VIN1 is the vinculin ortholog of the homoscleromorph sponge Oscarella pearsei, an 846-residue member of the vinculin/alpha-catenin family. It groups with animal vinculins in phylogenetic analyses and its 2.3 A crystal structure is more similar to vertebrate vinculin than to alpha-catenin, although it lacks domain D2, the helix bundle that otherwise distinguishes vinculins from alpha-catenins. Recombinant VIN1 is a monomer. Its N-terminal D1 domain binds a peptide from the vinculin-binding site of sponge talin (TLN) with high affinity, whereas full-length VIN1 binds the same peptide about ten-fold more weakly, indicating partial head-tail autoinhibition. VIN1 alone does not bind actin filaments, but talin peptide relieves this autoinhibition and allows F-actin binding, the same activation mechanism as in vertebrate vinculin. VIN1 does not bind beta-catenin. In sponge tissue the endogenous protein co-localizes with actin filaments in belt-like zones at cell-cell contacts of the outer epithelium (pinacoderm) and feeding epithelium (choanoderm), at the base of the microvillar collar of choanocytes, and in filopodial and lamellipodial extensions of migratory mesohyl cells. These properties suggest that VIN1 links adhesion complexes at cell-cell and cell-matrix contacts to the actin cytoskeleton, as vinculin does in other animals.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003779 actin binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the vinculin family signature. Correct but general; F-actin binding was shown directly for this protein in a talin-dependent manner. Reason: The more specific actin filament binding (GO:0051015) is supported by IDA in PMID:29880641, so this broader parent is consistent with the experimental data. Supporting Evidence: PMID:29880641 In the presence of Op talin peptide, full-length Op vinculin bound to F-actin filaments |
| GO:0005515 protein binding | IPI PMID:29880641 Analysis of a vinculin homolog in a sponge (phylum Porifera)... | MODIFY | Summary: ITC shows that full-length VIN1 and its D1 domain bind a synthetic peptide corresponding to the vinculin-binding site of O. pearsei talin (TLN residues 598-621); the D1 interaction has nanomolar affinity, comparable to the mammalian vinculin-talin interaction. Reason: Generic protein binding is uninformative. The interacting partner is specifically talin, and the paper treats this binding as the vinculin activation mechanism, so talin binding (GO:1990147) captures the function. The interaction was not shown with alpha-catenin or cadherin, so terms such as alpha-catenin binding or cadherin binding are not supported. Proposed replacements: talin binding Supporting Evidence: PMID:29880641 Full-length Op vinculin and Op vinculin D1 bound Op talin peptide PMID:29880641 Moreover, Op vinculin bound talin but not Ξ²-catenin |
| GO:0005856 cytoskeleton | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping; the underlying UniProt statement is based on co-localization of endogenous VIN1 with actin filaments in sponge tissue. Reason: General but correct; the more specific cortical cytoskeleton is annotated by IDA. Supporting Evidence: PMID:29880641 In each cellular context, Op vinculin appeared to co-localize with actin filaments, indicating an evolutionarily conserved interaction with the actin cytoskeleton. |
| GO:0005938 cell cortex | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping, reflecting the cortical actin belts at cell-cell contacts where VIN1 is found in sponge epithelia. Reason: Consistent with the immunostaining of endogenous protein in O. pearsei pinacoderm and choanoderm. Supporting Evidence: PMID:29880641 Immunofluorescence of O. pearsei tissue using an affinity-purified antibody raised against Op vinculin showed co-localization with cortical belts of actin filaments at cellβcell contacts in the pinacoderm and choanoderm tissues |
| GO:0007155 cell adhesion | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the vinculin/catenin domain. Vinculin in other animals connects cadherin- and integrin-based adhesions to actin; in the sponge, VIN1 is at cell-cell contacts and in migratory-cell protrusions and shows the conserved talin-activated F-actin binding. Reason: Vinculin does part of the work of adhesion (it is the actin-anchoring linker in adhesion complexes), so the general process term is appropriate for a vinculin ortholog with conserved biochemistry. The sponge data are localization and in vitro binding only; no loss-of-function test of adhesion exists, so the more specific adhesion subtypes are not asserted. Supporting Evidence: PMID:29880641 We propose that Op vinculin played a role in cell adhesion and tissue organization in the last common ancestor of sponges and other animals. PMID:29880641 Mammalian vinculin predominantly localizes to cellβECM contacts, where it anchors FA complexes to the actin cytoskeleton |
| GO:0030175 filopodium | IDA PMID:29880641 Analysis of a vinculin homolog in a sponge (phylum Porifera)... | ACCEPT | Summary: Immunostaining of endogenous VIN1 in fixed O. pearsei tissue (not heterologous expression) detects VIN1 with actin in filopodial and lamellipodial extensions of motile cells in the mesohyl. Reason: Directly observed in sponge cells with an antibody validated by Western blot, antigen competition and immunoprecipitation. The authors interpret this as cell-matrix (focal-adhesion-like) contacts in migrating cells, but this was not tested with other focal adhesion markers. Supporting Evidence: PMID:29880641 in filopodial/lamellopodial extensions of motile cells within the mesohyl |
| GO:0030175 filopodium | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping derived from the same immunostaining observation as the IDA row. Reason: Duplicates the IDA annotation and is correct. Supporting Evidence: PMID:29880641 in filopodial/lamellopodial extensions of motile cells within the mesohyl |
| GO:0030863 cortical cytoskeleton | IDA PMID:29880641 Analysis of a vinculin homolog in a sponge (phylum Porifera)... | ACCEPT | Summary: Endogenous VIN1 co-localizes with cortical belts of actin filaments at cell-cell contacts in sponge pinacoderm and choanoderm, shown by immunofluorescence with phalloidin co-stain in fixed O. pearsei tissue. Reason: Direct observation in the native organism; this is the principal location of the protein in sponge epithelia. Supporting Evidence: PMID:29880641 Immunofluorescence of O. pearsei tissue using an affinity-purified antibody raised against Op vinculin showed co-localization with cortical belts of actin filaments at cellβcell contacts in the pinacoderm and choanoderm tissues |
| GO:0051015 actin filament binding | IDA PMID:29880641 Analysis of a vinculin homolog in a sponge (phylum Porifera)... | ACCEPT | Summary: High-speed co-sedimentation with rabbit skeletal muscle F-actin: VIN1 alone does not bind F-actin, but binds in the presence of the sponge talin peptide, which relieves head-tail autoinhibition. Reason: Directly measured with recombinant protein. The activity is conditional on talin-mediated activation, as for vertebrate vinculin; this is the core molecular function of a vinculin. Supporting Evidence: PMID:29880641 Like vertebrate vinculins, Op vinculin did not bind F-actin significantly above background at concentrations up to 15 PMID:29880641 In the presence of Op talin peptide, full-length Op vinculin bound to F-actin filaments |
| GO:0051015 actin filament binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the vinculin/catenin domain; agrees with the direct experimental evidence. Reason: Confirmed by the IDA annotation from PMID:29880641. Supporting Evidence: PMID:29880641 Thus, binding of talin to Op vinculin D1 releases autoinhibition for F-actin binding, similar to the behavior of vertebrate vinculin. |
| GO:0005911 cell-cell junction | IDA PMID:29880641 Analysis of a vinculin homolog in a sponge (phylum Porifera)... | NEW | Summary: Endogenous VIN1 forms a belt-like zone at points of cell-cell contact in the pinacoderm and in the choanoderm of O. pearsei, co-localized with cortical actin. Reason: Not captured by existing annotations (cortical cytoskeleton and cell cortex do not convey the cell-cell contact location). Cell-cell junction is chosen rather than adherens junction because the contacts have not been defined ultrastructurally or with cadherin/catenin co-staining, and the authors themselves present an adherens junction only as a possibility. Supporting Evidence: PMID:29880641 a belt-like zone at points of cellβcell contact in the pinacoderm PMID:29880641 The localization of Op vinculin to cellβcell contacts in the pinacoderm and choanoderm is consistent with a possible AJ in these tissues, despite the lack of ultrastructural evidence |
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Download this section (compressed HTML)Q: Are the VIN1-positive belts at sponge cell-cell contacts cadherin-catenin adherens junctions? Do O. pearsei cadherin, beta-catenin and alpha-catenin co-localize with VIN1 there, and does VIN1 bind O. pearsei alpha-catenin?
Q: Are the VIN1-positive filopodia of migratory mesohyl cells integrin- and talin-containing focal-adhesion-like contacts?
Q: Given that VIN1 lacks domain D2, how does it achieve autoinhibition, and is its weaker autoinhibition physiologically relevant?
Experiment: Co-stain O. pearsei tissue for VIN1 with antibodies to TLN, integrin beta, cadherin and alpha-catenin to assign VIN1-positive contacts to cell-matrix or cell-cell adhesion structures; complement with immuno-electron microscopy.
Type: Co-immunolocalization
Experiment: Test binding of VIN1 to full-length O. pearsei talin rod fragments and to O. pearsei alpha-catenin, including under force (e.g. optical trap), and test F-actin binding with sponge actin.
Type: Binding assay
Experiment: Inhibit VIN1 (e.g. antibody or morpholino/RNAi delivery in tissue explants or reaggregating cells) and score epithelial integrity and cell migration.
Type: Functional perturbation
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