{"uniprot":"A6NM10","gene":"AQP12B","name":"Aquaporin-12B","organism":"Homo sapiens (Human)","status":"dark","length":295,"sequence":"MAGLNVSLSFFFATFTLCEAARRASKALLPVGAYEVFAREAMRTLVELGPWAGDFGPDLLLTLLFLLFLAHGVTLDGASANPTVSLQEFLMAEESLPGTLLKLAAQGLGMQAACTLTRLCWAWELSDLHLLQSLMAQSCSSALRTSVPHGALVEAACAFCFHLTLLHLRHSPPAYSGPAVALLVTVTAYTAGPFTSAFFNPALAASVTFACSGHTLLEYVQVYWLGPLTGMVLAVLLHQGRLPHLFQRNLFYGQKNKYRAPRGKPAPASGDTQTPAKGSSVREPGRSGVEGPHSS","function_summary":"An intracellular aquaporin-like tetrameric assembly that resides predominantly in the cytosol and uses a channel-derived scaffold to organize protein complexes rather than mediating bulk water flow. By forming stable homotetramers and engaging partner proteins, it modulates intracellular water/ion/osmolyte handling and assembles adhesion-regulatory machinery. This architecture supports enhanced cell–cell interface stability and macromolecular exchange, consistent with a role in intracellular processes that influence adhesion and intercellular transport.","plain_language":"AQP12B has barely been studied. The model's best guess: An intracellular aquaporin-like tetrameric assembly that resides predominantly in the cytosol and uses a channel-derived scaffold to organize protein complexes rather than mediating bulk water flow. By forming stable homotetramers and engaging partner proteins, it modulates intracellular water/ion/osmolyte handling and assembles adhesion-regulatory machinery.","uniprot_summary":"Intracellular aquaporin that most likely functions in non-water transport processes.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0010496","label":"intercellular transport"},{"id":"GO:0045785","label":"positive regulation of cell adhesion"},{"id":"GO:0051289","label":"protein homotetramerization"}],"cellular_component":[{"id":"GO:0005829","label":"cytosol"}]},"interpro":[{"id":"IPR023271","name":"Aquaporin-like","type":"homologous_superfamily","start":8,"end":256},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":1,"end":10},{"id":"IPR051883","name":"Aquaporin-11/12 water channel","type":"family","start":1,"end":268},{"id":"IPR016697","name":"Aquaporin 11/12","type":"family","start":2,"end":264},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":18,"end":28},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":32,"end":41},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":42,"end":55},{"id":"IPR000425","name":"Major intrinsic protein","type":"family","start":61,"end":241},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":87,"end":99},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":114,"end":127},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":131,"end":140},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":141,"end":150},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":168,"end":178},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":207,"end":219},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":238,"end":250},{"id":"IPR023265","name":"Aquaporin 12","type":"family","start":251,"end":264}],"reasoning":"I begin with the InterPro architecture. The core scaffold is IPR000425 (Major intrinsic protein family, residues 61–241), embedded within IPR023271 (Aquaporin-like homologous superfamily, residues 8–256). This aquaporin/MIP fold forms a six-helix, hourglass-shaped channel that typically assembles as homotetramers. Multiple aquaporin-11/12 family signatures—IPR016697 (Aquaporin 11/12 family, residues 2–264), IPR051883 (Aquaporin-11/12 water channel family, residues 1–268), and IPR023265 (Aquaporin 12 family, residues 1–10, 18–28, 32–41, 42–55)—span nearly the full length, specifying the AQP11/12 clade that has diverged from classical water channels. The dense run of AQP12-specific family hits at precise positions (IPR023265 entries at 87–99, 114–127, 131–140, 141–150, 168–178, 207–219, 238–250, 251–264) indicates conserved motifs that tune gating and oligomerization rather than bulk water transport. This architecture causally enforces homotetramerization (GO:0051289 protein homotetramerization) and creates a platform for multivalent contacts, supporting GO:0005515 protein binding as a basal molecular function.\n\nFrom this aquaporin-like scaffold, I infer process-level roles. The AQP11/12 clade is known for intracellular localization and assembly control rather than classical osmotic transport. The tetrameric assembly and cytosolic residence together enable regulation of adhesion machinery and membrane-proximal complexes. By stabilizing and organizing adhesion-modulatory assemblies, the channel-like core can positively regulate cell adhesion (GO:0045785), and by shaping cytosol–membrane interfaces it facilitates intercellular transport (GO:0010496) of macromolecular cargoes and signals. The aquaporin-like fold provides a conduit-like cavity and oligomeric symmetry that favor scaffolded interactions over solute permeation, aligning with a role in intracellular water/ion/osmolyte handling that indirectly governs adhesion and exchange.\n\nCellular location follows from both the fold and the annotations. The absence of secretion signals and the aquaporin-11/12 family’s known intracellular specialization point to a soluble pool in the cytosol (GO:0005829 cytosol), consistent with a cytoplasmic localization. A cytosolic tetramer can transiently dock to membranes and cytoskeletal hubs, explaining how it coordinates adhesion and intercellular exchange without requiring a classical plasma-membrane channel context.\n\nMechanistically, I hypothesize that the aquaporin-like tetramer forms a cytosolic assembly hub that binds partner proteins and organizes adhesion-regulatory pathways. Likely partners include cytoskeletal and trafficking adaptors that couple to membrane-proximal complexes; transient association with membrane trafficking modules and adhesion regulators would allow the tetramer to tune intracellular osmotic balance and cargo routing, thereby enhancing cell–cell interface stability and exchange dynamics.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-A6NM10.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/A6NM10"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/A6NM10/entry","atlas":"/p/A6NM10"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}