K9IFY6 is the common vampire bat orthologue of CCL28 (mucosae-associated epithelial chemokine, MEC), a secreted CC-motif chemokine. The 132-residue precursor comprises a signal peptide (residues 1-22), a chemokine interleukin-8-like domain (residues 28-87) with the canonical CC cysteine motif, and an unusually long, strongly basic C-terminal extension. It is highly homologous to human CCL28. Like other chemokines it is secreted and acts extracellularly as a receptor ligand, engaging CCR-family G protein-coupled receptors (CCR10 and CCR3 for mammalian CCL28) to direct leukocyte chemotaxis; in mammals CCL28 is characteristically expressed by mucosal epithelia and exocrine glands, where it recruits IgA-producing plasma cells. Human CCL28 additionally carries a histatin-like basic C-terminus with direct broad-spectrum antimicrobial activity, and the bat protein retains the equivalent basic extension. It was among the most abundant transcripts of the vampire bat submaxillary gland and was confirmed in the gland proteome, making it a likely antimicrobial and immune-modulating component of saliva delivered to the host bite wound.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0008009 chemokine activity | IEA GO_REF:0000002 | ACCEPT | Summary: The protein carries a chemokine interleukin-8-like domain (residues 28-87) with the CC cysteine signature (PROSITE PS00472 SMALL_CYTOKINES_CC), belongs to the intercrine beta family, and is the CCL28 orthologue. Chemokine activity is the informative molecular function for this protein. Reason: Domain architecture, family assignment, and orthology to CCL28 all converge on chemokine activity. This is the core molecular function. Supporting Evidence: file:DESRO/K9IFY6/K9IFY6-uniprot.txt /note="Chemokine interleukin-8-like" file:DESRO/K9IFY6/K9IFY6-uniprot.txt Belongs to the intercrine beta (chemokine CC) family. PMID:23411029 CCL28 is a chemokine signaling via CCR10 and CCR3 that is selectively expressed in certain mucosal tissues such as exocrine glands, trachea, and colon. |
| GO:0005125 cytokine activity | IEA GO_REF:0000043 | MODIFY | Summary: Cytokine activity is correct but is the parent of chemokine activity, which is already independently annotated and is directly supported by the IL8-like domain and the CC cysteine motif. Reason: Replace the generic parent with the specific child GO:0008009 chemokine activity, which conveys the receptor class and the chemotactic mode of action. Proposed replacements: chemokine activity Supporting Evidence: file:DESRO/K9IFY6/K9IFY6-uniprot.txt /note="Chemokine interleukin-8-like" file:DESRO/K9IFY6/K9IFY6-uniprot.txt Belongs to the intercrine beta (chemokine CC) family. |
| GO:0060326 cell chemotaxis | IEA GO_REF:0000108 | ACCEPT | Summary: Directing the migration of responding cells is the defining biological role of a chemokine, and the UniProt record carries the Chemotaxis keyword from the CC chemokine rule. For CCL28 specifically, the best-characterised activity is chemoattraction of IgA-producing plasma cells into mucosal lamina propria. Reason: Well supported at the family level and specifically for CCL28. This is the core biological process. Supporting Evidence: file:DESRO/K9IFY6/K9IFY6-uniprot.txt Chemotaxis {ECO:0000256|RuleBase:RU361150}; PMID:23411029 CCL28 is particularly abundant in SGs and plays an important role in mucosal immunity as a chemoattractant for IgA-producing plasma cells into the mucosal lamina propria |
| GO:0006935 chemotaxis | IEA GO_REF:0000043 | MODIFY | Summary: GO:0006935 chemotaxis is the general parent covering any cell or organism moving along a chemical gradient. The specific child GO:0060326 cell chemotaxis is already annotated and is the correct granularity for a leukocyte chemoattractant. Reason: Replace with GO:0060326 cell chemotaxis, which is what a chemokine actually mediates. Proposed replacements: cell chemotaxis Supporting Evidence: PMID:23411029 CCL28 is particularly abundant in SGs and plays an important role in mucosal immunity as a chemoattractant for IgA-producing plasma cells into the mucosal lamina propria |
| GO:0005615 extracellular space | IEA GO_REF:0000043 | ACCEPT | Summary: The precursor has a signal peptide (1-22) with a cleaved mature chain (23-132), UniProt records the subcellular location as Secreted, and salivary CCL28 was recovered from the D. rotundus submaxillary gland proteome, so the mature protein is a soluble extracellular species. Reason: Secretion is supported by signal peptide prediction, the UniProt subcellular location, and direct proteomic detection of CCL28 in bat salivary gland. Supporting Evidence: file:DESRO/K9IFY6/K9IFY6-uniprot.txt SUBCELLULAR LOCATION: Secreted PMID:23411029 In our analysis, bat salivary CCL28 was found to be abundant at the transcriptional (Table 4) and proteome (Figure 2A) levels. |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: A small soluble secreted chemokine; extracellular region is the appropriate location term. Reason: A soluble secreted protein; extracellular region is correct. GO has since obsoleted GO:0005615 extracellular space, the replacement previously proposed here, and merged it into GO:0005576 (replaced_by), so this term is now the correct location term. Supporting Evidence: file:DESRO/K9IFY6/K9IFY6-uniprot.txt SUBCELLULAR LOCATION: Secreted |
| GO:0006955 immune response | IEA GO_REF:0000002 | ACCEPT | Summary: Immune response is correct for a CC chemokine and is directly appropriate for CCL28, which is a mucosal immunity effector. The term is general, but the more specific descendants that would apply to CCL28 (mucosal IgA plasma cell recruitment, antibacterial humoral response) have not been demonstrated for the vampire bat protein, so the general term is the honest level of granularity here. Reason: Correct, if broad. Retained at this level rather than replaced with a speculative descendant, because no bat CCL28 has been assayed. Supporting Evidence: PMID:23411029 CCL28 is particularly abundant in SGs and plays an important role in mucosal immunity as a chemoattractant for IgA-producing plasma cells into the mucosal lamina propria file:DESRO/K9IFY6/K9IFY6-uniprot.txt Belongs to the intercrine beta (chemokine CC) family. |
| GO:0007165 signal transduction | IEA GO_REF:0000108 | MARK AS OVER ANNOTATED | Summary: This annotation comes from an inter-ontology logical inference from cytokine activity, not from evidence about this protein. Signal transduction is the process carried out by the responding cell after receptor engagement; a secreted ligand initiates that process rather than performing it. Its informative content for this protein is already captured by chemokine activity and cell chemotaxis. Reason: Root-level, ligand-inappropriate biological process term produced by automatic inter-ontology inference. It adds no information beyond the retained chemokine activity and cell chemotaxis annotations. Supporting Evidence: file:DESRO/K9IFY6/K9IFY6-uniprot.txt /note="Chemokine interleukin-8-like" |
| GO:0048020 CCR chemokine receptor binding | ISS PMID:23411029 The "Vampirome": Transcriptome and proteome analysis of the ... | NEW | Summary: Proposed new annotation. CCL28 signals through the CCR-family G protein-coupled receptors CCR10 and CCR3. K9IFY6 is the D. rotundus CCL28 orthologue (UniProt cross-references to NCBI Gene 112315258 and to PANTHER subfamily PTHR12015:SF205 C-C motif chemokine 28), and the Vampirome authors report that bat salivary CCL28 is highly homologous to the human protein. Receptor binding is the mechanistic basis of the accepted chemokine activity annotation and is worth stating explicitly. Reason: Adds mechanism to the generic chemokine activity call. The conservative parent GO:0048020 is proposed rather than GO:0031735 (CCR10 chemokine receptor binding), because the specific receptor has not been tested for the bat protein and mammalian CCL28 engages both CCR10 and CCR3. Supporting Evidence: PMID:23411029 CCL28 is a chemokine signaling via CCR10 and CCR3 that is selectively expressed in certain mucosal tissues such as exocrine glands, trachea, and colon. file:DESRO/K9IFY6/K9IFY6-uniprot.txt PANTHER; PTHR12015:SF205; C-C MOTIF CHEMOKINE 28; 1. PMID:23411029 It is highly homologous to the human counterpart according to a Clustal analysis (Figure 13A) and phylogenetic tree (Figure 13B). |
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Download this section (compressed HTML)Q: Is the abundant salivary CCL28 of Desmodus rotundus acting on the bat's own mucosal immunity, or is it delivered to the host bite wound where it would modulate host leukocyte recruitment?
Suggested experts: Ivo M. B. Francischetti, José M. C. Ribeiro
Q: Does the basic C-terminal extension of bat CCL28 have the direct antimicrobial activity described for the histatin-like tail of human CCL28, and is it under positive selection as vampire bat lysozyme is?
Q: Does bat CCL28 engage CCR10, CCR3, or both, and does it cross-react with the receptors of the mammalian hosts on which vampire bats feed?
Experiment: Express recombinant mature bat CCL28 and synthesise a peptide covering its basic C-terminal extension (approximately residues 88-132); measure killing of Candida albicans, Escherichia coli, and Staphylococcus aureus by radial diffusion and MIC assays at low ionic strength, alongside human CCL28 as a positive control and a C-terminally truncated bat construct as the structure-function test.
Hypothesis: Vampire bat CCL28 is a broad-spectrum antimicrobial protein, not only a chemoattractant.
Type: Antimicrobial activity assay with truncation mutants
Experiment: Assay recombinant bat CCL28 on HEK293 cells expressing bat or human CCR10 and CCR3 using calcium mobilisation and beta-arrestin recruitment readouts, and confirm functional consequences with transwell chemotaxis of primary leukocytes.
Hypothesis: Bat CCL28 signals through CCR10 and/or CCR3 to recruit leukocytes.
Type: Receptor pharmacology and chemotaxis assay
Experiment: Use targeted parallel reaction monitoring mass spectrometry on saliva expectorated by feeding bats, and immunohistochemistry of principal versus accessory submaxillary gland sections, to establish that CCL28 reaches the bite site.
Hypothesis: CCL28 is transferred to the host during feeding rather than merely being stored in the gland.
Type: Targeted proteomics and immunohistochemistry
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