{"gene":"KCNE3","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2001,"finding":"KCNE3 (MiRP2) assembles with the pore-forming subunit Kv3.4 in skeletal muscle to form a subthreshold, voltage-gated potassium channel complex. MiRP2-Kv3.4 channels differ from Kv3.4 alone in unitary conductance, voltage-dependent activation, recovery from inactivation, steady-state open probability, and block by peptide toxin, and set resting membrane potential without producing afterhyperpolarization or cumulative inactivation.","method":"Electrophysiology (patch-clamp), co-immunoprecipitation, heterologous expression","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional characterization with multiple electrophysiological parameters, channel complex formation confirmed, widely replicated in follow-up studies","pmids":["11207363"],"is_preprint":false},{"year":2001,"finding":"A missense mutation R83H in KCNE3 reduces current density of MiRP2-Kv3.4 complexes and diminishes their capacity to set resting membrane potential, segregating with familial periodic paralysis.","method":"Electrophysiology (patch-clamp), genetic segregation analysis","journal":"Cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional electrophysiology in heterologous system plus genetic co-segregation, but R83H pathogenicity later disputed by control studies","pmids":["11207363"],"is_preprint":false},{"year":2006,"finding":"KCNE3 (MiRP2) has a single functional PKC phosphorylation site at serine 82, and normal MiRP2-Kv3.4 function requires phosphorylation of this site. The R83H variant does not prevent PKC phosphorylation of S82 but endows MiRP2-Kv3.4 channels with sensitivity to intracellular pH changes across the physiological range (pKa ~7.3, consistent with histidine protonation), reducing single-channel current as internal pH is lowered.","method":"Electrophysiology (patch-clamp), mutagenesis, PKC phosphorylation assays","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of phosphorylation site combined with in vitro functional assays, two orthogonal approaches (PKC assay + electrophysiology)","pmids":["16449802"],"is_preprint":false},{"year":2004,"finding":"The KCNE3 transmembrane domain alone is sufficient for assembly with and constitutive activation (basal activation) of KCNQ1 channels; neither the N-terminal nor C-terminal regions are required for this modulation. This contrasts with KCNE1, where the transmembrane domain is passive and the C-terminus drives modulation, revealing a bipartite model of KCNQ1 modulation.","method":"Truncation mutagenesis, heterologous expression, whole-cell patch-clamp","journal":"The Journal of general physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic truncation panel with multiple mutants and functional electrophysiology, mechanistic conclusion supported by rescue experiment with KCNE1 LQT mutant","pmids":["15572349"],"is_preprint":false},{"year":2008,"finding":"KCNE3 physically interacts with Kv4.3 in human atrial tissue, demonstrated by co-immunoprecipitation. A missense mutation R99H in KCNE3 significantly increases Ito current density when co-expressed with KCND3 (Kv4.3), establishing a gain-of-function role in Brugada syndrome pathogenesis.","method":"Co-immunoprecipitation from human atrial tissue, whole-cell patch-clamp in CHO cells, heterologous co-transfection","journal":"Circulation. Arrhythmia and electrophysiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP in native human tissue combined with electrophysiology, two orthogonal methods","pmids":["19122847"],"is_preprint":false},{"year":2008,"finding":"KCNE3 V17M mutation increases activity of Kv4.3/KCNE3 and Kv11.1/KCNE3 channels in Xenopus oocytes, consistent with gain-of-function on multiple cardiac currents and susceptibility to atrial fibrillation.","method":"Two-electrode voltage-clamp in Xenopus laevis oocytes, heterologous expression","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean electrophysiology in oocyte system, single lab, single method","pmids":["18209471"],"is_preprint":false},{"year":2009,"finding":"KCNE3 mutation R99H reduces outward current through KCNQ1/KCNE3 complexes in CHO cells, representing a loss-of-function mechanism linked to long QT syndrome (LQTS). Mutation T4A showed no statistically significant change in current density.","method":"Whole-cell patch-clamp in CHO cells stably expressing KCNQ1, heterologous co-expression","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — electrophysiology in heterologous system, single lab, single method","pmids":["19306396"],"is_preprint":false},{"year":2010,"finding":"KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells. Kcne3 knockout mice show drastically reduced cAMP-stimulated electrogenic Cl- secretion across tracheal and intestinal epithelia, demonstrating that KCNE3 modification of KCNQ1 biophysical properties (not KCNQ1 abundance or localization) is essential for K+ recycling and transepithelial Cl- secretion.","method":"Kcne3 knockout mouse model, Ussing chamber Cl- secretion measurements, immunolocalization, membrane fractionation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with specific physiological readout, subcellular localization, confirmed KCNQ1 unchanged, multiple orthogonal methods","pmids":["20051516"],"is_preprint":false},{"year":2011,"finding":"KCNQ1 and KCNE3 co-associate in colonic crypts and 17β-estradiol (E2) rapidly (<15 min) dissociates KCNQ1:KCNE3 complexes specifically in female crypts. This dissociation underlies the sexual dimorphism in colonic Cl- secretion. KCNE3-S82A mutation (abolishing PKCδ phosphorylation site) causes rapid run-down and insensitivity to E2, implicating phosphorylation at S82 in estrogen-regulated channel dissociation.","method":"Co-immunoprecipitation, whole-cell patch-clamp, short-circuit current recording, co-expression in CHO cells","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus electrophysiology plus site-directed mutagenesis, two orthogonal approaches","pmids":["21911611"],"is_preprint":false},{"year":2012,"finding":"KCNE3 T4A mutation increases Ito reconstituted by co-expressing Kv4.3 + KChIP2b + KCNE3 in CHO cells, representing a gain-of-function mechanism associated with Brugada-pattern ECG.","method":"Whole-cell patch-clamp in CHO cells, heterologous co-expression","journal":"Circulation journal","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean electrophysiology, single lab, single method","pmids":["22987075"],"is_preprint":false},{"year":2013,"finding":"Kcne3 deletion in mice causes secondary hyperaldosteronism associated with adrenal-specific lymphocyte infiltration, which in turn impairs ventricular repolarization (QTc prolongation) and predisposes to post-ischemia ventricular tachycardia. This establishes an extracardiac, aldosterone-dependent arrhythmogenic mechanism for KCNE3 loss.","method":"Kcne3-/- mouse model, ECG, patch-clamp, qPCR, microarray, coronary artery ligation/reperfusion, blood analysis, histology","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple orthogonal readouts (ECG, patch-clamp, histology, blood assays), aldosterone dependence established","pmids":["24225147"],"is_preprint":false},{"year":2014,"finding":"KCNE3 null deletion abolishes characteristic wide variations in resting membrane potential of spiral ganglion neurons and causes age-dependent alterations in action potential and firing properties. KCNE3 regulates activity of Kv4.2 channels in spiral ganglion neurons, with null mutation resulting in enhanced outward K+ currents.","method":"Kcne3-/- mouse model, patch-clamp of spiral ganglion neurons, conductance analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with specific electrophysiological readouts, multiple firing properties measured, KChIP2-independent Kv4.2 regulation identified","pmids":["24727472"],"is_preprint":false},{"year":2015,"finding":"KCNE3 acts primarily by shifting the voltage dependence of S4 (voltage sensor) movement to extreme hyperpolarized potentials, making KCNQ1/KCNE3 channels constitutively conducting within the physiological voltage range. Two negatively charged residues D54 and D55 in KCNE3 are essential for this effect, exerting electrostatic interaction with R228 in the KCNQ1 S4 segment. KCNE3 directly affects voltage sensor movement and only indirectly affects the gate.","method":"Voltage clamp fluorometry, mutagenesis, PIP2 depletion, separation of S4 movement and gate opening","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — voltage clamp fluorometry directly reports S4 movement, mutagenesis identifies critical residues, PIP2 depletion as orthogonal tool, two orthogonal approaches","pmids":["26668384"],"is_preprint":false},{"year":2015,"finding":"KCNE1 and KCNE3 affect KCNQ1 gating by different mechanisms: KCNE1 affects both S4 movement and the gate, whereas KCNE3 affects S4 movement and only affects the gate if intact S4-to-gate coupling is present. A triple mutation in the middle of the KCNE3 transmembrane segment introduces KCNE1-like effects on the second S4 movement and the gate. Differences in two residues at the external end of KCNE transmembrane segments underlie differences in effects on the first S4 movement and voltage sensor-to-gate coupling.","method":"Voltage clamp fluorometry, mutagenesis (triple TM mutation), PIP2 depletion, separation of S4 movement and gate opening","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — voltage clamp fluorometry directly monitors S4 and gate, mutagenesis with domain-swap experiments, two independent PNAS papers (2015 and 2017) using same approach","pmids":["28808020"],"is_preprint":false},{"year":2016,"finding":"An integrative structural model of the KCNE3-KCNQ1 complex, built from NMR, computational, and electrophysiological data, shows that KCNE3 residues at both ends of its transmembrane domain directly interact with residues on the intra- and extracellular ends of the KCNQ1 voltage-sensing domain S4 helix, stabilizing the activated 'up' state of S4 and thereby inducing constitutive activation of the channel gate.","method":"Solution NMR structure, computational modeling, electrophysiology, mutagenesis","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 / Strong — integrative structural model with NMR, computation, and mutagenesis-guided electrophysiology, multiple orthogonal methods in one study","pmids":["27626070"],"is_preprint":false},{"year":2016,"finding":"Novel N-terminally extended (full-length) KCNE3 isoform, encoded by a previously undiscovered exon 1 protein-coding region adding 44 residues to the extracellular domain, preserves KCNQ1 constitutive activation but prevents KCNE3 inhibition of Kv4.2 and KCNQ4. This indicates the additional N-terminal segment modulates partner-channel specificity.","method":"Two-electrode voltage-clamp in Xenopus laevis oocytes, heterologous expression, RT-PCR/Western blot for tissue expression","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiology with multiple channel partners, tissue expression confirmed, single lab","pmids":["27162025"],"is_preprint":false},{"year":2016,"finding":"In Kcne3-/- mice, AF predisposition arises from increased aldosterone-dependent recycling of Kv1.5 channels to the Z-disc/T-tubulus region and lateral membrane via activation of the Akt/AS160 pathway and Rab4, -5, and -9 GTPases, leading to reduced atrial effective refractory period. Spironolactone treatment normalized these effects, confirming aldosterone dependence.","method":"Kcne3-/- mouse model, electrophysiology (invasive), co-immunoprecipitation, Western blot for Akt/AS160 phosphorylation, pharmacological rescue with spironolactone","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with pharmacological rescue, signaling pathway (Akt/AS160/Rab) identified mechanistically, multiple orthogonal methods","pmids":["26985008"],"is_preprint":false},{"year":2009,"finding":"KCNE1 and KCNE3 both regulate Kv12.2 (KCNH3) channel surface expression and gating: siRNA knockdown of KCNE1 or KCNE3 increases macroscopic Kv12.2 currents ~4-fold by increasing membrane surface expression (not total protein). Co-expression of both siRNAs produces ~9-fold increase (additive). Native co-immunoprecipitation from mouse brain membranes shows KCNE1 and KCNE3 interact with Kv12.2 simultaneously, suggesting tripartite complexes in vivo.","method":"siRNA knockdown in Xenopus oocytes, surface biotinylation assay, co-immunoprecipitation from mouse brain, electrophysiology","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP from native tissue combined with surface biotinylation and electrophysiology, multiple orthogonal methods","pmids":["19623261"],"is_preprint":false},{"year":2017,"finding":"KCNE3 deletion in mice impairs skeletal muscle function: Kcne3-/- mice show abnormal hindlimb clasping, loss of biphasic contractile force decline with repetitive stimulation in vivo and in vitro, and myoblasts from Kcne3-/- mice have faster-inactivating and smaller sustained outward K+ currents. Kcne3 deletion also specifically down-regulates KCNC4 (Kv3.4) and KCNH2 (mERG) alpha subunit expression and shifts muscle fiber type toward type IIa fast-twitch oxidative fibers.","method":"Kcne3-/- mouse model, in vivo/in vitro muscle force measurements, patch-clamp of myoblasts, microarray, immunofluorescence","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with specific contractile phenotype, electrophysiology, transcriptomics and fiber-type immunofluorescence, multiple orthogonal methods","pmids":["28356343"],"is_preprint":false},{"year":2002,"finding":"Ectopic expression of KCNE3 in cardiac myocytes (via adenoviral delivery) interacts with KCNQ1 to increase outward current and accelerate activation, reducing action potential duration >3-fold in transduced cells and abbreviating QT interval by ~10% in guinea pigs.","method":"Heterologous co-expression (CHO), adenoviral transduction in guinea pig ventricle, patch-clamp, ECG recording","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo functional consequence (QT shortening) combined with in vitro electrophysiology and quantitative modeling, two orthogonal approaches","pmids":["11956246"],"is_preprint":false},{"year":2022,"finding":"Optimized tight binding between the S1 segment of KCNQ1 and the transmembrane domain of KCNE3 is required for constitutive channel activity. Volume scanning mutagenesis of interacting residues at the S1-KCNE3 interface shows the inter-helical distance is precisely calibrated; two pairs of compensatory KCNQ1/KCNE3 mutants partially restore constitutive activity when co-expressed, confirming a direct physical interaction.","method":"Volume scanning mutagenesis, compensatory mutagenesis, electrophysiology, based on KCNQ1-KCNE3-calmodulin complex structure","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structure-guided mutagenesis with compensatory rescue experiments confirming direct contact, multiple mutants tested","pmids":["36331187"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM structures of KCNQ1-KCNE1 and reassessed KCNQ1-KCNE3 structures reveal two PIP2-binding sites in both complexes. KCNE3 contributes to a second, previously uncharacterized PIP2-binding site involving residues critical for voltage sensor-pore domain coupling. Through this site, KCNE3 converts KCNQ1 into a voltage-insensitive, PIP2-gated channel governed by GPCR signaling, maintaining ion homeostasis in non-excitable epithelial cells.","method":"Cryo-EM structure determination, electrophysiology, PIP2 binding site mutagenesis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — cryo-EM structural data plus electrophysiology, but preprint not yet peer-reviewed","pmids":[],"is_preprint":true}],"current_model":"KCNE3 (MiRP2) is a single-transmembrane regulatory β-subunit that assembles with multiple voltage-gated K+ channel α-subunits (primarily KCNQ1 and Kv3.4, but also Kv4.3, Kv12.2, and others) to profoundly alter their gating: in epithelial cells, KCNE3 stabilizes the activated 'up' state of the KCNQ1 voltage sensor S4 through direct electrostatic interactions (D54/D55 with R228) and tight contacts with the S1 segment, converting voltage-dependent KCNQ1 into a constitutively open, PIP2-gated K+ channel that drives basolateral K+ recycling for transepithelial Cl- secretion; in skeletal muscle, KCNE3 assembles with Kv3.4, shifts activation voltage, and requires PKC phosphorylation at S82 to set resting membrane potential; and in the heart it modulates Ito (via Kv4.3) and IKr, with disease-causing mutations producing gain- or loss-of-function effects linked to periodic paralysis, Brugada syndrome, long QT syndrome, and atrial fibrillation."},"narrative":{"mechanistic_narrative":"KCNE3 (MiRP2) is a single-transmembrane regulatory β-subunit that assembles with multiple voltage-gated K+ channel α-subunits to reshape their gating and set the electrical properties of epithelial, muscle, neuronal, and cardiac cells [PMID:11207363, PMID:20051516]. Its best-defined action is on KCNQ1: the KCNE3 transmembrane domain alone is sufficient to assemble with and constitutively activate KCNQ1, with neither terminus required [PMID:15572349], and it does so by shifting the voltage dependence of S4 voltage-sensor movement to extreme hyperpolarized potentials so the channel conducts across the physiological range [PMID:26668384]. This stabilization of the activated 'up' state of S4 is achieved through direct electrostatic and inter-helical contacts—the acidic KCNE3 residues D54/D55 engaging KCNQ1 S4 R228, contacts at both ends of the KCNE3 transmembrane domain with the voltage-sensing domain, and a precisely calibrated tight interface with the KCNQ1 S1 segment confirmed by compensatory mutagenesis [PMID:26668384, PMID:27626070, PMID:36331187]. In epithelia, KCNQ1/KCNE3 heteromers reside in the basolateral membrane and provide the K+ recycling required for cAMP-stimulated transepithelial Cl- secretion; Kcne3 knockout abolishes this secretion without altering KCNQ1 abundance, and 17β-estradiol acutely dissociates the complex via PKCδ phosphorylation of KCNE3 S82 to produce sexually dimorphic colonic secretion [PMID:20051516, PMID:21911611]. In skeletal muscle, KCNE3 assembles with Kv3.4 to form a subthreshold channel that sets resting membrane potential, an interaction dependent on PKC phosphorylation at S82 [PMID:11207363, PMID:16449802]. KCNE3 also modulates cardiac currents through Kv4.3 and Kv12.2 and regulates neuronal Kv4.2, and timeline disease findings link KCNE3 variants to familial periodic paralysis, Brugada syndrome, long QT syndrome, and atrial fibrillation through gain- or loss-of-function effects on these partner channels [PMID:11207363, PMID:19122847, PMID:19306396, PMID:19623261].","teleology":[{"year":2001,"claim":"Established KCNE3 as a functional β-subunit by showing it assembles with Kv3.4 to create a distinct subthreshold channel that sets skeletal muscle resting potential, and tied a KCNE3 variant to periodic paralysis.","evidence":"Patch-clamp, co-immunoprecipitation, heterologous expression and genetic segregation of R83H","pmids":["11207363"],"confidence":"High","gaps":["R83H pathogenicity later disputed","structural basis of Kv3.4 modulation not resolved"]},{"year":2002,"claim":"Demonstrated that KCNE3 modulation of KCNQ1 has direct physiological consequence by showing ectopic KCNE3 accelerates current and shortens action potential and QT interval in vivo.","evidence":"Heterologous co-expression, adenoviral transduction in guinea pig ventricle, patch-clamp and ECG","pmids":["11956246"],"confidence":"High","gaps":["ectopic rather than native cardiac context","mechanism of gating change not yet mapped to residues"]},{"year":2004,"claim":"Localized KCNQ1-activating function to the KCNE3 transmembrane domain, distinguishing it from the C-terminus-driven KCNE1 mechanism and defining a bipartite model.","evidence":"Truncation mutagenesis panel with whole-cell patch-clamp in heterologous cells","pmids":["15572349"],"confidence":"High","gaps":["specific contact residues not identified","did not resolve voltage-sensor versus gate target"]},{"year":2006,"claim":"Identified S82 as the functional PKC phosphorylation site required for MiRP2-Kv3.4 function and showed R83H confers pathological pH sensitivity rather than blocking phosphorylation.","evidence":"Mutagenesis, PKC phosphorylation assays and patch-clamp","pmids":["16449802"],"confidence":"High","gaps":["physiological trigger of S82 phosphorylation in muscle not defined","kinase identity in vivo not established"]},{"year":2008,"claim":"Extended KCNE3 partnerships to cardiac Kv4.3 and Kv11.1 and linked gain-of-function variants (R99H, V17M) to Brugada syndrome and atrial fibrillation.","evidence":"Co-IP from human atrial tissue and voltage-clamp of channel complexes in CHO and oocytes","pmids":["19122847","18209471"],"confidence":"Medium","gaps":["single-method electrophysiology for V17M","in vivo arrhythmic mechanism not tested"]},{"year":2009,"claim":"Showed the same R99H variant reduces KCNQ1/KCNE3 current (long QT mechanism) and that KCNE3 suppresses Kv12.2 surface expression in native brain, revealing partner-dependent and additive regulation.","evidence":"Patch-clamp in CHO cells; siRNA knockdown, surface biotinylation and brain co-IP for Kv12.2","pmids":["19306396","19623261"],"confidence":"Medium","gaps":["opposite directional effects of R99H across partners unreconciled","tripartite KCNE1/KCNE3/Kv12.2 stoichiometry not resolved"]},{"year":2010,"claim":"Proved in vivo that KCNE3 biophysical modulation of basolateral KCNQ1—not KCNQ1 abundance—is required for transepithelial Cl- secretion.","evidence":"Kcne3 knockout mice, Ussing chamber secretion assays, immunolocalization and membrane fractionation","pmids":["20051516"],"confidence":"High","gaps":["upstream signaling controlling complex activity in epithelia not yet defined"]},{"year":2011,"claim":"Revealed dynamic, hormone-regulated control of the complex: estradiol dissociates KCNQ1:KCNE3 via PKCδ phosphorylation of S82, explaining sexual dimorphism in colonic secretion.","evidence":"Co-IP, patch-clamp, short-circuit current and S82A mutagenesis in crypts and CHO cells","pmids":["21911611"],"confidence":"High","gaps":["estrogen receptor coupling to PKCδ not detailed","in vivo reversibility kinetics not measured"]},{"year":2013,"claim":"Uncovered an extracardiac arrhythmogenic mechanism whereby Kcne3 loss causes aldosterone-dependent adrenal pathology that impairs ventricular repolarization.","evidence":"Kcne3-/- mice with ECG, patch-clamp, histology, blood assays and ischemia-reperfusion","pmids":["24225147"],"confidence":"High","gaps":["link between KCNE3 channel function and aldosterone regulation not molecularly defined"]},{"year":2014,"claim":"Showed KCNE3 shapes neuronal excitability by regulating Kv4.2 in spiral ganglion neurons independent of KChIP2.","evidence":"Kcne3-/- mice with patch-clamp and conductance analysis of spiral ganglion neurons","pmids":["24727472"],"confidence":"High","gaps":["direct KCNE3-Kv4.2 binding not structurally mapped","behavioral/auditory consequence not assessed"]},{"year":2015,"claim":"Defined the gating mechanism: KCNE3 acts on KCNQ1 by hyperpolarizing S4 voltage-sensor movement via D54/D55–R228 electrostatics, affecting the gate only indirectly—mechanistically distinct from KCNE1.","evidence":"Voltage clamp fluorometry, mutagenesis, domain-swap and PIP2 depletion separating S4 movement from gating","pmids":["26668384","28808020"],"confidence":"High","gaps":["full atomic stoichiometry of S4 contacts addressed separately by structural work"]},{"year":2016,"claim":"Built an integrative structural model of the contacts driving constitutive activation, identified an N-terminally extended isoform that tunes partner specificity, and mapped the aldosterone/Akt/Rab pathway underlying AF in knockouts.","evidence":"NMR-guided modeling with electrophysiology; oocyte electrophysiology of isoforms; Kcne3-/- mice with co-IP, Western blot and spironolactone rescue","pmids":["27626070","27162025","26985008"],"confidence":"High","gaps":["isoform tissue distribution and abundance incompletely defined","high-resolution structure not yet available at this stage"]},{"year":2017,"claim":"Demonstrated KCNE3 is required for normal skeletal muscle contractile dynamics and controls Kv3.4/mERG subunit expression and fiber-type composition.","evidence":"Kcne3-/- mice with muscle force measurements, myoblast patch-clamp, microarray and fiber-type immunofluorescence","pmids":["28356343"],"confidence":"High","gaps":["transcriptional mechanism controlling Kv3.4/KCNH2 expression not defined"]},{"year":2022,"claim":"Confirmed that a precisely calibrated tight S1–KCNE3 transmembrane interface is required for constitutive activity, using compensatory mutant rescue to prove direct physical contact.","evidence":"Volume-scanning and compensatory mutagenesis with electrophysiology guided by the KCNQ1-KCNE3-calmodulin structure","pmids":["36331187"],"confidence":"High","gaps":["energetics of the interface not quantified","how S1 contact integrates with S4 stabilization not unified"]},{"year":2025,"claim":"Cryo-EM reassessment identified a second KCNE3-dependent PIP2-binding site, recasting KCNE3 as converting KCNQ1 into a voltage-insensitive, PIP2- and GPCR-gated channel.","evidence":"Cryo-EM, electrophysiology and PIP2 site mutagenesis (preprint)","pmids":[],"confidence":"Medium","gaps":["preprint not peer-reviewed","GPCR signaling coupling demonstrated only inferentially","functional contribution of second PIP2 site in native epithelia not tested"]},{"year":null,"claim":"How KCNE3 selects among its many partner α-subunits in different tissues, and how upstream signaling (PKC, estrogen, aldosterone, PIP2/GPCR) is integrated to dynamically gate these complexes in vivo, remains incompletely resolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["no unified model of partner selection across tissues","in vivo signaling integration not reconstituted","stoichiometry of multi-KCNE/multi-α complexes uncertain"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,7,12]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[7,17]}],"pathway":[],"complexes":["KCNQ1/KCNE3 channel","MiRP2-Kv3.4 channel"],"partners":["KCNQ1","KCNC4","KCND3","KCNH3","KCNH2","KCND2","CALM1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y6H6","full_name":"Potassium voltage-gated channel subfamily E member 3","aliases":["MinK-related peptide 2","MiRP2","Minimum potassium ion channel-related peptide 2","Potassium channel subunit beta MiRP2"],"length_aa":103,"mass_kda":11.7,"function":"Ancillary protein that functions as a regulatory subunit of the voltage-gated potassium (Kv) channel complex composed of pore-forming and potassium-conducting alpha subunits and of regulatory beta subunits. KCNE3 beta subunit modulates the gating kinetics and enhances stability of the channel complex (PubMed:10646604, PubMed:11207363, PubMed:12954870). Alters the gating of the delayed rectifier Kv channel containing KCNB1 alpha subunit (PubMed:12954870). Associates with KCNC4/Kv3.4 alpha subunit to form the subthreshold Kv channel in skeletal muscle and to establish the resting membrane potential (RMP) in muscle cells (PubMed:11207363). Association with KCNQ1/KCLQT1 alpha subunit may form the intestinal cAMP-stimulated potassium channel involved in chloride secretion that produces a current with nearly instantaneous activation with a linear current-voltage relationship (By similarity)","subcellular_location":"Cell membrane; Cytoplasm; Perikaryon; Cell projection, dendrite; Membrane raft","url":"https://www.uniprot.org/uniprotkb/Q9Y6H6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCNE3","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCNE3","total_profiled":1310},"omim":[{"mim_id":"613119","title":"BRUGADA SYNDROME 6; BRGDA6","url":"https://www.omim.org/entry/613119"},{"mim_id":"611451","title":"DEAFNESS, AUTOSOMAL RECESSIVE 63; DFNB63","url":"https://www.omim.org/entry/611451"},{"mim_id":"607554","title":"ATRIAL FIBRILLATION, FAMILIAL, 3; ATFB3","url":"https://www.omim.org/entry/607554"},{"mim_id":"607542","title":"POTASSIUM CHANNEL, VOLTAGE-GATED, KQT-LIKE SUBFAMILY, MEMBER 1; KCNQ1","url":"https://www.omim.org/entry/607542"},{"mim_id":"604433","title":"POTASSIUM CHANNEL, VOLTAGE-GATED, ISK-RELATED SUBFAMILY, MEMBER 3; KCNE3","url":"https://www.omim.org/entry/604433"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"intestine","ntpm":66.2},{"tissue":"stomach 1","ntpm":53.0}],"url":"https://www.proteinatlas.org/search/KCNE3"},"hgnc":{"alias_symbol":["MiRP2","HOKPP"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y6H6","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6H6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6H6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y6H6-F1-predicted_aligned_error_v6.png","plddt_mean":71.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCNE3","jax_strain_url":"https://www.jax.org/strain/search?query=KCNE3"},"sequence":{"accession":"Q9Y6H6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y6H6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y6H6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y6H6"}},"corpus_meta":[{"pmid":"11207363","id":"PMC_11207363","title":"MiRP2 forms potassium channels in skeletal muscle with Kv3.4 and is associated with periodic paralysis.","date":"2001","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/11207363","citation_count":240,"is_preprint":false},{"pmid":"19122847","id":"PMC_19122847","title":"Functional effects of KCNE3 mutation and its role in the development of Brugada syndrome.","date":"2008","source":"Circulation. 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MiRP2-Kv3.4 channels differ from Kv3.4 alone in unitary conductance, voltage-dependent activation, recovery from inactivation, steady-state open probability, and block by peptide toxin, and set resting membrane potential without producing afterhyperpolarization or cumulative inactivation.\",\n      \"method\": \"Electrophysiology (patch-clamp), co-immunoprecipitation, heterologous expression\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional characterization with multiple electrophysiological parameters, channel complex formation confirmed, widely replicated in follow-up studies\",\n      \"pmids\": [\"11207363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"A missense mutation R83H in KCNE3 reduces current density of MiRP2-Kv3.4 complexes and diminishes their capacity to set resting membrane potential, segregating with familial periodic paralysis.\",\n      \"method\": \"Electrophysiology (patch-clamp), genetic segregation analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrophysiology in heterologous system plus genetic co-segregation, but R83H pathogenicity later disputed by control studies\",\n      \"pmids\": [\"11207363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"KCNE3 (MiRP2) has a single functional PKC phosphorylation site at serine 82, and normal MiRP2-Kv3.4 function requires phosphorylation of this site. The R83H variant does not prevent PKC phosphorylation of S82 but endows MiRP2-Kv3.4 channels with sensitivity to intracellular pH changes across the physiological range (pKa ~7.3, consistent with histidine protonation), reducing single-channel current as internal pH is lowered.\",\n      \"method\": \"Electrophysiology (patch-clamp), mutagenesis, PKC phosphorylation assays\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of phosphorylation site combined with in vitro functional assays, two orthogonal approaches (PKC assay + electrophysiology)\",\n      \"pmids\": [\"16449802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The KCNE3 transmembrane domain alone is sufficient for assembly with and constitutive activation (basal activation) of KCNQ1 channels; neither the N-terminal nor C-terminal regions are required for this modulation. This contrasts with KCNE1, where the transmembrane domain is passive and the C-terminus drives modulation, revealing a bipartite model of KCNQ1 modulation.\",\n      \"method\": \"Truncation mutagenesis, heterologous expression, whole-cell patch-clamp\",\n      \"journal\": \"The Journal of general physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic truncation panel with multiple mutants and functional electrophysiology, mechanistic conclusion supported by rescue experiment with KCNE1 LQT mutant\",\n      \"pmids\": [\"15572349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"KCNE3 physically interacts with Kv4.3 in human atrial tissue, demonstrated by co-immunoprecipitation. A missense mutation R99H in KCNE3 significantly increases Ito current density when co-expressed with KCND3 (Kv4.3), establishing a gain-of-function role in Brugada syndrome pathogenesis.\",\n      \"method\": \"Co-immunoprecipitation from human atrial tissue, whole-cell patch-clamp in CHO cells, heterologous co-transfection\",\n      \"journal\": \"Circulation. Arrhythmia and electrophysiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP in native human tissue combined with electrophysiology, two orthogonal methods\",\n      \"pmids\": [\"19122847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"KCNE3 V17M mutation increases activity of Kv4.3/KCNE3 and Kv11.1/KCNE3 channels in Xenopus oocytes, consistent with gain-of-function on multiple cardiac currents and susceptibility to atrial fibrillation.\",\n      \"method\": \"Two-electrode voltage-clamp in Xenopus laevis oocytes, heterologous expression\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean electrophysiology in oocyte system, single lab, single method\",\n      \"pmids\": [\"18209471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"KCNE3 mutation R99H reduces outward current through KCNQ1/KCNE3 complexes in CHO cells, representing a loss-of-function mechanism linked to long QT syndrome (LQTS). Mutation T4A showed no statistically significant change in current density.\",\n      \"method\": \"Whole-cell patch-clamp in CHO cells stably expressing KCNQ1, heterologous co-expression\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — electrophysiology in heterologous system, single lab, single method\",\n      \"pmids\": [\"19306396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells. Kcne3 knockout mice show drastically reduced cAMP-stimulated electrogenic Cl- secretion across tracheal and intestinal epithelia, demonstrating that KCNE3 modification of KCNQ1 biophysical properties (not KCNQ1 abundance or localization) is essential for K+ recycling and transepithelial Cl- secretion.\",\n      \"method\": \"Kcne3 knockout mouse model, Ussing chamber Cl- secretion measurements, immunolocalization, membrane fractionation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with specific physiological readout, subcellular localization, confirmed KCNQ1 unchanged, multiple orthogonal methods\",\n      \"pmids\": [\"20051516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"KCNQ1 and KCNE3 co-associate in colonic crypts and 17β-estradiol (E2) rapidly (<15 min) dissociates KCNQ1:KCNE3 complexes specifically in female crypts. This dissociation underlies the sexual dimorphism in colonic Cl- secretion. KCNE3-S82A mutation (abolishing PKCδ phosphorylation site) causes rapid run-down and insensitivity to E2, implicating phosphorylation at S82 in estrogen-regulated channel dissociation.\",\n      \"method\": \"Co-immunoprecipitation, whole-cell patch-clamp, short-circuit current recording, co-expression in CHO cells\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus electrophysiology plus site-directed mutagenesis, two orthogonal approaches\",\n      \"pmids\": [\"21911611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"KCNE3 T4A mutation increases Ito reconstituted by co-expressing Kv4.3 + KChIP2b + KCNE3 in CHO cells, representing a gain-of-function mechanism associated with Brugada-pattern ECG.\",\n      \"method\": \"Whole-cell patch-clamp in CHO cells, heterologous co-expression\",\n      \"journal\": \"Circulation journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean electrophysiology, single lab, single method\",\n      \"pmids\": [\"22987075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Kcne3 deletion in mice causes secondary hyperaldosteronism associated with adrenal-specific lymphocyte infiltration, which in turn impairs ventricular repolarization (QTc prolongation) and predisposes to post-ischemia ventricular tachycardia. This establishes an extracardiac, aldosterone-dependent arrhythmogenic mechanism for KCNE3 loss.\",\n      \"method\": \"Kcne3-/- mouse model, ECG, patch-clamp, qPCR, microarray, coronary artery ligation/reperfusion, blood analysis, histology\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple orthogonal readouts (ECG, patch-clamp, histology, blood assays), aldosterone dependence established\",\n      \"pmids\": [\"24225147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"KCNE3 null deletion abolishes characteristic wide variations in resting membrane potential of spiral ganglion neurons and causes age-dependent alterations in action potential and firing properties. KCNE3 regulates activity of Kv4.2 channels in spiral ganglion neurons, with null mutation resulting in enhanced outward K+ currents.\",\n      \"method\": \"Kcne3-/- mouse model, patch-clamp of spiral ganglion neurons, conductance analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with specific electrophysiological readouts, multiple firing properties measured, KChIP2-independent Kv4.2 regulation identified\",\n      \"pmids\": [\"24727472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"KCNE3 acts primarily by shifting the voltage dependence of S4 (voltage sensor) movement to extreme hyperpolarized potentials, making KCNQ1/KCNE3 channels constitutively conducting within the physiological voltage range. Two negatively charged residues D54 and D55 in KCNE3 are essential for this effect, exerting electrostatic interaction with R228 in the KCNQ1 S4 segment. KCNE3 directly affects voltage sensor movement and only indirectly affects the gate.\",\n      \"method\": \"Voltage clamp fluorometry, mutagenesis, PIP2 depletion, separation of S4 movement and gate opening\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — voltage clamp fluorometry directly reports S4 movement, mutagenesis identifies critical residues, PIP2 depletion as orthogonal tool, two orthogonal approaches\",\n      \"pmids\": [\"26668384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"KCNE1 and KCNE3 affect KCNQ1 gating by different mechanisms: KCNE1 affects both S4 movement and the gate, whereas KCNE3 affects S4 movement and only affects the gate if intact S4-to-gate coupling is present. A triple mutation in the middle of the KCNE3 transmembrane segment introduces KCNE1-like effects on the second S4 movement and the gate. Differences in two residues at the external end of KCNE transmembrane segments underlie differences in effects on the first S4 movement and voltage sensor-to-gate coupling.\",\n      \"method\": \"Voltage clamp fluorometry, mutagenesis (triple TM mutation), PIP2 depletion, separation of S4 movement and gate opening\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — voltage clamp fluorometry directly monitors S4 and gate, mutagenesis with domain-swap experiments, two independent PNAS papers (2015 and 2017) using same approach\",\n      \"pmids\": [\"28808020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"An integrative structural model of the KCNE3-KCNQ1 complex, built from NMR, computational, and electrophysiological data, shows that KCNE3 residues at both ends of its transmembrane domain directly interact with residues on the intra- and extracellular ends of the KCNQ1 voltage-sensing domain S4 helix, stabilizing the activated 'up' state of S4 and thereby inducing constitutive activation of the channel gate.\",\n      \"method\": \"Solution NMR structure, computational modeling, electrophysiology, mutagenesis\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — integrative structural model with NMR, computation, and mutagenesis-guided electrophysiology, multiple orthogonal methods in one study\",\n      \"pmids\": [\"27626070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Novel N-terminally extended (full-length) KCNE3 isoform, encoded by a previously undiscovered exon 1 protein-coding region adding 44 residues to the extracellular domain, preserves KCNQ1 constitutive activation but prevents KCNE3 inhibition of Kv4.2 and KCNQ4. This indicates the additional N-terminal segment modulates partner-channel specificity.\",\n      \"method\": \"Two-electrode voltage-clamp in Xenopus laevis oocytes, heterologous expression, RT-PCR/Western blot for tissue expression\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiology with multiple channel partners, tissue expression confirmed, single lab\",\n      \"pmids\": [\"27162025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In Kcne3-/- mice, AF predisposition arises from increased aldosterone-dependent recycling of Kv1.5 channels to the Z-disc/T-tubulus region and lateral membrane via activation of the Akt/AS160 pathway and Rab4, -5, and -9 GTPases, leading to reduced atrial effective refractory period. Spironolactone treatment normalized these effects, confirming aldosterone dependence.\",\n      \"method\": \"Kcne3-/- mouse model, electrophysiology (invasive), co-immunoprecipitation, Western blot for Akt/AS160 phosphorylation, pharmacological rescue with spironolactone\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with pharmacological rescue, signaling pathway (Akt/AS160/Rab) identified mechanistically, multiple orthogonal methods\",\n      \"pmids\": [\"26985008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"KCNE1 and KCNE3 both regulate Kv12.2 (KCNH3) channel surface expression and gating: siRNA knockdown of KCNE1 or KCNE3 increases macroscopic Kv12.2 currents ~4-fold by increasing membrane surface expression (not total protein). Co-expression of both siRNAs produces ~9-fold increase (additive). Native co-immunoprecipitation from mouse brain membranes shows KCNE1 and KCNE3 interact with Kv12.2 simultaneously, suggesting tripartite complexes in vivo.\",\n      \"method\": \"siRNA knockdown in Xenopus oocytes, surface biotinylation assay, co-immunoprecipitation from mouse brain, electrophysiology\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP from native tissue combined with surface biotinylation and electrophysiology, multiple orthogonal methods\",\n      \"pmids\": [\"19623261\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"KCNE3 deletion in mice impairs skeletal muscle function: Kcne3-/- mice show abnormal hindlimb clasping, loss of biphasic contractile force decline with repetitive stimulation in vivo and in vitro, and myoblasts from Kcne3-/- mice have faster-inactivating and smaller sustained outward K+ currents. Kcne3 deletion also specifically down-regulates KCNC4 (Kv3.4) and KCNH2 (mERG) alpha subunit expression and shifts muscle fiber type toward type IIa fast-twitch oxidative fibers.\",\n      \"method\": \"Kcne3-/- mouse model, in vivo/in vitro muscle force measurements, patch-clamp of myoblasts, microarray, immunofluorescence\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with specific contractile phenotype, electrophysiology, transcriptomics and fiber-type immunofluorescence, multiple orthogonal methods\",\n      \"pmids\": [\"28356343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Ectopic expression of KCNE3 in cardiac myocytes (via adenoviral delivery) interacts with KCNQ1 to increase outward current and accelerate activation, reducing action potential duration >3-fold in transduced cells and abbreviating QT interval by ~10% in guinea pigs.\",\n      \"method\": \"Heterologous co-expression (CHO), adenoviral transduction in guinea pig ventricle, patch-clamp, ECG recording\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo functional consequence (QT shortening) combined with in vitro electrophysiology and quantitative modeling, two orthogonal approaches\",\n      \"pmids\": [\"11956246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Optimized tight binding between the S1 segment of KCNQ1 and the transmembrane domain of KCNE3 is required for constitutive channel activity. Volume scanning mutagenesis of interacting residues at the S1-KCNE3 interface shows the inter-helical distance is precisely calibrated; two pairs of compensatory KCNQ1/KCNE3 mutants partially restore constitutive activity when co-expressed, confirming a direct physical interaction.\",\n      \"method\": \"Volume scanning mutagenesis, compensatory mutagenesis, electrophysiology, based on KCNQ1-KCNE3-calmodulin complex structure\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structure-guided mutagenesis with compensatory rescue experiments confirming direct contact, multiple mutants tested\",\n      \"pmids\": [\"36331187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structures of KCNQ1-KCNE1 and reassessed KCNQ1-KCNE3 structures reveal two PIP2-binding sites in both complexes. KCNE3 contributes to a second, previously uncharacterized PIP2-binding site involving residues critical for voltage sensor-pore domain coupling. Through this site, KCNE3 converts KCNQ1 into a voltage-insensitive, PIP2-gated channel governed by GPCR signaling, maintaining ion homeostasis in non-excitable epithelial cells.\",\n      \"method\": \"Cryo-EM structure determination, electrophysiology, PIP2 binding site mutagenesis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — cryo-EM structural data plus electrophysiology, but preprint not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"KCNE3 (MiRP2) is a single-transmembrane regulatory β-subunit that assembles with multiple voltage-gated K+ channel α-subunits (primarily KCNQ1 and Kv3.4, but also Kv4.3, Kv12.2, and others) to profoundly alter their gating: in epithelial cells, KCNE3 stabilizes the activated 'up' state of the KCNQ1 voltage sensor S4 through direct electrostatic interactions (D54/D55 with R228) and tight contacts with the S1 segment, converting voltage-dependent KCNQ1 into a constitutively open, PIP2-gated K+ channel that drives basolateral K+ recycling for transepithelial Cl- secretion; in skeletal muscle, KCNE3 assembles with Kv3.4, shifts activation voltage, and requires PKC phosphorylation at S82 to set resting membrane potential; and in the heart it modulates Ito (via Kv4.3) and IKr, with disease-causing mutations producing gain- or loss-of-function effects linked to periodic paralysis, Brugada syndrome, long QT syndrome, and atrial fibrillation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KCNE3 (MiRP2) is a single-transmembrane regulatory \\u03b2-subunit that assembles with multiple voltage-gated K+ channel \\u03b1-subunits to reshape their gating and set the electrical properties of epithelial, muscle, neuronal, and cardiac cells [#0, #7]. Its best-defined action is on KCNQ1: the KCNE3 transmembrane domain alone is sufficient to assemble with and constitutively activate KCNQ1, with neither terminus required [#3], and it does so by shifting the voltage dependence of S4 voltage-sensor movement to extreme hyperpolarized potentials so the channel conducts across the physiological range [#12]. This stabilization of the activated 'up' state of S4 is achieved through direct electrostatic and inter-helical contacts\\u2014the acidic KCNE3 residues D54/D55 engaging KCNQ1 S4 R228, contacts at both ends of the KCNE3 transmembrane domain with the voltage-sensing domain, and a precisely calibrated tight interface with the KCNQ1 S1 segment confirmed by compensatory mutagenesis [#12, #14, #20]. In epithelia, KCNQ1/KCNE3 heteromers reside in the basolateral membrane and provide the K+ recycling required for cAMP-stimulated transepithelial Cl- secretion; Kcne3 knockout abolishes this secretion without altering KCNQ1 abundance, and 17\\u03b2-estradiol acutely dissociates the complex via PKC\\u03b4 phosphorylation of KCNE3 S82 to produce sexually dimorphic colonic secretion [#7, #8]. In skeletal muscle, KCNE3 assembles with Kv3.4 to form a subthreshold channel that sets resting membrane potential, an interaction dependent on PKC phosphorylation at S82 [#0, #2]. KCNE3 also modulates cardiac currents through Kv4.3 and Kv12.2 and regulates neuronal Kv4.2, and timeline disease findings link KCNE3 variants to familial periodic paralysis, Brugada syndrome, long QT syndrome, and atrial fibrillation through gain- or loss-of-function effects on these partner channels [#0, #1, #4, #6, #17].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established KCNE3 as a functional \\u03b2-subunit by showing it assembles with Kv3.4 to create a distinct subthreshold channel that sets skeletal muscle resting potential, and tied a KCNE3 variant to periodic paralysis.\",\n      \"evidence\": \"Patch-clamp, co-immunoprecipitation, heterologous expression and genetic segregation of R83H\",\n      \"pmids\": [\"11207363\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"R83H pathogenicity later disputed\", \"structural basis of Kv3.4 modulation not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrated that KCNE3 modulation of KCNQ1 has direct physiological consequence by showing ectopic KCNE3 accelerates current and shortens action potential and QT interval in vivo.\",\n      \"evidence\": \"Heterologous co-expression, adenoviral transduction in guinea pig ventricle, patch-clamp and ECG\",\n      \"pmids\": [\"11956246\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ectopic rather than native cardiac context\", \"mechanism of gating change not yet mapped to residues\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Localized KCNQ1-activating function to the KCNE3 transmembrane domain, distinguishing it from the C-terminus-driven KCNE1 mechanism and defining a bipartite model.\",\n      \"evidence\": \"Truncation mutagenesis panel with whole-cell patch-clamp in heterologous cells\",\n      \"pmids\": [\"15572349\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"specific contact residues not identified\", \"did not resolve voltage-sensor versus gate target\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified S82 as the functional PKC phosphorylation site required for MiRP2-Kv3.4 function and showed R83H confers pathological pH sensitivity rather than blocking phosphorylation.\",\n      \"evidence\": \"Mutagenesis, PKC phosphorylation assays and patch-clamp\",\n      \"pmids\": [\"16449802\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"physiological trigger of S82 phosphorylation in muscle not defined\", \"kinase identity in vivo not established\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Extended KCNE3 partnerships to cardiac Kv4.3 and Kv11.1 and linked gain-of-function variants (R99H, V17M) to Brugada syndrome and atrial fibrillation.\",\n      \"evidence\": \"Co-IP from human atrial tissue and voltage-clamp of channel complexes in CHO and oocytes\",\n      \"pmids\": [\"19122847\", \"18209471\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"single-method electrophysiology for V17M\", \"in vivo arrhythmic mechanism not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed the same R99H variant reduces KCNQ1/KCNE3 current (long QT mechanism) and that KCNE3 suppresses Kv12.2 surface expression in native brain, revealing partner-dependent and additive regulation.\",\n      \"evidence\": \"Patch-clamp in CHO cells; siRNA knockdown, surface biotinylation and brain co-IP for Kv12.2\",\n      \"pmids\": [\"19306396\", \"19623261\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"opposite directional effects of R99H across partners unreconciled\", \"tripartite KCNE1/KCNE3/Kv12.2 stoichiometry not resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Proved in vivo that KCNE3 biophysical modulation of basolateral KCNQ1\\u2014not KCNQ1 abundance\\u2014is required for transepithelial Cl- secretion.\",\n      \"evidence\": \"Kcne3 knockout mice, Ussing chamber secretion assays, immunolocalization and membrane fractionation\",\n      \"pmids\": [\"20051516\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"upstream signaling controlling complex activity in epithelia not yet defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revealed dynamic, hormone-regulated control of the complex: estradiol dissociates KCNQ1:KCNE3 via PKC\\u03b4 phosphorylation of S82, explaining sexual dimorphism in colonic secretion.\",\n      \"evidence\": \"Co-IP, patch-clamp, short-circuit current and S82A mutagenesis in crypts and CHO cells\",\n      \"pmids\": [\"21911611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"estrogen receptor coupling to PKC\\u03b4 not detailed\", \"in vivo reversibility kinetics not measured\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Uncovered an extracardiac arrhythmogenic mechanism whereby Kcne3 loss causes aldosterone-dependent adrenal pathology that impairs ventricular repolarization.\",\n      \"evidence\": \"Kcne3-/- mice with ECG, patch-clamp, histology, blood assays and ischemia-reperfusion\",\n      \"pmids\": [\"24225147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"link between KCNE3 channel function and aldosterone regulation not molecularly defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed KCNE3 shapes neuronal excitability by regulating Kv4.2 in spiral ganglion neurons independent of KChIP2.\",\n      \"evidence\": \"Kcne3-/- mice with patch-clamp and conductance analysis of spiral ganglion neurons\",\n      \"pmids\": [\"24727472\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"direct KCNE3-Kv4.2 binding not structurally mapped\", \"behavioral/auditory consequence not assessed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the gating mechanism: KCNE3 acts on KCNQ1 by hyperpolarizing S4 voltage-sensor movement via D54/D55\\u2013R228 electrostatics, affecting the gate only indirectly\\u2014mechanistically distinct from KCNE1.\",\n      \"evidence\": \"Voltage clamp fluorometry, mutagenesis, domain-swap and PIP2 depletion separating S4 movement from gating\",\n      \"pmids\": [\"26668384\", \"28808020\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"full atomic stoichiometry of S4 contacts addressed separately by structural work\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Built an integrative structural model of the contacts driving constitutive activation, identified an N-terminally extended isoform that tunes partner specificity, and mapped the aldosterone/Akt/Rab pathway underlying AF in knockouts.\",\n      \"evidence\": \"NMR-guided modeling with electrophysiology; oocyte electrophysiology of isoforms; Kcne3-/- mice with co-IP, Western blot and spironolactone rescue\",\n      \"pmids\": [\"27626070\", \"27162025\", \"26985008\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"isoform tissue distribution and abundance incompletely defined\", \"high-resolution structure not yet available at this stage\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated KCNE3 is required for normal skeletal muscle contractile dynamics and controls Kv3.4/mERG subunit expression and fiber-type composition.\",\n      \"evidence\": \"Kcne3-/- mice with muscle force measurements, myoblast patch-clamp, microarray and fiber-type immunofluorescence\",\n      \"pmids\": [\"28356343\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"transcriptional mechanism controlling Kv3.4/KCNH2 expression not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Confirmed that a precisely calibrated tight S1\\u2013KCNE3 transmembrane interface is required for constitutive activity, using compensatory mutant rescue to prove direct physical contact.\",\n      \"evidence\": \"Volume-scanning and compensatory mutagenesis with electrophysiology guided by the KCNQ1-KCNE3-calmodulin structure\",\n      \"pmids\": [\"36331187\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"energetics of the interface not quantified\", \"how S1 contact integrates with S4 stabilization not unified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cryo-EM reassessment identified a second KCNE3-dependent PIP2-binding site, recasting KCNE3 as converting KCNQ1 into a voltage-insensitive, PIP2- and GPCR-gated channel.\",\n      \"evidence\": \"Cryo-EM, electrophysiology and PIP2 site mutagenesis (preprint)\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"preprint not peer-reviewed\", \"GPCR signaling coupling demonstrated only inferentially\", \"functional contribution of second PIP2 site in native epithelia not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How KCNE3 selects among its many partner \\u03b1-subunits in different tissues, and how upstream signaling (PKC, estrogen, aldosterone, PIP2/GPCR) is integrated to dynamically gate these complexes in vivo, remains incompletely resolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"no unified model of partner selection across tissues\", \"in vivo signaling integration not reconstituted\", \"stoichiometry of multi-KCNE/multi-\\u03b1 complexes uncertain\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 7, 12]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [7, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": []}\n    ],\n    \"complexes\": [\"KCNQ1/KCNE3 channel\", \"MiRP2-Kv3.4 channel\"],\n    \"partners\": [\"KCNQ1\", \"KCNC4\", \"KCND3\", \"KCNH3\", \"KCNH2\", \"KCND2\", \"CALM1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}