{"gene":"ISCA1","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2012,"finding":"ISCA1, ISCA2, and IBA57 are specifically required for maturation of mitochondrial [4Fe-4S] proteins (aconitase, respiratory complex I, lipoic acid synthase) but not [2Fe-2S] proteins (ferrochelatase); RNAi depletion in HeLa cells caused massively swollen mitochondria devoid of cristae, and evidence was provided against a cytosolic localization or direct Fe/S maturation function of ISCA1/ISCA2 outside mitochondria.","method":"RNAi knockdown in HeLa cells, enzyme activity assays (aconitase, succinate dehydrogenase, lipoic acid synthase, ferrochelatase), heme content measurement, mitochondrial morphology by electron microscopy, subcellular fractionation","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (enzyme activity, morphology, fractionation), replicated across three proteins in the same pathway, consistent with yeast studies","pmids":["22323289"],"is_preprint":false},{"year":2011,"finding":"Yeast Isa1 and Isa2 form a complex required for maturation of mitochondrial [4Fe-4S] proteins (aconitase, homoaconitase) but dispensable for [2Fe-2S] proteins and cytosolic [4Fe-4S] proteins; Isa1-Isa2 bind iron in vivo, and this iron is required for de novo [4Fe-4S] cluster synthesis rather than [2Fe-2S] assembly on Isu1-Isu2; Iba57 specifically interacts with Isa1 and Isa2 and its depletion causes iron accumulation on Isa proteins.","method":"In vivo genetic analysis in S. cerevisiae, co-immunoprecipitation, iron-binding assays, mitochondrially targeted bacterial ferredoxin reporters, enzyme activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, multiple orthogonal in vivo assays, complementary bacterial ferredoxin targeting experiments, consistent across multiple genetic backgrounds","pmids":["21987576"],"is_preprint":false},{"year":2020,"finding":"In vitro reconstitution of mitochondrial [4Fe-4S] aconitase maturation demonstrated that GLRX5 (carrying [2Fe-2S] clusters) serves as cluster donor to ISCA1-ISCA2, electrons from FDX2 (but not FDX1) catalyze reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 in an IBA57-dependent fashion to form [4Fe-4S] clusters, and FDXR provides NADPH-coupled reducing equivalents; [2Fe-2S] transfer from GLRX5 to [2Fe-2S] apoproteins occurred spontaneously without ISC factors.","method":"In vitro reconstitution without artificial reductants, EPR/Mössbauer spectroscopy, activity assays for aconitase maturation, genetic complementation with FDX1 vs FDX2","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — full in vitro reconstitution with defined components, multiple spectroscopic methods, rigorous controls comparing FDX1 vs FDX2, single study with multiple orthogonal approaches","pmids":["32817474"],"is_preprint":false},{"year":2021,"finding":"NMR analysis showed ISCA1 is the central scaffold that interacts with both ISCA2 and NFU1; 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 a cluster-binding site formed jointly by ISCA1 and the C-terminal domain of NFU1, making the [4Fe-4S] cluster available to NFU1-dependent apo proteins.","method":"NMR spectroscopy, protein-protein interaction mapping, [4Fe-4S] cluster transfer assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structural/interaction data with cluster transfer assays, single lab but multiple orthogonal NMR and biochemical methods","pmids":["33711344"],"is_preprint":false},{"year":2020,"finding":"ISCA1 (ISCU2) directly donates [2Fe-2S] clusters to NFU1; ISCA1 interacts with NFU1 at a conserved hydrophobic patch on the C-terminal alpha-helix of NFU1, and mutagenesis of this interface abolished NFU1's ability to acquire its Fe-S cluster and impaired downstream lipoylation of pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and glycine cleavage complex components.","method":"Co-immunoprecipitation, site-directed mutagenesis of NFU1 interaction surface, biochemical Fe-S cluster transfer assays, lipoylation assays in HEK293 cells","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus mutagenesis and functional readout, single lab","pmids":["32776106"],"is_preprint":false},{"year":2000,"finding":"Yeast Isa1p is targeted to the mitochondrial matrix; three invariant cysteine residues in Isa1p (and Isa2p) are essential for function and may be involved in iron binding; isa1Δ mutants showed elevated mitochondrial iron, reduced aconitase and succinate dehydrogenase activities, and dependency on lysine and glutamate, consistent with a role in Fe-S cluster assembly.","method":"Genetic disruption of ISA1/ISA2 in S. cerevisiae, mitochondrial fractionation/import assays, enzyme activity assays, site-directed mutagenesis of cysteine residues, iron measurement","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (fractionation, mutagenesis, enzyme assays, iron measurement), replicated findings consistent across paralogs","pmids":["10805735"],"is_preprint":false},{"year":2010,"finding":"Human ISCA1 (hIscA1) binds mononuclear iron with an association constant of ~2×10^19 M⁻¹; iron-bound hIscA1 can donate iron to the IscU scaffold protein for in vitro Fe-S cluster assembly; hIscA1 partially complements an E. coli iscA deletion for aerobic growth on minimal medium.","method":"UV-visible absorption and EPR spectroscopy, iron-binding constant determination, in vitro Fe-S cluster assembly assay with IscU, E. coli complementation","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical reconstitution with spectroscopic validation and complementation, single lab","pmids":["20302570"],"is_preprint":false},{"year":2002,"finding":"S. pombe Isa1 is a multimeric protein carrying [2Fe-2S]²⁺ clusters as characterized by Mössbauer and optical spectroscopy; it forms a complex with a redox-active ferredoxin identified by crosslinking; site-directed mutagenesis of coordinating residues altered cluster coordination and stability.","method":"Protein purification, Mössbauer spectroscopy, UV-visible spectroscopy, chemical crosslinking, site-directed mutagenesis","journal":"Journal of biological inorganic chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro spectroscopic characterization with mutagenesis validation, single lab study on fission yeast ortholog","pmids":["11941510"],"is_preprint":false},{"year":2009,"finding":"Human ISCA1 is present in both cytosolic and mitochondrial fractions of HeLa cells; siRNA knockdown decreased activities of mitochondrial Fe-S enzymes (succinate dehydrogenase, mitochondrial aconitase) and also cytosolic aconitase; ISCA1 physically interacts with IOP1/NARFL, a cytosolic protein involved in cytosolic Fe-S protein assembly.","method":"siRNA knockdown in HeLa cells, subcellular fractionation, enzyme activity assays, co-immunoprecipitation with IOP1/NARFL","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus knockdown with functional readout, single lab; cytosolic localization conclusion contradicted by later more rigorous study (PMID:22323289)","pmids":["19864422"],"is_preprint":false},{"year":2010,"finding":"In S. pombe, Grx5 (monothiol glutaredoxin) interacts in vivo with Isa1 and Isa2 proteins in mitochondria; overexpression of isa1⁺ or isa2⁺ suppressed growth defects of Δgrx5 mutants and partly restored Fe-S enzyme activities, placing Grx5 upstream of or parallel to Isa1/Isa2 in the Fe-S assembly pathway.","method":"Bimolecular fluorescence complementation (BiFC) for in vivo interaction, multi-copy suppressor screen, genetic epistasis, enzyme activity assays","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — BiFC interaction plus genetic epistasis and enzyme activity, single lab","pmids":["20085751"],"is_preprint":false},{"year":2007,"finding":"In S. cerevisiae, Isa1 and Isa2 are required for the in vivo catalytic function of biotin synthase (Bio2) but not for de novo assembly of its [4Fe-4S] or [2Fe-2S] clusters; de novo Fe-S cluster assembly on Bio2 depended on Isu1/Isu2 scaffold proteins.","method":"Genetic screen, isa1/isa2 deletion analysis, biotin utilization assays, Bio2 overexpression complementation, Fe-S cluster assembly assays in yeast","journal":"Eukaryotic cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic dissection with functional enzymatic readouts and overexpression controls, single lab","pmids":["17259550"],"is_preprint":false},{"year":2004,"finding":"Human ISCA1 (hIscA) localizes to mitochondria and can functionally complement an isa1Δ null mutant in S. cerevisiae, demonstrating conserved function in Fe-S cluster biogenesis.","method":"Yeast functional complementation, subcellular localization by mitochondrial targeting signal analysis and expression studies","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional complementation in yeast is a direct assay but single lab with limited mechanistic depth","pmids":["15262227"],"is_preprint":false},{"year":2018,"finding":"A homozygous ISCA1 p.V10G mutation located in the uncleaved presequence severely impaired mitochondrial import and stability of ISCA1; RNAi knockdown of ISCA1 in HeLa cells impaired [4Fe-4S] protein biogenesis and was rescued by wild-type ISCA1 but only partially by the p.V10G mutant; patient fibroblasts showed defects in [4Fe-4S]-dependent respiratory complexes and lipoic acid synthesis.","method":"Targeted MitoExome sequencing, RNAi rescue experiments in HeLa cells, mitochondrial import assays, [4Fe-4S] enzyme activity assays, patient fibroblast biochemistry","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional rescue with wild-type vs mutant plus import assays and enzyme activity, single lab","pmids":["29767723"],"is_preprint":false},{"year":2020,"finding":"ISCA1 p.(Tyr101Cys) mutation decreased stability of the [2Fe-2S] cluster in purified recombinant human ISCA1 protein, establishing that the mutation directly destabilizes the iron-sulfur cluster on the protein; patient fibroblasts showed impaired lipoic acid synthesis and decreased activities of respiratory chain complexes I and II.","method":"Recombinant protein expression and purification, spectroscopic analysis of [2Fe-2S] cluster stability, patient fibroblast biochemistry","journal":"Mitochondrion","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro biochemical characterization of mutant protein cluster stability, single lab, limited mechanistic depth beyond cluster destabilization","pmids":["32092383"],"is_preprint":false},{"year":2023,"finding":"Human ISCA1, ISCA2, and ISCU proteins have strong copper-binding activity that inhibits iron-sulfur cluster assembly; excess copper (in Wilson's disease models including ATP7A⁻/⁻ lymphocytes and ATP7B knockdown cells and mouse model) suppressed Fe-S cluster assembly, decreased Fe-S enzyme activity, and disrupted mitochondrial function.","method":"Copper-binding assays with purified proteins, Fe-S enzyme activity assays in cell lines and mouse models, Wilson's disease mouse model (ATP7A⁻/⁻), siRNA knockdown of ATP7B","journal":"Free radical biology & medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct copper-binding assays with ISCA1 protein plus in vivo functional assays in multiple model systems, single lab","pmids":["37225108"],"is_preprint":false},{"year":2019,"finding":"ISCA1 knockout in rats caused early embryonic death at E8.5 with significant decrease in NDUFA9 (respiratory complex I subunit) protein and increase in aconitase 2 (ACO2), indicating ISCA1 is essential for respiratory chain complex integrity in vivo.","method":"CRISPR-Cas9 knockout rat generation, embryo morphology analysis, Western blot for mitochondrial proteins, fluorescence imaging using ISCA1 promoter-driven reporter","journal":"Animal models and experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean KO with specific protein-level readouts, single lab, limited mechanistic depth","pmids":["31016283"],"is_preprint":false},{"year":2023,"finding":"Neuron-specific Isca1 knockout rats developed epilepsy, memory impairment, massive neuronal death, mitochondrial fragmentation and cristae fracture, reduced respiratory chain complex protein content, and decreased ATP production; neuronal death occurred via oncosis.","method":"Conditional CRISPR-Cas9 knockout (Isca1flox/flox-NeuN-Cre), MRI, behavioral tests, electron microscopy, Western blot for respiratory chain complexes, ATP assay, immunofluorescence","journal":"Animal models and experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with multiple functional readouts (behavior, ultrastructure, biochemistry), single lab","pmids":["37140997"],"is_preprint":false},{"year":2011,"finding":"TbIsa1 and TbIsa2 in Trypanosoma brucei are required for Fe-S cluster assembly in mitochondrial aconitase, fumarase, and succinate dehydrogenase in the procyclic (active mitochondrion) form; their depletion did not affect cytosolic Fe-S proteins; human Isa orthologues partially rescued single TbIsa knockdowns, restoring aconitase and fumarase activities.","method":"RNAi knockdown in T. brucei, enzyme activity assays, heterologous rescue with human ISCA1/ISCA2, ROS measurement","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockdown with enzymatic readouts and cross-species rescue, single lab","pmids":["21790804"],"is_preprint":false}],"current_model":"ISCA1 is a mitochondrial iron-sulfur cluster assembly protein that, together with ISCA2 and IBA57, forms a late-acting ISC subsystem specifically dedicated to synthesizing [4Fe-4S] clusters: GLRX5 donates [2Fe-2S] clusters to the ISCA1-ISCA2 complex, FDX2-derived electrons catalyze reductive fusion of two [2Fe-2S] clusters into a [4Fe-4S] cluster on ISCA1-ISCA2 in an IBA57-dependent manner, and ISCA1 then acts as the central scaffold that bridges ISCA2 and NFU1 in a transient ternary complex to transfer the [4Fe-4S] cluster to NFU1 for delivery to downstream apo-proteins such as lipoic acid synthase and respiratory complex I subunits; ISCA1 also binds iron via conserved cysteine residues essential for function, and its deficiency causes loss of [4Fe-4S] enzyme activities, mitochondrial morphological collapse, and early embryonic lethality in vivo."},"narrative":{"mechanistic_narrative":"ISCA1 is a mitochondrial matrix protein that functions in a late-acting branch of the iron-sulfur cluster (ISC) assembly machinery specifically dedicated to maturing [4Fe-4S] proteins such as aconitase, respiratory complex I subunits, and lipoic acid synthase, while being dispensable for [2Fe-2S] protein maturation [PMID:22323289, PMID:21987576, PMID:10805735]. Together with ISCA2 and IBA57, ISCA1 forms a complex that catalyzes the reductive fusion of two [2Fe-2S] clusters into a single [4Fe-4S] cluster: GLRX5 donates [2Fe-2S] clusters to ISCA1-ISCA2, and electrons supplied by FDX2 (not FDX1) drive fusion in an IBA57-dependent manner [PMID:32817474, PMID:20085751]. ISCA1 then serves as the central scaffold of cluster handoff, bridging ISCA2 and NFU1 in a transient ternary complex and transferring the assembled cluster to a binding site formed jointly by ISCA1 and the NFU1 C-terminal domain, enabling downstream lipoylation of pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and the glycine cleavage system [PMID:33711344, PMID:32776106]. The protein binds iron with high affinity through conserved cysteine residues essential for function and harbors clusters whose stability depends on coordinating residues [PMID:10805735, PMID:20302570, PMID:11941510]. Copper binds ISCA1 and inhibits Fe-S cluster assembly, linking ISCA1 dysfunction to copper-overload pathology [PMID:37225108]. ISCA1 deficiency causes loss of [4Fe-4S] enzyme activities, mitochondrial cristae collapse, and is essential for viability, with knockout causing early embryonic lethality and neuron-specific loss producing neurodegeneration in vivo [PMID:22323289, PMID:31016283, PMID:37140997]; a homozygous presequence mutation impairing mitochondrial import causes a multiple mitochondrial dysfunctions syndrome in patients [PMID:29767723].","teleology":[{"year":2000,"claim":"Established that the Isa proteins reside in the mitochondrial matrix and that conserved cysteines are functionally essential, defining the protein's compartment and putative metal-binding residues.","evidence":"Genetic disruption, import/fractionation, cysteine mutagenesis and iron measurement in S. cerevisiae","pmids":["10805735"],"confidence":"High","gaps":["Did not establish whether cysteines coordinate iron directly versus a cluster","Specific [4Fe-4S] vs [2Fe-2S] role not yet distinguished"]},{"year":2002,"claim":"Showed that Isa1 itself carries [2Fe-2S] clusters and partners with a redox-active ferredoxin, providing the first spectroscopic evidence of a cluster-bearing, redox-coupled protein.","evidence":"Mössbauer/UV-vis spectroscopy, crosslinking and mutagenesis on S. pombe Isa1","pmids":["11941510"],"confidence":"Medium","gaps":["Functional consequence of the ferredoxin partnership not defined","Cluster role as substrate versus product unresolved"]},{"year":2004,"claim":"Demonstrated functional conservation of human ISCA1 by complementation of yeast isa1 deletion, validating model-organism findings for the human protein.","evidence":"Yeast functional complementation and targeting-signal analysis","pmids":["15262227"],"confidence":"Medium","gaps":["No mechanistic detail on human protein activity","Did not address substrate specificity"]},{"year":2007,"claim":"Distinguished Isa-dependent maturation from the upstream Isu scaffold, showing Isa proteins are needed for catalytic competence of [4Fe-4S] enzymes rather than de novo cluster assembly per se.","evidence":"Genetic dissection of biotin synthase maturation in S. cerevisiae","pmids":["17259550"],"confidence":"Medium","gaps":["Molecular step catalyzed by Isa proteins not defined","Did not explain how clusters reach Bio2"]},{"year":2010,"claim":"Defined high-affinity mononuclear iron binding by human ISCA1 and its capacity to donate iron to the IscU scaffold, framing an iron-carrier role.","evidence":"Spectroscopy, iron-binding constant determination, in vitro assembly with IscU and E. coli complementation","pmids":["20302570"],"confidence":"Medium","gaps":["Iron-donor model later superseded by cluster-transfer model","Physiological relevance of mononuclear iron binding unclear"]},{"year":2010,"claim":"Placed monothiol glutaredoxin Grx5 in interaction with Isa1/Isa2 and upstream/parallel in the pathway, foreshadowing GLRX5 as the cluster donor.","evidence":"BiFC, multi-copy suppressor and epistasis analysis in S. pombe","pmids":["20085751"],"confidence":"Medium","gaps":["Direction of cluster transfer not biochemically resolved","Nature of transferred species undefined"]},{"year":2011,"claim":"Established the [4Fe-4S]-specific function of the Isa1-Isa2-Iba57 module and demonstrated in vivo iron binding requisite for de novo [4Fe-4S] synthesis, with Iba57 as a specific interactor.","evidence":"Yeast genetics, reciprocal Co-IP, iron-binding assays and ferredoxin reporters","pmids":["21987576"],"confidence":"High","gaps":["Did not reconstitute the fusion reaction in vitro","Electron source for fusion not identified"]},{"year":2011,"claim":"Extended Isa-dependent [4Fe-4S] maturation to trypanosomes and confirmed cross-species functional conservation of human orthologues.","evidence":"RNAi, enzyme assays and heterologous human rescue in T. brucei","pmids":["21790804"],"confidence":"Medium","gaps":["No structural or biochemical mechanism","Cytosolic involvement excluded but not mechanistically explored"]},{"year":2012,"claim":"In human cells, rigorously assigned ISCA1/ISCA2/IBA57 to mitochondrial [4Fe-4S] (not [2Fe-2S]) maturation and tied deficiency to cristae-devoid swollen mitochondria, refuting a cytosolic maturation role.","evidence":"RNAi, enzyme activity panels, EM morphology and fractionation in HeLa cells","pmids":["22323289"],"confidence":"High","gaps":["Did not define the biochemical reaction catalyzed","Order of factor action not established"]},{"year":2018,"claim":"Linked ISCA1 to human mitochondrial disease via a presequence mutation impairing import and [4Fe-4S] biogenesis, establishing causality through rescue.","evidence":"MitoExome sequencing, RNAi rescue with WT vs mutant, import assays and patient fibroblast biochemistry","pmids":["29767723"],"confidence":"Medium","gaps":["Single mutation locus","Did not address neurological phenotype mechanism"]},{"year":2019,"claim":"Showed ISCA1 is essential for embryonic viability and respiratory complex integrity in a mammalian whole-organism model.","evidence":"CRISPR knockout rat, embryo morphology and Western blot for complex I subunit","pmids":["31016283"],"confidence":"Medium","gaps":["Lethality precludes tissue-level mechanism","Did not dissect cause of ACO2 increase"]},{"year":2020,"claim":"Reconstituted the complete [4Fe-4S] synthesis reaction in vitro, defining GLRX5 as cluster donor and FDX2-derived electrons as the driver of IBA57-dependent reductive fusion on ISCA1-ISCA2.","evidence":"Defined-component in vitro reconstitution with EPR/Mössbauer and FDX1-vs-FDX2 controls","pmids":["32817474"],"confidence":"High","gaps":["Did not resolve the cluster handoff to downstream carriers","Structural basis of fusion not solved"]},{"year":2020,"claim":"Mapped a direct ISCA1-NFU1 interface required for NFU1 cluster acquisition and downstream lipoylation, identifying the next acceptor in the pathway.","evidence":"Co-IP, interface mutagenesis, transfer assays and lipoylation readouts in HEK293","pmids":["32776106"],"confidence":"Medium","gaps":["Single lab","Cluster nuclearity transferred to NFU1 described differently across studies"]},{"year":2020,"claim":"Provided patient and biochemical evidence that an ISCA1 missense mutation destabilizes its bound cluster, connecting cluster instability to respiratory and lipoylation defects.","evidence":"Recombinant protein cluster-stability spectroscopy and patient fibroblast biochemistry","pmids":["32092383"],"confidence":"Medium","gaps":["Mechanism limited to cluster destabilization","Effect on assembly reaction not tested"]},{"year":2021,"claim":"Defined ISCA1 as the central scaffold bridging ISCA2 and NFU1 in a transient ternary complex that drives [4Fe-4S] transfer to a shared ISCA1-NFU1 site, resolving the cluster-handoff architecture.","evidence":"NMR interaction mapping and [4Fe-4S] cluster transfer assays","pmids":["33711344"],"confidence":"High","gaps":["No high-resolution complex structure","Kinetics of in vivo handoff not measured"]},{"year":2023,"claim":"Revealed copper binding to ISCA1 (and ISCA2/ISCU) as an inhibitory mechanism, linking copper overload to suppressed Fe-S assembly and mitochondrial dysfunction.","evidence":"Copper-binding assays, Fe-S enzyme activity in Wilson's disease models and ATP7B knockdown","pmids":["37225108"],"confidence":"Medium","gaps":["Copper-binding site on ISCA1 not mapped","Whether copper competes at the iron site unresolved"]},{"year":2023,"claim":"Established that neuronal ISCA1 loss causes epilepsy, neurodegeneration, mitochondrial fragmentation and energy failure, tying [4Fe-4S] biogenesis defects to brain pathology.","evidence":"Conditional neuron-specific CRISPR knockout rat with behavior, EM, biochemistry and ATP assays","pmids":["37140997"],"confidence":"Medium","gaps":["Mechanism of oncotic neuronal death not detailed","Cell-autonomy versus circuit effects not separated"]},{"year":null,"claim":"A high-resolution structure of the ISCA1-ISCA2-IBA57 fusion machine and of the ISCA1-ISCA2-NFU1 transfer complex remains undetermined, leaving the atomic mechanism of reductive cluster fusion and directional handoff open.","evidence":"","pmids":[],"confidence":"High","gaps":["No experimental structure of the assembly or transfer complexes","Copper inhibition site and competition with iron unmapped","Kinetic ordering of GLRX5 donation, fusion and NFU1 handoff not measured in a single system"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,3,4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,4]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3,1]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,5,11]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,16]}],"complexes":["ISCA1-ISCA2-IBA57 complex","ISCA1-ISCA2-NFU1 ternary complex"],"partners":["ISCA2","IBA57","NFU1","GLRX5","FDX2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BUE6","full_name":"Iron-sulfur cluster assembly 1 homolog, mitochondrial","aliases":["HESB-like domain-containing protein 2","Iron-sulfur assembly protein IscA","hIscA"],"length_aa":129,"mass_kda":14.2,"function":"Involved in the maturation of mitochondrial 4Fe-4S proteins functioning late in the iron-sulfur cluster assembly pathway. Probably involved in the binding of an intermediate of Fe/S cluster assembly","subcellular_location":"Mitochondrion","url":"https://www.uniprot.org/uniprotkb/Q9BUE6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ISCA1","classification":"Not Classified","n_dependent_lines":306,"n_total_lines":1208,"dependency_fraction":0.2533112582781457},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ISCA1","total_profiled":1310},"omim":[{"mim_id":"617613","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 5; MMDS5","url":"https://www.omim.org/entry/617613"},{"mim_id":"616370","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 4; MMDS4","url":"https://www.omim.org/entry/616370"},{"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":"611118","title":"NUCLEAR PRELAMIN A RECOGNITION FACTOR-LIKE; NARFL","url":"https://www.omim.org/entry/611118"}],"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/ISCA1"},"hgnc":{"alias_symbol":["MGC4276","ISA1","hIscA","hIscA1"],"prev_symbol":["HBLD2"]},"alphafold":{"accession":"Q9BUE6","domains":[{"cath_id":"2.60.300.12","chopping":"24-127","consensus_level":"high","plddt":93.6289,"start":24,"end":127}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BUE6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BUE6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BUE6-F1-predicted_aligned_error_v6.png","plddt_mean":89.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ISCA1","jax_strain_url":"https://www.jax.org/strain/search?query=ISCA1"},"sequence":{"accession":"Q9BUE6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BUE6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BUE6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BUE6"}},"corpus_meta":[{"pmid":"22323289","id":"PMC_22323289","title":"The human mitochondrial ISCA1, ISCA2, and IBA57 proteins are required for [4Fe-4S] protein maturation.","date":"2012","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/22323289","citation_count":172,"is_preprint":false},{"pmid":"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":"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":71,"is_preprint":false},{"pmid":"11941510","id":"PMC_11941510","title":"Iron-sulfur cluster biosynthesis: characterization of Schizosaccharomyces pombe Isa1.","date":"2002","source":"Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11941510","citation_count":68,"is_preprint":false},{"pmid":"28356563","id":"PMC_28356563","title":"Homozygous p.(Glu87Lys) variant in ISCA1 is associated with a multiple mitochondrial dysfunctions syndrome.","date":"2017","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/28356563","citation_count":54,"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":"24993830","id":"PMC_24993830","title":"Crystal structure of the Chlamydomonas starch debranching enzyme isoamylase ISA1 reveals insights into the mechanism of branch trimming and complex assembly.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24993830","citation_count":47,"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 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[4Fe-4S] cluster of NFU1 requires the coordinated donation of two [2Fe-2S] clusters from the scaffold proteins, ISCU2 and ISCA1.","date":"2020","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/32776106","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":"31016283","id":"PMC_31016283","title":"Knockout of ISCA1 causes early embryonic death in rats.","date":"2019","source":"Animal models and experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31016283","citation_count":13,"is_preprint":false},{"pmid":"33711344","id":"PMC_33711344","title":"ISCA1 Orchestrates ISCA2 and NFU1 in the Maturation of Human Mitochondrial [4Fe-4S] 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the rice planthopper, Nilaparvata lugens.","date":"2017","source":"Insect science","url":"https://pubmed.ncbi.nlm.nih.gov/29063672","citation_count":8,"is_preprint":false},{"pmid":"30105122","id":"PMC_30105122","title":"Report of the Third Family with Multiple Mitochondrial Dysfunctions Syndrome 5 Caused by the Founder Variant p.(Glu87Lys) in ISCA1.","date":"2018","source":"Journal of pediatric genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30105122","citation_count":8,"is_preprint":false},{"pmid":"37140997","id":"PMC_37140997","title":"A neuron-specific Isca1 knockout rat developments multiple mitochondrial dysfunction syndromes.","date":"2023","source":"Animal models and experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/37140997","citation_count":6,"is_preprint":false},{"pmid":"33410574","id":"PMC_33410574","title":"Transcriptomic analysis reveals the inhibition of reproduction in rice brown planthopper, Nilaparvata lugens, after silencing the gene of MagR 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journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36613634","citation_count":4,"is_preprint":false},{"pmid":"39891829","id":"PMC_39891829","title":"Long Noncoding RNA ISA1 Protects Against Ischemic Brain Damage by Promoting the Transformation of Microglia Toward Anti-inflammatory Phenotype via the SOCS3/JAK2/STAT3 Pathway.","date":"2025","source":"Neurochemical research","url":"https://pubmed.ncbi.nlm.nih.gov/39891829","citation_count":1,"is_preprint":false},{"pmid":"39766805","id":"PMC_39766805","title":"Comprehensive Analysis Reveals That ISCA1 Is Correlated with Ferroptosis-Related Genes Across Cancers and Is a Biomarker in Thyroid Carcinoma.","date":"2024","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/39766805","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.11.17.688664","title":"A scalable screening platform for discovering predominant miRNA target genes and druggable siRNA sequences","date":"2025-11-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.17.688664","citation_count":0,"is_preprint":true},{"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":17269,"output_tokens":4942,"usd":0.062968,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13293,"output_tokens":4798,"usd":0.093207,"stage2_stop_reason":"end_turn"},"total_usd":0.156175,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2012,\n      \"finding\": \"ISCA1, ISCA2, and IBA57 are specifically required for maturation of mitochondrial [4Fe-4S] proteins (aconitase, respiratory complex I, lipoic acid synthase) but not [2Fe-2S] proteins (ferrochelatase); RNAi depletion in HeLa cells caused massively swollen mitochondria devoid of cristae, and evidence was provided against a cytosolic localization or direct Fe/S maturation function of ISCA1/ISCA2 outside mitochondria.\",\n      \"method\": \"RNAi knockdown in HeLa cells, enzyme activity assays (aconitase, succinate dehydrogenase, lipoic acid synthase, ferrochelatase), heme content measurement, mitochondrial morphology by electron microscopy, subcellular fractionation\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (enzyme activity, morphology, fractionation), replicated across three proteins in the same pathway, consistent with yeast studies\",\n      \"pmids\": [\"22323289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Yeast Isa1 and Isa2 form a complex required for maturation of mitochondrial [4Fe-4S] proteins (aconitase, homoaconitase) but dispensable for [2Fe-2S] proteins and cytosolic [4Fe-4S] proteins; Isa1-Isa2 bind iron in vivo, and this iron is required for de novo [4Fe-4S] cluster synthesis rather than [2Fe-2S] assembly on Isu1-Isu2; Iba57 specifically interacts with Isa1 and Isa2 and its depletion causes iron accumulation on Isa proteins.\",\n      \"method\": \"In vivo genetic analysis in S. cerevisiae, co-immunoprecipitation, iron-binding assays, mitochondrially targeted bacterial ferredoxin reporters, enzyme activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, multiple orthogonal in vivo assays, complementary bacterial ferredoxin targeting experiments, consistent across multiple genetic backgrounds\",\n      \"pmids\": [\"21987576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"In vitro reconstitution of mitochondrial [4Fe-4S] aconitase maturation demonstrated that GLRX5 (carrying [2Fe-2S] clusters) serves as cluster donor to ISCA1-ISCA2, electrons from FDX2 (but not FDX1) catalyze reductive [2Fe-2S] cluster fusion on ISCA1-ISCA2 in an IBA57-dependent fashion to form [4Fe-4S] clusters, and FDXR provides NADPH-coupled reducing equivalents; [2Fe-2S] transfer from GLRX5 to [2Fe-2S] apoproteins occurred spontaneously without ISC factors.\",\n      \"method\": \"In vitro reconstitution without artificial reductants, EPR/Mössbauer spectroscopy, activity assays for aconitase maturation, genetic complementation with FDX1 vs FDX2\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — full in vitro reconstitution with defined components, multiple spectroscopic methods, rigorous controls comparing FDX1 vs FDX2, single study with multiple orthogonal approaches\",\n      \"pmids\": [\"32817474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NMR analysis showed ISCA1 is the central scaffold that interacts with both ISCA2 and NFU1; 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 a cluster-binding site formed jointly by ISCA1 and the C-terminal domain of NFU1, making the [4Fe-4S] cluster available to NFU1-dependent apo proteins.\",\n      \"method\": \"NMR spectroscopy, protein-protein interaction mapping, [4Fe-4S] cluster transfer assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structural/interaction data with cluster transfer assays, single lab but multiple orthogonal NMR and biochemical methods\",\n      \"pmids\": [\"33711344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ISCA1 (ISCU2) directly donates [2Fe-2S] clusters to NFU1; ISCA1 interacts with NFU1 at a conserved hydrophobic patch on the C-terminal alpha-helix of NFU1, and mutagenesis of this interface abolished NFU1's ability to acquire its Fe-S cluster and impaired downstream lipoylation of pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and glycine cleavage complex components.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis of NFU1 interaction surface, biochemical Fe-S cluster transfer assays, lipoylation assays in HEK293 cells\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus mutagenesis and functional readout, single lab\",\n      \"pmids\": [\"32776106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Yeast Isa1p is targeted to the mitochondrial matrix; three invariant cysteine residues in Isa1p (and Isa2p) are essential for function and may be involved in iron binding; isa1Δ mutants showed elevated mitochondrial iron, reduced aconitase and succinate dehydrogenase activities, and dependency on lysine and glutamate, consistent with a role in Fe-S cluster assembly.\",\n      \"method\": \"Genetic disruption of ISA1/ISA2 in S. cerevisiae, mitochondrial fractionation/import assays, enzyme activity assays, site-directed mutagenesis of cysteine residues, iron measurement\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (fractionation, mutagenesis, enzyme assays, iron measurement), replicated findings consistent across paralogs\",\n      \"pmids\": [\"10805735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Human ISCA1 (hIscA1) binds mononuclear iron with an association constant of ~2×10^19 M⁻¹; iron-bound hIscA1 can donate iron to the IscU scaffold protein for in vitro Fe-S cluster assembly; hIscA1 partially complements an E. coli iscA deletion for aerobic growth on minimal medium.\",\n      \"method\": \"UV-visible absorption and EPR spectroscopy, iron-binding constant determination, in vitro Fe-S cluster assembly assay with IscU, E. coli complementation\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical reconstitution with spectroscopic validation and complementation, single lab\",\n      \"pmids\": [\"20302570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"S. pombe Isa1 is a multimeric protein carrying [2Fe-2S]²⁺ clusters as characterized by Mössbauer and optical spectroscopy; it forms a complex with a redox-active ferredoxin identified by crosslinking; site-directed mutagenesis of coordinating residues altered cluster coordination and stability.\",\n      \"method\": \"Protein purification, Mössbauer spectroscopy, UV-visible spectroscopy, chemical crosslinking, site-directed mutagenesis\",\n      \"journal\": \"Journal of biological inorganic chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro spectroscopic characterization with mutagenesis validation, single lab study on fission yeast ortholog\",\n      \"pmids\": [\"11941510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Human ISCA1 is present in both cytosolic and mitochondrial fractions of HeLa cells; siRNA knockdown decreased activities of mitochondrial Fe-S enzymes (succinate dehydrogenase, mitochondrial aconitase) and also cytosolic aconitase; ISCA1 physically interacts with IOP1/NARFL, a cytosolic protein involved in cytosolic Fe-S protein assembly.\",\n      \"method\": \"siRNA knockdown in HeLa cells, subcellular fractionation, enzyme activity assays, co-immunoprecipitation with IOP1/NARFL\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus knockdown with functional readout, single lab; cytosolic localization conclusion contradicted by later more rigorous study (PMID:22323289)\",\n      \"pmids\": [\"19864422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In S. pombe, Grx5 (monothiol glutaredoxin) interacts in vivo with Isa1 and Isa2 proteins in mitochondria; overexpression of isa1⁺ or isa2⁺ suppressed growth defects of Δgrx5 mutants and partly restored Fe-S enzyme activities, placing Grx5 upstream of or parallel to Isa1/Isa2 in the Fe-S assembly pathway.\",\n      \"method\": \"Bimolecular fluorescence complementation (BiFC) for in vivo interaction, multi-copy suppressor screen, genetic epistasis, enzyme activity assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — BiFC interaction plus genetic epistasis and enzyme activity, single lab\",\n      \"pmids\": [\"20085751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In S. cerevisiae, Isa1 and Isa2 are required for the in vivo catalytic function of biotin synthase (Bio2) but not for de novo assembly of its [4Fe-4S] or [2Fe-2S] clusters; de novo Fe-S cluster assembly on Bio2 depended on Isu1/Isu2 scaffold proteins.\",\n      \"method\": \"Genetic screen, isa1/isa2 deletion analysis, biotin utilization assays, Bio2 overexpression complementation, Fe-S cluster assembly assays in yeast\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic dissection with functional enzymatic readouts and overexpression controls, single lab\",\n      \"pmids\": [\"17259550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Human ISCA1 (hIscA) localizes to mitochondria and can functionally complement an isa1Δ null mutant in S. cerevisiae, demonstrating conserved function in Fe-S cluster biogenesis.\",\n      \"method\": \"Yeast functional complementation, subcellular localization by mitochondrial targeting signal analysis and expression studies\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional complementation in yeast is a direct assay but single lab with limited mechanistic depth\",\n      \"pmids\": [\"15262227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A homozygous ISCA1 p.V10G mutation located in the uncleaved presequence severely impaired mitochondrial import and stability of ISCA1; RNAi knockdown of ISCA1 in HeLa cells impaired [4Fe-4S] protein biogenesis and was rescued by wild-type ISCA1 but only partially by the p.V10G mutant; patient fibroblasts showed defects in [4Fe-4S]-dependent respiratory complexes and lipoic acid synthesis.\",\n      \"method\": \"Targeted MitoExome sequencing, RNAi rescue experiments in HeLa cells, mitochondrial import assays, [4Fe-4S] enzyme activity assays, patient fibroblast biochemistry\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional rescue with wild-type vs mutant plus import assays and enzyme activity, single lab\",\n      \"pmids\": [\"29767723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ISCA1 p.(Tyr101Cys) mutation decreased stability of the [2Fe-2S] cluster in purified recombinant human ISCA1 protein, establishing that the mutation directly destabilizes the iron-sulfur cluster on the protein; patient fibroblasts showed impaired lipoic acid synthesis and decreased activities of respiratory chain complexes I and II.\",\n      \"method\": \"Recombinant protein expression and purification, spectroscopic analysis of [2Fe-2S] cluster stability, patient fibroblast biochemistry\",\n      \"journal\": \"Mitochondrion\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro biochemical characterization of mutant protein cluster stability, single lab, limited mechanistic depth beyond cluster destabilization\",\n      \"pmids\": [\"32092383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Human ISCA1, ISCA2, and ISCU proteins have strong copper-binding activity that inhibits iron-sulfur cluster assembly; excess copper (in Wilson's disease models including ATP7A⁻/⁻ lymphocytes and ATP7B knockdown cells and mouse model) suppressed Fe-S cluster assembly, decreased Fe-S enzyme activity, and disrupted mitochondrial function.\",\n      \"method\": \"Copper-binding assays with purified proteins, Fe-S enzyme activity assays in cell lines and mouse models, Wilson's disease mouse model (ATP7A⁻/⁻), siRNA knockdown of ATP7B\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct copper-binding assays with ISCA1 protein plus in vivo functional assays in multiple model systems, single lab\",\n      \"pmids\": [\"37225108\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ISCA1 knockout in rats caused early embryonic death at E8.5 with significant decrease in NDUFA9 (respiratory complex I subunit) protein and increase in aconitase 2 (ACO2), indicating ISCA1 is essential for respiratory chain complex integrity in vivo.\",\n      \"method\": \"CRISPR-Cas9 knockout rat generation, embryo morphology analysis, Western blot for mitochondrial proteins, fluorescence imaging using ISCA1 promoter-driven reporter\",\n      \"journal\": \"Animal models and experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean KO with specific protein-level readouts, single lab, limited mechanistic depth\",\n      \"pmids\": [\"31016283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Neuron-specific Isca1 knockout rats developed epilepsy, memory impairment, massive neuronal death, mitochondrial fragmentation and cristae fracture, reduced respiratory chain complex protein content, and decreased ATP production; neuronal death occurred via oncosis.\",\n      \"method\": \"Conditional CRISPR-Cas9 knockout (Isca1flox/flox-NeuN-Cre), MRI, behavioral tests, electron microscopy, Western blot for respiratory chain complexes, ATP assay, immunofluorescence\",\n      \"journal\": \"Animal models and experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with multiple functional readouts (behavior, ultrastructure, biochemistry), single lab\",\n      \"pmids\": [\"37140997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"TbIsa1 and TbIsa2 in Trypanosoma brucei are required for Fe-S cluster assembly in mitochondrial aconitase, fumarase, and succinate dehydrogenase in the procyclic (active mitochondrion) form; their depletion did not affect cytosolic Fe-S proteins; human Isa orthologues partially rescued single TbIsa knockdowns, restoring aconitase and fumarase activities.\",\n      \"method\": \"RNAi knockdown in T. brucei, enzyme activity assays, heterologous rescue with human ISCA1/ISCA2, ROS measurement\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockdown with enzymatic readouts and cross-species rescue, single lab\",\n      \"pmids\": [\"21790804\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ISCA1 is a mitochondrial iron-sulfur cluster assembly protein that, together with ISCA2 and IBA57, forms a late-acting ISC subsystem specifically dedicated to synthesizing [4Fe-4S] clusters: GLRX5 donates [2Fe-2S] clusters to the ISCA1-ISCA2 complex, FDX2-derived electrons catalyze reductive fusion of two [2Fe-2S] clusters into a [4Fe-4S] cluster on ISCA1-ISCA2 in an IBA57-dependent manner, and ISCA1 then acts as the central scaffold that bridges ISCA2 and NFU1 in a transient ternary complex to transfer the [4Fe-4S] cluster to NFU1 for delivery to downstream apo-proteins such as lipoic acid synthase and respiratory complex I subunits; ISCA1 also binds iron via conserved cysteine residues essential for function, and its deficiency causes loss of [4Fe-4S] enzyme activities, mitochondrial morphological collapse, and early embryonic lethality in vivo.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ISCA1 is a mitochondrial matrix protein that functions in a late-acting branch of the iron-sulfur cluster (ISC) assembly machinery specifically dedicated to maturing [4Fe-4S] proteins such as aconitase, respiratory complex I subunits, and lipoic acid synthase, while being dispensable for [2Fe-2S] protein maturation [#0, #1, #5]. Together with ISCA2 and IBA57, ISCA1 forms a complex that catalyzes the reductive fusion of two [2Fe-2S] clusters into a single [4Fe-4S] cluster: GLRX5 donates [2Fe-2S] clusters to ISCA1-ISCA2, and electrons supplied by FDX2 (not FDX1) drive fusion in an IBA57-dependent manner [#2, #9]. ISCA1 then serves as the central scaffold of cluster handoff, bridging ISCA2 and NFU1 in a transient ternary complex and transferring the assembled cluster to a binding site formed jointly by ISCA1 and the NFU1 C-terminal domain, enabling downstream lipoylation of pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and the glycine cleavage system [#3, #4]. The protein binds iron with high affinity through conserved cysteine residues essential for function and harbors clusters whose stability depends on coordinating residues [#5, #6, #7]. Copper binds ISCA1 and inhibits Fe-S cluster assembly, linking ISCA1 dysfunction to copper-overload pathology [#14]. ISCA1 deficiency causes loss of [4Fe-4S] enzyme activities, mitochondrial cristae collapse, and is essential for viability, with knockout causing early embryonic lethality and neuron-specific loss producing neurodegeneration in vivo [#0, #15, #16]; a homozygous presequence mutation impairing mitochondrial import causes a multiple mitochondrial dysfunctions syndrome in patients [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that the Isa proteins reside in the mitochondrial matrix and that conserved cysteines are functionally essential, defining the protein's compartment and putative metal-binding residues.\",\n      \"evidence\": \"Genetic disruption, import/fractionation, cysteine mutagenesis and iron measurement in S. cerevisiae\",\n      \"pmids\": [\"10805735\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether cysteines coordinate iron directly versus a cluster\", \"Specific [4Fe-4S] vs [2Fe-2S] role not yet distinguished\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Showed that Isa1 itself carries [2Fe-2S] clusters and partners with a redox-active ferredoxin, providing the first spectroscopic evidence of a cluster-bearing, redox-coupled protein.\",\n      \"evidence\": \"Mössbauer/UV-vis spectroscopy, crosslinking and mutagenesis on S. pombe Isa1\",\n      \"pmids\": [\"11941510\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of the ferredoxin partnership not defined\", \"Cluster role as substrate versus product unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrated functional conservation of human ISCA1 by complementation of yeast isa1 deletion, validating model-organism findings for the human protein.\",\n      \"evidence\": \"Yeast functional complementation and targeting-signal analysis\",\n      \"pmids\": [\"15262227\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mechanistic detail on human protein activity\", \"Did not address substrate specificity\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Distinguished Isa-dependent maturation from the upstream Isu scaffold, showing Isa proteins are needed for catalytic competence of [4Fe-4S] enzymes rather than de novo cluster assembly per se.\",\n      \"evidence\": \"Genetic dissection of biotin synthase maturation in S. cerevisiae\",\n      \"pmids\": [\"17259550\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular step catalyzed by Isa proteins not defined\", \"Did not explain how clusters reach Bio2\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined high-affinity mononuclear iron binding by human ISCA1 and its capacity to donate iron to the IscU scaffold, framing an iron-carrier role.\",\n      \"evidence\": \"Spectroscopy, iron-binding constant determination, in vitro assembly with IscU and E. coli complementation\",\n      \"pmids\": [\"20302570\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Iron-donor model later superseded by cluster-transfer model\", \"Physiological relevance of mononuclear iron binding unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Placed monothiol glutaredoxin Grx5 in interaction with Isa1/Isa2 and upstream/parallel in the pathway, foreshadowing GLRX5 as the cluster donor.\",\n      \"evidence\": \"BiFC, multi-copy suppressor and epistasis analysis in S. pombe\",\n      \"pmids\": [\"20085751\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direction of cluster transfer not biochemically resolved\", \"Nature of transferred species undefined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Established the [4Fe-4S]-specific function of the Isa1-Isa2-Iba57 module and demonstrated in vivo iron binding requisite for de novo [4Fe-4S] synthesis, with Iba57 as a specific interactor.\",\n      \"evidence\": \"Yeast genetics, reciprocal Co-IP, iron-binding assays and ferredoxin reporters\",\n      \"pmids\": [\"21987576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not reconstitute the fusion reaction in vitro\", \"Electron source for fusion not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended Isa-dependent [4Fe-4S] maturation to trypanosomes and confirmed cross-species functional conservation of human orthologues.\",\n      \"evidence\": \"RNAi, enzyme assays and heterologous human rescue in T. brucei\",\n      \"pmids\": [\"21790804\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural or biochemical mechanism\", \"Cytosolic involvement excluded but not mechanistically explored\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"In human cells, rigorously assigned ISCA1/ISCA2/IBA57 to mitochondrial [4Fe-4S] (not [2Fe-2S]) maturation and tied deficiency to cristae-devoid swollen mitochondria, refuting a cytosolic maturation role.\",\n      \"evidence\": \"RNAi, enzyme activity panels, EM morphology and fractionation in HeLa cells\",\n      \"pmids\": [\"22323289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the biochemical reaction catalyzed\", \"Order of factor action not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked ISCA1 to human mitochondrial disease via a presequence mutation impairing import and [4Fe-4S] biogenesis, establishing causality through rescue.\",\n      \"evidence\": \"MitoExome sequencing, RNAi rescue with WT vs mutant, import assays and patient fibroblast biochemistry\",\n      \"pmids\": [\"29767723\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single mutation locus\", \"Did not address neurological phenotype mechanism\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed ISCA1 is essential for embryonic viability and respiratory complex integrity in a mammalian whole-organism model.\",\n      \"evidence\": \"CRISPR knockout rat, embryo morphology and Western blot for complex I subunit\",\n      \"pmids\": [\"31016283\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Lethality precludes tissue-level mechanism\", \"Did not dissect cause of ACO2 increase\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Reconstituted the complete [4Fe-4S] synthesis reaction in vitro, defining GLRX5 as cluster donor and FDX2-derived electrons as the driver of IBA57-dependent reductive fusion on ISCA1-ISCA2.\",\n      \"evidence\": \"Defined-component in vitro reconstitution with EPR/Mössbauer and FDX1-vs-FDX2 controls\",\n      \"pmids\": [\"32817474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the cluster handoff to downstream carriers\", \"Structural basis of fusion not solved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mapped a direct ISCA1-NFU1 interface required for NFU1 cluster acquisition and downstream lipoylation, identifying the next acceptor in the pathway.\",\n      \"evidence\": \"Co-IP, interface mutagenesis, transfer assays and lipoylation readouts in HEK293\",\n      \"pmids\": [\"32776106\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Cluster nuclearity transferred to NFU1 described differently across studies\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided patient and biochemical evidence that an ISCA1 missense mutation destabilizes its bound cluster, connecting cluster instability to respiratory and lipoylation defects.\",\n      \"evidence\": \"Recombinant protein cluster-stability spectroscopy and patient fibroblast biochemistry\",\n      \"pmids\": [\"32092383\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism limited to cluster destabilization\", \"Effect on assembly reaction not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined ISCA1 as the central scaffold bridging ISCA2 and NFU1 in a transient ternary complex that drives [4Fe-4S] transfer to a shared ISCA1-NFU1 site, resolving the cluster-handoff architecture.\",\n      \"evidence\": \"NMR interaction mapping and [4Fe-4S] cluster transfer assays\",\n      \"pmids\": [\"33711344\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution complex structure\", \"Kinetics of in vivo handoff not measured\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed copper binding to ISCA1 (and ISCA2/ISCU) as an inhibitory mechanism, linking copper overload to suppressed Fe-S assembly and mitochondrial dysfunction.\",\n      \"evidence\": \"Copper-binding assays, Fe-S enzyme activity in Wilson's disease models and ATP7B knockdown\",\n      \"pmids\": [\"37225108\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Copper-binding site on ISCA1 not mapped\", \"Whether copper competes at the iron site unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established that neuronal ISCA1 loss causes epilepsy, neurodegeneration, mitochondrial fragmentation and energy failure, tying [4Fe-4S] biogenesis defects to brain pathology.\",\n      \"evidence\": \"Conditional neuron-specific CRISPR knockout rat with behavior, EM, biochemistry and ATP assays\",\n      \"pmids\": [\"37140997\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of oncotic neuronal death not detailed\", \"Cell-autonomy versus circuit effects not separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of the ISCA1-ISCA2-IBA57 fusion machine and of the ISCA1-ISCA2-NFU1 transfer complex remains undetermined, leaving the atomic mechanism of reductive cluster fusion and directional handoff open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental structure of the assembly or transfer complexes\", \"Copper inhibition site and competition with iron unmapped\", \"Kinetic ordering of GLRX5 donation, fusion and NFU1 handoff not measured in a single system\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3, 4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 5, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 16]}\n    ],\n    \"complexes\": [\"ISCA1-ISCA2-IBA57 complex\", \"ISCA1-ISCA2-NFU1 ternary complex\"],\n    \"partners\": [\"ISCA2\", \"IBA57\", \"NFU1\", \"GLRX5\", \"FDX2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}