{"uniprot":"P03979","gene":"TRGV3","name":"T cell receptor gamma variable 3","organism":"Homo sapiens (Human)","status":"dark","length":118,"sequence":"MRWALLVLLAFLSPASQKSSNLEGRTKSVTRQTGSSAEITCDLTVTNTFYIHWYLHQEGKAPQRLLYYDVSTARDVLESGLSPGKYYTHTPRRWSWILRLQNLIENDSGVYYCATWDR","function_summary":"An extracellular immunoglobulin-like recognition module that forms the gamma-chain component of a heterodimeric immune receptor complex. It presents a variable-type Ig fold that binds proteinaceous ligands at the cell surface, assembling with a partner chain to tune antigen recognition and initiate signaling that modulates lymphocyte responses. Displayed at the plasma membrane and exposed to the extracellular milieu, it likely operates by shaping ligand-binding avidity and coupling to membrane-proximal signaling assemblies that regulate immune responses.","plain_language":"TRGV3 has barely been studied. The model's best guess: An extracellular immunoglobulin-like recognition module that forms the gamma-chain component of a heterodimeric immune receptor complex. It presents a variable-type Ig fold that binds proteinaceous ligands at the cell surface, assembling with a partner chain to tune antigen recognition and initiate signaling that modulates lymphocyte responses.","uniprot_summary":"Involved in the immune response.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0006955","label":"immune response"}],"cellular_component":[{"id":"GO:0005576","label":"extracellular region"},{"id":"GO:0005886","label":"plasma membrane"}]},"interpro":[{"id":"IPR013783","name":"Immunoglobulin-like fold","type":"homologous_superfamily","start":17,"end":118},{"id":"IPR036179","name":"Immunoglobulin-like domain superfamily","type":"homologous_superfamily","start":27,"end":117},{"id":"IPR007110","name":"Immunoglobulin-like domain","type":"domain","start":14,"end":118},{"id":"IPR013106","name":"Immunoglobulin V-set domain","type":"domain","start":27,"end":115},{"id":"IPR051117","name":"T cell receptor gamma variable/constant region","type":"family","start":2,"end":117}],"reasoning":"I begin with the InterPro architecture. The polypeptide core from residues 14–118 is saturated with immunoglobulin-like signatures: IPR007110 (Immunoglobulin-like domain, residues 14–118) and IPR013783 (Immunoglobulin-like fold homologous superfamily, residues 17–118) define a beta-sandwich scaffold typical of cell-surface recognition modules. Within this scaffold, IPR013106 (Immunoglobulin V-set domain, residues 27–115) specifies a variable-type Ig fold that forms the ligand-recognition surface. The presence of IPR036179 (Immunoglobulin-like domain superfamily, residues 27–117) reinforces this fold assignment, and IPR051117 (T cell receptor gamma variable/constant region family, residues 2–117) ties the module explicitly to the gamma-chain architecture of a heterodimeric immune receptor. The ordered layout—an N-terminal TCR gamma-family signature leading into a V-set Ig domain—creates a rigid extracellular recognition module that pairs with a partner chain to form a high-affinity heterodimer.\n\nThis Ig V-set architecture causes avid protein binding as its primary molecular function. The solvent-exposed beta-sheet edges and loop regions of the V-set domain generate a composite binding surface that captures proteinaceous or glycoprotein ligands at the cell surface. This directly supports GO:0005515 protein binding as the operative molecular function.\n\nFrom this binding capacity, the biological role follows. A T cell receptor gamma-chain-like module that forms a heterodimer with a partner receptor naturally initiates and tunes antigen recognition and signaling in lymphocytes. Such recognition triggers downstream pathways that orchestrate lymphocyte activation and effector programs, situating the protein squarely within GO:0006955 immune response.\n\nCellular placement is dictated by the domain’s extracellular nature and the receptor’s assembly pathway. Ig-like V-set domains are secreted or displayed at the cell surface; in immune receptors they are presented on the outside of the plasma membrane as part of a multisubunit complex. This architecture therefore predicts a surface-exposed module that resides at the cell boundary, consistent with GO:0005886 plasma membrane and GO:0005576 extracellular region. The extracellular Ig fold explains membrane association via complex assembly rather than intrinsic transmembrane segments.\n\nMechanistically, the V-set domain forms a heterodimer with a partner Ig-like domain to create a composite ligand-binding site that samples extracellular ligands and transduces signals through associated signaling subunits. I hypothesize that it pairs with a delta-chain-like partner to assemble a heterodimer that recruits signaling modules analogous to canonical lymphocyte receptor complexes. Likely interaction partners include a delta-chain-like Ig module and membrane-proximal signaling assemblies that couple ligand engagement to intracellular pathways. This arrangement positions the complex to survey extracellular ligands and modulate immune signaling thresholds at the plasma membrane interface.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-P03979.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/P03979"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/P03979/entry","atlas":"/p/P03979"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}