{"uniprot":"Q3KPI0","gene":"CEACAM21","name":"Carcinoembryonic antigen-related cell adhesion molecule 21","organism":"Homo sapiens (Human)","status":"dark","length":293,"sequence":"MGPPSACPHRECIPWQGLLLTASLLTFWNAPTTAWLFIASAPFEVAEGENVHLSVVYLPENLYSYGWYKGKTVEPNQLIAAYVIDTHVRTPGPAYSGRETISPSGDLHFQNVTLEDTGYYNLQVTYRNSQIEQASHHLRVYESVAQPSIQASSTTVTEKGSVVLTCHTNNTGTSFQWIFNNQRLQVTKRMKLSWFNHVLTIDPIRQEDAGEYQCEVSNPVSSNRSDPLKLTVKSDDNTLGILIGVLVGSLLVAALVCFLLLRKTGRASDQSDFREQQPPASTPGHGPSDSSIS","function_summary":"A human cell-surface adhesion molecule that presents a tandem immunoglobulin architecture to mediate multivalent binding at the plasma membrane interface. By stabilizing adhesive contacts and capturing opsonized particles, it promotes phagocytic uptake and contributes to the maturation of dendritic cells. Its extracellular Ig-like modules organize cell–cell and cell–particle interactions that tune immune adhesion and uptake pathways at the cell surface.","plain_language":"CEACAM21 has barely been studied. The model's best guess: A human cell-surface adhesion molecule that presents a tandem immunoglobulin architecture to mediate multivalent binding at the plasma membrane interface. By stabilizing adhesive contacts and capturing opsonized particles, it promotes phagocytic uptake and contributes to the maturation of dendritic cells.","uniprot_summary":"May be involved in cell adhesion. Involved in maturation of dendritic cells (By similarity).","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0006909","label":"phagocytosis"}],"cellular_component":[{"id":"GO:0009986","label":"cell surface"}]},"interpro":[{"id":"IPR036179","name":"Immunoglobulin-like domain superfamily","type":"homologous_superfamily","start":36,"end":141},{"id":"IPR013783","name":"Immunoglobulin-like fold","type":"homologous_superfamily","start":39,"end":146},{"id":"IPR013783","name":"Immunoglobulin-like fold","type":"homologous_superfamily","start":147,"end":237},{"id":"IPR036179","name":"Immunoglobulin-like domain superfamily","type":"homologous_superfamily","start":151,"end":233},{"id":"IPR003599","name":"Immunoglobulin domain subtype","type":"domain","start":40,"end":141},{"id":"IPR013106","name":"Immunoglobulin V-set domain","type":"domain","start":40,"end":141},{"id":"IPR007110","name":"Immunoglobulin-like domain","type":"domain","start":147,"end":231},{"id":"IPR003599","name":"Immunoglobulin domain subtype","type":"domain","start":151,"end":233},{"id":"IPR003598","name":"Immunoglobulin subtype 2","type":"domain","start":157,"end":221},{"id":"IPR050831","name":"Carcinoembryonic antigen-related cell adhesion","type":"family","start":1,"end":234}],"reasoning":"I begin with the InterPro architecture. The N-terminal half contains a compact immunoglobulin V-set module: IPR013106 (Immunoglobulin V-set domain, residues 40–141) sits within broader immunoglobulin signatures IPR036179 (Immunoglobulin-like domain superfamily, residues 36–141) and IPR013783 (Immunoglobulin-like fold, residues 39–146), together with IPR003599 (Immunoglobulin domain subtype, residues 40–141). This arrangement defines a canonical V-set Ig domain that typically mediates high-affinity, calcium-independent adhesion and ligand recognition at the cell surface. The C-terminal half transitions into a second Ig-like region: IPR007110 (Immunoglobulin-like domain, residues 147–231) and IPR003599 (Immunoglobulin domain subtype, residues 151–233), further refined by IPR003598 (Immunoglobulin subtype 2, residues 157–221) and again encompassed by IPR036179 (Immunoglobulin-like domain superfamily, residues 151–233) and IPR013783 (Immunoglobulin-like fold, residues 147–237). The tandem IgV–IgL layout is characteristic of carcinoembryonic antigen-related adhesion molecules, captured by IPR050831 (Carcinoembryonic antigen-related cell adhesion family, residues 1–234). This two-module Ig scaffold causes avid, multivalent protein binding at the cell surface and is optimized for cell–cell and cell–particle interactions.\n\nFrom this architecture, the molecular function resolves as protein binding (GO:0005515). Ig-like domains in CEACAM-related families create adhesive interfaces and receptor–ligand contacts rather than catalysis; the V-set domain confers specificity and the C-terminal Ig-like domain stabilizes homotypic/heterotypic interactions. Such multivalent binding underlies both adhesion and opsonin-like recognition.\n\nThe biological process follows from how these Ig modules operate in immune and epithelial contexts. CEACAM-related adhesion molecules frequently bridge cells to opsonized targets and trigger uptake pathways. The tandem Ig arrangement supports avid capture of particles and phagocytic cup formation, aligning with phagocytosis (GO:0006909). The same adhesive and recognition properties explain roles in cell adhesion and in the maturation of dendritic cells, where surface receptor clustering and ligand presentation tune antigen-presenting functions.\n\nCellular localization is dictated by the extracellular Ig architecture and adhesion role. The absence of intracellular catalytic motifs and the presence of secreted/ECAM-like features point to a cell-surface exposure. This supports a cell surface assignment (GO:0009986), consistent with a secreted or membrane-associated adhesion molecule that operates at the plasma membrane interface.\n\nMechanistically, the protein likely functions as a cell-surface adhesion and recognition module that clusters at sites of cell–cell contact and cell–particle binding. By stabilizing adhesive junctions and presenting opsonized cargo, it promotes phagocytic uptake and influences dendritic cell maturation. I hypothesize that it forms homotypic/heterotypic complexes with other CEACAM family members and engages integrin-rich adhesion sites. Candidate partners include integrins (e.g., αvβ3/αvβ5) and cytoskeletal adaptors recruited downstream of CEACAM clustering. These assemblies would couple extracellular Ig-mediated adhesion to intracellular actin remodeling that drives phagocytosis and antigen-presenting cell maturation.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q3KPI0.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q3KPI0"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q3KPI0/entry","atlas":"/p/Q3KPI0"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}