{"gene":"NDUFS2","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2013,"finding":"NDUFAF7, a SAM-dependent methyltransferase, symmetrically dimethylates the ω-NG,NG' atoms of Arg-85 in NDUFS2. This methylation occurs early in complex I assembly and stabilizes a ~400-kDa subcomplex that forms the initial nucleus of the peripheral arm and its junction with the membrane arm.","method":"Mass spectrometry identification of methylated residue, confirmation of NDUFAF7 mitochondrial matrix localization, in vitro methyltransferase assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical identification of modified residue by MS, methyltransferase activity demonstrated in vitro, functionally linked to assembly intermediate; single lab but multiple orthogonal methods","pmids":["24089531"],"is_preprint":false},{"year":2011,"finding":"A homozygous Asp446Asn mutation in NDUFS2 reduces complex I enzymatic activity without reducing complex I abundance, and the mutated residue resides near the coenzyme Q (CoQ) binding pocket. The mutation does not alter the Km for CoQ analogs, suggesting it interferes with CoQ reduction or coupling of CoQ reduction to proton-pumping conformational changes. The enzymatic defect was rescued by transduction of wild-type NDUFS2.","method":"Patient fibroblast biochemical assays, 3D structural modeling of complex I catalytic core, kinetic Km measurements for CoQ analogs, wild-type NDUFS2 rescue by lentiviral transduction","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzymatic assays plus structural modeling plus genetic rescue in a single lab; Km measurement adds orthogonal evidence but model is in silico","pmids":["22036843"],"is_preprint":false},{"year":2019,"finding":"NDUFS2 functions as the molecular oxygen sensor in pulmonary artery smooth muscle cells (PASMCs). Acute hypoxia reduces cysteine residues of Ndufs2 and functionally inhibits complex I. siRNA knockdown of Ndufs2 decreases normoxic H2O2, prevents hypoxia-induced increases in intracellular Ca2+, decreases complex I activity, elevates NADH/NAD+ ratio, and decreases Kv1.5 expression — mimicking aspects of chronic hypoxia. Knockdown of other complex I subunits (Ndufs1) or putative O2 sensors (complex III Rieske Fe-S, COX4i2) had no effect on hypoxic Ca2+ increases, identifying Ndufs2 specifically as the O2-sensing subunit essential for hypoxic pulmonary vasoconstriction (HPV).","method":"siRNA knockdown in PASMCs, live-cell H2O2 and Ca2+ imaging, complex I activity assay, NADH/NAD+ measurement, in vivo siNdufs2 lung delivery with HPV assessment, mitochondria-conditioned media bioassay with catalase treatment","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (enzymatic, live imaging, in vivo), specific epistasis with other subunit knockdowns establishing unique role of NDUFS2, corroborated by separate preprint (2025)","pmids":["30922174"],"is_preprint":false},{"year":2019,"finding":"S100A4 regulates NDUFS2 expression, and NDUFS2 silencing inhibits mitochondrial complex I activity, reduces cellular ATP levels, shifts metabolism toward glycolysis (via hexokinase upregulation), and decreases invasive capacity of lung cancer cells in 3D culture and in vivo metastasis, phenocopying S100A4 silencing.","method":"siRNA knockdown of S100A4 and NDUFS2 in lung cancer cells, oxygen consumption rate measurement, ATP assay, 3D invasion assay, in vivo xenograft/metastasis model","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple cellular and in vivo assays in a single lab establishing functional pathway placement of NDUFS2 downstream of S100A4","pmids":["30885944"],"is_preprint":false},{"year":2021,"finding":"CRISPR/Cas9-mediated disruption of NDUFS2 in HEK293 cells significantly decreases complex I-specific respiration, glycolytic capacity, ATP pool, and cell membrane integrity, while increasing complex II respiration, ROS generation, apoptosis, and necrosis. Treatment with idebenone (a benzoquinone) partially restores growth, ATP pool, and oxygen consumption in NDUFS2-knockout cells.","method":"CRISPR/Cas9 knockout in HEK293 cells, Seahorse respirometry, ATP assay, flow cytometry (apoptosis/necrosis), idebenone rescue experiment","journal":"Mitochondrion","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with multiple defined cellular phenotypic readouts and pharmacological rescue, single lab","pmids":["33744462"],"is_preprint":false},{"year":2024,"finding":"OTUB1, a deubiquitinase, interacts with NDUFS2 and removes K48-linked polyubiquitin chains from NDUFS2, thereby stabilizing NDUFS2 protein. OTUB1 overexpression increases NDUFS2 protein levels; OTUB1 knockdown decreases them. This OTUB1/NDUFS2 axis promotes pancreatic cancer cell survival, proliferation, and migration by inhibiting mitochondrial cell death.","method":"Protein mass spectrometry, co-immunoprecipitation, OTUB1 overexpression/knockdown, ubiquitination assay (K48-linkage specificity), in vivo xenograft tumor growth","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, ubiquitin linkage assay, and in vivo validation in a single lab","pmids":["38653740"],"is_preprint":false},{"year":2024,"finding":"The lncRNA DCRT binds PTBP1 in the nucleus of cardiomyocytes, preventing PTBP1-mediated skipping of the third exon of NDUFS2. When DCRT is lost, exon 3 of NDUFS2 is skipped, producing a truncated/altered NDUFS2 isoform that competitively inhibits mitochondrial complex I activity and binds PRDX5 to suppress its antioxidant activity, causing mitochondrial dysfunction. Coenzyme Q10 partially rescues mitochondrial dysfunction caused by DCRT loss.","method":"CRISPR/Cas9 DCRT knockout mice, cardiac-specific DCRT transgenic mice, RNA immunoprecipitation, chromatin co-IP, isoform sequencing, Western blot, AAV overexpression, transverse aortic constriction model","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (RIP, isoform sequencing, genetic KO and transgenic mice, in vivo TAC model), mechanistically linking splicing regulation directly to NDUFS2 complex I function and PRDX5 interaction","pmids":["38841852"],"is_preprint":false},{"year":2023,"finding":"PTPMT1 co-immunoprecipitates with both SLC25A6 and NDUFS2 in pancreatic cancer cells, suggesting PTPMT1 modulates mitochondrial function via the SLC25A6-NDUFS2 axis.","method":"Co-immunoprecipitation, siRNA knockdown of PTPMT1, PTPMT1 inhibitor (alexidine dihydrochloride) treatment with mitochondrial function readouts","journal":"American journal of cancer research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP experiment identifying the interaction, limited mechanistic follow-up on NDUFS2 specifically","pmids":["37034225"],"is_preprint":false},{"year":2020,"finding":"Co-IP and LC-MS analysis showed that LASS2 interacts with NDUFS2; this interaction is associated with production of mitochondrial ROS (mtROS), which may promote AMPK phosphorylation to inhibit lipogenesis in hepatocytes.","method":"Co-immunoprecipitation, LC-MS, LASS2 overexpression/knockdown in hepatocytes, mtROS measurement","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP/LC-MS interaction, mechanistic link to NDUFS2 function is inferred rather than directly tested","pmids":["32279995"],"is_preprint":false},{"year":2022,"finding":"Disease-causing mutations in NDUFS2 (and the bacterial ortholog NuoCD) that map to subunit interfaces disrupt complex I assembly, as demonstrated in E. coli models. Compound heterozygote analysis in the bacterial system identified which of paired human mutations is more deleterious; alanine substitution allowed distinction between loss-of-original-residue versus gain-of-mutant-residue effects.","method":"Site-directed mutagenesis of E. coli nuoCD (NDUFS2 ortholog), NADH oxidase activity assay in membrane vesicles, co-immunoprecipitation assembly assay, time-delayed expression assay","journal":"Mitochondrion","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — reconstituted bacterial system with mutagenesis and functional assays; ortholog model limits direct translation to human protein","pmids":["36462614"],"is_preprint":false},{"year":2025,"finding":"siRNA knockdown of NDUFS2 (but not NDUFS1, NDUFS7, UQCRFS1, or COX4I2) uniquely inhibits O2-induced increases in intracellular Ca2+, cell shortening, and mitochondrial ROS production in human ductus arteriosus smooth muscle cells (DASMCs), establishing NDUFS2 as the mitochondrial oxygen sensor for O2-induced vasoconstriction in the DA.","method":"siRNA knockdown in human DASMCs, intracellular Ca2+ imaging, cell length measurement, mitochondrial ROS assay (MitoSOX), MitoTEMPO antioxidant rescue, micropolarimetry, complex I/III/IV activity assays, 3′RNA sequencing","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal readouts with specific epistasis against other subunit knockdowns; preprint, single lab, not yet peer-reviewed","pmids":["bio_10.1101_2025.07.08.663799"],"is_preprint":true},{"year":2025,"finding":"ndufs2-/- zebrafish (CRISPR/Cas9 knockout) show 80% reduced complex I enzyme activity, severe neuromuscular dysfunction, metabolic dysregulation (increased lactate, TCA intermediates, acyl-carnitines), and dysregulation of one-carbon metabolism. Folic acid treatment rescues the growth defect and hepatomegaly, implicating one-carbon metabolism in complex I disease pathophysiology.","method":"CRISPR/Cas9 ndufs2 knockout zebrafish, complex I enzyme activity assay, transcriptomics, unbiased metabolomics, folic acid rescue experiment","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with direct enzyme activity measurement, metabolomics, and pharmacological rescue; preprint, single lab","pmids":["40791373"],"is_preprint":true}],"current_model":"NDUFS2 is a core catalytic subunit of mitochondrial respiratory chain complex I (NADH:ubiquinone oxidoreductase) that harbors the rotenone/coenzyme Q binding site at the interface between the peripheral and membrane arms; it undergoes early-assembly symmetric dimethylation of Arg-85 by the methyltransferase NDUFAF7 (stabilizing a ~400-kDa assembly intermediate), is stabilized post-translationally by OTUB1-mediated K48-deubiquitylation, and its cysteine residues undergo redox changes during hypoxia that inhibit complex I activity, making NDUFS2 the specific mitochondrial oxygen sensor responsible for hypoxic pulmonary vasoconstriction and ductus arteriosus O2-sensing; loss of NDUFS2 function impairs complex I activity, elevates ROS, disrupts cellular ATP production and Ca2+ signaling, and pathogenic mutations at the CoQ-binding pocket cause Leigh syndrome by compromising CoQ reduction or proton-pumping coupling."},"narrative":{"mechanistic_narrative":"NDUFS2 is a core catalytic subunit of mitochondrial respiratory chain complex I (NADH:ubiquinone oxidoreductase), residing near the coenzyme Q (CoQ) binding pocket where it couples CoQ reduction to the conformational changes required for proton-pumping [PMID:22036843]. During complex I biogenesis, NDUFS2 is symmetrically dimethylated at Arg-85 by the SAM-dependent methyltransferase NDUFAF7, an early modification that stabilizes a ~400-kDa assembly intermediate forming the nucleus of the peripheral arm and its junction with the membrane arm [PMID:24089531]. Loss of NDUFS2 function — by knockout, knockdown, or disease mutation — selectively impairs complex I respiration while driving compensatory glycolysis, elevated ROS, ATP depletion, and apoptosis/necrosis, phenotypes partially rescued by quinone analogs such as idebenone and CoQ10 [PMID:30885944, PMID:33744462, PMID:38841852]. Beyond its catalytic role, NDUFS2 serves as the specific mitochondrial oxygen sensor: acute hypoxia reduces its cysteine residues and inhibits complex I, and NDUFS2 knockdown — but not knockdown of other complex I, III, or IV subunits — uniquely abolishes hypoxia/O2-induced Ca2+ signaling and ROS production underlying hypoxic pulmonary vasoconstriction and ductus arteriosus O2-sensing [PMID:30922174, PMID:bio_10.1101_2025.07.08.663799]. NDUFS2 abundance is set post-translationally by OTUB1, which removes K48-linked polyubiquitin to stabilize the protein [PMID:38653740], and by lncRNA/PTBP1-controlled splicing of exon 3, whose loss yields a dominant-negative isoform that inhibits complex I and binds PRDX5 [PMID:38841852]. Pathogenic mutations at the CoQ-binding interface reduce complex I activity without lowering complex abundance and are causative of complex I deficiency, with mutation effects validated by genetic rescue and bacterial ortholog models [PMID:22036843, PMID:36462614].","teleology":[{"year":2011,"claim":"Establishing how a point mutation in NDUFS2 causes complex I deficiency localized the protein's catalytic contribution to the CoQ-reduction/proton-pumping step rather than to complex stability.","evidence":"Patient fibroblast enzymology, CoQ-analog Km measurement, structural modeling, and wild-type rescue by lentiviral transduction","pmids":["22036843"],"confidence":"Medium","gaps":["Structural placement near the CoQ pocket rests on in silico modeling","Exact step (CoQ reduction vs proton-pump coupling) not directly resolved"]},{"year":2013,"claim":"Identifying NDUFAF7-mediated symmetric dimethylation of Arg-85 revealed a co-translational/early-assembly modification step required to stabilize the peripheral-arm nucleus, explaining how NDUFS2 maturation is gated.","evidence":"MS identification of the methylated residue, matrix localization of NDUFAF7, and in vitro methyltransferase assay","pmids":["24089531"],"confidence":"High","gaps":["Functional consequence of losing the methylation on mature enzyme activity not quantified","Single lab"]},{"year":2019,"claim":"Subunit-specific epistasis testing answered which complex I component senses oxygen, identifying NDUFS2 cysteine redox state as the molecular trigger for hypoxic pulmonary vasoconstriction.","evidence":"siRNA knockdown in PASMCs with live-cell H2O2/Ca2+ imaging, complex I activity, NADH/NAD+, and in vivo HPV assessment","pmids":["30922174"],"confidence":"High","gaps":["Which cysteine residues are redox-modified not pinpointed","Mechanism linking complex I inhibition to Kv1.5 and Ca2+ signaling incompletely mapped"]},{"year":2019,"claim":"Placing NDUFS2 downstream of S100A4 connected complex I activity to cancer cell metabolic phenotype and invasion, framing NDUFS2 as a node in the OXPHOS-to-glycolysis balance.","evidence":"siRNA knockdown of S100A4 and NDUFS2 in lung cancer cells, respirometry, ATP and 3D invasion assays, in vivo metastasis model","pmids":["30885944"],"confidence":"Medium","gaps":["Direct molecular link between S100A4 and NDUFS2 regulation not defined","Single lab"]},{"year":2021,"claim":"A clean CRISPR knockout quantified the cellular cost of losing NDUFS2 and demonstrated pharmacological bypass, supporting quinone supplementation as a functional rescue.","evidence":"CRISPR/Cas9 knockout in HEK293 cells, Seahorse respirometry, ATP/apoptosis assays, idebenone rescue","pmids":["33744462"],"confidence":"Medium","gaps":["Rescue is partial; mechanism of idebenone electron bypass not detailed","Single cell line"]},{"year":2023,"claim":"A co-IP placed NDUFS2 in a putative PTPMT1-SLC25A6 axis in pancreatic cancer, tentatively linking it to broader mitochondrial regulation.","evidence":"Co-immunoprecipitation, PTPMT1 knockdown and inhibitor treatment with mitochondrial readouts","pmids":["37034225"],"confidence":"Low","gaps":["Single co-IP without reciprocal validation specific to NDUFS2","No demonstrated functional consequence on NDUFS2 directly"]},{"year":2024,"claim":"Identifying OTUB1 as an NDUFS2 deubiquitinase revealed a post-translational stabilization mechanism setting NDUFS2 protein levels and linking it to cancer cell survival.","evidence":"MS, reciprocal co-IP, OTUB1 overexpression/knockdown, K48-linkage ubiquitination assay, in vivo xenograft","pmids":["38653740"],"confidence":"Medium","gaps":["Ubiquitin ligase that opposes OTUB1 not identified","Single lab"]},{"year":2024,"claim":"Demonstrating lncRNA DCRT/PTBP1 control of NDUFS2 exon 3 splicing established a regulatory layer in which a truncated isoform acts as a dominant-negative inhibitor of complex I and suppressor of PRDX5 antioxidant activity.","evidence":"DCRT knockout/transgenic mice, RIP, isoform sequencing, AAV overexpression, TAC cardiac stress model, CoQ10 rescue","pmids":["38841852"],"confidence":"High","gaps":["Structural basis of competitive inhibition by the truncated isoform unresolved","Generality beyond cardiomyocytes not established"]},{"year":2022,"claim":"Bacterial ortholog mutagenesis dissected how interface mutations disrupt complex I assembly and ranked the deleteriousness of paired human alleles, providing a tractable system for genotype-function interpretation.","evidence":"Site-directed mutagenesis of E. coli nuoCD, NADH oxidase activity, co-IP assembly assay, time-delayed expression","pmids":["36462614"],"confidence":"Medium","gaps":["Bacterial ortholog limits direct translation to human complex I","Assembly defects not validated in human cells for all mutants"]},{"year":2025,"claim":"Extending oxygen-sensing epistasis to human ductus arteriosus smooth muscle confirmed NDUFS2 as the specific O2 sensor for vasoconstriction across distinct vascular beds.","evidence":"siRNA knockdown in human DASMCs (vs NDUFS1/NDUFS7/UQCRFS1/COX4I2) with Ca2+ imaging, cell shortening, MitoSOX, MitoTEMPO rescue (preprint)","pmids":["bio_10.1101_2025.07.08.663799"],"confidence":"Medium","gaps":["Preprint, single lab, not peer-reviewed","Molecular redox event in DASMCs inferred from PASMC model"]},{"year":2025,"claim":"A zebrafish ndufs2 knockout modeled organismal complex I disease and implicated one-carbon metabolism, with folic acid rescuing growth and hepatomegaly.","evidence":"CRISPR/Cas9 ndufs2 knockout zebrafish, complex I enzyme activity, transcriptomics, metabolomics, folic acid rescue (preprint)","pmids":["40791373"],"confidence":"Medium","gaps":["Preprint, single lab","Mechanism connecting complex I loss to one-carbon metabolism dysregulation not defined"]},{"year":null,"claim":"How the redox state of specific NDUFS2 cysteines is transduced into complex I inhibition and downstream Ca2+/Kv channel signaling during oxygen sensing remains mechanistically unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Specific O2-sensing cysteine residues not mapped","Structural model of the redox-inhibited state lacking","Link between matrix redox change and plasma-membrane channel regulation unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[1,2,4]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[2,10]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,2,4]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1,3,4]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[2,10]}],"complexes":["mitochondrial respiratory chain complex I"],"partners":["NDUFAF7","OTUB1","PRDX5","PTBP1","PTPMT1","LASS2","SLC25A6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75306","full_name":"NADH dehydrogenase [ubiquinone] iron-sulfur protein 2, mitochondrial","aliases":["Complex I-49kD","CI-49kD","NADH-ubiquinone oxidoreductase 49 kDa subunit"],"length_aa":463,"mass_kda":52.5,"function":"Core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) which catalyzes electron transfer from NADH through the respiratory chain, using ubiquinone as an electron acceptor (PubMed:22036843, PubMed:28031252, PubMed:30922174). Essential for the catalytic activity of complex I (PubMed:22036843, PubMed:30922174). Essential for the assembly of complex I (By similarity). Redox-sensitive, critical component of the oxygen-sensing pathway in the pulmonary vasculature which plays a key role in acute pulmonary oxygen-sensing and hypoxic pulmonary vasoconstriction (PubMed:30922174). Plays an important role in carotid body sensing of hypoxia (By similarity). Essential for glia-like neural stem and progenitor cell proliferation, differentiation and subsequent oligodendrocyte or neuronal maturation (By similarity)","subcellular_location":"Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/O75306/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/NDUFS2","classification":"Common Essential","n_dependent_lines":561,"n_total_lines":1208,"dependency_fraction":0.4644039735099338},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NDUFS2","total_profiled":1310},"omim":[{"mim_id":"620569","title":"LEBER-LIKE HEREDITARY OPTIC NEUROPATHY, AUTOSOMAL RECESSIVE 2; LHONAR2","url":"https://www.omim.org/entry/620569"},{"mim_id":"620135","title":"MITOCHONDRIAL COMPLEX I DEFICIENCY, NUCLEAR TYPE 39; MC1DN39","url":"https://www.omim.org/entry/620135"},{"mim_id":"619382","title":"LEBER-LIKE HEREDITARY OPTIC NEUROPATHY, AUTOSOMAL RECESSIVE 1; LHONAR1","url":"https://www.omim.org/entry/619382"},{"mim_id":"618229","title":"MITOCHONDRIAL COMPLEX I DEFICIENCY, NUCLEAR TYPE 7; MC1DN7","url":"https://www.omim.org/entry/618229"},{"mim_id":"618228","title":"MITOCHONDRIAL COMPLEX I DEFICIENCY, NUCLEAR TYPE 6; MC1DN6","url":"https://www.omim.org/entry/618228"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"},{"location":"Calyx","reliability":"Additional"},{"location":"Connecting piece","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":435.2},{"tissue":"tongue","ntpm":591.6}],"url":"https://www.proteinatlas.org/search/NDUFS2"},"hgnc":{"alias_symbol":["CI-49"],"prev_symbol":[]},"alphafold":{"accession":"O75306","domains":[{"cath_id":"1.10.645.10","chopping":"85-463","consensus_level":"medium","plddt":93.8884,"start":85,"end":463}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75306","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75306-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75306-F1-predicted_aligned_error_v6.png","plddt_mean":89.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NDUFS2","jax_strain_url":"https://www.jax.org/strain/search?query=NDUFS2"},"sequence":{"accession":"O75306","fasta_url":"https://rest.uniprot.org/uniprotkb/O75306.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75306/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75306"}},"corpus_meta":[{"pmid":"11220739","id":"PMC_11220739","title":"Mutations in the complex I NDUFS2 gene of patients with cardiomyopathy and encephalomyopathy.","date":"2001","source":"Annals of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/11220739","citation_count":153,"is_preprint":false},{"pmid":"24089531","id":"PMC_24089531","title":"NDUFAF7 methylates arginine 85 in the NDUFS2 subunit of human complex I.","date":"2013","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24089531","citation_count":87,"is_preprint":false},{"pmid":"30922174","id":"PMC_30922174","title":"Ndufs2, a Core Subunit of Mitochondrial Complex I, Is Essential for Acute Oxygen-Sensing and Hypoxic Pulmonary Vasoconstriction.","date":"2019","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/30922174","citation_count":85,"is_preprint":false},{"pmid":"20819849","id":"PMC_20819849","title":"The p.M292T NDUFS2 mutation causes complex I-deficient Leigh syndrome in multiple families.","date":"2010","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/20819849","citation_count":71,"is_preprint":false},{"pmid":"30885944","id":"PMC_30885944","title":"S100A4 alters metabolism and promotes invasion of lung cancer cells by up-regulating mitochondrial complex I protein NDUFS2.","date":"2019","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30885944","citation_count":68,"is_preprint":false},{"pmid":"23266820","id":"PMC_23266820","title":"Leigh syndrome associated with mitochondrial complex I deficiency due to novel mutations In NDUFV1 and NDUFS2.","date":"2012","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/23266820","citation_count":49,"is_preprint":false},{"pmid":"28031252","id":"PMC_28031252","title":"Compound heterozygosity for severe and hypomorphic NDUFS2 mutations cause non-syndromic LHON-like optic neuropathy.","date":"2016","source":"Journal of medical 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enzyme.","date":"2022","source":"Mitochondrion","url":"https://pubmed.ncbi.nlm.nih.gov/36462614","citation_count":4,"is_preprint":false},{"pmid":"39789601","id":"PMC_39789601","title":"An integrated investigation of mitochondrial genes in COPD reveals the causal effect of NDUFS2 by regulating pulmonary macrophages.","date":"2025","source":"Biology direct","url":"https://pubmed.ncbi.nlm.nih.gov/39789601","citation_count":3,"is_preprint":false},{"pmid":"39226079","id":"PMC_39226079","title":"Decreased in Mitochondrial Complex I Subunit NDUFS2 Is Critical for Oocyte Quality During Postovulatory Aging in Pigs.","date":"2024","source":"Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada","url":"https://pubmed.ncbi.nlm.nih.gov/39226079","citation_count":1,"is_preprint":false},{"pmid":"40791373","id":"PMC_40791373","title":"ndufs2-/- zebrafish have impaired survival, neuromuscular activity, morphology, and one-carbon metabolism treatable with folic acid.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40791373","citation_count":1,"is_preprint":false},{"pmid":"41924720","id":"PMC_41924720","title":"Sodium butyrate promotes the function of NDUFS2 in bovine skeletal muscle fiber type transformation and mitochondrial biosynthesis.","date":"2026","source":"Frontiers in veterinary science","url":"https://pubmed.ncbi.nlm.nih.gov/41924720","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.16.664929","title":"<i>  ndufs2  <sup>-/-</sup>  </i>  zebrafish have impaired survival, neuromuscular activity, morphology, and one-carbon metabolism treatable with folic acid","date":"2025-07-18","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.16.664929","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.07.08.663799","title":"NDUFS2 (NADH:Ubiquinone oxidoreductase core subunit S2) in Mitochondrial Electron Transport Chain Complex I is Critical to Oxygen Responsiveness of Human Ductus Arteriosus Smooth Muscle Cells","date":"2025-07-14","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.08.663799","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14199,"output_tokens":3615,"usd":0.048411,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11378,"output_tokens":3891,"usd":0.077082,"stage2_stop_reason":"end_turn"},"total_usd":0.125493,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"NDUFAF7, a SAM-dependent methyltransferase, symmetrically dimethylates the ω-NG,NG' atoms of Arg-85 in NDUFS2. This methylation occurs early in complex I assembly and stabilizes a ~400-kDa subcomplex that forms the initial nucleus of the peripheral arm and its junction with the membrane arm.\",\n      \"method\": \"Mass spectrometry identification of methylated residue, confirmation of NDUFAF7 mitochondrial matrix localization, in vitro methyltransferase assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical identification of modified residue by MS, methyltransferase activity demonstrated in vitro, functionally linked to assembly intermediate; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"24089531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A homozygous Asp446Asn mutation in NDUFS2 reduces complex I enzymatic activity without reducing complex I abundance, and the mutated residue resides near the coenzyme Q (CoQ) binding pocket. The mutation does not alter the Km for CoQ analogs, suggesting it interferes with CoQ reduction or coupling of CoQ reduction to proton-pumping conformational changes. The enzymatic defect was rescued by transduction of wild-type NDUFS2.\",\n      \"method\": \"Patient fibroblast biochemical assays, 3D structural modeling of complex I catalytic core, kinetic Km measurements for CoQ analogs, wild-type NDUFS2 rescue by lentiviral transduction\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzymatic assays plus structural modeling plus genetic rescue in a single lab; Km measurement adds orthogonal evidence but model is in silico\",\n      \"pmids\": [\"22036843\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"NDUFS2 functions as the molecular oxygen sensor in pulmonary artery smooth muscle cells (PASMCs). Acute hypoxia reduces cysteine residues of Ndufs2 and functionally inhibits complex I. siRNA knockdown of Ndufs2 decreases normoxic H2O2, prevents hypoxia-induced increases in intracellular Ca2+, decreases complex I activity, elevates NADH/NAD+ ratio, and decreases Kv1.5 expression — mimicking aspects of chronic hypoxia. Knockdown of other complex I subunits (Ndufs1) or putative O2 sensors (complex III Rieske Fe-S, COX4i2) had no effect on hypoxic Ca2+ increases, identifying Ndufs2 specifically as the O2-sensing subunit essential for hypoxic pulmonary vasoconstriction (HPV).\",\n      \"method\": \"siRNA knockdown in PASMCs, live-cell H2O2 and Ca2+ imaging, complex I activity assay, NADH/NAD+ measurement, in vivo siNdufs2 lung delivery with HPV assessment, mitochondria-conditioned media bioassay with catalase treatment\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (enzymatic, live imaging, in vivo), specific epistasis with other subunit knockdowns establishing unique role of NDUFS2, corroborated by separate preprint (2025)\",\n      \"pmids\": [\"30922174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"S100A4 regulates NDUFS2 expression, and NDUFS2 silencing inhibits mitochondrial complex I activity, reduces cellular ATP levels, shifts metabolism toward glycolysis (via hexokinase upregulation), and decreases invasive capacity of lung cancer cells in 3D culture and in vivo metastasis, phenocopying S100A4 silencing.\",\n      \"method\": \"siRNA knockdown of S100A4 and NDUFS2 in lung cancer cells, oxygen consumption rate measurement, ATP assay, 3D invasion assay, in vivo xenograft/metastasis model\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple cellular and in vivo assays in a single lab establishing functional pathway placement of NDUFS2 downstream of S100A4\",\n      \"pmids\": [\"30885944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CRISPR/Cas9-mediated disruption of NDUFS2 in HEK293 cells significantly decreases complex I-specific respiration, glycolytic capacity, ATP pool, and cell membrane integrity, while increasing complex II respiration, ROS generation, apoptosis, and necrosis. Treatment with idebenone (a benzoquinone) partially restores growth, ATP pool, and oxygen consumption in NDUFS2-knockout cells.\",\n      \"method\": \"CRISPR/Cas9 knockout in HEK293 cells, Seahorse respirometry, ATP assay, flow cytometry (apoptosis/necrosis), idebenone rescue experiment\",\n      \"journal\": \"Mitochondrion\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with multiple defined cellular phenotypic readouts and pharmacological rescue, single lab\",\n      \"pmids\": [\"33744462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"OTUB1, a deubiquitinase, interacts with NDUFS2 and removes K48-linked polyubiquitin chains from NDUFS2, thereby stabilizing NDUFS2 protein. OTUB1 overexpression increases NDUFS2 protein levels; OTUB1 knockdown decreases them. This OTUB1/NDUFS2 axis promotes pancreatic cancer cell survival, proliferation, and migration by inhibiting mitochondrial cell death.\",\n      \"method\": \"Protein mass spectrometry, co-immunoprecipitation, OTUB1 overexpression/knockdown, ubiquitination assay (K48-linkage specificity), in vivo xenograft tumor growth\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, ubiquitin linkage assay, and in vivo validation in a single lab\",\n      \"pmids\": [\"38653740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The lncRNA DCRT binds PTBP1 in the nucleus of cardiomyocytes, preventing PTBP1-mediated skipping of the third exon of NDUFS2. When DCRT is lost, exon 3 of NDUFS2 is skipped, producing a truncated/altered NDUFS2 isoform that competitively inhibits mitochondrial complex I activity and binds PRDX5 to suppress its antioxidant activity, causing mitochondrial dysfunction. Coenzyme Q10 partially rescues mitochondrial dysfunction caused by DCRT loss.\",\n      \"method\": \"CRISPR/Cas9 DCRT knockout mice, cardiac-specific DCRT transgenic mice, RNA immunoprecipitation, chromatin co-IP, isoform sequencing, Western blot, AAV overexpression, transverse aortic constriction model\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (RIP, isoform sequencing, genetic KO and transgenic mice, in vivo TAC model), mechanistically linking splicing regulation directly to NDUFS2 complex I function and PRDX5 interaction\",\n      \"pmids\": [\"38841852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PTPMT1 co-immunoprecipitates with both SLC25A6 and NDUFS2 in pancreatic cancer cells, suggesting PTPMT1 modulates mitochondrial function via the SLC25A6-NDUFS2 axis.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown of PTPMT1, PTPMT1 inhibitor (alexidine dihydrochloride) treatment with mitochondrial function readouts\",\n      \"journal\": \"American journal of cancer research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP experiment identifying the interaction, limited mechanistic follow-up on NDUFS2 specifically\",\n      \"pmids\": [\"37034225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Co-IP and LC-MS analysis showed that LASS2 interacts with NDUFS2; this interaction is associated with production of mitochondrial ROS (mtROS), which may promote AMPK phosphorylation to inhibit lipogenesis in hepatocytes.\",\n      \"method\": \"Co-immunoprecipitation, LC-MS, LASS2 overexpression/knockdown in hepatocytes, mtROS measurement\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP/LC-MS interaction, mechanistic link to NDUFS2 function is inferred rather than directly tested\",\n      \"pmids\": [\"32279995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Disease-causing mutations in NDUFS2 (and the bacterial ortholog NuoCD) that map to subunit interfaces disrupt complex I assembly, as demonstrated in E. coli models. Compound heterozygote analysis in the bacterial system identified which of paired human mutations is more deleterious; alanine substitution allowed distinction between loss-of-original-residue versus gain-of-mutant-residue effects.\",\n      \"method\": \"Site-directed mutagenesis of E. coli nuoCD (NDUFS2 ortholog), NADH oxidase activity assay in membrane vesicles, co-immunoprecipitation assembly assay, time-delayed expression assay\",\n      \"journal\": \"Mitochondrion\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted bacterial system with mutagenesis and functional assays; ortholog model limits direct translation to human protein\",\n      \"pmids\": [\"36462614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"siRNA knockdown of NDUFS2 (but not NDUFS1, NDUFS7, UQCRFS1, or COX4I2) uniquely inhibits O2-induced increases in intracellular Ca2+, cell shortening, and mitochondrial ROS production in human ductus arteriosus smooth muscle cells (DASMCs), establishing NDUFS2 as the mitochondrial oxygen sensor for O2-induced vasoconstriction in the DA.\",\n      \"method\": \"siRNA knockdown in human DASMCs, intracellular Ca2+ imaging, cell length measurement, mitochondrial ROS assay (MitoSOX), MitoTEMPO antioxidant rescue, micropolarimetry, complex I/III/IV activity assays, 3′RNA sequencing\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal readouts with specific epistasis against other subunit knockdowns; preprint, single lab, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.07.08.663799\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ndufs2-/- zebrafish (CRISPR/Cas9 knockout) show 80% reduced complex I enzyme activity, severe neuromuscular dysfunction, metabolic dysregulation (increased lactate, TCA intermediates, acyl-carnitines), and dysregulation of one-carbon metabolism. Folic acid treatment rescues the growth defect and hepatomegaly, implicating one-carbon metabolism in complex I disease pathophysiology.\",\n      \"method\": \"CRISPR/Cas9 ndufs2 knockout zebrafish, complex I enzyme activity assay, transcriptomics, unbiased metabolomics, folic acid rescue experiment\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with direct enzyme activity measurement, metabolomics, and pharmacological rescue; preprint, single lab\",\n      \"pmids\": [\"40791373\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"NDUFS2 is a core catalytic subunit of mitochondrial respiratory chain complex I (NADH:ubiquinone oxidoreductase) that harbors the rotenone/coenzyme Q binding site at the interface between the peripheral and membrane arms; it undergoes early-assembly symmetric dimethylation of Arg-85 by the methyltransferase NDUFAF7 (stabilizing a ~400-kDa assembly intermediate), is stabilized post-translationally by OTUB1-mediated K48-deubiquitylation, and its cysteine residues undergo redox changes during hypoxia that inhibit complex I activity, making NDUFS2 the specific mitochondrial oxygen sensor responsible for hypoxic pulmonary vasoconstriction and ductus arteriosus O2-sensing; loss of NDUFS2 function impairs complex I activity, elevates ROS, disrupts cellular ATP production and Ca2+ signaling, and pathogenic mutations at the CoQ-binding pocket cause Leigh syndrome by compromising CoQ reduction or proton-pumping coupling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NDUFS2 is a core catalytic subunit of mitochondrial respiratory chain complex I (NADH:ubiquinone oxidoreductase), residing near the coenzyme Q (CoQ) binding pocket where it couples CoQ reduction to the conformational changes required for proton-pumping [#1]. During complex I biogenesis, NDUFS2 is symmetrically dimethylated at Arg-85 by the SAM-dependent methyltransferase NDUFAF7, an early modification that stabilizes a ~400-kDa assembly intermediate forming the nucleus of the peripheral arm and its junction with the membrane arm [#0]. Loss of NDUFS2 function — by knockout, knockdown, or disease mutation — selectively impairs complex I respiration while driving compensatory glycolysis, elevated ROS, ATP depletion, and apoptosis/necrosis, phenotypes partially rescued by quinone analogs such as idebenone and CoQ10 [#3, #4, #6]. Beyond its catalytic role, NDUFS2 serves as the specific mitochondrial oxygen sensor: acute hypoxia reduces its cysteine residues and inhibits complex I, and NDUFS2 knockdown — but not knockdown of other complex I, III, or IV subunits — uniquely abolishes hypoxia/O2-induced Ca2+ signaling and ROS production underlying hypoxic pulmonary vasoconstriction and ductus arteriosus O2-sensing [#2, #10]. NDUFS2 abundance is set post-translationally by OTUB1, which removes K48-linked polyubiquitin to stabilize the protein [#5], and by lncRNA/PTBP1-controlled splicing of exon 3, whose loss yields a dominant-negative isoform that inhibits complex I and binds PRDX5 [#6]. Pathogenic mutations at the CoQ-binding interface reduce complex I activity without lowering complex abundance and are causative of complex I deficiency, with mutation effects validated by genetic rescue and bacterial ortholog models [#1, #9].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Establishing how a point mutation in NDUFS2 causes complex I deficiency localized the protein's catalytic contribution to the CoQ-reduction/proton-pumping step rather than to complex stability.\",\n      \"evidence\": \"Patient fibroblast enzymology, CoQ-analog Km measurement, structural modeling, and wild-type rescue by lentiviral transduction\",\n      \"pmids\": [\"22036843\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural placement near the CoQ pocket rests on in silico modeling\", \"Exact step (CoQ reduction vs proton-pump coupling) not directly resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identifying NDUFAF7-mediated symmetric dimethylation of Arg-85 revealed a co-translational/early-assembly modification step required to stabilize the peripheral-arm nucleus, explaining how NDUFS2 maturation is gated.\",\n      \"evidence\": \"MS identification of the methylated residue, matrix localization of NDUFAF7, and in vitro methyltransferase assay\",\n      \"pmids\": [\"24089531\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of losing the methylation on mature enzyme activity not quantified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Subunit-specific epistasis testing answered which complex I component senses oxygen, identifying NDUFS2 cysteine redox state as the molecular trigger for hypoxic pulmonary vasoconstriction.\",\n      \"evidence\": \"siRNA knockdown in PASMCs with live-cell H2O2/Ca2+ imaging, complex I activity, NADH/NAD+, and in vivo HPV assessment\",\n      \"pmids\": [\"30922174\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which cysteine residues are redox-modified not pinpointed\", \"Mechanism linking complex I inhibition to Kv1.5 and Ca2+ signaling incompletely mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placing NDUFS2 downstream of S100A4 connected complex I activity to cancer cell metabolic phenotype and invasion, framing NDUFS2 as a node in the OXPHOS-to-glycolysis balance.\",\n      \"evidence\": \"siRNA knockdown of S100A4 and NDUFS2 in lung cancer cells, respirometry, ATP and 3D invasion assays, in vivo metastasis model\",\n      \"pmids\": [\"30885944\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link between S100A4 and NDUFS2 regulation not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A clean CRISPR knockout quantified the cellular cost of losing NDUFS2 and demonstrated pharmacological bypass, supporting quinone supplementation as a functional rescue.\",\n      \"evidence\": \"CRISPR/Cas9 knockout in HEK293 cells, Seahorse respirometry, ATP/apoptosis assays, idebenone rescue\",\n      \"pmids\": [\"33744462\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Rescue is partial; mechanism of idebenone electron bypass not detailed\", \"Single cell line\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A co-IP placed NDUFS2 in a putative PTPMT1-SLC25A6 axis in pancreatic cancer, tentatively linking it to broader mitochondrial regulation.\",\n      \"evidence\": \"Co-immunoprecipitation, PTPMT1 knockdown and inhibitor treatment with mitochondrial readouts\",\n      \"pmids\": [\"37034225\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single co-IP without reciprocal validation specific to NDUFS2\", \"No demonstrated functional consequence on NDUFS2 directly\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying OTUB1 as an NDUFS2 deubiquitinase revealed a post-translational stabilization mechanism setting NDUFS2 protein levels and linking it to cancer cell survival.\",\n      \"evidence\": \"MS, reciprocal co-IP, OTUB1 overexpression/knockdown, K48-linkage ubiquitination assay, in vivo xenograft\",\n      \"pmids\": [\"38653740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin ligase that opposes OTUB1 not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrating lncRNA DCRT/PTBP1 control of NDUFS2 exon 3 splicing established a regulatory layer in which a truncated isoform acts as a dominant-negative inhibitor of complex I and suppressor of PRDX5 antioxidant activity.\",\n      \"evidence\": \"DCRT knockout/transgenic mice, RIP, isoform sequencing, AAV overexpression, TAC cardiac stress model, CoQ10 rescue\",\n      \"pmids\": [\"38841852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of competitive inhibition by the truncated isoform unresolved\", \"Generality beyond cardiomyocytes not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Bacterial ortholog mutagenesis dissected how interface mutations disrupt complex I assembly and ranked the deleteriousness of paired human alleles, providing a tractable system for genotype-function interpretation.\",\n      \"evidence\": \"Site-directed mutagenesis of E. coli nuoCD, NADH oxidase activity, co-IP assembly assay, time-delayed expression\",\n      \"pmids\": [\"36462614\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Bacterial ortholog limits direct translation to human complex I\", \"Assembly defects not validated in human cells for all mutants\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extending oxygen-sensing epistasis to human ductus arteriosus smooth muscle confirmed NDUFS2 as the specific O2 sensor for vasoconstriction across distinct vascular beds.\",\n      \"evidence\": \"siRNA knockdown in human DASMCs (vs NDUFS1/NDUFS7/UQCRFS1/COX4I2) with Ca2+ imaging, cell shortening, MitoSOX, MitoTEMPO rescue (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.07.08.663799\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab, not peer-reviewed\", \"Molecular redox event in DASMCs inferred from PASMC model\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A zebrafish ndufs2 knockout modeled organismal complex I disease and implicated one-carbon metabolism, with folic acid rescuing growth and hepatomegaly.\",\n      \"evidence\": \"CRISPR/Cas9 ndufs2 knockout zebrafish, complex I enzyme activity, transcriptomics, metabolomics, folic acid rescue (preprint)\",\n      \"pmids\": [\"40791373\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab\", \"Mechanism connecting complex I loss to one-carbon metabolism dysregulation not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the redox state of specific NDUFS2 cysteines is transduced into complex I inhibition and downstream Ca2+/Kv channel signaling during oxygen sensing remains mechanistically unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific O2-sensing cysteine residues not mapped\", \"Structural model of the redox-inhibited state lacking\", \"Link between matrix redox change and plasma-membrane channel regulation unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [1, 2, 4]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [2, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 3, 4]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [2, 10]}\n    ],\n    \"complexes\": [\"mitochondrial respiratory chain complex I\"],\n    \"partners\": [\"NDUFAF7\", \"OTUB1\", \"PRDX5\", \"PTBP1\", \"PTPMT1\", \"LASS2\", \"SLC25A6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":6,"faith_pct":83.33333333333333}}