Affinage

TMC2

Transmembrane channel-like protein 2 · UniProt Q8TDI7

Length
906 aa
Mass
102.6 kDa
Annotated
2026-04-28
15 papers in source corpus 11 papers cited in narrative 11 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TMC2 is a pore-forming subunit of the mechanotransduction (MET) channel in inner ear hair cells, where it localizes to stereocilia tips and confers high calcium permeability, large single-channel conductance, and altered pharmacological sensitivity to the immature channel complex (PMID:23871232, PMID:26321635, PMID:29093662). Purified TMC2 reconstituted into proteoliposomes forms a mechanosensitive ion channel, and in heterologous cells TMC2 paired with the auxiliary subunit TMIE (whose palmitoylation is required for gating stimulation) recapitulates native MET channel biophysics (PMID:31761710, PMID:39999170). TMC2 assembles as a homodimer in complex with CALM-1/CIB2 and TMIE, and interacts directly with the tip-link protein PCDH15 via its N-terminal domain, coupling mechanical force to channel gating (PMID:38354260, PMID:25114259, PMID:28663585). TMC2 can rescue vestibular but not auditory mechanotransduction in the absence of TMC1, indicating non-redundant roles across hair cell populations (PMID:30108254).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2013 High

    Establishing that TMC proteins are channel components rather than mere trafficking factors resolved the identity of the long-sought hair cell MET channel pore: TMC2-expressing hair cells exhibited high Ca²⁺ permeability and large single-channel conductance, and TMC1/TMC2 co-expression produced a range of conductances consistent with heteromeric assemblies.

    Evidence Whole-cell and single-channel patch-clamp recordings from mouse hair cells of various Tmc genotypes

    PMID:23871232

    Open questions at the time
    • Whether TMC2 directly forms the pore or acts as an obligate accessory subunit was not resolved by cellular electrophysiology alone
    • Stoichiometry of TMC1–TMC2 heteromeric assemblies remained undefined
  2. 2014 High

    Identifying a direct physical link between the tip-link protein PCDH15 and TMC2 established the molecular basis for force transmission from the tip link to the channel complex.

    Evidence Yeast two-hybrid, co-immunoprecipitation, and in vivo overexpression in zebrafish with electrophysiological readout

    PMID:25114259

    Open questions at the time
    • Structural details of the PCDH15–TMC2 interface were unknown
    • Whether PCDH15 binding directly gates TMC2 or simply anchors it remained unclear
  3. 2015 High

    Demonstrating that TMC2 localizes to stereocilia tips — the precise site of mechanotransduction — provided spatial evidence consistent with a direct channel role and revealed developmental redistribution from shaft to tip.

    Evidence Live imaging and immunofluorescence of TMC2-AcGFP knock-in mice with MET current rescue in Tmc1/Tmc2 double-KO

    PMID:26321635

    Open questions at the time
    • Mechanism controlling TMC2 trafficking to stereocilia tips was not identified
    • Why TMC2 is excluded from the tallest stereocilia row was unexplained
  4. 2017 High

    Two advances in 2017 clarified TMC2's pore contribution and its auxiliary protein network: TMC2 altered intracellular and extracellular drug-binding sites in the MET pore, and CIB2 was identified as a direct TMC2 interactor required for MET channel function, with deafness mutations disrupting the interaction.

    Evidence MET recordings from Tmc2 KO vs. WT with dihydrostreptomycin block; co-immunoprecipitation and Cib2 KO/knock-in mice with MET recordings

    PMID:28663585 PMID:29093662

    Open questions at the time
    • How CIB2 modulates TMC2 gating at a structural level was unknown
    • Whether CIB2's role is Ca²⁺-dependent regulation or structural assembly was not resolved
  5. 2018 High

    Genetic rescue experiments revealed that TMC2 can substitute for TMC1 in vestibular but not cochlear hair cells, demonstrating that TMC1 and TMC2 fulfill non-redundant roles across sensory epithelia.

    Evidence Cre-inducible Tmc2 knock-in in Tmc1 KO mice with ABR, VsEP, and MET recordings

    PMID:30108230 PMID:30108254

    Open questions at the time
    • Molecular basis for cochlear-specific TMC1 requirement (e.g., conductance, tonotopic tuning) was not determined
    • Whether TMC2 is actively silenced in mature cochlear hair cells or simply down-regulated was unclear
  6. 2019 High

    Reconstitution of purified budgerigar TMC2 into liposomes provided definitive proof that TMC2 itself is a mechanosensitive pore-forming protein, independent of other hair cell components.

    Evidence Heterologous expression in insect cells, purification, liposome reconstitution, electrophysiology under applied pressure

    PMID:31761710

    Open questions at the time
    • Reconstituted channel properties differed from native MET channels, suggesting missing auxiliary subunits
    • Lipid requirements for mechanosensitivity were not systematically explored
  7. 2024 High

    The cryo-EM structure of the C. elegans TMC-2 complex revealed a homodimeric architecture with two TMC-2 pore subunits, CALM-1 (CIB2 ortholog), and TMIE, providing the first atomic-level view of the assembled mechanotransduction complex and identifying conserved protein–lipid interactions and a π-helical motif in pore helices.

    Evidence Single-particle cryo-EM of native TMC-2 complex from C. elegans

    PMID:38354260

    Open questions at the time
    • Structure was captured in a closed/resting state; an open-state structure is needed to understand gating conformational changes
    • Whether mammalian TMC2 adopts the same dimeric stoichiometry was not verified
  8. 2025 High

    Heterologous reconstitution of mouse TMC2 with TMIE in mammalian cells showed that TMIE is the key gating stimulator of TMC2, requiring palmitoylation at C76/C77, and that the TMC2+TMIE channel recapitulates native MET biophysics (24 pS conductance).

    Evidence Patch-clamp of Fyn-tagged TMC2 ± TMIE in HEK cells, palmitoylation-site mutagenesis

    PMID:39999170

    Open questions at the time
    • Whether PCDH15 further modulates TMC2+TMIE gating was not tested in this system
    • Role of CIB2 in the heterologous reconstitution was not assessed
  9. 2025 Medium

    Beyond ion conduction, TMC2 was shown to function as a cholesterol-regulated lipid scramblase that modulates phospholipid asymmetry in hair cell membranes, linking channel activity to membrane remodeling.

    Evidence Reconstituted proteoliposome scramblase assays, molecular dynamics simulations, phosphatidylserine externalization in murine hair cells (preprint)

    PMID:40631239

    Open questions at the time
    • Preprint findings have not been peer-reviewed or independently replicated
    • Physiological significance of scramblase activity for hearing or hair cell survival is undefined
    • Whether scramblase and ion channel activities occur through the same pore path is unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the open-state structure of the mammalian TMC2 channel complex, the molecular basis for cochlear-specific TMC1 dependence versus vestibular TMC2 sufficiency, and whether TMC2 scramblase activity has physiological relevance for hair cell function and survival.
  • No open-state structural model for mammalian TMC2
  • Mechanism of tonotopic or epithelium-specific TMC1 versus TMC2 functional divergence is undefined
  • Physiological role of TMC2 scramblase activity in vivo is untested

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005215 transporter activity 4 GO:0140299 molecular sensor activity 2
Localization
GO:0005886 plasma membrane 2 GO:0005929 cilium 1
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-9709957 Sensory Perception 3
Partners
CIB2PCDH15TMC1TMIE
Complex memberships
TMC MET channel complex (TMC2-TMIE-CIB2/CALM-1)

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 TMC1 and TMC2 are components of the mechanosensitive ion channel in inner ear hair cells: cells expressing TMC2 alone had high calcium permeability and large single-channel currents; cells with TMC1 and TMC2 together showed a broad range of single-channel currents suggesting heteromeric assemblies; mutant TMC1 reduced calcium permeability and single-channel conductance. Whole-cell and single-channel patch-clamp recordings from mouse hair cells expressing Tmc1, Tmc2, or mutant Tmc1 Neuron High 23871232
2015 TMC1 and TMC2 localize to stereocilia tips (the site of mechanotransduction) in developing hair cells, transitioning from along the full length of immature stereocilia to predominantly tip localization as hair cells mature; both are absent from the tallest stereocilia row where MET activity is undetectable. Live imaging and immunofluorescence of fluorescently tagged TMC1-mCherry and TMC2-AcGFP knock-in mice; functional rescue of MET currents in Tmc1Δ/Δ;Tmc2Δ/Δ mice confirmed tag functionality Cell reports High 26321635
2014 PCDH15 (tip-link protein protocadherin 15) directly interacts with TMC1 and TMC2; the interaction requires the cytoplasmic CD1 or CD3 domains of PCDH15 and the N-terminal region of TMC2; overexpression of the TMC2a N-terminus in zebrafish hair cells mislocalizes PCDH15 and reduces mechanosensitive responses. Membrane-based yeast two-hybrid screen, yeast two-hybrid assay, co-immunoprecipitation, and in vivo overexpression in zebrafish with electrophysiological readout Proceedings of the National Academy of Sciences of the United States of America High 25114259
2017 CIB2 (calcium and integrin-binding protein 2) physically interacts with TMC1 and TMC2, and this interaction is disrupted by deafness-causing CIB2 mutations; CIB2 is required for normal mechanotransducer channel operation in auditory hair cells. Co-immunoprecipitation; characterization of Cib2 knockout and Cib2 deafness-mutation knock-in mouse lines with MET current recordings Nature communications High 28663585
2019 TMC2 (budgerigar MuTMC2) is a pore-forming subunit of a mechanosensitive ion channel: purified, liposome-reconstituted MuTMC2 possesses ion channel activity and responds to mechanical pressure applied to proteoliposomes. Heterologous expression in insect cells, protein purification, liposome reconstitution, electrophysiology of proteoliposomes with applied pressure Neuron High 31761710
2017 TMC2 modifies permeation and pharmacology of the MET channel pore in neonatal cochlear outer hair cells: in the presence of TMC2, the channel blocker dihydrostreptomycin has lower affinity both extracellularly and intracellularly, indicating TMC2 contributes to pore-forming properties of the immature MET channel. MET current recordings from Tmc2 knockout mouse outer hair cells with pharmacological block by dihydrostreptomycin Frontiers in molecular neuroscience High 29093662
2024 Cryo-EM structure of the C. elegans TMC-2 complex reveals it as a homodimer containing two TMC-2 pore-forming subunits, the calcium and integrin binding protein CALM-1, and the transmembrane inner ear protein TMIE; conserved protein-lipid interactions and a π-helical structural motif in pore-forming helices suggest a mechanism for mechanosensory transduction. Single-particle cryo-electron microscopy of native TMC-2 complex isolated from C. elegans Proceedings of the National Academy of Sciences of the United States of America High 38354260
2025 Full-length mouse TMC2, when driven to the plasma membrane via a Fyn lipidation tag, functions as a mechanosensitive channel on its own; TMIE robustly stimulates TMC2 channel activity by modulating gating, and TMIE palmitoylation at C76/C77 is required for this stimulation. TMC2+TMIE forms 24 pS single channels with biophysical and pharmacological properties matching native MET channels. Heterologous expression in mammalian cells with Fyn lipidation tag for membrane targeting, patch-clamp electrophysiology, TMIE palmitoylation site mutagenesis Proceedings of the National Academy of Sciences of the United States of America High 39999170
2018 TMC2 can partially substitute for TMC1 in vestibular hair cells (restoring sensory transduction and balance), but cannot fully substitute for TMC1 in mature cochlear hair cells (no auditory rescue), demonstrating distinct functional requirements for TMC1 vs. TMC2 in different hair cell populations. Cre-inducible Tmc2 knock-in mouse crossed with Tmc1 KO; sensory transduction recordings, auditory brainstem responses, vestibular behavioral assays Scientific reports High 30108230 30108254
2025 TMC1 and TMC2 function as cholesterol-regulated lipid scramblases that facilitate phospholipid translocation across membrane bilayers; this activity modulates plasma membrane asymmetry (phosphatidylserine externalization) in murine auditory hair cells, and deafness-causing TMC1 mutations enhance scramblase activity. Reconstituted proteoliposomes, molecular dynamics simulations, phosphatidylserine externalization assay in murine auditory hair cells bioRxivpreprint Medium 40631239
2024 TMC1 and TMC2 act as mechanosensitive scramblases in stereocilia: scramblase activity depends on the MET channel being open, as demonstrated by developmental, genetic, electrophysiological, and pharmacological approaches using a membrane viscosity sensor (BODIPY 1c). Fluorescent membrane viscosity sensor (BODIPY 1c), pharmacological MET channel blockade, genetic KO of Tmc1/Tmc2, electrophysiology in inner ear hair cells bioRxivpreprint Medium

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 TMC1 and TMC2 are components of the mechanotransduction channel in hair cells of the mammalian inner ear. Neuron 340 23871232
2015 TMC1 and TMC2 Localize at the Site of Mechanotransduction in Mammalian Inner Ear Hair Cell Stereocilia. Cell reports 154 26321635
2017 CIB2 interacts with TMC1 and TMC2 and is essential for mechanotransduction in auditory hair cells. Nature communications 146 28663585
2014 Tip-link protein protocadherin 15 interacts with transmembrane channel-like proteins TMC1 and TMC2. Proceedings of the National Academy of Sciences of the United States of America 137 25114259
2019 TMC1 and TMC2 Proteins Are Pore-Forming Subunits of Mechanosensitive Ion Channels. Neuron 128 31761710
2008 TMC1 but not TMC2 is responsible for autosomal recessive nonsyndromic hearing impairment in Tunisian families. Audiology & neuro-otology 52 18259073
2017 TMC2 Modifies Permeation Properties of the Mechanoelectrical Transducer Channel in Early Postnatal Mouse Cochlear Outer Hair Cells. Frontiers in molecular neuroscience 30 29093662
2024 The structure of the Caenorhabditis elegans TMC-2 complex suggests roles of lipid-mediated subunit contacts in mechanosensory transduction. Proceedings of the National Academy of Sciences of the United States of America 27 38354260
2018 Tmc2 expression partially restores auditory function in a mouse model of DFNB7/B11 deafness caused by loss of Tmc1 function. Scientific reports 23 30108230
2018 Transgenic Tmc2 expression preserves inner ear hair cells and vestibular function in mice lacking Tmc1. Scientific reports 23 30108254
2025 Ectopic mouse TMC1 and TMC2 alone form mechanosensitive channels that are potently modulated by TMIE. Proceedings of the National Academy of Sciences of the United States of America 6 39999170
2025 TMC1 and TMC2 function as the mechano-electrical transduction ion channel in hearing. Current opinion in neurobiology 4 40280017
2023 Structure of C. elegans TMC-2 complex suggests roles of lipid-mediated subunit contacts in mechanosensory transduction. bioRxiv : the preprint server for biology 3 37645790
2025 TMC1 and TMC2 are cholesterol-dependent scramblases that regulate membrane homeostasis in auditory hair cells. bioRxiv : the preprint server for biology 1 40631239
2022 Functional consequences of Genetics variant in TMC1 and TMC2 within a United Arab Emirates family with Pre-lingual hearing loss. Saudi journal of biological sciences 0 36568409