts from Fut8-/- mice, gene expression analysis, Wnt inhibitor treatment, lectin blot, mass spectrometry of IgG glycans","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Wnt inhibitor epistasis establishes pathway regulation of GnT-III; in vivo mass spectrometry validates substrate modification; single lab","pmids":["24619415"],"is_preprint":false},{"year":2016,"finding":"DNA methylation at the MGAT3 transcription start site represses MGAT3 expression; treatment with the DNA methyltransferase inhibitor 5-Aza restores MGAT3 expression coinciding with reduced promoter methylation. Bisecting GlcNAc on released N-glycans (detected by LC-ESI-qTOF-MS/MS) appears in ovarian cancer cells only after MGAT3 re-expression following demethylation, establishing promoter methylation as a direct mechanism controlling bisecting GlcNAc biosynthesis.","method":"5-Aza treatment, bisulfite sequencing, LC-ESI-qTOF-MS/MS glycan analysis, expression analysis","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct mechanistic link between promoter methylation and enzymatic product detected by mass spectrometry; single lab, two orthogonal methods","pmids":["27429195"],"is_preprint":false},{"year":2017,"finding":"GnT-III expression controls expansion of cancer stem cells (side-population cells) in epithelial ovarian carcinoma. shRNA suppression of GnT-III reduces Notch receptor levels and signaling more potently than pharmacologic γ-secretase inhibition, by redirecting Notch receptor to the lysosome rather than to the cell surface, identifying a novel mechanism whereby bisecting glycosylation controls Notch receptor trafficking.","method":"Stable shRNA knockdown, flow cytometry for side-population cells, Western blot, γ-secretase inhibitor comparison, lysosome localization assay, primary tumor-derived cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined mechanistic pathway (lysosomal redirection of Notch); single lab, multiple cell models","pmids":["28842505"],"is_preprint":false},{"year":2017,"finding":"GLP-1 receptor agonists (exendin-4) downregulate aberrant GnT-III expression and bisecting GlcNAc levels in APP/PS1 mice and Aβ25-35-treated PC12 cells through the Akt/GSK-3β/β-catenin signaling pathway. β-catenin siRNA abolishes the effect of GLP-1RA on GnT-III, and PI3K inhibitor LY294002 attenuates these effects, establishing the Akt/GSK-3β/β-catenin axis as an upstream regulator of GnT-III expression.","method":"APP/PS1 transgenic mice, siRNA knockdown, PI3K inhibitor (LY294002), Western blot, phosphorylation analysis, behavioral testing","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis via siRNA and pharmacological inhibitor establishes pathway; single lab, multiple methods","pmids":["29223528"],"is_preprint":false},{"year":2020,"finding":"MGAT3-mediated glycosylation of CD82 at asparagine 157 is required for CD82-mediated inhibition of ovarian cancer cell migration and metastasis in vitro and in vivo. Mechanistically, glycosylated CD82 disrupts integrin α5β1-mediated cellular adhesion to fibronectin and inhibits integrin signaling-induced cytoskeletal rearrangements required for migration. MGAT3 was identified as the glycosyltransferase responsible for this CD82 glycosylation.","method":"Site-directed mutagenesis of CD82 glycosylation sites, in vitro migration/invasion assays, in vivo xenograft, integrin adhesion assays, Western blot, paired human tissue samples","journal":"Theranostics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis of specific glycosylation site, in vitro and in vivo functional validation, mechanistic pathway (integrin α5β1/fibronectin) identified; single lab with multiple orthogonal methods","pmids":["32483464"],"is_preprint":false},{"year":2021,"finding":"miR-23b directly targets the 3'-UTR of GnT-III mRNA (verified by dual-luciferase reporter assay), reducing GnT-III expression. miR-23b overexpression activates the Akt/GSK-3β signaling pathway to inhibit tau hyperphosphorylation and reduce oxidative stress in Alzheimer's disease models.","method":"Dual-luciferase reporter assay, bioinformatics, overexpression in Aβ1-42-induced mouse and PC12 cell models, Western blot","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct 3'-UTR targeting validated by reporter assay with downstream pathway analysis; single lab","pmids":["34153312"],"is_preprint":false},{"year":2024,"finding":"Structure-function analysis of GnT-III using AlphaFold2-based modeling and point mutagenesis identified E320 as the catalytic center of human GnT-III. A K346T mutant showed reduced in vitro activity but enhanced intracellular bisecting GlcNAc production; TurboID-based proximity labeling demonstrated that K346T is shifted to the cis-Golgi relative to wild-type, providing a mechanistic explanation for discordant in vitro vs. intracellular activity. Cycloheximide chase showed the K346T mutant has a shorter half-life.","method":"AlphaFold2 structure prediction, site-directed mutagenesis, in vitro activity assay, HPLC, UDP-Glo glycosyltransferase assay, glycomic analysis, TurboID proximity labeling, immunostaining, cycloheximide chase","journal":"Biochimica et biophysica acta. General subjects","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mutagenesis with in vitro activity and intracellular glycomic readouts plus proximity labeling for localization; single lab, multiple orthogonal methods; catalytic center identified by computational prediction + mutagenesis","pmids":["38936637"],"is_preprint":false},{"year":2024,"finding":"The middle loop (Loop) and C-terminal tail (Tail) of GnT-III play distinct functional roles: (1) deletion of Loop increases both in vitro and intracellular GnT-III activity, indicating Loop suppresses catalytic activity and contains the cleavage site for GnT-III shedding; (2) deletion of Tail reduces activity, increases ER localization, and accelerates protein degradation, indicating Tail is required for proper folding and Golgi localization.","method":"Deletion mutagenesis, HPLC activity assay, UDP-Glo assay, glycomic analysis, immunostaining for subcellular localization, degradation rate assay","journal":"Biochimica et biophysica acta. General subjects","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — deletion mutagenesis with enzymatic activity assays and subcellular localization; single lab, multiple methods","pmids":["39653250"],"is_preprint":false},{"year":2025,"finding":"Proximity labeling with biotin ligases (BASU and TurboID) identified 116 and 189 proteins in the MGAT3 proximitome in HEK293T cells, with 17 shared with a bisecting GlcNAc-bearing proteome. Four novel substrates—GOLM2, CCDC134, ASPH, and ERO1A—were confirmed to bear bisecting GlcNAc modification. MGAT3-mediated bisecting GlcNAc on α-galactosidase A (GLA) promotes GLA degradation, thereby inhibiting breast cancer progression.","method":"TurboID and BASU proximity labeling, intact glycopeptide enrichment, mass spectrometry, Western blot, breast cancer functional assays","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proximity labeling with MS identification and validation of substrates bearing bisecting GlcNAc; functional consequence established for GLA; single lab","pmids":["39851531"],"is_preprint":false},{"year":2025,"finding":"Chemoenzymatic experiments established that GnT-III can act on bi-, tri-, and tetra-antennary N-glycans as substrates and preferentially modifies bi-antennary glycans (kinetic experiments). GnT-III also accepts N-glycans having a β1,2-GlcNTFA or GlcN3 moiety at the α1,2Man- or α1,6Man-antenna, enabling synthesis of asymmetric bisecting glycans.","method":"Chemoenzymatic synthesis, kinetic activity assays, glycan microarray screening","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro enzymatic kinetics with defined substrates; preprint, single study, not yet peer-reviewed","pmids":["bio_10.1101_2025.06.26.661710"],"is_preprint":true}],"current_model":"MGAT3/GnT-III is a Golgi-resident glycosyltransferase (type II transmembrane protein) that catalyzes the β1,4-transfer of GlcNAc to the β-linked mannose of the trimannosyl N-glycan core, producing a bisecting GlcNAc that suppresses further N-glycan branching; its catalytic center requires Glu320 and Asp321/Asp323, its activity is suppressed by an internal loop and requires a C-terminal tail for proper folding/Golgi localization, and its expression is regulated epigenetically by promoter methylation and transcriptionally via Wnt/β-catenin and Akt/GSK-3β signaling; substrates include CD45, ICAM-1, E-cadherin, CD82 (at N157), haptoglobin, and GLA, with functional consequences including inhibition of EMT, suppression of integrin α5β1/fibronectin-mediated migration, control of Notch receptor lysosomal trafficking, and promotion of GLA degradation."},"narrative":{"mechanistic_narrative":"MGAT3 encodes GlcNAc-TIII (GnT-III), a Golgi-resident type II transmembrane glycosyltransferase that transfers N-acetylglucosamine in β1,4 linkage to the β-linked mannose of the trimannosyl N-glycan core to produce a bisecting GlcNAc residue that suppresses further N-glycan branching [PMID:8370666, PMID:7590346]. Catalysis depends on conserved acidic active-site residues—Glu320 as the catalytic center and Asp321/Asp323—mutation of which abolishes activity, with a catalytically dead Asp323 mutant acting dominant-negatively to block bisected-glycan formation [PMID:11784313, PMID:38936637]; an internal loop suppresses catalytic activity and harbors the shedding cleavage site, while a C-terminal tail is required for proper folding and Golgi retention, with its loss causing ER mislocalization and accelerated degradation [PMID:39653250]. Despite this molecular activity, bisecting GlcNAc is dispensable for normal mouse development, as Mgat3-null mice are viable and fertile [PMID:9061364]. GnT-III modifies a defined set of glycoprotein substrates—including CD45, E-cadherin, ICAM-1, haptoglobin, CD82 at Asn157, and α-galactosidase A (GLA)—and these modifications carry distinct functional consequences: bisecting glycosylation of E-cadherin and ICAM-1 restrains EMT and cell adhesion/migration [PMID:22427986, PMID:23300837], glycosylation of CD82 disrupts integrin α5β1-mediated adhesion to fibronectin to inhibit ovarian cancer migration and metastasis [PMID:32483464], control of Notch receptor trafficking redirects the receptor to the lysosome to limit cancer stem-cell expansion [PMID:28842505], and bisecting GlcNAc on GLA promotes its degradation to inhibit breast cancer progression [PMID:39851531]. MGAT3 expression is controlled epigenetically by promoter/transcription-start-site methylation and transcriptionally through Wnt/β-catenin and Akt/GSK-3β signaling, as well as post-transcriptionally by miR-23b targeting of its 3′-UTR [PMID:22427986, PMID:24619415, PMID:27429195, PMID:29223528, PMID:34153312].","teleology":[{"year":1993,"claim":"Establishing what MGAT3 is at the molecular level: cloning revealed it encodes a type II transmembrane glycosyltransferase that builds the bisecting GlcNAc on the N-glycan core.","evidence":"cDNA cloning, ORF analysis, and FISH mapping of human GnT-III","pmids":["8370666"],"confidence":"High","gaps":["Did not resolve active-site residues or catalytic mechanism","Substrate glycoproteins not yet identified"]},{"year":1995,"claim":"Confirmed the cloned ORF is the catalytic enzyme and not a regulatory factor by demonstrating that sense-orientation expression confers GlcNAc-TIII activity.","evidence":"Genomic cloning and sense/antisense transfection with enzymatic assay in CHO cells","pmids":["7590346"],"confidence":"High","gaps":["Tissue-restricted expression mechanism unexplained","No physiological substrate defined"]},{"year":1995,"claim":"Linked elevated GnT-III activity in hematologic malignancy to a concrete physiological substrate, identifying CD45 as bearing increased bisecting GlcNAc.","evidence":"Enzymatic assay, immunoprecipitation, and E4-PHA lectin blot in CML/myeloma cells","pmids":["7829256"],"confidence":"Medium","gaps":["Functional consequence of CD45 bisecting glycosylation not established","Single-lab characterization"]},{"year":1997,"claim":"Resolved whether bisecting GlcNAc is essential in vivo: knockout mice showed it is dispensable for development and homeostasis, redirecting the field toward conditional/disease roles.","evidence":"Cre/loxP gene targeting with lectin, flow, and histology readouts","pmids":["9061364"],"confidence":"High","gaps":["Phenotypes under stress, tumor, or aging not assessed","Compensation by other branching enzymes not excluded"]},{"year":2002,"claim":"Defined the catalytic chemistry by mapping required active-site aspartates and demonstrating dominant-negative suppression by an inactive mutant.","evidence":"Homology-guided site-directed mutagenesis with activity and N-glycan structural analysis","pmids":["11784313"],"confidence":"High","gaps":["Did not identify the principal catalytic residue (later Glu320)","No structural model of the active site"]},{"year":2002,"claim":"Connected GnT-III to tumor suppression in vivo and expanded the substrate repertoire by identifying haptoglobin as a bisected target.","evidence":"GnT-III transgenic DEN-hepatocarcinogenesis model with glycomic/immunoprecipitation substrate mapping","pmids":["12420740"],"confidence":"Medium","gaps":["Mechanism linking haptoglobin glycosylation to tumor suppression unclear","Single-lab study"]},{"year":2012,"claim":"Showed how MGAT3 is regulated and coupled to cell-state transitions: promoter methylation silences it during EMT and is reversed in MET, controlling E-cadherin glycosylation.","evidence":"Bisulfite sequencing and lectin/glycan analysis during TGF-β-induced EMT/MET","pmids":["22427986"],"confidence":"Medium","gaps":["Upstream signals driving methylation not defined","Causality of E-cadherin glycosylation in EMT not proven by rescue"]},{"year":2012,"claim":"Identified an inducible transcriptional route (ATRA/ERK) to GnT-III upregulation and tied ICAM-1 glycan remodeling to suppressed adhesion and transmigration.","evidence":"siRNA, gel mobility/PNGase F, adhesion and trans-endothelial migration assays with ERK inhibition","pmids":["23300837"],"confidence":"Medium","gaps":["Direct transcriptional effectors downstream of ERK not mapped","Single-lab characterization"]},{"year":2014,"claim":"Placed MGAT3 in a glycan crosstalk network: loss of core fucose induces GnT-III via Wnt/β-catenin, increasing bisecting GlcNAc on integrin and N-cadherin.","evidence":"Fut8-/- MEFs with Wnt-inhibitor epistasis and in vivo IgG mass spectrometry","pmids":["24619415"],"confidence":"Medium","gaps":["How loss of core fucose activates Wnt signaling not resolved","Single-lab study"]},{"year":2016,"claim":"Generalized methylation control of MGAT3 to cancer, directly tying promoter demethylation to restored bisecting-glycan biosynthesis.","evidence":"5-Aza treatment, bisulfite sequencing, and LC-MS/MS glycan detection in ovarian cancer cells","pmids":["27429195"],"confidence":"Medium","gaps":["Functional impact of restored MGAT3 in this model not measured","Single-lab study"]},{"year":2017,"claim":"Uncovered a trafficking-based mechanism for MGAT3's tumor-relevant role: bisecting glycosylation controls Notch receptor lysosomal routing to limit cancer stem-cell expansion.","evidence":"shRNA knockdown, side-population flow cytometry, lysosomal localization, and γ-secretase comparison in ovarian carcinoma cells","pmids":["28842505"],"confidence":"Medium","gaps":["Direct demonstration that Notch itself is bisected not shown","Single-lab study"]},{"year":2017,"claim":"Established an Akt/GSK-3β/β-catenin signaling axis as upstream regulator of GnT-III in a neurodegeneration context.","evidence":"APP/PS1 mice and Aβ-treated PC12 cells with β-catenin siRNA and PI3K inhibitor epistasis","pmids":["29223528"],"confidence":"Medium","gaps":["Direct substrate(s) mediating neural effects not identified","Single-lab study"]},{"year":2020,"claim":"Provided rigorous site-resolved substrate causality: MGAT3 glycosylation of CD82 at Asn157 is required to suppress integrin α5β1/fibronectin adhesion and metastasis.","evidence":"CD82 glycosite mutagenesis with in vitro/in vivo migration, adhesion assays, and paired tissues","pmids":["32483464"],"confidence":"High","gaps":["Structural basis of how the bisected glycan alters CD82-integrin interaction not defined","Single-lab study"]},{"year":2021,"claim":"Added post-transcriptional control by showing miR-23b directly targets the GnT-III 3′-UTR, with downstream effects on tau phosphorylation and oxidative stress.","evidence":"Dual-luciferase 3′-UTR reporter and overexpression in Aβ-induced AD models","pmids":["34153312"],"confidence":"Medium","gaps":["Whether GnT-III substrate changes mediate the tau/oxidative effects not shown","Single-lab study"]},{"year":2024,"claim":"Resolved the catalytic center and a localization-dependent activity mechanism: Glu320 is catalytic, and a K346T mutant shifts to the cis-Golgi to explain discordant in vitro vs intracellular activity.","evidence":"AlphaFold2 modeling, mutagenesis, in vitro/intracellular activity, TurboID localization, and cycloheximide chase","pmids":["38936637"],"confidence":"Medium","gaps":["No experimental crystal/cryo-EM structure","Single-lab study"]},{"year":2024,"claim":"Dissected domain-level regulation: an internal loop autoinhibits and is the shedding cleavage site, while the C-terminal tail is needed for folding and Golgi retention.","evidence":"Deletion mutagenesis with activity assays and subcellular localization in cells","pmids":["39653250"],"confidence":"Medium","gaps":["Protease responsible for loop-mediated shedding not identified","Single-lab study"]},{"year":2025,"claim":"Systematically expanded the substrate landscape via proximity labeling, identifying new bisected substrates and a functional GLA-degradation axis in breast cancer.","evidence":"BASU/TurboID proximity labeling, glycopeptide MS, and breast cancer functional assays","pmids":["39851531"],"confidence":"Medium","gaps":["Mechanism by which bisecting GlcNAc promotes GLA degradation unclear","Roles of GOLM2/CCDC134/ASPH/ERO1A modification untested"]},{"year":2025,"claim":"Defined acceptor-substrate specificity and kinetic preferences, showing GnT-III acts on multi-antennary and modified N-glycans, enabling asymmetric bisecting-glycan synthesis.","evidence":"Chemoenzymatic synthesis, kinetics, and glycan microarray screening (preprint)","pmids":["bio_10.1101_2025.06.26.661710"],"confidence":"Medium","gaps":["Not peer-reviewed","In vitro specificity may not reflect cellular acceptor availability"]},{"year":null,"claim":"How bisecting GlcNAc on individual substrates mechanistically alters protein trafficking, stability, and signaling—and the physiological consequences of MGAT3 dysregulation in disease—remains incompletely defined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No experimental high-resolution structure of the catalytic domain","Generalizable rules linking bisected glycan to substrate fate not established","In vivo disease causality from MGAT3 perturbation largely correlative"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,3,14,17]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[14,15]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[15]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,3]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,12,16]}],"complexes":[],"partners":["CD45","E-CADHERIN","ICAM-1","CD82","HAPTOGLOBIN","GLA","NOTCH"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q09327","full_name":"Beta-1,4-mannosyl-glycoprotein 4-beta-N-acetylglucosaminyltransferase","aliases":["N-glycosyl-oligosaccharide-glycoprotein N-acetylglucosaminyltransferase III","GNT-III","GlcNAc-T III","N-acetylglucosaminyltransferase III"],"length_aa":533,"mass_kda":61.3,"function":"It is involved in the regulation of the biosynthesis and biological function of glycoprotein oligosaccharides. Catalyzes the addition of N-acetylglucosamine in beta 1-4 linkage to the beta-linked mannose of the trimannosyl core of N-linked sugar chains, called bisecting N-acetylglucosamine (GlcNAc). It is one of the most important enzymes involved in the regulation of the biosynthesis of glycoprotein oligosaccharides. The addition of this bisecting GlcNAc residue alters not only the composition, but also the conformation of the N-glycan. The introduction of the bisecting GlcNAc residue results in the suppression of further processing and elongation of N-glycans, precluding the formation of beta-1,6 GlcNAc branching, catalyzed by MGAT5 since it is unable to use the bisected oligosaccharide as a substrate (PubMed:19403558). Addition of bisecting N-acetylglucosamine to CDH1/E-cadherin modulates CDH1 cell membrane location (PubMed:19403558). Inhibits NeuAc-alpha-2,3-Gal-beta-1,4-GlcNAc- formation which modulates sialylation levels and plays a role in cell migration regulation (PubMed:26801611). In brain, addition of bisecting N-acetylglucosamine to BACE1 blocks its lysosomal targeting in response to oxidative stress and further degradation which increases its location to early endosome and the APP cleavage (By similarity). Adds bisecting GlcNAc residue to complex-type N-linked-glycans attached on fragment crystallizable (Fc) of IgGs. Readily converts fucosylated and non-fucosylated core glycoforms with terminal GlcNAcs on both antennae. Prior galactosylation of GlcNAc on the alpha(1->3) Man branch prevents N-glycan bisection, whereas galactosylation of GlcNAc on the alpha(1->6) Man branch is permissive","subcellular_location":"Golgi apparatus, Golgi stack membrane","url":"https://www.uniprot.org/uniprotkb/Q09327/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MGAT3","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MGAT3","total_profiled":1310},"omim":[{"mim_id":"610184","title":"MONOACYLGLYCEROL O-ACYLTRANSFERASE 3; MOGAT3","url":"https://www.omim.org/entry/610184"},{"mim_id":"606822","title":"PROTEIN O-MANNOSE BETA-1,2-N-ACETYLGLUCOSAMINYLTRANSFERASE; POMGNT1","url":"https://www.omim.org/entry/606822"},{"mim_id":"604621","title":"BETA-1,4-@MANNOSYL-GLYCOPROTEIN BETA-1,4-N-ACETYLGLUCOSAMINYLTRANSFERASE; MGAT3","url":"https://www.omim.org/entry/604621"},{"mim_id":"604564","title":"GLUTATHIONE S-TRANSFERASE, MICROSOMAL, 3; MGST3","url":"https://www.omim.org/entry/604564"},{"mim_id":"601774","title":"ALPHA-1,6-@MANNOSYL-GLYCOPROTEIN BETA-1,6-N-ACETYLGLUCOSAMINYLTRANSFERASE; MGAT5","url":"https://www.omim.org/entry/601774"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":41.3},{"tissue":"intestine","ntpm":26.7}],"url":"https://www.proteinatlas.org/search/MGAT3"},"hgnc":{"alias_symbol":["GNT-III"],"prev_symbol":[]},"alphafold":{"accession":"Q09327","domains":[{"cath_id":"3.90.550","chopping":"85-106_192-423","consensus_level":"high","plddt":94.7194,"start":85,"end":423}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q09327","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q09327-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q09327-F1-predicted_aligned_error_v6.png","plddt_mean":78.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MGAT3","jax_strain_url":"https://www.jax.org/strain/search?query=MGAT3"},"sequence":{"accession":"Q09327","fasta_url":"https://rest.uniprot.org/uniprotkb/Q09327.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q09327/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q09327"}},"corpus_meta":[{"pmid":"15807771","id":"PMC_15807771","title":"Survival of adult islet grafts from transgenic pigs with N-acetylglucosaminyltransferase-III (GnT-III) in cynomolgus monkeys.","date":"2005","source":"Xenotransplantation","url":"https://pubmed.ncbi.nlm.nih.gov/15807771","citation_count":120,"is_preprint":false},{"pmid":"8370666","id":"PMC_8370666","title":"cDNA cloning, expression, and chromosomal localization of human N-acetylglucosaminyltransferase III (GnT-III).","date":"1993","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8370666","citation_count":95,"is_preprint":false},{"pmid":"22427986","id":"PMC_22427986","title":"Loss and recovery of Mgat3 and GnT-III Mediated E-cadherin N-glycosylation is a mechanism involved in epithelial-mesenchymal-epithelial transitions.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22427986","citation_count":87,"is_preprint":false},{"pmid":"9061364","id":"PMC_9061364","title":"Isolation, characterization and inactivation of the mouse Mgat3 gene: the bisecting N-acetylglucosamine in asparagine-linked oligosaccharides appears dispensable for viability and reproduction.","date":"1997","source":"Glycobiology","url":"https://pubmed.ncbi.nlm.nih.gov/9061364","citation_count":86,"is_preprint":false},{"pmid":"17170429","id":"PMC_17170429","title":"Catalytic properties of MGAT3, a putative triacylgycerol synthase.","date":"2006","source":"Journal of lipid research","url":"https://pubmed.ncbi.nlm.nih.gov/17170429","citation_count":76,"is_preprint":false},{"pmid":"29223528","id":"PMC_29223528","title":"GLP-1 receptor agonists downregulate aberrant GnT-III expression in Alzheimer's disease models through the Akt/GSK-3β/β-catenin signaling.","date":"2017","source":"Neuropharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/29223528","citation_count":52,"is_preprint":false},{"pmid":"32483464","id":"PMC_32483464","title":"MGAT3-mediated glycosylation of tetraspanin CD82 at asparagine 157 suppresses ovarian cancer metastasis by inhibiting the integrin signaling pathway.","date":"2020","source":"Theranostics","url":"https://pubmed.ncbi.nlm.nih.gov/32483464","citation_count":47,"is_preprint":false},{"pmid":"24619415","id":"PMC_24619415","title":"The absence of core fucose up-regulates GnT-III and Wnt target genes: a possible mechanism for an adaptive response in terms of glycan function.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24619415","citation_count":43,"is_preprint":false},{"pmid":"7590346","id":"PMC_7590346","title":"Cloning and chromosomal mapping of the mouse Mgat3 gene encoding N-acetylglucosaminyltransferase III.","date":"1995","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/7590346","citation_count":40,"is_preprint":false},{"pmid":"33649791","id":"PMC_33649791","title":"Exosomal miR‑663b exposed to TGF‑β1 promotes cervical cancer metastasis and epithelial‑mesenchymal transition by targeting MGAT3.","date":"2021","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/33649791","citation_count":40,"is_preprint":false},{"pmid":"28842505","id":"PMC_28842505","title":"The glycosyltransferase GnT-III activates Notch signaling and drives stem cell expansion to promote the growth and invasion of ovarian cancer.","date":"2017","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28842505","citation_count":40,"is_preprint":false},{"pmid":"33010941","id":"PMC_33010941","title":"True significance of N-acetylglucosaminyltransferases GnT-III, V and α1,6 fucosyltransferase in epithelial-mesenchymal transition and cancer.","date":"2020","source":"Molecular aspects of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33010941","citation_count":39,"is_preprint":false},{"pmid":"27429195","id":"PMC_27429195","title":"Epigenetic activation of MGAT3 and corresponding bisecting GlcNAc shortens the survival of cancer patients.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27429195","citation_count":30,"is_preprint":false},{"pmid":"34153312","id":"PMC_34153312","title":"MicroRNA-23b attenuates tau pathology and inhibits oxidative stress by targeting GnT-III in Alzheimer's disease.","date":"2021","source":"Neuropharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/34153312","citation_count":30,"is_preprint":false},{"pmid":"29991969","id":"PMC_29991969","title":"Promoter methylation of the MGAT3 and BACH2 genes correlates with the composition of the immunoglobulin G glycome in inflammatory bowel disease.","date":"2018","source":"Clinical epigenetics","url":"https://pubmed.ncbi.nlm.nih.gov/29991969","citation_count":30,"is_preprint":false},{"pmid":"7829256","id":"PMC_7829256","title":"High expression of UDP-N-acetylglucosamine: beta-D mannoside beta-1,4-N-acetylglucosaminyltransferase III (GnT-III) in chronic myelogenous leukemia in blast crisis.","date":"1995","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/7829256","citation_count":29,"is_preprint":false},{"pmid":"29743543","id":"PMC_29743543","title":"MiR-23a transcriptional activated by Runx2 increases metastatic potential of mouse hepatoma cell via directly targeting Mgat3.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/29743543","citation_count":28,"is_preprint":false},{"pmid":"21312067","id":"PMC_21312067","title":"The acyl coenzymeA:monoacylglycerol acyltransferase 3 (MGAT3) gene is a pseudogene in mice but encodes a functional enzyme in rats.","date":"2011","source":"Lipids","url":"https://pubmed.ncbi.nlm.nih.gov/21312067","citation_count":27,"is_preprint":false},{"pmid":"29502191","id":"PMC_29502191","title":"The glycomic effect of N-acetylglucosaminyltransferase III overexpression in metastatic melanoma cells. GnT-III modifies highly branched N-glycans.","date":"2018","source":"Glycoconjugate journal","url":"https://pubmed.ncbi.nlm.nih.gov/29502191","citation_count":27,"is_preprint":false},{"pmid":"27073020","id":"PMC_27073020","title":"DNA hypomethylation upregulates expression of the MGAT3 gene in HepG2 cells and leads to changes in N-glycosylation of secreted glycoproteins.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27073020","citation_count":26,"is_preprint":false},{"pmid":"11784313","id":"PMC_11784313","title":"A catalytically inactive beta 1,4-N-acetylglucosaminyltransferase III (GnT-III) behaves as a dominant negative GnT-III inhibitor.","date":"2002","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11784313","citation_count":23,"is_preprint":false},{"pmid":"7496137","id":"PMC_7496137","title":"Changes of beta-1,4-N-acetylglucosaminyltransferase III (GnT-III) in patients with leukaemia.","date":"1995","source":"Glycoconjugate journal","url":"https://pubmed.ncbi.nlm.nih.gov/7496137","citation_count":21,"is_preprint":false},{"pmid":"23300837","id":"PMC_23300837","title":"All-trans-retinoic acid modulates ICAM-1 N-glycan composition by influencing GnT-III levels and inhibits cell adhesion and trans-endothelial migration.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23300837","citation_count":19,"is_preprint":false},{"pmid":"35166206","id":"PMC_35166206","title":"Suppression of MGAT3 expression and the epithelial-mesenchymal transition of lung cancer cells by miR-188-5p.","date":"2020","source":"Biomedical journal","url":"https://pubmed.ncbi.nlm.nih.gov/35166206","citation_count":17,"is_preprint":false},{"pmid":"27184406","id":"PMC_27184406","title":"Biochemical characterization of human acyl coenzyme A: 2-monoacylglycerol acyltransferase-3 (MGAT3).","date":"2016","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/27184406","citation_count":17,"is_preprint":false},{"pmid":"31611608","id":"PMC_31611608","title":"Endogenous intronic antisense long non-coding RNA, MGAT3-AS1, and kidney transplantation.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31611608","citation_count":11,"is_preprint":false},{"pmid":"12420740","id":"PMC_12420740","title":"A glycomic approach to hepatic tumors in N-acetylglucosaminyltransferase III (GnT-III) transgenic mice induced by diethylnitrosamine (DEN): identification of haptoglobin as a target molecule of GnT-III.","date":"2002","source":"Free radical research","url":"https://pubmed.ncbi.nlm.nih.gov/12420740","citation_count":10,"is_preprint":false},{"pmid":"33305115","id":"PMC_33305115","title":"Prospective Study of Long Noncoding RNA, MGAT3-AS1, and Viremia of BK Polyomavirus and Cytomegalovirus in Living Donor Renal Transplant Recipients.","date":"2020","source":"Kidney international reports","url":"https://pubmed.ncbi.nlm.nih.gov/33305115","citation_count":9,"is_preprint":false},{"pmid":"38521909","id":"PMC_38521909","title":"Circ_0070934 promotes MGAT3 expression and inhibits epithelial-mesenchymal transition in bronchial epithelial cells by sponging miR-199a-5p.","date":"2024","source":"Allergy, asthma, and clinical immunology : official journal of the Canadian Society of Allergy and Clinical Immunology","url":"https://pubmed.ncbi.nlm.nih.gov/38521909","citation_count":4,"is_preprint":false},{"pmid":"38936637","id":"PMC_38936637","title":"The K346T mutant of GnT-III bearing weak in vitro and potent intracellular activity.","date":"2024","source":"Biochimica et biophysica acta. General subjects","url":"https://pubmed.ncbi.nlm.nih.gov/38936637","citation_count":4,"is_preprint":false},{"pmid":"33200553","id":"PMC_33200553","title":"Associations between genetic variants of KIF5B, FMN1, and MGAT3 in the cadherin pathway and pancreatic cancer risk.","date":"2020","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33200553","citation_count":4,"is_preprint":false},{"pmid":"39851531","id":"PMC_39851531","title":"Proximity Labeling-Based Identification of MGAT3 Substrates and Revelation of the Tumor-Suppressive Role of Bisecting GlcNAc in Breast Cancer via GLA Degradation.","date":"2025","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/39851531","citation_count":2,"is_preprint":false},{"pmid":"40199132","id":"PMC_40199132","title":"MGAT3 and MGAT5 overexpression alters the protein cargo of extracellular vesicles released by metastatic melanoma cells.","date":"2025","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/40199132","citation_count":0,"is_preprint":false},{"pmid":"40352502","id":"PMC_40352502","title":"Downregulation of MGAT3 Promotes Benzo[a]pyrene-Mediated Lung Carcinogenesis by Regulating Cell Invasion and Migration Activity.","date":"2025","source":"ACS omega","url":"https://pubmed.ncbi.nlm.nih.gov/40352502","citation_count":0,"is_preprint":false},{"pmid":"39653250","id":"PMC_39653250","title":"Functions of unique middle loop and C-terminal tail in GnT-III activity and secretion.","date":"2024","source":"Biochimica et biophysica acta. General subjects","url":"https://pubmed.ncbi.nlm.nih.gov/39653250","citation_count":0,"is_preprint":false},{"pmid":"30689164","id":"PMC_30689164","title":"N-Acetylglucosaminyltransferase III (GnT-III) but not N-Acetylgalactosaminyltransferase-6 and 8 are Differentially Expressed in Invasive and In Situ Ductal Carcinoma of the Breast.","date":"2019","source":"Pathology oncology research : POR","url":"https://pubmed.ncbi.nlm.nih.gov/30689164","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.26.661710","title":"Chemoenzymatic Synthesis of Asymmetric Bisecting Bi-, Tri-, and Tetra-Antennary  <i>N</i>  -Glycans","date":"2025-06-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.26.661710","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.02.15.638459","title":"N-Glycan Fingerprinting of the NIST monoclonal antibody (NISTmAb)","date":"2025-02-20","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.15.638459","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.08.22.609211","title":"Remodelling of the glycome of B-cell precursor acute lymphoblastic leukemia cells developing drug-tolerance","date":"2024-08-23","source":"bioRxiv","url":"https://doi.org/10.1101/2024.08.22.609211","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":23751,"output_tokens":5141,"usd":0.074184,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13438,"output_tokens":5051,"usd":0.096732,"stage2_stop_reason":"end_turn"},"total_usd":0.170916,"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\": 1993,\n      \"finding\": \"Human GnT-III (MGAT3) encodes a 531-amino acid type II transmembrane protein that catalyzes the addition of N-acetylglucosamine in β1,4 linkage to the β-linked mannose of the trimannosyl core of N-linked sugar chains, producing a bisecting GlcNAc residue. The amino-terminal transmembrane domain and catalytic domain are conserved between human and rat. The gene maps to chromosome 22q13.1.\",\n      \"method\": \"cDNA cloning, open reading frame analysis, chromosomal mapping by fluorescence in situ hybridization (FISH)\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct sequencing and functional characterization of human cDNA, replicated across species; foundational cloning paper\",\n      \"pmids\": [\"8370666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The mouse Mgat3 gene encodes GlcNAc-TIII and is expressed as a single-copy gene at high levels in kidney and brain. A sense-orientation ORF transfected into CHO cells confers GlcNAc-TIII enzymatic activity, demonstrating the ORF encodes the catalytic enzyme. Mouse Mgat3 maps to chromosome 15.\",\n      \"method\": \"Genomic cloning, mammalian expression transfection, enzymatic activity assay, Southern blot, FISH mapping\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct enzymatic activity confirmed by transfection with sense/antisense control, consistent with human gene characterization\",\n      \"pmids\": [\"7590346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Mgat3-deficient mice generated by Cre/loxP-mediated gene deletion lack GlcNAc-TIII activity and are deficient in E4-PHA-visualized GlcNAc-bisected N-linked oligosaccharides, yet are viable, fertile, and show no overt developmental, hematological, or organ morphology defects. This establishes that bisecting GlcNAc is dispensable for normal murine development and homeostasis.\",\n      \"method\": \"Gene targeting (Cre/loxP), enzymatic activity assay, lectin blotting, flow cytometry, histology\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with multiple orthogonal readouts; definitive loss-of-function study\",\n      \"pmids\": [\"9061364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Active-site mutagenesis of rat GnT-III identified two conserved aspartate residues (Asp321 and Asp323) as absolutely required for catalytic activity based on sequence homology with snail β1,4GlcNAc transferase and β1,4Gal transferase-1. Overexpression of the catalytically inactive Asp323-substituted mutant suppressed endogenous GnT-III activity (dominant negative effect) and specifically blocked formation of bisected N-glycans without reducing endogenous GnT-III expression levels.\",\n      \"method\": \"Sequence homology analysis, site-directed mutagenesis, enzymatic activity assay, overexpression in Huh6 cells, N-glycan structural analysis\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis with in vitro activity assay and structural glycan analysis in a single rigorous study\",\n      \"pmids\": [\"11784313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"GnT-III activity is elevated in CML blast crisis and multiple myeloma cells. Immunoprecipitation and lectin blot analysis showed that elevated GnT-III in KU812 (CML) cells results in increased bisecting GlcNAc on CD45, a major leukocyte surface glycoprotein, as its substrate.\",\n      \"method\": \"Enzymatic activity assay (HPLC), immunoprecipitation, Western/lectin blot with E4-PHA\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — immunoprecipitation plus lectin blot confirms CD45 as substrate; single lab, two orthogonal methods\",\n      \"pmids\": [\"7829256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"In GnT-III transgenic mice with DEN-induced hepatic tumors, glycomic analysis (2D gel electrophoresis, lectin blot, sequencing, immunoprecipitation) identified haptoglobin as a target glycoprotein modified by GnT-III-mediated bisecting GlcNAc addition, and GnT-III overexpression dramatically suppressed hepatic tumor incidence.\",\n      \"method\": \"Transgenic mouse model, 2D gel electrophoresis, lectin blot, sequence analysis, immunoprecipitation with E4-PHA lectin blot\",\n      \"journal\": \"Free radical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — glycomic approach with immunoprecipitation validation identifies haptoglobin as substrate; single lab study\",\n      \"pmids\": [\"12420740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"During epithelial-mesenchymal transition (EMT), Mgat3 promoter methylation causes dramatic reduction in Mgat3 expression and loss of GnT-III-mediated bisecting GlcNAc modification on E-cadherin; this is reversed during mesenchymal-epithelial transition (MET) by promoter demethylation. This identifies epigenetic regulation of Mgat3 as a mechanism controlling E-cadherin glycosylation during EMT/MET.\",\n      \"method\": \"Bisulfite sequencing, qPCR, Western blot, lectin blot, glycan analysis during TGF-β-induced EMT/MET in cell lines\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter methylation analysis linked to enzymatic product on defined substrate; single lab, multiple methods\",\n      \"pmids\": [\"22427986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"All-trans-retinoic acid (ATRA) upregulates GnT-III expression via the ERK signaling pathway, causing bisecting GlcNAc modification of ICAM-1 N-glycans (shown by reduced ICAM-1 molecular mass reversible by PNGase F and by GnT-III siRNA knockdown). This GnT-III-dependent ICAM-1 glycan remodeling inhibits cell adhesion and trans-endothelial migration.\",\n      \"method\": \"siRNA knockdown, qPCR, gel mobility shift assay, PNGase F treatment, cell adhesion assay, trans-endothelial migration assay, ERK inhibitor treatment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function (siRNA) links GnT-III to specific ICAM-1 glycan change and defined cellular phenotype; single lab, multiple methods\",\n      \"pmids\": [\"23300837\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In Fut8-deficient mouse embryonic fibroblasts (MEFs), loss of core fucose leads to upregulation of GnT-III expression via activation of Wnt/β-catenin signaling. A Wnt signaling inhibitor abrogates GnT-III upregulation. As a result, bisecting GlcNAc on β1-integrin and N-cadherin is increased; IgG1 glycan analysis by mass spectrometry confirms increased bisecting GlcNAc in Fut8-/- mouse serum in vivo.\",\n      \"method\": \"Mouse embryonic fibroblasts from Fut8-/- mice, gene expression analysis, Wnt inhibitor treatment, lectin blot, mass spectrometry of IgG glycans\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Wnt inhibitor epistasis establishes pathway regulation of GnT-III; in vivo mass spectrometry validates substrate modification; single lab\",\n      \"pmids\": [\"24619415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"DNA methylation at the MGAT3 transcription start site represses MGAT3 expression; treatment with the DNA methyltransferase inhibitor 5-Aza restores MGAT3 expression coinciding with reduced promoter methylation. Bisecting GlcNAc on released N-glycans (detected by LC-ESI-qTOF-MS/MS) appears in ovarian cancer cells only after MGAT3 re-expression following demethylation, establishing promoter methylation as a direct mechanism controlling bisecting GlcNAc biosynthesis.\",\n      \"method\": \"5-Aza treatment, bisulfite sequencing, LC-ESI-qTOF-MS/MS glycan analysis, expression analysis\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct mechanistic link between promoter methylation and enzymatic product detected by mass spectrometry; single lab, two orthogonal methods\",\n      \"pmids\": [\"27429195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GnT-III expression controls expansion of cancer stem cells (side-population cells) in epithelial ovarian carcinoma. shRNA suppression of GnT-III reduces Notch receptor levels and signaling more potently than pharmacologic γ-secretase inhibition, by redirecting Notch receptor to the lysosome rather than to the cell surface, identifying a novel mechanism whereby bisecting glycosylation controls Notch receptor trafficking.\",\n      \"method\": \"Stable shRNA knockdown, flow cytometry for side-population cells, Western blot, γ-secretase inhibitor comparison, lysosome localization assay, primary tumor-derived cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined mechanistic pathway (lysosomal redirection of Notch); single lab, multiple cell models\",\n      \"pmids\": [\"28842505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GLP-1 receptor agonists (exendin-4) downregulate aberrant GnT-III expression and bisecting GlcNAc levels in APP/PS1 mice and Aβ25-35-treated PC12 cells through the Akt/GSK-3β/β-catenin signaling pathway. β-catenin siRNA abolishes the effect of GLP-1RA on GnT-III, and PI3K inhibitor LY294002 attenuates these effects, establishing the Akt/GSK-3β/β-catenin axis as an upstream regulator of GnT-III expression.\",\n      \"method\": \"APP/PS1 transgenic mice, siRNA knockdown, PI3K inhibitor (LY294002), Western blot, phosphorylation analysis, behavioral testing\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via siRNA and pharmacological inhibitor establishes pathway; single lab, multiple methods\",\n      \"pmids\": [\"29223528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MGAT3-mediated glycosylation of CD82 at asparagine 157 is required for CD82-mediated inhibition of ovarian cancer cell migration and metastasis in vitro and in vivo. Mechanistically, glycosylated CD82 disrupts integrin α5β1-mediated cellular adhesion to fibronectin and inhibits integrin signaling-induced cytoskeletal rearrangements required for migration. MGAT3 was identified as the glycosyltransferase responsible for this CD82 glycosylation.\",\n      \"method\": \"Site-directed mutagenesis of CD82 glycosylation sites, in vitro migration/invasion assays, in vivo xenograft, integrin adhesion assays, Western blot, paired human tissue samples\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis of specific glycosylation site, in vitro and in vivo functional validation, mechanistic pathway (integrin α5β1/fibronectin) identified; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"32483464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"miR-23b directly targets the 3'-UTR of GnT-III mRNA (verified by dual-luciferase reporter assay), reducing GnT-III expression. miR-23b overexpression activates the Akt/GSK-3β signaling pathway to inhibit tau hyperphosphorylation and reduce oxidative stress in Alzheimer's disease models.\",\n      \"method\": \"Dual-luciferase reporter assay, bioinformatics, overexpression in Aβ1-42-induced mouse and PC12 cell models, Western blot\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct 3'-UTR targeting validated by reporter assay with downstream pathway analysis; single lab\",\n      \"pmids\": [\"34153312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Structure-function analysis of GnT-III using AlphaFold2-based modeling and point mutagenesis identified E320 as the catalytic center of human GnT-III. A K346T mutant showed reduced in vitro activity but enhanced intracellular bisecting GlcNAc production; TurboID-based proximity labeling demonstrated that K346T is shifted to the cis-Golgi relative to wild-type, providing a mechanistic explanation for discordant in vitro vs. intracellular activity. Cycloheximide chase showed the K346T mutant has a shorter half-life.\",\n      \"method\": \"AlphaFold2 structure prediction, site-directed mutagenesis, in vitro activity assay, HPLC, UDP-Glo glycosyltransferase assay, glycomic analysis, TurboID proximity labeling, immunostaining, cycloheximide chase\",\n      \"journal\": \"Biochimica et biophysica acta. General subjects\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis with in vitro activity and intracellular glycomic readouts plus proximity labeling for localization; single lab, multiple orthogonal methods; catalytic center identified by computational prediction + mutagenesis\",\n      \"pmids\": [\"38936637\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The middle loop (Loop) and C-terminal tail (Tail) of GnT-III play distinct functional roles: (1) deletion of Loop increases both in vitro and intracellular GnT-III activity, indicating Loop suppresses catalytic activity and contains the cleavage site for GnT-III shedding; (2) deletion of Tail reduces activity, increases ER localization, and accelerates protein degradation, indicating Tail is required for proper folding and Golgi localization.\",\n      \"method\": \"Deletion mutagenesis, HPLC activity assay, UDP-Glo assay, glycomic analysis, immunostaining for subcellular localization, degradation rate assay\",\n      \"journal\": \"Biochimica et biophysica acta. General subjects\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — deletion mutagenesis with enzymatic activity assays and subcellular localization; single lab, multiple methods\",\n      \"pmids\": [\"39653250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Proximity labeling with biotin ligases (BASU and TurboID) identified 116 and 189 proteins in the MGAT3 proximitome in HEK293T cells, with 17 shared with a bisecting GlcNAc-bearing proteome. Four novel substrates—GOLM2, CCDC134, ASPH, and ERO1A—were confirmed to bear bisecting GlcNAc modification. MGAT3-mediated bisecting GlcNAc on α-galactosidase A (GLA) promotes GLA degradation, thereby inhibiting breast cancer progression.\",\n      \"method\": \"TurboID and BASU proximity labeling, intact glycopeptide enrichment, mass spectrometry, Western blot, breast cancer functional assays\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proximity labeling with MS identification and validation of substrates bearing bisecting GlcNAc; functional consequence established for GLA; single lab\",\n      \"pmids\": [\"39851531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Chemoenzymatic experiments established that GnT-III can act on bi-, tri-, and tetra-antennary N-glycans as substrates and preferentially modifies bi-antennary glycans (kinetic experiments). GnT-III also accepts N-glycans having a β1,2-GlcNTFA or GlcN3 moiety at the α1,2Man- or α1,6Man-antenna, enabling synthesis of asymmetric bisecting glycans.\",\n      \"method\": \"Chemoenzymatic synthesis, kinetic activity assays, glycan microarray screening\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro enzymatic kinetics with defined substrates; preprint, single study, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.06.26.661710\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"MGAT3/GnT-III is a Golgi-resident glycosyltransferase (type II transmembrane protein) that catalyzes the β1,4-transfer of GlcNAc to the β-linked mannose of the trimannosyl N-glycan core, producing a bisecting GlcNAc that suppresses further N-glycan branching; its catalytic center requires Glu320 and Asp321/Asp323, its activity is suppressed by an internal loop and requires a C-terminal tail for proper folding/Golgi localization, and its expression is regulated epigenetically by promoter methylation and transcriptionally via Wnt/β-catenin and Akt/GSK-3β signaling; substrates include CD45, ICAM-1, E-cadherin, CD82 (at N157), haptoglobin, and GLA, with functional consequences including inhibition of EMT, suppression of integrin α5β1/fibronectin-mediated migration, control of Notch receptor lysosomal trafficking, and promotion of GLA degradation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MGAT3 encodes GlcNAc-TIII (GnT-III), a Golgi-resident type II transmembrane glycosyltransferase that transfers N-acetylglucosamine in \\u03b21,4 linkage to the \\u03b2-linked mannose of the trimannosyl N-glycan core to produce a bisecting GlcNAc residue that suppresses further N-glycan branching [#0, #1]. Catalysis depends on conserved acidic active-site residues\\u2014Glu320 as the catalytic center and Asp321/Asp323\\u2014mutation of which abolishes activity, with a catalytically dead Asp323 mutant acting dominant-negatively to block bisected-glycan formation [#3, #14]; an internal loop suppresses catalytic activity and harbors the shedding cleavage site, while a C-terminal tail is required for proper folding and Golgi retention, with its loss causing ER mislocalization and accelerated degradation [#15]. Despite this molecular activity, bisecting GlcNAc is dispensable for normal mouse development, as Mgat3-null mice are viable and fertile [#2]. GnT-III modifies a defined set of glycoprotein substrates\\u2014including CD45, E-cadherin, ICAM-1, haptoglobin, CD82 at Asn157, and \\u03b1-galactosidase A (GLA)\\u2014and these modifications carry distinct functional consequences: bisecting glycosylation of E-cadherin and ICAM-1 restrains EMT and cell adhesion/migration [#6, #7], glycosylation of CD82 disrupts integrin \\u03b15\\u03b21-mediated adhesion to fibronectin to inhibit ovarian cancer migration and metastasis [#12], control of Notch receptor trafficking redirects the receptor to the lysosome to limit cancer stem-cell expansion [#10], and bisecting GlcNAc on GLA promotes its degradation to inhibit breast cancer progression [#16]. MGAT3 expression is controlled epigenetically by promoter/transcription-start-site methylation and transcriptionally through Wnt/\\u03b2-catenin and Akt/GSK-3\\u03b2 signaling, as well as post-transcriptionally by miR-23b targeting of its 3\\u2032-UTR [#6, #8, #9, #11, #13].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Establishing what MGAT3 is at the molecular level: cloning revealed it encodes a type II transmembrane glycosyltransferase that builds the bisecting GlcNAc on the N-glycan core.\",\n      \"evidence\": \"cDNA cloning, ORF analysis, and FISH mapping of human GnT-III\",\n      \"pmids\": [\"8370666\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve active-site residues or catalytic mechanism\", \"Substrate glycoproteins not yet identified\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Confirmed the cloned ORF is the catalytic enzyme and not a regulatory factor by demonstrating that sense-orientation expression confers GlcNAc-TIII activity.\",\n      \"evidence\": \"Genomic cloning and sense/antisense transfection with enzymatic assay in CHO cells\",\n      \"pmids\": [\"7590346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-restricted expression mechanism unexplained\", \"No physiological substrate defined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Linked elevated GnT-III activity in hematologic malignancy to a concrete physiological substrate, identifying CD45 as bearing increased bisecting GlcNAc.\",\n      \"evidence\": \"Enzymatic assay, immunoprecipitation, and E4-PHA lectin blot in CML/myeloma cells\",\n      \"pmids\": [\"7829256\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of CD45 bisecting glycosylation not established\", \"Single-lab characterization\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Resolved whether bisecting GlcNAc is essential in vivo: knockout mice showed it is dispensable for development and homeostasis, redirecting the field toward conditional/disease roles.\",\n      \"evidence\": \"Cre/loxP gene targeting with lectin, flow, and histology readouts\",\n      \"pmids\": [\"9061364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phenotypes under stress, tumor, or aging not assessed\", \"Compensation by other branching enzymes not excluded\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined the catalytic chemistry by mapping required active-site aspartates and demonstrating dominant-negative suppression by an inactive mutant.\",\n      \"evidence\": \"Homology-guided site-directed mutagenesis with activity and N-glycan structural analysis\",\n      \"pmids\": [\"11784313\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the principal catalytic residue (later Glu320)\", \"No structural model of the active site\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Connected GnT-III to tumor suppression in vivo and expanded the substrate repertoire by identifying haptoglobin as a bisected target.\",\n      \"evidence\": \"GnT-III transgenic DEN-hepatocarcinogenesis model with glycomic/immunoprecipitation substrate mapping\",\n      \"pmids\": [\"12420740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking haptoglobin glycosylation to tumor suppression unclear\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed how MGAT3 is regulated and coupled to cell-state transitions: promoter methylation silences it during EMT and is reversed in MET, controlling E-cadherin glycosylation.\",\n      \"evidence\": \"Bisulfite sequencing and lectin/glycan analysis during TGF-\\u03b2-induced EMT/MET\",\n      \"pmids\": [\"22427986\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Upstream signals driving methylation not defined\", \"Causality of E-cadherin glycosylation in EMT not proven by rescue\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified an inducible transcriptional route (ATRA/ERK) to GnT-III upregulation and tied ICAM-1 glycan remodeling to suppressed adhesion and transmigration.\",\n      \"evidence\": \"siRNA, gel mobility/PNGase F, adhesion and trans-endothelial migration assays with ERK inhibition\",\n      \"pmids\": [\"23300837\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional effectors downstream of ERK not mapped\", \"Single-lab characterization\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Placed MGAT3 in a glycan crosstalk network: loss of core fucose induces GnT-III via Wnt/\\u03b2-catenin, increasing bisecting GlcNAc on integrin and N-cadherin.\",\n      \"evidence\": \"Fut8-/- MEFs with Wnt-inhibitor epistasis and in vivo IgG mass spectrometry\",\n      \"pmids\": [\"24619415\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How loss of core fucose activates Wnt signaling not resolved\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Generalized methylation control of MGAT3 to cancer, directly tying promoter demethylation to restored bisecting-glycan biosynthesis.\",\n      \"evidence\": \"5-Aza treatment, bisulfite sequencing, and LC-MS/MS glycan detection in ovarian cancer cells\",\n      \"pmids\": [\"27429195\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional impact of restored MGAT3 in this model not measured\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Uncovered a trafficking-based mechanism for MGAT3's tumor-relevant role: bisecting glycosylation controls Notch receptor lysosomal routing to limit cancer stem-cell expansion.\",\n      \"evidence\": \"shRNA knockdown, side-population flow cytometry, lysosomal localization, and \\u03b3-secretase comparison in ovarian carcinoma cells\",\n      \"pmids\": [\"28842505\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that Notch itself is bisected not shown\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established an Akt/GSK-3\\u03b2/\\u03b2-catenin signaling axis as upstream regulator of GnT-III in a neurodegeneration context.\",\n      \"evidence\": \"APP/PS1 mice and A\\u03b2-treated PC12 cells with \\u03b2-catenin siRNA and PI3K inhibitor epistasis\",\n      \"pmids\": [\"29223528\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct substrate(s) mediating neural effects not identified\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided rigorous site-resolved substrate causality: MGAT3 glycosylation of CD82 at Asn157 is required to suppress integrin \\u03b15\\u03b21/fibronectin adhesion and metastasis.\",\n      \"evidence\": \"CD82 glycosite mutagenesis with in vitro/in vivo migration, adhesion assays, and paired tissues\",\n      \"pmids\": [\"32483464\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of how the bisected glycan alters CD82-integrin interaction not defined\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Added post-transcriptional control by showing miR-23b directly targets the GnT-III 3\\u2032-UTR, with downstream effects on tau phosphorylation and oxidative stress.\",\n      \"evidence\": \"Dual-luciferase 3\\u2032-UTR reporter and overexpression in A\\u03b2-induced AD models\",\n      \"pmids\": [\"34153312\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether GnT-III substrate changes mediate the tau/oxidative effects not shown\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the catalytic center and a localization-dependent activity mechanism: Glu320 is catalytic, and a K346T mutant shifts to the cis-Golgi to explain discordant in vitro vs intracellular activity.\",\n      \"evidence\": \"AlphaFold2 modeling, mutagenesis, in vitro/intracellular activity, TurboID localization, and cycloheximide chase\",\n      \"pmids\": [\"38936637\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental crystal/cryo-EM structure\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Dissected domain-level regulation: an internal loop autoinhibits and is the shedding cleavage site, while the C-terminal tail is needed for folding and Golgi retention.\",\n      \"evidence\": \"Deletion mutagenesis with activity assays and subcellular localization in cells\",\n      \"pmids\": [\"39653250\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protease responsible for loop-mediated shedding not identified\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Systematically expanded the substrate landscape via proximity labeling, identifying new bisected substrates and a functional GLA-degradation axis in breast cancer.\",\n      \"evidence\": \"BASU/TurboID proximity labeling, glycopeptide MS, and breast cancer functional assays\",\n      \"pmids\": [\"39851531\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which bisecting GlcNAc promotes GLA degradation unclear\", \"Roles of GOLM2/CCDC134/ASPH/ERO1A modification untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined acceptor-substrate specificity and kinetic preferences, showing GnT-III acts on multi-antennary and modified N-glycans, enabling asymmetric bisecting-glycan synthesis.\",\n      \"evidence\": \"Chemoenzymatic synthesis, kinetics, and glycan microarray screening (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.06.26.661710\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not peer-reviewed\", \"In vitro specificity may not reflect cellular acceptor availability\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How bisecting GlcNAc on individual substrates mechanistically alters protein trafficking, stability, and signaling\\u2014and the physiological consequences of MGAT3 dysregulation in disease\\u2014remains incompletely defined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental high-resolution structure of the catalytic domain\", \"Generalizable rules linking bisected glycan to substrate fate not established\", \"In vivo disease causality from MGAT3 perturbation largely correlative\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 3, 14, 17]},\n      {\"term_id\": \"GO:0016757\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [14, 15]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 12, 16]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CD45\", \"E-cadherin\", \"ICAM-1\", \"CD82\", \"haptoglobin\", \"GLA\", \"Notch\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}