Affinage

NDUFS2

NADH dehydrogenase [ubiquinone] iron-sulfur protein 2, mitochondrial · UniProt O75306

Length
463 aa
Mass
52.5 kDa
Annotated
2026-06-10
20 papers in source corpus 12 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/6 claims corpus-supported (83%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2011 Medium

    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

    PMID:22036843

    Open questions at the time
    • Structural placement near the CoQ pocket rests on in silico modeling
    • Exact step (CoQ reduction vs proton-pump coupling) not directly resolved
  2. 2013 High

    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

    PMID:24089531

    Open questions at the time
    • Functional consequence of losing the methylation on mature enzyme activity not quantified
    • Single lab
  3. 2019 High

    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

    PMID:30922174

    Open questions at the time
    • Which cysteine residues are redox-modified not pinpointed
    • Mechanism linking complex I inhibition to Kv1.5 and Ca2+ signaling incompletely mapped
  4. 2019 Medium

    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

    PMID:30885944

    Open questions at the time
    • Direct molecular link between S100A4 and NDUFS2 regulation not defined
    • Single lab
  5. 2021 Medium

    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

    PMID:33744462

    Open questions at the time
    • Rescue is partial; mechanism of idebenone electron bypass not detailed
    • Single cell line
  6. 2023 Low

    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

    PMID:37034225

    Open questions at the time
    • Single co-IP without reciprocal validation specific to NDUFS2
    • No demonstrated functional consequence on NDUFS2 directly
  7. 2024 Medium

    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

    PMID:38653740

    Open questions at the time
    • Ubiquitin ligase that opposes OTUB1 not identified
    • Single lab
  8. 2024 High

    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

    PMID:38841852

    Open questions at the time
    • Structural basis of competitive inhibition by the truncated isoform unresolved
    • Generality beyond cardiomyocytes not established
  9. 2022 Medium

    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

    PMID:36462614

    Open questions at the time
    • Bacterial ortholog limits direct translation to human complex I
    • Assembly defects not validated in human cells for all mutants
  10. 2025 Medium

    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)

    PMID:bio_10.1101_2025.07.08.663799

    Open questions at the time
    • Preprint, single lab, not peer-reviewed
    • Molecular redox event in DASMCs inferred from PASMC model
  11. 2025 Medium

    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)

    PMID:40791373

    Open questions at the time
    • Preprint, single lab
    • Mechanism connecting complex I loss to one-carbon metabolism dysregulation not defined

Open questions

Synthesis pass · forward-looking unresolved questions
  • 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.
  • 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

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0016491 oxidoreductase activity 3 GO:0140299 molecular sensor activity 2
Localization
GO:0005739 mitochondrion 3
Pathway
R-HSA-1430728 Metabolism 3 R-HSA-8953897 Cellular responses to stimuli 2
Partners
LASS2NDUFAF7OTUB1PRDX5PTBP1PTPMT1SLC25A6
Complex memberships
mitochondrial respiratory chain complex I

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 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. Mass spectrometry identification of methylated residue, confirmation of NDUFAF7 mitochondrial matrix localization, in vitro methyltransferase assay The Journal of biological chemistry High 24089531
2011 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. 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 Biochimica et biophysica acta Medium 22036843
2019 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). 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 Circulation research High 30922174
2019 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. siRNA knockdown of S100A4 and NDUFS2 in lung cancer cells, oxygen consumption rate measurement, ATP assay, 3D invasion assay, in vivo xenograft/metastasis model The Journal of biological chemistry Medium 30885944
2021 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. CRISPR/Cas9 knockout in HEK293 cells, Seahorse respirometry, ATP assay, flow cytometry (apoptosis/necrosis), idebenone rescue experiment Mitochondrion Medium 33744462
2024 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. Protein mass spectrometry, co-immunoprecipitation, OTUB1 overexpression/knockdown, ubiquitination assay (K48-linkage specificity), in vivo xenograft tumor growth Cell death discovery Medium 38653740
2024 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. 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 Circulation High 38841852
2023 PTPMT1 co-immunoprecipitates with both SLC25A6 and NDUFS2 in pancreatic cancer cells, suggesting PTPMT1 modulates mitochondrial function via the SLC25A6-NDUFS2 axis. Co-immunoprecipitation, siRNA knockdown of PTPMT1, PTPMT1 inhibitor (alexidine dihydrochloride) treatment with mitochondrial function readouts American journal of cancer research Low 37034225
2020 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. Co-immunoprecipitation, LC-MS, LASS2 overexpression/knockdown in hepatocytes, mtROS measurement Biochemical and biophysical research communications Low 32279995
2022 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. Site-directed mutagenesis of E. coli nuoCD (NDUFS2 ortholog), NADH oxidase activity assay in membrane vesicles, co-immunoprecipitation assembly assay, time-delayed expression assay Mitochondrion Medium 36462614
2025 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. 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 bioRxivpreprint Medium bio_10.1101_2025.07.08.663799
2025 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. CRISPR/Cas9 ndufs2 knockout zebrafish, complex I enzyme activity assay, transcriptomics, unbiased metabolomics, folic acid rescue experiment bioRxivpreprint Medium 40791373

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2001 Mutations in the complex I NDUFS2 gene of patients with cardiomyopathy and encephalomyopathy. Annals of neurology 153 11220739
2013 NDUFAF7 methylates arginine 85 in the NDUFS2 subunit of human complex I. The Journal of biological chemistry 87 24089531
2019 Ndufs2, a Core Subunit of Mitochondrial Complex I, Is Essential for Acute Oxygen-Sensing and Hypoxic Pulmonary Vasoconstriction. Circulation research 85 30922174
2010 The p.M292T NDUFS2 mutation causes complex I-deficient Leigh syndrome in multiple families. Brain : a journal of neurology 71 20819849
2019 S100A4 alters metabolism and promotes invasion of lung cancer cells by up-regulating mitochondrial complex I protein NDUFS2. The Journal of biological chemistry 68 30885944
2012 Leigh syndrome associated with mitochondrial complex I deficiency due to novel mutations In NDUFV1 and NDUFS2. Gene 49 23266820
2016 Compound heterozygosity for severe and hypomorphic NDUFS2 mutations cause non-syndromic LHON-like optic neuropathy. Journal of medical genetics 47 28031252
2021 Complex I protein NDUFS2 is vital for growth, ROS generation, membrane integrity, apoptosis, and mitochondrial energetics. Mitochondrion 36 33744462
2011 A catalytic defect in mitochondrial respiratory chain complex I due to a mutation in NDUFS2 in a patient with Leigh syndrome. Biochimica et biophysica acta 28 22036843
2024 LncRNA DCRT Protects Against Dilated Cardiomyopathy by Preventing NDUFS2 Alternative Splicing by Binding to PTBP1. Circulation 27 38841852
2022 Reduced expression of mitochondrial complex I subunit Ndufs2 does not impact healthspan in mice. Scientific reports 27 35338200
2024 OTUB1/NDUFS2 axis promotes pancreatic tumorigenesis through protecting against mitochondrial cell death. Cell death discovery 9 38653740
2023 PTPMT1 regulates mitochondrial death through the SLC25A6-NDUFS2 axis in pancreatic cancer cells. American journal of cancer research 6 37034225
2024 NUDT21 interacts with NDUFS2 to activate the PI3K/AKT pathway and promotes pancreatic cancer pathogenesis. Journal of cancer research and clinical oncology 5 38195952
2020 LASS2 regulates hepatocyte steatosis by interacting with NDUFS2/OXPHOS related proteins. Biochemical and biophysical research communications 5 32279995
2022 Analysis of compound heterozygous and homozygous mutations found in peripheral subunits of human respiratory Complex I, NDUFS1, NDUFS2, NDUFS8 and NDUFV1, by modeling in the E. coli enzyme. Mitochondrion 4 36462614
2025 An integrated investigation of mitochondrial genes in COPD reveals the causal effect of NDUFS2 by regulating pulmonary macrophages. Biology direct 3 39789601
2025 ndufs2-/- zebrafish have impaired survival, neuromuscular activity, morphology, and one-carbon metabolism treatable with folic acid. bioRxiv : the preprint server for biology 1 40791373
2024 Decreased in Mitochondrial Complex I Subunit NDUFS2 Is Critical for Oocyte Quality During Postovulatory Aging in Pigs. Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada 1 39226079
2026 Sodium butyrate promotes the function of NDUFS2 in bovine skeletal muscle fiber type transformation and mitochondrial biosynthesis. Frontiers in veterinary science 0 41924720

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