{"gene":"P2RX5","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1996,"finding":"P2X5 is an ATP-gated ion channel with two transmembrane segments and a large extracellular loop; it desensitizes slowly and does not respond to alpha,beta-methylene-ATP, distinguishing it from P2X1/P2X3.","method":"cDNA cloning, heterologous expression, electrophysiology","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — foundational cloning and functional characterization replicated across subsequent studies","pmids":["8786426"],"is_preprint":false},{"year":1998,"finding":"P2X1 and P2X5 subunits co-assemble to form a novel heteromeric ATP-gated ion channel with distinct pharmacology (biphasic currents, non-desensitizing plateau) compared to homomeric P2X1; heteromeric assembly confirmed by co-immunoprecipitation of epitope-tagged subunits.","method":"Heterologous co-expression in HEK293 cells, patch-clamp electrophysiology, co-immunoprecipitation","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Strong — biochemical (Co-IP) and functional (electrophysiology) evidence in same study, independently replicated by at least two other groups","pmids":["9855626"],"is_preprint":false},{"year":1999,"finding":"P2X1 and P2X5 subunits form hetero-oligomeric channels with the pharmacology of P2X1 (sensitivity to alpha,beta-methylene-ATP and TNP-ATP) but the slow desensitization kinetics of P2X5; physical co-assembly confirmed by reciprocal subunit-specific co-purification of epitope-tagged subunits in HEK-293A cells.","method":"Expression in Xenopus oocytes, two-electrode voltage clamp, reciprocal co-purification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reciprocal biochemical co-purification plus functional electrophysiology, independently corroborating the Torres 1998 finding","pmids":["10336430"],"is_preprint":false},{"year":1999,"finding":"The heteromeric P2X1/5 receptor displays a distinct agonist rank order (ATP ≥ 2-methylthio-ATP > ATPγS > alpha,beta-meATP), is less sensitive to TNP-ATP than P2X1 alone, and plateau currents are potentiated by low PPADS concentrations and elevated extracellular Ca2+.","method":"Patch-clamp electrophysiology in HEK293 cells, concentration-response curves for agonists and antagonists","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — rigorous pharmacological characterization but single lab, extending prior Torres 1998 study","pmids":["10496954"],"is_preprint":false},{"year":2002,"finding":"Extracellular Ca2+ sensitizes the rat P2X5 homomeric receptor: replacement of Ca2+ with Ba2+ or Mg2+ produces very small agonist responses, while Ca2+-pulse conditioning restores robust responses; Zn2+ potentiates then inhibits ATP responses concentration-dependently, and lowering pH reduces ATP potency and efficacy.","method":"Two-electrode voltage clamp in Xenopus oocytes, ion substitution and modulator experiments","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — detailed in vitro electrophysiology with multiple orthogonal ion substitution experiments, single lab","pmids":["12237343"],"is_preprint":false},{"year":2002,"finding":"Activation of P2X5 receptors on rat skeletal muscle satellite cells inhibits proliferation, stimulates expression of differentiation markers (myogenin, p21, myosin heavy chain), increases myotube formation, and rapidly increases p38 MAPK phosphorylation; inhibition of p38 prevents the effect of ATP on cell number.","method":"Primary satellite cell cultures, immunocytochemistry, RT-PCR, electrophysiology, p38 inhibitor experiments","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (electrophysiology, biochemistry, inhibitor rescue), single lab","pmids":["12135987"],"is_preprint":false},{"year":2003,"finding":"Full-length human P2X5 (including exon 10) forms a functional ATP-gated cation channel permeable to Ca2+ (PCa/PNa=1.5), Na+, NMDG (PNMDG/PNa=0.4), and Cl- (PCl/PNa=0.5) but not gluconate; it shows slow desensitization, is blocked by suramin, PPADS, and Brilliant Blue G, and rapidly accumulates YO-PRO-1 dye upon ATP application.","method":"Patch-clamp recording, fluorescence imaging, reversal potential measurements in HEK293 cells","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — comprehensive electrophysiological and permeability characterization with multiple ion substitution experiments, single lab but multiple orthogonal methods","pmids":["12761352"],"is_preprint":false},{"year":2005,"finding":"A frameshift polymorphism in P2X5 (exon 10 skipping) results in absence of protein expression in donor hematopoietic cells; differential P2X5 protein expression between donor and recipient generates the minor histocompatibility antigen LRH-1, which is presented by HLA class I and elicits an allogeneic CD8+ CTL response.","method":"Genetic linkage analysis, tetramer analysis of CTL responses, protein expression studies in hematopoietic cells","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and immunological evidence in patient samples with functional CTL assays, single study","pmids":["16322791"],"is_preprint":false},{"year":2006,"finding":"P2X5 homotrimerization requires formation of a complete second transmembrane domain (TM2); the truncated human variant (lacking the C-terminal end of TM2 due to exon 10 skipping) is prone to subunit aggregation because the residual TM2 is too short to insert into the membrane. A single conserved aspartate residue (Asp355) in TM2 supports homotrimerization in a side-chain-specific manner.","method":"Systematic mutagenesis, hydrophobic stretch addition, biochemical analysis of trimerization in heterologous expression system","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with biochemical trimerization assays, multiple mutants tested, single lab","pmids":["17001079"],"is_preprint":false},{"year":2008,"finding":"P2X1 and P2X5 subunits together form the functional P2X receptor mediating ATP-induced currents in mouse cortical astrocytes; astrocyte ATP responses show high sensitivity (EC50 ~40 nM), biphasic kinetics, and PPADS sensitivity consistent with P2X1/5 heteromers. Quantitative PCR confirmed strong P2X1 and P2X5 mRNA expression in these cells.","method":"Whole-cell voltage clamp in acutely isolated astrocytes from transgenic mice, quantitative RT-PCR","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electrophysiology plus qPCR in native cells, pharmacological profile matches known P2X1/5 heteromer, single lab","pmids":["18495881"],"is_preprint":false},{"year":2010,"finding":"The exon 10-deleted human P2X5 isoform (lacking 22 aa of TM2) is non-functional and localizes to the cytoplasm, whereas full-length P2X5 (containing exon 10) localizes to the cell surface and produces robust ATP-evoked currents and Ca2+ influx. Most humans carry the G-allele at the exon 10 splice site, resulting in exclusive expression of the non-functional isoform.","method":"Genotyping, RT-PCR, immunofluorescence of stably expressing cell lines, electrophysiology, fluorometric Ca2+ imaging","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (localization, electrophysiology, Ca2+ imaging, genotyping) in single study establishing isoform-specific function and localization","pmids":["20223879"],"is_preprint":false},{"year":2012,"finding":"P2X5 and P2X2 subunits interact to form heteromeric receptors with alternate stoichiometries at the plasma membrane; P2X2/5 receptors display pore dilatation, membrane blebbing, and phosphatidylserine exposure—functional hallmarks previously attributed exclusively to P2X7 receptors. P2X2 and P2X5 subunits colocalize and physically interact in specific mouse neuronal populations in vivo.","method":"Bioluminescence resonance energy transfer (BRET), bifunctional fluorescence complementation, protein biochemistry, confocal colocalization in mouse brain","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — three orthogonal biochemical/biophysical methods (BRET, BiFC, protein biochemistry) plus in vivo colocalization, single rigorous study","pmids":["22442090"],"is_preprint":false},{"year":2014,"finding":"Human P2RX5 (truncation variant lacking exon 10) is upregulated at mRNA and protein levels during T cell activation, is recruited to the cell surface, and siRNA-mediated knockdown of P2RX5 in CD4+ T cells leads to twofold increased IL-10 production, indicating a role in T cell immunoregulation.","method":"Flow cytometry, siRNA knockdown, ELISA for IL-10, surface expression analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with specific cytokine phenotype and surface recruitment, multiple methods, single lab","pmids":["25181038"],"is_preprint":false},{"year":2017,"finding":"P2X5 is required for ATP-mediated inflammasome activation and IL-1β production in osteoclasts; P2X5-deficient osteoclasts show defective hyper-multinucleation under inflammatory conditions, and this maturation defect is rescued in vitro by addition of exogenous IL-1β.","method":"P2rx5 knockout mice, osteoclast differentiation assays, inflammasome activation assays, IL-1β rescue experiment","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with rescue experiment, multiple functional readouts (multinucleation, inflammasome, IL-1β), replicated in subsequent studies","pmids":["28298636"],"is_preprint":false},{"year":2019,"finding":"Methylosome protein 50 (MEP50), a cofactor of PRMT5, physically associates with P2X5 via its C-terminal intracellular region; RNAi knockdown of MEP50 decreases mature osteoclast formation, and the defective osteoclast maturation in P2X5-deficient cells is rescued by full-length P2X5 but not by a C-terminal deletion mutant.","method":"Co-immunoprecipitation, RNAi knockdown, transduction with full-length vs. C-terminal deletion mutant P2X5, osteoclast differentiation assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus domain-mapping rescue experiments, single lab, multiple approaches","pmids":["31432503"],"is_preprint":false},{"year":2019,"finding":"Weak ATP responses of rat P2X5 are due to altered allostery of the left flipper (LF) domain; single amino acid substitutions S191F or F195H (replacing rat residues with corresponding human P2X5 residues) significantly enhance current amplitude. Engineered disulfide cross-linking and molecular modeling show that these substitutions alter LF domain allostery to allow full pore opening.","method":"Site-directed mutagenesis, patch-clamp electrophysiology, engineered disulfide cross-linking, single-channel recording, molecular modeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis with functional electrophysiology and structural cross-linking experiments, multiple orthogonal methods in single study","pmids":["31727741"],"is_preprint":false},{"year":2020,"finding":"P2X5 is required for cytosolic killing of Listeria monocytogenes by macrophages and for L. monocytogenes-induced inflammasome activation and IL-1β/IL-18 production; defective killing in P2X5-deficient macrophages is substantially rescued by exogenous IL-1β or IL-18. This P2X5-dependent pathway is independent of ATP-P2X7 inflammasome activation.","method":"P2rx5 knockout mice, bone marrow-derived macrophage killing assays, inflammasome activation assays, cytokine rescue experiments, P2X7 deficiency comparison","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with cytokine rescue, parallel comparison to P2X7 pathway, multiple functional readouts in vivo and in vitro","pmids":["32540996"],"is_preprint":false},{"year":2022,"finding":"Dihydropyridines isradipine and nimodipine potentiate ATP-induced currents through the full-length human P2X5 receptor at low micromolar concentrations, while amlodipine inhibits only at high (300 µM) concentrations. The full-length hP2X5 receptor shows Cl- permeability and gating kinetics consistent with prior reports.","method":"Two-microelectrode voltage clamp in Xenopus oocytes expressing hP2X5FL, pharmacological screening","journal":"Molecules","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro electrophysiology with multiple compounds, single lab, no mechanistic follow-up on binding site","pmids":["35335209"],"is_preprint":false},{"year":2022,"finding":"Using BRET-based probes, concentration- and time-dependent ligand bias in cationic selectivity (differential Ca2+ vs. K+ permeability) was detected in P2X5 when activated by benzoyl-ATP (Bz-ATP), indicating dynamic ion selectivity changes dependent on ligand identity.","method":"BRET-based ion concentration probes in live cells during drug challenge","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — novel BRET approach demonstrates functional ligand bias, single study, P2X5 is secondary to TRPV1 focus","pmids":["36343259"],"is_preprint":false},{"year":2024,"finding":"P2RX5 knockout in mice causes reduced brown adipocyte differentiation in vitro and reduced browning in vivo; P2RX5 agonism exerts an anti-obesity effect under thermoneutral conditions with enhanced BAT recruitment, indicating P2RX5 mediates brown adipocyte differentiation and function.","method":"P2rx5 knockout mice, in vitro brown adipocyte differentiation assays, metabolic characterization, in vivo agonist treatment","journal":"Adipocyte","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout plus in vitro and in vivo agonist experiments, multiple readouts, single lab","pmids":["39484996"],"is_preprint":false},{"year":2025,"finding":"P2X5 modulates glucose metabolism in brown adipose tissue (BAT): both global and brown adipocyte-specific P2rx5 deficiency results in lower UCP1 expression and impaired glucose tolerance, with reduced glucose disposal specifically into BAT but not other organs.","method":"Global and tissue-specific knockout mice, indirect calorimetry, glucose tolerance tests, organ-specific glucose uptake measurements","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — tissue-specific knockout and global KO with multiple metabolic readouts, single lab","pmids":["40650249"],"is_preprint":false},{"year":2025,"finding":"ATP-sensitive P2X5 isoforms exist across species including humans: in mice ~90% of P2X5 transcripts encode the ATP-sensitive mP2X5 G317 form; in rats an exon 3-containing variant accounts for >70%; in human cell lines ATP-sensitive isoforms retaining exons 3, 7, and 10 represent ~15-30% of transcripts. These findings challenge the prevailing assumption that P2X5 is universally ATP-insensitive.","method":"Gene profiling, next-generation sequencing (NGS), RNA-seq from human tissues","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, sequencing-based identification without full functional reconstitution for all variants, single study","pmids":["bio_10.1101_2025.01.10.632374"],"is_preprint":true}],"current_model":"P2RX5 (P2X5) is an ATP-gated trimeric cation channel with two transmembrane domains that can form homomeric channels (when full-length, including exon 10) or heteromeric channels with P2X1, P2X2, or P2X4 subunits; its functional state depends critically on TM2 integrity and left-flipper domain allostery, the human truncated isoform (lacking exon 10) is non-functional and cytoplasmic, the full-length receptor is permeable to Ca2+, Na+, NMDG, and Cl-, is modulated by extracellular Ca2+, Zn2+, and pH, and in immune and musculoskeletal contexts P2X5 mediates inflammasome activation and IL-1β production, interacts with MEP50 via its C-terminal intracellular domain to regulate osteoclast maturation, controls skeletal muscle satellite cell differentiation via p38 MAPK, and regulates T cell IL-10 production and brown adipocyte differentiation/glucose metabolism."},"narrative":{"mechanistic_narrative":"P2RX5 (P2X5) is an ATP-gated cation channel of the P2X family that signals through purinergic ATP sensing to control differentiation and inflammatory output across muscle, immune, and adipose tissues [PMID:8786426, PMID:12135987, PMID:28298636]. The receptor has the canonical two-transmembrane topology with a large extracellular ATP-binding loop, desensitizes slowly, and is insensitive to alpha,beta-methylene-ATP, distinguishing it from P2X1/P2X3 [PMID:8786426]. Functional assembly requires a complete second transmembrane domain: trimerization depends on TM2 integrity and a conserved aspartate (Asp355), so that full-length human P2X5 (retaining exon 10) traffics to the cell surface and forms a channel permeable to Ca2+, Na+, NMDG, and Cl-, whereas the common exon-10-skipped human isoform lacks part of TM2, aggregates, remains cytoplasmic, and is non-functional [PMID:12761352, PMID:17001079, PMID:20223879]. Gating is tuned by extracellular Ca2+, Zn2+, and pH and by left-flipper domain allostery, where human-type residues in this region permit fuller pore opening [PMID:12237343, PMID:31727741]. Beyond homomers, P2X5 co-assembles into heteromeric channels with P2X1, P2X2, or P2X4, conferring hybrid pharmacology and kinetics, and P2X2/5 heteromers acquire pore-dilatation and phosphatidylserine-exposure properties; such P2X1/5 heteromers underlie native ATP currents in astrocytes [PMID:9855626, PMID:10336430, PMID:22442090, PMID:18495881]. Physiologically, ATP activation of P2X5 drives p38 MAPK-dependent skeletal muscle satellite cell differentiation [PMID:12135987], licenses inflammasome activation and IL-1beta production required for osteoclast hyper-multinucleation and for macrophage cytosolic killing of Listeria monocytogenes [PMID:28298636, PMID:32540996], and in osteoclasts the C-terminal intracellular region binds the PRMT5 cofactor MEP50 to support maturation [PMID:31432503]. P2X5 also regulates T cell IL-10 production and is required for brown adipocyte differentiation, BAT browning, and glucose disposal into brown adipose tissue [PMID:25181038, PMID:39484996, PMID:40650249]. A genetic polymorphism creating the exon-10-skipped non-functional isoform underlies the minor histocompatibility antigen LRH-1, which is presented by HLA class I and elicits allogeneic CD8+ CTL responses [PMID:16322791].","teleology":[{"year":1996,"claim":"Established that P2X5 is a distinct ATP-gated ion channel, defining its existence as a slowly-desensitizing purinergic receptor with a unique pharmacology separating it from other P2X subunits.","evidence":"cDNA cloning, heterologous expression, and electrophysiology","pmids":["8786426"],"confidence":"High","gaps":["Native cell type of action not established","No physiological function assigned"]},{"year":1999,"claim":"Resolved that P2X5 is not solely a homomeric channel but co-assembles with P2X1 into heteromers, explaining hybrid ATP-current kinetics and broadening the receptor's functional repertoire.","evidence":"Heterologous co-expression, patch-clamp/two-electrode voltage clamp, and reciprocal co-immunoprecipitation/co-purification of epitope-tagged subunits","pmids":["9855626","10336430","10496954"],"confidence":"High","gaps":["Subunit stoichiometry within the heteromer not defined","In vivo relevance not yet shown at this stage"]},{"year":2002,"claim":"Defined how the homomeric channel is gated allosterically by the extracellular environment, showing Ca2+, Zn2+, and pH tune ATP responsiveness.","evidence":"Two-electrode voltage clamp in Xenopus oocytes with ion substitution and modulator experiments","pmids":["12237343"],"confidence":"Medium","gaps":["Structural basis of modulator binding sites not mapped","Studied for rat receptor only"]},{"year":2002,"claim":"Assigned the first physiological role to P2X5 activation: linking ATP sensing to a p38 MAPK-driven switch from proliferation to differentiation in muscle satellite cells.","evidence":"Primary satellite cell cultures with immunocytochemistry, RT-PCR, electrophysiology, and p38 inhibitor rescue","pmids":["12135987"],"confidence":"Medium","gaps":["Direct coupling between channel ion flux and p38 activation not established","Single lab, rat cells"]},{"year":2003,"claim":"Characterized the full-length human receptor as a genuinely functional, broadly permeable channel (Ca2+, Na+, NMDG, Cl-), establishing the human ortholog's biophysical baseline.","evidence":"Patch-clamp, fluorescence imaging, and reversal-potential measurements in HEK293 cells","pmids":["12761352"],"confidence":"High","gaps":["Did not address why most humans express a non-functional isoform"]},{"year":2006,"claim":"Explained at the molecular level why the truncated human variant fails: trimerization requires a complete TM2, and the exon-10-skipped form is too short to insert and aggregates.","evidence":"Systematic mutagenesis, hydrophobic-stretch addition, and biochemical trimerization assays in heterologous cells","pmids":["17001079"],"confidence":"High","gaps":["Role of Asp355 in the assembled trimer's gating not defined"]},{"year":2010,"claim":"Connected genotype to subcellular fate, showing the exon-10-deleted human isoform is cytoplasmic and non-functional while full-length P2X5 reaches the surface, and that most humans express only the non-functional form.","evidence":"Genotyping, RT-PCR, immunofluorescence, electrophysiology, and Ca2+ imaging in stable cell lines","pmids":["20223879"],"confidence":"High","gaps":["Functional consequences in human tissues of carrying the non-functional allele not resolved"]},{"year":2005,"claim":"Showed the human expression polymorphism has direct immunological consequence, generating the LRH-1 minor histocompatibility antigen that drives allogeneic CD8+ CTL responses.","evidence":"Genetic linkage, tetramer CTL analysis, and protein expression studies in hematopoietic cells","pmids":["16322791"],"confidence":"Medium","gaps":["Mechanism linking exon-10 skipping to antigen presentation not detailed","Single study"]},{"year":2012,"claim":"Expanded heteromer biology by demonstrating P2X2/5 channels with alternate stoichiometries that acquire pore-dilatation and phosphatidylserine-exposure properties previously attributed only to P2X7.","evidence":"BRET, bifunctional fluorescence complementation, protein biochemistry, and confocal colocalization in mouse brain","pmids":["22442090"],"confidence":"High","gaps":["Functional output of P2X2/5 in specific neuronal circuits not defined"]},{"year":2017,"claim":"Established a genetic in vivo requirement for P2X5 in inflammatory signaling, linking it to inflammasome activation, IL-1beta production, and osteoclast hyper-multinucleation.","evidence":"P2rx5 knockout mice, osteoclast differentiation and inflammasome assays, and IL-1beta rescue","pmids":["28298636"],"confidence":"High","gaps":["Molecular link from channel activity to inflammasome assembly not mapped"]},{"year":2019,"claim":"Identified an intracellular protein partner, showing the P2X5 C-terminus binds MEP50 to support osteoclast maturation beyond its channel role.","evidence":"Co-immunoprecipitation, RNAi, and domain-mapping rescue with C-terminal deletion mutant","pmids":["31432503"],"confidence":"Medium","gaps":["Whether MEP50/PRMT5 activity is modulated by P2X5 binding not shown","Reciprocal validation limited"]},{"year":2019,"claim":"Explained the species difference in ATP sensitivity mechanistically, attributing weak rat P2X5 responses to left-flipper domain allostery that human-type residues relieve to permit full pore opening.","evidence":"Site-directed mutagenesis, patch-clamp, engineered disulfide cross-linking, single-channel recording, and molecular modeling","pmids":["31727741"],"confidence":"High","gaps":["No high-resolution structure of the gating transition"]},{"year":2020,"claim":"Generalized the inflammatory role to host defense, showing P2X5 is required for macrophage cytosolic killing of Listeria via an inflammasome/IL-1beta/IL-18 pathway independent of ATP-P2X7.","evidence":"P2rx5 knockout mice, macrophage killing and inflammasome assays, cytokine rescue, and P2X7 comparison","pmids":["32540996"],"confidence":"High","gaps":["Trigger that activates P2X5 during intracellular infection unclear"]},{"year":2014,"claim":"Implicated P2X5 in adaptive immune regulation, showing the human truncation variant is induced on activated T cells and restrains IL-10 production.","evidence":"Flow cytometry, siRNA knockdown, IL-10 ELISA, and surface expression analysis","pmids":["25181038"],"confidence":"Medium","gaps":["How a non-functional channel isoform exerts this effect not explained","Single lab"]},{"year":2022,"claim":"Identified small-molecule modulators (dihydropyridines) and ligand-dependent ion-selectivity bias, revealing the channel's gating output is tunable by both pharmacology and agonist identity.","evidence":"Two-microelectrode voltage clamp in oocytes and BRET-based ion probes in live cells","pmids":["35335209","36343259"],"confidence":"Medium","gaps":["Binding sites for dihydropyridines not localized","Physiological relevance of ligand bias unknown"]},{"year":2025,"claim":"Defined a metabolic role, showing P2X5 is required for brown adipocyte differentiation, BAT browning, and glucose disposal into brown fat, positioning it as an anti-obesity target.","evidence":"Global and brown-adipocyte-specific P2rx5 knockout mice, in vitro differentiation, calorimetry, glucose tolerance, and organ-specific uptake; in vivo agonist treatment","pmids":["39484996","40650249"],"confidence":"Medium","gaps":["Whether the metabolic effect requires channel ion flux or a scaffolding function not resolved","Single lab"]},{"year":2025,"claim":"Challenged the assumption of universal ATP-insensitivity by cataloguing ATP-sensitive splice isoforms across species, including a minority of functional human transcripts.","evidence":"Gene profiling, NGS, and RNA-seq from human tissues (preprint)","pmids":["bio_10.1101_2025.01.10.632374"],"confidence":"Low","gaps":["Awaits full functional reconstitution of all variants","Preprint, not peer-reviewed","Tissue-level protein expression not confirmed"]},{"year":null,"claim":"How a predominantly non-functional human isoform mediates immune and metabolic phenotypes, and whether the C-terminal MEP50 interaction and channel gating are mechanistically coupled, remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of an assembled human P2X5 channel","Channel-independent (scaffolding) functions not separated from ion-flux functions","Endogenous activation trigger in disease contexts undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,6,10]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,6,18]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,2,8,11]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[10,11]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[13,16]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,19]}],"complexes":["P2X1/5 heteromeric receptor","P2X2/5 heteromeric receptor","P2X5 homotrimer"],"partners":["P2RX1","P2RX2","P2RX4","MEP50"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q93086","full_name":"P2X purinoceptor 5","aliases":["ATP receptor","Purinergic receptor"],"length_aa":444,"mass_kda":49.3,"function":"ATP-gated nonselective transmembrane cation channel permeable to potassium, sodium and calcium (PubMed:12761352). Unlike other P2RX receptors, the P2X5 receptor is also permeable to chloride (PubMed:12761352). May play a supporting role in the inflammatory response (By similarity) Non-functional","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q93086/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/P2RX5","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/P2RX5","total_profiled":1310},"omim":[{"mim_id":"611741","title":"ACID-SENSING ION CHANNEL, SUBUNIT 3; ASIC3","url":"https://www.omim.org/entry/611741"},{"mim_id":"602836","title":"PURINERGIC RECEPTOR P2X, LIGAND-GATED ION CHANNEL, 5; P2RX5","url":"https://www.omim.org/entry/602836"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"intestine","ntpm":23.7},{"tissue":"lymphoid tissue","ntpm":73.8}],"url":"https://www.proteinatlas.org/search/P2RX5"},"hgnc":{"alias_symbol":["P2X5","LRH-1"],"prev_symbol":[]},"alphafold":{"accession":"Q93086","domains":[{"cath_id":"2.60.490.10","chopping":"64-113_190-332","consensus_level":"high","plddt":89.9916,"start":64,"end":332},{"cath_id":"-","chopping":"122-170","consensus_level":"high","plddt":90.8833,"start":122,"end":170}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q93086","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q93086-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q93086-F1-predicted_aligned_error_v6.png","plddt_mean":81.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=P2RX5","jax_strain_url":"https://www.jax.org/strain/search?query=P2RX5"},"sequence":{"accession":"Q93086","fasta_url":"https://rest.uniprot.org/uniprotkb/Q93086.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q93086/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q93086"}},"corpus_meta":[{"pmid":"8786426","id":"PMC_8786426","title":"Cloning OF P2X5 and P2X6 receptors and the distribution and properties of an extended family of ATP-gated ion channels.","date":"1996","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/8786426","citation_count":768,"is_preprint":false},{"pmid":"25080478","id":"PMC_25080478","title":"ASC-1, PAT2, and P2RX5 are cell surface markers for white, beige, and brown adipocytes.","date":"2014","source":"Science translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/25080478","citation_count":163,"is_preprint":false},{"pmid":"18495881","id":"PMC_18495881","title":"P2X1 and P2X5 subunits form the functional P2X receptor in mouse cortical astrocytes.","date":"2008","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/18495881","citation_count":142,"is_preprint":false},{"pmid":"16322791","id":"PMC_16322791","title":"A frameshift 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\"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — foundational cloning and functional characterization replicated across subsequent studies\",\n      \"pmids\": [\"8786426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"P2X1 and P2X5 subunits co-assemble to form a novel heteromeric ATP-gated ion channel with distinct pharmacology (biphasic currents, non-desensitizing plateau) compared to homomeric P2X1; heteromeric assembly confirmed by co-immunoprecipitation of epitope-tagged subunits.\",\n      \"method\": \"Heterologous co-expression in HEK293 cells, patch-clamp electrophysiology, co-immunoprecipitation\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biochemical (Co-IP) and functional (electrophysiology) evidence in same study, independently replicated by at least two other groups\",\n      \"pmids\": [\"9855626\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"P2X1 and P2X5 subunits form hetero-oligomeric channels with the pharmacology of P2X1 (sensitivity to alpha,beta-methylene-ATP and TNP-ATP) but the slow desensitization kinetics of P2X5; physical co-assembly confirmed by reciprocal subunit-specific co-purification of epitope-tagged subunits in HEK-293A cells.\",\n      \"method\": \"Expression in Xenopus oocytes, two-electrode voltage clamp, reciprocal co-purification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reciprocal biochemical co-purification plus functional electrophysiology, independently corroborating the Torres 1998 finding\",\n      \"pmids\": [\"10336430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The heteromeric P2X1/5 receptor displays a distinct agonist rank order (ATP ≥ 2-methylthio-ATP > ATPγS > alpha,beta-meATP), is less sensitive to TNP-ATP than P2X1 alone, and plateau currents are potentiated by low PPADS concentrations and elevated extracellular Ca2+.\",\n      \"method\": \"Patch-clamp electrophysiology in HEK293 cells, concentration-response curves for agonists and antagonists\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — rigorous pharmacological characterization but single lab, extending prior Torres 1998 study\",\n      \"pmids\": [\"10496954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Extracellular Ca2+ sensitizes the rat P2X5 homomeric receptor: replacement of Ca2+ with Ba2+ or Mg2+ produces very small agonist responses, while Ca2+-pulse conditioning restores robust responses; Zn2+ potentiates then inhibits ATP responses concentration-dependently, and lowering pH reduces ATP potency and efficacy.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, ion substitution and modulator experiments\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — detailed in vitro electrophysiology with multiple orthogonal ion substitution experiments, single lab\",\n      \"pmids\": [\"12237343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Activation of P2X5 receptors on rat skeletal muscle satellite cells inhibits proliferation, stimulates expression of differentiation markers (myogenin, p21, myosin heavy chain), increases myotube formation, and rapidly increases p38 MAPK phosphorylation; inhibition of p38 prevents the effect of ATP on cell number.\",\n      \"method\": \"Primary satellite cell cultures, immunocytochemistry, RT-PCR, electrophysiology, p38 inhibitor experiments\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (electrophysiology, biochemistry, inhibitor rescue), single lab\",\n      \"pmids\": [\"12135987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Full-length human P2X5 (including exon 10) forms a functional ATP-gated cation channel permeable to Ca2+ (PCa/PNa=1.5), Na+, NMDG (PNMDG/PNa=0.4), and Cl- (PCl/PNa=0.5) but not gluconate; it shows slow desensitization, is blocked by suramin, PPADS, and Brilliant Blue G, and rapidly accumulates YO-PRO-1 dye upon ATP application.\",\n      \"method\": \"Patch-clamp recording, fluorescence imaging, reversal potential measurements in HEK293 cells\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — comprehensive electrophysiological and permeability characterization with multiple ion substitution experiments, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"12761352\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"A frameshift polymorphism in P2X5 (exon 10 skipping) results in absence of protein expression in donor hematopoietic cells; differential P2X5 protein expression between donor and recipient generates the minor histocompatibility antigen LRH-1, which is presented by HLA class I and elicits an allogeneic CD8+ CTL response.\",\n      \"method\": \"Genetic linkage analysis, tetramer analysis of CTL responses, protein expression studies in hematopoietic cells\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and immunological evidence in patient samples with functional CTL assays, single study\",\n      \"pmids\": [\"16322791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"P2X5 homotrimerization requires formation of a complete second transmembrane domain (TM2); the truncated human variant (lacking the C-terminal end of TM2 due to exon 10 skipping) is prone to subunit aggregation because the residual TM2 is too short to insert into the membrane. A single conserved aspartate residue (Asp355) in TM2 supports homotrimerization in a side-chain-specific manner.\",\n      \"method\": \"Systematic mutagenesis, hydrophobic stretch addition, biochemical analysis of trimerization in heterologous expression system\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with biochemical trimerization assays, multiple mutants tested, single lab\",\n      \"pmids\": [\"17001079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"P2X1 and P2X5 subunits together form the functional P2X receptor mediating ATP-induced currents in mouse cortical astrocytes; astrocyte ATP responses show high sensitivity (EC50 ~40 nM), biphasic kinetics, and PPADS sensitivity consistent with P2X1/5 heteromers. Quantitative PCR confirmed strong P2X1 and P2X5 mRNA expression in these cells.\",\n      \"method\": \"Whole-cell voltage clamp in acutely isolated astrocytes from transgenic mice, quantitative RT-PCR\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electrophysiology plus qPCR in native cells, pharmacological profile matches known P2X1/5 heteromer, single lab\",\n      \"pmids\": [\"18495881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The exon 10-deleted human P2X5 isoform (lacking 22 aa of TM2) is non-functional and localizes to the cytoplasm, whereas full-length P2X5 (containing exon 10) localizes to the cell surface and produces robust ATP-evoked currents and Ca2+ influx. Most humans carry the G-allele at the exon 10 splice site, resulting in exclusive expression of the non-functional isoform.\",\n      \"method\": \"Genotyping, RT-PCR, immunofluorescence of stably expressing cell lines, electrophysiology, fluorometric Ca2+ imaging\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (localization, electrophysiology, Ca2+ imaging, genotyping) in single study establishing isoform-specific function and localization\",\n      \"pmids\": [\"20223879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"P2X5 and P2X2 subunits interact to form heteromeric receptors with alternate stoichiometries at the plasma membrane; P2X2/5 receptors display pore dilatation, membrane blebbing, and phosphatidylserine exposure—functional hallmarks previously attributed exclusively to P2X7 receptors. P2X2 and P2X5 subunits colocalize and physically interact in specific mouse neuronal populations in vivo.\",\n      \"method\": \"Bioluminescence resonance energy transfer (BRET), bifunctional fluorescence complementation, protein biochemistry, confocal colocalization in mouse brain\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — three orthogonal biochemical/biophysical methods (BRET, BiFC, protein biochemistry) plus in vivo colocalization, single rigorous study\",\n      \"pmids\": [\"22442090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Human P2RX5 (truncation variant lacking exon 10) is upregulated at mRNA and protein levels during T cell activation, is recruited to the cell surface, and siRNA-mediated knockdown of P2RX5 in CD4+ T cells leads to twofold increased IL-10 production, indicating a role in T cell immunoregulation.\",\n      \"method\": \"Flow cytometry, siRNA knockdown, ELISA for IL-10, surface expression analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with specific cytokine phenotype and surface recruitment, multiple methods, single lab\",\n      \"pmids\": [\"25181038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"P2X5 is required for ATP-mediated inflammasome activation and IL-1β production in osteoclasts; P2X5-deficient osteoclasts show defective hyper-multinucleation under inflammatory conditions, and this maturation defect is rescued in vitro by addition of exogenous IL-1β.\",\n      \"method\": \"P2rx5 knockout mice, osteoclast differentiation assays, inflammasome activation assays, IL-1β rescue experiment\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with rescue experiment, multiple functional readouts (multinucleation, inflammasome, IL-1β), replicated in subsequent studies\",\n      \"pmids\": [\"28298636\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Methylosome protein 50 (MEP50), a cofactor of PRMT5, physically associates with P2X5 via its C-terminal intracellular region; RNAi knockdown of MEP50 decreases mature osteoclast formation, and the defective osteoclast maturation in P2X5-deficient cells is rescued by full-length P2X5 but not by a C-terminal deletion mutant.\",\n      \"method\": \"Co-immunoprecipitation, RNAi knockdown, transduction with full-length vs. C-terminal deletion mutant P2X5, osteoclast differentiation assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus domain-mapping rescue experiments, single lab, multiple approaches\",\n      \"pmids\": [\"31432503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Weak ATP responses of rat P2X5 are due to altered allostery of the left flipper (LF) domain; single amino acid substitutions S191F or F195H (replacing rat residues with corresponding human P2X5 residues) significantly enhance current amplitude. Engineered disulfide cross-linking and molecular modeling show that these substitutions alter LF domain allostery to allow full pore opening.\",\n      \"method\": \"Site-directed mutagenesis, patch-clamp electrophysiology, engineered disulfide cross-linking, single-channel recording, molecular modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis with functional electrophysiology and structural cross-linking experiments, multiple orthogonal methods in single study\",\n      \"pmids\": [\"31727741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"P2X5 is required for cytosolic killing of Listeria monocytogenes by macrophages and for L. monocytogenes-induced inflammasome activation and IL-1β/IL-18 production; defective killing in P2X5-deficient macrophages is substantially rescued by exogenous IL-1β or IL-18. This P2X5-dependent pathway is independent of ATP-P2X7 inflammasome activation.\",\n      \"method\": \"P2rx5 knockout mice, bone marrow-derived macrophage killing assays, inflammasome activation assays, cytokine rescue experiments, P2X7 deficiency comparison\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with cytokine rescue, parallel comparison to P2X7 pathway, multiple functional readouts in vivo and in vitro\",\n      \"pmids\": [\"32540996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Dihydropyridines isradipine and nimodipine potentiate ATP-induced currents through the full-length human P2X5 receptor at low micromolar concentrations, while amlodipine inhibits only at high (300 µM) concentrations. The full-length hP2X5 receptor shows Cl- permeability and gating kinetics consistent with prior reports.\",\n      \"method\": \"Two-microelectrode voltage clamp in Xenopus oocytes expressing hP2X5FL, pharmacological screening\",\n      \"journal\": \"Molecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro electrophysiology with multiple compounds, single lab, no mechanistic follow-up on binding site\",\n      \"pmids\": [\"35335209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Using BRET-based probes, concentration- and time-dependent ligand bias in cationic selectivity (differential Ca2+ vs. K+ permeability) was detected in P2X5 when activated by benzoyl-ATP (Bz-ATP), indicating dynamic ion selectivity changes dependent on ligand identity.\",\n      \"method\": \"BRET-based ion concentration probes in live cells during drug challenge\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — novel BRET approach demonstrates functional ligand bias, single study, P2X5 is secondary to TRPV1 focus\",\n      \"pmids\": [\"36343259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"P2RX5 knockout in mice causes reduced brown adipocyte differentiation in vitro and reduced browning in vivo; P2RX5 agonism exerts an anti-obesity effect under thermoneutral conditions with enhanced BAT recruitment, indicating P2RX5 mediates brown adipocyte differentiation and function.\",\n      \"method\": \"P2rx5 knockout mice, in vitro brown adipocyte differentiation assays, metabolic characterization, in vivo agonist treatment\",\n      \"journal\": \"Adipocyte\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout plus in vitro and in vivo agonist experiments, multiple readouts, single lab\",\n      \"pmids\": [\"39484996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"P2X5 modulates glucose metabolism in brown adipose tissue (BAT): both global and brown adipocyte-specific P2rx5 deficiency results in lower UCP1 expression and impaired glucose tolerance, with reduced glucose disposal specifically into BAT but not other organs.\",\n      \"method\": \"Global and tissue-specific knockout mice, indirect calorimetry, glucose tolerance tests, organ-specific glucose uptake measurements\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — tissue-specific knockout and global KO with multiple metabolic readouts, single lab\",\n      \"pmids\": [\"40650249\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ATP-sensitive P2X5 isoforms exist across species including humans: in mice ~90% of P2X5 transcripts encode the ATP-sensitive mP2X5 G317 form; in rats an exon 3-containing variant accounts for >70%; in human cell lines ATP-sensitive isoforms retaining exons 3, 7, and 10 represent ~15-30% of transcripts. These findings challenge the prevailing assumption that P2X5 is universally ATP-insensitive.\",\n      \"method\": \"Gene profiling, next-generation sequencing (NGS), RNA-seq from human tissues\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, sequencing-based identification without full functional reconstitution for all variants, single study\",\n      \"pmids\": [\"bio_10.1101_2025.01.10.632374\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"P2RX5 (P2X5) is an ATP-gated trimeric cation channel with two transmembrane domains that can form homomeric channels (when full-length, including exon 10) or heteromeric channels with P2X1, P2X2, or P2X4 subunits; its functional state depends critically on TM2 integrity and left-flipper domain allostery, the human truncated isoform (lacking exon 10) is non-functional and cytoplasmic, the full-length receptor is permeable to Ca2+, Na+, NMDG, and Cl-, is modulated by extracellular Ca2+, Zn2+, and pH, and in immune and musculoskeletal contexts P2X5 mediates inflammasome activation and IL-1β production, interacts with MEP50 via its C-terminal intracellular domain to regulate osteoclast maturation, controls skeletal muscle satellite cell differentiation via p38 MAPK, and regulates T cell IL-10 production and brown adipocyte differentiation/glucose metabolism.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"P2RX5 (P2X5) is an ATP-gated cation channel of the P2X family that signals through purinergic ATP sensing to control differentiation and inflammatory output across muscle, immune, and adipose tissues [#0, #5, #13]. The receptor has the canonical two-transmembrane topology with a large extracellular ATP-binding loop, desensitizes slowly, and is insensitive to alpha,beta-methylene-ATP, distinguishing it from P2X1/P2X3 [#0]. Functional assembly requires a complete second transmembrane domain: trimerization depends on TM2 integrity and a conserved aspartate (Asp355), so that full-length human P2X5 (retaining exon 10) traffics to the cell surface and forms a channel permeable to Ca2+, Na+, NMDG, and Cl-, whereas the common exon-10-skipped human isoform lacks part of TM2, aggregates, remains cytoplasmic, and is non-functional [#6, #8, #10]. Gating is tuned by extracellular Ca2+, Zn2+, and pH and by left-flipper domain allostery, where human-type residues in this region permit fuller pore opening [#4, #15]. Beyond homomers, P2X5 co-assembles into heteromeric channels with P2X1, P2X2, or P2X4, conferring hybrid pharmacology and kinetics, and P2X2/5 heteromers acquire pore-dilatation and phosphatidylserine-exposure properties; such P2X1/5 heteromers underlie native ATP currents in astrocytes [#1, #2, #11, #9]. Physiologically, ATP activation of P2X5 drives p38 MAPK-dependent skeletal muscle satellite cell differentiation [#5], licenses inflammasome activation and IL-1beta production required for osteoclast hyper-multinucleation and for macrophage cytosolic killing of Listeria monocytogenes [#13, #16], and in osteoclasts the C-terminal intracellular region binds the PRMT5 cofactor MEP50 to support maturation [#14]. P2X5 also regulates T cell IL-10 production and is required for brown adipocyte differentiation, BAT browning, and glucose disposal into brown adipose tissue [#12, #19, #20]. A genetic polymorphism creating the exon-10-skipped non-functional isoform underlies the minor histocompatibility antigen LRH-1, which is presented by HLA class I and elicits allogeneic CD8+ CTL responses [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established that P2X5 is a distinct ATP-gated ion channel, defining its existence as a slowly-desensitizing purinergic receptor with a unique pharmacology separating it from other P2X subunits.\",\n      \"evidence\": \"cDNA cloning, heterologous expression, and electrophysiology\",\n      \"pmids\": [\"8786426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native cell type of action not established\", \"No physiological function assigned\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Resolved that P2X5 is not solely a homomeric channel but co-assembles with P2X1 into heteromers, explaining hybrid ATP-current kinetics and broadening the receptor's functional repertoire.\",\n      \"evidence\": \"Heterologous co-expression, patch-clamp/two-electrode voltage clamp, and reciprocal co-immunoprecipitation/co-purification of epitope-tagged subunits\",\n      \"pmids\": [\"9855626\", \"10336430\", \"10496954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subunit stoichiometry within the heteromer not defined\", \"In vivo relevance not yet shown at this stage\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined how the homomeric channel is gated allosterically by the extracellular environment, showing Ca2+, Zn2+, and pH tune ATP responsiveness.\",\n      \"evidence\": \"Two-electrode voltage clamp in Xenopus oocytes with ion substitution and modulator experiments\",\n      \"pmids\": [\"12237343\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of modulator binding sites not mapped\", \"Studied for rat receptor only\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Assigned the first physiological role to P2X5 activation: linking ATP sensing to a p38 MAPK-driven switch from proliferation to differentiation in muscle satellite cells.\",\n      \"evidence\": \"Primary satellite cell cultures with immunocytochemistry, RT-PCR, electrophysiology, and p38 inhibitor rescue\",\n      \"pmids\": [\"12135987\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct coupling between channel ion flux and p38 activation not established\", \"Single lab, rat cells\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Characterized the full-length human receptor as a genuinely functional, broadly permeable channel (Ca2+, Na+, NMDG, Cl-), establishing the human ortholog's biophysical baseline.\",\n      \"evidence\": \"Patch-clamp, fluorescence imaging, and reversal-potential measurements in HEK293 cells\",\n      \"pmids\": [\"12761352\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address why most humans express a non-functional isoform\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Explained at the molecular level why the truncated human variant fails: trimerization requires a complete TM2, and the exon-10-skipped form is too short to insert and aggregates.\",\n      \"evidence\": \"Systematic mutagenesis, hydrophobic-stretch addition, and biochemical trimerization assays in heterologous cells\",\n      \"pmids\": [\"17001079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of Asp355 in the assembled trimer's gating not defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected genotype to subcellular fate, showing the exon-10-deleted human isoform is cytoplasmic and non-functional while full-length P2X5 reaches the surface, and that most humans express only the non-functional form.\",\n      \"evidence\": \"Genotyping, RT-PCR, immunofluorescence, electrophysiology, and Ca2+ imaging in stable cell lines\",\n      \"pmids\": [\"20223879\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences in human tissues of carrying the non-functional allele not resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed the human expression polymorphism has direct immunological consequence, generating the LRH-1 minor histocompatibility antigen that drives allogeneic CD8+ CTL responses.\",\n      \"evidence\": \"Genetic linkage, tetramer CTL analysis, and protein expression studies in hematopoietic cells\",\n      \"pmids\": [\"16322791\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking exon-10 skipping to antigen presentation not detailed\", \"Single study\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Expanded heteromer biology by demonstrating P2X2/5 channels with alternate stoichiometries that acquire pore-dilatation and phosphatidylserine-exposure properties previously attributed only to P2X7.\",\n      \"evidence\": \"BRET, bifunctional fluorescence complementation, protein biochemistry, and confocal colocalization in mouse brain\",\n      \"pmids\": [\"22442090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional output of P2X2/5 in specific neuronal circuits not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established a genetic in vivo requirement for P2X5 in inflammatory signaling, linking it to inflammasome activation, IL-1beta production, and osteoclast hyper-multinucleation.\",\n      \"evidence\": \"P2rx5 knockout mice, osteoclast differentiation and inflammasome assays, and IL-1beta rescue\",\n      \"pmids\": [\"28298636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link from channel activity to inflammasome assembly not mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified an intracellular protein partner, showing the P2X5 C-terminus binds MEP50 to support osteoclast maturation beyond its channel role.\",\n      \"evidence\": \"Co-immunoprecipitation, RNAi, and domain-mapping rescue with C-terminal deletion mutant\",\n      \"pmids\": [\"31432503\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MEP50/PRMT5 activity is modulated by P2X5 binding not shown\", \"Reciprocal validation limited\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Explained the species difference in ATP sensitivity mechanistically, attributing weak rat P2X5 responses to left-flipper domain allostery that human-type residues relieve to permit full pore opening.\",\n      \"evidence\": \"Site-directed mutagenesis, patch-clamp, engineered disulfide cross-linking, single-channel recording, and molecular modeling\",\n      \"pmids\": [\"31727741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of the gating transition\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Generalized the inflammatory role to host defense, showing P2X5 is required for macrophage cytosolic killing of Listeria via an inflammasome/IL-1beta/IL-18 pathway independent of ATP-P2X7.\",\n      \"evidence\": \"P2rx5 knockout mice, macrophage killing and inflammasome assays, cytokine rescue, and P2X7 comparison\",\n      \"pmids\": [\"32540996\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trigger that activates P2X5 during intracellular infection unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Implicated P2X5 in adaptive immune regulation, showing the human truncation variant is induced on activated T cells and restrains IL-10 production.\",\n      \"evidence\": \"Flow cytometry, siRNA knockdown, IL-10 ELISA, and surface expression analysis\",\n      \"pmids\": [\"25181038\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a non-functional channel isoform exerts this effect not explained\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified small-molecule modulators (dihydropyridines) and ligand-dependent ion-selectivity bias, revealing the channel's gating output is tunable by both pharmacology and agonist identity.\",\n      \"evidence\": \"Two-microelectrode voltage clamp in oocytes and BRET-based ion probes in live cells\",\n      \"pmids\": [\"35335209\", \"36343259\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding sites for dihydropyridines not localized\", \"Physiological relevance of ligand bias unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a metabolic role, showing P2X5 is required for brown adipocyte differentiation, BAT browning, and glucose disposal into brown fat, positioning it as an anti-obesity target.\",\n      \"evidence\": \"Global and brown-adipocyte-specific P2rx5 knockout mice, in vitro differentiation, calorimetry, glucose tolerance, and organ-specific uptake; in vivo agonist treatment\",\n      \"pmids\": [\"39484996\", \"40650249\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the metabolic effect requires channel ion flux or a scaffolding function not resolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Challenged the assumption of universal ATP-insensitivity by cataloguing ATP-sensitive splice isoforms across species, including a minority of functional human transcripts.\",\n      \"evidence\": \"Gene profiling, NGS, and RNA-seq from human tissues (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.01.10.632374\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Awaits full functional reconstitution of all variants\", \"Preprint, not peer-reviewed\", \"Tissue-level protein expression not confirmed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a predominantly non-functional human isoform mediates immune and metabolic phenotypes, and whether the C-terminal MEP50 interaction and channel gating are mechanistically coupled, remains unresolved.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of an assembled human P2X5 channel\", \"Channel-independent (scaffolding) functions not separated from ion-flux functions\", \"Endogenous activation trigger in disease contexts undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 6, 10]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 6, 18]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 2, 8, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [10, 11]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [13, 16]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 19]}\n    ],\n    \"complexes\": [\"P2X1/5 heteromeric receptor\", \"P2X2/5 heteromeric receptor\", \"P2X5 homotrimer\"],\n    \"partners\": [\"P2RX1\", \"P2RX2\", \"P2RX4\", \"MEP50\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}