{"gene":"NFS1","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":1993,"finding":"NifS (NFS1 ortholog) is a pyridoxal phosphate-containing homodimer that catalyzes the formation of L-alanine and elemental sulfur from L-cysteine; activity is abolished by thiol-specific alkylating reagents, implicating an active-site cysteinyl thiolate; proposed to supply inorganic sulfide for nitrogenase metallocluster (Fe-S cluster) biosynthesis.","method":"In vitro enzyme assay, chemical modification with thiol-specific alkylating reagents, pyridoxal phosphate cofactor identification","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro biochemical reconstitution with cofactor identification and active-site chemical modification; foundational mechanistic study replicated by multiple subsequent labs","pmids":["8464885"],"is_preprint":false},{"year":1994,"finding":"The catalytic mechanism of NifS (NFS1 ortholog) involves: (1) nucleophilic attack by active-site Cys325 on a PLP-bound cysteine substrate, (2) formation of an enzyme-bound cysteinyl persulfide intermediate, and (3) generation of an enamine intermediate yielding L-alanine; Cys325 identified as the essential catalytic residue by site-directed mutagenesis and specific alkylation.","method":"Substrate analog inhibition (L-allylglycine, vinylglycine), site-directed mutagenesis of Cys325, in vitro enzyme assays, identification of persulfide intermediate","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis and intermediate trapping; defines catalytic mechanism at residue level","pmids":["8161529"],"is_preprint":false},{"year":1998,"finding":"Human NFS1 is synthesized from a single transcript as different isoforms that localize either to mitochondria or to the cytosol/nucleus through initiation at alternative in-frame AUGs; isoform selection varies with cytosolic pH, providing a mechanism for redistribution of NFS1 between compartments in response to metabolic changes.","method":"cDNA cloning, subcellular fractionation, alternative AUG mapping, pH manipulation experiments","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct subcellular fractionation with functional localization linked to alternative AUG utilization; single lab but multiple orthogonal approaches","pmids":["9885568"],"is_preprint":false},{"year":2000,"finding":"NifS directs assembly of a transient [2Fe-2S] cluster on the scaffold protein NifU in vitro when incubated with ferric ion and L-cysteine; NifU interacts physically with NifS; the transient cluster is labile and rapidly released upon reduction, supporting a model where NifS-assembled clusters on NifU are transferred to nitrogenase component proteins.","method":"In vitro Fe-S cluster assembly assay, UV-vis and EPR spectroscopy, protein interaction studies","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with spectroscopic characterization of cluster intermediate; foundational study","pmids":["10639125"],"is_preprint":false},{"year":2001,"finding":"E. coli IscS (NFS1 ortholog) directly transfers persulfide sulfur to the scaffold protein IscU via a high-affinity protein-protein interaction (Kd ~2 µM); transfer requires cysteinyl residues of IscU and is inhibited by iodoacetamide treatment of IscU; the C-terminal region of IscS (residues 376-413) is important for IscU binding and efficient sulfur transfer.","method":"35S-cysteine radiotracer sulfur transfer assay, surface plasmon resonance, isothermal titration calorimetry, IscS C-terminal deletion mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct sulfur transfer assay combined with binding measurements and mutagenesis; multiple orthogonal methods","pmids":["11577100"],"is_preprint":false},{"year":1999,"finding":"IscS is required for the biosynthesis of 4-thiouridine (s4U) in tRNA, thiamine (specifically the thiazole moiety), and NAD in E. coli; IscS mobilizes sulfur for transfer to ThiS (the direct sulfur donor in thiazole biosynthesis), with ThiI stimulating the IscS-to-ThiS sulfur transfer ~7-fold; neither of the other two nifS-like E. coli genes can complement iscS deletion.","method":"iscS deletion mutant phenotypic analysis, in vitro reconstitution of ThiS thiocarboxylate synthesis, genetic complementation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro reconstitution of sulfur transfer pathway combined with in vivo genetic deletion and complementation; replicated in multiple subsequent studies","pmids":["10781607"],"is_preprint":false},{"year":1999,"finding":"IscS acts as a tRNA sulfurtransferase for 4-thiouridine biosynthesis; purified IscS catalyzes sulfur transfer from cysteine to tRNA in vitro; among E. coli proteins with cysteine desulfurase activity, only IscS can mobilize sulfur for tRNA thiolation.","method":"Protein purification, in vitro tRNA thiolation assay, HPLC nucleoside analysis, N-terminal sequencing","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with chemical product identification; single lab but orthogonal methods","pmids":["10600118"],"is_preprint":false},{"year":2000,"finding":"IscS transfers sulfane sulfur (persulfide) sequentially to ThiI, which then transfers it to tRNA during 4-thiouridine biosynthesis; ThiI contains a reactive cysteine required for catalysis/binding protected by ATP and tRNA; IscS-generated persulfide is the direct sulfur source for ThiI.","method":"Fluorescent alkylating agent inhibition of ThiI, gel shift and protease protection assays, in vitro sulfur transfer reconstitution","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of sequential sulfur relay with biochemical intermediate trapping; single lab with multiple orthogonal methods","pmids":["10753862"],"is_preprint":false},{"year":2003,"finding":"Crystal structure of E. coli IscS (NFS1 ortholog) solved at 2.1 Å; the catalytic Cys328 resides on a flexible surface loop >17 Å from the PLP cofactor, requiring a large conformational change for catalysis; structural modeling suggests loop rotation brings Cys328 to ~3 Å of PLP cofactor.","method":"X-ray crystallography at 2.1 Å resolution","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — atomic-resolution crystal structure providing mechanistic insight into catalytic loop flexibility; single lab but definitive structural method","pmids":["12860127"],"is_preprint":false},{"year":2003,"finding":"Frataxin ortholog Yfh1 specifically binds to the core ISC assembly complex composed of scaffold protein Isu1 and cysteine desulfurase Nfs1; binding is markedly increased by ferrous iron; Yfh1 is involved in de novo Fe-S cluster synthesis on Isu1, suggesting frataxin provides iron to the Isu scaffold.","method":"Co-immunoprecipitation, in vivo functional analysis of ISC synthesis on Isu1, iron-dependence assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP with functional validation in vivo; single lab with multiple methods","pmids":["12947415"],"is_preprint":false},{"year":2003,"finding":"MnmA and IscS are both required for in vitro 2-thiouridine (s2U) biosynthesis in E. coli tRNA; IscS-generated persulfide can provide sulfur for s2U synthesis in the absence of free cysteine; MnmA binds tRNA substrates with low micromolar affinity and requires ATP.","method":"In vitro s2U biosynthesis reconstitution with purified components, 35S radiotracer, HPLC analysis, gel mobility shift","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with defined components and product identification; single lab with multiple orthogonal methods","pmids":["12549933"],"is_preprint":false},{"year":2005,"finding":"Isd11 forms a stable complex with Nfs1 in mitochondria; in the absence of Isd11, Nfs1 is prone to aggregation; Isd11 depletion causes strong reduction in Fe-S protein activities (aconitase, succinate dehydrogenase, Rieske protein); Isd11 acts with Nfs1 in an early step of Fe-S cluster biogenesis.","method":"Yeast genetics (Isd11 depletion), enzyme activity assays, co-immunoprecipitation, protein stability assessment","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — protein interaction plus functional loss-of-function with multiple Fe-S enzyme activity readouts; replicated by multiple subsequent labs","pmids":["16341090"],"is_preprint":false},{"year":2006,"finding":"Human Nfs1 (huNfs1) is located predominantly in mitochondria with small amounts in cytosol/nucleus; siRNA depletion of huNfs1 in HeLa cells strongly impairs both mitochondrial and cytosolic Fe-S protein activities and causes growth retardation and mitochondrial morphology changes; Nfs1 must be inside mitochondria to support Fe-S protein maturation—cytosolic Nfs1 lacking the mitochondrial presequence cannot complement.","method":"siRNA knockdown, enzyme activity assays for mitochondrial and cytosolic Fe-S proteins, subcellular fractionation, complementation with presequence-deleted Nfs1","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — siRNA depletion with multiple Fe-S enzyme activity readouts and localization-function dissection; single lab but multiple orthogonal approaches","pmids":["16847322"],"is_preprint":false},{"year":2006,"finding":"Depletion of mammalian m-Nfs1 by siRNA in cultured fibroblasts significantly inhibits activities of mitochondrial respiratory chain complexes I and II, mitochondrial aconitase, cytosolic xanthine oxidase (a [2Fe-2S] enzyme), and converts IRP-1 from its [4Fe-4S] aconitase form to its RNA-binding form; cytosolic Fe-S activities are affected earlier than mitochondrial activities.","method":"siRNA gene silencing, enzyme activity assays, IRP-1 RNA-binding assay, ferritin mRNA regulation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — loss-of-function with multiple Fe-S enzyme readouts across compartments; single lab with multiple orthogonal methods","pmids":["16787928"],"is_preprint":false},{"year":2008,"finding":"Human NFS1 (purified with Isd11) interacts specifically with the rhodanese-like domain (RLD) of MOCS3, a cytosolic protein involved in molybdenum cofactor biosynthesis; sulfur is transferred from L-cysteine to MOCS3-RLD via an NFS1-bound persulfide intermediate; cytosolic NFS1 acts as sulfur donor for Moco biosynthesis.","method":"Protein-protein interaction studies, in vitro sulfur transfer assay, kinetic parameter determination","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct protein interaction combined with in vitro sulfur transfer reconstitution via persulfide intermediate; single lab with multiple methods","pmids":["18650437"],"is_preprint":false},{"year":2009,"finding":"Yeast Nfs1 undergoes dual targeting to mitochondria and nucleus from a single translation product; the minor nuclear/cytosolic subpopulation arises via partial mitochondrial entry followed by retrograde translocation; mitochondrial processing peptidase cleaves Nfs1, and the novel processing enzyme Icp55 subsequently removes three additional N-terminal amino acids.","method":"Alpha-complementation assay, subcellular fractionation, Edman degradation of N-terminal sequence, discovery of Icp55 protease","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct fractionation and N-terminal sequencing identifying novel processing enzyme; single lab with multiple methods in yeast","pmids":["19720832"],"is_preprint":false},{"year":2009,"finding":"Bacterial frataxin CyaY acts as an iron-dependent inhibitor of Fe-S cluster formation by binding to the desulfurase IscS; the interaction involves the iron-binding surface of CyaY; CyaY acts as an iron sensor/regulator that fine-tunes Fe-S cluster formation.","method":"Biochemical and biophysical interaction studies, in vitro Fe-S cluster assembly assays","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple biophysical methods demonstrating inhibitory mechanism with defined binding site; single lab with rigorous controls","pmids":["19305405"],"is_preprint":false},{"year":2010,"finding":"Crystal structures of IscS-IscU and IscS-TusA complexes reveal that IscS interacts with multiple partner proteins through an extensive surface area centered on catalytic Cys328; partner proteins approach Cys328 from different directions; the conformational plasticity of the active-site loop containing Cys328 is essential for sulfur transfer to multiple acceptors; sulfur acceptors (IscU, TusA) bind IscS one at a time (mutually exclusive), while frataxin/CyaY and IscX can form ternary complexes with IscU and IscS.","method":"X-ray crystallography of IscS-IscU and IscS-TusA complexes, exhaustive IscS surface mutagenesis, biochemical binding and activity assays","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures of two distinct complexes with comprehensive mutagenesis and biochemical validation; multiple orthogonal methods in one rigorous study","pmids":["20404999"],"is_preprint":false},{"year":2011,"finding":"Mammalian frataxin interacts with the preformed ISCU/NFS1/ISD11 core Fe-S assembly complex (not individual components); the quaternary complex has a molecular mass of ~190 kDa; the mature FXN(81-210) form is the essential functional form in vivo.","method":"Co-immunoprecipitation from mammalian cells, heterologous expression system, molecular mass determination, in vivo complementation","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP combined with in vivo functional validation; single lab with multiple orthogonal approaches","pmids":["21298097"],"is_preprint":false},{"year":2013,"finding":"Human NFS1 (cysteine desulfurase) binds preferentially to the disordered (D-state) conformation of ISCU scaffold protein; ISD11 does not interact directly with ISCU but the NFS1-ISD11 complex also binds the D-state of ISCU; in vitro Fe-S cluster assembly on ISCU is catalyzed by NFS1 alone and at higher rate by the NFS1-ISD11 complex.","method":"NMR spectroscopy, ISCU conformational state variants (D39V, N90A, D39A, H105A), in vitro Fe-S cluster assembly assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structural/interaction analysis combined with in vitro activity assay; single lab with multiple orthogonal methods","pmids":["23940031"],"is_preprint":false},{"year":2013,"finding":"Binding of Jac1 (J-protein co-chaperone) and Nfs1 to the scaffold protein Isu is mutually exclusive; both proteins require the same hydrophobic patch on Isu surface; Jac1 and Nfs1 compete for Isu binding in vitro; competition between Jac1 and Nfs1 for Isu is proposed to transition the machinery from cluster assembly to Hsp70-mediated cluster transfer.","method":"In vitro binding assays with purified proteins, competition assays, Isu hydrophobic patch mutagenesis, in vivo functional validation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vitro competition assays with mutagenesis and in vivo validation; single lab with multiple orthogonal methods","pmids":["23946486"],"is_preprint":false},{"year":2013,"finding":"NFS1 physical interaction (not enzymatic activity) with Isu protects Isu from degradation by the Pim1/Lon protease; when Fe-S cluster biogenesis is disrupted, increased Isu stability depends on its interaction with Nfs1.","method":"Yeast genetics, Pim1 protease identification, protein stability assays under various conditions including Nfs1 enzymatic mutants","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and biochemical dissection of interaction vs. enzymatic activity; single lab with multiple conditions","pmids":["22689995"],"is_preprint":false},{"year":2013,"finding":"Cytosolic NFS1 colocalizes and interacts with MOCS3 in the cytosol of human cells; NFS1 localization in cytosol confirmed by FRET, split-EGFP, immunodetection of fractionated cells, and confocal microscopy; purified NFS1 can reconstitute molybdoenzyme activity in Neurospora crassa nit-1 mutant.","method":"FRET, split-EGFP, immunofluorescence/confocal microscopy, cell fractionation, in vitro molybdoenzyme reconstitution","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal localization methods plus functional reconstitution; single lab","pmids":["23593335"],"is_preprint":false},{"year":2015,"finding":"Mammalian frataxin directly enhances the rate of sulfur transfer from NFS1 persulfide to both ISCU (accumulating a persulfide on ISCU Cys104) and to small free thiols (DTT, L-cysteine, GSH); frataxin acts as an enhancer of sulfur transfer within the NFS1-ISD11-ISCU complex rather than primarily as an iron donor.","method":"Maleimide-peptide trapping of cysteine-persulfide intermediates combined with mass spectrometry, in vitro sulfur transfer kinetics","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct persulfide intermediate trapping by mass spectrometry with kinetic analysis; single lab with orthogonal chemical biology and MS methods","pmids":["25597503"],"is_preprint":false},{"year":2017,"finding":"NFS1 activity is critical for maintaining Fe-S cofactors in multiple cell-essential proteins under high oxygen conditions; NFS1 suppression activates the iron-starvation response and, in combination with inhibition of glutathione biosynthesis, triggers ferroptosis; NFS1 is amplified in lung adenocarcinoma and protects against ferroptosis under high-oxygen tension.","method":"RNA interference loss-of-function screening, in vivo tumor growth experiments, genetic cooperation assays (NFS1 suppression + cysteine transport inhibition), iron-starvation response measurements","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function in multiple in vivo and in vitro systems with defined molecular phenotypes (Fe-S cofactor loss, iron-starvation response, ferroptosis); multiple labs cite and replicate","pmids":["29168506"],"is_preprint":false},{"year":2013,"finding":"Ferredoxin (Fdx) competes with frataxin CyaY for binding to the desulfurase IscS; Fdx binds in a cavity close to the enzyme active site overlapping the CyaY binding site; in vivo mutagenesis confirms importance of this interaction surface for Fe-S cluster formation.","method":"Biophysical characterization (SAXS, NMR, other), mutagenesis, in vivo complementation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biophysical methods with in vivo validation; single lab","pmids":["23839945"],"is_preprint":false},{"year":2015,"finding":"Ferredoxin (Fdx), together with NADPH and ferredoxin-NADP reductase, transfers electrons to the IscS/IscU complex to promote Fe-S cluster assembly; this electron transfer trio is sufficient to sustain in vitro Fe-S cluster assembly; Fdx does not interfere with CyaY inhibitory activity despite overlapping binding sites on IscS.","method":"In vitro Fe-S cluster assembly assay using physiological electron transfer chain (NADPH/FNR/Fdx), comparison with DTT-mediated assembly","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with physiological electron donor system; single lab","pmids":["25688831"],"is_preprint":false},{"year":2022,"finding":"During FeS cluster biogenesis in yeast, ferredoxin (Yah1) and frataxin (Yfh1) share an evolutionarily conserved interaction site on Nfs1; Yah1 and Yfh1 can each displace the other from Nfs1, demonstrating mutually exclusive binding; this binding mode mirrors bacterial CyaY/Fdx competition at IscS.","method":"In vitro competition assays with purified WT and variant Nfs1/Yah1/Yfh1 proteins, biochemical binding assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro competition assays with mutagenesis; single lab","pmids":["35026224"],"is_preprint":false},{"year":2013,"finding":"NFS1 deficiency (c.215G>A, p.Arg72Gln mutation) identified as causative for infantile mitochondrial complex II/III deficiency, establishing that loss of NFS1 cysteine desulfurase activity impairs respiratory chain function in humans.","method":"Autozygosity mapping, exome sequencing, in silico analyses, population studies, functional tests","journal":"Molecular genetics & genomic medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human disease mutation with functional validation; single study","pmids":["24498631"],"is_preprint":false},{"year":2015,"finding":"ISD11 residues in helix 1 (Phe-40), helix 3 (Leu-63, Arg-68, Gln-69, Ile-72, Tyr-76), and C-terminal segment (Leu-81, Glu-84) are critical for interaction with NFS1; mutation of these residues compromises ISD11-NFS1 complex stability, causing NFS1 aggregation and reduced Fe-S cluster biosynthesis; the COXPD19-associated ISD11 R68L mutation reduces affinity for NFS1 and causes mitochondrial dysfunction.","method":"Site-directed mutagenesis of ISD11, co-immunoprecipitation, enzyme activity assays (ETC complexes), mitochondrial iron/ROS measurements","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis with functional and interaction assays; single lab","pmids":["26342079"],"is_preprint":false},{"year":2017,"finding":"The first 10 N-terminal amino acids of ISD11, including the conserved 'LYR' motif, are indispensable for NFS1 activity and formation of a stable, active NFS1-ISD11 complex; the N-terminus of ISD11 also contains its mitochondrial targeting sequence.","method":"In vitro purified protein interaction studies, in vivo cellular complementation, mutagenesis of ISD11 N-terminus","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — combination of in vitro and in vivo studies; single lab","pmids":["28271877"],"is_preprint":false},{"year":2022,"finding":"Oxaliplatin-induced oxidative stress enhances phosphorylation of NFS1 at serine residue S293; phosphorylation at S293 prevents PANoptosis (apoptosis, necroptosis, pyroptosis, ferroptosis) in colorectal cancer cells; NFS1 transcription is regulated by MYC; NFS1 deficiency combined with oxaliplatin triggers PANoptosis by increasing intracellular ROS.","method":"CRISPR-Cas9 metabolic enzyme screen in vivo, site-directed mutagenesis of S293, in vitro and in vivo functional assays, ROS measurement, phosphorylation site identification","journal":"Signal transduction and targeted therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR screen combined with mutagenesis and functional validation; single lab","pmids":["35221331"],"is_preprint":false},{"year":2022,"finding":"Eprenetapopt (APR-246) inhibits the cysteine desulfurase activity of NFS1, limiting Fe-S cluster biogenesis and potentiating ferroptosis; this effect is independent of its reported mutant-p53 reactivation activity.","method":"Unbiased genetic screen, glutathione turnover assays, NFS1 cysteine desulfurase activity assay, ferroptosis cell death assays","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — unbiased genetic approach plus biochemical NFS1 activity assay; single lab","pmids":["36103522"],"is_preprint":false},{"year":2023,"finding":"OPA3 (mitochondrial membrane protein) interacts with NFS1 and regulates ferroptosis; DOX promotes OPA3 ubiquitination and downregulates NFS1; H2S antagonizes OPA3 ubiquitination via S-sulfhydration, restoring NFS1 expression and inhibiting ferroptosis; NFS1 deficiency increases cardiomyocyte susceptibility to ferroptosis.","method":"Co-immunoprecipitation (OPA3-NFS1 interaction), overexpression/knockdown in cardiomyocytes, in vivo DOX cardiotoxicity model, ubiquitination and S-sulfhydration assays","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP interaction plus functional in vivo/in vitro assays; single lab","pmids":["36924813"],"is_preprint":false},{"year":2025,"finding":"Nuclear YAP and YY1 interact and bind to the NFS1 promoter, mediating transcriptional downregulation of NFS1 upon Hippo pathway activation; NFS1 downregulation causes insufficient Fe-S cluster biosynthesis leading to cardiomyocyte ferroptosis and dilated cardiomyopathy; AAV9-mediated restoration of NFS1 expression alleviates ferroptosis and DCM phenotype in mice.","method":"Transcriptome analysis, ChIP/promoter binding assays, AAV9-Nfs1 rescue in Mst1-TG mice, ferroptosis assays, Mst1/dnMst1 transgenic mouse models","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter binding, in vivo gene therapy rescue, and multiple mouse models; single lab","pmids":["40107016"],"is_preprint":false},{"year":2018,"finding":"Zinc(II)-bound ISCU inhibits NFS1-ISD11-ACP-ISCU (SDAU) desulfurase activity; removal of zinc from ISCU causes a moderate but significant increase in NFS1 desulfurase activity; frataxin can activate both zinc-depleted and zinc-bound forms of ISCU complexed to NFS1-ISD11-ACP. Human ISCU Met140 variants (M140I, M140L, M140V) do not show FXN-bypass effect on NFS1 desulfurase activity in vitro.","method":"In vitro desulfurase activity assays with zinc-depleted vs zinc-bound ISCU, mutagenesis of ISCU Met140, biochemical/biophysical characterization","journal":"Biochimie","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical assays with defined components; single lab, single study","pmids":["30031876"],"is_preprint":false}],"current_model":"NFS1 is a pyridoxal phosphate-dependent homodimeric cysteine desulfurase that catalyzes the conversion of L-cysteine to L-alanine via an enzyme-bound persulfide intermediate at the catalytic cysteine (Cys328 in bacteria; active-site loop undergoes large conformational changes to reach the PLP cofactor); in mitochondria, NFS1 forms a core complex with ISD11 (which prevents NFS1 aggregation and stabilizes its structure), ISCU (the Fe-S cluster scaffold, to which NFS1 transfers persulfide sulfur directly), and frataxin (which enhances persulfide sulfur transfer and whose binding is mutually exclusive with ferredoxin binding on a shared NFS1 surface); this complex is the primary sulfur donor for mitochondrial Fe-S cluster biogenesis; cytosolic NFS1 isoforms (produced by alternative AUG utilization) additionally supply sulfur for molybdenum cofactor biosynthesis via MOCS3 and for tRNA thiolation; NFS1 activity protects cells from ferroptosis by maintaining Fe-S cofactors under oxidative stress, and its transcriptional downregulation (e.g., by the YAP/YY1 axis) or post-translational phosphorylation at S293 modulates ferroptosis susceptibility in cardiac and cancer contexts."},"narrative":{"mechanistic_narrative":"NFS1 is a pyridoxal-phosphate-dependent homodimeric cysteine desulfurase that mobilizes sulfur from L-cysteine to drive the biosynthesis of iron-sulfur cofactors and other sulfur-containing biomolecules [PMID:8464885, PMID:8161529]. Catalysis proceeds through nucleophilic attack of an active-site cysteine (Cys325/Cys328) on a PLP-bound substrate to generate L-alanine and an enzyme-bound cysteinyl persulfide intermediate; this catalytic cysteine sits on a flexible surface loop that must undergo a large conformational change to reach the PLP cofactor and to deliver sulfane sulfur to diverse acceptors [PMID:8161529, PMID:12860127, PMID:20404999]. In mitochondria, NFS1 nucleates the core Fe-S cluster assembly machinery: ISD11 binds NFS1 to prevent its aggregation and stabilize the active enzyme, while NFS1 transfers persulfide sulfur directly to the scaffold protein ISCU, on which transient Fe-S clusters are built and later released for transfer [PMID:10639125, PMID:11577100, PMID:16341090, PMID:23940031]. Frataxin associates with the preassembled NFS1-ISD11-ISCU complex and accelerates persulfide sulfur transfer onto ISCU, competing with ferredoxin for a shared, evolutionarily conserved surface on NFS1 [PMID:21298097, PMID:25597503, PMID:35026224]. NFS1 must reside inside mitochondria to support maturation of both mitochondrial and cytosolic Fe-S proteins, and its depletion collapses respiratory-chain, aconitase, and other Fe-S enzyme activities while activating the iron-starvation response [PMID:16847322, PMID:16787928, PMID:29168506]. Alternative in-frame AUG utilization generates cytosolic/nuclear NFS1 isoforms that additionally donate sulfur to MOCS3 for molybdenum cofactor biosynthesis and to ThiI/MnmA-type pathways for tRNA thiolation [PMID:9885568, PMID:18650437, PMID:23593335, PMID:10753862, PMID:12549933]. By sustaining Fe-S cofactors under oxidative stress, NFS1 protects cells from ferroptosis, and its expression and activity are modulated in cancer and cardiac disease through transcriptional control (YAP/YY1, MYC) and post-translational regulation (S293 phosphorylation), making it a target of ferroptosis-inducing agents [PMID:29168506, PMID:35221331, PMID:36103522, PMID:40107016]. Loss-of-function mutation of NFS1 causes infantile mitochondrial complex II/III deficiency in humans [PMID:24498631].","teleology":[{"year":1994,"claim":"Establishing how a cysteine desulfurase chemically mobilizes sulfur defined the enzymatic basis for all downstream Fe-S and sulfur-transfer biology.","evidence":"In vitro enzyme assays with PLP cofactor identification, thiol-alkylation, and site-directed mutagenesis of the catalytic Cys in the NifS ortholog","pmids":["8464885","8161529"],"confidence":"High","gaps":["Defined in a bacterial ortholog; human NFS1 catalytic residues inferred","Did not address partner-dependent sulfur delivery"]},{"year":2000,"claim":"Identifying direct sulfur transfer from the desulfurase to a scaffold protein revealed how persulfide sulfur is committed to Fe-S cluster assembly.","evidence":"In vitro Fe-S assembly with spectroscopy, 35S sulfur-transfer assays, binding measurements, and C-terminal deletion mutagenesis of IscS","pmids":["10639125","11577100"],"confidence":"High","gaps":["Bacterial system; mammalian scaffold transfer kinetics characterized later","Mechanism of cluster release from scaffold not defined here"]},{"year":2000,"claim":"Demonstrating that the same desulfurase feeds tRNA thiolation, thiamine, and molybdenum cofactor pathways established NFS1 as a central sulfur hub beyond Fe-S clusters.","evidence":"iscS deletion/complementation, in vitro reconstitution of ThiS/ThiI/MnmA sulfur relays, HPLC nucleoside analysis","pmids":["10781607","10600118","10753862","12549933"],"confidence":"High","gaps":["Defined in E. coli; human pathway partners only partly mapped","Compartment-specific isoform contribution not addressed"]},{"year":1998,"claim":"Discovering alternative AUG-driven isoform targeting explained how a single gene supplies sulfur to both mitochondrial and cytosolic/nuclear pathways.","evidence":"cDNA cloning, subcellular fractionation, alternative AUG mapping, and pH manipulation; in yeast, retrograde translocation and Icp55 processing","pmids":["9885568","19720832"],"confidence":"Medium","gaps":["Physiological trigger for pH-dependent redistribution unconfirmed in vivo","Yeast dual-targeting mechanism may differ from human"]},{"year":2006,"claim":"Loss-of-function in mammalian cells showed NFS1 is required, from within mitochondria, for maturation of Fe-S proteins across compartments.","evidence":"siRNA depletion in HeLa and fibroblasts with multiple Fe-S enzyme readouts, IRP-1 switching, and presequence-deletion complementation","pmids":["16847322","16787928"],"confidence":"High","gaps":["Mechanism linking mitochondrial NFS1 to cytosolic Fe-S maturation not resolved here","Did not address the molybdenum cofactor role of cytosolic NFS1"]},{"year":2008,"claim":"Identifying NFS1-MOCS3 sulfur transfer assigned a direct cytosolic function to NFS1 in molybdenum cofactor biosynthesis.","evidence":"Protein interaction studies with MOCS3-RLD, in vitro persulfide-mediated sulfur transfer, and cytosolic colocalization plus molybdoenzyme reconstitution","pmids":["18650437","23593335"],"confidence":"High","gaps":["Quantitative contribution of cytosolic vs mitochondrial NFS1 to Moco in vivo unclear"]},{"year":2006,"claim":"Characterizing ISD11 as an obligate NFS1 partner explained how the desulfurase is stabilized in mitochondria.","evidence":"Yeast Isd11 depletion, co-IP, NFS1 aggregation/stability assays, ISD11 mutagenesis, and a COXPD19-associated R68L variant","pmids":["16341090","26342079","28271877"],"confidence":"High","gaps":["How ISD11/LYR-motif binding mechanistically promotes catalysis not fully resolved","Disease variant effects shown in cells, not whole organisms"]},{"year":2015,"claim":"Resolving frataxin's role redefined it as an enhancer of sulfur transfer within the NFS1-ISD11-ISCU complex rather than purely an iron donor.","evidence":"Co-IP showing frataxin binds the preformed core complex; persulfide intermediate trapping by mass spectrometry and sulfur-transfer kinetics","pmids":["12947415","21298097","23940031","25597503"],"confidence":"High","gaps":["Whether frataxin also contributes iron in vivo not excluded","Regulation of frataxin engagement under iron status incompletely defined"]},{"year":2010,"claim":"Structural and competition studies revealed how a flexible active-site loop and a shared NFS1 surface coordinate sulfur delivery to multiple acceptors.","evidence":"Crystal structures of IscS-IscU and IscS-TusA with surface mutagenesis; mutually exclusive binding of acceptors, Jac1/Nfs1 competition, and ferredoxin/frataxin competition for a conserved site","pmids":["12860127","20404999","23946486","23839945","35026224"],"confidence":"High","gaps":["High-resolution structure of the full mammalian core complex not described here","Order of acceptor engagement in vivo not directly observed"]},{"year":2015,"claim":"Defining the ferredoxin electron-transfer input and ISCU conformational/zinc regulation clarified additional control layers on cluster assembly.","evidence":"In vitro Fe-S assembly with NADPH/FNR/Fdx; NMR of ISCU conformational states; zinc-depletion desulfurase assays and ISCU Met140 variant analysis","pmids":["25688831","26342079","30031876"],"confidence":"Medium","gaps":["In vivo electron-supply stoichiometry not established","Physiological role of ISCU zinc occupancy unresolved"]},{"year":2013,"claim":"A causative human mutation linked NFS1 desulfurase loss directly to mitochondrial respiratory chain disease.","evidence":"Autozygosity mapping, exome sequencing, and functional tests identifying p.Arg72Gln in infantile complex II/III deficiency","pmids":["24498631"],"confidence":"Medium","gaps":["Single family/study","Direct enzymatic deficit of the variant not biochemically quantified here"]},{"year":2017,"claim":"Connecting NFS1 to ferroptosis established its protective role in maintaining Fe-S cofactors under oxidative stress and its relevance to cancer.","evidence":"RNAi loss-of-function screens, in vivo lung adenocarcinoma tumor growth, iron-starvation response readouts, and genetic cooperation with cysteine/glutathione limitation","pmids":["29168506"],"confidence":"High","gaps":["Which specific Fe-S clients gate ferroptosis sensitivity not fully resolved"]},{"year":2025,"claim":"Mapping transcriptional and post-translational control of NFS1 explained how its ferroptosis-protective output is tuned in cardiac and cancer disease.","evidence":"CRISPR screen with S293 phosphosite mutagenesis (oxaliplatin/PANoptosis), OPA3 co-IP and ubiquitination assays, and YAP/YY1 promoter binding with AAV9-NFS1 rescue in mouse DCM models","pmids":["35221331","36924813","40107016","36103522"],"confidence":"Medium","gaps":["Mechanistic link between S293 phosphorylation and desulfurase activity not defined","Single-lab models for each regulatory axis; cross-context generality untested"]},{"year":null,"claim":"How the conformational cycle of the catalytic loop is choreographed in the assembled mammalian NFS1-ISD11-ISCU-frataxin-ferredoxin machinery to hand off sulfur and release clusters in vivo remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No high-resolution structure of the complete mammalian core complex in the corpus","Temporal coordination of acceptor exchange in living cells not directly observed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,4,14,23]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4,14,23]},{"term_id":"GO:0016829","term_label":"lyase activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[2,11,12,15]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2,12,14,22]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,15]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,3,14,24]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[5,6,7,10]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[24,31,33,34]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[28,29,34]}],"complexes":["NFS1-ISD11-ISCU core Fe-S assembly complex","NFS1-ISD11-ISCU-frataxin quaternary complex"],"partners":["ISCU","ISD11","FXN","MOCS3","THII","OPA3","FERREDOXIN","MNMA"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y697","full_name":"Cysteine desulfurase","aliases":[],"length_aa":457,"mass_kda":50.2,"function":"Cysteine desulfurase, of the core iron-sulfur cluster (ISC) assembly complex, that catalyzes the desulfuration of L-cysteine to L-alanine, as component of the cysteine desulfurase complex, leading to the formation of a cysteine persulfide intermediate at the active site cysteine residue and participates in the [2Fe-2S] clusters assembly on the scaffolding protein ISCU (PubMed:18650437, PubMed:29097656, PubMed:31101807). The persulfide is then transferred on the flexible Cys loop from the catalytic site of NFS1 to the surface of NFS1 (PubMed:29097656). After the NFS1-linked persulfide sulfur is transferred to one of the conserved Cys residues of the scaffold, a reaction assisted by FXN (By similarity). The core iron-sulfur cluster (ISC) assembly complex is involved in the de novo synthesis of a [2Fe-2S] cluster, the first step of the mitochondrial iron-sulfur protein biogenesis. This process is initiated by the cysteine desulfurase complex (NFS1:LYRM4:NDUFAB1) that produces persulfide which is delivered on the scaffold protein ISCU in a FXN-dependent manner. Then this complex is stabilized by FDX2 which provides reducing equivalents to accomplish the [2Fe-2S] cluster assembly. Finally, the [2Fe-2S] cluster is transferred from ISCU to chaperone proteins, including HSCB, HSPA9 and GLRX5 (By similarity) May catalyze the desulfuration of L-cysteine to L-alanine as component of the cysteine desulfurase complex (NFS1:LYRM4), leading to the formation of a cysteine persulfide intermediate (PubMed:16527810, PubMed:18650437). Acts as a sulfur donor for MOCS3 by transferring the sulfur of the cysteine persulfide intermediate on MOCS3 (PubMed:18650437, PubMed:23593335)","subcellular_location":"Cytoplasm, cytosol; Nucleus; Cytoplasm, cytoskeleton, microtubule organizing center, centrosome","url":"https://www.uniprot.org/uniprotkb/Q9Y697/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/NFS1","classification":"Common Essential","n_dependent_lines":1203,"n_total_lines":1208,"dependency_fraction":0.9958609271523179},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NFS1","total_profiled":1310},"omim":[{"mim_id":"619386","title":"COMBINED OXIDATIVE PHOSPHORYLATION DEFICIENCY 52; COXPD52","url":"https://www.omim.org/entry/619386"},{"mim_id":"615595","title":"COMBINED OXIDATIVE PHOSPHORYLATION DEFICIENCY 19; COXPD19","url":"https://www.omim.org/entry/615595"},{"mim_id":"613311","title":"LYR MOTIF-CONTAINING PROTEIN 4; LYRM4","url":"https://www.omim.org/entry/613311"},{"mim_id":"613274","title":"MOLYBDENUM COFACTOR SULFURASE; MOCOS","url":"https://www.omim.org/entry/613274"},{"mim_id":"611911","title":"IRON-SULFUR CLUSTER ASSEMBLY ENZYME; ISCU","url":"https://www.omim.org/entry/611911"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NFS1"},"hgnc":{"alias_symbol":["NifS","IscS"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y697","domains":[{"cath_id":"3.40.640.10","chopping":"72-311","consensus_level":"medium","plddt":98.4951,"start":72,"end":311},{"cath_id":"3.90.1150.10","chopping":"316-450","consensus_level":"medium","plddt":91.9019,"start":316,"end":450}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y697","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y697-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y697-F1-predicted_aligned_error_v6.png","plddt_mean":88.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NFS1","jax_strain_url":"https://www.jax.org/strain/search?query=NFS1"},"sequence":{"accession":"Q9Y697","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y697.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y697/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y697"}},"corpus_meta":[{"pmid":"29168506","id":"PMC_29168506","title":"NFS1 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catalyzes the formation of L-alanine and elemental sulfur from L-cysteine; activity is abolished by thiol-specific alkylating reagents, implicating an active-site cysteinyl thiolate; proposed to supply inorganic sulfide for nitrogenase metallocluster (Fe-S cluster) biosynthesis.\",\n      \"method\": \"In vitro enzyme assay, chemical modification with thiol-specific alkylating reagents, pyridoxal phosphate cofactor identification\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro biochemical reconstitution with cofactor identification and active-site chemical modification; foundational mechanistic study replicated by multiple subsequent labs\",\n      \"pmids\": [\"8464885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The catalytic mechanism of NifS (NFS1 ortholog) involves: (1) nucleophilic attack by active-site Cys325 on a PLP-bound cysteine substrate, (2) formation of an enzyme-bound cysteinyl persulfide intermediate, and (3) generation of an enamine intermediate yielding L-alanine; Cys325 identified as the essential catalytic residue by site-directed mutagenesis and specific alkylation.\",\n      \"method\": \"Substrate analog inhibition (L-allylglycine, vinylglycine), site-directed mutagenesis of Cys325, in vitro enzyme assays, identification of persulfide intermediate\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis and intermediate trapping; defines catalytic mechanism at residue level\",\n      \"pmids\": [\"8161529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human NFS1 is synthesized from a single transcript as different isoforms that localize either to mitochondria or to the cytosol/nucleus through initiation at alternative in-frame AUGs; isoform selection varies with cytosolic pH, providing a mechanism for redistribution of NFS1 between compartments in response to metabolic changes.\",\n      \"method\": \"cDNA cloning, subcellular fractionation, alternative AUG mapping, pH manipulation experiments\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct subcellular fractionation with functional localization linked to alternative AUG utilization; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"9885568\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"NifS directs assembly of a transient [2Fe-2S] cluster on the scaffold protein NifU in vitro when incubated with ferric ion and L-cysteine; NifU interacts physically with NifS; the transient cluster is labile and rapidly released upon reduction, supporting a model where NifS-assembled clusters on NifU are transferred to nitrogenase component proteins.\",\n      \"method\": \"In vitro Fe-S cluster assembly assay, UV-vis and EPR spectroscopy, protein interaction studies\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with spectroscopic characterization of cluster intermediate; foundational study\",\n      \"pmids\": [\"10639125\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"E. coli IscS (NFS1 ortholog) directly transfers persulfide sulfur to the scaffold protein IscU via a high-affinity protein-protein interaction (Kd ~2 µM); transfer requires cysteinyl residues of IscU and is inhibited by iodoacetamide treatment of IscU; the C-terminal region of IscS (residues 376-413) is important for IscU binding and efficient sulfur transfer.\",\n      \"method\": \"35S-cysteine radiotracer sulfur transfer assay, surface plasmon resonance, isothermal titration calorimetry, IscS C-terminal deletion mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct sulfur transfer assay combined with binding measurements and mutagenesis; multiple orthogonal methods\",\n      \"pmids\": [\"11577100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"IscS is required for the biosynthesis of 4-thiouridine (s4U) in tRNA, thiamine (specifically the thiazole moiety), and NAD in E. coli; IscS mobilizes sulfur for transfer to ThiS (the direct sulfur donor in thiazole biosynthesis), with ThiI stimulating the IscS-to-ThiS sulfur transfer ~7-fold; neither of the other two nifS-like E. coli genes can complement iscS deletion.\",\n      \"method\": \"iscS deletion mutant phenotypic analysis, in vitro reconstitution of ThiS thiocarboxylate synthesis, genetic complementation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro reconstitution of sulfur transfer pathway combined with in vivo genetic deletion and complementation; replicated in multiple subsequent studies\",\n      \"pmids\": [\"10781607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"IscS acts as a tRNA sulfurtransferase for 4-thiouridine biosynthesis; purified IscS catalyzes sulfur transfer from cysteine to tRNA in vitro; among E. coli proteins with cysteine desulfurase activity, only IscS can mobilize sulfur for tRNA thiolation.\",\n      \"method\": \"Protein purification, in vitro tRNA thiolation assay, HPLC nucleoside analysis, N-terminal sequencing\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with chemical product identification; single lab but orthogonal methods\",\n      \"pmids\": [\"10600118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"IscS transfers sulfane sulfur (persulfide) sequentially to ThiI, which then transfers it to tRNA during 4-thiouridine biosynthesis; ThiI contains a reactive cysteine required for catalysis/binding protected by ATP and tRNA; IscS-generated persulfide is the direct sulfur source for ThiI.\",\n      \"method\": \"Fluorescent alkylating agent inhibition of ThiI, gel shift and protease protection assays, in vitro sulfur transfer reconstitution\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of sequential sulfur relay with biochemical intermediate trapping; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"10753862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Crystal structure of E. coli IscS (NFS1 ortholog) solved at 2.1 Å; the catalytic Cys328 resides on a flexible surface loop >17 Å from the PLP cofactor, requiring a large conformational change for catalysis; structural modeling suggests loop rotation brings Cys328 to ~3 Å of PLP cofactor.\",\n      \"method\": \"X-ray crystallography at 2.1 Å resolution\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — atomic-resolution crystal structure providing mechanistic insight into catalytic loop flexibility; single lab but definitive structural method\",\n      \"pmids\": [\"12860127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Frataxin ortholog Yfh1 specifically binds to the core ISC assembly complex composed of scaffold protein Isu1 and cysteine desulfurase Nfs1; binding is markedly increased by ferrous iron; Yfh1 is involved in de novo Fe-S cluster synthesis on Isu1, suggesting frataxin provides iron to the Isu scaffold.\",\n      \"method\": \"Co-immunoprecipitation, in vivo functional analysis of ISC synthesis on Isu1, iron-dependence assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP with functional validation in vivo; single lab with multiple methods\",\n      \"pmids\": [\"12947415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"MnmA and IscS are both required for in vitro 2-thiouridine (s2U) biosynthesis in E. coli tRNA; IscS-generated persulfide can provide sulfur for s2U synthesis in the absence of free cysteine; MnmA binds tRNA substrates with low micromolar affinity and requires ATP.\",\n      \"method\": \"In vitro s2U biosynthesis reconstitution with purified components, 35S radiotracer, HPLC analysis, gel mobility shift\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with defined components and product identification; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"12549933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Isd11 forms a stable complex with Nfs1 in mitochondria; in the absence of Isd11, Nfs1 is prone to aggregation; Isd11 depletion causes strong reduction in Fe-S protein activities (aconitase, succinate dehydrogenase, Rieske protein); Isd11 acts with Nfs1 in an early step of Fe-S cluster biogenesis.\",\n      \"method\": \"Yeast genetics (Isd11 depletion), enzyme activity assays, co-immunoprecipitation, protein stability assessment\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — protein interaction plus functional loss-of-function with multiple Fe-S enzyme activity readouts; replicated by multiple subsequent labs\",\n      \"pmids\": [\"16341090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human Nfs1 (huNfs1) is located predominantly in mitochondria with small amounts in cytosol/nucleus; siRNA depletion of huNfs1 in HeLa cells strongly impairs both mitochondrial and cytosolic Fe-S protein activities and causes growth retardation and mitochondrial morphology changes; Nfs1 must be inside mitochondria to support Fe-S protein maturation—cytosolic Nfs1 lacking the mitochondrial presequence cannot complement.\",\n      \"method\": \"siRNA knockdown, enzyme activity assays for mitochondrial and cytosolic Fe-S proteins, subcellular fractionation, complementation with presequence-deleted Nfs1\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA depletion with multiple Fe-S enzyme activity readouts and localization-function dissection; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"16847322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Depletion of mammalian m-Nfs1 by siRNA in cultured fibroblasts significantly inhibits activities of mitochondrial respiratory chain complexes I and II, mitochondrial aconitase, cytosolic xanthine oxidase (a [2Fe-2S] enzyme), and converts IRP-1 from its [4Fe-4S] aconitase form to its RNA-binding form; cytosolic Fe-S activities are affected earlier than mitochondrial activities.\",\n      \"method\": \"siRNA gene silencing, enzyme activity assays, IRP-1 RNA-binding assay, ferritin mRNA regulation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with multiple Fe-S enzyme readouts across compartments; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"16787928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human NFS1 (purified with Isd11) interacts specifically with the rhodanese-like domain (RLD) of MOCS3, a cytosolic protein involved in molybdenum cofactor biosynthesis; sulfur is transferred from L-cysteine to MOCS3-RLD via an NFS1-bound persulfide intermediate; cytosolic NFS1 acts as sulfur donor for Moco biosynthesis.\",\n      \"method\": \"Protein-protein interaction studies, in vitro sulfur transfer assay, kinetic parameter determination\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct protein interaction combined with in vitro sulfur transfer reconstitution via persulfide intermediate; single lab with multiple methods\",\n      \"pmids\": [\"18650437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Yeast Nfs1 undergoes dual targeting to mitochondria and nucleus from a single translation product; the minor nuclear/cytosolic subpopulation arises via partial mitochondrial entry followed by retrograde translocation; mitochondrial processing peptidase cleaves Nfs1, and the novel processing enzyme Icp55 subsequently removes three additional N-terminal amino acids.\",\n      \"method\": \"Alpha-complementation assay, subcellular fractionation, Edman degradation of N-terminal sequence, discovery of Icp55 protease\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct fractionation and N-terminal sequencing identifying novel processing enzyme; single lab with multiple methods in yeast\",\n      \"pmids\": [\"19720832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Bacterial frataxin CyaY acts as an iron-dependent inhibitor of Fe-S cluster formation by binding to the desulfurase IscS; the interaction involves the iron-binding surface of CyaY; CyaY acts as an iron sensor/regulator that fine-tunes Fe-S cluster formation.\",\n      \"method\": \"Biochemical and biophysical interaction studies, in vitro Fe-S cluster assembly assays\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple biophysical methods demonstrating inhibitory mechanism with defined binding site; single lab with rigorous controls\",\n      \"pmids\": [\"19305405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structures of IscS-IscU and IscS-TusA complexes reveal that IscS interacts with multiple partner proteins through an extensive surface area centered on catalytic Cys328; partner proteins approach Cys328 from different directions; the conformational plasticity of the active-site loop containing Cys328 is essential for sulfur transfer to multiple acceptors; sulfur acceptors (IscU, TusA) bind IscS one at a time (mutually exclusive), while frataxin/CyaY and IscX can form ternary complexes with IscU and IscS.\",\n      \"method\": \"X-ray crystallography of IscS-IscU and IscS-TusA complexes, exhaustive IscS surface mutagenesis, biochemical binding and activity assays\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures of two distinct complexes with comprehensive mutagenesis and biochemical validation; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"20404999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mammalian frataxin interacts with the preformed ISCU/NFS1/ISD11 core Fe-S assembly complex (not individual components); the quaternary complex has a molecular mass of ~190 kDa; the mature FXN(81-210) form is the essential functional form in vivo.\",\n      \"method\": \"Co-immunoprecipitation from mammalian cells, heterologous expression system, molecular mass determination, in vivo complementation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP combined with in vivo functional validation; single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"21298097\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Human NFS1 (cysteine desulfurase) binds preferentially to the disordered (D-state) conformation of ISCU scaffold protein; ISD11 does not interact directly with ISCU but the NFS1-ISD11 complex also binds the D-state of ISCU; in vitro Fe-S cluster assembly on ISCU is catalyzed by NFS1 alone and at higher rate by the NFS1-ISD11 complex.\",\n      \"method\": \"NMR spectroscopy, ISCU conformational state variants (D39V, N90A, D39A, H105A), in vitro Fe-S cluster assembly assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structural/interaction analysis combined with in vitro activity assay; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"23940031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Binding of Jac1 (J-protein co-chaperone) and Nfs1 to the scaffold protein Isu is mutually exclusive; both proteins require the same hydrophobic patch on Isu surface; Jac1 and Nfs1 compete for Isu binding in vitro; competition between Jac1 and Nfs1 for Isu is proposed to transition the machinery from cluster assembly to Hsp70-mediated cluster transfer.\",\n      \"method\": \"In vitro binding assays with purified proteins, competition assays, Isu hydrophobic patch mutagenesis, in vivo functional validation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro competition assays with mutagenesis and in vivo validation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"23946486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NFS1 physical interaction (not enzymatic activity) with Isu protects Isu from degradation by the Pim1/Lon protease; when Fe-S cluster biogenesis is disrupted, increased Isu stability depends on its interaction with Nfs1.\",\n      \"method\": \"Yeast genetics, Pim1 protease identification, protein stability assays under various conditions including Nfs1 enzymatic mutants\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and biochemical dissection of interaction vs. enzymatic activity; single lab with multiple conditions\",\n      \"pmids\": [\"22689995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Cytosolic NFS1 colocalizes and interacts with MOCS3 in the cytosol of human cells; NFS1 localization in cytosol confirmed by FRET, split-EGFP, immunodetection of fractionated cells, and confocal microscopy; purified NFS1 can reconstitute molybdoenzyme activity in Neurospora crassa nit-1 mutant.\",\n      \"method\": \"FRET, split-EGFP, immunofluorescence/confocal microscopy, cell fractionation, in vitro molybdoenzyme reconstitution\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal localization methods plus functional reconstitution; single lab\",\n      \"pmids\": [\"23593335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Mammalian frataxin directly enhances the rate of sulfur transfer from NFS1 persulfide to both ISCU (accumulating a persulfide on ISCU Cys104) and to small free thiols (DTT, L-cysteine, GSH); frataxin acts as an enhancer of sulfur transfer within the NFS1-ISD11-ISCU complex rather than primarily as an iron donor.\",\n      \"method\": \"Maleimide-peptide trapping of cysteine-persulfide intermediates combined with mass spectrometry, in vitro sulfur transfer kinetics\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct persulfide intermediate trapping by mass spectrometry with kinetic analysis; single lab with orthogonal chemical biology and MS methods\",\n      \"pmids\": [\"25597503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NFS1 activity is critical for maintaining Fe-S cofactors in multiple cell-essential proteins under high oxygen conditions; NFS1 suppression activates the iron-starvation response and, in combination with inhibition of glutathione biosynthesis, triggers ferroptosis; NFS1 is amplified in lung adenocarcinoma and protects against ferroptosis under high-oxygen tension.\",\n      \"method\": \"RNA interference loss-of-function screening, in vivo tumor growth experiments, genetic cooperation assays (NFS1 suppression + cysteine transport inhibition), iron-starvation response measurements\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function in multiple in vivo and in vitro systems with defined molecular phenotypes (Fe-S cofactor loss, iron-starvation response, ferroptosis); multiple labs cite and replicate\",\n      \"pmids\": [\"29168506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Ferredoxin (Fdx) competes with frataxin CyaY for binding to the desulfurase IscS; Fdx binds in a cavity close to the enzyme active site overlapping the CyaY binding site; in vivo mutagenesis confirms importance of this interaction surface for Fe-S cluster formation.\",\n      \"method\": \"Biophysical characterization (SAXS, NMR, other), mutagenesis, in vivo complementation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biophysical methods with in vivo validation; single lab\",\n      \"pmids\": [\"23839945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ferredoxin (Fdx), together with NADPH and ferredoxin-NADP reductase, transfers electrons to the IscS/IscU complex to promote Fe-S cluster assembly; this electron transfer trio is sufficient to sustain in vitro Fe-S cluster assembly; Fdx does not interfere with CyaY inhibitory activity despite overlapping binding sites on IscS.\",\n      \"method\": \"In vitro Fe-S cluster assembly assay using physiological electron transfer chain (NADPH/FNR/Fdx), comparison with DTT-mediated assembly\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with physiological electron donor system; single lab\",\n      \"pmids\": [\"25688831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"During FeS cluster biogenesis in yeast, ferredoxin (Yah1) and frataxin (Yfh1) share an evolutionarily conserved interaction site on Nfs1; Yah1 and Yfh1 can each displace the other from Nfs1, demonstrating mutually exclusive binding; this binding mode mirrors bacterial CyaY/Fdx competition at IscS.\",\n      \"method\": \"In vitro competition assays with purified WT and variant Nfs1/Yah1/Yfh1 proteins, biochemical binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro competition assays with mutagenesis; single lab\",\n      \"pmids\": [\"35026224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"NFS1 deficiency (c.215G>A, p.Arg72Gln mutation) identified as causative for infantile mitochondrial complex II/III deficiency, establishing that loss of NFS1 cysteine desulfurase activity impairs respiratory chain function in humans.\",\n      \"method\": \"Autozygosity mapping, exome sequencing, in silico analyses, population studies, functional tests\",\n      \"journal\": \"Molecular genetics & genomic medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human disease mutation with functional validation; single study\",\n      \"pmids\": [\"24498631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ISD11 residues in helix 1 (Phe-40), helix 3 (Leu-63, Arg-68, Gln-69, Ile-72, Tyr-76), and C-terminal segment (Leu-81, Glu-84) are critical for interaction with NFS1; mutation of these residues compromises ISD11-NFS1 complex stability, causing NFS1 aggregation and reduced Fe-S cluster biosynthesis; the COXPD19-associated ISD11 R68L mutation reduces affinity for NFS1 and causes mitochondrial dysfunction.\",\n      \"method\": \"Site-directed mutagenesis of ISD11, co-immunoprecipitation, enzyme activity assays (ETC complexes), mitochondrial iron/ROS measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis with functional and interaction assays; single lab\",\n      \"pmids\": [\"26342079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The first 10 N-terminal amino acids of ISD11, including the conserved 'LYR' motif, are indispensable for NFS1 activity and formation of a stable, active NFS1-ISD11 complex; the N-terminus of ISD11 also contains its mitochondrial targeting sequence.\",\n      \"method\": \"In vitro purified protein interaction studies, in vivo cellular complementation, mutagenesis of ISD11 N-terminus\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — combination of in vitro and in vivo studies; single lab\",\n      \"pmids\": [\"28271877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Oxaliplatin-induced oxidative stress enhances phosphorylation of NFS1 at serine residue S293; phosphorylation at S293 prevents PANoptosis (apoptosis, necroptosis, pyroptosis, ferroptosis) in colorectal cancer cells; NFS1 transcription is regulated by MYC; NFS1 deficiency combined with oxaliplatin triggers PANoptosis by increasing intracellular ROS.\",\n      \"method\": \"CRISPR-Cas9 metabolic enzyme screen in vivo, site-directed mutagenesis of S293, in vitro and in vivo functional assays, ROS measurement, phosphorylation site identification\",\n      \"journal\": \"Signal transduction and targeted therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR screen combined with mutagenesis and functional validation; single lab\",\n      \"pmids\": [\"35221331\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Eprenetapopt (APR-246) inhibits the cysteine desulfurase activity of NFS1, limiting Fe-S cluster biogenesis and potentiating ferroptosis; this effect is independent of its reported mutant-p53 reactivation activity.\",\n      \"method\": \"Unbiased genetic screen, glutathione turnover assays, NFS1 cysteine desulfurase activity assay, ferroptosis cell death assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — unbiased genetic approach plus biochemical NFS1 activity assay; single lab\",\n      \"pmids\": [\"36103522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"OPA3 (mitochondrial membrane protein) interacts with NFS1 and regulates ferroptosis; DOX promotes OPA3 ubiquitination and downregulates NFS1; H2S antagonizes OPA3 ubiquitination via S-sulfhydration, restoring NFS1 expression and inhibiting ferroptosis; NFS1 deficiency increases cardiomyocyte susceptibility to ferroptosis.\",\n      \"method\": \"Co-immunoprecipitation (OPA3-NFS1 interaction), overexpression/knockdown in cardiomyocytes, in vivo DOX cardiotoxicity model, ubiquitination and S-sulfhydration assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP interaction plus functional in vivo/in vitro assays; single lab\",\n      \"pmids\": [\"36924813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Nuclear YAP and YY1 interact and bind to the NFS1 promoter, mediating transcriptional downregulation of NFS1 upon Hippo pathway activation; NFS1 downregulation causes insufficient Fe-S cluster biosynthesis leading to cardiomyocyte ferroptosis and dilated cardiomyopathy; AAV9-mediated restoration of NFS1 expression alleviates ferroptosis and DCM phenotype in mice.\",\n      \"method\": \"Transcriptome analysis, ChIP/promoter binding assays, AAV9-Nfs1 rescue in Mst1-TG mice, ferroptosis assays, Mst1/dnMst1 transgenic mouse models\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter binding, in vivo gene therapy rescue, and multiple mouse models; single lab\",\n      \"pmids\": [\"40107016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Zinc(II)-bound ISCU inhibits NFS1-ISD11-ACP-ISCU (SDAU) desulfurase activity; removal of zinc from ISCU causes a moderate but significant increase in NFS1 desulfurase activity; frataxin can activate both zinc-depleted and zinc-bound forms of ISCU complexed to NFS1-ISD11-ACP. Human ISCU Met140 variants (M140I, M140L, M140V) do not show FXN-bypass effect on NFS1 desulfurase activity in vitro.\",\n      \"method\": \"In vitro desulfurase activity assays with zinc-depleted vs zinc-bound ISCU, mutagenesis of ISCU Met140, biochemical/biophysical characterization\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical assays with defined components; single lab, single study\",\n      \"pmids\": [\"30031876\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NFS1 is a pyridoxal phosphate-dependent homodimeric cysteine desulfurase that catalyzes the conversion of L-cysteine to L-alanine via an enzyme-bound persulfide intermediate at the catalytic cysteine (Cys328 in bacteria; active-site loop undergoes large conformational changes to reach the PLP cofactor); in mitochondria, NFS1 forms a core complex with ISD11 (which prevents NFS1 aggregation and stabilizes its structure), ISCU (the Fe-S cluster scaffold, to which NFS1 transfers persulfide sulfur directly), and frataxin (which enhances persulfide sulfur transfer and whose binding is mutually exclusive with ferredoxin binding on a shared NFS1 surface); this complex is the primary sulfur donor for mitochondrial Fe-S cluster biogenesis; cytosolic NFS1 isoforms (produced by alternative AUG utilization) additionally supply sulfur for molybdenum cofactor biosynthesis via MOCS3 and for tRNA thiolation; NFS1 activity protects cells from ferroptosis by maintaining Fe-S cofactors under oxidative stress, and its transcriptional downregulation (e.g., by the YAP/YY1 axis) or post-translational phosphorylation at S293 modulates ferroptosis susceptibility in cardiac and cancer contexts.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NFS1 is a pyridoxal-phosphate-dependent homodimeric cysteine desulfurase that mobilizes sulfur from L-cysteine to drive the biosynthesis of iron-sulfur cofactors and other sulfur-containing biomolecules [#0, #1]. Catalysis proceeds through nucleophilic attack of an active-site cysteine (Cys325/Cys328) on a PLP-bound substrate to generate L-alanine and an enzyme-bound cysteinyl persulfide intermediate; this catalytic cysteine sits on a flexible surface loop that must undergo a large conformational change to reach the PLP cofactor and to deliver sulfane sulfur to diverse acceptors [#1, #8, #17]. In mitochondria, NFS1 nucleates the core Fe-S cluster assembly machinery: ISD11 binds NFS1 to prevent its aggregation and stabilize the active enzyme, while NFS1 transfers persulfide sulfur directly to the scaffold protein ISCU, on which transient Fe-S clusters are built and later released for transfer [#3, #4, #11, #19]. Frataxin associates with the preassembled NFS1-ISD11-ISCU complex and accelerates persulfide sulfur transfer onto ISCU, competing with ferredoxin for a shared, evolutionarily conserved surface on NFS1 [#18, #23, #27]. NFS1 must reside inside mitochondria to support maturation of both mitochondrial and cytosolic Fe-S proteins, and its depletion collapses respiratory-chain, aconitase, and other Fe-S enzyme activities while activating the iron-starvation response [#12, #13, #24]. Alternative in-frame AUG utilization generates cytosolic/nuclear NFS1 isoforms that additionally donate sulfur to MOCS3 for molybdenum cofactor biosynthesis and to ThiI/MnmA-type pathways for tRNA thiolation [#2, #14, #22, #7, #10]. By sustaining Fe-S cofactors under oxidative stress, NFS1 protects cells from ferroptosis, and its expression and activity are modulated in cancer and cardiac disease through transcriptional control (YAP/YY1, MYC) and post-translational regulation (S293 phosphorylation), making it a target of ferroptosis-inducing agents [#24, #31, #32, #34]. Loss-of-function mutation of NFS1 causes infantile mitochondrial complex II/III deficiency in humans [#28].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Establishing how a cysteine desulfurase chemically mobilizes sulfur defined the enzymatic basis for all downstream Fe-S and sulfur-transfer biology.\",\n      \"evidence\": \"In vitro enzyme assays with PLP cofactor identification, thiol-alkylation, and site-directed mutagenesis of the catalytic Cys in the NifS ortholog\",\n      \"pmids\": [\"8464885\", \"8161529\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Defined in a bacterial ortholog; human NFS1 catalytic residues inferred\", \"Did not address partner-dependent sulfur delivery\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identifying direct sulfur transfer from the desulfurase to a scaffold protein revealed how persulfide sulfur is committed to Fe-S cluster assembly.\",\n      \"evidence\": \"In vitro Fe-S assembly with spectroscopy, 35S sulfur-transfer assays, binding measurements, and C-terminal deletion mutagenesis of IscS\",\n      \"pmids\": [\"10639125\", \"11577100\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Bacterial system; mammalian scaffold transfer kinetics characterized later\", \"Mechanism of cluster release from scaffold not defined here\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstrating that the same desulfurase feeds tRNA thiolation, thiamine, and molybdenum cofactor pathways established NFS1 as a central sulfur hub beyond Fe-S clusters.\",\n      \"evidence\": \"iscS deletion/complementation, in vitro reconstitution of ThiS/ThiI/MnmA sulfur relays, HPLC nucleoside analysis\",\n      \"pmids\": [\"10781607\", \"10600118\", \"10753862\", \"12549933\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Defined in E. coli; human pathway partners only partly mapped\", \"Compartment-specific isoform contribution not addressed\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Discovering alternative AUG-driven isoform targeting explained how a single gene supplies sulfur to both mitochondrial and cytosolic/nuclear pathways.\",\n      \"evidence\": \"cDNA cloning, subcellular fractionation, alternative AUG mapping, and pH manipulation; in yeast, retrograde translocation and Icp55 processing\",\n      \"pmids\": [\"9885568\", \"19720832\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological trigger for pH-dependent redistribution unconfirmed in vivo\", \"Yeast dual-targeting mechanism may differ from human\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Loss-of-function in mammalian cells showed NFS1 is required, from within mitochondria, for maturation of Fe-S proteins across compartments.\",\n      \"evidence\": \"siRNA depletion in HeLa and fibroblasts with multiple Fe-S enzyme readouts, IRP-1 switching, and presequence-deletion complementation\",\n      \"pmids\": [\"16847322\", \"16787928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking mitochondrial NFS1 to cytosolic Fe-S maturation not resolved here\", \"Did not address the molybdenum cofactor role of cytosolic NFS1\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identifying NFS1-MOCS3 sulfur transfer assigned a direct cytosolic function to NFS1 in molybdenum cofactor biosynthesis.\",\n      \"evidence\": \"Protein interaction studies with MOCS3-RLD, in vitro persulfide-mediated sulfur transfer, and cytosolic colocalization plus molybdoenzyme reconstitution\",\n      \"pmids\": [\"18650437\", \"23593335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of cytosolic vs mitochondrial NFS1 to Moco in vivo unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Characterizing ISD11 as an obligate NFS1 partner explained how the desulfurase is stabilized in mitochondria.\",\n      \"evidence\": \"Yeast Isd11 depletion, co-IP, NFS1 aggregation/stability assays, ISD11 mutagenesis, and a COXPD19-associated R68L variant\",\n      \"pmids\": [\"16341090\", \"26342079\", \"28271877\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ISD11/LYR-motif binding mechanistically promotes catalysis not fully resolved\", \"Disease variant effects shown in cells, not whole organisms\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolving frataxin's role redefined it as an enhancer of sulfur transfer within the NFS1-ISD11-ISCU complex rather than purely an iron donor.\",\n      \"evidence\": \"Co-IP showing frataxin binds the preformed core complex; persulfide intermediate trapping by mass spectrometry and sulfur-transfer kinetics\",\n      \"pmids\": [\"12947415\", \"21298097\", \"23940031\", \"25597503\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether frataxin also contributes iron in vivo not excluded\", \"Regulation of frataxin engagement under iron status incompletely defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Structural and competition studies revealed how a flexible active-site loop and a shared NFS1 surface coordinate sulfur delivery to multiple acceptors.\",\n      \"evidence\": \"Crystal structures of IscS-IscU and IscS-TusA with surface mutagenesis; mutually exclusive binding of acceptors, Jac1/Nfs1 competition, and ferredoxin/frataxin competition for a conserved site\",\n      \"pmids\": [\"12860127\", \"20404999\", \"23946486\", \"23839945\", \"35026224\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the full mammalian core complex not described here\", \"Order of acceptor engagement in vivo not directly observed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defining the ferredoxin electron-transfer input and ISCU conformational/zinc regulation clarified additional control layers on cluster assembly.\",\n      \"evidence\": \"In vitro Fe-S assembly with NADPH/FNR/Fdx; NMR of ISCU conformational states; zinc-depletion desulfurase assays and ISCU Met140 variant analysis\",\n      \"pmids\": [\"25688831\", \"26342079\", \"30031876\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo electron-supply stoichiometry not established\", \"Physiological role of ISCU zinc occupancy unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A causative human mutation linked NFS1 desulfurase loss directly to mitochondrial respiratory chain disease.\",\n      \"evidence\": \"Autozygosity mapping, exome sequencing, and functional tests identifying p.Arg72Gln in infantile complex II/III deficiency\",\n      \"pmids\": [\"24498631\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single family/study\", \"Direct enzymatic deficit of the variant not biochemically quantified here\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Connecting NFS1 to ferroptosis established its protective role in maintaining Fe-S cofactors under oxidative stress and its relevance to cancer.\",\n      \"evidence\": \"RNAi loss-of-function screens, in vivo lung adenocarcinoma tumor growth, iron-starvation response readouts, and genetic cooperation with cysteine/glutathione limitation\",\n      \"pmids\": [\"29168506\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific Fe-S clients gate ferroptosis sensitivity not fully resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mapping transcriptional and post-translational control of NFS1 explained how its ferroptosis-protective output is tuned in cardiac and cancer disease.\",\n      \"evidence\": \"CRISPR screen with S293 phosphosite mutagenesis (oxaliplatin/PANoptosis), OPA3 co-IP and ubiquitination assays, and YAP/YY1 promoter binding with AAV9-NFS1 rescue in mouse DCM models\",\n      \"pmids\": [\"35221331\", \"36924813\", \"40107016\", \"36103522\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between S293 phosphorylation and desulfurase activity not defined\", \"Single-lab models for each regulatory axis; cross-context generality untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the conformational cycle of the catalytic loop is choreographed in the assembled mammalian NFS1-ISD11-ISCU-frataxin-ferredoxin machinery to hand off sulfur and release clusters in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No high-resolution structure of the complete mammalian core complex in the corpus\", \"Temporal coordination of acceptor exchange in living cells not directly observed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 4, 14, 23]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4, 14, 23]},\n      {\"term_id\": \"GO:0016829\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [2, 11, 12, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2, 12, 14, 22]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 3, 14, 24]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [5, 6, 7, 10]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [24, 31, 33, 34]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [28, 29, 34]}\n    ],\n    \"complexes\": [\n      \"NFS1-ISD11-ISCU core Fe-S assembly complex\",\n      \"NFS1-ISD11-ISCU-frataxin quaternary complex\"\n    ],\n    \"partners\": [\n      \"ISCU\",\n      \"ISD11\",\n      \"FXN\",\n      \"MOCS3\",\n      \"ThiI\",\n      \"OPA3\",\n      \"ferredoxin\",\n      \"MnmA\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}