{"gene":"BTN3A1","run_date":"2026-04-28T17:12:38","timeline":{"discoveries":[{"year":2012,"finding":"BTN3A1 is the specific CD277 isoform required for phosphoantigen (PAg)-induced Vγ9Vδ2 T cell activation; FRAP experiments showed that intracellular PAg accumulation causes decreased BTN3A1 membrane mobility, and CD277 knockdown plus domain-shuffling confirmed BTN3A1's key role in PAg sensing.","method":"FRAP, CD277 knockdown, domain-shuffling, antibody agonist/antagonist functional assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (FRAP, KD, domain-swap) in highly cited foundational paper","pmids":["22767497"],"is_preprint":false},{"year":2012,"finding":"BTN3A1 (and the other two BTN3A isoforms) form V-shaped homodimers in solution, associating through the membrane-proximal C-type Ig domain; agonist antibody 20.1 and antagonist antibody 103.2 bind to separate epitopes on the BTN3A Ig-V domain with high affinity but different valencies.","method":"X-ray crystallography, solution biochemistry (SEC), antibody binding studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with functional antibody binding characterization","pmids":["22846996"],"is_preprint":false},{"year":2015,"finding":"Phosphoantigens bind directly to the intracellular B30.2 domain of BTN3A1 (HMBPP at 1.1 μM affinity, IPP at 627 μM affinity); periplakin interacts with a membrane-proximal di-leucine motif in the BTN3A1 cytoplasmic tail (not present in BTN3A2/3), and a BTN3A1 variant lacking this motif fails to restore γδ T cell responses in knockdown cells.","method":"In vitro binding assays, yeast two-hybrid, knockdown/re-expression, coculture functional assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding measurements combined with yeast two-hybrid identification and functional rescue experiments","pmids":["25637025"],"is_preprint":false},{"year":2017,"finding":"Phosphoantigen binding to the B30.2 intracellular domain of BTN3A1 induces a global conformational change propagating from the pAg-binding pocket to distal parts of the domain and disrupting a preexisting dimer interface; the extracellular domains adopt a V-shaped conformation at rest, and locking them in this resting conformation without perturbing membrane reorganization diminishes pAg-induced T cell activation.","method":"NMR spectroscopy, X-ray crystallography, molecular dynamics simulations, biochemical and cellular assays","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 1 — reconstitution + NMR + crystal structures + MD + cellular validation in one study","pmids":["28807997"],"is_preprint":false},{"year":2017,"finding":"The intracellular B30.2 domain of BTN3A1 discriminates phosphoantigens from nonantigenic small molecules via a conformational sensor: while many negatively charged molecules bind the positively charged pocket, only pAgs induce a specific conformational change that propagates to distal parts of the domain.","method":"NMR chemical shift perturbation analysis, X-ray crystallography","journal":"ACS chemical biology","confidence":"High","confidence_rationale":"Tier 1 — NMR and crystallography with mechanistic discrimination demonstrated","pmids":["28862425"],"is_preprint":false},{"year":2017,"finding":"The juxtamembrane domain of BTN3A1 (distinct from the transmembrane domain) is required for correct γδ T cell-related function; mutations in this region, which includes a possible dimerization interface near the B30.2 domain start, markedly enhance or reduce γδ T cell reactivity.","method":"Site-directed mutagenesis, T cell activation functional assays","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — mutagenesis with functional readout but single lab","pmids":["28461569"],"is_preprint":false},{"year":2016,"finding":"BTN3A1 constitutively associates with TBK1 at rest; upon nucleic acid stimulation, the BTN3A1-TBK1 complex redistributes to the perinuclear region via MAP4-regulated dynein-dependent transport, where BTN3A1 mediates TBK1-IRF3 interaction and IRF3 phosphorylation, promoting type I IFN production. Depletion of BTN3A1 inhibits IFN-β production.","method":"Co-immunoprecipitation, siRNA knockdown, subcellular fractionation/imaging, IFN-β reporter assays","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP + KD + localization with functional consequence, multiple orthogonal methods","pmids":["27911820"],"is_preprint":false},{"year":2016,"finding":"Internalization of HMBPP into target cells is required for BTN3A1-dependent lysis by Vγ9Vδ2 effector T cells; a cell-permeable prodrug that bypasses energy-dependent uptake routes restores BTN3A1-dependent killing even at 4°C, supporting an inside-out signaling model.","method":"Cytotoxicity assays, BTN3A1 disruption, temperature-dependent uptake experiments, prodrug comparison","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — clean functional assay with BTN3A1 disruption and mechanistic prodrug comparison","pmids":["27271567"],"is_preprint":false},{"year":2014,"finding":"BTN3A1 expression alone is sufficient for Vγ9Vδ2 T cell activation by agonist antibody 20.1, but PAg-mediated activation additionally requires gene(s) on human chromosome 6 besides BTN3A1, established by comparing BTN3A1-transduced CHO cells with CHO cells carrying the full human chromosome 6.","method":"Genetic complementation/epistasis using BTN3A1 transduction and chromosome transfer in CHO cells","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with transduction and chromosome 6 complementation","pmids":["24890657"],"is_preprint":false},{"year":2019,"finding":"Residue H381 in the BTN3A1 B30.2 domain is critical for phosphoantigen ligand binding; mutations to charged surface residues impact diphosphate interactions. Monophosphonate analogs bind similarly to BTN3A1 but differ in antigenicity, demonstrating binding and efficacy are not linearly correlated.","method":"Molecular docking, site-directed mutagenesis, fluorescence polarization binding assay, T cell proliferation assays","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1–2 — mutagenesis with direct binding assay and functional validation","pmids":["31268699"],"is_preprint":false},{"year":2020,"finding":"BTN3A1 inhibits tumor-reactive αβ T cell receptor activation by preventing segregation of N-glycosylated CD45 from the immune synapse; CD277-specific antibodies restore αβ T cell effector activity and elicit BTN2A1-dependent γδ lymphocyte cytotoxicity against BTN3A1+ cancer cells.","method":"Genetic KO/KD, immune synapse imaging, in vitro and in vivo tumor models, antibody functional assays","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including mechanistic imaging and in vivo validation in high-impact journal","pmids":["32820120"],"is_preprint":false},{"year":2020,"finding":"NLRC5 regulates transcription of BTN3A1-3 genes through an atypical regulatory motif in their promoters; forced NLRC5 expression promotes Vγ9Vδ2 T cell-mediated killing of tumor cells in a BTN3A-dependent manner.","method":"Promoter analysis, overexpression, gene knockdown, T cell killing assays","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 — promoter functional analysis combined with BTN3A-dependent killing assay","pmids":["33364588"],"is_preprint":false},{"year":2022,"finding":"BTN3A1 promotes radioresistance in esophageal squamous cell carcinoma by activating autophagy through interaction with ULK1 and promoting ULK1 phosphorylation; HIF-1α directly promotes BTN3A1 transcription upon irradiation.","method":"Immunoprecipitation, mass spectrometry, western blotting, ChIP, luciferase reporter assay, KO/OE functional assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP/MS identification of ULK1 interaction + ChIP for transcriptional regulation with functional validation","pmids":["36418890"],"is_preprint":false},{"year":2023,"finding":"BTN2A1 B30.2 domain forms a homodimer; HMBPP binds to BTN3A1 B30.2 but not BTN2A1 B30.2; the BTN2A1 L325G mutation prevents both BTN2A1 internal domain homodimerization and binding to HMBPP-bound BTN3A1, linking BTN2A1 homodimerization to its cytoplasmic interaction with pAg-bound BTN3A1.","method":"NMR (31P-NMR, solution NMR), size exclusion chromatography, isothermal titration calorimetry, site-directed mutagenesis, T cell IFN-γ ELISA","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 — multiple biophysical methods (NMR, ITC, SEC) plus functional validation with mutagenesis","pmids":["37171180"],"is_preprint":false},{"year":2025,"finding":"19F NMR of BTN3A1 point mutants revealed that residues W421, T449, and T506 in the B30.2 domain undergo conformational/dynamic changes upon HMBPP and BTN2A1 association; W421 is at the BTN2A1 binding interface, and T506 changes indicate a larger conformational rearrangement propagating from the pAg-binding site. Juxtamembrane residues T304 and G323 are unaffected, localizing the conformational change within the B30.2 domain.","method":"19F solution NMR, site-directed mutagenesis, binding affinity measurements","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 1 — NMR with mutagenesis revealing specific residues involved in conformational change, single study","pmids":["40079188"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures show that HMBPP bridges the intracellular B30.2 domains of BTN3A1 and BTN2A1 within a full-length BTN3A1-BTN3A2-BTN2A1 complex; upon Vγ9Vδ2 TCR engagement, the BTN3A2-BTN2A1 ectodomain interaction dissociates, allowing BTN2A1 to bind the lateral surface of the Vγ9 chain and BTN3A2 to bind the apical surface of the Vδ2 chain in a 'pliers-like gripping' mechanism.","method":"Cryo-electron microscopy structural determination","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 — cryo-EM structure with functional antibody complexes, but preprint without peer review","pmids":["bio_10.1101_2024.10.02.616253"],"is_preprint":true},{"year":2025,"finding":"The agonist antibody ICT01 binds a unique region in the extracellular domain of BTN3As, destabilizing the BTN2A1-BTN3As interface and facilitating Vγ9Vδ2 TCR engagement to activate Vγ9Vδ2 T cells independently of phosphoantigens.","method":"Structural analysis (crystallography/cryo-EM implied), biochemical assays, cellular activation assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1–2 — structural and biochemical characterization, but preprint without peer review","pmids":["bio_10.1101_2025.10.21.681109"],"is_preprint":true},{"year":2024,"finding":"Juxtamembrane (JTM) amino acid phosphorylation of BTN3A1 is required for activating heterodimerization of BTN2A1 and BTN3A1 that leads to full Vγ9Vδ2 TCR activation; PHLDB2, SYNJ2, and CARMIL1 were identified as key players controlling surface dynamics of BTN2A1 and BTN3A1 during early oncogenic transformation.","method":"Protein interactome mapping, step-wise oncogenic mutagenesis organoid models, surface expression analysis, T cell activation assays","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — interactome mapping with functional assays but preprint, single study","pmids":["bio_10.1101_2024.11.19.624272"],"is_preprint":true},{"year":2011,"finding":"BTN3A1 (but not BTN3A2, which lacks the B30.2 intracellular domain) triggers co-stimulatory effects on TCR-induced T cell activation; differential expression of BTN3A isoforms between T cells (all three isoforms) and NK cells (mostly BTN3A2) explains differential CD277 functions, with BTN3A2-specific engagement decreasing NKp30-induced cytokine production in NK cells.","method":"Flow cytometry, isoform-selective antibody engagement, cytokine/proliferation assays","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 — isoform-specific functional characterization with mechanistic domain explanation","pmids":["21918970"],"is_preprint":false}],"current_model":"BTN3A1 is a transmembrane immune receptor that acts as an intracellular phosphoantigen (pAg) sensor via its B30.2 domain, which directly binds pyrophosphate metabolites (HMBPP, IPP) and undergoes a conformational change that propagates to the extracellular domains, triggering heterodimerization with BTN2A1 (requiring BTN2A1 B30.2 homodimerization) and ultimately presenting an activating surface to the Vγ9Vδ2 TCR; BTN3A1 additionally serves as a co-stimulatory molecule for αβ T cells (while inhibiting αβ TCR signaling by retaining CD45 at the immune synapse), interacts with periplakin via a di-leucine cytoplasmic motif to link the cytoskeleton to γδ T cell activation, constitutively associates with TBK1 and mediates its dynein-dependent perinuclear redistribution upon nucleic acid sensing to promote IRF3 phosphorylation and type I IFN production, and promotes radioresistance in cancer cells through ULK1 interaction and autophagy activation."},"narrative":{"teleology":[{"year":2011,"claim":"Establishing that BTN3A1, uniquely among CD277 isoforms, has co-stimulatory activity on αβ T cells dependent on its B30.2 domain resolved why CD277 engagement has different effects on T cells versus NK cells.","evidence":"Isoform-selective antibody engagement with cytokine/proliferation readouts in T and NK cells","pmids":["21918970"],"confidence":"Medium","gaps":["Co-stimulatory mechanism not defined at molecular level","No ligand for extracellular domain identified"]},{"year":2012,"claim":"Identifying BTN3A1 as the specific isoform required for phosphoantigen-induced Vγ9Vδ2 T cell activation, and showing that intracellular pAg accumulation reduces BTN3A1 membrane mobility, established the inside-out sensing paradigm.","evidence":"FRAP, CD277 knockdown, domain-shuffling, and agonist/antagonist antibody assays; crystal structures of BTN3A homodimers and antibody-binding epitopes","pmids":["22767497","22846996"],"confidence":"High","gaps":["Direct pAg–B30.2 binding not yet demonstrated","Identity of additional chromosome 6 genes required for pAg response unknown"]},{"year":2014,"claim":"Genetic complementation showed BTN3A1 alone suffices for agonist antibody-mediated activation but pAg-mediated activation requires additional human chromosome 6 gene(s), separating antibody-triggered from pAg-triggered pathways.","evidence":"BTN3A1 transduction versus full chromosome 6 transfer in CHO cells with γδ T cell activation readout","pmids":["24890657"],"confidence":"Medium","gaps":["Identity of the additional chromosome 6 factor(s) not determined at this point","Mechanism of cooperation unknown"]},{"year":2015,"claim":"Direct measurement of pAg binding to the B30.2 domain (HMBPP ~1 μM, IPP ~627 μM) and identification of periplakin as a cytoplasmic interactor via a di-leucine motif established the molecular basis of intracellular sensing and linked cytoskeletal coupling to γδ T cell activation.","evidence":"In vitro binding assays, yeast two-hybrid, knockdown/re-expression with coculture functional assays","pmids":["25637025"],"confidence":"High","gaps":["How periplakin interaction transmits signal to the extracellular face unknown","Structural basis of pAg binding not yet resolved"]},{"year":2016,"claim":"Discovery that BTN3A1 constitutively associates with TBK1 and mediates its dynein-dependent perinuclear redistribution upon nucleic acid sensing to drive IRF3 phosphorylation and IFN-β production revealed a second, innate-immune signaling function independent of γδ T cell activation.","evidence":"Reciprocal co-IP, siRNA knockdown, subcellular fractionation/imaging, IFN-β reporter assays","pmids":["27911820"],"confidence":"High","gaps":["Whether TBK1 and pAg-sensing functions are coordinated or independent is unclear","MAP4 regulatory mechanism not fully defined"]},{"year":2016,"claim":"Demonstration that HMBPP must be internalized for BTN3A1-dependent target cell lysis, bypassed by a cell-permeable prodrug, strengthened the inside-out model of pAg sensing.","evidence":"Cytotoxicity assays with BTN3A1 disruption, temperature-dependent uptake, prodrug comparison","pmids":["27271567"],"confidence":"Medium","gaps":["Identity and regulation of the pAg uptake transporter not established"]},{"year":2017,"claim":"NMR and crystallography revealed that pAg binding induces a global conformational change in the B30.2 domain distinct from nonspecific charge-driven binding, disrupting the intracellular dimer interface and propagating to extracellular domains, explaining how intracellular sensing triggers surface presentation.","evidence":"NMR chemical shift perturbation, X-ray crystallography, molecular dynamics, juxtamembrane mutagenesis with T cell activation assays","pmids":["28807997","28862425","28461569"],"confidence":"High","gaps":["Structural linkage from B30.2 rearrangement through transmembrane to extracellular domains not atomically resolved","Role of juxtamembrane dimerization interface incompletely defined"]},{"year":2020,"claim":"BTN3A1 was shown to inhibit αβ T cell activation by preventing CD45 exclusion from the immune synapse, while anti-CD277 antibodies restore αβ effector function and elicit BTN2A1-dependent γδ cytotoxicity, unifying its dual role as immunosuppressive for αβ and immunoactivating for γδ T cells in cancer.","evidence":"Genetic KO/KD, immune synapse imaging, in vitro and in vivo tumor models, antibody functional assays","pmids":["32820120"],"confidence":"High","gaps":["Structural mechanism of CD45 retention at the synapse not defined","Relative importance of αβ inhibition versus γδ activation in tumor immunity unclear"]},{"year":2022,"claim":"Identification of ULK1 as a BTN3A1 interactor that promotes autophagy-mediated radioresistance downstream of HIF-1α-driven BTN3A1 transcription extended BTN3A1 function to cancer cell-intrinsic stress responses.","evidence":"Co-IP/mass spectrometry, ChIP, luciferase reporter, KO/OE functional assays in esophageal squamous cell carcinoma","pmids":["36418890"],"confidence":"Medium","gaps":["Mechanism of ULK1 phosphorylation by BTN3A1 interaction not defined","Generalizability to other cancer types not established","Relationship to immune functions of BTN3A1 unexplored"]},{"year":2023,"claim":"Biophysical demonstration that HMBPP bridges BTN3A1 and BTN2A1 B30.2 domains, and that BTN2A1 B30.2 homodimerization is prerequisite for this interaction, resolved the molecular logic of the BTN3A1–BTN2A1 partnership required for γδ T cell activation.","evidence":"31P-NMR, solution NMR, SEC, ITC, site-directed mutagenesis, T cell IFN-γ ELISA","pmids":["37171180"],"confidence":"High","gaps":["Full-length heterodimer structure not resolved","Stoichiometry at the cell surface unknown"]},{"year":2025,"claim":"19F NMR mapping of specific B30.2 residues (W421, T449, T506) undergoing conformational changes upon HMBPP and BTN2A1 binding localized the allosteric propagation pathway within the B30.2 domain, while juxtamembrane residues were unaffected.","evidence":"19F solution NMR with site-directed mutagenesis and binding affinity measurements","pmids":["40079188"],"confidence":"Medium","gaps":["How conformational change in B30.2 propagates through transmembrane domain to ectodomains remains unresolved","Dynamic measurements limited to selected point mutants"]},{"year":null,"claim":"The complete structural mechanism by which intracellular pAg-induced B30.2 conformational changes propagate through the transmembrane region to reorganize BTN3A1 ectodomains for TCR engagement remains unresolved at atomic resolution in a full-length membrane-embedded context.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length BTN3A1 structure in a lipid membrane environment","Mechanism of juxtamembrane phosphorylation and its regulatory role not established in peer-reviewed literature","Identity and regulation of the pAg uptake transporter still unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,2,3,4,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[6,10]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[10,12]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,10,18]}],"pathway":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[6]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,2,7,10,13]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,18]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[12]}],"complexes":["BTN3A1-BTN2A1 heterodimer","BTN3A1-TBK1 complex"],"partners":["BTN2A1","BTN3A2","TBK1","ULK1","PPL","CD45","IRF3"],"other_free_text":[]},"mechanistic_narrative":"BTN3A1 is a transmembrane immunoreceptor that functions as an intracellular phosphoantigen sensor to activate Vγ9Vδ2 T cells, while also modulating αβ T cell responses and innate immune signaling. Its intracellular B30.2 domain directly binds pyrophosphate metabolites (HMBPP with ~1 μM affinity, IPP with ~627 μM affinity), and only bona fide phosphoantigens induce a specific conformational change that propagates through the B30.2 domain to disrupt a preexisting homodimer interface, ultimately triggering heterodimerization with BTN2A1 via HMBPP-bridged B30.2 domain interactions [PMID:25637025, PMID:28807997, PMID:28862425, PMID:37171180]. Beyond γδ T cell activation, BTN3A1 inhibits αβ TCR signaling by retaining N-glycosylated CD45 at the immune synapse, constitutively associates with TBK1 to promote dynein-dependent perinuclear redistribution and IRF3-mediated type I interferon production upon nucleic acid sensing, and interacts with periplakin through a cytoplasmic di-leucine motif required for γδ T cell responses [PMID:32820120, PMID:27911820, PMID:25637025]. BTN3A1 also promotes radioresistance in esophageal squamous cell carcinoma through ULK1 interaction and autophagy activation downstream of HIF-1α-driven transcription [PMID:36418890]."},"prefetch_data":{"uniprot":{"accession":"O00481","full_name":"Butyrophilin subfamily 3 member A1","aliases":[],"length_aa":513,"mass_kda":57.7,"function":"Plays a role in T-cell activation and in the adaptive immune response. Regulates the proliferation of activated T-cells. Regulates the release of cytokines and IFNG by activated T-cells. Mediates the response of T-cells toward infected and transformed cells that are characterized by high levels of phosphorylated metabolites, such as isopentenyl pyrophosphate","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O00481/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/BTN3A1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/BTN3A1","total_profiled":1310},"omim":[{"mim_id":"613595","title":"BUTYROPHILIN, SUBFAMILY 3, MEMBER A3; BTN3A3","url":"https://www.omim.org/entry/613595"},{"mim_id":"613593","title":"BUTYROPHILIN, SUBFAMILY 3, MEMBER A1; BTN3A1","url":"https://www.omim.org/entry/613593"},{"mim_id":"613590","title":"BUTYROPHILIN, SUBFAMILY 2, MEMBER A1; BTN2A1","url":"https://www.omim.org/entry/613590"},{"mim_id":"191390","title":"INFLAMMATORY BOWEL DISEASE 11; IBD11","url":"https://www.omim.org/entry/191390"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Vesicles","reliability":"Uncertain"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/BTN3A1"},"hgnc":{"alias_symbol":["BT3.1","BTF5","CD277","BTN3.1"],"prev_symbol":[]},"alphafold":{"accession":"O00481","domains":[{"cath_id":"2.60.40.10","chopping":"33-145","consensus_level":"high","plddt":95.3199,"start":33,"end":145},{"cath_id":"2.60.40.10","chopping":"152-241","consensus_level":"high","plddt":89.9124,"start":152,"end":241},{"cath_id":"2.60.120.920","chopping":"327-512","consensus_level":"high","plddt":95.7384,"start":327,"end":512},{"cath_id":"1.20.5","chopping":"247-322","consensus_level":"high","plddt":73.2692,"start":247,"end":322}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00481","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00481-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00481-F1-predicted_aligned_error_v6.png","plddt_mean":89.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=BTN3A1","jax_strain_url":"https://www.jax.org/strain/search?query=BTN3A1"},"sequence":{"accession":"O00481","fasta_url":"https://rest.uniprot.org/uniprotkb/O00481.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00481/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00481"}},"corpus_meta":[{"pmid":"22767497","id":"PMC_22767497","title":"Key implication of CD277/butyrophilin-3 (BTN3A) in cellular stress sensing by a major human γδ T-cell subset.","date":"2012","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/22767497","citation_count":477,"is_preprint":false},{"pmid":"22846996","id":"PMC_22846996","title":"The molecular basis for modulation of human Vγ9Vδ2 T cell responses by CD277/butyrophilin-3 (BTN3A)-specific antibodies.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22846996","citation_count":146,"is_preprint":false},{"pmid":"32820120","id":"PMC_32820120","title":"BTN3A1 governs antitumor responses by coordinating αβ and γδ T cells.","date":"2020","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/32820120","citation_count":129,"is_preprint":false},{"pmid":"25637025","id":"PMC_25637025","title":"Activation of human γδ T cells by cytosolic interactions of BTN3A1 with soluble phosphoantigens and the cytoskeletal adaptor periplakin.","date":"2015","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/25637025","citation_count":125,"is_preprint":false},{"pmid":"28807997","id":"PMC_28807997","title":"Phosphoantigen-induced conformational change of butyrophilin 3A1 (BTN3A1) and its implication on Vγ9Vδ2 T cell activation.","date":"2017","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/28807997","citation_count":102,"is_preprint":false},{"pmid":"24890657","id":"PMC_24890657","title":"Vγ9Vδ2 TCR-activation by phosphorylated antigens requires butyrophilin 3 A1 (BTN3A1) and additional genes on human chromosome 6.","date":"2014","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/24890657","citation_count":71,"is_preprint":false},{"pmid":"21918970","id":"PMC_21918970","title":"Differential role for CD277 as a co-regulator of the immune signal in T and NK cells.","date":"2011","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/21918970","citation_count":69,"is_preprint":false},{"pmid":"33178494","id":"PMC_33178494","title":"Baseline plasma levels of soluble PD-1, PD-L1, and BTN3A1 predict response to nivolumab treatment in patients with metastatic renal cell carcinoma: a step toward a biomarker for therapeutic decisions.","date":"2020","source":"Oncoimmunology","url":"https://pubmed.ncbi.nlm.nih.gov/33178494","citation_count":60,"is_preprint":false},{"pmid":"28862425","id":"PMC_28862425","title":"BTN3A1 Discriminates γδ T Cell Phosphoantigens from Nonantigenic Small Molecules via a Conformational Sensor in Its B30.2 Domain.","date":"2017","source":"ACS chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/28862425","citation_count":59,"is_preprint":false},{"pmid":"28386905","id":"PMC_28386905","title":"Butyrophilin 3A (BTN3A, CD277)-specific antibody 20.1 differentially activates Vγ9Vδ2 TCR clonotypes and interferes with phosphoantigen activation.","date":"2017","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/28386905","citation_count":53,"is_preprint":false},{"pmid":"27619996","id":"PMC_27619996","title":"Butyrophilin 3A/CD277-Dependent Activation of Human γδ T Cells: Accessory Cell Capacity of Distinct Leukocyte Populations.","date":"2016","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/27619996","citation_count":42,"is_preprint":false},{"pmid":"27271567","id":"PMC_27271567","title":"HMBPP Analog Prodrugs Bypass Energy-Dependent Uptake To Promote Efficient BTN3A1-Mediated Malignant Cell Lysis by Vγ9Vδ2 T Lymphocyte Effectors.","date":"2016","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/27271567","citation_count":41,"is_preprint":false},{"pmid":"28461569","id":"PMC_28461569","title":"The Juxtamembrane Domain of Butyrophilin BTN3A1 Controls Phosphoantigen-Mediated Activation of Human Vγ9Vδ2 T Cells.","date":"2017","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/28461569","citation_count":39,"is_preprint":false},{"pmid":"27911820","id":"PMC_27911820","title":"MAP4-regulated dynein-dependent trafficking of BTN3A1 controls the TBK1-IRF3 signaling axis.","date":"2016","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/27911820","citation_count":29,"is_preprint":false},{"pmid":"33364588","id":"PMC_33364588","title":"NLRC5 promotes transcription of BTN3A1-3 genes and Vγ9Vδ2 T cell-mediated killing.","date":"2020","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/33364588","citation_count":23,"is_preprint":false},{"pmid":"36418890","id":"PMC_36418890","title":"BTN3A1 promotes tumor progression and radiation resistance in esophageal squamous cell carcinoma by regulating ULK1-mediated autophagy.","date":"2022","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/36418890","citation_count":22,"is_preprint":false},{"pmid":"36288286","id":"PMC_36288286","title":"Up-regulation of BTN3A1 on CD14+ cells promotes Vγ9Vδ2 T cell activation in psoriasis.","date":"2022","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/36288286","citation_count":22,"is_preprint":false},{"pmid":"36096643","id":"PMC_36096643","title":"Cutting Edge: Bispecific γδ T Cell Engager Containing Heterodimeric BTN2A1 and BTN3A1 Promotes Targeted Activation of Vγ9Vδ2+ T Cells in the Presence of Costimulation by CD28 or NKG2D.","date":"2022","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/36096643","citation_count":21,"is_preprint":false},{"pmid":"34293829","id":"PMC_34293829","title":"Comprehensive analysis of BTN3A1 in cancers: mining of omics data and validation in patient samples and cellular models.","date":"2021","source":"FEBS open bio","url":"https://pubmed.ncbi.nlm.nih.gov/34293829","citation_count":20,"is_preprint":false},{"pmid":"29670629","id":"PMC_29670629","title":"Regulation of Human γδ T Cells by BTN3A1 Protein Stability and ATP-Binding Cassette Transporters.","date":"2018","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/29670629","citation_count":18,"is_preprint":false},{"pmid":"29937767","id":"PMC_29937767","title":"ABCA1, apoA-I, and BTN3A1: A Legitimate Ménage à Trois in Dendritic Cells.","date":"2018","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/29937767","citation_count":16,"is_preprint":false},{"pmid":"34240204","id":"PMC_34240204","title":"Long noncoding RNA HOXA-AS2 accelerates cervical cancer by the miR-509-3p/BTN3A1 axis.","date":"2021","source":"The Journal of pharmacy and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/34240204","citation_count":14,"is_preprint":false},{"pmid":"31268699","id":"PMC_31268699","title":"Probing the Ligand-Binding Pocket of BTN3A1.","date":"2019","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31268699","citation_count":11,"is_preprint":false},{"pmid":"37171180","id":"PMC_37171180","title":"Mutations to the BTN2A1 Linker Region Impact Its Homodimerization and Its Cytoplasmic Interaction with Phospho-Antigen-Bound BTN3A1.","date":"2023","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/37171180","citation_count":9,"is_preprint":false},{"pmid":"39342337","id":"PMC_39342337","title":"BTN3A1 expressed in cervical cancer cells promotes Vγ9Vδ2 T cells exhaustion through upregulating transcription factors NR4A2/3 downstream of TCR signaling.","date":"2024","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/39342337","citation_count":9,"is_preprint":false},{"pmid":"35178171","id":"PMC_35178171","title":"Synthesis and Metabolism of BTN3A1 Ligands: Studies on Diene Modifications to the Phosphoantigen Scaffold.","date":"2022","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/35178171","citation_count":8,"is_preprint":false},{"pmid":"35920929","id":"PMC_35920929","title":"CD277 agonist enhances the immunogenicity of relapsed/refractory acute myeloid leukemia towards Vδ2+ T cell cytotoxicity.","date":"2022","source":"Annals of hematology","url":"https://pubmed.ncbi.nlm.nih.gov/35920929","citation_count":7,"is_preprint":false},{"pmid":"37688767","id":"PMC_37688767","title":"Synergistic effects of BTN3A1, SHP2, CD274, and STAT3 gene polymorphisms on the risk of systemic lupus erythematosus: a multifactorial dimensional reduction analysis.","date":"2023","source":"Clinical rheumatology","url":"https://pubmed.ncbi.nlm.nih.gov/37688767","citation_count":5,"is_preprint":false},{"pmid":"34545848","id":"PMC_34545848","title":"Elevated Expressions of BTN3A1 and RhoB in Psoriasis Vulgaris Lesions by an Immunohistochemical Study.","date":"2022","source":"Applied immunohistochemistry & molecular morphology : AIMM","url":"https://pubmed.ncbi.nlm.nih.gov/34545848","citation_count":5,"is_preprint":false},{"pmid":"28631855","id":"PMC_28631855","title":"A Photo-Crosslinkable Biotin Derivative of the Phosphoantigen (E)-4-Hydroxy-3-Methylbut-2-Enyl Diphosphate (HMBPP) Activates Vγ9Vδ2 T Cells and Binds to the HMBPP Site of BTN3A1.","date":"2017","source":"Chemistry (Weinheim an der Bergstrasse, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/28631855","citation_count":4,"is_preprint":false},{"pmid":"40091603","id":"PMC_40091603","title":"Autologous Peripheral Vγ9Vδ2 T Cell Synergizes with αβ T Cell Through Antigen Presentation and BTN3A1 Blockade in Immunotherapy of Cervical Cancer.","date":"2025","source":"Advanced science (Weinheim, Baden-Wurttemberg, Germany)","url":"https://pubmed.ncbi.nlm.nih.gov/40091603","citation_count":4,"is_preprint":false},{"pmid":"41226733","id":"PMC_41226733","title":"BTN2A1 and BTN3A1 as Novel Coeliac Disease Risk Loci: An In Silico Analysis.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/41226733","citation_count":2,"is_preprint":false},{"pmid":"32958123","id":"PMC_32958123","title":"[Butyrophilin 3A1 (BTN3A1) enhances activation and proliferation of human peripheral blood Vγ9Vδ2 T cells induced by MTB-HAg].","date":"2020","source":"Xi bao yu fen zi mian yi xue za zhi = Chinese journal of cellular and molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/32958123","citation_count":2,"is_preprint":false},{"pmid":"28597565","id":"PMC_28597565","title":"BTN3A1-antibodies and phosphoantigens: TCRVγ9Vδ2 \"see\" the difference.","date":"2017","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/28597565","citation_count":2,"is_preprint":false},{"pmid":"39417845","id":"PMC_39417845","title":"A regulatory variant rs9379874 in T1D risk region 6p22.2 affects BTN3A1 expression regulating T cell function.","date":"2024","source":"Acta diabetologica","url":"https://pubmed.ncbi.nlm.nih.gov/39417845","citation_count":1,"is_preprint":false},{"pmid":"39919440","id":"PMC_39919440","title":"Synthesis and evaluation of triazole-containing aryl/acyloxy prodrugs of a BTN3A1 ligand.","date":"2025","source":"European journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39919440","citation_count":0,"is_preprint":false},{"pmid":"40079188","id":"PMC_40079188","title":"Investigation of structural and dynamic properties of the Butyrophilin BTN3A1/BTN2A1 cytoplasmic complex by 19F solution NMR.","date":"2025","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/40079188","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.10.21.681109","title":"Molecular Mechanisms Underlying Human Vγ9Vδ2 T Cell Activation by Butyrophilin-3 (BTN3) Targeted Antibodies","date":"2025-10-21","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.21.681109","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.06.12.659293","title":"The early human interferon gamma response to <i>Toxoplasma gondii</i> is driven by Vγ9Vδ2 T-cell sensing of host phosphoantigens and subsequent NK-cell activation","date":"2025-06-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.12.659293","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.11.19.624272","title":"Sensitivity to Vγ9Vδ2TCR T cells is imprinted after single mutations during early oncogenesis","date":"2024-11-21","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.19.624272","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.05.05.652251","title":"γδ T Cells Target and Ablate Senescent Cells in Aging and Alleviate Pulmonary Fibrosis","date":"2025-05-09","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.05.652251","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.10.02.616253","title":"Cryo-EM structural insights into Vγ9Vδ2 TCR activation via multiple butyrophilins","date":"2024-10-03","source":"bioRxiv","url":"https://doi.org/10.1101/2024.10.02.616253","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":24185,"output_tokens":4551,"usd":0.07041},"stage2":{"model":"claude-opus-4-6","input_tokens":8148,"output_tokens":3047,"usd":0.175372},"total_usd":0.245782,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"BTN3A1 is the specific CD277 isoform required for phosphoantigen (PAg)-induced Vγ9Vδ2 T cell activation; FRAP experiments showed that intracellular PAg accumulation causes decreased BTN3A1 membrane mobility, and CD277 knockdown plus domain-shuffling confirmed BTN3A1's key role in PAg sensing.\",\n      \"method\": \"FRAP, CD277 knockdown, domain-shuffling, antibody agonist/antagonist functional assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (FRAP, KD, domain-swap) in highly cited foundational paper\",\n      \"pmids\": [\"22767497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"BTN3A1 (and the other two BTN3A isoforms) form V-shaped homodimers in solution, associating through the membrane-proximal C-type Ig domain; agonist antibody 20.1 and antagonist antibody 103.2 bind to separate epitopes on the BTN3A Ig-V domain with high affinity but different valencies.\",\n      \"method\": \"X-ray crystallography, solution biochemistry (SEC), antibody binding studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with functional antibody binding characterization\",\n      \"pmids\": [\"22846996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Phosphoantigens bind directly to the intracellular B30.2 domain of BTN3A1 (HMBPP at 1.1 μM affinity, IPP at 627 μM affinity); periplakin interacts with a membrane-proximal di-leucine motif in the BTN3A1 cytoplasmic tail (not present in BTN3A2/3), and a BTN3A1 variant lacking this motif fails to restore γδ T cell responses in knockdown cells.\",\n      \"method\": \"In vitro binding assays, yeast two-hybrid, knockdown/re-expression, coculture functional assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding measurements combined with yeast two-hybrid identification and functional rescue experiments\",\n      \"pmids\": [\"25637025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Phosphoantigen binding to the B30.2 intracellular domain of BTN3A1 induces a global conformational change propagating from the pAg-binding pocket to distal parts of the domain and disrupting a preexisting dimer interface; the extracellular domains adopt a V-shaped conformation at rest, and locking them in this resting conformation without perturbing membrane reorganization diminishes pAg-induced T cell activation.\",\n      \"method\": \"NMR spectroscopy, X-ray crystallography, molecular dynamics simulations, biochemical and cellular assays\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution + NMR + crystal structures + MD + cellular validation in one study\",\n      \"pmids\": [\"28807997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The intracellular B30.2 domain of BTN3A1 discriminates phosphoantigens from nonantigenic small molecules via a conformational sensor: while many negatively charged molecules bind the positively charged pocket, only pAgs induce a specific conformational change that propagates to distal parts of the domain.\",\n      \"method\": \"NMR chemical shift perturbation analysis, X-ray crystallography\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR and crystallography with mechanistic discrimination demonstrated\",\n      \"pmids\": [\"28862425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The juxtamembrane domain of BTN3A1 (distinct from the transmembrane domain) is required for correct γδ T cell-related function; mutations in this region, which includes a possible dimerization interface near the B30.2 domain start, markedly enhance or reduce γδ T cell reactivity.\",\n      \"method\": \"Site-directed mutagenesis, T cell activation functional assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis with functional readout but single lab\",\n      \"pmids\": [\"28461569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"BTN3A1 constitutively associates with TBK1 at rest; upon nucleic acid stimulation, the BTN3A1-TBK1 complex redistributes to the perinuclear region via MAP4-regulated dynein-dependent transport, where BTN3A1 mediates TBK1-IRF3 interaction and IRF3 phosphorylation, promoting type I IFN production. Depletion of BTN3A1 inhibits IFN-β production.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, subcellular fractionation/imaging, IFN-β reporter assays\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP + KD + localization with functional consequence, multiple orthogonal methods\",\n      \"pmids\": [\"27911820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Internalization of HMBPP into target cells is required for BTN3A1-dependent lysis by Vγ9Vδ2 effector T cells; a cell-permeable prodrug that bypasses energy-dependent uptake routes restores BTN3A1-dependent killing even at 4°C, supporting an inside-out signaling model.\",\n      \"method\": \"Cytotoxicity assays, BTN3A1 disruption, temperature-dependent uptake experiments, prodrug comparison\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean functional assay with BTN3A1 disruption and mechanistic prodrug comparison\",\n      \"pmids\": [\"27271567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"BTN3A1 expression alone is sufficient for Vγ9Vδ2 T cell activation by agonist antibody 20.1, but PAg-mediated activation additionally requires gene(s) on human chromosome 6 besides BTN3A1, established by comparing BTN3A1-transduced CHO cells with CHO cells carrying the full human chromosome 6.\",\n      \"method\": \"Genetic complementation/epistasis using BTN3A1 transduction and chromosome transfer in CHO cells\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with transduction and chromosome 6 complementation\",\n      \"pmids\": [\"24890657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Residue H381 in the BTN3A1 B30.2 domain is critical for phosphoantigen ligand binding; mutations to charged surface residues impact diphosphate interactions. Monophosphonate analogs bind similarly to BTN3A1 but differ in antigenicity, demonstrating binding and efficacy are not linearly correlated.\",\n      \"method\": \"Molecular docking, site-directed mutagenesis, fluorescence polarization binding assay, T cell proliferation assays\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis with direct binding assay and functional validation\",\n      \"pmids\": [\"31268699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"BTN3A1 inhibits tumor-reactive αβ T cell receptor activation by preventing segregation of N-glycosylated CD45 from the immune synapse; CD277-specific antibodies restore αβ T cell effector activity and elicit BTN2A1-dependent γδ lymphocyte cytotoxicity against BTN3A1+ cancer cells.\",\n      \"method\": \"Genetic KO/KD, immune synapse imaging, in vitro and in vivo tumor models, antibody functional assays\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including mechanistic imaging and in vivo validation in high-impact journal\",\n      \"pmids\": [\"32820120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"NLRC5 regulates transcription of BTN3A1-3 genes through an atypical regulatory motif in their promoters; forced NLRC5 expression promotes Vγ9Vδ2 T cell-mediated killing of tumor cells in a BTN3A-dependent manner.\",\n      \"method\": \"Promoter analysis, overexpression, gene knockdown, T cell killing assays\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter functional analysis combined with BTN3A-dependent killing assay\",\n      \"pmids\": [\"33364588\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"BTN3A1 promotes radioresistance in esophageal squamous cell carcinoma by activating autophagy through interaction with ULK1 and promoting ULK1 phosphorylation; HIF-1α directly promotes BTN3A1 transcription upon irradiation.\",\n      \"method\": \"Immunoprecipitation, mass spectrometry, western blotting, ChIP, luciferase reporter assay, KO/OE functional assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP/MS identification of ULK1 interaction + ChIP for transcriptional regulation with functional validation\",\n      \"pmids\": [\"36418890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"BTN2A1 B30.2 domain forms a homodimer; HMBPP binds to BTN3A1 B30.2 but not BTN2A1 B30.2; the BTN2A1 L325G mutation prevents both BTN2A1 internal domain homodimerization and binding to HMBPP-bound BTN3A1, linking BTN2A1 homodimerization to its cytoplasmic interaction with pAg-bound BTN3A1.\",\n      \"method\": \"NMR (31P-NMR, solution NMR), size exclusion chromatography, isothermal titration calorimetry, site-directed mutagenesis, T cell IFN-γ ELISA\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple biophysical methods (NMR, ITC, SEC) plus functional validation with mutagenesis\",\n      \"pmids\": [\"37171180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"19F NMR of BTN3A1 point mutants revealed that residues W421, T449, and T506 in the B30.2 domain undergo conformational/dynamic changes upon HMBPP and BTN2A1 association; W421 is at the BTN2A1 binding interface, and T506 changes indicate a larger conformational rearrangement propagating from the pAg-binding site. Juxtamembrane residues T304 and G323 are unaffected, localizing the conformational change within the B30.2 domain.\",\n      \"method\": \"19F solution NMR, site-directed mutagenesis, binding affinity measurements\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — NMR with mutagenesis revealing specific residues involved in conformational change, single study\",\n      \"pmids\": [\"40079188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures show that HMBPP bridges the intracellular B30.2 domains of BTN3A1 and BTN2A1 within a full-length BTN3A1-BTN3A2-BTN2A1 complex; upon Vγ9Vδ2 TCR engagement, the BTN3A2-BTN2A1 ectodomain interaction dissociates, allowing BTN2A1 to bind the lateral surface of the Vγ9 chain and BTN3A2 to bind the apical surface of the Vδ2 chain in a 'pliers-like gripping' mechanism.\",\n      \"method\": \"Cryo-electron microscopy structural determination\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure with functional antibody complexes, but preprint without peer review\",\n      \"pmids\": [\"bio_10.1101_2024.10.02.616253\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The agonist antibody ICT01 binds a unique region in the extracellular domain of BTN3As, destabilizing the BTN2A1-BTN3As interface and facilitating Vγ9Vδ2 TCR engagement to activate Vγ9Vδ2 T cells independently of phosphoantigens.\",\n      \"method\": \"Structural analysis (crystallography/cryo-EM implied), biochemical assays, cellular activation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — structural and biochemical characterization, but preprint without peer review\",\n      \"pmids\": [\"bio_10.1101_2025.10.21.681109\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Juxtamembrane (JTM) amino acid phosphorylation of BTN3A1 is required for activating heterodimerization of BTN2A1 and BTN3A1 that leads to full Vγ9Vδ2 TCR activation; PHLDB2, SYNJ2, and CARMIL1 were identified as key players controlling surface dynamics of BTN2A1 and BTN3A1 during early oncogenic transformation.\",\n      \"method\": \"Protein interactome mapping, step-wise oncogenic mutagenesis organoid models, surface expression analysis, T cell activation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — interactome mapping with functional assays but preprint, single study\",\n      \"pmids\": [\"bio_10.1101_2024.11.19.624272\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"BTN3A1 (but not BTN3A2, which lacks the B30.2 intracellular domain) triggers co-stimulatory effects on TCR-induced T cell activation; differential expression of BTN3A isoforms between T cells (all three isoforms) and NK cells (mostly BTN3A2) explains differential CD277 functions, with BTN3A2-specific engagement decreasing NKp30-induced cytokine production in NK cells.\",\n      \"method\": \"Flow cytometry, isoform-selective antibody engagement, cytokine/proliferation assays\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — isoform-specific functional characterization with mechanistic domain explanation\",\n      \"pmids\": [\"21918970\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"BTN3A1 is a transmembrane immune receptor that acts as an intracellular phosphoantigen (pAg) sensor via its B30.2 domain, which directly binds pyrophosphate metabolites (HMBPP, IPP) and undergoes a conformational change that propagates to the extracellular domains, triggering heterodimerization with BTN2A1 (requiring BTN2A1 B30.2 homodimerization) and ultimately presenting an activating surface to the Vγ9Vδ2 TCR; BTN3A1 additionally serves as a co-stimulatory molecule for αβ T cells (while inhibiting αβ TCR signaling by retaining CD45 at the immune synapse), interacts with periplakin via a di-leucine cytoplasmic motif to link the cytoskeleton to γδ T cell activation, constitutively associates with TBK1 and mediates its dynein-dependent perinuclear redistribution upon nucleic acid sensing to promote IRF3 phosphorylation and type I IFN production, and promotes radioresistance in cancer cells through ULK1 interaction and autophagy activation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"BTN3A1 is a transmembrane immunoreceptor that functions as an intracellular phosphoantigen sensor to activate Vγ9Vδ2 T cells, while also modulating αβ T cell responses and innate immune signaling. Its intracellular B30.2 domain directly binds pyrophosphate metabolites (HMBPP with ~1 μM affinity, IPP with ~627 μM affinity), and only bona fide phosphoantigens induce a specific conformational change that propagates through the B30.2 domain to disrupt a preexisting homodimer interface, ultimately triggering heterodimerization with BTN2A1 via HMBPP-bridged B30.2 domain interactions [PMID:25637025, PMID:28807997, PMID:28862425, PMID:37171180]. Beyond γδ T cell activation, BTN3A1 inhibits αβ TCR signaling by retaining N-glycosylated CD45 at the immune synapse, constitutively associates with TBK1 to promote dynein-dependent perinuclear redistribution and IRF3-mediated type I interferon production upon nucleic acid sensing, and interacts with periplakin through a cytoplasmic di-leucine motif required for γδ T cell responses [PMID:32820120, PMID:27911820, PMID:25637025]. BTN3A1 also promotes radioresistance in esophageal squamous cell carcinoma through ULK1 interaction and autophagy activation downstream of HIF-1α-driven transcription [PMID:36418890].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Establishing that BTN3A1, uniquely among CD277 isoforms, has co-stimulatory activity on αβ T cells dependent on its B30.2 domain resolved why CD277 engagement has different effects on T cells versus NK cells.\",\n      \"evidence\": \"Isoform-selective antibody engagement with cytokine/proliferation readouts in T and NK cells\",\n      \"pmids\": [\"21918970\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Co-stimulatory mechanism not defined at molecular level\", \"No ligand for extracellular domain identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identifying BTN3A1 as the specific isoform required for phosphoantigen-induced Vγ9Vδ2 T cell activation, and showing that intracellular pAg accumulation reduces BTN3A1 membrane mobility, established the inside-out sensing paradigm.\",\n      \"evidence\": \"FRAP, CD277 knockdown, domain-shuffling, and agonist/antagonist antibody assays; crystal structures of BTN3A homodimers and antibody-binding epitopes\",\n      \"pmids\": [\"22767497\", \"22846996\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct pAg–B30.2 binding not yet demonstrated\", \"Identity of additional chromosome 6 genes required for pAg response unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Genetic complementation showed BTN3A1 alone suffices for agonist antibody-mediated activation but pAg-mediated activation requires additional human chromosome 6 gene(s), separating antibody-triggered from pAg-triggered pathways.\",\n      \"evidence\": \"BTN3A1 transduction versus full chromosome 6 transfer in CHO cells with γδ T cell activation readout\",\n      \"pmids\": [\"24890657\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of the additional chromosome 6 factor(s) not determined at this point\", \"Mechanism of cooperation unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Direct measurement of pAg binding to the B30.2 domain (HMBPP ~1 μM, IPP ~627 μM) and identification of periplakin as a cytoplasmic interactor via a di-leucine motif established the molecular basis of intracellular sensing and linked cytoskeletal coupling to γδ T cell activation.\",\n      \"evidence\": \"In vitro binding assays, yeast two-hybrid, knockdown/re-expression with coculture functional assays\",\n      \"pmids\": [\"25637025\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How periplakin interaction transmits signal to the extracellular face unknown\", \"Structural basis of pAg binding not yet resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that BTN3A1 constitutively associates with TBK1 and mediates its dynein-dependent perinuclear redistribution upon nucleic acid sensing to drive IRF3 phosphorylation and IFN-β production revealed a second, innate-immune signaling function independent of γδ T cell activation.\",\n      \"evidence\": \"Reciprocal co-IP, siRNA knockdown, subcellular fractionation/imaging, IFN-β reporter assays\",\n      \"pmids\": [\"27911820\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TBK1 and pAg-sensing functions are coordinated or independent is unclear\", \"MAP4 regulatory mechanism not fully defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstration that HMBPP must be internalized for BTN3A1-dependent target cell lysis, bypassed by a cell-permeable prodrug, strengthened the inside-out model of pAg sensing.\",\n      \"evidence\": \"Cytotoxicity assays with BTN3A1 disruption, temperature-dependent uptake, prodrug comparison\",\n      \"pmids\": [\"27271567\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity and regulation of the pAg uptake transporter not established\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"NMR and crystallography revealed that pAg binding induces a global conformational change in the B30.2 domain distinct from nonspecific charge-driven binding, disrupting the intracellular dimer interface and propagating to extracellular domains, explaining how intracellular sensing triggers surface presentation.\",\n      \"evidence\": \"NMR chemical shift perturbation, X-ray crystallography, molecular dynamics, juxtamembrane mutagenesis with T cell activation assays\",\n      \"pmids\": [\"28807997\", \"28862425\", \"28461569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural linkage from B30.2 rearrangement through transmembrane to extracellular domains not atomically resolved\", \"Role of juxtamembrane dimerization interface incompletely defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"BTN3A1 was shown to inhibit αβ T cell activation by preventing CD45 exclusion from the immune synapse, while anti-CD277 antibodies restore αβ effector function and elicit BTN2A1-dependent γδ cytotoxicity, unifying its dual role as immunosuppressive for αβ and immunoactivating for γδ T cells in cancer.\",\n      \"evidence\": \"Genetic KO/KD, immune synapse imaging, in vitro and in vivo tumor models, antibody functional assays\",\n      \"pmids\": [\"32820120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural mechanism of CD45 retention at the synapse not defined\", \"Relative importance of αβ inhibition versus γδ activation in tumor immunity unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of ULK1 as a BTN3A1 interactor that promotes autophagy-mediated radioresistance downstream of HIF-1α-driven BTN3A1 transcription extended BTN3A1 function to cancer cell-intrinsic stress responses.\",\n      \"evidence\": \"Co-IP/mass spectrometry, ChIP, luciferase reporter, KO/OE functional assays in esophageal squamous cell carcinoma\",\n      \"pmids\": [\"36418890\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of ULK1 phosphorylation by BTN3A1 interaction not defined\", \"Generalizability to other cancer types not established\", \"Relationship to immune functions of BTN3A1 unexplored\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Biophysical demonstration that HMBPP bridges BTN3A1 and BTN2A1 B30.2 domains, and that BTN2A1 B30.2 homodimerization is prerequisite for this interaction, resolved the molecular logic of the BTN3A1–BTN2A1 partnership required for γδ T cell activation.\",\n      \"evidence\": \"31P-NMR, solution NMR, SEC, ITC, site-directed mutagenesis, T cell IFN-γ ELISA\",\n      \"pmids\": [\"37171180\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length heterodimer structure not resolved\", \"Stoichiometry at the cell surface unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"19F NMR mapping of specific B30.2 residues (W421, T449, T506) undergoing conformational changes upon HMBPP and BTN2A1 binding localized the allosteric propagation pathway within the B30.2 domain, while juxtamembrane residues were unaffected.\",\n      \"evidence\": \"19F solution NMR with site-directed mutagenesis and binding affinity measurements\",\n      \"pmids\": [\"40079188\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How conformational change in B30.2 propagates through transmembrane domain to ectodomains remains unresolved\", \"Dynamic measurements limited to selected point mutants\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The complete structural mechanism by which intracellular pAg-induced B30.2 conformational changes propagate through the transmembrane region to reorganize BTN3A1 ectodomains for TCR engagement remains unresolved at atomic resolution in a full-length membrane-embedded context.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length BTN3A1 structure in a lipid membrane environment\", \"Mechanism of juxtamembrane phosphorylation and its regulatory role not established in peer-reviewed literature\", \"Identity and regulation of the pAg uptake transporter still unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 3, 4, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [6, 10]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [10, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 10, 18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 2, 7, 10, 13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 18]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [\n      \"BTN3A1-BTN2A1 heterodimer\",\n      \"BTN3A1-TBK1 complex\"\n    ],\n    \"partners\": [\n      \"BTN2A1\",\n      \"BTN3A2\",\n      \"TBK1\",\n      \"ULK1\",\n      \"PPL\",\n      \"CD45\",\n      \"IRF3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}