Affinage

NDUFA9

NADH dehydrogenase [ubiquinone] 1 alpha subcomplex subunit 9, mitochondrial · UniProt Q16795

Round 2 corrected
Length
377 aa
Mass
42.5 kDa
Annotated
2026-04-29
40 papers in source corpus 9 papers cited in narrative 9 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NDUFA9 is an accessory subunit of mitochondrial respiratory chain Complex I that occupies the Q-module at the junction between the peripheral matrix arm and the membrane arm, where it is indispensable for late-stage Complex I assembly and activity. TALEN- and CRISPR-mediated knockout studies show that loss of NDUFA9 causes accumulation of incomplete membrane-arm subcomplexes while preventing incorporation of matrix-arm subunits, and re-expression rescues full Complex I assembly and oxidative phosphorylation (PMID:23223238, PMID:27626371). NDUFA9 is a direct substrate of the mitochondrial deacetylase SIRT3, and its activity is further modulated by competing crotonylation (activating) and acetylation (inhibitory) post-translational modifications that tune Complex I function in contexts such as adipocyte thermogenesis (PMID:18794531, PMID:38657899). Biallelic loss-of-function mutations in NDUFA9 cause Leigh syndrome with isolated Complex I deficiency (PMID:22114105, PMID:28671271).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2008 High

    Identifying SIRT3 as a direct NDUFA9 interactor and deacetylase established that reversible lysine acetylation regulates Complex I activity, linking NAD⁺-dependent signalling to oxidative phosphorylation.

    Evidence Co-immunoprecipitation of SIRT3 with NDUFA9; Complex I activity and ATP measurements in Sirt3-knockout MEFs and tissues with wild-type vs. catalytically dead SIRT3 rescue

    PMID:18794531

    Open questions at the time
    • Specific NDUFA9 lysine residues targeted by SIRT3 were not mapped
    • Whether SIRT3-mediated deacetylation affects Complex I assembly or only catalytic activity was not resolved
  2. 2011 High

    Discovery that a homozygous NDUFA9 missense variant (Arg321Pro) causes fatal Leigh syndrome with isolated Complex I deficiency proved that NDUFA9 integrity is essential for Complex I function in humans.

    Evidence Homozygosity mapping in a consanguineous family; lentiviral wild-type vs. mutant NDUFA9 complementation in patient fibroblasts with Complex I activity rescue

    PMID:22114105

    Open questions at the time
    • Mechanism by which the Arg321Pro substitution disrupts Complex I was not determined at structural level
    • Whether residual Complex I assembly persists in patient cells was not characterized
  3. 2012 High

    TALEN-mediated knockout revealed that NDUFA9 acts at a late assembly step, stabilizing the junction between the membrane and matrix arms of Complex I — cells lacking NDUFA9 accumulate an incomplete membrane-arm subcomplex.

    Evidence Biallelic NDUFA9 KO in HEK293T; BN-PAGE subcomplex profiling; galactose growth assay; rescue by NDUFA9 re-expression

    PMID:23223238

    Open questions at the time
    • The precise molecular contacts through which NDUFA9 bridges the two arms were not resolved
    • Whether NDUFA9 loss also affects supercomplex formation was not tested
  4. 2016 High

    A systematic CRISPR screen of all 31 accessory subunits confirmed NDUFA9 as strictly essential and assigned it to the Q-module, showing that its loss destabilises co-modular subunits.

    Evidence CRISPR/Cas9 KO of each accessory subunit in HEK293T; TMT-based quantitative proteomics; BN-PAGE

    PMID:27626371

    Open questions at the time
    • Order of NDUFA9 incorporation relative to other Q-module subunits during assembly was not resolved
  5. 2017 High

    High-resolution cryo-EM of the human respiratory megacomplex provided the first atomic-level view of NDUFA9 within the Q-module, confirming its position at the membrane-matrix arm interface and enabling rationalisation of disease mutations.

    Evidence Single-particle cryo-EM of purified human megacomplex I₂III₂IV₂

    PMID:28844695

    Open questions at the time
    • Dynamic conformational changes of NDUFA9 during the catalytic cycle (A/D transition) were not captured
  6. 2017 High

    Analysis of two additional patient NDUFA9 alleles demonstrated that variant severity correlates with the degree of Complex I assembly disruption, extending the genotype-phenotype relationship and confirming Q-module subassembly accumulation as a diagnostic signature.

    Evidence BN-PAGE assembly profiling and lentiviral rescue in fibroblasts from patients with two distinct NDUFA9 missense variants

    PMID:28671271

    Open questions at the time
    • Threshold level of residual NDUFA9 function compatible with survival was not defined
  7. 2024 Medium

    Demonstration that crotonylation activates and acetylation inhibits NDUFA9 function in adipocytes revealed a PTM-based switch controlling Complex I-dependent thermogenesis, extending the regulatory framework beyond SIRT3-mediated deacetylation.

    Evidence NDUFA9 overexpression/knockdown in white adipocytes; pharmacological induction of crotonylation vs. acetylation; OCR, ATP, and Complex I activity measurements; in vivo browning model

    PMID:38657899

    Open questions at the time
    • Specific crotonylated and acetylated lysine sites on NDUFA9 were not identified by site-directed mutagenesis
    • Whether these PTMs alter NDUFA9 assembly into Complex I or only its catalytic contribution is unknown
    • Results rely on pharmacological PTM induction rather than site-specific modification
  8. 2025 Medium

    Expanded patient cohort analysis with structural modelling identified Arg360 as a mutational hotspot and showed that pathogenic variants cause NDUFA9 misfolding or disruption of inter-subunit binding interfaces, providing a structural rationale for disease severity.

    Evidence Patient fibroblast BN-PAGE and Complex I activity assays; in silico protein structural modelling of multiple NDUFA9 variants

    PMID:41069424

    Open questions at the time
    • Structural predictions have not been validated by experimental structure determination of mutant forms
    • Functional rescue with site-directed mutants of Arg360 was not performed
  9. 2026 Medium

    Identification of YY1 as a direct transcriptional activator of NDUFA9 and demonstration that NDUFA9 depletion suppresses Akt-mTOR signalling placed NDUFA9 as a node coupling mitochondrial ATP output to growth-factor signalling in cancer cells.

    Evidence ChIP and luciferase reporter assays for YY1 binding; NDUFA9 KD/KO and overexpression in NSCLC lines; OCR, ATP, ROS, phospho-Akt/S6K immunoblotting; xenograft model

    PMID:42014681

    Open questions at the time
    • Whether YY1-driven NDUFA9 expression is relevant outside NSCLC contexts is untested
    • Whether the Akt-mTOR effect is specific to NDUFA9 or a general consequence of Complex I deficiency is not distinguished

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key open questions include the identity and functional impact of specific NDUFA9 lysine residues modified by SIRT3, crotonylation, and acetylation; the conformational dynamics of NDUFA9 during the active/deactive transition of Complex I; and whether NDUFA9 has roles beyond Complex I (e.g. in supercomplex organisation or signalling).
  • No site-specific mutagenesis of individual PTM sites has been performed
  • Conformational dynamics of NDUFA9 during the A/D transition remain unresolved
  • Potential scaffolding or signalling functions independent of Complex I catalysis have not been investigated

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 4
Localization
GO:0005739 mitochondrion 9
Pathway
R-HSA-1430728 Metabolism 6 R-HSA-1852241 Organelle biogenesis and maintenance 3
Partners
SIRT3YY1
Complex memberships
Complex I (NADH:ubiquinone oxidoreductase)Respiratory megacomplex I2III2IV2

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 SIRT3, the mitochondrial NAD-dependent deacetylase, physically interacts with NDUFA9 (the 39-kDa Complex I subunit) and deacetylates multiple Complex I components; loss of SIRT3 increases acetylation of Complex I subunits and selectively inhibits Complex I activity, while exogenous SIRT3 augments Complex I activity, establishing NDUFA9 as a SIRT3 substrate/interactor that links protein acetylation to Complex I regulation. Co-immunoprecipitation of SIRT3 with NDUFA9; reconstitution with wild-type vs. deacetylase-deficient SIRT3 in Sirt3-/- MEFs; measurement of Complex I activity and ATP levels in knockout mice tissues Proceedings of the National Academy of Sciences of the United States of America High 18794531
2011 A homozygous missense mutation in NDUFA9 (Arg321Pro) causes neonatally fatal Leigh syndrome with Complex I deficiency; lentiviral complementation with wild-type but not mutant NDUFA9 restored Complex I activity in patient fibroblasts, establishing NDUFA9 as an essential structural/functional subunit of Complex I whose integrity is required for Complex I activity. Homozygosity mapping; functional complementation with wild-type vs. mutant NDUFA9 via lentiviral transduction; Complex I enzyme activity assay in patient fibroblasts Journal of medical genetics High 22114105
2012 TALEN-mediated knockout of NDUFA9 in HEK293T cells demonstrated that NDUFA9 is required for stabilizing the junction between the membrane arm and matrix arm of Complex I; cells lacking NDUFA9 accumulated a membrane arm subcomplex but lacked matrix arm marker subunits, and re-expression of NDUFA9 restored full Complex I assembly, identifying NDUFA9's role as a late assembly step critical for Complex I biogenesis. TALEN-mediated gene knockout; Blue-Native PAGE and immunoblotting of Complex I subcomplexes; galactose growth assay; rescue by re-expression of NDUFA9 The Journal of biological chemistry High 23223238
2016 Systematic knockout of all 31 accessory subunits of human Complex I confirmed NDUFA9 as strictly required for assembly of a functional Complex I; proteomic analysis showed that loss of NDUFA9 destabilizes subunits within the same Q-module structural module. CRISPR/Cas9 gene editing of each accessory subunit; quantitative proteomic analysis (TMT-based MS); Blue-Native PAGE Nature High 27626371
2017 Cryo-EM structure of the human respiratory megacomplex I2III2IV2 enabled precise subunit assignment within Complex I, including NDUFA9 as part of the Q-module at the junction between the peripheral matrix arm and the membrane arm. Single-particle cryo-electron microscopy of purified human megacomplex I2III2IV2 Cell High 28844695
2017 Patient fibroblast studies with two different NDUFA9 missense variants showed that NDUFA9 is a Q-module subunit whose dysfunction causes accumulation of Q-module subassemblies; the more severe variant additionally caused P-module subassembly accumulation, demonstrating that the severity of the NDUFA9 variant correlates with the extent of Complex I assembly disruption. Lentiviral complementation with wild-type NDUFA9 rescued both Complex I deficiency and assembly defects. Patient fibroblast BN-PAGE complex I assembly analysis; lentiviral complementation with wild-type NDUFA9; exome sequencing for variant identification Clinical genetics High 28671271
2024 NDUFA9 promotes browning of white adipocytes by enhancing mitochondrial Complex I activity, ATP synthesis, and mitochondrial respiration; crotonylation of NDUFA9 (induced by SAHA + sodium crotonate treatment) promotes white adipocyte browning, whereas acetylation of NDUFA9 inhibits this process, revealing a competition between these two PTMs as a regulatory switch for NDUFA9 function in adipocyte thermogenesis. NDUFA9 overexpression/knockdown in white adipocyte cell lines; SAHA + sodium crotonate or SAHA + sodium acetate treatment; measurement of mitochondrial Complex I activity, OCR, ATP production; in vivo fat browning mouse model The international journal of biochemistry & cell biology Medium 38657899
2025 Functional studies in fibroblasts from individuals with biallelic NDUFA9 variants showed loss of fully assembled Complex I, decreased steady-state NDUFA9 protein levels, and/or reduced Complex I activity; protein structural modelling indicated that pathogenic variants cause NDUFA9 misfolding and/or disruption of binding interfaces, with Arg360 identified as a mutational hotspot critical for protein stability/interactions. Patient fibroblast Complex I activity assay; BN-PAGE steady-state assembly analysis; in silico protein structural modelling of variant effects Brain communications Medium 41069424
2026 YY1 transcription factor directly binds the NDUFA9 promoter and drives its transcriptional upregulation in NSCLC; NDUFA9 depletion impairs mitochondrial Complex I activity, reduces oxygen consumption and ATP production, increases ROS, and suppresses Akt-mTOR signalling, while NDUFA9 overexpression enhances mitochondrial function and promotes Akt-mTOR activation, placing NDUFA9 as a positive regulator coupling mitochondrial metabolism to the Akt-mTOR pathway in cancer cells. ChIP and luciferase reporter assays for YY1-NDUFA9 promoter binding; shRNA/CRISPR KO and overexpression in NSCLC cells; measurement of OCR, Complex I activity, ATP, ROS, mitochondrial membrane potential, mtDNA; phospho-immunoblotting of Akt/S6K/mTOR; xenograft mouse tumour model Cell death & disease Medium 42014681

Source papers

Stage 0 corpus · 40 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2015 The BioPlex Network: A Systematic Exploration of the Human Interactome. Cell 1118 26186194
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2008 A role for the mitochondrial deacetylase Sirt3 in regulating energy homeostasis. Proceedings of the National Academy of Sciences of the United States of America 1078 18794531
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2009 A genome-wide RNAi screen identifies multiple synthetic lethal interactions with the Ras oncogene. Cell 843 19490893
2018 VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation. Cell discovery 829 29507755
2007 Large-scale mapping of human protein-protein interactions by mass spectrometry. Molecular systems biology 733 17353931
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2018 High-Density Proximity Mapping Reveals the Subcellular Organization of mRNA-Associated Granules and Bodies. Molecular cell 580 29395067
2016 Accessory subunits are integral for assembly and function of human mitochondrial complex I. Nature 450 27626371
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2015 A Dynamic Protein Interaction Landscape of the Human Centrosome-Cilium Interface. Cell 433 26638075
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
2017 Architecture of Human Mitochondrial Respiratory Megacomplex I2III2IV2. Cell 391 28844695
1994 Purification of CpG islands using a methylated DNA binding column. Nature genetics 363 8012384
2021 A proximity-dependent biotinylation map of a human cell. Nature 339 34079125
2007 Huntingtin interacting proteins are genetic modifiers of neurodegeneration. PLoS genetics 325 17500595
2008 The SDR (short-chain dehydrogenase/reductase and related enzymes) nomenclature initiative. Chemico-biological interactions 315 19027726
2016 Identification of Zika Virus and Dengue Virus Dependency Factors using Functional Genomics. Cell reports 306 27342126
2021 Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context. Cell metabolism 239 34800366
2018 Mapping the Genetic Landscape of Human Cells. Cell 225 30033366
2007 hORFeome v3.1: a resource of human open reading frames representing over 10,000 human genes. Genomics 222 17207965
2016 Mitochondrial Protein Interaction Mapping Identifies Regulators of Respiratory Chain Function. Molecular cell 220 27499296
2016 An organelle-specific protein landscape identifies novel diseases and molecular mechanisms. Nature communications 211 27173435
2015 ∆F508 CFTR interactome remodelling promotes rescue of cystic fibrosis. Nature 209 26618866
2009 Proteomic analysis of integrin-associated complexes identifies RCC2 as a dual regulator of Rac1 and Arf6. Science signaling 207 19738201
2012 Gene knockout using transcription activator-like effector nucleases (TALENs) reveals that human NDUFA9 protein is essential for stabilizing the junction between membrane and matrix arms of complex I. The Journal of biological chemistry 68 23223238
2015 Identification of Coq11, a new coenzyme Q biosynthetic protein in the CoQ-synthome in Saccharomyces cerevisiae. The Journal of biological chemistry 64 25631044
2011 Defective NDUFA9 as a novel cause of neonatally fatal complex I disease. Journal of medical genetics 44 22114105
2017 NDUFA9 point mutations cause a variable mitochondrial complex I assembly defect. Clinical genetics 34 28671271
2020 COQ11 deletion mitigates respiratory deficiency caused by mutations in the gene encoding the coenzyme Q chaperone protein Coq10. The Journal of biological chemistry 15 32205446
2022 HIV-1 Tat and cocaine impact astrocytic energy reservoirs and epigenetic regulation by influencing the LINC01133-hsa-miR-4726-5p-NDUFA9 axis. Molecular therapy. Nucleic acids 10 35892093
2024 NDUFA9 and its crotonylation modification promote browning of white adipocytes by activating mitochondrial function in mice. The international journal of biochemistry & cell biology 5 38657899
2023 Identification of novel coenzyme Q10 biosynthetic proteins Coq11 and Coq12 in Schizosaccharomyces pombe. The Journal of biological chemistry 4 37156397
2026 YY1-mediated NDUFA9 upregulation promotes NSCLC cell growth through mitochondrial and Akt-mTOR pathway modulation. Cell death & disease 0 42014681
2025 Biallelic NDUFA9 variants cause a progressive neurodevelopmental disorder with prominent dystonia and mitochondrial complex I deficiency. Brain communications 0 41069424