NDUFS4

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005739 mitochondrion	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for mitochondrial localization. NDUFS4 is a nuclear-encoded mitochondrial protein with an N-terminal transit peptide (residues 1-42) that targets it to the mitochondrion (UniProt O43181). The protein is confirmed as mitochondrial by immunopurification (PMID:12611891), structural studies (PMID:28844695), and high-confidence mitochondrial proteomics (PMID:34800366). The IBA annotation is phylogenetically informed and accurate. Reason: Core cellular component annotation. NDUFS4 is unambiguously a mitochondrial protein, confirmed by multiple experimental approaches. The IBA annotation is sound and consistent with all available evidence. Supporting Evidence: PMID:12611891 we describe an immunocapture procedure for isolating this multisubunit membrane-bound complex from human tissue PMID:28844695 Architecture of Human Mitochondrial Respiratory Megacomplex I(2)III(2)IV(2)
GO:0022904 respiratory electron transport chain	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for involvement in the respiratory electron transport chain. NDUFS4 is an accessory subunit of Complex I, the first enzyme of the respiratory chain. While NDUFS4 itself does not catalyze electron transfer, it is essential for assembly and stability of a functional Complex I that carries out NADH-to-ubiquinone electron transfer. Loss of NDUFS4 causes substantially reduced NADH:ubiquinone oxidoreductase activity (PMID:11181577, PMID:16478720) and ~50% reduction of intact Complex I abundance (Yin et al. 2024, EMBO J). Reason: Core biological process. NDUFS4 is essential for the function of Complex I within the respiratory electron transport chain. Although it is not a catalytic core subunit, its structural and regulatory role is indispensable for the pathway. The IBA annotation is phylogenetically well supported. Supporting Evidence: PMID:11181577 Fibroblast cultures from the patient exhibited severe reduction of the rotenone-sensitive NADH-->UQ oxidoreductase activity of complex I PMID:16478720 the NDUFS4 mutation prevented complete assembly of the complex and caused full suppression of the activity
GO:0032981 mitochondrial respiratory chain complex I assembly	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for involvement in Complex I assembly. Recent cryo-EM structural analyses of Ndufs4-/- mouse tissue (Yin et al. 2024, EMBO J) reveal that NDUFS4 is critical for the late-stage maturation of Complex I. Loss of NDUFS4 prevents the displacement of the assembly factor NDUFAF2 and results in failure to incorporate NDUFA12, yielding incomplete assembly intermediates. Multiple patient studies show that NDUFS4 mutations abolish normal Complex I assembly (PMID:11181577, PMID:11112787, PMID:15038602). Reason: Core biological process. This is one of the most important functions of NDUFS4. The protein is essential for the final maturation step of Complex I assembly. The IBA annotation is phylogenetically sound and strongly supported by experimental evidence from both human patient fibroblasts and mouse knockout models. Supporting Evidence: PMID:11181577 Two-dimensional electrophoresis showed the absence of detectable normally assembled complex I in the inner mitochondrial membrane. These findings show that the expression of the NDUFS4 gene is essential for the assembly of a functional complex I. PMID:15038602 All the NDUFS4 mutations resulted in impairment of the assembly of a functional complex file:human/NDUFS4/NDUFS4-deep-research-falcon.md knockout complexes lack NDUFA12 in all visualized classes and adopt distinct assembly states where either the assembly factor NDUFAF2 remains bound or NDUFS6 is incompletely associated
GO:0045271 respiratory chain complex I	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for NDUFS4 being part of respiratory chain Complex I. NDUFS4 is one of the 45 subunits of human Complex I, specifically an accessory subunit located within the iron-sulfur protein (IP) fragment at the interface of the N- and Q-modules (PMID:27626371, PMID:12611891, PMID:28844695). The IBA annotation is phylogenetically well supported and correct. Reason: Core cellular component. NDUFS4 is an integral subunit of Complex I, identified by mass spectrometry in immunopurified complex (PMID:12611891) and resolved in cryo-EM structures (PMID:28844695). The IBA annotation is accurate. Supporting Evidence: PMID:27626371 Complex I (NADH:ubiquinone oxidoreductase) is the first enzyme of the mitochondrial respiratory chain and is composed of 45 subunits in humans PMID:12611891 we can resolve and identify the human homologues of 42 polypeptides detected so far in the more extensively studied beef heart complex I
GO:1902600 proton transmembrane transport	IEA GO_REF:0000108	ACCEPT	Summary: IEA annotation inferred from logical inference based on GO:0008137 (NADH dehydrogenase (ubiquinone) activity). Complex I couples electron transfer from NADH to ubiquinone with proton translocation across the inner mitochondrial membrane. While NDUFS4 is in the N-module (hydrophilic arm) rather than the proton-pumping membrane arm, the complex as a whole carries out proton transmembrane transport. As an accessory subunit essential for Complex I function, NDUFS4 contributes to this activity indirectly. Reason: The annotation is acceptable as a broader process annotation for a Complex I subunit. While NDUFS4 is not directly in the proton-pumping domain, the complex as a whole performs proton transmembrane transport, and NDUFS4 is essential for a functional complex. The IEA inference from the complex-level MF is reasonable.
GO:0005743 mitochondrial inner membrane	IEA GO_REF:0000044	ACCEPT	Summary: IEA annotation based on UniProtKB subcellular location mapping. NDUFS4 is localized to the mitochondrial inner membrane as a peripheral membrane protein on the matrix side (UniProt O43181, PMID:12611891). This is well supported by multiple experimental studies. Reason: Correct localization. NDUFS4 is a peripheral membrane protein on the matrix side of the mitochondrial inner membrane, confirmed by subcellular fractionation and structural studies. Supporting Evidence: PMID:12611891 we describe an immunocapture procedure for isolating this multisubunit membrane-bound complex from human tissue
GO:0022900 electron transport chain	IEA GO_REF:0000002	ACCEPT	Summary: IEA annotation from InterPro mapping (IPR006885). GO:0022900 (electron transport chain) is a parent term of GO:0022904 (respiratory electron transport chain). Given that the more specific IBA annotation to GO:0022904 is already present, this broader IEA annotation is redundant but not incorrect. Reason: Correct but broader than the IBA annotation to GO:0022904. As an IEA annotation it provides additional automated support. It is consistent with the known role of NDUFS4 as a Complex I subunit in the electron transport chain.
GO:0022904 respiratory electron transport chain	IEA GO_REF:0000043	ACCEPT	Summary: IEA annotation based on UniProtKB keyword mapping (KW-0679, Respiratory chain). This duplicates the IBA annotation to the same term. The IEA mapping is correct for NDUFS4 as a Complex I subunit. Reason: Correct annotation, consistent with the IBA annotation to the same term. Duplicate GO IDs with different evidence codes are acceptable.
GO:0045271 respiratory chain complex I	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation from ARBA machine learning models. NDUFS4 is a confirmed subunit of respiratory chain Complex I. This duplicates the IBA annotation to the same term but with a different evidence source. Reason: Correct annotation. NDUFS4 is an established subunit of Complex I. Duplicate with different evidence code is acceptable.
GO:0072593 reactive oxygen species metabolic process	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: IEA annotation from ARBA machine learning models for ROS metabolic process. Complex I is a major source of reactive oxygen species in mitochondria. However, NDUFS4 loss (which abolishes Complex I activity) actually prevented ROS production in one study (PMID:16478720), contrasting with the NDUFS1 mutant which showed increased ROS. The relationship between NDUFS4 and ROS is complex and context-dependent. The deep research report also notes that ROS phenotypes may be tissue/context dependent. Reason: While Complex I is a well-established source of ROS, the relationship between NDUFS4 specifically and ROS is indirect and context-dependent. NDUFS4 loss can either increase or decrease ROS depending on conditions (PMID:16478720). ROS metabolism is a secondary consequence of Complex I dysfunction, not a core function of NDUFS4. Consistent with the IMP annotation to the same term. Supporting Evidence: PMID:16478720 No ROS increase was observed in the NDUFS4 mutation
GO:0005739 mitochondrion	IDA GO_REF:0000052	ACCEPT	Summary: IDA annotation based on immunofluorescence data from the Human Protein Atlas. Mitochondrial localization is well established for NDUFS4 from multiple lines of evidence. Reason: Correct localization supported by immunofluorescence data. Consistent with all other evidence for mitochondrial localization of NDUFS4.
GO:0005743 mitochondrial inner membrane	IDA PMID:28844695 Architecture of Human Mitochondrial Respiratory Megacomplex ...	ACCEPT	Summary: IDA annotation from ComplexPortal based on cryo-EM structural data. Guo et al. (2017) determined the architecture of the human respiratory megacomplex I2III2IV2, which resolves all Complex I subunits including NDUFS4 within the inner membrane-associated complex. This structural data directly confirms NDUFS4 localization to the mitochondrial inner membrane. Reason: Strong structural evidence from cryo-EM. NDUFS4 is resolved as a peripheral subunit on the matrix side of the inner membrane within the intact Complex I structure. Supporting Evidence: PMID:28844695 The structure not only reveals the precise assignment of individual subunits of human CI and CIII, but also enables future in-depth analysis of the electron transport chain as a whole
GO:0009060 aerobic respiration	NAS PMID:30030361 Assembly of mammalian oxidative phosphorylation complexes I-...	ACCEPT	Summary: NAS annotation from ComplexPortal based on a review of OXPHOS complex assembly (Signes & Fernandez-Vizarra, 2018). NDUFS4 is an accessory subunit of Complex I, which is part of the oxidative phosphorylation system that carries out aerobic respiration. This is a broad but correct process annotation for a Complex I subunit. Reason: Correct broad biological process. Complex I is the first enzyme in the OXPHOS system which is central to aerobic respiration. NDUFS4 is essential for a functional Complex I. Supporting Evidence: PMID:30030361 The assembly of the five oxidative phosphorylation system (OXPHOS) complexes in the inner mitochondrial membrane is an intricate process
GO:0042776 proton motive force-driven mitochondrial ATP synthesis	NAS PMID:30030361 Assembly of mammalian oxidative phosphorylation complexes I-...	KEEP AS NON CORE	Summary: NAS annotation from ComplexPortal. Complex I contributes to the proton motive force by pumping protons across the inner membrane, which drives ATP synthase (Complex V). NDUFS4 is not directly involved in proton pumping or ATP synthesis but is essential for Complex I function. This annotation is somewhat indirect for an accessory subunit that resides in the hydrophilic arm rather than the proton-pumping membrane domain. Reason: While technically accurate that loss of NDUFS4 impairs proton motive force generation (because it collapses Complex I), this annotation is more of a downstream consequence than a direct function of NDUFS4. The primary role of NDUFS4 is in Complex I assembly and stability, not directly in ATP synthesis. Keeping as non-core reflects that this is an indirect contribution. Supporting Evidence: PMID:30030361 complexes I, III and IV interact with each other, forming the so-called respiratory supercomplexes or 'respirasomes'
GO:0005739 mitochondrion	HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an...	ACCEPT	Summary: HTP annotation from high-throughput mitochondrial proteomics (Morgenstern et al. 2021). NDUFS4 was identified as part of the high-confidence human mitochondrial proteome. This is consistent with all other evidence. Reason: Correct localization confirmed by quantitative proteomics. Consistent with all other evidence for NDUFS4 mitochondrial localization. Supporting Evidence: PMID:34800366 Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context
GO:0045271 respiratory chain complex I	IMP PMID:11112787 Human complex I defects can be resolved by monoclonal antibo...	ACCEPT	Summary: IMP annotation based on Triepels et al. (2001), who used monoclonal antibodies against Complex I subunits to analyze assembly patterns in patients with Complex I defects, including NDUFS4 mutant patients. The study demonstrated that NDUFS4 mutations cause distinct subunit assembly patterns, providing indirect evidence that NDUFS4 is part of Complex I (its loss disrupts the complex). Reason: Valid experimental evidence. The monoclonal antibody analysis and sucrose gradient studies in NDUFS4 mutant patient cells demonstrate that NDUFS4 is a component whose loss disrupts Complex I assembly, confirming its membership in the complex. Supporting Evidence: PMID:11112787 different mutations in the same gene are shown to give very similar subunit profiles
GO:0045271 respiratory chain complex I	IDA PMID:12611891 The subunit composition of the human NADH dehydrogenase obta...	ACCEPT	Summary: IDA annotation based on Murray et al. (2003), who used immunocapture followed by mass spectrometry to identify NDUFS4 as one of the subunits of immunopurified human Complex I. This is direct experimental evidence for NDUFS4 as a Complex I component. Reason: Strong direct evidence. NDUFS4 was identified by MALDI-TOF and LC-MS/MS in immunopurified human Complex I, directly demonstrating its presence as a subunit of the complex. Supporting Evidence: PMID:12611891 Using small amounts of immunoisolated protein, one-dimensional and two-dimensional gel electrophoresis, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) peptide mass finger printing (PMF), and nanoflow liquid chromatography mass spectrometry/mass spectrometry (LC-MS/MS), we can resolve and identify the human homologues of 42 polypeptides
GO:0045271 respiratory chain complex I	IMP PMID:16478720 Dysfunctions of cellular oxidative metabolism in patients wi...	ACCEPT	Summary: IMP annotation based on Iuso et al. (2006), who studied the effects of NDUFS4 mutations on Complex I in patient fibroblasts. The NDUFS4 G44A nonsense mutation prevented complete assembly and caused full suppression of Complex I activity, providing mutant phenotype evidence that NDUFS4 is an essential component of Complex I. Reason: Valid mutant phenotype evidence confirming NDUFS4 as an essential Complex I subunit. Loss of NDUFS4 abolishes Complex I assembly and activity. Supporting Evidence: PMID:16478720 the NDUFS4 mutation prevented complete assembly of the complex and caused full suppression of the activity
GO:0045271 respiratory chain complex I	IDA PMID:27626371 Accessory subunits are integral for assembly and function of...	ACCEPT	Summary: IDA annotation based on Stroud et al. (2016), who used gene editing to generate knockout cell lines for all Complex I accessory subunits and performed quantitative proteomics. NDUFS4 was shown to be one of 25 accessory subunits strictly required for assembly of a functional complex. This study provides both identification of NDUFS4 within the complex and functional evidence for its essentiality. Reason: Strong experimental evidence from a systematic gene-editing and proteomics study. NDUFS4 knockout cells showed loss of functional Complex I, confirming it as an essential accessory subunit. Supporting Evidence: PMID:27626371 We show that 25 subunits are strictly required for assembly of a functional complex and 1 subunit is essential for cell viability
GO:0005515 protein binding	IPI PMID:31206022 BAP31 regulates mitochondrial function via interaction with ...	MARK AS OVER ANNOTATED	Summary: IPI annotation for protein binding, based on Namba (2019) who showed that NDUFS4 interacts with BAP31 (BCAP31, UniProtKB:P51572) and TOMM40 via co-immunoprecipitation. BAP31 acts as an ER-mitochondria bridging factor that stimulates translocation of NDUFS4 from the cytosol to mitochondria through interaction with Tom40. However, "protein binding" (GO:0005515) is uninformative and does not capture the specific nature of these interactions. Reason: The generic "protein binding" term does not convey useful information about the biological context. The NDUFS4-BAP31-TOMM40 interaction relates to mitochondrial protein import and is better captured by more specific terms. Per project guidelines, generic protein binding annotations should be flagged as over-annotated. Supporting Evidence: PMID:31206022 BAP31 interacts with mitochondria-localized proteins, including Tom40, to stimulate the translocation of NDUFS4, the component of complex I from the cytosol to the mitochondria
GO:0005739 mitochondrion	IDA PMID:31206022 BAP31 regulates mitochondrial function via interaction with ...	ACCEPT	Summary: IDA annotation for mitochondrial localization based on Namba (2019). The study used subcellular fractionation and showed NDUFS4 localization in the mitochondria-associated ER membrane (MAM) and mitochondrial fractions. BAP31 knockout reduced NDUFS4 in the mitochondrial fraction, confirming its normal mitochondrial localization. Reason: Valid experimental evidence from subcellular fractionation confirming NDUFS4 mitochondrial localization. Consistent with all other evidence. Supporting Evidence: PMID:31206022 NDUFS4 and Tom40 were localized to the MAM and mitochondria
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-163217	ACCEPT	Summary: TAS annotation from Reactome pathway R-HSA-163217 (Complex I oxidises NADH to NAD+, reduces CoQ to CoQH2). NDUFS4 is annotated as part of Complex I which functions at the mitochondrial inner membrane. This is consistent with all structural and biochemical evidence. Reason: Correct localization supported by Reactome pathway annotation. NDUFS4 is a peripheral membrane protein on the matrix side of the inner mitochondrial membrane as part of Complex I.
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-6799179	ACCEPT	Summary: TAS annotation from Reactome pathway R-HSA-6799179 (Peripheral arm subunits bind the 815kDa complex to form a 980kDa complex). This Reactome entry describes the assembly step where peripheral arm subunits including NDUFS4 are incorporated into the growing Complex I at the inner membrane. Reason: Correct localization. The Reactome assembly pathway places NDUFS4 at the mitochondrial inner membrane during Complex I biogenesis.
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-6799196	ACCEPT	Summary: TAS annotation from Reactome pathway R-HSA-6799196 (The MCIA complex, NDUFAF2-7 all dissociate from the 980kDa complex, resulting in Complex I). This represents the final maturation step of Complex I assembly where assembly factors dissociate. NDUFS4 is critical for this step, as its incorporation helps displace NDUFAF2. Reason: Correct localization. Consistent with the role of NDUFS4 in the final maturation of Complex I at the mitochondrial inner membrane.
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-6800870	ACCEPT	Summary: TAS annotation from Reactome pathway R-HSA-6800870 (NDUF subunits bind to form the FP subcomplex). This refers to early assembly of the flavoprotein subcomplex. NDUFS4 is part of the iron-sulfur protein fragment rather than the FP subcomplex, but the overall annotation of inner membrane localization is still correct. Reason: Correct localization. While NDUFS4 is in the IP fragment rather than the FP subcomplex, the annotation of mitochondrial inner membrane localization is accurate regardless.
GO:0072593 reactive oxygen species metabolic process	IMP PMID:16870178 cAMP controls oxygen metabolism in mammalian cells.	KEEP AS NON CORE	Summary: IMP annotation based on Piccoli et al. (2006). This study found that a missense genetic defect in the NDUFS4 subunit suppressed Complex I activity and prevented ROS production, while cAMP-dependent activation of Complex I was associated with reduced ROS accumulation. Notably, the NDUFS4 mutation decreased ROS rather than increasing it, in contrast to the NDUFS1 mutant. This shows NDUFS4 mutations alter ROS metabolism, but the direction of effect depends on context. Reason: While NDUFS4 mutations do affect ROS metabolism, this appears to be a secondary consequence of Complex I dysfunction rather than a direct function of NDUFS4. The relationship is complex since NDUFS4 loss can either increase or decrease ROS depending on the tissue and conditions. This is not a core function but a downstream phenotypic consequence. Supporting Evidence: PMID:16870178 A missense genetic defect in the NDUFS4 subunit, putative substrate of PKA, suppressed, on the other hand, the activity of the complex and prevented ROS production
GO:0032981 mitochondrial respiratory chain complex I assembly	IMP PMID:11112787 Human complex I defects can be resolved by monoclonal antibo...	ACCEPT	Summary: IMP annotation based on Triepels et al. (2001), who analyzed Complex I assembly patterns in NDUFS4 mutant patients using monoclonal antibodies against Complex I subunits. The NDUFS4 mutations caused distinct assembly defects, demonstrating that NDUFS4 is required for normal Complex I assembly. Reason: Valid experimental evidence showing that NDUFS4 mutations disrupt Complex I assembly, as revealed by altered subunit profiles. Complex I assembly is a core function of NDUFS4. Supporting Evidence: PMID:11112787 Western blotting with these antibodies, particularly when used in conjunction with sucrose gradient studies and enzymatic activity measurements, helps distinguish catalytic versus assembly defects
GO:0032981 mitochondrial respiratory chain complex I assembly	IMP PMID:15038602 Respiratory complex I in brain development and genetic disea...	ACCEPT	Summary: IMP annotation based on Papa et al. (2004), who studied Complex I expression, activity, and assembly during brain development and in children with inherited encephalopathies carrying NDUFS4 mutations. All NDUFS4 mutations studied resulted in impairment of the assembly of a functional complex. Reason: Core function confirmed by multiple NDUFS4 mutations all resulting in impaired Complex I assembly. This is consistent with the structural role of NDUFS4 in the late-stage maturation of Complex I. Supporting Evidence: PMID:15038602 All the NDUFS4 mutations resulted in impairment of the assembly of a functional complex
GO:0006120 mitochondrial electron transport, NADH to ubiquinone	NAS PMID:9463323 Demonstration of a new pathogenic mutation in human complex ...	ACCEPT	Summary: NAS annotation based on van den Heuvel et al. (1998), the original cloning and mutation report for NDUFS4. The paper describes NDUFS4 as encoding the 18 kDa subunit of mitochondrial respiratory chain Complex I, which carries out NADH to ubiquinone electron transport. While NDUFS4 itself does not catalyze this reaction, it is essential for the function of the complex that does. Reason: Correct biological process annotation. NDUFS4 is essential for Complex I function, and Complex I catalyzes NADH to ubiquinone electron transfer. NAS evidence code is appropriate for this literature-based inference. Supporting Evidence: PMID:9463323 We report the cDNA cloning, chromosomal localization, and a mutation in the human nuclear gene encoding the 18-kD (AQDQ) subunit of the mitochondrial respiratory chain complex I
GO:0007420 brain development	IMP PMID:14765537 Clinical heterogeneity in patients with mutations in the NDU...	MARK AS OVER ANNOTATED	Summary: IMP annotation based on Budde et al. (2003), who compared clinical presentation of NDUFS4 mutation patients. The paper describes marked clinical heterogeneity in patients with NDUFS4 mutations, with neurological presentations including Leigh syndrome. However, brain development impairment in these patients is a disease consequence of global Complex I deficiency, not a direct developmental function of NDUFS4. NDUFS4 is expressed ubiquitously (HPA shows low tissue specificity), and its role in brain development is secondary to its essential role in Complex I function in metabolically demanding tissues. Reason: Brain development impairment in NDUFS4 patients is a downstream consequence of Complex I deficiency in metabolically demanding neural tissue, not a direct developmental function of NDUFS4. The gene is ubiquitously expressed and has no brain-specific function. Annotating NDUFS4 to brain development conflates disease phenotype with gene function. Supporting Evidence: PMID:14765537 A comparison of the clinical presentation, disease course and results of laboratory and imaging studies of all patients so far published with a NDUFS4 mutation are presented. This reveals marked clinical heterogeneity, even in patients with the same genotype.
GO:0008137 NADH dehydrogenase (ubiquinone) activity	IMP PMID:15038602 Respiratory complex I in brain development and genetic disea...	ACCEPT	Summary: IMP annotation with contributes_to qualifier based on Papa et al. (2004). The study showed that NDUFS4 mutations impair Complex I assembly and thus NADH dehydrogenase activity. The contributes_to qualifier is appropriate because NDUFS4 is an accessory subunit that does not directly catalyze the reaction but contributes to the complex-level enzymatic activity through its structural and assembly role. Reason: The contributes_to qualifier is correctly applied for an accessory subunit. NDUFS4 does not directly catalyze NADH oxidation but is essential for the assembly and stability of the complex that does. This is consistent with GO annotation practices for multi-subunit enzyme complexes where accessory subunits use contributes_to. Supporting Evidence: PMID:15038602 All the NDUFS4 mutations resulted in impairment of the assembly of a functional complex
GO:0008137 NADH dehydrogenase (ubiquinone) activity	IMP PMID:16870178 cAMP controls oxygen metabolism in mammalian cells.	ACCEPT	Summary: IMP annotation with contributes_to qualifier based on Piccoli et al. (2006). The study showed that an NDUFS4 missense defect suppressed Complex I NADH-ubiquinone oxidoreductase activity. The contributes_to qualifier is appropriate for this accessory subunit. Reason: Correct annotation with appropriate contributes_to qualifier. NDUFS4 mutations suppress Complex I activity, confirming that NDUFS4 contributes to the complex-level enzymatic activity. Supporting Evidence: PMID:16870178 A missense genetic defect in the NDUFS4 subunit, putative substrate of PKA, suppressed, on the other hand, the activity of the complex
GO:0051591 response to cAMP	IMP PMID:11165261 Mutation in the NDUFS4 gene of complex I abolishes cAMP-depe...	ACCEPT	Summary: IMP annotation based on Papa et al. (2001), who showed that mutation in NDUFS4 abolishes cAMP-dependent phosphorylation of the protein and cAMP-dependent activation of Complex I. NDUFS4 contains a PKA phosphorylation site (Ser-173), and cAMP-dependent phosphorylation of this site activates Complex I. The NDUFS4 mutation abolished this cAMP-dependent response, providing evidence that NDUFS4 mediates the response of Complex I to cAMP signaling. Reason: Valid experimental evidence. NDUFS4 is a direct substrate of PKA, and its phosphorylation at Ser-173 mediates cAMP-dependent activation of Complex I. This is a genuine regulatory function of NDUFS4 as a signal-responsive subunit. Supporting Evidence: PMID:11165261 the homozygous 5 bp duplication in the cDNA of the NDUFS4 18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of this protein and activation of the complex. These findings show for the first time that human complex I is regulated via phosphorylation of the subunit encoded by the NDUFS4 gene.
GO:0051591 response to cAMP	IMP PMID:11181577 A nonsense mutation in the NDUFS4 gene encoding the 18 kDa (...	ACCEPT	Summary: IMP annotation based on Petruzzella et al. (2001), who showed that a nonsense mutation in NDUFS4 resulted in Complex I activity that was insensitive to cAMP stimulation. Since NDUFS4 is the PKA substrate through which cAMP activates Complex I, its loss abolishes this response. Reason: Valid experimental evidence confirming that NDUFS4 is required for the cAMP-dependent regulation of Complex I. The loss of NDUFS4 eliminated cAMP responsiveness of Complex I activity. Supporting Evidence: PMID:11181577 Fibroblast cultures from the patient exhibited severe reduction of the rotenone-sensitive NADH-->UQ oxidoreductase activity of complex I, which was insensitive to cAMP stimulation
GO:0006120 mitochondrial electron transport, NADH to ubiquinone	NAS PMID:9878551 cDNA of eight nuclear encoded subunits of NADH:ubiquinone ox...	ACCEPT	Summary: NAS annotation based on Loeffen et al. (1998), who completed the cDNA characterization of all nuclear-encoded Complex I subunits. The paper describes NDUFS4 in the context of NADH:ubiquinone oxidoreductase function but does not specifically study NDUFS4 function. The NAS code is appropriate. Reason: Correct biological process annotation. NDUFS4 is a subunit of NADH:ubiquinone oxidoreductase, which catalyzes mitochondrial electron transport from NADH to ubiquinone. NAS evidence code is appropriate for this literature-based characterization. Supporting Evidence: PMID:9878551 NADH:ubiquinone oxidoreductase (complex I) is an extremely complicated multiprotein complex located in the inner mitochondrial membrane. Its main function is the transport of electrons from NADH to ubiquinone
GO:0008137 NADH dehydrogenase (ubiquinone) activity	IMP PMID:16478720 Dysfunctions of cellular oxidative metabolism in patients wi...	ACCEPT	Summary: IMP annotation based on Iuso et al. (2006), showing that NDUFS4 mutation prevents complete Complex I assembly and fully suppresses Complex I activity. This supports NDUFS4 participation in the complex-level NADH dehydrogenase function. Reason: The GO term is supported by strong experimental evidence that NDUFS4 loss causes complete suppression of Complex I activity. As a supernumerary subunit, NDUFS4 supports the complex-level activity through assembly/stability rather than direct catalysis, consistent with other accepted GO:0008137 entries for this gene. Supporting Evidence: PMID:16478720 the NDUFS4 mutation prevented complete assembly of the complex and caused full suppression of the activity
GO:0001932 regulation of protein phosphorylation	IMP PMID:11165261 Mutation in the NDUFS4 gene of complex I abolishes cAMP-depe...	MARK AS OVER ANNOTATED	Summary: IMP annotation from MGI for regulation of protein phosphorylation, based on Papa et al. (2001). The GOA TSV shows the qualifier acts_upstream_of_or_within, suggesting this is an indirect involvement. The study showed that NDUFS4 mutation abolishes cAMP-dependent phosphorylation of the NDUFS4 protein itself and activation of Complex I. NDUFS4 is a phosphorylation substrate, not a kinase or phosphatase. The annotation seems to conflate being a substrate of phosphorylation with regulating phosphorylation. NDUFS4 does not regulate protein phosphorylation; rather, its own phosphorylation by PKA regulates Complex I activity. Reason: NDUFS4 is a substrate of PKA phosphorylation at Ser-173, not a regulator of protein phosphorylation. The annotation conflates being phosphorylated (a substrate) with regulating phosphorylation (a kinase/phosphatase/regulatory function). The cAMP/PKA-dependent phosphorylation of NDUFS4 is better captured by the response to cAMP annotations (GO:0051591). Supporting Evidence: PMID:11165261 the homozygous 5 bp duplication in the cDNA of the NDUFS4 18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of this protein and activation of the complex

Core Functions

NDUFS4 is a supernumerary accessory subunit required for late-stage maturation and stability of mitochondrial Complex I. Although it is not a catalytic redox subunit, NDUFS4 is essential for assembly of a functional holoenzyme and therefore contributes_to the complex-level NADH dehydrogenase (ubiquinone) activity carried out by Complex I.

Molecular Function:

NADH dehydrogenase (ubiquinone) activity

Directly Involved In:

mitochondrial respiratory chain complex I assembly respiratory electron transport chain

Cellular Locations:

mitochondrial inner membrane

In Complex:

respiratory chain complex I

Supporting Evidence:

PMID:11181577
Two-dimensional electrophoresis showed the absence of detectable normally assembled complex I in the inner mitochondrial membrane. These findings show that the expression of the NDUFS4 gene is essential for the assembly of a functional complex I.
file:human/NDUFS4/NDUFS4-deep-research-falcon.md
knockout complexes lack NDUFA12 in all visualized classes and adopt distinct assembly states where either the assembly factor NDUFAF2 remains bound or NDUFS6 is incompletely associated

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

GO_REF:0000052

Gene Ontology annotation based on curation of immunofluorescence data

GO_REF:0000108

Automatic assignment of GO terms using logical inference, based on on inter-ontology links

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

file:human/NDUFS4/NDUFS4-deep-research-falcon.md

Falcon deep research synthesis for human NDUFS4

PMID:11112787

Human complex I defects can be resolved by monoclonal antibody analysis into distinct subunit assembly patterns.

Monoclonal antibody analysis and sucrose gradient studies of NDUFS4 mutant patient cells showed distinct subunit assembly defects, demonstrating NDUFS4 is required for normal Complex I assembly.

"Western blotting with these antibodies, particularly when used in conjunction with sucrose gradient studies and enzymatic activity measurements, helps distinguish catalytic versus assembly defects and further distinguishes between mutations in different subunits"

PMID:11165261

Mutation in the NDUFS4 gene of complex I abolishes cAMP-dependent activation of the complex in a child with fatal neurological syndrome.

NDUFS4 mutation abolishes cAMP-dependent phosphorylation of the NDUFS4 protein and cAMP-dependent activation of Complex I, showing for the first time that human Complex I is regulated via phosphorylation of NDUFS4.

"the homozygous 5 bp duplication in the cDNA of the NDUFS4 18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of this protein and activation of the complex. These findings show for the first time that human complex I is regulated via phosphorylation of the subunit encoded by the NDUFS4 gene."

PMID:11181577

A nonsense mutation in the NDUFS4 gene encoding the 18 kDa (AQDQ) subunit of complex I abolishes assembly and activity of the complex in a patient with Leigh-like syndrome.

Nonsense mutation in NDUFS4 causes complete absence of normally assembled Complex I in the inner mitochondrial membrane, severe reduction of NADH:UQ oxidoreductase activity, and insensitivity to cAMP stimulation, demonstrating that NDUFS4 is essential for assembly of a functional Complex I.

"Two-dimensional electrophoresis showed the absence of detectable normally assembled complex I in the inner mitochondrial membrane. These findings show that the expression of the NDUFS4 gene is essential for the assembly of a functional complex I."

PMID:12611891

The subunit composition of the human NADH dehydrogenase obtained by rapid one-step immunopurification.

NDUFS4 was identified as a subunit of human Complex I by immunocapture followed by MALDI-TOF and LC-MS/MS mass spectrometry.

"we can resolve and identify the human homologues of 42 polypeptides detected so far in the more extensively studied beef heart complex I"

PMID:14765537

Clinical heterogeneity in patients with mutations in the NDUFS4 gene of mitochondrial complex I.

Marked clinical heterogeneity exists among patients with NDUFS4 mutations, including neurological presentations consistent with Leigh syndrome, even among patients with the same genotype.

"A comparison of the clinical presentation, disease course and results of laboratory and imaging studies of all patients so far published with a NDUFS4 mutation are presented. This reveals marked clinical heterogeneity, even in patients with the same genotype."

PMID:15038602

Respiratory complex I in brain development and genetic disease.

All NDUFS4 mutations studied resulted in impairment of Complex I assembly. Complex I expression and activity markedly increase during brain cell differentiation.

"All the NDUFS4 mutations resulted in impairment of the assembly of a functional complex"

PMID:16478720

Dysfunctions of cellular oxidative metabolism in patients with mutations in the NDUFS1 and NDUFS4 genes of complex I.

NDUFS4 G44A nonsense mutation prevents complete Complex I assembly and fully suppresses activity. Unlike NDUFS1 mutation, no ROS increase was observed with the NDUFS4 mutation.

"the NDUFS4 mutation prevented complete assembly of the complex and caused full suppression of the activity...No ROS increase was observed in the NDUFS4 mutation"

PMID:16870178

cAMP controls oxygen metabolism in mammalian cells.

NDUFS4 missense defect suppresses Complex I activity and prevents ROS production. cAMP activates NADH-ubiquinone oxidoreductase activity, and this activation is abolished by NDUFS4 mutation.

"A missense genetic defect in the NDUFS4 subunit, putative substrate of PKA, suppressed, on the other hand, the activity of the complex and prevented ROS production"

PMID:27626371

Accessory subunits are integral for assembly and function of human mitochondrial complex I.

Systematic gene editing study showed 25 of 31 accessory subunits (including NDUFS4) are strictly required for assembly of a functional Complex I. Loss of each subunit affects stability of other subunits in the same structural module.

"We show that 25 subunits are strictly required for assembly of a functional complex and 1 subunit is essential for cell viability"

PMID:28844695

Architecture of Human Mitochondrial Respiratory Megacomplex I(2)III(2)IV(2).

Cryo-EM structure of the human respiratory megacomplex at 3.4 A resolution reveals precise assignment of all Complex I subunits including NDUFS4 in the mitochondrial inner membrane.

"The structure not only reveals the precise assignment of individual subunits of human CI and CIII, but also enables future in-depth analysis of the electron transport chain as a whole"

PMID:30030361

Assembly of mammalian oxidative phosphorylation complexes I-V and supercomplexes.

Review of the assembly pathways for all five OXPHOS complexes. Complex I assembly involves multiple intermediate stages with numerous assembly factors, and supernumerary subunits play essential roles in assembly, regulation, and stability.

"The assembly of the five oxidative phosphorylation system (OXPHOS) complexes in the inner mitochondrial membrane is an intricate process"

PMID:31206022

BAP31 regulates mitochondrial function via interaction with Tom40 within ER-mitochondria contact sites.

BAP31 interacts with NDUFS4 and Tom40 to form an ER-mitochondria bridging complex that stimulates translocation of NDUFS4 from the cytosol to mitochondria. Loss of BAP31 reduces NDUFS4 in the mitochondrial fraction and suppresses Complex I activity.

"BAP31 interacts with mitochondria-localized proteins, including Tom40, to stimulate the translocation of NDUFS4, the component of complex I from the cytosol to the mitochondria"

PMID:34800366

Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context.

NDUFS4 identified as part of the high-confidence human mitochondrial proteome by quantitative proteomics.

"Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context"

PMID:9463323

Demonstration of a new pathogenic mutation in human complex I deficiency: a 5-bp duplication in the nuclear gene encoding the 18-kD (AQDQ) subunit.

First report of NDUFS4 cDNA cloning, chromosomal localization (chromosome 5), and identification of a pathogenic homozygous 5-bp duplication destroying a consensus phosphorylation site, causing Complex I deficiency.

"We report the cDNA cloning, chromosomal localization, and a mutation in the human nuclear gene encoding the 18-kD (AQDQ) subunit of the mitochondrial respiratory chain complex I...A homozygous 5-bp duplication, destroying a consensus phosphorylation site"

PMID:9878551

cDNA of eight nuclear encoded subunits of NADH:ubiquinone oxidoreductase: human complex I cDNA characterization completed.

Completed characterization of all nuclear-encoded Complex I subunit cDNAs. NDUFS4 encodes the 18 kDa subunit of NADH:ubiquinone oxidoreductase.

"NADH:ubiquinone oxidoreductase (complex I) is an extremely complicated multiprotein complex located in the inner mitochondrial membrane. Its main function is the transport of electrons from NADH to ubiquinone"

Reactome:R-HSA-163217

Complex I oxidises NADH to NAD+, reduces CoQ to CoQH2

Reactome:R-HSA-6799179

Peripheral arm subunits bind the 815kDa complex to form a 980kDa complex

Reactome:R-HSA-6799196

The MCIA complex, NDUFAF2-7 all dissociate from the 980kDa complex, resulting in Complex I

Reactome:R-HSA-6800870

NDUF subunits bind to form the FP subcomplex

Deep Research

Falcon

(NDUFS4-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 32 citations 2026-02-11T09:05:16.234902

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Comprehensive research report: Human NDUFS4 (UniProt O43181)

Plan overview
- We verified the identity of the target (NDUFS4, UniProt O43181) in Homo sapiens and aligned nomenclature, structure, family placement, and localization with recent structural literature. We then prioritized 2023–2024 primary papers and authoritative reviews to detail function, pathways, localization, recent advances (cryo-EM, immune and organ-specific findings), and translational developments. Finally, we consolidated quantitative data and embedded a summary artifact for rapid reference (URLs and dates included where available).

1) Key concepts, definitions, and current understanding
- Identity and localization. NDUFS4 (NADH dehydrogenase [ubiquinone] iron–sulfur protein 4) is an ~18 kDa supernumerary subunit of mitochondrial Complex I (NADH:ubiquinone oxidoreductase) localized on the matrix-facing side at the interface between the NADH dehydrogenase module (N-module) and the quinone reduction module (Q-module). Human NDUFS4 contains a canonical PKA site at Ser131, and its structural elements act as a rivet that helps anchor the N-module to the rest of the enzyme while lying within ~8–12 Å of multiple Fe–S clusters (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4). These placements explain how NDUFS4 can influence stability and catalysis despite not being a catalytic core subunit (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4). (yin2024structuralinsightsinto pages 1-2, yin2024structuralinsightsinto pages 2-3)
- Primary function within Complex I. As an accessory subunit, NDUFS4 contributes to Complex I stability, assembly maturation, and proper positioning/dynamics of the N-module relative to the membrane domain; by bridging N- and Q-modules and interacting near Fe–S sites, it helps sustain efficient NADH-to-ubiquinone electron transfer and overall enzyme stability rather than catalyzing a distinct reaction itself (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4). (yin2024structuralinsightsinto pages 1-2, yin2024structuralinsightsinto pages 2-3)
- Cellular compartment. NDUFS4 functions in the mitochondrial inner membrane as part of Complex I, with the polypeptide oriented toward the matrix-facing hydrophilic arm (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4). (yin2024structuralinsightsinto pages 2-3)

2) Recent developments and latest research (2023–2024)
- Cryo-EM structural and assembly insights. High-resolution analyses in the Ndufs4−/− mouse reveal that loss of NDUFS4 destabilizes attachment of the N-module and prevents normal maturation: knockout complexes lack NDUFA12 in all visualized classes and adopt distinct assembly states where either the assembly factor NDUFAF2 remains bound or NDUFS6 is incompletely associated—consistent with NDUFAF2 recruiting the N-module late in assembly and being displaced during maturation by NDUFS4/NDUFS6/NDUFA12 (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4; preprint version, Jul 2023, https://doi.org/10.1101/2023.07.17.549284). Quantitatively, intact Complex I abundance was reduced by ~50% in Ndufs4−/− tissues, with BN-PAGE consistently showing ~1 MDa (WT) and, in knockout, ~800 kDa “QP” and ~200 kDa N-module species, and with substantially reduced NADH:ubiquinone oxidoreductase activity in the knockout preparations (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4; preprint, Jul 2023, https://doi.org/10.1101/2023.07.17.549284). (yin2024structuralinsightsinto pages 2-3, yin2024structuralinsightsinto pages 1-2, yin2024structuralinsightsinto pages 22-25, yin2024structuralinsightsinto pages 11-12, yin2023structuralinsightsinto pages 14-16, yin2023structuralinsightsinto pages 16-19)
- Blood–brain barrier (BBB) integrity. Contrary to expectations from acute pharmacological Complex I inhibition models, 1-month-old Ndufs4−/− mice exhibit preserved BBB structure and function: systemic AAV9-GFP (5.0×10^13 vg/kg) poorly transduced the brain in both genotypes, and Evans blue extravasation and endogenous albumin assays showed no increased permeability (Evans blue absorbance 0.049 ± 0.002 in Ndufs4−/− vs 0.053 ± 0.003 in controls; p>0.05). Vascular architecture (3D clearing, histology) and junctional protein levels were comparable to controls (IJMS, Apr 2024, https://doi.org/10.3390/ijms25094828). The authors note these conclusions apply to early disease and do not exclude later-stage changes (IJMS, Apr 2024, https://doi.org/10.3390/ijms25094828). (reynauddulaurier2024theblood–brainbarrier pages 2-4, reynauddulaurier2024theblood–brainbarrier pages 4-7, reynauddulaurier2024theblood–brainbarrier pages 1-2, reynauddulaurier2024theblood–brainbarrier pages 10-12)
- Cardiac electrophysiology and oxidative stress. In germline Ndufs4−/− mice, mitochondrial/total ROS rose markedly during ex vivo hypoxia–reoxygenation and correlated with progression to high-degree AV block and sinus node dysfunction. Mitochondria-targeted antioxidant MitoTempo abolished MitoSOX/DCFDA signals, restored sinus rhythm, and—together with SS-31 (elamipretide)—significantly extended lifespan with chronic treatment (Antioxidants, Apr 2023, https://doi.org/10.3390/antiox12051001). Mechanistic proposals include ROS-mediated or NAD+/Sirt1-dependent modulation of Nav1.5 (INa) affecting conduction (Antioxidants, Apr 2023, https://doi.org/10.3390/antiox12051001). (chen2023mitochondrialoxidativestress pages 8-10)
- Kidney and cristae remodeling. In diabetic mouse models, podocyte-specific overexpression of Ndufs4 improved cristae morphology, mitochondrial dynamics, and albuminuria, and proximity labeling connected NDUFS4 to the cristae-shaping factor STOML2, nominating NDUFS4 as a regulator of cristae status in this context (Nature Communications, Mar 2024, https://doi.org/10.1038/s41467-024-46366-w). (serranolorenzo2023developmentofa pages 14-15)
- Mitochondria transfer-based therapies. Intercellular/exogenous mitochondria transfer reduced morbidity and mortality in Ndufs4−/− models, supporting organelle replacement as a candidate therapeutic approach for Leigh syndrome (Nature Metabolism, Sep 2024, https://doi.org/10.1038/s42255-024-01125-5). (nakai2024mitochondriatransferbasedtherapies pages 24-25)

3) Current applications and real-world implementations
- CNS gene therapy context. AAV-mediated CNS gene replacement in OXPHOS-deficient mouse models (e.g., Complex I subunit Ndufs3 or Complex IV Cox10 conditional knockouts) extended survival from ~5–6 months to >15 months, with extensive phenotypic rescue despite transducing ~30% of neurons. These results illustrate that partial neuronal correction can yield outsized benefit and frame feasibility for gene therapy strategies in mitochondrial encephalopathies (EMBO Molecular Medicine, Aug 2024, https://doi.org/10.1038/s44321-024-00111-4). Although not an Ndufs4 therapy per se, they contextualize AAV-based approaches for Complex I deficiencies including NDUFS4-related disease (EMBO Molecular Medicine, Aug 2024, https://doi.org/10.1038/s44321-024-00111-4). (reynauddulaurier2024theblood–brainbarrier pages 2-4)
- Small-molecule and physiological interventions. In Complex I–deficient/Leigh models, several strategies have shown benefit in preclinical settings, including chronic hypoxia and mTOR inhibition; both have been reported to ameliorate features of Ndufs4−/− disease (reported in structural and cardiac studies that reference these interventions) (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4; Antioxidants, Apr 2023, https://doi.org/10.3390/antiox12051001). (yin2024structuralinsightsinto pages 2-3, chen2023mitochondrialoxidativestress pages 8-10)
- BBB targeting implications. Because the BBB appears intact at early disease stages in Ndufs4−/− mice, gene and drug delivery to the CNS may require vectors or routes that bypass the barrier (e.g., serotypes or direct administration), rather than relying on disease-related permeability (IJMS, Apr 2024, https://doi.org/10.3390/ijms25094828). (reynauddulaurier2024theblood–brainbarrier pages 1-2, reynauddulaurier2024theblood–brainbarrier pages 2-4, reynauddulaurier2024theblood–brainbarrier pages 4-7)

4) Expert opinions and authoritative analyses
- Consensus gene–disease curation. An expert panel curated 113 primary mitochondrial disease genes for the Leigh syndrome spectrum, underscoring the robustness of gene–disease assertions that include NDUFS4 among established nuclear Complex I causes (Annals of Neurology, Aug 2023, https://doi.org/10.1002/ana.26716). (serranolorenzo2023developmentofa pages 4-5)
- Structural biology perspective on assembly. Recent cryo-EM–based analyses propose a late-stage maturation mechanism in which NDUFAF2 initially recruits and stabilizes the N-module; subsequent incorporation of NDUFS4, NDUFS6, and NDUFA12 displaces NDUFAF2 to yield the mature, fully assembled Complex I. The NDUFS4 β-hairpin and contacts with NDUFS6/NDUFA12 appear to be critical for this transition (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4; preprint, Jul 2023, https://doi.org/10.1101/2023.07.17.549284). (yin2024structuralinsightsinto pages 2-3, yin2023structuralinsightsinto pages 16-19)
- Immunology and metabolism (models). Work in Ndufs4−/− macrophage cell lines shows that Complex I deficiency skews effector functions toward pro-inflammatory responses and increases phagocytic capacity, supporting tissue- and cell-type–specific consequences of NDUFS4 loss that may contribute to systemic disease (PLOS ONE, Sep 2023, https://doi.org/10.1371/journal.pone.0291442). (serranolorenzo2023developmentofa pages 14-15, serranolorenzo2023developmentofa pages 4-5)

5) Relevant statistics and quantitative data (recent studies)
- Complex I abundance and activity in Ndufs4−/− tissues: ~50% reduction of intact Complex I, with BN-PAGE revealing ~1 MDa (wild type) versus ~800 kDa (QP subcomplex) and ~200 kDa (N-module) species in the knockout, and substantially lower NADH:ubiquinone oxidoreductase activity in purified knockout Complex I (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4; preprint, Jul 2023, https://doi.org/10.1101/2023.07.17.549284). (yin2024structuralinsightsinto pages 11-12, yin2023structuralinsightsinto pages 14-16, yin2023structuralinsightsinto pages 16-19)
- BBB permeability in 1-month-old Ndufs4−/− mice: Evans blue absorbance 0.049 ± 0.002 (Ndufs4−/−) vs 0.053 ± 0.003 (controls), p>0.05; systemic AAV9 (5.0×10^13 vg/kg) yielded rare brain GFP+ cells in both genotypes, consistent with intact BBB and limited vector access at this dose (IJMS, Apr 2024, https://doi.org/10.3390/ijms25094828). (reynauddulaurier2024theblood–brainbarrier pages 4-7, reynauddulaurier2024theblood–brainbarrier pages 2-4)
- Cardiac electrophysiology rescue by mitochondrial antioxidants (model): Ex vivo MitoTempo abolished MitoSOX/DCFDA signals and restored normal sinus rhythm; continuous treatment with MitoTempo or SS-31 significantly extended lifespan in Leigh syndrome mice (Antioxidants, Apr 2023, https://doi.org/10.3390/antiox12051001). (chen2023mitochondrialoxidativestress pages 8-10)

Mechanistic consequences of NDUFS4 loss and pathway placement
- Assembly, stability, and electron transfer. NDUFS4 anchors the N-module at the N–Q interface and is essential for transitioning from an assembly-factor–stabilized intermediate (with NDUFAF2 bound) to a mature enzyme containing NDUFS4/NDUFS6/NDUFA12. Loss of NDUFS4 leads to insufficient retention/incorporation of NDUFA12, compositional heterogeneity with retained assembly factor (NDUFAF2) or altered NDUFS6, loosening of the N-module, and markedly decreased NADH:Q oxidoreductase activity—all consistent with a primary role in complex I assembly and stability rather than direct catalytic chemistry (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4; preprint, Jul 2023, https://doi.org/10.1101/2023.07.17.549284). (yin2024structuralinsightsinto pages 2-3, yin2024structuralinsightsinto pages 1-2, yin2024structuralinsightsinto pages 22-25, yin2024structuralinsightsinto pages 11-12, yin2023structuralinsightsinto pages 16-19)
- Tissue- and cell-type–specific phenotypes. In hearts, Ndufs4 loss perturbs conduction under stress via mitochondrial ROS, with antioxidant therapies restoring rhythm and improving survival; in podocytes, Ndufs4 overexpression enhances cristae structure and function in diabetic kidney disease; in macrophages, Ndufs4 knockout decreases respiration and shifts inflammatory responses—together highlighting that NDUFS4 impacts both bioenergetics and organelle ultrastructure with context-dependent outcomes (Antioxidants, Apr 2023, https://doi.org/10.3390/antiox12051001; Nature Communications, Mar 2024, https://doi.org/10.1038/s41467-024-46366-w; PLOS ONE, Sep 2023, https://doi.org/10.1371/journal.pone.0291442). (chen2023mitochondrialoxidativestress pages 8-10, serranolorenzo2023developmentofa pages 14-15)
- CNS pathology and BBB. Early-stage BBB integrity appears preserved in Ndufs4−/− mice, implying that neurodegeneration and lesions in this model (a hallmark of Leigh syndrome) may not require overt BBB breakdown and that delivery of therapeutics to the brain is likely to demand BBB-aware strategies (IJMS, Apr 2024, https://doi.org/10.3390/ijms25094828). (reynauddulaurier2024theblood–brainbarrier pages 1-2, reynauddulaurier2024theblood–brainbarrier pages 2-4, reynauddulaurier2024theblood–brainbarrier pages 4-7)

Embedded summary artifact
| Topic | Key finding | Quantitative / example data | Source (DOI URL + context ID) |
|---|---|---:|---|
| Identity / verification | NDUFS4: ~18 kDa supernumerary mitochondrial Complex I subunit; matrix‑facing at the N–Q interface; contains a PKA site (Ser131); lies near multiple Fe–S clusters. | Structural mapping places NDUFS4 within ~8–12 Å of several Fe–S clusters; described as a "rivet" anchoring N‑module to Q‑module. | https://doi.org/10.1038/s44318-023-00001-4 (yin2024structuralinsightsinto pages 1-2), https://doi.org/10.1101/2023.07.17.549284 (yin2023structuralinsightsinto pages 1-4) |
| Assembly / structural consequences of NDUFS4 loss | NDUFS4 loss → loosely attached N‑module, failure to mature complete enzyme; NDUFA12 absent; assembly-factor NDUFAF2 retained in classes or NDUFS6 altered; QP subcomplex observed. | Intact complex I abundance ≈50% reduced in ndufs4−/− tissues; BN‑PAGE shows ~1 MDa (WT), ~800 kDa (QP) and ~200 kDa (N‑module) bands; NADH→ubiquinone activity substantially lower. | https://doi.org/10.1038/s44318-023-00001-4 (yin2023structuralinsightsinto pages 14-16, yin2024structuralinsightsinto pages 11-12), https://doi.org/10.1101/2023.07.17.549284 (yin2023structuralinsightsinto pages 16-19) |
| Disease association (Leigh syndrome) | Biallelic NDUFS4 loss‑of‑function causes early‑onset Leigh or Leigh‑like encephalopathy with severe neurodegeneration and respiratory failure. | Clinical phenotype: early pediatric neurodegeneration with brainstem/basal ganglia lesions; NDUFS4 protein often absent in pathogenic cases. | https://doi.org/10.1038/s44318-023-00001-4 (yin2024structuralinsightsinto pages 2-3), https://doi.org/10.1002/ana.26716 (serranolorenzo2023developmentofa pages 4-5) |
| Cardiac bradyarrhythmia & antioxidant rescue (model) | Ndufs4−/− mice display sinus‑node dysfunction and intermittent/high‑degree AV block linked to mitochondrial ROS; mitochondrial antioxidants (MitoTempo) and SS‑31 restore rhythm and extend survival. | Ex vivo Mitotempo abolished MitoSOX/DCFDA ROS signals and restored sinus rhythm; continuous Mitotempo or SS‑31 treatment significantly extended lifespan in reported mouse experiments. | https://doi.org/10.3390/antiox12051001 (chen2023mitochondrialoxidativestress pages 8-10) |
| Blood–brain barrier integrity (1‑month Ndufs4−/− mice) | Multiple permeability assays indicate preserved BBB structure and function at 1 month; AAV9 systemic delivery produced only rare brain transduction in both genotypes. | Evans blue absorbance (brain) 0.049 ± 0.002 (Ndufs4−/−) vs 0.053 ± 0.003 (control), p > 0.05; AAV9 (5.0 × 10^13 vg/kg) transduced liver robustly but produced rare GFP+ brain cells. | https://doi.org/10.3390/ijms25094828 (reynauddulaurier2024theblood–brainbarrier pages 2-4, reynauddulaurier2024theblood–brainbarrier pages 4-7) |
| Macrophage cell model evidence (RAW264.7 Ndufs4−/−) | Ndufs4 knockout macrophages show impaired Complex I assembly/activity, lower maximal respiration, a shift to proinflammatory cytokine responses, and increased phagocytosis. | CI activity assessed by in‑gel NADH/NBT and spectrophotometry (normalized to citrate synthase); LPS (100 ng/mL) induced altered cytokine mRNA/protein and increased FITC‑E. coli phagocytosis. | https://doi.org/10.1371/journal.pone.0291442 (serranolorenzo2023developmentofa pages 14-15) |
| Mitochondria transfer therapy (preclinical) | Exogenous/intercellular mitochondrial transfer interventions reduced morbidity and mortality in Ndufs4−/− preclinical models, supporting organelle‑replacement strategies. | Reported reductions in morbidity and mortality in treated Ndufs4−/− mice (preclinical, model‑level outcomes). | https://doi.org/10.1038/s42255-024-01125-5 (nakai2024mitochondriatransferbasedtherapies pages 24-25) |

Table: Concise, citation‑linked summary table of 2023–2024 experimental findings for human NDUFS4 (UniProt O43181), covering identity, assembly/structural effects of loss, disease association, selected model phenotypes, and recent therapeutic/preclinical observations.

Verification of gene/protein identity and domain/family alignment
- The reviewed literature consistently matches the UniProt-specified target: human NDUFS4 (O43181), a supernumerary 18 kDa Complex I subunit (CI-18 kDa/AQDQ), matrix-facing at the N–Q interface, with a PKA site (Ser131) and proximal to Fe–S clusters, belonging to the Complex I NDUFS4 subunit family (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4; preprint, Jul 2023, https://doi.org/10.1101/2023.07.17.549284). No conflicting gene-symbol usage was identified for Homo sapiens in these sources, and the structural/functional assignments align with known NDUFS4 family features (supernumerary complex I subunit) (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4). (yin2024structuralinsightsinto pages 1-2, yin2024structuralinsightsinto pages 2-3, yin2023structuralinsightsinto pages 1-4)

Notes on limitations and open questions
- ROS phenotypes may be tissue/context dependent: while some preclinical tissues/cells show increased ROS with Ndufs4 loss, direct respiratory-membrane/Complex I measurements in certain preparations did not show large ROS increases even as turnover decreased—highlighting the importance of model and assay conditions (EMBO Journal, Jan 2024, https://doi.org/10.1038/s44318-023-00001-4) (yin2023structuralinsightsinto pages 14-16, yin2024structuralinsightsinto pages 11-12).
- BBB findings currently apply to young Ndufs4−/− mice; later disease stages and other LS genotypes require evaluation before generalizing preserved barrier integrity (IJMS, Apr 2024, https://doi.org/10.3390/ijms25094828) (reynauddulaurier2024theblood–brainbarrier pages 9-10).

References (URLs and publication dates)
- EMBO Journal (Jan 2024): Structural insights into respiratory Complex I deficiency and assembly from the Ndufs4−/− mouse. https://doi.org/10.1038/s44318-023-00001-4 (supports identity, localization, assembly, activity, and quantitative BN-PAGE/kinetics) (yin2024structuralinsightsinto pages 2-3, yin2024structuralinsightsinto pages 1-2, yin2024structuralinsightsinto pages 22-25, yin2024structuralinsightsinto pages 11-12).
- bioRxiv (Jul 2023): Structural insights into Complex I deficiency and assembly from the disease-related ndufs4−/− mouse. https://doi.org/10.1101/2023.07.17.549284 (complements assembly-pathway and class observations; NDUFAF2/NDUFS6 roles) (yin2023structuralinsightsinto pages 9-11, yin2023structuralinsightsinto pages 4-6, yin2023structuralinsightsinto pages 1-4, yin2023structuralinsightsinto pages 14-16, yin2023structuralinsightsinto pages 16-19).
- International Journal of Molecular Sciences (Apr 2024): The blood–brain barrier is unaffected in the Ndufs4−/− mouse model of Leigh syndrome. https://doi.org/10.3390/ijms25094828 (BBB permeability, AAV9, Evans blue quantification) (reynauddulaurier2024theblood–brainbarrier pages 1-2, reynauddulaurier2024theblood–brainbarrier pages 2-4, reynauddulaurier2024theblood–brainbarrier pages 4-7, reynauddulaurier2024theblood–brainbarrier pages 10-12).
- Antioxidants (Apr 2023): Mitochondrial oxidative stress mediates bradyarrhythmia in Leigh syndrome mice. https://doi.org/10.3390/antiox12051001 (bradyarrhythmia phenotypes and antioxidant rescue) (chen2023mitochondrialoxidativestress pages 8-10).
- Nature Communications (Mar 2024): NDUFS4 regulates cristae remodeling in diabetic kidney disease. https://doi.org/10.1038/s41467-024-46366-w (podocyte overexpression improves cristae and albuminuria) (serranolorenzo2023developmentofa pages 14-15).
- Nature Metabolism (Sep 2024): Mitochondria transfer-based therapies reduce morbidity and mortality of Leigh syndrome. https://doi.org/10.1038/s42255-024-01125-5 (organelle-transfer therapy in Ndufs4−/− models) (nakai2024mitochondriatransferbasedtherapies pages 24-25).
- EMBO Molecular Medicine (Aug 2024): Restoration of defective OXPHOS to a subset of neurons prevents mitochondrial encephalopathy. https://doi.org/10.1038/s44321-024-00111-4 (AAV CNS gene replacement context) (reynauddulaurier2024theblood–brainbarrier pages 2-4).
- Annals of Neurology (Aug 2023): Expert panel curation of 113 primary mitochondrial disease genes for Leigh syndrome spectrum. https://doi.org/10.1002/ana.26716 (authoritative gene–disease curation) (serranolorenzo2023developmentofa pages 4-5).

References

(yin2024structuralinsightsinto pages 1-2): Zhan Yin, Ahmed-Noor A Agip, Hannah R Bridges, and Judy Hirst. Structural insights into respiratory complex i deficiency and assembly from the mitochondrial disease-related ndufs4−/− mouse. The EMBO Journal, 43:225-249, Jan 2024. URL: https://doi.org/10.1038/s44318-023-00001-4, doi:10.1038/s44318-023-00001-4. This article has 30 citations.
(yin2024structuralinsightsinto pages 2-3): Zhan Yin, Ahmed-Noor A Agip, Hannah R Bridges, and Judy Hirst. Structural insights into respiratory complex i deficiency and assembly from the mitochondrial disease-related ndufs4−/− mouse. The EMBO Journal, 43:225-249, Jan 2024. URL: https://doi.org/10.1038/s44318-023-00001-4, doi:10.1038/s44318-023-00001-4. This article has 30 citations.
(yin2024structuralinsightsinto pages 22-25): Zhan Yin, Ahmed-Noor A Agip, Hannah R Bridges, and Judy Hirst. Structural insights into respiratory complex i deficiency and assembly from the mitochondrial disease-related ndufs4−/− mouse. The EMBO Journal, 43:225-249, Jan 2024. URL: https://doi.org/10.1038/s44318-023-00001-4, doi:10.1038/s44318-023-00001-4. This article has 30 citations.
(yin2024structuralinsightsinto pages 11-12): Zhan Yin, Ahmed-Noor A Agip, Hannah R Bridges, and Judy Hirst. Structural insights into respiratory complex i deficiency and assembly from the mitochondrial disease-related ndufs4−/− mouse. The EMBO Journal, 43:225-249, Jan 2024. URL: https://doi.org/10.1038/s44318-023-00001-4, doi:10.1038/s44318-023-00001-4. This article has 30 citations.
(yin2023structuralinsightsinto pages 14-16): Zhan Yin, Ahmed-Noor A. Agip, Hannah R. Bridges, and Judy Hirst. Structural insights into complex i deficiency and assembly from the disease-related ndufs4-/- mouse. bioRxiv, Jul 2023. URL: https://doi.org/10.1101/2023.07.17.549284, doi:10.1101/2023.07.17.549284. This article has 0 citations and is from a poor quality or predatory journal.
(yin2023structuralinsightsinto pages 16-19): Zhan Yin, Ahmed-Noor A. Agip, Hannah R. Bridges, and Judy Hirst. Structural insights into complex i deficiency and assembly from the disease-related ndufs4-/- mouse. bioRxiv, Jul 2023. URL: https://doi.org/10.1101/2023.07.17.549284, doi:10.1101/2023.07.17.549284. This article has 0 citations and is from a poor quality or predatory journal.
(reynauddulaurier2024theblood–brainbarrier pages 2-4): Robin Reynaud-Dulaurier, Romain Clément, Sara Yjjou, Cassandra Cresson, Yasmina Saoudi, Mathilde Faideau, and Michael Decressac. The blood–brain barrier is unaffected in the ndufs4−/− mouse model of leigh syndrome. International Journal of Molecular Sciences, 25:4828, Apr 2024. URL: https://doi.org/10.3390/ijms25094828, doi:10.3390/ijms25094828. This article has 3 citations and is from a poor quality or predatory journal.
(reynauddulaurier2024theblood–brainbarrier pages 4-7): Robin Reynaud-Dulaurier, Romain Clément, Sara Yjjou, Cassandra Cresson, Yasmina Saoudi, Mathilde Faideau, and Michael Decressac. The blood–brain barrier is unaffected in the ndufs4−/− mouse model of leigh syndrome. International Journal of Molecular Sciences, 25:4828, Apr 2024. URL: https://doi.org/10.3390/ijms25094828, doi:10.3390/ijms25094828. This article has 3 citations and is from a poor quality or predatory journal.
(reynauddulaurier2024theblood–brainbarrier pages 1-2): Robin Reynaud-Dulaurier, Romain Clément, Sara Yjjou, Cassandra Cresson, Yasmina Saoudi, Mathilde Faideau, and Michael Decressac. The blood–brain barrier is unaffected in the ndufs4−/− mouse model of leigh syndrome. International Journal of Molecular Sciences, 25:4828, Apr 2024. URL: https://doi.org/10.3390/ijms25094828, doi:10.3390/ijms25094828. This article has 3 citations and is from a poor quality or predatory journal.
(reynauddulaurier2024theblood–brainbarrier pages 10-12): Robin Reynaud-Dulaurier, Romain Clément, Sara Yjjou, Cassandra Cresson, Yasmina Saoudi, Mathilde Faideau, and Michael Decressac. The blood–brain barrier is unaffected in the ndufs4−/− mouse model of leigh syndrome. International Journal of Molecular Sciences, 25:4828, Apr 2024. URL: https://doi.org/10.3390/ijms25094828, doi:10.3390/ijms25094828. This article has 3 citations and is from a poor quality or predatory journal.
(chen2023mitochondrialoxidativestress pages 8-10): Biyi Chen, Nastaran Daneshgar, Hsiang-Chun Lee, Long-Sheng Song, and Dao-Fu Dai. Mitochondrial oxidative stress mediates bradyarrhythmia in leigh syndrome mitochondrial disease mice. Antioxidants, 12:1001, Apr 2023. URL: https://doi.org/10.3390/antiox12051001, doi:10.3390/antiox12051001. This article has 13 citations and is from a poor quality or predatory journal.
(serranolorenzo2023developmentofa pages 14-15): Pablo Serrano-Lorenzo, Dino Gobelli, Rocío Garrido-Moraga, María J. Esteban-Amo, José R. López-López, Antonio Orduña, Miguel A. de la Fuente, Miguel A. Martín, and María Simarro. Development of a novel in vitro model to study the modulatory role of the respiratory complex i in macrophage effector functions. PLOS ONE, 18:e0291442, Sep 2023. URL: https://doi.org/10.1371/journal.pone.0291442, doi:10.1371/journal.pone.0291442. This article has 1 citations and is from a peer-reviewed journal.
(nakai2024mitochondriatransferbasedtherapies pages 24-25): Ritsuko Nakai, Stella Varnum, Rachael L. Field, Henyun Shi, Rocky Giwa, Wentong Jia, Samantha J. Krysa, Eva F. Cohen, Nicholas Borcherding, Russell P. Saneto, Rick C. Tsai, Masashi Suganuma, Hisashi Ohta, Takafumi Yokota, and Jonathan R. Brestoff. Mitochondria transfer-based therapies reduce the morbidity and mortality of leigh syndrome. Nature metabolism, 6:1886-1896, Sep 2024. URL: https://doi.org/10.1038/s42255-024-01125-5, doi:10.1038/s42255-024-01125-5. This article has 40 citations and is from a domain leading peer-reviewed journal.
(serranolorenzo2023developmentofa pages 4-5): Pablo Serrano-Lorenzo, Dino Gobelli, Rocío Garrido-Moraga, María J. Esteban-Amo, José R. López-López, Antonio Orduña, Miguel A. de la Fuente, Miguel A. Martín, and María Simarro. Development of a novel in vitro model to study the modulatory role of the respiratory complex i in macrophage effector functions. PLOS ONE, 18:e0291442, Sep 2023. URL: https://doi.org/10.1371/journal.pone.0291442, doi:10.1371/journal.pone.0291442. This article has 1 citations and is from a peer-reviewed journal.
(yin2023structuralinsightsinto pages 1-4): Zhan Yin, Ahmed-Noor A. Agip, Hannah R. Bridges, and Judy Hirst. Structural insights into complex i deficiency and assembly from the disease-related ndufs4-/- mouse. bioRxiv, Jul 2023. URL: https://doi.org/10.1101/2023.07.17.549284, doi:10.1101/2023.07.17.549284. This article has 0 citations and is from a poor quality or predatory journal.
(reynauddulaurier2024theblood–brainbarrier pages 9-10): Robin Reynaud-Dulaurier, Romain Clément, Sara Yjjou, Cassandra Cresson, Yasmina Saoudi, Mathilde Faideau, and Michael Decressac. The blood–brain barrier is unaffected in the ndufs4−/− mouse model of leigh syndrome. International Journal of Molecular Sciences, 25:4828, Apr 2024. URL: https://doi.org/10.3390/ijms25094828, doi:10.3390/ijms25094828. This article has 3 citations and is from a poor quality or predatory journal.
(yin2023structuralinsightsinto pages 9-11): Zhan Yin, Ahmed-Noor A. Agip, Hannah R. Bridges, and Judy Hirst. Structural insights into complex i deficiency and assembly from the disease-related ndufs4-/- mouse. bioRxiv, Jul 2023. URL: https://doi.org/10.1101/2023.07.17.549284, doi:10.1101/2023.07.17.549284. This article has 0 citations and is from a poor quality or predatory journal.
(yin2023structuralinsightsinto pages 4-6): Zhan Yin, Ahmed-Noor A. Agip, Hannah R. Bridges, and Judy Hirst. Structural insights into complex i deficiency and assembly from the disease-related ndufs4-/- mouse. bioRxiv, Jul 2023. URL: https://doi.org/10.1101/2023.07.17.549284, doi:10.1101/2023.07.17.549284. This article has 0 citations and is from a poor quality or predatory journal.

Citations

yin2024structuralinsightsinto pages 2-3
chen2023mitochondrialoxidativestress pages 8-10
serranolorenzo2023developmentofa pages 14-15
nakai2024mitochondriatransferbasedtherapies pages 24-25
serranolorenzo2023developmentofa pages 4-5
yin2024structuralinsightsinto pages 1-2
yin2023structuralinsightsinto pages 1-4
yin2023structuralinsightsinto pages 16-19
yin2024structuralinsightsinto pages 22-25
yin2024structuralinsightsinto pages 11-12
yin2023structuralinsightsinto pages 14-16
yin2023structuralinsightsinto pages 9-11
yin2023structuralinsightsinto pages 4-6
ubiquinone
https://doi.org/10.1038/s44318-023-00001-4
https://doi.org/10.1038/s44318-023-00001-4;
https://doi.org/10.1101/2023.07.17.549284
https://doi.org/10.3390/ijms25094828
https://doi.org/10.3390/antiox12051001
https://doi.org/10.1038/s41467-024-46366-w
https://doi.org/10.1038/s42255-024-01125-5
https://doi.org/10.1038/s44321-024-00111-4
https://doi.org/10.1002/ana.26716
https://doi.org/10.1371/journal.pone.0291442
https://doi.org/10.3390/antiox12051001;
https://doi.org/10.1038/s41467-024-46366-w;
https://doi.org/10.1038/s44318-023-00001-4,
https://doi.org/10.1101/2023.07.17.549284,
https://doi.org/10.3390/ijms25094828,
https://doi.org/10.3390/antiox12051001,
https://doi.org/10.1371/journal.pone.0291442,
https://doi.org/10.1038/s42255-024-01125-5,

📄 View Raw YAML

---
id: O43181
gene_symbol: NDUFS4
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: NDUFS4 (NADH dehydrogenase [ubiquinone] iron-sulfur protein 4) is an
  18 kDa accessory (supernumerary) subunit of mitochondrial Complex I (NADH:ubiquinone
  oxidoreductase). It is not a catalytic core subunit but plays a critical structural
  and regulatory role, acting as a rivet that anchors the N-module to the Q-module
  at the matrix-facing side of the enzyme. NDUFS4 is essential for the late-stage
  maturation of Complex I, where its incorporation (together with NDUFS6 and NDUFA12)
  displaces the assembly factor NDUFAF2 to yield the fully assembled, catalytically
  competent enzyme. Loss of NDUFS4 leads to destabilization and partial loss of the
  N-module, substantially reduced NADH:ubiquinone oxidoreductase activity, and is
  the most common nuclear-encoded Complex I gene cause of Leigh syndrome (MC1DN1).
  NDUFS4 also contains a PKA phosphorylation site at Ser-173 (Ser-131 in the mature
  form), through which cAMP signaling can regulate Complex I activity. The protein
  is a component of the iron-sulfur fragment of Complex I, localized to the mitochondrial
  inner membrane on the matrix side.
existing_annotations:
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: IBA annotation for mitochondrial localization. NDUFS4 is a nuclear-encoded
        mitochondrial protein with an N-terminal transit peptide (residues 1-42) that
        targets it to the mitochondrion (UniProt O43181). The protein is confirmed
        as mitochondrial by immunopurification (PMID:12611891), structural studies
        (PMID:28844695), and high-confidence mitochondrial proteomics (PMID:34800366).
        The IBA annotation is phylogenetically informed and accurate.
      action: ACCEPT
      reason: Core cellular component annotation. NDUFS4 is unambiguously a mitochondrial
        protein, confirmed by multiple experimental approaches. The IBA annotation
        is sound and consistent with all available evidence.
      supported_by:
        - reference_id: PMID:12611891
          supporting_text: we describe an immunocapture procedure for isolating this
            multisubunit membrane-bound complex from human tissue
        - reference_id: PMID:28844695
          supporting_text: Architecture of Human Mitochondrial Respiratory Megacomplex
            I(2)III(2)IV(2)
  - term:
      id: GO:0022904
      label: respiratory electron transport chain
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: IBA annotation for involvement in the respiratory electron transport
        chain. NDUFS4 is an accessory subunit of Complex I, the first enzyme of the
        respiratory chain. While NDUFS4 itself does not catalyze electron transfer,
        it is essential for assembly and stability of a functional Complex I that
        carries out NADH-to-ubiquinone electron transfer. Loss of NDUFS4 causes substantially
        reduced NADH:ubiquinone oxidoreductase activity (PMID:11181577, PMID:16478720)
        and ~50% reduction of intact Complex I abundance (Yin et al. 2024, EMBO J).
      action: ACCEPT
      reason: Core biological process. NDUFS4 is essential for the function of Complex
        I within the respiratory electron transport chain. Although it is not a catalytic
        core subunit, its structural and regulatory role is indispensable for the
        pathway. The IBA annotation is phylogenetically well supported.
      supported_by:
        - reference_id: PMID:11181577
          supporting_text: Fibroblast cultures from the patient exhibited severe reduction
            of the rotenone-sensitive NADH-->UQ oxidoreductase activity of complex
            I
        - reference_id: PMID:16478720
          supporting_text: the NDUFS4 mutation prevented complete assembly of the
            complex and caused full suppression of the activity
  - term:
      id: GO:0032981
      label: mitochondrial respiratory chain complex I assembly
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: IBA annotation for involvement in Complex I assembly. Recent cryo-EM
        structural analyses of Ndufs4-/- mouse tissue (Yin et al. 2024, EMBO J) reveal
        that NDUFS4 is critical for the late-stage maturation of Complex I. Loss of
        NDUFS4 prevents the displacement of the assembly factor NDUFAF2 and results
        in failure to incorporate NDUFA12, yielding incomplete assembly intermediates.
        Multiple patient studies show that NDUFS4 mutations abolish normal Complex
        I assembly (PMID:11181577, PMID:11112787, PMID:15038602).
      action: ACCEPT
      reason: Core biological process. This is one of the most important functions
        of NDUFS4. The protein is essential for the final maturation step of Complex
        I assembly. The IBA annotation is phylogenetically sound and strongly supported
        by experimental evidence from both human patient fibroblasts and mouse knockout
        models.
      additional_reference_ids:
        - file:human/NDUFS4/NDUFS4-deep-research-falcon.md
      supported_by:
        - reference_id: PMID:11181577
          supporting_text: Two-dimensional electrophoresis showed the absence of detectable
            normally assembled complex I in the inner mitochondrial membrane. These
            findings show that the expression of the NDUFS4 gene is essential for
            the assembly of a functional complex I.
        - reference_id: PMID:15038602
          supporting_text: All the NDUFS4 mutations resulted in impairment of the
            assembly of a functional complex
        - reference_id: file:human/NDUFS4/NDUFS4-deep-research-falcon.md
          supporting_text: knockout complexes lack NDUFA12 in all visualized classes
            and adopt distinct assembly states where either the assembly factor NDUFAF2
            remains bound or NDUFS6 is incompletely associated
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: IBA annotation for NDUFS4 being part of respiratory chain Complex I.
        NDUFS4 is one of the 45 subunits of human Complex I, specifically an accessory
        subunit located within the iron-sulfur protein (IP) fragment at the interface
        of the N- and Q-modules (PMID:27626371, PMID:12611891, PMID:28844695). The
        IBA annotation is phylogenetically well supported and correct.
      action: ACCEPT
      reason: Core cellular component. NDUFS4 is an integral subunit of Complex I,
        identified by mass spectrometry in immunopurified complex (PMID:12611891)
        and resolved in cryo-EM structures (PMID:28844695). The IBA annotation is
        accurate.
      supported_by:
        - reference_id: PMID:27626371
          supporting_text: Complex I (NADH:ubiquinone oxidoreductase) is the first
            enzyme of the mitochondrial respiratory chain and is composed of 45 subunits
            in humans
        - reference_id: PMID:12611891
          supporting_text: we can resolve and identify the human homologues of 42
            polypeptides detected so far in the more extensively studied beef heart
            complex I
  - term:
      id: GO:1902600
      label: proton transmembrane transport
    evidence_type: IEA
    original_reference_id: GO_REF:0000108
    review:
      summary: IEA annotation inferred from logical inference based on GO:0008137
        (NADH dehydrogenase (ubiquinone) activity). Complex I couples electron transfer
        from NADH to ubiquinone with proton translocation across the inner mitochondrial
        membrane. While NDUFS4 is in the N-module (hydrophilic arm) rather than the
        proton-pumping membrane arm, the complex as a whole carries out proton transmembrane
        transport. As an accessory subunit essential for Complex I function, NDUFS4
        contributes to this activity indirectly.
      action: ACCEPT
      reason: The annotation is acceptable as a broader process annotation for a Complex
        I subunit. While NDUFS4 is not directly in the proton-pumping domain, the
        complex as a whole performs proton transmembrane transport, and NDUFS4 is
        essential for a functional complex. The IEA inference from the complex-level
        MF is reasonable.
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: IEA annotation based on UniProtKB subcellular location mapping. NDUFS4
        is localized to the mitochondrial inner membrane as a peripheral membrane
        protein on the matrix side (UniProt O43181, PMID:12611891). This is well supported
        by multiple experimental studies.
      action: ACCEPT
      reason: Correct localization. NDUFS4 is a peripheral membrane protein on the
        matrix side of the mitochondrial inner membrane, confirmed by subcellular
        fractionation and structural studies.
      supported_by:
        - reference_id: PMID:12611891
          supporting_text: we describe an immunocapture procedure for isolating this
            multisubunit membrane-bound complex from human tissue
  - term:
      id: GO:0022900
      label: electron transport chain
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    review:
      summary: IEA annotation from InterPro mapping (IPR006885). GO:0022900 (electron
        transport chain) is a parent term of GO:0022904 (respiratory electron transport
        chain). Given that the more specific IBA annotation to GO:0022904 is already
        present, this broader IEA annotation is redundant but not incorrect.
      action: ACCEPT
      reason: Correct but broader than the IBA annotation to GO:0022904. As an IEA
        annotation it provides additional automated support. It is consistent with
        the known role of NDUFS4 as a Complex I subunit in the electron transport
        chain.
  - term:
      id: GO:0022904
      label: respiratory electron transport chain
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: IEA annotation based on UniProtKB keyword mapping (KW-0679, Respiratory
        chain). This duplicates the IBA annotation to the same term. The IEA mapping
        is correct for NDUFS4 as a Complex I subunit.
      action: ACCEPT
      reason: Correct annotation, consistent with the IBA annotation to the same term.
        Duplicate GO IDs with different evidence codes are acceptable.
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: IEA annotation from ARBA machine learning models. NDUFS4 is a confirmed
        subunit of respiratory chain Complex I. This duplicates the IBA annotation
        to the same term but with a different evidence source.
      action: ACCEPT
      reason: Correct annotation. NDUFS4 is an established subunit of Complex I. Duplicate
        with different evidence code is acceptable.
  - term:
      id: GO:0072593
      label: reactive oxygen species metabolic process
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    review:
      summary: IEA annotation from ARBA machine learning models for ROS metabolic
        process. Complex I is a major source of reactive oxygen species in mitochondria.
        However, NDUFS4 loss (which abolishes Complex I activity) actually prevented
        ROS production in one study (PMID:16478720), contrasting with the NDUFS1 mutant
        which showed increased ROS. The relationship between NDUFS4 and ROS is complex
        and context-dependent. The deep research report also notes that ROS phenotypes
        may be tissue/context dependent.
      action: KEEP_AS_NON_CORE
      reason: While Complex I is a well-established source of ROS, the relationship
        between NDUFS4 specifically and ROS is indirect and context-dependent. NDUFS4
        loss can either increase or decrease ROS depending on conditions (PMID:16478720).
        ROS metabolism is a secondary consequence of Complex I dysfunction, not a
        core function of NDUFS4. Consistent with the IMP annotation to the same term.
      supported_by:
        - reference_id: PMID:16478720
          supporting_text: No ROS increase was observed in the NDUFS4 mutation
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: IDA
    original_reference_id: GO_REF:0000052
    review:
      summary: IDA annotation based on immunofluorescence data from the Human Protein
        Atlas. Mitochondrial localization is well established for NDUFS4 from multiple
        lines of evidence.
      action: ACCEPT
      reason: Correct localization supported by immunofluorescence data. Consistent
        with all other evidence for mitochondrial localization of NDUFS4.
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: IDA
    original_reference_id: PMID:28844695
    review:
      summary: IDA annotation from ComplexPortal based on cryo-EM structural data.
        Guo et al. (2017) determined the architecture of the human respiratory megacomplex
        I2III2IV2, which resolves all Complex I subunits including NDUFS4 within the
        inner membrane-associated complex. This structural data directly confirms
        NDUFS4 localization to the mitochondrial inner membrane.
      action: ACCEPT
      reason: Strong structural evidence from cryo-EM. NDUFS4 is resolved as a peripheral
        subunit on the matrix side of the inner membrane within the intact Complex
        I structure.
      supported_by:
        - reference_id: PMID:28844695
          supporting_text: The structure not only reveals the precise assignment of
            individual subunits of human CI and CIII, but also enables future in-depth
            analysis of the electron transport chain as a whole
  - term:
      id: GO:0009060
      label: aerobic respiration
    evidence_type: NAS
    original_reference_id: PMID:30030361
    review:
      summary: NAS annotation from ComplexPortal based on a review of OXPHOS complex
        assembly (Signes & Fernandez-Vizarra, 2018). NDUFS4 is an accessory subunit
        of Complex I, which is part of the oxidative phosphorylation system that carries
        out aerobic respiration. This is a broad but correct process annotation for
        a Complex I subunit.
      action: ACCEPT
      reason: Correct broad biological process. Complex I is the first enzyme in the
        OXPHOS system which is central to aerobic respiration. NDUFS4 is essential
        for a functional Complex I.
      supported_by:
        - reference_id: PMID:30030361
          supporting_text: The assembly of the five oxidative phosphorylation system
            (OXPHOS) complexes in the inner mitochondrial membrane is an intricate
            process
  - term:
      id: GO:0042776
      label: proton motive force-driven mitochondrial ATP synthesis
    evidence_type: NAS
    original_reference_id: PMID:30030361
    review:
      summary: NAS annotation from ComplexPortal. Complex I contributes to the proton
        motive force by pumping protons across the inner membrane, which drives ATP
        synthase (Complex V). NDUFS4 is not directly involved in proton pumping or
        ATP synthesis but is essential for Complex I function. This annotation is
        somewhat indirect for an accessory subunit that resides in the hydrophilic
        arm rather than the proton-pumping membrane domain.
      action: KEEP_AS_NON_CORE
      reason: While technically accurate that loss of NDUFS4 impairs proton motive
        force generation (because it collapses Complex I), this annotation is more
        of a downstream consequence than a direct function of NDUFS4. The primary
        role of NDUFS4 is in Complex I assembly and stability, not directly in ATP
        synthesis. Keeping as non-core reflects that this is an indirect contribution.
      supported_by:
        - reference_id: PMID:30030361
          supporting_text: complexes I, III and IV interact with each other, forming
            the so-called respiratory supercomplexes or 'respirasomes'
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: HTP
    original_reference_id: PMID:34800366
    review:
      summary: HTP annotation from high-throughput mitochondrial proteomics (Morgenstern
        et al. 2021). NDUFS4 was identified as part of the high-confidence human mitochondrial
        proteome. This is consistent with all other evidence.
      action: ACCEPT
      reason: Correct localization confirmed by quantitative proteomics. Consistent
        with all other evidence for NDUFS4 mitochondrial localization.
      supported_by:
        - reference_id: PMID:34800366
          supporting_text: Quantitative high-confidence human mitochondrial proteome
            and its dynamics in cellular context
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IMP
    original_reference_id: PMID:11112787
    review:
      summary: IMP annotation based on Triepels et al. (2001), who used monoclonal
        antibodies against Complex I subunits to analyze assembly patterns in patients
        with Complex I defects, including NDUFS4 mutant patients. The study demonstrated
        that NDUFS4 mutations cause distinct subunit assembly patterns, providing
        indirect evidence that NDUFS4 is part of Complex I (its loss disrupts the
        complex).
      action: ACCEPT
      reason: Valid experimental evidence. The monoclonal antibody analysis and sucrose
        gradient studies in NDUFS4 mutant patient cells demonstrate that NDUFS4 is
        a component whose loss disrupts Complex I assembly, confirming its membership
        in the complex.
      supported_by:
        - reference_id: PMID:11112787
          supporting_text: different mutations in the same gene are shown to give
            very similar subunit profiles
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IDA
    original_reference_id: PMID:12611891
    review:
      summary: IDA annotation based on Murray et al. (2003), who used immunocapture
        followed by mass spectrometry to identify NDUFS4 as one of the subunits of
        immunopurified human Complex I. This is direct experimental evidence for NDUFS4
        as a Complex I component.
      action: ACCEPT
      reason: Strong direct evidence. NDUFS4 was identified by MALDI-TOF and LC-MS/MS
        in immunopurified human Complex I, directly demonstrating its presence as
        a subunit of the complex.
      supported_by:
        - reference_id: PMID:12611891
          supporting_text: Using small amounts of immunoisolated protein, one-dimensional
            and two-dimensional gel electrophoresis, matrix-assisted laser desorption
            ionization time-of-flight (MALDI-TOF) peptide mass finger printing (PMF),
            and nanoflow liquid chromatography mass spectrometry/mass spectrometry
            (LC-MS/MS), we can resolve and identify the human homologues of 42 polypeptides
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IMP
    original_reference_id: PMID:16478720
    review:
      summary: IMP annotation based on Iuso et al. (2006), who studied the effects
        of NDUFS4 mutations on Complex I in patient fibroblasts. The NDUFS4 G44A nonsense
        mutation prevented complete assembly and caused full suppression of Complex
        I activity, providing mutant phenotype evidence that NDUFS4 is an essential
        component of Complex I.
      action: ACCEPT
      reason: Valid mutant phenotype evidence confirming NDUFS4 as an essential Complex
        I subunit. Loss of NDUFS4 abolishes Complex I assembly and activity.
      supported_by:
        - reference_id: PMID:16478720
          supporting_text: the NDUFS4 mutation prevented complete assembly of the
            complex and caused full suppression of the activity
  - term:
      id: GO:0045271
      label: respiratory chain complex I
    evidence_type: IDA
    original_reference_id: PMID:27626371
    review:
      summary: IDA annotation based on Stroud et al. (2016), who used gene editing
        to generate knockout cell lines for all Complex I accessory subunits and performed
        quantitative proteomics. NDUFS4 was shown to be one of 25 accessory subunits
        strictly required for assembly of a functional complex. This study provides
        both identification of NDUFS4 within the complex and functional evidence for
        its essentiality.
      action: ACCEPT
      reason: Strong experimental evidence from a systematic gene-editing and proteomics
        study. NDUFS4 knockout cells showed loss of functional Complex I, confirming
        it as an essential accessory subunit.
      supported_by:
        - reference_id: PMID:27626371
          supporting_text: We show that 25 subunits are strictly required for assembly
            of a functional complex and 1 subunit is essential for cell viability
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:31206022
    review:
      summary: IPI annotation for protein binding, based on Namba (2019) who showed
        that NDUFS4 interacts with BAP31 (BCAP31, UniProtKB:P51572) and TOMM40 via
        co-immunoprecipitation. BAP31 acts as an ER-mitochondria bridging factor that
        stimulates translocation of NDUFS4 from the cytosol to mitochondria through
        interaction with Tom40. However, "protein binding" (GO:0005515) is uninformative
        and does not capture the specific nature of these interactions.
      action: MARK_AS_OVER_ANNOTATED
      reason: The generic "protein binding" term does not convey useful information
        about the biological context. The NDUFS4-BAP31-TOMM40 interaction relates
        to mitochondrial protein import and is better captured by more specific terms.
        Per project guidelines, generic protein binding annotations should be flagged
        as over-annotated.
      supported_by:
        - reference_id: PMID:31206022
          supporting_text: BAP31 interacts with mitochondria-localized proteins, including
            Tom40, to stimulate the translocation of NDUFS4, the component of complex
            I from the cytosol to the mitochondria
  - term:
      id: GO:0005739
      label: mitochondrion
    evidence_type: IDA
    original_reference_id: PMID:31206022
    review:
      summary: IDA annotation for mitochondrial localization based on Namba (2019).
        The study used subcellular fractionation and showed NDUFS4 localization in
        the mitochondria-associated ER membrane (MAM) and mitochondrial fractions.
        BAP31 knockout reduced NDUFS4 in the mitochondrial fraction, confirming its
        normal mitochondrial localization.
      action: ACCEPT
      reason: Valid experimental evidence from subcellular fractionation confirming
        NDUFS4 mitochondrial localization. Consistent with all other evidence.
      supported_by:
        - reference_id: PMID:31206022
          supporting_text: NDUFS4 and Tom40 were localized to the MAM and mitochondria
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-163217
    review:
      summary: TAS annotation from Reactome pathway R-HSA-163217 (Complex I oxidises
        NADH to NAD+, reduces CoQ to CoQH2). NDUFS4 is annotated as part of Complex
        I which functions at the mitochondrial inner membrane. This is consistent
        with all structural and biochemical evidence.
      action: ACCEPT
      reason: Correct localization supported by Reactome pathway annotation. NDUFS4
        is a peripheral membrane protein on the matrix side of the inner mitochondrial
        membrane as part of Complex I.
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799179
    review:
      summary: TAS annotation from Reactome pathway R-HSA-6799179 (Peripheral arm
        subunits bind the 815kDa complex to form a 980kDa complex). This Reactome
        entry describes the assembly step where peripheral arm subunits including
        NDUFS4 are incorporated into the growing Complex I at the inner membrane.
      action: ACCEPT
      reason: Correct localization. The Reactome assembly pathway places NDUFS4 at
        the mitochondrial inner membrane during Complex I biogenesis.
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6799196
    review:
      summary: TAS annotation from Reactome pathway R-HSA-6799196 (The MCIA complex,
        NDUFAF2-7 all dissociate from the 980kDa complex, resulting in Complex I).
        This represents the final maturation step of Complex I assembly where assembly
        factors dissociate. NDUFS4 is critical for this step, as its incorporation
        helps displace NDUFAF2.
      action: ACCEPT
      reason: Correct localization. Consistent with the role of NDUFS4 in the final
        maturation of Complex I at the mitochondrial inner membrane.
  - term:
      id: GO:0005743
      label: mitochondrial inner membrane
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-6800870
    review:
      summary: TAS annotation from Reactome pathway R-HSA-6800870 (NDUF subunits bind
        to form the FP subcomplex). This refers to early assembly of the flavoprotein
        subcomplex. NDUFS4 is part of the iron-sulfur protein fragment rather than
        the FP subcomplex, but the overall annotation of inner membrane localization
        is still correct.
      action: ACCEPT
      reason: Correct localization. While NDUFS4 is in the IP fragment rather than
        the FP subcomplex, the annotation of mitochondrial inner membrane localization
        is accurate regardless.
  - term:
      id: GO:0072593
      label: reactive oxygen species metabolic process
    evidence_type: IMP
    original_reference_id: PMID:16870178
    review:
      summary: IMP annotation based on Piccoli et al. (2006). This study found that
        a missense genetic defect in the NDUFS4 subunit suppressed Complex I activity
        and prevented ROS production, while cAMP-dependent activation of Complex I
        was associated with reduced ROS accumulation. Notably, the NDUFS4 mutation
        decreased ROS rather than increasing it, in contrast to the NDUFS1 mutant.
        This shows NDUFS4 mutations alter ROS metabolism, but the direction of effect
        depends on context.
      action: KEEP_AS_NON_CORE
      reason: While NDUFS4 mutations do affect ROS metabolism, this appears to be
        a secondary consequence of Complex I dysfunction rather than a direct function
        of NDUFS4. The relationship is complex since NDUFS4 loss can either increase
        or decrease ROS depending on the tissue and conditions. This is not a core
        function but a downstream phenotypic consequence.
      supported_by:
        - reference_id: PMID:16870178
          supporting_text: A missense genetic defect in the NDUFS4 subunit, putative
            substrate of PKA, suppressed, on the other hand, the activity of the complex
            and prevented ROS production
  - term:
      id: GO:0032981
      label: mitochondrial respiratory chain complex I assembly
    evidence_type: IMP
    original_reference_id: PMID:11112787
    review:
      summary: IMP annotation based on Triepels et al. (2001), who analyzed Complex
        I assembly patterns in NDUFS4 mutant patients using monoclonal antibodies
        against Complex I subunits. The NDUFS4 mutations caused distinct assembly
        defects, demonstrating that NDUFS4 is required for normal Complex I assembly.
      action: ACCEPT
      reason: Valid experimental evidence showing that NDUFS4 mutations disrupt Complex
        I assembly, as revealed by altered subunit profiles. Complex I assembly is
        a core function of NDUFS4.
      supported_by:
        - reference_id: PMID:11112787
          supporting_text: Western blotting with these antibodies, particularly when
            used in conjunction with sucrose gradient studies and enzymatic activity
            measurements, helps distinguish catalytic versus assembly defects
  - term:
      id: GO:0032981
      label: mitochondrial respiratory chain complex I assembly
    evidence_type: IMP
    original_reference_id: PMID:15038602
    review:
      summary: IMP annotation based on Papa et al. (2004), who studied Complex I expression,
        activity, and assembly during brain development and in children with inherited
        encephalopathies carrying NDUFS4 mutations. All NDUFS4 mutations studied resulted
        in impairment of the assembly of a functional complex.
      action: ACCEPT
      reason: Core function confirmed by multiple NDUFS4 mutations all resulting in
        impaired Complex I assembly. This is consistent with the structural role of
        NDUFS4 in the late-stage maturation of Complex I.
      supported_by:
        - reference_id: PMID:15038602
          supporting_text: All the NDUFS4 mutations resulted in impairment of the
            assembly of a functional complex
  - term:
      id: GO:0006120
      label: mitochondrial electron transport, NADH to ubiquinone
    evidence_type: NAS
    original_reference_id: PMID:9463323
    review:
      summary: NAS annotation based on van den Heuvel et al. (1998), the original
        cloning and mutation report for NDUFS4. The paper describes NDUFS4 as encoding
        the 18 kDa subunit of mitochondrial respiratory chain Complex I, which carries
        out NADH to ubiquinone electron transport. While NDUFS4 itself does not catalyze
        this reaction, it is essential for the function of the complex that does.
      action: ACCEPT
      reason: Correct biological process annotation. NDUFS4 is essential for Complex
        I function, and Complex I catalyzes NADH to ubiquinone electron transfer.
        NAS evidence code is appropriate for this literature-based inference.
      supported_by:
        - reference_id: PMID:9463323
          supporting_text: We report the cDNA cloning, chromosomal localization, and
            a mutation in the human nuclear gene encoding the 18-kD (AQDQ) subunit
            of the mitochondrial respiratory chain complex I
  - term:
      id: GO:0007420
      label: brain development
    evidence_type: IMP
    original_reference_id: PMID:14765537
    review:
      summary: IMP annotation based on Budde et al. (2003), who compared clinical
        presentation of NDUFS4 mutation patients. The paper describes marked clinical
        heterogeneity in patients with NDUFS4 mutations, with neurological presentations
        including Leigh syndrome. However, brain development impairment in these patients
        is a disease consequence of global Complex I deficiency, not a direct developmental
        function of NDUFS4. NDUFS4 is expressed ubiquitously (HPA shows low tissue
        specificity), and its role in brain development is secondary to its essential
        role in Complex I function in metabolically demanding tissues.
      action: MARK_AS_OVER_ANNOTATED
      reason: Brain development impairment in NDUFS4 patients is a downstream consequence
        of Complex I deficiency in metabolically demanding neural tissue, not a direct
        developmental function of NDUFS4. The gene is ubiquitously expressed and has
        no brain-specific function. Annotating NDUFS4 to brain development conflates
        disease phenotype with gene function.
      supported_by:
        - reference_id: PMID:14765537
          supporting_text: A comparison of the clinical presentation, disease course
            and results of laboratory and imaging studies of all patients so far published
            with a NDUFS4 mutation are presented. This reveals marked clinical heterogeneity,
            even in patients with the same genotype.
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IMP
    original_reference_id: PMID:15038602
    qualifier: contributes_to
    review:
      summary: IMP annotation with contributes_to qualifier based on Papa et al. (2004).
        The study showed that NDUFS4 mutations impair Complex I assembly and thus
        NADH dehydrogenase activity. The contributes_to qualifier is appropriate because
        NDUFS4 is an accessory subunit that does not directly catalyze the reaction
        but contributes to the complex-level enzymatic activity through its structural
        and assembly role.
      action: ACCEPT
      reason: The contributes_to qualifier is correctly applied for an accessory subunit.
        NDUFS4 does not directly catalyze NADH oxidation but is essential for the
        assembly and stability of the complex that does. This is consistent with GO
        annotation practices for multi-subunit enzyme complexes where accessory subunits
        use contributes_to.
      supported_by:
        - reference_id: PMID:15038602
          supporting_text: All the NDUFS4 mutations resulted in impairment of the
            assembly of a functional complex
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IMP
    original_reference_id: PMID:16870178
    qualifier: contributes_to
    review:
      summary: IMP annotation with contributes_to qualifier based on Piccoli et al.
        (2006). The study showed that an NDUFS4 missense defect suppressed Complex
        I NADH-ubiquinone oxidoreductase activity. The contributes_to qualifier is
        appropriate for this accessory subunit.
      action: ACCEPT
      reason: Correct annotation with appropriate contributes_to qualifier. NDUFS4
        mutations suppress Complex I activity, confirming that NDUFS4 contributes
        to the complex-level enzymatic activity.
      supported_by:
        - reference_id: PMID:16870178
          supporting_text: A missense genetic defect in the NDUFS4 subunit, putative
            substrate of PKA, suppressed, on the other hand, the activity of the complex
  - term:
      id: GO:0051591
      label: response to cAMP
    evidence_type: IMP
    original_reference_id: PMID:11165261
    review:
      summary: IMP annotation based on Papa et al. (2001), who showed that mutation
        in NDUFS4 abolishes cAMP-dependent phosphorylation of the protein and cAMP-dependent
        activation of Complex I. NDUFS4 contains a PKA phosphorylation site (Ser-173),
        and cAMP-dependent phosphorylation of this site activates Complex I. The NDUFS4
        mutation abolished this cAMP-dependent response, providing evidence that NDUFS4
        mediates the response of Complex I to cAMP signaling.
      action: ACCEPT
      reason: Valid experimental evidence. NDUFS4 is a direct substrate of PKA, and
        its phosphorylation at Ser-173 mediates cAMP-dependent activation of Complex
        I. This is a genuine regulatory function of NDUFS4 as a signal-responsive
        subunit.
      supported_by:
        - reference_id: PMID:11165261
          supporting_text: the homozygous 5 bp duplication in the cDNA of the NDUFS4
            18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of
            this protein and activation of the complex. These findings show for the
            first time that human complex I is regulated via phosphorylation of the
            subunit encoded by the NDUFS4 gene.
  - term:
      id: GO:0051591
      label: response to cAMP
    evidence_type: IMP
    original_reference_id: PMID:11181577
    review:
      summary: IMP annotation based on Petruzzella et al. (2001), who showed that
        a nonsense mutation in NDUFS4 resulted in Complex I activity that was insensitive
        to cAMP stimulation. Since NDUFS4 is the PKA substrate through which cAMP
        activates Complex I, its loss abolishes this response.
      action: ACCEPT
      reason: Valid experimental evidence confirming that NDUFS4 is required for the
        cAMP-dependent regulation of Complex I. The loss of NDUFS4 eliminated cAMP
        responsiveness of Complex I activity.
      supported_by:
        - reference_id: PMID:11181577
          supporting_text: Fibroblast cultures from the patient exhibited severe reduction
            of the rotenone-sensitive NADH-->UQ oxidoreductase activity of complex
            I, which was insensitive to cAMP stimulation
  - term:
      id: GO:0006120
      label: mitochondrial electron transport, NADH to ubiquinone
    evidence_type: NAS
    original_reference_id: PMID:9878551
    review:
      summary: NAS annotation based on Loeffen et al. (1998), who completed the cDNA
        characterization of all nuclear-encoded Complex I subunits. The paper describes
        NDUFS4 in the context of NADH:ubiquinone oxidoreductase function but does
        not specifically study NDUFS4 function. The NAS code is appropriate.
      action: ACCEPT
      reason: Correct biological process annotation. NDUFS4 is a subunit of NADH:ubiquinone
        oxidoreductase, which catalyzes mitochondrial electron transport from NADH
        to ubiquinone. NAS evidence code is appropriate for this literature-based
        characterization.
      supported_by:
        - reference_id: PMID:9878551
          supporting_text: NADH:ubiquinone oxidoreductase (complex I) is an extremely
            complicated multiprotein complex located in the inner mitochondrial membrane.
            Its main function is the transport of electrons from NADH to ubiquinone
  - term:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    evidence_type: IMP
    original_reference_id: PMID:16478720
    review:
      summary: IMP annotation based on Iuso et al. (2006), showing that NDUFS4 mutation
        prevents complete Complex I assembly and fully suppresses Complex I activity.
        This supports NDUFS4 participation in the complex-level NADH dehydrogenase
        function.
      action: ACCEPT
      reason: The GO term is supported by strong experimental evidence that NDUFS4
        loss causes complete suppression of Complex I activity. As a supernumerary
        subunit, NDUFS4 supports the complex-level activity through assembly/stability
        rather than direct catalysis, consistent with other accepted GO:0008137 entries
        for this gene.
      supported_by:
        - reference_id: PMID:16478720
          supporting_text: the NDUFS4 mutation prevented complete assembly of the
            complex and caused full suppression of the activity
  - term:
      id: GO:0001932
      label: regulation of protein phosphorylation
    evidence_type: IMP
    original_reference_id: PMID:11165261
    review:
      summary: IMP annotation from MGI for regulation of protein phosphorylation,
        based on Papa et al. (2001). The GOA TSV shows the qualifier acts_upstream_of_or_within,
        suggesting this is an indirect involvement. The study showed that NDUFS4 mutation
        abolishes cAMP-dependent phosphorylation of the NDUFS4 protein itself and
        activation of Complex I. NDUFS4 is a phosphorylation substrate, not a kinase
        or phosphatase. The annotation seems to conflate being a substrate of phosphorylation
        with regulating phosphorylation. NDUFS4 does not regulate protein phosphorylation;
        rather, its own phosphorylation by PKA regulates Complex I activity.
      action: MARK_AS_OVER_ANNOTATED
      reason: NDUFS4 is a substrate of PKA phosphorylation at Ser-173, not a regulator
        of protein phosphorylation. The annotation conflates being phosphorylated
        (a substrate) with regulating phosphorylation (a kinase/phosphatase/regulatory
        function). The cAMP/PKA-dependent phosphorylation of NDUFS4 is better captured
        by the response to cAMP annotations (GO:0051591).
      supported_by:
        - reference_id: PMID:11165261
          supporting_text: the homozygous 5 bp duplication in the cDNA of the NDUFS4
            18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of
            this protein and activation of the complex
references:
  - id: GO_REF:0000002
    title: Gene Ontology annotation through association of InterPro records with GO
      terms
    findings: []
  - id: GO_REF:0000033
    title: Annotation inferences using phylogenetic trees
    findings: []
  - id: GO_REF:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
    findings: []
  - id: GO_REF:0000044
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
      vocabulary mapping, accompanied by conservative changes to GO terms applied
      by UniProt
    findings: []
  - id: GO_REF:0000052
    title: Gene Ontology annotation based on curation of immunofluorescence data
    findings: []
  - id: GO_REF:0000108
    title: Automatic assignment of GO terms using logical inference, based on on inter-ontology
      links
    findings: []
  - id: GO_REF:0000117
    title: Electronic Gene Ontology annotations created by ARBA machine learning models
    findings: []
  - id: file:human/NDUFS4/NDUFS4-deep-research-falcon.md
    title: Falcon deep research synthesis for human NDUFS4
    findings: []
  - id: PMID:11112787
    title: Human complex I defects can be resolved by monoclonal antibody analysis
      into distinct subunit assembly patterns.
    findings:
      - statement: Monoclonal antibody analysis and sucrose gradient studies of NDUFS4
          mutant patient cells showed distinct subunit assembly defects, demonstrating
          NDUFS4 is required for normal Complex I assembly.
        supporting_text: Western blotting with these antibodies, particularly when
          used in conjunction with sucrose gradient studies and enzymatic activity
          measurements, helps distinguish catalytic versus assembly defects and further
          distinguishes between mutations in different subunits
  - id: PMID:11165261
    title: Mutation in the NDUFS4 gene of complex I abolishes cAMP-dependent activation
      of the complex in a child with fatal neurological syndrome.
    findings:
      - statement: NDUFS4 mutation abolishes cAMP-dependent phosphorylation of the
          NDUFS4 protein and cAMP-dependent activation of Complex I, showing for the
          first time that human Complex I is regulated via phosphorylation of NDUFS4.
        supporting_text: the homozygous 5 bp duplication in the cDNA of the NDUFS4
          18 kDa subunit of complex I abolishes cAMP-dependent phosphorylation of
          this protein and activation of the complex. These findings show for the
          first time that human complex I is regulated via phosphorylation of the
          subunit encoded by the NDUFS4 gene.
  - id: PMID:11181577
    title: A nonsense mutation in the NDUFS4 gene encoding the 18 kDa (AQDQ) subunit
      of complex I abolishes assembly and activity of the complex in a patient with
      Leigh-like syndrome.
    findings:
      - statement: Nonsense mutation in NDUFS4 causes complete absence of normally
          assembled Complex I in the inner mitochondrial membrane, severe reduction
          of NADH:UQ oxidoreductase activity, and insensitivity to cAMP stimulation,
          demonstrating that NDUFS4 is essential for assembly of a functional Complex
          I.
        supporting_text: Two-dimensional electrophoresis showed the absence of detectable
          normally assembled complex I in the inner mitochondrial membrane. These
          findings show that the expression of the NDUFS4 gene is essential for the
          assembly of a functional complex I.
  - id: PMID:12611891
    title: The subunit composition of the human NADH dehydrogenase obtained by rapid
      one-step immunopurification.
    findings:
      - statement: NDUFS4 was identified as a subunit of human Complex I by immunocapture
          followed by MALDI-TOF and LC-MS/MS mass spectrometry.
        supporting_text: we can resolve and identify the human homologues of 42 polypeptides
          detected so far in the more extensively studied beef heart complex I
  - id: PMID:14765537
    title: Clinical heterogeneity in patients with mutations in the NDUFS4 gene of
      mitochondrial complex I.
    findings:
      - statement: Marked clinical heterogeneity exists among patients with NDUFS4
          mutations, including neurological presentations consistent with Leigh syndrome,
          even among patients with the same genotype.
        supporting_text: A comparison of the clinical presentation, disease course
          and results of laboratory and imaging studies of all patients so far published
          with a NDUFS4 mutation are presented. This reveals marked clinical heterogeneity,
          even in patients with the same genotype.
  - id: PMID:15038602
    title: Respiratory complex I in brain development and genetic disease.
    findings:
      - statement: All NDUFS4 mutations studied resulted in impairment of Complex
          I assembly. Complex I expression and activity markedly increase during brain
          cell differentiation.
        supporting_text: All the NDUFS4 mutations resulted in impairment of the assembly
          of a functional complex
  - id: PMID:16478720
    title: Dysfunctions of cellular oxidative metabolism in patients with mutations
      in the NDUFS1 and NDUFS4 genes of complex I.
    findings:
      - statement: NDUFS4 G44A nonsense mutation prevents complete Complex I assembly
          and fully suppresses activity. Unlike NDUFS1 mutation, no ROS increase was
          observed with the NDUFS4 mutation.
        supporting_text: the NDUFS4 mutation prevented complete assembly of the complex
          and caused full suppression of the activity...No ROS increase was observed
          in the NDUFS4 mutation
  - id: PMID:16870178
    title: cAMP controls oxygen metabolism in mammalian cells.
    findings:
      - statement: NDUFS4 missense defect suppresses Complex I activity and prevents
          ROS production. cAMP activates NADH-ubiquinone oxidoreductase activity,
          and this activation is abolished by NDUFS4 mutation.
        supporting_text: A missense genetic defect in the NDUFS4 subunit, putative
          substrate of PKA, suppressed, on the other hand, the activity of the complex
          and prevented ROS production
  - id: PMID:27626371
    title: Accessory subunits are integral for assembly and function of human mitochondrial
      complex I.
    findings:
      - statement: Systematic gene editing study showed 25 of 31 accessory subunits
          (including NDUFS4) are strictly required for assembly of a functional Complex
          I. Loss of each subunit affects stability of other subunits in the same
          structural module.
        supporting_text: We show that 25 subunits are strictly required for assembly
          of a functional complex and 1 subunit is essential for cell viability
  - id: PMID:28844695
    title: Architecture of Human Mitochondrial Respiratory Megacomplex I(2)III(2)IV(2).
    findings:
      - statement: Cryo-EM structure of the human respiratory megacomplex at 3.4 A
          resolution reveals precise assignment of all Complex I subunits including
          NDUFS4 in the mitochondrial inner membrane.
        supporting_text: The structure not only reveals the precise assignment of
          individual subunits of human CI and CIII, but also enables future in-depth
          analysis of the electron transport chain as a whole
  - id: PMID:30030361
    title: Assembly of mammalian oxidative phosphorylation complexes I-V and supercomplexes.
    findings:
      - statement: Review of the assembly pathways for all five OXPHOS complexes.
          Complex I assembly involves multiple intermediate stages with numerous assembly
          factors, and supernumerary subunits play essential roles in assembly, regulation,
          and stability.
        supporting_text: The assembly of the five oxidative phosphorylation system
          (OXPHOS) complexes in the inner mitochondrial membrane is an intricate process
  - id: PMID:31206022
    title: BAP31 regulates mitochondrial function via interaction with Tom40 within
      ER-mitochondria contact sites.
    findings:
      - statement: BAP31 interacts with NDUFS4 and Tom40 to form an ER-mitochondria
          bridging complex that stimulates translocation of NDUFS4 from the cytosol
          to mitochondria. Loss of BAP31 reduces NDUFS4 in the mitochondrial fraction
          and suppresses Complex I activity.
        supporting_text: BAP31 interacts with mitochondria-localized proteins, including
          Tom40, to stimulate the translocation of NDUFS4, the component of complex
          I from the cytosol to the mitochondria
  - id: PMID:34800366
    title: Quantitative high-confidence human mitochondrial proteome and its dynamics
      in cellular context.
    findings:
      - statement: NDUFS4 identified as part of the high-confidence human mitochondrial
          proteome by quantitative proteomics.
        supporting_text: Quantitative high-confidence human mitochondrial proteome
          and its dynamics in cellular context
  - id: PMID:9463323
    title: 'Demonstration of a new pathogenic mutation in human complex I deficiency:
      a 5-bp duplication in the nuclear gene encoding the 18-kD (AQDQ) subunit.'
    findings:
      - statement: First report of NDUFS4 cDNA cloning, chromosomal localization (chromosome
          5), and identification of a pathogenic homozygous 5-bp duplication destroying
          a consensus phosphorylation site, causing Complex I deficiency.
        supporting_text: We report the cDNA cloning, chromosomal localization, and
          a mutation in the human nuclear gene encoding the 18-kD (AQDQ) subunit of
          the mitochondrial respiratory chain complex I...A homozygous 5-bp duplication,
          destroying a consensus phosphorylation site
  - id: PMID:9878551
    title: 'cDNA of eight nuclear encoded subunits of NADH:ubiquinone oxidoreductase:
      human complex I cDNA characterization completed.'
    findings:
      - statement: Completed characterization of all nuclear-encoded Complex I subunit
          cDNAs. NDUFS4 encodes the 18 kDa subunit of NADH:ubiquinone oxidoreductase.
        supporting_text: NADH:ubiquinone oxidoreductase (complex I) is an extremely
          complicated multiprotein complex located in the inner mitochondrial membrane.
          Its main function is the transport of electrons from NADH to ubiquinone
  - id: Reactome:R-HSA-163217
    title: Complex I oxidises NADH to NAD+, reduces CoQ to CoQH2
    findings: []
  - id: Reactome:R-HSA-6799179
    title: Peripheral arm subunits bind the 815kDa complex to form a 980kDa complex
    findings: []
  - id: Reactome:R-HSA-6799196
    title: The MCIA complex, NDUFAF2-7 all dissociate from the 980kDa complex, resulting
      in Complex I
    findings: []
  - id: Reactome:R-HSA-6800870
    title: NDUF subunits bind to form the FP subcomplex
    findings: []
core_functions:
  - molecular_function:
      id: GO:0008137
      label: NADH dehydrogenase (ubiquinone) activity
    directly_involved_in:
      - id: GO:0032981
        label: mitochondrial respiratory chain complex I assembly
      - id: GO:0022904
        label: respiratory electron transport chain
    locations:
      - id: GO:0005743
        label: mitochondrial inner membrane
    description: >-
      NDUFS4 is a supernumerary accessory subunit required for late-stage maturation
      and stability of mitochondrial Complex I. Although it is not a catalytic redox
      subunit, NDUFS4 is essential for assembly of a functional holoenzyme and
      therefore contributes_to the complex-level NADH dehydrogenase (ubiquinone)
      activity carried out by Complex I.
    supported_by:
      - reference_id: PMID:11181577
        supporting_text: >-
          Two-dimensional electrophoresis showed the absence of detectable normally
          assembled complex I in the inner mitochondrial membrane. These findings
          show
          that the expression of the NDUFS4 gene is essential for the assembly of
          a
          functional complex I.
      - reference_id: file:human/NDUFS4/NDUFS4-deep-research-falcon.md
        supporting_text: >-
          knockout complexes lack NDUFA12 in all visualized classes and adopt distinct
          assembly states where either the assembly factor NDUFAF2 remains bound or
          NDUFS6 is incompletely associated
    in_complex:
      id: GO:0045271
      label: respiratory chain complex I

Gene Description

Existing Annotations Review

Core Functions

References

Deep Research

Falcon

Citations

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