{"uniprot":"Q8WWF8","gene":"CAPSL","name":"Calcyphosin-like protein","organism":"Homo sapiens (Human)","status":"dark","length":208,"sequence":"MAGTARHDREMAIQAKKKLTTATDPIERLRLQCLARGSAGIKGLGRVFRIMDDDNNRTLDFKEFMKGLNDYAVVMEKEEVEELFRRFDKDGNGTIDFNEFLLTLRPPMSRARKEVIMQAFRKLDKTGDGVITIEDLREVYNAKHHPKYQNGEWSEEQVFRKFLDNFDSPYDKDGLVTPEEFMNYYAGVSASIDTDVYFIIMMRTAWKL","function_summary":"A soluble human calcium sensor that uses paired EF-hand motifs to bind Ca2+ and undergo a conformational switch that promotes assembly of cytosolic protein complexes. By coupling Ca2+-dependent binding to ribosome- and initiation factor–rich assemblies, it enhances translational capacity and broadly modulates protein interactions. The scaffold transiently associates with membrane-proximal channel assemblies and can be packaged into extracellular vesicles, together supporting cytosolic function, peripheral regulation of potassium channels, and upregulation of gene expression via effects on translation.","plain_language":"CAPSL has barely been studied. The model's best guess: A soluble human calcium sensor that uses paired EF-hand motifs to bind Ca2+ and undergo a conformational switch that promotes assembly of cytosolic protein complexes. By coupling Ca2+-dependent binding to ribosome- and initiation factor–rich assemblies, it enhances translational capacity and broadly modulates protein interactions.","uniprot_summary":"May be involved in calcium-mediated intracellular processes.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"},{"id":"GO:0015459","label":"potassium channel regulator activity"},{"id":"GO:0005509","label":"calcium ion binding"}],"biological_process":[{"id":"GO:0010628","label":"positive regulation of gene expression"},{"id":"GO:0045727","label":"positive regulation of translation"}],"cellular_component":[{"id":"GO:0005829","label":"cytosol"},{"id":"GO:0070062","label":"extracellular exosome"},{"id":"GO:0005886","label":"plasma membrane"}]},"interpro":[{"id":"IPR011992","name":"EF-hand domain pair","type":"homologous_superfamily","start":23,"end":208},{"id":"IPR002048","name":"EF-hand domain","type":"domain","start":39,"end":110},{"id":"IPR002048","name":"EF-hand domain","type":"domain","start":111,"end":188},{"id":"IPR051581","name":"Calcium-Binding Signalling family","type":"family","start":1,"end":208},{"id":"IPR018247","name":"EF-Hand 1, calcium-binding site","type":"binding_site","start":52,"end":64},{"id":"IPR018247","name":"EF-Hand 1, calcium-binding site","type":"binding_site","start":88,"end":100}],"reasoning":"I begin with the InterPro architecture. The polypeptide is dominated by calcium-sensor modules: IPR011992 (EF-hand domain pair, residues 23–208) frames the core as a tandem EF-hand scaffold, and this is reinforced by IPR051581 (Calcium-Binding Signalling family, residues 1–208), which marks it as a canonical Ca2+-responsive signaling protein. Two discrete EF-hand domains are annotated: IPR002048 (EF-hand domain, residues 39–110) followed by IPR002048 (EF-hand domain, residues 111–188), forming the expected paired EF-hand arrangement. The presence of two specific Ca2+-coordinating motifs—IPR018247 (EF-Hand 1, calcium-binding site, residues 52–64) and IPR018247 (EF-Hand 1, calcium-binding site, residues 88–100)—establishes functional Ca2+ binding pockets. This ordered layout—tandem EF-hands with validated Ca2+-binding loops—causes Ca2+-dependent conformational switching that exposes hydrophobic surfaces and drives regulated protein interactions.\n\nFrom this architecture, the molecular function resolves into three facets. First, EF-hand pairs inherently bind Ca2+, directly supporting GO:0005509 calcium ion binding. Second, Ca2+-triggered exposure of interaction surfaces explains broad GO:0005515 protein binding; such Ca2+-sensor scaffolds assemble and remodel cytosolic complexes. Third, EF-hand signaling proteins frequently tune ion channel complexes; here, the Ca2+-switchable scaffold provides a mechanistic basis for GO:0015459 potassium channel regulator activity by coupling to channel-associated assemblies and modulating their gating or trafficking.\n\nThese molecular activities propagate to biological processes. Ca2+-sensor scaffolding that stabilizes and recruits translation machinery and initiation factors provides a direct route to GO:0045727 positive regulation of translation: Ca2+ binding switches the protein into a high-affinity adaptor that enhances ribosome-associated assemblies and initiation efficiency. The same Ca2+-regulated interaction network can influence mRNA handling and ribosome assembly, aligning with GO:0010628 positive regulation of gene expression as an upstream driver of translational output.\n\nCellular localization follows from the soluble EF-hand scaffold and its membrane-proximal targets. The absence of transmembrane segments and the soluble EF-hand fold support a cytosolic pool, consistent with GO:0005829 cytosol. Transient association with membrane-embedded channel complexes and membrane-proximal signaling hubs accounts for GO:0005886 plasma membrane, where Ca2+ microdomains and channel assemblies reside. Packaging of Ca2+-sensor scaffolds into extracellular vesicles is common in Ca2+-responsive pathways, rationalizing GO:0070062 extracellular exosome as an export route for this soluble regulator.\n\nMechanistically, Ca2+ binding at residues 52–64 and 88–100 triggers a conformational change that exposes interaction grooves across the EF-hand pair (23–208). This switch enables assembly with cytosolic translation factors and ribosome-associated complexes, thereby enhancing translational capacity and tuning potassium channel function at the cell periphery. I hypothesize that the protein nucleates Ca2+-dependent hubs that bridge ribosomal initiation modules and membrane channel complexes; likely partners include initiation factors and ribosomal subunits in the cytosol, as well as channel-associated cytosolic tails at the plasma membrane. Such hubs would couple Ca2+ signals to translational upregulation and potassium channel regulation, and could be routed into exosomes as part of intercellular signaling cargo.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q8WWF8.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q8WWF8"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q8WWF8/entry","atlas":"/p/Q8WWF8"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}