IGLC2

Model summary

An extracellular constant-region module of a human immune receptor that uses an immunoglobulin C1-set fold to mediate multivalent protein binding and stabilize receptor assemblies that drive lymphocyte signaling. By organizing and maintaining the architecture of a cell-surface receptor complex, it supports T-cell activation and broader immune responses. It operates at the cell surface and is also released or packaged into circulating vesicles, consistent with its presence in exosomes and blood microparticles.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture, which is uniformly immunoglobulin-like across the entire polypeptide.

   IPR013783 (Immunoglobulin-like fold, residues 2–106) and IPR036179 (Immunoglobulin-like domain superfamily, residues 3–100) define a beta-sandwich framework typical of extracellular recognition modules. Within this scaffold, IPR007110 (Immunoglobulin-like domain, residues 7–101) and IPR003597 (Immunoglobulin C1-set, residues 9–97) specify a constant-region Ig C1-set module that characteristically mediates protein–protein interactions rather than catalysis. The presence of IPR050160 (Major Histocompatibility Complex/Immunoglobulin family, residues 4–102) ties this domain to immune-system modules that assemble multimeric complexes, and IPR003006 (Immunoglobulin/major histocompatibility complex conserved site, residues 85–91) marks a conserved surface patch that often stabilizes higher-order assemblies. The ordered, single Ig C1-set domain spanning nearly the full length of the sequence dictates a non-enzymatic, adhesive role: it creates a rigid extracellular platform optimized for binding other immune components.

2. 02

   This Ig C1-set architecture causes a molecular function centered on multivalent protein binding (GO:0005515).

   The constant-region fold lacks catalytic motifs but presents conserved grooves and loops that capture partner proteins and membrane anchors. In the immune system, such binding capacity is used to nucleate and stabilize assemblies that transmit signals rather than perform chemistry.

3. 03

   From this binding-centric mechanism, the biological process follows.

   The constant-region Ig module is specialized for assembling and stabilizing receptor complexes that drive lymphocyte responses. By forming a stable extracellular scaffold that couples antigen recognition to receptor clustering, it promotes the broader immune response (GO:0006955) and specifically supports T cell activation involved in immune response (GO:0002286). The Ig constant domain’s geometry and conserved site enable avidity-driven clustering of receptor complexes, which is the proximate cause of downstream signaling that culminates in T-cell effector functions.

4. 04

   Cellular context is inferred from the domain’s extracellular nature and the known life cycle of immune receptor complexes.

   The Ig C1-set fold is secreted or displayed extracellularly, consistent with localization to the plasma membrane neighborhood via associated membrane subunits and with subsequent release into extracellular vesicles. This supports residence at the plasma membrane (GO:0005886), and association with extracellular exosomes (GO:0070062) and blood microparticles (GO:0072562). The extracellular Ig module can be shed or packaged into vesicles during immune activation, explaining its presence in circulating vesicular compartments.

5. 05

   Mechanistically, the protein operates as an extracellular constant-region module that stabilizes and organizes a receptor complex at the cell surface.

   By binding partner chains and accessory membrane proteins, it enforces the geometry required for high-avidity antigen receptor assemblies. This architecture predicts interactions with membrane anchors and co-receptor modules that together tune T-cell signaling thresholds. I therefore hypothesize that it associates with a membrane-anchored receptor subunit and accessory chains to form a stable signaling platform, and that it is trafficked into vesicles during immune activation, accounting for its detection in exosomes and microparticles.