{"uniprot":"B3GLJ2","gene":"PATE3","name":"Prostate and testis expressed protein 3","organism":"Homo sapiens (Human)","status":"dark","length":98,"sequence":"MNKHFLFLFLLYCLIVAVTSLQCITCHLRTRTDRCRRGFGVCTAQKGEACMLLRIYQRNTLQISYMVCQKFCRDMTFDLRNRTYVHTCCNYNYCNFKL","function_summary":"A secreted human extracellular regulator that uses a Ly-6/uPA receptor-like fold to bind and modulate acetylcholine receptor assemblies. By docking onto receptor ectodomains, it fine-tunes assembly efficiency and gating behavior, thereby shaping receptor-mediated signaling pathways at the cell surface. Its action is non-enzymatic and relies on high-affinity extracellular interactions that stabilize and adjust receptor function within local membrane microenvironments.","plain_language":"PATE3 has barely been studied. The model's best guess: A secreted human extracellular regulator that uses a Ly-6/uPA receptor-like fold to bind and modulate acetylcholine receptor assemblies. By docking onto receptor ectodomains, it fine-tunes assembly efficiency and gating behavior, thereby shaping receptor-mediated signaling pathways at the cell surface.","uniprot_summary":"May be involved in acetylcholine receptor-mediated signal transduction.","go_terms":{"molecular_function":[{"id":"GO:0030548","label":"acetylcholine receptor regulator activity"}],"biological_process":[{"id":"GO:0099601","label":"regulation of neurotransmitter receptor activity"}],"cellular_component":[{"id":"GO:0005615","label":"extracellular space"}]},"interpro":[{"id":"IPR016054","name":"Ly-6 antigen/uPA receptor-like","type":"domain","start":20,"end":96}],"reasoning":"I begin with the InterPro architecture: a single IPR016054 Ly-6 antigen/uPA receptor-like domain spanning residues 20–96. This LU/Ly6 domain is a cystine-rich, disulfide-stabilized module that folds into a three-fingered scaffold typical of LU-family proteins. Such LU modules are secreted or GPI-anchored extracellular regulators that bind and modulate receptor complexes at the cell surface. Their rigid, solvent-exposed loops and absence of catalytic motifs steer the protein toward non-enzymatic, affinity-based regulation of membrane receptors.\n\nThis LU architecture causally supports acetylcholine receptor regulator activity (GO:0030548). LU domains commonly tune ligand-gated ion channel assemblies by docking to extracellular loops of receptor subunits, thereby altering gating kinetics, assembly efficiency, and surface stability. The presence of a single, dominant LU domain and the lack of intracellular enzymatic signatures indicate that the primary molecular function is allosteric modulation rather than signal transduction or catalysis.\n\nFrom this molecular function, the biological role follows: regulation of neurotransmitter receptor activity (GO:0099601). By stabilizing or biasing acetylcholine receptor assemblies and tuning their responsiveness, the protein directly governs receptor-mediated signaling cascades. LU-mediated modulation of receptor complexes generalizes beyond cholinergic systems and provides a mechanistic basis for broader control of receptor pathways at epithelial and neuronal interfaces.\n\nThe LU fold is classically extracellular. LU-family proteins are secreted or tethered to the exterior leaflet of the plasma membrane, and here the architecture and functional logic point to a soluble extracellular regulator. This supports localization to the extracellular space (GO:0005615), consistent with a secreted protein that operates by binding receptor ectodomains rather than traversing membranes or engaging cytosolic machinery.\n\nMechanistically, the LU domain’s three-fingered surface likely docks onto acetylcholine receptor ectodomains to modulate assembly and gating. I hypothesize that it transiently associates with nicotinic acetylcholine receptor subunits to promote proper folding/assembly and to fine-tune channel open probability and desensitization. Additional transient contacts with extracellular matrix or other LU-family proteins could scaffold these interactions and concentrate the regulator near receptor-rich membrane microdomains.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-B3GLJ2.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/B3GLJ2"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/B3GLJ2/entry","atlas":"/p/B3GLJ2"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}