Fel d 7, a secreted lipocalin of the domestic cat (calycin superfamily, lipocalin family) and a minor cat allergen, abundant in cat urine. It is closely related (~63% identity) and cross-reactive to the dog allergen Can f 1. Its beta-barrel calyx is open and positively charged and binds fatty acids (with preference for palmitic and oleic acid; ~2:1 fatty acid:protein), as shown by the crystal structure (PDB:8EPV), fluorescence and NMR studies; the carried lipid may influence allergenicity. The crystal structure also contains coordinated Zn(2+), although the zinc derives from the zinc-acetate crystallization buffer so its physiological relevance is uncertain. The native in-vivo ligand and biological role remain to be confirmed.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: Fel d 7 is a secreted lipocalin (abundant in cat urine); extracellular localization is appropriate. Reason: Secretory lipocalin acting in the extracellular space. Supporting Evidence: file:FELCA/Feld7/Feld7-uniprot.txt SUBCELLULAR LOCATION: Secreted |
| GO:0036094 small molecule binding | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Generic small-molecule-binding term. A specific ligand class is now experimentally established (fatty acids; see the NEW annotation below), so the uninformative parent is superseded. Reason: Uninformative broad parent; the specific fatty-acid binding activity is now demonstrated and annotated. |
| GO:0005504 fatty acid binding | IDA PMID:36960093 Structural and ligand binding analysis of the pet allergens ... | NEW | Summary: NEW (proposed). Crystallographic, fluorescence (ANS-displacement) and NMR analyses show Fel d 7 binds fatty acids in its calyx, preferring palmitic acid (16:0) and oleic acid (18:1), with ~2:1 fatty acid:protein stoichiometry. Reason: Direct experimental demonstration of fatty-acid binding (Min et al. 2023); the specific molecular function of this lipocalin's calyx. Supporting Evidence: PMID:36960093 Can f 1 and Fel d 7 bind multiple ligands with |
| GO:0008270 zinc ion binding | IDA PMID:36960093 Structural and ligand binding analysis of the pet allergens ... | NEW | Summary: NEW (proposed). The Fel d 7 crystal structure (PDB:8EPV) contains coordinated Zn(2+) at five residues (113, 137, 142, 143, 146), and UniProt records the protein as zinc/metal-binding (GO:0046872). Caveat: the zinc derives from the zinc-acetate crystallization buffer, so this captures a demonstrated structural metal-coordination capacity whose physiological relevance is not established. Reason: Structurally demonstrated zinc coordination (five Zn-binding residues in PDB:8EPV); the specific term zinc ion binding is preferred over the generic metal ion binding (GO:0046872) keyword annotation. Physiological relevance flagged as uncertain (crystallization-derived). Supporting Evidence: file:FELCA/Feld7/Feld7-uniprot.txt IN COMPLEX WITH ZN(2+) |
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Download this section (compressed HTML)Q: What endogenous fatty acid (or other lipid) does Fel d 7 carry in vivo, and does the carried ligand modulate its allergenicity (as proposed for lipocalin allergens)?
Experiment: Identify lipids co-purifying with native Fel d 7 from cat urine by LC-MS and test whether ligand-loaded vs delipidated Fel d 7 differ in dendritic-cell activation / sensitization assays.
Hypothesis: Fel d 7 carries a specific endogenous fatty-acid ligand in cat secretions that influences sensitization.
Type: ligand identification / immunological assay
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