KCNK6

KCNK6 (TWIK-2/K2P6.1) is a two-pore-domain potassium channel that forms a homodimer with extremely low single-channel conductance and contributes to background K+ flux that shapes cellular excitability and tone (PMID:10075682, PMID:10887187). Heterologous expression established it as a weak inward rectifier that inactivates at depolarized potentials with temperature-sensitive kinetics, is inhibited by intracellular but not extracellular acidification, and depends on an external-loop cysteine (C53) for functional surface expression (PMID:10075682, PMID:10887187); subsequent functional work confirmed voltage-dependent gating that is insensitive to extracellular pH (PMID:41617707). Cryo-EM structures of the human channel reveal a distinctive selectivity-filter (SF1) conformation and a 'lipid plug' of two-chain lipids occupying the central cavity and lateral fenestrations, which renders the channel inactive; an R257A mutation repositions this plug and increases channel function, and removal of the plug is required to form an ion-permeable pore [PMID:bio_10.1101_2025.06.11.659167]. These fenestrations also serve as the access route for hydrophobic inhibitors: the antipsychotic pimozide displaces the acyl chains and binds below the selectivity filter to block ion conduction [PMID:bio_10.1101_2025.02.24.639991]. Physiologically, TWIK-2 promotes K+ efflux that activates the NLRP3 inflammasome in macrophages, with its expression controlled by METTL3-mediated m6A modification acting through YTHDF2 and by histone lactylation (PMID:39269733), and its genetic loss in mice causes pulmonary hypertension and vascular remodeling through a Rho-kinase-dependent mechanism (PMID:25245387).

1. 1999 High

   Established the molecular identity and basic biophysical class of KCNK6, defining it as a two-pore-domain weak inward rectifier K+ channel distinct from TWIK-1.

   Evidence Cloning from human brain cDNA and electrophysiology/pharmacological profiling in Xenopus oocytes

   PMID:10075682

   Open questions at the time

   • Native cell type and physiological function not addressed
   • No structural basis for gating
   • pH sensitivity restricted to heterologous context
2. 2000 High

   Defined inactivation, rectification, and low conductance as intrinsic channel properties and identified a residue (C53) required for functional expression but not subunit assembly.

   Evidence Whole-cell and single-channel patch clamp with site-directed mutagenesis in COS cells across human and rat isoforms

   PMID:10887187

   Open questions at the time

   • Mechanism linking C53 to surface trafficking unresolved
   • Physiological role still unknown
   • Endogenous modulators not identified
3. 2004 Medium

   Provided the first tissue localization, placing TWIK-2 protein in the cochlear stria vascularis and implicating it in potassium recycling, while excluding it as a DFNA4 disease gene.

   Evidence RT-PCR, immunoblot, and immunohistochemistry of mouse cochlea plus mutation screening of DFNA4 families

   PMID:14689445

   Open questions at the time

   • Functional contribution to endolymph K+ inferential, no KO or electrophysiology in cochlea
   • No causative human disease mutation found
4. 2009 Medium

   Extended characterization to vascular tissue, showing arachidonic acid enhances TWIK-2 currents and defining its pharmacological insensitivity profile.

   Evidence Cloning from rat middle cerebral artery and whole-cell patch clamp in CHO cells

   PMID:19934370

   Open questions at the time

   • Arachidonic acid modulation not independently replicated
   • Single lab, single study
   • Mechanism of lipid enhancement undefined
5. 2014 High

   Connected channel loss to a whole-organism cardiovascular phenotype, placing TWIK-2 upstream of Rho-kinase in regulating pulmonary vascular tone.

   Evidence TWIK-2 knockout mice with hemodynamic and morphometric phenotyping and pharmacological epistasis using Rho-kinase inhibitors

   PMID:25245387

   Open questions at the time

   • Molecular link between K+ flux and Rho-kinase activation not defined
   • Cell-autonomous site of action in vasculature unresolved
6. 2024 Medium

   Assigned TWIK-2 a role in innate immune signaling, showing its K+ efflux drives NLRP3 inflammasome activation and that its expression is controlled by m6A and histone lactylation.

   Evidence Kcnk6 knockout macrophages, AOM/DSS colitis-cancer model, m6A and YTHDF2-binding assays, histone lactylation analysis

   PMID:39269733

   Open questions at the time

   • Some mechanistic claims rely on abstract-level description
   • Direct demonstration that channel-mediated efflux is the trigger not fully detailed
   • Link to TWIK-2 biophysics not integrated
7. 2026 High

   Resolved the molecular architecture and gating logic of TWIK-2, revealing a lipid plug that inactivates the channel, a route for hydrophobic drug access through fenestrations, and pH-insensitive voltage-dependent gating.

   Evidence Cryo-EM structures (peer-reviewed and preprint, including pimozide-bound and R257A/plasma-membrane-targeting mutants) with automated patch clamp and mutagenesis

   PMID:41617707 PMID:bio_10.1101_2025.02.24.639991 PMID:bio_10.1101_2025.06.11.659167

   Open questions at the time

   • Physiological trigger for lipid plug removal in vivo unknown
   • Whether lipid gating links to NLRP3 or vascular roles not tested
   • Endogenous regulators that open the channel undefined

• It remains unknown how the structurally defined lipid-plug gating mechanism is physiologically controlled and how it mechanistically connects K+ efflux to NLRP3 inflammasome activation and Rho-kinase-dependent vascular tone.
• Endogenous signal that displaces the lipid plug unidentified
• Molecular intermediates between channel activity and Rho-kinase unknown
• Cell-type-specific contributions not dissected