Affinage

NDUFB9

NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 9 · UniProt Q9Y6M9

Length
179 aa
Mass
21.8 kDa
Annotated
2026-06-10
26 papers in source corpus 8 papers cited in narrative 8 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NDUFB9 (B22) is an accessory subunit of mitochondrial complex I (NADH:ubiquinone oxidoreductase) that is required for the enzyme's assembly, abundance, and catalytic activity (PMID:22200994, PMID:8661098). Its LYR domain mediates a direct interaction with the neighbouring complex I subunit SDAP1 (mitochondrial acyl carrier protein), and an LYR-domain mutant fails to rescue complex I deficiency, establishing this interaction as central to NDUFB9's structural role in the assembled complex (PMID:39981882). A pathogenic NDUFB9 mutation reduces NDUFB9 protein and both the amount and activity of complex I, defects that are corrected by re-expression of wild-type NDUFB9 in patient fibroblasts (PMID:22200994). Loss of NDUFB9 disrupts complex I integrity with broad metabolic consequences: it elevates mitochondrial ROS, disturbs the NAD+/NADH balance, and depletes mitochondrial DNA, driving pro-proliferative and pro-migratory phenotypes (PMID:26641458), while NDUFB9 knockout reduces intracellular aspartate and, in the brain microenvironment, restricts nucleotide biosynthesis to suppress metastatic outgrowth (PMID:42103753). Beyond its respiratory-chain function, NDUFB9 physically interacts with and stabilizes PINK1 to promote PINK1/Parkin-dependent mitophagy (PMID:40825941), and its expression is dynamically regulated during cellular differentiation programs, declining during erythroid differentiation (PMID:11911854) and rising during adipogenesis where it acts upstream of SCD1 (PMID:35122619).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1996 Medium

    Established the molecular identity and genomic location of NDUFB9, assigning it as a respiratory-chain complex I subunit before any functional characterization existed.

    Evidence Cosmid hybrid selection, cDNA isolation, and sequence similarity to the bovine B22 subunit; chromosomal mapping to 8q13.3

    PMID:8661098

    Open questions at the time
    • No functional assay confirming complex I role
    • Assignment rests on cross-species sequence similarity only
  2. 2002 Low

    Linked NDUFB9 expression to a differentiation program, showing the subunit gene is transcriptionally repressed as cells exit proliferation and commit to erythroid maturation.

    Evidence Northern blot during DMSO-induced MEL cell differentiation, with N6-methyladenosine inhibitor abrogating repression

    PMID:11911854

    Open questions at the time
    • Single method (Northern blot), no mechanistic dissection of the repression
    • Transcription factors and cis-elements controlling repression unidentified
    • Functional consequence of reduced complex I subunit during erythropoiesis not tested
  3. 2011 High

    Demonstrated causally that NDUFB9 is required for complex I integrity, resolving whether the subunit is structurally essential rather than merely associated.

    Evidence Functional complementation with wild-type cDNA in patient-derived fibroblasts restoring both protein level and enzymatic activity

    PMID:22200994

    Open questions at the time
    • Did not define which assembly intermediate requires NDUFB9
    • Structural basis of the requirement not resolved
  4. 2015 Medium

    Connected loss of NDUFB9 to downstream redox and metabolic disturbance, showing complex I dysfunction propagates to ROS, NAD+/NADH imbalance and tumor-cell phenotypes.

    Evidence siRNA knockdown in MDA-MB-231 cells with proteomics, ROS, NAD+/NADH and mtDNA measurements plus migration/invasion assays

    PMID:26641458

    Open questions at the time
    • Akt/mTOR/p70S6K and EMT placement inferred, not genetically confirmed
    • Single cell line and single lab
    • Direct causal link between ROS and phenotype not isolated
  5. 2022 Medium

    Identified a regulatory role for NDUFB9 in adipogenesis, positioning it upstream of a lipogenic enzyme rather than purely as a bioenergetic component.

    Evidence siRNA knockdown in OP9 cells and adipose-derived stem cells with transcriptomics, lipidomics, and SCD1-inhibitor phenocopy

    PMID:35122619

    Open questions at the time
    • Mechanism linking complex I subunit to SCD1 regulation unresolved
    • Single lab
    • Whether the effect is bioenergetic or signaling not separated
  6. 2025 High

    Defined the structural mechanism of NDUFB9 within complex I, identifying the LYR domain as the determinant that anchors SDAP1.

    Evidence Arabidopsis T-DNA knockout/knockdown, LYR-domain mutant complementation, protein interaction assays, and parallel SDAP1 knockdown converging on the same conclusion

    PMID:39981882

    Open questions at the time
    • Structural detail of the LYR–SDAP1 interface not solved
    • Demonstrated in plant system; conservation of the interface assumed across species
  7. 2025 Medium

    Revealed a moonlighting function beyond the respiratory chain, showing NDUFB9 stabilizes PINK1 to drive mitophagy.

    Evidence AAV-mediated overexpression in a CUMS mouse model with reciprocal Co-IP, protein half-life assay, mitophagy inhibitor experiments, and behavioral readouts

    PMID:40825941

    Open questions at the time
    • Domain/region of NDUFB9 mediating PINK1 binding unmapped
    • Whether stabilization is direct or via complex I status unclear
    • Single lab
  8. 2026 High

    Placed NDUFB9 loss within a context-specific metabolic circuit, showing complex I disruption depletes aspartate and, in the brain, restricts nucleotide biosynthesis to limit metastasis.

    Evidence In vivo CRISPR loss-of-function screen, NDUFB9 knockout lines, metabolomics, ASNS expression analysis, and orthotopic brain vs extracranial metastasis models

    PMID:42103753

    Open questions at the time
    • Generalizability beyond TNBC brain metastasis not established
    • Direct flux from aspartate to nucleotides not isotopically traced in all contexts

Open questions

Synthesis pass · forward-looking unresolved questions
  • How NDUFB9's bioenergetic role is mechanistically coupled to its differentiation-regulatory (SCD1, erythroid) and mitophagy (PINK1) functions remains unresolved.
  • No unified mechanism linking complex I subunit status to PINK1 stabilization
  • No structural model of the human NDUFB9–SDAP1 interface
  • Transcriptional regulators of NDUFB9 across tissues unidentified

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3 GO:0140096 catalytic activity, acting on a protein 1
Localization
GO:0005739 mitochondrion 3
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-9612973 Autophagy 1
Partners
PINK1SDAP1
Complex memberships
mitochondrial respiratory chain complex I

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2011 A causal mutation in NDUFB9 (encoding a complex I subunit) results in reduction of NDUFB9 protein and both amount and activity of mitochondrial complex I; these defects were rescued by expression of wild-type NDUFB9 in patient-derived fibroblasts, confirming NDUFB9 as a structural/functional subunit required for complex I integrity and activity. Functional complementation assay in patient-derived fibroblasts; Sanger sequencing; high-resolution melting curve analysis Journal of medical genetics High 22200994
2015 Loss of NDUFB9 promotes breast cancer cell proliferation, migration, and invasion by elevating mitochondrial ROS (mtROS), disturbing the NAD+/NADH balance, and depleting mitochondrial DNA; the Akt/mTOR/p70S6K signaling pathway and epithelial-mesenchymal transition (EMT) are implicated downstream. siRNA-mediated knockdown of NDUFB9 in MDA-MB-231 cells; quantitative proteomic analysis; cell proliferation, migration, and invasion assays; ROS and NAD+/NADH measurements PloS one Medium 26641458
2022 NDUFB9 is upregulated during adipogenesis; silencing Ndufb9 inhibits adipogenesis, and this effect is mediated through stearoyl-CoA desaturase 1 (SCD1), placing NDUFB9 upstream of SCD1 in the adipogenic pathway. siRNA knockdown of Ndufb9 (83% silencing efficiency) in OP9 cells and adipose-derived stem cells; transcriptomics; lipidomics; SCD1 inhibitor (Aramchol) phenocopy experiment Journal of physiology and biochemistry Medium 35122619
2025 The LYR (leucine/tyrosine/arginine) domain of the NDUFB9/B22 subunit of mitochondrial complex I is essential for complex I function and assembly; this domain mediates a direct protein–protein interaction with the neighbouring complex I subunit SDAP1 (mitochondrial acyl carrier protein), as shown by the inability of an LYR-domain mutant to rescue CI deficiency and by protein interaction assays. T-DNA insertional knockout/knockdown lines in Arabidopsis; complementation with LYR-domain mutant B22 variant; protein interaction assays; CI activity and abundance measurements The Plant journal : for cell and molecular biology High 39981882
2025 NDUFB9 overexpression in a CUMS mouse model alleviates depressive-like behavior by restoring mitochondrial function and enhancing mitophagy via the PINK1/Parkin pathway; co-immunoprecipitation and protein half-life assays revealed that NDUFB9 physically interacts with and stabilizes the PINK1 protein, thereby promoting mitophagy. CUMS mouse model; AAV-mediated NDUFB9 overexpression; Co-IP; protein half-life assay; autophagy/mitophagy inhibitor experiments; behavioral assays Translational psychiatry Medium 40825941
2026 NDUFB9 knockout selectively disrupts mitochondrial complex I and reduces intracellular aspartate in TNBC cells; in the brain microenvironment, lower asparagine concentration triggers compensatory upregulation of asparagine synthetase (ASNS), which diverts the already-depleted aspartate pool toward asparagine biosynthesis, thereby restricting nucleotide biosynthesis and suppressing brain metastasis outgrowth — a brain-specific dual-hit mechanism. High-throughput in vivo CRISPR loss-of-function screen; NDUFB9 knockout cell lines; metabolomics (aspartate, asparagine measurement); ASNS expression analysis; orthotopic brain and extracranial metastasis mouse models Nature communications High 42103753
1996 The human NDUFB9 (B22 subunit) gene was physically mapped to chromosome 8q13.3, and the encoded protein was identified as a subunit of the mitochondrial NADH-ubiquinone oxidoreductase (complex I) respiratory chain, based on 89% sequence similarity to the bovine B22 subunit. Hybrid selection using cosmid genomic clones; cDNA isolation; sequence similarity analysis Genomics Medium 8661098
2002 B22 (NDUFB9) gene expression declines progressively during terminal erythroid differentiation of MEL cells induced by DMSO, indicating transcriptional repression of this complex I subunit gene during erythropoiesis; this repression was abrogated by N6-methyladenosine (an inhibitor of commitment and RNA methylation), linking B22 repression to the differentiation program. Northern blot analysis; MEL cell differentiation assay with DMSO and chemical inhibitors; cDNA cloning and sequencing of B22 fragment Biochemical pharmacology Low 11911854

Source papers

Stage 0 corpus · 26 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 Mutation screening of 75 candidate genes in 152 complex I deficiency cases identifies pathogenic variants in 16 genes including NDUFB9. Journal of medical genetics 85 22200994
2015 Down-Regulation of NDUFB9 Promotes Breast Cancer Cell Proliferation, Metastasis by Mediating Mitochondrial Metabolism. PloS one 66 26641458
2014 T cell inactivation by poxviral B22 family proteins increases viral virulence. PLoS pathogens 48 24832205
2013 Coarse-grained model for colloidal protein interactions, B(22), and protein cluster formation. The journal of physical chemistry. B 41 24289039
2003 Influence of human leukocyte antigen-B22 alleles on the course of human immunodeficiency virus type 1 infection in 3 cohorts of white men. The Journal of infectious diseases 27 12964117
2015 From osmotic second virial coefficient (B22 ) to phase behavior of a monoclonal antibody. Biotechnology progress 24 25683855
1996 The human B22 subunit of the NADH-ubiquinone oxidoreductase maps to the region of chromosome 8 involved in branchio-oto-renal syndrome. Genomics 24 8661098
2009 Fragmentation of doubly-protonated Pro-His-Xaa tripeptides: formation of b(2)(2+) ions. Journal of the American Society for Mass Spectrometry 22 19683937
2014 Priming-mediated systemic resistance in cucumber induced by Pseudomonas azotoformans GC-B19 and Paenibacillus elgii MM-B22 against Colletotrichum orbiculare. Phytopathology 18 24502209
1999 Human NDUFB9 gene: genomic organization and a possible candidate gene associated with deafness disorder mapped to chromosome 8q13. Human heredity 17 10077726
1997 Five HLA-B22 group alleles in Japanese. Tissue antigens 17 9151389
2020 Agricultural waste materials enhance protease production by Bacillus subtilis B22 in submerged fermentation under blue light-emitting diodes. Bioprocess and biosystems engineering 14 31919603
2023 Effects of resveratrol on DLD and NDUFB9 decrease in frozen semen of Mongolian sheep. Cryobiology 11 37956782
2022 Blockage of NDUFB9-SCD1 pathway inhibits adipogenesis : Blockage of NDUFB9-SCD1 pathway inhibits adipogenesis. Journal of physiology and biochemistry 11 35122619
2016 A homolog of the variola virus B22 membrane protein contributes to ectromelia virus pathogenicity in the mouse footpad model. Virology 10 27898336
2002 Differentiation-dependent repression of c-myc, B22, COX II and COX IV genes in murine erythroleukemia (MEL) cells. Biochemical pharmacology 7 11911854
2022 Predicting Experimental B22 Values and the Effects of Histidine Charge States for Monoclonal Antibodies Using Coarse-Grained Molecular Simulations. Molecular pharmaceutics 6 36194430
1999 HLA-B22 diversity including a novel B54 variant (B*5507) in the Korean population. Human immunology 6 10439319
1996 Lambda clone B22 contains a 7676 bp genomic fragment of Saccharomyces cerevisiae chromosome VII spanning the VAM7-SPM2 intergenic region and containing three novel transcribed open reading frames. Yeast (Chichester, England) 6 8813766
2025 Dissecting the High Esterase/Lipase Activity and Probiotic Traits in Lactiplantibacillus plantarum B22: A Genome-Guided Functional Characterization. Foods (Basel, Switzerland) 5 40647106
1999 Regression of melanoma, but not keratoacanthoma, is associated with increased HLA-B22 and decreased HLA-B27 and HLA-DR1. Melanoma research 4 10661764
1982 [B22-D-arginine]insulin: synthesis and biological properties. Hoppe-Seyler's Zeitschrift fur physiologische Chemie 4 6761262
2025 The complex I subunit B22 contains a LYR domain that is crucial for an interaction with the mitochondrial acyl carrier protein SDAP1. The Plant journal : for cell and molecular biology 2 39981882
2025 NDUFB9 ameliorates CUMS-induced depression-like behavior by promoting mitophagy. Translational psychiatry 2 40825941
2026 Complex I protein NDUFB9 is a metabolic vulnerability in triple negative breast cancer brain metastases. Nature communications 0 42103753
2025 The B22 Dilemma: Structural Basis for Conformational Differences in Proinsulin B-Chain Arg22 Mutants. Biomolecules 0 40305339

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