{"gene":"SIMC1","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2012,"finding":"C5orf25 (SIMC1) contains clustered SUMO-interacting motifs (SIMs) that form a distinct SUMO-binding domain capable of recognizing diverse forms of protein sumoylation, including polysumoylation. Dominant SIMs in the cluster contain a pentameric VIDLT core sequence. A FRET-based assay later confirmed that the SIM clusters of C5orf25 can bind to adjacent subunits of a SUMO chain.","method":"Computational string search, biochemical analysis of SIM clusters, FRET sensor assay with di-SUMO","journal":"The Journal of biological chemistry; Chembiochem","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — computational identification followed by biochemical validation (FRET sensor) in two independent studies, single-method each but orthogonal approaches","pmids":["23086935","29120074"],"is_preprint":false},{"year":2013,"finding":"PLEIAD/SIMC1/C5orf25 binds CAPN3 (skeletal-muscle-specific calpain-3) and suppresses its autolytic protease activity. PLEIAD also interacts with CTBP1 (a CAPN3 substrate and transcriptional co-regulator), scaffolding it for proteolysis by CAPN3 in COS7 cells. Thus PLEIAD can function as either a CAPN3 inhibitor or a substrate-recruitment scaffold depending on cellular context.","method":"Co-immunoprecipitation, in-cell proteolysis assay (COS7 cells expressing CAPN3), database/evolutionary conservation analysis, identification of CTBP1 cleavage sites","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal binding demonstrated plus functional proteolysis readout in cells, single lab with two orthogonal methods","pmids":["23707407"],"is_preprint":false},{"year":2022,"finding":"SIMC1 is a novel subunit of the human SMC5/6 complex. Its N-terminal SIMs and C-terminal Nse5-like domain together localize SMC5/6 to polyomavirus replication centers (PyVRCs) at SUMO-rich PML nuclear bodies. The Nse5-like domain of SIMC1 binds SLF2 (the putative human Nse6 orthologue) to form an anti-parallel helical dimer structurally resembling yeast Nse5/6. Structure-based mutagenesis of the SIMC1-SLF2 interface identified a conserved surface region at the N-terminus of SIMC1's helical domain that is required for SMC5/6 localization to PyVRCs. SLF1 binds SLF2 analogously to SIMC1, forming a separate, mutually exclusive Nse5/6-like complex that recruits SMC5/6 to chromosomal DNA lesions instead.","method":"Proteomic isolation from polyomavirus LT-induced compartments, Co-IP, cryo-EM/structural analysis of SIMC1-SLF2 dimer, structure-based mutagenesis, fluorescence microscopy localization","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — structure determination combined with mutagenesis, reciprocal Co-IP, and functional localization assays in a single rigorous study","pmids":["36373674"],"is_preprint":false},{"year":2025,"finding":"SMC5/6-mediated repression of plasmid transcription (extrachromosomal circular DNA silencing) depends exclusively on the SIMC1-SLF2 subcomplex; the SLF1/2 subcomplex is dispensable for this function. SIMC1-SLF2 does not participate in SMC5/6 recruitment to chromosomal DNA lesions, establishing functional specialization of the two Nse5/6-like subcomplexes. Plasmid silencing requires a conserved SIMC1-SLF2–SMC6 interaction and depends on the SUMO pathway but not on PML nuclear bodies. SV40 large T antigen interacts with SMC5/6 and antagonizes SIMC1-SLF2-dependent plasmid silencing.","method":"Genetic depletion/knockout of SIMC1-SLF2 vs. SLF1/2, transcription reporter assays for plasmid silencing, Co-IP for LT–SMC5/6 interaction, epistasis with SUMO pathway and PML NB perturbation","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal genetic and biochemical approaches in a single study, peer-reviewed publication replicating and extending prior findings from the same group","pmids":["41294034"],"is_preprint":false}],"current_model":"SIMC1 (PLEIAD/C5orf25) is a multifunctional scaffold protein: it acts as a regulatory subunit of the human SMC5/6 complex by forming an anti-parallel helical Nse5/6-like dimer with SLF2, using its N-terminal SIMs to sense SUMO-rich environments and its Nse5-like domain to bind SLF2, thereby directing SMC5/6 specifically to PML nuclear bodies and extrachromosomal DNA (viral and plasmid) for transcriptional silencing via the SUMO pathway; separately, in muscle cells it binds calpain-3 (CAPN3) to suppress its autolytic activity and can scaffold CAPN3 substrates such as CTBP1 for proteolysis."},"narrative":{"mechanistic_narrative":"SIMC1 (PLEIAD/C5orf25) is a SUMO-sensing scaffold that directs the human SMC5/6 complex to extrachromosomal DNA for transcriptional silencing [PMID:36373674, PMID:41294034]. Its N-terminal clustered SUMO-interacting motifs (SIMs), built around a pentameric VIDLT core, constitute a distinct SUMO-binding module that recognizes diverse sumoylation states, including polySUMO chains, by engaging adjacent subunits of a SUMO chain [PMID:23086935, PMID:29120074]. SIMC1 functions as a regulatory subunit of SMC5/6 through its C-terminal Nse5-like domain, which binds SLF2 (the putative human Nse6 orthologue) to form an anti-parallel helical dimer structurally resembling the yeast Nse5/6 module; a conserved surface at the N-terminus of this helical domain is required to localize SMC5/6 to SUMO-rich PML nuclear bodies and polyomavirus replication centers [PMID:36373674]. The SIMC1-SLF2 subcomplex is functionally specialized: it is exclusively required for SMC5/6-mediated silencing of plasmid (extrachromosomal circular DNA) transcription via a conserved SIMC1-SLF2–SMC6 interaction and the SUMO pathway, whereas the alternative, mutually exclusive SLF1-SLF2 subcomplex instead recruits SMC5/6 to chromosomal DNA lesions; SV40 large T antigen interacts with SMC5/6 and antagonizes this silencing [PMID:36373674, PMID:41294034]. Independently, in skeletal muscle SIMC1 binds calpain-3 (CAPN3) and suppresses its autolytic protease activity while also scaffolding the CAPN3 substrate CTBP1 for proteolysis, acting as either inhibitor or substrate-recruitment scaffold depending on context [PMID:23707407].","teleology":[{"year":2012,"claim":"Establishing how SIMC1 reads the SUMO landscape, this work defined its clustered SIMs as a dedicated SUMO-binding domain capable of recognizing polysumoylation rather than a single SUMO moiety.","evidence":"Computational SIM-cluster identification plus FRET sensor assay with di-SUMO","pmids":["23086935","29120074"],"confidence":"Medium","gaps":["Did not connect SUMO binding to any cellular complex or substrate","No structural model of the SIM cluster engaging a SUMO chain","In vivo relevance of polySUMO recognition untested at this stage"]},{"year":2013,"claim":"The first functional role assigned to PLEIAD/SIMC1 placed it in muscle calpain regulation, showing it can both inhibit CAPN3 autolysis and act as a substrate-delivery scaffold.","evidence":"Co-IP, in-cell proteolysis assay in COS7 cells, CTBP1 cleavage-site mapping","pmids":["23707407"],"confidence":"Medium","gaps":["Switch between inhibitor and scaffold modes not mechanistically defined","Relationship between the CAPN3 role and the SUMO-binding function unaddressed","Physiological consequence in muscle tissue not demonstrated"]},{"year":2022,"claim":"This study redefined SIMC1 as a bona fide SMC5/6 subunit, explaining how its SIMs and Nse5-like domain jointly target the complex to SUMO-rich nuclear bodies and viral replication centers.","evidence":"Proteomic isolation from polyomavirus compartments, reciprocal Co-IP, cryo-EM/structure of the SIMC1-SLF2 dimer, structure-based mutagenesis, microscopy","pmids":["36373674"],"confidence":"High","gaps":["Did not establish the transcriptional or silencing output of the localized complex","Functional distinction from the SLF1-SLF2 subcomplex not yet tested","Mechanism by which SUMO sensing is integrated with SLF2 binding incompletely resolved"]},{"year":2025,"claim":"By dissecting the two Nse5/6-like subcomplexes, this work showed the SIMC1-SLF2 module is specialized for silencing extrachromosomal DNA transcription, separating it functionally from the chromosomal-lesion role of SLF1-SLF2.","evidence":"Selective depletion/knockout of SIMC1-SLF2 vs SLF1/2, plasmid transcription reporters, Co-IP of LT–SMC5/6, epistasis with SUMO pathway and PML NB perturbation","pmids":["41294034"],"confidence":"High","gaps":["How the SUMO pathway acts independently of PML nuclear bodies in silencing is unresolved","Mechanism by which SV40 large T antigen antagonizes silencing not defined at molecular level","Whether the muscle CAPN3 role and the SMC5/6 role share regulatory inputs remains unconnected"]},{"year":null,"claim":"How SIMC1 integrates its SUMO-sensing, SMC5/6-targeting, and CAPN3-regulatory activities into a unified physiological program remains unknown.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No tissue-level phenotype linking the two functional arms","Structural basis of SUMO-chain recognition driving complex localization undefined","Determinants selecting between inhibitor and scaffold modes for CAPN3 unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,3]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[3]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[2,3]}],"complexes":["SMC5/6 complex","SIMC1-SLF2 (Nse5/6-like) subcomplex"],"partners":["SLF2","SMC6","CAPN3","CTBP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NDZ2","full_name":"SUMO-interacting motif-containing protein 1","aliases":["Platform element for inhibition of autolytic degradation"],"length_aa":872,"mass_kda":96.8,"function":"Plays a role in SMC5-SMC6 complex recruitment for viral restriction. Forms a complex with SLF2 and this complex is required to recruit SMC5-SMC6 complex to PML nuclear bodies and sites of viral replication Inhibits the protease activity of CAPN3 Inhibits the protease activity of CAPN3","subcellular_location":"Cytoplasm; Cytoplasm, myofibril, sarcomere","url":"https://www.uniprot.org/uniprotkb/Q8NDZ2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SIMC1","classification":"Not Classified","n_dependent_lines":99,"n_total_lines":1208,"dependency_fraction":0.08195364238410596},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SIMC1","total_profiled":1310},"omim":[{"mim_id":"618102","title":"SUMO-INTERACTING MOTIFS-CONTAINING PROTEIN 1; SIMC1","url":"https://www.omim.org/entry/618102"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nucleoli fibrillar center","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"ovary","ntpm":38.7}],"url":"https://www.proteinatlas.org/search/SIMC1"},"hgnc":{"alias_symbol":["FLJ44216","OOMA1","PLEIAD"],"prev_symbol":["C5orf25"]},"alphafold":{"accession":"Q8NDZ2","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NDZ2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NDZ2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NDZ2-F1-predicted_aligned_error_v6.png","plddt_mean":58.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SIMC1","jax_strain_url":"https://www.jax.org/strain/search?query=SIMC1"},"sequence":{"accession":"Q8NDZ2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NDZ2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NDZ2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NDZ2"}},"corpus_meta":[{"pmid":"9278244","id":"PMC_9278244","title":"The use of confocal microscopy in the investigation of cell structure and function in the heart, vascular endothelium and smooth muscle cells.","date":"1997","source":"Molecular and cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9278244","citation_count":93,"is_preprint":false},{"pmid":"23086935","id":"PMC_23086935","title":"Poly-small ubiquitin-like modifier (PolySUMO)-binding proteins identified through a string search.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23086935","citation_count":86,"is_preprint":false},{"pmid":"36373674","id":"PMC_36373674","title":"The Nse5/6-like SIMC1-SLF2 complex localizes SMC5/6 to viral replication centers.","date":"2022","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/36373674","citation_count":26,"is_preprint":false},{"pmid":"32605009","id":"PMC_32605009","title":"miR-615 Fine-Tunes Growth and Development and Has a Role in Cancer and in Neural Repair.","date":"2020","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/32605009","citation_count":22,"is_preprint":false},{"pmid":"23707407","id":"PMC_23707407","title":"PLEIAD/SIMC1/C5orf25, a novel autolysis regulator for a skeletal-muscle-specific calpain, CAPN3, scaffolds a CAPN3 substrate, CTBP1.","date":"2013","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/23707407","citation_count":20,"is_preprint":false},{"pmid":"24551045","id":"PMC_24551045","title":"Molecular evidence of RNA editing in Bombyx chemosensory protein family.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24551045","citation_count":18,"is_preprint":false},{"pmid":"38397182","id":"PMC_38397182","title":"HERVs: Expression Control Mechanisms and Interactions in Diseases and Human Immunodeficiency Virus Infection.","date":"2024","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/38397182","citation_count":11,"is_preprint":false},{"pmid":"36382659","id":"PMC_36382659","title":"Omega-3 pleiad: The multipoint anti-inflammatory strategy.","date":"2022","source":"Critical reviews in food science and nutrition","url":"https://pubmed.ncbi.nlm.nih.gov/36382659","citation_count":10,"is_preprint":false},{"pmid":"29120074","id":"PMC_29120074","title":"A FRET Sensor to Monitor Bivalent SUMO-SIM Interactions in SUMO Chain Binding.","date":"2017","source":"Chembiochem : a European journal of chemical biology","url":"https://pubmed.ncbi.nlm.nih.gov/29120074","citation_count":8,"is_preprint":false},{"pmid":"37191775","id":"PMC_37191775","title":"Characterization of the conserved features of the NSE6 subunit of the Physcomitrium patens SMC5/6 complex.","date":"2023","source":"The Plant journal : for cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/37191775","citation_count":7,"is_preprint":false},{"pmid":"38858852","id":"PMC_38858852","title":"NSE5 subunit interacts with distant regions of the SMC arms in the Physcomitrium patens SMC5/6 complex.","date":"2024","source":"The Plant journal : for cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/38858852","citation_count":4,"is_preprint":false},{"pmid":"39162072","id":"PMC_39162072","title":"A semen-specific deoxyribonucleic acid methylation model for epigenetic age estimation and its robustness under environmental challenges.","date":"2024","source":"Electrophoresis","url":"https://pubmed.ncbi.nlm.nih.gov/39162072","citation_count":3,"is_preprint":false},{"pmid":"41294034","id":"PMC_41294034","title":"SMC5/6-mediated plasmid silencing is directed by SIMC1-SLF2 and antagonized by the SV40 large T antigen.","date":"2025","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/41294034","citation_count":1,"is_preprint":false},{"pmid":"40196500","id":"PMC_40196500","title":"SMC5/6-Mediated Plasmid Silencing is Directed by SIMC1-SLF2 and Antagonized by LT.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40196500","citation_count":0,"is_preprint":false},{"pmid":"41481677","id":"PMC_41481677","title":"B chromosome retrotransposed sequences persist through speciation, contributing to genomic and regulatory innovations in the fish genus Psalidodon (Characiformes, Acestrorhamphidae).","date":"2026","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/41481677","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9223,"output_tokens":1544,"usd":0.025414,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8230,"output_tokens":2407,"usd":0.050662,"stage2_stop_reason":"end_turn"},"total_usd":0.076076,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"C5orf25 (SIMC1) contains clustered SUMO-interacting motifs (SIMs) that form a distinct SUMO-binding domain capable of recognizing diverse forms of protein sumoylation, including polysumoylation. Dominant SIMs in the cluster contain a pentameric VIDLT core sequence. A FRET-based assay later confirmed that the SIM clusters of C5orf25 can bind to adjacent subunits of a SUMO chain.\",\n      \"method\": \"Computational string search, biochemical analysis of SIM clusters, FRET sensor assay with di-SUMO\",\n      \"journal\": \"The Journal of biological chemistry; Chembiochem\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — computational identification followed by biochemical validation (FRET sensor) in two independent studies, single-method each but orthogonal approaches\",\n      \"pmids\": [\"23086935\", \"29120074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PLEIAD/SIMC1/C5orf25 binds CAPN3 (skeletal-muscle-specific calpain-3) and suppresses its autolytic protease activity. PLEIAD also interacts with CTBP1 (a CAPN3 substrate and transcriptional co-regulator), scaffolding it for proteolysis by CAPN3 in COS7 cells. Thus PLEIAD can function as either a CAPN3 inhibitor or a substrate-recruitment scaffold depending on cellular context.\",\n      \"method\": \"Co-immunoprecipitation, in-cell proteolysis assay (COS7 cells expressing CAPN3), database/evolutionary conservation analysis, identification of CTBP1 cleavage sites\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding demonstrated plus functional proteolysis readout in cells, single lab with two orthogonal methods\",\n      \"pmids\": [\"23707407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIMC1 is a novel subunit of the human SMC5/6 complex. Its N-terminal SIMs and C-terminal Nse5-like domain together localize SMC5/6 to polyomavirus replication centers (PyVRCs) at SUMO-rich PML nuclear bodies. The Nse5-like domain of SIMC1 binds SLF2 (the putative human Nse6 orthologue) to form an anti-parallel helical dimer structurally resembling yeast Nse5/6. Structure-based mutagenesis of the SIMC1-SLF2 interface identified a conserved surface region at the N-terminus of SIMC1's helical domain that is required for SMC5/6 localization to PyVRCs. SLF1 binds SLF2 analogously to SIMC1, forming a separate, mutually exclusive Nse5/6-like complex that recruits SMC5/6 to chromosomal DNA lesions instead.\",\n      \"method\": \"Proteomic isolation from polyomavirus LT-induced compartments, Co-IP, cryo-EM/structural analysis of SIMC1-SLF2 dimer, structure-based mutagenesis, fluorescence microscopy localization\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — structure determination combined with mutagenesis, reciprocal Co-IP, and functional localization assays in a single rigorous study\",\n      \"pmids\": [\"36373674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SMC5/6-mediated repression of plasmid transcription (extrachromosomal circular DNA silencing) depends exclusively on the SIMC1-SLF2 subcomplex; the SLF1/2 subcomplex is dispensable for this function. SIMC1-SLF2 does not participate in SMC5/6 recruitment to chromosomal DNA lesions, establishing functional specialization of the two Nse5/6-like subcomplexes. Plasmid silencing requires a conserved SIMC1-SLF2–SMC6 interaction and depends on the SUMO pathway but not on PML nuclear bodies. SV40 large T antigen interacts with SMC5/6 and antagonizes SIMC1-SLF2-dependent plasmid silencing.\",\n      \"method\": \"Genetic depletion/knockout of SIMC1-SLF2 vs. SLF1/2, transcription reporter assays for plasmid silencing, Co-IP for LT–SMC5/6 interaction, epistasis with SUMO pathway and PML NB perturbation\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal genetic and biochemical approaches in a single study, peer-reviewed publication replicating and extending prior findings from the same group\",\n      \"pmids\": [\"41294034\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIMC1 (PLEIAD/C5orf25) is a multifunctional scaffold protein: it acts as a regulatory subunit of the human SMC5/6 complex by forming an anti-parallel helical Nse5/6-like dimer with SLF2, using its N-terminal SIMs to sense SUMO-rich environments and its Nse5-like domain to bind SLF2, thereby directing SMC5/6 specifically to PML nuclear bodies and extrachromosomal DNA (viral and plasmid) for transcriptional silencing via the SUMO pathway; separately, in muscle cells it binds calpain-3 (CAPN3) to suppress its autolytic activity and can scaffold CAPN3 substrates such as CTBP1 for proteolysis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SIMC1 (PLEIAD/C5orf25) is a SUMO-sensing scaffold that directs the human SMC5/6 complex to extrachromosomal DNA for transcriptional silencing [#2, #3]. Its N-terminal clustered SUMO-interacting motifs (SIMs), built around a pentameric VIDLT core, constitute a distinct SUMO-binding module that recognizes diverse sumoylation states, including polySUMO chains, by engaging adjacent subunits of a SUMO chain [#0]. SIMC1 functions as a regulatory subunit of SMC5/6 through its C-terminal Nse5-like domain, which binds SLF2 (the putative human Nse6 orthologue) to form an anti-parallel helical dimer structurally resembling the yeast Nse5/6 module; a conserved surface at the N-terminus of this helical domain is required to localize SMC5/6 to SUMO-rich PML nuclear bodies and polyomavirus replication centers [#2]. The SIMC1-SLF2 subcomplex is functionally specialized: it is exclusively required for SMC5/6-mediated silencing of plasmid (extrachromosomal circular DNA) transcription via a conserved SIMC1-SLF2\\u2013SMC6 interaction and the SUMO pathway, whereas the alternative, mutually exclusive SLF1-SLF2 subcomplex instead recruits SMC5/6 to chromosomal DNA lesions; SV40 large T antigen interacts with SMC5/6 and antagonizes this silencing [#2, #3]. Independently, in skeletal muscle SIMC1 binds calpain-3 (CAPN3) and suppresses its autolytic protease activity while also scaffolding the CAPN3 substrate CTBP1 for proteolysis, acting as either inhibitor or substrate-recruitment scaffold depending on context [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing how SIMC1 reads the SUMO landscape, this work defined its clustered SIMs as a dedicated SUMO-binding domain capable of recognizing polysumoylation rather than a single SUMO moiety.\",\n      \"evidence\": \"Computational SIM-cluster identification plus FRET sensor assay with di-SUMO\",\n      \"pmids\": [\"23086935\", \"29120074\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Did not connect SUMO binding to any cellular complex or substrate\",\n        \"No structural model of the SIM cluster engaging a SUMO chain\",\n        \"In vivo relevance of polySUMO recognition untested at this stage\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The first functional role assigned to PLEIAD/SIMC1 placed it in muscle calpain regulation, showing it can both inhibit CAPN3 autolysis and act as a substrate-delivery scaffold.\",\n      \"evidence\": \"Co-IP, in-cell proteolysis assay in COS7 cells, CTBP1 cleavage-site mapping\",\n      \"pmids\": [\"23707407\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Switch between inhibitor and scaffold modes not mechanistically defined\",\n        \"Relationship between the CAPN3 role and the SUMO-binding function unaddressed\",\n        \"Physiological consequence in muscle tissue not demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"This study redefined SIMC1 as a bona fide SMC5/6 subunit, explaining how its SIMs and Nse5-like domain jointly target the complex to SUMO-rich nuclear bodies and viral replication centers.\",\n      \"evidence\": \"Proteomic isolation from polyomavirus compartments, reciprocal Co-IP, cryo-EM/structure of the SIMC1-SLF2 dimer, structure-based mutagenesis, microscopy\",\n      \"pmids\": [\"36373674\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not establish the transcriptional or silencing output of the localized complex\",\n        \"Functional distinction from the SLF1-SLF2 subcomplex not yet tested\",\n        \"Mechanism by which SUMO sensing is integrated with SLF2 binding incompletely resolved\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"By dissecting the two Nse5/6-like subcomplexes, this work showed the SIMC1-SLF2 module is specialized for silencing extrachromosomal DNA transcription, separating it functionally from the chromosomal-lesion role of SLF1-SLF2.\",\n      \"evidence\": \"Selective depletion/knockout of SIMC1-SLF2 vs SLF1/2, plasmid transcription reporters, Co-IP of LT\\u2013SMC5/6, epistasis with SUMO pathway and PML NB perturbation\",\n      \"pmids\": [\"41294034\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"How the SUMO pathway acts independently of PML nuclear bodies in silencing is unresolved\",\n        \"Mechanism by which SV40 large T antigen antagonizes silencing not defined at molecular level\",\n        \"Whether the muscle CAPN3 role and the SMC5/6 role share regulatory inputs remains unconnected\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SIMC1 integrates its SUMO-sensing, SMC5/6-targeting, and CAPN3-regulatory activities into a unified physiological program remains unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No tissue-level phenotype linking the two functional arms\",\n        \"Structural basis of SUMO-chain recognition driving complex localization undefined\",\n        \"Determinants selecting between inhibitor and scaffold modes for CAPN3 unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"complexes\": [\n      \"SMC5/6 complex\",\n      \"SIMC1-SLF2 (Nse5/6-like) subcomplex\"\n    ],\n    \"partners\": [\n      \"SLF2\",\n      \"SMC6\",\n      \"CAPN3\",\n      \"CTBP1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}