{"gene":"IBA57","run_date":"2026-04-28T18:06:53","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, functioning late in the ISC assembly pathway in mitochondria.","method":"RNAi depletion in HeLa cells with measurement of [4Fe-4S] and [2Fe-2S] enzyme activities; mitochondrial morphology assessment","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — clean KD with defined biochemical phenotype, replicated across multiple [4Fe-4S] substrates, strong citation record indicating replication","pmids":["22323289"],"is_preprint":false},{"year":2018,"finding":"IBA57 forms a heterodimeric complex with ISCA2 bridged by a [2Fe-2S] cluster; the conserved cysteine of IBA57 and the three conserved cysteines of ISCA2 act as cluster ligands. The [2Fe-2S] ISCA2-IBA57 complex is formed via a transfer pathway involving GLRX5 → ISCA2 → IBA57, and the complex is capable of reactivating apo aconitase in vitro.","method":"In vitro reconstitution, NMR, UV-visible spectroscopy, mutagenesis of cysteine residues, aconitase activity assay","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in vitro with mutagenesis and functional assay (aconitase reactivation), multiple orthogonal biophysical methods","pmids":["30269484"],"is_preprint":false},{"year":2019,"finding":"The human mitochondrial [2Fe-2S] ISCA2-IBA57 complex adopts a dimer-of-dimers structural organization as determined by SAXS, with ISCA2 providing the homodimerization core and the [2Fe-2S] cluster shared between ISCA2 and IBA57 at the heterodimer interface. The pathogenic Arg146Trp IBA57 mutation disrupts this interface.","method":"Small-angle X-ray scattering (SAXS), bioinformatics-driven docking, structural modeling","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 method (structural), but low-resolution SAXS model without crystal/cryo-EM validation; single study","pmids":["31831856"],"is_preprint":false},{"year":2022,"finding":"Mitochondrial IBA57/Iba57, despite structural similarity to tetrahydrofolate (THF)-dependent enzymes (GcvT family), does not require folate for [4Fe-4S] protein assembly. The crystal structure of Iba57 from Chaetomium thermophilum shows a constricted THF-binding pocket; mutations in conserved residues essential for THF-dependent catalysis in GcvT do not impair Iba57 function, while mutation of the invariant surface-exposed cysteine does.","method":"Crystal structure determination, in vivo yeast genetic complementation, site-directed mutagenesis, biochemical assays in Saccharomyces cerevisiae folate mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with mutagenesis and in vivo genetic tests across multiple lines of evidence in a single study","pmids":["36075292"],"is_preprint":false},{"year":2013,"finding":"A pathogenic IBA57 mutation (p.Gln314Pro) leads to excessive proteolytic degradation of IBA57 protein, which can be ameliorated by protease inhibitors; the resulting IBA57 deficiency causes decreased activity of mitochondrial [4Fe-4S] proteins and reduced protein lipoylation (dependent on [4Fe-4S] lipoic acid synthase).","method":"Patient cell studies, HeLa RNAi depletion and complementation, protease inhibitor treatment, western blotting, enzyme activity assays","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 — complementation and protease inhibitor experiments in patient-derived and HeLa cells, single lab","pmids":["23462291"],"is_preprint":false},{"year":2017,"finding":"IBA57 deficiency in patient myoblasts and fibroblasts leads to decreased NFU1 protein expression, which in turn affects SDH (complex II) activity and lipoic acid synthase (LIAS) expression, placing IBA57 upstream of NFU1 in the mitochondrial ISC biogenesis pathway.","method":"Immunoblotting, enzyme activity staining, SDH activity in rescued myoblasts","journal":"Neurology. Genetics","confidence":"Medium","confidence_rationale":"Tier 2 — pathway epistasis via protein-level analysis in patient cells and rescued cells, single lab","pmids":["28913435"],"is_preprint":false},{"year":2024,"finding":"The pathogenic Gly104Cys variant of IBA57 does not impair formation of the IBA57-[2Fe-2S]-ISCA2 heterodimer but significantly reduces the stability of IBA57 both in isolation and in complex with ISCA2, explaining the severe MMDS3 phenotype associated with this mutation.","method":"Size exclusion chromatography, multi-angle light scattering (SEC-MALS), NMR, circular dichroism, fluorescence spectroscopy","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1 methods (biophysical characterization), but single study and single variant analyzed","pmids":["39408793"],"is_preprint":false}],"current_model":"IBA57 is a mitochondrial iron-sulfur cluster assembly factor that acts late in the ISC pathway to specifically mature [4Fe-4S] proteins (but not [2Fe-2S] proteins): it forms a [2Fe-2S]-bridged heterodimer with ISCA2 (receiving the cluster from GLRX5 via ISCA2), uses its conserved surface cysteine as a cluster ligand, does not require tetrahydrofolate for its function despite structural similarity to THF-binding enzymes, and is required upstream of NFU1 for the assembly of [4Fe-4S]-dependent enzymes including respiratory complexes I/II and lipoic acid synthase."},"narrative":{"teleology":[{"year":2012,"claim":"Establishing that IBA57 (with ISCA1/ISCA2) is specifically required for mitochondrial [4Fe-4S] but not [2Fe-2S] protein maturation resolved its position as a late-acting, substrate-specific factor in the ISC pathway.","evidence":"RNAi depletion in HeLa cells with measurement of multiple [4Fe-4S] and [2Fe-2S] enzyme activities","pmids":["22323289"],"confidence":"High","gaps":["Biochemical mechanism of IBA57 action (cluster transfer vs. scaffold) was not determined","Physical interactions among ISCA1, ISCA2, and IBA57 were not characterized","Relationship to downstream factors such as NFU1 was unknown"]},{"year":2013,"claim":"Demonstrating that the pathogenic Q314P mutation destabilizes IBA57 protein and that the resulting deficiency impairs [4Fe-4S] enzyme activities and protein lipoylation linked IBA57 loss to human disease (MMDS3) and confirmed lipoic acid synthase as a downstream target.","evidence":"Patient cell studies, HeLa RNAi complementation, protease inhibitor rescue, enzyme activity assays","pmids":["23462291"],"confidence":"Medium","gaps":["Only a single pathogenic variant was studied; generalizability of proteolytic degradation mechanism to other variants was unclear","Molecular basis of IBA57 instability caused by Q314P was not structurally resolved"]},{"year":2017,"claim":"Placing IBA57 upstream of NFU1 in the [4Fe-4S] assembly hierarchy established a linear epistatic order (IBA57→NFU1→target enzymes) for mitochondrial Fe-S cluster delivery.","evidence":"Immunoblotting and SDH activity measurements in IBA57-deficient patient myoblasts/fibroblasts with rescue","pmids":["28913435"],"confidence":"Medium","gaps":["Direct physical interaction between IBA57 and NFU1 was not demonstrated","Whether IBA57 transfers clusters directly to NFU1 or acts indirectly remained unknown"]},{"year":2018,"claim":"Reconstituting the [2Fe-2S]-bridged ISCA2-IBA57 heterodimer and mapping the GLRX5→ISCA2→IBA57 cluster transfer pathway defined the molecular mechanism by which IBA57 receives its iron-sulfur cluster and reactivates apo-[4Fe-4S] targets.","evidence":"In vitro reconstitution with NMR, UV-visible spectroscopy, cysteine mutagenesis, and aconitase reactivation assay","pmids":["30269484"],"confidence":"High","gaps":["Conversion of the [2Fe-2S] cluster to a [4Fe-4S] cluster on target proteins was not mechanistically resolved","Role of ISCA1 relative to the ISCA2-IBA57 complex remained unclear","High-resolution structure of the complex was not obtained"]},{"year":2019,"claim":"SAXS-based structural modeling revealed a dimer-of-dimers architecture for the ISCA2-IBA57 complex and showed that the pathogenic R146W mutation disrupts the heterodimer interface, linking structural organization to disease.","evidence":"Small-angle X-ray scattering with bioinformatics-driven docking and structural modeling","pmids":["31831856"],"confidence":"Medium","gaps":["Low-resolution SAXS envelope lacks atomic detail; no crystal or cryo-EM structure of the complex exists","Functional consequences of R146W on cluster transfer activity were not directly tested"]},{"year":2022,"claim":"Solving the crystal structure of Iba57 established that despite GcvT-family fold homology, the THF-binding pocket is constricted and folate is dispensable for function, while the invariant surface cysteine is essential—clarifying the catalytic residues versus the inherited structural scaffold.","evidence":"X-ray crystallography of Chaetomium thermophilum Iba57, site-directed mutagenesis, yeast genetic complementation including folate auxotrophs","pmids":["36075292"],"confidence":"High","gaps":["Structure of human IBA57 or its complex with ISCA2 at atomic resolution has not been determined","How the surface cysteine participates in [2Fe-2S] to [4Fe-4S] cluster conversion is not mechanistically resolved"]},{"year":2024,"claim":"Biophysical characterization of the G104C pathogenic variant showed that it destabilizes IBA57 without preventing ISCA2 complex formation, establishing protein stability as a disease-determining parameter distinct from cluster-binding competence.","evidence":"SEC-MALS, NMR, circular dichroism, and fluorescence spectroscopy on recombinant wild-type and G104C IBA57","pmids":["39408793"],"confidence":"Medium","gaps":["Single variant analyzed; unclear whether stability loss is a general mechanism across MMDS3 mutations","In vivo consequences of the G104C stability defect on [4Fe-4S] target maturation were not measured"]},{"year":null,"claim":"The mechanism by which the [2Fe-2S]-bridged ISCA2-IBA57 complex converts to or delivers a [4Fe-4S] cluster to target apoproteins, and whether ISCA1 participates in this step, remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No atomic-resolution structure of the human ISCA2-IBA57 complex exists","The [2Fe-2S] to [4Fe-4S] cluster conversion mechanism is not reconstituted","Direct physical handoff from IBA57 complex to NFU1 or target apoproteins has not been demonstrated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,3,4,5]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,5]}],"complexes":["ISCA2-IBA57 [2Fe-2S]-bridged heterodimer"],"partners":["ISCA2","ISCA1","GLRX5","NFU1"],"other_free_text":[]},"mechanistic_narrative":"IBA57 is a mitochondrial iron-sulfur cluster assembly factor that functions late in the ISC pathway to specifically mature [4Fe-4S] proteins—including aconitase, respiratory complexes I and II, and lipoic acid synthase—without affecting [2Fe-2S] protein biogenesis [PMID:22323289]. It forms a [2Fe-2S]-bridged heterodimeric complex with ISCA2, receiving the cluster via a GLRX5→ISCA2→IBA57 transfer pathway, with its conserved surface cysteine serving as a cluster ligand essential for function [PMID:30269484, PMID:36075292]. IBA57 acts upstream of NFU1 in the mitochondrial [4Fe-4S] assembly hierarchy, and despite structural homology to tetrahydrofolate-dependent GcvT enzymes, it does not require folate for its function [PMID:28913435, PMID:36075292]. Biallelic loss-of-function mutations in IBA57 cause multiple mitochondrial dysfunctions syndrome 3 (MMDS3), characterized by impaired [4Fe-4S] enzyme activities and reduced protein lipoylation [PMID:23462291, PMID:39408793]."},"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":171,"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":93,"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":"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":"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":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":8,"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":"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":4,"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":"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":"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":"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":"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":"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":10495,"output_tokens":1836,"usd":0.029513},"stage2":{"model":"claude-opus-4-6","input_tokens":5088,"output_tokens":2215,"usd":0.121222},"total_usd":0.150735,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","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, functioning late in the ISC assembly pathway in mitochondria.\",\n      \"method\": \"RNAi depletion in HeLa cells with measurement of [4Fe-4S] and [2Fe-2S] enzyme activities; mitochondrial morphology assessment\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined biochemical phenotype, replicated across multiple [4Fe-4S] substrates, strong citation record indicating replication\",\n      \"pmids\": [\"22323289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IBA57 forms a heterodimeric complex with ISCA2 bridged by a [2Fe-2S] cluster; the conserved cysteine of IBA57 and the three conserved cysteines of ISCA2 act as cluster ligands. The [2Fe-2S] ISCA2-IBA57 complex is formed via a transfer pathway involving GLRX5 → ISCA2 → IBA57, and the complex is capable of reactivating apo aconitase in vitro.\",\n      \"method\": \"In vitro reconstitution, NMR, UV-visible spectroscopy, mutagenesis of cysteine residues, aconitase activity assay\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in vitro with mutagenesis and functional assay (aconitase reactivation), multiple orthogonal biophysical methods\",\n      \"pmids\": [\"30269484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The human mitochondrial [2Fe-2S] ISCA2-IBA57 complex adopts a dimer-of-dimers structural organization as determined by SAXS, with ISCA2 providing the homodimerization core and the [2Fe-2S] cluster shared between ISCA2 and IBA57 at the heterodimer interface. The pathogenic Arg146Trp IBA57 mutation disrupts this interface.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS), bioinformatics-driven docking, structural modeling\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 method (structural), but low-resolution SAXS model without crystal/cryo-EM validation; single study\",\n      \"pmids\": [\"31831856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Mitochondrial IBA57/Iba57, despite structural similarity to tetrahydrofolate (THF)-dependent enzymes (GcvT family), does not require folate for [4Fe-4S] protein assembly. The crystal structure of Iba57 from Chaetomium thermophilum shows a constricted THF-binding pocket; mutations in conserved residues essential for THF-dependent catalysis in GcvT do not impair Iba57 function, while mutation of the invariant surface-exposed cysteine does.\",\n      \"method\": \"Crystal structure determination, in vivo yeast genetic complementation, site-directed mutagenesis, biochemical assays in Saccharomyces cerevisiae folate mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with mutagenesis and in vivo genetic tests across multiple lines of evidence in a single study\",\n      \"pmids\": [\"36075292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A pathogenic IBA57 mutation (p.Gln314Pro) leads to excessive proteolytic degradation of IBA57 protein, which can be ameliorated by protease inhibitors; the resulting IBA57 deficiency causes decreased activity of mitochondrial [4Fe-4S] proteins and reduced protein lipoylation (dependent on [4Fe-4S] lipoic acid synthase).\",\n      \"method\": \"Patient cell studies, HeLa RNAi depletion and complementation, protease inhibitor treatment, western blotting, enzyme activity assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — complementation and protease inhibitor experiments in patient-derived and HeLa cells, single lab\",\n      \"pmids\": [\"23462291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IBA57 deficiency in patient myoblasts and fibroblasts leads to decreased NFU1 protein expression, which in turn affects SDH (complex II) activity and lipoic acid synthase (LIAS) expression, placing IBA57 upstream of NFU1 in the mitochondrial ISC biogenesis pathway.\",\n      \"method\": \"Immunoblotting, enzyme activity staining, SDH activity in rescued myoblasts\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway epistasis via protein-level analysis in patient cells and rescued cells, single lab\",\n      \"pmids\": [\"28913435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The pathogenic Gly104Cys variant of IBA57 does not impair formation of the IBA57-[2Fe-2S]-ISCA2 heterodimer but significantly reduces the stability of IBA57 both in isolation and in complex with ISCA2, explaining the severe MMDS3 phenotype associated with this mutation.\",\n      \"method\": \"Size exclusion chromatography, multi-angle light scattering (SEC-MALS), NMR, circular dichroism, fluorescence spectroscopy\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 methods (biophysical characterization), but single study and single variant analyzed\",\n      \"pmids\": [\"39408793\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IBA57 is a mitochondrial iron-sulfur cluster assembly factor that acts late in the ISC pathway to specifically mature [4Fe-4S] proteins (but not [2Fe-2S] proteins): it forms a [2Fe-2S]-bridged heterodimer with ISCA2 (receiving the cluster from GLRX5 via ISCA2), uses its conserved surface cysteine as a cluster ligand, does not require tetrahydrofolate for its function despite structural similarity to THF-binding enzymes, and is required upstream of NFU1 for the assembly of [4Fe-4S]-dependent enzymes including respiratory complexes I/II and lipoic acid synthase.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"IBA57 is a mitochondrial iron-sulfur cluster assembly factor that functions late in the ISC pathway to specifically mature [4Fe-4S] proteins—including aconitase, respiratory complexes I and II, and lipoic acid synthase—without affecting [2Fe-2S] protein biogenesis [PMID:22323289]. It forms a [2Fe-2S]-bridged heterodimeric complex with ISCA2, receiving the cluster via a GLRX5→ISCA2→IBA57 transfer pathway, with its conserved surface cysteine serving as a cluster ligand essential for function [PMID:30269484, PMID:36075292]. IBA57 acts upstream of NFU1 in the mitochondrial [4Fe-4S] assembly hierarchy, and despite structural homology to tetrahydrofolate-dependent GcvT enzymes, it does not require folate for its function [PMID:28913435, PMID:36075292]. Biallelic loss-of-function mutations in IBA57 cause multiple mitochondrial dysfunctions syndrome 3 (MMDS3), characterized by impaired [4Fe-4S] enzyme activities and reduced protein lipoylation [PMID:23462291, PMID:39408793].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing that IBA57 (with ISCA1/ISCA2) is specifically required for mitochondrial [4Fe-4S] but not [2Fe-2S] protein maturation resolved its position as a late-acting, substrate-specific factor in the ISC pathway.\",\n      \"evidence\": \"RNAi depletion in HeLa cells with measurement of multiple [4Fe-4S] and [2Fe-2S] enzyme activities\",\n      \"pmids\": [\"22323289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Biochemical mechanism of IBA57 action (cluster transfer vs. scaffold) was not determined\",\n        \"Physical interactions among ISCA1, ISCA2, and IBA57 were not characterized\",\n        \"Relationship to downstream factors such as NFU1 was unknown\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrating that the pathogenic Q314P mutation destabilizes IBA57 protein and that the resulting deficiency impairs [4Fe-4S] enzyme activities and protein lipoylation linked IBA57 loss to human disease (MMDS3) and confirmed lipoic acid synthase as a downstream target.\",\n      \"evidence\": \"Patient cell studies, HeLa RNAi complementation, protease inhibitor rescue, enzyme activity assays\",\n      \"pmids\": [\"23462291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Only a single pathogenic variant was studied; generalizability of proteolytic degradation mechanism to other variants was unclear\",\n        \"Molecular basis of IBA57 instability caused by Q314P was not structurally resolved\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Placing IBA57 upstream of NFU1 in the [4Fe-4S] assembly hierarchy established a linear epistatic order (IBA57→NFU1→target enzymes) for mitochondrial Fe-S cluster delivery.\",\n      \"evidence\": \"Immunoblotting and SDH activity measurements in IBA57-deficient patient myoblasts/fibroblasts with rescue\",\n      \"pmids\": [\"28913435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct physical interaction between IBA57 and NFU1 was not demonstrated\",\n        \"Whether IBA57 transfers clusters directly to NFU1 or acts indirectly remained unknown\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Reconstituting the [2Fe-2S]-bridged ISCA2-IBA57 heterodimer and mapping the GLRX5→ISCA2→IBA57 cluster transfer pathway defined the molecular mechanism by which IBA57 receives its iron-sulfur cluster and reactivates apo-[4Fe-4S] targets.\",\n      \"evidence\": \"In vitro reconstitution with NMR, UV-visible spectroscopy, cysteine mutagenesis, and aconitase reactivation assay\",\n      \"pmids\": [\"30269484\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Conversion of the [2Fe-2S] cluster to a [4Fe-4S] cluster on target proteins was not mechanistically resolved\",\n        \"Role of ISCA1 relative to the ISCA2-IBA57 complex remained unclear\",\n        \"High-resolution structure of the complex was not obtained\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"SAXS-based structural modeling revealed a dimer-of-dimers architecture for the ISCA2-IBA57 complex and showed that the pathogenic R146W mutation disrupts the heterodimer interface, linking structural organization to disease.\",\n      \"evidence\": \"Small-angle X-ray scattering with bioinformatics-driven docking and structural modeling\",\n      \"pmids\": [\"31831856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Low-resolution SAXS envelope lacks atomic detail; no crystal or cryo-EM structure of the complex exists\",\n        \"Functional consequences of R146W on cluster transfer activity were not directly tested\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Solving the crystal structure of Iba57 established that despite GcvT-family fold homology, the THF-binding pocket is constricted and folate is dispensable for function, while the invariant surface cysteine is essential—clarifying the catalytic residues versus the inherited structural scaffold.\",\n      \"evidence\": \"X-ray crystallography of Chaetomium thermophilum Iba57, site-directed mutagenesis, yeast genetic complementation including folate auxotrophs\",\n      \"pmids\": [\"36075292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure of human IBA57 or its complex with ISCA2 at atomic resolution has not been determined\",\n        \"How the surface cysteine participates in [2Fe-2S] to [4Fe-4S] cluster conversion is not mechanistically resolved\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Biophysical characterization of the G104C pathogenic variant showed that it destabilizes IBA57 without preventing ISCA2 complex formation, establishing protein stability as a disease-determining parameter distinct from cluster-binding competence.\",\n      \"evidence\": \"SEC-MALS, NMR, circular dichroism, and fluorescence spectroscopy on recombinant wild-type and G104C IBA57\",\n      \"pmids\": [\"39408793\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single variant analyzed; unclear whether stability loss is a general mechanism across MMDS3 mutations\",\n        \"In vivo consequences of the G104C stability defect on [4Fe-4S] target maturation were not measured\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The mechanism by which the [2Fe-2S]-bridged ISCA2-IBA57 complex converts to or delivers a [4Fe-4S] cluster to target apoproteins, and whether ISCA1 participates in this step, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No atomic-resolution structure of the human ISCA2-IBA57 complex exists\",\n        \"The [2Fe-2S] to [4Fe-4S] cluster conversion mechanism is not reconstituted\",\n        \"Direct physical handoff from IBA57 complex to NFU1 or target apoproteins has not been demonstrated\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\n        \"term_id\": \"GO:0140104\",\n        \"supporting_discovery_ids\": [0, 1]\n      }\n    ],\n    \"localization\": [\n      {\n        \"term_id\": \"GO:0005739\",\n        \"supporting_discovery_ids\": [0, 1, 3, 4, 5]\n      }\n    ],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-1430728\",\n        \"supporting_discovery_ids\": [0, 1, 5]\n      }\n    ],\n    \"complexes\": [\n      \"ISCA2-IBA57 [2Fe-2S]-bridged heterodimer\"\n    ],\n    \"partners\": [\n      \"ISCA2\",\n      \"ISCA1\",\n      \"GLRX5\",\n      \"NFU1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}