{"gene":"MVB12A","run_date":"2026-06-10T05:19:51","timeline":{"discoveries":[{"year":2007,"finding":"MVB12A (and MVB12B) are identified as the fourth class of metazoan ESCRT-I subunits, forming a stoichiometric heterotetramer (one copy each) with TSG101, VPS28, and VPS37. MVB12 subunits associate with the core region of the binary TSG101-VPS37 complex through conserved C-terminal sequence elements. Both depletion and overexpression of MVB12 inhibit HIV-1 infectivity and induce aberrant virion morphologies and altered Gag protein processing.","method":"Hydrodynamic studies, co-immunoprecipitation, siRNA depletion, overexpression, viral infectivity and morphology assays","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, hydrodynamic analysis, loss-of-function and gain-of-function with defined cellular phenotypes, replicated across multiple orthogonal methods in one focused study","pmids":["18005716"],"is_preprint":false},{"year":2010,"finding":"Tyrosine-204 phosphorylation of MVB12A in response to EGF stimulation affects its binding to CD2AP, which in turn regulates the amount of EGF receptor bound to ESCRT-I. MVB12A is also involved in the aggregation of the ubiquitination-prone MVB12B protein.","method":"Phosphorylation site mutagenesis, co-immunoprecipitation, EGF stimulation assays, ubiquitination assays in COS-7 cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP and mutagenesis in a single lab, single study with no independent replication","pmids":["20654576"],"is_preprint":false},{"year":2011,"finding":"UBAP1 defines an endosome-specific ESCRT-I complex that contains VPS37A but excludes MVB12A/MVB12B. UBAP1 (not MVB12A/B) is required for MVB sorting of EGFR and endosomal ubiquitin homeostasis, establishing that ESCRT-I variants with different MVB12-family members have distinct functional specializations.","method":"siRNA depletion, co-immunoprecipitation, EGFR degradation assay, ubiquitin homeostasis assay","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus functional siRNA knockdown with defined cellular phenotypes, multiple orthogonal methods, defines pathway position of MVB12A by exclusion from endosome-specific complex","pmids":["21757351"],"is_preprint":false},{"year":2012,"finding":"The MABP (MVB12-associated β-prism) domain of MVB12A and MVB12B binds acidic lipid-containing liposomes in vitro in a negative-charge-density-dependent manner and autonomously localizes to subcellular puncta and the plasma membrane. The 1.3-Å crystal structure of the MVB12B MABP domain reveals a β-prism fold with a hydrophobic membrane-anchoring loop and an electropositive phosphoinositide-binding patch that senses charge density without lipid-head-group stereoselectivity.","method":"Crystal structure determination (1.3 Å), in vitro liposome-binding assay, subcellular localization imaging","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic-resolution crystal structure combined with in vitro reconstituted lipid-binding assay and subcellular localization experiment in a single rigorous study","pmids":["22232651"],"is_preprint":false},{"year":2013,"finding":"The incorporation of MVB12A into ESCRT-I is highly selective with respect to its VPS37 partner. siRNA-mediated depletion of MVB12A (and MVB12B together) does not disrupt ubiquitin-dependent MVB sorting, in contrast to UBAP1 depletion, demonstrating that MVB12A-containing ESCRT-I is functionally distinct from the UBAP1-VPS37A endosome-specific complex.","method":"siRNA depletion, co-immunoprecipitation, domain-mapping experiments, MVB cargo-sorting assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, domain mapping, and functional siRNA knockdown with defined phenotypic readout, independently replicating and extending findings from PMID 21757351","pmids":["24284069"],"is_preprint":false},{"year":2020,"finding":"Crystal structure of the human ESCRT-I headpiece comprising TSG101-VPS28-VPS37B-MVB12A reveals that ESCRT-I forms a helical assembly with a 12-molecule repeat. ESCRT-I subcomplexes form helical filaments in solution (confirmed by EM). Mutation of VPS28 helical interface residues blocks filament formation in vitro and impairs autophagosome closure and HIV-1 release in human cells, demonstrating that ESCRT-I has an essential scaffolding and mechanical role beyond bridging.","method":"Crystal structure determination, electron microscopy, in vitro filament formation assay, VPS28 interface mutagenesis, autophagosome closure assay, HIV-1 budding assay","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure of complex containing MVB12A, EM validation, mutagenesis with in vitro and cellular functional readouts, multiple orthogonal methods in one rigorous study","pmids":["32424346"],"is_preprint":false},{"year":2025,"finding":"Knockdown of MVB12A does not affect β-coronavirus (OC43) virion assembly but inhibits virion egress, placing MVB12A specifically in the egress step of the ESCRT-dependent coronavirus life cycle.","method":"siRNA knockdown, electron microscopy of virion assembly, virion-like particle production assay, coronavirus replication assay","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean knockdown with defined phenotypic readout (egress vs. assembly), single study, single lab, no independent replication yet","pmids":["40407327"],"is_preprint":false}],"current_model":"MVB12A is the fourth subunit of human ESCRT-I, forming a stoichiometric heterotetramer with TSG101, VPS28, and VPS37 via conserved C-terminal elements; its MABP domain directly binds acidic membranes via charge-density sensing, enabling ESCRT-I to act as a coincidence detector at endosomes and the plasma membrane; within the cell, MVB12A-containing ESCRT-I complexes are functionally distinct from the endosome-specific UBAP1-VPS37A complex and are not required for ubiquitin-dependent MVB cargo sorting; MVB12A participates in the ESCRT-I helical scaffold that templates ESCRT-III assembly for membrane scission during HIV-1 budding and autophagosome closure; EGF-induced Tyr204 phosphorylation of MVB12A modulates its binding to CD2AP and thereby regulates EGFR association with ESCRT-I; and MVB12A is specifically required for β-coronavirus egress but not assembly."},"narrative":{"mechanistic_narrative":"MVB12A is the fourth, stoichiometric subunit of human ESCRT-I, completing a one-copy-each heterotetramer with TSG101, VPS28, and VPS37 through conserved C-terminal elements [PMID:18005716]. Its MABP (MVB12-associated β-prism) domain directly engages acidic, phosphoinositide-containing membranes by sensing negative charge density rather than specific lipid head groups, using a hydrophobic anchoring loop and an electropositive patch, and is sufficient to localize autonomously to puncta and the plasma membrane [PMID:22232651]. Through this membrane-sensing module MVB12A-containing ESCRT-I is functionally distinct from the endosome-specific UBAP1–VPS37A complex and is not required for ubiquitin-dependent MVB cargo sorting, marking a division of labor among ESCRT-I variants defined by their MVB12-family subunit [PMID:21757351, PMID:24284069]. Within the assembled complex, MVB12A is part of an ESCRT-I helical scaffold with a 12-molecule repeat whose integrity is required for autophagosome closure and HIV-1 release, giving ESCRT-I a mechanical scaffolding role in membrane scission [PMID:32424346], and MVB12A is specifically required for β-coronavirus egress but not virion assembly [PMID:40407327]. EGF-induced phosphorylation of MVB12A at Tyr204 modulates its binding to CD2AP and thereby tunes the amount of EGF receptor associated with ESCRT-I [PMID:20654576].","teleology":[{"year":2007,"claim":"Established that metazoan ESCRT-I is a heterotetramer by identifying MVB12A/B as a fourth subunit class, defining the complex's composition and a role in viral budding.","evidence":"Hydrodynamic analysis, reciprocal co-immunoprecipitation, and siRNA/overexpression with HIV-1 infectivity and morphology readouts","pmids":["18005716"],"confidence":"High","gaps":["Did not resolve how MVB12A contacts membranes","Mechanism of the budding defect at the structural level unresolved"]},{"year":2010,"claim":"Connected MVB12A to receptor-level signaling by showing EGF-triggered Tyr204 phosphorylation regulates CD2AP binding and the loading of EGFR onto ESCRT-I.","evidence":"Phospho-site mutagenesis, co-immunoprecipitation, and EGF/ubiquitination assays in COS-7 cells","pmids":["20654576"],"confidence":"Medium","gaps":["Single lab, no independent replication","Kinase responsible for Tyr204 phosphorylation not identified","Functional consequence for cargo fate not measured"]},{"year":2011,"claim":"Resolved that ESCRT-I exists in functionally specialized variants by showing UBAP1/VPS37A — excluding MVB12A/B — drives endosomal MVB sorting and ubiquitin homeostasis.","evidence":"siRNA depletion, co-immunoprecipitation, and EGFR degradation / ubiquitin homeostasis assays","pmids":["21757351"],"confidence":"High","gaps":["Did not define the positive cellular role of MVB12A-containing ESCRT-I","Basis of subunit-selective complex assembly unresolved"]},{"year":2012,"claim":"Defined the molecular basis of MVB12A membrane recognition, revealing the MABP β-prism domain as a charge-density-sensing membrane anchor.","evidence":"1.3-Å crystal structure of the MVB12B MABP domain, in vitro liposome-binding, and subcellular localization imaging","pmids":["22232651"],"confidence":"High","gaps":["In vivo contribution of MABP binding within the intact ESCRT-I complex not directly tested","How charge-sensing integrates with cargo recognition unresolved"]},{"year":2013,"claim":"Confirmed selective incorporation of MVB12A with specific VPS37 partners and that its loss leaves ubiquitin-dependent MVB sorting intact, cementing a distinct function from UBAP1-VPS37A complexes.","evidence":"siRNA depletion, co-immunoprecipitation, domain mapping, and MVB cargo-sorting assays","pmids":["24284069"],"confidence":"High","gaps":["Positive cargo or process uniquely served by MVB12A-ESCRT-I not identified","Rules governing VPS37-MVB12 pairing not fully defined"]},{"year":2020,"claim":"Revealed that MVB12A-containing ESCRT-I forms a helical filament scaffold with mechanical function, not merely a bridging adaptor, linking it to membrane scission.","evidence":"Crystal structure of TSG101-VPS28-VPS37B-MVB12A headpiece, EM, in vitro filament assay, VPS28 interface mutagenesis with autophagosome closure and HIV-1 budding readouts","pmids":["32424346"],"confidence":"High","gaps":["Specific contribution of MVB12A to filament mechanics not isolated from other subunits","How the helical scaffold templates ESCRT-III not fully resolved"]},{"year":2025,"claim":"Placed MVB12A specifically at the egress step of the β-coronavirus life cycle, distinguishing it from virion assembly.","evidence":"siRNA knockdown of MVB12A with EM of assembly and virion-like-particle / replication egress assays for OC43","pmids":["40407327"],"confidence":"Medium","gaps":["Single study, no independent replication","Molecular target of MVB12A at the egress membrane unidentified","Whether the MABP domain mediates the egress role untested"]},{"year":null,"claim":"The endogenous cellular cargo or membrane process uniquely dependent on MVB12A-containing ESCRT-I — as opposed to its role in viral budding and autophagosome closure — remains undefined.","evidence":"","pmids":[],"confidence":"High","gaps":["No cellular substrate specific to MVB12A-ESCRT-I identified","Physiological signal controlling Tyr204 phosphorylation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[5]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,6]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[2,4]}],"complexes":["ESCRT-I"],"partners":["TSG101","VPS28","VPS37B","MVB12B","CD2AP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96EY5","full_name":"Multivesicular body subunit 12A","aliases":["CIN85/CD2AP family-binding protein","ESCRT-I complex subunit MVB12A","Protein FAM125A"],"length_aa":273,"mass_kda":28.8,"function":"Component of the ESCRT-I complex, a regulator of vesicular trafficking process. Required for the sorting of endocytic ubiquitinated cargos into multivesicular bodies. May be involved in the ligand-mediated internalization and down-regulation of EGF receptor","subcellular_location":"Cytoplasm; Nucleus; Endosome; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome; Late endosome membrane","url":"https://www.uniprot.org/uniprotkb/Q96EY5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MVB12A","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000141971","cell_line_id":"CID000782","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"VPS28","stoichiometry":10.0},{"gene":"TSG101","stoichiometry":10.0},{"gene":"VPS37B","stoichiometry":10.0},{"gene":"CCAR1","stoichiometry":0.2},{"gene":"GOLGA2","stoichiometry":0.2},{"gene":"STAM2","stoichiometry":0.2},{"gene":"HGS","stoichiometry":0.2},{"gene":"STAM","stoichiometry":0.2},{"gene":"IST1","stoichiometry":0.2},{"gene":"CEP55","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000782","total_profiled":1310},"omim":[{"mim_id":"621543","title":"UBIQUITIN-ASSOCIATED PROTEIN 1-LIKE PROTEIN; UBAP1L","url":"https://www.omim.org/entry/621543"},{"mim_id":"621454","title":"MULTIVESICULAR BODY SUBUNIT 12B; MVB12B","url":"https://www.omim.org/entry/621454"},{"mim_id":"621453","title":"MULTIVESICULAR BODY SUBUNIT 12A; MVB12A","url":"https://www.omim.org/entry/621453"},{"mim_id":"609787","title":"UBIQUITIN-ASSOCIATED PROTEIN 1; UBAP1","url":"https://www.omim.org/entry/609787"},{"mim_id":"604241","title":"CD2-ASSOCIATED PROTEIN; CD2AP","url":"https://www.omim.org/entry/604241"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MVB12A"},"hgnc":{"alias_symbol":["FLJ32495"],"prev_symbol":["FAM125A"]},"alphafold":{"accession":"Q96EY5","domains":[{"cath_id":"2.100.10.50","chopping":"11-150","consensus_level":"high","plddt":92.307,"start":11,"end":150}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96EY5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96EY5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96EY5-F1-predicted_aligned_error_v6.png","plddt_mean":77.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MVB12A","jax_strain_url":"https://www.jax.org/strain/search?query=MVB12A"},"sequence":{"accession":"Q96EY5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96EY5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96EY5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96EY5"}},"corpus_meta":[{"pmid":"21757351","id":"PMC_21757351","title":"UBAP1 is a component of an endosome-specific ESCRT-I complex that is essential for MVB sorting.","date":"2011","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/21757351","citation_count":110,"is_preprint":false},{"pmid":"18005716","id":"PMC_18005716","title":"Identification of human MVB12 proteins as ESCRT-I subunits that function in HIV budding.","date":"2007","source":"Cell host & microbe","url":"https://pubmed.ncbi.nlm.nih.gov/18005716","citation_count":99,"is_preprint":false},{"pmid":"32424346","id":"PMC_32424346","title":"A helical assembly of human ESCRT-I scaffolds reverse-topology membrane scission.","date":"2020","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/32424346","citation_count":48,"is_preprint":false},{"pmid":"22232651","id":"PMC_22232651","title":"Structural basis for membrane targeting by the MVB12-associated β-prism domain of the human ESCRT-I MVB12 subunit.","date":"2012","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/22232651","citation_count":43,"is_preprint":false},{"pmid":"24284069","id":"PMC_24284069","title":"The molecular basis for selective assembly of the UBAP1-containing endosome-specific ESCRT-I complex.","date":"2013","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/24284069","citation_count":30,"is_preprint":false},{"pmid":"20654576","id":"PMC_20654576","title":"Distinct functions of human MVB12A and MVB12B in the ESCRT-I dependent on their posttranslational modifications.","date":"2010","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/20654576","citation_count":26,"is_preprint":false},{"pmid":"35923698","id":"PMC_35923698","title":"Transcriptome Analysis Reveals Hub Genes Regulating Autophagy in Patients With Severe COVID-19.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35923698","citation_count":10,"is_preprint":false},{"pmid":"40407327","id":"PMC_40407327","title":"β-Coronaviruses exploit ESCRT for virion assembly and egress.","date":"2025","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/40407327","citation_count":2,"is_preprint":false},{"pmid":"41558077","id":"PMC_41558077","title":"Positive effects of bile acids alleviating heat stress in laying hens by enhancing immunity via metabolome and transcriptome integration.","date":"2026","source":"Poultry science","url":"https://pubmed.ncbi.nlm.nih.gov/41558077","citation_count":1,"is_preprint":false},{"pmid":"42030266","id":"PMC_42030266","title":"Distinct tumor genomic signatures underlie canine macrophage polarization.","date":"2026","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/42030266","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.06.25329102","title":"The development of childhood internalising problems: A meta-analysis of epigenome-wide-association-studies","date":"2025-06-06","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.06.25329102","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8327,"output_tokens":2088,"usd":0.02815,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9063,"output_tokens":2719,"usd":0.056645,"stage2_stop_reason":"end_turn"},"total_usd":0.084795,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"MVB12A (and MVB12B) are identified as the fourth class of metazoan ESCRT-I subunits, forming a stoichiometric heterotetramer (one copy each) with TSG101, VPS28, and VPS37. MVB12 subunits associate with the core region of the binary TSG101-VPS37 complex through conserved C-terminal sequence elements. Both depletion and overexpression of MVB12 inhibit HIV-1 infectivity and induce aberrant virion morphologies and altered Gag protein processing.\",\n      \"method\": \"Hydrodynamic studies, co-immunoprecipitation, siRNA depletion, overexpression, viral infectivity and morphology assays\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, hydrodynamic analysis, loss-of-function and gain-of-function with defined cellular phenotypes, replicated across multiple orthogonal methods in one focused study\",\n      \"pmids\": [\"18005716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Tyrosine-204 phosphorylation of MVB12A in response to EGF stimulation affects its binding to CD2AP, which in turn regulates the amount of EGF receptor bound to ESCRT-I. MVB12A is also involved in the aggregation of the ubiquitination-prone MVB12B protein.\",\n      \"method\": \"Phosphorylation site mutagenesis, co-immunoprecipitation, EGF stimulation assays, ubiquitination assays in COS-7 cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP and mutagenesis in a single lab, single study with no independent replication\",\n      \"pmids\": [\"20654576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"UBAP1 defines an endosome-specific ESCRT-I complex that contains VPS37A but excludes MVB12A/MVB12B. UBAP1 (not MVB12A/B) is required for MVB sorting of EGFR and endosomal ubiquitin homeostasis, establishing that ESCRT-I variants with different MVB12-family members have distinct functional specializations.\",\n      \"method\": \"siRNA depletion, co-immunoprecipitation, EGFR degradation assay, ubiquitin homeostasis assay\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus functional siRNA knockdown with defined cellular phenotypes, multiple orthogonal methods, defines pathway position of MVB12A by exclusion from endosome-specific complex\",\n      \"pmids\": [\"21757351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The MABP (MVB12-associated β-prism) domain of MVB12A and MVB12B binds acidic lipid-containing liposomes in vitro in a negative-charge-density-dependent manner and autonomously localizes to subcellular puncta and the plasma membrane. The 1.3-Å crystal structure of the MVB12B MABP domain reveals a β-prism fold with a hydrophobic membrane-anchoring loop and an electropositive phosphoinositide-binding patch that senses charge density without lipid-head-group stereoselectivity.\",\n      \"method\": \"Crystal structure determination (1.3 Å), in vitro liposome-binding assay, subcellular localization imaging\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic-resolution crystal structure combined with in vitro reconstituted lipid-binding assay and subcellular localization experiment in a single rigorous study\",\n      \"pmids\": [\"22232651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The incorporation of MVB12A into ESCRT-I is highly selective with respect to its VPS37 partner. siRNA-mediated depletion of MVB12A (and MVB12B together) does not disrupt ubiquitin-dependent MVB sorting, in contrast to UBAP1 depletion, demonstrating that MVB12A-containing ESCRT-I is functionally distinct from the UBAP1-VPS37A endosome-specific complex.\",\n      \"method\": \"siRNA depletion, co-immunoprecipitation, domain-mapping experiments, MVB cargo-sorting assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, domain mapping, and functional siRNA knockdown with defined phenotypic readout, independently replicating and extending findings from PMID 21757351\",\n      \"pmids\": [\"24284069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structure of the human ESCRT-I headpiece comprising TSG101-VPS28-VPS37B-MVB12A reveals that ESCRT-I forms a helical assembly with a 12-molecule repeat. ESCRT-I subcomplexes form helical filaments in solution (confirmed by EM). Mutation of VPS28 helical interface residues blocks filament formation in vitro and impairs autophagosome closure and HIV-1 release in human cells, demonstrating that ESCRT-I has an essential scaffolding and mechanical role beyond bridging.\",\n      \"method\": \"Crystal structure determination, electron microscopy, in vitro filament formation assay, VPS28 interface mutagenesis, autophagosome closure assay, HIV-1 budding assay\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure of complex containing MVB12A, EM validation, mutagenesis with in vitro and cellular functional readouts, multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"32424346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Knockdown of MVB12A does not affect β-coronavirus (OC43) virion assembly but inhibits virion egress, placing MVB12A specifically in the egress step of the ESCRT-dependent coronavirus life cycle.\",\n      \"method\": \"siRNA knockdown, electron microscopy of virion assembly, virion-like particle production assay, coronavirus replication assay\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean knockdown with defined phenotypic readout (egress vs. assembly), single study, single lab, no independent replication yet\",\n      \"pmids\": [\"40407327\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MVB12A is the fourth subunit of human ESCRT-I, forming a stoichiometric heterotetramer with TSG101, VPS28, and VPS37 via conserved C-terminal elements; its MABP domain directly binds acidic membranes via charge-density sensing, enabling ESCRT-I to act as a coincidence detector at endosomes and the plasma membrane; within the cell, MVB12A-containing ESCRT-I complexes are functionally distinct from the endosome-specific UBAP1-VPS37A complex and are not required for ubiquitin-dependent MVB cargo sorting; MVB12A participates in the ESCRT-I helical scaffold that templates ESCRT-III assembly for membrane scission during HIV-1 budding and autophagosome closure; EGF-induced Tyr204 phosphorylation of MVB12A modulates its binding to CD2AP and thereby regulates EGFR association with ESCRT-I; and MVB12A is specifically required for β-coronavirus egress but not assembly.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MVB12A is the fourth, stoichiometric subunit of human ESCRT-I, completing a one-copy-each heterotetramer with TSG101, VPS28, and VPS37 through conserved C-terminal elements [#0]. Its MABP (MVB12-associated β-prism) domain directly engages acidic, phosphoinositide-containing membranes by sensing negative charge density rather than specific lipid head groups, using a hydrophobic anchoring loop and an electropositive patch, and is sufficient to localize autonomously to puncta and the plasma membrane [#3]. Through this membrane-sensing module MVB12A-containing ESCRT-I is functionally distinct from the endosome-specific UBAP1–VPS37A complex and is not required for ubiquitin-dependent MVB cargo sorting, marking a division of labor among ESCRT-I variants defined by their MVB12-family subunit [#2, #4]. Within the assembled complex, MVB12A is part of an ESCRT-I helical scaffold with a 12-molecule repeat whose integrity is required for autophagosome closure and HIV-1 release, giving ESCRT-I a mechanical scaffolding role in membrane scission [#5], and MVB12A is specifically required for β-coronavirus egress but not virion assembly [#6]. EGF-induced phosphorylation of MVB12A at Tyr204 modulates its binding to CD2AP and thereby tunes the amount of EGF receptor associated with ESCRT-I [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established that metazoan ESCRT-I is a heterotetramer by identifying MVB12A/B as a fourth subunit class, defining the complex's composition and a role in viral budding.\",\n      \"evidence\": \"Hydrodynamic analysis, reciprocal co-immunoprecipitation, and siRNA/overexpression with HIV-1 infectivity and morphology readouts\",\n      \"pmids\": [\"18005716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how MVB12A contacts membranes\", \"Mechanism of the budding defect at the structural level unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected MVB12A to receptor-level signaling by showing EGF-triggered Tyr204 phosphorylation regulates CD2AP binding and the loading of EGFR onto ESCRT-I.\",\n      \"evidence\": \"Phospho-site mutagenesis, co-immunoprecipitation, and EGF/ubiquitination assays in COS-7 cells\",\n      \"pmids\": [\"20654576\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, no independent replication\", \"Kinase responsible for Tyr204 phosphorylation not identified\", \"Functional consequence for cargo fate not measured\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Resolved that ESCRT-I exists in functionally specialized variants by showing UBAP1/VPS37A — excluding MVB12A/B — drives endosomal MVB sorting and ubiquitin homeostasis.\",\n      \"evidence\": \"siRNA depletion, co-immunoprecipitation, and EGFR degradation / ubiquitin homeostasis assays\",\n      \"pmids\": [\"21757351\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the positive cellular role of MVB12A-containing ESCRT-I\", \"Basis of subunit-selective complex assembly unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the molecular basis of MVB12A membrane recognition, revealing the MABP β-prism domain as a charge-density-sensing membrane anchor.\",\n      \"evidence\": \"1.3-Å crystal structure of the MVB12B MABP domain, in vitro liposome-binding, and subcellular localization imaging\",\n      \"pmids\": [\"22232651\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of MABP binding within the intact ESCRT-I complex not directly tested\", \"How charge-sensing integrates with cargo recognition unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Confirmed selective incorporation of MVB12A with specific VPS37 partners and that its loss leaves ubiquitin-dependent MVB sorting intact, cementing a distinct function from UBAP1-VPS37A complexes.\",\n      \"evidence\": \"siRNA depletion, co-immunoprecipitation, domain mapping, and MVB cargo-sorting assays\",\n      \"pmids\": [\"24284069\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Positive cargo or process uniquely served by MVB12A-ESCRT-I not identified\", \"Rules governing VPS37-MVB12 pairing not fully defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Revealed that MVB12A-containing ESCRT-I forms a helical filament scaffold with mechanical function, not merely a bridging adaptor, linking it to membrane scission.\",\n      \"evidence\": \"Crystal structure of TSG101-VPS28-VPS37B-MVB12A headpiece, EM, in vitro filament assay, VPS28 interface mutagenesis with autophagosome closure and HIV-1 budding readouts\",\n      \"pmids\": [\"32424346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific contribution of MVB12A to filament mechanics not isolated from other subunits\", \"How the helical scaffold templates ESCRT-III not fully resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placed MVB12A specifically at the egress step of the β-coronavirus life cycle, distinguishing it from virion assembly.\",\n      \"evidence\": \"siRNA knockdown of MVB12A with EM of assembly and virion-like-particle / replication egress assays for OC43\",\n      \"pmids\": [\"40407327\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single study, no independent replication\", \"Molecular target of MVB12A at the egress membrane unidentified\", \"Whether the MABP domain mediates the egress role untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The endogenous cellular cargo or membrane process uniquely dependent on MVB12A-containing ESCRT-I — as opposed to its role in viral budding and autophagosome closure — remains undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cellular substrate specific to MVB12A-ESCRT-I identified\", \"Physiological signal controlling Tyr204 phosphorylation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [\"ESCRT-I\"],\n    \"partners\": [\"TSG101\", \"VPS28\", \"VPS37B\", \"MVB12B\", \"CD2AP\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}