{"gene":"ISCA2","run_date":"2026-04-28T18:06:54","timeline":{"discoveries":[{"year":2012,"finding":"Human ISCA2 (along with ISCA1 and IBA57) is specifically required for maturation of mitochondrial [4Fe-4S] proteins (aconitase, respiratory complex I, lipoic acid synthase), but not [2Fe-2S] proteins (ferrochelatase), functioning late in the ISC assembly pathway. Depletion by RNAi caused massively swollen, cristae-devoid mitochondria and loss of [4Fe-4S] enzyme activities.","method":"RNA interference knockdown in HeLa cells, enzyme activity assays, mitochondrial morphology analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — clean KD with defined cellular phenotype, replicated across multiple [4Fe-4S] substrates, consistent with yeast and human studies","pmids":["22323289"],"is_preprint":false},{"year":2000,"finding":"Yeast Isa2p (ISCA2 ortholog) localizes to the mitochondrial intermembrane space via a bipartite N-terminal leader sequence (mitochondrial import signal + IMS-targeting sequence), both signals required for function. Three invariant cysteine residues in Isa2p are essential for function and likely involved in iron binding.","method":"Deletion mutagenesis, subcellular fractionation, genetic complementation, growth assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (fractionation, mutagenesis, genetic rescue), foundational paper with 148 citations","pmids":["10805735"],"is_preprint":false},{"year":2011,"finding":"Yeast Isa1 and Isa2 (ISCA2 ortholog) form a complex that binds iron in vivo; this iron is required for de novo synthesis of [4Fe-4S] clusters in mitochondria but is not donated to [2Fe-2S] scaffold proteins Isu1-Isu2. The Isa1-Isa2 complex is specifically dedicated to maturation of mitochondrial [4Fe-4S] proteins (aconitase, homoaconitase), not [2Fe-2S] proteins or cytosolic [4Fe-4S] proteins.","method":"In vivo iron-binding assays, genetic epistasis, targeted ferredoxin expression, comprehensive deletion analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal in vivo methods, 135 citations, defines mechanistic role of the complex","pmids":["21987576"],"is_preprint":false},{"year":2018,"finding":"Human IBA57 recruits ISCA2 to form a heterodimeric complex bridged by a [2Fe-2S] cluster. The conserved cysteine of IBA57 and the three conserved cysteines of ISCA2 act as cluster ligands. [2Fe-2S] cluster binding is absolutely required for complex formation. The [2Fe-2S] ISCA2-IBA57 complex can reactivate apo aconitase in vitro and is resistant to highly oxidative environments.","method":"In vitro reconstitution, spectroscopic characterization, mutagenesis of cluster-coordinating cysteines, aconitase reactivation assay","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis and functional validation","pmids":["30269484"],"is_preprint":false},{"year":2020,"finding":"Mitochondrial [4Fe-4S] cluster assembly on ISCA1-ISCA2 proceeds via reductive fusion of two [2Fe-2S] clusters donated by GLRX5, requiring electrons from ferredoxin FDX2 (not FDX1) coupled to FDXR (NADPH-dependent). IBA57 is required for this FDX2-dependent reductive fusion. This reconstituted the complete in vitro maturation of aconitase without artificial reductants.","method":"In vitro reconstitution of [4Fe-4S] aconitase maturation without artificial reductants, spectroscopic assays, substitution of individual ISC components","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — complete in vitro reconstitution with defined components, mechanistic dissection with multiple controls","pmids":["32817474"],"is_preprint":false},{"year":2019,"finding":"The [2Fe-2S] ISCA2-IBA57 complex adopts a dimer-of-dimers architecture in solution, with ISCA2 providing the homodimerization core and the [2Fe-2S] cluster shared between ISCA2 and IBA57 at the dimer interface. The pathogenic IBA57 Arg146Trp mutation disrupts this specific interaction interface.","method":"Small-angle X-ray scattering (SAXS), bioinformatics-driven docking, structural modeling","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 method (SAXS structural determination) but low-resolution model without crystallographic validation","pmids":["31831856"],"is_preprint":false},{"year":2021,"finding":"ISCA1 acts as the central orchestrator of [4Fe-4S] cluster maturation: it interacts with both ISCA2 and NFU1, whereas ISCA2 and NFU1 do not interact directly. ISCA1 promotes formation of a transient ISCA1-ISCA2-NFU1 ternary complex and drives [4Fe-4S] cluster transfer from the ISCA1-ISCA2 assembly site to NFU1 via ISCA1's interaction with NFU1's C-terminal cluster-binding domain.","method":"NMR-based interaction mapping, protein-protein interaction studies, cluster transfer assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — NMR structural/interaction study with defined molecular mechanism of cluster handoff","pmids":["33711344"],"is_preprint":false},{"year":2021,"finding":"Human ISCA2 (as [2Fe-2S]-bound form) can donate clusters to reconstitute human lipoyl synthase (LIAS), enabling complete LIAS product turnover. ISCU (also [2Fe-2S]-bound) is also a donor; auxiliary cluster addition to LIAS precedes the reducing [4Fe-4S] center.","method":"In vitro cluster reconstitution, LC-MS activity assay, EPR spectroscopy of LIAS variants","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1 in vitro assay, single lab study","pmids":["33562493"],"is_preprint":false},{"year":2010,"finding":"Fission yeast Isa2 (ISCA2 ortholog) interacts in vivo with Grx5 (monothiol glutaredoxin) in mitochondria, as demonstrated by bimolecular fluorescence complementation. Overexpression of isa2+ suppresses growth defects of Δgrx5 mutant and partially restores Fe-S enzyme activities.","method":"Bimolecular fluorescence complementation (BiFC), genetic suppressor analysis, enzyme activity assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct in vivo interaction imaging plus genetic epistasis, single lab","pmids":["20085751"],"is_preprint":false},{"year":2014,"finding":"A missense founder mutation in ISCA2 causes mitochondrial depletion and reduced complex I activity, and decreases expression of ISCA2, ISCA1, and IBA57 in patient fibroblasts, establishing ISCA2 deficiency as cause of hereditary mitochondrial neurodegenerative white matter disease.","method":"Exome sequencing, immunohistochemistry, quantitative PCR, complex I dipstick assay, patient fibroblast analysis","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 — patient-derived cells with biochemical validation of pathway disruption","pmids":["25539947"],"is_preprint":false},{"year":2018,"finding":"Loss of ISCA2 in patient cells and siRNA knockdown models specifically impairs [4Fe-4S] protein function (but not [2Fe-2S] proteins), diminishes mitochondrial membrane potential, respiratory complex II and IV activities, and causes mtDNA depletion.","method":"Patient fibroblast analysis, siRNA knockdown, enzyme activity assays, mitochondrial membrane potential measurement, respiratory flux assays","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods, patient cells plus knockdown model","pmids":["29297947"],"is_preprint":false},{"year":2023,"finding":"Human ISCA2 protein directly binds copper with high affinity, and excess copper binding to ISCA2 (as well as ISCA1 and ISCU) inhibits iron-sulfur cluster assembly, explaining copper cytotoxicity in the context of Wilson's disease.","method":"In vitro copper-binding assays, cellular Fe-S enzyme activity measurement, mouse model of Wilson's disease, lymphocyte cell lines","journal":"Free radical biology & medicine","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro binding combined with cellular and in vivo models, single lab","pmids":["37225108"],"is_preprint":false},{"year":2022,"finding":"ISCA2 knockdown in K562 erythroid cells disrupts [4Fe-4S] cluster formation, leading to ROS accumulation that inactivates cytoplasmic aconitase/IRP1, which then represses ALAS2 translation via iron-responsive element binding, thereby blocking heme synthesis and erythroid differentiation.","method":"siRNA knockdown in K562 cells, ROS measurement, IRP1 activity assay, ALAS2 expression analysis, heme synthesis assays","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 2 — mechanistic pathway placement with multiple readouts, single lab","pmids":["35714932"],"is_preprint":false},{"year":2022,"finding":"Pharmacological inhibition or siRNA knockdown of ISCA2 in clear cell renal carcinoma decreases HIF-2α protein levels by blocking iron-responsive element (IRE)-dependent translation, and at higher concentrations decreases HIF-1α translation; ISCA2 inhibition also triggers an iron starvation response leading to ferroptosis.","method":"High-throughput chemical screen, siRNA knockdown, protein level analysis, xenograft tumor model, lipid peroxidation assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological and genetic inhibition with mechanistic readout, in vivo validation","pmids":["36097192"],"is_preprint":false},{"year":2007,"finding":"Yeast Isa2 (ISCA2 ortholog) is required for the in vivo function of biotin synthase (Bio2) but not for de novo Fe/S cluster synthesis on Bio2 (which depends on Isu1/Isu2). Loss of Isa2 reduces Bio2 protein levels, but overexpression of BIO2 does not rescue the biotin synthesis defect, indicating Isa2 acts on Bio2 catalytic activity rather than cluster assembly.","method":"Genetic screen, growth assays, enzyme activity assays, overexpression epistasis","journal":"Eukaryotic cell","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with multiple experimental tests distinguishing assembly from function","pmids":["17259550"],"is_preprint":false}],"current_model":"ISCA2 is a mitochondrial [4Fe-4S] cluster assembly factor that, together with ISCA1 and IBA57, forms a late-acting ISC subsystem: GLRX5 donates [2Fe-2S] clusters to the ISCA1-ISCA2 heterodimer, where FDX2/FDXR-driven electron transfer catalyzes reductive fusion to form [4Fe-4S] clusters that are then transferred—via a transient ISCA1-ISCA2-NFU1 ternary complex orchestrated by ISCA1—into [4Fe-4S] apoproteins such as aconitase and lipoyl synthase, while IBA57 participates by bridging a [2Fe-2S] cluster with ISCA2 in a heterodimeric intermediate required for this process."},"narrative":{"teleology":[{"year":2000,"claim":"Establishing the subcellular location and essential residues of the ISCA2 ortholog: yeast Isa2p was shown to localize to mitochondria via a bipartite leader sequence, with three invariant cysteines required for function, providing the first molecular handle on this protein family.","evidence":"Deletion mutagenesis, subcellular fractionation, and genetic complementation in S. cerevisiae","pmids":["10805735"],"confidence":"High","gaps":["Precise sub-mitochondrial localization of the human ortholog was not resolved","Iron-binding capacity not yet demonstrated","Molecular partners unknown"]},{"year":2007,"claim":"Yeast Isa2 was shown to be required for the catalytic function of the [4Fe-4S] enzyme biotin synthase (Bio2), acting downstream of initial cluster assembly, hinting that the Isa proteins serve a late cluster-maturation or delivery role rather than de novo scaffold function.","evidence":"Genetic epistasis, enzyme activity assays, and overexpression studies in S. cerevisiae","pmids":["17259550"],"confidence":"Medium","gaps":["Whether Isa2 directly contacts Bio2 was not tested","Mechanism of action on Bio2 catalysis versus stability unresolved"]},{"year":2010,"claim":"The physical interaction between the ISCA2 ortholog and the [2Fe-2S] donor GLRX5 was demonstrated in vivo, connecting the late ISC assembly system to the upstream cluster scaffold pathway.","evidence":"Bimolecular fluorescence complementation and genetic suppression in fission yeast","pmids":["20085751"],"confidence":"Medium","gaps":["Direction of cluster transfer not established","Interaction stoichiometry unknown","Human ortholog interaction not validated"]},{"year":2011,"claim":"The yeast Isa1–Isa2 complex was shown to bind iron in vivo and to function specifically in de novo mitochondrial [4Fe-4S] cluster synthesis, not [2Fe-2S] protein maturation or cytosolic Fe-S assembly, establishing the dedicated role of this complex.","evidence":"In vivo iron-binding assays, comprehensive deletion analysis, and enzyme activity measurements in S. cerevisiae","pmids":["21987576"],"confidence":"High","gaps":["Whether iron binding is direct or cluster-mediated was unclear","Biochemical reconstitution of the assembly reaction not yet achieved"]},{"year":2012,"claim":"Human ISCA2 (with ISCA1 and IBA57) was confirmed as specifically required for mitochondrial [4Fe-4S] protein maturation in mammalian cells, with depletion causing dramatic mitochondrial morphological collapse, translating the yeast findings to human biology.","evidence":"RNAi knockdown in HeLa cells with enzyme activity assays and electron microscopy","pmids":["22323289"],"confidence":"High","gaps":["Individual contributions of ISCA1, ISCA2, and IBA57 were not separated","Mechanism of mitochondrial morphology disruption unknown"]},{"year":2014,"claim":"A causative link between ISCA2 deficiency and human disease was established: a founder missense mutation caused mitochondrial neurodegenerative white matter disease with reduced complex I activity and decreased expression of the entire late ISC machinery (ISCA1, ISCA2, IBA57).","evidence":"Exome sequencing, patient fibroblast biochemistry, and immunohistochemistry","pmids":["25539947"],"confidence":"Medium","gaps":["Rescue experiment not performed","Whether ISCA2 mutation destabilizes the entire late ISC complex or triggers secondary transcriptional effects unknown"]},{"year":2018,"claim":"The molecular basis of ISCA2–IBA57 interaction was revealed: the two proteins form a heterodimer bridged by a [2Fe-2S] cluster coordinated by ISCA2's three conserved cysteines and IBA57's conserved cysteine, and this complex can reactivate apo-aconitase, defining a cluster-bridged intermediate in the assembly pathway.","evidence":"In vitro reconstitution with spectroscopic characterization and cysteine mutagenesis","pmids":["30269484"],"confidence":"High","gaps":["Relationship of this [2Fe-2S] intermediate to the final [4Fe-4S] product not resolved","Whether this complex forms in vivo not confirmed"]},{"year":2018,"claim":"Further patient and knockdown studies confirmed ISCA2 loss specifically impairs [4Fe-4S] but not [2Fe-2S] proteins, and additionally causes mtDNA depletion and reduced mitochondrial membrane potential, broadening the phenotypic consequences.","evidence":"Patient fibroblast analysis, siRNA knockdown, respiratory complex activity assays","pmids":["29297947"],"confidence":"Medium","gaps":["Mechanism linking [4Fe-4S] cluster deficiency to mtDNA depletion not established"]},{"year":2019,"claim":"Low-resolution structural characterization revealed that the ISCA2–IBA57 complex adopts a dimer-of-dimers quaternary structure with ISCA2 providing the homodimerization core, and the pathogenic IBA57 R146W mutation was mapped to this interface.","evidence":"SAXS and computational docking","pmids":["31831856"],"confidence":"Medium","gaps":["No high-resolution crystal or cryo-EM structure available","Dimer-of-dimers stoichiometry not validated by independent method"]},{"year":2020,"claim":"The complete [4Fe-4S] cluster assembly mechanism was reconstituted in vitro: GLRX5 donates two [2Fe-2S] clusters to the ISCA1–ISCA2 complex, and FDX2 (not FDX1) coupled to FDXR provides electrons for reductive fusion to form [4Fe-4S], with IBA57 required; this was the first artificial-reductant-free reconstitution of mitochondrial [4Fe-4S] maturation.","evidence":"Complete in vitro reconstitution with defined human ISC components and spectroscopic monitoring","pmids":["32817474"],"confidence":"High","gaps":["Kinetic parameters and rate-limiting steps not determined","Structural mechanism of reductive fusion not resolved"]},{"year":2021,"claim":"The cluster handoff mechanism was elucidated: ISCA1 acts as the central orchestrator, interacting with both ISCA2 and NFU1 to form a transient ternary complex through which [4Fe-4S] clusters are transferred to downstream acceptors; ISCA2 and NFU1 do not interact directly.","evidence":"NMR-based interaction mapping and cluster transfer assays with purified human proteins","pmids":["33711344"],"confidence":"High","gaps":["Whether ISCA1 also transfers clusters to targets other than NFU1 not addressed","Ternary complex structure not determined"]},{"year":2022,"claim":"Downstream consequences of ISCA2 deficiency were connected to iron homeostasis: ISCA2 knockdown impairs cytoplasmic aconitase/IRP1, which then represses ALAS2 translation and heme synthesis in erythroid cells, and separately decreases HIF-2α translation via IRE-dependent mechanisms in renal carcinoma, with ISCA2 inhibition also triggering ferroptosis.","evidence":"siRNA knockdown in K562 and renal carcinoma cells, IRP1 activity assays, HIF-2α protein measurements, xenograft models","pmids":["35714932","36097192"],"confidence":"Medium","gaps":["Whether ferroptosis is a direct consequence of [4Fe-4S] loss or secondary iron dysregulation is unclear","In vivo relevance in normal erythropoiesis not validated"]},{"year":2023,"claim":"ISCA2 was identified as a direct target of copper toxicity: high-affinity copper binding to ISCA2 inhibits iron-sulfur cluster assembly, providing a molecular explanation for Fe-S deficits in copper overload conditions such as Wilson's disease.","evidence":"In vitro copper-binding assays, cellular Fe-S activity measurements, and Wilson's disease mouse model","pmids":["37225108"],"confidence":"Medium","gaps":["Structural basis of copper versus iron discrimination unknown","Whether copper binding is reversible in vivo not tested","Relative contribution of ISCA2 versus ISCA1/ISCU copper inhibition not separated"]},{"year":null,"claim":"Key unresolved questions include the high-resolution structure of the ISCA1–ISCA2 heterodimer and its [4Fe-4S]-bound state, the structural mechanism of reductive [2Fe-2S]-to-[4Fe-4S] cluster fusion, the full range of [4Fe-4S] client proteins receiving clusters through this pathway, and the mechanism by which ISCA2 deficiency leads to mtDNA depletion and mitochondrial morphological collapse.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution structure of ISCA1–ISCA2 complex","Reductive fusion mechanism structurally unresolved","Complete client protein inventory unknown","mtDNA depletion mechanism not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[3,4,6,7]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,2,8]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,4,7]}],"complexes":["ISCA1-ISCA2 heterodimer","ISCA2-IBA57 [2Fe-2S]-bridged complex","ISCA1-ISCA2-NFU1 transient ternary complex"],"partners":["ISCA1","IBA57","NFU1","GLRX5","FDX2","FDXR"],"other_free_text":[]},"mechanistic_narrative":"ISCA2 is a mitochondrial iron-sulfur cluster assembly factor that functions late in the ISC pathway, specifically dedicated to the maturation of [4Fe-4S] proteins including aconitase, respiratory complexes, lipoyl synthase, and biotin synthase, while dispensable for [2Fe-2S] protein biogenesis [PMID:22323289, PMID:21987576]. ISCA2 forms a heterodimer with ISCA1 that receives [2Fe-2S] clusters from GLRX5 and catalyzes their reductive fusion into [4Fe-4S] clusters via FDX2/FDXR-dependent electron transfer, with IBA57 required for this process; ISCA2 also forms a [2Fe-2S]-bridged complex with IBA57 through its three conserved cysteine residues [PMID:32817474, PMID:30269484]. ISCA1 orchestrates transfer of the assembled [4Fe-4S] cluster from the ISCA1–ISCA2 complex to downstream acceptors such as NFU1 through a transient ternary complex [PMID:33711344]. Biallelic loss-of-function mutations in ISCA2 cause a mitochondrial neurodegenerative white matter disease characterized by mitochondrial depletion, loss of respiratory chain activities, and impaired [4Fe-4S] enzyme function [PMID:25539947, PMID:29297947]."},"prefetch_data":{"uniprot":{"accession":"Q86U28","full_name":"Iron-sulfur cluster assembly 2 homolog, mitochondrial","aliases":["HESB-like domain-containing protein 1"],"length_aa":154,"mass_kda":16.5,"function":"Involved in the maturation of mitochondrial 4Fe-4S proteins functioning late in the iron-sulfur cluster assembly pathway. May be involved in the binding of an intermediate of Fe/S cluster assembly","subcellular_location":"Mitochondrion","url":"https://www.uniprot.org/uniprotkb/Q86U28/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/ISCA2","classification":"Common Essential","n_dependent_lines":921,"n_total_lines":1208,"dependency_fraction":0.7624172185430463},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ISCA2","total_profiled":1310},"omim":[{"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"},{"mim_id":"611006","title":"IRON-SULFUR CLUSTER ASSEMBLY 1; ISCA1","url":"https://www.omim.org/entry/611006"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ISCA2"},"hgnc":{"alias_symbol":["ISA2"],"prev_symbol":["HBLD1"]},"alphafold":{"accession":"Q86U28","domains":[{"cath_id":"2.60.300.12","chopping":"52-153","consensus_level":"high","plddt":90.576,"start":52,"end":153}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86U28","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q86U28-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q86U28-F1-predicted_aligned_error_v6.png","plddt_mean":77.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ISCA2","jax_strain_url":"https://www.jax.org/strain/search?query=ISCA2"},"sequence":{"accession":"Q86U28","fasta_url":"https://rest.uniprot.org/uniprotkb/Q86U28.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q86U28/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q86U28"}},"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":"10805735","id":"PMC_10805735","title":"Role of Saccharomyces cerevisiae ISA1 and ISA2 in iron homeostasis.","date":"2000","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10805735","citation_count":148,"is_preprint":false},{"pmid":"21987576","id":"PMC_21987576","title":"Specialized function of yeast Isa1 and Isa2 proteins in the maturation of mitochondrial [4Fe-4S] proteins.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21987576","citation_count":135,"is_preprint":false},{"pmid":"25539947","id":"PMC_25539947","title":"ISCA2 mutation causes infantile neurodegenerative mitochondrial disorder.","date":"2014","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25539947","citation_count":80,"is_preprint":false},{"pmid":"32817474","id":"PMC_32817474","title":"Mitochondrial [4Fe-4S] protein assembly involves reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 by electron flow from ferredoxin FDX2.","date":"2020","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/32817474","citation_count":69,"is_preprint":false},{"pmid":"20085751","id":"PMC_20085751","title":"Monothiol glutaredoxin Grx5 interacts with Fe-S scaffold proteins Isa1 and Isa2 and supports Fe-S assembly and DNA integrity in mitochondria of fission yeast.","date":"2010","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/20085751","citation_count":53,"is_preprint":false},{"pmid":"36097192","id":"PMC_36097192","title":"ISCA2 inhibition decreases HIF and induces ferroptosis in clear cell renal carcinoma.","date":"2022","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/36097192","citation_count":48,"is_preprint":false},{"pmid":"17259550","id":"PMC_17259550","title":"The ISC [corrected] proteins Isa1 and Isa2 are required for the function but not for the de novo synthesis of the Fe/S clusters of biotin synthase in Saccharomyces cerevisiae.","date":"2007","source":"Eukaryotic cell","url":"https://pubmed.ncbi.nlm.nih.gov/17259550","citation_count":47,"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":"21790804","id":"PMC_21790804","title":"Stage-specific requirement for Isa1 and Isa2 proteins in the mitochondrion of Trypanosoma brucei and heterologous rescue by human and Blastocystis orthologues.","date":"2011","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/21790804","citation_count":33,"is_preprint":false},{"pmid":"37225108","id":"PMC_37225108","title":"Copper exerts cytotoxicity through inhibition of iron-sulfur cluster biogenesis on ISCA1/ISCA2/ISCU assembly proteins.","date":"2023","source":"Free radical biology & medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37225108","citation_count":31,"is_preprint":false},{"pmid":"12966069","id":"PMC_12966069","title":"A HEAT-repeats containing protein, IaiH, stabilizes the iron-sulfur cluster bound to the cyanobacterial IscA homologue, IscA2.","date":"2003","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12966069","citation_count":24,"is_preprint":false},{"pmid":"29297947","id":"PMC_29297947","title":"Loss-of-function mutations in ISCA2 disrupt 4Fe-4S cluster machinery and cause a fatal leukodystrophy with hyperglycinemia and mtDNA depletion.","date":"2018","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/29297947","citation_count":23,"is_preprint":false},{"pmid":"29122497","id":"PMC_29122497","title":"Further delineation of the phenotypic spectrum of ISCA2 defect: A report of ten new cases.","date":"2017","source":"European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society","url":"https://pubmed.ncbi.nlm.nih.gov/29122497","citation_count":23,"is_preprint":false},{"pmid":"33562493","id":"PMC_33562493","title":"Characterization and Reconstitution of Human Lipoyl Synthase (LIAS) Supports ISCA2 and ISCU as Primary Cluster Donors and an Ordered Mechanism of Cluster Assembly.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33562493","citation_count":22,"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":"24642810","id":"PMC_24642810","title":"Replacement of the endogenous starch debranching enzymes ISA1 and ISA2 of Arabidopsis with the rice orthologs reveals a degree of functional conservation during starch synthesis.","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24642810","citation_count":21,"is_preprint":false},{"pmid":"23952574","id":"PMC_23952574","title":"Function of isoamylase-type starch debranching enzymes ISA1 and ISA2 in the Zea mays leaf.","date":"2013","source":"The New phytologist","url":"https://pubmed.ncbi.nlm.nih.gov/23952574","citation_count":20,"is_preprint":false},{"pmid":"29359243","id":"PMC_29359243","title":"Neonatal mitochondrial leukoencephalopathy with brain and spinal involvement and high lactate: expanding the phenotype of ISCA2 gene mutations.","date":"2018","source":"Metabolic brain disease","url":"https://pubmed.ncbi.nlm.nih.gov/29359243","citation_count":20,"is_preprint":false},{"pmid":"28708852","id":"PMC_28708852","title":"Simultaneous silencing of isoamylases ISA1, ISA2 and ISA3 by multi-target RNAi in potato tubers leads to decreased starch content and an early sprouting phenotype.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/28708852","citation_count":19,"is_preprint":false},{"pmid":"31106229","id":"PMC_31106229","title":"Multiple Mitochondrial Dysfunctions Syndrome 4 Due to ISCA2 Gene Defects: A Review.","date":"2019","source":"Child neurology open","url":"https://pubmed.ncbi.nlm.nih.gov/31106229","citation_count":15,"is_preprint":false},{"pmid":"33711344","id":"PMC_33711344","title":"ISCA1 Orchestrates ISCA2 and NFU1 in the Maturation of Human Mitochondrial [4Fe-4S] Proteins.","date":"2021","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/33711344","citation_count":11,"is_preprint":false},{"pmid":"31279336","id":"PMC_31279336","title":"A novel ISCA2 variant responsible for an early-onset neurodegenerative mitochondrial disorder: a case report of multiple mitochondrial dysfunctions syndrome 4.","date":"2019","source":"BMC neurology","url":"https://pubmed.ncbi.nlm.nih.gov/31279336","citation_count":10,"is_preprint":false},{"pmid":"35714932","id":"PMC_35714932","title":"ISCA2 deficiency leads to heme synthesis defects and impaired erythroid differentiation in K562 cells by indirect ROS-mediated IRP1 activation.","date":"2022","source":"Biochimica et biophysica acta. Molecular cell research","url":"https://pubmed.ncbi.nlm.nih.gov/35714932","citation_count":8,"is_preprint":false},{"pmid":"40595605","id":"PMC_40595605","title":"Amylopectin branch trimming and biosynthesis elucidated by the rice isoamylase ISA1-ISA2 heterocomplex.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/40595605","citation_count":4,"is_preprint":false},{"pmid":"36613634","id":"PMC_36613634","title":"Foliar Application of dsRNA Targeting Endogenous Potato (Solanum tuberosum) Isoamylase Genes ISA1, ISA2, and ISA3 Confers Transgenic Phenotype.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36613634","citation_count":4,"is_preprint":false},{"pmid":"39544370","id":"PMC_39544370","title":"A novel missense mutation in ISCA2 causes aberrant splicing and leads to multiple mitochondrial dysfunctions syndrome 4.","date":"2024","source":"Frontiers in psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/39544370","citation_count":2,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.23.661224","title":"LIKE EARLY STARVATION is involved in the regulation of starch initiation in potato ( <i>Solanum tuberosum</i> cv. Désirée) tubers","date":"2025-06-24","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.23.661224","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15738,"output_tokens":3607,"usd":0.05066},"stage2":{"model":"claude-opus-4-6","input_tokens":7014,"output_tokens":3202,"usd":0.17268},"total_usd":0.22334,"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 ISCA2 (along with ISCA1 and IBA57) is specifically required for maturation of mitochondrial [4Fe-4S] proteins (aconitase, respiratory complex I, lipoic acid synthase), but not [2Fe-2S] proteins (ferrochelatase), functioning late in the ISC assembly pathway. Depletion by RNAi caused massively swollen, cristae-devoid mitochondria and loss of [4Fe-4S] enzyme activities.\",\n      \"method\": \"RNA interference knockdown in HeLa cells, enzyme activity assays, mitochondrial morphology analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined cellular phenotype, replicated across multiple [4Fe-4S] substrates, consistent with yeast and human studies\",\n      \"pmids\": [\"22323289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Yeast Isa2p (ISCA2 ortholog) localizes to the mitochondrial intermembrane space via a bipartite N-terminal leader sequence (mitochondrial import signal + IMS-targeting sequence), both signals required for function. Three invariant cysteine residues in Isa2p are essential for function and likely involved in iron binding.\",\n      \"method\": \"Deletion mutagenesis, subcellular fractionation, genetic complementation, growth assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (fractionation, mutagenesis, genetic rescue), foundational paper with 148 citations\",\n      \"pmids\": [\"10805735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Yeast Isa1 and Isa2 (ISCA2 ortholog) form a complex that binds iron in vivo; this iron is required for de novo synthesis of [4Fe-4S] clusters in mitochondria but is not donated to [2Fe-2S] scaffold proteins Isu1-Isu2. The Isa1-Isa2 complex is specifically dedicated to maturation of mitochondrial [4Fe-4S] proteins (aconitase, homoaconitase), not [2Fe-2S] proteins or cytosolic [4Fe-4S] proteins.\",\n      \"method\": \"In vivo iron-binding assays, genetic epistasis, targeted ferredoxin expression, comprehensive deletion analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal in vivo methods, 135 citations, defines mechanistic role of the complex\",\n      \"pmids\": [\"21987576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Human IBA57 recruits ISCA2 to form a heterodimeric complex bridged by a [2Fe-2S] cluster. The conserved cysteine of IBA57 and the three conserved cysteines of ISCA2 act as cluster ligands. [2Fe-2S] cluster binding is absolutely required for complex formation. The [2Fe-2S] ISCA2-IBA57 complex can reactivate apo aconitase in vitro and is resistant to highly oxidative environments.\",\n      \"method\": \"In vitro reconstitution, spectroscopic characterization, mutagenesis of cluster-coordinating cysteines, aconitase reactivation assay\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis and functional validation\",\n      \"pmids\": [\"30269484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Mitochondrial [4Fe-4S] cluster assembly on ISCA1-ISCA2 proceeds via reductive fusion of two [2Fe-2S] clusters donated by GLRX5, requiring electrons from ferredoxin FDX2 (not FDX1) coupled to FDXR (NADPH-dependent). IBA57 is required for this FDX2-dependent reductive fusion. This reconstituted the complete in vitro maturation of aconitase without artificial reductants.\",\n      \"method\": \"In vitro reconstitution of [4Fe-4S] aconitase maturation without artificial reductants, spectroscopic assays, substitution of individual ISC components\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — complete in vitro reconstitution with defined components, mechanistic dissection with multiple controls\",\n      \"pmids\": [\"32817474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The [2Fe-2S] ISCA2-IBA57 complex adopts a dimer-of-dimers architecture in solution, with ISCA2 providing the homodimerization core and the [2Fe-2S] cluster shared between ISCA2 and IBA57 at the dimer interface. The pathogenic IBA57 Arg146Trp mutation disrupts this specific interaction 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 (SAXS structural determination) but low-resolution model without crystallographic validation\",\n      \"pmids\": [\"31831856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ISCA1 acts as the central orchestrator of [4Fe-4S] cluster maturation: it interacts with both ISCA2 and NFU1, whereas ISCA2 and NFU1 do not interact directly. ISCA1 promotes formation of a transient ISCA1-ISCA2-NFU1 ternary complex and drives [4Fe-4S] cluster transfer from the ISCA1-ISCA2 assembly site to NFU1 via ISCA1's interaction with NFU1's C-terminal cluster-binding domain.\",\n      \"method\": \"NMR-based interaction mapping, protein-protein interaction studies, cluster transfer assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural/interaction study with defined molecular mechanism of cluster handoff\",\n      \"pmids\": [\"33711344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Human ISCA2 (as [2Fe-2S]-bound form) can donate clusters to reconstitute human lipoyl synthase (LIAS), enabling complete LIAS product turnover. ISCU (also [2Fe-2S]-bound) is also a donor; auxiliary cluster addition to LIAS precedes the reducing [4Fe-4S] center.\",\n      \"method\": \"In vitro cluster reconstitution, LC-MS activity assay, EPR spectroscopy of LIAS variants\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 in vitro assay, single lab study\",\n      \"pmids\": [\"33562493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Fission yeast Isa2 (ISCA2 ortholog) interacts in vivo with Grx5 (monothiol glutaredoxin) in mitochondria, as demonstrated by bimolecular fluorescence complementation. Overexpression of isa2+ suppresses growth defects of Δgrx5 mutant and partially restores Fe-S enzyme activities.\",\n      \"method\": \"Bimolecular fluorescence complementation (BiFC), genetic suppressor analysis, enzyme activity assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vivo interaction imaging plus genetic epistasis, single lab\",\n      \"pmids\": [\"20085751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"A missense founder mutation in ISCA2 causes mitochondrial depletion and reduced complex I activity, and decreases expression of ISCA2, ISCA1, and IBA57 in patient fibroblasts, establishing ISCA2 deficiency as cause of hereditary mitochondrial neurodegenerative white matter disease.\",\n      \"method\": \"Exome sequencing, immunohistochemistry, quantitative PCR, complex I dipstick assay, patient fibroblast analysis\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — patient-derived cells with biochemical validation of pathway disruption\",\n      \"pmids\": [\"25539947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Loss of ISCA2 in patient cells and siRNA knockdown models specifically impairs [4Fe-4S] protein function (but not [2Fe-2S] proteins), diminishes mitochondrial membrane potential, respiratory complex II and IV activities, and causes mtDNA depletion.\",\n      \"method\": \"Patient fibroblast analysis, siRNA knockdown, enzyme activity assays, mitochondrial membrane potential measurement, respiratory flux assays\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, patient cells plus knockdown model\",\n      \"pmids\": [\"29297947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Human ISCA2 protein directly binds copper with high affinity, and excess copper binding to ISCA2 (as well as ISCA1 and ISCU) inhibits iron-sulfur cluster assembly, explaining copper cytotoxicity in the context of Wilson's disease.\",\n      \"method\": \"In vitro copper-binding assays, cellular Fe-S enzyme activity measurement, mouse model of Wilson's disease, lymphocyte cell lines\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro binding combined with cellular and in vivo models, single lab\",\n      \"pmids\": [\"37225108\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ISCA2 knockdown in K562 erythroid cells disrupts [4Fe-4S] cluster formation, leading to ROS accumulation that inactivates cytoplasmic aconitase/IRP1, which then represses ALAS2 translation via iron-responsive element binding, thereby blocking heme synthesis and erythroid differentiation.\",\n      \"method\": \"siRNA knockdown in K562 cells, ROS measurement, IRP1 activity assay, ALAS2 expression analysis, heme synthesis assays\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — mechanistic pathway placement with multiple readouts, single lab\",\n      \"pmids\": [\"35714932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Pharmacological inhibition or siRNA knockdown of ISCA2 in clear cell renal carcinoma decreases HIF-2α protein levels by blocking iron-responsive element (IRE)-dependent translation, and at higher concentrations decreases HIF-1α translation; ISCA2 inhibition also triggers an iron starvation response leading to ferroptosis.\",\n      \"method\": \"High-throughput chemical screen, siRNA knockdown, protein level analysis, xenograft tumor model, lipid peroxidation assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic inhibition with mechanistic readout, in vivo validation\",\n      \"pmids\": [\"36097192\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Yeast Isa2 (ISCA2 ortholog) is required for the in vivo function of biotin synthase (Bio2) but not for de novo Fe/S cluster synthesis on Bio2 (which depends on Isu1/Isu2). Loss of Isa2 reduces Bio2 protein levels, but overexpression of BIO2 does not rescue the biotin synthesis defect, indicating Isa2 acts on Bio2 catalytic activity rather than cluster assembly.\",\n      \"method\": \"Genetic screen, growth assays, enzyme activity assays, overexpression epistasis\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple experimental tests distinguishing assembly from function\",\n      \"pmids\": [\"17259550\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ISCA2 is a mitochondrial [4Fe-4S] cluster assembly factor that, together with ISCA1 and IBA57, forms a late-acting ISC subsystem: GLRX5 donates [2Fe-2S] clusters to the ISCA1-ISCA2 heterodimer, where FDX2/FDXR-driven electron transfer catalyzes reductive fusion to form [4Fe-4S] clusters that are then transferred—via a transient ISCA1-ISCA2-NFU1 ternary complex orchestrated by ISCA1—into [4Fe-4S] apoproteins such as aconitase and lipoyl synthase, while IBA57 participates by bridging a [2Fe-2S] cluster with ISCA2 in a heterodimeric intermediate required for this process.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ISCA2 is a mitochondrial iron-sulfur cluster assembly factor that functions late in the ISC pathway, specifically dedicated to the maturation of [4Fe-4S] proteins including aconitase, respiratory complexes, lipoyl synthase, and biotin synthase, while dispensable for [2Fe-2S] protein biogenesis [PMID:22323289, PMID:21987576]. ISCA2 forms a heterodimer with ISCA1 that receives [2Fe-2S] clusters from GLRX5 and catalyzes their reductive fusion into [4Fe-4S] clusters via FDX2/FDXR-dependent electron transfer, with IBA57 required for this process; ISCA2 also forms a [2Fe-2S]-bridged complex with IBA57 through its three conserved cysteine residues [PMID:32817474, PMID:30269484]. ISCA1 orchestrates transfer of the assembled [4Fe-4S] cluster from the ISCA1–ISCA2 complex to downstream acceptors such as NFU1 through a transient ternary complex [PMID:33711344]. Biallelic loss-of-function mutations in ISCA2 cause a mitochondrial neurodegenerative white matter disease characterized by mitochondrial depletion, loss of respiratory chain activities, and impaired [4Fe-4S] enzyme function [PMID:25539947, PMID:29297947].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing the subcellular location and essential residues of the ISCA2 ortholog: yeast Isa2p was shown to localize to mitochondria via a bipartite leader sequence, with three invariant cysteines required for function, providing the first molecular handle on this protein family.\",\n      \"evidence\": \"Deletion mutagenesis, subcellular fractionation, and genetic complementation in S. cerevisiae\",\n      \"pmids\": [\"10805735\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise sub-mitochondrial localization of the human ortholog was not resolved\", \"Iron-binding capacity not yet demonstrated\", \"Molecular partners unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Yeast Isa2 was shown to be required for the catalytic function of the [4Fe-4S] enzyme biotin synthase (Bio2), acting downstream of initial cluster assembly, hinting that the Isa proteins serve a late cluster-maturation or delivery role rather than de novo scaffold function.\",\n      \"evidence\": \"Genetic epistasis, enzyme activity assays, and overexpression studies in S. cerevisiae\",\n      \"pmids\": [\"17259550\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Isa2 directly contacts Bio2 was not tested\", \"Mechanism of action on Bio2 catalysis versus stability unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The physical interaction between the ISCA2 ortholog and the [2Fe-2S] donor GLRX5 was demonstrated in vivo, connecting the late ISC assembly system to the upstream cluster scaffold pathway.\",\n      \"evidence\": \"Bimolecular fluorescence complementation and genetic suppression in fission yeast\",\n      \"pmids\": [\"20085751\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direction of cluster transfer not established\", \"Interaction stoichiometry unknown\", \"Human ortholog interaction not validated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The yeast Isa1–Isa2 complex was shown to bind iron in vivo and to function specifically in de novo mitochondrial [4Fe-4S] cluster synthesis, not [2Fe-2S] protein maturation or cytosolic Fe-S assembly, establishing the dedicated role of this complex.\",\n      \"evidence\": \"In vivo iron-binding assays, comprehensive deletion analysis, and enzyme activity measurements in S. cerevisiae\",\n      \"pmids\": [\"21987576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether iron binding is direct or cluster-mediated was unclear\", \"Biochemical reconstitution of the assembly reaction not yet achieved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Human ISCA2 (with ISCA1 and IBA57) was confirmed as specifically required for mitochondrial [4Fe-4S] protein maturation in mammalian cells, with depletion causing dramatic mitochondrial morphological collapse, translating the yeast findings to human biology.\",\n      \"evidence\": \"RNAi knockdown in HeLa cells with enzyme activity assays and electron microscopy\",\n      \"pmids\": [\"22323289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Individual contributions of ISCA1, ISCA2, and IBA57 were not separated\", \"Mechanism of mitochondrial morphology disruption unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A causative link between ISCA2 deficiency and human disease was established: a founder missense mutation caused mitochondrial neurodegenerative white matter disease with reduced complex I activity and decreased expression of the entire late ISC machinery (ISCA1, ISCA2, IBA57).\",\n      \"evidence\": \"Exome sequencing, patient fibroblast biochemistry, and immunohistochemistry\",\n      \"pmids\": [\"25539947\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Rescue experiment not performed\", \"Whether ISCA2 mutation destabilizes the entire late ISC complex or triggers secondary transcriptional effects unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The molecular basis of ISCA2–IBA57 interaction was revealed: the two proteins form a heterodimer bridged by a [2Fe-2S] cluster coordinated by ISCA2's three conserved cysteines and IBA57's conserved cysteine, and this complex can reactivate apo-aconitase, defining a cluster-bridged intermediate in the assembly pathway.\",\n      \"evidence\": \"In vitro reconstitution with spectroscopic characterization and cysteine mutagenesis\",\n      \"pmids\": [\"30269484\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship of this [2Fe-2S] intermediate to the final [4Fe-4S] product not resolved\", \"Whether this complex forms in vivo not confirmed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Further patient and knockdown studies confirmed ISCA2 loss specifically impairs [4Fe-4S] but not [2Fe-2S] proteins, and additionally causes mtDNA depletion and reduced mitochondrial membrane potential, broadening the phenotypic consequences.\",\n      \"evidence\": \"Patient fibroblast analysis, siRNA knockdown, respiratory complex activity assays\",\n      \"pmids\": [\"29297947\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking [4Fe-4S] cluster deficiency to mtDNA depletion not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Low-resolution structural characterization revealed that the ISCA2–IBA57 complex adopts a dimer-of-dimers quaternary structure with ISCA2 providing the homodimerization core, and the pathogenic IBA57 R146W mutation was mapped to this interface.\",\n      \"evidence\": \"SAXS and computational docking\",\n      \"pmids\": [\"31831856\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution crystal or cryo-EM structure available\", \"Dimer-of-dimers stoichiometry not validated by independent method\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The complete [4Fe-4S] cluster assembly mechanism was reconstituted in vitro: GLRX5 donates two [2Fe-2S] clusters to the ISCA1–ISCA2 complex, and FDX2 (not FDX1) coupled to FDXR provides electrons for reductive fusion to form [4Fe-4S], with IBA57 required; this was the first artificial-reductant-free reconstitution of mitochondrial [4Fe-4S] maturation.\",\n      \"evidence\": \"Complete in vitro reconstitution with defined human ISC components and spectroscopic monitoring\",\n      \"pmids\": [\"32817474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetic parameters and rate-limiting steps not determined\", \"Structural mechanism of reductive fusion not resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The cluster handoff mechanism was elucidated: ISCA1 acts as the central orchestrator, interacting with both ISCA2 and NFU1 to form a transient ternary complex through which [4Fe-4S] clusters are transferred to downstream acceptors; ISCA2 and NFU1 do not interact directly.\",\n      \"evidence\": \"NMR-based interaction mapping and cluster transfer assays with purified human proteins\",\n      \"pmids\": [\"33711344\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ISCA1 also transfers clusters to targets other than NFU1 not addressed\", \"Ternary complex structure not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Downstream consequences of ISCA2 deficiency were connected to iron homeostasis: ISCA2 knockdown impairs cytoplasmic aconitase/IRP1, which then represses ALAS2 translation and heme synthesis in erythroid cells, and separately decreases HIF-2α translation via IRE-dependent mechanisms in renal carcinoma, with ISCA2 inhibition also triggering ferroptosis.\",\n      \"evidence\": \"siRNA knockdown in K562 and renal carcinoma cells, IRP1 activity assays, HIF-2α protein measurements, xenograft models\",\n      \"pmids\": [\"35714932\", \"36097192\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether ferroptosis is a direct consequence of [4Fe-4S] loss or secondary iron dysregulation is unclear\", \"In vivo relevance in normal erythropoiesis not validated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"ISCA2 was identified as a direct target of copper toxicity: high-affinity copper binding to ISCA2 inhibits iron-sulfur cluster assembly, providing a molecular explanation for Fe-S deficits in copper overload conditions such as Wilson's disease.\",\n      \"evidence\": \"In vitro copper-binding assays, cellular Fe-S activity measurements, and Wilson's disease mouse model\",\n      \"pmids\": [\"37225108\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of copper versus iron discrimination unknown\", \"Whether copper binding is reversible in vivo not tested\", \"Relative contribution of ISCA2 versus ISCA1/ISCU copper inhibition not separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the high-resolution structure of the ISCA1–ISCA2 heterodimer and its [4Fe-4S]-bound state, the structural mechanism of reductive [2Fe-2S]-to-[4Fe-4S] cluster fusion, the full range of [4Fe-4S] client proteins receiving clusters through this pathway, and the mechanism by which ISCA2 deficiency leads to mtDNA depletion and mitochondrial morphological collapse.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of ISCA1–ISCA2 complex\", \"Reductive fusion mechanism structurally unresolved\", \"Complete client protein inventory unknown\", \"mtDNA depletion mechanism not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [3, 4, 6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 2, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 4, 7]}\n    ],\n    \"complexes\": [\n      \"ISCA1-ISCA2 heterodimer\",\n      \"ISCA2-IBA57 [2Fe-2S]-bridged complex\",\n      \"ISCA1-ISCA2-NFU1 transient ternary complex\"\n    ],\n    \"partners\": [\n      \"ISCA1\",\n      \"IBA57\",\n      \"NFU1\",\n      \"GLRX5\",\n      \"FDX2\",\n      \"FDXR\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}