{"gene":"MGAT4B","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2006,"finding":"GnT-IVb (MGAT4B) catalyzes formation of the GlcNAcβ1-4 branch on the GlcNAcβ1-2Manα1-3 arm of N-glycan core structures; kinetic characterization showed Km for UDP-GlcNAc of 0.24 mM (2-fold higher than GnT-IVa), and Km values for pyridylaminated acceptor sugar chains were 3- to 6-fold higher than GnT-IVa, indicating lower affinity for both donor and acceptor substrates compared to GnT-IVa despite similar acceptor substrate specificities.","method":"In vitro enzyme assay using recombinant full-length and soluble flag-tagged enzymes expressed in COS7 cells, kinetic parameter determination with 14 PA-sugar chain acceptors","journal":"Glycoconjugate journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro reconstitution with recombinant enzymes and systematic kinetic analysis with multiple substrates in a single focused study","pmids":["17006639"],"is_preprint":false},{"year":2009,"finding":"GnT-IVb (MGAT4B) is broadly expressed among organs (unlike GnT-IVa which is restricted to gastrointestinal tissues); GnT-IVb deficiency in mice induces compensatory aberrant GnT-IVa expression corresponding to the GnT-IVb distribution pattern, attributed to increased Ets-1 activating the Mgat4a promoter, thereby preserving apparent GnT-IV activity. GnT-IVa/IVb double deficiency completely abolished GnT-IV activity and eliminated the GlcNAcβ1-4 branch on the Manα1-3 arm.","method":"Engineered GnT-IVb-deficient mice, GnT-IVa/-IVb double-deficient mice, MALDI-TOF MS and GC-MS linkage analyses, comprehensive glycomic analyses, RT-PCR for Ets-1 and glycosyltransferases","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout models with multiple orthogonal biochemical readouts (MS, glycomics, gene expression) replicated across single/double KO","pmids":["20015870"],"is_preprint":false},{"year":2015,"finding":"MGAT4B forms complexes in close proximity to UDP-galactose transporter (SLC35A2/UGT) splice variants UGT1 and UGT2, and to UDP-N-acetylglucosamine transporter (SLC35A3/NGT) in the Golgi membrane. Notably, MGAT4B was the only Mgat tested that occurs in close proximity to UGT2 (distance <10 nm by FLIM-FRET), while MGAT1, MGAT2, and MGAT5 are more distant from UGT2.","method":"In situ proximity ligation assay and FLIM-FRET in cultured cells at endogenous levels and upon overexpression","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal proximity methods (PLA and FLIM-FRET), single lab, endogenous and overexpressed conditions tested","pmids":["25944901"],"is_preprint":false},{"year":2015,"finding":"GnT1IP-L (MGAT4D) did not generate a FRET signal with MGAT4B in medial Golgi GlcNAc-transferase interaction assays, indicating MGAT4B does not interact with the MGAT1 inhibitor GnT1IP-L, in contrast to MGAT1 which does interact.","method":"Dynamic FRET and bimolecular fluorescence complementation (BiFC) assays in transfected cells","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — negative result for MGAT4B-GnT1IP-L interaction established by FRET/BiFC, single lab","pmids":["26371870"],"is_preprint":false},{"year":2019,"finding":"MGAT4B participates in multi-enzyme assemblies with MGAT1, MGAT2, MGAT3 and Golgi alpha-mannosidase IIX (MAN2A2) in Golgi membranes in vivo; MAN2A2 acts as a central hub for these interactions. Novel ternary complexes between MGATs themselves and between MGATs and nucleotide sugar transporters (SLC35A2, SLC35A3, SLC35A4) were also identified.","method":"High-throughput FRET- and BiFC-based interaction screens in live cells","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal interaction methods (FRET and BiFC), single lab, multiple partner proteins tested systematically","pmids":["30737517"],"is_preprint":false},{"year":2020,"finding":"MGAT4B shares the PSLFQ sequence motif present in MGAT4D-L but does not inhibit MGAT1 activity in transfected CHO cells, demonstrating that the PSLFQ motif alone is insufficient to confer MGAT1-inhibitory activity to MGAT4B.","method":"Transfection of MGAT4B into CHO cells with GNA lectin binding assay for MGAT1 inhibition","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — negative result established by functional cell assay, single lab, single method","pmids":["32763972"],"is_preprint":false},{"year":2022,"finding":"GnT-IVa (MGAT4A) and GnT-IVb (MGAT4B) exhibit distinct glycoprotein substrate preferences both in cells and in vitro; GnT-IVb acts efficiently on glycoproteins bearing N-glycans pre-modified by GnT-IV. A nonconserved amino acid in the GnT-IVb C-terminal lectin domain governs this differential substrate selectivity: replacement of this residue with the corresponding GnT-IVa residue shifted GnT-IVb glycoprotein preference to resemble GnT-IVa.","method":"UDP-Glo enzyme assays in vitro and cellular glycosylation assays; site-directed mutagenesis of the C-terminal lectin domain","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzyme assay combined with mutagenesis and cellular assays, two orthogonal approaches, single lab","pmids":["35988645"],"is_preprint":false},{"year":2022,"finding":"The C-terminal region (CBML/lectin domain) of human GnT-IVa (and by homology MGAT4B) adopts a β-sandwich fold similar to CBM32 carbohydrate-binding module family proteins and binds β-N-acetylglucosamine; GlcNAc-binding residues are conserved across GnT-IVa, GnT-IVb (MGAT4B), and GnT-IVc.","method":"Crystal structure determination at 1.97 Å (human GnT-IVa CBML), 1.47 Å (Bombyx mori CBML), and 1.15 Å (B. mori CBML–β-GlcNAc complex); sugar-binding assays","journal":"Glycobiology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — high-resolution crystal structures with ligand; direct structural data on GnT-IVa lectin domain with inference by conservation to MGAT4B, not directly crystallized","pmids":["36106687"],"is_preprint":false},{"year":2024,"finding":"The C-terminal lectin domain of MGAT4B (and MGAT4A) is required for enzymatic activity toward glycoprotein substrates but not toward free N-glycans. The lectin domain carries an N-glycan that acts as a self-ligand interacting with the lectin domain's binding site in a glycan structure-dependent manner, and this self-ligand interaction suppresses GnT-IVa (MGAT4A) activity toward glycoprotein substrates, revealing a lectin-assisted self-regulatory mechanism.","method":"UDP-Glo enzyme assays with glycan-remodeled enzymes; functional domain deletion and glycan remodeling experiments","journal":"iScience","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with glycan-remodeled enzymes plus domain functional analysis, multiple orthogonal assays, single lab","pmids":["39669865"],"is_preprint":false},{"year":2025,"finding":"MGAT4B regulates directional cell migration and establishment of the melanocyte stem cell pool during zebrafish development; its disruption causes migratory melanocyte progenitors marked by galectin expression to fail to persist. MGAT4B controls N-glycosylation of key melanocyte proteins GPNMB, KIT, and TYRP1. MGAT4B loss causes mislocalization of junctional plakoglobin (JUP), explaining defects in cell adhesion and migration, a phenotype not produced by loss of its isozyme MGAT4A.","method":"Zebrafish targeted disruption of mgat4b, scRNA sequencing, lectin affinity proteomic analysis, confocal localization of JUP, small-molecule N-glycosylation inhibitor, in vivo BRAFV600E tumor model (MAZERATI platform)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function in vivo with multiple orthogonal readouts (scRNA-seq, proteomics, localization, tumor model), isozyme specificity established by comparison to MGAT4A","pmids":["40424122"],"is_preprint":false},{"year":2024,"finding":"Mgat4b mediated selective N-glycosylation regulates melanocyte development and melanoma progression (preprint version corroborating PMID:40424122 findings including GPNMB, KIT, TYRP1 glycosylation and JUP mislocalization under mgat4b disruption).","method":"Zebrafish mgat4b disruption, lectin affinity proteomics, scRNA-seq, in vivo BRAFV600E melanoma model","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — preprint; findings replicated in peer-reviewed PMID:40424122, lowering standalone confidence","pmids":["bio_10.1101_2024.10.10.617552"],"is_preprint":true},{"year":2026,"finding":"MGAT4B knockout (CRISPR/Cas9) in NB4 leukemia cells did not suppress ATRA-induced differentiation (as measured by CD11b and CD11c expression), in contrast to MGAT4A KO which markedly suppressed differentiation, indicating MGAT4B is dispensable for this process.","method":"CRISPR/Cas9 knockout of MGAT4B in NB4 cells, flow cytometry for CD11b/CD11c upon ATRA treatment","journal":"Biomolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — negative result for MGAT4B in APL differentiation established by clean KO with defined cellular phenotype readout, single lab","pmids":["42194104"],"is_preprint":false}],"current_model":"MGAT4B (GnT-IVb) is a Golgi-localized glycosyltransferase that catalyzes addition of a GlcNAcβ1-4 branch to the Manα1-3 arm of N-glycan core structures with lower donor and acceptor affinity than its isozyme MGAT4A; its unique C-terminal lectin domain (adopting a CBM32-like β-sandwich fold) is essential for activity toward glycoprotein substrates, selectively recognizes GnT-IV product glycans to confer differential substrate preferences distinct from MGAT4A, and mediates self-regulation through interaction with the enzyme's own N-glycan; MGAT4B forms multi-enzyme/multi-transporter assemblies with other MGATs, MAN2A2, and nucleotide sugar transporters in the Golgi membrane; in vivo, it controls N-glycosylation of GPNMB, KIT, TYRP1, and junctional plakoglobin (JUP) to regulate melanocyte migration, stem cell maintenance, and melanoma initiation in a manner not compensated by MGAT4A."},"narrative":{"mechanistic_narrative":"MGAT4B (GnT-IVb) is a Golgi-resident glycosyltransferase that catalyzes addition of a GlcNAcβ1-4 branch to the GlcNAcβ1-2Manα1-3 arm of N-glycan core structures, displaying lower donor and acceptor affinity than its isozyme MGAT4A [PMID:17006639]. Genetic ablation studies established that MGAT4B and MGAT4A together account for all GnT-IV activity and the Manα1-3 arm GlcNAcβ1-4 branch, with MGAT4B broadly expressed across organs and capable of triggering compensatory MGAT4A upregulation in its absence [PMID:20015870]. Its activity toward glycoprotein substrates depends on a C-terminal lectin domain that adopts a CBM32-like β-sandwich fold and binds β-N-acetylglucosamine [PMID:36106687]; a single nonconserved residue within this domain dictates the distinct glycoprotein substrate preference of MGAT4B versus MGAT4A, biasing it toward N-glycans already modified by GnT-IV [PMID:35988645]. This lectin domain also carries a self-ligand N-glycan whose interaction with the domain's binding site provides a glycan-structure-dependent self-regulatory mechanism that tunes activity toward glycoproteins [PMID:39669865]. Within the Golgi membrane MGAT4B assembles into multi-enzyme and enzyme-transporter complexes with other MGATs, the α-mannosidase MAN2A2, and nucleotide-sugar transporters [PMID:30737517, PMID:25944901]. In vivo, MGAT4B controls N-glycosylation of GPNMB, KIT, and TYRP1 and governs junctional plakoglobin (JUP) localization to direct melanocyte progenitor migration, stem cell pool establishment, and BRAFV600E melanoma initiation, a role not compensated by MGAT4A [PMID:40424122].","teleology":[{"year":2006,"claim":"Defined the core catalytic reaction of MGAT4B and showed it is a lower-affinity counterpart to MGAT4A, establishing that the two isozymes are kinetically distinct despite similar acceptor specificity.","evidence":"In vitro enzyme assays with recombinant flag-tagged enzymes and kinetic analysis across 14 PA-sugar chain acceptors","pmids":["17006639"],"confidence":"High","gaps":["Did not address glycoprotein (versus free glycan) substrate selectivity","No structural basis for the affinity difference"]},{"year":2009,"claim":"Genetic knockout established the physiological scope of MGAT4B activity and revealed a compensatory MGAT4A upregulation circuit, distinguishing the broad-tissue MGAT4B from gastrointestinal-restricted MGAT4A.","evidence":"GnT-IVb single and GnT-IVa/IVb double-deficient mice with MALDI-TOF/GC-MS glycomics and Ets-1 expression analysis","pmids":["20015870"],"confidence":"High","gaps":["Did not identify specific endogenous glycoprotein substrates","Mechanism of Ets-1-driven compensation not dissected at the regulatory level"]},{"year":2015,"claim":"Showed MGAT4B is physically organized with specific nucleotide-sugar transporters in the Golgi, implicating supramolecular assembly in channeling its activity, with selective proximity to UGT2 distinguishing it from other MGATs.","evidence":"In situ proximity ligation assay and FLIM-FRET at endogenous and overexpressed levels","pmids":["25944901"],"confidence":"Medium","gaps":["Proximity does not establish functional substrate channeling","Stoichiometry and architecture of assemblies undefined"]},{"year":2015,"claim":"Demonstrated by negative result that MGAT4B does not engage the MGAT1 inhibitor GnT1IP-L, separating MGAT4B from the GnT1IP-mediated regulatory axis acting on MGAT1.","evidence":"Dynamic FRET and BiFC assays in transfected cells","pmids":["26371870"],"confidence":"Medium","gaps":["Negative interaction result from a single lab/method pair","Does not address other potential regulators of MGAT4B"]},{"year":2019,"claim":"Mapped MGAT4B into a defined Golgi multi-enzyme network organized around MAN2A2 as a hub, placing it within the spatial logic of N-glycan branch processing.","evidence":"High-throughput FRET- and BiFC-based interaction screens in live cells","pmids":["30737517"],"confidence":"Medium","gaps":["Functional consequence of each interaction for glycan output not measured","Single-lab screen without orthogonal biochemical isolation of complexes"]},{"year":2020,"claim":"Excluded MGAT4B as an MGAT1 inhibitor despite sharing the PSLFQ motif of MGAT4D-L, establishing that sequence-motif sharing does not confer inhibitory function and reinforcing MGAT4B's dedicated catalytic role.","evidence":"MGAT4B transfection into CHO cells with GNA lectin binding assay for MGAT1 inhibition","pmids":["32763972"],"confidence":"Medium","gaps":["Negative functional result; structural reason for lack of inhibition not resolved","Single method readout"]},{"year":2022,"claim":"Identified the C-terminal lectin domain, and specifically a single nonconserved residue within it, as the determinant of the distinct glycoprotein substrate preference that separates MGAT4B from MGAT4A.","evidence":"UDP-Glo in vitro and cellular glycosylation assays with site-directed mutagenesis of the lectin domain","pmids":["35988645"],"confidence":"High","gaps":["Structural mechanism by which the residue alters preference not solved","Full repertoire of preferred glycoprotein substrates not enumerated"]},{"year":2022,"claim":"Provided the structural framework for the lectin domain as a CBM32-like β-sandwich that binds β-GlcNAc, with binding residues conserved across the GnT-IV family including MGAT4B.","evidence":"Crystal structures of human GnT-IVa CBML and Bombyx mori CBML with β-GlcNAc plus sugar-binding assays","pmids":["36106687"],"confidence":"Medium","gaps":["MGAT4B lectin domain not directly crystallized; assignment is by conservation","No full-length enzyme structure"]},{"year":2024,"claim":"Revealed a lectin-assisted self-regulatory mechanism in which the lectin domain's own N-glycan acts as a self-ligand to modulate activity toward glycoprotein substrates, linking the lectin domain's requirement for glycoprotein activity to autoregulation.","evidence":"UDP-Glo assays with glycan-remodeled enzymes plus domain deletion and glycan remodeling experiments","pmids":["39669865"],"confidence":"High","gaps":["Self-regulation directly demonstrated for MGAT4A; extent to which it tunes MGAT4B in vivo not fully resolved","Physiological glycan states triggering autoregulation unknown"]},{"year":2025,"claim":"Established the non-redundant in vivo role of MGAT4B in melanocyte biology, identifying its glycoprotein substrates (GPNMB, KIT, TYRP1) and the JUP-mislocalization mechanism underlying defective migration and melanoma initiation.","evidence":"Zebrafish mgat4b disruption with scRNA-seq, lectin-affinity proteomics, JUP confocal localization, and a BRAFV600E MAZERATI tumor model, with MGAT4A comparison","pmids":["40424122"],"confidence":"High","gaps":["Causal glycosylation site(s) on JUP regulators not pinpointed","Conservation of the melanoma role in mammalian systems untested"]},{"year":2026,"claim":"Showed MGAT4B is dispensable for ATRA-induced myeloid differentiation, in contrast to MGAT4A, demonstrating functional divergence of the isozymes in a hematopoietic context.","evidence":"CRISPR/Cas9 MGAT4B knockout in NB4 leukemia cells with flow cytometry for CD11b/CD11c","pmids":["42194104"],"confidence":"Medium","gaps":["Negative result in a single cell line","Does not exclude MGAT4B roles in other myeloid or differentiation programs"]},{"year":null,"claim":"How the Golgi multi-enzyme/transporter assemblies, the lectin-domain self-regulation, and tissue-specific substrate selection are integrated to determine which glycoproteins MGAT4B modifies in a given cell remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of full-length MGAT4B or its complexes","Mammalian in vivo substrate map beyond melanocyte proteins undefined","Quantitative link between complex assembly and catalytic output not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,6,8]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,8,9]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2,4]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,8]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[9]}],"complexes":[],"partners":["MAN2A2","MGAT1","MGAT2","MGAT3","SLC35A2","SLC35A3","SLC35A4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UQ53","full_name":"Alpha-1,3-mannosyl-glycoprotein 4-beta-N-acetylglucosaminyltransferase B","aliases":["N-glycosyl-oligosaccharide-glycoprotein N-acetylglucosaminyltransferase IVb","GlcNAc-T IVb","GnT-IVb","N-acetylglucosaminyltransferase IVb","UDP-N-acetylglucosamine: alpha-1,3-D-mannoside beta-1,4-N-acetylglucosaminyltransferase IVb"],"length_aa":548,"mass_kda":63.2,"function":"Glycosyltransferase that catalyzes the transfer of GlcNAc from UDP-GlcNAc to the GlcNAcbeta1-2Manalpha1-3 arm of the core structure of N-linked glycans through a beta1-4 linkage and participates in the production of tri- and tetra-antennary N-linked sugar chains (PubMed:10372966, PubMed:17006639). Prefers complex-type N-glycans over hybrid-types (PubMed:17006639). Has lower affinities for donors or acceptors than MGAT4A, suggesting that, under physiological conditions, it is not the main contributor in N-glycan biosynthesis (PubMed:17006639)","subcellular_location":"Golgi apparatus membrane","url":"https://www.uniprot.org/uniprotkb/Q9UQ53/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MGAT4B","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MGAT4B","total_profiled":1310},"omim":[{"mim_id":"606822","title":"PROTEIN O-MANNOSE BETA-1,2-N-ACETYLGLUCOSAMINYLTRANSFERASE; POMGNT1","url":"https://www.omim.org/entry/606822"},{"mim_id":"604623","title":"ALPHA-1,3-@MANNOSYL-GLYCOPROTEIN BETA-1,4-N-ACETYLGLUCOSAMINYLTRANSFERASE, ISOZYME A; MGAT4A","url":"https://www.omim.org/entry/604623"},{"mim_id":"604561","title":"ALPHA-1,3-@MANNOSYL-GLYCOPROTEIN BETA-1,4-N-ACETYLGLUCOSAMINYLTRANSFERASE, ISOZYME B; MGAT4B","url":"https://www.omim.org/entry/604561"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Golgi apparatus","reliability":"Additional"},{"location":"Vesicles","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"liver","ntpm":281.1}],"url":"https://www.proteinatlas.org/search/MGAT4B"},"hgnc":{"alias_symbol":["GnT-Ivb"],"prev_symbol":[]},"alphafold":{"accession":"Q9UQ53","domains":[{"cath_id":"3.90.550.10","chopping":"115-367","consensus_level":"high","plddt":93.6862,"start":115,"end":367},{"cath_id":"2.60.120.260","chopping":"400-545","consensus_level":"high","plddt":86.4535,"start":400,"end":545}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UQ53","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UQ53-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UQ53-F1-predicted_aligned_error_v6.png","plddt_mean":83.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MGAT4B","jax_strain_url":"https://www.jax.org/strain/search?query=MGAT4B"},"sequence":{"accession":"Q9UQ53","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UQ53.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UQ53/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UQ53"}},"corpus_meta":[{"pmid":"24206759","id":"PMC_24206759","title":"Identification and characterization of genes that control fat deposition in chickens.","date":"2013","source":"Journal of animal science and biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/24206759","citation_count":113,"is_preprint":false},{"pmid":"17488527","id":"PMC_17488527","title":"N-glycan alterations are associated with drug resistance in human hepatocellular carcinoma.","date":"2007","source":"Molecular cancer","url":"https://pubmed.ncbi.nlm.nih.gov/17488527","citation_count":63,"is_preprint":false},{"pmid":"20015870","id":"PMC_20015870","title":"Physiological and glycomic characterization of N-acetylglucosaminyltransferase-IVa and -IVb double deficient mice.","date":"2009","source":"Glycobiology","url":"https://pubmed.ncbi.nlm.nih.gov/20015870","citation_count":48,"is_preprint":false},{"pmid":"25944901","id":"PMC_25944901","title":"UDP-galactose (SLC35A2) and UDP-N-acetylglucosamine (SLC35A3) Transporters Form Glycosylation-related Complexes with Mannoside 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America","url":"https://pubmed.ncbi.nlm.nih.gov/40424122","citation_count":1,"is_preprint":false},{"pmid":"42194104","id":"PMC_42194104","title":"Upregulation of GnT-IVa and Its Critical Roles in ATRA-Induced Differentiation of Acute Promyelocytic Leukemia Cells.","date":"2026","source":"Biomolecules","url":"https://pubmed.ncbi.nlm.nih.gov/42194104","citation_count":0,"is_preprint":false},{"pmid":"41244580","id":"PMC_41244580","title":"Evolutionary analyses of the animal glycosyltransferase family 54 reveals two β1,4-N-acetylglucosaminyltransferase families.","date":"2025","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/41244580","citation_count":0,"is_preprint":false},{"pmid":"42007565","id":"PMC_42007565","title":"Replication of 10 novel loci involved in human plasma protein N-glycosylation using MALDI-MS and UHPLC-FD data.","date":"2026","source":"Glycobiology","url":"https://pubmed.ncbi.nlm.nih.gov/42007565","citation_count":0,"is_preprint":false},{"pmid":"41305834","id":"PMC_41305834","title":"Identification of shared molecular biomarkers and pathogenic mechanisms between gastroesophageal reflux disease and ischemic stroke via integrated machine learning.","date":"2025","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41305834","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.10.10.617552","title":"Mgat4b mediated selective  <i>N</i>  -glycosylation regulates melanocyte development and melanoma progression","date":"2024-10-11","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.10.617552","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15772,"output_tokens":3619,"usd":0.0508,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11097,"output_tokens":3791,"usd":0.07513,"stage2_stop_reason":"end_turn"},"total_usd":0.12593,"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\": 2006,\n      \"finding\": \"GnT-IVb (MGAT4B) catalyzes formation of the GlcNAcβ1-4 branch on the GlcNAcβ1-2Manα1-3 arm of N-glycan core structures; kinetic characterization showed Km for UDP-GlcNAc of 0.24 mM (2-fold higher than GnT-IVa), and Km values for pyridylaminated acceptor sugar chains were 3- to 6-fold higher than GnT-IVa, indicating lower affinity for both donor and acceptor substrates compared to GnT-IVa despite similar acceptor substrate specificities.\",\n      \"method\": \"In vitro enzyme assay using recombinant full-length and soluble flag-tagged enzymes expressed in COS7 cells, kinetic parameter determination with 14 PA-sugar chain acceptors\",\n      \"journal\": \"Glycoconjugate journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro reconstitution with recombinant enzymes and systematic kinetic analysis with multiple substrates in a single focused study\",\n      \"pmids\": [\"17006639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GnT-IVb (MGAT4B) is broadly expressed among organs (unlike GnT-IVa which is restricted to gastrointestinal tissues); GnT-IVb deficiency in mice induces compensatory aberrant GnT-IVa expression corresponding to the GnT-IVb distribution pattern, attributed to increased Ets-1 activating the Mgat4a promoter, thereby preserving apparent GnT-IV activity. GnT-IVa/IVb double deficiency completely abolished GnT-IV activity and eliminated the GlcNAcβ1-4 branch on the Manα1-3 arm.\",\n      \"method\": \"Engineered GnT-IVb-deficient mice, GnT-IVa/-IVb double-deficient mice, MALDI-TOF MS and GC-MS linkage analyses, comprehensive glycomic analyses, RT-PCR for Ets-1 and glycosyltransferases\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout models with multiple orthogonal biochemical readouts (MS, glycomics, gene expression) replicated across single/double KO\",\n      \"pmids\": [\"20015870\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"MGAT4B forms complexes in close proximity to UDP-galactose transporter (SLC35A2/UGT) splice variants UGT1 and UGT2, and to UDP-N-acetylglucosamine transporter (SLC35A3/NGT) in the Golgi membrane. Notably, MGAT4B was the only Mgat tested that occurs in close proximity to UGT2 (distance <10 nm by FLIM-FRET), while MGAT1, MGAT2, and MGAT5 are more distant from UGT2.\",\n      \"method\": \"In situ proximity ligation assay and FLIM-FRET in cultured cells at endogenous levels and upon overexpression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal proximity methods (PLA and FLIM-FRET), single lab, endogenous and overexpressed conditions tested\",\n      \"pmids\": [\"25944901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GnT1IP-L (MGAT4D) did not generate a FRET signal with MGAT4B in medial Golgi GlcNAc-transferase interaction assays, indicating MGAT4B does not interact with the MGAT1 inhibitor GnT1IP-L, in contrast to MGAT1 which does interact.\",\n      \"method\": \"Dynamic FRET and bimolecular fluorescence complementation (BiFC) assays in transfected cells\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — negative result for MGAT4B-GnT1IP-L interaction established by FRET/BiFC, single lab\",\n      \"pmids\": [\"26371870\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MGAT4B participates in multi-enzyme assemblies with MGAT1, MGAT2, MGAT3 and Golgi alpha-mannosidase IIX (MAN2A2) in Golgi membranes in vivo; MAN2A2 acts as a central hub for these interactions. Novel ternary complexes between MGATs themselves and between MGATs and nucleotide sugar transporters (SLC35A2, SLC35A3, SLC35A4) were also identified.\",\n      \"method\": \"High-throughput FRET- and BiFC-based interaction screens in live cells\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal interaction methods (FRET and BiFC), single lab, multiple partner proteins tested systematically\",\n      \"pmids\": [\"30737517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MGAT4B shares the PSLFQ sequence motif present in MGAT4D-L but does not inhibit MGAT1 activity in transfected CHO cells, demonstrating that the PSLFQ motif alone is insufficient to confer MGAT1-inhibitory activity to MGAT4B.\",\n      \"method\": \"Transfection of MGAT4B into CHO cells with GNA lectin binding assay for MGAT1 inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — negative result established by functional cell assay, single lab, single method\",\n      \"pmids\": [\"32763972\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GnT-IVa (MGAT4A) and GnT-IVb (MGAT4B) exhibit distinct glycoprotein substrate preferences both in cells and in vitro; GnT-IVb acts efficiently on glycoproteins bearing N-glycans pre-modified by GnT-IV. A nonconserved amino acid in the GnT-IVb C-terminal lectin domain governs this differential substrate selectivity: replacement of this residue with the corresponding GnT-IVa residue shifted GnT-IVb glycoprotein preference to resemble GnT-IVa.\",\n      \"method\": \"UDP-Glo enzyme assays in vitro and cellular glycosylation assays; site-directed mutagenesis of the C-terminal lectin domain\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzyme assay combined with mutagenesis and cellular assays, two orthogonal approaches, single lab\",\n      \"pmids\": [\"35988645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The C-terminal region (CBML/lectin domain) of human GnT-IVa (and by homology MGAT4B) adopts a β-sandwich fold similar to CBM32 carbohydrate-binding module family proteins and binds β-N-acetylglucosamine; GlcNAc-binding residues are conserved across GnT-IVa, GnT-IVb (MGAT4B), and GnT-IVc.\",\n      \"method\": \"Crystal structure determination at 1.97 Å (human GnT-IVa CBML), 1.47 Å (Bombyx mori CBML), and 1.15 Å (B. mori CBML–β-GlcNAc complex); sugar-binding assays\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — high-resolution crystal structures with ligand; direct structural data on GnT-IVa lectin domain with inference by conservation to MGAT4B, not directly crystallized\",\n      \"pmids\": [\"36106687\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The C-terminal lectin domain of MGAT4B (and MGAT4A) is required for enzymatic activity toward glycoprotein substrates but not toward free N-glycans. The lectin domain carries an N-glycan that acts as a self-ligand interacting with the lectin domain's binding site in a glycan structure-dependent manner, and this self-ligand interaction suppresses GnT-IVa (MGAT4A) activity toward glycoprotein substrates, revealing a lectin-assisted self-regulatory mechanism.\",\n      \"method\": \"UDP-Glo enzyme assays with glycan-remodeled enzymes; functional domain deletion and glycan remodeling experiments\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with glycan-remodeled enzymes plus domain functional analysis, multiple orthogonal assays, single lab\",\n      \"pmids\": [\"39669865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MGAT4B regulates directional cell migration and establishment of the melanocyte stem cell pool during zebrafish development; its disruption causes migratory melanocyte progenitors marked by galectin expression to fail to persist. MGAT4B controls N-glycosylation of key melanocyte proteins GPNMB, KIT, and TYRP1. MGAT4B loss causes mislocalization of junctional plakoglobin (JUP), explaining defects in cell adhesion and migration, a phenotype not produced by loss of its isozyme MGAT4A.\",\n      \"method\": \"Zebrafish targeted disruption of mgat4b, scRNA sequencing, lectin affinity proteomic analysis, confocal localization of JUP, small-molecule N-glycosylation inhibitor, in vivo BRAFV600E tumor model (MAZERATI platform)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function in vivo with multiple orthogonal readouts (scRNA-seq, proteomics, localization, tumor model), isozyme specificity established by comparison to MGAT4A\",\n      \"pmids\": [\"40424122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Mgat4b mediated selective N-glycosylation regulates melanocyte development and melanoma progression (preprint version corroborating PMID:40424122 findings including GPNMB, KIT, TYRP1 glycosylation and JUP mislocalization under mgat4b disruption).\",\n      \"method\": \"Zebrafish mgat4b disruption, lectin affinity proteomics, scRNA-seq, in vivo BRAFV600E melanoma model\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — preprint; findings replicated in peer-reviewed PMID:40424122, lowering standalone confidence\",\n      \"pmids\": [\"bio_10.1101_2024.10.10.617552\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MGAT4B knockout (CRISPR/Cas9) in NB4 leukemia cells did not suppress ATRA-induced differentiation (as measured by CD11b and CD11c expression), in contrast to MGAT4A KO which markedly suppressed differentiation, indicating MGAT4B is dispensable for this process.\",\n      \"method\": \"CRISPR/Cas9 knockout of MGAT4B in NB4 cells, flow cytometry for CD11b/CD11c upon ATRA treatment\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — negative result for MGAT4B in APL differentiation established by clean KO with defined cellular phenotype readout, single lab\",\n      \"pmids\": [\"42194104\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MGAT4B (GnT-IVb) is a Golgi-localized glycosyltransferase that catalyzes addition of a GlcNAcβ1-4 branch to the Manα1-3 arm of N-glycan core structures with lower donor and acceptor affinity than its isozyme MGAT4A; its unique C-terminal lectin domain (adopting a CBM32-like β-sandwich fold) is essential for activity toward glycoprotein substrates, selectively recognizes GnT-IV product glycans to confer differential substrate preferences distinct from MGAT4A, and mediates self-regulation through interaction with the enzyme's own N-glycan; MGAT4B forms multi-enzyme/multi-transporter assemblies with other MGATs, MAN2A2, and nucleotide sugar transporters in the Golgi membrane; in vivo, it controls N-glycosylation of GPNMB, KIT, TYRP1, and junctional plakoglobin (JUP) to regulate melanocyte migration, stem cell maintenance, and melanoma initiation in a manner not compensated by MGAT4A.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MGAT4B (GnT-IVb) is a Golgi-resident glycosyltransferase that catalyzes addition of a GlcNAcβ1-4 branch to the GlcNAcβ1-2Manα1-3 arm of N-glycan core structures, displaying lower donor and acceptor affinity than its isozyme MGAT4A [#0]. Genetic ablation studies established that MGAT4B and MGAT4A together account for all GnT-IV activity and the Manα1-3 arm GlcNAcβ1-4 branch, with MGAT4B broadly expressed across organs and capable of triggering compensatory MGAT4A upregulation in its absence [#1]. Its activity toward glycoprotein substrates depends on a C-terminal lectin domain that adopts a CBM32-like β-sandwich fold and binds β-N-acetylglucosamine [#7]; a single nonconserved residue within this domain dictates the distinct glycoprotein substrate preference of MGAT4B versus MGAT4A, biasing it toward N-glycans already modified by GnT-IV [#6]. This lectin domain also carries a self-ligand N-glycan whose interaction with the domain's binding site provides a glycan-structure-dependent self-regulatory mechanism that tunes activity toward glycoproteins [#8]. Within the Golgi membrane MGAT4B assembles into multi-enzyme and enzyme-transporter complexes with other MGATs, the α-mannosidase MAN2A2, and nucleotide-sugar transporters [#4, #2]. In vivo, MGAT4B controls N-glycosylation of GPNMB, KIT, and TYRP1 and governs junctional plakoglobin (JUP) localization to direct melanocyte progenitor migration, stem cell pool establishment, and BRAFV600E melanoma initiation, a role not compensated by MGAT4A [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined the core catalytic reaction of MGAT4B and showed it is a lower-affinity counterpart to MGAT4A, establishing that the two isozymes are kinetically distinct despite similar acceptor specificity.\",\n      \"evidence\": \"In vitro enzyme assays with recombinant flag-tagged enzymes and kinetic analysis across 14 PA-sugar chain acceptors\",\n      \"pmids\": [\"17006639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address glycoprotein (versus free glycan) substrate selectivity\", \"No structural basis for the affinity difference\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Genetic knockout established the physiological scope of MGAT4B activity and revealed a compensatory MGAT4A upregulation circuit, distinguishing the broad-tissue MGAT4B from gastrointestinal-restricted MGAT4A.\",\n      \"evidence\": \"GnT-IVb single and GnT-IVa/IVb double-deficient mice with MALDI-TOF/GC-MS glycomics and Ets-1 expression analysis\",\n      \"pmids\": [\"20015870\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify specific endogenous glycoprotein substrates\", \"Mechanism of Ets-1-driven compensation not dissected at the regulatory level\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed MGAT4B is physically organized with specific nucleotide-sugar transporters in the Golgi, implicating supramolecular assembly in channeling its activity, with selective proximity to UGT2 distinguishing it from other MGATs.\",\n      \"evidence\": \"In situ proximity ligation assay and FLIM-FRET at endogenous and overexpressed levels\",\n      \"pmids\": [\"25944901\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Proximity does not establish functional substrate channeling\", \"Stoichiometry and architecture of assemblies undefined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated by negative result that MGAT4B does not engage the MGAT1 inhibitor GnT1IP-L, separating MGAT4B from the GnT1IP-mediated regulatory axis acting on MGAT1.\",\n      \"evidence\": \"Dynamic FRET and BiFC assays in transfected cells\",\n      \"pmids\": [\"26371870\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative interaction result from a single lab/method pair\", \"Does not address other potential regulators of MGAT4B\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mapped MGAT4B into a defined Golgi multi-enzyme network organized around MAN2A2 as a hub, placing it within the spatial logic of N-glycan branch processing.\",\n      \"evidence\": \"High-throughput FRET- and BiFC-based interaction screens in live cells\",\n      \"pmids\": [\"30737517\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of each interaction for glycan output not measured\", \"Single-lab screen without orthogonal biochemical isolation of complexes\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Excluded MGAT4B as an MGAT1 inhibitor despite sharing the PSLFQ motif of MGAT4D-L, establishing that sequence-motif sharing does not confer inhibitory function and reinforcing MGAT4B's dedicated catalytic role.\",\n      \"evidence\": \"MGAT4B transfection into CHO cells with GNA lectin binding assay for MGAT1 inhibition\",\n      \"pmids\": [\"32763972\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative functional result; structural reason for lack of inhibition not resolved\", \"Single method readout\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified the C-terminal lectin domain, and specifically a single nonconserved residue within it, as the determinant of the distinct glycoprotein substrate preference that separates MGAT4B from MGAT4A.\",\n      \"evidence\": \"UDP-Glo in vitro and cellular glycosylation assays with site-directed mutagenesis of the lectin domain\",\n      \"pmids\": [\"35988645\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism by which the residue alters preference not solved\", \"Full repertoire of preferred glycoprotein substrates not enumerated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided the structural framework for the lectin domain as a CBM32-like β-sandwich that binds β-GlcNAc, with binding residues conserved across the GnT-IV family including MGAT4B.\",\n      \"evidence\": \"Crystal structures of human GnT-IVa CBML and Bombyx mori CBML with β-GlcNAc plus sugar-binding assays\",\n      \"pmids\": [\"36106687\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"MGAT4B lectin domain not directly crystallized; assignment is by conservation\", \"No full-length enzyme structure\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a lectin-assisted self-regulatory mechanism in which the lectin domain's own N-glycan acts as a self-ligand to modulate activity toward glycoprotein substrates, linking the lectin domain's requirement for glycoprotein activity to autoregulation.\",\n      \"evidence\": \"UDP-Glo assays with glycan-remodeled enzymes plus domain deletion and glycan remodeling experiments\",\n      \"pmids\": [\"39669865\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Self-regulation directly demonstrated for MGAT4A; extent to which it tunes MGAT4B in vivo not fully resolved\", \"Physiological glycan states triggering autoregulation unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established the non-redundant in vivo role of MGAT4B in melanocyte biology, identifying its glycoprotein substrates (GPNMB, KIT, TYRP1) and the JUP-mislocalization mechanism underlying defective migration and melanoma initiation.\",\n      \"evidence\": \"Zebrafish mgat4b disruption with scRNA-seq, lectin-affinity proteomics, JUP confocal localization, and a BRAFV600E MAZERATI tumor model, with MGAT4A comparison\",\n      \"pmids\": [\"40424122\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal glycosylation site(s) on JUP regulators not pinpointed\", \"Conservation of the melanoma role in mammalian systems untested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showed MGAT4B is dispensable for ATRA-induced myeloid differentiation, in contrast to MGAT4A, demonstrating functional divergence of the isozymes in a hematopoietic context.\",\n      \"evidence\": \"CRISPR/Cas9 MGAT4B knockout in NB4 leukemia cells with flow cytometry for CD11b/CD11c\",\n      \"pmids\": [\"42194104\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative result in a single cell line\", \"Does not exclude MGAT4B roles in other myeloid or differentiation programs\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the Golgi multi-enzyme/transporter assemblies, the lectin-domain self-regulation, and tissue-specific substrate selection are integrated to determine which glycoproteins MGAT4B modifies in a given cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of full-length MGAT4B or its complexes\", \"Mammalian in vivo substrate map beyond melanocyte proteins undefined\", \"Quantitative link between complex assembly and catalytic output not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 6, 8]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 8, 9]},\n      {\"term_id\": \"GO:0030246\", \"supporting_discovery_ids\": [7, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 8]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"MAN2A2\", \"MGAT1\", \"MGAT2\", \"MGAT3\", \"SLC35A2\", \"SLC35A3\", \"SLC35A4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":{"gene":"MGAT4B","tier":"GROUNDING","verdict":"Evidence-grounding concern","subtype":"fabrication","uniprot_band":"medium","rules_fired":"R7","issue":"R7: fabricated (no corpus paper): 39669865"},"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}