K9IWX5 is a secreted cysteine-rich protein of the CAP/SCP/TAPS superfamily (antigen 5 / CRISP subfamily) encoded in the submaxillary salivary gland transcriptome of the common vampire bat. The 241-residue precursor carries a predicted N-terminal signal peptide (residues 1-22), a CAP/PR-1 domain, and a C-terminal cysteine-rich ShKT module (residues 206-239) stabilised by two disulfide bonds, giving the canonical two-domain CRISP architecture. Antigen 5/CRISP proteins were recovered both as transcripts and as peptides in the principal submaxillary gland proteome of D. rotundus, so the family is translated and not merely transcribed in the gland; delivery of this specific protein into expectorated saliva has not been directly demonstrated. Its molecular activity is not established: CAP-superfamily members in vertebrate reproductive tracts, snake venoms, and the salivary glands of blood-feeding arthropods have been variously reported to bind lipids or divalent cations through the CAP cavity and to modulate ion channels through the cysteine-rich domain, but no activity has been demonstrated for any vampire bat CRISP, and the family is explicitly described as functionally uncharacterised in hematophagous salivary glands. The ShKT module of this protein is itself degenerate at residues that are conserved in canonical ShKT domains.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | IEA GO_REF:0000002 | ACCEPT | Summary: Secretion is well supported for this protein and is independent of the UniProt CAUTION. The precursor has a SignalP-predicted signal peptide (residues 1-22) with a cleaved 23-241 chain, the CRISP family is a family of secreted proteins, and antigen-5/CRISP peptides were recovered from the principal submaxillary gland proteome of D. rotundus by LC-MS/MS. The CAUTION in the UniProt record refers to PROSITE ProRule PRU01005, i.e. the ShKT domain feature annotation, not to subcellular localisation. Reason: Signal peptide prediction, CRISP family membership, and direct proteomic detection of antigen-5/CRISP family members in vampire bat salivary gland secretions all support extracellular localisation. The generic parent term GO:0005576 is retained rather than the child GO:0005615 (extracellular space) because there is no evidence distinguishing the soluble salivary pool from matrix-associated forms. Supporting Evidence: file:DESRO/K9IWX5/K9IWX5-uniprot.txt SIGNAL 1..22 file:DESRO/K9IWX5/K9IWX5-uniprot.txt Belongs to the CRISP family. PMID:23411029 secretoglobin (65 ions) and antigen-5/CRISP families (57) |
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Download this section (compressed HTML)Q: Is the abundant salivary antigen-5/CRISP of Desmodus rotundus active on host hemostasis, vascular tone, or nociception at the bite site, or is it a functionally inert secretory product?
Suggested experts: Ivo M. B. Francischetti, José M. C. Ribeiro
Q: Do vampire bat salivary CRISPs show the signature of positive selection seen in vampire bat lysozyme, which would indicate adaptation to sanguivory rather than neutral retention?
Q: Does the degenerate ShKT module of K9IWX5 retain any ion-channel activity, and if not, has the CAP domain taken over as the functional module?
Experiment: Express the mature 23-241 chain in a eukaryotic system that supports extensive disulfide bonding (UniProt annotates only the two ShKT bonds 215-233 and 224-237, but the mature chain carries 16 cysteines, so up to eight bonds are expected for the CRISP fold; e.g. Drosophila S2 or Expi293), confirm fold by circular dichroism, then screen against a panel of host K+ (BKCa, Kv1.1, Kv1.3) and Ca2+ channels by whole-cell patch clamp, and on cytokine release from human monocytes.
Hypothesis: Recombinant mature K9IWX5 modulates host ion channels or inflammatory signalling at the feeding site, analogous to characterised venom CRISPs.
Type: Recombinant expression plus electrophysiology and cytokine assay
Experiment: Perform lipidomic pull-down on recombinant K9IWX5 from host plasma and skin homogenate, and test binding of candidate prohemostatic prostaglandins (PGE2, PGF2-alpha, thromboxane) by isothermal titration calorimetry, using a CAP-cavity histidine mutant as the negative control.
Hypothesis: The CAP cavity of K9IWX5 binds a small hydrophobic ligand (sterol, fatty acid, or eicosanoid) that it scavenges or delivers at the bite site.
Type: Ligand pull-down and isothermal titration calorimetry
Experiment: Raise antibodies against recombinant K9IWX5 and assay saliva collected directly from feeding vampire bats by Western blot and targeted parallel reaction monitoring mass spectrometry, comparing principal and accessory gland extracts with expectorated saliva.
Hypothesis: K9IWX5 is secreted into saliva rather than retained in the gland, and is transferred to the host during feeding.
Type: Targeted proteomics of expectorated saliva
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