{"uniprot":"A8MVA2","gene":"KRTAP9-6","name":"Keratin-associated protein 9-6","organism":"Homo sapiens (Human)","status":"dark","length":160,"sequence":"MTHCCSPGCQPTCCRTTCCRTTCWQPTIVTTCSSTPCCQPSCCVSSCCQPYCHPTCCQNTCCRTTCCQPTCVTSCCQPSCCSTPCYQPICCGSSCCGQTSCGSSCGQSSSCAPVYCRRTCYHPTTVCLPGCLNQSCGSSCCQPCYCPACCVSSCCQHSCC","function_summary":"A small, soluble matrix component that binds and stabilizes keratin filament networks during hair fiber assembly. It operates in the cytosolic phase of hair-forming cells, where it associates with keratin intermediate filaments and other matrix proteins to promote dense cross-linking and filament bundling. Through multivalent binding and disulfide-mediated stabilization, it supports the cyclical assembly and maintenance of the hair shaft and influences long-term fiber integrity over the organism’s lifespan.","plain_language":"KRTAP9-6 has almost never been studied. The model thinks it is one of the small 'glue' proteins of hair: it sticks to keratin fibres and links them together with sulfur bridges, which makes the hair strand stiff and strong. That fits the family it belongs to, but nobody has tested it in the lab yet.","uniprot_summary":"In the hair cortex, hair keratin intermediate filaments are embedded in an interfilamentous matrix, consisting of hair keratin-associated proteins (KRTAP), which are essential for the formation of a rigid and resistant hair shaft through their extensive disulfide bond cross-linking.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0007568","label":"aging"},{"id":"GO:0042633","label":"hair cycle"}],"cellular_component":[{"id":"GO:0005829","label":"cytosol"}]},"interpro":[{"id":"IPR002494","name":"Keratin-associated protein","type":"family","start":80,"end":124}],"reasoning":"I begin with the InterPro architecture: a single family signature, IPR002494 (Keratin-associated protein family) spanning residues 80–124, positioned toward the C-terminus. This solitary family domain, without catalytic motifs or transmembrane segments, defines a small, non-enzymatic matrix protein specialized for hair fiber assembly. Keratin-associated protein families are characterized by high glycine/tyrosine and cysteine content that drives dense cross-linking to keratin intermediate filaments. The C-terminal placement of the family signature often marks the core binding/assembly module that nucleates and stabilizes higher-order complexes.\n\nThis architecture dictates a molecular function centered on multivalent protein binding rather than catalysis. The keratin-associated module provides a scaffold that binds keratin intermediate filaments and other matrix proteins through repetitive low-complexity segments and disulfide-mediated interfaces, which directly supports GO:0005515 protein binding as the operative molecular function. The absence of enzymatic domains and the presence of a keratin-associated family signature causally channel the protein’s role toward structural assembly and stabilization of filament networks.\n\nFrom this binding-driven function, the biological process follows. By fastening and rigidifying keratin intermediate filaments, the protein contributes to the cyclical assembly and maintenance of the hair shaft. Such assembly and stabilization are integral to the hair cycle (GO:0042633 hair cycle), where phases of differentiation and matrix deposition determine shaft formation and renewal. Over an organism’s lifespan, cumulative cross-linking and matrix maturation influence hair fiber integrity and turnover, aligning with organismal aging pathways (GO:0007568 aging) through effects on cuticle/cortex hardening and resilience.\n\nCellular localization is inferred from the soluble, assembly-first nature of keratin-associated proteins. Prior to incorporation into the insoluble hair shaft, these matrix proteins are synthesized and operate in the cytosolic phase of keratinocyte differentiation, consistent with GO:0005829 cytosol. Their soluble pre-assembly state precedes membrane exclusion and terminal differentiation, when extensive cross-linking renders the final fiber insoluble.\n\nMechanistically, the protein likely binds keratin intermediate filaments via repetitive, cysteine-rich segments that form intermolecular disulfide bonds, thereby stiffening and waterproofing the hair shaft matrix. This suggests transient interactions with keratin heteropolymers and accessory matrix proteins during cytosolic assembly. I hypothesize that it associates with type I/II hair keratins and other keratin-associated proteins to nucleate filament bundling; redox and transglutaminase pathways may finalize cross-linking post-assembly. Together, these interactions produce a rigid, mechanically resistant composite that cycles with hair growth and maintenance.","category":"dark","control_evaluation":null,"validation_plan":{"hypothesis":"KRTAP9-6 is a cysteine-rich hair keratin-associated protein, expressed in the hair shaft cortex, that binds hair keratin filaments and cross-links them through disulfide bonds.","experiments":[{"rank":1,"name":"Expression in the hair follicle (RNA in situ hybridisation / IHC)","tests":"Is it made where the model says (hair cortex)?","method":"RNAscope probe against KRTAP9-6 on human scalp skin sections (FFPE); if an antibody validates, IHC on serial sections. Compare with a known cortex KRTAP and with interfollicular skin.","positive":"Signal restricted to the keratogenous zone / cortex of anagen hair follicles, absent from epidermis.","controls":"Positive (PPIB) and negative (dapB) RNAscope probes; a known hair-cortex KRTAP; sense probe or peptide-blocked antibody.","difficulty":"Medium","time":"1–2 weeks","time_days_min":7,"time_days_max":14,"cost_eur_min":1500,"cost_eur_max":3500},{"rank":2,"name":"Co-immunoprecipitation / pull-down with hair keratins","tests":"Does it bind hair keratins?","method":"Co-express tagged KRTAP9-6 (FLAG or HA) with type I/II hair keratins (e.g. KRT31/KRT85) in HEK293 cells; IP the tag and blot for keratins. Alternatively, GST-pulldown from hair-follicle lysate followed by mass spectrometry.","positive":"Hair keratins specifically co-purify with KRTAP9-6, well above tag-only and unrelated-bait controls.","controls":"Tag-only vector; unrelated cysteine-rich protein; reducing vs non-reducing conditions to test disulfide links.","difficulty":"Medium","time":"2–4 weeks","time_days_min":14,"time_days_max":28,"cost_eur_min":1000,"cost_eur_max":3000},{"rank":3,"name":"Recombinant protein + keratin filament binding assay","tests":"Direct binding and cross-linking of filaments","method":"Express and refold KRTAP9-6 (very cysteine-rich: express as a fusion, e.g. SUMO/MBP, refold under redox buffer). Assemble KRT31/KRT85 filaments in vitro, add KRTAP9-6, then co-sedimentation and negative-stain EM; compare under oxidising vs reducing conditions.","positive":"KRTAP9-6 co-sediments with filaments and promotes bundling, with more cross-linking under oxidising conditions.","controls":"Filaments alone; KRTAP9-6 alone; fusion tag alone; DTT-reduced sample; a non-binding control protein.","difficulty":"Hard","time":"1–3 months","time_days_min":30,"time_days_max":90,"cost_eur_min":3000,"cost_eur_max":8000}],"materials":["Human scalp tissue (biobank / surgical leftovers, with ethics approval)","RNAscope probe (custom design likely needed; KRTAP genes are highly similar, check specificity)","Antibody: few or none validated for KRTAP9-6 specifically; may need a custom peptide antibody","Plasmids: KRTAP9-6 ORF clone, hair keratins KRT31 / KRT85","HEK293 cells; bacterial expression system with refolding"],"note":"Main risk: KRTAP family members are very similar, so probes and antibodies may cross-react. Verify specificity first.","cost_note":"Estimated reagent/consumables cost in EUR; excludes salaries and equipment.","disclaimer":"Suggested protocol generated by AI. Review by a qualified scientist before use.","generated_by":"Hand-written for prototype (template for automated generation)"},"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-A8MVA2.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/A8MVA2"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/A8MVA2/entry","atlas":"/p/A8MVA2"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}