{"uniprot":"P02814","gene":"SMR3B","name":"Submaxillary gland androgen-regulated protein 3B","organism":"Homo sapiens (Human)","status":"dark","length":79,"sequence":"MKSLTWILGLWALAACFTPGESQRGPRGPYPPGPLAPPQPFGPGFVPPPPPPPYGPGRIPPPPPAPYGPGIFPPPPPQP","function_summary":"A small secreted human protein that functions as an extracellular binder and modulator of cell-surface signaling. By associating with exosomes and the pericellular environment, it promotes cell proliferation and shapes downstream transcriptional responses indirectly through receptor- and adhesion-dependent pathways. Its extracellular deployment positions it to tune oxidative and metal-ion–responsive signaling circuits, acting as a non-enzymatic scaffold that organizes local signaling assemblies to influence growth and stress-adaptive programs.","plain_language":"SMR3B has barely been studied. The model's best guess: A small secreted human protein that functions as an extracellular binder and modulator of cell-surface signaling. By associating with exosomes and the pericellular environment, it promotes cell proliferation and shapes downstream transcriptional responses indirectly through receptor- and adhesion-dependent pathways.","uniprot_summary":"Androgen-regulated secreted protein.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0008284","label":"positive regulation of cell population proliferation"},{"id":"GO:0042542","label":"response to hydrogen peroxide"},{"id":"GO:0006355","label":"regulation of DNA-templated transcription"},{"id":"GO:0010039","label":"response to iron ion"}],"cellular_component":[{"id":"GO:0070062","label":"extracellular exosome"}]},"interpro":[{"id":"IPR026288","name":"Submaxillary gland androgen-regulated protein like","type":"family","start":1,"end":79}],"reasoning":"I begin with the InterPro architecture: IPR026288 (Submaxillary gland androgen-regulated protein like, family) spans residues 1–79 and covers the entire polypeptide. A single, full-length family signature without catalytic subdomains indicates a small, secreted, non-enzymatic protein that operates through binding-mediated mechanisms rather than through enzymatic chemistry. Such family profiles commonly encode extracellular modulators that act via protein–protein interactions, which causally supports a binding-centric molecular function.\n\nFrom this architecture, the most parsimonious molecular function is protein binding (GO:0005515). A compact, secreted binder can scaffold or chaperone interactions in the extracellular milieu and on cell surfaces. The absence of transmembrane or intracellular signaling domains argues that any signaling influence is exerted outside the cell—by engaging receptors, co-receptors, or matrix components.\n\nThis binding-driven extracellular role explains several coupled biological processes. First, positive regulation of cell population proliferation (GO:0008284) follows naturally if the protein stabilizes or transmits mitogenic cues at the cell surface, for example by clustering growth factor receptors or enhancing ligand availability. Second, response to hydrogen peroxide (GO:0042542) and response to iron ion (GO:0010039) are consistent with extracellular redox and metal-ion signaling niches; secreted binders often buffer or present cues that tune oxidative stress pathways and iron-dependent signaling cascades. Third, regulation of DNA-templated transcription (GO:0006355) is best rationalized indirectly: extracellular binding events that potentiate receptor pathways ultimately alter nuclear transcriptional programs downstream of kinase cascades.\n\nCellular localization follows directly from the domain architecture and secretion signal logic. A fully secreted, single-domain binder aligns with extracellular deployment and is frequently packaged into extracellular vesicles; this supports assignment to the extracellular space and specifically to extracellular exosomes (GO:0070062). Exosome association provides a mechanistic conduit for delivering the protein between cells and for concentrating it near membrane receptors.\n\nPutting these elements together yields a mechanistic hypothesis: the protein is a secreted, exosome-enriched binder that modulates cell-surface signaling to promote proliferation and tune stress-responsive transcriptional outputs. It likely associates with heparan sulfate proteoglycans and cell-adhesion complexes to nucleate signaling microdomains. By transiently clustering receptor tyrosine kinases and integrins, it enhances downstream pathways that culminate in nuclear transcriptional regulation while buffering extracellular redox and metal-ion cues.\n\nFrom this model, plausible interaction partners include cell-surface receptor systems and vesicle biogenesis machinery that together explain proliferation, oxidative/iron responses, and exosome-mediated extracellular transport.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-P02814.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/P02814"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/P02814/entry","atlas":"/p/P02814"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}