{"gene":"P2RX2","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1995,"finding":"Co-expression of P2X2 and P2X3 subunits in Xenopus oocytes produced ATP-gated currents that closely resembled those in sensory neurons; these properties could not be accounted for by addition of the two homomeric channels, indicating that P2X2 and P2X3 subunits heteropolymerize to form a new channel with distinct properties.","method":"Heterologous co-expression in Xenopus oocytes, electrophysiology","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — functional reconstitution in heterologous system, replicated across multiple subsequent studies","pmids":["7566120"],"is_preprint":false},{"year":1997,"finding":"P2X2 and P2X3 subunits were directly shown to co-assemble into heteromeric channels by cross-immunoprecipitation of epitope-tagged subunits expressed via baculovirus in insect cells; co-infected cells showed ATP-evoked currents with agonist sensitivity and desensitization distinct from either homomer.","method":"Baculovirus expression in Sf9 insect cells, cross-immunoprecipitation with epitope tags, whole-cell patch clamp","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical (co-IP) plus functional reconstitution with distinct pharmacological fingerprint, replicated across labs","pmids":["9254665"],"is_preprint":false},{"year":1997,"finding":"Three splice variants of the P2X2 receptor were isolated from rat cerebellum; only the P2X2(b) variant (with a 69-amino acid C-terminal deletion) formed functional homomeric channels in oocytes and showed faster desensitization compared to P2X2(a), indicating that the C-terminal serine/proline-rich region regulates desensitization kinetics.","method":"cDNA cloning from rat cerebellum, heterologous expression in Xenopus oocytes and mammalian cells, two-electrode voltage clamp, in situ hybridization","journal":"Molecular Pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Strong — functional expression with mutagenesis-equivalent splice deletion, confirmed in two expression systems","pmids":["9271346"],"is_preprint":false},{"year":1997,"finding":"Extracellular acidification (lowered pH) enhanced the activity of all agonists at the recombinant P2X2 receptor expressed in Xenopus oocytes (~5-fold increase in ATP affinity at pH 6.5, apparent pKa ~7.05), consistent with protonation of the receptor itself rather than the agonist, while only suramin antagonism was significantly affected by pH.","method":"Two-electrode voltage clamp in Xenopus oocytes expressing recombinant P2X2, systematic pH variation with agonist and antagonist concentration-response curves","journal":"British Journal of Pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — rigorous pharmacological characterization in reconstituted system, single lab with multiple agonists and antagonists tested","pmids":["9257926"],"is_preprint":false},{"year":1997,"finding":"The putative extracellular domain (ECD) of P2X2 expressed as a recombinant protein bound [α-32P]ATP specifically and competably by antagonists suramin and cibacron blue, indicating that the extracellular domain contains the ATP-binding site.","method":"Bacterial expression, metal-affinity purification, UV-crosslinking with [α-32P]ATP, gel filtration / analytical ultracentrifugation","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical binding assay with competition, but isolated ECD may not fully recapitulate native receptor; single lab","pmids":["9398614"],"is_preprint":false},{"year":1998,"finding":"N-linked glycosylation at three asparagine residues (N182, N239, N298) in the extracellular domain of P2X2 is essential for cell-surface expression; tunicamycin treatment or mutagenesis of all three sites abolished ATP responses and caused intracellular retention of the non-glycosylated receptor.","method":"Stable HEK-293 transfection, tunicamycin treatment, site-directed mutagenesis, cell-surface biotin labeling, indirect immunofluorescence","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with two independent surface-trafficking readouts in mammalian cells, single lab","pmids":["9778359"],"is_preprint":false},{"year":1998,"finding":"PKA phosphorylation of Ser431 in the intracellular C-terminus of rat P2X2 reduces ATP-activated current amplitude; site-directed S431C mutation abolished the current reduction induced by 8-bromo-cAMP or purified PKA catalytic subunit without affecting inactivation kinetics or reversal potential.","method":"Whole-cell voltage clamp of stably transfected HEK-293 cells, intracellular perfusion of 8-bromo-cAMP and PKA, site-directed mutagenesis","journal":"Journal of Neurochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — phosphorylation site identified by mutagenesis with direct functional readout; single lab with two orthogonal pharmacological approaches","pmids":["9603227"],"is_preprint":false},{"year":1998,"finding":"The P2X2 splice variant P2X2-2 (P2X2b), lacking the Val370-Gln438 C-terminal sequence, desensitizes rapidly and completely compared to the slowly desensitizing wild-type channel when expressed in anterior pituitary GT1 or HEK293 cells, demonstrating that the C-terminal domain controls desensitization rate.","method":"Expression in GT1 and HEK293 cells, single-cell Ca2+ imaging, whole-cell patch clamp, RT-PCR from enriched pituitary cell fractions","journal":"Molecular Endocrinology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — functional expression with deletion variant in two cell systems plus native cell verification; single lab","pmids":["9658396"],"is_preprint":false},{"year":1998,"finding":"Homomeric P2X2 receptors have higher Ca2+ permeability (PCa/PNa ~2.5) compared to P2X3 (~1.2–1.5) or heteromeric P2X2/3 receptors (~1.2–1.5); external Ca2+ blocks P2X2 with half-maximal concentration ~5 mM, while the Ca2+ block of the heteromeric P2X2/3 receptor (~15 mM) matched that of native nodose neurones, supporting that Ca2+ block involves both subunits.","method":"Whole-cell recording from stably transfected HEK-293 cells and cultured rat nodose neurones, reversal-potential measurements with NMDG and Ca2+ substitution","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — rigorous ion permeation analysis in recombinant and native systems with multiple ionic conditions","pmids":["9625864"],"is_preprint":false},{"year":1999,"finding":"Specific amino acids in the C-terminal region of P2X2 regulate desensitization: Val370 immediately after the Lys369 splice site slows desensitization via interaction with an intracellular hydrophobic site; truncation at Lys369 accelerated desensitization >100-fold; neutralization of nearby lysines (especially Lys365) also markedly accelerated desensitization.","method":"Site-directed mutagenesis, truncation analysis, peptide injection into Xenopus oocytes, two-electrode voltage clamp","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic mutagenesis and peptide competition in reconstituted system; single lab with multiple constructs","pmids":["10517803"],"is_preprint":false},{"year":1999,"finding":"P2X2 receptor expression in the cochlea is concentrated on hair cell stereocilia (endolymphatic surface), inner sulcus cells, and spiral ganglion neurons; voltage-clamped guinea pig hair cells exhibited P2X2-compatible pharmacology, and immunoelectron microscopy localized P2X2 subunits to postsynaptic junctions at both inner and outer hair cells.","method":"RT-PCR, whole-cell voltage clamp, immunohistochemistry with P2X2-specific antiserum, immunoelectron microscopy","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, immunoEM, RT-PCR) in the same tissue, functionally linked to cochlear physiology","pmids":["10493739"],"is_preprint":false},{"year":1999,"finding":"Both Cu2+ and Zn2+ potentiate P2X2 receptor currents in Xenopus oocytes with EC50 ~16–20 µM by increasing apparent ATP affinity (leftward shift of concentration-response curve) in a voltage-independent manner; Cu2+ did not further potentiate in the presence of maximal Zn2+, suggesting a shared binding site or mechanism. This modulation is distinct from P2X4, which is potentiated by Zn2+ but not Cu2+.","method":"Two-electrode voltage clamp in Xenopus oocytes, concentration-response analysis, voltage-independence testing","journal":"Journal of Neurophysiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — rigorous pharmacological characterization in reconstituted system, differential comparison with P2X4; single lab","pmids":["10322050"],"is_preprint":false},{"year":2000,"finding":"Co-expression of P2X2 and P2X6 subunits in Xenopus oocytes formed a heteromeric P2X2/6 receptor with significantly different agonist potencies, biphasic ATP-evoked currents (especially with Zn2+ or low pH), altered pH modulation range, and changed suramin sensitivity compared to the P2X2 homomer, demonstrating that P2X6 modifies P2X2 channel phenotype.","method":"Two-electrode voltage clamp in Xenopus oocytes, pharmacological characterization with agonists and antagonists, pH and Zn2+ modulation","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Moderate — functional heteromer characterization with multiple pharmacological probes; single lab","pmids":["10864944"],"is_preprint":false},{"year":2001,"finding":"P2X2 receptor mediates ATP-stimulated parasensory cation absorption in cochlear outer sulcus cells and vestibular transitional cells; ATP but not selective P2Y agonists stimulated transepithelial current (Isc) with a potency order consistent with P2X2 pharmacology, and this response was blocked by suramin or gadolinium.","method":"Vibrating probe technique for transepithelial current measurement, pharmacological profiling with P2X/P2Y agonists and antagonists","journal":"The Journal of Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional readout in native tissue with pharmacological dissection matching P2X2; single lab","pmids":["11717350"],"is_preprint":false},{"year":2001,"finding":"Noise exposure (90–120 dB) up-regulated P2X2 receptor mRNA and protein in rat cochlea organ of Corti and spiral ganglion; confocal immunofluorescence showed increased P2X2R labeling on outer hair cell stereocilia and cuticular plates, and whole-cell voltage clamp of OHCs confirmed noise-induced up-regulation of ATP-gated inward currents, indicating adaptive regulation of P2X2 expression by acoustic trauma.","method":"RT-PCR, western blot, confocal immunofluorescence, whole-cell voltage clamp of isolated outer hair cells","journal":"Neuroreport","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods linking noise-induced expression changes to functional current increase in native cells; single lab","pmids":["12858039"],"is_preprint":false},{"year":2003,"finding":"P2X2 subunits are required for fast excitatory postsynaptic potentials (fEPSPs) mediated by ATP in myenteric S neurons of the mouse small intestine; in P2X2 knockout mice, fEPSPs were insensitive to the P2X antagonist PPADS and ATP failed to depolarize S neurons, while peristaltic contractions were impaired in vitro.","method":"P2X2 knockout mice, intracellular electrophysiology, pharmacology with PPADS and mecamylamine, RT-PCR, immunohistochemistry, in vitro motility assay","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with clean electrophysiological and motility phenotype, replicated across multiple experimental paradigms","pmids":["12937291"],"is_preprint":false},{"year":2004,"finding":"Homomeric P2X2 receptors (and P2X4, P2X5) are trimers of identical subunits, as are heteromeric P2X1+2 receptors; P2X6 subunits fail to form homotrimers and instead are retained in the ER as tetramers/aggregates, establishing trimeric architecture as the structural hallmark of functional P2X receptors.","method":"Biochemical analysis (cross-linking, gel electrophoresis, PAGE) in Xenopus oocytes and transfected cells","journal":"Journal of Molecular Biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical stoichiometry determination with multiple subunit types; single lab","pmids":["15313628"],"is_preprint":false},{"year":2004,"finding":"Co-activation of P2X2 and GABAA receptors containing β subunits (αβ or αβγ) causes cross-inhibition of P2X2 channels, dependent on the C-terminal domain of P2X2 and the intracellular loop of GABAA β subunits; overexpression of minigenes encoding these domains disrupted the cross-inhibition, and the interaction also induced co-clustering of P2X2 and rho1-β3 chimeric receptors at surface clusters in hippocampal neurons.","method":"Co-expression in Xenopus oocytes, two-electrode voltage clamp, minigene overexpression, co-expression in hippocampal neurons with imaging","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — functional cross-inhibition mapped to specific domains by dominant-negative minigenes plus co-clustering in neurons; single lab with two orthogonal approaches","pmids":["15456793"],"is_preprint":false},{"year":2004,"finding":"Pore properties of the P2X2 channel (permeability to large cations, inward rectification, ligand sensitivity) change dynamically depending on channel expression density; Ile328 at the outer mouth of the pore was identified by mutagenesis as critical for these density-dependent changes.","method":"Two-electrode voltage clamp in Xenopus oocytes with varying cRNA injection levels, site-directed mutagenesis at Ile328","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis linked to functional pore property changes in reconstituted system; single lab","pmids":["15107474"],"is_preprint":false},{"year":2005,"finding":"The zinc-binding site in rat P2X2 receptors is intersubunit, requiring His120 and His213 from adjacent subunits; mixing H120A and H213A mutant subunits rescued zinc potentiation; trimeric concatamers showed zinc potentiation correlated with the number of intersubunit histidine pairs; H120C/H213C double mutant formed ectopic disulfide bonds between adjacent subunits confirming their proximity.","method":"Mutagenesis, co-expression of mixed subunits, trimeric concatamers, two-electrode voltage clamp in Xenopus oocytes, disulfide-trapping with immunoblot under non-reducing conditions","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — five independent lines of evidence including disulfide trapping and concatamer analysis; single lab with multiple orthogonal methods","pmids":["15899882"],"is_preprint":false},{"year":2005,"finding":"Heteromeric P2X2/3 receptors require lysine residues from two different subunits for function; single-lysine mutations in P2X2 (K69A or K308A) were rescued by wild-type P2X3 co-expression, but not vice versa, indicating the heteromeric channel contains one P2X2 and two P2X3 subunits.","method":"Whole-cell recording from HEK cells, co-expression of wild-type and lysine-to-alanine mutant subunits","journal":"Molecular Pharmacology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic rescue approach with reciprocal mutant combinations establishing 1:2 P2X2:P2X3 stoichiometry; single lab","pmids":["16840712"],"is_preprint":false},{"year":2005,"finding":"ATP application to dendrites of hippocampal neurons expressing P2X2-GFP caused receptor redistribution and formation of varicose hot spots with higher receptor density; this redistribution was accompanied by activation-dependent enhancement of ATP-evoked current; the T18A substate-specific mutant showed neither redistribution nor activation-dependent current enhancement.","method":"Live-cell fluorescence imaging of P2X2-GFP in hippocampal neurons, whole-cell voltage clamp, T18A mutant analysis","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 / Moderate — simultaneous live imaging and electrophysiology with mutant validation; single lab","pmids":["11296257"],"is_preprint":false},{"year":2005,"finding":"P2X2 and P2X3 knockout mice showed reduced urinary bladder reflexes and decreased pelvic afferent nerve activity in response to bladder distension, and reduced pain behavior in the formalin test; P2X2-/- mice lacked sustained ATP-evoked inward currents in nodose, coeliac, and SCG neurons, while DRG neurons retained only transient currents.","method":"P2X2 knockout and P2X2/P2X3 double knockout mice, patch-clamp electrophysiology of ganglia neurons, cystometry, pelvic nerve recording, behavioral pain assays","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple knockout models with electrophysiological and behavioral phenotypes across multiple sensory paradigms","pmids":["15961431"],"is_preprint":false},{"year":2005,"finding":"Fe65 (β-amyloid precursor protein-binding protein) directly interacts with the P2X2 C-terminal domain (but not the naturally occurring P2X2b splice variant lacking part of this domain) as shown by yeast two-hybrid and GST pull-down; Fe65 co-localizes with P2X2 subunits at postsynaptic specializations of excitatory synapses in CA1 hippocampus; co-expression of Fe65 inhibited the time- and activation-dependent increase in ionic selectivity of P2X2 receptors.","method":"Yeast two-hybrid, GST pull-down, postembedding immunogold electron microscopy, co-immunoprecipitation from brain membrane extracts, co-expression in HEK cells with electrophysiology","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Y2H, GST pulldown, co-IP from brain, immunoEM, functional electrophysiology) in single study","pmids":["16330549"],"is_preprint":false},{"year":2005,"finding":"Visualization by electron microscopy of purified P2X2 protein from baculovirus-Sf9 cells confirmed the trimeric composition of the P2X2 receptor; averaged negative-stain images showed an inverted three-sided pyramid (~215 Å height) with a crown-shaped extracellular domain and three-fold symmetry.","method":"Baculovirus-Sf9 expression, affinity purification, chemical cross-linking, negative-stain electron microscopy, single-particle averaging","journal":"Biochemical and Biophysical Research Communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct structural visualization by EM with biochemical cross-linking confirmation; single lab","pmids":["16219297"],"is_preprint":false},{"year":2006,"finding":"Membrane phosphoinositides (PIPs, PIP2) regulate P2X2 channel activity and pore dilation through electrostatic interaction with positively charged residues (Lys365, Lys369) in the proximal C-terminal cytoplasmic domain; PI3K inhibition or K365Q/K369Q mutations accelerated channel desensitization and sped up the decrease in NMDG permeability (pore dilation); GST-tagged C-terminal fusion proteins bound PIPs in vitro and this binding was abolished by K365Q/K369Q mutations.","method":"Two-electrode voltage clamp in Xenopus oocytes, PI3K inhibition (wortmannin, LY294002), site-directed mutagenesis, GST-fusion protein lipid binding assay, fluorescence membrane association assay in COS-7 cells","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis, in vitro lipid binding, and live-cell imaging converge on same mechanism; single lab with multiple orthogonal methods","pmids":["16857707"],"is_preprint":false},{"year":2007,"finding":"The Thr339Ser mutation in the second transmembrane domain (TM2) of rat P2X2 causes constitutive (spontaneous) channel opening; the additional K308A mutation (but not K69A) abolished this spontaneous activity and also blocked the agonist-like action of suramin and TNP-ATP at T339S receptors, indicating that Lys308 plays a critical role in channel gating distinct from ATP binding.","method":"Single-channel and whole-cell recording in HEK-293 cells, double and single mutagenesis, pharmacological testing with suramin and TNP-ATP","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Moderate — constitutively active mutant rescued by second-site mutation, establishing gating role for K308; single lab with functional and pharmacological validation","pmids":["18032665"],"is_preprint":false},{"year":2008,"finding":"The neuronal calcium sensor VILIP1 interacts with P2X2 receptors; VILIP1 was identified by proteomic pull-down, confirmed to form a complex in vitro and in vivo with P2X2 receptors, and was shown to regulate P2X2 receptor sensitivity to ATP, peak response, surface expression, and lateral diffusion; the interaction is constitutive but enhanced in an activation- and calcium-dependent manner due to exposure of the VILIP1-binding segment in P2X2; interaction is also enhanced in hippocampal neurons during action potential firing.","method":"Proteomic pull-down, co-immunoprecipitation from brain tissue, surface expression assays, whole-cell electrophysiology, live-cell imaging of receptor diffusion in hippocampal neurons","journal":"Science Signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — proteomic identification confirmed by co-IP from brain, with functional regulation shown by multiple readouts; single lab with multiple orthogonal methods","pmids":["18922787"],"is_preprint":false},{"year":2009,"finding":"The C-terminus of P2X2 binds directly to PIP2, PIP3, and other phosphoinositides in a lipid-binding assay, while the C-terminus of P2X3 does not; wortmannin inhibition reduced P2X2/3 heteromeric receptor currents in DRG neurons and Xenopus oocytes via both PI3K and PI4K pathways, and PIP2 or PIP3 application partially reversed this inhibition.","method":"Lipid binding assay with C-terminal GST-fusion proteins, whole-cell patch clamp in DRG neurons, two-electrode voltage clamp in Xenopus oocytes, PI3K/PI4K inhibition","journal":"Molecular Pain","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct lipid binding biochemistry combined with native cell electrophysiology; single lab","pmids":["19671169"],"is_preprint":false},{"year":2009,"finding":"Systematic mutagenesis of polar and charged residues in TM2 of rat P2X2 identified Asn333 and Asp349 as located in external and internal vestibules respectively; substitutions at Asn333, Thr336, Ser340 were most likely to cause spontaneously active channels; introduction of positive charges at Thr336, Thr339, Ser340 (by Arg/Lys/His substitution or MTSEA modification of Cys) greatly enhanced outward currents, indicating these residues face the permeation pathway in the open channel.","method":"Single-channel and whole-cell recording in HEK-293 cells, systematic site-directed mutagenesis of TM2, MTSEA modification of cysteine substitutions","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — comprehensive systematic mutagenesis with functional readouts interpreted against crystal structure of related P2X4; single lab","pmids":["19906973"],"is_preprint":false},{"year":2011,"finding":"ATP-activated cation current in mouse spermatozoa midpiece is mediated by P2X2; the current was absent in P2rx2-/- mice; the slowly desensitizing, outwardly rectifying current matched biophysical and pharmacological properties of heterologously expressed mouse P2X2; P2rx2-/- males showed normal sperm motility but reduced fertility with frequent mating.","method":"Whole-cell patch clamp of mouse spermatozoa, P2rx2 knockout mice, pharmacological characterization","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout abolishes current, pharmacological match to recombinant P2X2; two orthogonal approaches (electrophysiology + genetics)","pmids":["21831833"],"is_preprint":false},{"year":2011,"finding":"Colchicine (microtubule disruptor) did not affect ionic currents generated by ATP at P2X2 receptors but inhibited dye (Yo-Pro-1) uptake in Xenopus oocytes and HEK293 cells expressing P2X2, indicating that microtubule integrity is required for the macropore/dye-uptake function of P2X2 but not for its ion channel function.","method":"Whole-cell electrophysiology and Yo-Pro-1 dye uptake assay in Xenopus oocytes and HEK293 cells, colchicine treatment","journal":"British Journal of Pharmacology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection of two distinct channel functions (ion current vs macropore) in two heterologous systems; single lab","pmids":["21306580"],"is_preprint":false},{"year":2011,"finding":"P2X2 and P2X5 subunits interact to form heteromeric receptors at the plasma membrane with alternate stoichiometries, as shown by bioluminescence resonance energy transfer (BRET), bimolecular fluorescence complementation, and protein biochemistry; P2X2/5 receptors display pore dilatation, membrane blebbing, and phosphatidylserine exposure—properties previously thought specific to P2X7 receptors.","method":"BRET, bimolecular fluorescence complementation (BiFC), protein biochemistry, live-cell imaging of membrane blebbing and phosphatidylserine exposure","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Moderate — three orthogonal methods for assembly determination plus functional characterization; single lab","pmids":["22090499"],"is_preprint":false},{"year":2011,"finding":"P2X2 receptor lateral mobility in hippocampal neuron dendrites is mostly Brownian, consists of mobile and slowly-mobile pools, is P2X2-subunit and cell-type specific, and is increased in an activation-dependent manner; VILIP1 calcium-binding protein regulates this lateral mobility.","method":"Single-molecule quantum dot imaging with simultaneous whole-cell voltage clamp in rat hippocampal neurons","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Moderate — single-molecule imaging with simultaneous electrophysiology, mutant P2X2 and VILIP1 regulation tested; single lab","pmids":["22090499"],"is_preprint":false},{"year":2011,"finding":"ATP-binding sites of P2X2 receptors are located at intersubunit interfaces; a thiol-reactive ATP analog (NCS-ATP) covalently labeled Asn140 and Leu186 from two adjacent subunits; tethering at these positions had distinct functional consequences—labeling N140 impeded subsequent ATP function while labeling L186 enhanced subsequent ATP function.","method":"Proximity-dependent tethering with NCS-ATP, single cysteine mutagenesis, whole-cell and single-channel recording in HEK cells, homology modeling","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — chemical biology approach with functional validation; identifies ATP binding pocket residues from two subunits in closed state; single lab","pmids":["21576497"],"is_preprint":false},{"year":2012,"finding":"Glu167 and Arg290 form a salt bridge in the closed state of rat P2X2 receptor that is disrupted upon ATP binding and channel opening; charge-reversal mutations, mutant-cycle analysis, and disulfide trapping confirmed their close proximity in the closed but not open state; the Arg290/ATP ionic interaction replaces the Glu167/Arg290 salt bridge to promote channel opening.","method":"Homology modeling, charge-reversal mutagenesis, mutant cycle analysis, disulfide trapping, whole-cell electrophysiology","journal":"Molecular Pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Strong — disulfide trapping plus mutant cycle analysis demonstrate state-dependent interaction; multiple experimental approaches; single lab","pmids":["23041661"],"is_preprint":false},{"year":2012,"finding":"P2X2/3 heteromeric receptors have a 1:2 stoichiometry (one P2X2, two P2X3 subunits) while P2X2/6 receptors have a 2:1 stoichiometry (two P2X2, one P2X6 subunit); determined by co-expression of WT and ATP-binding-site Ala mutants in HEK293 cells and Xenopus oocytes—only selective mutations in the majority subunit abolished agonist responses.","method":"Site-directed mutagenesis of ATP-binding sites, co-expression of WT and mutant subunits in HEK293 cells and Xenopus oocytes, patch clamp, Ca2+ imaging, protein labeling/PAGE","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic approach with multiple subunit combinations confirmed by biochemical gel analysis; multiple orthogonal methods in one study","pmids":["22378790"],"is_preprint":false},{"year":2013,"finding":"The P2RX2 missense mutation p.V60L abolishes two hallmark P2X2 functions—ATP-evoked inward current and ATP-stimulated macropore permeability (FM1-43 dye uptake); co-expression of mutant and WT P2X2 subunits significantly reduced ATP-activated membrane permeability, indicating dominant-negative effect. P2RX2-null mice developed severe progressive hearing loss, and early noise exposure caused high-frequency hearing loss in young adults.","method":"Functional expression in heterologous cells, whole-cell electrophysiology, FM1-43 dye uptake assay, P2RX2 knockout mice, audiological testing, linkage analysis in human families","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 / Strong — human genetics confirmed by functional characterization of mutant in reconstituted system plus knockout mouse phenotype; multiple orthogonal methods","pmids":["23345450"],"is_preprint":false},{"year":2020,"finding":"ATP activates P2X2 receptors on enteric glial cells to trigger a p38 MAPK-dependent pathway causing cytokine release and a gliosis phenotype; pharmacological blockade and genetic depletion of P2X2 prevented ATP-induced enteric gliosis, inflammation, and dysmotility in postoperative ileus models in mice and humans; ambroxol was identified as a novel P2X2 antagonist.","method":"P2X2 receptor antagonism and genetic depletion in murine EGCs and human intestinal tissue, p38 MAPK pathway analysis, cytokine quantification, motility assays, pharmacological screening","journal":"EMBO Molecular Medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — both pharmacological and genetic approaches converge on P2X2 as the relevant receptor, with defined downstream pathway (p38 MAPK) and validated in human tissue","pmids":["33332729"],"is_preprint":false},{"year":2022,"finding":"P2X2 receptors in medial prefrontal cortex pyramidal neurons regulate vulnerability to chronic stress-induced depressive-like behavior; conditional knockout of P2X2 in pyramidal neurons promoted resilience, while pyramidal neuron-specific P2X2 overexpression increased vulnerability; in vivo fiber-photometry and electrophysiology showed P2X2 regulates mPFC neuronal activity and synapse function.","method":"Conditional knockout (CamkIIα-Cre), AAV-mediated overexpression, chronic social defeat stress model, in vivo fiber-photometry, patch-clamp electrophysiology, neuronal morphometry","journal":"Theranostics","confidence":"High","confidence_rationale":"Tier 2 / Strong — bidirectional (KO and OE) genetic manipulation with in vivo functional readouts; multiple behavioral and electrophysiological assays","pmids":["35664080"],"is_preprint":false}],"current_model":"P2X2 (P2RX2) is a trimeric, ATP-gated non-selective cation channel that functions as a homomeric trimer or, critically, as a 1P2X2:2P2X3 heterotrimer with distinct pharmacological and biophysical properties; its gating involves intersubunit ATP-binding pockets (contributed by N140/L186 from adjacent subunits), a state-dependent Glu167/Arg290 salt bridge that breaks upon ATP binding, and TM2 residues (especially Thr339) at the gate, while channel activity is regulated post-translationally by PKA phosphorylation at Ser431, membrane phosphoinositides interacting with C-terminal Lys365/Lys369, the neuronal calcium sensor VILIP1 (which controls receptor surface expression and lateral mobility in an activation/Ca²⁺-dependent manner), and intersubunit Zn²⁺/Cu²⁺ binding at His120/His213; alternative C-terminal splicing controls desensitization rate (Val370 is a key hydrophobic anchor); the receptor mediates fast ATP-gated synaptic transmission in enteric and sensory neurons, cochlear endolymphatic homeostasis and protection from noise, taste signal transmission to gustatory nerves, ATP-dependent spermatozoa cation currents, enteric glial gliosis via p38 MAPK signaling, and stress vulnerability in prefrontal cortex pyramidal neurons, with loss-of-function mutations causing autosomal dominant progressive sensorineural hearing loss (DFNA41)."},"narrative":{"mechanistic_narrative":"P2X2 (P2RX2) is an ATP-gated non-selective cation channel that mediates fast purinergic signaling in sensory, enteric, and central neurons as well as cochlear epithelia [PMID:7566120, PMID:12937291]. The functional receptor is a trimer, assembling as a homotrimer or, by co-assembly with other P2X subunits, as heteromeric channels with distinct pharmacology and ion permeation—including a 1P2X2:2P2X3 channel that reconstitutes the ATP currents of native sensory neurons and a 2P2X2:1P2X6 channel [PMID:7566120, PMID:9254665, PMID:15313628, PMID:16840712, PMID:22378790]. ATP binds at intersubunit pockets formed by N140 and L186 contributed by adjacent subunits within the extracellular domain [PMID:9398614, PMID:21576497]; binding disrupts a closed-state Glu167/Arg290 salt bridge, with Arg290 then coordinating ATP to promote gating [PMID:23041661], and channel opening proceeds through the second transmembrane segment, where TM2 residues including Thr339 line the permeation pathway and define the gate [PMID:18032665, PMID:19906973]. Homomeric P2X2 is notably Ca2+-permeable and exhibits an activation-dependent dilation to a large-cation/dye-permeant pore [PMID:9625864, PMID:23345450]. Channel behavior is shaped post-translationally: PKA phosphorylation of Ser431 reduces current [PMID:9603227], C-terminal phosphoinositides binding Lys365/Lys369 control desensitization and pore dilation [PMID:16857707], alternative C-terminal splicing (with Val370/Lys369 as key determinants) sets desensitization rate [PMID:9271346, PMID:10517803], and intersubunit His120/His213 pairs mediate Zn2+/Cu2+ potentiation [PMID:10322050, PMID:15899882]. Surface expression and lateral mobility are governed by N-linked glycosylation and by the neuronal calcium sensor VILIP1, whose activation/Ca2+-dependent association tunes ATP sensitivity and trafficking [PMID:9778359, PMID:18922787, PMID:22090499]. Physiologically, P2X2 drives ATP-mediated fast excitatory transmission in myenteric neurons and bladder/sensory afferents, cochlear endolymphatic ion transport and noise protection, spermatozoa cation currents, enteric glial p38 MAPK–dependent gliosis, and prefrontal-cortex stress vulnerability [PMID:12937291, PMID:15961431, PMID:12858039, PMID:21831833, PMID:33332729, PMID:35664080]. A dominant-negative P2RX2 missense mutation that abolishes ATP-gated current and macropore function causes autosomal dominant progressive sensorineural hearing loss, recapitulated by P2RX2-null mice [PMID:23345450].","teleology":[{"year":1995,"claim":"Established that P2X2 does not act alone but co-assembles with P2X3 to generate a channel reproducing native sensory-neuron ATP currents, answering why recombinant homomers failed to match physiology.","evidence":"Co-expression of P2X2 and P2X3 in Xenopus oocytes with electrophysiology","pmids":["7566120"],"confidence":"High","gaps":["Stoichiometry of the heteromer not determined","Direct physical association not yet shown biochemically"]},{"year":1997,"claim":"Confirmed direct physical co-assembly of P2X2 and P2X3 subunits, converting the functional inference into a biochemically demonstrated heteromer.","evidence":"Cross-immunoprecipitation of epitope-tagged subunits in Sf9 cells with whole-cell patch clamp","pmids":["9254665"],"confidence":"High","gaps":["Subunit ratio not established","Native heteromer composition in neurons not directly confirmed"]},{"year":1997,"claim":"Localized ATP binding and identified the C-terminus as the desensitization controller, separating ligand recognition (ECD) from kinetic regulation (intracellular tail).","evidence":"Recombinant ECD ATP UV-crosslinking with antagonist competition; cerebellar splice-variant cloning and oocyte expression","pmids":["9398614","9271346"],"confidence":"Medium","gaps":["Isolated ECD may not recapitulate native binding pocket geometry","Exact ECD residues contacting ATP not yet mapped"]},{"year":1998,"claim":"Defined surface-trafficking and post-translational control of the channel, showing glycosylation is required for surface expression and PKA phosphorylation of Ser431 down-modulates current.","evidence":"Mutagenesis of N182/N239/N298 with surface labeling; S431C mutation with PKA/8-Br-cAMP perfusion in HEK-293 cells","pmids":["9778359","9603227"],"confidence":"High","gaps":["Kinase coupling and physiological trigger for Ser431 phosphorylation in neurons not defined","Glycan structural requirement vs simple folding role unresolved"]},{"year":1998,"claim":"Quantified ion permeation, establishing high Ca2+ permeability of homomeric P2X2 and subunit-dependent Ca2+ block matching native nodose neurons.","evidence":"Whole-cell reversal-potential measurements in HEK-293 and rat nodose neurons with ion substitution","pmids":["9625864"],"confidence":"High","gaps":["Structural basis of Ca2+ selectivity not mapped"]},{"year":1999,"claim":"Pinpointed C-terminal residues (Val370, Lys365/Lys369) governing desensitization kinetics, providing a molecular mechanism for splice-variant differences.","evidence":"Site-directed mutagenesis, truncation, and peptide injection in oocytes; expression of P2X2b in GT1/HEK293 cells","pmids":["10517803","9658396"],"confidence":"High","gaps":["Identity of the intracellular hydrophobic partner for Val370 unknown"]},{"year":1999,"claim":"Defined trace-metal modulation (Zn2+/Cu2+ potentiation) of P2X2, distinguishing it pharmacologically from P2X4.","evidence":"Two-electrode voltage clamp concentration-response analysis in oocytes","pmids":["10322050"],"confidence":"High","gaps":["Binding site not yet localized at this stage","Physiological relevance of Cu2+/Zn2+ modulation in vivo not established"]},{"year":1999,"claim":"Connected P2X2 to cochlear physiology by localizing it to hair-cell stereocilia and synaptic junctions, implicating it in endolymphatic ATP signaling.","evidence":"RT-PCR, hair-cell voltage clamp, immunohistochemistry and immunoEM in cochlea","pmids":["10493739"],"confidence":"High","gaps":["Causal role in hearing not yet tested genetically","Functional output of stereociliary receptors unresolved"]},{"year":2001,"claim":"Linked P2X2 to functional cochlear/vestibular ion transport and showed expression is adaptively up-regulated by acoustic trauma.","evidence":"Vibrating-probe transepithelial current with P2X/P2Y pharmacology; noise exposure with RT-PCR, western, immunofluorescence, OHC voltage clamp","pmids":["11717350","12858039"],"confidence":"Medium","gaps":["Receptor identity inferred pharmacologically, not by genetic deletion in these assays","Signal driving noise-induced upregulation unknown"]},{"year":2004,"claim":"Established trimeric architecture as the structural hallmark of functional P2X channels and defined a density-dependent pore property controlled by Ile328.","evidence":"Cross-linking/PAGE stoichiometry; oocyte expression with varied cRNA and I328 mutagenesis","pmids":["15313628","15107474"],"confidence":"High","gaps":["Physiological setting where expression density alters pore properties unclear"]},{"year":2004,"claim":"Revealed functional cross-talk between P2X2 and GABA-A receptors, mapping cross-inhibition and co-clustering to specific intracellular domains.","evidence":"Co-expression in oocytes and hippocampal neurons, minigene dominant-negatives, imaging","pmids":["15456793"],"confidence":"High","gaps":["Direct physical interaction vs functional coupling not fully distinguished","Endogenous neuronal relevance not quantified"]},{"year":2005,"claim":"Defined the intersubunit Zn2+ site (His120/His213 from adjacent subunits) and confirmed 1P2X2:2P2X3 heteromer stoichiometry, anchoring the trimer's functional interfaces.","evidence":"Mixed-subunit and concatamer expression, disulfide trapping; lysine-mutant rescue in HEK cells","pmids":["15899882","16840712"],"confidence":"High","gaps":["Whether multiple metal sites coexist not resolved","Heteromer stoichiometry in native tissue confirmed only indirectly"]},{"year":2005,"claim":"Demonstrated activation-dependent receptor redistribution/clustering and identified Fe65 as a C-terminal interactor regulating ionic selectivity, expanding regulatory partners.","evidence":"Live imaging of P2X2-GFP with electrophysiology and T18A mutant; Y2H, GST pulldown, co-IP from brain, immunoEM","pmids":["11296257","16330549"],"confidence":"High","gaps":["Functional significance of Fe65 binding in vivo unclear","Mechanism coupling activation to redistribution not defined"]},{"year":2005,"claim":"Provided the first direct structural visualization of the trimeric P2X2 receptor as an inverted pyramid with crown-shaped ECD.","evidence":"Affinity-purified P2X2 with cross-linking and negative-stain EM single-particle averaging","pmids":["16219297"],"confidence":"High","gaps":["Low resolution; no atomic model from this study","Conformational states not resolved"]},{"year":2005,"claim":"Established P2X2's role in vivo in fast enteric and visceral sensory transmission using knockout mice, linking the channel to peristalsis, bladder reflexes, and pain.","evidence":"P2X2 and P2X2/3 knockout mice with ganglion electrophysiology, cystometry, motility, and behavioral pain assays","pmids":["12937291","15961431"],"confidence":"High","gaps":["Relative contribution of homomeric vs heteromeric channels in each tissue not dissected"]},{"year":2006,"claim":"Identified membrane phosphoinositides as direct regulators of desensitization and pore dilation via C-terminal Lys365/Lys369.","evidence":"Oocyte electrophysiology with PI3K inhibition, K365Q/K369Q mutagenesis, GST-fusion lipid binding, COS-7 imaging","pmids":["16857707"],"confidence":"High","gaps":["Which endogenous lipid species dominates regulation in neurons unclear"]},{"year":2007,"claim":"Assigned a gating role to TM2 by showing the Thr339Ser mutation causes constitutive opening rescuable by K308A, separating gating from ATP binding.","evidence":"Single-channel and whole-cell recording in HEK-293 with double/single mutagenesis and antagonist testing","pmids":["18032665"],"confidence":"High","gaps":["Detailed gate motion not directly visualized"]},{"year":2009,"claim":"Mapped TM2 vestibule and permeation-pathway residues (Asn333, Asp349, Thr336/Thr339/Ser340) and showed P2X2 (but not P2X3) C-terminus binds phosphoinositides, extending lipid regulation to heteromers.","evidence":"Systematic TM2 mutagenesis with MTSEA in HEK cells; GST-fusion lipid binding and DRG/oocyte electrophysiology with PI3K/PI4K inhibition","pmids":["19906973","19671169"],"confidence":"High","gaps":["Structural model relied on related P2X4 crystal structure rather than P2X2 itself"]},{"year":2011,"claim":"Established VILIP1 as a calcium-sensor regulator of P2X2 surface expression and lateral mobility, and demonstrated microtubule dependence of the macropore but not the ion-channel function.","evidence":"Single-molecule quantum-dot imaging with electrophysiology; colchicine treatment with Yo-Pro-1 uptake assays","pmids":["22090499","21306580"],"confidence":"High","gaps":["Molecular mechanism linking microtubules to macropore formation unknown"]},{"year":2011,"claim":"Extended heteromerization to P2X2/5 with P2X7-like pore dilation/blebbing and defined P2X2's role in spermatozoa, broadening physiological scope.","evidence":"BRET/BiFC and biochemistry for P2X2/5 assembly; P2rx2-/- mouse spermatozoa patch clamp","pmids":["22090499","21831833"],"confidence":"High","gaps":["P2X2/5 native expression sites not established","Mechanism of sperm fertility reduction not defined"]},{"year":2011,"claim":"Localized the ATP-binding pocket to the intersubunit interface (Asn140 and Leu186 from adjacent subunits) using chemical tethering.","evidence":"NCS-ATP proximity tethering with single-cysteine mutagenesis and recording in HEK cells, homology modeling","pmids":["21576497"],"confidence":"High","gaps":["Conformational coupling from binding to gate not directly observed"]},{"year":2012,"claim":"Resolved the conformational logic of gating—Glu167/Arg290 salt bridge breaks on ATP binding—and established subunit ratios of P2X2/3 (1:2) and P2X2/6 (2:1) heteromers.","evidence":"Charge-reversal mutagenesis, mutant-cycle analysis, disulfide trapping; WT/mutant co-expression in HEK and oocytes with biochemistry","pmids":["23041661","22378790"],"confidence":"High","gaps":["Full open-state structure not determined at this stage"]},{"year":2013,"claim":"Identified P2RX2 as a Mendelian deafness gene, with a dominant-negative p.V60L mutation abolishing both ion current and macropore function and recapitulated by null mice.","evidence":"Human linkage with functional expression (electrophysiology, FM1-43 dye uptake) and P2RX2 knockout mice with audiology","pmids":["23345450"],"confidence":"High","gaps":["Which cochlear cell type's P2X2 loss drives hearing loss not pinpointed"]},{"year":2020,"claim":"Defined a non-neuronal disease mechanism whereby ATP activation of P2X2 on enteric glia drives p38 MAPK–dependent gliosis and dysmotility in postoperative ileus.","evidence":"Pharmacological and genetic depletion in murine and human EGCs, p38 pathway and cytokine analysis, motility assays","pmids":["33332729"],"confidence":"High","gaps":["Whether glial P2X2 is homomeric or heteromeric not determined","Coupling of cation flux to p38 activation not mechanistically detailed"]},{"year":2022,"claim":"Implicated prefrontal-cortex P2X2 in stress-induced depressive vulnerability through bidirectional genetic manipulation.","evidence":"Pyramidal-neuron conditional knockout and AAV overexpression in chronic social defeat stress with fiber-photometry and electrophysiology","pmids":["35664080"],"confidence":"High","gaps":["ATP source and circuit-level signaling driving the phenotype unresolved"]},{"year":null,"claim":"How the discrete regulatory inputs (PIP/PKA/VILIP1/metals/heteromerization) are integrated in specific native cell types to set physiological output, and the high-resolution structural basis of P2X2 pore dilation, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No high-resolution P2X2-specific structure in defined gating states in the corpus","Cell-type-specific subunit composition in vivo not mapped","Mechanism converting macropore/ion flux into downstream signaling (e.g., p38) unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,8,15,30]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,34,35]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[16,24]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,10,32,33]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[10,14]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[15,22,39]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[8,13]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,27,38]}],"complexes":["P2X2 homotrimer","P2X2/P2X3 heterotrimer (1:2)","P2X2/P2X6 heterotrimer (2:1)","P2X2/P2X5 heteromer"],"partners":["P2RX3","P2RX6","P2RX5","VILIP1","FE65","GABRB"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UBL9","full_name":"P2X purinoceptor 2","aliases":["ATP receptor","Purinergic receptor"],"length_aa":471,"mass_kda":51.8,"function":"ATP-gated nonselective transmembrane cation channel permeable to potassium, sodium and calcium (PubMed:10570044, PubMed:31636190). Activation by extracellular ATP induces a variety of cellular responses, such as excitatory postsynaptic responses in sensory neurons, neuromuscular junctions (NMJ) formation, hearing, perception of taste and peristalsis (By similarity). In the inner ear, regulates sound transduction and auditory neurotransmission, outer hair cell electromotility, inner ear gap junctions, and K(+) recycling (PubMed:23345450). Mediates synaptic transmission between neurons and from neurons to smooth muscle (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9UBL9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/P2RX2","classification":"Not Classified","n_dependent_lines":32,"n_total_lines":1208,"dependency_fraction":0.026490066225165563},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/P2RX2","total_profiled":1310},"omim":[{"mim_id":"608224","title":"DEAFNESS, AUTOSOMAL DOMINANT 41; DFNA41","url":"https://www.omim.org/entry/608224"},{"mim_id":"603149","title":"INTERLEUKIN 17A; IL17A","url":"https://www.omim.org/entry/603149"},{"mim_id":"600844","title":"PURINERGIC RECEPTOR P2X, LIGAND-GATED ION CHANNEL, 2; P2RX2","url":"https://www.omim.org/entry/600844"},{"mim_id":"600843","title":"PURINERGIC RECEPTOR P2X, LIGAND-GATED ION CHANNEL, 3; P2RX3","url":"https://www.omim.org/entry/600843"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":12.3},{"tissue":"epididymis","ntpm":20.6},{"tissue":"prostate","ntpm":14.1}],"url":"https://www.proteinatlas.org/search/P2RX2"},"hgnc":{"alias_symbol":["P2X2"],"prev_symbol":["DFNA41"]},"alphafold":{"accession":"Q9UBL9","domains":[{"cath_id":"1.10.287.940","chopping":"40-68_338-378","consensus_level":"high","plddt":90.082,"start":40,"end":378},{"cath_id":"2.60.490.10","chopping":"76-118_183-335","consensus_level":"high","plddt":92.506,"start":76,"end":335},{"cath_id":"-","chopping":"129-178","consensus_level":"medium","plddt":91.4978,"start":129,"end":178}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UBL9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UBL9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UBL9-F1-predicted_aligned_error_v6.png","plddt_mean":79.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=P2RX2","jax_strain_url":"https://www.jax.org/strain/search?query=P2RX2"},"sequence":{"accession":"Q9UBL9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UBL9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UBL9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UBL9"}},"corpus_meta":[{"pmid":"7566120","id":"PMC_7566120","title":"Coexpression of P2X2 and P2X3 receptor subunits can account for ATP-gated currents in sensory neurons.","date":"1995","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/7566120","citation_count":869,"is_preprint":false},{"pmid":"12482951","id":"PMC_12482951","title":"A-317491, a novel potent and selective non-nucleotide antagonist of P2X3 and P2X2/3 receptors, reduces chronic inflammatory and neuropathic pain in the rat.","date":"2002","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/12482951","citation_count":393,"is_preprint":false},{"pmid":"9364478","id":"PMC_9364478","title":"Immunohistochemical study of the P2X2 and P2X3 receptor subunits in rat and monkey sensory neurons and their central terminals.","date":"1997","source":"Neuropharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/9364478","citation_count":368,"is_preprint":false},{"pmid":"15961431","id":"PMC_15961431","title":"P2X2 knockout mice and P2X2/P2X3 double knockout mice reveal a role for the P2X2 receptor subunit in mediating multiple sensory effects of ATP.","date":"2005","source":"The Journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/15961431","citation_count":309,"is_preprint":false},{"pmid":"10213185","id":"PMC_10213185","title":"Distribution of the P2X2 receptor subunit of the ATP-gated ion channels in the rat central nervous system.","date":"1999","source":"The Journal of comparative neurology","url":"https://pubmed.ncbi.nlm.nih.gov/10213185","citation_count":226,"is_preprint":false},{"pmid":"16000618","id":"PMC_16000618","title":"Dual presynaptic control by ATP of glutamate release via facilitatory P2X1, P2X2/3, and P2X3 and inhibitory P2Y1, P2Y2, and/or P2Y4 receptors in the rat hippocampus.","date":"2005","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/16000618","citation_count":187,"is_preprint":false},{"pmid":"10493739","id":"PMC_10493739","title":"Expression of the P2X(2) receptor subunit of the ATP-gated ion channel in the cochlea: implications for sound transduction and auditory neurotransmission.","date":"1999","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/10493739","citation_count":150,"is_preprint":false},{"pmid":"14623769","id":"PMC_14623769","title":"Effects of A-317491, a novel and selective P2X3/P2X2/3 receptor antagonist, on neuropathic, inflammatory and chemogenic nociception following intrathecal and intraplantar administration.","date":"2003","source":"British journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/14623769","citation_count":148,"is_preprint":false},{"pmid":"12849743","id":"PMC_12849743","title":"Up-regulation of P2X2, P2X4 receptor and ischemic cell death: prevention by P2 antagonists.","date":"2003","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/12849743","citation_count":135,"is_preprint":false},{"pmid":"18689601","id":"PMC_18689601","title":"P2X2 receptors differentiate placodal vs. neural crest C-fiber phenotypes innervating guinea pig lungs and esophagus.","date":"2008","source":"American journal of physiology. 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these properties could not be accounted for by addition of the two homomeric channels, indicating that P2X2 and P2X3 subunits heteropolymerize to form a new channel with distinct properties.\",\n      \"method\": \"Heterologous co-expression in Xenopus oocytes, electrophysiology\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — functional reconstitution in heterologous system, replicated across multiple subsequent studies\",\n      \"pmids\": [\"7566120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"P2X2 and P2X3 subunits were directly shown to co-assemble into heteromeric channels by cross-immunoprecipitation of epitope-tagged subunits expressed via baculovirus in insect cells; co-infected cells showed ATP-evoked currents with agonist sensitivity and desensitization distinct from either homomer.\",\n      \"method\": \"Baculovirus expression in Sf9 insect cells, cross-immunoprecipitation with epitope tags, whole-cell patch clamp\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical (co-IP) plus functional reconstitution with distinct pharmacological fingerprint, replicated across labs\",\n      \"pmids\": [\"9254665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Three splice variants of the P2X2 receptor were isolated from rat cerebellum; only the P2X2(b) variant (with a 69-amino acid C-terminal deletion) formed functional homomeric channels in oocytes and showed faster desensitization compared to P2X2(a), indicating that the C-terminal serine/proline-rich region regulates desensitization kinetics.\",\n      \"method\": \"cDNA cloning from rat cerebellum, heterologous expression in Xenopus oocytes and mammalian cells, two-electrode voltage clamp, in situ hybridization\",\n      \"journal\": \"Molecular Pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — functional expression with mutagenesis-equivalent splice deletion, confirmed in two expression systems\",\n      \"pmids\": [\"9271346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Extracellular acidification (lowered pH) enhanced the activity of all agonists at the recombinant P2X2 receptor expressed in Xenopus oocytes (~5-fold increase in ATP affinity at pH 6.5, apparent pKa ~7.05), consistent with protonation of the receptor itself rather than the agonist, while only suramin antagonism was significantly affected by pH.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes expressing recombinant P2X2, systematic pH variation with agonist and antagonist concentration-response curves\",\n      \"journal\": \"British Journal of Pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous pharmacological characterization in reconstituted system, single lab with multiple agonists and antagonists tested\",\n      \"pmids\": [\"9257926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The putative extracellular domain (ECD) of P2X2 expressed as a recombinant protein bound [α-32P]ATP specifically and competably by antagonists suramin and cibacron blue, indicating that the extracellular domain contains the ATP-binding site.\",\n      \"method\": \"Bacterial expression, metal-affinity purification, UV-crosslinking with [α-32P]ATP, gel filtration / analytical ultracentrifugation\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical binding assay with competition, but isolated ECD may not fully recapitulate native receptor; single lab\",\n      \"pmids\": [\"9398614\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"N-linked glycosylation at three asparagine residues (N182, N239, N298) in the extracellular domain of P2X2 is essential for cell-surface expression; tunicamycin treatment or mutagenesis of all three sites abolished ATP responses and caused intracellular retention of the non-glycosylated receptor.\",\n      \"method\": \"Stable HEK-293 transfection, tunicamycin treatment, site-directed mutagenesis, cell-surface biotin labeling, indirect immunofluorescence\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with two independent surface-trafficking readouts in mammalian cells, single lab\",\n      \"pmids\": [\"9778359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PKA phosphorylation of Ser431 in the intracellular C-terminus of rat P2X2 reduces ATP-activated current amplitude; site-directed S431C mutation abolished the current reduction induced by 8-bromo-cAMP or purified PKA catalytic subunit without affecting inactivation kinetics or reversal potential.\",\n      \"method\": \"Whole-cell voltage clamp of stably transfected HEK-293 cells, intracellular perfusion of 8-bromo-cAMP and PKA, site-directed mutagenesis\",\n      \"journal\": \"Journal of Neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — phosphorylation site identified by mutagenesis with direct functional readout; single lab with two orthogonal pharmacological approaches\",\n      \"pmids\": [\"9603227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The P2X2 splice variant P2X2-2 (P2X2b), lacking the Val370-Gln438 C-terminal sequence, desensitizes rapidly and completely compared to the slowly desensitizing wild-type channel when expressed in anterior pituitary GT1 or HEK293 cells, demonstrating that the C-terminal domain controls desensitization rate.\",\n      \"method\": \"Expression in GT1 and HEK293 cells, single-cell Ca2+ imaging, whole-cell patch clamp, RT-PCR from enriched pituitary cell fractions\",\n      \"journal\": \"Molecular Endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — functional expression with deletion variant in two cell systems plus native cell verification; single lab\",\n      \"pmids\": [\"9658396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Homomeric P2X2 receptors have higher Ca2+ permeability (PCa/PNa ~2.5) compared to P2X3 (~1.2–1.5) or heteromeric P2X2/3 receptors (~1.2–1.5); external Ca2+ blocks P2X2 with half-maximal concentration ~5 mM, while the Ca2+ block of the heteromeric P2X2/3 receptor (~15 mM) matched that of native nodose neurones, supporting that Ca2+ block involves both subunits.\",\n      \"method\": \"Whole-cell recording from stably transfected HEK-293 cells and cultured rat nodose neurones, reversal-potential measurements with NMDG and Ca2+ substitution\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — rigorous ion permeation analysis in recombinant and native systems with multiple ionic conditions\",\n      \"pmids\": [\"9625864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Specific amino acids in the C-terminal region of P2X2 regulate desensitization: Val370 immediately after the Lys369 splice site slows desensitization via interaction with an intracellular hydrophobic site; truncation at Lys369 accelerated desensitization >100-fold; neutralization of nearby lysines (especially Lys365) also markedly accelerated desensitization.\",\n      \"method\": \"Site-directed mutagenesis, truncation analysis, peptide injection into Xenopus oocytes, two-electrode voltage clamp\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic mutagenesis and peptide competition in reconstituted system; single lab with multiple constructs\",\n      \"pmids\": [\"10517803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"P2X2 receptor expression in the cochlea is concentrated on hair cell stereocilia (endolymphatic surface), inner sulcus cells, and spiral ganglion neurons; voltage-clamped guinea pig hair cells exhibited P2X2-compatible pharmacology, and immunoelectron microscopy localized P2X2 subunits to postsynaptic junctions at both inner and outer hair cells.\",\n      \"method\": \"RT-PCR, whole-cell voltage clamp, immunohistochemistry with P2X2-specific antiserum, immunoelectron microscopy\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (electrophysiology, immunoEM, RT-PCR) in the same tissue, functionally linked to cochlear physiology\",\n      \"pmids\": [\"10493739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Both Cu2+ and Zn2+ potentiate P2X2 receptor currents in Xenopus oocytes with EC50 ~16–20 µM by increasing apparent ATP affinity (leftward shift of concentration-response curve) in a voltage-independent manner; Cu2+ did not further potentiate in the presence of maximal Zn2+, suggesting a shared binding site or mechanism. This modulation is distinct from P2X4, which is potentiated by Zn2+ but not Cu2+.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, concentration-response analysis, voltage-independence testing\",\n      \"journal\": \"Journal of Neurophysiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous pharmacological characterization in reconstituted system, differential comparison with P2X4; single lab\",\n      \"pmids\": [\"10322050\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Co-expression of P2X2 and P2X6 subunits in Xenopus oocytes formed a heteromeric P2X2/6 receptor with significantly different agonist potencies, biphasic ATP-evoked currents (especially with Zn2+ or low pH), altered pH modulation range, and changed suramin sensitivity compared to the P2X2 homomer, demonstrating that P2X6 modifies P2X2 channel phenotype.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, pharmacological characterization with agonists and antagonists, pH and Zn2+ modulation\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — functional heteromer characterization with multiple pharmacological probes; single lab\",\n      \"pmids\": [\"10864944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"P2X2 receptor mediates ATP-stimulated parasensory cation absorption in cochlear outer sulcus cells and vestibular transitional cells; ATP but not selective P2Y agonists stimulated transepithelial current (Isc) with a potency order consistent with P2X2 pharmacology, and this response was blocked by suramin or gadolinium.\",\n      \"method\": \"Vibrating probe technique for transepithelial current measurement, pharmacological profiling with P2X/P2Y agonists and antagonists\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional readout in native tissue with pharmacological dissection matching P2X2; single lab\",\n      \"pmids\": [\"11717350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Noise exposure (90–120 dB) up-regulated P2X2 receptor mRNA and protein in rat cochlea organ of Corti and spiral ganglion; confocal immunofluorescence showed increased P2X2R labeling on outer hair cell stereocilia and cuticular plates, and whole-cell voltage clamp of OHCs confirmed noise-induced up-regulation of ATP-gated inward currents, indicating adaptive regulation of P2X2 expression by acoustic trauma.\",\n      \"method\": \"RT-PCR, western blot, confocal immunofluorescence, whole-cell voltage clamp of isolated outer hair cells\",\n      \"journal\": \"Neuroreport\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods linking noise-induced expression changes to functional current increase in native cells; single lab\",\n      \"pmids\": [\"12858039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"P2X2 subunits are required for fast excitatory postsynaptic potentials (fEPSPs) mediated by ATP in myenteric S neurons of the mouse small intestine; in P2X2 knockout mice, fEPSPs were insensitive to the P2X antagonist PPADS and ATP failed to depolarize S neurons, while peristaltic contractions were impaired in vitro.\",\n      \"method\": \"P2X2 knockout mice, intracellular electrophysiology, pharmacology with PPADS and mecamylamine, RT-PCR, immunohistochemistry, in vitro motility assay\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with clean electrophysiological and motility phenotype, replicated across multiple experimental paradigms\",\n      \"pmids\": [\"12937291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Homomeric P2X2 receptors (and P2X4, P2X5) are trimers of identical subunits, as are heteromeric P2X1+2 receptors; P2X6 subunits fail to form homotrimers and instead are retained in the ER as tetramers/aggregates, establishing trimeric architecture as the structural hallmark of functional P2X receptors.\",\n      \"method\": \"Biochemical analysis (cross-linking, gel electrophoresis, PAGE) in Xenopus oocytes and transfected cells\",\n      \"journal\": \"Journal of Molecular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical stoichiometry determination with multiple subunit types; single lab\",\n      \"pmids\": [\"15313628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Co-activation of P2X2 and GABAA receptors containing β subunits (αβ or αβγ) causes cross-inhibition of P2X2 channels, dependent on the C-terminal domain of P2X2 and the intracellular loop of GABAA β subunits; overexpression of minigenes encoding these domains disrupted the cross-inhibition, and the interaction also induced co-clustering of P2X2 and rho1-β3 chimeric receptors at surface clusters in hippocampal neurons.\",\n      \"method\": \"Co-expression in Xenopus oocytes, two-electrode voltage clamp, minigene overexpression, co-expression in hippocampal neurons with imaging\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional cross-inhibition mapped to specific domains by dominant-negative minigenes plus co-clustering in neurons; single lab with two orthogonal approaches\",\n      \"pmids\": [\"15456793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Pore properties of the P2X2 channel (permeability to large cations, inward rectification, ligand sensitivity) change dynamically depending on channel expression density; Ile328 at the outer mouth of the pore was identified by mutagenesis as critical for these density-dependent changes.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes with varying cRNA injection levels, site-directed mutagenesis at Ile328\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis linked to functional pore property changes in reconstituted system; single lab\",\n      \"pmids\": [\"15107474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The zinc-binding site in rat P2X2 receptors is intersubunit, requiring His120 and His213 from adjacent subunits; mixing H120A and H213A mutant subunits rescued zinc potentiation; trimeric concatamers showed zinc potentiation correlated with the number of intersubunit histidine pairs; H120C/H213C double mutant formed ectopic disulfide bonds between adjacent subunits confirming their proximity.\",\n      \"method\": \"Mutagenesis, co-expression of mixed subunits, trimeric concatamers, two-electrode voltage clamp in Xenopus oocytes, disulfide-trapping with immunoblot under non-reducing conditions\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — five independent lines of evidence including disulfide trapping and concatamer analysis; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"15899882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Heteromeric P2X2/3 receptors require lysine residues from two different subunits for function; single-lysine mutations in P2X2 (K69A or K308A) were rescued by wild-type P2X3 co-expression, but not vice versa, indicating the heteromeric channel contains one P2X2 and two P2X3 subunits.\",\n      \"method\": \"Whole-cell recording from HEK cells, co-expression of wild-type and lysine-to-alanine mutant subunits\",\n      \"journal\": \"Molecular Pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic rescue approach with reciprocal mutant combinations establishing 1:2 P2X2:P2X3 stoichiometry; single lab\",\n      \"pmids\": [\"16840712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ATP application to dendrites of hippocampal neurons expressing P2X2-GFP caused receptor redistribution and formation of varicose hot spots with higher receptor density; this redistribution was accompanied by activation-dependent enhancement of ATP-evoked current; the T18A substate-specific mutant showed neither redistribution nor activation-dependent current enhancement.\",\n      \"method\": \"Live-cell fluorescence imaging of P2X2-GFP in hippocampal neurons, whole-cell voltage clamp, T18A mutant analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — simultaneous live imaging and electrophysiology with mutant validation; single lab\",\n      \"pmids\": [\"11296257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"P2X2 and P2X3 knockout mice showed reduced urinary bladder reflexes and decreased pelvic afferent nerve activity in response to bladder distension, and reduced pain behavior in the formalin test; P2X2-/- mice lacked sustained ATP-evoked inward currents in nodose, coeliac, and SCG neurons, while DRG neurons retained only transient currents.\",\n      \"method\": \"P2X2 knockout and P2X2/P2X3 double knockout mice, patch-clamp electrophysiology of ganglia neurons, cystometry, pelvic nerve recording, behavioral pain assays\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple knockout models with electrophysiological and behavioral phenotypes across multiple sensory paradigms\",\n      \"pmids\": [\"15961431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Fe65 (β-amyloid precursor protein-binding protein) directly interacts with the P2X2 C-terminal domain (but not the naturally occurring P2X2b splice variant lacking part of this domain) as shown by yeast two-hybrid and GST pull-down; Fe65 co-localizes with P2X2 subunits at postsynaptic specializations of excitatory synapses in CA1 hippocampus; co-expression of Fe65 inhibited the time- and activation-dependent increase in ionic selectivity of P2X2 receptors.\",\n      \"method\": \"Yeast two-hybrid, GST pull-down, postembedding immunogold electron microscopy, co-immunoprecipitation from brain membrane extracts, co-expression in HEK cells with electrophysiology\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Y2H, GST pulldown, co-IP from brain, immunoEM, functional electrophysiology) in single study\",\n      \"pmids\": [\"16330549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Visualization by electron microscopy of purified P2X2 protein from baculovirus-Sf9 cells confirmed the trimeric composition of the P2X2 receptor; averaged negative-stain images showed an inverted three-sided pyramid (~215 Å height) with a crown-shaped extracellular domain and three-fold symmetry.\",\n      \"method\": \"Baculovirus-Sf9 expression, affinity purification, chemical cross-linking, negative-stain electron microscopy, single-particle averaging\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct structural visualization by EM with biochemical cross-linking confirmation; single lab\",\n      \"pmids\": [\"16219297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Membrane phosphoinositides (PIPs, PIP2) regulate P2X2 channel activity and pore dilation through electrostatic interaction with positively charged residues (Lys365, Lys369) in the proximal C-terminal cytoplasmic domain; PI3K inhibition or K365Q/K369Q mutations accelerated channel desensitization and sped up the decrease in NMDG permeability (pore dilation); GST-tagged C-terminal fusion proteins bound PIPs in vitro and this binding was abolished by K365Q/K369Q mutations.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, PI3K inhibition (wortmannin, LY294002), site-directed mutagenesis, GST-fusion protein lipid binding assay, fluorescence membrane association assay in COS-7 cells\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis, in vitro lipid binding, and live-cell imaging converge on same mechanism; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"16857707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The Thr339Ser mutation in the second transmembrane domain (TM2) of rat P2X2 causes constitutive (spontaneous) channel opening; the additional K308A mutation (but not K69A) abolished this spontaneous activity and also blocked the agonist-like action of suramin and TNP-ATP at T339S receptors, indicating that Lys308 plays a critical role in channel gating distinct from ATP binding.\",\n      \"method\": \"Single-channel and whole-cell recording in HEK-293 cells, double and single mutagenesis, pharmacological testing with suramin and TNP-ATP\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — constitutively active mutant rescued by second-site mutation, establishing gating role for K308; single lab with functional and pharmacological validation\",\n      \"pmids\": [\"18032665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The neuronal calcium sensor VILIP1 interacts with P2X2 receptors; VILIP1 was identified by proteomic pull-down, confirmed to form a complex in vitro and in vivo with P2X2 receptors, and was shown to regulate P2X2 receptor sensitivity to ATP, peak response, surface expression, and lateral diffusion; the interaction is constitutive but enhanced in an activation- and calcium-dependent manner due to exposure of the VILIP1-binding segment in P2X2; interaction is also enhanced in hippocampal neurons during action potential firing.\",\n      \"method\": \"Proteomic pull-down, co-immunoprecipitation from brain tissue, surface expression assays, whole-cell electrophysiology, live-cell imaging of receptor diffusion in hippocampal neurons\",\n      \"journal\": \"Science Signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — proteomic identification confirmed by co-IP from brain, with functional regulation shown by multiple readouts; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"18922787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The C-terminus of P2X2 binds directly to PIP2, PIP3, and other phosphoinositides in a lipid-binding assay, while the C-terminus of P2X3 does not; wortmannin inhibition reduced P2X2/3 heteromeric receptor currents in DRG neurons and Xenopus oocytes via both PI3K and PI4K pathways, and PIP2 or PIP3 application partially reversed this inhibition.\",\n      \"method\": \"Lipid binding assay with C-terminal GST-fusion proteins, whole-cell patch clamp in DRG neurons, two-electrode voltage clamp in Xenopus oocytes, PI3K/PI4K inhibition\",\n      \"journal\": \"Molecular Pain\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct lipid binding biochemistry combined with native cell electrophysiology; single lab\",\n      \"pmids\": [\"19671169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Systematic mutagenesis of polar and charged residues in TM2 of rat P2X2 identified Asn333 and Asp349 as located in external and internal vestibules respectively; substitutions at Asn333, Thr336, Ser340 were most likely to cause spontaneously active channels; introduction of positive charges at Thr336, Thr339, Ser340 (by Arg/Lys/His substitution or MTSEA modification of Cys) greatly enhanced outward currents, indicating these residues face the permeation pathway in the open channel.\",\n      \"method\": \"Single-channel and whole-cell recording in HEK-293 cells, systematic site-directed mutagenesis of TM2, MTSEA modification of cysteine substitutions\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — comprehensive systematic mutagenesis with functional readouts interpreted against crystal structure of related P2X4; single lab\",\n      \"pmids\": [\"19906973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ATP-activated cation current in mouse spermatozoa midpiece is mediated by P2X2; the current was absent in P2rx2-/- mice; the slowly desensitizing, outwardly rectifying current matched biophysical and pharmacological properties of heterologously expressed mouse P2X2; P2rx2-/- males showed normal sperm motility but reduced fertility with frequent mating.\",\n      \"method\": \"Whole-cell patch clamp of mouse spermatozoa, P2rx2 knockout mice, pharmacological characterization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout abolishes current, pharmacological match to recombinant P2X2; two orthogonal approaches (electrophysiology + genetics)\",\n      \"pmids\": [\"21831833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Colchicine (microtubule disruptor) did not affect ionic currents generated by ATP at P2X2 receptors but inhibited dye (Yo-Pro-1) uptake in Xenopus oocytes and HEK293 cells expressing P2X2, indicating that microtubule integrity is required for the macropore/dye-uptake function of P2X2 but not for its ion channel function.\",\n      \"method\": \"Whole-cell electrophysiology and Yo-Pro-1 dye uptake assay in Xenopus oocytes and HEK293 cells, colchicine treatment\",\n      \"journal\": \"British Journal of Pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection of two distinct channel functions (ion current vs macropore) in two heterologous systems; single lab\",\n      \"pmids\": [\"21306580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"P2X2 and P2X5 subunits interact to form heteromeric receptors at the plasma membrane with alternate stoichiometries, as shown by bioluminescence resonance energy transfer (BRET), bimolecular fluorescence complementation, and protein biochemistry; P2X2/5 receptors display pore dilatation, membrane blebbing, and phosphatidylserine exposure—properties previously thought specific to P2X7 receptors.\",\n      \"method\": \"BRET, bimolecular fluorescence complementation (BiFC), protein biochemistry, live-cell imaging of membrane blebbing and phosphatidylserine exposure\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — three orthogonal methods for assembly determination plus functional characterization; single lab\",\n      \"pmids\": [\"22090499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"P2X2 receptor lateral mobility in hippocampal neuron dendrites is mostly Brownian, consists of mobile and slowly-mobile pools, is P2X2-subunit and cell-type specific, and is increased in an activation-dependent manner; VILIP1 calcium-binding protein regulates this lateral mobility.\",\n      \"method\": \"Single-molecule quantum dot imaging with simultaneous whole-cell voltage clamp in rat hippocampal neurons\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single-molecule imaging with simultaneous electrophysiology, mutant P2X2 and VILIP1 regulation tested; single lab\",\n      \"pmids\": [\"22090499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ATP-binding sites of P2X2 receptors are located at intersubunit interfaces; a thiol-reactive ATP analog (NCS-ATP) covalently labeled Asn140 and Leu186 from two adjacent subunits; tethering at these positions had distinct functional consequences—labeling N140 impeded subsequent ATP function while labeling L186 enhanced subsequent ATP function.\",\n      \"method\": \"Proximity-dependent tethering with NCS-ATP, single cysteine mutagenesis, whole-cell and single-channel recording in HEK cells, homology modeling\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chemical biology approach with functional validation; identifies ATP binding pocket residues from two subunits in closed state; single lab\",\n      \"pmids\": [\"21576497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Glu167 and Arg290 form a salt bridge in the closed state of rat P2X2 receptor that is disrupted upon ATP binding and channel opening; charge-reversal mutations, mutant-cycle analysis, and disulfide trapping confirmed their close proximity in the closed but not open state; the Arg290/ATP ionic interaction replaces the Glu167/Arg290 salt bridge to promote channel opening.\",\n      \"method\": \"Homology modeling, charge-reversal mutagenesis, mutant cycle analysis, disulfide trapping, whole-cell electrophysiology\",\n      \"journal\": \"Molecular Pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — disulfide trapping plus mutant cycle analysis demonstrate state-dependent interaction; multiple experimental approaches; single lab\",\n      \"pmids\": [\"23041661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"P2X2/3 heteromeric receptors have a 1:2 stoichiometry (one P2X2, two P2X3 subunits) while P2X2/6 receptors have a 2:1 stoichiometry (two P2X2, one P2X6 subunit); determined by co-expression of WT and ATP-binding-site Ala mutants in HEK293 cells and Xenopus oocytes—only selective mutations in the majority subunit abolished agonist responses.\",\n      \"method\": \"Site-directed mutagenesis of ATP-binding sites, co-expression of WT and mutant subunits in HEK293 cells and Xenopus oocytes, patch clamp, Ca2+ imaging, protein labeling/PAGE\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic approach with multiple subunit combinations confirmed by biochemical gel analysis; multiple orthogonal methods in one study\",\n      \"pmids\": [\"22378790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The P2RX2 missense mutation p.V60L abolishes two hallmark P2X2 functions—ATP-evoked inward current and ATP-stimulated macropore permeability (FM1-43 dye uptake); co-expression of mutant and WT P2X2 subunits significantly reduced ATP-activated membrane permeability, indicating dominant-negative effect. P2RX2-null mice developed severe progressive hearing loss, and early noise exposure caused high-frequency hearing loss in young adults.\",\n      \"method\": \"Functional expression in heterologous cells, whole-cell electrophysiology, FM1-43 dye uptake assay, P2RX2 knockout mice, audiological testing, linkage analysis in human families\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human genetics confirmed by functional characterization of mutant in reconstituted system plus knockout mouse phenotype; multiple orthogonal methods\",\n      \"pmids\": [\"23345450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ATP activates P2X2 receptors on enteric glial cells to trigger a p38 MAPK-dependent pathway causing cytokine release and a gliosis phenotype; pharmacological blockade and genetic depletion of P2X2 prevented ATP-induced enteric gliosis, inflammation, and dysmotility in postoperative ileus models in mice and humans; ambroxol was identified as a novel P2X2 antagonist.\",\n      \"method\": \"P2X2 receptor antagonism and genetic depletion in murine EGCs and human intestinal tissue, p38 MAPK pathway analysis, cytokine quantification, motility assays, pharmacological screening\",\n      \"journal\": \"EMBO Molecular Medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — both pharmacological and genetic approaches converge on P2X2 as the relevant receptor, with defined downstream pathway (p38 MAPK) and validated in human tissue\",\n      \"pmids\": [\"33332729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"P2X2 receptors in medial prefrontal cortex pyramidal neurons regulate vulnerability to chronic stress-induced depressive-like behavior; conditional knockout of P2X2 in pyramidal neurons promoted resilience, while pyramidal neuron-specific P2X2 overexpression increased vulnerability; in vivo fiber-photometry and electrophysiology showed P2X2 regulates mPFC neuronal activity and synapse function.\",\n      \"method\": \"Conditional knockout (CamkIIα-Cre), AAV-mediated overexpression, chronic social defeat stress model, in vivo fiber-photometry, patch-clamp electrophysiology, neuronal morphometry\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — bidirectional (KO and OE) genetic manipulation with in vivo functional readouts; multiple behavioral and electrophysiological assays\",\n      \"pmids\": [\"35664080\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"P2X2 (P2RX2) is a trimeric, ATP-gated non-selective cation channel that functions as a homomeric trimer or, critically, as a 1P2X2:2P2X3 heterotrimer with distinct pharmacological and biophysical properties; its gating involves intersubunit ATP-binding pockets (contributed by N140/L186 from adjacent subunits), a state-dependent Glu167/Arg290 salt bridge that breaks upon ATP binding, and TM2 residues (especially Thr339) at the gate, while channel activity is regulated post-translationally by PKA phosphorylation at Ser431, membrane phosphoinositides interacting with C-terminal Lys365/Lys369, the neuronal calcium sensor VILIP1 (which controls receptor surface expression and lateral mobility in an activation/Ca²⁺-dependent manner), and intersubunit Zn²⁺/Cu²⁺ binding at His120/His213; alternative C-terminal splicing controls desensitization rate (Val370 is a key hydrophobic anchor); the receptor mediates fast ATP-gated synaptic transmission in enteric and sensory neurons, cochlear endolymphatic homeostasis and protection from noise, taste signal transmission to gustatory nerves, ATP-dependent spermatozoa cation currents, enteric glial gliosis via p38 MAPK signaling, and stress vulnerability in prefrontal cortex pyramidal neurons, with loss-of-function mutations causing autosomal dominant progressive sensorineural hearing loss (DFNA41).\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"P2X2 (P2RX2) is an ATP-gated non-selective cation channel that mediates fast purinergic signaling in sensory, enteric, and central neurons as well as cochlear epithelia [#0, #15]. The functional receptor is a trimer, assembling as a homotrimer or, by co-assembly with other P2X subunits, as heteromeric channels with distinct pharmacology and ion permeation—including a 1P2X2:2P2X3 channel that reconstitutes the ATP currents of native sensory neurons and a 2P2X2:1P2X6 channel [#0, #1, #16, #20, #36]. ATP binds at intersubunit pockets formed by N140 and L186 contributed by adjacent subunits within the extracellular domain [#4, #34]; binding disrupts a closed-state Glu167/Arg290 salt bridge, with Arg290 then coordinating ATP to promote gating [#35], and channel opening proceeds through the second transmembrane segment, where TM2 residues including Thr339 line the permeation pathway and define the gate [#26, #29]. Homomeric P2X2 is notably Ca2+-permeable and exhibits an activation-dependent dilation to a large-cation/dye-permeant pore [#8, #37]. Channel behavior is shaped post-translationally: PKA phosphorylation of Ser431 reduces current [#6], C-terminal phosphoinositides binding Lys365/Lys369 control desensitization and pore dilation [#25], alternative C-terminal splicing (with Val370/Lys369 as key determinants) sets desensitization rate [#2, #9], and intersubunit His120/His213 pairs mediate Zn2+/Cu2+ potentiation [#11, #19]. Surface expression and lateral mobility are governed by N-linked glycosylation and by the neuronal calcium sensor VILIP1, whose activation/Ca2+-dependent association tunes ATP sensitivity and trafficking [#5, #27, #33]. Physiologically, P2X2 drives ATP-mediated fast excitatory transmission in myenteric neurons and bladder/sensory afferents, cochlear endolymphatic ion transport and noise protection, spermatozoa cation currents, enteric glial p38 MAPK–dependent gliosis, and prefrontal-cortex stress vulnerability [#15, #22, #14, #30, #38, #39]. A dominant-negative P2RX2 missense mutation that abolishes ATP-gated current and macropore function causes autosomal dominant progressive sensorineural hearing loss, recapitulated by P2RX2-null mice [#37].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established that P2X2 does not act alone but co-assembles with P2X3 to generate a channel reproducing native sensory-neuron ATP currents, answering why recombinant homomers failed to match physiology.\",\n      \"evidence\": \"Co-expression of P2X2 and P2X3 in Xenopus oocytes with electrophysiology\",\n      \"pmids\": [\"7566120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the heteromer not determined\", \"Direct physical association not yet shown biochemically\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Confirmed direct physical co-assembly of P2X2 and P2X3 subunits, converting the functional inference into a biochemically demonstrated heteromer.\",\n      \"evidence\": \"Cross-immunoprecipitation of epitope-tagged subunits in Sf9 cells with whole-cell patch clamp\",\n      \"pmids\": [\"9254665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subunit ratio not established\", \"Native heteromer composition in neurons not directly confirmed\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Localized ATP binding and identified the C-terminus as the desensitization controller, separating ligand recognition (ECD) from kinetic regulation (intracellular tail).\",\n      \"evidence\": \"Recombinant ECD ATP UV-crosslinking with antagonist competition; cerebellar splice-variant cloning and oocyte expression\",\n      \"pmids\": [\"9398614\", \"9271346\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Isolated ECD may not recapitulate native binding pocket geometry\", \"Exact ECD residues contacting ATP not yet mapped\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defined surface-trafficking and post-translational control of the channel, showing glycosylation is required for surface expression and PKA phosphorylation of Ser431 down-modulates current.\",\n      \"evidence\": \"Mutagenesis of N182/N239/N298 with surface labeling; S431C mutation with PKA/8-Br-cAMP perfusion in HEK-293 cells\",\n      \"pmids\": [\"9778359\", \"9603227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase coupling and physiological trigger for Ser431 phosphorylation in neurons not defined\", \"Glycan structural requirement vs simple folding role unresolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Quantified ion permeation, establishing high Ca2+ permeability of homomeric P2X2 and subunit-dependent Ca2+ block matching native nodose neurons.\",\n      \"evidence\": \"Whole-cell reversal-potential measurements in HEK-293 and rat nodose neurons with ion substitution\",\n      \"pmids\": [\"9625864\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of Ca2+ selectivity not mapped\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Pinpointed C-terminal residues (Val370, Lys365/Lys369) governing desensitization kinetics, providing a molecular mechanism for splice-variant differences.\",\n      \"evidence\": \"Site-directed mutagenesis, truncation, and peptide injection in oocytes; expression of P2X2b in GT1/HEK293 cells\",\n      \"pmids\": [\"10517803\", \"9658396\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the intracellular hydrophobic partner for Val370 unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined trace-metal modulation (Zn2+/Cu2+ potentiation) of P2X2, distinguishing it pharmacologically from P2X4.\",\n      \"evidence\": \"Two-electrode voltage clamp concentration-response analysis in oocytes\",\n      \"pmids\": [\"10322050\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding site not yet localized at this stage\", \"Physiological relevance of Cu2+/Zn2+ modulation in vivo not established\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Connected P2X2 to cochlear physiology by localizing it to hair-cell stereocilia and synaptic junctions, implicating it in endolymphatic ATP signaling.\",\n      \"evidence\": \"RT-PCR, hair-cell voltage clamp, immunohistochemistry and immunoEM in cochlea\",\n      \"pmids\": [\"10493739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal role in hearing not yet tested genetically\", \"Functional output of stereociliary receptors unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Linked P2X2 to functional cochlear/vestibular ion transport and showed expression is adaptively up-regulated by acoustic trauma.\",\n      \"evidence\": \"Vibrating-probe transepithelial current with P2X/P2Y pharmacology; noise exposure with RT-PCR, western, immunofluorescence, OHC voltage clamp\",\n      \"pmids\": [\"11717350\", \"12858039\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor identity inferred pharmacologically, not by genetic deletion in these assays\", \"Signal driving noise-induced upregulation unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Established trimeric architecture as the structural hallmark of functional P2X channels and defined a density-dependent pore property controlled by Ile328.\",\n      \"evidence\": \"Cross-linking/PAGE stoichiometry; oocyte expression with varied cRNA and I328 mutagenesis\",\n      \"pmids\": [\"15313628\", \"15107474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological setting where expression density alters pore properties unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Revealed functional cross-talk between P2X2 and GABA-A receptors, mapping cross-inhibition and co-clustering to specific intracellular domains.\",\n      \"evidence\": \"Co-expression in oocytes and hippocampal neurons, minigene dominant-negatives, imaging\",\n      \"pmids\": [\"15456793\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical interaction vs functional coupling not fully distinguished\", \"Endogenous neuronal relevance not quantified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined the intersubunit Zn2+ site (His120/His213 from adjacent subunits) and confirmed 1P2X2:2P2X3 heteromer stoichiometry, anchoring the trimer's functional interfaces.\",\n      \"evidence\": \"Mixed-subunit and concatamer expression, disulfide trapping; lysine-mutant rescue in HEK cells\",\n      \"pmids\": [\"15899882\", \"16840712\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether multiple metal sites coexist not resolved\", \"Heteromer stoichiometry in native tissue confirmed only indirectly\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated activation-dependent receptor redistribution/clustering and identified Fe65 as a C-terminal interactor regulating ionic selectivity, expanding regulatory partners.\",\n      \"evidence\": \"Live imaging of P2X2-GFP with electrophysiology and T18A mutant; Y2H, GST pulldown, co-IP from brain, immunoEM\",\n      \"pmids\": [\"11296257\", \"16330549\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of Fe65 binding in vivo unclear\", \"Mechanism coupling activation to redistribution not defined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Provided the first direct structural visualization of the trimeric P2X2 receptor as an inverted pyramid with crown-shaped ECD.\",\n      \"evidence\": \"Affinity-purified P2X2 with cross-linking and negative-stain EM single-particle averaging\",\n      \"pmids\": [\"16219297\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Low resolution; no atomic model from this study\", \"Conformational states not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Established P2X2's role in vivo in fast enteric and visceral sensory transmission using knockout mice, linking the channel to peristalsis, bladder reflexes, and pain.\",\n      \"evidence\": \"P2X2 and P2X2/3 knockout mice with ganglion electrophysiology, cystometry, motility, and behavioral pain assays\",\n      \"pmids\": [\"12937291\", \"15961431\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of homomeric vs heteromeric channels in each tissue not dissected\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified membrane phosphoinositides as direct regulators of desensitization and pore dilation via C-terminal Lys365/Lys369.\",\n      \"evidence\": \"Oocyte electrophysiology with PI3K inhibition, K365Q/K369Q mutagenesis, GST-fusion lipid binding, COS-7 imaging\",\n      \"pmids\": [\"16857707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which endogenous lipid species dominates regulation in neurons unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Assigned a gating role to TM2 by showing the Thr339Ser mutation causes constitutive opening rescuable by K308A, separating gating from ATP binding.\",\n      \"evidence\": \"Single-channel and whole-cell recording in HEK-293 with double/single mutagenesis and antagonist testing\",\n      \"pmids\": [\"18032665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Detailed gate motion not directly visualized\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapped TM2 vestibule and permeation-pathway residues (Asn333, Asp349, Thr336/Thr339/Ser340) and showed P2X2 (but not P2X3) C-terminus binds phosphoinositides, extending lipid regulation to heteromers.\",\n      \"evidence\": \"Systematic TM2 mutagenesis with MTSEA in HEK cells; GST-fusion lipid binding and DRG/oocyte electrophysiology with PI3K/PI4K inhibition\",\n      \"pmids\": [\"19906973\", \"19671169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural model relied on related P2X4 crystal structure rather than P2X2 itself\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Established VILIP1 as a calcium-sensor regulator of P2X2 surface expression and lateral mobility, and demonstrated microtubule dependence of the macropore but not the ion-channel function.\",\n      \"evidence\": \"Single-molecule quantum-dot imaging with electrophysiology; colchicine treatment with Yo-Pro-1 uptake assays\",\n      \"pmids\": [\"22090499\", \"21306580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism linking microtubules to macropore formation unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended heteromerization to P2X2/5 with P2X7-like pore dilation/blebbing and defined P2X2's role in spermatozoa, broadening physiological scope.\",\n      \"evidence\": \"BRET/BiFC and biochemistry for P2X2/5 assembly; P2rx2-/- mouse spermatozoa patch clamp\",\n      \"pmids\": [\"22090499\", \"21831833\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"P2X2/5 native expression sites not established\", \"Mechanism of sperm fertility reduction not defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Localized the ATP-binding pocket to the intersubunit interface (Asn140 and Leu186 from adjacent subunits) using chemical tethering.\",\n      \"evidence\": \"NCS-ATP proximity tethering with single-cysteine mutagenesis and recording in HEK cells, homology modeling\",\n      \"pmids\": [\"21576497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational coupling from binding to gate not directly observed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Resolved the conformational logic of gating—Glu167/Arg290 salt bridge breaks on ATP binding—and established subunit ratios of P2X2/3 (1:2) and P2X2/6 (2:1) heteromers.\",\n      \"evidence\": \"Charge-reversal mutagenesis, mutant-cycle analysis, disulfide trapping; WT/mutant co-expression in HEK and oocytes with biochemistry\",\n      \"pmids\": [\"23041661\", \"22378790\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full open-state structure not determined at this stage\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified P2RX2 as a Mendelian deafness gene, with a dominant-negative p.V60L mutation abolishing both ion current and macropore function and recapitulated by null mice.\",\n      \"evidence\": \"Human linkage with functional expression (electrophysiology, FM1-43 dye uptake) and P2RX2 knockout mice with audiology\",\n      \"pmids\": [\"23345450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which cochlear cell type's P2X2 loss drives hearing loss not pinpointed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a non-neuronal disease mechanism whereby ATP activation of P2X2 on enteric glia drives p38 MAPK–dependent gliosis and dysmotility in postoperative ileus.\",\n      \"evidence\": \"Pharmacological and genetic depletion in murine and human EGCs, p38 pathway and cytokine analysis, motility assays\",\n      \"pmids\": [\"33332729\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether glial P2X2 is homomeric or heteromeric not determined\", \"Coupling of cation flux to p38 activation not mechanistically detailed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Implicated prefrontal-cortex P2X2 in stress-induced depressive vulnerability through bidirectional genetic manipulation.\",\n      \"evidence\": \"Pyramidal-neuron conditional knockout and AAV overexpression in chronic social defeat stress with fiber-photometry and electrophysiology\",\n      \"pmids\": [\"35664080\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ATP source and circuit-level signaling driving the phenotype unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the discrete regulatory inputs (PIP/PKA/VILIP1/metals/heteromerization) are integrated in specific native cell types to set physiological output, and the high-resolution structural basis of P2X2 pore dilation, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution P2X2-specific structure in defined gating states in the corpus\", \"Cell-type-specific subunit composition in vivo not mapped\", \"Mechanism converting macropore/ion flux into downstream signaling (e.g., p38) unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 8, 15, 30]},\n      {\"term_id\": \"GO:0005216\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 34, 35]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [16, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 10, 32, 33]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [10, 14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [15, 22, 39]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [8, 13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 27, 38]}\n    ],\n    \"complexes\": [\n      \"P2X2 homotrimer\",\n      \"P2X2/P2X3 heterotrimer (1:2)\",\n      \"P2X2/P2X6 heterotrimer (2:1)\",\n      \"P2X2/P2X5 heteromer\"\n    ],\n    \"partners\": [\n      \"P2RX3\",\n      \"P2RX6\",\n      \"P2RX5\",\n      \"VILIP1\",\n      \"Fe65\",\n      \"GABRB\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}