Predicted high-sulfur (B2-type) keratin-associated protein (KAP/KRTAP) of the giant panda. The protein is short (419 aa) and built almost entirely from cysteine-rich pentapeptide-like repeats (e.g. CCKPVCCTPVCC), the diagnostic sequence signature of trichocyte hard-keratin matrix proteins, and carries the Pfam high-sulfur B2 keratin domain (PF13885, Keratin_B2_2) and the InterPro keratin-associated protein signature (IPR002494). Keratin-associated proteins are the structural matrix in which keratin intermediate filaments are embedded in hard (trichocyte) keratins such as hair, fur, claw, horn and hoof; the high-sulfur, cysteine-rich members cross-link adjacent keratin intermediate filaments through inter- and intramolecular disulfide bonds, organizing them into macrofibrils and giving the keratinized structure its mechanical rigidity, hardness and toughness. The protein is uncharacterized at the protein level and all functional inference is by family/domain homology; it most plausibly contributes to pelage (fur) and/or claw hard-keratin structure in the giant panda.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0045095 keratin filament | IEA GO_REF:0000002 | ACCEPT | Summary: ACCEPT. Keratin-associated proteins are the matrix that surrounds and cross-links keratin intermediate filaments, so the keratin-filament cellular-component term is the standard, well-supported localization for this family. The InterPro IPR002494 (KAP) -> keratin filament mapping is the same mapping that places human KRTAPs at the keratin filament. Reason: The protein is a high-sulfur (B2) keratin-associated protein (Pfam PF13885, InterPro IPR002494) whose biological role is structural cross-linking of keratin intermediate filaments into the hard-keratin matrix [PMID:29797269]. Keratin filament is the appropriate, conventional cellular-component term for KAPs (cross-checked against human KRTAP4-3, UniProtKB:Q9BYR4, which carries the identical InterPro keratin-filament annotation). This is the most informative existing annotation and reflects the core localization, though no panda-specific experimental data exist. Supporting Evidence: file:AILME/A0A7N5KEZ3_AILME/A0A7N5KEZ3_AILME-uniprot.txt GO; GO:0045095; C:keratin filament; IEA:InterPro. PMID:29797269 keratin intermediate filaments (IF) of diameter 7.5 nm are embedded in a matrix formed from at least 89 different types of keratin-associated proteins (KAPs) |
| GO:0005829 cytosol | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: MARK_AS_OVER_ANNOTATED. A generic, low-information localization that ARBA assigns broadly across keratin-associated proteins (human KRTAPs carry the same ARBA cytosol annotation, additionally given TAS by Reactome). It is not wrong enough to remove, but it does not represent the core function or the informative localization of a structural hard-keratin matrix protein. Reason: Biologically the relevant location of a KAP is the cross-linked keratin matrix of the cornified hair/claw, captured by the keratin-filament term, not free cytosol. The cytosol annotation is a broad ARBA rule-based assignment (GO_REF:0000117) seen across the KRTAP family rather than a gene-specific finding, so it is a generic over-annotation rather than an informative, gene-specific localization. Supporting Evidence: file:AILME/A0A7N5KEZ3_AILME/A0A7N5KEZ3_AILME-uniprot.txt GO; GO:0005829; C:cytosol; IEA:UniProtKB-ARBA. |
| GO:0005198 structural molecule activity | ISS PMID:29797269 Trichocyte Keratin-Associated Proteins (KAPs). | NEW | Summary: NEW. Proposed molecular function for this protein as a structural high-sulfur keratin-associated (matrix) protein. KAPs have no enzymatic activity; their function is structural - cross-linking keratin intermediate filaments into the hard-keratin matrix - so structural molecule activity is the appropriate (and only defensible) molecular-function term. Reason: Inferred by family/domain homology (Pfam PF13885 high-sulfur B2 keratin, InterPro IPR002494 KAP, cysteine-pentapeptide repeats). KAPs are matrix structural proteins that crosslink keratin intermediate filaments via disulfide bonds [PMID:29797269; PMID:12895003]; structural molecule activity captures this non-catalytic role. No panda-specific experimental evidence exists, hence ISS; note GO does not currently assert an MF on human KRTAPs, so this is a proposed, homology-based addition. The ISS basis (supporting_entities) is the defining KAP domain signature InterPro:IPR002494 together with a characterized human high-sulfur KAP family member, UniProtKB:Q9BYR4 (KRTAP4-3); note Q9BYR4 is a paralogous family exemplar rather than a strict 1:1 ortholog, and the structural role is established for the family as a whole. Supporting Evidence: file:AILME/A0A7N5KEZ3_AILME/A0A7N5KEZ3_AILME-uniprot.txt Pfam; PF13885; Keratin_B2_2; 1. PMID:29797269 keratin intermediate filaments (IF) of diameter 7.5 nm are embedded in a matrix formed from at least 89 different types of keratin-associated proteins (KAPs) |
Loading supporting content…
Download this section (compressed HTML)Q: In which giant panda hard-keratin structure(s) is this gene expressed - pelage (fur) shaft, claw, or footpad - and does its expression track the hair cycle as seen for mammalian KRTAPs?
Q: Which human/mammalian high-sulfur KAP subfamily (e.g. KRTAP1/2/3 B2 high-sulfur group) is the true ortholog of this protein, and is the cysteine-repeat copy number lineage-specific in Ursidae?
Experiment: RNA in situ hybridization or single-cell/bulk RNA-seq of giant panda skin and claw to localize expression to specific trichocyte compartments and confirm a hair/claw keratinization context.
Experiment: Phylogenetic and domain-architecture analysis placing this protein within the mammalian KRTAP high-sulfur (B2) family tree to assign the correct subfamily and quantify the cysteine-repeat expansion.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)