{"gene":"SUCLG1","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":2010,"finding":"SUCLG1 encodes the alpha subunit of succinate-CoA ligase (SUCL), a heterodimer in the mitochondrial matrix that catalyzes the reversible conversion of succinyl-CoA to succinate; in the absence of SUCLG1 protein, SUCLA2 protein is also absent in fibroblasts (by western blot), consistent with degradation of the beta subunit when its heterodimer partner is missing.","method":"Western blot analysis of patient fibroblasts; minigene expression system to confirm splice mutation","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — western blot and minigene assay in patient fibroblasts, single lab, two orthogonal methods confirming protein interdependence","pmids":["20693550"],"is_preprint":false},{"year":2018,"finding":"Pathogenic mutation in SUCLG1 (p.Ala209Glu) abolishes SUCLG1 protein, strongly reduces SUCLA2 and SUCLG2 protein levels, impairs mitochondrial substrate-level phosphorylation (mSLP) in fibroblasts, and causes mislocalization of SUCLG2 away from the mitochondrial network along with increased mitochondrial fragmentation, without changes in mtDNA levels or respiratory complex activities when standard substrates are used.","method":"Immunoblot, confocal immunocytochemistry, oxygen consumption/extracellular acidification rate assay, enzyme activity assay in patient fibroblasts","journal":"Molecular genetics and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (immunoblot, confocal imaging, respirometry, enzyme assay) in a single lab on patient-derived cells","pmids":["30470562"],"is_preprint":false},{"year":2016,"finding":"Loss of SUCLG1 protein in patient fibroblasts leads to significantly reduced SUCLA2 and SUCLG2 protein levels, essentially undetectable SCS enzyme activity, mtDNA depletion, and cellular respiration defects; ectopic expression of wild-type SUCLG1 rescues all these abnormal phenotypes, functionally confirming SUCLG1 as necessary for SUCL complex stability and activity.","method":"Western blot, SCS enzyme activity assay, mtDNA quantification, cellular respiration assay, rescue by ectopic WT SUCLG1 expression in patient fibroblasts","journal":"Molecular genetics and metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods plus genetic rescue experiment confirming mechanistic role, single lab but rigorous design","pmids":["27484306"],"is_preprint":false},{"year":2024,"finding":"SUCLG1 restricts succinyl-CoA levels to suppress succinylation of mitochondrial RNA polymerase (POLRMT) at lysine 622; this succinylation disrupts POLRMT interaction with mtDNA and mitochondrial transcription factors, while SUCLG1-mediated POLRMT hyposuccinylation maintains mtDNA transcription and mitochondrial biogenesis. FLT3 mutations upregulate SUCLG1 expression to reduce succinyl-CoA and POLRMT succinylation, enhancing mitobiogenesis and leukemia progression.","method":"Succinylation site mapping (K622), co-immunoprecipitation of POLRMT with mtDNA and transcription factors, genetic depletion of SUCLG1 and POLRMT in mouse and humanized leukemia models, succinyl-CoA and POLRMT succinylation measurement in FLT3-mutated clinical samples","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — site-specific PTM identification, Co-IP, in vivo genetic models, and clinical sample validation across multiple orthogonal methods in a single rigorous study","pmids":["38649537"],"is_preprint":false},{"year":2026,"finding":"SUCLG1 is hyperbutyrylated at lysine K90 in a mouse HFpEF model, which impairs its enzymatic function in the TCA cycle, resulting in reduced succinate and ATP production. SIRT4 acts as a debutyrylase for SUCLG1-K90, and downregulated SIRT4 leads to SUCLG1 hyperbutyrylation; restoration of SIRT4 activity (by ginsenoside Rb3 binding) reverses SUCLG1 hyperbutyrylation and restores TCA cycle flux.","method":"Butyrylome proteomic screening, SIRT4 inhibitor and overexpression experiments, metabolite (succinate, ATP) measurement, in vivo HFpEF mouse model and in vitro cellular model","journal":"Pharmacological research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — PTM site identified by proteomics with functional validation via enzyme inhibitor/overexpression, single lab, multiple methods","pmids":["41991142"],"is_preprint":false},{"year":2025,"finding":"SUCLG1 promotes mitochondrial quality, mitochondrial fusion, aerobic respiration (without affecting glycolysis), and proliferation/migration of plexiform neurofibroma cells; knockdown reduces these effects, and elevated SUCLG1 upregulates SLC25A1 expression.","method":"SUCLG1 knockdown and overexpression, Seahorse assay, western blotting, immunofluorescence, electron microscopy, flow cytometry, qPCR in PNF cell lines","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — multiple orthogonal functional assays in a single lab with KD/OE, but pathway placement is limited and SLC25A1 regulation is a single indirect observation","pmids":["39749698"],"is_preprint":false},{"year":2017,"finding":"In silico and computational analysis predicted that the SUCLG1 p.M14T mutation (located at the mitochondrial targeting sequence) alters protein stability and mitochondrial translocation; mtDNA copy number was reduced in patients' peripheral blood leukocytes.","method":"In silico structural/stability prediction, real-time PCR for mtDNA quantification in patient blood","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 4 / Weak — primarily computational prediction with supporting qPCR; no direct functional validation of mitochondrial import defect","pmids":["29217198"],"is_preprint":false}],"current_model":"SUCLG1 encodes the alpha subunit of the mitochondrial succinate-CoA ligase (SUCL) heterodimer, which is required for the stability of the beta subunits (SUCLA2 and SUCLG2); beyond its canonical TCA cycle role, SUCLG1 controls succinyl-CoA levels to restrict succinylation of POLRMT at K622—thereby sustaining mtDNA transcription and mitochondrial biogenesis—and its own enzymatic activity is regulated by SIRT4-dependent debutyrylation at K90, linking metabolic flux to post-translational control of mitochondrial function."},"narrative":{"mechanistic_narrative":"SUCLG1 encodes the alpha subunit of the mitochondrial matrix succinate-CoA ligase (SUCL), a heterodimer that catalyzes the reversible conversion of succinyl-CoA to succinate and thereby contributes to mitochondrial substrate-level phosphorylation [PMID:20693550, PMID:30470562]. SUCLG1 is structurally indispensable to the complex: loss of SUCLG1 protein leads to concurrent loss of the partner beta subunits SUCLA2 and SUCLG2, abolished SCS enzyme activity, mtDNA depletion, and respiration defects, all of which are reversed by ectopic wild-type SUCLG1, establishing SUCLG1 as required for SUCL stability and function [PMID:27484306]. Pathogenic SUCLG1 mutations cause this loss of SUCL, impairing mitochondrial substrate-level phosphorylation and producing SUCLG2 mislocalization with increased mitochondrial fragmentation [PMID:30470562]. Beyond its catalytic role, SUCLG1 governs the succinyl-CoA pool to restrict succinylation of mitochondrial RNA polymerase POLRMT at K622; by keeping POLRMT hyposuccinylated it preserves POLRMT engagement with mtDNA and transcription factors, sustaining mtDNA transcription and mitochondrial biogenesis—a circuit exploited by FLT3-mutant leukemia, which upregulates SUCLG1 to drive mitobiogenesis and disease progression [PMID:38649537]. SUCLG1 enzymatic activity is itself subject to acyl-lysine regulation, with hyperbutyrylation at K90 impairing TCA flux and SIRT4 acting as the debutyrylase that restores activity [PMID:41991142]. SUCLG1 supports mitochondrial fusion, mitochondrial quality, and aerobic respiration in proliferating tumor cells [PMID:39749698].","teleology":[{"year":2010,"claim":"Established that SUCLG1 is the alpha subunit of mitochondrial succinate-CoA ligase and that the complex is interdependent, since loss of SUCLG1 also eliminates the SUCLA2 beta subunit.","evidence":"Western blot and minigene splice analysis in patient fibroblasts","pmids":["20693550"],"confidence":"Medium","gaps":["Did not directly measure enzyme activity loss","Interdependence with SUCLG2 not yet examined","Mechanism of beta-subunit degradation not defined"]},{"year":2016,"claim":"Demonstrated through genetic rescue that SUCLG1 is necessary for SUCL complex stability, SCS enzyme activity, mtDNA maintenance, and respiration, moving beyond correlation to causation.","evidence":"Western blot, SCS activity assay, mtDNA quantification, respiration assay, and ectopic WT SUCLG1 rescue in patient fibroblasts","pmids":["27484306"],"confidence":"High","gaps":["Mechanism linking SUCL loss to mtDNA depletion not resolved","Single patient-derived cell background","No structural basis for complex stabilization"]},{"year":2018,"claim":"Connected a specific pathogenic mutation to functional consequences, showing SUCLG1 loss reduces both beta subunits, impairs substrate-level phosphorylation, and disrupts mitochondrial morphology.","evidence":"Immunoblot, confocal imaging, respirometry, and enzyme assays in patient fibroblasts carrying p.Ala209Glu","pmids":["30470562"],"confidence":"Medium","gaps":["Causal link between SUCL loss and SUCLG2 mislocalization unexplained","mtDNA levels and standard complex activities unchanged here, contrasting earlier findings","Mechanism of mitochondrial fragmentation not defined"]},{"year":2024,"claim":"Revealed a non-canonical regulatory role: SUCLG1 controls the succinyl-CoA pool to limit POLRMT K622 succinylation, thereby sustaining mtDNA transcription and mitochondrial biogenesis, a circuit hijacked in FLT3-mutant leukemia.","evidence":"Succinylation site mapping, POLRMT Co-IP with mtDNA and transcription factors, genetic depletion in mouse/humanized leukemia models, and clinical FLT3-mutant sample analysis","pmids":["38649537"],"confidence":"High","gaps":["Whether non-enzymatic succinyl-CoA buffering is the sole mechanism not established","Generality beyond leukemia contexts untested","Direct enzyme writer for POLRMT succinylation not identified"]},{"year":2025,"claim":"Showed SUCLG1 supports mitochondrial fusion, quality, aerobic respiration, and tumor cell proliferation/migration in plexiform neurofibroma, extending its role into mitochondrial dynamics and cancer cell metabolism.","evidence":"Knockdown/overexpression with Seahorse, immunofluorescence, electron microscopy, flow cytometry, and qPCR in PNF cell lines","pmids":["39749698"],"confidence":"Medium","gaps":["SLC25A1 regulation is a single indirect observation","Mechanism connecting SUCLG1 to fusion machinery unknown","Pathway placement limited to one tumor model"]},{"year":2026,"claim":"Identified acyl-lysine control of SUCLG1 enzymatic activity, with K90 hyperbutyrylation impairing TCA flux and SIRT4 acting as the debutyrylase that restores it, linking metabolic signaling to SUCLG1 function in heart failure.","evidence":"Butyrylome proteomics, SIRT4 inhibitor/overexpression, succinate/ATP measurement in HFpEF mouse and cellular models","pmids":["41991142"],"confidence":"Medium","gaps":["Direct demonstration that K90 butyrylation alters catalysis at the structural level absent","Butyryl-CoA source and writer enzyme not identified","Generality beyond HFpEF context untested"]},{"year":null,"claim":"How SUCLG1's catalytic and succinyl-CoA-buffering activities are integrated across tissues, and the structural basis for both complex stabilization and PTM-dependent regulation, remain open.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model integrating heterodimer assembly with K90/K622 PTM regulation","Mechanism by which SUCL loss causes mtDNA depletion versus normal mtDNA in different studies unreconciled","Writer enzymes for SUCLG1 and POLRMT acylation unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1,2]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2,4]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[3]}],"complexes":["succinate-CoA ligase (SUCL)"],"partners":["SUCLA2","SUCLG2","POLRMT","SIRT4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P53597","full_name":"Succinate--CoA ligase [ADP/GDP-forming] subunit alpha, mitochondrial","aliases":["Itaconyl--CoA ligase [ADP/GDP-forming] subunit alpha","Malyl--CoA ligase [ADP/GDP-forming] subunit alpha","Succinyl-CoA synthetase subunit alpha","SCS-alpha"],"length_aa":346,"mass_kda":36.2,"function":"Succinyl-CoA synthetase functions in the citric acid cycle (TCA), coupling the hydrolysis of succinyl-CoA to the synthesis of either ATP or GTP and thus represents the only step of substrate-level phosphorylation in the TCA (PubMed:34492704, PubMed:40108300). The alpha subunit of the enzyme binds the substrates coenzyme A and phosphate, while succinate binding and specificity for either ATP or GTP is provided by different beta subunits (By similarity). Also able to act as an itaconyl- and malyl-CoA synthetase (PubMed:40108300)","subcellular_location":"Mitochondrion","url":"https://www.uniprot.org/uniprotkb/P53597/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SUCLG1","classification":"Not Classified","n_dependent_lines":83,"n_total_lines":1208,"dependency_fraction":0.06870860927152318},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SUCLG1","total_profiled":1310},"omim":[{"mim_id":"612073","title":"MITOCHONDRIAL DNA DEPLETION SYNDROME 5 (ENCEPHALOMYOPATHIC WITH OR WITHOUT METHYLMALONIC ACIDURIA); MTDPS5","url":"https://www.omim.org/entry/612073"},{"mim_id":"611224","title":"SUCCINATE-CoA LIGASE, GDP/ADP-FORMING, SUBUNIT ALPHA; SUCLG1","url":"https://www.omim.org/entry/611224"},{"mim_id":"603922","title":"SUCCINATE-CoA LIGASE, GDP-FORMING, SUBUNIT BETA; SUCLG2","url":"https://www.omim.org/entry/603922"},{"mim_id":"603921","title":"SUCCINATE-CoA LIGASE, ADP-FORMING, SUBUNIT BETA; SUCLA2","url":"https://www.omim.org/entry/603921"},{"mim_id":"603041","title":"MITOCHONDRIAL DNA DEPLETION SYNDROME 1 (MNGIE TYPE); MTDPS1","url":"https://www.omim.org/entry/603041"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Mitochondria","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"kidney","ntpm":516.6}],"url":"https://www.proteinatlas.org/search/SUCLG1"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P53597","domains":[{"cath_id":"3.40.50.720","chopping":"47-172","consensus_level":"medium","plddt":98.5886,"start":47,"end":172},{"cath_id":"3.40.50.261","chopping":"191-346","consensus_level":"medium","plddt":97.7631,"start":191,"end":346}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P53597","model_url":"https://alphafold.ebi.ac.uk/files/AF-P53597-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P53597-F1-predicted_aligned_error_v6.png","plddt_mean":91.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SUCLG1","jax_strain_url":"https://www.jax.org/strain/search?query=SUCLG1"},"sequence":{"accession":"P53597","fasta_url":"https://rest.uniprot.org/uniprotkb/P53597.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P53597/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P53597"}},"corpus_meta":[{"pmid":"26475597","id":"PMC_26475597","title":"Succinate-CoA ligase deficiency due to mutations in SUCLA2 and SUCLG1: phenotype and genotype correlations in 71 patients.","date":"2015","source":"Journal of inherited metabolic disease","url":"https://pubmed.ncbi.nlm.nih.gov/26475597","citation_count":71,"is_preprint":false},{"pmid":"19526370","id":"PMC_19526370","title":"A novel missense mutation in SUCLG1 associated with mitochondrial DNA depletion, encephalomyopathic form, with methylmalonic aciduria.","date":"2009","source":"European journal of pediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/19526370","citation_count":42,"is_preprint":false},{"pmid":"20693550","id":"PMC_20693550","title":"The severity of phenotype linked to SUCLG1 mutations could be correlated with residual amount of SUCLG1 protein.","date":"2010","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20693550","citation_count":41,"is_preprint":false},{"pmid":"20197121","id":"PMC_20197121","title":"New SUCLG1 patients expanding the phenotypic spectrum of this rare cause of mild methylmalonic aciduria.","date":"2010","source":"Mitochondrion","url":"https://pubmed.ncbi.nlm.nih.gov/20197121","citation_count":33,"is_preprint":false},{"pmid":"38649537","id":"PMC_38649537","title":"SUCLG1 restricts POLRMT succinylation to enhance mitochondrial biogenesis and leukemia progression.","date":"2024","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/38649537","citation_count":30,"is_preprint":false},{"pmid":"20227526","id":"PMC_20227526","title":"Marked mitochondrial DNA depletion associated with a novel SUCLG1 gene mutation resulting in lethal neonatal acidosis, multi-organ failure, and interrupted aortic arch.","date":"2010","source":"Mitochondrion","url":"https://pubmed.ncbi.nlm.nih.gov/20227526","citation_count":27,"is_preprint":false},{"pmid":"30470562","id":"PMC_30470562","title":"Mutated SUCLG1 causes mislocalization of SUCLG2 protein, morphological alterations of mitochondria and an early-onset severe neurometabolic disorder.","date":"2018","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/30470562","citation_count":25,"is_preprint":false},{"pmid":"21639866","id":"PMC_21639866","title":"Neonatal lactic acidosis with methylmalonic aciduria due to novel mutations in the SUCLG1 gene.","date":"2011","source":"Pediatrics international : official journal of the Japan Pediatric Society","url":"https://pubmed.ncbi.nlm.nih.gov/21639866","citation_count":20,"is_preprint":false},{"pmid":"27484306","id":"PMC_27484306","title":"Expanding the phenotypic spectrum of Succinyl-CoA ligase deficiency through functional validation of a new SUCLG1 variant.","date":"2016","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/27484306","citation_count":16,"is_preprint":false},{"pmid":"27896121","id":"PMC_27896121","title":"A SUCLG1 mutation in a patient with mitochondrial DNA depletion and congenital anomalies.","date":"2014","source":"Molecular genetics and metabolism reports","url":"https://pubmed.ncbi.nlm.nih.gov/27896121","citation_count":15,"is_preprint":false},{"pmid":"21093335","id":"PMC_21093335","title":"Fatal infantile lactic acidosis and a novel homozygous mutation in the SUCLG1 gene: a mitochondrial DNA depletion disorder.","date":"2010","source":"Molecular genetics and metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/21093335","citation_count":15,"is_preprint":false},{"pmid":"33230783","id":"PMC_33230783","title":"SUCLG1 mutations and mitochondrial encephalomyopathy: a case study and review of the literature.","date":"2020","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/33230783","citation_count":10,"is_preprint":false},{"pmid":"26028457","id":"PMC_26028457","title":"Five novel SUCLG1 mutations in three Chinese patients with succinate-CoA ligase deficiency noticed by mild methylmalonic aciduria.","date":"2015","source":"Brain & development","url":"https://pubmed.ncbi.nlm.nih.gov/26028457","citation_count":10,"is_preprint":false},{"pmid":"29217198","id":"PMC_29217198","title":"Clinical, Molecular, and Computational Analysis in two cases with mitochondrial encephalomyopathy associated with SUCLG1 mutation in a consanguineous family.","date":"2017","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/29217198","citation_count":9,"is_preprint":false},{"pmid":"35762302","id":"PMC_35762302","title":"Novel compound heterozygous SUCLG1 variants may contribute to mitochondria DNA depletion syndrome-9.","date":"2022","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/35762302","citation_count":5,"is_preprint":false},{"pmid":"39749698","id":"PMC_39749698","title":"SUCLG1 promotes aerobic respiration and progression in plexiform neurofibroma.","date":"2025","source":"International journal of 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debutyrylation of SUCLG1 rescues myocardial energy failure in HFpEF: Ginsenoside Rb3 as a novel SIRT4-interacting regulator.","date":"2026","source":"Pharmacological research","url":"https://pubmed.ncbi.nlm.nih.gov/41991142","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.05.29.656916","title":"Reverse remodelling of the mitochondria and cytoskeleton after respiratory heart rate variability pacing of the failing sheep heart","date":"2025-05-30","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.29.656916","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12224,"output_tokens":2019,"usd":0.033479,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9014,"output_tokens":2809,"usd":0.057647,"stage2_stop_reason":"end_turn"},"total_usd":0.091126,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"SUCLG1 encodes the alpha subunit of succinate-CoA ligase (SUCL), a heterodimer in the mitochondrial matrix that catalyzes the reversible conversion of succinyl-CoA to succinate; in the absence of SUCLG1 protein, SUCLA2 protein is also absent in fibroblasts (by western blot), consistent with degradation of the beta subunit when its heterodimer partner is missing.\",\n      \"method\": \"Western blot analysis of patient fibroblasts; minigene expression system to confirm splice mutation\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — western blot and minigene assay in patient fibroblasts, single lab, two orthogonal methods confirming protein interdependence\",\n      \"pmids\": [\"20693550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Pathogenic mutation in SUCLG1 (p.Ala209Glu) abolishes SUCLG1 protein, strongly reduces SUCLA2 and SUCLG2 protein levels, impairs mitochondrial substrate-level phosphorylation (mSLP) in fibroblasts, and causes mislocalization of SUCLG2 away from the mitochondrial network along with increased mitochondrial fragmentation, without changes in mtDNA levels or respiratory complex activities when standard substrates are used.\",\n      \"method\": \"Immunoblot, confocal immunocytochemistry, oxygen consumption/extracellular acidification rate assay, enzyme activity assay in patient fibroblasts\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (immunoblot, confocal imaging, respirometry, enzyme assay) in a single lab on patient-derived cells\",\n      \"pmids\": [\"30470562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of SUCLG1 protein in patient fibroblasts leads to significantly reduced SUCLA2 and SUCLG2 protein levels, essentially undetectable SCS enzyme activity, mtDNA depletion, and cellular respiration defects; ectopic expression of wild-type SUCLG1 rescues all these abnormal phenotypes, functionally confirming SUCLG1 as necessary for SUCL complex stability and activity.\",\n      \"method\": \"Western blot, SCS enzyme activity assay, mtDNA quantification, cellular respiration assay, rescue by ectopic WT SUCLG1 expression in patient fibroblasts\",\n      \"journal\": \"Molecular genetics and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods plus genetic rescue experiment confirming mechanistic role, single lab but rigorous design\",\n      \"pmids\": [\"27484306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SUCLG1 restricts succinyl-CoA levels to suppress succinylation of mitochondrial RNA polymerase (POLRMT) at lysine 622; this succinylation disrupts POLRMT interaction with mtDNA and mitochondrial transcription factors, while SUCLG1-mediated POLRMT hyposuccinylation maintains mtDNA transcription and mitochondrial biogenesis. FLT3 mutations upregulate SUCLG1 expression to reduce succinyl-CoA and POLRMT succinylation, enhancing mitobiogenesis and leukemia progression.\",\n      \"method\": \"Succinylation site mapping (K622), co-immunoprecipitation of POLRMT with mtDNA and transcription factors, genetic depletion of SUCLG1 and POLRMT in mouse and humanized leukemia models, succinyl-CoA and POLRMT succinylation measurement in FLT3-mutated clinical samples\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — site-specific PTM identification, Co-IP, in vivo genetic models, and clinical sample validation across multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"38649537\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SUCLG1 is hyperbutyrylated at lysine K90 in a mouse HFpEF model, which impairs its enzymatic function in the TCA cycle, resulting in reduced succinate and ATP production. SIRT4 acts as a debutyrylase for SUCLG1-K90, and downregulated SIRT4 leads to SUCLG1 hyperbutyrylation; restoration of SIRT4 activity (by ginsenoside Rb3 binding) reverses SUCLG1 hyperbutyrylation and restores TCA cycle flux.\",\n      \"method\": \"Butyrylome proteomic screening, SIRT4 inhibitor and overexpression experiments, metabolite (succinate, ATP) measurement, in vivo HFpEF mouse model and in vitro cellular model\",\n      \"journal\": \"Pharmacological research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — PTM site identified by proteomics with functional validation via enzyme inhibitor/overexpression, single lab, multiple methods\",\n      \"pmids\": [\"41991142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SUCLG1 promotes mitochondrial quality, mitochondrial fusion, aerobic respiration (without affecting glycolysis), and proliferation/migration of plexiform neurofibroma cells; knockdown reduces these effects, and elevated SUCLG1 upregulates SLC25A1 expression.\",\n      \"method\": \"SUCLG1 knockdown and overexpression, Seahorse assay, western blotting, immunofluorescence, electron microscopy, flow cytometry, qPCR in PNF cell lines\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — multiple orthogonal functional assays in a single lab with KD/OE, but pathway placement is limited and SLC25A1 regulation is a single indirect observation\",\n      \"pmids\": [\"39749698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In silico and computational analysis predicted that the SUCLG1 p.M14T mutation (located at the mitochondrial targeting sequence) alters protein stability and mitochondrial translocation; mtDNA copy number was reduced in patients' peripheral blood leukocytes.\",\n      \"method\": \"In silico structural/stability prediction, real-time PCR for mtDNA quantification in patient blood\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — primarily computational prediction with supporting qPCR; no direct functional validation of mitochondrial import defect\",\n      \"pmids\": [\"29217198\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SUCLG1 encodes the alpha subunit of the mitochondrial succinate-CoA ligase (SUCL) heterodimer, which is required for the stability of the beta subunits (SUCLA2 and SUCLG2); beyond its canonical TCA cycle role, SUCLG1 controls succinyl-CoA levels to restrict succinylation of POLRMT at K622—thereby sustaining mtDNA transcription and mitochondrial biogenesis—and its own enzymatic activity is regulated by SIRT4-dependent debutyrylation at K90, linking metabolic flux to post-translational control of mitochondrial function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SUCLG1 encodes the alpha subunit of the mitochondrial matrix succinate-CoA ligase (SUCL), a heterodimer that catalyzes the reversible conversion of succinyl-CoA to succinate and thereby contributes to mitochondrial substrate-level phosphorylation [#0, #1]. SUCLG1 is structurally indispensable to the complex: loss of SUCLG1 protein leads to concurrent loss of the partner beta subunits SUCLA2 and SUCLG2, abolished SCS enzyme activity, mtDNA depletion, and respiration defects, all of which are reversed by ectopic wild-type SUCLG1, establishing SUCLG1 as required for SUCL stability and function [#2]. Pathogenic SUCLG1 mutations cause this loss of SUCL, impairing mitochondrial substrate-level phosphorylation and producing SUCLG2 mislocalization with increased mitochondrial fragmentation [#1]. Beyond its catalytic role, SUCLG1 governs the succinyl-CoA pool to restrict succinylation of mitochondrial RNA polymerase POLRMT at K622; by keeping POLRMT hyposuccinylated it preserves POLRMT engagement with mtDNA and transcription factors, sustaining mtDNA transcription and mitochondrial biogenesis—a circuit exploited by FLT3-mutant leukemia, which upregulates SUCLG1 to drive mitobiogenesis and disease progression [#3]. SUCLG1 enzymatic activity is itself subject to acyl-lysine regulation, with hyperbutyrylation at K90 impairing TCA flux and SIRT4 acting as the debutyrylase that restores activity [#4]. SUCLG1 supports mitochondrial fusion, mitochondrial quality, and aerobic respiration in proliferating tumor cells [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 2010,\n      \"claim\": \"Established that SUCLG1 is the alpha subunit of mitochondrial succinate-CoA ligase and that the complex is interdependent, since loss of SUCLG1 also eliminates the SUCLA2 beta subunit.\",\n      \"evidence\": \"Western blot and minigene splice analysis in patient fibroblasts\",\n      \"pmids\": [\"20693550\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not directly measure enzyme activity loss\", \"Interdependence with SUCLG2 not yet examined\", \"Mechanism of beta-subunit degradation not defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated through genetic rescue that SUCLG1 is necessary for SUCL complex stability, SCS enzyme activity, mtDNA maintenance, and respiration, moving beyond correlation to causation.\",\n      \"evidence\": \"Western blot, SCS activity assay, mtDNA quantification, respiration assay, and ectopic WT SUCLG1 rescue in patient fibroblasts\",\n      \"pmids\": [\"27484306\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking SUCL loss to mtDNA depletion not resolved\", \"Single patient-derived cell background\", \"No structural basis for complex stabilization\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected a specific pathogenic mutation to functional consequences, showing SUCLG1 loss reduces both beta subunits, impairs substrate-level phosphorylation, and disrupts mitochondrial morphology.\",\n      \"evidence\": \"Immunoblot, confocal imaging, respirometry, and enzyme assays in patient fibroblasts carrying p.Ala209Glu\",\n      \"pmids\": [\"30470562\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal link between SUCL loss and SUCLG2 mislocalization unexplained\", \"mtDNA levels and standard complex activities unchanged here, contrasting earlier findings\", \"Mechanism of mitochondrial fragmentation not defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a non-canonical regulatory role: SUCLG1 controls the succinyl-CoA pool to limit POLRMT K622 succinylation, thereby sustaining mtDNA transcription and mitochondrial biogenesis, a circuit hijacked in FLT3-mutant leukemia.\",\n      \"evidence\": \"Succinylation site mapping, POLRMT Co-IP with mtDNA and transcription factors, genetic depletion in mouse/humanized leukemia models, and clinical FLT3-mutant sample analysis\",\n      \"pmids\": [\"38649537\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether non-enzymatic succinyl-CoA buffering is the sole mechanism not established\", \"Generality beyond leukemia contexts untested\", \"Direct enzyme writer for POLRMT succinylation not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed SUCLG1 supports mitochondrial fusion, quality, aerobic respiration, and tumor cell proliferation/migration in plexiform neurofibroma, extending its role into mitochondrial dynamics and cancer cell metabolism.\",\n      \"evidence\": \"Knockdown/overexpression with Seahorse, immunofluorescence, electron microscopy, flow cytometry, and qPCR in PNF cell lines\",\n      \"pmids\": [\"39749698\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SLC25A1 regulation is a single indirect observation\", \"Mechanism connecting SUCLG1 to fusion machinery unknown\", \"Pathway placement limited to one tumor model\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified acyl-lysine control of SUCLG1 enzymatic activity, with K90 hyperbutyrylation impairing TCA flux and SIRT4 acting as the debutyrylase that restores it, linking metabolic signaling to SUCLG1 function in heart failure.\",\n      \"evidence\": \"Butyrylome proteomics, SIRT4 inhibitor/overexpression, succinate/ATP measurement in HFpEF mouse and cellular models\",\n      \"pmids\": [\"41991142\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that K90 butyrylation alters catalysis at the structural level absent\", \"Butyryl-CoA source and writer enzyme not identified\", \"Generality beyond HFpEF context untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SUCLG1's catalytic and succinyl-CoA-buffering activities are integrated across tissues, and the structural basis for both complex stabilization and PTM-dependent regulation, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model integrating heterodimer assembly with K90/K622 PTM regulation\", \"Mechanism by which SUCL loss causes mtDNA depletion versus normal mtDNA in different studies unreconciled\", \"Writer enzymes for SUCLG1 and POLRMT acylation unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2, 4]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [\"succinate-CoA ligase (SUCL)\"],\n    \"partners\": [\"SUCLA2\", \"SUCLG2\", \"POLRMT\", \"SIRT4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}