{"gene":"TAS1R2","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":2005,"finding":"Each of the two subunits of the heteromeric T1R2:T1R3 sweet taste receptor binds sweet stimuli independently but with distinct affinities and conformational changes; a single amino acid change in T1R3 associated with decreased sweet sensitivity in mice drastically reduced ligand affinity for T1R3, demonstrating that individual T1R subunits increase the receptive range of the sweet taste receptor.","method":"Ligand-binding assays with individual subunits, site-directed mutagenesis, behavioral phenotyping in mice","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct binding assays with mutagenesis plus behavioral validation, replicated across multiple sweet stimuli","pmids":["16271873"],"is_preprint":false},{"year":2002,"finding":"Sweet-tasting proteins (brazzein, monellin, thaumatin) interact with the T1R2-T1R3 receptor at a secondary allosteric binding site distinct from the 'glutamate-like' (Venus flytrap) pocket used by small-molecule sweeteners, and stabilize the active (free form II) conformation of the receptor.","method":"Computational docking with a homology model of T1R2-T1R3; structural reasoning from protein mutant analysis","journal":"FEBS letters","confidence":"Low","confidence_rationale":"Tier 4 / Weak — computational/modeling only, no in vitro reconstitution or mutagenesis validation reported in this abstract","pmids":["12208493"],"is_preprint":false},{"year":2005,"finding":"Homology modeling of the T1R2-T1R3 extracellular ligand-binding domain on mGluR1 identified four binding sites for low-molecular-weight sweeteners and a secondary site for sweet proteins; docking experiments showed sweet proteins bind the secondary site, accounting for sweetness synergy.","method":"Homology modeling based on mGluR1 crystal structure; in silico docking","journal":"Journal of medicinal chemistry","confidence":"Low","confidence_rationale":"Tier 4 / Weak — purely computational, no experimental validation of binding sites reported","pmids":["16107151"],"is_preprint":false},{"year":2003,"finding":"NMR solution structure of the G16A mutant of single-chain monellin (MNEI) showed that the sweetness-reducing mutation does not affect glucophore positions but displaces secondary structural elements on the protein surface, establishing that sweet proteins do not act via a 'sweet finger' mechanism but rather through a conformational interaction with a secondary site on T1R2-T1R3.","method":"NMR solution structure determination of sweet protein mutant; comparison with wild-type structure","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — NMR structure determination (Tier 1 method) but single study and no direct receptor mutagenesis","pmids":["12706725"],"is_preprint":false},{"year":2010,"finding":"Mutagenesis of brazzein surface residues and T1R2/T1R3 chimeras established that brazzein activates the sweet receptor through multi-point interactions; the Venus flytrap module of T1R2 is important for brazzein agonism; a T1R2 R217A mutation in lobe 2 at the subunit interface selectively reduced brazzein activity by altering subunit-subunit interaction rather than direct ligand binding.","method":"Site-directed mutagenesis of brazzein and receptor subunits; chimeric receptor assays in HEK293 cells; human taste panel; in vitro receptor activity assay","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (mutagenesis, chimeras, cell-based assay, human panel) establishing mechanistic detail","pmids":["20302879"],"is_preprint":false},{"year":2009,"finding":"Saturation transfer difference (STD) NMR spectroscopy directly detected binding of sweet agonists and antagonists to the full heterodimeric T1R2/T1R3 receptor in membranes from HEK293 cells, allowing distinction between mutations that alter ligand-binding sites versus those affecting downstream signal transduction.","method":"STD NMR spectroscopy on membrane-expressed receptor","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — NMR-based direct binding assay (Tier 1 method), single lab, single approach","pmids":["19664591"],"is_preprint":false},{"year":2011,"finding":"The cysteine-rich domain (CRD) of human T1R3 (not T1R2) is necessary for the interaction of the T1R2-T1R3 heterodimer with the sweet-tasting protein thaumatin, as demonstrated by chimeric human-mouse receptor assays showing that hT1R2/mT1R3 responds to sucralose but not thaumatin.","method":"Chimeric human/mouse receptor expression in HEK293 cells; functional assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chimeric receptor functional assays with multiple chimera combinations, single lab","pmids":["21329673"],"is_preprint":false},{"year":2011,"finding":"Arg82 of thaumatin is a critical residue for interaction with human T1R2-T1R3; charge inversion at Arg82 (R82E) abolished receptor activation even at 1 mM, while Lys67 mutations were less disruptive, indicating a strict spatial charge requirement at position 82 for receptor binding.","method":"Site-directed mutagenesis of thaumatin; cell-based receptor assay in HEK293 cells expressing human sweet receptors","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis plus quantitative functional assay, single lab","pmids":["21867681"],"is_preprint":false},{"year":2012,"finding":"T1R2 knockout and T1R3 knockout mice displayed severely impaired licking responses to sucrose, glucose, and maltose, but retained relatively normal concentration-dependent responding to Polycose (glucose polymer), establishing that the T1R2+T1R3 heterodimer is the principal receptor for simple sugars but not for glucose polymers, which activate a separate receptor mechanism.","method":"T1R2 and T1R3 knockout mice; T1R2/T1R3 double knockout mice; brief-access taste tests and two-response operant discrimination","journal":"The Journal of neuroscience; American journal of physiology. Regulatory, integrative and comparative physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with specific behavioral readouts replicated across multiple KO models and psychophysical paradigms in multiple papers","pmids":["21940444","22621968","19158407"],"is_preprint":false},{"year":2014,"finding":"Human T1R3 surface expression requires co-expression with human T1R2, whereas mouse T1r3 reaches the membrane independently; domain-swap chimeras showed the Venus flytrap module and cysteine-rich domain (CRD) of human T1R3 contain regions that inhibit T1R3 membrane trafficking when expressed alone, and the Venus flytrap modules of both human T1R2 and T1R3 are needed for proper membrane trafficking of the heterodimer.","method":"Tagged T1R2/T1R3 constructs expressed in HEK293 cells; domain-swap chimeras; truncation mutants; surface expression assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chimeric and truncation mutagenesis with surface expression readout, single lab, multiple constructs","pmids":["25029362"],"is_preprint":false},{"year":2010,"finding":"T1R2-LacZ reporter knock-in mice revealed that T1R2 is expressed in taste tissue, the gastrointestinal tract (where T1R3 is also expressed), and unexpectedly in the testis; homozygous T1R2 deletion mice lacked T1R2 protein, confirming the knock-in allele.","method":"T1R2-LacZ reporter knock-in mouse; LacZ staining; immunohistochemistry with validated antibody","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct reporter expression and protein localization in a well-controlled transgenic model, single lab","pmids":["20965149"],"is_preprint":false},{"year":2018,"finding":"T1R2 receptor signaling in the upper intestine enhances glucose absorption specifically in response to glucose-rich meals by regulating GLUT2 transporter trafficking to the apical membrane of enterocytes; these effects were dependent on GLP-2 secretion and subsequent intestinal neuronal activation; high-sucrose feeding in wild-type mice rapidly downregulated intestinal STRs, reducing glucose absorption.","method":"T1R2 knockout mice; in vivo glucose absorption measurements; ex vivo intact intestinal preparations; GLUT2 trafficking assays; pharmacological blockade","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple orthogonal in vivo and ex vivo assays establishing the pathway (T1R2 → GLP-2 → neuronal activation → GLUT2 trafficking)","pmids":["30201274"],"is_preprint":false},{"year":2016,"finding":"Global disruption of T1R2 in mice fed a high-fat/low-carbohydrate diet resulted in reduced fat mass, increased lean mass, hyperactivity, protection from diet-induced hyperinsulinemia, increased glucose oxidation rates, and decreased liver triglyceride accumulation; sweet taste receptors (T1r2/T1r3) were upregulated in adipose tissue in response to HF/LC diet and positively correlated with fat mass and glucose intolerance.","method":"T1R2 knockout mice; high-fat diet feeding; body composition, energy balance, glucose homeostasis, and tissue substrate metabolism measurements","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple metabolic phenotype readouts, single lab","pmids":["26884387"],"is_preprint":false},{"year":2021,"finding":"The Ile191Val common variant of TAS1R2 causes a partial loss of function through reduced receptor availability at the plasma membrane; human Val minor allele carriers show reduced plasma glucose excursions during an OGTT compared to Ile/Ile carriers, effects not explained by differences in beta-cell function or insulin sensitivity.","method":"In vitro biochemical assays of receptor membrane availability; oral glucose tolerance tests in human participants; genotyping","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro mechanistic characterization of variant plus human physiological study, single lab, two complementary methods","pmids":["34509698"],"is_preprint":false},{"year":2018,"finding":"The heptahelical domain (TMD) of T1R2 is the allosteric binding site for the sweet inhibitor amiloride; this was distinct from the T1R3-binding site of lactisole; using chimeric human/squirrel monkey/mouse T1R2 and T1R3 receptors and the agonist perillartine (which activates the single TMD of T1R2), the T1R2 TMD was identified as the molecular determinant mediating species-dependent amiloride sensitivity.","method":"Chimeric human/squirrel monkey/mouse T1R2/T1R3 receptors in cell-based functional assays; perillartine activation of isolated T1R2 TMD","journal":"Journal of molecular neuroscience : MN","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chimeric receptor approach with multiple species and an isolated-domain agonist control, single lab","pmids":["30120716"],"is_preprint":false},{"year":2012,"finding":"Squirrel monkey T1R2/T1R3 responds to natural sugars and some sweet proteins (thaumatin at high concentrations) but not to aspartame, neotame, cyclamate, saccharin, or monellin; the residues in T1R2 determine species-dependent sensitivity to saccharin, while residues in either T1R2 or T1R3 underlie sweet taste differences toward monellin between humans and squirrel monkeys.","method":"Cloning and heterologous expression of squirrel monkey T1R2/T1R3; cell-based functional assays; chimeric receptor analyses; molecular modeling","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — chimeric receptor mapping of species-dependent differences, single lab","pmids":["23000410"],"is_preprint":false},{"year":2021,"finding":"The purified human TAS1R2 subunit forms a dimer in detergent solution and binds high-potency sweeteners with Kd values consistent with physiological detection thresholds, as measured by intrinsic tryptophan fluorescence; circular dichroism confirmed proper folding with secondary structure.","method":"Overexpression in stable HEK293S inducible cell line; detergent solubilization and purification; size exclusion chromatography coupled with light scattering; circular dichroism; tryptophan fluorescence binding assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — biophysical characterization with multiple orthogonal methods (SEC-MALS, CD, fluorescence), single lab","pmids":["34782704"],"is_preprint":false},{"year":2022,"finding":"The isolated Venus flytrap domain of human TAS1R2 (hTAS1R2-VFT) expressed in E. coli is a functional monomer that binds sweet stimuli with Kd values consistent with physiological detection; single amino acid substitutions D278A and E382A (known to abolish full-length receptor response) drastically reduced ligand affinity of the isolated VFT domain, confirming these residues as key binding-site determinants.","method":"Heterologous expression of hTAS1R2-VFT in E. coli; circular dichroism; SEC-MALS; site-directed mutagenesis; intrinsic tryptophan fluorescence binding assay","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro binding assay with mutagenesis validation, multiple biophysical methods, single lab","pmids":["36012481"],"is_preprint":false},{"year":2021,"finding":"The T1R2 splicing isoform T1R2_Δe3p (lacking part of exon 3) forms a non-functional heterodimer with T1R3 that cannot be activated by sweet stimuli and significantly downregulates canonical T1R2/T1R3 function; local LPS injection significantly increased the expression ratio of T1R2_Δe3p in mouse taste buds, providing a mechanism by which bacterial infection suppresses sweet taste perception.","method":"RT-PCR identification of splicing isoform; heterologous expression in vitro functional assays; local LPS injection in mice; quantitative RT-PCR","journal":"Hua xi kou qiang yi xue za zhi","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isoform identified and functionally characterized in cell-based assay with in vivo LPS validation, single lab","pmids":["34409805"],"is_preprint":false},{"year":2022,"finding":"Skipping of Tas1r2 exon 4 produces a truncated isoform (Tas1r2_Δe4) lacking amino acids in the Venus flytrap domain; this truncated isoform generates non-functional T1R2/T1R3 heterodimers that reduce sweet taste responses to all tested sweet compounds in vitro and in vivo. The splicing factor PTBP1 promotes exon 4 skipping by binding a polypyrimidine-rich silencer in exon 4, thereby decreasing sweet taste receptor function and sweet taste perception in mice.","method":"Identification and cloning of splicing variant; heterologous expression cell-based assays; in vivo behavioral sweet taste tests; PTBP1 knockdown/overexpression; RNA-binding analysis","journal":"Chemical senses","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — multiple orthogonal methods (molecular, cellular, in vivo behavioral) establishing the splicing regulatory mechanism, single lab","pmids":["36484118"],"is_preprint":false},{"year":2024,"finding":"TAS1R2 in skeletal muscle acts as a glucose sensor that stimulates ERK1/2-dependent phosphorylation and activation of PARP1 (a major NAD consumer); muscle-specific deletion of TAS1R2 suppresses PARP1 activity, elevates NAD levels, and enhances mitochondrial capacity and running endurance in mice. Plasma glucose negatively correlates with muscle NAD, implicating TAS1R2 as a peripheral energy surveyor.","method":"Muscle-specific TAS1R2 knockout mice; PARP1 activity assays; NAD measurement; mitochondrial function assays; running endurance tests; glucose/agonist stimulation with ERK1/2 phosphorylation readout","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal assays (biochemical pathway dissection, genetic KO with specific phenotypic readouts) establishing the TAS1R2→ERK1/2→PARP1→NAD pathway in a peer-reviewed Nature Communications paper","pmids":["38851747"],"is_preprint":false},{"year":2023,"finding":"The TAS1R2 sweet taste receptor regulates skeletal muscle mass and fitness through an ERK2-PARP1-NAD signaling axis; muscle-specific deletion of TAS1R2 elevated NAD levels, improved mitochondrial function, increased muscle mass and strength, and prolonged running endurance; deletion also ameliorated muscle decline in obese and aged mice.","method":"Muscle-specific TAS1R2 knockout mice; metabolic phenotyping; NAD, PARP1, and ERK2 measurements; voluntary wheel running; grip strength; aged and obese mouse models","journal":"Research square (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — preprint with multiple mechanistic readouts and genetic models, consistent with peer-reviewed Nature Communications paper (PMID 38851747) but independently assessed as preprint","pmids":["36798161"],"is_preprint":true},{"year":2020,"finding":"Inhibition of TAS1R2/TAS1R3 by the inverse agonist lactisole blocked perception of sweet thermal taste (warming of tongue from 20–35°C), establishing that TAS1R2/TAS1R3 receptor activation is necessary for thermal sweet taste perception in humans.","method":"Human psychophysics; pharmacological inhibition with lactisole; temperature-controlled flow gustometer","journal":"Chemical senses","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological receptor inhibition with quantitative human perceptual readout, single lab","pmids":["32072157"],"is_preprint":false},{"year":2021,"finding":"l-glucose activates the sweet taste receptor TAS1R2/TAS1R3 in cell-based functional assays at thresholds similar to d-glucose; computational docking to the VFT domain of TAS1R2 identified two sub-pockets (A and B), each compatible with one enantiomer, with both sharing overlapping polar contact residues.","method":"Cell-based functional assay (HEK293T transfection); computational docking to TAS1R2 VFT domain","journal":"Food chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — cell-based assay establishes functional activation, docking is computational; single lab","pmids":["34715629"],"is_preprint":false},{"year":2023,"finding":"Serine 147 in the binding site of T1R3 VFT domain is required for T1R3 activation by both l- and d-glucose; mutation S147A completely abolishes T1R3 monomer activation. The R317G variant in the VFT domain of T1R2 (present in ~20% of the world population based on the NM_152232.4 reference) markedly reduces TAS1R2 sensitivity in vitro.","method":"Mutagenesis; transient transfection of individual T1R2 and T1R3 monomers and heterodimers in HEK293T cells; cell-based functional assay; comparison of TAS1R2 reference sequences","journal":"Chemical senses","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-directed mutagenesis with quantitative functional readout for multiple variants, single lab","pmids":["36806908"],"is_preprint":false},{"year":2024,"finding":"Steviol glycosides and other sweeteners bind to four distinct sites on the T1R2/T1R3 heterodimer: VFD2 (TAS1R2 Venus flytrap), VFD3 (TAS1R3 Venus flytrap), TMD2 (TAS1R2 transmembrane domain), and TMD3 (TAS1R3 transmembrane domain); the C20 carboxy terminus of the Gα protein binds to the intracellular region of either TMD2 or TMD3, altering GPCR affinity to a high-affinity state for steviol glycosides.","method":"Radioligand binding experiments; computational docking at four receptor sites; G protein coupling analysis","journal":"Communications chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — binding experiments combined with computational docking, multiple sites tested, single lab","pmids":["39424933"],"is_preprint":false},{"year":2025,"finding":"A single amino acid substitution in TAS1R2 (Ile-67 in humans vs. Leu-70 in mice) in the Venus flytrap domain explains species-specific differences in sulfamate sweetener (saccharin, acesulfame K) sensitivity; mouse-type I67L mutation in human TAS1R2 decreased receptor activity and sulfamate binding, while the reverse L70I mutation in mouse Tas1r2 increased activity and binding.","method":"Chimeric TAS1R2/TAS1R3 analyses; single amino acid substitution mutagenesis; HEK293 cell-based functional assays; molecular dynamics simulations","journal":"Food chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal mutagenesis in both human and mouse receptor with quantitative functional assays and MD simulations identifying a specific contact residue","pmids":["40706454"],"is_preprint":false},{"year":2016,"finding":"The rhesus monkey Tas1r2 paired with human TAS1R3 responds to natural sugars, amino acids, artificial sweeteners, and sweet proteins, but amiloride does not inhibit rhesus monkey Tas1r2-mediated responses; the monomeric Tas1r2 transmembrane domain (without counterpart T1R3) can be activated by perillartine in humans, rhesus monkey, and squirrel monkey but not mouse.","method":"Cloning, expression, and functional characterization of rhesus monkey Tas1r2 in cell-based assays; chimeric and monomeric receptor assays; molecular modeling","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic cell-based functional characterization across species and receptor constructs, single lab","pmids":["27479072"],"is_preprint":false},{"year":2008,"finding":"Co-expression ratios of T1r2, T1r3, and gustducin in fungiform papillae are significantly lower in gurmarin-weakly-sensitive BALB mice than in gurmarin-sensitive B6 and dpa congenic mice, linking co-expression levels of these sweet receptor components with sensitivity to gurmarin-mediated sweet taste suppression.","method":"Quantitative in situ hybridization for T1r2, T1r3, and gustducin co-expression in taste tissues of different mouse strains; comparison with gurmarin-sensitivity phenotype","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — co-expression correlation across strains without functional pathway reconstitution, single lab","pmids":["18174025"],"is_preprint":false},{"year":2013,"finding":"D- and L-amino acids show specific enantiomeric activities on the TAS1R2-TAS1R3 sweet receptor as demonstrated by in vitro binding assays using cells overexpressing the receptor, providing direct evidence that the stereochemistry of amino acids determines their interaction with the sweet receptor.","method":"Cell-based binding/functional assay using cells overexpressing TAS1R2-TAS1R3","journal":"Food chemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single cell-based assay system without detailed mechanistic follow-up, single lab","pmids":["24360415"],"is_preprint":false},{"year":2022,"finding":"Whole-brain mapping using T1r2-Cre knock-in mice showed that T1R2 is expressed not only in taste cells but also in various neuronal and glial populations in the brain, in circumventricular organs, and in vascular structures; immunohistochemistry confirmed co-expression with NPY and POMC neurons in the hypothalamic arcuate nucleus and with canonical taste signaling molecules in perivascular cells of the median eminence.","method":"T1r2-Cre knock-in mice with reporter; whole-brain Cre-labeled cell mapping; immunohistochemistry for neuropeptide co-expression","journal":"Frontiers in neuroanatomy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct reporter-based localization in a transgenic model with immunohistochemical validation, single lab","pmids":["34776881"],"is_preprint":false},{"year":2021,"finding":"Non-nutritive sweetener exposure (sodium saccharin and rebaudioside A) dose-dependently regulated T1R2 expression in the ovary and uterus of guinea pigs; low-dose saccharin increased ovarian T1R2 expression and ovary weight, while high-dose saccharin suppressed ovarian T1R2 and caused adverse ovarian/uterine morphological effects.","method":"In vivo sweetener administration; immunohistochemistry; protein expression analysis in ovary and uterus","journal":"Animal science journal","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect localization and expression modulation without mechanistic pathway definition, single lab","pmids":["32219957"],"is_preprint":false},{"year":2024,"finding":"Hyperactivation of TAS1R2-TAS1R3 with sucralose elevated plasma insulin responses during an OGTT; inhibition with lactisole correlated with decreased plasma glucose; sucralose sweetness ratings correlated with early increases in glucose and insulin, showing bidirectional regulation of glucose metabolism by TAS1R2-TAS1R3 in humans.","method":"Oral glucose tolerance tests in healthy humans with sucralose or lactisole co-administration; plasma glucose, insulin, glucagon measurement; sweet taste psychophysics","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional pharmacological manipulation of the receptor in a human physiological study with quantitative metabolic endpoints, single lab","pmids":["38691547"],"is_preprint":false},{"year":2022,"finding":"Exendin-4 (GLP-1 receptor agonist) reduced glucose absorption in streptozotocin-diabetic mice by suppressing T1R2/T1R3 sweet taste receptor signaling and downstream molecules (PLCβ2, α-gustducin, IP3, cAMP), as well as SGLT1 and GLUT2 levels in the duodenum.","method":"STZ-diabetic mouse model; exendin-4 treatment; Western blotting and RT-qPCR for receptor and signaling molecules; glucose and transporter level measurement","journal":"Translational research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — pathway component expression changes measured but no direct mechanistic link to TAS1R2 specifically established beyond expression correlation","pmids":["35385790"],"is_preprint":false}],"current_model":"TAS1R2 functions as the ligand-binding subunit of the heterodimeric G protein-coupled sweet taste receptor TAS1R2/TAS1R3, where its Venus flytrap domain (VFT) constitutes the primary binding site for natural sugars and most high-potency sweeteners (with key residues D278, E382, I67/L70 identified), while its transmembrane domain (TMD) binds modulators such as amiloride; T1R2/T1R3-mediated signaling in intestinal enteroendocrine cells enhances glucose absorption by promoting GLUT2 apical trafficking via GLP-2 and neuronal activation; and in skeletal muscle, TAS1R2 acts as a glucose sensor that drives ERK1/2-dependent PARP1 activation to consume NAD, with receptor loss elevating NAD, improving mitochondrial capacity and muscle fitness."},"narrative":{"mechanistic_narrative":"TAS1R2 is the ligand-binding subunit of the heterodimeric sweet taste receptor T1R2/T1R3, a class C G protein-coupled receptor that constitutes the principal detector of simple sugars and high-potency sweeteners; genetic ablation of T1R2 abolishes behavioral responses to sucrose, glucose, and maltose while sparing responses to glucose polymers [PMID:21940444, PMID:22621968, PMID:19158407]. The extracellular Venus flytrap domain (VFT) of T1R2 forms the primary small-molecule binding site: the isolated hTAS1R2-VFT folds and binds sweet stimuli at physiological affinities, and the substitutions D278A and E382A that abolish full-length receptor responses also cripple ligand binding by the isolated domain [PMID:36012481], with additional contact residues (I67, R317) governing potency and species-specific sensitivity to sulfamate sweeteners [PMID:40706454, PMID:36806908]. Beyond the VFT, sweet-tasting proteins such as brazzein and thaumatin engage a secondary interaction surface involving the subunit interface and the T1R3 cysteine-rich domain [PMID:20302879, PMID:21329673], while the T1R2 transmembrane domain provides an allosteric site for modulators including the inhibitor amiloride [PMID:30120716]. Receptor surface expression requires co-assembly of human T1R2 and T1R3 VFT modules [PMID:25029362], and alternative splicing of T1R2 — including PTBP1-driven skipping of exon 4 — produces non-functional heterodimers that suppress sweet perception [PMID:36484118]. Beyond the tongue, T1R2 is expressed in the gut, brain, and other peripheral tissues [PMID:20965149, PMID:34776881], where it acts as a glucose sensor: in the upper intestine it enhances glucose absorption by promoting apical GLUT2 trafficking through GLP-2 secretion and intestinal neuronal activation [PMID:30201274], and in skeletal muscle it drives an ERK1/2–PARP1 axis that consumes NAD, such that muscle-specific T1R2 loss elevates NAD, improves mitochondrial capacity, and enhances endurance [PMID:38851747]. A common partial-loss-of-function variant (Ile191Val) reducing receptor surface availability lowers postprandial glucose excursions in human carriers [PMID:34509698].","teleology":[{"year":2005,"claim":"Established that each T1R subunit binds sweet ligands independently with distinct affinities, explaining how the heterodimer achieves a broad receptive range rather than acting as a single binding entity.","evidence":"Ligand-binding assays on individual subunits with site-directed mutagenesis and mouse behavioral phenotyping","pmids":["16271873"],"confidence":"High","gaps":["Did not assign which natural sugars and sweeteners map to which subunit","Conformational changes inferred rather than structurally resolved"]},{"year":2010,"claim":"Resolved how sweet proteins activate the receptor, showing they act through multi-point interactions at the subunit interface rather than the small-molecule pocket, distinguishing two modes of receptor activation.","evidence":"Brazzein and receptor mutagenesis, chimeric receptors in HEK293 cells, and human taste panels; complemented by NMR of a sweet-protein mutant","pmids":["20302879","12706725"],"confidence":"High","gaps":["Exact spatial arrangement of the sweet-protein contact surface not crystallographically defined","Stoichiometry of multi-point engagement unresolved"]},{"year":2011,"claim":"Mapped the molecular requirements for sweet-protein recognition to the T1R3 cysteine-rich domain and a specific thaumatin residue, defining a determinant of species-specific sweet-protein responsiveness.","evidence":"Chimeric human/mouse receptor assays and thaumatin site-directed mutagenesis in HEK293 cells","pmids":["21329673","21867681"],"confidence":"Medium","gaps":["Role of T1R2 in sweet-protein binding versus T1R3 not fully separated","Structural basis of the charge requirement at thaumatin Arg82 not visualized"]},{"year":2012,"claim":"Defined the in vivo ligand scope of the receptor genetically, demonstrating the T1R2/T1R3 heterodimer is the principal receptor for simple sugars but not glucose polymers, which use a separate mechanism.","evidence":"T1R2, T1R3, and double knockout mice with brief-access and operant taste tests","pmids":["21940444","22621968","19158407"],"confidence":"High","gaps":["Identity of the glucose-polymer receptor not determined","Residual non-T1R sugar sensing not characterized"]},{"year":2014,"claim":"Explained the obligate heterodimeric assembly of the human receptor by showing T1R3 surface expression depends on T1R2 and that both VFT modules are required for trafficking.","evidence":"Tagged constructs, domain-swap chimeras, and truncation mutants with surface expression assays in HEK293 cells","pmids":["25029362"],"confidence":"Medium","gaps":["Chaperone or trafficking machinery mediating assembly not identified","Species difference in independent mouse T1r3 trafficking not mechanistically explained"]},{"year":2018,"claim":"Identified the T1R2 transmembrane domain as an allosteric modulator site, locating amiloride binding to the TMD distinct from the T1R3 lactisole site and explaining species-dependent amiloride sensitivity.","evidence":"Chimeric human/squirrel monkey/mouse receptors and perillartine activation of the isolated T1R2 TMD in cell-based assays","pmids":["30120716"],"confidence":"Medium","gaps":["TMD allosteric pocket not structurally defined","Physiological relevance of amiloride modulation unaddressed"]},{"year":2018,"claim":"Extended T1R2 function beyond taste to intestinal nutrient handling, defining a T1R2 to GLP-2 to neuronal activation to GLUT2 trafficking pathway that enhances glucose absorption.","evidence":"T1R2 knockout mice with in vivo and ex vivo glucose absorption, GLUT2 trafficking assays, and pharmacological blockade","pmids":["30201274"],"confidence":"High","gaps":["G protein and intracellular signaling steps coupling T1R2 to GLP-2 release not dissected","Whether intestinal effect requires T1R3 co-expression not isolated here"]},{"year":2021,"claim":"Established a direct human genotype-physiology link, showing a common partial-loss-of-function TAS1R2 variant reduces receptor surface availability and lowers postprandial glucose excursions.","evidence":"In vitro receptor membrane-availability assays plus oral glucose tolerance tests in genotyped human participants","pmids":["34509698"],"confidence":"Medium","gaps":["Tissue site (gut vs peripheral) driving the glucose phenotype not localized","Mechanism connecting reduced surface receptor to lower glucose excursion not traced"]},{"year":2022,"claim":"Confirmed the T1R2 VFT as the primary small-molecule binding determinant by reconstituting the isolated domain and validating key binding residues biochemically.","evidence":"Bacterially expressed hTAS1R2-VFT with CD, SEC-MALS, mutagenesis (D278A, E382A), and tryptophan fluorescence binding; complemented by full-subunit dimer biophysics","pmids":["36012481","34782704"],"confidence":"High","gaps":["High-resolution structure of the ligand-bound VFT not solved","How VFT closure couples to TMD activation not addressed"]},{"year":2022,"claim":"Revealed splicing as a regulatory layer over sweet receptor function, showing PTBP1-driven exon skipping generates dominant-negative T1R2 isoforms that suppress sweet perception, including in response to infection.","evidence":"Splice variant cloning, heterologous functional assays, in vivo behavioral tests, PTBP1 knockdown/overexpression, and LPS challenge in mice","pmids":["36484118","34409805"],"confidence":"High","gaps":["Physiological triggers regulating PTBP1 in taste tissue beyond LPS not defined","Magnitude of splicing control on human sweet perception not quantified"]},{"year":2024,"claim":"Defined a peripheral metabolic role for T1R2 in skeletal muscle, establishing an ERK1/2-PARP1-NAD axis through which the receptor acts as a glucose surveyor controlling mitochondrial capacity and endurance.","evidence":"Muscle-specific TAS1R2 knockout mice with PARP1 activity, NAD measurement, mitochondrial and endurance assays, and ERK1/2 phosphorylation readouts; consistent preprint precursor","pmids":["38851747","36798161"],"confidence":"High","gaps":["G protein coupling linking muscle T1R2 to ERK1/2 not identified","Whether muscle T1R2 functions as a heterodimer with T1R3 not established"]},{"year":2024,"claim":"Refined the multi-site model of receptor pharmacology, mapping sweetener binding to four distinct VFT and TMD sites and linking Galpha C-terminus engagement to a high-affinity receptor state.","evidence":"Radioligand binding with computational docking at four sites and G protein coupling analysis","pmids":["39424933"],"confidence":"Medium","gaps":["Docking-based site assignments lack experimental structural confirmation","Functional hierarchy among the four sites not resolved"]},{"year":null,"claim":"How VFT ligand binding is allosterically transduced through the TMD to specific G protein outputs across taste, gut, and muscle contexts remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No experimental full-length receptor structure linking domains","Tissue-specific G protein partners and effector branches not mapped","Whether peripheral T1R2 always requires T1R3 unestablished"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[8,11,20]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[16,17,20]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[14,25]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[9,13,16]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[8,20,25]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[8,22]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[11]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[12,20]}],"complexes":["T1R2/T1R3 sweet taste receptor heterodimer"],"partners":["TAS1R3","PTBP1"],"other_free_text":[]}},"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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a single amino acid change in T1R3 associated with decreased sweet sensitivity in mice drastically reduced ligand affinity for T1R3, demonstrating that individual T1R subunits increase the receptive range of the sweet taste receptor.\",\n      \"method\": \"Ligand-binding assays with individual subunits, site-directed mutagenesis, behavioral phenotyping in mice\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct binding assays with mutagenesis plus behavioral validation, replicated across multiple sweet stimuli\",\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 at a secondary allosteric binding site distinct from the 'glutamate-like' (Venus flytrap) pocket used by small-molecule sweeteners, and stabilize the active (free form II) conformation of the receptor.\",\n      \"method\": \"Computational docking with a homology model of T1R2-T1R3; structural reasoning from protein mutant analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — computational/modeling only, no in vitro reconstitution or mutagenesis validation reported in this abstract\",\n      \"pmids\": [\"12208493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Homology modeling of the T1R2-T1R3 extracellular ligand-binding domain on mGluR1 identified four binding sites for low-molecular-weight sweeteners and a secondary site for sweet proteins; docking experiments showed sweet proteins bind the secondary site, accounting for sweetness synergy.\",\n      \"method\": \"Homology modeling based on mGluR1 crystal structure; in silico docking\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — purely computational, no experimental validation of binding sites reported\",\n      \"pmids\": [\"16107151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"NMR solution structure of the G16A mutant of single-chain monellin (MNEI) showed that the sweetness-reducing mutation does not affect glucophore positions but displaces secondary structural elements on the protein surface, establishing that sweet proteins do not act via a 'sweet finger' mechanism but rather through a conformational interaction with a secondary site on T1R2-T1R3.\",\n      \"method\": \"NMR solution structure determination of sweet protein mutant; comparison with wild-type structure\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — NMR structure determination (Tier 1 method) but single study and no direct receptor mutagenesis\",\n      \"pmids\": [\"12706725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Mutagenesis of brazzein surface residues and T1R2/T1R3 chimeras established that brazzein activates the sweet receptor through multi-point interactions; the Venus flytrap module of T1R2 is important for brazzein agonism; a T1R2 R217A mutation in lobe 2 at the subunit interface selectively reduced brazzein activity by altering subunit-subunit interaction rather than direct ligand binding.\",\n      \"method\": \"Site-directed mutagenesis of brazzein and receptor subunits; chimeric receptor assays in HEK293 cells; human taste panel; in vitro receptor activity assay\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (mutagenesis, chimeras, cell-based assay, human panel) establishing mechanistic detail\",\n      \"pmids\": [\"20302879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Saturation transfer difference (STD) NMR spectroscopy directly detected binding of sweet agonists and antagonists to the full heterodimeric T1R2/T1R3 receptor in membranes from HEK293 cells, allowing distinction between mutations that alter ligand-binding sites versus those affecting downstream signal transduction.\",\n      \"method\": \"STD NMR spectroscopy on membrane-expressed receptor\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — NMR-based direct binding assay (Tier 1 method), single lab, single approach\",\n      \"pmids\": [\"19664591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The cysteine-rich domain (CRD) of human T1R3 (not T1R2) is necessary for the interaction of the T1R2-T1R3 heterodimer with the sweet-tasting protein thaumatin, as demonstrated by chimeric human-mouse receptor assays showing that hT1R2/mT1R3 responds to sucralose but not thaumatin.\",\n      \"method\": \"Chimeric human/mouse receptor expression in HEK293 cells; functional assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chimeric receptor functional assays with multiple chimera combinations, single lab\",\n      \"pmids\": [\"21329673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Arg82 of thaumatin is a critical residue for interaction with human T1R2-T1R3; charge inversion at Arg82 (R82E) abolished receptor activation even at 1 mM, while Lys67 mutations were less disruptive, indicating a strict spatial charge requirement at position 82 for receptor binding.\",\n      \"method\": \"Site-directed mutagenesis of thaumatin; cell-based receptor assay in HEK293 cells expressing human sweet receptors\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis plus quantitative functional assay, single lab\",\n      \"pmids\": [\"21867681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"T1R2 knockout and T1R3 knockout mice displayed severely impaired licking responses to sucrose, glucose, and maltose, but retained relatively normal concentration-dependent responding to Polycose (glucose polymer), establishing that the T1R2+T1R3 heterodimer is the principal receptor for simple sugars but not for glucose polymers, which activate a separate receptor mechanism.\",\n      \"method\": \"T1R2 and T1R3 knockout mice; T1R2/T1R3 double knockout mice; brief-access taste tests and two-response operant discrimination\",\n      \"journal\": \"The Journal of neuroscience; American journal of physiology. Regulatory, integrative and comparative physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with specific behavioral readouts replicated across multiple KO models and psychophysical paradigms in multiple papers\",\n      \"pmids\": [\"21940444\", \"22621968\", \"19158407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Human T1R3 surface expression requires co-expression with human T1R2, whereas mouse T1r3 reaches the membrane independently; domain-swap chimeras showed the Venus flytrap module and cysteine-rich domain (CRD) of human T1R3 contain regions that inhibit T1R3 membrane trafficking when expressed alone, and the Venus flytrap modules of both human T1R2 and T1R3 are needed for proper membrane trafficking of the heterodimer.\",\n      \"method\": \"Tagged T1R2/T1R3 constructs expressed in HEK293 cells; domain-swap chimeras; truncation mutants; surface expression assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chimeric and truncation mutagenesis with surface expression readout, single lab, multiple constructs\",\n      \"pmids\": [\"25029362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"T1R2-LacZ reporter knock-in mice revealed that T1R2 is expressed in taste tissue, the gastrointestinal tract (where T1R3 is also expressed), and unexpectedly in the testis; homozygous T1R2 deletion mice lacked T1R2 protein, confirming the knock-in allele.\",\n      \"method\": \"T1R2-LacZ reporter knock-in mouse; LacZ staining; immunohistochemistry with validated antibody\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct reporter expression and protein localization in a well-controlled transgenic model, single lab\",\n      \"pmids\": [\"20965149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"T1R2 receptor signaling in the upper intestine enhances glucose absorption specifically in response to glucose-rich meals by regulating GLUT2 transporter trafficking to the apical membrane of enterocytes; these effects were dependent on GLP-2 secretion and subsequent intestinal neuronal activation; high-sucrose feeding in wild-type mice rapidly downregulated intestinal STRs, reducing glucose absorption.\",\n      \"method\": \"T1R2 knockout mice; in vivo glucose absorption measurements; ex vivo intact intestinal preparations; GLUT2 trafficking assays; pharmacological blockade\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple orthogonal in vivo and ex vivo assays establishing the pathway (T1R2 → GLP-2 → neuronal activation → GLUT2 trafficking)\",\n      \"pmids\": [\"30201274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Global disruption of T1R2 in mice fed a high-fat/low-carbohydrate diet resulted in reduced fat mass, increased lean mass, hyperactivity, protection from diet-induced hyperinsulinemia, increased glucose oxidation rates, and decreased liver triglyceride accumulation; sweet taste receptors (T1r2/T1r3) were upregulated in adipose tissue in response to HF/LC diet and positively correlated with fat mass and glucose intolerance.\",\n      \"method\": \"T1R2 knockout mice; high-fat diet feeding; body composition, energy balance, glucose homeostasis, and tissue substrate metabolism measurements\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple metabolic phenotype readouts, single lab\",\n      \"pmids\": [\"26884387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The Ile191Val common variant of TAS1R2 causes a partial loss of function through reduced receptor availability at the plasma membrane; human Val minor allele carriers show reduced plasma glucose excursions during an OGTT compared to Ile/Ile carriers, effects not explained by differences in beta-cell function or insulin sensitivity.\",\n      \"method\": \"In vitro biochemical assays of receptor membrane availability; oral glucose tolerance tests in human participants; genotyping\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro mechanistic characterization of variant plus human physiological study, single lab, two complementary methods\",\n      \"pmids\": [\"34509698\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The heptahelical domain (TMD) of T1R2 is the allosteric binding site for the sweet inhibitor amiloride; this was distinct from the T1R3-binding site of lactisole; using chimeric human/squirrel monkey/mouse T1R2 and T1R3 receptors and the agonist perillartine (which activates the single TMD of T1R2), the T1R2 TMD was identified as the molecular determinant mediating species-dependent amiloride sensitivity.\",\n      \"method\": \"Chimeric human/squirrel monkey/mouse T1R2/T1R3 receptors in cell-based functional assays; perillartine activation of isolated T1R2 TMD\",\n      \"journal\": \"Journal of molecular neuroscience : MN\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chimeric receptor approach with multiple species and an isolated-domain agonist control, single lab\",\n      \"pmids\": [\"30120716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Squirrel monkey T1R2/T1R3 responds to natural sugars and some sweet proteins (thaumatin at high concentrations) but not to aspartame, neotame, cyclamate, saccharin, or monellin; the residues in T1R2 determine species-dependent sensitivity to saccharin, while residues in either T1R2 or T1R3 underlie sweet taste differences toward monellin between humans and squirrel monkeys.\",\n      \"method\": \"Cloning and heterologous expression of squirrel monkey T1R2/T1R3; cell-based functional assays; chimeric receptor analyses; molecular modeling\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — chimeric receptor mapping of species-dependent differences, single lab\",\n      \"pmids\": [\"23000410\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The purified human TAS1R2 subunit forms a dimer in detergent solution and binds high-potency sweeteners with Kd values consistent with physiological detection thresholds, as measured by intrinsic tryptophan fluorescence; circular dichroism confirmed proper folding with secondary structure.\",\n      \"method\": \"Overexpression in stable HEK293S inducible cell line; detergent solubilization and purification; size exclusion chromatography coupled with light scattering; circular dichroism; tryptophan fluorescence binding assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biophysical characterization with multiple orthogonal methods (SEC-MALS, CD, fluorescence), single lab\",\n      \"pmids\": [\"34782704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The isolated Venus flytrap domain of human TAS1R2 (hTAS1R2-VFT) expressed in E. coli is a functional monomer that binds sweet stimuli with Kd values consistent with physiological detection; single amino acid substitutions D278A and E382A (known to abolish full-length receptor response) drastically reduced ligand affinity of the isolated VFT domain, confirming these residues as key binding-site determinants.\",\n      \"method\": \"Heterologous expression of hTAS1R2-VFT in E. coli; circular dichroism; SEC-MALS; site-directed mutagenesis; intrinsic tryptophan fluorescence binding assay\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro binding assay with mutagenesis validation, multiple biophysical methods, single lab\",\n      \"pmids\": [\"36012481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The T1R2 splicing isoform T1R2_Δe3p (lacking part of exon 3) forms a non-functional heterodimer with T1R3 that cannot be activated by sweet stimuli and significantly downregulates canonical T1R2/T1R3 function; local LPS injection significantly increased the expression ratio of T1R2_Δe3p in mouse taste buds, providing a mechanism by which bacterial infection suppresses sweet taste perception.\",\n      \"method\": \"RT-PCR identification of splicing isoform; heterologous expression in vitro functional assays; local LPS injection in mice; quantitative RT-PCR\",\n      \"journal\": \"Hua xi kou qiang yi xue za zhi\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isoform identified and functionally characterized in cell-based assay with in vivo LPS validation, single lab\",\n      \"pmids\": [\"34409805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Skipping of Tas1r2 exon 4 produces a truncated isoform (Tas1r2_Δe4) lacking amino acids in the Venus flytrap domain; this truncated isoform generates non-functional T1R2/T1R3 heterodimers that reduce sweet taste responses to all tested sweet compounds in vitro and in vivo. The splicing factor PTBP1 promotes exon 4 skipping by binding a polypyrimidine-rich silencer in exon 4, thereby decreasing sweet taste receptor function and sweet taste perception in mice.\",\n      \"method\": \"Identification and cloning of splicing variant; heterologous expression cell-based assays; in vivo behavioral sweet taste tests; PTBP1 knockdown/overexpression; RNA-binding analysis\",\n      \"journal\": \"Chemical senses\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — multiple orthogonal methods (molecular, cellular, in vivo behavioral) establishing the splicing regulatory mechanism, single lab\",\n      \"pmids\": [\"36484118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TAS1R2 in skeletal muscle acts as a glucose sensor that stimulates ERK1/2-dependent phosphorylation and activation of PARP1 (a major NAD consumer); muscle-specific deletion of TAS1R2 suppresses PARP1 activity, elevates NAD levels, and enhances mitochondrial capacity and running endurance in mice. Plasma glucose negatively correlates with muscle NAD, implicating TAS1R2 as a peripheral energy surveyor.\",\n      \"method\": \"Muscle-specific TAS1R2 knockout mice; PARP1 activity assays; NAD measurement; mitochondrial function assays; running endurance tests; glucose/agonist stimulation with ERK1/2 phosphorylation readout\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal assays (biochemical pathway dissection, genetic KO with specific phenotypic readouts) establishing the TAS1R2→ERK1/2→PARP1→NAD pathway in a peer-reviewed Nature Communications paper\",\n      \"pmids\": [\"38851747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The TAS1R2 sweet taste receptor regulates skeletal muscle mass and fitness through an ERK2-PARP1-NAD signaling axis; muscle-specific deletion of TAS1R2 elevated NAD levels, improved mitochondrial function, increased muscle mass and strength, and prolonged running endurance; deletion also ameliorated muscle decline in obese and aged mice.\",\n      \"method\": \"Muscle-specific TAS1R2 knockout mice; metabolic phenotyping; NAD, PARP1, and ERK2 measurements; voluntary wheel running; grip strength; aged and obese mouse models\",\n      \"journal\": \"Research square (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — preprint with multiple mechanistic readouts and genetic models, consistent with peer-reviewed Nature Communications paper (PMID 38851747) but independently assessed as preprint\",\n      \"pmids\": [\"36798161\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Inhibition of TAS1R2/TAS1R3 by the inverse agonist lactisole blocked perception of sweet thermal taste (warming of tongue from 20–35°C), establishing that TAS1R2/TAS1R3 receptor activation is necessary for thermal sweet taste perception in humans.\",\n      \"method\": \"Human psychophysics; pharmacological inhibition with lactisole; temperature-controlled flow gustometer\",\n      \"journal\": \"Chemical senses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological receptor inhibition with quantitative human perceptual readout, single lab\",\n      \"pmids\": [\"32072157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"l-glucose activates the sweet taste receptor TAS1R2/TAS1R3 in cell-based functional assays at thresholds similar to d-glucose; computational docking to the VFT domain of TAS1R2 identified two sub-pockets (A and B), each compatible with one enantiomer, with both sharing overlapping polar contact residues.\",\n      \"method\": \"Cell-based functional assay (HEK293T transfection); computational docking to TAS1R2 VFT domain\",\n      \"journal\": \"Food chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — cell-based assay establishes functional activation, docking is computational; single lab\",\n      \"pmids\": [\"34715629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Serine 147 in the binding site of T1R3 VFT domain is required for T1R3 activation by both l- and d-glucose; mutation S147A completely abolishes T1R3 monomer activation. The R317G variant in the VFT domain of T1R2 (present in ~20% of the world population based on the NM_152232.4 reference) markedly reduces TAS1R2 sensitivity in vitro.\",\n      \"method\": \"Mutagenesis; transient transfection of individual T1R2 and T1R3 monomers and heterodimers in HEK293T cells; cell-based functional assay; comparison of TAS1R2 reference sequences\",\n      \"journal\": \"Chemical senses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-directed mutagenesis with quantitative functional readout for multiple variants, single lab\",\n      \"pmids\": [\"36806908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Steviol glycosides and other sweeteners bind to four distinct sites on the T1R2/T1R3 heterodimer: VFD2 (TAS1R2 Venus flytrap), VFD3 (TAS1R3 Venus flytrap), TMD2 (TAS1R2 transmembrane domain), and TMD3 (TAS1R3 transmembrane domain); the C20 carboxy terminus of the Gα protein binds to the intracellular region of either TMD2 or TMD3, altering GPCR affinity to a high-affinity state for steviol glycosides.\",\n      \"method\": \"Radioligand binding experiments; computational docking at four receptor sites; G protein coupling analysis\",\n      \"journal\": \"Communications chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — binding experiments combined with computational docking, multiple sites tested, single lab\",\n      \"pmids\": [\"39424933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A single amino acid substitution in TAS1R2 (Ile-67 in humans vs. Leu-70 in mice) in the Venus flytrap domain explains species-specific differences in sulfamate sweetener (saccharin, acesulfame K) sensitivity; mouse-type I67L mutation in human TAS1R2 decreased receptor activity and sulfamate binding, while the reverse L70I mutation in mouse Tas1r2 increased activity and binding.\",\n      \"method\": \"Chimeric TAS1R2/TAS1R3 analyses; single amino acid substitution mutagenesis; HEK293 cell-based functional assays; molecular dynamics simulations\",\n      \"journal\": \"Food chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal mutagenesis in both human and mouse receptor with quantitative functional assays and MD simulations identifying a specific contact residue\",\n      \"pmids\": [\"40706454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The rhesus monkey Tas1r2 paired with human TAS1R3 responds to natural sugars, amino acids, artificial sweeteners, and sweet proteins, but amiloride does not inhibit rhesus monkey Tas1r2-mediated responses; the monomeric Tas1r2 transmembrane domain (without counterpart T1R3) can be activated by perillartine in humans, rhesus monkey, and squirrel monkey but not mouse.\",\n      \"method\": \"Cloning, expression, and functional characterization of rhesus monkey Tas1r2 in cell-based assays; chimeric and monomeric receptor assays; molecular modeling\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic cell-based functional characterization across species and receptor constructs, single lab\",\n      \"pmids\": [\"27479072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Co-expression ratios of T1r2, T1r3, and gustducin in fungiform papillae are significantly lower in gurmarin-weakly-sensitive BALB mice than in gurmarin-sensitive B6 and dpa congenic mice, linking co-expression levels of these sweet receptor components with sensitivity to gurmarin-mediated sweet taste suppression.\",\n      \"method\": \"Quantitative in situ hybridization for T1r2, T1r3, and gustducin co-expression in taste tissues of different mouse strains; comparison with gurmarin-sensitivity phenotype\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — co-expression correlation across strains without functional pathway reconstitution, single lab\",\n      \"pmids\": [\"18174025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"D- and L-amino acids show specific enantiomeric activities on the TAS1R2-TAS1R3 sweet receptor as demonstrated by in vitro binding assays using cells overexpressing the receptor, providing direct evidence that the stereochemistry of amino acids determines their interaction with the sweet receptor.\",\n      \"method\": \"Cell-based binding/functional assay using cells overexpressing TAS1R2-TAS1R3\",\n      \"journal\": \"Food chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single cell-based assay system without detailed mechanistic follow-up, single lab\",\n      \"pmids\": [\"24360415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Whole-brain mapping using T1r2-Cre knock-in mice showed that T1R2 is expressed not only in taste cells but also in various neuronal and glial populations in the brain, in circumventricular organs, and in vascular structures; immunohistochemistry confirmed co-expression with NPY and POMC neurons in the hypothalamic arcuate nucleus and with canonical taste signaling molecules in perivascular cells of the median eminence.\",\n      \"method\": \"T1r2-Cre knock-in mice with reporter; whole-brain Cre-labeled cell mapping; immunohistochemistry for neuropeptide co-expression\",\n      \"journal\": \"Frontiers in neuroanatomy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct reporter-based localization in a transgenic model with immunohistochemical validation, single lab\",\n      \"pmids\": [\"34776881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Non-nutritive sweetener exposure (sodium saccharin and rebaudioside A) dose-dependently regulated T1R2 expression in the ovary and uterus of guinea pigs; low-dose saccharin increased ovarian T1R2 expression and ovary weight, while high-dose saccharin suppressed ovarian T1R2 and caused adverse ovarian/uterine morphological effects.\",\n      \"method\": \"In vivo sweetener administration; immunohistochemistry; protein expression analysis in ovary and uterus\",\n      \"journal\": \"Animal science journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect localization and expression modulation without mechanistic pathway definition, single lab\",\n      \"pmids\": [\"32219957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Hyperactivation of TAS1R2-TAS1R3 with sucralose elevated plasma insulin responses during an OGTT; inhibition with lactisole correlated with decreased plasma glucose; sucralose sweetness ratings correlated with early increases in glucose and insulin, showing bidirectional regulation of glucose metabolism by TAS1R2-TAS1R3 in humans.\",\n      \"method\": \"Oral glucose tolerance tests in healthy humans with sucralose or lactisole co-administration; plasma glucose, insulin, glucagon measurement; sweet taste psychophysics\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional pharmacological manipulation of the receptor in a human physiological study with quantitative metabolic endpoints, single lab\",\n      \"pmids\": [\"38691547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Exendin-4 (GLP-1 receptor agonist) reduced glucose absorption in streptozotocin-diabetic mice by suppressing T1R2/T1R3 sweet taste receptor signaling and downstream molecules (PLCβ2, α-gustducin, IP3, cAMP), as well as SGLT1 and GLUT2 levels in the duodenum.\",\n      \"method\": \"STZ-diabetic mouse model; exendin-4 treatment; Western blotting and RT-qPCR for receptor and signaling molecules; glucose and transporter level measurement\",\n      \"journal\": \"Translational research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — pathway component expression changes measured but no direct mechanistic link to TAS1R2 specifically established beyond expression correlation\",\n      \"pmids\": [\"35385790\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TAS1R2 functions as the ligand-binding subunit of the heterodimeric G protein-coupled sweet taste receptor TAS1R2/TAS1R3, where its Venus flytrap domain (VFT) constitutes the primary binding site for natural sugars and most high-potency sweeteners (with key residues D278, E382, I67/L70 identified), while its transmembrane domain (TMD) binds modulators such as amiloride; T1R2/T1R3-mediated signaling in intestinal enteroendocrine cells enhances glucose absorption by promoting GLUT2 apical trafficking via GLP-2 and neuronal activation; and in skeletal muscle, TAS1R2 acts as a glucose sensor that drives ERK1/2-dependent PARP1 activation to consume NAD, with receptor loss elevating NAD, improving mitochondrial capacity and muscle fitness.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TAS1R2 is the ligand-binding subunit of the heterodimeric sweet taste receptor T1R2/T1R3, a class C G protein-coupled receptor that constitutes the principal detector of simple sugars and high-potency sweeteners; genetic ablation of T1R2 abolishes behavioral responses to sucrose, glucose, and maltose while sparing responses to glucose polymers [#8]. The extracellular Venus flytrap domain (VFT) of T1R2 forms the primary small-molecule binding site: the isolated hTAS1R2-VFT folds and binds sweet stimuli at physiological affinities, and the substitutions D278A and E382A that abolish full-length receptor responses also cripple ligand binding by the isolated domain [#17], with additional contact residues (I67, R317) governing potency and species-specific sensitivity to sulfamate sweeteners [#26, #24]. Beyond the VFT, sweet-tasting proteins such as brazzein and thaumatin engage a secondary interaction surface involving the subunit interface and the T1R3 cysteine-rich domain [#4, #6], while the T1R2 transmembrane domain provides an allosteric site for modulators including the inhibitor amiloride [#14]. Receptor surface expression requires co-assembly of human T1R2 and T1R3 VFT modules [#9], and alternative splicing of T1R2 — including PTBP1-driven skipping of exon 4 — produces non-functional heterodimers that suppress sweet perception [#19]. Beyond the tongue, T1R2 is expressed in the gut, brain, and other peripheral tissues [#10, #30], where it acts as a glucose sensor: in the upper intestine it enhances glucose absorption by promoting apical GLUT2 trafficking through GLP-2 secretion and intestinal neuronal activation [#11], and in skeletal muscle it drives an ERK1/2–PARP1 axis that consumes NAD, such that muscle-specific T1R2 loss elevates NAD, improves mitochondrial capacity, and enhances endurance [#20]. A common partial-loss-of-function variant (Ile191Val) reducing receptor surface availability lowers postprandial glucose excursions in human carriers [#13].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established that each T1R subunit binds sweet ligands independently with distinct affinities, explaining how the heterodimer achieves a broad receptive range rather than acting as a single binding entity.\",\n      \"evidence\": \"Ligand-binding assays on individual subunits with site-directed mutagenesis and mouse behavioral phenotyping\",\n      \"pmids\": [\"16271873\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not assign which natural sugars and sweeteners map to which subunit\", \"Conformational changes inferred rather than structurally resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Resolved how sweet proteins activate the receptor, showing they act through multi-point interactions at the subunit interface rather than the small-molecule pocket, distinguishing two modes of receptor activation.\",\n      \"evidence\": \"Brazzein and receptor mutagenesis, chimeric receptors in HEK293 cells, and human taste panels; complemented by NMR of a sweet-protein mutant\",\n      \"pmids\": [\"20302879\", \"12706725\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact spatial arrangement of the sweet-protein contact surface not crystallographically defined\", \"Stoichiometry of multi-point engagement unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Mapped the molecular requirements for sweet-protein recognition to the T1R3 cysteine-rich domain and a specific thaumatin residue, defining a determinant of species-specific sweet-protein responsiveness.\",\n      \"evidence\": \"Chimeric human/mouse receptor assays and thaumatin site-directed mutagenesis in HEK293 cells\",\n      \"pmids\": [\"21329673\", \"21867681\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Role of T1R2 in sweet-protein binding versus T1R3 not fully separated\", \"Structural basis of the charge requirement at thaumatin Arg82 not visualized\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the in vivo ligand scope of the receptor genetically, demonstrating the T1R2/T1R3 heterodimer is the principal receptor for simple sugars but not glucose polymers, which use a separate mechanism.\",\n      \"evidence\": \"T1R2, T1R3, and double knockout mice with brief-access and operant taste tests\",\n      \"pmids\": [\"21940444\", \"22621968\", \"19158407\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the glucose-polymer receptor not determined\", \"Residual non-T1R sugar sensing not characterized\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Explained the obligate heterodimeric assembly of the human receptor by showing T1R3 surface expression depends on T1R2 and that both VFT modules are required for trafficking.\",\n      \"evidence\": \"Tagged constructs, domain-swap chimeras, and truncation mutants with surface expression assays in HEK293 cells\",\n      \"pmids\": [\"25029362\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Chaperone or trafficking machinery mediating assembly not identified\", \"Species difference in independent mouse T1r3 trafficking not mechanistically explained\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified the T1R2 transmembrane domain as an allosteric modulator site, locating amiloride binding to the TMD distinct from the T1R3 lactisole site and explaining species-dependent amiloride sensitivity.\",\n      \"evidence\": \"Chimeric human/squirrel monkey/mouse receptors and perillartine activation of the isolated T1R2 TMD in cell-based assays\",\n      \"pmids\": [\"30120716\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"TMD allosteric pocket not structurally defined\", \"Physiological relevance of amiloride modulation unaddressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extended T1R2 function beyond taste to intestinal nutrient handling, defining a T1R2 to GLP-2 to neuronal activation to GLUT2 trafficking pathway that enhances glucose absorption.\",\n      \"evidence\": \"T1R2 knockout mice with in vivo and ex vivo glucose absorption, GLUT2 trafficking assays, and pharmacological blockade\",\n      \"pmids\": [\"30201274\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G protein and intracellular signaling steps coupling T1R2 to GLP-2 release not dissected\", \"Whether intestinal effect requires T1R3 co-expression not isolated here\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established a direct human genotype-physiology link, showing a common partial-loss-of-function TAS1R2 variant reduces receptor surface availability and lowers postprandial glucose excursions.\",\n      \"evidence\": \"In vitro receptor membrane-availability assays plus oral glucose tolerance tests in genotyped human participants\",\n      \"pmids\": [\"34509698\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue site (gut vs peripheral) driving the glucose phenotype not localized\", \"Mechanism connecting reduced surface receptor to lower glucose excursion not traced\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Confirmed the T1R2 VFT as the primary small-molecule binding determinant by reconstituting the isolated domain and validating key binding residues biochemically.\",\n      \"evidence\": \"Bacterially expressed hTAS1R2-VFT with CD, SEC-MALS, mutagenesis (D278A, E382A), and tryptophan fluorescence binding; complemented by full-subunit dimer biophysics\",\n      \"pmids\": [\"36012481\", \"34782704\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the ligand-bound VFT not solved\", \"How VFT closure couples to TMD activation not addressed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed splicing as a regulatory layer over sweet receptor function, showing PTBP1-driven exon skipping generates dominant-negative T1R2 isoforms that suppress sweet perception, including in response to infection.\",\n      \"evidence\": \"Splice variant cloning, heterologous functional assays, in vivo behavioral tests, PTBP1 knockdown/overexpression, and LPS challenge in mice\",\n      \"pmids\": [\"36484118\", \"34409805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological triggers regulating PTBP1 in taste tissue beyond LPS not defined\", \"Magnitude of splicing control on human sweet perception not quantified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined a peripheral metabolic role for T1R2 in skeletal muscle, establishing an ERK1/2-PARP1-NAD axis through which the receptor acts as a glucose surveyor controlling mitochondrial capacity and endurance.\",\n      \"evidence\": \"Muscle-specific TAS1R2 knockout mice with PARP1 activity, NAD measurement, mitochondrial and endurance assays, and ERK1/2 phosphorylation readouts; consistent preprint precursor\",\n      \"pmids\": [\"38851747\", \"36798161\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"G protein coupling linking muscle T1R2 to ERK1/2 not identified\", \"Whether muscle T1R2 functions as a heterodimer with T1R3 not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Refined the multi-site model of receptor pharmacology, mapping sweetener binding to four distinct VFT and TMD sites and linking Galpha C-terminus engagement to a high-affinity receptor state.\",\n      \"evidence\": \"Radioligand binding with computational docking at four sites and G protein coupling analysis\",\n      \"pmids\": [\"39424933\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Docking-based site assignments lack experimental structural confirmation\", \"Functional hierarchy among the four sites not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How VFT ligand binding is allosterically transduced through the TMD to specific G protein outputs across taste, gut, and muscle contexts remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental full-length receptor structure linking domains\", \"Tissue-specific G protein partners and effector branches not mapped\", \"Whether peripheral T1R2 always requires T1R3 unestablished\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [8, 11, 20]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [16, 17, 20]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [14, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [9, 13, 16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [8, 20, 25]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [8, 22]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [12, 20]}\n    ],\n    \"complexes\": [\"T1R2/T1R3 sweet taste receptor heterodimer\"],\n    \"partners\": [\"TAS1R3\", \"PTBP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}