{"gene":"BOLA2","run_date":"2026-06-09T22:02:45","timeline":{"discoveries":[{"year":2019,"finding":"PCBP1 coordinates iron via conserved cysteine and glutamate residues with a noncovalently bound glutathione (GSH) molecule, and the Fe-GSH-bound form of PCBP1 complexes with cytosolic BolA2 via a bridging Fe ligand, forming a PCBP1-Fe-GSH-BolA2 intermediate required for assembly of [2Fe-2S] clusters on the BolA2-Glrx3 complex.","method":"Proteomics/Co-IP identification of PCBP1-BolA2 interaction; in vitro biochemical reconstitution; mutagenesis of PCBP1 iron-coordinating residues; cell-based assays","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution, mutagenesis, and cell-based validation in a single rigorous study; mechanistic intermediate characterized biochemically","pmids":["31406370"],"is_preprint":false},{"year":2012,"finding":"Human BolA2 forms [2Fe-2S]-bridged heterodimeric complexes with each Grx-like domain of human Glrx3, and apo BolA2 binds to [2Fe-2S] Glrx3 homodimer to form a [2Fe-2S] BolA2-Glrx3 heterotrimer; the Fe-S coordination environment is virtually identical to the analogous yeast complexes.","method":"UV-visible absorption/CD spectroscopy, resonance Raman spectroscopy, EPR spectroscopy of recombinant proteins; in vitro reconstitution of complexes","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal spectroscopic methods plus in vitro reconstitution establishing iron-sulfur cluster coordination geometry","pmids":["22309771"],"is_preprint":false},{"year":2016,"finding":"Cytosolic Glrx3·BolA2 functions as a [2Fe-2S] chaperone complex in human cells; complex formation requires Fe-S cluster coordination; cellular Glrx3·BolA2 complexes increase 6–8-fold in response to iron; the complex transfers [2Fe-2S] clusters to the apoprotein Ciapin1, acting upstream in the cytosolic Fe-S assembly pathway.","method":"Quantitative immunoprecipitation; live-cell proximity-dependent biotinylation (BioID); iron-titration experiments; functional Fe-S transfer assays in human cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, BioID proximity labeling, and functional transfer assays; iron-responsive behavior characterized with two orthogonal methods","pmids":["27519415"],"is_preprint":false},{"year":2015,"finding":"Apo BolA2 and apo GRX3 form a heterotrimeric complex (two BOLA2 molecules per one GRX3 molecule) that binds two [2Fe-2S]2+ clusters bridged between each BOLA2 molecule and a monothiol glutaredoxin domain of GRX3; this heterotrimer transfers both [2Fe-2S]2+ clusters to apo-anamorsin (Ciapin1), producing its mature holo state.","method":"NMR structural characterization of complex at atomic level; in vitro reconstitution; cluster transfer assays to apo-anamorsin","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR-based structural characterization with functional cluster transfer reconstitution, single lab but multiple orthogonal methods","pmids":["26613676"],"is_preprint":false},{"year":2021,"finding":"Iron coordination by PCBP1 (via specific cysteine/glutamate residues on each structural domain) is required for binding BolA2 and ferritin; PCBP1 variants lacking iron-binding activity fail to interact with BolA2 and lose the ability to control cell cycle progression and suppress DNA damage, while nucleic acid-binding activity is separately required for cell viability.","method":"Site-directed mutagenesis of PCBP1 iron-coordinating residues; Co-IP binding assays with BolA2 and ferritin; functional rescue experiments in PCBP1-depleted human cells and mouse tissues","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis plus Co-IP plus functional rescue in both cell and mouse models; two independent activity modules delineated","pmids":["34161287"],"is_preprint":false},{"year":2019,"finding":"BOLA2 participates in iron homeostasis in vivo; Bola2-deficient mice exhibit iron deficiency signs including decreased hemoglobin, lower plasma iron, microcytosis, and increased red blood cell zinc-protoporphyrin-to-heme ratio; human 16p11.2 deletion carriers with lower BOLA2 copy number show increased prevalence of iron-deficiency anemia.","method":"Mouse knockout (Bola2+/- and Bola2-/-) with hematological phenotyping; human 16p11.2 CNV carrier cohort analysis stratified by BOLA2 copy number","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined hematological phenotype in mice, supported by human CNV cohort; mechanistic pathway not fully resolved in vivo","pmids":["31668704"],"is_preprint":false},{"year":2016,"finding":"BOLA2 is a human-specific gene duplication (duplicated exclusively in Homo sapiens ~282 ka); BOLA2 copy number positively correlates with RNA expression (r=0.36) and protein level (r=0.65), with the greatest expression difference between human and chimpanzee in stem cells; the duplication also generated a novel human-specific in-frame fusion transcript.","method":"Comparative genomic sequencing; BOLA2 copy number vs. RNA/protein quantification across individuals; evolutionary timing analysis","journal":"Nature","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct quantification of copy number vs. protein level with good correlation; genomic/evolutionary characterization in a single large study","pmids":["27487209"],"is_preprint":false},{"year":2025,"finding":"In breast cancer cells, sulfatide (SM4) suppresses BOLA2 expression by inhibiting β1 integrin–STAT5 signaling; STAT5 directly binds and activates the BOLA2 promoter (demonstrated by EMSA); overexpression of BOLA2 confers resistance to doxorubicin-induced apoptosis, placing BOLA2 downstream of β1 integrin–STAT5 in the CIAPIN1 apoptotic pathway.","method":"RNA sequencing; RT-qPCR; Western blot; luciferase promoter assay; EMSA (STAT5 binding to BOLA2 promoter); BOLA2 overexpression rescue of apoptosis; β1 integrin re-expression epistasis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — EMSA for direct promoter binding, luciferase assay, functional rescue by BOLA2 OE, and epistasis via β1 integrin re-expression; single lab","pmids":["41465298"],"is_preprint":false},{"year":2017,"finding":"The monothiol glutaredoxin Glrx3 and BolA2 together function as a [2Fe-2S] chaperone complex representing a core component of the cytosolic iron cofactor distribution system in mammalian cells.","method":"Review/synthesis of biochemical and cell-biological evidence (fractionation, Co-IP, in vitro reconstitution cited across studies)","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — review paper consolidating multiple prior experimental findings; no new primary data but synthesizes replicated evidence","pmids":["28615454"],"is_preprint":false}],"current_model":"BOLA2 is a cytosolic iron-sulfur ([2Fe-2S]) cluster chaperone that forms a heterotrimer with two BOLA2 molecules and one GRX3/Glrx3 molecule, each bridging a [2Fe-2S] cluster; it receives iron from a PCBP1-Fe-GSH intermediate and transfers [2Fe-2S] clusters to apoproteins such as Ciapin1/anamorsin in the cytosolic Fe-S assembly pathway; its transcription is regulated by a β1 integrin–STAT5 axis, and its loss in vivo causes iron-deficiency anemia, while its human-specific copy-number expansion appears to protect against iron deficiency."},"narrative":{"mechanistic_narrative":"BOLA2 is a cytosolic [2Fe-2S] cluster chaperone that operates in the cytosolic iron-sulfur protein assembly pathway by partnering with the monothiol glutaredoxin GRX3/Glrx3 [PMID:27519415, PMID:28615454]. Human BOLA2 forms [2Fe-2S]-bridged complexes with each glutaredoxin-like domain of Glrx3, assembling a heterotrimer of two BOLA2 molecules and one GRX3 molecule that coordinates two [2Fe-2S] clusters, each bridged between a BOLA2 subunit and a glutaredoxin domain [PMID:22309771, PMID:26613676]. This complex acquires iron upstream from an iron-loaded, glutathione-bound form of PCBP1, which docks onto BOLA2 through a bridging iron ligand to form a PCBP1-Fe-GSH-BolA2 intermediate required for [2Fe-2S] cluster assembly on the BOLA2-Glrx3 complex [PMID:31406370, PMID:34161287]. The mature holo-heterotrimer then transfers both [2Fe-2S] clusters to apo-anamorsin/Ciapin1, maturing it as a downstream client, and cellular GRX3·BOLA2 complexes increase several-fold in response to iron [PMID:27519415, PMID:26613676]. Loss of Bola2 in mice produces iron-deficiency anemia with reduced hemoglobin, low plasma iron, and microcytosis, and reduced BOLA2 copy number in human 16p11.2 deletion carriers is associated with increased iron-deficiency anemia [PMID:31668704]. BOLA2 arose from a human-specific gene duplication whose copy number scales with RNA and protein levels [PMID:27487209], and in breast cancer cells its transcription is activated directly by STAT5 downstream of β1 integrin signaling, with BOLA2 overexpression conferring resistance to doxorubicin-induced apoptosis [PMID:41465298].","teleology":[{"year":2012,"claim":"Whether human BOLA2 and Glrx3 physically assemble into a defined iron-sulfur cluster complex was unknown; this work established the coordination geometry of a [2Fe-2S]-bridged BOLA2-Glrx3 assembly.","evidence":"Multiple orthogonal spectroscopies (UV-vis/CD, resonance Raman, EPR) on reconstituted recombinant proteins","pmids":["22309771"],"confidence":"High","gaps":["Did not establish the cellular function or downstream clients of the complex","Stoichiometry of the in-cell heterotrimer not yet resolved"]},{"year":2015,"claim":"The atomic architecture and catalytic output of the assembly were unresolved; NMR defined a two-BOLA2/one-GRX3 heterotrimer carrying two [2Fe-2S] clusters and showed it transfers them to apo-anamorsin to produce the holo protein.","evidence":"Atomic-level NMR structural characterization, in vitro reconstitution, and cluster transfer assays to apo-anamorsin/Ciapin1","pmids":["26613676"],"confidence":"High","gaps":["Iron source feeding the complex not identified","Transfer kinetics and directionality regulation not defined"]},{"year":2016,"claim":"Whether the GRX3·BOLA2 complex acts in cells as a chaperone and responds to iron was open; quantitative IP and BioID showed iron-dependent complex formation and functional [2Fe-2S] transfer to Ciapin1 in human cells.","evidence":"Quantitative immunoprecipitation, live-cell BioID proximity labeling, iron titration, and functional Fe-S transfer assays in human cells","pmids":["27519415"],"confidence":"High","gaps":["Mechanism of iron-responsive complex induction not defined","Full client repertoire beyond Ciapin1 unknown"]},{"year":2016,"claim":"The evolutionary origin of BOLA2 was unknown; comparative genomics showed it is a human-specific duplication whose copy number scales with RNA and protein expression.","evidence":"Comparative genomic sequencing, copy-number versus RNA/protein quantification, and evolutionary timing analysis","pmids":["27487209"],"confidence":"Medium","gaps":["Functional consequence of the expansion not tested in this study","Role of the novel fusion transcript uncharacterized"]},{"year":2017,"claim":"This synthesis consolidated GRX3 and BOLA2 as a core [2Fe-2S] chaperone module of the cytosolic iron cofactor distribution system.","evidence":"Review integrating fractionation, Co-IP, and in vitro reconstitution evidence","pmids":["28615454"],"confidence":"Medium","gaps":["No new primary data","In vivo physiological role not addressed"]},{"year":2019,"claim":"How iron is delivered to the BOLA2-Glrx3 complex was unknown; this work identified an iron-loaded, glutathione-bound PCBP1 that docks onto BolA2 through a bridging iron to form the intermediate required for [2Fe-2S] assembly.","evidence":"Proteomics/Co-IP, in vitro reconstitution, and mutagenesis of PCBP1 iron-coordinating residues with cell-based assays","pmids":["31406370"],"confidence":"High","gaps":["Structural detail of the iron hand-off step not resolved","Kinetics of intermediate turnover not defined"]},{"year":2019,"claim":"Whether BOLA2 has a physiological role in iron homeostasis was untested; Bola2 knockout mice and human CNV cohort analysis linked BOLA2 loss to iron-deficiency anemia.","evidence":"Bola2 knockout mice with hematological phenotyping plus human 16p11.2 CNV carrier cohort stratified by BOLA2 copy number","pmids":["31668704"],"confidence":"Medium","gaps":["In vivo molecular pathway connecting BOLA2 loss to anemia not fully resolved","Tissue-specific contributions not delineated"]},{"year":2021,"claim":"Whether PCBP1 iron coordination is functionally required for its interaction with BolA2 was unclear; mutagenesis showed iron binding is necessary for BolA2 (and ferritin) binding and for cell-cycle/DNA-damage control, separable from nucleic-acid-binding activity.","evidence":"Site-directed mutagenesis of PCBP1 iron-coordinating residues, Co-IP, and functional rescue in PCBP1-depleted cells and mouse tissues","pmids":["34161287"],"confidence":"High","gaps":["Direct contribution of BOLA2 to the cell-cycle/DNA-damage phenotype not isolated","Quantitative flux through the PCBP1-BolA2 route in vivo unknown"]},{"year":2025,"claim":"How BOLA2 transcription is controlled was unknown; this work placed BOLA2 downstream of β1 integrin–STAT5 signaling, with STAT5 directly activating the BOLA2 promoter and BOLA2 overexpression conferring apoptosis resistance.","evidence":"RNA-seq, luciferase promoter assay, EMSA for STAT5 promoter binding, BOLA2 overexpression rescue of apoptosis, and β1 integrin re-expression epistasis in breast cancer cells","pmids":["41465298"],"confidence":"Medium","gaps":["Whether the apoptosis resistance depends on BOLA2 Fe-S chaperone activity not tested","Generalizability beyond breast cancer cells unknown"]},{"year":null,"claim":"It remains unknown how the iron-responsive induction of the GRX3·BOLA2 complex is mechanistically regulated and how broadly its chaperone activity supplies cytosolic Fe-S clients beyond Ciapin1/anamorsin.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Full Fe-S client repertoire undefined","Link between transcriptional control and cluster-transfer flux unresolved","In vivo iron-homeostasis mechanism not fully mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[1,2,3]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3,8]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,2,8]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,5,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[7]}],"complexes":["BOLA2-GRX3 [2Fe-2S] heterotrimer","PCBP1-Fe-GSH-BolA2 intermediate"],"partners":["GLRX3","PCBP1","CIAPIN1","STAT5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H3K6","full_name":"BolA-like protein 2","aliases":[],"length_aa":86,"mass_kda":10.1,"function":"Acts as a cytosolic iron-sulfur (Fe-S) cluster assembly factor that facilitates [2Fe-2S] cluster insertion into a subset of cytosolic proteins (PubMed:26613676, PubMed:27519415). Acts together with the monothiol glutaredoxin GLRX3 (PubMed:26613676, PubMed:27519415)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9H3K6/entry"},"depmap":{"release":"DepMap","has_data":false,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/BOLA2"},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/BOLA2","total_profiled":1310},"omim":[{"mim_id":"613183","title":"BOLA FAMILY MEMBER 3; BOLA3","url":"https://www.omim.org/entry/613183"},{"mim_id":"613182","title":"BOLA FAMILY MEMBER 2; BOLA2","url":"https://www.omim.org/entry/613182"},{"mim_id":"613181","title":"BOLA FAMILY MEMBER 1; BOLA1","url":"https://www.omim.org/entry/613181"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/BOLA2"},"hgnc":{"alias_symbol":["My016","BOLA2A"],"prev_symbol":[]},"alphafold":{"accession":"Q9H3K6","domains":[{"cath_id":"3.30.300.90","chopping":"6-82","consensus_level":"high","plddt":93.3325,"start":6,"end":82}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3K6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3K6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H3K6-F1-predicted_aligned_error_v6.png","plddt_mean":92.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=BOLA2","jax_strain_url":"https://www.jax.org/strain/search?query=BOLA2"},"sequence":{"accession":"Q9H3K6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H3K6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H3K6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H3K6"}},"corpus_meta":[{"pmid":"28586827","id":"PMC_28586827","title":"Genome-wide Pleiotropy Between 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susceptibility.","date":"2016","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/27487209","citation_count":99,"is_preprint":false},{"pmid":"22309771","id":"PMC_22309771","title":"Human glutaredoxin 3 forms [2Fe-2S]-bridged complexes with human BolA2.","date":"2012","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22309771","citation_count":85,"is_preprint":false},{"pmid":"27519415","id":"PMC_27519415","title":"A Glutaredoxin·BolA Complex Serves as an Iron-Sulfur Cluster Chaperone for the Cytosolic Cluster Assembly Machinery.","date":"2016","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27519415","citation_count":64,"is_preprint":false},{"pmid":"26613676","id":"PMC_26613676","title":"Elucidating the Molecular Function of Human BOLA2 in GRX3-Dependent Anamorsin Maturation Pathway.","date":"2015","source":"Journal of the American Chemical 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in vitro biochemical reconstitution; mutagenesis of PCBP1 iron-coordinating residues; cell-based assays\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution, mutagenesis, and cell-based validation in a single rigorous study; mechanistic intermediate characterized biochemically\",\n      \"pmids\": [\"31406370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human BolA2 forms [2Fe-2S]-bridged heterodimeric complexes with each Grx-like domain of human Glrx3, and apo BolA2 binds to [2Fe-2S] Glrx3 homodimer to form a [2Fe-2S] BolA2-Glrx3 heterotrimer; the Fe-S coordination environment is virtually identical to the analogous yeast complexes.\",\n      \"method\": \"UV-visible absorption/CD spectroscopy, resonance Raman spectroscopy, EPR spectroscopy of recombinant proteins; in vitro reconstitution of complexes\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal spectroscopic methods plus in vitro reconstitution establishing iron-sulfur cluster coordination geometry\",\n      \"pmids\": [\"22309771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Cytosolic Glrx3·BolA2 functions as a [2Fe-2S] chaperone complex in human cells; complex formation requires Fe-S cluster coordination; cellular Glrx3·BolA2 complexes increase 6–8-fold in response to iron; the complex transfers [2Fe-2S] clusters to the apoprotein Ciapin1, acting upstream in the cytosolic Fe-S assembly pathway.\",\n      \"method\": \"Quantitative immunoprecipitation; live-cell proximity-dependent biotinylation (BioID); iron-titration experiments; functional Fe-S transfer assays in human cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, BioID proximity labeling, and functional transfer assays; iron-responsive behavior characterized with two orthogonal methods\",\n      \"pmids\": [\"27519415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Apo BolA2 and apo GRX3 form a heterotrimeric complex (two BOLA2 molecules per one GRX3 molecule) that binds two [2Fe-2S]2+ clusters bridged between each BOLA2 molecule and a monothiol glutaredoxin domain of GRX3; this heterotrimer transfers both [2Fe-2S]2+ clusters to apo-anamorsin (Ciapin1), producing its mature holo state.\",\n      \"method\": \"NMR structural characterization of complex at atomic level; in vitro reconstitution; cluster transfer assays to apo-anamorsin\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR-based structural characterization with functional cluster transfer reconstitution, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"26613676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Iron coordination by PCBP1 (via specific cysteine/glutamate residues on each structural domain) is required for binding BolA2 and ferritin; PCBP1 variants lacking iron-binding activity fail to interact with BolA2 and lose the ability to control cell cycle progression and suppress DNA damage, while nucleic acid-binding activity is separately required for cell viability.\",\n      \"method\": \"Site-directed mutagenesis of PCBP1 iron-coordinating residues; Co-IP binding assays with BolA2 and ferritin; functional rescue experiments in PCBP1-depleted human cells and mouse tissues\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis plus Co-IP plus functional rescue in both cell and mouse models; two independent activity modules delineated\",\n      \"pmids\": [\"34161287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"BOLA2 participates in iron homeostasis in vivo; Bola2-deficient mice exhibit iron deficiency signs including decreased hemoglobin, lower plasma iron, microcytosis, and increased red blood cell zinc-protoporphyrin-to-heme ratio; human 16p11.2 deletion carriers with lower BOLA2 copy number show increased prevalence of iron-deficiency anemia.\",\n      \"method\": \"Mouse knockout (Bola2+/- and Bola2-/-) with hematological phenotyping; human 16p11.2 CNV carrier cohort analysis stratified by BOLA2 copy number\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined hematological phenotype in mice, supported by human CNV cohort; mechanistic pathway not fully resolved in vivo\",\n      \"pmids\": [\"31668704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"BOLA2 is a human-specific gene duplication (duplicated exclusively in Homo sapiens ~282 ka); BOLA2 copy number positively correlates with RNA expression (r=0.36) and protein level (r=0.65), with the greatest expression difference between human and chimpanzee in stem cells; the duplication also generated a novel human-specific in-frame fusion transcript.\",\n      \"method\": \"Comparative genomic sequencing; BOLA2 copy number vs. RNA/protein quantification across individuals; evolutionary timing analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct quantification of copy number vs. protein level with good correlation; genomic/evolutionary characterization in a single large study\",\n      \"pmids\": [\"27487209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In breast cancer cells, sulfatide (SM4) suppresses BOLA2 expression by inhibiting β1 integrin–STAT5 signaling; STAT5 directly binds and activates the BOLA2 promoter (demonstrated by EMSA); overexpression of BOLA2 confers resistance to doxorubicin-induced apoptosis, placing BOLA2 downstream of β1 integrin–STAT5 in the CIAPIN1 apoptotic pathway.\",\n      \"method\": \"RNA sequencing; RT-qPCR; Western blot; luciferase promoter assay; EMSA (STAT5 binding to BOLA2 promoter); BOLA2 overexpression rescue of apoptosis; β1 integrin re-expression epistasis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — EMSA for direct promoter binding, luciferase assay, functional rescue by BOLA2 OE, and epistasis via β1 integrin re-expression; single lab\",\n      \"pmids\": [\"41465298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The monothiol glutaredoxin Glrx3 and BolA2 together function as a [2Fe-2S] chaperone complex representing a core component of the cytosolic iron cofactor distribution system in mammalian cells.\",\n      \"method\": \"Review/synthesis of biochemical and cell-biological evidence (fractionation, Co-IP, in vitro reconstitution cited across studies)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — review paper consolidating multiple prior experimental findings; no new primary data but synthesizes replicated evidence\",\n      \"pmids\": [\"28615454\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"BOLA2 is a cytosolic iron-sulfur ([2Fe-2S]) cluster chaperone that forms a heterotrimer with two BOLA2 molecules and one GRX3/Glrx3 molecule, each bridging a [2Fe-2S] cluster; it receives iron from a PCBP1-Fe-GSH intermediate and transfers [2Fe-2S] clusters to apoproteins such as Ciapin1/anamorsin in the cytosolic Fe-S assembly pathway; its transcription is regulated by a β1 integrin–STAT5 axis, and its loss in vivo causes iron-deficiency anemia, while its human-specific copy-number expansion appears to protect against iron deficiency.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"BOLA2 is a cytosolic [2Fe-2S] cluster chaperone that operates in the cytosolic iron-sulfur protein assembly pathway by partnering with the monothiol glutaredoxin GRX3/Glrx3 [#2, #8]. Human BOLA2 forms [2Fe-2S]-bridged complexes with each glutaredoxin-like domain of Glrx3, assembling a heterotrimer of two BOLA2 molecules and one GRX3 molecule that coordinates two [2Fe-2S] clusters, each bridged between a BOLA2 subunit and a glutaredoxin domain [#1, #3]. This complex acquires iron upstream from an iron-loaded, glutathione-bound form of PCBP1, which docks onto BOLA2 through a bridging iron ligand to form a PCBP1-Fe-GSH-BolA2 intermediate required for [2Fe-2S] cluster assembly on the BOLA2-Glrx3 complex [#0, #4]. The mature holo-heterotrimer then transfers both [2Fe-2S] clusters to apo-anamorsin/Ciapin1, maturing it as a downstream client, and cellular GRX3·BOLA2 complexes increase several-fold in response to iron [#2, #3]. Loss of Bola2 in mice produces iron-deficiency anemia with reduced hemoglobin, low plasma iron, and microcytosis, and reduced BOLA2 copy number in human 16p11.2 deletion carriers is associated with increased iron-deficiency anemia [#5]. BOLA2 arose from a human-specific gene duplication whose copy number scales with RNA and protein levels [#6], and in breast cancer cells its transcription is activated directly by STAT5 downstream of β1 integrin signaling, with BOLA2 overexpression conferring resistance to doxorubicin-induced apoptosis [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Whether human BOLA2 and Glrx3 physically assemble into a defined iron-sulfur cluster complex was unknown; this work established the coordination geometry of a [2Fe-2S]-bridged BOLA2-Glrx3 assembly.\",\n      \"evidence\": \"Multiple orthogonal spectroscopies (UV-vis/CD, resonance Raman, EPR) on reconstituted recombinant proteins\",\n      \"pmids\": [\"22309771\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the cellular function or downstream clients of the complex\", \"Stoichiometry of the in-cell heterotrimer not yet resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The atomic architecture and catalytic output of the assembly were unresolved; NMR defined a two-BOLA2/one-GRX3 heterotrimer carrying two [2Fe-2S] clusters and showed it transfers them to apo-anamorsin to produce the holo protein.\",\n      \"evidence\": \"Atomic-level NMR structural characterization, in vitro reconstitution, and cluster transfer assays to apo-anamorsin/Ciapin1\",\n      \"pmids\": [\"26613676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Iron source feeding the complex not identified\", \"Transfer kinetics and directionality regulation not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Whether the GRX3·BOLA2 complex acts in cells as a chaperone and responds to iron was open; quantitative IP and BioID showed iron-dependent complex formation and functional [2Fe-2S] transfer to Ciapin1 in human cells.\",\n      \"evidence\": \"Quantitative immunoprecipitation, live-cell BioID proximity labeling, iron titration, and functional Fe-S transfer assays in human cells\",\n      \"pmids\": [\"27519415\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of iron-responsive complex induction not defined\", \"Full client repertoire beyond Ciapin1 unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"The evolutionary origin of BOLA2 was unknown; comparative genomics showed it is a human-specific duplication whose copy number scales with RNA and protein expression.\",\n      \"evidence\": \"Comparative genomic sequencing, copy-number versus RNA/protein quantification, and evolutionary timing analysis\",\n      \"pmids\": [\"27487209\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the expansion not tested in this study\", \"Role of the novel fusion transcript uncharacterized\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"This synthesis consolidated GRX3 and BOLA2 as a core [2Fe-2S] chaperone module of the cytosolic iron cofactor distribution system.\",\n      \"evidence\": \"Review integrating fractionation, Co-IP, and in vitro reconstitution evidence\",\n      \"pmids\": [\"28615454\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No new primary data\", \"In vivo physiological role not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"How iron is delivered to the BOLA2-Glrx3 complex was unknown; this work identified an iron-loaded, glutathione-bound PCBP1 that docks onto BolA2 through a bridging iron to form the intermediate required for [2Fe-2S] assembly.\",\n      \"evidence\": \"Proteomics/Co-IP, in vitro reconstitution, and mutagenesis of PCBP1 iron-coordinating residues with cell-based assays\",\n      \"pmids\": [\"31406370\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural detail of the iron hand-off step not resolved\", \"Kinetics of intermediate turnover not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Whether BOLA2 has a physiological role in iron homeostasis was untested; Bola2 knockout mice and human CNV cohort analysis linked BOLA2 loss to iron-deficiency anemia.\",\n      \"evidence\": \"Bola2 knockout mice with hematological phenotyping plus human 16p11.2 CNV carrier cohort stratified by BOLA2 copy number\",\n      \"pmids\": [\"31668704\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo molecular pathway connecting BOLA2 loss to anemia not fully resolved\", \"Tissue-specific contributions not delineated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Whether PCBP1 iron coordination is functionally required for its interaction with BolA2 was unclear; mutagenesis showed iron binding is necessary for BolA2 (and ferritin) binding and for cell-cycle/DNA-damage control, separable from nucleic-acid-binding activity.\",\n      \"evidence\": \"Site-directed mutagenesis of PCBP1 iron-coordinating residues, Co-IP, and functional rescue in PCBP1-depleted cells and mouse tissues\",\n      \"pmids\": [\"34161287\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct contribution of BOLA2 to the cell-cycle/DNA-damage phenotype not isolated\", \"Quantitative flux through the PCBP1-BolA2 route in vivo unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"How BOLA2 transcription is controlled was unknown; this work placed BOLA2 downstream of β1 integrin–STAT5 signaling, with STAT5 directly activating the BOLA2 promoter and BOLA2 overexpression conferring apoptosis resistance.\",\n      \"evidence\": \"RNA-seq, luciferase promoter assay, EMSA for STAT5 promoter binding, BOLA2 overexpression rescue of apoptosis, and β1 integrin re-expression epistasis in breast cancer cells\",\n      \"pmids\": [\"41465298\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the apoptosis resistance depends on BOLA2 Fe-S chaperone activity not tested\", \"Generalizability beyond breast cancer cells unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how the iron-responsive induction of the GRX3·BOLA2 complex is mechanistically regulated and how broadly its chaperone activity supplies cytosolic Fe-S clients beyond Ciapin1/anamorsin.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full Fe-S client repertoire undefined\", \"Link between transcriptional control and cluster-transfer flux unresolved\", \"In vivo iron-homeostasis mechanism not fully mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 5, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\n      \"BOLA2-GRX3 [2Fe-2S] heterotrimer\",\n      \"PCBP1-Fe-GSH-BolA2 intermediate\"\n    ],\n    \"partners\": [\n      \"GLRX3\",\n      \"PCBP1\",\n      \"CIAPIN1\",\n      \"STAT5\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}