Affinage

PPTC7

Protein phosphatase PTC7 homolog · UniProt Q8NI37

Length
304 aa
Mass
32.6 kDa
Annotated
2026-06-10
11 papers in source corpus 9 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2018 High

    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

    PMID:30267671

    Open questions at the time
    • Did not establish in vivo physiological requirement
    • Other matrix substrates not yet defined
  2. 2019 High

    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

    PMID:31324765

    Open questions at the time
    • Timm50 not confirmed by full in vitro dephosphorylation reconstitution
    • Causal substrate driving the lethal metabolic phenotype unresolved
  3. 2023 High

    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

    PMID:37833277

    Open questions at the time
    • Whether dephosphorylation versus other mechanism controls receptor turnover not resolved
    • Subcellular site of action not yet localized
  4. 2023 High

    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

    PMID:38151018

    Open questions at the time
    • Stoichiometry and assembly order of the holocomplex not fully defined
    • How precursor trapping at OMM is regulated unclear
  5. 2024 High

    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

    PMID:38991726

    Open questions at the time
    • Determinants partitioning PPTC7 between matrix and OMM not fully mapped
    • Dynamics of receptor association under physiological stress incomplete
  6. 2025 High

    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

    PMID:40025034

    Open questions at the time
    • Structural basis of PPTC7-FBXL4 cooperation unknown
    • Reconciliation of catalytic versus scaffold contributions to receptor regulation not settled
  7. 2025 High

    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

    PMID:39776116

    Open questions at the time
    • How a mitochondrially-associated phosphatase accesses cytosolic VPS4A not explained
    • Physiological context of this non-mitochondrial role in vivo unaddressed
  8. 2025 Medium

    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

    PMID:41496208

    Open questions at the time
    • Mechanism of PPTC7-driven PHB2 degradation not reconstituted
    • Single study, no reciprocal or in vivo validation
  9. 2026 Medium

    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)

    PMID:41756425

    Open questions at the time
    • Single preprint without independent replication
    • Full clinical spectrum and genotype-phenotype correlation undefined

Open questions

Synthesis pass · forward-looking unresolved questions
  • 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.
  • No structural model of compartment-specific complexes
  • Mechanism setting matrix-versus-OMM localization incompletely defined
  • Full in vivo substrate repertoire unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140096 catalytic activity, acting on a protein 3 GO:0016787 hydrolase activity 2 GO:0060090 molecular adaptor activity 2
Localization
GO:0005739 mitochondrion 2 GO:0005768 endosome 1
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-392499 Metabolism of proteins 2 R-HSA-9612973 Autophagy 2 R-HSA-5653656 Vesicle-mediated transport 1
Partners
BNIP3BNIP3L/NIXCOQ7FBXL4PHB2TIMM50VPS4A
Complex memberships
SCFFBXL4 E3 ubiquitin ligase complex

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2019 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. CRISPR-Cas9 knockout mice, phosphoproteomics, mitochondrial fractionation Nature communications High 31324765
2019 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. Phosphoproteomics, in vitro import assay, Pptc7 knockout mice Nature communications Medium 31324765
2018 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. In vitro phosphatase assay, PPTC7 overexpression and knockdown, CoQ10 quantification Biochimica et biophysica acta. Bioenergetics High 30267671
2023 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. Inducible knockout mice, MEF double-knockout genetic rescue, phosphoproteomics, Co-IP, in vitro dephosphorylation assay Nature communications High 37833277
2023 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. Genetic rescue in mice (NIX KO x PPTC7 KO), biochemical fractionation, Co-IP, protein stability assays Molecular cell High 38151018
2024 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. Fluorescence co-localization, proximity labeling (BioID), organelle fractionation, catalytic mutant overexpression, chimeric OMM-anchored PPTC7 construct Life science alliance High 38991726
2025 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. Co-IP, in vitro cell culture, Pptc7 knockout mouse model, ubiquitination assay, phosphatase-dead mutant Cell death & disease High 40025034
2025 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. Co-IP, in vitro dephosphorylation, phosphomimetic/phosphodead mutants, subcellular fractionation/localization, EGFR trafficking assay, cell proliferation/migration assay Journal of cell science High 39776116
2025 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. Mass spectrometry, Co-immunoprecipitation, shRNA knockdown, ubiquitination assay Redox biology Medium 41496208
2026 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. Patient fibroblasts, CRISPR knock-in cell models, mt-Keima mitophagy flux assay, rescue with exogenous PPTC7, enzymatic phosphatase assay Research squarepreprint Medium 41756425

Source papers

Stage 0 corpus · 11 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2023 A mitophagy sensor PPTC7 controls BNIP3 and NIX degradation to regulate mitochondrial mass. Molecular cell 67 38151018
2019 Pptc7 is an essential phosphatase for promoting mammalian mitochondrial metabolism and biogenesis. Nature communications 54 31324765
2018 The mitochondrial phosphatase PPTC7 orchestrates mitochondrial metabolism regulating coenzyme Q10 biosynthesis. Biochimica et biophysica acta. Bioenergetics 29 30267671
2023 PPTC7 maintains mitochondrial protein content by suppressing receptor-mediated mitophagy. Nature communications 24 37833277
2024 Dual-localized PPTC7 limits mitophagy through proximal and dynamic interactions with BNIP3 and NIX. Life science alliance 13 38991726
2025 PPTC7 acts as an essential co-factor of the SCFFBXL4 ubiquitin ligase complex to restrict BNIP3/3L-dependent mitophagy. Cell death & disease 4 40025034
2023 Pptc7 maintains mitochondrial protein content by suppressing receptor-mediated mitophagy. bioRxiv : the preprint server for biology 2 36909604
2025 Mitochondrial phosphatase PPTC7 promotes EGFR recycling by facilitating VPS4A endosomal localization. Journal of cell science 1 39776116
2024 PPTC7 limits mitophagy through proximal and dynamic interactions with BNIP3 and NIX. bioRxiv : the preprint server for biology 1 38328188
2026 Recessive PPTC7 deficiency triggers excessive mitophagy to cause a severe inborn error of metabolism with hypomyelinating leukodystrophy. Research square 0 41756425
2025 Upregulation of PPTC7 in brain microvascular endothelial cell aggravates diabetic cognitive dysfunction by impairing PHB2 mediated mitochondrial function. Redox biology 0 41496208

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