{"gene":"IBA57","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2012,"finding":"Human IBA57, together with ISCA1 and ISCA2, is specifically required for the maturation of mitochondrial [4Fe-4S] proteins (including aconitase, respiratory complex I, and lipoic acid synthase) but not [2Fe-2S] proteins (ferrochelatase), placing IBA57 in a late step of the mitochondrial ISC assembly pathway.","method":"RNAi depletion in HeLa cells with enzymatic activity assays for [4Fe-4S] and [2Fe-2S] proteins; mitochondrial morphology assessment by microscopy","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KD with defined biochemical phenotype, multiple [4Fe-4S] enzyme readouts, replicated across multiple depletion conditions and confirmed by independent clinical studies","pmids":["22323289"],"is_preprint":false},{"year":2018,"finding":"IBA57 forms a heterodimeric complex with ISCA2 bridging a [2Fe-2S] cluster; [2Fe-2S] cluster binding is absolutely required for complex formation; the conserved cysteine of the IBA57 family motif and the three conserved cysteines of ISCA2 serve as cluster ligands. The [2Fe-2S] ISCA2-IBA57 complex forms via a transfer pathway involving GLRX5 → ISCA2 → IBA57 and is capable of reactivating apo-aconitase in vitro.","method":"In vitro reconstitution, UV-visible spectroscopy, iron/sulfur quantification, site-directed mutagenesis of cysteine ligands, in vitro aconitase reactivation assay, Co-IP/pulldown","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis, multiple spectroscopic methods, functional aconitase reactivation assay, replicated by structural study (PMID:31831856)","pmids":["30269484"],"is_preprint":false},{"year":2019,"finding":"Low-resolution structural model of the [2Fe-2S]2+ ISCA2-IBA57 heterodimeric complex was determined using SAXS and bioinformatics-driven docking; the complex adopts a dimer-of-dimers organization with ISCA2 providing the homodimerization core and the [2Fe-2S] cluster bridging at the ISCA2-IBA57 interface. The pathogenic Arg146Trp IBA57 mutation disrupts key interaction contacts at this interface.","method":"Small-angle X-ray scattering (SAXS), bioinformatics-driven docking, biochemical validation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — low-resolution structural model (SAXS, not crystal/cryo-EM), single lab, supported by prior biochemical work (PMID:30269484)","pmids":["31831856"],"is_preprint":false},{"year":2022,"finding":"Crystal structure of Iba57 from Chaetomium thermophilum showed that the THF-binding pocket is constricted relative to canonical THF-dependent enzymes (GcvT); genetic studies in yeast showed folate-deficient mutants have no defect in mitochondrial [4Fe-4S] protein maturation; mutations in conserved residues essential for THF-dependent catalysis in GcvT did not impair Iba57 function in vivo; mutation of the invariant surface-exposed cysteine did impair function. Conclusion: mitochondrial Iba57 does not utilize tetrahydrofolate for its [4Fe-4S] assembly function.","method":"Crystal structure determination of fungal Iba57; yeast genetic studies with folate-deficient mutants; in vivo mutagenesis of conserved active-site residues; [4Fe-4S] enzyme activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with in vivo mutagenesis and genetic epistasis in yeast, multiple orthogonal lines of evidence in a single rigorous study","pmids":["36075292"],"is_preprint":false},{"year":2013,"finding":"A missense mutation (p.Gln314Pro) in IBA57 causes excessive proteolytic degradation of the IBA57 protein below physiologically critical levels, leading to reduced mitochondrial [4Fe-4S] protein activities and loss of lipoic acid-modified proteins; the biochemical defects were complemented by wild-type IBA57 and partially by mutant IBA57; protease inhibitors ameliorated protein degradation.","method":"Patient fibroblast and HeLa cell biochemical complementation assays, immunoblotting, enzyme activity assays, protease inhibitor treatment","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complementation in cell model with multiple enzyme readouts, single lab, consistent with PMID:22323289","pmids":["23462291"],"is_preprint":false},{"year":2015,"finding":"A loss-of-function splice-site mutation in IBA57 results in severely reduced [4Fe-4S] protein activities (complexes I and II) in patient lymphoblasts while mitochondrial [2Fe-2S] proteins remain normal, confirming the specific role of IBA57 in [4Fe-4S] but not [2Fe-2S] protein maturation in a human disease context.","method":"mRNA splice analysis, immunoblotting, enzyme activity assays in patient lymphoblasts","journal":"Neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient cell biochemistry with specific enzyme readouts, consistent with PMID:22323289, single lab","pmids":["25609768"],"is_preprint":false},{"year":2015,"finding":"The p.Arg146Trp IBA57 mutation causes loss-of-function; mutant IBA57 is unable to restore biochemical phenotype (respiratory complex I/II activities and protein lipoylation) in IBA57-depleted HeLa cells, establishing this as a null-equivalent allele at the protein function level.","method":"Complementation assay in IBA57-depleted HeLa cells, enzyme activity assays, immunoblotting for lipoylated proteins","journal":"Journal of inherited metabolic disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional complementation with defined biochemical readouts, single lab","pmids":["25971455"],"is_preprint":false},{"year":2017,"finding":"IBA57 deficiency leads to reduced NFU1 protein expression, which in turn decreases SDH (complex II) activity and LIAS (lipoic acid synthase) expression, revealing a regulatory relationship between IBA57 and NFU1 within the mitochondrial ISC assembly pathway.","method":"Immunoblotting in patient myoblasts/fibroblasts, enzyme activity staining (SDH), rescue experiments in patient-derived myoblasts","journal":"Neurology. Genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — immunoblotting in patient cells only, single lab, no direct mechanistic dissection of how IBA57 affects NFU1","pmids":["28913435"],"is_preprint":false},{"year":2024,"finding":"The pathogenic p.Gly104Cys IBA57 variant does not impair formation of the IBA57-[2Fe-2S]-ISCA2 heterodimer but significantly destabilizes IBA57 protein in both its isolated form and within the ISCA2 complex, providing a structural rationale for the severe MMDS3 phenotype.","method":"Size exclusion chromatography-MALS, NMR, circular dichroism, fluorescence spectroscopy, in vitro reconstitution of IBA57-ISCA2 complex","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple biophysical methods in a single study, single lab, no in vivo functional validation","pmids":["39408793"],"is_preprint":false}],"current_model":"IBA57 is a mitochondrial iron-sulfur cluster assembly factor that acts in a late step of the ISC pathway, functioning together with ISCA1, ISCA2, and GLRX5 to specifically mature [4Fe-4S] proteins (including respiratory complexes I and II, aconitase, and lipoic acid synthase) but not [2Fe-2S] proteins; mechanistically, IBA57 receives a [2Fe-2S] cluster from GLRX5-loaded ISCA2 to form a bridged [2Fe-2S] ISCA2-IBA57 heterodimeric complex—with the conserved IBA57 cysteine and three ISCA2 cysteines acting as cluster ligands—and this complex can donate the cluster to activate apo-[4Fe-4S] target proteins; despite structural homology to tetrahydrofolate-dependent enzymes, IBA57 does not use folate as a cofactor, and its invariant surface-exposed cysteine is essential for function."},"narrative":{"mechanistic_narrative":"IBA57 is a mitochondrial iron-sulfur cluster (ISC) assembly factor that acts at a late step of the pathway to specifically mature [4Fe-4S] proteins—including respiratory complexes I and II, aconitase, and lipoic acid synthase—while being dispensable for [2Fe-2S] protein maturation [PMID:22323289, PMID:25609768]. It functions together with ISCA1 and ISCA2 [PMID:22323289], and forms a heterodimeric complex with ISCA2 that bridges a [2Fe-2S] cluster, with the conserved IBA57 family cysteine and three conserved ISCA2 cysteines serving as cluster ligands; cluster binding is required for complex formation, and the assembled [2Fe-2S]-ISCA2-IBA57 complex—generated via a GLRX5 → ISCA2 → IBA57 transfer pathway—can reactivate apo-aconitase in vitro [PMID:30269484]. Structurally the complex adopts a dimer-of-dimers organization with ISCA2 providing the homodimerization core and the cluster bridging the ISCA2-IBA57 interface [PMID:31831856]. Despite structural homology to tetrahydrofolate-dependent enzymes, IBA57 does not use folate as a cofactor: its THF-binding pocket is constricted, folate-deficient and THF-catalytic-residue mutants retain function, whereas mutation of the invariant surface-exposed cysteine impairs [4Fe-4S] assembly [PMID:36075292]. Loss-of-function mutations in IBA57 cause multiple mitochondrial dysfunctions syndrome (MMDS3), acting through protein destabilization or disruption of interface contacts that reduce [4Fe-4S] enzyme activities and protein lipoylation [PMID:23462291, PMID:25971455, PMID:39408793].","teleology":[{"year":2012,"claim":"Established the central question of where IBA57 acts—defining it as a late-acting, [4Fe-4S]-specific maturation factor rather than a general ISC component.","evidence":"RNAi depletion in HeLa cells with [4Fe-4S] and [2Fe-2S] enzyme activity readouts","pmids":["22323289"],"confidence":"High","gaps":["Did not define the molecular partners or the biochemical mechanism of cluster transfer","Did not resolve how specificity for [4Fe-4S] over [2Fe-2S] targets is achieved"]},{"year":2013,"claim":"Demonstrated that a patient missense allele acts by triggering proteolytic loss of IBA57 below a critical threshold, linking protein abundance to ISC function in disease.","evidence":"Complementation in patient fibroblasts/HeLa, immunoblotting, protease inhibitor treatment, enzyme assays","pmids":["23462291"],"confidence":"Medium","gaps":["Did not identify the protease responsible for degradation","Single-lab cell-model study"]},{"year":2015,"claim":"Confirmed in independent human disease contexts that IBA57 loss selectively impairs [4Fe-4S] (complex I/II) maturation and lipoylation while sparing [2Fe-2S] proteins, and that R146W is a null-equivalent allele.","evidence":"Splice analysis and complementation in patient lymphoblasts and IBA57-depleted HeLa cells with enzyme/lipoylation readouts","pmids":["25609768","25971455"],"confidence":"Medium","gaps":["Did not map why specific residues are required at the molecular level","Patient-cell biochemistry without reconstitution"]},{"year":2017,"claim":"Began addressing how IBA57 connects to other ISC factors by showing IBA57 deficiency lowers NFU1 and downstream SDH/LIAS.","evidence":"Immunoblotting and SDH activity staining in patient myoblasts/fibroblasts with rescue","pmids":["28913435"],"confidence":"Low","gaps":["No direct mechanism for how IBA57 controls NFU1 levels","Correlative immunoblot data in patient cells only, single lab"]},{"year":2018,"claim":"Resolved the core biochemical mechanism—reconstituting the [2Fe-2S]-bridged ISCA2-IBA57 heterodimer, identifying the cluster ligands, the GLRX5 → ISCA2 → IBA57 transfer route, and showing functional apo-aconitase reactivation.","evidence":"In vitro reconstitution, UV-vis spectroscopy, Fe/S quantification, cysteine mutagenesis, aconitase reactivation, Co-IP","pmids":["30269484"],"confidence":"High","gaps":["Did not provide an atomic-resolution structure of the complex","Mechanism of cluster donation to specific [4Fe-4S] apo-targets not detailed"]},{"year":2019,"claim":"Provided a structural framework for the complex, defining a dimer-of-dimers architecture with the cluster at the ISCA2-IBA57 interface and rationalizing the R146W pathogenic mutation.","evidence":"SAXS, bioinformatics-driven docking, biochemical validation","pmids":["31831856"],"confidence":"Medium","gaps":["Low-resolution model, not crystal/cryo-EM","Interface contacts inferred from docking rather than directly resolved"]},{"year":2022,"claim":"Settled whether IBA57's THF-enzyme homology reflects a folate-dependent mechanism—showing it does not, and pinpointing the invariant surface cysteine as the functionally essential residue.","evidence":"Crystal structure of fungal Iba57, yeast folate/active-site mutant genetics, [4Fe-4S] enzyme assays","pmids":["36075292"],"confidence":"High","gaps":["Did not establish the catalytic role, if any, of the surface cysteine beyond cluster ligation","Structure is of a fungal ortholog"]},{"year":2024,"claim":"Extended the structure-function picture by showing a pathogenic variant (G104C) destabilizes IBA57 protein without blocking heterodimer assembly, separating folding/stability defects from complex-formation defects.","evidence":"SEC-MALS, NMR, CD, fluorescence spectroscopy, in vitro reconstitution","pmids":["39408793"],"confidence":"Medium","gaps":["No in vivo functional validation of the variant","Single-lab biophysical study"]},{"year":null,"claim":"How the [2Fe-2S]-ISCA2-IBA57 complex selectively converts to and donates a [4Fe-4S] cluster to specific apo-target proteins, and the atomic-resolution structure of the cluster-bound complex, remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of the cluster-bound human complex","Mechanism of reductive [2Fe-2S]→[4Fe-4S] conversion and target selection undefined","Direct mechanism linking IBA57 to NFU1 regulation unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,3]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0]}],"complexes":["ISCA2-IBA57 heterodimer"],"partners":["ISCA2","ISCA1","GLRX5","NFU1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q5T440","full_name":"Iron-sulfur cluster assembly factor IBA57, mitochondrial","aliases":["Iron-sulfur cluster assembly factor homolog"],"length_aa":356,"mass_kda":38.2,"function":"Mitochondrial protein involved in the maturation of mitochondrial [4Fe-4S]-proteins in the late stage of the iron-sulfur cluster assembly pathway (PubMed:22323289, PubMed:23462291). Operates in cooperation with ISCA2 in the maturation of [4Fe-4S] proteins (PubMed:30269484) Involved in the maturation of mitochondrial 2Fe-2S proteins in the late stage of the iron-sulfur cluster assembly pathway","subcellular_location":"Mitochondrion","url":"https://www.uniprot.org/uniprotkb/Q5T440/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IBA57","classification":"Not Classified","n_dependent_lines":263,"n_total_lines":1208,"dependency_fraction":0.21771523178807947},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IBA57","total_profiled":1310},"omim":[{"mim_id":"616451","title":"SPASTIC PARAPLEGIA 74, AUTOSOMAL RECESSIVE; SPG74","url":"https://www.omim.org/entry/616451"},{"mim_id":"616370","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 4; MMDS4","url":"https://www.omim.org/entry/616370"},{"mim_id":"615330","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 3; MMDS3","url":"https://www.omim.org/entry/615330"},{"mim_id":"615317","title":"IRON-SULFUR CLUSTER ASSEMBLY 2; ISCA2","url":"https://www.omim.org/entry/615317"},{"mim_id":"615316","title":"IRON-SULFUR CLUSTER ASSEMBLY FACTOR IBA57; IBA57","url":"https://www.omim.org/entry/615316"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Mitochondria","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/IBA57"},"hgnc":{"alias_symbol":["FLJ12734"],"prev_symbol":["C1orf69"]},"alphafold":{"accession":"Q5T440","domains":[{"cath_id":"3.30.1360.120","chopping":"49-227","consensus_level":"high","plddt":91.1215,"start":49,"end":227},{"cath_id":"2.40.30.110","chopping":"277-351","consensus_level":"medium","plddt":94.2496,"start":277,"end":351}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T440","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T440-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q5T440-F1-predicted_aligned_error_v6.png","plddt_mean":85.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IBA57","jax_strain_url":"https://www.jax.org/strain/search?query=IBA57"},"sequence":{"accession":"Q5T440","fasta_url":"https://rest.uniprot.org/uniprotkb/Q5T440.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q5T440/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q5T440"}},"corpus_meta":[{"pmid":"22323289","id":"PMC_22323289","title":"The human mitochondrial ISCA1, ISCA2, and IBA57 proteins are required for [4Fe-4S] protein maturation.","date":"2012","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/22323289","citation_count":172,"is_preprint":false},{"pmid":"23462291","id":"PMC_23462291","title":"Mutation of the iron-sulfur cluster assembly gene IBA57 causes severe myopathy and encephalopathy.","date":"2013","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23462291","citation_count":94,"is_preprint":false},{"pmid":"25609768","id":"PMC_25609768","title":"Fe/S protein assembly gene IBA57 mutation causes hereditary spastic paraplegia.","date":"2015","source":"Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/25609768","citation_count":60,"is_preprint":false},{"pmid":"30269484","id":"PMC_30269484","title":"IBA57 Recruits ISCA2 to Form a [2Fe-2S] Cluster-Mediated Complex.","date":"2018","source":"Journal of the American Chemical Society","url":"https://pubmed.ncbi.nlm.nih.gov/30269484","citation_count":44,"is_preprint":false},{"pmid":"25971455","id":"PMC_25971455","title":"Mutation of the iron-sulfur cluster assembly gene IBA57 causes fatal infantile leukodystrophy.","date":"2015","source":"Journal of inherited metabolic disease","url":"https://pubmed.ncbi.nlm.nih.gov/25971455","citation_count":42,"is_preprint":false},{"pmid":"27785568","id":"PMC_27785568","title":"Novel mutations in IBA57 are associated with leukodystrophy and variable clinical phenotypes.","date":"2016","source":"Journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/27785568","citation_count":41,"is_preprint":false},{"pmid":"28913435","id":"PMC_28913435","title":"IBA57 mutations abrogate iron-sulfur cluster assembly leading to cavitating leukoencephalopathy.","date":"2017","source":"Neurology. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28913435","citation_count":30,"is_preprint":false},{"pmid":"28671726","id":"PMC_28671726","title":"Phenotypic spectrum of mutations in IBA57, a candidate gene for cavitating leukoencephalopathy.","date":"2017","source":"Clinical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28671726","citation_count":25,"is_preprint":false},{"pmid":"31831856","id":"PMC_31831856","title":"Structural properties of [2Fe-2S] ISCA2-IBA57: a complex of the mitochondrial iron-sulfur cluster assembly machinery.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/31831856","citation_count":21,"is_preprint":false},{"pmid":"34709542","id":"PMC_34709542","title":"Novel IBA57 mutations in two chinese patients and literature review of multiple mitochondrial dysfunction syndrome.","date":"2021","source":"Metabolic brain disease","url":"https://pubmed.ncbi.nlm.nih.gov/34709542","citation_count":9,"is_preprint":false},{"pmid":"36075292","id":"PMC_36075292","title":"The iron-sulfur cluster assembly (ISC) protein Iba57 executes a tetrahydrofolate-independent function in mitochondrial [4Fe-4S] protein maturation.","date":"2022","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/36075292","citation_count":6,"is_preprint":false},{"pmid":"37588046","id":"PMC_37588046","title":"A novel IBA57 variant is associated with mitochondrial iron-sulfur protein deficiency and necrotizing myelopathy in dogs.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37588046","citation_count":5,"is_preprint":false},{"pmid":"41559004","id":"PMC_41559004","title":"Multiple Mitochondrial Dysfunction Syndrome Caused by IBA57 Gene Mutation: A Case Report and Literature Review.","date":"2026","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41559004","citation_count":1,"is_preprint":false},{"pmid":"39227420","id":"PMC_39227420","title":"Phenotypic spectrum of iron-sulfur cluster assembly gene IBA57 mutations: c.286 T > C identified as a hotspot mutation in Chinese patients with a stable natural history.","date":"2024","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39227420","citation_count":1,"is_preprint":false},{"pmid":"39408793","id":"PMC_39408793","title":"Defects in the Maturation of Mitochondrial Iron-Sulfur Proteins: Biophysical Investigation of the MMDS3 Causing Gly104Cys Variant of IBA57.","date":"2024","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/39408793","citation_count":0,"is_preprint":false},{"pmid":"39779339","id":"PMC_39779339","title":"[Clinical characteristics and genetic analysis of two children with Multiple mitochondrial dysfunction syndrome due to variants of IBA57 gene].","date":"2025","source":"Zhonghua yi xue yi chuan xue za zhi = Zhonghua yixue yichuanxue zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/39779339","citation_count":0,"is_preprint":false},{"pmid":"40602968","id":"PMC_40602968","title":"The first report of a successful birth by preimplantation genetic testing for leukodystrophy induced by IBA57 gene.","date":"2025","source":"Taiwanese journal of obstetrics & gynecology","url":"https://pubmed.ncbi.nlm.nih.gov/40602968","citation_count":0,"is_preprint":false},{"pmid":"41108822","id":"PMC_41108822","title":"Establishment of human induced pluripotent stem cell line, NIMHi020-A from fibroblasts of a patient with IBA57 variant (p.Tyr113Cys).","date":"2025","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/41108822","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11258,"output_tokens":2560,"usd":0.036087,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9771,"output_tokens":2940,"usd":0.061178,"stage2_stop_reason":"end_turn"},"total_usd":0.097265,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"Human IBA57, together with ISCA1 and ISCA2, is specifically required for the maturation of mitochondrial [4Fe-4S] proteins (including aconitase, respiratory complex I, and lipoic acid synthase) but not [2Fe-2S] proteins (ferrochelatase), placing IBA57 in a late step of the mitochondrial ISC assembly pathway.\",\n      \"method\": \"RNAi depletion in HeLa cells with enzymatic activity assays for [4Fe-4S] and [2Fe-2S] proteins; mitochondrial morphology assessment by microscopy\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KD with defined biochemical phenotype, multiple [4Fe-4S] enzyme readouts, replicated across multiple depletion conditions and confirmed by independent clinical studies\",\n      \"pmids\": [\"22323289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IBA57 forms a heterodimeric complex with ISCA2 bridging a [2Fe-2S] cluster; [2Fe-2S] cluster binding is absolutely required for complex formation; the conserved cysteine of the IBA57 family motif and the three conserved cysteines of ISCA2 serve as cluster ligands. The [2Fe-2S] ISCA2-IBA57 complex forms via a transfer pathway involving GLRX5 → ISCA2 → IBA57 and is capable of reactivating apo-aconitase in vitro.\",\n      \"method\": \"In vitro reconstitution, UV-visible spectroscopy, iron/sulfur quantification, site-directed mutagenesis of cysteine ligands, in vitro aconitase reactivation assay, Co-IP/pulldown\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis, multiple spectroscopic methods, functional aconitase reactivation assay, replicated by structural study (PMID:31831856)\",\n      \"pmids\": [\"30269484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Low-resolution structural model of the [2Fe-2S]2+ ISCA2-IBA57 heterodimeric complex was determined using SAXS and bioinformatics-driven docking; the complex adopts a dimer-of-dimers organization with ISCA2 providing the homodimerization core and the [2Fe-2S] cluster bridging at the ISCA2-IBA57 interface. The pathogenic Arg146Trp IBA57 mutation disrupts key interaction contacts at this interface.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS), bioinformatics-driven docking, biochemical validation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — low-resolution structural model (SAXS, not crystal/cryo-EM), single lab, supported by prior biochemical work (PMID:30269484)\",\n      \"pmids\": [\"31831856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Crystal structure of Iba57 from Chaetomium thermophilum showed that the THF-binding pocket is constricted relative to canonical THF-dependent enzymes (GcvT); genetic studies in yeast showed folate-deficient mutants have no defect in mitochondrial [4Fe-4S] protein maturation; mutations in conserved residues essential for THF-dependent catalysis in GcvT did not impair Iba57 function in vivo; mutation of the invariant surface-exposed cysteine did impair function. Conclusion: mitochondrial Iba57 does not utilize tetrahydrofolate for its [4Fe-4S] assembly function.\",\n      \"method\": \"Crystal structure determination of fungal Iba57; yeast genetic studies with folate-deficient mutants; in vivo mutagenesis of conserved active-site residues; [4Fe-4S] enzyme activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with in vivo mutagenesis and genetic epistasis in yeast, multiple orthogonal lines of evidence in a single rigorous study\",\n      \"pmids\": [\"36075292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A missense mutation (p.Gln314Pro) in IBA57 causes excessive proteolytic degradation of the IBA57 protein below physiologically critical levels, leading to reduced mitochondrial [4Fe-4S] protein activities and loss of lipoic acid-modified proteins; the biochemical defects were complemented by wild-type IBA57 and partially by mutant IBA57; protease inhibitors ameliorated protein degradation.\",\n      \"method\": \"Patient fibroblast and HeLa cell biochemical complementation assays, immunoblotting, enzyme activity assays, protease inhibitor treatment\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complementation in cell model with multiple enzyme readouts, single lab, consistent with PMID:22323289\",\n      \"pmids\": [\"23462291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A loss-of-function splice-site mutation in IBA57 results in severely reduced [4Fe-4S] protein activities (complexes I and II) in patient lymphoblasts while mitochondrial [2Fe-2S] proteins remain normal, confirming the specific role of IBA57 in [4Fe-4S] but not [2Fe-2S] protein maturation in a human disease context.\",\n      \"method\": \"mRNA splice analysis, immunoblotting, enzyme activity assays in patient lymphoblasts\",\n      \"journal\": \"Neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient cell biochemistry with specific enzyme readouts, consistent with PMID:22323289, single lab\",\n      \"pmids\": [\"25609768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The p.Arg146Trp IBA57 mutation causes loss-of-function; mutant IBA57 is unable to restore biochemical phenotype (respiratory complex I/II activities and protein lipoylation) in IBA57-depleted HeLa cells, establishing this as a null-equivalent allele at the protein function level.\",\n      \"method\": \"Complementation assay in IBA57-depleted HeLa cells, enzyme activity assays, immunoblotting for lipoylated proteins\",\n      \"journal\": \"Journal of inherited metabolic disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional complementation with defined biochemical readouts, single lab\",\n      \"pmids\": [\"25971455\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IBA57 deficiency leads to reduced NFU1 protein expression, which in turn decreases SDH (complex II) activity and LIAS (lipoic acid synthase) expression, revealing a regulatory relationship between IBA57 and NFU1 within the mitochondrial ISC assembly pathway.\",\n      \"method\": \"Immunoblotting in patient myoblasts/fibroblasts, enzyme activity staining (SDH), rescue experiments in patient-derived myoblasts\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — immunoblotting in patient cells only, single lab, no direct mechanistic dissection of how IBA57 affects NFU1\",\n      \"pmids\": [\"28913435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The pathogenic p.Gly104Cys IBA57 variant does not impair formation of the IBA57-[2Fe-2S]-ISCA2 heterodimer but significantly destabilizes IBA57 protein in both its isolated form and within the ISCA2 complex, providing a structural rationale for the severe MMDS3 phenotype.\",\n      \"method\": \"Size exclusion chromatography-MALS, NMR, circular dichroism, fluorescence spectroscopy, in vitro reconstitution of IBA57-ISCA2 complex\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple biophysical methods in a single study, single lab, no in vivo functional validation\",\n      \"pmids\": [\"39408793\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IBA57 is a mitochondrial iron-sulfur cluster assembly factor that acts in a late step of the ISC pathway, functioning together with ISCA1, ISCA2, and GLRX5 to specifically mature [4Fe-4S] proteins (including respiratory complexes I and II, aconitase, and lipoic acid synthase) but not [2Fe-2S] proteins; mechanistically, IBA57 receives a [2Fe-2S] cluster from GLRX5-loaded ISCA2 to form a bridged [2Fe-2S] ISCA2-IBA57 heterodimeric complex—with the conserved IBA57 cysteine and three ISCA2 cysteines acting as cluster ligands—and this complex can donate the cluster to activate apo-[4Fe-4S] target proteins; despite structural homology to tetrahydrofolate-dependent enzymes, IBA57 does not use folate as a cofactor, and its invariant surface-exposed cysteine is essential for function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IBA57 is a mitochondrial iron-sulfur cluster (ISC) assembly factor that acts at a late step of the pathway to specifically mature [4Fe-4S] proteins—including respiratory complexes I and II, aconitase, and lipoic acid synthase—while being dispensable for [2Fe-2S] protein maturation [#0, #5]. It functions together with ISCA1 and ISCA2 [#0], and forms a heterodimeric complex with ISCA2 that bridges a [2Fe-2S] cluster, with the conserved IBA57 family cysteine and three conserved ISCA2 cysteines serving as cluster ligands; cluster binding is required for complex formation, and the assembled [2Fe-2S]-ISCA2-IBA57 complex—generated via a GLRX5 → ISCA2 → IBA57 transfer pathway—can reactivate apo-aconitase in vitro [#1]. Structurally the complex adopts a dimer-of-dimers organization with ISCA2 providing the homodimerization core and the cluster bridging the ISCA2-IBA57 interface [#2]. Despite structural homology to tetrahydrofolate-dependent enzymes, IBA57 does not use folate as a cofactor: its THF-binding pocket is constricted, folate-deficient and THF-catalytic-residue mutants retain function, whereas mutation of the invariant surface-exposed cysteine impairs [4Fe-4S] assembly [#3]. Loss-of-function mutations in IBA57 cause multiple mitochondrial dysfunctions syndrome (MMDS3), acting through protein destabilization or disruption of interface contacts that reduce [4Fe-4S] enzyme activities and protein lipoylation [#4, #6, #8].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established the central question of where IBA57 acts—defining it as a late-acting, [4Fe-4S]-specific maturation factor rather than a general ISC component.\",\n      \"evidence\": \"RNAi depletion in HeLa cells with [4Fe-4S] and [2Fe-2S] enzyme activity readouts\",\n      \"pmids\": [\"22323289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the molecular partners or the biochemical mechanism of cluster transfer\", \"Did not resolve how specificity for [4Fe-4S] over [2Fe-2S] targets is achieved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated that a patient missense allele acts by triggering proteolytic loss of IBA57 below a critical threshold, linking protein abundance to ISC function in disease.\",\n      \"evidence\": \"Complementation in patient fibroblasts/HeLa, immunoblotting, protease inhibitor treatment, enzyme assays\",\n      \"pmids\": [\"23462291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the protease responsible for degradation\", \"Single-lab cell-model study\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Confirmed in independent human disease contexts that IBA57 loss selectively impairs [4Fe-4S] (complex I/II) maturation and lipoylation while sparing [2Fe-2S] proteins, and that R146W is a null-equivalent allele.\",\n      \"evidence\": \"Splice analysis and complementation in patient lymphoblasts and IBA57-depleted HeLa cells with enzyme/lipoylation readouts\",\n      \"pmids\": [\"25609768\", \"25971455\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not map why specific residues are required at the molecular level\", \"Patient-cell biochemistry without reconstitution\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Began addressing how IBA57 connects to other ISC factors by showing IBA57 deficiency lowers NFU1 and downstream SDH/LIAS.\",\n      \"evidence\": \"Immunoblotting and SDH activity staining in patient myoblasts/fibroblasts with rescue\",\n      \"pmids\": [\"28913435\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct mechanism for how IBA57 controls NFU1 levels\", \"Correlative immunoblot data in patient cells only, single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Resolved the core biochemical mechanism—reconstituting the [2Fe-2S]-bridged ISCA2-IBA57 heterodimer, identifying the cluster ligands, the GLRX5 → ISCA2 → IBA57 transfer route, and showing functional apo-aconitase reactivation.\",\n      \"evidence\": \"In vitro reconstitution, UV-vis spectroscopy, Fe/S quantification, cysteine mutagenesis, aconitase reactivation, Co-IP\",\n      \"pmids\": [\"30269484\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not provide an atomic-resolution structure of the complex\", \"Mechanism of cluster donation to specific [4Fe-4S] apo-targets not detailed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided a structural framework for the complex, defining a dimer-of-dimers architecture with the cluster at the ISCA2-IBA57 interface and rationalizing the R146W pathogenic mutation.\",\n      \"evidence\": \"SAXS, bioinformatics-driven docking, biochemical validation\",\n      \"pmids\": [\"31831856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Low-resolution model, not crystal/cryo-EM\", \"Interface contacts inferred from docking rather than directly resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Settled whether IBA57's THF-enzyme homology reflects a folate-dependent mechanism—showing it does not, and pinpointing the invariant surface cysteine as the functionally essential residue.\",\n      \"evidence\": \"Crystal structure of fungal Iba57, yeast folate/active-site mutant genetics, [4Fe-4S] enzyme assays\",\n      \"pmids\": [\"36075292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the catalytic role, if any, of the surface cysteine beyond cluster ligation\", \"Structure is of a fungal ortholog\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended the structure-function picture by showing a pathogenic variant (G104C) destabilizes IBA57 protein without blocking heterodimer assembly, separating folding/stability defects from complex-formation defects.\",\n      \"evidence\": \"SEC-MALS, NMR, CD, fluorescence spectroscopy, in vitro reconstitution\",\n      \"pmids\": [\"39408793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vivo functional validation of the variant\", \"Single-lab biophysical study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the [2Fe-2S]-ISCA2-IBA57 complex selectively converts to and donates a [4Fe-4S] cluster to specific apo-target proteins, and the atomic-resolution structure of the cluster-bound complex, remain unresolved.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of the cluster-bound human complex\", \"Mechanism of reductive [2Fe-2S]→[4Fe-4S] conversion and target selection undefined\", \"Direct mechanism linking IBA57 to NFU1 regulation unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [\"ISCA2-IBA57 heterodimer\"],\n    \"partners\": [\"ISCA2\", \"ISCA1\", \"GLRX5\", \"NFU1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}