id: P82615
gene_symbol: Equc4
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:9796
  label: Equus caballus
description: >-
  Equ c 4 / latherin, a secreted horse protein of the BPI/LBP/PLUNC superfamily
  (PLUNC family) and a horse allergen. It is the major protein of horse sweat (and
  saliva), a highly surface-active biosurfactant that lowers surface tension to make
  the water-repellent coat wettable, promoting sweat spreading and evaporative
  cooling (thermoregulation). It is the prototype of the latherin/PLUNC family that
  also includes cat Fel d 8.
existing_annotations:
- term:
    id: GO:0043129
    label: surfactant homeostasis
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: Latherin is a biosurfactant; surfactant homeostasis is consistent with its family and direct characterization.
    action: ACCEPT
    reason: Supported by phylogeny and the experimentally demonstrated surfactant function.
    supported_by:
    - reference_id: file:HORSE/Equc4/Equc4-uniprot.txt
      supporting_text: Major protein in sweat, has surfactant properties. Has a role
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Latherin is secreted into sweat/saliva; extracellular localization is correct.
    action: ACCEPT
    reason: Consistent with secretion into sweat and saliva.
    supported_by:
    - reference_id: file:HORSE/Equc4/Equc4-uniprot.txt
      supporting_text: Major protein in sweat, has surfactant properties. Has a role
- term:
    id: GO:0008289
    label: lipid binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: BPI/LBP/PLUNC-superfamily proteins bind lipids; lipid binding is consistent with latherin's surfactant fold.
    action: ACCEPT
    reason: Consistent with the lipid-binding PLUNC fold and surfactant activity.
    supported_by:
    - reference_id: file:HORSE/Equc4/Equc4-uniprot.txt
      supporting_text: Belongs to the BPI/LBP/Plunc superfamily. Plunc family.
- term:
    id: GO:0001659
    label: temperature homeostasis
  evidence_type: IDA
  original_reference_id: PMID:3753435
  qualifier: involved_in
  review:
    summary: >-
      Latherin's surfactant activity wets the water-repellent coat and promotes
      sweat spreading/evaporation, contributing directly to evaporative cooling and
      temperature regulation.
    action: ACCEPT
    reason: Experimentally supported role in thermoregulation via sweat surfactant activity.
    supported_by:
    - reference_id: file:HORSE/Equc4/Equc4-uniprot.txt
      supporting_text: Major protein in sweat, has surfactant properties. Has a role
- term:
    id: GO:0043129
    label: surfactant homeostasis
  evidence_type: IDA
  original_reference_id: PMID:3753435
  qualifier: involved_in
  review:
    summary: Direct (IDA) demonstration of latherin's surfactant function in sweat.
    action: ACCEPT
    reason: Experimentally demonstrated surfactant activity.
    supported_by:
    - reference_id: file:HORSE/Equc4/Equc4-uniprot.txt
      supporting_text: Major protein in sweat, has surfactant properties. Has a role
core_functions:
- description: >-
    Secreted biosurfactant (latherin/PLUNC family) that lowers surface tension to
    wet the hydrophobic coat, promoting sweat spreading and evaporative cooling;
    binds lipids consistent with the PLUNC fold.
  molecular_function:
    id: GO:0008289
    label: lipid binding
  directly_involved_in:
  - id: GO:0043129
    label: surfactant homeostasis
  - id: GO:0001659
    label: temperature homeostasis
  supported_by:
  - reference_id: file:HORSE/Equc4/Equc4-uniprot.txt
    supporting_text: Major protein in sweat, has surfactant properties. Has a role
  locations:
  - id: GO:0005576
    label: extracellular region
proposed_new_terms: []
suggested_questions:
- question: How does latherin's PLUNC fold achieve its exceptional surface activity, and does Fel d 8 share the mechanism?
  experts: []
suggested_experiments:
- hypothesis: Equ c 4 / latherin reduces surface tension via a PLUNC-family lipid/air-water interface mechanism shared with Fel d 8.
  description: Compare surface-tension reduction (pendant drop) and lipid binding of recombinant latherin and Fel d 8.
  experiment_type: biophysical / surfactant assay
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
  findings: []
- id: PMID:3753435
  title: Isolation and characterization of latherin, a surface-active protein from horse sweat.
  findings:
  - statement: Latherin is the major surfactant protein of horse sweat, functioning in thermoregulation by wetting the coat for evaporative cooling.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Primary characterization of latherin's surfactant function and thermoregulatory role.
- id: file:HORSE/Equc4/Equc4-uniprot.txt
  title: UniProt entry P82615 (Latherin / Equ c 4), Equus caballus
  findings:
  - statement: Latherin is a secreted BPI/LBP/PLUNC-family surfactant protein of horse sweat with a role in temperature regulation.
    supporting_text: Major protein in sweat, has surfactant properties. Has a role
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Curated UniProt record; source for the surfactant/lipid-binding/thermoregulation functions and PLUNC family.