{"uniprot":"P04437","gene":"TRAV29DV5","name":"T cell receptor alpha variable 29/delta variable 5","organism":"Homo sapiens (Human)","status":"dark","length":119,"sequence":"MAMLLGASVLILWLQPDWVNSQQKNDDQQVKQNSPSLSVQEGRISILNCDYTNSMFDYFLWYKKYPAEGPTFLISISSIKDKNEDGRFTVFLNKSAKHLSLHIVPSQPGDSAVYFCAAS","function_summary":"A variable immunoglobulin-like recognition module of a human cell-surface antigen receptor that binds extracellular ligands and initiates signaling to drive lymphocyte activation. By forming a high-specificity binding site through its variable loops, it detects peptide–MHC complexes and triggers downstream pathways that execute cytotoxic effector functions within the immune system. The module operates at the cell surface as part of a larger receptor assembly that couples extracellular recognition to intracellular signaling from the plasma membrane.","plain_language":"TRAV29DV5 has barely been studied. The model's best guess: A variable immunoglobulin-like recognition module of a human cell-surface antigen receptor that binds extracellular ligands and initiates signaling to drive lymphocyte activation. By forming a high-specificity binding site through its variable loops, it detects peptide–MHC complexes and triggers downstream pathways that execute cytotoxic effector functions within the immune system.","uniprot_summary":"Variable region of a cell surface antigen receptor.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"},{"id":"GO:0004888","label":"transmembrane signaling receptor activity"}],"biological_process":[{"id":"GO:0006955","label":"immune response"}],"cellular_component":[{"id":"GO:0005886","label":"plasma membrane"}]},"interpro":[{"id":"IPR013783","name":"Immunoglobulin-like fold","type":"homologous_superfamily","start":15,"end":118},{"id":"IPR036179","name":"Immunoglobulin-like domain superfamily","type":"homologous_superfamily","start":27,"end":118},{"id":"IPR007110","name":"Immunoglobulin-like domain","type":"domain","start":16,"end":119},{"id":"IPR013106","name":"Immunoglobulin V-set domain","type":"domain","start":32,"end":118},{"id":"IPR051006","name":"T cell receptor variable domain","type":"family","start":1,"end":119}],"reasoning":"I begin with the InterPro architecture. The sequence is dominated by immunoglobulin-type modules: IPR013783 (Immunoglobulin-like fold, residues 15–118) and IPR036179 (Immunoglobulin-like domain superfamily, residues 27–118) define a β-sandwich scaffold typical of extracellular recognition domains. Within this scaffold sits IPR007110 (Immunoglobulin-like domain, residues 16–119), and more specifically IPR013106 (Immunoglobulin V-set domain, residues 32–118), which is the hallmark of variable (V) regions that mediate antigen recognition. The entire polypeptide is classified by IPR051006 (T cell receptor variable domain family, residues 1–119), indicating that this is a V-set module specialized for antigen-binding and signaling initiation. The ordered layout—an N-terminal TCR-variable family signature encompassing a single V-set Ig-like domain—establishes a soluble or extracellularly exposed recognition unit that pairs with a membrane-anchored signaling module.\n\nThis V-set architecture causes high-affinity, shape-complementary binding to proteinaceous or peptide–MHC ligands and necessitates multivalent protein interactions, supporting GO:0005515 protein binding as a core molecular function. Because a V-set TCR variable domain couples ligand recognition to intracellular signaling via associated transmembrane subunits, it fulfills GO:0004888 transmembrane signaling receptor activity: extracellular binding triggers intracellular cascades through the receptor complex rather than intrinsic catalytic motifs.\n\nFrom this molecular function, the biological role follows. Ligand engagement by this variable domain initiates the canonical signaling cascade that drives clonal activation and effector programming of cytotoxic lymphocytes, placing the protein squarely in GO:0006955 immune response. The V-set module’s specificity determines which peptide–MHC complexes are recognized, thereby gating downstream pathways that orchestrate cytotoxicity and cytokine production.\n\nCellular localization is dictated by the receptor’s topology. The V-set domain is extracellular and typically tethered through assembly with membrane-spanning partners; thus the functional complex resides at the cell surface, consistent with GO:0005886 plasma membrane. The absence of transmembrane features in the V-set itself suggests that membrane anchoring is achieved via associated chains, but the operational site remains the plasma membrane where ligand sampling and signaling occur.\n\nMechanistically, the V-set domain forms a heterodimeric recognition head with a partner variable domain, creating a composite binding site whose specificity arises from the variable loops. Ligand binding stabilizes a signaling-competent complex that recruits cytoplasmic adaptors and kinases through its associated transmembrane subunits. I therefore hypothesize that this variable module partners with a complementary TCR variable domain and constant chains to form the full receptor complex, and that it signals through cytoplasmic adaptors such as PAG1 and the Lck/ZAP-70 kinase axis. Likely extracellular partners include peptide–MHC complexes on antigen-presenting cells, while intracellular partners assemble at the inner leaflet of the plasma membrane to propagate the signal.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-P04437.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/P04437"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/P04437/entry","atlas":"/p/P04437"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}