id: A0A3G2LGI8 gene_symbol: TLN product_type: PROTEIN status: DRAFT aliases: - Op talin - TLN_OSCPE taxon: id: NCBITaxon:1940113 label: Oscarella pearsei description: >- TLN is the talin of the homoscleromorph sponge Oscarella pearsei, a 2531-residue cytoskeletal adaptor with the domain organization of animal talins: an N-terminal FERM head, followed by a talin rod made of helical bundles that carry vinculin-binding sites, and a C-terminal I/LWEQ actin-binding domain. It also has a predicted phosphotyrosine-binding domain just after the FERM domain that is absent from mouse talin. A peptide corresponding to its principal vinculin-binding site (residues 598-621) binds the D1 domain of sponge vinculin (VIN1) with nanomolar affinity and activates F-actin binding by VIN1, reproducing the talin-vinculin activation mechanism of vertebrate focal adhesions. By homology with talins of other animals, TLN is expected to bind integrin beta-subunit cytoplasmic tails and membrane lipids through its head and actin filaments through its rod and C-terminus, linking integrin-based cell-matrix adhesions to the actin cytoskeleton; these activities have not been tested for the sponge protein. references: - id: GO_REF:0000002 title: Gene Ontology annotation through association of InterPro records with GO terms findings: [] - id: GO_REF:0000044 title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt findings: [] - id: GO_REF:0000117 title: Electronic Gene Ontology annotations created by ARBA machine learning models findings: [] - id: GO_REF:0000118 title: TreeGrafter-generated GO annotations findings: [] - id: GO_REF:0000120 title: Combined Automated Annotation using Multiple IEA Methods findings: [] - id: PMID:29880641 title: Analysis of a vinculin homolog in a sponge (phylum Porifera) reveals that vertebrate-like cell adhesions emerged early in animal evolution. findings: - statement: >- TLN has the conserved talin domain organization, plus an additional predicted PTB domain. supporting_text: >- As in their mammalian counterparts, Op talin has an N-terminal FERM domain followed by a talin middle domain, vinculin-binding sites, and an I/WLEQ domain. - statement: >- The tested TLN fragment is a synthetic peptide of residues 598-621, homologous to the mouse talin vinculin-binding site. supporting_text: >- In a MUSCLE alignment Mm talin 605–628 correspond to residues 598–621 in Op talin - statement: >- The TLN peptide binds VIN1 and activates VIN1 binding to F-actin. supporting_text: >- In the presence of Op talin peptide, full-length Op vinculin bound to F-actin filaments reference_review: relevance: HIGH correctness: VERIFIED review_notes: >- Only paper on this protein; full text cached (PMC6066325) and matches the UniProt RN citation for TLN_OSCPE. The paper is focused on VIN1; TLN was studied only as a synthetic 24-residue vinculin-binding-site peptide in ITC and co-sedimentation assays. TLN localization and other activities were not examined. existing_annotations: - term: id: GO:0001726 label: ruffle evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: located_in supporting_entities: - InterPro:IPR015224 review: summary: >- InterPro2GO mapping from the talin central domain. No localization data exist for sponge talin. action: MARK_AS_OVER_ANNOTATED reason: >- Ruffle is a peripheral, context-dependent location of talin in cultured vertebrate cells, and a domain signature is a poor predictor of it. The characteristic talin location (focal adhesion / anchoring junction) is already annotated, and no ruffle-like structure has been described for O. pearsei talin. - term: id: GO:0003779 label: actin binding evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: enables supporting_entities: - InterPro:IPR002558 - InterPro:IPR035964 review: summary: >- InterPro2GO mapping from the I/LWEQ actin-binding domain, which TLN has at its C-terminus. action: ACCEPT reason: >- The I/LWEQ domain is the conserved talin F-actin-binding module and is present in TLN; untested in sponge but well-founded by homology. supported_by: - reference_id: PMID:29880641 supporting_text: >- As in their mammalian counterparts, Op talin has an N-terminal FERM domain followed by a talin middle domain, vinculin-binding sites, and an I/WLEQ domain. - term: id: GO:0005178 label: integrin binding evidence_type: IEA original_reference_id: GO_REF:0000118 qualifier: enables supporting_entities: - PANTHER:PTN001072690 review: summary: >- TreeGrafter (PANTHER) propagation from the talin family node. Integrin beta tail binding by the talin FERM head is the defining talin activity. action: ACCEPT reason: >- TLN retains the FERM head and the talin domain architecture, and sponges are inside the animal clade in which talin-integrin linkage is conserved. No target-specific evidence of loss. Not experimentally tested in sponge. supported_by: - reference_id: PMID:29880641 supporting_text: >- integrins anchor to the actin cytoskeleton through interactions with a large number of cytoplasmic proteins including talin, vinculin, and paxillin - term: id: GO:0005200 label: structural constituent of cytoskeleton evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: enables supporting_entities: - InterPro:IPR015224 review: summary: >- InterPro2GO mapping from the talin central domain. action: MARK_AS_OVER_ANNOTATED reason: >- Talin is an adaptor that links integrins and membrane to actin filaments and recruits vinculin; it is not a polymer-forming or lattice structural constituent of the cytoskeleton. Its activity is better described by integrin binding, actin filament binding and vinculin binding, all of which are annotated. - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:29880641 qualifier: enables supporting_entities: - UniProtKB:A0A3B6UES5 review: summary: >- ITC with a synthetic peptide of TLN residues 598-621 (the homolog of the mouse talin vinculin-binding site) and recombinant VIN1 or its D1 domain shows direct binding; the peptide also activates VIN1 F-actin binding. action: MODIFY reason: >- Generic protein binding is uninformative. The partner is vinculin and the tested segment is a vinculin-binding site, so vinculin binding (GO:0017166) describes the function. Caveat: evidence is from a peptide, not full-length TLN, whose vinculin-binding sites in other talins are cryptic until the rod is unfolded by force. proposed_replacement_terms: - id: GO:0017166 label: vinculin binding supported_by: - reference_id: PMID:29880641 supporting_text: >- Full-length Op vinculin and Op vinculin D1 bound Op talin peptide - reference_id: PMID:29880641 supporting_text: >- In a MUSCLE alignment Mm talin 605–628 correspond to residues 598–621 in Op talin - term: id: GO:0005737 label: cytoplasm evidence_type: IEA original_reference_id: GO_REF:0000118 qualifier: located_in supporting_entities: - PANTHER:PTN001072690 review: summary: >- TreeGrafter propagation; talin is a cytoplasmic protein. action: ACCEPT reason: >- Correct, if general, for a soluble cytoskeletal adaptor. - term: id: GO:0005856 label: cytoskeleton evidence_type: IEA original_reference_id: GO_REF:0000044 qualifier: located_in supporting_entities: - UniProtKB-SubCell:SL-0090 review: summary: >- UniProt subcellular location by similarity (UniProtKB:P0CE95); no sponge data. action: ACCEPT reason: >- Talins associate with the actin cytoskeleton throughout eukaryotes; general and consistent with the conserved actin-binding domains. - term: id: GO:0005886 label: plasma membrane evidence_type: IEA original_reference_id: GO_REF:0000118 qualifier: located_in supporting_entities: - PANTHER:PTN001072690 review: summary: >- TreeGrafter propagation; talin heads associate with the inner face of the plasma membrane at integrin adhesions. action: ACCEPT reason: >- Consistent with the conserved FERM head (membrane- and integrin-binding) in TLN. Not tested in sponge. - term: id: GO:0005925 label: focal adhesion evidence_type: IEA original_reference_id: GO_REF:0000120 qualifier: located_in supporting_entities: - InterPro:IPR015224 - PANTHER:PTN001072690 review: summary: >- Combined InterPro/PANTHER automatic annotation. Focal adhesion is the principal location of talin in other animals. action: ACCEPT reason: >- Talin is a core focal adhesion component across animals. Focal-adhesion-like structures in O. pearsei are not defined molecularly; VIN1, the talin partner, is found in filopodia of migratory cells that the authors interpret as cell-ECM contacts. Accepted as the family-level location. supported_by: - reference_id: PMID:29880641 supporting_text: >- The AJ (containing cadherins and catenins) and FAs (comprising integrins, talin, and paxillin) differ in protein composition - term: id: GO:0005938 label: cell cortex evidence_type: IEA original_reference_id: GO_REF:0000044 qualifier: located_in supporting_entities: - UniProtKB-SubCell:SL-0138 review: summary: >- UniProt subcellular location by similarity (UniProtKB:P0CE95); no sponge data. action: ACCEPT reason: >- Talins act at the membrane-cortex interface; general and plausible. - term: id: GO:0007155 label: cell adhesion evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: involved_in supporting_entities: - InterPro:IPR036723 review: summary: >- InterPro2GO mapping from the alpha-catenin/vinculin-like superfamily (talin rod bundles). action: ACCEPT reason: >- Talin does part of the work of integrin-mediated adhesion (it links and activates integrins and recruits vinculin and actin), so the general term is appropriate for a talin with conserved domain architecture. supported_by: - reference_id: PMID:29880641 supporting_text: >- integrins anchor to the actin cytoskeleton through interactions with a large number of cytoplasmic proteins including talin, vinculin, and paxillin - term: id: GO:0030036 label: actin cytoskeleton organization evidence_type: IEA original_reference_id: GO_REF:0000118 qualifier: involved_in supporting_entities: - PANTHER:PTN001072690 review: summary: >- TreeGrafter propagation from the talin family node. action: KEEP_AS_NON_CORE reason: >- Talin anchors actin filaments at adhesions and so contributes to actin organization, but this is a consequence of its adaptor role rather than its core function; untested in sponge. - term: id: GO:0051015 label: actin filament binding evidence_type: IEA original_reference_id: GO_REF:0000002 qualifier: enables supporting_entities: - InterPro:IPR036723 review: summary: >- InterPro2GO mapping. Talins bind F-actin through rod and I/LWEQ domains. action: ACCEPT reason: >- TLN has the I/LWEQ domain and talin rod; conserved activity, not tested in sponge. - term: id: GO:0070161 label: anchoring junction evidence_type: IEA original_reference_id: GO_REF:0000117 qualifier: located_in supporting_entities: - ARBA:ARBA00027154 review: summary: >- ARBA machine-learning rule; general parent of focal adhesion. action: ACCEPT reason: >- Correct at this general level and consistent with the focal adhesion annotation. - term: id: GO:0098609 label: cell-cell adhesion evidence_type: IEA original_reference_id: GO_REF:0000118 qualifier: involved_in supporting_entities: - PANTHER:PTN001072690 review: summary: >- TreeGrafter propagation from the talin family node. action: MODIFY reason: >- Talin's established role is in integrin-based attachment of cells to the extracellular matrix, whereas cell-cell contacts (adherens junctions) are built on cadherins and catenins. Nothing links O. pearsei talin to cell-cell contacts. The essence (adhesion) is right, but cell-matrix adhesion is the appropriate process. proposed_replacement_terms: - id: GO:0007160 label: cell-matrix adhesion supported_by: - reference_id: PMID:29880641 supporting_text: >- The AJ (containing cadherins and catenins) and FAs (comprising integrins, talin, and paxillin) differ in protein composition propagation_review: root_cause: TERM_SCOPING_PROBLEM failure_modes: - GRANULARITY_MISMATCH source_entities: - source_id: PANTHER:PTN001072690 source_label: talin family node source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET comment: >- The family-node adhesion term is right in essence, but talin acts at integrin-matrix adhesions; cell-cell adhesion is the wrong sibling for this sponge protein. core_functions: - description: >- Vinculin binding. The TLN vinculin-binding site (residues 598-621) binds the D1 domain of sponge vinculin with nanomolar affinity and releases vinculin autoinhibition so that vinculin binds F-actin, the conserved talin-vinculin reinforcement mechanism of integrin adhesions. molecular_function: id: GO:0017166 label: vinculin binding supported_by: - reference_id: PMID:29880641 supporting_text: >- Full-length Op vinculin and Op vinculin D1 bound Op talin peptide - reference_id: PMID:29880641 supporting_text: >- In the presence of Op talin peptide, full-length Op vinculin bound to F-actin filaments knowledge_gaps: - gap_statement: >- Shown only with a 24-residue synthetic peptide. Whether full-length TLN binds VIN1, whether its vinculin-binding sites are cryptic and force-exposed as in vertebrate talin, and how many functional sites the rod carries are unknown. - description: >- Predicted integrin-actin adaptor at cell-matrix adhesions, by homology to animal talins: integrin beta-tail and membrane binding through the FERM head, and actin filament binding through the rod and C-terminal I/LWEQ domain. molecular_function: id: GO:0005178 label: integrin binding locations: - id: GO:0005925 label: focal adhesion supported_by: - reference_id: PMID:29880641 supporting_text: >- As in their mammalian counterparts, Op talin has an N-terminal FERM domain followed by a talin middle domain, vinculin-binding sites, and an I/WLEQ domain. - reference_id: PMID:29880641 supporting_text: >- integrins anchor to the actin cytoskeleton through interactions with a large number of cytoplasmic proteins including talin, vinculin, and paxillin knowledge_gaps: - gap_statement: >- None of these activities or the focal adhesion location has been tested for O. pearsei talin; the role of the extra PTB domain is unknown. suggested_questions: - question: >- Does full-length O. pearsei talin localize with VIN1 in the filopodia of migratory mesohyl cells and at basal contacts with the collagen IV-containing basal lamina, i.e. are these focal-adhesion-like contacts? - question: >- What does the additional PTB domain after the FERM domain of sponge talin bind? suggested_experiments: - experiment_type: Immunolocalization description: >- Raise an antibody to O. pearsei talin and co-stain with VIN1, integrin beta and phalloidin in sponge tissue. - experiment_type: Binding assay description: >- Test binding of the recombinant TLN FERM head to O. pearsei integrin beta cytoplasmic tails and to PIP2-containing membranes, and map vinculin binding across rod fragments with and without force (magnetic tweezers).