{"gene":"NDUFB9","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":2011,"finding":"A causal mutation in NDUFB9 (encoding a complex I subunit) results in reduction of NDUFB9 protein and both amount and activity of mitochondrial complex I; these defects were rescued by expression of wild-type NDUFB9 in patient-derived fibroblasts, confirming NDUFB9 as a structural/functional subunit required for complex I integrity and activity.","method":"Functional complementation assay in patient-derived fibroblasts; Sanger sequencing; high-resolution melting curve analysis","journal":"Journal of medical genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional rescue experiment with wild-type cDNA in patient fibroblasts demonstrating both protein-level and enzymatic activity rescue; peer-reviewed, replicated in patient cohort","pmids":["22200994"],"is_preprint":false},{"year":2015,"finding":"Loss of NDUFB9 promotes breast cancer cell proliferation, migration, and invasion by elevating mitochondrial ROS (mtROS), disturbing the NAD+/NADH balance, and depleting mitochondrial DNA; the Akt/mTOR/p70S6K signaling pathway and epithelial-mesenchymal transition (EMT) are implicated downstream.","method":"siRNA-mediated knockdown of NDUFB9 in MDA-MB-231 cells; quantitative proteomic analysis; cell proliferation, migration, and invasion assays; ROS and NAD+/NADH measurements","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with multiple phenotypic readouts (ROS, NAD+/NADH, mtDNA, migration, invasion) in single lab; pathway placement inferred but not genetically confirmed","pmids":["26641458"],"is_preprint":false},{"year":2022,"finding":"NDUFB9 is upregulated during adipogenesis; silencing Ndufb9 inhibits adipogenesis, and this effect is mediated through stearoyl-CoA desaturase 1 (SCD1), placing NDUFB9 upstream of SCD1 in the adipogenic pathway.","method":"siRNA knockdown of Ndufb9 (83% silencing efficiency) in OP9 cells and adipose-derived stem cells; transcriptomics; lipidomics; SCD1 inhibitor (Aramchol) phenocopy experiment","journal":"Journal of physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with transcriptomic and lipidomic orthogonal methods, and pharmacological phenocopy via SCD1 inhibitor; single lab","pmids":["35122619"],"is_preprint":false},{"year":2025,"finding":"The LYR (leucine/tyrosine/arginine) domain of the NDUFB9/B22 subunit of mitochondrial complex I is essential for complex I function and assembly; this domain mediates a direct protein–protein interaction with the neighbouring complex I subunit SDAP1 (mitochondrial acyl carrier protein), as shown by the inability of an LYR-domain mutant to rescue CI deficiency and by protein interaction assays.","method":"T-DNA insertional knockout/knockdown lines in Arabidopsis; complementation with LYR-domain mutant B22 variant; protein interaction assays; CI activity and abundance measurements","journal":"The Plant journal : for cell and molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vivo complementation with domain-mutant, protein interaction assays, and parallel knockdown of interacting partner (SDAP1) all converge on the same mechanistic conclusion; multiple orthogonal methods in one study","pmids":["39981882"],"is_preprint":false},{"year":2025,"finding":"NDUFB9 overexpression in a CUMS mouse model alleviates depressive-like behavior by restoring mitochondrial function and enhancing mitophagy via the PINK1/Parkin pathway; co-immunoprecipitation and protein half-life assays revealed that NDUFB9 physically interacts with and stabilizes the PINK1 protein, thereby promoting mitophagy.","method":"CUMS mouse model; AAV-mediated NDUFB9 overexpression; Co-IP; protein half-life assay; autophagy/mitophagy inhibitor experiments; behavioral assays","journal":"Translational psychiatry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and protein stability assay identify NDUFB9–PINK1 interaction; in vivo rescue with defined pathway inhibitor follow-up; single lab","pmids":["40825941"],"is_preprint":false},{"year":2026,"finding":"NDUFB9 knockout selectively disrupts mitochondrial complex I and reduces intracellular aspartate in TNBC cells; in the brain microenvironment, lower asparagine concentration triggers compensatory upregulation of asparagine synthetase (ASNS), which diverts the already-depleted aspartate pool toward asparagine biosynthesis, thereby restricting nucleotide biosynthesis and suppressing brain metastasis outgrowth — a brain-specific dual-hit mechanism.","method":"High-throughput in vivo CRISPR loss-of-function screen; NDUFB9 knockout cell lines; metabolomics (aspartate, asparagine measurement); ASNS expression analysis; orthotopic brain and extracranial metastasis mouse models","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vivo CRISPR screen plus mechanistic validation with metabolomics and genetic models, multiple orthogonal methods establishing pathway position; peer-reviewed","pmids":["42103753"],"is_preprint":false},{"year":1996,"finding":"The human NDUFB9 (B22 subunit) gene was physically mapped to chromosome 8q13.3, and the encoded protein was identified as a subunit of the mitochondrial NADH-ubiquinone oxidoreductase (complex I) respiratory chain, based on 89% sequence similarity to the bovine B22 subunit.","method":"Hybrid selection using cosmid genomic clones; cDNA isolation; sequence similarity analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — sequence-based identification and chromosomal mapping; no functional assay performed, but similarity to bovine ortholog is strong; replicated by subsequent papers","pmids":["8661098"],"is_preprint":false},{"year":2002,"finding":"B22 (NDUFB9) gene expression declines progressively during terminal erythroid differentiation of MEL cells induced by DMSO, indicating transcriptional repression of this complex I subunit gene during erythropoiesis; this repression was abrogated by N6-methyladenosine (an inhibitor of commitment and RNA methylation), linking B22 repression to the differentiation program.","method":"Northern blot analysis; MEL cell differentiation assay with DMSO and chemical inhibitors; cDNA cloning and sequencing of B22 fragment","journal":"Biochemical pharmacology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method (Northern blot); no direct mechanistic dissection of the transcriptional repression mechanism","pmids":["11911854"],"is_preprint":false}],"current_model":"NDUFB9 (also known as B22/LYRM3/UQOR22) is an accessory subunit of mitochondrial complex I (NADH:ubiquinone oxidoreductase) whose LYR domain directly binds the neighbouring subunit SDAP1 (mitochondrial acyl carrier protein) and is essential for complex I assembly and activity; loss of NDUFB9 disrupts complex I, elevates mitochondrial ROS and perturbs the NAD⁺/NADH balance, and in specific metabolic contexts (brain microenvironment) reduces intracellular aspartate and restricts nucleotide biosynthesis; NDUFB9 also physically stabilizes PINK1 to promote PINK1/Parkin-dependent mitophagy, and its expression is transcriptionally regulated during erythroid differentiation and adipogenesis (acting upstream of SCD1 in the latter context)."},"narrative":{"mechanistic_narrative":"NDUFB9 (B22) is an accessory subunit of mitochondrial complex I (NADH:ubiquinone oxidoreductase) that is required for the enzyme's assembly, abundance, and catalytic activity [PMID:22200994, PMID:8661098]. Its LYR domain mediates a direct interaction with the neighbouring complex I subunit SDAP1 (mitochondrial acyl carrier protein), and an LYR-domain mutant fails to rescue complex I deficiency, establishing this interaction as central to NDUFB9's structural role in the assembled complex [PMID:39981882]. A pathogenic NDUFB9 mutation reduces NDUFB9 protein and both the amount and activity of complex I, defects that are corrected by re-expression of wild-type NDUFB9 in patient fibroblasts [PMID:22200994]. Loss of NDUFB9 disrupts complex I integrity with broad metabolic consequences: it elevates mitochondrial ROS, disturbs the NAD+/NADH balance, and depletes mitochondrial DNA, driving pro-proliferative and pro-migratory phenotypes [PMID:26641458], while NDUFB9 knockout reduces intracellular aspartate and, in the brain microenvironment, restricts nucleotide biosynthesis to suppress metastatic outgrowth [PMID:42103753]. Beyond its respiratory-chain function, NDUFB9 physically interacts with and stabilizes PINK1 to promote PINK1/Parkin-dependent mitophagy [PMID:40825941], and its expression is dynamically regulated during cellular differentiation programs, declining during erythroid differentiation [PMID:11911854] and rising during adipogenesis where it acts upstream of SCD1 [PMID:35122619].","teleology":[{"year":1996,"claim":"Established the molecular identity and genomic location of NDUFB9, assigning it as a respiratory-chain complex I subunit before any functional characterization existed.","evidence":"Cosmid hybrid selection, cDNA isolation, and sequence similarity to the bovine B22 subunit; chromosomal mapping to 8q13.3","pmids":["8661098"],"confidence":"Medium","gaps":["No functional assay confirming complex I role","Assignment rests on cross-species sequence similarity only"]},{"year":2002,"claim":"Linked NDUFB9 expression to a differentiation program, showing the subunit gene is transcriptionally repressed as cells exit proliferation and commit to erythroid maturation.","evidence":"Northern blot during DMSO-induced MEL cell differentiation, with N6-methyladenosine inhibitor abrogating repression","pmids":["11911854"],"confidence":"Low","gaps":["Single method (Northern blot), no mechanistic dissection of the repression","Transcription factors and cis-elements controlling repression unidentified","Functional consequence of reduced complex I subunit during erythropoiesis not tested"]},{"year":2011,"claim":"Demonstrated causally that NDUFB9 is required for complex I integrity, resolving whether the subunit is structurally essential rather than merely associated.","evidence":"Functional complementation with wild-type cDNA in patient-derived fibroblasts restoring both protein level and enzymatic activity","pmids":["22200994"],"confidence":"High","gaps":["Did not define which assembly intermediate requires NDUFB9","Structural basis of the requirement not resolved"]},{"year":2015,"claim":"Connected loss of NDUFB9 to downstream redox and metabolic disturbance, showing complex I dysfunction propagates to ROS, NAD+/NADH imbalance and tumor-cell phenotypes.","evidence":"siRNA knockdown in MDA-MB-231 cells with proteomics, ROS, NAD+/NADH and mtDNA measurements plus migration/invasion assays","pmids":["26641458"],"confidence":"Medium","gaps":["Akt/mTOR/p70S6K and EMT placement inferred, not genetically confirmed","Single cell line and single lab","Direct causal link between ROS and phenotype not isolated"]},{"year":2022,"claim":"Identified a regulatory role for NDUFB9 in adipogenesis, positioning it upstream of a lipogenic enzyme rather than purely as a bioenergetic component.","evidence":"siRNA knockdown in OP9 cells and adipose-derived stem cells with transcriptomics, lipidomics, and SCD1-inhibitor phenocopy","pmids":["35122619"],"confidence":"Medium","gaps":["Mechanism linking complex I subunit to SCD1 regulation unresolved","Single lab","Whether the effect is bioenergetic or signaling not separated"]},{"year":2025,"claim":"Defined the structural mechanism of NDUFB9 within complex I, identifying the LYR domain as the determinant that anchors SDAP1.","evidence":"Arabidopsis T-DNA knockout/knockdown, LYR-domain mutant complementation, protein interaction assays, and parallel SDAP1 knockdown converging on the same conclusion","pmids":["39981882"],"confidence":"High","gaps":["Structural detail of the LYR–SDAP1 interface not solved","Demonstrated in plant system; conservation of the interface assumed across species"]},{"year":2025,"claim":"Revealed a moonlighting function beyond the respiratory chain, showing NDUFB9 stabilizes PINK1 to drive mitophagy.","evidence":"AAV-mediated overexpression in a CUMS mouse model with reciprocal Co-IP, protein half-life assay, mitophagy inhibitor experiments, and behavioral readouts","pmids":["40825941"],"confidence":"Medium","gaps":["Domain/region of NDUFB9 mediating PINK1 binding unmapped","Whether stabilization is direct or via complex I status unclear","Single lab"]},{"year":2026,"claim":"Placed NDUFB9 loss within a context-specific metabolic circuit, showing complex I disruption depletes aspartate and, in the brain, restricts nucleotide biosynthesis to limit metastasis.","evidence":"In vivo CRISPR loss-of-function screen, NDUFB9 knockout lines, metabolomics, ASNS expression analysis, and orthotopic brain vs extracranial metastasis models","pmids":["42103753"],"confidence":"High","gaps":["Generalizability beyond TNBC brain metastasis not established","Direct flux from aspartate to nucleotides not isotopically traced in all contexts"]},{"year":null,"claim":"How NDUFB9's bioenergetic role is mechanistically coupled to its differentiation-regulatory (SCD1, erythroid) and mitophagy (PINK1) functions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified mechanism linking complex I subunit status to PINK1 stabilization","No structural model of the human NDUFB9–SDAP1 interface","Transcriptional regulators of NDUFB9 across tissues unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,3,6]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,3,6]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1,5]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4]}],"complexes":["mitochondrial respiratory chain complex I"],"partners":["SDAP1","PINK1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y6M9","full_name":"NADH dehydrogenase [ubiquinone] 1 beta subcomplex subunit 9","aliases":["Complex I-B22","CI-B22","LYR motif-containing protein 3","NADH-ubiquinone oxidoreductase B22 subunit"],"length_aa":179,"mass_kda":21.8,"function":"Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed to be not involved in catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone","subcellular_location":"Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/Q9Y6M9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/NDUFB9","classification":"Common Essential","n_dependent_lines":670,"n_total_lines":1208,"dependency_fraction":0.554635761589404},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/NDUFB9","total_profiled":1310},"omim":[{"mim_id":"618245","title":"MITOCHONDRIAL COMPLEX I DEFICIENCY, NUCLEAR TYPE 24; MC1DN24","url":"https://www.omim.org/entry/618245"},{"mim_id":"601445","title":"NADH-UBIQUINONE OXIDOREDUCTASE SUBUNIT B9; NDUFB9","url":"https://www.omim.org/entry/601445"},{"mim_id":"252010","title":"MITOCHONDRIAL COMPLEX I DEFICIENCY, NUCLEAR TYPE 1; MC1DN1","url":"https://www.omim.org/entry/252010"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Mitochondria","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":1286.6},{"tissue":"tongue","ntpm":1386.4}],"url":"https://www.proteinatlas.org/search/NDUFB9"},"hgnc":{"alias_symbol":["B22","UQOR22","LYRM3"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y6M9","domains":[{"cath_id":"-","chopping":"96-173","consensus_level":"high","plddt":96.5428,"start":96,"end":173},{"cath_id":"1.10.12","chopping":"13-75","consensus_level":"high","plddt":98.037,"start":13,"end":75}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6M9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6M9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6M9-F1-predicted_aligned_error_v6.png","plddt_mean":95.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NDUFB9","jax_strain_url":"https://www.jax.org/strain/search?query=NDUFB9"},"sequence":{"accession":"Q9Y6M9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y6M9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y6M9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6M9"}},"corpus_meta":[{"pmid":"22200994","id":"PMC_22200994","title":"Mutation screening of 75 candidate genes in 152 complex I deficiency cases identifies pathogenic variants in 16 genes including NDUFB9.","date":"2011","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22200994","citation_count":85,"is_preprint":false},{"pmid":"26641458","id":"PMC_26641458","title":"Down-Regulation of NDUFB9 Promotes Breast Cancer Cell Proliferation, Metastasis by Mediating Mitochondrial Metabolism.","date":"2015","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/26641458","citation_count":66,"is_preprint":false},{"pmid":"24832205","id":"PMC_24832205","title":"T cell inactivation by poxviral B22 family proteins increases viral virulence.","date":"2014","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/24832205","citation_count":48,"is_preprint":false},{"pmid":"24289039","id":"PMC_24289039","title":"Coarse-grained model for colloidal protein interactions, B(22), and protein cluster formation.","date":"2013","source":"The journal of physical chemistry. 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syndrome.","date":"1996","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/8661098","citation_count":24,"is_preprint":false},{"pmid":"19683937","id":"PMC_19683937","title":"Fragmentation of doubly-protonated Pro-His-Xaa tripeptides: formation of b(2)(2+) ions.","date":"2009","source":"Journal of the American Society for Mass Spectrometry","url":"https://pubmed.ncbi.nlm.nih.gov/19683937","citation_count":22,"is_preprint":false},{"pmid":"24502209","id":"PMC_24502209","title":"Priming-mediated systemic resistance in cucumber induced by Pseudomonas azotoformans GC-B19 and Paenibacillus elgii MM-B22 against Colletotrichum orbiculare.","date":"2014","source":"Phytopathology","url":"https://pubmed.ncbi.nlm.nih.gov/24502209","citation_count":18,"is_preprint":false},{"pmid":"10077726","id":"PMC_10077726","title":"Human NDUFB9 gene: genomic organization and a possible candidate gene associated with deafness disorder mapped to chromosome 8q13.","date":"1999","source":"Human heredity","url":"https://pubmed.ncbi.nlm.nih.gov/10077726","citation_count":17,"is_preprint":false},{"pmid":"9151389","id":"PMC_9151389","title":"Five HLA-B22 group alleles in Japanese.","date":"1997","source":"Tissue antigens","url":"https://pubmed.ncbi.nlm.nih.gov/9151389","citation_count":17,"is_preprint":false},{"pmid":"31919603","id":"PMC_31919603","title":"Agricultural waste materials enhance protease production by Bacillus subtilis B22 in submerged fermentation under blue light-emitting diodes.","date":"2020","source":"Bioprocess and biosystems engineering","url":"https://pubmed.ncbi.nlm.nih.gov/31919603","citation_count":14,"is_preprint":false},{"pmid":"35122619","id":"PMC_35122619","title":"Blockage of NDUFB9-SCD1 pathway inhibits adipogenesis : Blockage of NDUFB9-SCD1 pathway inhibits adipogenesis.","date":"2022","source":"Journal of physiology and 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and activity.\",\n      \"method\": \"Functional complementation assay in patient-derived fibroblasts; Sanger sequencing; high-resolution melting curve analysis\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional rescue experiment with wild-type cDNA in patient fibroblasts demonstrating both protein-level and enzymatic activity rescue; peer-reviewed, replicated in patient cohort\",\n      \"pmids\": [\"22200994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Loss of NDUFB9 promotes breast cancer cell proliferation, migration, and invasion by elevating mitochondrial ROS (mtROS), disturbing the NAD+/NADH balance, and depleting mitochondrial DNA; the Akt/mTOR/p70S6K signaling pathway and epithelial-mesenchymal transition (EMT) are implicated downstream.\",\n      \"method\": \"siRNA-mediated knockdown of NDUFB9 in MDA-MB-231 cells; quantitative proteomic analysis; cell proliferation, migration, and invasion assays; ROS and NAD+/NADH measurements\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with multiple phenotypic readouts (ROS, NAD+/NADH, mtDNA, migration, invasion) in single lab; pathway placement inferred but not genetically confirmed\",\n      \"pmids\": [\"26641458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NDUFB9 is upregulated during adipogenesis; silencing Ndufb9 inhibits adipogenesis, and this effect is mediated through stearoyl-CoA desaturase 1 (SCD1), placing NDUFB9 upstream of SCD1 in the adipogenic pathway.\",\n      \"method\": \"siRNA knockdown of Ndufb9 (83% silencing efficiency) in OP9 cells and adipose-derived stem cells; transcriptomics; lipidomics; SCD1 inhibitor (Aramchol) phenocopy experiment\",\n      \"journal\": \"Journal of physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with transcriptomic and lipidomic orthogonal methods, and pharmacological phenocopy via SCD1 inhibitor; single lab\",\n      \"pmids\": [\"35122619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The LYR (leucine/tyrosine/arginine) domain of the NDUFB9/B22 subunit of mitochondrial complex I is essential for complex I function and assembly; this domain mediates a direct protein–protein interaction with the neighbouring complex I subunit SDAP1 (mitochondrial acyl carrier protein), as shown by the inability of an LYR-domain mutant to rescue CI deficiency and by protein interaction assays.\",\n      \"method\": \"T-DNA insertional knockout/knockdown lines in Arabidopsis; complementation with LYR-domain mutant B22 variant; protein interaction assays; CI activity and abundance measurements\",\n      \"journal\": \"The Plant journal : for cell and molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vivo complementation with domain-mutant, protein interaction assays, and parallel knockdown of interacting partner (SDAP1) all converge on the same mechanistic conclusion; multiple orthogonal methods in one study\",\n      \"pmids\": [\"39981882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"NDUFB9 overexpression in a CUMS mouse model alleviates depressive-like behavior by restoring mitochondrial function and enhancing mitophagy via the PINK1/Parkin pathway; co-immunoprecipitation and protein half-life assays revealed that NDUFB9 physically interacts with and stabilizes the PINK1 protein, thereby promoting mitophagy.\",\n      \"method\": \"CUMS mouse model; AAV-mediated NDUFB9 overexpression; Co-IP; protein half-life assay; autophagy/mitophagy inhibitor experiments; behavioral assays\",\n      \"journal\": \"Translational psychiatry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and protein stability assay identify NDUFB9–PINK1 interaction; in vivo rescue with defined pathway inhibitor follow-up; single lab\",\n      \"pmids\": [\"40825941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"NDUFB9 knockout selectively disrupts mitochondrial complex I and reduces intracellular aspartate in TNBC cells; in the brain microenvironment, lower asparagine concentration triggers compensatory upregulation of asparagine synthetase (ASNS), which diverts the already-depleted aspartate pool toward asparagine biosynthesis, thereby restricting nucleotide biosynthesis and suppressing brain metastasis outgrowth — a brain-specific dual-hit mechanism.\",\n      \"method\": \"High-throughput in vivo CRISPR loss-of-function screen; NDUFB9 knockout cell lines; metabolomics (aspartate, asparagine measurement); ASNS expression analysis; orthotopic brain and extracranial metastasis mouse models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vivo CRISPR screen plus mechanistic validation with metabolomics and genetic models, multiple orthogonal methods establishing pathway position; peer-reviewed\",\n      \"pmids\": [\"42103753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The human NDUFB9 (B22 subunit) gene was physically mapped to chromosome 8q13.3, and the encoded protein was identified as a subunit of the mitochondrial NADH-ubiquinone oxidoreductase (complex I) respiratory chain, based on 89% sequence similarity to the bovine B22 subunit.\",\n      \"method\": \"Hybrid selection using cosmid genomic clones; cDNA isolation; sequence similarity analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — sequence-based identification and chromosomal mapping; no functional assay performed, but similarity to bovine ortholog is strong; replicated by subsequent papers\",\n      \"pmids\": [\"8661098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"B22 (NDUFB9) gene expression declines progressively during terminal erythroid differentiation of MEL cells induced by DMSO, indicating transcriptional repression of this complex I subunit gene during erythropoiesis; this repression was abrogated by N6-methyladenosine (an inhibitor of commitment and RNA methylation), linking B22 repression to the differentiation program.\",\n      \"method\": \"Northern blot analysis; MEL cell differentiation assay with DMSO and chemical inhibitors; cDNA cloning and sequencing of B22 fragment\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method (Northern blot); no direct mechanistic dissection of the transcriptional repression mechanism\",\n      \"pmids\": [\"11911854\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NDUFB9 (also known as B22/LYRM3/UQOR22) is an accessory subunit of mitochondrial complex I (NADH:ubiquinone oxidoreductase) whose LYR domain directly binds the neighbouring subunit SDAP1 (mitochondrial acyl carrier protein) and is essential for complex I assembly and activity; loss of NDUFB9 disrupts complex I, elevates mitochondrial ROS and perturbs the NAD⁺/NADH balance, and in specific metabolic contexts (brain microenvironment) reduces intracellular aspartate and restricts nucleotide biosynthesis; NDUFB9 also physically stabilizes PINK1 to promote PINK1/Parkin-dependent mitophagy, and its expression is transcriptionally regulated during erythroid differentiation and adipogenesis (acting upstream of SCD1 in the latter context).\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NDUFB9 (B22) is an accessory subunit of mitochondrial complex I (NADH:ubiquinone oxidoreductase) that is required for the enzyme's assembly, abundance, and catalytic activity [#0, #6]. Its LYR domain mediates a direct interaction with the neighbouring complex I subunit SDAP1 (mitochondrial acyl carrier protein), and an LYR-domain mutant fails to rescue complex I deficiency, establishing this interaction as central to NDUFB9's structural role in the assembled complex [#3]. A pathogenic NDUFB9 mutation reduces NDUFB9 protein and both the amount and activity of complex I, defects that are corrected by re-expression of wild-type NDUFB9 in patient fibroblasts [#0]. Loss of NDUFB9 disrupts complex I integrity with broad metabolic consequences: it elevates mitochondrial ROS, disturbs the NAD+/NADH balance, and depletes mitochondrial DNA, driving pro-proliferative and pro-migratory phenotypes [#1], while NDUFB9 knockout reduces intracellular aspartate and, in the brain microenvironment, restricts nucleotide biosynthesis to suppress metastatic outgrowth [#5]. Beyond its respiratory-chain function, NDUFB9 physically interacts with and stabilizes PINK1 to promote PINK1/Parkin-dependent mitophagy [#4], and its expression is dynamically regulated during cellular differentiation programs, declining during erythroid differentiation [#7] and rising during adipogenesis where it acts upstream of SCD1 [#2].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established the molecular identity and genomic location of NDUFB9, assigning it as a respiratory-chain complex I subunit before any functional characterization existed.\",\n      \"evidence\": \"Cosmid hybrid selection, cDNA isolation, and sequence similarity to the bovine B22 subunit; chromosomal mapping to 8q13.3\",\n      \"pmids\": [\"8661098\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional assay confirming complex I role\", \"Assignment rests on cross-species sequence similarity only\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Linked NDUFB9 expression to a differentiation program, showing the subunit gene is transcriptionally repressed as cells exit proliferation and commit to erythroid maturation.\",\n      \"evidence\": \"Northern blot during DMSO-induced MEL cell differentiation, with N6-methyladenosine inhibitor abrogating repression\",\n      \"pmids\": [\"11911854\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single method (Northern blot), no mechanistic dissection of the repression\", \"Transcription factors and cis-elements controlling repression unidentified\", \"Functional consequence of reduced complex I subunit during erythropoiesis not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated causally that NDUFB9 is required for complex I integrity, resolving whether the subunit is structurally essential rather than merely associated.\",\n      \"evidence\": \"Functional complementation with wild-type cDNA in patient-derived fibroblasts restoring both protein level and enzymatic activity\",\n      \"pmids\": [\"22200994\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which assembly intermediate requires NDUFB9\", \"Structural basis of the requirement not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected loss of NDUFB9 to downstream redox and metabolic disturbance, showing complex I dysfunction propagates to ROS, NAD+/NADH imbalance and tumor-cell phenotypes.\",\n      \"evidence\": \"siRNA knockdown in MDA-MB-231 cells with proteomics, ROS, NAD+/NADH and mtDNA measurements plus migration/invasion assays\",\n      \"pmids\": [\"26641458\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Akt/mTOR/p70S6K and EMT placement inferred, not genetically confirmed\", \"Single cell line and single lab\", \"Direct causal link between ROS and phenotype not isolated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified a regulatory role for NDUFB9 in adipogenesis, positioning it upstream of a lipogenic enzyme rather than purely as a bioenergetic component.\",\n      \"evidence\": \"siRNA knockdown in OP9 cells and adipose-derived stem cells with transcriptomics, lipidomics, and SCD1-inhibitor phenocopy\",\n      \"pmids\": [\"35122619\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking complex I subunit to SCD1 regulation unresolved\", \"Single lab\", \"Whether the effect is bioenergetic or signaling not separated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined the structural mechanism of NDUFB9 within complex I, identifying the LYR domain as the determinant that anchors SDAP1.\",\n      \"evidence\": \"Arabidopsis T-DNA knockout/knockdown, LYR-domain mutant complementation, protein interaction assays, and parallel SDAP1 knockdown converging on the same conclusion\",\n      \"pmids\": [\"39981882\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural detail of the LYR–SDAP1 interface not solved\", \"Demonstrated in plant system; conservation of the interface assumed across species\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed a moonlighting function beyond the respiratory chain, showing NDUFB9 stabilizes PINK1 to drive mitophagy.\",\n      \"evidence\": \"AAV-mediated overexpression in a CUMS mouse model with reciprocal Co-IP, protein half-life assay, mitophagy inhibitor experiments, and behavioral readouts\",\n      \"pmids\": [\"40825941\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Domain/region of NDUFB9 mediating PINK1 binding unmapped\", \"Whether stabilization is direct or via complex I status unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Placed NDUFB9 loss within a context-specific metabolic circuit, showing complex I disruption depletes aspartate and, in the brain, restricts nucleotide biosynthesis to limit metastasis.\",\n      \"evidence\": \"In vivo CRISPR loss-of-function screen, NDUFB9 knockout lines, metabolomics, ASNS expression analysis, and orthotopic brain vs extracranial metastasis models\",\n      \"pmids\": [\"42103753\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generalizability beyond TNBC brain metastasis not established\", \"Direct flux from aspartate to nucleotides not isotopically traced in all contexts\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How NDUFB9's bioenergetic role is mechanistically coupled to its differentiation-regulatory (SCD1, erythroid) and mitophagy (PINK1) functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified mechanism linking complex I subunit status to PINK1 stabilization\", \"No structural model of the human NDUFB9–SDAP1 interface\", \"Transcriptional regulators of NDUFB9 across tissues unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 3, 6]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 3, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 5]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [\"mitochondrial respiratory chain complex I\"],\n    \"partners\": [\"SDAP1\", \"PINK1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}