{"gene":"TAS1R2","run_date":"2026-04-28T21:42:58","timeline":{"discoveries":[{"year":2005,"finding":"T1R2 and T1R3 subunits each bind sweet stimuli independently but with distinct affinities and conformational changes; ligand affinities for T1R3 are drastically reduced by a single amino acid change associated with decreased sweet taste sensitivity in mice, indicating individual subunits increase the receptive range of the sweet taste receptor.","method":"Ligand binding assays, site-directed mutagenesis, conformational change measurements on individual subunits","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 — in vitro binding assays with mutagenesis, multiple orthogonal methods","pmids":["16271873"],"is_preprint":false},{"year":2002,"finding":"Sweet-tasting proteins (brazzein, monellin, thaumatin) interact with the T1R2-T1R3 receptor not via the 'glutamate-like' pocket but by stabilizing the active form of the receptor at a secondary binding site, a mechanism distinct from small molecular weight sweeteners.","method":"Computational docking with homology model of T1R2-T1R3 receptor based on mGluR1 template","journal":"FEBS letters","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only, no direct experimental validation in this paper","pmids":["12208493"],"is_preprint":false},{"year":2005,"finding":"Homology modeling of the T1R2-T1R3 heterodimer identified four ligand binding sites for low-molecular-weight sweeteners in the extracellular domain, and sweet proteins interact with a secondary site; models account for sweetness synergy.","method":"Homology modeling based on mGluR1 crystal structure, computational docking","journal":"Journal of medicinal chemistry","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only","pmids":["16107151"],"is_preprint":false},{"year":2010,"finding":"Key amino acid residues in brazzein at three interaction sites (Loop43, N/C-termini/Loop33, Loop9-19) are essential for activation of the T1R2-T1R3 sweet receptor; the Venus flytrap module of T1R2 is important for brazzein agonism; hT1R2 R217A mutation in lobe 2 affects subunit-subunit interaction rather than direct brazzein binding, supporting multi-point interaction mechanism.","method":"Site-directed mutagenesis of brazzein and receptor subunits, human taste panel, cell-based receptor assay in HEK293 cells, receptor chimeras","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in cell-based assay, mutagenesis of both ligand and receptor, validated by sensory panel","pmids":["20302879"],"is_preprint":false},{"year":2009,"finding":"Direct binding of sweet agonists and antagonists to the full heterodimeric T1R2-T1R3 receptor in native membranes from HEK293 cells was detected; STD NMR can distinguish mutations that alter ligand-binding sites from those affecting downstream signal transduction.","method":"Saturation transfer difference (STD) NMR spectroscopy on membranes from HEK293 cells expressing T1R2-T1R3","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 — direct biophysical binding assay on native membranes","pmids":["19664591"],"is_preprint":false},{"year":2009,"finding":"T1R2 knockout mice display severely blunted licking responses to sucrose and Na-saccharin but retain relatively normal concentration-dependent licking to Polycose (glucose polymer mixture), indicating T1R2+T1R3 heterodimer is the principal receptor for sweet-tasting ligands but is individually unnecessary for normal Polycose responsiveness.","method":"T1R2 knockout mice, brief-access taste tests","journal":"American journal of physiology. Regulatory, integrative and comparative physiology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined behavioral phenotype, replicated across multiple stimuli","pmids":["19158407"],"is_preprint":false},{"year":2011,"finding":"T1R2 knockout and T1R3 knockout mice show severely impaired responding to glucose, maltose, and maltotriose, but T1R2+T1R3 double KO mice still display concentration-dependent responding to Polycose, demonstrating that glucose polymers stimulate a taste receptor independent of the T1R2+T1R3 heterodimer.","method":"T1R2 KO, T1R3 KO, T1R2/T1R3 double KO mice, brief-access taste tests","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — multiple KO genotypes with defined behavioral phenotype, clear epistasis","pmids":["21940444"],"is_preprint":false},{"year":2012,"finding":"T1R2 KO and T1R3 KO mice show markedly decreased sensitivity to discriminate water from sucrose, glucose, or maltose in an operant procedure, but have normal EC50 values for Polycose, confirming T1R2+T1R3 heterodimer is the principal receptor for natural sweeteners but not all carbohydrate stimuli.","method":"T1R2 KO and T1R3 KO mice, operant two-response taste discrimination task","journal":"American journal of physiology. Regulatory, integrative and comparative physiology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with operant psychophysical phenotype, replicated across multiple stimuli","pmids":["22621968"],"is_preprint":false},{"year":2011,"finding":"The cysteine-rich domain (CRD) of human T1R3 (not T1R2) is necessary for interaction with sweet-tasting protein thaumatin, as demonstrated by chimeric human-mouse sweet receptor constructs in HEK293 cells.","method":"Chimeric human-mouse T1R2/T1R3 receptor constructs expressed in HEK293 cells, functional assay","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — chimeric receptor mapping with functional readout in cell-based assay","pmids":["21329673"],"is_preprint":false},{"year":2011,"finding":"Arg82 in thaumatin plays a central role in interaction with human T1R2-T1R3 sweet receptors; charge inversion at Arg82 (R82E) abolished receptor response even at 1 mM, while mutations at Lys67 had less effect.","method":"Site-directed mutagenesis of thaumatin, cell-based assay using HEK293 cells expressing human sweet receptors","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with quantitative cell-based functional assay","pmids":["21867681"],"is_preprint":false},{"year":2014,"finding":"Human T1R3 surface expression requires coexpression with human T1R2 (but not vice versa for mouse), and both the Venus flytrap module and cysteine-rich domain of human T1R3 contain regions regulating membrane trafficking; the Venus flytrap module of both human T1R2 and T1R3 are needed for proper membrane trafficking, revealing distinct human and mouse trafficking systems.","method":"Tagged receptor constructs in HEK293 cells, domain-swapped chimeras, truncation mutants, surface expression assays","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — chimeric receptor and deletion analysis with direct surface expression measurement","pmids":["25029362"],"is_preprint":false},{"year":2013,"finding":"In vitro binding assays demonstrated specific enantiomeric activities of D- and L-amino acids on the TAS1R2-TAS1R3 sweet receptor, showing direct ligand-receptor interaction for multiple amino acid stereoisomers.","method":"Cell-based in vitro assay with HEK293 cells overexpressing TAS1R2/TAS1R3, binding assay","journal":"Food chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based functional assay, systematic enantiomer analysis","pmids":["24360415"],"is_preprint":false},{"year":2015,"finding":"Sugar-induced cephalic-phase insulin release (CPIR) occurs in T1R3 knockout mice (lacking functional T1R2+T1R3 heterodimer) following oral but not intragastric glucose administration, demonstrating that CPIR is mediated by a T1R2+T1R3-independent taste transduction pathway.","method":"T1R3 KO mice, oral vs. intragastric glucose administration, insulin measurement, chorda tympani nerve recordings","journal":"American journal of physiology. Regulatory, integrative and comparative physiology","confidence":"High","confidence_rationale":"Tier 2 — KO model with multiple physiological readouts and epistasis","pmids":["26157055"],"is_preprint":false},{"year":2018,"finding":"T1R2-mediated glucose sensing in the upper intestine enhances glucose absorption by regulating GLUT2 transporter trafficking to the apical membrane of enterocytes; this effect is dependent on GLP-2 secretion and subsequent intestinal neuronal activation, as demonstrated in T1R2 knockout mice.","method":"T1R2 knockout mice, in vivo glucose absorption assay, ex vivo intact intestinal preparations, GLUT2 localization","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 — KO model with mechanistic pathway established (GLUT2 trafficking, GLP-2, neuronal activation), multiple orthogonal methods","pmids":["30201274"],"is_preprint":false},{"year":2016,"finding":"Disruption of T1R2 in mice fed a high-fat/low-carbohydrate diet protects against diet-induced hyperinsulinemia and alters substrate utilization (increased glucose oxidation, decreased liver triglyceride accumulation); sweet taste receptors (T1r2/T1r3) are upregulated in adipose tissue in response to HF/LC diet and correlate with fat mass and glucose intolerance.","method":"T1R2 global knockout mice, metabolic phenotyping, body composition, glucose homeostasis assays","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"High","confidence_rationale":"Tier 2 — clean KO with defined metabolic phenotypes and tissue-level receptor expression correlation","pmids":["26884387"],"is_preprint":false},{"year":2021,"finding":"The TAS1R2 Ile191Val variant causes partial loss of function through reduced receptor availability in the plasma membrane (not altered ligand binding); Val allele carriers have reduced glucose excursions during OGTT, supporting a peripheral (intestinal) role for TAS1R2 in metabolic regulation.","method":"In vitro biochemical assays for receptor membrane availability, oral glucose tolerance tests in human participants stratified by genotype","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 — biochemical mechanism (membrane trafficking) validated with human physiological data","pmids":["34509698"],"is_preprint":false},{"year":2024,"finding":"TAS1R2 in skeletal muscle acts as an ambient glucose sensor; receptor stimulation induces ERK1/2-dependent phosphorylation and activation of PARP1, a major NAD consumer; muscle-specific TAS1R2 deletion suppresses PARP1 activity, elevates NAD levels, and enhances mitochondrial capacity and running endurance.","method":"Muscle-specific TAS1R2 knockout mice, ERK1/2 phosphorylation assays, PARP1 activity assays, NAD measurements, exercise endurance testing","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific KO with defined molecular pathway (ERK1/2-PARP1-NAD) and multiple orthogonal phenotypes","pmids":["38851747"],"is_preprint":false},{"year":2018,"finding":"The heptahelical (transmembrane) domain of T1R2 is the allosteric binding site for amiloride, a sweet taste inhibitor, and mediates species-dependent sensitivity; this site is distinct from the lactisole binding site on T1R3, as shown using human/squirrel monkey/mouse chimeric receptors.","method":"Chimeric T1R2/T1R3 receptors from human, squirrel monkey, and mouse expressed in HEK293 cells; perillartine as T1R2 TMD-specific agonist; functional assays","journal":"Journal of molecular neuroscience : MN","confidence":"High","confidence_rationale":"Tier 1 — chimeric receptor mapping to specific domain with functional validation","pmids":["30120716"],"is_preprint":false},{"year":2021,"finding":"L-glucose activates the TAS1R2/TAS1R3 sweet taste receptor in a dose-dependent manner in cell-based functional assays; computational docking to the VFT domain of TAS1R2 suggests two sub-pockets, each compatible with one glucose enantiomer, with shared hydrogen-bond interactions explaining similar detection thresholds for D- and L-glucose.","method":"Cell-based functional assay with TAS1R2/TAS1R3, human sensory detection thresholds, computational docking","journal":"Food chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based functional assay plus computational modeling, single lab","pmids":["34715629"],"is_preprint":false},{"year":2021,"finding":"Human TAS1R2 expressed and purified as a dimer from HEK293S cells is properly folded and capable of binding high-potency sweeteners with Kd values consistent with physiological detection thresholds, as measured by intrinsic tryptophan fluorescence and size-exclusion chromatography coupled to light scattering.","method":"Recombinant protein expression in stable tetracycline-inducible HEK293S cells, protein purification, circular dichroism, size-exclusion chromatography with light scattering, intrinsic tryptophan fluorescence","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 — direct biophysical characterization of purified receptor, single lab","pmids":["34782704"],"is_preprint":false},{"year":2022,"finding":"The Venus Flytrap domain of TAS1R2 (hTAS1R2-VFT) expressed as a monomer binds sweet stimuli with Kd values consistent with physiological detection; point mutations D278A and E382A that abolish full-length receptor response also drastically reduce VFT ligand affinity, confirming VFT as the primary sweet compound binding site.","method":"Recombinant hTAS1R2-VFT expression in E. coli, site-directed mutagenesis, intrinsic tryptophan fluorescence, size-exclusion chromatography with light scattering, circular dichroism","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 1 — reconstituted isolated domain with mutagenesis validation, biophysical binding quantification","pmids":["36012481"],"is_preprint":false},{"year":2024,"finding":"Steviol glycosides bind to four distinct sites on the T1R2/T1R3 heterodimer (VFD2, VFD3, TMD2, TMD3); the C20 carboxy terminus of the Gα protein can bind to the intracellular region of either TMD2 or TMD3, shifting the receptor to high-affinity state for steviol glycosides.","method":"Competitive binding experiments with radiolabeled ligands, computational docking studies","journal":"Communications chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — experimental binding combined with computational docking, single lab","pmids":["39424933"],"is_preprint":false},{"year":2012,"finding":"Species-dependent sweet taste responses are determined by specific subunits: residues in T1R2 determine species-dependent saccharin responses, while residues in either T1R2 or T1R3 mediate species-dependent responses to monellin; squirrel monkey sweet receptor does not respond to aspartame, neotame, cyclamate, saccharin, or monellin, but responds to thaumatin.","method":"Cloning and functional characterization of squirrel monkey T1R2/T1R3, chimeric receptor assays in HEK293 cells, molecular modeling","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — chimeric receptor domain-swap with functional assays, clear subunit attribution","pmids":["23000410"],"is_preprint":false},{"year":2010,"finding":"T1R2-LacZ knock-in mouse revealed T1R2 expression in taste tissue, gastrointestinal tract (where T1R3 is co-expressed), and unexpectedly in testis; homozygous T1R2 deletion mice lack T1R2 protein, confirming T1R2 as a required component of the sweet taste receptor system.","method":"T1R2-LacZ reporter knock-in mouse generation, immunohistochemistry with anti-T1R2 antibody","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct reporter and antibody-based localization in KO-validated system","pmids":["20965149"],"is_preprint":false},{"year":2024,"finding":"Activation of TAS1R2-TAS1R3 with sucralose during OGTT elevated plasma insulin responses, and individual sucralose sweetness ratings correlated with early glucose and insulin increases; inhibition with lactisole was correlated with decreased plasma glucose, demonstrating bidirectional regulation of glucose metabolism by intestinal TAS1R2-TAS1R3 signaling in humans.","method":"Randomized human OGTT with sucralose or lactisole, plasma glucose/insulin/glucagon measurement, individual sweetness response assessment","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological activation/inhibition of receptor in humans with physiological endpoints, small sample size","pmids":["38691547"],"is_preprint":false}],"current_model":"TAS1R2 forms a heterodimeric G protein-coupled receptor with TAS1R3; TAS1R2 provides the primary sweet ligand-binding site in its Venus Flytrap domain (with additional allosteric sites in its transmembrane domain), the heterodimer signals through gustducin to mediate sweet taste perception for sugars and diverse sweeteners, and beyond taste buds TAS1R2 functions as a nutrient sensor in intestinal enteroendocrine cells (enhancing GLUT2-mediated glucose absorption via GLP-2 and neuronal signaling) and in skeletal muscle (sensing ambient glucose to drive ERK1/2-PARP1-dependent NAD consumption and regulate mitochondrial capacity)."},"narrative":{"teleology":[{"year":2005,"claim":"Demonstrating that each subunit of the sweet receptor independently binds ligands resolved how a single heterodimer recognizes a chemically diverse set of sweeteners.","evidence":"Ligand binding assays and mutagenesis on individual T1R2 and T1R3 subunits","pmids":["16271873"],"confidence":"High","gaps":["Relative contribution of each subunit to signaling efficacy was not quantified","Binding stoichiometry for asymmetric ligands unresolved"]},{"year":2009,"claim":"Loss-of-function studies in T1R2 knockout mice established TAS1R2 as a required component of the principal sweet taste receptor while revealing a T1R2-independent pathway for glucose polymer taste.","evidence":"T1R2 KO mice with brief-access and operant taste discrimination tests across multiple stimuli","pmids":["19158407","21940444","22621968"],"confidence":"High","gaps":["Identity of the T1R2-independent Polycose receptor remains unknown","Neural circuit differences between sweet and Polycose pathways not mapped"]},{"year":2010,"claim":"Reporter knock-in mice revealed TAS1R2 expression beyond taste buds—in the gastrointestinal tract and testis—raising the question of non-gustatory function.","evidence":"T1R2-LacZ knock-in mouse with immunohistochemistry","pmids":["20965149"],"confidence":"Medium","gaps":["Functional significance of testicular expression unknown","Cell-type resolution in GI tract limited"]},{"year":2010,"claim":"Mutagenesis of both the sweet protein brazzein and the TAS1R2 Venus Flytrap domain identified a multi-point interaction mechanism, mapping the primary agonist-binding locus to the T1R2 subunit.","evidence":"Site-directed mutagenesis of brazzein and hT1R2 residues, cell-based assay in HEK293 cells, human taste panel, chimeric receptors","pmids":["20302879"],"confidence":"High","gaps":["No crystal or cryo-EM structure of VFT–protein sweetener complex","Allosteric coupling between VFT closure and TMD activation unresolved"]},{"year":2012,"claim":"Cross-species chimeric receptor experiments attributed species-specific sweetener selectivity to defined residues in TAS1R2, distinguishing VFT-mediated and TMD-mediated ligand recognition.","evidence":"Squirrel monkey/human/mouse chimeric T1R2/T1R3 constructs in HEK293 cells","pmids":["23000410","30120716"],"confidence":"High","gaps":["Structural basis for species selectivity at atomic resolution lacking","Role of CRD linker in signal transmission between VFT and TMD not tested"]},{"year":2014,"claim":"Domain-swap and truncation analysis revealed that human T1R3 surface expression depends on co-expression with T1R2, establishing obligate heterodimerization for membrane trafficking in human cells.","evidence":"Tagged receptor constructs, domain-swapped chimeras, surface expression assays in HEK293 cells","pmids":["25029362"],"confidence":"High","gaps":["Chaperone or ER-quality-control factors mediating co-dependence not identified","Whether trafficking requirement is conserved beyond primates is unclear"]},{"year":2018,"claim":"Intestinal TAS1R2 was shown to regulate glucose absorption by controlling apical GLUT2 trafficking through a GLP-2 and neuronal signaling cascade, establishing a mechanistic link between sweet taste receptor signaling and nutrient uptake.","evidence":"T1R2 KO mice, in vivo glucose absorption, GLUT2 localization in intact intestinal preparations","pmids":["30201274"],"confidence":"High","gaps":["Specific enteroendocrine cell type(s) mediating GLP-2 release not isolated","Downstream G protein (gustducin vs. others) in intestinal cells not confirmed"]},{"year":2021,"claim":"The human Ile191Val variant was shown to reduce TAS1R2 membrane availability without altering ligand binding, and Val carriers exhibited reduced glucose excursions, linking receptor trafficking efficiency to metabolic outcomes in humans.","evidence":"In vitro membrane availability assays, human OGTT stratified by genotype","pmids":["34509698"],"confidence":"High","gaps":["Effect size in diverse populations not replicated","Whether variant affects intestinal vs. taste bud function differentially is unknown"]},{"year":2022,"claim":"Biophysical reconstitution of the isolated TAS1R2 Venus Flytrap domain confirmed it as the primary sweet-ligand binding site, with D278A and E382A mutations drastically reducing affinity, closing a long-standing question about which domain confers sweet specificity.","evidence":"Recombinant hTAS1R2-VFT expressed in E. coli, mutagenesis, intrinsic tryptophan fluorescence binding assays","pmids":["36012481"],"confidence":"High","gaps":["No structure of VFT in ligand-bound versus unbound state","Cooperativity between monomeric VFT binding and heterodimer activation not measured"]},{"year":2024,"claim":"Muscle-specific TAS1R2 deletion revealed a glucose-sensing pathway in skeletal muscle that signals through ERK1/2 to activate PARP1, consuming NAD and limiting mitochondrial capacity—an entirely new extra-gustatory role for the receptor.","evidence":"Muscle-specific TAS1R2 KO mice, ERK1/2 and PARP1 activity assays, NAD measurements, exercise endurance testing","pmids":["38851747"],"confidence":"High","gaps":["G protein coupling partner in skeletal muscle not identified","Whether TAS1R3 is the obligate partner in muscle is untested","Physiological glucose concentration range that activates the pathway in vivo not delineated"]},{"year":2024,"claim":"Pharmacological activation and inhibition of intestinal TAS1R2-TAS1R3 in humans during OGTT bidirectionally modulated plasma glucose and insulin, providing direct translational evidence for the receptor's metabolic role.","evidence":"Randomized human OGTT with sucralose or lactisole, plasma glucose/insulin measurement","pmids":["38691547"],"confidence":"Medium","gaps":["Small sample size limits generalizability","Cannot fully exclude extra-intestinal contributions of sucralose/lactisole"]},{"year":null,"claim":"No high-resolution experimental structure of TAS1R2 (alone or in the heterodimer) exists, and the G protein coupling specificity and downstream signaling cascades in extra-gustatory tissues remain incompletely characterized.","evidence":"","pmids":[],"confidence":"High","gaps":["Cryo-EM or crystal structure of TAS1R2-TAS1R3 heterodimer needed","G protein identity in intestine and muscle unknown","Role of TAS1R2 in testis entirely unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,4,5,20]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[13,16]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[10,15]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[16,13,24]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[5,6,7]},{"term_id":"R-HSA-8963743","term_label":"Digestion and absorption","supporting_discovery_ids":[13]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[13,15]}],"complexes":["TAS1R2-TAS1R3 heterodimer"],"partners":["TAS1R3","GLUT2","ERK1","ERK2","PARP1"],"other_free_text":[]},"mechanistic_narrative":"TAS1R2 encodes the ligand-binding subunit of the TAS1R2–TAS1R3 heterodimeric G protein-coupled receptor that serves as the principal mammalian sweet taste receptor and a metabolic nutrient sensor in extra-gustatory tissues. The Venus Flytrap domain of TAS1R2 constitutes the primary orthosteric binding site for sugars, amino acids, and high-potency sweeteners, with critical residues D278 and E382 required for ligand affinity, while the transmembrane domain harbors a distinct allosteric site for modulators such as amiloride [PMID:36012481, PMID:30120716]. Knockout studies demonstrate that TAS1R2 is essential for behavioral responses to sucrose, glucose, and saccharin but dispensable for Polycose detection; in the intestine, TAS1R2 promotes GLUT2-mediated glucose absorption through GLP-2 secretion and neuronal signaling, and in skeletal muscle it senses ambient glucose to activate ERK1/2–PARP1-dependent NAD consumption, thereby limiting mitochondrial capacity [PMID:19158407, PMID:30201274, PMID:38851747]. A common human TAS1R2 Ile191Val variant reduces receptor plasma-membrane availability without altering ligand binding and is associated with attenuated oral glucose excursions, linking receptor trafficking to metabolic regulation [PMID:34509698]."},"prefetch_data":{"uniprot":{"accession":"Q8TE23","full_name":"Taste receptor type 1 member 2","aliases":["G-protein coupled receptor 71","Sweet taste receptor T1R2"],"length_aa":839,"mass_kda":95.2,"function":"Putative taste receptor. 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chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34715629","citation_count":17,"is_preprint":false},{"pmid":"27479072","id":"PMC_27479072","title":"Characterization of the Sweet Taste Receptor Tas1r2 from an Old World Monkey Species Rhesus Monkey and Species-Dependent Activation of the Monomeric Receptor by an Intense Sweetener Perillartine.","date":"2016","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/27479072","citation_count":17,"is_preprint":false},{"pmid":"34509698","id":"PMC_34509698","title":"The Ile191Val is a partial loss-of-function variant of the TAS1R2 sweet-taste receptor and is associated with reduced glucose excursions in humans.","date":"2021","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/34509698","citation_count":16,"is_preprint":false},{"pmid":"36432589","id":"PMC_36432589","title":"Associations between Sweet Taste Sensitivity and Polymorphisms (SNPs) in the TAS1R2 and TAS1R3 Genes, Gender, PROP Taster Status, and Density of Fungiform Papillae in a Genetically Homogeneous Sardinian Cohort.","date":"2022","source":"Nutrients","url":"https://pubmed.ncbi.nlm.nih.gov/36432589","citation_count":16,"is_preprint":false},{"pmid":"16317770","id":"PMC_16317770","title":"Ligand-independent orphan receptor TR2 activation by phosphorylation at the DNA-binding domain.","date":"2006","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/16317770","citation_count":15,"is_preprint":false},{"pmid":"39424933","id":"PMC_39424933","title":"Steviol rebaudiosides bind to four different sites of the human sweet taste receptor (T1R2/T1R3) complex explaining confusing experiments.","date":"2024","source":"Communications chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39424933","citation_count":15,"is_preprint":false},{"pmid":"19204783","id":"PMC_19204783","title":"HDAC3 as a molecular chaperone for shuttling phosphorylated TR2 to PML: a novel deacetylase activity-independent function of HDAC3.","date":"2009","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/19204783","citation_count":15,"is_preprint":false},{"pmid":"27040630","id":"PMC_27040630","title":"Oxaliplatin Alters Expression of T1R2 Receptor and Sensitivity to Sweet Taste in Rats.","date":"2016","source":"Biological & pharmaceutical bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/27040630","citation_count":15,"is_preprint":false},{"pmid":"16130175","id":"PMC_16130175","title":"Protein kinase C-mediated phosphorylation of orphan nuclear receptor TR2: effects on receptor stability and activity.","date":"2005","source":"Proteomics","url":"https://pubmed.ncbi.nlm.nih.gov/16130175","citation_count":15,"is_preprint":false},{"pmid":"16839558","id":"PMC_16839558","title":"SmTR2/4, a Schistosoma mansoni homologue of TR2/TR4 orphan nuclear receptor.","date":"2006","source":"International journal for parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/16839558","citation_count":14,"is_preprint":false},{"pmid":"32219957","id":"PMC_32219957","title":"Influences of non-nutritive sweeteners on ovarian and uterine expression of T1R2 and T1R3 in peripubertal female guinea pigs.","date":"2020","source":"Animal science journal = Nihon chikusan Gakkaiho","url":"https://pubmed.ncbi.nlm.nih.gov/32219957","citation_count":14,"is_preprint":false},{"pmid":"10391141","id":"PMC_10391141","title":"Identification of the histamine H1 receptor gene as a differentially repressed target of the human TR2 orphan receptor.","date":"1999","source":"Molecular and cellular biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10391141","citation_count":14,"is_preprint":false},{"pmid":"38691547","id":"PMC_38691547","title":"Activation and inhibition of the sweet taste receptor TAS1R2-TAS1R3 differentially affect glucose tolerance in humans.","date":"2024","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/38691547","citation_count":12,"is_preprint":false},{"pmid":"34776881","id":"PMC_34776881","title":"Whole-Brain Mapping of the Expression Pattern of T1R2, a Subunit Specific to the Sweet Taste Receptor.","date":"2021","source":"Frontiers in neuroanatomy","url":"https://pubmed.ncbi.nlm.nih.gov/34776881","citation_count":12,"is_preprint":false},{"pmid":"36012481","id":"PMC_36012481","title":"Functional Characterization of the Venus Flytrap Domain of the Human TAS1R2 Sweet Taste Receptor.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36012481","citation_count":12,"is_preprint":false},{"pmid":"9704569","id":"PMC_9704569","title":"The genomic structure and chromosomal location of the human TR2 orphan receptor, a member of the steroid receptor superfamily.","date":"1998","source":"Endocrine","url":"https://pubmed.ncbi.nlm.nih.gov/9704569","citation_count":12,"is_preprint":false},{"pmid":"17010934","id":"PMC_17010934","title":"Transcriptional regulation of the human TR2 orphan receptor gene by nuclear factor 1-A.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/17010934","citation_count":11,"is_preprint":false},{"pmid":"38508871","id":"PMC_38508871","title":"Rethinking Sweetener Discovering: Multiparameter Modeling of Molecular Docking Results between the T1R2-T1R3 Receptor and Compounds with Different Tastes.","date":"2024","source":"Journal of agricultural and food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/38508871","citation_count":11,"is_preprint":false},{"pmid":"31098002","id":"PMC_31098002","title":"Unnatural Tripeptides as Potent Positive Allosteric Modulators of T1R2/T1R3.","date":"2019","source":"ACS medicinal chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/31098002","citation_count":11,"is_preprint":false},{"pmid":"38851747","id":"PMC_38851747","title":"The TAS1R2 G-protein-coupled receptor is an ambient glucose sensor in skeletal muscle that regulates NAD homeostasis and mitochondrial capacity.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38851747","citation_count":10,"is_preprint":false},{"pmid":"33486192","id":"PMC_33486192","title":"Non-nutritive sweetener activation of the pig sweet taste receptor T1R2-T1R3 in vitro mirrors sweetener stimulation of the gut-expressed receptor in vivo.","date":"2021","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/33486192","citation_count":10,"is_preprint":false},{"pmid":"7841789","id":"PMC_7841789","title":"Molecular cloning of a novel member of the nuclear receptor superfamily related to the orphan receptor, TR2.","date":"1994","source":"Gene 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heterodimer.","date":"2017","source":"American journal of physiology. Regulatory, integrative and comparative physiology","url":"https://pubmed.ncbi.nlm.nih.gov/28768658","citation_count":9,"is_preprint":false},{"pmid":"38931195","id":"PMC_38931195","title":"Artificial and Natural Sweeteners Biased T1R2/T1R3 Taste Receptors Transactivate Glycosylated Receptors on Cancer Cells to Induce Epithelial-Mesenchymal Transition of Metastatic Phenotype.","date":"2024","source":"Nutrients","url":"https://pubmed.ncbi.nlm.nih.gov/38931195","citation_count":9,"is_preprint":false},{"pmid":"28551284","id":"PMC_28551284","title":"The nuclear hormone receptor gene Nr2c1 (Tr2) is a critical regulator of early retina cell patterning.","date":"2017","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/28551284","citation_count":9,"is_preprint":false},{"pmid":"33110140","id":"PMC_33110140","title":"An in-silico layer-by-layer adsorption study of the interaction between Rebaudioside A and the T1R2 human sweet taste receptor: modelling and biosensing perspectives.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33110140","citation_count":9,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":46613,"output_tokens":5532,"usd":0.111409},"stage2":{"model":"claude-opus-4-6","input_tokens":9114,"output_tokens":2702,"usd":0.16968},"total_usd":0.281089,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"T1R2 and T1R3 subunits each bind sweet stimuli independently but with distinct affinities and conformational changes; ligand affinities for T1R3 are drastically reduced by a single amino acid change associated with decreased sweet taste sensitivity in mice, indicating individual subunits increase the receptive range of the sweet taste receptor.\",\n      \"method\": \"Ligand binding assays, site-directed mutagenesis, conformational change measurements on individual subunits\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding assays with mutagenesis, multiple orthogonal methods\",\n      \"pmids\": [\"16271873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Sweet-tasting proteins (brazzein, monellin, thaumatin) interact with the T1R2-T1R3 receptor not via the 'glutamate-like' pocket but by stabilizing the active form of the receptor at a secondary binding site, a mechanism distinct from small molecular weight sweeteners.\",\n      \"method\": \"Computational docking with homology model of T1R2-T1R3 receptor based on mGluR1 template\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only, no direct experimental validation in this paper\",\n      \"pmids\": [\"12208493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Homology modeling of the T1R2-T1R3 heterodimer identified four ligand binding sites for low-molecular-weight sweeteners in the extracellular domain, and sweet proteins interact with a secondary site; models account for sweetness synergy.\",\n      \"method\": \"Homology modeling based on mGluR1 crystal structure, computational docking\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only\",\n      \"pmids\": [\"16107151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Key amino acid residues in brazzein at three interaction sites (Loop43, N/C-termini/Loop33, Loop9-19) are essential for activation of the T1R2-T1R3 sweet receptor; the Venus flytrap module of T1R2 is important for brazzein agonism; hT1R2 R217A mutation in lobe 2 affects subunit-subunit interaction rather than direct brazzein binding, supporting multi-point interaction mechanism.\",\n      \"method\": \"Site-directed mutagenesis of brazzein and receptor subunits, human taste panel, cell-based receptor assay in HEK293 cells, receptor chimeras\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in cell-based assay, mutagenesis of both ligand and receptor, validated by sensory panel\",\n      \"pmids\": [\"20302879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Direct binding of sweet agonists and antagonists to the full heterodimeric T1R2-T1R3 receptor in native membranes from HEK293 cells was detected; STD NMR can distinguish mutations that alter ligand-binding sites from those affecting downstream signal transduction.\",\n      \"method\": \"Saturation transfer difference (STD) NMR spectroscopy on membranes from HEK293 cells expressing T1R2-T1R3\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — direct biophysical binding assay on native membranes\",\n      \"pmids\": [\"19664591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"T1R2 knockout mice display severely blunted licking responses to sucrose and Na-saccharin but retain relatively normal concentration-dependent licking to Polycose (glucose polymer mixture), indicating T1R2+T1R3 heterodimer is the principal receptor for sweet-tasting ligands but is individually unnecessary for normal Polycose responsiveness.\",\n      \"method\": \"T1R2 knockout mice, brief-access taste tests\",\n      \"journal\": \"American journal of physiology. Regulatory, integrative and comparative physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined behavioral phenotype, replicated across multiple stimuli\",\n      \"pmids\": [\"19158407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"T1R2 knockout and T1R3 knockout mice show severely impaired responding to glucose, maltose, and maltotriose, but T1R2+T1R3 double KO mice still display concentration-dependent responding to Polycose, demonstrating that glucose polymers stimulate a taste receptor independent of the T1R2+T1R3 heterodimer.\",\n      \"method\": \"T1R2 KO, T1R3 KO, T1R2/T1R3 double KO mice, brief-access taste tests\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple KO genotypes with defined behavioral phenotype, clear epistasis\",\n      \"pmids\": [\"21940444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"T1R2 KO and T1R3 KO mice show markedly decreased sensitivity to discriminate water from sucrose, glucose, or maltose in an operant procedure, but have normal EC50 values for Polycose, confirming T1R2+T1R3 heterodimer is the principal receptor for natural sweeteners but not all carbohydrate stimuli.\",\n      \"method\": \"T1R2 KO and T1R3 KO mice, operant two-response taste discrimination task\",\n      \"journal\": \"American journal of physiology. Regulatory, integrative and comparative physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with operant psychophysical phenotype, replicated across multiple stimuli\",\n      \"pmids\": [\"22621968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The cysteine-rich domain (CRD) of human T1R3 (not T1R2) is necessary for interaction with sweet-tasting protein thaumatin, as demonstrated by chimeric human-mouse sweet receptor constructs in HEK293 cells.\",\n      \"method\": \"Chimeric human-mouse T1R2/T1R3 receptor constructs expressed in HEK293 cells, functional assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — chimeric receptor mapping with functional readout in cell-based assay\",\n      \"pmids\": [\"21329673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Arg82 in thaumatin plays a central role in interaction with human T1R2-T1R3 sweet receptors; charge inversion at Arg82 (R82E) abolished receptor response even at 1 mM, while mutations at Lys67 had less effect.\",\n      \"method\": \"Site-directed mutagenesis of thaumatin, cell-based assay using HEK293 cells expressing human sweet receptors\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with quantitative cell-based functional assay\",\n      \"pmids\": [\"21867681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Human T1R3 surface expression requires coexpression with human T1R2 (but not vice versa for mouse), and both the Venus flytrap module and cysteine-rich domain of human T1R3 contain regions regulating membrane trafficking; the Venus flytrap module of both human T1R2 and T1R3 are needed for proper membrane trafficking, revealing distinct human and mouse trafficking systems.\",\n      \"method\": \"Tagged receptor constructs in HEK293 cells, domain-swapped chimeras, truncation mutants, surface expression assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — chimeric receptor and deletion analysis with direct surface expression measurement\",\n      \"pmids\": [\"25029362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In vitro binding assays demonstrated specific enantiomeric activities of D- and L-amino acids on the TAS1R2-TAS1R3 sweet receptor, showing direct ligand-receptor interaction for multiple amino acid stereoisomers.\",\n      \"method\": \"Cell-based in vitro assay with HEK293 cells overexpressing TAS1R2/TAS1R3, binding assay\",\n      \"journal\": \"Food chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based functional assay, systematic enantiomer analysis\",\n      \"pmids\": [\"24360415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Sugar-induced cephalic-phase insulin release (CPIR) occurs in T1R3 knockout mice (lacking functional T1R2+T1R3 heterodimer) following oral but not intragastric glucose administration, demonstrating that CPIR is mediated by a T1R2+T1R3-independent taste transduction pathway.\",\n      \"method\": \"T1R3 KO mice, oral vs. intragastric glucose administration, insulin measurement, chorda tympani nerve recordings\",\n      \"journal\": \"American journal of physiology. Regulatory, integrative and comparative physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO model with multiple physiological readouts and epistasis\",\n      \"pmids\": [\"26157055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"T1R2-mediated glucose sensing in the upper intestine enhances glucose absorption by regulating GLUT2 transporter trafficking to the apical membrane of enterocytes; this effect is dependent on GLP-2 secretion and subsequent intestinal neuronal activation, as demonstrated in T1R2 knockout mice.\",\n      \"method\": \"T1R2 knockout mice, in vivo glucose absorption assay, ex vivo intact intestinal preparations, GLUT2 localization\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO model with mechanistic pathway established (GLUT2 trafficking, GLP-2, neuronal activation), multiple orthogonal methods\",\n      \"pmids\": [\"30201274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Disruption of T1R2 in mice fed a high-fat/low-carbohydrate diet protects against diet-induced hyperinsulinemia and alters substrate utilization (increased glucose oxidation, decreased liver triglyceride accumulation); sweet taste receptors (T1r2/T1r3) are upregulated in adipose tissue in response to HF/LC diet and correlate with fat mass and glucose intolerance.\",\n      \"method\": \"T1R2 global knockout mice, metabolic phenotyping, body composition, glucose homeostasis assays\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined metabolic phenotypes and tissue-level receptor expression correlation\",\n      \"pmids\": [\"26884387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The TAS1R2 Ile191Val variant causes partial loss of function through reduced receptor availability in the plasma membrane (not altered ligand binding); Val allele carriers have reduced glucose excursions during OGTT, supporting a peripheral (intestinal) role for TAS1R2 in metabolic regulation.\",\n      \"method\": \"In vitro biochemical assays for receptor membrane availability, oral glucose tolerance tests in human participants stratified by genotype\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — biochemical mechanism (membrane trafficking) validated with human physiological data\",\n      \"pmids\": [\"34509698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TAS1R2 in skeletal muscle acts as an ambient glucose sensor; receptor stimulation induces ERK1/2-dependent phosphorylation and activation of PARP1, a major NAD consumer; muscle-specific TAS1R2 deletion suppresses PARP1 activity, elevates NAD levels, and enhances mitochondrial capacity and running endurance.\",\n      \"method\": \"Muscle-specific TAS1R2 knockout mice, ERK1/2 phosphorylation assays, PARP1 activity assays, NAD measurements, exercise endurance testing\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific KO with defined molecular pathway (ERK1/2-PARP1-NAD) and multiple orthogonal phenotypes\",\n      \"pmids\": [\"38851747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The heptahelical (transmembrane) domain of T1R2 is the allosteric binding site for amiloride, a sweet taste inhibitor, and mediates species-dependent sensitivity; this site is distinct from the lactisole binding site on T1R3, as shown using human/squirrel monkey/mouse chimeric receptors.\",\n      \"method\": \"Chimeric T1R2/T1R3 receptors from human, squirrel monkey, and mouse expressed in HEK293 cells; perillartine as T1R2 TMD-specific agonist; functional assays\",\n      \"journal\": \"Journal of molecular neuroscience : MN\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — chimeric receptor mapping to specific domain with functional validation\",\n      \"pmids\": [\"30120716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"L-glucose activates the TAS1R2/TAS1R3 sweet taste receptor in a dose-dependent manner in cell-based functional assays; computational docking to the VFT domain of TAS1R2 suggests two sub-pockets, each compatible with one glucose enantiomer, with shared hydrogen-bond interactions explaining similar detection thresholds for D- and L-glucose.\",\n      \"method\": \"Cell-based functional assay with TAS1R2/TAS1R3, human sensory detection thresholds, computational docking\",\n      \"journal\": \"Food chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based functional assay plus computational modeling, single lab\",\n      \"pmids\": [\"34715629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Human TAS1R2 expressed and purified as a dimer from HEK293S cells is properly folded and capable of binding high-potency sweeteners with Kd values consistent with physiological detection thresholds, as measured by intrinsic tryptophan fluorescence and size-exclusion chromatography coupled to light scattering.\",\n      \"method\": \"Recombinant protein expression in stable tetracycline-inducible HEK293S cells, protein purification, circular dichroism, size-exclusion chromatography with light scattering, intrinsic tryptophan fluorescence\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — direct biophysical characterization of purified receptor, single lab\",\n      \"pmids\": [\"34782704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The Venus Flytrap domain of TAS1R2 (hTAS1R2-VFT) expressed as a monomer binds sweet stimuli with Kd values consistent with physiological detection; point mutations D278A and E382A that abolish full-length receptor response also drastically reduce VFT ligand affinity, confirming VFT as the primary sweet compound binding site.\",\n      \"method\": \"Recombinant hTAS1R2-VFT expression in E. coli, site-directed mutagenesis, intrinsic tryptophan fluorescence, size-exclusion chromatography with light scattering, circular dichroism\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted isolated domain with mutagenesis validation, biophysical binding quantification\",\n      \"pmids\": [\"36012481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Steviol glycosides bind to four distinct sites on the T1R2/T1R3 heterodimer (VFD2, VFD3, TMD2, TMD3); the C20 carboxy terminus of the Gα protein can bind to the intracellular region of either TMD2 or TMD3, shifting the receptor to high-affinity state for steviol glycosides.\",\n      \"method\": \"Competitive binding experiments with radiolabeled ligands, computational docking studies\",\n      \"journal\": \"Communications chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — experimental binding combined with computational docking, single lab\",\n      \"pmids\": [\"39424933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Species-dependent sweet taste responses are determined by specific subunits: residues in T1R2 determine species-dependent saccharin responses, while residues in either T1R2 or T1R3 mediate species-dependent responses to monellin; squirrel monkey sweet receptor does not respond to aspartame, neotame, cyclamate, saccharin, or monellin, but responds to thaumatin.\",\n      \"method\": \"Cloning and functional characterization of squirrel monkey T1R2/T1R3, chimeric receptor assays in HEK293 cells, molecular modeling\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — chimeric receptor domain-swap with functional assays, clear subunit attribution\",\n      \"pmids\": [\"23000410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"T1R2-LacZ knock-in mouse revealed T1R2 expression in taste tissue, gastrointestinal tract (where T1R3 is co-expressed), and unexpectedly in testis; homozygous T1R2 deletion mice lack T1R2 protein, confirming T1R2 as a required component of the sweet taste receptor system.\",\n      \"method\": \"T1R2-LacZ reporter knock-in mouse generation, immunohistochemistry with anti-T1R2 antibody\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct reporter and antibody-based localization in KO-validated system\",\n      \"pmids\": [\"20965149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Activation of TAS1R2-TAS1R3 with sucralose during OGTT elevated plasma insulin responses, and individual sucralose sweetness ratings correlated with early glucose and insulin increases; inhibition with lactisole was correlated with decreased plasma glucose, demonstrating bidirectional regulation of glucose metabolism by intestinal TAS1R2-TAS1R3 signaling in humans.\",\n      \"method\": \"Randomized human OGTT with sucralose or lactisole, plasma glucose/insulin/glucagon measurement, individual sweetness response assessment\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological activation/inhibition of receptor in humans with physiological endpoints, small sample size\",\n      \"pmids\": [\"38691547\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TAS1R2 forms a heterodimeric G protein-coupled receptor with TAS1R3; TAS1R2 provides the primary sweet ligand-binding site in its Venus Flytrap domain (with additional allosteric sites in its transmembrane domain), the heterodimer signals through gustducin to mediate sweet taste perception for sugars and diverse sweeteners, and beyond taste buds TAS1R2 functions as a nutrient sensor in intestinal enteroendocrine cells (enhancing GLUT2-mediated glucose absorption via GLP-2 and neuronal signaling) and in skeletal muscle (sensing ambient glucose to drive ERK1/2-PARP1-dependent NAD consumption and regulate mitochondrial capacity).\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TAS1R2 encodes the ligand-binding subunit of the TAS1R2–TAS1R3 heterodimeric G protein-coupled receptor that serves as the principal mammalian sweet taste receptor and a metabolic nutrient sensor in extra-gustatory tissues. The Venus Flytrap domain of TAS1R2 constitutes the primary orthosteric binding site for sugars, amino acids, and high-potency sweeteners, with critical residues D278 and E382 required for ligand affinity, while the transmembrane domain harbors a distinct allosteric site for modulators such as amiloride [PMID:36012481, PMID:30120716]. Knockout studies demonstrate that TAS1R2 is essential for behavioral responses to sucrose, glucose, and saccharin but dispensable for Polycose detection; in the intestine, TAS1R2 promotes GLUT2-mediated glucose absorption through GLP-2 secretion and neuronal signaling, and in skeletal muscle it senses ambient glucose to activate ERK1/2–PARP1-dependent NAD consumption, thereby limiting mitochondrial capacity [PMID:19158407, PMID:30201274, PMID:38851747]. A common human TAS1R2 Ile191Val variant reduces receptor plasma-membrane availability without altering ligand binding and is associated with attenuated oral glucose excursions, linking receptor trafficking to metabolic regulation [PMID:34509698].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrating that each subunit of the sweet receptor independently binds ligands resolved how a single heterodimer recognizes a chemically diverse set of sweeteners.\",\n      \"evidence\": \"Ligand binding assays and mutagenesis on individual T1R2 and T1R3 subunits\",\n      \"pmids\": [\"16271873\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of each subunit to signaling efficacy was not quantified\", \"Binding stoichiometry for asymmetric ligands unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Loss-of-function studies in T1R2 knockout mice established TAS1R2 as a required component of the principal sweet taste receptor while revealing a T1R2-independent pathway for glucose polymer taste.\",\n      \"evidence\": \"T1R2 KO mice with brief-access and operant taste discrimination tests across multiple stimuli\",\n      \"pmids\": [\"19158407\", \"21940444\", \"22621968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the T1R2-independent Polycose receptor remains unknown\", \"Neural circuit differences between sweet and Polycose pathways not mapped\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Reporter knock-in mice revealed TAS1R2 expression beyond taste buds—in the gastrointestinal tract and testis—raising the question of non-gustatory function.\",\n      \"evidence\": \"T1R2-LacZ knock-in mouse with immunohistochemistry\",\n      \"pmids\": [\"20965149\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional significance of testicular expression unknown\", \"Cell-type resolution in GI tract limited\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mutagenesis of both the sweet protein brazzein and the TAS1R2 Venus Flytrap domain identified a multi-point interaction mechanism, mapping the primary agonist-binding locus to the T1R2 subunit.\",\n      \"evidence\": \"Site-directed mutagenesis of brazzein and hT1R2 residues, cell-based assay in HEK293 cells, human taste panel, chimeric receptors\",\n      \"pmids\": [\"20302879\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of VFT–protein sweetener complex\", \"Allosteric coupling between VFT closure and TMD activation unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Cross-species chimeric receptor experiments attributed species-specific sweetener selectivity to defined residues in TAS1R2, distinguishing VFT-mediated and TMD-mediated ligand recognition.\",\n      \"evidence\": \"Squirrel monkey/human/mouse chimeric T1R2/T1R3 constructs in HEK293 cells\",\n      \"pmids\": [\"23000410\", \"30120716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for species selectivity at atomic resolution lacking\", \"Role of CRD linker in signal transmission between VFT and TMD not tested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Domain-swap and truncation analysis revealed that human T1R3 surface expression depends on co-expression with T1R2, establishing obligate heterodimerization for membrane trafficking in human cells.\",\n      \"evidence\": \"Tagged receptor constructs, domain-swapped chimeras, surface expression assays in HEK293 cells\",\n      \"pmids\": [\"25029362\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Chaperone or ER-quality-control factors mediating co-dependence not identified\", \"Whether trafficking requirement is conserved beyond primates is unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Intestinal TAS1R2 was shown to regulate glucose absorption by controlling apical GLUT2 trafficking through a GLP-2 and neuronal signaling cascade, establishing a mechanistic link between sweet taste receptor signaling and nutrient uptake.\",\n      \"evidence\": \"T1R2 KO mice, in vivo glucose absorption, GLUT2 localization in intact intestinal preparations\",\n      \"pmids\": [\"30201274\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific enteroendocrine cell type(s) mediating GLP-2 release not isolated\", \"Downstream G protein (gustducin vs. others) in intestinal cells not confirmed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The human Ile191Val variant was shown to reduce TAS1R2 membrane availability without altering ligand binding, and Val carriers exhibited reduced glucose excursions, linking receptor trafficking efficiency to metabolic outcomes in humans.\",\n      \"evidence\": \"In vitro membrane availability assays, human OGTT stratified by genotype\",\n      \"pmids\": [\"34509698\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effect size in diverse populations not replicated\", \"Whether variant affects intestinal vs. taste bud function differentially is unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Biophysical reconstitution of the isolated TAS1R2 Venus Flytrap domain confirmed it as the primary sweet-ligand binding site, with D278A and E382A mutations drastically reducing affinity, closing a long-standing question about which domain confers sweet specificity.\",\n      \"evidence\": \"Recombinant hTAS1R2-VFT expressed in E. coli, mutagenesis, intrinsic tryptophan fluorescence binding assays\",\n      \"pmids\": [\"36012481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of VFT in ligand-bound versus unbound state\", \"Cooperativity between monomeric VFT binding and heterodimer activation not measured\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Muscle-specific TAS1R2 deletion revealed a glucose-sensing pathway in skeletal muscle that signals through ERK1/2 to activate PARP1, consuming NAD and limiting mitochondrial capacity—an entirely new extra-gustatory role for the receptor.\",\n      \"evidence\": \"Muscle-specific TAS1R2 KO mice, ERK1/2 and PARP1 activity assays, NAD measurements, exercise endurance testing\",\n      \"pmids\": [\"38851747\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G protein coupling partner in skeletal muscle not identified\", \"Whether TAS1R3 is the obligate partner in muscle is untested\", \"Physiological glucose concentration range that activates the pathway in vivo not delineated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Pharmacological activation and inhibition of intestinal TAS1R2-TAS1R3 in humans during OGTT bidirectionally modulated plasma glucose and insulin, providing direct translational evidence for the receptor's metabolic role.\",\n      \"evidence\": \"Randomized human OGTT with sucralose or lactisole, plasma glucose/insulin measurement\",\n      \"pmids\": [\"38691547\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Small sample size limits generalizability\", \"Cannot fully exclude extra-intestinal contributions of sucralose/lactisole\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"No high-resolution experimental structure of TAS1R2 (alone or in the heterodimer) exists, and the G protein coupling specificity and downstream signaling cascades in extra-gustatory tissues remain incompletely characterized.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cryo-EM or crystal structure of TAS1R2-TAS1R3 heterodimer needed\", \"G protein identity in intestine and muscle unknown\", \"Role of TAS1R2 in testis entirely unexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 4, 5, 20]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [13, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [10, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0009579\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [16, 13, 24]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [5, 6, 7]},\n      {\"term_id\": \"R-HSA-8963743\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [13, 15]}\n    ],\n    \"complexes\": [\n      \"TAS1R2-TAS1R3 heterodimer\"\n    ],\n    \"partners\": [\n      \"TAS1R3\",\n      \"GLUT2\",\n      \"ERK1\",\n      \"ERK2\",\n      \"PARP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}