{"gene":"MGAT5","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2001,"finding":"MGAT5 (GlcNAc-TV) initiates β1,6 GlcNAc branching on N-glycans of the TCR complex, increasing N-acetyllactosamine ligands for galectins; galectin-3 associates with the TCR complex at the cell surface in an MGAT5-dependent manner, forming a galectin-glycoprotein lattice that restricts TCR clustering at the antigen presentation site, thereby raising T-cell activation thresholds. Mgat5-/- mice showed enhanced TCR clustering, actin microfilament reorganization, and autoimmune disease.","method":"Mgat5 knockout mice, lactose competition assay (phenocopy), co-immunoprecipitation of galectin-3 with TCR, TCR recruitment to agonist-coated beads, signaling and proliferation assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — reciprocal evidence from KO mice, co-IP, and pharmacological phenocopy; replicated across multiple orthogonal readouts in a highly cited foundational study","pmids":["11217864"],"is_preprint":false},{"year":2000,"finding":"MGAT5-derived β1,6GlcNAc-branched N-glycans stimulate membrane ruffling and PI3K-PKB (Akt) activation, creating a positive feedback loop that amplifies oncogene signaling; Mgat5-deficient mice show markedly reduced mammary tumor growth and metastasis in a polyomavirus middle T oncogene model.","method":"Targeted gene knockout mice crossed with PyMT transgenic mice; PI3K/PKB activity assays; membrane ruffling assays; in vivo tumor growth and metastasis measurements","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function in vivo with defined signaling readout, replicated with multiple tumor endpoints","pmids":["10700233"],"is_preprint":false},{"year":2006,"finding":"Galectin-3 binding to Mgat5-modified β1,6GlcNAc-branched N-glycans on fibronectin receptors regulates fibronectin fibrillogenesis and tumor cell motility by activating FAK and PI3K, recruiting conformationally active α5β1-integrin to fibrillar adhesions, and increasing F-actin turnover. Blocking Mgat5 or competing for galectin binding inhibits these processes.","method":"Mgat5-/- mammary epithelial tumor cells, swainsonine treatment, exogenous galectin-3 addition, RGD peptide inhibition, anti-galectin-3 antibodies, FAK/PI3K activity assays, fibronectin matrix remodeling assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KO cells, pharmacological inhibition, antibody blockade, exogenous protein addition) converging on the same mechanism","pmids":["16581792"],"is_preprint":false},{"year":1987,"finding":"GnT-V (MGAT5) catalyzes transfer of GlcNAc in β1,6 linkage from UDP-GlcNAc onto α-mannoside acceptors (N-glycan precursors), as demonstrated by cell-free enzyme assays using a synthetic trisaccharide acceptor and UDP-[3H]-GlcNAc, producing a radiolabeled tetrasaccharide product.","method":"In vitro enzymatic assay with cell extracts, synthetic trisaccharide acceptor, UDP-[3H]-GlcNAc, reverse-phase chromatography product separation","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — direct in vitro enzymatic assay establishing catalytic activity","pmids":["2956949"],"is_preprint":false},{"year":2002,"finding":"Secreted (soluble) GnT-V protein itself promotes tumor angiogenesis in vitro and in vivo at physiological concentrations independent of its glycosyltransferase activity, via its highly basic domain inducing release of FGF-2 from heparan sulfate proteoglycan on the cell surface/extracellular matrix.","method":"In vitro angiogenesis assays, in vivo angiogenesis models, addition of purified soluble GnT-V protein, domain analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — recombinant protein functional assay with domain-level mechanistic insight; single lab","pmids":["11872751"],"is_preprint":false},{"year":2006,"finding":"GnT-V is cleaved at its transmembrane/stem region boundary (at His31) by γ-secretase (presenilin-containing complex), generating the secreted ~100 kDa soluble form. Presenilin-1/2 double-deficient cells (no γ-secretase activity) completely lack soluble GnT-V secretion; FAD-linked presenilin-1 overexpression increases GnT-V secretion.","method":"N-terminal protein sequencing of purified soluble GnT-V, γ-secretase inhibitor (DFK-167) treatment, presenilin knockout cells, presenilin-1 overexpression, site-directed mutagenesis of cleavage site","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 — protein sequencing of cleavage site combined with genetic and pharmacological validation in multiple cell models","pmids":["17142794"],"is_preprint":false},{"year":2004,"finding":"MGAT5-mediated β1,6GlcNAc N-glycans on the TCR negatively regulate TCR signaling, promoting Th2 over Th1 differentiation; Mgat5-/- T cells produce more IFN-γ and less IL-4. Swainsonine (Golgi α-mannosidase II inhibitor blocking β1,6GlcNAc expression) phenocopies this increase in IFN-γ in human and mouse T cells, but has no additional effect in Mgat5-/- cells, confirming pathway specificity.","method":"Mgat5 knockout mice, cytokine ELISAs, swainsonine pharmacological inhibition, Th1/Th2 polarization assays, anti-CD3 stimulation of human T cells","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO confirmed by pharmacological epistasis in both mouse and human T cells","pmids":["15585841"],"is_preprint":false},{"year":1999,"finding":"The transcription factor Ets-1 regulates GnT-V (MGAT5) gene expression in cancer cells; Ets-1 mRNA levels correlate tightly with GnT-V mRNA across 16 cancer cell lines (r=0.97), and overexpression of Ets-1 enhances GnT-V expression while dominant-negative Ets-1 reduces it.","method":"Correlation analysis across cancer cell lines, Ets-1 cDNA transfection, dominant-negative Ets-1 transfection, RT-PCR","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function of transcription factor with defined gene expression readout; single lab","pmids":["10438459"],"is_preprint":false},{"year":2007,"finding":"Mgat5 and PTEN interact functionally to regulate PI3K/Akt signaling, cell spreading, and proliferation: Pten heterozygosity enhances adhesion-dependent PI3K/Akt signaling and cell spreading, while Mgat5 deficiency normalizes these responses in Pten+/- cells. Pten heterozygosity is also associated with increased surface β1,6GlcNAc-branched N-glycans, suggesting positive feedback from PI3K signaling to N-glycan branching.","method":"Pten/Mgat5 double-mutant mouse embryonic fibroblasts, PI3K/Akt activity assays, cell spreading assays, L-PHA lectin staining, in vivo longevity analysis","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis in double-mutant cells with biochemical readouts; single lab","pmids":["17400585"],"is_preprint":false},{"year":2009,"finding":"GnT-V (MGAT5) and its paralog GnT-Vb (GnT-IX) have distinct catalytic properties: GnT-V is fully active without exogenous cations (pH optimum 6.5–7.0), while GnT-Vb is stimulated by Mn²⁺ (pH optimum 8.0) and has ~2.5-fold higher Km for biantennary N-glycan acceptors but much greater efficiency on O-mannosyl glycopeptide substrates. Both transfer GlcNAc in β1,6 linkage to the Man of GlcNAcβ1,2Man moiety.","method":"In vitro enzymatic assays with purified enzymes, synthetic and natural glycan acceptors, kinetic measurements (Km, Vmax), EDTA/cation dependence, pH profiles, product characterization","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 1 — rigorous in vitro enzyme kinetics with purified proteins and defined substrates","pmids":["19846580"],"is_preprint":false},{"year":2012,"finding":"In vivo, GnT-V (MGAT5) and GnT-Vb (GnT-IX) have complementary substrate specificities: GnT-V null brains lack N-linked β1,6-glycans but have normal O-Man β1,6-branched structures; GnT-Vb null brains have normal N-linked β1,6-glycans but reduced O-Man β1,6-branched glycans. Only deletion of both enzymes eliminates all β1,6-branched glycans.","method":"GnT-V and GnT-Vb single and double knockout mice, glycan structural analysis, antibody binding assays (IIH6C4), laminin binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — genetic epistasis via double-KO mice with glycan structural analysis","pmids":["22715095"],"is_preprint":false},{"year":2022,"finding":"GnT-V (MGAT5) in small extracellular vesicles (sEVs) is a cleaved (secreted) form generated by SPPL3 protease cleavage; GnT-V is selectively enriched in non-exosomal sEVs among various glycosyltransferases. Enzymatically active GnT-V in sEVs is transferred to recipient cells and remodels their N-glycan structures to express GnT-V-produced β1,6-branched glycans.","method":"Glycosyltransferase activity measurements in sEV fractions, SPPL3 knockdown/knockout, single-particle imaging, fractionation experiments, recipient cell glycan structural analysis","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 — enzymatic activity assays combined with genetic manipulation and functional transfer experiment; single lab","pmids":["36590176"],"is_preprint":false},{"year":2018,"finding":"GnT-V enhances gemcitabine chemosensitivity in bladder cancer cells by adding β1,6-GlcNAc branches to the nucleoside transporter hENT1, which increases hENT1 accumulation at the plasma membrane and thus gemcitabine uptake. GnT-V silencing reduces β1,6-GlcNAc on hENT1 and decreases membrane hENT1 levels and drug uptake.","method":"GnT-V shRNA knockdown, lectin blot for β1,6-GlcNAc on hENT1, membrane fractionation, drug uptake assays, cell viability assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — specific substrate identified with glycan modification, membrane localization and functional drug uptake linked; single lab","pmids":["30143259"],"is_preprint":false},{"year":2021,"finding":"MGAT5-catalyzed β1,6-branched N-glycan production is required for stiffness-dependent invasion of glioblastoma stem-like cells (GSCs). CRISPR-Cas9 deletion of MGAT5 suppressed stiffness dependence of migration on 166 kPa nanofiber scaffolds and abolished associated focal adhesion (FA) maturation and EMT protein expression, demonstrating MGAT5 as a critical mediator of mechanotransduction.","method":"CRISPR-Cas9 MGAT5 deletion in GSCs, 3D nanofiber scaffolds with tunable stiffness, cell migration assays, galectin-3 binding, FA and EMT protein expression analysis","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype and molecular readouts; single lab","pmids":["33894774"],"is_preprint":false},{"year":2023,"finding":"Loss of MGAT5 in neural stem/progenitor cells (NSPCs) shifts differentiation toward neurons and away from astrocytes in vitro and in vivo, leading to accelerated neuronal differentiation, depletion of the NSPC niche, and a shift in cortical neuron layers in Mgat5-null mice.","method":"Mgat5 homozygous null mice, NSPC culture differentiation assays, in vivo cortical neuron layer analysis, cell fate marker immunostaining","journal":"Stem cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with defined in vitro and in vivo differentiation phenotypes; single lab","pmids":["37172586"],"is_preprint":false},{"year":2024,"finding":"Mgat5 is required for in vivo tumor growth of pancreatic ductal adenocarcinoma (PDAC) but not for in vitro growth; Mgat5-deficient tumor cells show increased sensitivity to TNF superfamily-mediated cell death and are cleared by T cells and dendritic cells, with NK cells playing an early role. Mgat5 knockout in an immunotherapy-resistant PDAC line restored sensitivity to immune checkpoint blockade.","method":"Mgat5 knockout clonal cell lines, in vivo vs. in vitro growth comparison, T cell/NK cell/dendritic cell depletion experiments, TNF family cell death pathway assays, immune checkpoint blockade treatment","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with multiple orthogonal in vivo immune depletion experiments and defined cell death mechanism; single lab","pmids":["38912584"],"is_preprint":false},{"year":2023,"finding":"GnT-V (MGAT5) recognizes the N-glycan core via residues outside its catalytic pocket, and UDP binding affects acceptor orientation through a conformational change at the Manα1,6-Man linkage, as determined by molecular dynamics simulations validated by biochemical experiments with site-specifically mutated residues.","method":"Molecular dynamics simulations, biochemical mutagenesis experiments, HPLC-based enzyme activity assays","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 1-2 — simulation plus mutagenesis validation; single lab, moderate evidence","pmids":["37974463"],"is_preprint":false},{"year":2022,"finding":"UDP-GlcNAc analogs with increased hydrophobicity (phosphate groups replaced by hydrophobic groups) selectively inhibit GnT-V enzymatic activity compared to other GnT family members (GnT-I–IV), indicating GnT-V is uniquely tolerant of hydrophobicity in the donor substrate and that its catalytic pocket is structurally distinct.","method":"Purified truncated enzyme HPLC-based activity assays for GnT-I–V, synthesis of 10 UDP-GlcNAc analogs, docking models","journal":"Biochimica et biophysica acta. General subjects","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro assay with purified enzymes and panel of synthesized inhibitors; single lab","pmids":["35248671"],"is_preprint":false},{"year":2021,"finding":"IGF2BP1 binds directly to MGAT5 mRNA and stabilizes it through m6A RNA methylation modification, promoting MGAT5 expression and consequently the liver cancer stem cell phenotype (self-renewal, chemoresistance, tumorigenesis).","method":"MeRIP-qPCR for IGF2BP1-MGAT5 mRNA binding, MGAT5 mRNA stability assays, IGF2BP1 shRNA knockdown, stemness and tumorigenesis assays","journal":"Stem cells and development","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding of RNA-binding protein to MGAT5 mRNA via m6A demonstrated by MeRIP; single lab","pmids":["34514861"],"is_preprint":false},{"year":2001,"finding":"GnT-V overexpression in hepatocellular carcinoma (7721) cells enhances cell migration and increases surface integrin α5 subunit ~2.9-fold without altering β1 subunit levels, and also elevates E-cadherin and β-catenin expression, linking MGAT5-mediated N-glycan branching to adhesion molecule regulation and migration.","method":"GnT-V cDNA transfection, agarose drop migration assay, flow cytometry for integrin subunits, immunocytochemistry for E-cadherin, Western blot for β-catenin","journal":"Shi yan sheng wu xue bao","confidence":"Low","confidence_rationale":"Tier 3 — single lab, single overexpression approach with no complementary loss-of-function or glycan structural confirmation","pmids":["12549224"],"is_preprint":false},{"year":2025,"finding":"GnT-V (MGAT5) selectively modifies the major kidney tubule apical surface metalloproteases ANPEP and MEP1A at highly accessible, C-terminal domain glycosylation sites. Upon epithelial cell polarization, GnT-V products accumulate to the apical side, suggesting polarized subcellular trafficking contributes to selective substrate modification in vivo.","method":"Lectin-assisted proteomics in Mgat5-null mouse kidney, single-cell transcriptomics, glycosite mapping, epithelial cell polarization experiments with apical/basolateral fractionation","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 — proteomics-based substrate identification in KO tissue combined with cell biology; single lab","pmids":["41323266"],"is_preprint":false},{"year":2025,"finding":"GnT-V (MGAT5) catalyzes β1,6-GlcNAc branching at N121 and N336 of PSMA, which is critical for PSMA protein stability (non-N-glycosylated PSMA is degraded via the autophagy-lysosome pathway). PSMA directly interacts with JAK2 (confirmed by co-immunoprecipitation), which activates STAT3 transcriptional activation, driving PSMA overexpression and aberrant N-glycosylation in a positive feedback loop.","method":"Site-specific N-glycosylation mapping of PSMA, GnT-V inhibition/knockdown, autophagy-lysosome pathway inhibitors, co-immunoprecipitation of PSMA and JAK2, STAT3 activity assays","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 2 — specific glycosylation sites identified with functional degradation consequence, plus co-IP of substrate-signaling partner interaction; single lab","pmids":["40112979"],"is_preprint":false},{"year":2024,"finding":"GnT-V (MGAT5) binds to TIMP-1 (confirmed by GST pull-down) and promotes N-glycosylation of TIMP-1; this aberrant GnT-V-mediated N-glycosylation of TIMP-1 activates the VEGF signaling pathway and promotes retinal microvascular endothelial cell angiogenesis in diabetic retinopathy. Kifunensine treatment, GnT-V knockdown, or TIMP-1 mutation reverses these effects.","method":"GST pull-down assay for GnT-V/TIMP-1 interaction, lectin blot for TIMP-1 glycosylation, GnT-V knockdown, TIMP-1 glycosylation-site mutants, angiogenesis assays, VEGF ELISA, in vivo DR model","journal":"Molecular biology reports","confidence":"Medium","confidence_rationale":"Tier 2 — substrate interaction confirmed by pull-down with functional glycosylation consequence; single lab","pmids":["38499842"],"is_preprint":false}],"current_model":"MGAT5 (GnT-V) is a Golgi UDP-GlcNAc:α-mannoside β1,6-N-acetylglucosaminyltransferase that catalyzes the addition of β1,6-linked GlcNAc branches onto N-glycans of cell-surface and secreted glycoproteins; these branched N-glycans serve as high-avidity ligands for galectins, forming a galectin-glycoprotein lattice that controls receptor clustering, surface residency, and signaling thresholds (e.g., restricting TCR clustering and Th1 responses, and promoting integrin-FAK-PI3K/Akt signaling in tumor cells); MGAT5 is shed from the Golgi membrane by γ-secretase/SPPL3 cleavage to generate a secreted form capable of FGF-2-dependent angiogenesis and transfer of enzymatic activity via small extracellular vesicles, and its expression is transcriptionally regulated by Ets-1 and post-transcriptionally stabilized by IGF2BP1 via m6A modification."},"narrative":{"teleology":[{"year":1987,"claim":"The fundamental catalytic activity of MGAT5 was established: transfer of GlcNAc in β1,6 linkage from UDP-GlcNAc onto α-mannoside acceptors, defining it as the glycosyltransferase responsible for initiating the β1,6 branch on N-glycans.","evidence":"Cell-free enzymatic assay with synthetic trisaccharide acceptor and radiolabeled UDP-GlcNAc, product characterization by reverse-phase chromatography","pmids":["2956949"],"confidence":"High","gaps":["No protein purification or cloning at this stage","Substrate specificity beyond synthetic acceptor not defined","In vivo relevance not yet demonstrated"]},{"year":1999,"claim":"Transcriptional regulation of MGAT5 by Ets-1 was identified, explaining how oncogenic signaling could upregulate β1,6 branching in cancer cells.","evidence":"Ets-1 mRNA correlation with GnT-V across 16 cancer lines (r=0.97), gain- and dominant-negative loss-of-function of Ets-1","pmids":["10438459"],"confidence":"Medium","gaps":["Direct promoter binding by Ets-1 not shown","Other transcription factors not excluded","Regulation in non-cancer cell types not addressed"]},{"year":2000,"claim":"Genetic loss-of-function in mice demonstrated that MGAT5-derived β1,6 branching amplifies oncogenic PI3K/Akt signaling and is required for efficient mammary tumor growth and metastasis, establishing MGAT5 as a functional mediator—not merely a marker—of malignancy.","evidence":"Mgat5 knockout mice crossed with PyMT transgenic mice; PI3K/Akt activity, membrane ruffling, tumor growth and metastasis endpoints","pmids":["10700233"],"confidence":"High","gaps":["Specific glycoprotein substrates mediating the PI3K feedback not identified","Mechanism of PI3K activation by β1,6 glycans not resolved","Immune contribution vs. cell-autonomous effects not distinguished"]},{"year":2001,"claim":"The galectin–glycoprotein lattice model was established: MGAT5-produced β1,6 N-glycans on the TCR recruit galectin-3 to restrict TCR clustering, setting T-cell activation thresholds and preventing autoimmunity.","evidence":"Mgat5 knockout mice showing enhanced TCR clustering and autoimmune disease, co-immunoprecipitation of galectin-3 with TCR, lactose competition phenocopy","pmids":["11217864"],"confidence":"High","gaps":["Specific TCR subunit(s) carrying the critical glycosylation sites not mapped","Galectin-3 vs. other galectins not fully distinguished","Mechanism linking lattice to actin reorganization incomplete"]},{"year":2002,"claim":"A transferase-independent function was discovered: soluble (secreted) GnT-V promotes angiogenesis by liberating FGF-2 from heparan sulfate via a basic domain, revealing a non-catalytic role for the protein.","evidence":"Purified soluble GnT-V protein in vitro and in vivo angiogenesis assays, domain analysis","pmids":["11872751"],"confidence":"Medium","gaps":["Physiological source and regulation of soluble GnT-V secretion not defined at this point","FGF-2 release mechanism not structurally resolved","In vivo contribution vs. catalytic function not separated"]},{"year":2004,"claim":"MGAT5-dependent glycan branching was shown to skew T helper differentiation toward Th2 by suppressing IFN-γ and promoting IL-4, with pharmacological epistasis confirming pathway specificity.","evidence":"Mgat5 knockout mice, swainsonine treatment of human and mouse T cells, cytokine ELISAs, Th1/Th2 polarization assays","pmids":["15585841"],"confidence":"High","gaps":["Downstream signaling intermediates between lattice and cytokine transcription not mapped","Contribution of individual galectin family members not resolved"]},{"year":2006,"claim":"Two advances converged: (1) the galectin-3/MGAT5 lattice was shown to control integrin-mediated focal adhesion signaling (FAK/PI3K) and fibronectin fibrillogenesis; (2) γ-secretase (presenilin complex) was identified as the protease that cleaves GnT-V at His31 to generate its secreted form.","evidence":"Mgat5-/- tumor cells with galectin-3 add-back and antibody blockade for integrin mechanism; N-terminal sequencing of soluble GnT-V, presenilin KO cells, γ-secretase inhibitor for cleavage mechanism","pmids":["16581792","17142794"],"confidence":"High","gaps":["Whether γ-secretase cleavage is regulated by signaling cues unknown","Relative contributions of lattice-dependent vs. lattice-independent integrin regulation not fully resolved"]},{"year":2007,"claim":"Genetic epistasis between Mgat5 and Pten established a bidirectional feedback loop: PI3K/Akt signaling increases β1,6 branching, and β1,6 branching amplifies PI3K/Akt signaling.","evidence":"Pten/Mgat5 double-mutant MEFs, PI3K/Akt assays, L-PHA lectin staining","pmids":["17400585"],"confidence":"Medium","gaps":["Molecular mechanism by which PI3K signaling upregulates β1,6 glycan output not identified","In vivo tumor relevance of the double-mutant interaction not tested"]},{"year":2009,"claim":"Rigorous enzyme kinetics distinguished MGAT5 from its paralog GnT-Vb (GnT-IX): MGAT5 is cation-independent and optimally active at Golgi pH, while GnT-Vb prefers O-mannosyl substrates, resolving potential functional redundancy.","evidence":"Purified enzyme kinetics with defined glycan acceptors, pH and cation-dependence profiles","pmids":["19846580"],"confidence":"High","gaps":["No crystal structure available to explain selectivity differences","Tissue-specific substrate partitioning in vivo not addressed"]},{"year":2012,"claim":"In vivo substrate partitioning was confirmed: MGAT5 accounts for N-linked β1,6 branching and GnT-Vb for O-mannosyl β1,6 branching in brain, with double knockout eliminating all β1,6 products.","evidence":"Single and double knockout mice, glycan structural analysis, laminin binding assays","pmids":["22715095"],"confidence":"High","gaps":["Functional consequences of brain-specific β1,6 N-glycan loss not deeply explored","Compensation mechanisms in peripheral tissues not examined"]},{"year":2018,"claim":"A specific transporter substrate was identified: MGAT5-catalyzed β1,6 branching on hENT1 stabilizes it at the plasma membrane, increasing gemcitabine uptake and chemosensitivity in bladder cancer.","evidence":"GnT-V shRNA knockdown, lectin blot for β1,6-GlcNAc on hENT1, membrane fractionation, drug uptake assays","pmids":["30143259"],"confidence":"Medium","gaps":["Specific glycosylation sites on hENT1 not mapped","Galectin involvement in hENT1 retention not tested","Clinical validation absent"]},{"year":2021,"claim":"Two findings expanded MGAT5 biology: (1) MGAT5 mediates stiffness-dependent glioblastoma invasion via focal adhesion maturation and EMT; (2) IGF2BP1 stabilizes MGAT5 mRNA via m6A modification, linking epitranscriptomic regulation to cancer stemness.","evidence":"CRISPR KO in glioblastoma stem cells on tunable nanofiber scaffolds; MeRIP-qPCR for IGF2BP1-MGAT5 mRNA binding and mRNA stability assays in liver cancer cells","pmids":["33894774","34514861"],"confidence":"Medium","gaps":["Specific m6A sites on MGAT5 mRNA not mapped","How mechanotransduction feeds back to MGAT5 expression unknown","Single-lab findings for each"]},{"year":2022,"claim":"SPPL3 was identified as a second protease (alongside γ-secretase) that cleaves GnT-V to generate its secreted form, which is selectively loaded into non-exosomal small extracellular vesicles capable of intercellular glycan remodeling.","evidence":"SPPL3 knockdown/knockout, sEV fractionation, enzymatic activity assays, recipient cell glycan analysis","pmids":["36590176"],"confidence":"Medium","gaps":["Relative contributions of γ-secretase vs. SPPL3 to GnT-V secretion not quantified","Physiological range and target cell specificity of sEV-mediated glycan transfer unknown"]},{"year":2023,"claim":"Structural insights into substrate recognition emerged: molecular dynamics simulations combined with mutagenesis revealed that GnT-V recognizes the N-glycan core via residues outside the catalytic pocket, and UDP binding induces a conformational change affecting acceptor orientation; separately, hydrophobic UDP-GlcNAc analogs were shown to selectively inhibit GnT-V over GnT-I–IV.","evidence":"MD simulations validated by site-directed mutagenesis and HPLC activity assays; purified enzyme panel assays with synthetic donor analogs","pmids":["37974463","35248671"],"confidence":"Medium","gaps":["No experimental crystal or cryo-EM structure of GnT-V with bound acceptor","Selectivity of inhibitors not tested in cellular context"]},{"year":2024,"claim":"MGAT5 was shown to shield tumors from immune surveillance: Mgat5-deficient pancreatic tumors become sensitive to TNF superfamily-mediated killing by T cells and dendritic cells, and Mgat5 knockout restores responsiveness to immune checkpoint blockade in resistant PDAC.","evidence":"Mgat5 KO clonal PDAC lines, in vivo growth, immune cell depletion experiments, TNF family death pathway assays, anti-PD-1/CTLA-4 treatment","pmids":["38912584"],"confidence":"Medium","gaps":["Specific glycoprotein substrates mediating immune evasion not identified","Mechanism linking β1,6 glycans to TNF pathway sensitivity unknown","Human tumor validation absent"]},{"year":2025,"claim":"Specific in vivo substrates of MGAT5 were mapped in kidney (ANPEP, MEP1A at accessible C-terminal glycosites) and in prostate cancer (PSMA at N121/N336), with β1,6 branching controlling PSMA stability via the autophagy-lysosome pathway and TIMP-1 glycosylation driving VEGF-mediated angiogenesis in diabetic retinopathy.","evidence":"Lectin-assisted proteomics in Mgat5-null kidney, site-specific glycosite mapping, PSMA glycosylation/degradation assays, GST pull-down of GnT-V/TIMP-1, in vivo diabetic retinopathy model","pmids":["41323266","40112979","38499842"],"confidence":"Medium","gaps":["Full in vivo substrate repertoire beyond kidney and select cancer substrates remains unmapped","Structural basis for substrate selectivity at specific glycosites not determined","TIMP-1 and PSMA findings each from single laboratories"]},{"year":null,"claim":"No high-resolution experimental structure of MGAT5 with bound acceptor glycan exists, the full in vivo substrate repertoire is unmapped, and the molecular mechanism by which β1,6-branched glycans sensitize tumor cells to TNF-family-mediated immune killing remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["Experimental 3D structure with acceptor glycan needed","Systematic in vivo substrate identification across tissues lacking","Mechanism linking glycan branching to TNF pathway death sensitivity undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[3,9,10,17]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,6]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[3,5,9,20]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4,5,11]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,9,10,17]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,2,8]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,6,15]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,13,15]}],"complexes":[],"partners":["LGALS3","TIMP1","SPPL3","PSEN1","IGF2BP1","FOLH1","ANPEP","MEP1A"],"other_free_text":[]},"mechanistic_narrative":"MGAT5 (GnT-V) is a Golgi-resident UDP-GlcNAc:α-mannoside β1,6-N-acetylglucosaminyltransferase that catalyzes the addition of β1,6-linked GlcNAc branches onto N-glycans, thereby generating high-avidity ligands for galectins and establishing a galectin–glycoprotein lattice that controls receptor clustering, surface residency, and signaling thresholds across immune, epithelial, and tumor cell contexts [PMID:2956949, PMID:11217864, PMID:16581792]. In T cells, MGAT5-modified N-glycans on the TCR recruit galectin-3 to restrain TCR clustering and bias differentiation toward Th2 responses, while in tumor cells β1,6-branched glycans on integrins, hENT1, PSMA, TIMP-1, and kidney metalloproteases (ANPEP, MEP1A) promote FAK–PI3K/Akt signaling, membrane retention of transporters, protein stability, and motility [PMID:11217864, PMID:15585841, PMID:10700233, PMID:30143259, PMID:40112979, PMID:38499842, PMID:41323266]. MGAT5 is released from the Golgi membrane by γ-secretase (presenilin complex) and SPPL3 cleavage to yield a secreted form that promotes FGF-2-dependent angiogenesis and can be delivered to recipient cells via small extracellular vesicles to remodel their glycan landscape [PMID:17142794, PMID:11872751, PMID:36590176]. Loss of Mgat5 in vivo suppresses mammary and pancreatic tumor growth, restores sensitivity to immune checkpoint blockade, and shifts neural stem cell differentiation toward neurons at the expense of astrocytes [PMID:10700233, PMID:38912584, PMID:37172586]."},"prefetch_data":{"uniprot":{"accession":"Q09328","full_name":"Alpha-1,6-mannosylglycoprotein 6-beta-N-acetylglucosaminyltransferase A","aliases":["Alpha-mannoside beta-1,6-N-acetylglucosaminyltransferase V","GlcNAc-T V","GNT-V","Mannoside acetylglucosaminyltransferase 5","N-acetylglucosaminyl-transferase V"],"length_aa":741,"mass_kda":84.5,"function":"Catalyzes the addition of N-acetylglucosamine (GlcNAc) in beta 1-6 linkage to the alpha-linked mannose of biantennary N-linked oligosaccharides (PubMed:10395745, PubMed:30140003). Catalyzes an important step in the biosynthesis of branched, complex-type N-glycans, such as those found on EGFR, TGFR (TGF-beta receptor) and CDH2 (PubMed:10395745, PubMed:22614033, PubMed:30140003). Via its role in the biosynthesis of complex N-glycans, plays an important role in the activation of cellular signaling pathways, reorganization of the actin cytoskeleton, cell-cell adhesion and cell migration. MGAT5-dependent EGFR N-glycosylation enhances the interaction between EGFR and LGALS3 and thereby prevents rapid EGFR endocytosis and prolongs EGFR signaling. Required for efficient interaction between TGFB1 and its receptor. Enhances activation of intracellular signaling pathways by several types of growth factors, including FGF2, PDGF, IGF, TGFB1 and EGF. MGAT5-dependent CDH2 N-glycosylation inhibits CDH2-mediated homotypic cell-cell adhesion and contributes to the regulation of downstream signaling pathways. Promotes cell migration. Contributes to the regulation of the inflammatory response. MGAT5-dependent TCR N-glycosylation enhances the interaction between TCR and LGALS3, limits agonist-induced TCR clustering, and thereby dampens TCR-mediated responses to antigens. Required for normal leukocyte evasation and accumulation at sites of inflammation (By similarity). Inhibits attachment of monocytes to the vascular endothelium and subsequent monocyte diapedesis (PubMed:22614033) Promotes proliferation of umbilical vein endothelial cells and angiogenesis, at least in part by promoting the release of the growth factor FGF2 from the extracellular matrix","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q09328/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MGAT5","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MGAT5","total_profiled":1310},"omim":[{"mim_id":"615553","title":"ARTHROGRYPOSIS, IMPAIRED INTELLECTUAL DEVELOPMENT, AND SEIZURES; AMRS","url":"https://www.omim.org/entry/615553"},{"mim_id":"612441","title":"ALPHA-1,6-@MANNOSYL-GLYCOPROTEIN BETA-1,6-N-ACETYLGLUCOSAMINYLTRANSFERASE, ISOZYME B; MGAT5B","url":"https://www.omim.org/entry/612441"},{"mim_id":"606822","title":"PROTEIN O-MANNOSE BETA-1,2-N-ACETYLGLUCOSAMINYLTRANSFERASE; POMGNT1","url":"https://www.omim.org/entry/606822"},{"mim_id":"605632","title":"SOLUTE CARRIER FAMILY 35 (UDP-N-ACETYLGLUCOSAMINE TRANSPORTER), MEMBER 3; SLC35A3","url":"https://www.omim.org/entry/605632"},{"mim_id":"604621","title":"BETA-1,4-@MANNOSYL-GLYCOPROTEIN BETA-1,4-N-ACETYLGLUCOSAMINYLTRANSFERASE; MGAT3","url":"https://www.omim.org/entry/604621"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MGAT5"},"hgnc":{"alias_symbol":["GNT-V","MGAT5A"],"prev_symbol":[]},"alphafold":{"accession":"Q09328","domains":[{"cath_id":"-","chopping":"154-207","consensus_level":"high","plddt":84.6309,"start":154,"end":207},{"cath_id":"-","chopping":"221-378","consensus_level":"high","plddt":89.6456,"start":221,"end":378},{"cath_id":"3.40.50.2000","chopping":"433-602","consensus_level":"high","plddt":91.2704,"start":433,"end":602},{"cath_id":"-","chopping":"631-726","consensus_level":"high","plddt":94.0986,"start":631,"end":726}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q09328","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q09328-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q09328-F1-predicted_aligned_error_v6.png","plddt_mean":83.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MGAT5","jax_strain_url":"https://www.jax.org/strain/search?query=MGAT5"},"sequence":{"accession":"Q09328","fasta_url":"https://rest.uniprot.org/uniprotkb/Q09328.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q09328/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q09328"}},"corpus_meta":[{"pmid":"11217864","id":"PMC_11217864","title":"Negative 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General subjects","url":"https://pubmed.ncbi.nlm.nih.gov/39233219","citation_count":4,"is_preprint":false},{"pmid":"38499842","id":"PMC_38499842","title":"GnT-V-mediated aberrant N-glycosylation of TIMP-1 promotes diabetic retinopathy progression.","date":"2024","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/38499842","citation_count":2,"is_preprint":false},{"pmid":"12122020","id":"PMC_12122020","title":"Sequences of the mouse N-acetylglucosaminyltransferase V (Mgat5) mRNA and an mRNA expressed by an Mgat5-deficient cell line.","date":"2002","source":"Glycobiology","url":"https://pubmed.ncbi.nlm.nih.gov/12122020","citation_count":2,"is_preprint":false},{"pmid":"41323266","id":"PMC_41323266","title":"Selective modification of glycoprotein substrates by GnT-V in mouse kidney.","date":"2025","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/41323266","citation_count":1,"is_preprint":false},{"pmid":"37427332","id":"PMC_37427332","title":"ISLR interacts with MGAT5 to promote the malignant progression of human gastric cancer AGS cells.","date":"2023","source":"Iranian journal of basic medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37427332","citation_count":1,"is_preprint":false},{"pmid":"12549224","id":"PMC_12549224","title":"[GnT-V overexpression in human hepatocarcinoma cells affects its migration and expression of cell adhesion molecules].","date":"2001","source":"Shi yan sheng wu xue bao","url":"https://pubmed.ncbi.nlm.nih.gov/12549224","citation_count":1,"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":"18655794","id":"PMC_18655794","title":"Evidence for tyrosinase as a beta1,6 branch containing glycoprotein: substrate of GnT-V.","date":"2008","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/18655794","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":30016,"output_tokens":6312,"usd":0.092364},"stage2":{"model":"claude-opus-4-6","input_tokens":9983,"output_tokens":4369,"usd":0.23871},"total_usd":0.331074,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"MGAT5 (GlcNAc-TV) initiates β1,6 GlcNAc branching on N-glycans of the TCR complex, increasing N-acetyllactosamine ligands for galectins; galectin-3 associates with the TCR complex at the cell surface in an MGAT5-dependent manner, forming a galectin-glycoprotein lattice that restricts TCR clustering at the antigen presentation site, thereby raising T-cell activation thresholds. Mgat5-/- mice showed enhanced TCR clustering, actin microfilament reorganization, and autoimmune disease.\",\n      \"method\": \"Mgat5 knockout mice, lactose competition assay (phenocopy), co-immunoprecipitation of galectin-3 with TCR, TCR recruitment to agonist-coated beads, signaling and proliferation assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal evidence from KO mice, co-IP, and pharmacological phenocopy; replicated across multiple orthogonal readouts in a highly cited foundational study\",\n      \"pmids\": [\"11217864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MGAT5-derived β1,6GlcNAc-branched N-glycans stimulate membrane ruffling and PI3K-PKB (Akt) activation, creating a positive feedback loop that amplifies oncogene signaling; Mgat5-deficient mice show markedly reduced mammary tumor growth and metastasis in a polyomavirus middle T oncogene model.\",\n      \"method\": \"Targeted gene knockout mice crossed with PyMT transgenic mice; PI3K/PKB activity assays; membrane ruffling assays; in vivo tumor growth and metastasis measurements\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function in vivo with defined signaling readout, replicated with multiple tumor endpoints\",\n      \"pmids\": [\"10700233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Galectin-3 binding to Mgat5-modified β1,6GlcNAc-branched N-glycans on fibronectin receptors regulates fibronectin fibrillogenesis and tumor cell motility by activating FAK and PI3K, recruiting conformationally active α5β1-integrin to fibrillar adhesions, and increasing F-actin turnover. Blocking Mgat5 or competing for galectin binding inhibits these processes.\",\n      \"method\": \"Mgat5-/- mammary epithelial tumor cells, swainsonine treatment, exogenous galectin-3 addition, RGD peptide inhibition, anti-galectin-3 antibodies, FAK/PI3K activity assays, fibronectin matrix remodeling assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KO cells, pharmacological inhibition, antibody blockade, exogenous protein addition) converging on the same mechanism\",\n      \"pmids\": [\"16581792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"GnT-V (MGAT5) catalyzes transfer of GlcNAc in β1,6 linkage from UDP-GlcNAc onto α-mannoside acceptors (N-glycan precursors), as demonstrated by cell-free enzyme assays using a synthetic trisaccharide acceptor and UDP-[3H]-GlcNAc, producing a radiolabeled tetrasaccharide product.\",\n      \"method\": \"In vitro enzymatic assay with cell extracts, synthetic trisaccharide acceptor, UDP-[3H]-GlcNAc, reverse-phase chromatography product separation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro enzymatic assay establishing catalytic activity\",\n      \"pmids\": [\"2956949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Secreted (soluble) GnT-V protein itself promotes tumor angiogenesis in vitro and in vivo at physiological concentrations independent of its glycosyltransferase activity, via its highly basic domain inducing release of FGF-2 from heparan sulfate proteoglycan on the cell surface/extracellular matrix.\",\n      \"method\": \"In vitro angiogenesis assays, in vivo angiogenesis models, addition of purified soluble GnT-V protein, domain analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — recombinant protein functional assay with domain-level mechanistic insight; single lab\",\n      \"pmids\": [\"11872751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GnT-V is cleaved at its transmembrane/stem region boundary (at His31) by γ-secretase (presenilin-containing complex), generating the secreted ~100 kDa soluble form. Presenilin-1/2 double-deficient cells (no γ-secretase activity) completely lack soluble GnT-V secretion; FAD-linked presenilin-1 overexpression increases GnT-V secretion.\",\n      \"method\": \"N-terminal protein sequencing of purified soluble GnT-V, γ-secretase inhibitor (DFK-167) treatment, presenilin knockout cells, presenilin-1 overexpression, site-directed mutagenesis of cleavage site\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — protein sequencing of cleavage site combined with genetic and pharmacological validation in multiple cell models\",\n      \"pmids\": [\"17142794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"MGAT5-mediated β1,6GlcNAc N-glycans on the TCR negatively regulate TCR signaling, promoting Th2 over Th1 differentiation; Mgat5-/- T cells produce more IFN-γ and less IL-4. Swainsonine (Golgi α-mannosidase II inhibitor blocking β1,6GlcNAc expression) phenocopies this increase in IFN-γ in human and mouse T cells, but has no additional effect in Mgat5-/- cells, confirming pathway specificity.\",\n      \"method\": \"Mgat5 knockout mice, cytokine ELISAs, swainsonine pharmacological inhibition, Th1/Th2 polarization assays, anti-CD3 stimulation of human T cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO confirmed by pharmacological epistasis in both mouse and human T cells\",\n      \"pmids\": [\"15585841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The transcription factor Ets-1 regulates GnT-V (MGAT5) gene expression in cancer cells; Ets-1 mRNA levels correlate tightly with GnT-V mRNA across 16 cancer cell lines (r=0.97), and overexpression of Ets-1 enhances GnT-V expression while dominant-negative Ets-1 reduces it.\",\n      \"method\": \"Correlation analysis across cancer cell lines, Ets-1 cDNA transfection, dominant-negative Ets-1 transfection, RT-PCR\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function of transcription factor with defined gene expression readout; single lab\",\n      \"pmids\": [\"10438459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mgat5 and PTEN interact functionally to regulate PI3K/Akt signaling, cell spreading, and proliferation: Pten heterozygosity enhances adhesion-dependent PI3K/Akt signaling and cell spreading, while Mgat5 deficiency normalizes these responses in Pten+/- cells. Pten heterozygosity is also associated with increased surface β1,6GlcNAc-branched N-glycans, suggesting positive feedback from PI3K signaling to N-glycan branching.\",\n      \"method\": \"Pten/Mgat5 double-mutant mouse embryonic fibroblasts, PI3K/Akt activity assays, cell spreading assays, L-PHA lectin staining, in vivo longevity analysis\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in double-mutant cells with biochemical readouts; single lab\",\n      \"pmids\": [\"17400585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GnT-V (MGAT5) and its paralog GnT-Vb (GnT-IX) have distinct catalytic properties: GnT-V is fully active without exogenous cations (pH optimum 6.5–7.0), while GnT-Vb is stimulated by Mn²⁺ (pH optimum 8.0) and has ~2.5-fold higher Km for biantennary N-glycan acceptors but much greater efficiency on O-mannosyl glycopeptide substrates. Both transfer GlcNAc in β1,6 linkage to the Man of GlcNAcβ1,2Man moiety.\",\n      \"method\": \"In vitro enzymatic assays with purified enzymes, synthetic and natural glycan acceptors, kinetic measurements (Km, Vmax), EDTA/cation dependence, pH profiles, product characterization\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — rigorous in vitro enzyme kinetics with purified proteins and defined substrates\",\n      \"pmids\": [\"19846580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In vivo, GnT-V (MGAT5) and GnT-Vb (GnT-IX) have complementary substrate specificities: GnT-V null brains lack N-linked β1,6-glycans but have normal O-Man β1,6-branched structures; GnT-Vb null brains have normal N-linked β1,6-glycans but reduced O-Man β1,6-branched glycans. Only deletion of both enzymes eliminates all β1,6-branched glycans.\",\n      \"method\": \"GnT-V and GnT-Vb single and double knockout mice, glycan structural analysis, antibody binding assays (IIH6C4), laminin binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic epistasis via double-KO mice with glycan structural analysis\",\n      \"pmids\": [\"22715095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GnT-V (MGAT5) in small extracellular vesicles (sEVs) is a cleaved (secreted) form generated by SPPL3 protease cleavage; GnT-V is selectively enriched in non-exosomal sEVs among various glycosyltransferases. Enzymatically active GnT-V in sEVs is transferred to recipient cells and remodels their N-glycan structures to express GnT-V-produced β1,6-branched glycans.\",\n      \"method\": \"Glycosyltransferase activity measurements in sEV fractions, SPPL3 knockdown/knockout, single-particle imaging, fractionation experiments, recipient cell glycan structural analysis\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — enzymatic activity assays combined with genetic manipulation and functional transfer experiment; single lab\",\n      \"pmids\": [\"36590176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GnT-V enhances gemcitabine chemosensitivity in bladder cancer cells by adding β1,6-GlcNAc branches to the nucleoside transporter hENT1, which increases hENT1 accumulation at the plasma membrane and thus gemcitabine uptake. GnT-V silencing reduces β1,6-GlcNAc on hENT1 and decreases membrane hENT1 levels and drug uptake.\",\n      \"method\": \"GnT-V shRNA knockdown, lectin blot for β1,6-GlcNAc on hENT1, membrane fractionation, drug uptake assays, cell viability assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific substrate identified with glycan modification, membrane localization and functional drug uptake linked; single lab\",\n      \"pmids\": [\"30143259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MGAT5-catalyzed β1,6-branched N-glycan production is required for stiffness-dependent invasion of glioblastoma stem-like cells (GSCs). CRISPR-Cas9 deletion of MGAT5 suppressed stiffness dependence of migration on 166 kPa nanofiber scaffolds and abolished associated focal adhesion (FA) maturation and EMT protein expression, demonstrating MGAT5 as a critical mediator of mechanotransduction.\",\n      \"method\": \"CRISPR-Cas9 MGAT5 deletion in GSCs, 3D nanofiber scaffolds with tunable stiffness, cell migration assays, galectin-3 binding, FA and EMT protein expression analysis\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype and molecular readouts; single lab\",\n      \"pmids\": [\"33894774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss of MGAT5 in neural stem/progenitor cells (NSPCs) shifts differentiation toward neurons and away from astrocytes in vitro and in vivo, leading to accelerated neuronal differentiation, depletion of the NSPC niche, and a shift in cortical neuron layers in Mgat5-null mice.\",\n      \"method\": \"Mgat5 homozygous null mice, NSPC culture differentiation assays, in vivo cortical neuron layer analysis, cell fate marker immunostaining\",\n      \"journal\": \"Stem cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined in vitro and in vivo differentiation phenotypes; single lab\",\n      \"pmids\": [\"37172586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Mgat5 is required for in vivo tumor growth of pancreatic ductal adenocarcinoma (PDAC) but not for in vitro growth; Mgat5-deficient tumor cells show increased sensitivity to TNF superfamily-mediated cell death and are cleared by T cells and dendritic cells, with NK cells playing an early role. Mgat5 knockout in an immunotherapy-resistant PDAC line restored sensitivity to immune checkpoint blockade.\",\n      \"method\": \"Mgat5 knockout clonal cell lines, in vivo vs. in vitro growth comparison, T cell/NK cell/dendritic cell depletion experiments, TNF family cell death pathway assays, immune checkpoint blockade treatment\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple orthogonal in vivo immune depletion experiments and defined cell death mechanism; single lab\",\n      \"pmids\": [\"38912584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GnT-V (MGAT5) recognizes the N-glycan core via residues outside its catalytic pocket, and UDP binding affects acceptor orientation through a conformational change at the Manα1,6-Man linkage, as determined by molecular dynamics simulations validated by biochemical experiments with site-specifically mutated residues.\",\n      \"method\": \"Molecular dynamics simulations, biochemical mutagenesis experiments, HPLC-based enzyme activity assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — simulation plus mutagenesis validation; single lab, moderate evidence\",\n      \"pmids\": [\"37974463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"UDP-GlcNAc analogs with increased hydrophobicity (phosphate groups replaced by hydrophobic groups) selectively inhibit GnT-V enzymatic activity compared to other GnT family members (GnT-I–IV), indicating GnT-V is uniquely tolerant of hydrophobicity in the donor substrate and that its catalytic pocket is structurally distinct.\",\n      \"method\": \"Purified truncated enzyme HPLC-based activity assays for GnT-I–V, synthesis of 10 UDP-GlcNAc analogs, docking models\",\n      \"journal\": \"Biochimica et biophysica acta. General subjects\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro assay with purified enzymes and panel of synthesized inhibitors; single lab\",\n      \"pmids\": [\"35248671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IGF2BP1 binds directly to MGAT5 mRNA and stabilizes it through m6A RNA methylation modification, promoting MGAT5 expression and consequently the liver cancer stem cell phenotype (self-renewal, chemoresistance, tumorigenesis).\",\n      \"method\": \"MeRIP-qPCR for IGF2BP1-MGAT5 mRNA binding, MGAT5 mRNA stability assays, IGF2BP1 shRNA knockdown, stemness and tumorigenesis assays\",\n      \"journal\": \"Stem cells and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding of RNA-binding protein to MGAT5 mRNA via m6A demonstrated by MeRIP; single lab\",\n      \"pmids\": [\"34514861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"GnT-V overexpression in hepatocellular carcinoma (7721) cells enhances cell migration and increases surface integrin α5 subunit ~2.9-fold without altering β1 subunit levels, and also elevates E-cadherin and β-catenin expression, linking MGAT5-mediated N-glycan branching to adhesion molecule regulation and migration.\",\n      \"method\": \"GnT-V cDNA transfection, agarose drop migration assay, flow cytometry for integrin subunits, immunocytochemistry for E-cadherin, Western blot for β-catenin\",\n      \"journal\": \"Shi yan sheng wu xue bao\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single overexpression approach with no complementary loss-of-function or glycan structural confirmation\",\n      \"pmids\": [\"12549224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GnT-V (MGAT5) selectively modifies the major kidney tubule apical surface metalloproteases ANPEP and MEP1A at highly accessible, C-terminal domain glycosylation sites. Upon epithelial cell polarization, GnT-V products accumulate to the apical side, suggesting polarized subcellular trafficking contributes to selective substrate modification in vivo.\",\n      \"method\": \"Lectin-assisted proteomics in Mgat5-null mouse kidney, single-cell transcriptomics, glycosite mapping, epithelial cell polarization experiments with apical/basolateral fractionation\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomics-based substrate identification in KO tissue combined with cell biology; single lab\",\n      \"pmids\": [\"41323266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GnT-V (MGAT5) catalyzes β1,6-GlcNAc branching at N121 and N336 of PSMA, which is critical for PSMA protein stability (non-N-glycosylated PSMA is degraded via the autophagy-lysosome pathway). PSMA directly interacts with JAK2 (confirmed by co-immunoprecipitation), which activates STAT3 transcriptional activation, driving PSMA overexpression and aberrant N-glycosylation in a positive feedback loop.\",\n      \"method\": \"Site-specific N-glycosylation mapping of PSMA, GnT-V inhibition/knockdown, autophagy-lysosome pathway inhibitors, co-immunoprecipitation of PSMA and JAK2, STAT3 activity assays\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific glycosylation sites identified with functional degradation consequence, plus co-IP of substrate-signaling partner interaction; single lab\",\n      \"pmids\": [\"40112979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GnT-V (MGAT5) binds to TIMP-1 (confirmed by GST pull-down) and promotes N-glycosylation of TIMP-1; this aberrant GnT-V-mediated N-glycosylation of TIMP-1 activates the VEGF signaling pathway and promotes retinal microvascular endothelial cell angiogenesis in diabetic retinopathy. Kifunensine treatment, GnT-V knockdown, or TIMP-1 mutation reverses these effects.\",\n      \"method\": \"GST pull-down assay for GnT-V/TIMP-1 interaction, lectin blot for TIMP-1 glycosylation, GnT-V knockdown, TIMP-1 glycosylation-site mutants, angiogenesis assays, VEGF ELISA, in vivo DR model\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — substrate interaction confirmed by pull-down with functional glycosylation consequence; single lab\",\n      \"pmids\": [\"38499842\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MGAT5 (GnT-V) is a Golgi UDP-GlcNAc:α-mannoside β1,6-N-acetylglucosaminyltransferase that catalyzes the addition of β1,6-linked GlcNAc branches onto N-glycans of cell-surface and secreted glycoproteins; these branched N-glycans serve as high-avidity ligands for galectins, forming a galectin-glycoprotein lattice that controls receptor clustering, surface residency, and signaling thresholds (e.g., restricting TCR clustering and Th1 responses, and promoting integrin-FAK-PI3K/Akt signaling in tumor cells); MGAT5 is shed from the Golgi membrane by γ-secretase/SPPL3 cleavage to generate a secreted form capable of FGF-2-dependent angiogenesis and transfer of enzymatic activity via small extracellular vesicles, and its expression is transcriptionally regulated by Ets-1 and post-transcriptionally stabilized by IGF2BP1 via m6A modification.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MGAT5 (GnT-V) is a Golgi-resident UDP-GlcNAc:α-mannoside β1,6-N-acetylglucosaminyltransferase that catalyzes the addition of β1,6-linked GlcNAc branches onto N-glycans, thereby generating high-avidity ligands for galectins and establishing a galectin–glycoprotein lattice that controls receptor clustering, surface residency, and signaling thresholds across immune, epithelial, and tumor cell contexts [PMID:2956949, PMID:11217864, PMID:16581792]. In T cells, MGAT5-modified N-glycans on the TCR recruit galectin-3 to restrain TCR clustering and bias differentiation toward Th2 responses, while in tumor cells β1,6-branched glycans on integrins, hENT1, PSMA, TIMP-1, and kidney metalloproteases (ANPEP, MEP1A) promote FAK–PI3K/Akt signaling, membrane retention of transporters, protein stability, and motility [PMID:11217864, PMID:15585841, PMID:10700233, PMID:30143259, PMID:40112979, PMID:38499842, PMID:41323266]. MGAT5 is released from the Golgi membrane by γ-secretase (presenilin complex) and SPPL3 cleavage to yield a secreted form that promotes FGF-2-dependent angiogenesis and can be delivered to recipient cells via small extracellular vesicles to remodel their glycan landscape [PMID:17142794, PMID:11872751, PMID:36590176]. Loss of Mgat5 in vivo suppresses mammary and pancreatic tumor growth, restores sensitivity to immune checkpoint blockade, and shifts neural stem cell differentiation toward neurons at the expense of astrocytes [PMID:10700233, PMID:38912584, PMID:37172586].\",\n  \"teleology\": [\n    {\n      \"year\": 1987,\n      \"claim\": \"The fundamental catalytic activity of MGAT5 was established: transfer of GlcNAc in β1,6 linkage from UDP-GlcNAc onto α-mannoside acceptors, defining it as the glycosyltransferase responsible for initiating the β1,6 branch on N-glycans.\",\n      \"evidence\": \"Cell-free enzymatic assay with synthetic trisaccharide acceptor and radiolabeled UDP-GlcNAc, product characterization by reverse-phase chromatography\",\n      \"pmids\": [\"2956949\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No protein purification or cloning at this stage\", \"Substrate specificity beyond synthetic acceptor not defined\", \"In vivo relevance not yet demonstrated\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Transcriptional regulation of MGAT5 by Ets-1 was identified, explaining how oncogenic signaling could upregulate β1,6 branching in cancer cells.\",\n      \"evidence\": \"Ets-1 mRNA correlation with GnT-V across 16 cancer lines (r=0.97), gain- and dominant-negative loss-of-function of Ets-1\",\n      \"pmids\": [\"10438459\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct promoter binding by Ets-1 not shown\", \"Other transcription factors not excluded\", \"Regulation in non-cancer cell types not addressed\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Genetic loss-of-function in mice demonstrated that MGAT5-derived β1,6 branching amplifies oncogenic PI3K/Akt signaling and is required for efficient mammary tumor growth and metastasis, establishing MGAT5 as a functional mediator—not merely a marker—of malignancy.\",\n      \"evidence\": \"Mgat5 knockout mice crossed with PyMT transgenic mice; PI3K/Akt activity, membrane ruffling, tumor growth and metastasis endpoints\",\n      \"pmids\": [\"10700233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific glycoprotein substrates mediating the PI3K feedback not identified\", \"Mechanism of PI3K activation by β1,6 glycans not resolved\", \"Immune contribution vs. cell-autonomous effects not distinguished\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The galectin–glycoprotein lattice model was established: MGAT5-produced β1,6 N-glycans on the TCR recruit galectin-3 to restrict TCR clustering, setting T-cell activation thresholds and preventing autoimmunity.\",\n      \"evidence\": \"Mgat5 knockout mice showing enhanced TCR clustering and autoimmune disease, co-immunoprecipitation of galectin-3 with TCR, lactose competition phenocopy\",\n      \"pmids\": [\"11217864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific TCR subunit(s) carrying the critical glycosylation sites not mapped\", \"Galectin-3 vs. other galectins not fully distinguished\", \"Mechanism linking lattice to actin reorganization incomplete\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"A transferase-independent function was discovered: soluble (secreted) GnT-V promotes angiogenesis by liberating FGF-2 from heparan sulfate via a basic domain, revealing a non-catalytic role for the protein.\",\n      \"evidence\": \"Purified soluble GnT-V protein in vitro and in vivo angiogenesis assays, domain analysis\",\n      \"pmids\": [\"11872751\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological source and regulation of soluble GnT-V secretion not defined at this point\", \"FGF-2 release mechanism not structurally resolved\", \"In vivo contribution vs. catalytic function not separated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"MGAT5-dependent glycan branching was shown to skew T helper differentiation toward Th2 by suppressing IFN-γ and promoting IL-4, with pharmacological epistasis confirming pathway specificity.\",\n      \"evidence\": \"Mgat5 knockout mice, swainsonine treatment of human and mouse T cells, cytokine ELISAs, Th1/Th2 polarization assays\",\n      \"pmids\": [\"15585841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling intermediates between lattice and cytokine transcription not mapped\", \"Contribution of individual galectin family members not resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Two advances converged: (1) the galectin-3/MGAT5 lattice was shown to control integrin-mediated focal adhesion signaling (FAK/PI3K) and fibronectin fibrillogenesis; (2) γ-secretase (presenilin complex) was identified as the protease that cleaves GnT-V at His31 to generate its secreted form.\",\n      \"evidence\": \"Mgat5-/- tumor cells with galectin-3 add-back and antibody blockade for integrin mechanism; N-terminal sequencing of soluble GnT-V, presenilin KO cells, γ-secretase inhibitor for cleavage mechanism\",\n      \"pmids\": [\"16581792\", \"17142794\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether γ-secretase cleavage is regulated by signaling cues unknown\", \"Relative contributions of lattice-dependent vs. lattice-independent integrin regulation not fully resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Genetic epistasis between Mgat5 and Pten established a bidirectional feedback loop: PI3K/Akt signaling increases β1,6 branching, and β1,6 branching amplifies PI3K/Akt signaling.\",\n      \"evidence\": \"Pten/Mgat5 double-mutant MEFs, PI3K/Akt assays, L-PHA lectin staining\",\n      \"pmids\": [\"17400585\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism by which PI3K signaling upregulates β1,6 glycan output not identified\", \"In vivo tumor relevance of the double-mutant interaction not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Rigorous enzyme kinetics distinguished MGAT5 from its paralog GnT-Vb (GnT-IX): MGAT5 is cation-independent and optimally active at Golgi pH, while GnT-Vb prefers O-mannosyl substrates, resolving potential functional redundancy.\",\n      \"evidence\": \"Purified enzyme kinetics with defined glycan acceptors, pH and cation-dependence profiles\",\n      \"pmids\": [\"19846580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure available to explain selectivity differences\", \"Tissue-specific substrate partitioning in vivo not addressed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"In vivo substrate partitioning was confirmed: MGAT5 accounts for N-linked β1,6 branching and GnT-Vb for O-mannosyl β1,6 branching in brain, with double knockout eliminating all β1,6 products.\",\n      \"evidence\": \"Single and double knockout mice, glycan structural analysis, laminin binding assays\",\n      \"pmids\": [\"22715095\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences of brain-specific β1,6 N-glycan loss not deeply explored\", \"Compensation mechanisms in peripheral tissues not examined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"A specific transporter substrate was identified: MGAT5-catalyzed β1,6 branching on hENT1 stabilizes it at the plasma membrane, increasing gemcitabine uptake and chemosensitivity in bladder cancer.\",\n      \"evidence\": \"GnT-V shRNA knockdown, lectin blot for β1,6-GlcNAc on hENT1, membrane fractionation, drug uptake assays\",\n      \"pmids\": [\"30143259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific glycosylation sites on hENT1 not mapped\", \"Galectin involvement in hENT1 retention not tested\", \"Clinical validation absent\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Two findings expanded MGAT5 biology: (1) MGAT5 mediates stiffness-dependent glioblastoma invasion via focal adhesion maturation and EMT; (2) IGF2BP1 stabilizes MGAT5 mRNA via m6A modification, linking epitranscriptomic regulation to cancer stemness.\",\n      \"evidence\": \"CRISPR KO in glioblastoma stem cells on tunable nanofiber scaffolds; MeRIP-qPCR for IGF2BP1-MGAT5 mRNA binding and mRNA stability assays in liver cancer cells\",\n      \"pmids\": [\"33894774\", \"34514861\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific m6A sites on MGAT5 mRNA not mapped\", \"How mechanotransduction feeds back to MGAT5 expression unknown\", \"Single-lab findings for each\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"SPPL3 was identified as a second protease (alongside γ-secretase) that cleaves GnT-V to generate its secreted form, which is selectively loaded into non-exosomal small extracellular vesicles capable of intercellular glycan remodeling.\",\n      \"evidence\": \"SPPL3 knockdown/knockout, sEV fractionation, enzymatic activity assays, recipient cell glycan analysis\",\n      \"pmids\": [\"36590176\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of γ-secretase vs. SPPL3 to GnT-V secretion not quantified\", \"Physiological range and target cell specificity of sEV-mediated glycan transfer unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Structural insights into substrate recognition emerged: molecular dynamics simulations combined with mutagenesis revealed that GnT-V recognizes the N-glycan core via residues outside the catalytic pocket, and UDP binding induces a conformational change affecting acceptor orientation; separately, hydrophobic UDP-GlcNAc analogs were shown to selectively inhibit GnT-V over GnT-I–IV.\",\n      \"evidence\": \"MD simulations validated by site-directed mutagenesis and HPLC activity assays; purified enzyme panel assays with synthetic donor analogs\",\n      \"pmids\": [\"37974463\", \"35248671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental crystal or cryo-EM structure of GnT-V with bound acceptor\", \"Selectivity of inhibitors not tested in cellular context\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"MGAT5 was shown to shield tumors from immune surveillance: Mgat5-deficient pancreatic tumors become sensitive to TNF superfamily-mediated killing by T cells and dendritic cells, and Mgat5 knockout restores responsiveness to immune checkpoint blockade in resistant PDAC.\",\n      \"evidence\": \"Mgat5 KO clonal PDAC lines, in vivo growth, immune cell depletion experiments, TNF family death pathway assays, anti-PD-1/CTLA-4 treatment\",\n      \"pmids\": [\"38912584\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific glycoprotein substrates mediating immune evasion not identified\", \"Mechanism linking β1,6 glycans to TNF pathway sensitivity unknown\", \"Human tumor validation absent\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Specific in vivo substrates of MGAT5 were mapped in kidney (ANPEP, MEP1A at accessible C-terminal glycosites) and in prostate cancer (PSMA at N121/N336), with β1,6 branching controlling PSMA stability via the autophagy-lysosome pathway and TIMP-1 glycosylation driving VEGF-mediated angiogenesis in diabetic retinopathy.\",\n      \"evidence\": \"Lectin-assisted proteomics in Mgat5-null kidney, site-specific glycosite mapping, PSMA glycosylation/degradation assays, GST pull-down of GnT-V/TIMP-1, in vivo diabetic retinopathy model\",\n      \"pmids\": [\"41323266\", \"40112979\", \"38499842\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full in vivo substrate repertoire beyond kidney and select cancer substrates remains unmapped\", \"Structural basis for substrate selectivity at specific glycosites not determined\", \"TIMP-1 and PSMA findings each from single laboratories\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No high-resolution experimental structure of MGAT5 with bound acceptor glycan exists, the full in vivo substrate repertoire is unmapped, and the molecular mechanism by which β1,6-branched glycans sensitize tumor cells to TNF-family-mediated immune killing remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Experimental 3D structure with acceptor glycan needed\", \"Systematic in vivo substrate identification across tissues lacking\", \"Mechanism linking glycan branching to TNF pathway death sensitivity undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [3, 9, 10, 17]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [3, 5, 9, 20]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4, 5, 11]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 9, 10, 17]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 2, 8]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 6, 15]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 13, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"LGALS3\",\n      \"TIMP1\",\n      \"SPPL3\",\n      \"PSEN1\",\n      \"IGF2BP1\",\n      \"FOLH1\",\n      \"ANPEP\",\n      \"MEP1A\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}