Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005540 hyaluronic acid binding	IEA GO_REF:0000002	ACCEPT	Summary: Hyaluronan binding is the defining activity of the Link module, and the Link module of this protein is intact and confidently detected (PROSITE PS50963, residues 36-129, with both canonical disulfides annotated). The human orthologue TNFAIP6 carries this term from direct assay. The UniProt CAUTION does not bear on this call: it is scoped to PROSITE ProRule PRU00059, which is the CUB domain rule, not the Link rule (PRU00323) that supports the Link module features here. Reason: Intact, well-detected Link module plus direct experimental support in the human orthologue. The earlier UNDECIDED reflected a misreading of the CAUTION, which concerns the CUB domain. Supporting Evidence: file:DESRO/K9IIP0/K9IIP0-uniprot.txt DOMAIN 36..129 PMID:23411029 The N-terminal domain of TSG-6 represents a structural motif known as the Link module, which confers affinity for hyaluronan. file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md The Link module mediates binding to hyaluronan (HA) and other glycosaminoglycans
GO:0005615 extracellular space	IEA GO_REF:0000118	ACCEPT	Summary: The precursor has a SignalP-predicted signal peptide (1-17) with a cleaved 18-277 mature chain, TSG-6 is a classical secreted matrix protein, the human orthologue is annotated to the extracellular region from direct assay, and TSG-6 was recovered from the D. rotundus principal submaxillary gland proteome by LC-MS/MS. As with the hyaluronan binding call, the CAUTION concerns the CUB domain and says nothing about localisation. Reason: Signal peptide, family behaviour, and orthologue annotation all agree. The LC-MS/MS detection was made on principal gland tissue, so strictly it is expression evidence rather than localisation evidence; it corroborates that the protein is made in quantity here, while the secreted localisation itself rests on the signal peptide, the classical secreted family, and the direct-assay annotation of the human orthologue. Upgraded from UNDECIDED. Supporting Evidence: file:DESRO/K9IIP0/K9IIP0-uniprot.txt SIGNAL 1..17 PMID:23411029 Of note, expression of TSG-6 was confirmed by the proteome of the PS gland (Figure 2A). file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md It is secreted into the extracellular space and acts in the ECM and pericellular matrix.
GO:0050728 negative regulation of inflammatory response	IEA GO_REF:0000118	ACCEPT	Summary: Anti-inflammatory action is the best-characterised biology of TSG-6, not a peripheral inference: the Link module binds chemokines and blocks their presentation on endothelial glycosaminoglycans, suppressing neutrophil transendothelial migration, and the protein inhibits inflammation across several in vivo models. The human orthologue carries this exact term both from direct assay (PMID:21569482) and by phylogenetic inference, so the TreeGrafter propagation to the bat protein is a legitimate transfer rather than an over-propagation. An earlier version of this review removed the term; there is no biological argument against it. Reason: Well-supported family function with experimental backing in the human orthologue and an identified mechanism that depends on the Link module, which is intact in this protein. REMOVE is reserved for annotations that can be argued against on biological grounds; this one cannot. Supporting Evidence: PMID:23411029 TSG-6 inhibits inflammation, according to several in vivo models PMID:23411029 TSG-6 also inhibits neutrophil migration to interact with macrophage CD44
GO:0016787 hydrolase activity	IEA GO_REF:0000043	MODIFY	Summary: This keyword-derived term is uninformative but, contrary to an earlier version of this review, it is not wrong. TSG-6 does catalyse a covalent chemical step: it transfers inter-alpha-inhibitor heavy chains onto hyaluronan via a TSG-6-heavy-chain ester intermediate. The human orthologue TNFAIP6 is annotated to GO:0106435 carboxylesterase activity from two independent direct assays (PMID:16873769, PMID:20463016), and GO:0106435 is a descendant of GO:0016787. The UniProt record for this very protein states that the ITIH2/HC2 interaction is required for transesterification of the heavy chain to hyaluronan. Reason: Replace the root-level hydrolase term with the specific child GO:0106435 carboxylesterase activity, which is the term the GO consortium uses for the experimentally demonstrated heavy-chain transfer activity of the human orthologue. Removing the annotation, as previously proposed, would have discarded a real catalytic function. Caveat to record explicitly: carboxylesterase activity is defined as ester hydrolysis, whereas TSG-6 performs two sequential transesterifications with no net hydrolysis, the heavy chain moving from the chondroitin sulfate of inter-alpha-inhibitor onto hyaluronan through a covalent TSG-6-heavy-chain ester intermediate. GO:0106435 is used here because it is the term the consortium applies to the human orthologue, not because the chemistry is a good fit; a transferase-branch term would describe the reaction better (see suggested_questions). Proposed replacements: carboxylesterase activity Supporting Evidence: file:DESRO/K9IIP0/K9IIP0-uniprot.txt is required for transesterification of the HC to hyaluronan. file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md enzymatic transesterase activity transferring I PMID:20463016 In concert with HC2, TSG-6 have a unique catalytic activity transferring HCs from bikunin proteins to hyaluronan (HA). PMID:20463016 The reaction involves two divalent cation-dependent transesterifications and a covalent intermediate composed of TSG-6 and the HC to be transferred PMID:26468290 TSG-6 was shown to play a direct role in the transfer of HCs from IαI onto HA via the formation of covalent intermediates
GO:0007155 cell adhesion	IEA GO_REF:0000120	MARK AS OVER ANNOTATED	Summary: This comes from the UniProt Cell adhesion keyword. Even in the human orthologue the term has never risen above electronic evidence, and the documented matrix biology of TSG-6 is hyaluronan binding, cross-linking, and heavy-chain transfer rather than adhesion between cells. Any effect on adhesion is indirect, through the altered hyaluronan matrix, and is better captured by the hyaluronan terms. Reason: Keyword-derived, unsupported by experiment in any species, and attributing to the protein a role that is a downstream consequence of its matrix remodelling rather than its own activity. Supporting Evidence: file:DESRO/K9IIP0/K9IIP0-uniprot.txt Cell adhesion {ECO:0000256\|ARBA:ARBA00022889}; file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md The Link module mediates binding to hyaluronan (HA) and other glycosaminoglycans
GO:0030212 hyaluronan metabolic process	ISS PMID:20463016 The TSG-6/HC2-mediated transfer is a dynamic process shuffli...	NEW	Summary: Proposed new annotation. The heavy-chain transfer reaction covalently modifies hyaluronan to form heavy chain-hyaluronan complexes, which is a hyaluronan metabolic process; the human orthologue carries this term from two direct assays (PMID:20463016, PMID:26468290). This is the biological process counterpart of the carboxylesterase activity proposed above, and the GOA record for this protein has no term covering it. Reason: Completes the molecular function to biological process link for the heavy-chain transfer activity, and mirrors the experimentally supported annotation of the human orthologue. Anchored to the orthologue experimental evidence (PMID:20463016, PMID:26468290) rather than to the deep-research survey, since the justification is orthologue transfer. Supporting Evidence: file:DESRO/K9IIP0/K9IIP0-uniprot.txt is required for transesterification of the HC to hyaluronan. PMID:20463016 can be transferred to different hyaluronan (HA) molecules by TSG-6/HC2 PMID:26468290 both HC1 and HC2 of IαI can be covalently transferred onto the C6-hydroxyls of the N-acetyl glucosamine sugars in HA

Core Functions

Secreted hyaladherin that binds hyaluronan through its Link module and remodels hyaluronan-rich extracellular matrix, both by non-covalent cross-linking and by covalently transferring inter-alpha-inhibitor heavy chains onto hyaluronan. The same module sequesters C-X-C and C-C chemokines and blocks their presentation on endothelial glycosaminoglycans, suppressing neutrophil recruitment and damping inflammation. In the vampire bat the protein is an abundant product of the principal submaxillary salivary gland.

Molecular Function:

hyaluronic acid binding

Directly Involved In:

negative regulation of inflammatory response

Cellular Locations:

extracellular space

Supporting Evidence:

PMID:23411029
The N-terminal domain of TSG-6 represents a structural motif known as the Link module, which confers affinity for hyaluronan.
PMID:23411029
TSG-6 inhibits inflammation, according to several in vivo models
file:DESRO/K9IIP0/K9IIP0-uniprot.txt
is required for transesterification of the HC to hyaluronan.

Catalyses the covalent transfer of inter-alpha-inhibitor heavy chains onto hyaluronan, through two divalent cation-dependent transesterifications that proceed via a covalent TSG-6-heavy-chain ester intermediate, building the heavy chain-hyaluronan complexes that stabilise and cross-link hyaluronan-rich matrices. This is a distinct catalytic function from the non-covalent hyaluronan binding of the Link module, and for the bat protein it is inferred by orthology: the activity is experimentally established for mammalian TSG-6 and the corresponding UniProt statement is made for this record, but the bat protein itself has not been assayed. The GO term is the one the consortium applies to the human orthologue; chemically the reaction is a transesterification rather than the net hydrolysis that carboxylesterase activity denotes.

Molecular Function:

carboxylesterase activity

Directly Involved In:

hyaluronan metabolic process

Cellular Locations:

extracellular space

Supporting Evidence:

file:DESRO/K9IIP0/K9IIP0-uniprot.txt
is required for transesterification of the HC to hyaluronan.
PMID:20463016
In concert with HC2, TSG-6 have a unique catalytic activity transferring HCs from bikunin proteins to hyaluronan (HA).
PMID:20463016
The reaction involves two divalent cation-dependent transesterifications and a covalent intermediate composed of TSG-6 and the HC to be transferred
PMID:26468290
TSG-6 was shown to play a direct role in the transfer of HCs from IαI onto HA via the formation of covalent intermediates

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

Hyaluronic acid binding was inferred from the Link domain InterPro signature IPR000538, which is confidently matched in this protein.

"InterPro; IPR000538; Link_dom."

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

The root-level hydrolase activity annotation derives from the ARBA Hydrolase keyword. The keyword itself is defensible for TSG-6, whose heavy-chain transfer proceeds through an ester intermediate, but the term is far less informative than the carboxylesterase activity term used for the human orthologue.

"Hydrolase {ECO:0000256|ARBA:ARBA00022801};"

GO_REF:0000118

TreeGrafter-generated GO annotations

Extracellular space and negative regulation of inflammatory response were propagated from the PANTHER TSG-6 subfamily PTHR46908:SF4. The human orthologue carries the inflammatory-response term from direct assay as well as by phylogenetic inference, so this propagation rests on experimental evidence rather than on prediction alone.

"PANTHER; PTHR46908:SF4; TUMOR NECROSIS FACTOR-INDUCIBLE GENE 6 PROTEIN; 1."

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

The cell adhesion annotation derives from combined automated methods applied to the Cell adhesion keyword; no experimental evidence for this process exists for TSG-6 in any species.

"Cell adhesion {ECO:0000256|ARBA:ARBA00022889};"

PMID:23411029

The "Vampirome": Transcriptome and proteome analysis of the principal and accessory submaxillary glands of the vampire bat Desmodus rotundus, a vector of human rabies.

At least two TSG-6 family members are transcribed in D. rotundus salivary gland, and TSG-6 was confirmed in the principal gland proteome by LC-MS/MS (101 ions, the fourth most abundant protein family identified, after semaphorin at 855 ions, plasminogen activator at 597 and lipocalin at 163). This is the study whose EMBL submission (JAA46157.1, salivary gland) underlies the K9IIP0 accession.

"Of note, expression of TSG-6 was confirmed by the proteome of the PS gland (Figure 2A)."
The Link module is the hyaluronan-binding module that defines the hyaladherin family, and it is the N-terminal half of TSG-6.

"The N-terminal domain of TSG-6 represents a structural motif known as the Link module, which confers affinity for hyaluronan."
TSG-6 suppresses neutrophil migration and inhibits inflammation in multiple in vivo models, which is the basis for the anti-inflammatory annotation.

"TSG-6 inhibits inflammation, according to several in vivo models"
TSG-6 potentiates the antiplasmin activity of inter-alpha-inhibitor through a Link module to bikunin interaction, linking the protein to fibrinolysis regulation as well as inflammation - potentially relevant in a saliva that also contains a plasminogen activator.

"TSG-6 has been found to potentiate the antiplasmin activity of inter"
The function of the C-terminal CUB domain of TSG-6 remains unidentified. This is the domain to which the UniProt CAUTION for this protein is scoped.

"The C terminal half of TSG-6 forms a CUB (complement subcomponents C1r/C1s, Uegf, BMP-1) domain whose function remains unidentified"
The authors propose an anti-inflammatory role for the protein in bat saliva specifically, but state it as a possibility rather than a measurement.

"In bat saliva, this protein may function as an anti-inflammatory molecule."

PMID:20463016

The TSG-6/HC2-mediated transfer is a dynamic process shuffling heavy chains between glycosaminoglycans.

TSG-6, acting with heavy chain 2, has a catalytic activity that transfers inter-alpha-inhibitor heavy chains onto hyaluronan. This is the direct experimental basis for the carboxylesterase activity term on the human orthologue and, by orthology, for the proposed replacement term here.

"In concert with HC2, TSG-6 have a unique catalytic activity transferring HCs from bikunin proteins to hyaluronan (HA)."
The reaction proceeds by two divalent cation-dependent transesterifications through a covalent TSG-6-heavy-chain intermediate, which is why the chemistry is transesterification rather than the net hydrolysis that GO:0106435 formally describes.

"The reaction involves two divalent cation-dependent transesterifications and a covalent intermediate composed of TSG-6 and the HC to be transferred"
Heavy chains are transferred onto hyaluronan and can be further shuffled between glycosaminoglycans, so the activity covalently modifies hyaluronan itself - the basis of the proposed hyaluronan metabolic process annotation.

"can be transferred to different hyaluronan (HA) molecules by TSG-6/HC2"

PMID:26468290

Metal Ion-dependent Heavy Chain Transfer Activity of TSG-6 Mediates Assembly of the Cumulus-Oocyte Matrix.

TSG-6 acts as a catalyst in the transfer of heavy chains from inter-alpha-inhibitor onto hyaluronan through covalent heavy-chain-TSG-6 intermediates, and is the only known transferase able to produce heavy chain-hyaluronan complexes.

"TSG-6 was shown to play a direct role in the transfer of HCs from IαI onto HA via the formation of covalent intermediates"
The heavy chains are attached covalently to hyaluronan sugars, so the reaction is a covalent modification of the hyaluronan polymer and falls under hyaluronan metabolic process.

"both HC1 and HC2 of IαI can be covalently transferred onto the C6-hydroxyls of the N-acetyl glucosamine sugars in HA"
The heavy-chain transferase activity, rather than hyaluronan binding, is the activity required for cumulus-oocyte complex expansion in mice, establishing the catalytic function as physiologically load-bearing.

"it is the HC transferase activity of TSG-6, rather than HA binding, that is crucial for murine COC expansion"

PMID:16873769

TSG-6 potentiates the antitissue kallikrein activity of inter-alpha-inhibitor through bikunin release.

TSG-6 forms covalent complexes with inter-alpha-inhibitor and pre-alpha-inhibitor heavy chains and potentiates the antiplasmin activity of bikunin, corroborating both the covalent heavy-chain chemistry and the fibrinolysis link noted for the salivary protein.

"potentiating the antiplasmin activity of this serine protease inhibitor"

file:DESRO/K9IIP0/K9IIP0-uniprot.txt

UniProtKB record for K9IIP0 (K9IIP0_DESRO)

The protein is TSG-6/TNFAIP6 with a signal peptide (1-17), a Link domain (36-129) carrying the 58-127 and 82-103 disulfides, and a CUB domain (135-247).

"RecName: Full=Tumor necrosis factor-inducible gene 6 protein"
The record states that the ITIH2/HC2 interaction is required for transesterification of the inter-alpha-inhibitor heavy chain onto hyaluronan, which is the covalent catalytic step behind the carboxylesterase activity annotation of the human orthologue.

"is required for transesterification of the HC to hyaluronan."
The Link module is also recorded as binding a broad panel of C-X-C and C-C chemokines, interfering with their binding to glycosaminoglycans - the mechanism of TSG-6's anti-inflammatory action.

"interferes with chemokine binding to glycosaminoglycans. Interacts"
The UniProt CAUTION is scoped to PROSITE ProRule PRU00059, which is the CUB domain rule (PROSITE PS01180). It therefore limits confidence in CUB-derived feature transfer, and does not bear on the Link module (rule PRU00323), on secretion, or on hyaluronan binding.

"feature annotation. {ECO:0000256|PROSITE-ProRule:PRU00059}."

file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md

Deep research report on K9IIP0

TSG-6 is a secreted inflammation-inducible glycoprotein whose Link module binds hyaluronan and other glycosaminoglycans, and which acts in the extracellular matrix and pericellular matrix.

"The Link module mediates binding to hyaluronan (HA) and other glycosaminoglycans"
The report enumerates enzymatic transesterase activity transferring inter-alpha-inhibitor heavy chains to hyaluronan among the biochemical activities of TSG-6, independently corroborating the catalytic call.

"enzymatic transesterase activity transferring I"
The report is explicit that direct bat-specific primary literature is limited and that its functional annotation is inferred from conserved domain architecture plus mammalian TSG-6 data.

"Direct bat-specific primary literature is limited; therefore, functional annotation is inferred from conserved domain architecture and extensive mammalian data on TSG-6."

Suggested Experiments

Experiment: Express recombinant full-length bat TSG-6 and its isolated Link module, incubate each with inter-alpha-inhibitor and hyaluronan in the presence of magnesium, and detect heavy chain-hyaluronan complex formation by Western blot against inter-alpha-inhibitor heavy chains, using human TSG-6 as the positive control.

Hypothesis: Vampire bat salivary TSG-6 retains the heavy-chain transferase activity of mammalian TSG-6 despite the flagged CUB domain divergence.

Type: In vitro heavy-chain transfer assay

Experiment: Measure binding of recombinant bat TSG-6 to a panel of host C-X-C and C-C chemokines by surface plasmon resonance, then test whether it inhibits chemokine-driven neutrophil transendothelial migration across a host endothelial monolayer.

Hypothesis: Salivary TSG-6 suppresses host leukocyte recruitment at the bite site.

Type: Surface plasmon resonance and transendothelial migration assay

Experiment: Align the bat CUB domain against characterised CUB domains to identify which conserved residues are missing, model the domain with AlphaFold, and compare full-length bat TSG-6 with a CUB-deleted construct in fibronectin binding and heavy-chain transfer assays.

Hypothesis: The C-terminal CUB domain of the bat protein is degenerate, specialising it toward Link-module functions.

Type: Comparative sequence and structure analysis with domain-deletion assays

Deep Research

Falcon

(K9IIP0-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 17 citations 2026-01-21T12:03:41.135284

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Plan and verification. We verified that UniProt accession K9IIP0 corresponds to tumor necrosis factor alpha-induced protein 6 (TNFAIP6/TSG-6) from Desmodus rotundus (vampire bat), with hallmark Link and CUB domains and hyaluronan-binding/link module and CUB superfamily annotations. Direct bat-specific primary literature is limited; therefore, functional annotation is inferred from conserved domain architecture and extensive mammalian data on TSG-6.

Key concepts and definitions. TNFAIP6/TSG-6 is a secreted, inflammation-inducible glycoprotein (~35 kDa) composed of an N-terminal region followed by a hyaluronan-binding Link module and a CUB domain. The Link module mediates binding to hyaluronan (HA) and other glycosaminoglycans; residues Lys11, Tyr12, Tyr59, Phe70, Tyr78, and Arg81 contribute to HA binding and function. TSG-6 binds inter-α-inhibitor (IαI) and catalyzes covalent transfer of IαI heavy chains (HCs) onto HA to form HC·HA complexes (also termed SHAP-HA), via a TSG-6·HC intermediate, thereby remodeling extracellular matrices at sites of inflammation and ovulation. TSG-6 also noncovalently crosslinks HA via induced TSG-6 oligomerization and binds chemokines (e.g., CXCL8/IL-8), modulating leukocyte trafficking. It is secreted into the extracellular space and acts in the ECM and pericellular matrix. (dong2020investigationoftsg6 pages 25-28, albtoush2018inhibitingthefunction pages 21-32)

Mechanistic functions and pathways. The Link module’s HA binding is pH- and residue-specific and can lead to noncovalent HA networking; full-length TSG-6, but not isolated Link_TSG6, mediates HC transfer from IαI to HA. HC transfer enhances leukocyte adhesion to HA matrices and is increased in inflamed synovial fluid and tissues. TSG-6 directly binds CXCL8 at its GAG-binding site (KD ~25 nM) to inhibit chemokine presentation on endothelial GAGs and suppress neutrophil transendothelial migration, delineating an anti-inflammatory pathway. In osteoarthritis and other inflammatory conditions, the TNF-α–TSG-6–HC·HA axis is upregulated; TSG-6 modulates matrix proteolysis (e.g., plasmin/MMP pathways) and can be chondroprotective in models. In the gut, HA-mediated mucosal healing requires TSG-6, consistent with a role in epithelial regeneration. (dyer2014tsg6inhibitsneutrophil pages 1-2, dong2020investigationoftsg6 pages 25-28, fasanello2021hyaluronicacidsynthesis pages 1-2, sammarco2019hyaluronanacceleratesintestinal pages 15-17, albtoush2018inhibitingthefunction pages 21-32)

Recent developments (2023–2024). In 2024, Ilg et al. reported that TGF-β1 induces formation of TSG-6–enriched extracellular vesicles from fibroblasts; these EVs prevent myofibroblast transformation by inhibiting ERK1/2 phosphorylation, suggesting an EV-mediated, anti-fibrotic mechanism for TSG-6. In 2024, Dodd et al. provided chemical/structural insights: specific chemical modifications to HA oligosaccharides increased affinity for Link_TSG6 (distinct from CD44_HABD), with docking implicating Arg81 in salt-bridge formation; select modifications turned short HA oligos into substrates for HC transfer, indicating a means to tune TSG-6 enzymatic activity. A 2024 cancer review highlights TSG-6’s roles in constructing inflammatory ECM niches through HC·HA and promoting CD44-dependent adhesion, with implications in metastasis. (ilg2024tgfβ1inducesformation pages 11-12, dodd2024chemicalmodificationof pages 1-3, xu2024hyaluronicacidinteracting pages 20-21)

Localization. TSG-6 is secreted, present in extracellular fluid/ECM, and can be stored in neutrophil granules for rapid release; it localizes to HA-rich matrices, synovial fluid, and wounded tissues where it participates in ECM remodeling. (dong2020investigationoftsg6 pages 25-28, fasanello2021hyaluronicacidsynthesis pages 1-2)

Biochemical activities and specificity. TSG-6 exhibits: (1) HA binding via the Link module; (2) noncovalent HA crosslinking through TSG-6 oligomerization; (3) enzymatic transesterase activity transferring IαI heavy chains to HA to form HC·HA; (4) chemokine binding (e.g., CXCL8) to inhibit neutrophil migration; and (5) modulation of protease pathways via effects on inter-α-inhibitor/plasmin activity. Substrate specificity includes HA as the principal glycosaminoglycan ligand for Link-mediated functions, with competition by certain chondroitin sulfates; IαI serves as heavy-chain donor for covalent modification of HA. (dong2020investigationoftsg6 pages 28-33, dyer2014tsg6inhibitsneutrophil pages 1-2, dong2020investigationoftsg6 pages 25-28, albtoush2018inhibitingthefunction pages 21-32)

Roles in disease and physiology. In osteoarthritis, TSG-6 expression and HC·HA formation increase in synovial fluid and tissues; the axis is TNF-α inducible, and HC·HA localizes to synovium and chondrocyte surfaces. In mucosal injury and ulcerative colitis models, HA treatment accelerates healing in a TSG-6–dependent manner; deleting TSG-6 abrogates HA’s benefit. In acute inflammation, TSG-6’s binding to CXCL8 and interference with GAG-mediated chemokine presentation reduces neutrophil trafficking, providing tissue protection. (fasanello2021hyaluronicacidsynthesis pages 1-2, sammarco2019hyaluronanacceleratesintestinal pages 15-17, dyer2014tsg6inhibitsneutrophil pages 1-2)

Current applications and implementations. Mesenchymal stromal cells (MSCs) secrete TSG-6, which contributes to MSCs’ anti-inflammatory and tissue-protective effects across models; mechanism includes suppression of neutrophil transendothelial migration and modulation of macrophage NF-κB signaling. In the clinic, a TSG-6–mimetic peptide (ALY688) progressed to ophthalmic trials for dry eye disease (Phase 1/2a NCT04201574: completed; Phase 2/3 NCT04899518: completed) and a systemic formulation trial (NCT04855565: terminated), indicating translational interest in TSG-6 pathway agonism. (dyer2014tsg6inhibitsneutrophil pages 1-2)

Expert opinions and authoritative analyses. The mechanistic body of work positions TSG-6 as a multifunctional hyaladherin and inflammation-modifying enzyme that remodels HA matrices through both covalent (HC transfer) and noncovalent (crosslinking) mechanisms and tempers neutrophil recruitment by chemokine sequestration. 2024 advances indicate that EV-associated TSG-6 may be a lever to modulate fibroblast activation via ERK1/2, and that chemical editing of HA can selectively tune TSG-6 binding and HC transfer, opening paths for rational biomaterials and therapeutics targeting HA–TSG-6 axes. (ilg2024tgfβ1inducesformation pages 11-12, dodd2024chemicalmodificationof pages 1-3)

Statistics and specific data points. Dyer et al. quantified TSG-6–CXCL8 binding with KD ~25 nM and demonstrated inhibition of chemokine transcytosis and neutrophil migration across endothelium. Fasanello et al. showed elevated TSG-6 expression and HC·HA presence in OA synovial fluid/tissues with localization to synovium and superficial chondrocytes and observed that HA concentration, rather than HA MW or HC·HA crosslinking, primarily determines synovial fluid viscosity. Ilg et al. reported ~7.3-fold upregulation of TNFAIP6 in myofibroblast-derived EVs under TGF-β1 and inhibition of ERK1/2 phosphorylation dependent on EV uptake. Dodd et al. identified HA modifications that increased Link_TSG6 affinity and enabled HC-transfer activity from modified HA oligos, with docking implicating Arg81 interactions. (dyer2014tsg6inhibitsneutrophil pages 1-2, fasanello2021hyaluronicacidsynthesis pages 1-2, ilg2024tgfβ1inducesformation pages 11-12, dodd2024chemicalmodificationof pages 1-3)

Relevance to Desmodus rotundus (K9IIP0). The vampire bat protein retains the defining Link and CUB domains and hyaluronan-binding/link-fold annotations, supporting conservation of HA binding, noncovalent crosslinking, and HC-transfer functions observed in mammals. Therefore, K9IIP0 is most likely a secreted ECM-modifying and inflammation-modulating protein with roles in HA-rich matrices analogous to human TSG-6. (dong2020investigationoftsg6 pages 25-28, albtoush2018inhibitingthefunction pages 21-32)

Key references with URLs and dates. Dyer et al., The Journal of Immunology, 2014-03-01. URL: https://doi.org/10.4049/jimmunol.1300194. (dyer2014tsg6inhibitsneutrophil pages 1-2). Fasanello et al., Arthritis Research & Therapy, 2021-08-24. URL: https://doi.org/10.1186/s13075-021-02588-7. (fasanello2021hyaluronicacidsynthesis pages 1-2). Sammarco et al., Cells, 2019-09-10. URL: https://doi.org/10.3390/cells8091074. (sammarco2019hyaluronanacceleratesintestinal pages 1-3, sammarco2019hyaluronanacceleratesintestinal pages 15-17). Dodd et al., The Journal of Biological Chemistry, 2024-03-12 (preprint DOI). URL: https://doi.org/10.1101/2024.03.12.584658. (dodd2024chemicalmodificationof pages 1-3). Ilg et al., Scientific Reports, 2024-05-17. URL: https://doi.org/10.1038/s41598-024-62123-x. (ilg2024tgfβ1inducesformation pages 11-12). Dong (compilation), 2020. (dong2020investigationoftsg6 pages 28-33, dong2020investigationoftsg6 pages 25-28).

Limitations and open questions. Bat-specific expression patterns, post-translational modifications, and interaction partners have not been resolved; research would benefit from sequencing/ortholog alignment and expression profiling in bat tissues. 2023–2024 literature emphasizes chemical modulation of HA–TSG-6 interactions and EV-mediated signaling, but detailed in vivo efficacy and safety data for TSG-6-targeted therapies remain sparse outside ophthalmology.

References

(dong2020investigationoftsg6 pages 25-28): Y Dong. Investigation of tsg-6 as a potential biomarker and therapeutic target in osteoarthritis. Unknown journal, 2020.
(albtoush2018inhibitingthefunction pages 21-32): NI Albtoush. Inhibiting the function of tsg-6 in inflammatory models as a possible therapeutic intervention. Unknown journal, 2018.
(dyer2014tsg6inhibitsneutrophil pages 1-2): Douglas P Dyer, Jennifer M Thomson, Aurelie Hermant, Thomas A Jowitt, Tracy M Handel, Amanda E I Proudfoot, Anthony J Day, and Caroline M Milner. Tsg-6 inhibits neutrophil migration via direct interaction with the chemokine cxcl8. The Journal of Immunology, 192:2177-2185, Mar 2014. URL: https://doi.org/10.4049/jimmunol.1300194, doi:10.4049/jimmunol.1300194. This article has 229 citations.
(fasanello2021hyaluronicacidsynthesis pages 1-2): Diana C. Fasanello, Jin Su, Siyu Deng, Rose Yin, Marshall J. Colville, Joshua M. Berenson, Carolyn M. Kelly, Heather Freer, Alicia Rollins, Bettina Wagner, Felipe Rivas, Adam R. Hall, Elaheh Rahbar, Paul L. DeAngelis, Matthew J. Paszek, and Heidi L. Reesink. Hyaluronic acid synthesis, degradation, and crosslinking in equine osteoarthritis: tnf-α-tsg-6-mediated hc-ha formation. Arthritis Research & Therapy, Aug 2021. URL: https://doi.org/10.1186/s13075-021-02588-7, doi:10.1186/s13075-021-02588-7. This article has 26 citations and is from a domain leading peer-reviewed journal.
(sammarco2019hyaluronanacceleratesintestinal pages 15-17): Giusy Sammarco, Mohammad Shalaby, Sudharshan Elangovan, Luciana Petti, Giulia Roda, Silvia Restelli, Vincenzo Arena, Federica Ungaro, Gionata Fiorino, Anthony J. Day, Silvia D’Alessio, and Stefania Vetrano. Hyaluronan accelerates intestinal mucosal healing through interaction with tsg-6. Cells, 8:1074, Sep 2019. URL: https://doi.org/10.3390/cells8091074, doi:10.3390/cells8091074. This article has 20 citations and is from a poor quality or predatory journal.
(ilg2024tgfβ1inducesformation pages 11-12): Marcus M. Ilg, Stephen A. Bustin, David J. Ralph, and Selim Cellek. Tgf-β1 induces formation of tsg-6-enriched extracellular vesicles in fibroblasts which can prevent myofibroblast transformation by modulating erk1/2 phosphorylation. Scientific Reports, May 2024. URL: https://doi.org/10.1038/s41598-024-62123-x, doi:10.1038/s41598-024-62123-x. This article has 11 citations and is from a peer-reviewed journal.
(dodd2024chemicalmodificationof pages 1-3): R. Dodd, C. Blundell, Benedict M. Sattelle, J. Enghild, C. Milner, and Anthony J. Day. Chemical modification of hyaluronan oligosaccharides differentially modulates hyaluronan–hyaladherin interactions. The Journal of Biological Chemistry, Mar 2024. URL: https://doi.org/10.1101/2024.03.12.584658, doi:10.1101/2024.03.12.584658. This article has 9 citations.
(xu2024hyaluronicacidinteracting pages 20-21): Yali Xu, Johannes Benedikt, and Lin Ye. Hyaluronic acid interacting molecules mediated crosstalk between cancer cells and microenvironment from primary tumour to distant metastasis. Cancers, 16:1907, May 2024. URL: https://doi.org/10.3390/cancers16101907, doi:10.3390/cancers16101907. This article has 17 citations and is from a poor quality or predatory journal.
(dong2020investigationoftsg6 pages 28-33): Y Dong. Investigation of tsg-6 as a potential biomarker and therapeutic target in osteoarthritis. Unknown journal, 2020.
(sammarco2019hyaluronanacceleratesintestinal pages 1-3): Giusy Sammarco, Mohammad Shalaby, Sudharshan Elangovan, Luciana Petti, Giulia Roda, Silvia Restelli, Vincenzo Arena, Federica Ungaro, Gionata Fiorino, Anthony J. Day, Silvia D’Alessio, and Stefania Vetrano. Hyaluronan accelerates intestinal mucosal healing through interaction with tsg-6. Cells, 8:1074, Sep 2019. URL: https://doi.org/10.3390/cells8091074, doi:10.3390/cells8091074. This article has 20 citations and is from a poor quality or predatory journal.

Citations

fasanello2021hyaluronicacidsynthesis pages 1-2
dodd2024chemicalmodificationof pages 1-3
albtoush2018inhibitingthefunction pages 21-32
sammarco2019hyaluronanacceleratesintestinal pages 15-17
xu2024hyaluronicacidinteracting pages 20-21
sammarco2019hyaluronanacceleratesintestinal pages 1-3
https://doi.org/10.4049/jimmunol.1300194.
https://doi.org/10.1186/s13075-021-02588-7.
https://doi.org/10.3390/cells8091074.
https://doi.org/10.1101/2024.03.12.584658.
https://doi.org/10.1038/s41598-024-62123-x.
https://doi.org/10.4049/jimmunol.1300194,
https://doi.org/10.1186/s13075-021-02588-7,
https://doi.org/10.3390/cells8091074,
https://doi.org/10.1038/s41598-024-62123-x,
https://doi.org/10.1101/2024.03.12.584658,
https://doi.org/10.3390/cancers16101907,

📚 Additional Documentation

Notes

(K9IIP0-notes.md)

K9IIP0 Research Notes

Key findings

UniProt names this protein Tumor necrosis factor-inducible gene 6 protein [file:DESRO/K9IIP0/K9IIP0-uniprot.txt "RecName: Full=Tumor necrosis factor-inducible gene 6 protein"].
Deep research identifies K9IIP0 as TNFAIP6/TSG-6 with Link and CUB domains [file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md "UniProt accession K9IIP0 corresponds to tumor necrosis factor alpha-induced protein 6 (TNFAIP6/TSG-6) from Desmodus rotundus (vampire bat), with hallmark Link and CUB domains and hyaluronan-binding/link module and CUB superfamily annotations."].
Deep research notes TSG-6 is secreted and inflammation-inducible [file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md "TNFAIP6/TSG-6 is a secreted, inflammation-inducible glycoprotein"]

2026-07-31 compliance review

The UniProt CAUTION was being over-read. The previous version used
[file:DESRO/K9IIP0/K9IIP0-uniprot.txt "CAUTION: Lacks conserved residue(s)
required for the propagation of"] to justify UNDECIDED on hyaluronan binding and
on secretion, and REMOVE on the anti-inflammatory term. But the caution is
scoped to PROSITE-ProRule:PRU00059, and PRU00059 is the CUB rule (it maps
to PROSITE PS01180; confirmed at prosite.expasy.org/unirule/PRU00059). The Link
module features in the same record cite a different rule, PRU00323. So the
caution constrains CUB-derived transfer only — not the Link module, not
secretion, not hyaluronan binding. Same pattern as K9IWX5, where the caution was
scoped to the ShKT rule.

Cross-checked every call against human TNFAIP6 (P98066) in QuickGO:

Term	Human evidence	Old call	New call
`GO:0005540` HA binding	IDA ×2 (26468290, 26823460)	UNDECIDED	ACCEPT
`GO:0005615` extracellular space	`GO:0005576` IDA (1730767)	UNDECIDED	ACCEPT
`GO:0050728` neg. reg. inflammatory response	IDA (21569482) + IBA	REMOVE	ACCEPT
`GO:0016787` hydrolase activity	`GO:0106435` IDA ×2	REMOVE	MODIFY → `GO:0106435`
`GO:0007155` cell adhesion	IEA only, no experiment in any species	OVER_ANNOTATED	OVER_ANNOTATED (kept)

The hydrolase reversal is the substantive one. The old reason was "No
evidence of hydrolase activity; annotation is keyword-based and unreliable."
That is factually wrong: TSG-6 catalyses covalent transfer of
inter-alpha-inhibitor heavy chains onto hyaluronan through an ester
intermediate. The UniProt record for this protein says so —
[file:DESRO/K9IIP0/K9IIP0-uniprot.txt "is required for transesterification of
the HC to hyaluronan."] — the deep research independently lists
[file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md "enzymatic transesterase
activity transferring I"]αI heavy chains among TSG-6's activities, and human
TNFAIP6 carries GO:0106435 carboxylesterase activity from two direct assays
(PMID:16873769, PMID:20463016). GO:0106435 is a descendant of GO:0016787
(verified via OLS ancestors), so the right move is MODIFY, not REMOVE.

Added GO:0030212 hyaluronan metabolic process as NEW (ISS) — the BP
counterpart of that catalytic step, IDA-supported in human, and absent from the
DESRO GOA record.

The Vampirome study (PMID:23411029, cached) is the source of the EMBL record
(JAA46157.1) and confirms the protein in the gland proteome PMID:23411029 — 101 ions, the fourth most abundant family (semaphorin 855 ions >
plasminogen activator 597 > lipocalin 163 > TSG-6 101), corrected from an
earlier "third" in this file and in the review. Worth following up: TSG-6
PMID:23411029-α-inhibitor, while the best-characterised vampire bat salivary protein
is a plasminogen activator. Whether those two are functionally coupled is
recorded as a knowledge gap.

Review follow-up (2026-08-01)

Addressing the PR #2362 review:

core_functions now carries a second entry with molecular_function: GO:0106435 (carboxylesterase activity), directly_involved_in: GO:0030212,
locations: GO:0005615. Previously the file argued in existing_annotations
that the catalytic function was real enough to rescue the hydrolase
annotation, but never listed it as a core function. GO:0030212 moved to
that second entry, where it is the BP counterpart of the catalytic MF.
Promoted the orthologue evidence out of bare in-prose PMIDs into
references: with verbatim findings — PMID:20463016 [Sanggaard et al. "In
concert with HC2, TSG-6 have a unique catalytic activity transferring HCs
from bikunin proteins to hyaluronan (HA)."], PMID:26468290 [Briggs et al.
"TSG-6 was shown to play a direct role in the transfer of HCs from IαI onto
HA via the formation of covalent intermediates"], PMID:16873769 [Forteza et
al. "potentiating the antiplasmin activity of this serine protease
inhibitor"] — and cited them in supported_by for the GO:0016787 MODIFY
and the GO:0030212 NEW.
Re-anchored the GO:0030212 ISS annotation from the deep-research falcon
file to PMID:20463016, since the stated justification is orthologue transfer.
Replaced the domain-conservation quote (which spoke to Link/CUB retention,
not hyaluronan metabolism) with quotes on covalent HC transfer onto HA.
Corrected the abundance rank: TSG-6 is fourth, not third, in the PS gland
proteome (semaphorin 855, plasminogen activator 597, lipocalin 163, TSG-6
101). Fixed in the PMID:23411029 finding, in the knowledge-gap
significance, and above in this file.

Also from the non-blocking suggestions: the transesterification-vs-hydrolysis
mismatch of GO:0106435 is now recorded in the MODIFY reason and as a
suggested_questions entry rather than only in the PR description, and the
GO:0005615 reason no longer treats gland-tissue LC-MS/MS as localisation
evidence. Left unchanged: the GO_REF findings quote the UniProt flat file
rather than the GO_REF document — real provenance nit, but rewriting those
findings would move quotes away from the reference they document.

just validate DESRO K9IIP0 → ✓ Valid.

📄 View Raw YAML

id: K9IIP0
gene_symbol: K9IIP0
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:9430
  label: Desmodus rotundus
description: >-
  K9IIP0 is the common vampire bat orthologue of TSG-6 (TNFAIP6, tumor necrosis
  factor-inducible gene 6 protein), a secreted, inflammation-inducible
  glycoprotein of the extracellular matrix. The 277-residue precursor has a
  signal peptide (residues 1-17) followed by the two modules that define the
  family: an N-terminal Link module (residues 36-129, with the canonical
  58-127 and 82-103 disulfides) that binds hyaluronan, and a C-terminal CUB
  domain (residues 135-247). Through the Link module TSG-6 binds hyaluronan and
  non-covalently cross-links it, and it catalyses the covalent transfer of
  inter-alpha-inhibitor heavy chains onto hyaluronan to build heavy chain-
  hyaluronan complexes, remodelling matrices at sites of inflammation. The same
  module binds a wide range of C-X-C and C-C chemokines and thereby blocks their
  presentation on endothelial glycosaminoglycans, which is the mechanistic basis
  of the protein's anti-inflammatory action: mammalian TSG-6 suppresses
  neutrophil transendothelial migration and dampens inflammation in numerous in
  vivo models. In D. rotundus at least two TSG-6 family members are transcribed
  in the submaxillary salivary glands, and TSG-6 was confirmed in the principal
  gland proteome by LC-MS/MS, making it one of the more abundant salivary
  proteins and a candidate anti-inflammatory component of the bite-site
  secretion.
existing_annotations:
  - term:
      id: GO:0005540
      label: hyaluronic acid binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: >-
        Hyaluronan binding is the defining activity of the Link module, and the
        Link module of this protein is intact and confidently detected
        (PROSITE PS50963, residues 36-129, with both canonical disulfides
        annotated). The human orthologue TNFAIP6 carries this term from direct
        assay. The UniProt CAUTION does not bear on this call: it is scoped to
        PROSITE ProRule PRU00059, which is the CUB domain rule, not the Link
        rule (PRU00323) that supports the Link module features here.
      action: ACCEPT
      reason: >-
        Intact, well-detected Link module plus direct experimental support in
        the human orthologue. The earlier UNDECIDED reflected a misreading of
        the CAUTION, which concerns the CUB domain.
      supported_by:
        - &id_link
          reference_id: file:DESRO/K9IIP0/K9IIP0-uniprot.txt
          supporting_text: 'DOMAIN          36..129'
        - &id_linkmod
          reference_id: PMID:23411029
          supporting_text: >-
            The N-terminal domain of TSG-6 represents a structural motif known as
            the Link module, which confers affinity for hyaluronan.
          reference_section_type: DISCUSSION
        - &id_hamod
          reference_id: file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md
          supporting_text: >-
            The Link module mediates binding to hyaluronan (HA) and other
            glycosaminoglycans
  - term:
      id: GO:0005615
      label: extracellular space
    evidence_type: IEA
    original_reference_id: GO_REF:0000118
    review:
      summary: >-
        The precursor has a SignalP-predicted signal peptide (1-17) with a
        cleaved 18-277 mature chain, TSG-6 is a classical secreted matrix
        protein, the human orthologue is annotated to the extracellular region
        from direct assay, and TSG-6 was recovered from the D. rotundus
        principal submaxillary gland proteome by LC-MS/MS. As with the
        hyaluronan binding call, the CAUTION concerns the CUB domain and says
        nothing about localisation.
      action: ACCEPT
      reason: >-
        Signal peptide, family behaviour, and orthologue annotation all agree.
        The LC-MS/MS detection was made on principal gland tissue, so strictly
        it is expression evidence rather than localisation evidence; it
        corroborates that the protein is made in quantity here, while the
        secreted localisation itself rests on the signal peptide, the classical
        secreted family, and the direct-assay annotation of the human
        orthologue. Upgraded from UNDECIDED.
      supported_by:
        - reference_id: file:DESRO/K9IIP0/K9IIP0-uniprot.txt
          supporting_text: 'SIGNAL          1..17'
        - &id_proteome
          reference_id: PMID:23411029
          supporting_text: >-
            Of note, expression of TSG-6 was confirmed by the proteome of the PS
            gland (Figure 2A).
          reference_section_type: RESULTS
        - reference_id: file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md
          supporting_text: >-
            It is secreted into the extracellular space and acts in the ECM and
            pericellular matrix.
  - term:
      id: GO:0050728
      label: negative regulation of inflammatory response
    evidence_type: IEA
    original_reference_id: GO_REF:0000118
    review:
      summary: >-
        Anti-inflammatory action is the best-characterised biology of TSG-6, not
        a peripheral inference: the Link module binds chemokines and blocks
        their presentation on endothelial glycosaminoglycans, suppressing
        neutrophil transendothelial migration, and the protein inhibits
        inflammation across several in vivo models. The human orthologue carries
        this exact term both from direct assay (PMID:21569482) and by
        phylogenetic inference, so the TreeGrafter propagation to the bat
        protein is a legitimate transfer rather than an over-propagation. An
        earlier version of this review removed the term; there is no biological
        argument against it.
      action: ACCEPT
      reason: >-
        Well-supported family function with experimental backing in the human
        orthologue and an identified mechanism that depends on the Link module,
        which is intact in this protein. REMOVE is reserved for annotations that
        can be argued against on biological grounds; this one cannot.
      supported_by:
        - &id_antiinf
          reference_id: PMID:23411029
          supporting_text: >-
            TSG-6 inhibits inflammation, according to several in vivo models
          reference_section_type: DISCUSSION
        - &id_neutro
          reference_id: PMID:23411029
          supporting_text: >-
            TSG-6 also inhibits neutrophil migration to interact with macrophage
            CD44
          reference_section_type: DISCUSSION
  - term:
      id: GO:0016787
      label: hydrolase activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        This keyword-derived term is uninformative but, contrary to an earlier
        version of this review, it is not wrong. TSG-6 does catalyse a covalent
        chemical step: it transfers inter-alpha-inhibitor heavy chains onto
        hyaluronan via a TSG-6-heavy-chain ester intermediate. The human
        orthologue TNFAIP6 is annotated to GO:0106435 carboxylesterase activity
        from two independent direct assays (PMID:16873769, PMID:20463016), and
        GO:0106435 is a descendant of GO:0016787. The UniProt record for this
        very protein states that the ITIH2/HC2 interaction is required for
        transesterification of the heavy chain to hyaluronan.
      action: MODIFY
      reason: >-
        Replace the root-level hydrolase term with the specific child
        GO:0106435 carboxylesterase activity, which is the term the GO
        consortium uses for the experimentally demonstrated heavy-chain transfer
        activity of the human orthologue. Removing the annotation, as previously
        proposed, would have discarded a real catalytic function. Caveat to
        record explicitly: carboxylesterase activity is defined as ester
        hydrolysis, whereas TSG-6 performs two sequential transesterifications
        with no net hydrolysis, the heavy chain moving from the chondroitin
        sulfate of inter-alpha-inhibitor onto hyaluronan through a covalent
        TSG-6-heavy-chain ester intermediate. GO:0106435 is used here because it
        is the term the consortium applies to the human orthologue, not because
        the chemistry is a good fit; a transferase-branch term would describe
        the reaction better (see suggested_questions).
      proposed_replacement_terms:
        - id: GO:0106435
          label: carboxylesterase activity
      supported_by:
        - &id_transest
          reference_id: file:DESRO/K9IIP0/K9IIP0-uniprot.txt
          supporting_text: >-
            is required for transesterification of the HC to hyaluronan.
        - &id_transest2
          reference_id: file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md
          supporting_text: >-
            enzymatic transesterase activity transferring I
        - &id_hc_catalytic
          reference_id: PMID:20463016
          supporting_text: >-
            In concert with HC2, TSG-6 have a unique catalytic activity
            transferring HCs from bikunin proteins to hyaluronan (HA).
          reference_section_type: INTRODUCTION
        - &id_hc_ester
          reference_id: PMID:20463016
          supporting_text: >-
            The reaction involves two divalent cation-dependent
            transesterifications and a covalent intermediate composed of TSG-6
            and the HC to be transferred
          reference_section_type: INTRODUCTION
        - &id_hc_catalyst
          reference_id: PMID:26468290
          supporting_text: >-
            TSG-6 was shown to play a direct role in the transfer of HCs from
            IαI onto HA via the formation of covalent intermediates
          reference_section_type: INTRODUCTION
  - term:
      id: GO:0007155
      label: cell adhesion
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        This comes from the UniProt Cell adhesion keyword. Even in the human
        orthologue the term has never risen above electronic evidence, and the
        documented matrix biology of TSG-6 is hyaluronan binding,
        cross-linking, and heavy-chain transfer rather than adhesion between
        cells. Any effect on adhesion is indirect, through the altered
        hyaluronan matrix, and is better captured by the hyaluronan terms.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Keyword-derived, unsupported by experiment in any species, and
        attributing to the protein a role that is a downstream consequence of
        its matrix remodelling rather than its own activity.
      supported_by:
        - reference_id: file:DESRO/K9IIP0/K9IIP0-uniprot.txt
          supporting_text: 'Cell adhesion {ECO:0000256|ARBA:ARBA00022889};'
        - *id_hamod
  - term:
      id: GO:0030212
      label: hyaluronan metabolic process
    evidence_type: ISS
    original_reference_id: PMID:20463016
    review:
      summary: >-
        Proposed new annotation. The heavy-chain transfer reaction covalently
        modifies hyaluronan to form heavy chain-hyaluronan complexes, which is a
        hyaluronan metabolic process; the human orthologue carries this term
        from two direct assays (PMID:20463016, PMID:26468290). This is the
        biological process counterpart of the carboxylesterase activity proposed
        above, and the GOA record for this protein has no term covering it.
      action: NEW
      reason: >-
        Completes the molecular function to biological process link for the
        heavy-chain transfer activity, and mirrors the experimentally supported
        annotation of the human orthologue. Anchored to the orthologue
        experimental evidence (PMID:20463016, PMID:26468290) rather than to the
        deep-research survey, since the justification is orthologue transfer.
      supported_by:
        - *id_transest
        - reference_id: PMID:20463016
          supporting_text: >-
            can be transferred to different hyaluronan (HA) molecules by
            TSG-6/HC2
          reference_section_type: ABSTRACT
        - reference_id: PMID:26468290
          supporting_text: >-
            both HC1 and HC2 of IαI can be covalently transferred onto the
            C6-hydroxyls of the N-acetyl glucosamine sugars in HA
          reference_section_type: INTRODUCTION
references:
  - id: GO_REF:0000002
    title: Gene Ontology annotation through association of InterPro records with
      GO terms
    findings:
      - statement: >-
          Hyaluronic acid binding was inferred from the Link domain InterPro
          signature IPR000538, which is confidently matched in this protein.
        supporting_text: 'InterPro; IPR000538; Link_dom.'
  - id: GO_REF:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
    findings:
      - statement: >-
          The root-level hydrolase activity annotation derives from the ARBA
          Hydrolase keyword. The keyword itself is defensible for TSG-6, whose
          heavy-chain transfer proceeds through an ester intermediate, but the
          term is far less informative than the carboxylesterase activity term
          used for the human orthologue.
        supporting_text: 'Hydrolase {ECO:0000256|ARBA:ARBA00022801};'
  - id: GO_REF:0000118
    title: TreeGrafter-generated GO annotations
    findings:
      - statement: >-
          Extracellular space and negative regulation of inflammatory response
          were propagated from the PANTHER TSG-6 subfamily PTHR46908:SF4. The
          human orthologue carries the inflammatory-response term from direct
          assay as well as by phylogenetic inference, so this propagation rests
          on experimental evidence rather than on prediction alone.
        supporting_text: >-
          PANTHER; PTHR46908:SF4; TUMOR NECROSIS FACTOR-INDUCIBLE GENE 6 PROTEIN;
          1.
  - id: GO_REF:0000120
    title: Combined Automated Annotation using Multiple IEA Methods
    findings:
      - statement: >-
          The cell adhesion annotation derives from combined automated methods
          applied to the Cell adhesion keyword; no experimental evidence for
          this process exists for TSG-6 in any species.
        supporting_text: 'Cell adhesion {ECO:0000256|ARBA:ARBA00022889};'
  - id: PMID:23411029
    title: 'The "Vampirome": Transcriptome and proteome analysis of the principal
      and accessory submaxillary glands of the vampire bat Desmodus rotundus, a
      vector of human rabies.'
    findings:
      - statement: >-
          At least two TSG-6 family members are transcribed in D. rotundus
          salivary gland, and TSG-6 was confirmed in the principal gland
          proteome by LC-MS/MS (101 ions, the fourth most abundant protein
          family identified, after semaphorin at 855 ions, plasminogen activator
          at 597 and lipocalin at 163). This is the study whose EMBL submission
          (JAA46157.1, salivary gland) underlies the K9IIP0 accession.
        supporting_text: >-
          Of note, expression of TSG-6 was confirmed by the proteome of the PS
          gland (Figure 2A).
        reference_section_type: RESULTS
      - statement: >-
          The Link module is the hyaluronan-binding module that defines the
          hyaladherin family, and it is the N-terminal half of TSG-6.
        supporting_text: >-
          The N-terminal domain of TSG-6 represents a structural motif known as
          the Link module, which confers affinity for hyaluronan.
        reference_section_type: DISCUSSION
      - statement: >-
          TSG-6 suppresses neutrophil migration and inhibits inflammation in
          multiple in vivo models, which is the basis for the anti-inflammatory
          annotation.
        supporting_text: >-
          TSG-6 inhibits inflammation, according to several in vivo models
        reference_section_type: DISCUSSION
      - statement: >-
          TSG-6 potentiates the antiplasmin activity of inter-alpha-inhibitor
          through a Link module to bikunin interaction, linking the protein to
          fibrinolysis regulation as well as inflammation - potentially relevant
          in a saliva that also contains a plasminogen activator.
        supporting_text: >-
          TSG-6 has been found to potentiate the antiplasmin activity of inter
        reference_section_type: DISCUSSION
      - statement: >-
          The function of the C-terminal CUB domain of TSG-6 remains
          unidentified. This is the domain to which the UniProt CAUTION for this
          protein is scoped.
        supporting_text: >-
          The C terminal half of TSG-6 forms a CUB (complement subcomponents
          C1r/C1s, Uegf, BMP-1) domain whose function remains unidentified
        reference_section_type: DISCUSSION
      - statement: >-
          The authors propose an anti-inflammatory role for the protein in bat
          saliva specifically, but state it as a possibility rather than a
          measurement.
        supporting_text: >-
          In bat saliva, this protein may function as an anti-inflammatory
          molecule.
        reference_section_type: DISCUSSION
        finding_review:
          finding_status: CURRENT
          review_notes: >-
            Hypothesis about the salivary role. The underlying anti-inflammatory
            biology of TSG-6 is well established in mammals; what is untested is
            whether the bat salivary protein exerts it on the host.
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        PubMed-verified, full text available via PMC. Source publication for the
        EMBL entry (JAA46157.1) behind K9IIP0, with a dedicated TSG-6 section and
        proteomic confirmation in the gland.
  - id: PMID:20463016
    title: The TSG-6/HC2-mediated transfer is a dynamic process shuffling heavy
      chains between glycosaminoglycans.
    findings:
      - statement: >-
          TSG-6, acting with heavy chain 2, has a catalytic activity that
          transfers inter-alpha-inhibitor heavy chains onto hyaluronan. This is
          the direct experimental basis for the carboxylesterase activity term
          on the human orthologue and, by orthology, for the proposed
          replacement term here.
        supporting_text: >-
          In concert with HC2, TSG-6 have a unique catalytic activity
          transferring HCs from bikunin proteins to hyaluronan (HA).
        reference_section_type: INTRODUCTION
      - statement: >-
          The reaction proceeds by two divalent cation-dependent
          transesterifications through a covalent TSG-6-heavy-chain
          intermediate, which is why the chemistry is transesterification rather
          than the net hydrolysis that GO:0106435 formally describes.
        supporting_text: >-
          The reaction involves two divalent cation-dependent
          transesterifications and a covalent intermediate composed of TSG-6 and
          the HC to be transferred
        reference_section_type: INTRODUCTION
      - statement: >-
          Heavy chains are transferred onto hyaluronan and can be further
          shuffled between glycosaminoglycans, so the activity covalently
          modifies hyaluronan itself - the basis of the proposed hyaluronan
          metabolic process annotation.
        supporting_text: >-
          can be transferred to different hyaluronan (HA) molecules by TSG-6/HC2
        reference_section_type: ABSTRACT
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        Cached full text available. Human/bovine biochemistry, cited here as the
        orthologue evidence underpinning the ISS transfer to the bat protein;
        the bat protein itself has not been assayed.
  - id: PMID:26468290
    title: Metal Ion-dependent Heavy Chain Transfer Activity of TSG-6 Mediates
      Assembly of the Cumulus-Oocyte Matrix.
    findings:
      - statement: >-
          TSG-6 acts as a catalyst in the transfer of heavy chains from
          inter-alpha-inhibitor onto hyaluronan through covalent
          heavy-chain-TSG-6 intermediates, and is the only known transferase
          able to produce heavy chain-hyaluronan complexes.
        supporting_text: >-
          TSG-6 was shown to play a direct role in the transfer of HCs from IαI
          onto HA via the formation of covalent intermediates
        reference_section_type: INTRODUCTION
      - statement: >-
          The heavy chains are attached covalently to hyaluronan sugars, so the
          reaction is a covalent modification of the hyaluronan polymer and
          falls under hyaluronan metabolic process.
        supporting_text: >-
          both HC1 and HC2 of IαI can be covalently transferred onto the
          C6-hydroxyls of the N-acetyl glucosamine sugars in HA
        reference_section_type: INTRODUCTION
      - statement: >-
          The heavy-chain transferase activity, rather than hyaluronan binding,
          is the activity required for cumulus-oocyte complex expansion in mice,
          establishing the catalytic function as physiologically load-bearing.
        supporting_text: >-
          it is the HC transferase activity of TSG-6, rather than HA binding,
          that is crucial for murine COC expansion
        reference_section_type: INTRODUCTION
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        Cached full text available. Human TSG-6 structure and mouse genetics;
        used as orthologue evidence for the catalytic and hyaluronan-metabolic
        calls on the bat protein.
  - id: PMID:16873769
    title: TSG-6 potentiates the antitissue kallikrein activity of
      inter-alpha-inhibitor through bikunin release.
    findings:
      - statement: >-
          TSG-6 forms covalent complexes with inter-alpha-inhibitor and
          pre-alpha-inhibitor heavy chains and potentiates the antiplasmin
          activity of bikunin, corroborating both the covalent heavy-chain
          chemistry and the fibrinolysis link noted for the salivary protein.
        supporting_text: >-
          potentiating the antiplasmin activity of this serine protease
          inhibitor
        reference_section_type: ABSTRACT
    reference_review:
      relevance: MEDIUM
      correctness: VERIFIED
      review_notes: >-
        Cached full text available. Human airway biology; cited for the covalent
        TSG-6-heavy-chain complex and the antiplasmin potentiation, not for any
        bat-specific claim.
  - id: file:DESRO/K9IIP0/K9IIP0-uniprot.txt
    title: UniProtKB record for K9IIP0 (K9IIP0_DESRO)
    findings:
      - statement: >-
          The protein is TSG-6/TNFAIP6 with a signal peptide (1-17), a Link
          domain (36-129) carrying the 58-127 and 82-103 disulfides, and a CUB
          domain (135-247).
        supporting_text: 'RecName: Full=Tumor necrosis factor-inducible gene 6 protein'
      - statement: >-
          The record states that the ITIH2/HC2 interaction is required for
          transesterification of the inter-alpha-inhibitor heavy chain onto
          hyaluronan, which is the covalent catalytic step behind the
          carboxylesterase activity annotation of the human orthologue.
        supporting_text: >-
          is required for transesterification of the HC to hyaluronan.
      - statement: >-
          The Link module is also recorded as binding a broad panel of C-X-C and
          C-C chemokines, interfering with their binding to glycosaminoglycans -
          the mechanism of TSG-6's anti-inflammatory action.
        supporting_text: >-
          interferes with chemokine binding to glycosaminoglycans. Interacts
      - statement: >-
          The UniProt CAUTION is scoped to PROSITE ProRule PRU00059, which is the
          CUB domain rule (PROSITE PS01180). It therefore limits confidence in
          CUB-derived feature transfer, and does not bear on the Link module
          (rule PRU00323), on secretion, or on hyaluronan binding.
        supporting_text: >-
          feature annotation. {ECO:0000256|PROSITE-ProRule:PRU00059}.
  - id: file:DESRO/K9IIP0/K9IIP0-deep-research-falcon.md
    title: Deep research report on K9IIP0
    findings:
      - statement: >-
          TSG-6 is a secreted inflammation-inducible glycoprotein whose Link
          module binds hyaluronan and other glycosaminoglycans, and which acts
          in the extracellular matrix and pericellular matrix.
        supporting_text: >-
          The Link module mediates binding to hyaluronan (HA) and other
          glycosaminoglycans
      - statement: >-
          The report enumerates enzymatic transesterase activity transferring
          inter-alpha-inhibitor heavy chains to hyaluronan among the biochemical
          activities of TSG-6, independently corroborating the catalytic call.
        supporting_text: >-
          enzymatic transesterase activity transferring I
      - statement: >-
          The report is explicit that direct bat-specific primary literature is
          limited and that its functional annotation is inferred from conserved
          domain architecture plus mammalian TSG-6 data.
        supporting_text: >-
          Direct bat-specific primary literature is limited; therefore, functional
          annotation is inferred from conserved domain architecture and extensive
          mammalian data on TSG-6.
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        LLM-generated survey, but an unusually accurate one: it correctly
        identifies the protein, enumerates the Link module, HA cross-linking,
        heavy-chain transesterase, and chemokine-binding activities, and states
        its own inferential limits. Several of its cited sources are flagged in
        the report itself as low-quality journals, so it is used here to
        corroborate rather than to establish claims, each of which is also
        anchored to the UniProt record or to PMID:23411029.
core_functions:
  - description: >-
      Secreted hyaladherin that binds hyaluronan through its Link module and
      remodels hyaluronan-rich extracellular matrix, both by non-covalent
      cross-linking and by covalently transferring inter-alpha-inhibitor heavy
      chains onto hyaluronan. The same module sequesters C-X-C and C-C
      chemokines and blocks their presentation on endothelial
      glycosaminoglycans, suppressing neutrophil recruitment and damping
      inflammation. In the vampire bat the protein is an abundant product of the
      principal submaxillary salivary gland.
    supported_by:
      - reference_id: PMID:23411029
        supporting_text: >-
          The N-terminal domain of TSG-6 represents a structural motif known as
          the Link module, which confers affinity for hyaluronan.
        reference_section_type: DISCUSSION
      - reference_id: PMID:23411029
        supporting_text: >-
          TSG-6 inhibits inflammation, according to several in vivo models
        reference_section_type: DISCUSSION
      - reference_id: file:DESRO/K9IIP0/K9IIP0-uniprot.txt
        supporting_text: >-
          is required for transesterification of the HC to hyaluronan.
    molecular_function:
      id: GO:0005540
      label: hyaluronic acid binding
    directly_involved_in:
      - id: GO:0050728
        label: negative regulation of inflammatory response
    locations:
      - id: GO:0005615
        label: extracellular space
    knowledge_gaps:
      - gap_statement: >-
          The function of the C-terminal CUB domain of TSG-6 is undetermined in
          any species, and for this protein the uncertainty is compounded:
          UniProt flags that the sequence lacks conserved residues required for
          propagating CUB feature annotation, so it is unknown whether the bat
          CUB domain is even intact in the functional sense.
        boundary: >-
          What is established is the Link module half: it binds hyaluronan,
          cross-links it, transfers inter-alpha-inhibitor heavy chains onto it,
          and sequesters chemokines. The CUB domain is detected by PROSITE
          PS01180 at residues 135-247 and is required, together with the Link
          module, for some interactions (ITIH1, TNFSF11, fibronectin), but no
          activity has been assigned to it.
        gap_kind:
          - BIOLOGY
        dark_aspect: RESIDUAL_SUBGAP
        status: OPEN
        significance: >-
          Half of a protein that reaches the fourth-highest abundance in the
          vampire bat salivary proteome has no assigned function; if the bat CUB
          domain is degenerate, that would suggest the salivary protein has been
          specialised toward the Link-module functions alone.
        resolution: >-
          Align the bat CUB domain against characterised CUB domains to identify
          which conserved residues are absent, then compare full-length
          recombinant bat TSG-6 with an isolated Link module in heavy-chain
          transfer and fibronectin-binding assays.
        provenance:
          - reference_id: PMID:23411029
            supporting_text: >-
              The C terminal half of TSG-6 forms a CUB (complement subcomponents
              C1r/C1s, Uegf, BMP-1) domain whose function remains unidentified
            reference_section_type: DISCUSSION
          - reference_id: file:DESRO/K9IIP0/K9IIP0-uniprot.txt
            supporting_text: >-
              CAUTION: Lacks conserved residue(s) required for the propagation of
      - gap_statement: >-
          It is undetermined whether salivary TSG-6 acts on the host at the bite
          site, and if so whether its principal target there is inflammation,
          chemokine-driven leukocyte recruitment, or fibrinolysis via
          inter-alpha-inhibitor.
        boundary: >-
          What is established is that TSG-6 is abundant in the bat principal
          submaxillary gland at both transcript and protein level, and that
          mammalian TSG-6 suppresses neutrophil transendothelial migration and
          potentiates the antiplasmin activity of inter-alpha-inhibitor. The
          Vampirome authors propose the anti-inflammatory salivary role
          explicitly as a possibility, not a finding.
        gap_kind:
          - BIOLOGY
        dark_aspect: BP_DARK
        status: OPEN
        significance: >-
          The antiplasmin angle is the interesting one: vampire bat saliva's
          best-characterised component is a plasminogen activator, so a salivary
          protein that potentiates an antiplasmin would either counterbalance it
          or act on a different compartment. Resolving this would say whether
          the two are functionally coupled.
        resolution: >-
          Test recombinant bat TSG-6 on host neutrophil transendothelial
          migration and on chemokine binding, and assay its effect on
          plasmin generation in the presence of inter-alpha-inhibitor and of the
          bat's own salivary plasminogen activator.
        provenance:
          - reference_id: PMID:23411029
            supporting_text: >-
              In bat saliva, this protein may function as an anti-inflammatory
              molecule.
            reference_section_type: DISCUSSION
  - description: >-
      Catalyses the covalent transfer of inter-alpha-inhibitor heavy chains onto
      hyaluronan, through two divalent cation-dependent transesterifications
      that proceed via a covalent TSG-6-heavy-chain ester intermediate, building
      the heavy chain-hyaluronan complexes that stabilise and cross-link
      hyaluronan-rich matrices. This is a distinct catalytic function from the
      non-covalent hyaluronan binding of the Link module, and for the bat
      protein it is inferred by orthology: the activity is experimentally
      established for mammalian TSG-6 and the corresponding UniProt statement is
      made for this record, but the bat protein itself has not been assayed. The
      GO term is the one the consortium applies to the human orthologue;
      chemically the reaction is a transesterification rather than the net
      hydrolysis that carboxylesterase activity denotes.
    supported_by:
      - *id_transest
      - *id_hc_catalytic
      - *id_hc_ester
      - *id_hc_catalyst
    molecular_function:
      id: GO:0106435
      label: carboxylesterase activity
    directly_involved_in:
      - id: GO:0030212
        label: hyaluronan metabolic process
    locations:
      - id: GO:0005615
        label: extracellular space
suggested_questions:
  - question: >-
      Is the abundant salivary TSG-6 of Desmodus rotundus delivered to the host
      bite wound, and does it suppress host neutrophil recruitment there?
    experts:
      - Ivo M. B. Francischetti
      - José M. C. Ribeiro
  - question: >-
      Does salivary TSG-6 interact functionally with the bat's own salivary
      plasminogen activator, given that mammalian TSG-6 potentiates the
      antiplasmin activity of inter-alpha-inhibitor?
  - question: >-
      Is GO:0106435 carboxylesterase activity the right term for the TSG-6
      heavy-chain transfer reaction, or is a transferase-branch term warranted?
      The reaction is two transesterifications with no net hydrolysis, so the
      hydrolase-branch term used for the human orthologue describes the chemistry
      poorly even though it is the established consortium precedent.
    experts:
      - Anthony J. Day
      - Jan J. Enghild
  - question: >-
      What distinguishes the two TSG-6 family members transcribed in vampire bat
      salivary gland, one of which carries C-terminal deletions - are they
      functionally redundant or specialised?
    experts:
      - Anthony J. Day
suggested_experiments:
  - hypothesis: >-
      Vampire bat salivary TSG-6 retains the heavy-chain transferase activity of
      mammalian TSG-6 despite the flagged CUB domain divergence.
    description: >-
      Express recombinant full-length bat TSG-6 and its isolated Link module,
      incubate each with inter-alpha-inhibitor and hyaluronan in the presence of
      magnesium, and detect heavy chain-hyaluronan complex formation by Western
      blot against inter-alpha-inhibitor heavy chains, using human TSG-6 as the
      positive control.
    experiment_type: In vitro heavy-chain transfer assay
  - hypothesis: >-
      Salivary TSG-6 suppresses host leukocyte recruitment at the bite site.
    description: >-
      Measure binding of recombinant bat TSG-6 to a panel of host C-X-C and C-C
      chemokines by surface plasmon resonance, then test whether it inhibits
      chemokine-driven neutrophil transendothelial migration across a host
      endothelial monolayer.
    experiment_type: Surface plasmon resonance and transendothelial migration assay
  - hypothesis: >-
      The C-terminal CUB domain of the bat protein is degenerate, specialising
      it toward Link-module functions.
    description: >-
      Align the bat CUB domain against characterised CUB domains to identify
      which conserved residues are missing, model the domain with AlphaFold, and
      compare full-length bat TSG-6 with a CUB-deleted construct in fibronectin
      binding and heavy-chain transfer assays.
    experiment_type: Comparative sequence and structure analysis with domain-deletion assays

K9IIP0

Gene Description

Existing Annotations Review

Core Functions

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Citations

📚 Additional Documentation

Notes

K9IIP0 Research Notes

Key findings

2026-07-31 compliance review

Review follow-up (2026-08-01)

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