Affinage

TMEM63B

Mechanosensitive cation channel TMEM63B · UniProt Q5T3F8

Length
832 aa
Mass
95.0 kDa
Annotated
2026-06-10
18 papers in source corpus 14 papers cited in narrative 14 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

TMEM63B is a mechanosensitive and osmosensitive nonselective cation channel that converts membrane physical stimuli — hypo-osmotic swelling and membrane stretch — into Ca2+ influx to drive tissue-specific physiological responses (PMID:32375046, PMID:39985646, PMID:42067058). In cochlear outer hair cells it serves as the inner-ear osmosensor, mediating hypo-osmolarity-induced Ca2+ entry that activates Ca2+-dependent K+ channels for regulatory volume decrease; its loss causes outer hair cell necroptosis and progressive hearing loss (PMID:32375046). The same channel activity underlies stretch-evoked Ca2+ influx that triggers lamellar body fusion and pulmonary surfactant secretion in alveolar type II cells (PMID:38127458, PMID:42067058), glucose-swelling-induced depolarization and insulin secretion in pancreatic β-cells (PMID:39985646), and it additionally stabilizes nucleocytoplasmic transport machinery (the Ran-XPO1 complex) to permit p21 nuclear export and trophoblast proliferation (PMID:42259794). Beyond ion conduction, TMEM63B is a membrane-structure-responsive lipid scramblase that catalyzes bidirectional phospholipid translocation in response to changes in membrane curvature and thickness, a function requiring palmitoylated intracellular cysteine clusters and resolved by cryo-EM structures capturing open and closed states with a defined lipid translocation pathway (PMID:39424995). The channel is autoinhibited at rest by a C-terminal AQVLQD motif whose Leu776 packs against intracellular helices; disrupting this motif yields constitutive scrambling (PMID:42248451). Activity is further tuned post-transcriptionally by brain-specific exon 4 alternative splicing — the exon-4 isoform carries an RXR-type COPI-dependent ER retention signal limiting surface expression — coupled to ADAR2-dependent Q/R A-to-I editing that occurs almost exclusively in the exon-4-lacking isoform (PMID:33100268, PMID:36496074). Heterozygous transmembrane missense variants act as gain-of-function alleles producing isotonic leak currents (PMID:37421948), whereas bi-allelic loss-of-function variants cause a syndromic surfactant dysfunction disorder with neonatal respiratory failure paralleling the knockout mouse (PMID:42259295).

Mechanistic history

Synthesis pass · year-by-year structured walk · 14 steps
  1. 2016 Medium

    Established the TMEM63 family as candidate osmolarity-activated channels, raising the question of whether subunits act independently or cooperatively.

    Evidence Heterologous co-expression of TMEM63A/B/C in HEK293 cells with patch-clamp

    PMID:27045885

    Open questions at the time
    • Inferred obligate three-subunit requirement was contradicted by later evidence that TMEM63B functions independently
    • No native tissue context tested
  2. 2019 Medium

    Showed TMEM63B is a plasma-membrane Ca2+-permeable channel responsive to hyperosmolarity and capable of promoting cell migration, defining it as an independent functional unit.

    Evidence Immunofluorescence, Ca2+ imaging, and wound-healing assays with overexpression in HEK293T cells

    PMID:31243992

    Open questions at the time
    • Single overexpression system without endogenous validation
    • Mechanism linking channel activity to migration not resolved
  3. 2020 High

    Defined the physiological role of TMEM63B as the inner-ear osmosensor, answering what process its channel activity serves in vivo.

    Evidence Knockout mouse, electrophysiology, Ca2+ imaging, and volume assays in outer hair cells

    PMID:32375046

    Open questions at the time
    • Selectivity filter and gating residues not mapped
    • Link from Ca2+ influx to necroptosis not mechanistically detailed
  4. 2020 High

    Revealed that channel properties are post-transcriptionally tuned, answering how Ca2+ permeability and osmosensitivity are regulated in a tissue-specific manner.

    Evidence RT-PCR/sequencing, ADAR2 knockout mice, and electrophysiology in cerebellar granule neurons

    PMID:33100268

    Open questions at the time
    • Functional consequence in intact neural circuits not established
    • Structural basis of Q/R-site effect on permeation unknown at the time
  5. 2022 High

    Explained how alternative splicing controls surface availability, linking exon 4 to a COPI-dependent ER retention signal and to heterodimer-mediated suppression.

    Evidence Mutagenesis, surface biotinylation, co-IP, COPI binding assays, and electrophysiology

    PMID:36496074

    Open questions at the time
    • In vivo significance of isoform ratios per tissue not quantified
    • Stoichiometry of long/short heterodimers undefined
  6. 2023 High

    Connected TMEM63B to human neurodevelopmental disease through gain-of-function transmembrane variants producing isotonic leak currents.

    Evidence Patch-clamp and Ca2+ imaging in Neuro2a cells plus Drosophila lethality assay

    PMID:37421948

    Open questions at the time
    • Channel-pore residues underlying leak not structurally localized in this study
    • Genotype-phenotype correlation across variant positions incomplete
  7. 2024 High

    Identified an organelle-membrane role: TMEM63B as a stretch sensor on lamellar body membranes driving surfactant and ATP release in the lung.

    Evidence Knockout mice, confocal localization, electrophysiology, surfactant/ATP release and Ca2+ imaging in AT2 cells

    PMID:38127458

    Open questions at the time
    • Relative contribution of TMEM63A vs TMEM63B not separated
    • Direct gating by membrane tension at the LB membrane not reconstituted
  8. 2024 High

    Expanded the molecular function beyond ion conduction by demonstrating lipid scramblase activity and providing open/closed cryo-EM structures.

    Evidence Cryo-EM, scramblase assays, palmitoylation-site mutagenesis, and phospholipid distribution analysis in deficient cells

    PMID:39424995

    Open questions at the time
    • Relationship between ion conduction and lipid scrambling pathways not fully resolved
    • Physiological readout of scrambling in native tissues limited
  9. 2025 High

    Extended the stretch-channel role to metabolism, showing glucose-induced swelling activates TMEM63B to promote β-cell depolarization and insulin secretion.

    Evidence Conditional knockout mice, patch-clamp, Ca2+ imaging, and insulin secretion assays

    PMID:39985646

    Open questions at the time
    • Coupling between swelling and channel gating in β-cells not directly measured
    • Contribution relative to canonical KATP-dependent secretion unclear
  10. 2025 Medium

    Tested whether TMEM63B contributes to bladder mechanosensation, returning a well-controlled negative result that bounds its functional scope.

    Evidence Tissue-specific conditional knockouts with void-spot assays under cyclophosphamide stress

    PMID:41348674

    Open questions at the time
    • Possible redundancy with other mechanosensors not excluded
    • Subthreshold or compensatory roles not assayed
  11. 2026 High

    Confirmed TMEM63B as the primary stretch sensor on the AT2 plasma membrane and dissociated mechanical sensing from downstream ATP signaling.

    Evidence Conditional knockout, patch-clamp, Ca2+ imaging, and LB fusion/surfactant assays in AT2 cells

    PMID:42067058

    Open questions at the time
    • Molecular force-transduction mechanism not defined
    • Integration with the earlier LB-membrane localization model not fully reconciled
  12. 2026 Medium

    Uncovered a non-channel role in nucleocytoplasmic transport, linking TMEM63B loss to Ran/XPO1 destabilization and impaired p21 export in trophoblasts.

    Evidence Knockout mice, co-IP of Ran-XPO1, immunofluorescence shuttling, and trophoblast proliferation assays

    PMID:42259794

    Open questions at the time
    • Mechanism by which a membrane channel stabilizes Ran is unresolved
    • Single lab; direct physical interaction not established
  13. 2026 High

    Defined the autoinhibitory switch, showing the C-terminal AQVLQD motif (Leu776) holds TMEM63B inactive via intracellular helix contacts.

    Evidence Mutagenesis/truncations, scramblase assays, and cryo-EM structural analysis

    PMID:42248451

    Open questions at the time
    • How physiological stimuli relieve autoinhibition not shown
    • Effect of the motif on ion conduction versus scrambling not separated
  14. 2026 Medium

    Established a recessive human disease link, showing bi-allelic loss-of-function variants cause syndromic surfactant dysfunction matching the knockout phenotype.

    Evidence Functional splice/nonsense variant evaluation and clinical genotype-phenotype correlation with KO mouse comparison

    PMID:42259295

    Open questions at the time
    • Limited functional detail beyond loss-of-function confirmation
    • Spectrum of biallelic phenotypes not fully delineated

Open questions

Synthesis pass · forward-looking unresolved questions
  • How a single protein partitions between ion conduction, lipid scrambling, and a non-channel role in nucleocytoplasmic transport — and how stimulus-specific relief of C-terminal autoinhibition selects among these outputs — remains unresolved.
  • No unified model coupling mechanosensing to choice of ion vs lipid output
  • Mechanism connecting a membrane channel to Ran/XPO1 stability unknown
  • Stimulus-to-gating transduction not reconstituted in vitro

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005215 transporter activity 4 GO:0140299 molecular sensor activity 4 GO:0140096 catalytic activity, acting on a protein 2 GO:0008289 lipid binding 1 GO:0098772 molecular function regulator activity 1
Localization
GO:0005886 plasma membrane 3 GO:0005764 lysosome 1 GO:0005783 endoplasmic reticulum 1 GO:0031410 cytoplasmic vesicle 1
Pathway
R-HSA-8953897 Cellular responses to stimuli 3 R-HSA-162582 Signal Transduction 2 R-HSA-1643685 Disease 2 R-HSA-8953854 Metabolism of RNA 1 R-HSA-9609507 Protein localization 1
Partners
ADAR2RANXPO1

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2020 TMEM63B functions as an osmosensitive nonselective cation channel (NSCC) activated by hypotonic stress. Genetic deletion of TMEM63B in mice causes necroptosis of outer hair cells (OHCs) and progressive hearing loss. Mechanistically, TMEM63B mediates hypo-osmolarity-induced Ca2+ influx, which activates Ca2+-dependent K+ channels required for maintenance of OHC morphology, establishing TMEM63B as the osmosensor of the mammalian inner ear and the cation channel mediating Ca2+-dependent regulatory volume decrease (RVD). Electrophysiology, genetic knockout (KO) mouse, Ca2+ imaging, cell volume assays Cell reports High 32375046
2016 Co-expression of all three mouse TMEM63 family members (TMEM63A, TMEM63B, and TMEM63C) together in HEK293 cells confers hyperosmolarity-activated ion currents; expression of any two subtypes alone is insufficient to produce these currents, suggesting all three are required to constitute a functional hyperosmolarity-activated ion channel. Heterologous expression in HEK293 cells, patch-clamp electrophysiology Cell biochemistry and function Medium 27045885
2019 TMEM63B localizes to the plasma membrane and associates with F-actin in HEK293T cells. It functions as a Ca2+-permeable channel that mediates Ca2+ influx in response to hyperosmolarity and extracellular Ca2+ concentration. Overexpression of TMEM63B significantly enhances cell migration and wound healing. Immunofluorescence, Ca2+ imaging, wound healing/migration assays, overexpression in HEK293T cells Biochemistry Medium 31243992
2020 TMEM63B pre-mRNA undergoes brain-specific A-to-I RNA editing at exon 20 (Q/R site) catalyzed by ADAR2 (ADARB1), requiring an editing site complementary sequence in intron 20. A brain-specific alternative splicing of exon 4 (~80% of brain mRNAs lack exon 4) is coupled to this editing: the Q/R editing occurs almost exclusively in the exon-4-lacking isoform. The splicing plays the dominant role (exon 4 inclusion suppresses Q/R editing). The two modifications coordinately regulate Ca2+ permeability and osmosensitivity of the channel. RT-PCR, sequencing, ADAR2 knockout mice, transfection in cerebellar granule neurons, electrophysiology, Ca2+ imaging The Journal of biological chemistry High 33100268
2022 The exon 4-containing long isoform of TMEM63B contains an RXR-type ER retention signal (RER motif) within the exon 4-encoded sequence that binds COPI retrieval vesicles, causing retrotranslocation to the ER and reduced surface expression. The short isoform (lacking exon 4) exhibits stronger plasma membrane surface expression and enhanced responses to hypoosmotic stimulation. Additionally, long TMEM63B isoforms can form heterodimers with short isoforms and reduce their surface expression. Mutagenesis screening, surface biotinylation, co-immunoprecipitation, COPI binding assay, electrophysiology The Journal of biological chemistry High 36496074
2023 Disease-associated heterozygous missense variants in TMEM63B transmembrane domains (e.g., p.Val44Met, p.Arg433His, p.Thr481Asn, p.Gly580Ser, p.Arg660Thr, p.Phe697Leu) produce inward leak cation currents in isotonic conditions (gain-of-function), while impairing the hypo-osmotic challenge response and reducing Ca2+ transients under hypo-osmotic stimulation. Expression of p.Val44Met and p.Gly580Cys variants in Drosophila causes early death. Patch-clamp electrophysiology in transfected Neuro2a cells, Ca2+ imaging, Drosophila ectopic expression lethality assay American journal of human genetics High 37421948
2024 TMEM63A and TMEM63B are mechanosensitive channels predominantly localized at the limiting membrane of the lamellar body (LB) in alveolar type 2 (AT2) cells. Loss of TMEM63A/B results in atelectasis and respiratory failure in mice due to surfactant secretion deficit. Activation of TMEM63A/B during cell stretch facilitates surfactant and ATP release from LBs fused with the plasma membrane; released ATP evokes Ca2+ signaling in AT2 cells, potentiating exocytic fusion of more LBs. Genetic KO mice, immunofluorescence/confocal localization, electrophysiology, surfactant secretion assays, ATP release assays, Ca2+ imaging The Journal of clinical investigation High 38127458
2024 TMEM63B functions as a membrane structure-responsive lipid scramblase localized at the plasma membrane and lysosomes, activating bidirectional lipid translocation in response to changes in membrane curvature and thickness. TMEM63B contains two intracellular loops with palmitoylated cysteine residue clusters essential for its scrambling function. TMEM63B deficiency alters phosphatidylcholine and sphingomyelin distributions in the plasma membrane. The disease variant p.Val44Met confers constitutive scramblase activity, disrupting plasma membrane phospholipid asymmetry. Cryo-EM structures of TMEM63B in open and closed conformations reveal a lipid translocation pathway formed in response to membrane environment changes. Cryo-EM structure determination, lipid scramblase assay (phosphatidylserine externalization, fluorescent lipid incorporation), mutagenesis of palmitoylation sites, TMEM63B-deficient cells, phospholipid distribution analysis Nature structural & molecular biology High 39424995
2025 TMEM63B is a stretch-activated cation channel (SAC) expressed in pancreatic β-cells. Deletion of TMEM63B impairs insulin secretion in response to high glucose. Mechanistically, glucose metabolism induces cell swelling, which activates TMEM63B, leading to Ca2+ influx, β-cell depolarization, and insulin secretion. TMEM63B deletion eliminates the increased Ca2+ influx and firing frequency normally induced by high glucose. Conditional KO mice, patch-clamp electrophysiology, Ca2+ imaging, insulin secretion assays Science China. Life sciences High 39985646
2026 TMEM63B functions as the primary mechanosensor on the plasma membrane of alveolar type II (AT2) cells. Stretch induces significant currents in AT2 cells that are abolished by TMEM63B deletion. TMEM63B activation causes Ca2+ influx, lamellar body (LB) fusion, and pulmonary surfactant secretion. ATP-induced Ca2+ influx and LB fusion are unaffected by TMEM63B deletion, indicating TMEM63B specifically senses mechanical stretch rather than ATP signaling in this context. Conditional KO (Tmem63bHA-fl/HA-fl mice), patch-clamp electrophysiology in AT2 cells, Ca2+ imaging, LB fusion assay, surfactant secretion assay Journal of genetics and genomics High 42067058
2026 TMEM63B modulates nucleocytoplasmic transport (NCT) by stabilizing NCT components. Loss of TMEM63B compromises Ran protein expression and the Ran-XPO1 complex, impairing nuclear export of CDKN1A/p21, leading to defective trophoblast proliferation, placental dysfunction, and perinatal lethality in mice. Genetic KO mice, co-immunoprecipitation (Ran-XPO1 complex), immunofluorescence (nuclear shuttling), western blot (Ran levels, p21 localization), trophoblast proliferation assays Nature communications Medium 42259794
2026 The C-terminal tail of TMEM63B contains an autoinhibitory AQVLQD motif (residues 773-778). Deletion of the adjacent LQD motif (Δ776-778) or substitution of Leu776 with alanine induces constitutive lipid scrambling (phosphatidylserine externalization and enhanced phosphatidylcholine incorporation), while substitutions at Gln777 or Asp778 have minimal effects. Cryo-EM structural analysis positions the AQVLQD motif adjacent to conserved intracellular helices in the open conformation, with Leu776 near hydrophobic residues, suggesting the C-terminal tail maintains TMEM63B in an inactive state through interactions with intracellular helices. Mutagenesis (chimeric constructs, truncations, internal deletions), lipid scramblase functional assays (phosphatidylserine externalization, fluorescent phosphatidylcholine incorporation), cryo-EM structural analysis, antibody epitope mapping The Journal of biological chemistry High 42248451
2026 Bi-allelic loss-of-function variants in TMEM63B cause a syndromic surfactant dysfunction disorder in humans with early-onset respiratory distress. Functional evaluation of splice donor and nonsense variants confirmed loss-of-function mechanism. The pulmonary phenotype parallels Tmem63b-knockout mice with neonatal respiratory failure due to impaired surfactant secretion. Functional variant evaluation (splice/nonsense variant testing), clinical genotype-phenotype correlation, parallel KO mouse comparison American journal of human genetics Medium 42259295
2025 TMEM63B is expressed in the urothelium of the bladder and dorsal root ganglia sensory neurons innervating the bladder. However, conditional deletion of TMEM63B in urothelium or sensory neurons does not produce a demonstrable voiding phenotype, even under cyclophosphamide-induced stress (negative result for bladder mechanosensory function). Conditional KO mice, void-spot screening assay, immunofluorescence PloS one Medium 41348674

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2020 The Cation Channel TMEM63B Is an Osmosensor Required for Hearing. Cell reports 72 32375046
2023 Stretch-activated ion channel TMEM63B associates with developmental and epileptic encephalopathies and progressive neurodegeneration. American journal of human genetics 39 37421948
2024 Mechanosensitive channels TMEM63A and TMEM63B mediate lung inflation-induced surfactant secretion. The Journal of clinical investigation 38 38127458
2016 Co-expression of mouse TMEM63A, TMEM63B and TMEM63C confers hyperosmolarity activated ion currents in HEK293 cells. Cell biochemistry and function 31 27045885
2024 Membrane structure-responsive lipid scrambling by TMEM63B to control plasma membrane lipid distribution. Nature structural & molecular biology 23 39424995
2020 Distant coupling between RNA editing and alternative splicing of the osmosensitive cation channel Tmem63b. The Journal of biological chemistry 23 33100268
2012 Association of genes on chromosome 6, GRIK2 , TMEM217 and TMEM63B (linked to MRPL14 ) with diabetic retinopathy. Ophthalmologica. Journal international d'ophtalmologie. International journal of ophthalmology. Zeitschrift fur Augenheilkunde 19 23037145
2019 Overexpression of Osmosensitive Ca2+-Permeable Channel TMEM63B Promotes Migration in HEK293T Cells. Biochemistry 13 31243992
2022 A splicing-dependent ER retention signal regulates surface expression of the mechanosensitive TMEM63B cation channel. The Journal of biological chemistry 12 36496074
2025 Osmosensor TMEM63B facilitates insulin secretion in pancreatic β-cells. Science China. Life sciences 6 39985646
2024 Expression and localization of the mechanosensitive/osmosensitive ion channel TMEM63B in the mouse urinary tract. Physiological reports 4 38724885
2025 Targeting Tmem63b and Piezo2 in C-fiber low-threshold mechanoreceptors: Limitation of Vglut3-IRES-Cre. Biophysical journal 1 41176617
2026 TMEM63B channel is the mechanosensor in alveolar epithelial type II cells. Journal of genetics and genomics = Yi chuan xue bao 0 42067058
2026 Autoinhibition of the mechanosensitive lipid scramblase TMEM63B by its C-terminal tail. The Journal of biological chemistry 0 42248451
2026 Bi-allelic loss-of-function variants in TMEM63B cause syndromic surfactant dysfunction disorder. American journal of human genetics 0 42259295
2026 TMEM63B regulates nucleocytoplasmic transport and placental development. Nature communications 0 42259794
2025 Targeting Tmem63b and Piezo2 in C-fiber low threshold mechanoreceptor: limitation of Vglut3-IRES-Cre. bioRxiv : the preprint server for biology 0 40766537
2025 Conditional deletion of Tmem63b does not impact mouse voiding behavior. PloS one 0 41348674

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