{"gene":"NFU1","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":2011,"finding":"NFU1 functions as a late-acting maturation factor for a specific subset of mitochondrial Fe-S proteins. RNAi depletion of NFU1 in human cells markedly decreased lipoic acid synthase (LAS) activity and in turn pyruvate dehydrogenase complex (PDHC) activity, and reduced succinate dehydrogenase (SDH) amount, but did not affect other Fe-S proteins tested. By contrast, depletion of the general scaffold ISCU severely affected all tested Fe-S proteins, demonstrating that NFU1 has a specialized rather than general role in mitochondrial Fe-S cluster maturation.","method":"RNA interference in human cell culture, enzymatic activity assays, protein quantification; yeast NFU1 deletion with lipoylation and SDH activity measurements; yeast missense mutant functional complementation","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (RNAi, yeast KO, yeast complementation) across two model systems, independently replicated in a second paper (PMID:21944046)","pmids":["22077971"],"is_preprint":false},{"year":2011,"finding":"Both NFU1 (mitochondrial isoform) and BOLA3 (isoform 1) are required for the maturation of lipoate-containing 2-oxoacid dehydrogenases and for respiratory chain complex assembly. Retroviral transduction with the mitochondrial isoform of NFU1, but not the cytosolic isoform, restored respiratory chain function and oxoacid dehydrogenase complex activity in patient fibroblasts.","method":"Retroviral complementation of patient fibroblast lines with isoform-specific NFU1 constructs; enzymatic activity assays for respiratory chain and oxoacid dehydrogenase complexes","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 — isoform-specific functional rescue with enzymatic readouts, replicated by companion paper (PMID:22077971)","pmids":["21944046"],"is_preprint":false},{"year":2016,"finding":"Human mitochondrial NFU1 binds and transfers a [4Fe-4S] cluster. The C-terminal domain contains the two cysteines that coordinate one [4Fe-4S] cluster bridging two NFU1 subunits to form a cluster-linked dimer; three such dimers associate via their N-terminal domains to form hexameric holo-NFU1. Holo-NFU1 can activate apo-aconitase in vitro, confirming its cluster-transfer activity.","method":"NMR spectroscopy (3D structures of N- and C-terminal domains), small-angle X-ray scattering (SAXS), size-exclusion chromatography, in vitro aconitase activation assay","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — NMR structure determination combined with SAXS and functional in vitro reconstitution assay in single study","pmids":["27818104"],"is_preprint":false},{"year":2016,"finding":"Yeast Nfu1 functions in a late step of [4Fe-4S] cluster biogenesis and physically interacts with components of the ISA [4Fe-4S] assembly complex and with [4Fe-4S] client proteins. Bol3 (human BOLA3 ortholog) functions together with Nfu1 in this late step, whereas Bol1 functions earlier with the monothiol glutaredoxin Grx5.","method":"Genetic studies in yeast (deletion mutants, growth under oxidative metabolism), proteomic interaction studies (mass spectrometry-based), epistasis analysis","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis combined with proteomics-based physical interaction mapping, multiple orthogonal approaches","pmids":["27532773"],"is_preprint":false},{"year":2020,"finding":"Human ISCU (ISCU2) directly interacts with NFU1 (Kd ~1.1 µM as measured by ITC), and ISCU[4Fe-4S] transfers its Fe-S cluster to apo-NFU1 in the absence of a chaperone to form holo-NFU1. ISCU[2Fe-2S] does not transfer its cluster to apo-NFU1. The interaction site maps to the cluster-binding region of ISCU and two α-helices in the C-terminal domain of NFU1.","method":"NMR spectroscopy, SAXS, size-exclusion chromatography, isothermal titration calorimetry (ITC), in vitro Fe-S cluster transfer assay","journal":"Journal of structural biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of cluster transfer with structural mapping by NMR/SAXS and quantitative binding by ITC","pmids":["32151725"],"is_preprint":false},{"year":2020,"finding":"ISCU2 and ISCA1 are the direct sequential donors of [2Fe-2S] clusters to mitochondrial NFU1, which dimerizes and reductively forms a bridging [4Fe-4S] cluster aided by ferredoxin 2. The interaction site maps to a conserved hydrophobic patch at the end of the C-terminal α-helix of NFU1; mutagenesis at this site abolishes cluster acquisition and downstream maturation of lipoic acid synthase (LIAS), thereby impairing lipoylation of PDH, α-KGDH, and glycine cleavage complex components.","method":"Genetic knockdown/knockout in human cells, biochemical pulldown/co-IP, site-directed mutagenesis of NFU1, Fe-S cluster transfer assays, enzymatic activity assays for LIAS-dependent lipoylation","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction mapping with mutagenesis confirming functional site, multiple client proteins assessed, consistent with structural studies (PMID:33711344, PMID:37211204)","pmids":["32776106"],"is_preprint":false},{"year":2021,"finding":"ISCA1 is the key orchestrator of mitochondrial [4Fe-4S] protein maturation: it interacts with both NFU1 and ISCA2 (which do not interact with each other), 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 between ISCA1 and the C-terminal domain of NFU1.","method":"NMR spectroscopy (interaction mapping and structural modeling of complexes), in vitro Fe-S cluster transfer assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — NMR-based structural characterization of binary and ternary complexes combined with in vitro functional cluster transfer assays","pmids":["33711344"],"is_preprint":false},{"year":2022,"finding":"Human NFU1 forms a tight complex with human lipoyl synthase (LIAS) in vitro and efficiently restores the auxiliary [4Fe-4S] cluster of LIAS during catalytic turnover, enabling multiple rounds of lipoyl cofactor synthesis. BOLA3 has no direct effect on Fe-S cluster transfer from NFU1 to LIAS.","method":"In vitro reconstitution of LIAS activity in the presence of NFU1 (radical SAM assay), protein complex formation assay, Fe-S cluster transfer assay","journal":"ACS bio & med chem Au","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution demonstrating direct catalytic support of LIAS by NFU1, with multiple turnover readout and controls excluding BOLA3","pmids":["36281303"],"is_preprint":false},{"year":2023,"finding":"NFU1 functions in inserting the [4Fe-4S] cluster into the mitoribosome assembly factor METTL17, via the ISCA1-NFU1 node, thereby indirectly supporting mitoribosome small subunit assembly and mitochondrial protein synthesis. Fibroblasts from NFU1-deficient patients show previously unrecognized attenuation of mitochondrial protein synthesis.","method":"siRNA silencing of Fe-S cluster biosynthetic and delivery factors, mitoribosome assembly assays, mitochondrial translation assays, structure-function correlation studies, patient fibroblast analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — functional silencing studies with mitoribosome assembly and translation readouts, but NFU1-METTL17 interaction not directly reconstituted","pmids":["37823603"],"is_preprint":false},{"year":2023,"finding":"Structural plasticity of NFU1's N-terminal domain is required for protein partner recognition during [4Fe-4S] cluster transfer. SAXS and paramagnetic NMR reveal structural models of ISCA1-ISCA2, ISCA1-ISCA2-NFU1, and ISCA1-NFU1 apo complexes; the terminal stable species is the ISCA1-NFU1 complex carrying the [4Fe-4S] cluster, and the N-terminal domain of NFU1 acts as a modulator of cluster transfer.","method":"Small-angle X-ray scattering (SEC-SAXS), paramagnetic NMR, structural modeling of apo and holo complexes","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — structural characterization of multiple complex states by orthogonal biophysical methods (SAXS + paramagnetic NMR) in a single study","pmids":["37211204"],"is_preprint":false},{"year":2017,"finding":"The MMDS1 disease-causing Gly208Cys substitution in NFU1 increases propensity to dimerize and perturbs secondary structure, severely impairing the ability of NFU1 to accept a [4Fe-4S] cluster from physiologically relevant sources (ISCU, ISCA). The additional cysteine at position 208 does not contribute to cluster coordination; rather the structural change prevents cluster acquisition and downstream trafficking.","method":"In vitro biochemical characterization: protein stability assays, oligomeric state analysis (SEC), secondary structure analysis (CD spectroscopy), Fe-S cluster reconstitution assays, site-directed mutagenesis","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal in vitro methods with mutagenesis panel dissecting mechanism of pathogenic variant","pmids":["28161430"],"is_preprint":false},{"year":2017,"finding":"The MMDS1 disease-causing Gly189Arg substitution in NFU1 increases structural flexibility, decreases stability, and shifts the monomer-dimer equilibrium toward monomer, thereby impairing the ability of NFU1 to receive a [4Fe-4S] cluster from physiologically relevant sources.","method":"In vitro biochemical characterization: protein stability, oligomeric state, secondary structure (CD), Fe-S cluster reconstitution assays, site-directed mutagenesis","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 1 methods but single lab, and complementary to PMID:28161430 from same group","pmids":["28906594"],"is_preprint":false},{"year":2003,"finding":"The C-terminal NifU-like domain of the cytosolic protein HIRIP5 interacts with the N-terminal CBD-4 domain of laforin (EPM2A phosphatase) both in vitro (pull-down) and in vivo (co-immunoprecipitation); laforin dephosphorylates HIRIP5 in vitro, suggesting that NFU1/HIRIP5-related proteins participate in a phosphorylation-regulated interaction with laforin.","method":"Yeast two-hybrid, in vitro pulldown, co-immunoprecipitation, in vitro phosphatase assay","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 3 — interaction confirmed by multiple methods including in vivo co-IP, but functional significance for NFU1 itself remains indirect (study focused on HIRIP5, not NFU1 directly)","pmids":["12915448"],"is_preprint":false},{"year":2023,"finding":"C. elegans nfu-1 (NFU1 ortholog) is required for normal acetylcholine signaling at neuromuscular junctions. Patient-specific point variants Gly147Arg and Gly166Cys cause allele-specific neuromuscular dysfunction: Gly147Arg causes hypersensitivity to acetylcholine at the presynaptic level (rescued by acetylcholine release knockdown), while Gly166Cys causes postsynaptic acetylcholine hypersensitivity.","method":"CRISPR knock-in of patient variants in C. elegans, acetylcholine sensitivity assays, genetic epistasis (knockdown of acetylcholine release), motility assays","journal":"Disease models & mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis in C. elegans ortholog with patient-specific alleles and defined neuromuscular phenotype, but mechanism linking Fe-S cluster deficiency to cholinergic signaling not fully resolved","pmids":["36645076"],"is_preprint":false}],"current_model":"Human mitochondrial NFU1 is a late-acting [4Fe-4S] cluster carrier that receives two [2Fe-2S] clusters sequentially from ISCU2 and ISCA1 (the latter orchestrating a transient ISCA1-ISCA2-NFU1 ternary complex), reductively assembles them into a bridging [4Fe-4S] cluster held between two NFU1 subunits in a dimer, and then directly transfers this cluster to a specific subset of mitochondrial client proteins—most critically lipoic acid synthase (LIAS), whose regenerated auxiliary cluster enables multi-turnover lipoylation of pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and the glycine cleavage complex—as well as to complex II (SDH) and the mitoribosome assembly factor METTL17, with its N-terminal domain modulating partner recognition and its C-terminal CXXC motif providing the cluster-binding site."},"narrative":{"teleology":[{"year":2011,"claim":"Establishing that NFU1 is not a general Fe-S scaffold but a specialized late-acting maturation factor for a restricted subset of mitochondrial [4Fe-4S] clients — primarily lipoic acid synthase and SDH — resolved its position in the Fe-S biogenesis pathway and linked its loss to defective lipoylation.","evidence":"RNAi in human cells and yeast deletion mutants with enzymatic activity assays for LAS/PDHC/SDH, plus isoform-specific retroviral complementation in patient fibroblasts","pmids":["22077971","21944046"],"confidence":"High","gaps":["Whether NFU1 directly binds and transfers a [4Fe-4S] cluster was not demonstrated","The donor(s) of the cluster to NFU1 were unknown","Full client repertoire beyond LAS and SDH was not defined"]},{"year":2016,"claim":"Structural determination revealed that NFU1's C-terminal CXXC domain coordinates a bridging [4Fe-4S] cluster between two subunits forming a cluster-linked dimer, and that holo-NFU1 can activate apo-aconitase, proving its cluster-transfer competence in vitro.","evidence":"NMR structure of N- and C-terminal domains, SAXS, SEC, and in vitro aconitase activation assay; yeast genetic and proteomic interaction mapping with ISA complex and client proteins","pmids":["27818104","27532773"],"confidence":"High","gaps":["The physiological cluster donor to NFU1 remained unidentified","Whether NFU1 directly interacts with LIAS was not tested","The role of the N-terminal domain in partner selectivity was unclear"]},{"year":2017,"claim":"Biochemical dissection of MMDS1-causing mutations (Gly208Cys and Gly189Arg) showed they impair cluster acquisition not by altering the cluster-binding cysteines but by disrupting dimerization and structural integrity, establishing the mechanistic basis of disease pathogenesis.","evidence":"In vitro SEC, CD spectroscopy, Fe-S reconstitution assays, and site-directed mutagenesis panels for both pathogenic variants","pmids":["28161430","28906594"],"confidence":"High","gaps":["Whether these mutations also impair downstream cluster transfer to clients was not directly tested","Impact on the full client repertoire in patient cells was not assessed","G189R finding from a single lab (Medium confidence individually)"]},{"year":2020,"claim":"Identification of ISCU2 and ISCA1 as sequential [2Fe-2S] cluster donors to NFU1, with ferredoxin 2-assisted reductive coupling into a [4Fe-4S] cluster, defined the complete upstream delivery pathway and mapped the interaction site to a conserved hydrophobic patch on NFU1's C-terminal α-helix.","evidence":"NMR interaction mapping, ITC (Kd ~1.1 µM), in vitro Fe-S cluster transfer assays, site-directed mutagenesis abolishing cluster acquisition and downstream LIAS-dependent lipoylation in human cells","pmids":["32151725","32776106"],"confidence":"High","gaps":["The reductive coupling mechanism and precise role of ferredoxin 2 were not structurally resolved","Whether ISCU transfers a [4Fe-4S] or two sequential [2Fe-2S] clusters was debated between the two studies"]},{"year":2021,"claim":"NMR-based structural characterization showed that ISCA1 orchestrates a transient ISCA1-ISCA2-NFU1 ternary complex that channels the [4Fe-4S] cluster from the ISCA1-ISCA2 assembly site to an ISCA1-NFU1 intermediate, clarifying the handoff mechanism in the late biogenesis pathway.","evidence":"NMR interaction mapping and structural modeling of binary and ternary apo/holo complexes, in vitro cluster transfer assays","pmids":["33711344"],"confidence":"High","gaps":["Kinetics and directionality of cluster transfer within the ternary complex were not quantified","Role of ferredoxin 2 in the ternary complex context was not addressed"]},{"year":2022,"claim":"In vitro reconstitution demonstrated that NFU1 forms a tight complex with LIAS and regenerates its auxiliary [4Fe-4S] cluster during catalytic turnover, enabling multiple rounds of lipoyl cofactor synthesis — establishing NFU1 as a catalytic partner rather than a one-shot donor.","evidence":"Radical SAM activity assay for LIAS with NFU1, protein complex formation assay, Fe-S cluster transfer assay; BOLA3 shown to have no direct effect","pmids":["36281303"],"confidence":"High","gaps":["Structural basis of the NFU1-LIAS complex is not resolved","Whether multi-turnover regeneration occurs in cellulo was not shown","Role of BOLA3 in vivo remains unexplained despite no in vitro effect"]},{"year":2023,"claim":"Discovery that NFU1 delivers a [4Fe-4S] cluster to METTL17 expanded the client repertoire beyond metabolic enzymes to mitoribosome assembly, revealing a previously unrecognized role in mitochondrial translation that explains some NFU1-deficiency phenotypes.","evidence":"siRNA silencing of Fe-S biogenesis factors, mitoribosome assembly and mitochondrial translation assays, NFU1-patient fibroblast analysis","pmids":["37823603"],"confidence":"Medium","gaps":["Direct physical interaction between NFU1 and METTL17 was not reconstituted in vitro","Quantitative contribution of translation defects versus lipoylation defects to MMDS1 pathology is unknown"]},{"year":2023,"claim":"SAXS and paramagnetic NMR structural models of the ISCA1-ISCA2-NFU1 assembly intermediates revealed that NFU1's N-terminal domain undergoes structural rearrangements that modulate partner recognition and cluster transfer, assigning a functional role to the previously enigmatic N-terminal domain.","evidence":"SEC-SAXS, paramagnetic NMR, structural modeling of apo and holo complexes","pmids":["37211204"],"confidence":"High","gaps":["High-resolution atomic structure of the full holo-NFU1 in complex with clients is lacking","Whether N-terminal domain plasticity differs for different client proteins is untested"]},{"year":2023,"claim":"C. elegans studies showed that NFU1 orthologue loss-of-function affects neuromuscular junction acetylcholine signaling, with patient-specific alleles causing distinct pre- versus post-synaptic defects, extending the phenotypic impact of NFU1 deficiency to the nervous system.","evidence":"CRISPR knock-in of patient variants in C. elegans, acetylcholine sensitivity assays, genetic epistasis","pmids":["36645076"],"confidence":"Medium","gaps":["The molecular link between mitochondrial Fe-S cluster deficiency and cholinergic signaling is unknown","Whether these neuromuscular phenotypes are conserved in mammals has not been tested"]},{"year":null,"claim":"Key unresolved questions include the complete client repertoire of NFU1 in human mitochondria, the high-resolution structural basis of NFU1-client recognition (especially NFU1-LIAS), the in vivo mechanism by which BOLA3 cooperates with NFU1 despite lacking direct in vitro effects on cluster transfer, and how NFU1 deficiency leads to neuromuscular phenotypes.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of an NFU1-client complex exists","BOLA3's in vivo role in NFU1-dependent cluster delivery is mechanistically unexplained","Full inventory of NFU1 client proteins in human cells has not been systematically determined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[0,2,5,7]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,2,5]}],"pathway":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,7]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,11]}],"complexes":["ISCA1-ISCA2-NFU1 ternary complex","ISCA1-NFU1 binary complex","NFU1-LIAS complex"],"partners":["ISCA1","ISCA2","ISCU","LIAS","BOLA3","METTL17","FDX2"],"other_free_text":[]},"mechanistic_narrative":"NFU1 is a mitochondrial late-acting iron-sulfur cluster carrier that receives [2Fe-2S] clusters sequentially from ISCU2 and ISCA1, reductively assembles them into a bridging [4Fe-4S] cluster coordinated by its C-terminal CXXC motif between two NFU1 subunits, and delivers this cluster to a specific subset of mitochondrial client proteins [PMID:22077971, PMID:27818104, PMID:32776106, PMID:33711344]. Its most critical client is lipoic acid synthase (LIAS), whose auxiliary [4Fe-4S] cluster is regenerated by NFU1 during catalytic turnover to enable multi-round lipoylation of pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and the glycine cleavage complex; additional clients include succinate dehydrogenase (complex II) and the mitoribosome assembly factor METTL17 [PMID:36281303, PMID:21944046, PMID:37823603]. The N-terminal domain modulates partner recognition during cluster transfer through structural plasticity, while ISCA1 orchestrates a transient ISCA1-ISCA2-NFU1 ternary complex that channels [4Fe-4S] clusters to the ISCA1-NFU1 delivery intermediate [PMID:37211204, PMID:33711344]. Pathogenic missense mutations (e.g., Gly208Cys, Gly189Arg) cause multiple mitochondrial dysfunctions syndrome 1 (MMDS1) by disrupting NFU1 dimerization or stability and thereby abolishing cluster acquisition [PMID:28161430, PMID:28906594]."},"prefetch_data":{"uniprot":{"accession":"Q9UMS0","full_name":"NFU1 iron-sulfur cluster scaffold homolog, mitochondrial","aliases":["HIRA-interacting protein 5"],"length_aa":254,"mass_kda":28.5,"function":"Iron-sulfur cluster scaffold protein which can assemble [4Fe-4S] clusters and deliver them to target proteins","subcellular_location":"Mitochondrion; Cytoplasm, cytosol","url":"https://www.uniprot.org/uniprotkb/Q9UMS0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NFU1","classification":"Not Classified","n_dependent_lines":170,"n_total_lines":1208,"dependency_fraction":0.14072847682119205},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NFU1","total_profiled":1310},"omim":[{"mim_id":"620938","title":"SPASTIC PARAPLEGIA 93, AUTOSOMAL RECESSIVE; SPG93","url":"https://www.omim.org/entry/620938"},{"mim_id":"615330","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 3; MMDS3","url":"https://www.omim.org/entry/615330"},{"mim_id":"615316","title":"IRON-SULFUR CLUSTER ASSEMBLY FACTOR IBA57; IBA57","url":"https://www.omim.org/entry/615316"},{"mim_id":"614299","title":"MULTIPLE MITOCHONDRIAL DYSFUNCTIONS SYNDROME 2 WITH HYPERGLYCINEMIA; MMDS2","url":"https://www.omim.org/entry/614299"},{"mim_id":"613183","title":"BOLA FAMILY MEMBER 3; BOLA3","url":"https://www.omim.org/entry/613183"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NFU1"},"hgnc":{"alias_symbol":["CGI-33","NifU","NIFUC"],"prev_symbol":["HIRIP5"]},"alphafold":{"accession":"Q9UMS0","domains":[{"cath_id":"3.30.1370.70","chopping":"63-148","consensus_level":"medium","plddt":95.132,"start":63,"end":148},{"cath_id":"3.30.300.130","chopping":"169-241","consensus_level":"medium","plddt":93.5827,"start":169,"end":241}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UMS0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UMS0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UMS0-F1-predicted_aligned_error_v6.png","plddt_mean":78.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NFU1","jax_strain_url":"https://www.jax.org/strain/search?query=NFU1"},"sequence":{"accession":"Q9UMS0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UMS0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UMS0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UMS0"}},"corpus_meta":[{"pmid":"10639125","id":"PMC_10639125","title":"NifS-directed assembly of a transient [2Fe-2S] cluster within the NifU protein.","date":"2000","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/10639125","citation_count":267,"is_preprint":false},{"pmid":"22077971","id":"PMC_22077971","title":"A fatal mitochondrial disease is associated with defective NFU1 function in the maturation of a subset of mitochondrial Fe-S proteins.","date":"2011","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22077971","citation_count":225,"is_preprint":false},{"pmid":"21944046","id":"PMC_21944046","title":"Mutations in iron-sulfur cluster scaffold genes NFU1 and BOLA3 cause a fatal deficiency of multiple respiratory chain and 2-oxoacid dehydrogenase enzymes.","date":"2011","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21944046","citation_count":220,"is_preprint":false},{"pmid":"7947754","id":"PMC_7947754","title":"nifU gene product from Azotobacter vinelandii is a homodimer that contains two identical [2Fe-2S] clusters.","date":"1994","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/7947754","citation_count":129,"is_preprint":false},{"pmid":"15031412","id":"PMC_15031412","title":"The Arabidopsis chloroplastic NifU-like protein CnfU, which can act as an iron-sulfur cluster scaffold protein, is required for biogenesis of ferredoxin and photosystem I.","date":"2004","source":"The Plant cell","url":"https://pubmed.ncbi.nlm.nih.gov/15031412","citation_count":117,"is_preprint":false},{"pmid":"16185064","id":"PMC_16185064","title":"NifS-mediated assembly of [4Fe-4S] clusters in the N- and C-terminal domains of the NifU scaffold protein.","date":"2005","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16185064","citation_count":114,"is_preprint":false},{"pmid":"14993221","id":"PMC_14993221","title":"Iron-sulfur cluster assembly: NifU-directed activation of the nitrogenase Fe protein.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/14993221","citation_count":111,"is_preprint":false},{"pmid":"27532773","id":"PMC_27532773","title":"Role of Nfu1 and Bol3 in iron-sulfur cluster transfer to mitochondrial clients.","date":"2016","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/27532773","citation_count":106,"is_preprint":false},{"pmid":"10819462","id":"PMC_10819462","title":"Modular organization and identification of a mononuclear iron-binding site within the NifU protein.","date":"2000","source":"Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10819462","citation_count":104,"is_preprint":false},{"pmid":"2553733","id":"PMC_2553733","title":"Nitrogen fixation (nif) genes of the cyanobacterium Anabaena species strain PCC 7120. 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RNAi depletion of NFU1 in human cells markedly decreased lipoic acid synthase (LAS) activity and in turn pyruvate dehydrogenase complex (PDHC) activity, and reduced succinate dehydrogenase (SDH) amount, but did not affect other Fe-S proteins tested. By contrast, depletion of the general scaffold ISCU severely affected all tested Fe-S proteins, demonstrating that NFU1 has a specialized rather than general role in mitochondrial Fe-S cluster maturation.\",\n      \"method\": \"RNA interference in human cell culture, enzymatic activity assays, protein quantification; yeast NFU1 deletion with lipoylation and SDH activity measurements; yeast missense mutant functional complementation\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (RNAi, yeast KO, yeast complementation) across two model systems, independently replicated in a second paper (PMID:21944046)\",\n      \"pmids\": [\"22077971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Both NFU1 (mitochondrial isoform) and BOLA3 (isoform 1) are required for the maturation of lipoate-containing 2-oxoacid dehydrogenases and for respiratory chain complex assembly. Retroviral transduction with the mitochondrial isoform of NFU1, but not the cytosolic isoform, restored respiratory chain function and oxoacid dehydrogenase complex activity in patient fibroblasts.\",\n      \"method\": \"Retroviral complementation of patient fibroblast lines with isoform-specific NFU1 constructs; enzymatic activity assays for respiratory chain and oxoacid dehydrogenase complexes\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — isoform-specific functional rescue with enzymatic readouts, replicated by companion paper (PMID:22077971)\",\n      \"pmids\": [\"21944046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Human mitochondrial NFU1 binds and transfers a [4Fe-4S] cluster. The C-terminal domain contains the two cysteines that coordinate one [4Fe-4S] cluster bridging two NFU1 subunits to form a cluster-linked dimer; three such dimers associate via their N-terminal domains to form hexameric holo-NFU1. Holo-NFU1 can activate apo-aconitase in vitro, confirming its cluster-transfer activity.\",\n      \"method\": \"NMR spectroscopy (3D structures of N- and C-terminal domains), small-angle X-ray scattering (SAXS), size-exclusion chromatography, in vitro aconitase activation assay\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure determination combined with SAXS and functional in vitro reconstitution assay in single study\",\n      \"pmids\": [\"27818104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Yeast Nfu1 functions in a late step of [4Fe-4S] cluster biogenesis and physically interacts with components of the ISA [4Fe-4S] assembly complex and with [4Fe-4S] client proteins. Bol3 (human BOLA3 ortholog) functions together with Nfu1 in this late step, whereas Bol1 functions earlier with the monothiol glutaredoxin Grx5.\",\n      \"method\": \"Genetic studies in yeast (deletion mutants, growth under oxidative metabolism), proteomic interaction studies (mass spectrometry-based), epistasis analysis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis combined with proteomics-based physical interaction mapping, multiple orthogonal approaches\",\n      \"pmids\": [\"27532773\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Human ISCU (ISCU2) directly interacts with NFU1 (Kd ~1.1 µM as measured by ITC), and ISCU[4Fe-4S] transfers its Fe-S cluster to apo-NFU1 in the absence of a chaperone to form holo-NFU1. ISCU[2Fe-2S] does not transfer its cluster to apo-NFU1. The interaction site maps to the cluster-binding region of ISCU and two α-helices in the C-terminal domain of NFU1.\",\n      \"method\": \"NMR spectroscopy, SAXS, size-exclusion chromatography, isothermal titration calorimetry (ITC), in vitro Fe-S cluster transfer assay\",\n      \"journal\": \"Journal of structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of cluster transfer with structural mapping by NMR/SAXS and quantitative binding by ITC\",\n      \"pmids\": [\"32151725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ISCU2 and ISCA1 are the direct sequential donors of [2Fe-2S] clusters to mitochondrial NFU1, which dimerizes and reductively forms a bridging [4Fe-4S] cluster aided by ferredoxin 2. The interaction site maps to a conserved hydrophobic patch at the end of the C-terminal α-helix of NFU1; mutagenesis at this site abolishes cluster acquisition and downstream maturation of lipoic acid synthase (LIAS), thereby impairing lipoylation of PDH, α-KGDH, and glycine cleavage complex components.\",\n      \"method\": \"Genetic knockdown/knockout in human cells, biochemical pulldown/co-IP, site-directed mutagenesis of NFU1, Fe-S cluster transfer assays, enzymatic activity assays for LIAS-dependent lipoylation\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction mapping with mutagenesis confirming functional site, multiple client proteins assessed, consistent with structural studies (PMID:33711344, PMID:37211204)\",\n      \"pmids\": [\"32776106\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ISCA1 is the key orchestrator of mitochondrial [4Fe-4S] protein maturation: it interacts with both NFU1 and ISCA2 (which do not interact with each other), 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 between ISCA1 and the C-terminal domain of NFU1.\",\n      \"method\": \"NMR spectroscopy (interaction mapping and structural modeling of complexes), in vitro Fe-S cluster transfer assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR-based structural characterization of binary and ternary complexes combined with in vitro functional cluster transfer assays\",\n      \"pmids\": [\"33711344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Human NFU1 forms a tight complex with human lipoyl synthase (LIAS) in vitro and efficiently restores the auxiliary [4Fe-4S] cluster of LIAS during catalytic turnover, enabling multiple rounds of lipoyl cofactor synthesis. BOLA3 has no direct effect on Fe-S cluster transfer from NFU1 to LIAS.\",\n      \"method\": \"In vitro reconstitution of LIAS activity in the presence of NFU1 (radical SAM assay), protein complex formation assay, Fe-S cluster transfer assay\",\n      \"journal\": \"ACS bio & med chem Au\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution demonstrating direct catalytic support of LIAS by NFU1, with multiple turnover readout and controls excluding BOLA3\",\n      \"pmids\": [\"36281303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NFU1 functions in inserting the [4Fe-4S] cluster into the mitoribosome assembly factor METTL17, via the ISCA1-NFU1 node, thereby indirectly supporting mitoribosome small subunit assembly and mitochondrial protein synthesis. Fibroblasts from NFU1-deficient patients show previously unrecognized attenuation of mitochondrial protein synthesis.\",\n      \"method\": \"siRNA silencing of Fe-S cluster biosynthetic and delivery factors, mitoribosome assembly assays, mitochondrial translation assays, structure-function correlation studies, patient fibroblast analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional silencing studies with mitoribosome assembly and translation readouts, but NFU1-METTL17 interaction not directly reconstituted\",\n      \"pmids\": [\"37823603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Structural plasticity of NFU1's N-terminal domain is required for protein partner recognition during [4Fe-4S] cluster transfer. SAXS and paramagnetic NMR reveal structural models of ISCA1-ISCA2, ISCA1-ISCA2-NFU1, and ISCA1-NFU1 apo complexes; the terminal stable species is the ISCA1-NFU1 complex carrying the [4Fe-4S] cluster, and the N-terminal domain of NFU1 acts as a modulator of cluster transfer.\",\n      \"method\": \"Small-angle X-ray scattering (SEC-SAXS), paramagnetic NMR, structural modeling of apo and holo complexes\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural characterization of multiple complex states by orthogonal biophysical methods (SAXS + paramagnetic NMR) in a single study\",\n      \"pmids\": [\"37211204\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The MMDS1 disease-causing Gly208Cys substitution in NFU1 increases propensity to dimerize and perturbs secondary structure, severely impairing the ability of NFU1 to accept a [4Fe-4S] cluster from physiologically relevant sources (ISCU, ISCA). The additional cysteine at position 208 does not contribute to cluster coordination; rather the structural change prevents cluster acquisition and downstream trafficking.\",\n      \"method\": \"In vitro biochemical characterization: protein stability assays, oligomeric state analysis (SEC), secondary structure analysis (CD spectroscopy), Fe-S cluster reconstitution assays, site-directed mutagenesis\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal in vitro methods with mutagenesis panel dissecting mechanism of pathogenic variant\",\n      \"pmids\": [\"28161430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The MMDS1 disease-causing Gly189Arg substitution in NFU1 increases structural flexibility, decreases stability, and shifts the monomer-dimer equilibrium toward monomer, thereby impairing the ability of NFU1 to receive a [4Fe-4S] cluster from physiologically relevant sources.\",\n      \"method\": \"In vitro biochemical characterization: protein stability, oligomeric state, secondary structure (CD), Fe-S cluster reconstitution assays, site-directed mutagenesis\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 methods but single lab, and complementary to PMID:28161430 from same group\",\n      \"pmids\": [\"28906594\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The C-terminal NifU-like domain of the cytosolic protein HIRIP5 interacts with the N-terminal CBD-4 domain of laforin (EPM2A phosphatase) both in vitro (pull-down) and in vivo (co-immunoprecipitation); laforin dephosphorylates HIRIP5 in vitro, suggesting that NFU1/HIRIP5-related proteins participate in a phosphorylation-regulated interaction with laforin.\",\n      \"method\": \"Yeast two-hybrid, in vitro pulldown, co-immunoprecipitation, in vitro phosphatase assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — interaction confirmed by multiple methods including in vivo co-IP, but functional significance for NFU1 itself remains indirect (study focused on HIRIP5, not NFU1 directly)\",\n      \"pmids\": [\"12915448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"C. elegans nfu-1 (NFU1 ortholog) is required for normal acetylcholine signaling at neuromuscular junctions. Patient-specific point variants Gly147Arg and Gly166Cys cause allele-specific neuromuscular dysfunction: Gly147Arg causes hypersensitivity to acetylcholine at the presynaptic level (rescued by acetylcholine release knockdown), while Gly166Cys causes postsynaptic acetylcholine hypersensitivity.\",\n      \"method\": \"CRISPR knock-in of patient variants in C. elegans, acetylcholine sensitivity assays, genetic epistasis (knockdown of acetylcholine release), motility assays\",\n      \"journal\": \"Disease models & mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in C. elegans ortholog with patient-specific alleles and defined neuromuscular phenotype, but mechanism linking Fe-S cluster deficiency to cholinergic signaling not fully resolved\",\n      \"pmids\": [\"36645076\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Human mitochondrial NFU1 is a late-acting [4Fe-4S] cluster carrier that receives two [2Fe-2S] clusters sequentially from ISCU2 and ISCA1 (the latter orchestrating a transient ISCA1-ISCA2-NFU1 ternary complex), reductively assembles them into a bridging [4Fe-4S] cluster held between two NFU1 subunits in a dimer, and then directly transfers this cluster to a specific subset of mitochondrial client proteins—most critically lipoic acid synthase (LIAS), whose regenerated auxiliary cluster enables multi-turnover lipoylation of pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and the glycine cleavage complex—as well as to complex II (SDH) and the mitoribosome assembly factor METTL17, with its N-terminal domain modulating partner recognition and its C-terminal CXXC motif providing the cluster-binding site.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NFU1 is a mitochondrial late-acting iron-sulfur cluster carrier that receives [2Fe-2S] clusters sequentially from ISCU2 and ISCA1, reductively assembles them into a bridging [4Fe-4S] cluster coordinated by its C-terminal CXXC motif between two NFU1 subunits, and delivers this cluster to a specific subset of mitochondrial client proteins [PMID:22077971, PMID:27818104, PMID:32776106, PMID:33711344]. Its most critical client is lipoic acid synthase (LIAS), whose auxiliary [4Fe-4S] cluster is regenerated by NFU1 during catalytic turnover to enable multi-round lipoylation of pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and the glycine cleavage complex; additional clients include succinate dehydrogenase (complex II) and the mitoribosome assembly factor METTL17 [PMID:36281303, PMID:21944046, PMID:37823603]. The N-terminal domain modulates partner recognition during cluster transfer through structural plasticity, while ISCA1 orchestrates a transient ISCA1-ISCA2-NFU1 ternary complex that channels [4Fe-4S] clusters to the ISCA1-NFU1 delivery intermediate [PMID:37211204, PMID:33711344]. Pathogenic missense mutations (e.g., Gly208Cys, Gly189Arg) cause multiple mitochondrial dysfunctions syndrome 1 (MMDS1) by disrupting NFU1 dimerization or stability and thereby abolishing cluster acquisition [PMID:28161430, PMID:28906594].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Establishing that NFU1 is not a general Fe-S scaffold but a specialized late-acting maturation factor for a restricted subset of mitochondrial [4Fe-4S] clients — primarily lipoic acid synthase and SDH — resolved its position in the Fe-S biogenesis pathway and linked its loss to defective lipoylation.\",\n      \"evidence\": \"RNAi in human cells and yeast deletion mutants with enzymatic activity assays for LAS/PDHC/SDH, plus isoform-specific retroviral complementation in patient fibroblasts\",\n      \"pmids\": [\"22077971\", \"21944046\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether NFU1 directly binds and transfers a [4Fe-4S] cluster was not demonstrated\",\n        \"The donor(s) of the cluster to NFU1 were unknown\",\n        \"Full client repertoire beyond LAS and SDH was not defined\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Structural determination revealed that NFU1's C-terminal CXXC domain coordinates a bridging [4Fe-4S] cluster between two subunits forming a cluster-linked dimer, and that holo-NFU1 can activate apo-aconitase, proving its cluster-transfer competence in vitro.\",\n      \"evidence\": \"NMR structure of N- and C-terminal domains, SAXS, SEC, and in vitro aconitase activation assay; yeast genetic and proteomic interaction mapping with ISA complex and client proteins\",\n      \"pmids\": [\"27818104\", \"27532773\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The physiological cluster donor to NFU1 remained unidentified\",\n        \"Whether NFU1 directly interacts with LIAS was not tested\",\n        \"The role of the N-terminal domain in partner selectivity was unclear\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Biochemical dissection of MMDS1-causing mutations (Gly208Cys and Gly189Arg) showed they impair cluster acquisition not by altering the cluster-binding cysteines but by disrupting dimerization and structural integrity, establishing the mechanistic basis of disease pathogenesis.\",\n      \"evidence\": \"In vitro SEC, CD spectroscopy, Fe-S reconstitution assays, and site-directed mutagenesis panels for both pathogenic variants\",\n      \"pmids\": [\"28161430\", \"28906594\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether these mutations also impair downstream cluster transfer to clients was not directly tested\",\n        \"Impact on the full client repertoire in patient cells was not assessed\",\n        \"G189R finding from a single lab (Medium confidence individually)\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identification of ISCU2 and ISCA1 as sequential [2Fe-2S] cluster donors to NFU1, with ferredoxin 2-assisted reductive coupling into a [4Fe-4S] cluster, defined the complete upstream delivery pathway and mapped the interaction site to a conserved hydrophobic patch on NFU1's C-terminal α-helix.\",\n      \"evidence\": \"NMR interaction mapping, ITC (Kd ~1.1 µM), in vitro Fe-S cluster transfer assays, site-directed mutagenesis abolishing cluster acquisition and downstream LIAS-dependent lipoylation in human cells\",\n      \"pmids\": [\"32151725\", \"32776106\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The reductive coupling mechanism and precise role of ferredoxin 2 were not structurally resolved\",\n        \"Whether ISCU transfers a [4Fe-4S] or two sequential [2Fe-2S] clusters was debated between the two studies\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"NMR-based structural characterization showed that ISCA1 orchestrates a transient ISCA1-ISCA2-NFU1 ternary complex that channels the [4Fe-4S] cluster from the ISCA1-ISCA2 assembly site to an ISCA1-NFU1 intermediate, clarifying the handoff mechanism in the late biogenesis pathway.\",\n      \"evidence\": \"NMR interaction mapping and structural modeling of binary and ternary apo/holo complexes, in vitro cluster transfer assays\",\n      \"pmids\": [\"33711344\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Kinetics and directionality of cluster transfer within the ternary complex were not quantified\",\n        \"Role of ferredoxin 2 in the ternary complex context was not addressed\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"In vitro reconstitution demonstrated that NFU1 forms a tight complex with LIAS and regenerates its auxiliary [4Fe-4S] cluster during catalytic turnover, enabling multiple rounds of lipoyl cofactor synthesis — establishing NFU1 as a catalytic partner rather than a one-shot donor.\",\n      \"evidence\": \"Radical SAM activity assay for LIAS with NFU1, protein complex formation assay, Fe-S cluster transfer assay; BOLA3 shown to have no direct effect\",\n      \"pmids\": [\"36281303\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the NFU1-LIAS complex is not resolved\",\n        \"Whether multi-turnover regeneration occurs in cellulo was not shown\",\n        \"Role of BOLA3 in vivo remains unexplained despite no in vitro effect\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that NFU1 delivers a [4Fe-4S] cluster to METTL17 expanded the client repertoire beyond metabolic enzymes to mitoribosome assembly, revealing a previously unrecognized role in mitochondrial translation that explains some NFU1-deficiency phenotypes.\",\n      \"evidence\": \"siRNA silencing of Fe-S biogenesis factors, mitoribosome assembly and mitochondrial translation assays, NFU1-patient fibroblast analysis\",\n      \"pmids\": [\"37823603\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct physical interaction between NFU1 and METTL17 was not reconstituted in vitro\",\n        \"Quantitative contribution of translation defects versus lipoylation defects to MMDS1 pathology is unknown\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"SAXS and paramagnetic NMR structural models of the ISCA1-ISCA2-NFU1 assembly intermediates revealed that NFU1's N-terminal domain undergoes structural rearrangements that modulate partner recognition and cluster transfer, assigning a functional role to the previously enigmatic N-terminal domain.\",\n      \"evidence\": \"SEC-SAXS, paramagnetic NMR, structural modeling of apo and holo complexes\",\n      \"pmids\": [\"37211204\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"High-resolution atomic structure of the full holo-NFU1 in complex with clients is lacking\",\n        \"Whether N-terminal domain plasticity differs for different client proteins is untested\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"C. elegans studies showed that NFU1 orthologue loss-of-function affects neuromuscular junction acetylcholine signaling, with patient-specific alleles causing distinct pre- versus post-synaptic defects, extending the phenotypic impact of NFU1 deficiency to the nervous system.\",\n      \"evidence\": \"CRISPR knock-in of patient variants in C. elegans, acetylcholine sensitivity assays, genetic epistasis\",\n      \"pmids\": [\"36645076\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The molecular link between mitochondrial Fe-S cluster deficiency and cholinergic signaling is unknown\",\n        \"Whether these neuromuscular phenotypes are conserved in mammals has not been tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the complete client repertoire of NFU1 in human mitochondria, the high-resolution structural basis of NFU1-client recognition (especially NFU1-LIAS), the in vivo mechanism by which BOLA3 cooperates with NFU1 despite lacking direct in vitro effects on cluster transfer, and how NFU1 deficiency leads to neuromuscular phenotypes.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of an NFU1-client complex exists\",\n        \"BOLA3's in vivo role in NFU1-dependent cluster delivery is mechanistically unexplained\",\n        \"Full inventory of NFU1 client proteins in human cells has not been systematically determined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [0, 2, 5, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 2, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 7]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 11]}\n    ],\n    \"complexes\": [\n      \"ISCA1-ISCA2-NFU1 ternary complex\",\n      \"ISCA1-NFU1 binary complex\",\n      \"NFU1-LIAS complex\"\n    ],\n    \"partners\": [\n      \"ISCA1\",\n      \"ISCA2\",\n      \"ISCU\",\n      \"LIAS\",\n      \"BOLA3\",\n      \"METTL17\",\n      \"FDX2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}