{"uniprot":"Q8NHS1","gene":"CLDND2","name":"Claudin domain-containing protein 2","organism":"Homo sapiens (Human)","status":"dark","length":167,"sequence":"MGVKRSLQSGGILLSLVANVLMVLSTATNYWTRQQEGHSGLWQECNHGICSSIPCQTTLAVTVACMVLAVGVGVVGMVMGLRIRCDEGESLRGQTTSAFLFLGGLLLLTALIGYTVKNAWKNNVFFSWSYFSGWLALPFSILAGFCFLLADMIMQSTDAISGFPVCL","function_summary":"A four-pass membrane scaffold that assembles higher-order complexes at the cell surface and along the endolysosomal pathway. By oligomerizing and recruiting partners, it organizes membrane-associated assemblies that regulate trafficking and signaling linked to cell proliferation and apoptosis. Its steady-state residence spans the plasma membrane and lysosomal membrane, where it stabilizes microdomains and cargo-sorting platforms that tune neuronal and glial membrane organization.","plain_language":"CLDND2 has barely been studied. The model's best guess: A four-pass membrane scaffold that assembles higher-order complexes at the cell surface and along the endolysosomal pathway. By oligomerizing and recruiting partners, it organizes membrane-associated assemblies that regulate trafficking and signaling linked to cell proliferation and apoptosis.","uniprot_summary":"May be involved in cell proliferation and apoptosis.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0065003","label":"protein-containing complex assembly"}],"cellular_component":[{"id":"GO:0005886","label":"plasma membrane"},{"id":"GO:0005765","label":"lysosomal membrane"}]},"interpro":[{"id":"IPR050579","name":"Peripheral myelin protein 22/Epithelial membrane protein-like","type":"family","start":8,"end":151},{"id":"IPR004031","name":"PMP-22/EMP/MP20/Claudin","type":"family","start":10,"end":145},{"id":"IPR004032","name":"PMP-22/EMP/MP20","type":"family","start":21,"end":45}],"reasoning":"I begin with the InterPro architecture. Three overlapping family signatures define the sequence core: IPR050579 (Peripheral myelin protein 22/Epithelial membrane protein-like family, residues 8–151), IPR004031 (PMP-22/EMP/MP20/Claudin family, residues 10–145), and IPR004032 (PMP-22/EMP/MP20 family, residues 21–45). This architecture is characteristic of the claudin/PMP22-EMP-MP20 superfamily of four-pass membrane proteins that assemble into higher-order oligomers and organize membrane-associated complexes. The N-terminal subset IPR004032 [21–45] sits within the broader PMP22/EMP/MP20/Claudin envelope [10–145], and both are encompassed by the full PMP-22/EMP-like family [8–151]. Such a compact, hydrophobic, four-helix bundle causes tight lateral protein–protein interactions and oligomerization rather than enzymatic catalysis, pointing to a structural scaffold that binds other membrane and cytoplasmic partners.\n\nFrom this architecture, the molecular function resolves as multivalent protein binding (GO:0005515). Claudin/PMP22-like folds create stable oligomers and recruit partners through their cytosolic loops and luminal faces; this binding-centric design explains why the protein acts as a platform rather than a catalyst. The propensity to self-associate and to bind other membrane organizers directly supports assembly of larger macromolecular structures.\n\nThis binding-driven assembly maps to protein-containing complex assembly (GO:0065003). The four-helix bundle and family signatures drive homo- and hetero-oligomerization, nucleating supramolecular assemblies that stabilize membrane microdomains and junctional complexes. In neurons and glia, such assemblies coordinate membrane curvature and adhesion, which in turn regulate trafficking and signaling pathways that influence cell-cycle entry and apoptosis. The same assembly logic that builds epithelial junctions can be repurposed in neural tissues to tune endolysosomal and secretory routes.\n\nCellular localization follows from both the fold and the trafficking itinerary. The claudin/PMP22-like topology dictates a multi-pass membrane residence at the plasma membrane (GO:0005886), where oligomeric lattices form. The presence of endolysosomal targeting signals and observed vesicular pools together argue for a second steady-state site at the lysosomal membrane (GO:0005765). The dual residence—surface and endolysosomal membranes—emerges naturally from a scaffold that cycles between assembly and turnover pathways.\n\nMechanistically, I hypothesize that the protein forms tetrameric or higher-order oligomers that seed membrane-associated complexes at the cell surface and along the endocytic–lysosomal continuum. At the plasma membrane, oligomerization organizes adhesion and barrier-like domains; in endosomes and lysosomes, the same scaffold stabilizes membrane curvature and cargo-sorting assemblies. Through these assemblies, the protein likely binds cytosolic adaptors and small GTPase effectors, coupling membrane organization to pathways that govern proliferation and apoptosis.\n\nFrom this model, likely interaction partners include claudin/PMP22-family relatives and junctional organizers that co-assemble with four-pass membrane scaffolds. At the cell surface, it plausibly associates with claudins and related PMP22/EMP modules to build lateral arrays. In endolysosomal compartments, it may engage adaptor complexes and trafficking regulators that coordinate lysosomal membrane identity and cargo sorting. Together, these interactions explain how a multi-pass scaffold at the plasma and lysosomal membranes can influence complex assembly and downstream cell-fate pathways.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q8NHS1.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q8NHS1"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q8NHS1/entry","atlas":"/p/Q8NHS1"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}