{"gene":"PPTC7","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2019,"finding":"Pptc7 is a mitochondrial matrix phosphatase essential for mitochondrial biogenesis and metabolism; knockout mice die shortly after birth with hypoketotic hypoglycemia, elevated acylcarnitines, diminished mitochondrial size and protein content, and aberrantly elevated phosphorylation on select mitochondrial proteins despite normal transcript levels.","method":"CRISPR-Cas9 knockout mice, phosphoproteomics, mitochondrial fractionation","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout with multiple orthogonal metabolic and molecular readouts, replicated across tissues","pmids":["31324765"],"is_preprint":false},{"year":2019,"finding":"The protein translocase subunit Timm50 is identified as a putative Pptc7 substrate; its phosphorylation reduces mitochondrial import activity, and phosphorylation within or near mitochondrial targeting sequences of multiple proteins disrupts their import rates and matrix processing.","method":"Phosphoproteomics, in vitro import assay, Pptc7 knockout mice","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — phosphoproteomics and import assay in single study, Timm50 identified as putative substrate without full in vitro dephosphorylation reconstitution","pmids":["31324765"],"is_preprint":false},{"year":2018,"finding":"PPTC7 is a bona fide protein phosphatase that directly dephosphorylates COQ7 in vitro, and controls cellular CoQ10 content; PPTC7 expression/activity facilitates human cell adaptation to respiratory conditions and starvation by regulating CoQ10 biosynthesis.","method":"In vitro phosphatase assay, PPTC7 overexpression and knockdown, CoQ10 quantification","journal":"Biochimica et biophysica acta. Bioenergetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro phosphatase assay demonstrating direct dephosphorylation, corroborated by expression modulation experiments in human cells","pmids":["30267671"],"is_preprint":false},{"year":2023,"finding":"Loss of Pptc7 in adult mice causes marked reduction in mitochondrial mass and elevated BNIP3 and NIX mitophagy receptors; Pptc7-/- MEFs display a major increase in mitophagy that is reversed upon deletion of BNIP3 and NIX, and PPTC7 directly interacts with and dephosphorylates BNIP3 and NIX.","method":"Inducible knockout mice, MEF double-knockout genetic rescue, phosphoproteomics, Co-IP, in vitro dephosphorylation assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis (double KO rescue), direct interaction by Co-IP, phosphoproteomics across multiple tissue types, multiple orthogonal methods","pmids":["37833277"],"is_preprint":false},{"year":2023,"finding":"PPTC7 knockout causes perinatal lethality in mice that is rescued by NIX knockout, establishing a genetic epistasis relationship; the PPTC7 precursor is trapped by BNIP3 and NIX at the mitochondrial outer membrane, where PPTC7 scaffolds assembly of a substrate-PPTC7-SCFFBXL4 holocomplex to promote degradation of BNIP3 and NIX. PPTC7 possesses an unusually weak mitochondrial targeting sequence that facilitates its outer membrane retention.","method":"Genetic rescue in mice (NIX KO x PPTC7 KO), biochemical fractionation, Co-IP, protein stability assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic rescue with double-KO mice plus biochemical reconstitution of holocomplex, multiple orthogonal methods","pmids":["38151018"],"is_preprint":false},{"year":2024,"finding":"PPTC7 is dual-localized to the outer mitochondrial membrane (OMM) and the matrix; anchoring PPTC7 to the OMM is sufficient to suppress BNIP3 and NIX accumulation. PPTC7-mediated suppression requires an intact PP2C catalytic motif but is independent of full mitochondrial matrix targeting. Proximity labeling and fluorescence co-localization show dynamic associations of PPTC7 with BNIP3 and NIX that are enhanced under conditions promoting their turnover.","method":"Fluorescence co-localization, proximity labeling (BioID), organelle fractionation, catalytic mutant overexpression, chimeric OMM-anchored PPTC7 construct","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal localization and functional methods (proximity labeling, live-cell imaging, domain mutagenesis) in a single study","pmids":["38991726"],"is_preprint":false},{"year":2025,"finding":"PPTC7 acts as a co-factor of the SCFFBXL4 E3 ubiquitin ligase complex at the outer mitochondrial membrane, interacting with FBXL4 and BNIP3/3L; PPTC7 facilitates SCFFBXL4-mediated ubiquitin-proteasomal degradation of BNIP3/3L in a phosphatase activity-independent manner.","method":"Co-IP, in vitro cell culture, Pptc7 knockout mouse model, ubiquitination assay, phosphatase-dead mutant","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating direct FBXL4 interaction, phosphatase-dead mutant showing activity-independence, in vivo KO corroboration","pmids":["40025034"],"is_preprint":false},{"year":2025,"finding":"PPTC7 has a non-mitochondrial role: it interacts with and dephosphorylates VPS4A (an ESCRT-associated ATPase) at serine 335; this dephosphorylation is required for VPS4A stability and its localization to early endosomes. Loss of PPTC7 or constitutively phosphorylated VPS4A causes defective EGFR recycling, re-routing EGFR to lysosomes, and impairs AKT signaling and cell proliferation/migration.","method":"Co-IP, in vitro dephosphorylation, phosphomimetic/phosphodead mutants, subcellular fractionation/localization, EGFR trafficking assay, cell proliferation/migration assay","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro phosphatase assay on VPS4A-S335, Co-IP, phosphomutant functional rescue, multiple orthogonal readouts in a single study","pmids":["39776116"],"is_preprint":false},{"year":2025,"finding":"PPTC7 interacts with prohibitin 2 (PHB2) as identified by mass spectrometry and Co-IP; PPTC7 promotes ubiquitin-proteasome-mediated degradation of PHB2, disrupting mitochondrial function in brain microvascular endothelial cells.","method":"Mass spectrometry, Co-immunoprecipitation, shRNA knockdown, ubiquitination assay","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — Co-IP and ubiquitination data from single study; mechanism of PPTC7-driven PHB2 degradation not fully reconstituted","pmids":["41496208"],"is_preprint":false},{"year":2026,"finding":"The PPTC7 missense variant p.D158N, affecting a conserved metal-binding residue, disrupts both enzymatic phosphatase activity and PPTC7's ability to negatively regulate BNIP3 and NIX, establishing that metal coordination is required for full PPTC7 function; patient fibroblasts and CRISPR knock-in cells show excessive BNIP3/NIX-mediated mitophagy rescued by exogenous wild-type PPTC7 expression.","method":"Patient fibroblasts, CRISPR knock-in cell models, mt-Keima mitophagy flux assay, rescue with exogenous PPTC7, enzymatic phosphatase assay","journal":"Research square","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional patient variants with cellular rescue, but single preprint study without independent replication","pmids":["41756425"],"is_preprint":true}],"current_model":"PPTC7 is a dual-localized PP2C-type phosphatase that resides in both the mitochondrial matrix and the outer mitochondrial membrane (OMM); in the matrix it dephosphorylates substrates such as COQ7 (to regulate CoQ10 biosynthesis) and Timm50 (to support mitochondrial protein import), while at the OMM it scaffolds assembly of a substrate-PPTC7-SCFFBXL4 holocomplex that promotes ubiquitin-proteasomal degradation of the mitophagy receptors BNIP3 and NIX, thereby suppressing receptor-mediated mitophagy and maintaining mitochondrial mass; outside mitochondria, PPTC7 also dephosphorylates VPS4A at S335 to support EGFR recycling and AKT signaling."},"narrative":{"mechanistic_narrative":"PPTC7 is a dual-localized PP2C-type protein phosphatase that governs mitochondrial mass and metabolism through both catalytic and scaffolding functions [PMID:31324765, PMID:38991726]. In the mitochondrial matrix it is essential for biogenesis and metabolic homeostasis: its loss in mice causes perinatal lethality with hypoketotic hypoglycemia, elevated acylcarnitines, reduced mitochondrial content, and hyperphosphorylation of select mitochondrial proteins [PMID:31324765]. Among its matrix-relevant activities, PPTC7 directly dephosphorylates COQ7 to control cellular CoQ10 content and adaptation to respiratory and starvation conditions [PMID:30267671], and dephosphorylates the import translocase subunit Timm50 to support mitochondrial protein import [PMID:31324765]. At the outer mitochondrial membrane—where an unusually weak targeting sequence promotes its retention—PPTC7 directly binds and suppresses the mitophagy receptors BNIP3 and NIX, restraining receptor-mediated mitophagy; double deletion of BNIP3 and NIX, or NIX knockout alone, reverses the excess mitophagy and rescues the lethality of PPTC7 loss [PMID:37833277, PMID:38151018]. Mechanistically, PPTC7 acts as a co-factor of the SCFFBXL4 E3 ubiquitin ligase, scaffolding a substrate-PPTC7-SCFFBXL4 holocomplex that drives ubiquitin-proteasomal degradation of BNIP3/NIX in a manner independent of its phosphatase activity [PMID:38151018, PMID:40025034]. Beyond mitochondria, PPTC7 dephosphorylates VPS4A at serine 335 to maintain VPS4A stability and endosomal localization, thereby supporting EGFR recycling, AKT signaling, and cell proliferation and migration [PMID:39776116]. A patient-derived missense variant (p.D158N) at a conserved metal-coordinating residue disrupts both phosphatase activity and BNIP3/NIX regulation, causing excessive mitophagy in patient fibroblasts that is rescued by wild-type PPTC7 [PMID:41756425].","teleology":[{"year":2018,"claim":"Established that PPTC7 is a genuine catalytic phosphatase with a defined substrate, answering whether it acts enzymatically and linking it to a metabolic output (CoQ10 biosynthesis).","evidence":"In vitro phosphatase assay on COQ7 plus expression modulation and CoQ10 quantification in human cells","pmids":["30267671"],"confidence":"High","gaps":["Did not establish in vivo physiological requirement","Other matrix substrates not yet defined"]},{"year":2019,"claim":"Defined PPTC7 as a matrix phosphatase essential for mitochondrial biogenesis in vivo and implicated it in regulating protein import via phosphorylation of targeting sequences.","evidence":"CRISPR-Cas9 knockout mice with phosphoproteomics, mitochondrial fractionation, and in vitro import assays identifying Timm50 as a putative substrate","pmids":["31324765"],"confidence":"High","gaps":["Timm50 not confirmed by full in vitro dephosphorylation reconstitution","Causal substrate driving the lethal metabolic phenotype unresolved"]},{"year":2023,"claim":"Revealed that PPTC7 loss drives mitochondrial depletion through unleashed receptor-mediated mitophagy, identifying BNIP3 and NIX as direct interactors and the relevant effectors.","evidence":"Inducible knockout mice, MEF BNIP3/NIX double-knockout genetic rescue, phosphoproteomics, Co-IP, and in vitro dephosphorylation","pmids":["37833277"],"confidence":"High","gaps":["Whether dephosphorylation versus other mechanism controls receptor turnover not resolved","Subcellular site of action not yet localized"]},{"year":2023,"claim":"Showed that PPTC7 functions at the outer membrane as a scaffold within an SCFFBXL4 holocomplex that degrades BNIP3/NIX, and that NIX knockout rescues PPTC7-null lethality, defining the genetic epistasis.","evidence":"NIX-KO x PPTC7-KO genetic rescue, biochemical fractionation, Co-IP, and protein stability assays","pmids":["38151018"],"confidence":"High","gaps":["Stoichiometry and assembly order of the holocomplex not fully defined","How precursor trapping at OMM is regulated unclear"]},{"year":2024,"claim":"Resolved the localization question by showing dual OMM/matrix distribution and that OMM anchoring alone suffices to suppress BNIP3/NIX, separating the receptor-regulating function from matrix targeting.","evidence":"Proximity labeling (BioID), fluorescence co-localization, organelle fractionation, catalytic mutant and chimeric OMM-anchored constructs","pmids":["38991726"],"confidence":"High","gaps":["Determinants partitioning PPTC7 between matrix and OMM not fully mapped","Dynamics of receptor association under physiological stress incomplete"]},{"year":2025,"claim":"Defined PPTC7's mechanistic role in the SCFFBXL4 complex as a phosphatase-independent co-factor promoting ubiquitin-proteasomal degradation of BNIP3/3L.","evidence":"Co-IP with FBXL4 and BNIP3/3L, ubiquitination assays, phosphatase-dead mutant, and Pptc7 knockout mouse corroboration","pmids":["40025034"],"confidence":"High","gaps":["Structural basis of PPTC7-FBXL4 cooperation unknown","Reconciliation of catalytic versus scaffold contributions to receptor regulation not settled"]},{"year":2025,"claim":"Extended PPTC7 function beyond mitochondria by identifying VPS4A-S335 as a substrate whose dephosphorylation supports endosomal trafficking, EGFR recycling, and AKT signaling.","evidence":"Co-IP, in vitro dephosphorylation, phosphomimetic/phosphodead mutants, subcellular localization, EGFR trafficking and proliferation/migration assays","pmids":["39776116"],"confidence":"High","gaps":["How a mitochondrially-associated phosphatase accesses cytosolic VPS4A not explained","Physiological context of this non-mitochondrial role in vivo unaddressed"]},{"year":2025,"claim":"Reported a PPTC7-PHB2 interaction with PPTC7 promoting PHB2 degradation, extending its degradation-promoting activity to another mitochondrial protein.","evidence":"Mass spectrometry, Co-IP, shRNA knockdown, and ubiquitination assay in brain microvascular endothelial cells","pmids":["41496208"],"confidence":"Medium","gaps":["Mechanism of PPTC7-driven PHB2 degradation not reconstituted","Single study, no reciprocal or in vivo validation"]},{"year":2026,"claim":"Linked PPTC7 to human disease by showing a metal-binding-residue variant abolishes both phosphatase activity and BNIP3/NIX regulation, causing pathological mitophagy rescued by wild-type protein.","evidence":"Patient fibroblasts, CRISPR knock-in cells, mt-Keima mitophagy flux, enzymatic assay, and exogenous PPTC7 rescue (preprint)","pmids":["41756425"],"confidence":"Medium","gaps":["Single preprint without independent replication","Full clinical spectrum and genotype-phenotype correlation undefined"]},{"year":null,"claim":"How PPTC7 balances its catalytic (COQ7, Timm50, VPS4A) and non-catalytic scaffolding (SCFFBXL4) functions across compartments, and what determines its partitioning and substrate selection, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of compartment-specific complexes","Mechanism setting matrix-versus-OMM localization incompletely defined","Full in vivo substrate repertoire unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,3,7]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[2,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,6]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,5]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[7]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,6]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[7]}],"complexes":["SCFFBXL4 E3 ubiquitin ligase complex"],"partners":["BNIP3","BNIP3L/NIX","FBXL4","COQ7","TIMM50","VPS4A","PHB2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NI37","full_name":"Protein phosphatase PTC7 homolog","aliases":["T-cell activation protein phosphatase 2C","TA-PP2C","T-cell activation protein phosphatase 2C-like"],"length_aa":304,"mass_kda":32.6,"function":"Protein phosphatase that plays an essential role in mitochondrial metabolism and biogenesis (PubMed:30267671). Positively regulates biosynthesis of the ubiquinone, coenzyme Q (PubMed:30267671). Dephosphorylates the ubiquinone biosynthesis protein COQ7 which is likely to lead to its activation (PubMed:30267671). Serves as a crucial sensor for mitophagy, though the underlying mechanism remains ambiguous (By similarity). May dephosphorylate BNIP3 and NIX and thereby directly regulates mitophagy receptor function and stability (By similarity). Alternatively, promotes SCF-FBXL4-dependent ubiquitination and degradation of BNIP3 and NIX independently of its catalytic activity to restrain mitophagy (PubMed:38992176)","subcellular_location":"Mitochondrion matrix","url":"https://www.uniprot.org/uniprotkb/Q8NI37/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PPTC7","classification":"Not Classified","n_dependent_lines":49,"n_total_lines":1208,"dependency_fraction":0.04056291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PPTC7","total_profiled":1310},"omim":[{"mim_id":"609668","title":"PROTEIN PHOSPHATASE TARGETING COQ7; PPTC7","url":"https://www.omim.org/entry/609668"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"tongue","ntpm":130.9}],"url":"https://www.proteinatlas.org/search/PPTC7"},"hgnc":{"alias_symbol":["TA-PP2C"],"prev_symbol":[]},"alphafold":{"accession":"Q8NI37","domains":[{"cath_id":"3.60.40.10","chopping":"33-223_241-258_291-300","consensus_level":"high","plddt":93.8869,"start":33,"end":300}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NI37","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NI37-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NI37-F1-predicted_aligned_error_v6.png","plddt_mean":88.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPTC7","jax_strain_url":"https://www.jax.org/strain/search?query=PPTC7"},"sequence":{"accession":"Q8NI37","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NI37.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NI37/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NI37"}},"corpus_meta":[{"pmid":"38151018","id":"PMC_38151018","title":"A mitophagy sensor PPTC7 controls BNIP3 and NIX degradation to regulate mitochondrial mass.","date":"2023","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/38151018","citation_count":67,"is_preprint":false},{"pmid":"31324765","id":"PMC_31324765","title":"Pptc7 is an essential phosphatase for promoting mammalian mitochondrial metabolism and biogenesis.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/31324765","citation_count":54,"is_preprint":false},{"pmid":"30267671","id":"PMC_30267671","title":"The mitochondrial phosphatase PPTC7 orchestrates mitochondrial metabolism regulating coenzyme Q10 biosynthesis.","date":"2018","source":"Biochimica et biophysica acta. Bioenergetics","url":"https://pubmed.ncbi.nlm.nih.gov/30267671","citation_count":29,"is_preprint":false},{"pmid":"37833277","id":"PMC_37833277","title":"PPTC7 maintains mitochondrial protein content by suppressing receptor-mediated mitophagy.","date":"2023","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/37833277","citation_count":24,"is_preprint":false},{"pmid":"38991726","id":"PMC_38991726","title":"Dual-localized PPTC7 limits mitophagy through proximal and dynamic interactions with BNIP3 and NIX.","date":"2024","source":"Life science alliance","url":"https://pubmed.ncbi.nlm.nih.gov/38991726","citation_count":13,"is_preprint":false},{"pmid":"40025034","id":"PMC_40025034","title":"PPTC7 acts as an essential co-factor of the SCFFBXL4 ubiquitin ligase complex to restrict BNIP3/3L-dependent mitophagy.","date":"2025","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/40025034","citation_count":4,"is_preprint":false},{"pmid":"36909604","id":"PMC_36909604","title":"Pptc7 maintains mitochondrial protein content by suppressing receptor-mediated mitophagy.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/36909604","citation_count":2,"is_preprint":false},{"pmid":"38328188","id":"PMC_38328188","title":"PPTC7 limits mitophagy through proximal and dynamic interactions with BNIP3 and NIX.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/38328188","citation_count":1,"is_preprint":false},{"pmid":"39776116","id":"PMC_39776116","title":"Mitochondrial phosphatase PPTC7 promotes EGFR recycling by facilitating VPS4A endosomal localization.","date":"2025","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/39776116","citation_count":1,"is_preprint":false},{"pmid":"41496208","id":"PMC_41496208","title":"Upregulation of PPTC7 in brain microvascular endothelial cell aggravates diabetic cognitive dysfunction by impairing PHB2 mediated mitochondrial function.","date":"2025","source":"Redox biology","url":"https://pubmed.ncbi.nlm.nih.gov/41496208","citation_count":0,"is_preprint":false},{"pmid":"41756425","id":"PMC_41756425","title":"Recessive PPTC7 deficiency triggers excessive mitophagy to cause a severe inborn error of metabolism with hypomyelinating leukodystrophy.","date":"2026","source":"Research square","url":"https://pubmed.ncbi.nlm.nih.gov/41756425","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.06.20.599818","title":"PPTC7 acts as an essential co-factor of the SCF  <sup>FBXL4</sup>  ubiquitin ligase complex to restrict BNIP3/BNIP3L-dependent mitophagy","date":"2024-06-21","source":"bioRxiv","url":"https://doi.org/10.1101/2024.06.20.599818","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8121,"output_tokens":2739,"usd":0.032724,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9932,"output_tokens":3634,"usd":0.070255,"stage2_stop_reason":"end_turn"},"total_usd":0.102979,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2019,\n      \"finding\": \"Pptc7 is a mitochondrial matrix phosphatase essential for mitochondrial biogenesis and metabolism; knockout mice die shortly after birth with hypoketotic hypoglycemia, elevated acylcarnitines, diminished mitochondrial size and protein content, and aberrantly elevated phosphorylation on select mitochondrial proteins despite normal transcript levels.\",\n      \"method\": \"CRISPR-Cas9 knockout mice, phosphoproteomics, mitochondrial fractionation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout with multiple orthogonal metabolic and molecular readouts, replicated across tissues\",\n      \"pmids\": [\"31324765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The protein translocase subunit Timm50 is identified as a putative Pptc7 substrate; its phosphorylation reduces mitochondrial import activity, and phosphorylation within or near mitochondrial targeting sequences of multiple proteins disrupts their import rates and matrix processing.\",\n      \"method\": \"Phosphoproteomics, in vitro import assay, Pptc7 knockout mice\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — phosphoproteomics and import assay in single study, Timm50 identified as putative substrate without full in vitro dephosphorylation reconstitution\",\n      \"pmids\": [\"31324765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PPTC7 is a bona fide protein phosphatase that directly dephosphorylates COQ7 in vitro, and controls cellular CoQ10 content; PPTC7 expression/activity facilitates human cell adaptation to respiratory conditions and starvation by regulating CoQ10 biosynthesis.\",\n      \"method\": \"In vitro phosphatase assay, PPTC7 overexpression and knockdown, CoQ10 quantification\",\n      \"journal\": \"Biochimica et biophysica acta. Bioenergetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphatase assay demonstrating direct dephosphorylation, corroborated by expression modulation experiments in human cells\",\n      \"pmids\": [\"30267671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Loss of Pptc7 in adult mice causes marked reduction in mitochondrial mass and elevated BNIP3 and NIX mitophagy receptors; Pptc7-/- MEFs display a major increase in mitophagy that is reversed upon deletion of BNIP3 and NIX, and PPTC7 directly interacts with and dephosphorylates BNIP3 and NIX.\",\n      \"method\": \"Inducible knockout mice, MEF double-knockout genetic rescue, phosphoproteomics, Co-IP, in vitro dephosphorylation assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis (double KO rescue), direct interaction by Co-IP, phosphoproteomics across multiple tissue types, multiple orthogonal methods\",\n      \"pmids\": [\"37833277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PPTC7 knockout causes perinatal lethality in mice that is rescued by NIX knockout, establishing a genetic epistasis relationship; the PPTC7 precursor is trapped by BNIP3 and NIX at the mitochondrial outer membrane, where PPTC7 scaffolds assembly of a substrate-PPTC7-SCFFBXL4 holocomplex to promote degradation of BNIP3 and NIX. PPTC7 possesses an unusually weak mitochondrial targeting sequence that facilitates its outer membrane retention.\",\n      \"method\": \"Genetic rescue in mice (NIX KO x PPTC7 KO), biochemical fractionation, Co-IP, protein stability assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic rescue with double-KO mice plus biochemical reconstitution of holocomplex, multiple orthogonal methods\",\n      \"pmids\": [\"38151018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PPTC7 is dual-localized to the outer mitochondrial membrane (OMM) and the matrix; anchoring PPTC7 to the OMM is sufficient to suppress BNIP3 and NIX accumulation. PPTC7-mediated suppression requires an intact PP2C catalytic motif but is independent of full mitochondrial matrix targeting. Proximity labeling and fluorescence co-localization show dynamic associations of PPTC7 with BNIP3 and NIX that are enhanced under conditions promoting their turnover.\",\n      \"method\": \"Fluorescence co-localization, proximity labeling (BioID), organelle fractionation, catalytic mutant overexpression, chimeric OMM-anchored PPTC7 construct\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal localization and functional methods (proximity labeling, live-cell imaging, domain mutagenesis) in a single study\",\n      \"pmids\": [\"38991726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PPTC7 acts as a co-factor of the SCFFBXL4 E3 ubiquitin ligase complex at the outer mitochondrial membrane, interacting with FBXL4 and BNIP3/3L; PPTC7 facilitates SCFFBXL4-mediated ubiquitin-proteasomal degradation of BNIP3/3L in a phosphatase activity-independent manner.\",\n      \"method\": \"Co-IP, in vitro cell culture, Pptc7 knockout mouse model, ubiquitination assay, phosphatase-dead mutant\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating direct FBXL4 interaction, phosphatase-dead mutant showing activity-independence, in vivo KO corroboration\",\n      \"pmids\": [\"40025034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PPTC7 has a non-mitochondrial role: it interacts with and dephosphorylates VPS4A (an ESCRT-associated ATPase) at serine 335; this dephosphorylation is required for VPS4A stability and its localization to early endosomes. Loss of PPTC7 or constitutively phosphorylated VPS4A causes defective EGFR recycling, re-routing EGFR to lysosomes, and impairs AKT signaling and cell proliferation/migration.\",\n      \"method\": \"Co-IP, in vitro dephosphorylation, phosphomimetic/phosphodead mutants, subcellular fractionation/localization, EGFR trafficking assay, cell proliferation/migration assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro phosphatase assay on VPS4A-S335, Co-IP, phosphomutant functional rescue, multiple orthogonal readouts in a single study\",\n      \"pmids\": [\"39776116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PPTC7 interacts with prohibitin 2 (PHB2) as identified by mass spectrometry and Co-IP; PPTC7 promotes ubiquitin-proteasome-mediated degradation of PHB2, disrupting mitochondrial function in brain microvascular endothelial cells.\",\n      \"method\": \"Mass spectrometry, Co-immunoprecipitation, shRNA knockdown, ubiquitination assay\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Co-IP and ubiquitination data from single study; mechanism of PPTC7-driven PHB2 degradation not fully reconstituted\",\n      \"pmids\": [\"41496208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The PPTC7 missense variant p.D158N, affecting a conserved metal-binding residue, disrupts both enzymatic phosphatase activity and PPTC7's ability to negatively regulate BNIP3 and NIX, establishing that metal coordination is required for full PPTC7 function; patient fibroblasts and CRISPR knock-in cells show excessive BNIP3/NIX-mediated mitophagy rescued by exogenous wild-type PPTC7 expression.\",\n      \"method\": \"Patient fibroblasts, CRISPR knock-in cell models, mt-Keima mitophagy flux assay, rescue with exogenous PPTC7, enzymatic phosphatase assay\",\n      \"journal\": \"Research square\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional patient variants with cellular rescue, but single preprint study without independent replication\",\n      \"pmids\": [\"41756425\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PPTC7 is a dual-localized PP2C-type phosphatase that resides in both the mitochondrial matrix and the outer mitochondrial membrane (OMM); in the matrix it dephosphorylates substrates such as COQ7 (to regulate CoQ10 biosynthesis) and Timm50 (to support mitochondrial protein import), while at the OMM it scaffolds assembly of a substrate-PPTC7-SCFFBXL4 holocomplex that promotes ubiquitin-proteasomal degradation of the mitophagy receptors BNIP3 and NIX, thereby suppressing receptor-mediated mitophagy and maintaining mitochondrial mass; outside mitochondria, PPTC7 also dephosphorylates VPS4A at S335 to support EGFR recycling and AKT signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PPTC7 is a dual-localized PP2C-type protein phosphatase that governs mitochondrial mass and metabolism through both catalytic and scaffolding functions [#0, #5]. In the mitochondrial matrix it is essential for biogenesis and metabolic homeostasis: its loss in mice causes perinatal lethality with hypoketotic hypoglycemia, elevated acylcarnitines, reduced mitochondrial content, and hyperphosphorylation of select mitochondrial proteins [#0]. Among its matrix-relevant activities, PPTC7 directly dephosphorylates COQ7 to control cellular CoQ10 content and adaptation to respiratory and starvation conditions [#2], and dephosphorylates the import translocase subunit Timm50 to support mitochondrial protein import [#1]. At the outer mitochondrial membrane—where an unusually weak targeting sequence promotes its retention—PPTC7 directly binds and suppresses the mitophagy receptors BNIP3 and NIX, restraining receptor-mediated mitophagy; double deletion of BNIP3 and NIX, or NIX knockout alone, reverses the excess mitophagy and rescues the lethality of PPTC7 loss [#3, #4]. Mechanistically, PPTC7 acts as a co-factor of the SCFFBXL4 E3 ubiquitin ligase, scaffolding a substrate-PPTC7-SCFFBXL4 holocomplex that drives ubiquitin-proteasomal degradation of BNIP3/NIX in a manner independent of its phosphatase activity [#4, #6]. Beyond mitochondria, PPTC7 dephosphorylates VPS4A at serine 335 to maintain VPS4A stability and endosomal localization, thereby supporting EGFR recycling, AKT signaling, and cell proliferation and migration [#7]. A patient-derived missense variant (p.D158N) at a conserved metal-coordinating residue disrupts both phosphatase activity and BNIP3/NIX regulation, causing excessive mitophagy in patient fibroblasts that is rescued by wild-type PPTC7 [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2018,\n      \"claim\": \"Established that PPTC7 is a genuine catalytic phosphatase with a defined substrate, answering whether it acts enzymatically and linking it to a metabolic output (CoQ10 biosynthesis).\",\n      \"evidence\": \"In vitro phosphatase assay on COQ7 plus expression modulation and CoQ10 quantification in human cells\",\n      \"pmids\": [\"30267671\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish in vivo physiological requirement\", \"Other matrix substrates not yet defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined PPTC7 as a matrix phosphatase essential for mitochondrial biogenesis in vivo and implicated it in regulating protein import via phosphorylation of targeting sequences.\",\n      \"evidence\": \"CRISPR-Cas9 knockout mice with phosphoproteomics, mitochondrial fractionation, and in vitro import assays identifying Timm50 as a putative substrate\",\n      \"pmids\": [\"31324765\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Timm50 not confirmed by full in vitro dephosphorylation reconstitution\", \"Causal substrate driving the lethal metabolic phenotype unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed that PPTC7 loss drives mitochondrial depletion through unleashed receptor-mediated mitophagy, identifying BNIP3 and NIX as direct interactors and the relevant effectors.\",\n      \"evidence\": \"Inducible knockout mice, MEF BNIP3/NIX double-knockout genetic rescue, phosphoproteomics, Co-IP, and in vitro dephosphorylation\",\n      \"pmids\": [\"37833277\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether dephosphorylation versus other mechanism controls receptor turnover not resolved\", \"Subcellular site of action not yet localized\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed that PPTC7 functions at the outer membrane as a scaffold within an SCFFBXL4 holocomplex that degrades BNIP3/NIX, and that NIX knockout rescues PPTC7-null lethality, defining the genetic epistasis.\",\n      \"evidence\": \"NIX-KO x PPTC7-KO genetic rescue, biochemical fractionation, Co-IP, and protein stability assays\",\n      \"pmids\": [\"38151018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and assembly order of the holocomplex not fully defined\", \"How precursor trapping at OMM is regulated unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the localization question by showing dual OMM/matrix distribution and that OMM anchoring alone suffices to suppress BNIP3/NIX, separating the receptor-regulating function from matrix targeting.\",\n      \"evidence\": \"Proximity labeling (BioID), fluorescence co-localization, organelle fractionation, catalytic mutant and chimeric OMM-anchored constructs\",\n      \"pmids\": [\"38991726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants partitioning PPTC7 between matrix and OMM not fully mapped\", \"Dynamics of receptor association under physiological stress incomplete\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined PPTC7's mechanistic role in the SCFFBXL4 complex as a phosphatase-independent co-factor promoting ubiquitin-proteasomal degradation of BNIP3/3L.\",\n      \"evidence\": \"Co-IP with FBXL4 and BNIP3/3L, ubiquitination assays, phosphatase-dead mutant, and Pptc7 knockout mouse corroboration\",\n      \"pmids\": [\"40025034\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PPTC7-FBXL4 cooperation unknown\", \"Reconciliation of catalytic versus scaffold contributions to receptor regulation not settled\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended PPTC7 function beyond mitochondria by identifying VPS4A-S335 as a substrate whose dephosphorylation supports endosomal trafficking, EGFR recycling, and AKT signaling.\",\n      \"evidence\": \"Co-IP, in vitro dephosphorylation, phosphomimetic/phosphodead mutants, subcellular localization, EGFR trafficking and proliferation/migration assays\",\n      \"pmids\": [\"39776116\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a mitochondrially-associated phosphatase accesses cytosolic VPS4A not explained\", \"Physiological context of this non-mitochondrial role in vivo unaddressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Reported a PPTC7-PHB2 interaction with PPTC7 promoting PHB2 degradation, extending its degradation-promoting activity to another mitochondrial protein.\",\n      \"evidence\": \"Mass spectrometry, Co-IP, shRNA knockdown, and ubiquitination assay in brain microvascular endothelial cells\",\n      \"pmids\": [\"41496208\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of PPTC7-driven PHB2 degradation not reconstituted\", \"Single study, no reciprocal or in vivo validation\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Linked PPTC7 to human disease by showing a metal-binding-residue variant abolishes both phosphatase activity and BNIP3/NIX regulation, causing pathological mitophagy rescued by wild-type protein.\",\n      \"evidence\": \"Patient fibroblasts, CRISPR knock-in cells, mt-Keima mitophagy flux, enzymatic assay, and exogenous PPTC7 rescue (preprint)\",\n      \"pmids\": [\"41756425\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single preprint without independent replication\", \"Full clinical spectrum and genotype-phenotype correlation undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PPTC7 balances its catalytic (COQ7, Timm50, VPS4A) and non-catalytic scaffolding (SCFFBXL4) functions across compartments, and what determines its partitioning and substrate selection, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of compartment-specific complexes\", \"Mechanism setting matrix-versus-OMM localization incompletely defined\", \"Full in vivo substrate repertoire unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3, 7]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [2, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0005741\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 6]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\"SCFFBXL4 E3 ubiquitin ligase complex\"],\n    \"partners\": [\"BNIP3\", \"BNIP3L/NIX\", \"FBXL4\", \"COQ7\", \"TIMM50\", \"VPS4A\", \"PHB2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}