NDUFA4

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0045277 respiratory chain complex IV	IBA GO_REF:0000033	ACCEPT	Summary: NDUFA4 is the 14th subunit of Complex IV (cytochrome c oxidase), established by Balsa et al. (2012, PMID:22902835) and structurally confirmed by Zong et al. (2018, PMID:30030519). IBA annotation from phylogenetic inference correctly assigns NDUFA4 as part of Complex IV, consistent with the reclassification from Complex I. Reason: Core annotation. NDUFA4 is a bona fide structural subunit of Complex IV. The IBA annotation reflects the phylogenetically supported reclassification. Balsa et al. demonstrated via proteomic, genetic, evolutionary, and biochemical analyses that NDUFA4 is a CIV subunit (PMID:22902835), and Zong et al. provided 3.3 Angstrom cryo-EM structural confirmation (PMID:30030519). Supporting Evidence: PMID:22902835 NDUFA4, formerly considered a constituent of NADH Dehydrogenase (CI), is instead a component of the cytochrome c oxidase (CIV). Deletion of NDUFA4 does not perturb CI. Rather, proteomic, genetic, evolutionary, and biochemical analyses reveal that NDUFA4 plays a role in CIV function and biogenesis. PMID:30030519 Combining previous structural and biochemical data shown by us and other groups, we propose that the intact complex-IV is a monomer containing 14 subunits. file:human/NDUFA4/NDUFA4-deep-research-falcon.md Belongs to the complex IV COXFA4 subunit family.
GO:1902600 proton transmembrane transport	IEA GO_REF:0000108	ACCEPT	Summary: Complex IV pumps protons across the inner mitochondrial membrane coupled to electron transfer from cytochrome c to O2. NDUFA4 does not directly pump protons (catalytic core subunits MT-CO1/2/3 perform that), but as a structural subunit it is required for complex integrity and optimal activity. The IEA annotation is logically inferred from the cytochrome-c oxidase activity annotation. Reason: Appropriate biological process annotation. Complex IV couples electron transfer to proton pumping. As a structural subunit essential for CIV maintenance, NDUFA4 is involved in this process. This parallels the accepted annotation pattern for COX5B (P10606). Supporting Evidence: PMID:30030519 It accepts electrons from cytochrome c to reduce the oxygen to water and meanwhile pumps two protons from the matrix side to the intermembrane space (IMS) PMID:22902835 NDUFA4 plays a role in CIV function and biogenesis
GO:0005743 mitochondrial inner membrane	IEA GO_REF:0000044	ACCEPT	Summary: NDUFA4 is localized to the mitochondrial inner membrane as a single-pass transmembrane protein within Complex IV. UniProt and structural data confirm inner membrane localization. Reason: Core localization. Cryo-EM structure (PMID:30030519) resolves NDUFA4 residues 3-81 within CIV on the inner membrane. UniProt records NDUFA4 as a single-pass membrane protein in the inner mitochondrial membrane, with matrix-facing N-terminus (residues 1-14) and IMS-facing C-terminus (residues 38-81). Supporting Evidence: file:human/NDUFA4/NDUFA4-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion inner membrane; Single-pass membrane protein PMID:30030519 Here we obtained the 3.3 Å resolution structure of complex-IV derived from the human supercomplex I 1 III 2 IV 1 and assigned the NDUFA4 subunit into complex-IV
GO:0022904 respiratory electron transport chain	IEA GO_REF:0000043	KEEP AS NON CORE	Summary: NDUFA4 participates in the respiratory electron transport chain as a subunit of Complex IV. This is a broad but correct annotation inferred from UniProt keyword mapping. Reason: This term is too general. The more specific term GO:0006123 (mitochondrial electron transport, cytochrome c to oxygen) is already annotated and better captures the precise step of the ETC in which NDUFA4 participates. However, the annotation is not wrong -- NDUFA4 does function in the respiratory electron transport chain through CIV. Supporting Evidence: PMID:22902835 NDUFA4 plays a role in CIV function and biogenesis file:human/NDUFA4/NDUFA4-uniprot.txt Component of the cytochrome c oxidase, the last enzyme in the mitochondrial electron transport chain which drives oxidative phosphorylation
GO:0005515 protein binding	IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ...	MARK AS OVER ANNOTATED	Summary: This annotation derives from a large-scale neurodegenerative disease interactome study (Haenig et al. 2020) that mapped ~30,000 interactions among ~5,000 proteins. The with/from column indicates interaction with DPF1 (Q92782-2). This is a generic protein binding annotation from high-throughput yeast two-hybrid screening. Reason: Generic protein binding from a high-throughput neurodegenerative disease interactome study. Per curation guidelines, protein binding is not informative about the actual molecular function. The interaction with DPF1 has no known functional significance for NDUFA4's role as a Complex IV subunit. Supporting Evidence: PMID:32814053 Interactome maps are valuable resources to elucidate protein function and disease mechanisms.
GO:0045271 respiratory chain complex I	IEA GO_REF:0000107	REMOVE	Summary: This annotation incorrectly assigns NDUFA4 to Complex I. NDUFA4 was conclusively reclassified from Complex I to Complex IV by Balsa et al. (2012, PMID:22902835). Deletion of NDUFA4 does not perturb Complex I. The IEA annotation persists from ortholog transfer of an outdated annotation via Ensembl Compara, propagating the historical misclassification. Reason: Incorrect annotation based on historical misclassification. Balsa et al. (2012) definitively demonstrated that NDUFA4 is not a Complex I subunit: "Deletion of NDUFA4 does not perturb CI." Zong et al. (2018) structurally placed NDUFA4 in Complex IV. UniProt now explicitly states: "Was initially believed to be a subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (complex I)." The correct annotation is GO:0045277 (respiratory chain complex IV), which is already present. Supporting Evidence: PMID:22902835 NDUFA4, formerly considered a constituent of NADH Dehydrogenase (CI), is instead a component of the cytochrome c oxidase (CIV). Deletion of NDUFA4 does not perturb CI. file:human/NDUFA4/NDUFA4-uniprot.txt Was initially believed to be a subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (complex I).
GO:0045277 respiratory chain complex IV	IEA GO_REF:0000120	ACCEPT	Summary: IEA annotation from combined automated methods correctly placing NDUFA4 in Complex IV. Consistent with the IBA and IDA annotations for the same term. Reason: Correct annotation. Same term as IBA (GO_REF:0000033) and IDA (PMID:22902835) annotations. Acceptable redundancy from automated pipeline that correctly reflects NDUFA4's reclassification as a CIV subunit. Supporting Evidence: PMID:22902835 NDUFA4, formerly considered a constituent of NADH Dehydrogenase (CI), is instead a component of the cytochrome c oxidase (CIV).
GO:0005739 mitochondrion	IDA GO_REF:0000052	ACCEPT	Summary: NDUFA4 localizes to mitochondria as confirmed by immunofluorescence data (HPA). This is a broad but correct localization. Reason: Direct experimental evidence (IDA) from immunofluorescence confirms mitochondrial localization. While broad, this is valid. More specific inner membrane localization is captured by separate annotations. Supporting Evidence: file:human/NDUFA4/NDUFA4-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion inner membrane; Single-pass membrane protein
GO:0006123 mitochondrial electron transport, cytochrome c to oxygen	NAS PMID:30030519 Structure of the intact 14-subunit human cytochrome c oxidas...	ACCEPT	Summary: NDUFA4 is a structural subunit of Complex IV, which catalyzes the terminal step of the ETC -- transfer of electrons from cytochrome c to molecular oxygen. Zong et al. (2018, PMID:30030519) resolved the 14-subunit CIV structure including NDUFA4 and confirmed its role in this process. As a CIV subunit, NDUFA4 is involved in this specific electron transport step. Reason: Core biological process annotation. NDUFA4 is essential for this process as a structural subunit of Complex IV. Knockdown of NDUFA4 specifically reduces CIV activity (PMID:22902835), and loss-of-function mutations cause isolated CIV deficiency (MC4DN21) with reduced COX activity in patient fibroblasts. Supporting Evidence: PMID:30030519 CIV is the terminal oxidase of the electron transport chain in mitochondria. PMID:22902835 proteomic, genetic, evolutionary, and biochemical analyses reveal that NDUFA4 plays a role in CIV function and biogenesis
GO:0031966 mitochondrial membrane	IDA PMID:30030519 Structure of the intact 14-subunit human cytochrome c oxidas...	MODIFY	Summary: NDUFA4 is specifically on the mitochondrial inner membrane. This term (mitochondrial membrane) is broader, encompassing both inner and outer membranes. Reason: While technically correct, this term is less precise than GO:0005743 (mitochondrial inner membrane), which is already annotated with multiple lines of evidence. NDUFA4 is specifically a single-pass transmembrane protein of the inner mitochondrial membrane, as shown by the cryo-EM structure (PMID:30030519) and UniProt annotation. Following the same pattern as COX5B review. Proposed replacements: mitochondrial inner membrane Supporting Evidence: PMID:30030519 Here we obtained the 3.3 Å resolution structure of complex-IV derived from the human supercomplex I 1 III 2 IV 1 and assigned the NDUFA4 subunit into complex-IV file:human/NDUFA4/NDUFA4-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion inner membrane; Single-pass membrane protein
GO:0045333 cellular respiration	NAS PMID:30030519 Structure of the intact 14-subunit human cytochrome c oxidas...	KEEP AS NON CORE	Summary: Very broad biological process term. NDUFA4 participates in cellular respiration as a subunit of Complex IV, but more specific terms exist to capture its role. Reason: Too general. More precise annotations for GO:0006123 (mitochondrial electron transport, cytochrome c to oxygen) and GO:1902600 (proton transmembrane transport) better describe NDUFA4's specific role. Keep as valid but non-core annotation, following the same pattern as COX5B review. Supporting Evidence: PMID:30030519 CIV is the terminal oxidase of the electron transport chain in mitochondria.
GO:0005739 mitochondrion	HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an...	ACCEPT	Summary: NDUFA4 identified in quantitative high-confidence human mitochondrial proteome (Morgenstern et al. 2021). High-throughput proteomics data confirming mitochondrial localization. Reason: High-confidence mitochondrial proteomics data from reputable study. HTP evidence code indicates high-throughput but the study is rigorous and well-validated. Confirms core localization. Supporting Evidence: PMID:34800366 Quantitative high-confidence human mitochondrial proteome and its dynamics in cellular context
GO:0045277 respiratory chain complex IV	IDA PMID:22902835 NDUFA4 is a subunit of complex IV of the mammalian electron ...	ACCEPT	Summary: Balsa et al. (2012) provided the foundational experimental evidence that NDUFA4 is a subunit of Complex IV, not Complex I. This landmark paper used proteomic, genetic, evolutionary, and biochemical analyses to demonstrate CIV membership. IDA from the primary reclassification study. Reason: Core annotation with strongest experimental evidence. This is the definitive study reclassifying NDUFA4 from CI to CIV. NDUFA4 knockdown specifically reduced CIV levels and activity without affecting CI. This is the most important single annotation for NDUFA4. Supporting Evidence: PMID:22902835 NDUFA4, formerly considered a constituent of NADH Dehydrogenase (CI), is instead a component of the cytochrome c oxidase (CIV). Deletion of NDUFA4 does not perturb CI. Rather, proteomic, genetic, evolutionary, and biochemical analyses reveal that NDUFA4 plays a role in CIV function and biogenesis.
GO:0005515 protein binding	IPI PMID:31536960 Rewiring of the Human Mitochondrial Interactome during Neuro...	MARK AS OVER ANNOTATED	Summary: Moutaoufik et al. (2019) performed systematic mass spectrometry-based co-fractionation profiling of mitochondrial proteins. The with/from column indicates interaction with RAB5IF (Q9BUV8). UniProt confirms NDUFA4 interacts with RAB5IF. This is a high-throughput interactome study of mitochondrial proteins during neuronal reprogramming. Reason: Generic protein binding from a high-throughput mitochondrial interactome study. While the interaction with RAB5IF was confirmed by UniProt, the protein binding term itself is uninformative about NDUFA4's actual molecular function as a CIV subunit. Per curation guidelines, protein binding does not tell us about actual function. Supporting Evidence: PMID:31536960 Association of CI subunit (NDUFA4) or TFAM with the components of the respirasome file:human/NDUFA4/NDUFA4-uniprot.txt Interacts with RAB5IF
GO:0044877 protein-containing complex binding	IDA PMID:23209302 KIF14 negatively regulates Rap1a-Radil signaling during brea...	REMOVE	Summary: PMID:23209302 (Ahmed et al. 2012) is about KIF14 regulation of Rap1a-Radil signaling in breast cancer. This publication has no relevance to NDUFA4/COXFA4 function. Searching the full text of the paper reveals no mention of NDUFA4, COXFA4, or O00483. This annotation appears to be a misattribution -- possibly transferred from a different protein erroneously. Reason: Likely erroneous annotation. The cited reference (PMID:23209302) is about KIF14 and Rap1a-Radil signaling in breast cancer and has no connection to NDUFA4. The paper does not mention NDUFA4, COXFA4, or cytochrome c oxidase anywhere. This appears to be a curation error where the annotation was incorrectly assigned to NDUFA4. The term protein-containing complex binding is also vague and uninformative. Supporting Evidence: PMID:23209302 KIF14 negatively regulates Rap1a-Radil signaling during breast cancer progression
GO:0005515 protein binding	IPI PMID:19822128 DJ-1 binds to mitochondrial complex I and maintains its acti...	MARK AS OVER ANNOTATED	Summary: Hayashi et al. (2009) reported that DJ-1 (PARK7, Q99497) directly binds to NDUFA4 and ND1. However, this study was performed when NDUFA4 was still classified as a Complex I subunit. The finding that DJ-1 binds NDUFA4 is of some interest but the functional interpretation (DJ-1 maintaining CI activity through NDUFA4) is outdated given NDUFA4's reclassification to CIV. The protein binding annotation itself is generic. Reason: Generic protein binding annotation. The DJ-1 interaction with NDUFA4 was reported in the context of Complex I biology, which is now known to be incorrect for NDUFA4. While the physical interaction may be real, the protein binding term is uninformative about NDUFA4's core function as a CIV subunit. The functional context of the interaction (CI activity maintenance) has been invalidated by NDUFA4 reclassification. Supporting Evidence: PMID:19822128 DJ-1 directly bound to NDUFA4 and ND1, nuclear and mitochondrial DNA-encoding subunits of mitochondrial complex I, respectively PMID:22902835 NDUFA4, formerly considered a constituent of NADH Dehydrogenase (CI), is instead a component of the cytochrome c oxidase (CIV).
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-163214	ACCEPT	Summary: Reactome pathway for electron transfer from reduced cytochrome c to molecular oxygen, documenting Complex IV at the inner mitochondrial membrane. Reason: Traceable author statement from Reactome curated pathway. NDUFA4 is part of Complex IV which localizes to and functions at the inner mitochondrial membrane. Appropriate and precise localization annotation. Supporting Evidence: Reactome:R-HSA-163214 Electron transfer from reduced cytochrome c to molecular oxygen
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-9709406	ACCEPT	Summary: Reactome reaction documenting CO binding to cytochrome c oxidase at the inner membrane. Reason: Valid TAS evidence for NDUFA4 localization as subunit of Complex IV at the inner mitochondrial membrane. Reactome curated reaction. Supporting Evidence: Reactome:R-HSA-9709406 CO binds to Cytochrome c oxidase
GO:0005743 mitochondrial inner membrane	TAS Reactome:R-HSA-9865663	ACCEPT	Summary: Reactome reaction for Complex IV assembly -- MT-CO3, COX6A, COX6B, COX7A and NDUFA4 bind to the holo-MT-CO1,2 complex at the inner membrane. This directly documents NDUFA4 incorporation into CIV. Reason: Directly relevant Reactome reaction documenting NDUFA4 assembly into Complex IV at the inner mitochondrial membrane. Strong support for both localization and CIV membership. Supporting Evidence: Reactome:R-HSA-9865663 MT-CO3, COX6A,B,7A and NDUFA4 bind to holo-MT-CO1,2 complex
GO:0005739 mitochondrion	IDA PMID:16729965 Novel localization of OCTN1, an organic cation/carnitine tra...	ACCEPT	Summary: PMID:16729965 (Lamhonwah and Tein 2006) is about OCTN1 (organic cation/carnitine transporter) localization to mitochondria. While this study may have incidentally identified NDUFA4 in mitochondrial fractions, the paper is primarily about OCTN1. The mitochondrial localization of NDUFA4 is well-established from other sources. Reason: Although the cited reference focuses on OCTN1, the mitochondrial localization of NDUFA4 is robustly supported by multiple independent lines of evidence including the cryo-EM structure (PMID:30030519), immunofluorescence (GO_REF:0000052), and proteomics (PMID:34800366). The broad mitochondrion term is valid. Supporting Evidence: file:human/NDUFA4/NDUFA4-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion inner membrane; Single-pass membrane protein PMID:16729965 Novel localization of OCTN1, an organic cation/carnitine transporter, to mammalian mitochondria.
GO:0006120 mitochondrial electron transport, NADH to ubiquinone	NAS PMID:9878551 cDNA of eight nuclear encoded subunits of NADH:ubiquinone ox...	REMOVE	Summary: This annotation reflects the outdated classification of NDUFA4 as a Complex I subunit. PMID:9878551 (Loeffen et al. 1998) reported cDNA sequences for nuclear encoded CI subunits including NDUFA4, based on the now-incorrect assumption that NDUFA4 was a Complex I component. Balsa et al. (2012) subsequently demonstrated that NDUFA4 is not involved in the NADH-to-ubiquinone electron transport step. Reason: Incorrect annotation based on historical misclassification. NDUFA4 is not a Complex I subunit and does not participate in mitochondrial electron transport from NADH to ubiquinone. Balsa et al. (2012) showed "Deletion of NDUFA4 does not perturb CI." The correct process annotation is GO:0006123 (mitochondrial electron transport, cytochrome c to oxygen), which is already annotated. Supporting Evidence: PMID:22902835 NDUFA4, formerly considered a constituent of NADH Dehydrogenase (CI), is instead a component of the cytochrome c oxidase (CIV). Deletion of NDUFA4 does not perturb CI. PMID:9878551 cDNA of eight nuclear encoded subunits of NADH:ubiquinone oxidoreductase: human complex I cDNA characterization completed [predates the reclassification]
GO:0008137 NADH dehydrogenase (ubiquinone) activity	NAS PMID:9878551 cDNA of eight nuclear encoded subunits of NADH:ubiquinone ox...	REMOVE	Summary: This annotation reflects the outdated classification of NDUFA4 as a Complex I subunit with NADH dehydrogenase activity. PMID:9878551 (Loeffen et al. 1998) characterized NDUFA4 cDNA as part of CI, which has since been disproved. Reason: Incorrect annotation based on historical misclassification. NDUFA4 does not have NADH dehydrogenase (ubiquinone) activity. It is a subunit of Complex IV (cytochrome c oxidase), not Complex I (NADH dehydrogenase). Balsa et al. (2012) definitively showed NDUFA4 deletion does not perturb CI. UniProt now explicitly cautions: "Was initially believed to be a subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (complex I)." Supporting Evidence: PMID:22902835 Deletion of NDUFA4 does not perturb CI. Rather, proteomic, genetic, evolutionary, and biochemical analyses reveal that NDUFA4 plays a role in CIV function and biogenesis. file:human/NDUFA4/NDUFA4-uniprot.txt Was initially believed to be a subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (complex I).
GO:0008137 NADH dehydrogenase (ubiquinone) activity	TAS PMID:9352085 Cloning of the human cDNA sequence encoding the NADH:ubiquin...	REMOVE	Summary: PMID:9352085 (Kim et al. 1997) cloned the human NDUFA4 cDNA and described it as encoding the NADH:ubiquinone oxidoreductase MLRQ subunit. This was the initial characterization of NDUFA4, predating the reclassification by 15 years. Reason: Incorrect annotation based on original misclassification. Kim et al. (1997) characterized NDUFA4 under the assumption it was a Complex I subunit. Balsa et al. (2012) subsequently demonstrated this was incorrect. NDUFA4 does not contribute to NADH dehydrogenase activity; it is a cytochrome c oxidase subunit. The gene name NDUFA4 persists for historical reasons but is misleading. Supporting Evidence: PMID:9352085 A cDNA clone encoding human NADH:ubiquinone oxidoreductase (complex I of mitochondrial respiratory chain) MLRQ subunit was isolated [predates reclassification] PMID:22902835 The change in the attribution of the NDUFA4 protein requires renaming of the gene and reconsideration of the structure of CIV.
GO:0004129 cytochrome-c oxidase activity	IDA PMID:22902835 NDUFA4 is a subunit of complex IV of the mammalian electron ...	NEW	Summary: As a structural subunit of Complex IV, NDUFA4 contributes to cytochrome-c oxidase activity. Balsa et al. (2012) showed that knockdown of NDUFA4 reduces CIV activity. Following GO annotation conventions for complex subunits (contributes_to qualifier), NDUFA4 should be annotated to the molecular function of the complex it enables. This annotation is present in UniProt GO cross-references but is missing from the GOA file. Reason: NDUFA4 is a subunit of Complex IV whose primary molecular function is cytochrome-c oxidase activity (GO:0004129). Following the pattern established for other CIV subunits like COX5B (P10606), which is annotated to GO:0004129, NDUFA4 should have this molecular function annotation. Balsa et al. showed NDUFA4 knockdown reduces CIV activity, and mutations cause MC4DN21 with reduced COX activity. Note this should use the contributes_to qualifier since NDUFA4 is a structural subunit, not the catalytic core. Supporting Evidence: PMID:22902835 proteomic, genetic, evolutionary, and biochemical analyses reveal that NDUFA4 plays a role in CIV function and biogenesis file:human/NDUFA4/NDUFA4-uniprot.txt Cytochrome c oxidase is the component of the respiratory chain that catalyzes the reduction of oxygen to water. COXFA4 is required for complex IV maintenance.

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