{"gene":"TAS1R1","run_date":"2026-04-28T21:42:58","timeline":{"discoveries":[{"year":2012,"finding":"The heterodimeric GPCR T1R1/T1R3 functions as a direct sensor of extracellular amino acid availability and regulates mTORC1 signaling; knockdown of T1R1/T1R3 reduces amino acid-stimulated mTORC1 activation, alters mTORC1 localization, downregulates pathway inhibitors, upregulates amino acid transporters, blocks translation initiation, and induces autophagy.","method":"siRNA knockdown in cell lines, mTORC1 localization imaging, phosphorylation assays, autophagy assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (knockdown, localization, pathway readouts) in a single study; replicated conceptually in a companion commentary","pmids":["22959271"],"is_preprint":false},{"year":2012,"finding":"TAS1R1-TAS1R3 senses extracellular amino acids at the cell surface, activates mTORC1, and inhibits autophagy; fasted TAS1R3−/− mice show increased autophagy in heart, skeletal muscle and liver, confirming the in vivo role.","method":"Knockout mouse model, autophagy assays in multiple tissues","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined in vivo phenotypic readout, corroborating the companion Molecular Cell paper","pmids":["23222068"],"is_preprint":false},{"year":2012,"finding":"T1R1-T1R3 expressed in gut enteroendocrine (STC-1) cells senses L-amino acids (Phe, Leu, Glu but not Trp) and drives CCK secretion; siRNA knockdown of T1R1 in STC-1 cells significantly reduces Phe-, Leu-, and Glu-stimulated (but not Trp-stimulated) CCK release; IMP potentiates this response, consistent with canonical T1R1/T1R3 pharmacology.","method":"siRNA knockdown, CCK ELISA, pharmacological inhibition (gurmarin), intestinal tissue explants","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 2 — siRNA KD with specific phenotypic readout, pharmacological corroboration, and ex vivo tissue validation","pmids":["23203156"],"is_preprint":false},{"year":2013,"finding":"T1R1/T1R3 ligand specificity is determined by two distinct determinants in the Venus flytrap (VFT) domain of T1R1: an orthosteric ligand-binding site controlling acidic amino acid selectivity, and non-orthosteric sites that modulate receptor activity independently of IMP allosteric modulation; 12 key residues were identified by chimeric receptor and point-mutant analysis.","method":"Chimeric human-mouse receptor analysis, site-directed mutagenesis, heterologous receptor expression assays, molecular modeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with mutagenesis and molecular modeling; multiple orthogonal mutant series","pmids":["24214976"],"is_preprint":false},{"year":2013,"finding":"T1R1-knockout mice show a severe deficit in IMP-elicited umami synergy in gustatory nerve recordings but retain substantial residual glutamate responses mediated by metabotropic glutamate receptors (mGluR1/mGluR4); T1R1-expressing taste cells also contribute partly to sweet sensitivity.","method":"T1R1 knockout mouse, chorda tympani and glossopharyngeal nerve recordings, mGluR antagonist pharmacology, single-cell RT-PCR, conditioned taste aversion","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1-2 — full KO with electrophysiological recordings and pharmacological dissection of receptor contributions","pmids":["23339178"],"is_preprint":false},{"year":2012,"finding":"Tas1r1 and Tas1r3 are expressed in murine and human spermatozoa, localized to the flagellum and acrosomal cap; Tas1r1-null spermatozoa display spermatogenic abnormalities, increased spontaneous acrosomal reaction, and significantly elevated basal cytosolic Ca²⁺ and cAMP concentrations, indicating that Tas1r1 maintains sperm quiescence through constitutive or tonic receptor activity.","method":"Tas1r1-deficient mCherry reporter mouse, acrosomal reaction assays, intracellular Ca²⁺ and cAMP measurements, immunofluorescence localization","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple quantitative cellular phenotype readouts and subcellular localization data","pmids":["22427794"],"is_preprint":false},{"year":2014,"finding":"Activation of luminal T1R1/T1R3 by monosodium glutamate or L-cysteine in the distal colon initiates the peristaltic reflex (ascending contraction, descending relaxation) and CGRP release; T1R1-knockout mice fail to show MSG-evoked peristaltic reflex, confirming receptor necessity.","method":"T1R1 knockout mice, flat-sheet colonic preparation, electrophysiology, CGRP ELISA, video pellet propulsion recording","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"High","confidence_rationale":"Tier 2 — KO mouse with specific physiological readouts and pharmacological corroboration","pmids":["25324508"],"is_preprint":false},{"year":2016,"finding":"Methionine activates mTORC1 via the T1R1/T1R3 → PLCβ → Ca²⁺ → ERK1/2 signal transduction cascade in C2C12 myotubes; siRNA knockdown of T1R1 abolishes Met-induced mTORC1 activation.","method":"siRNA knockdown, Ca²⁺ measurement, ERK1/2 phosphorylation assay, mTORC1 activity assay","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD with defined signaling readouts, single lab","pmids":["27727170"],"is_preprint":false},{"year":2018,"finding":"Methionine and valine activate mTOR signaling in bovine mammary epithelial cells through TAS1R1/TAS1R3 by elevating intracellular Ca²⁺; TAS1R1 siRNA knockdown decreases intracellular Ca²⁺ and reduces mTOR, S6K1, and 4EBP1 phosphorylation, as well as β-casein (CSN2) mRNA abundance.","method":"siRNA knockdown, intracellular Ca²⁺ measurement, Western blot for mTOR pathway components, RT-qPCR","journal":"Journal of dairy science","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA KD with multiple downstream readouts, single lab","pmids":["30268610"],"is_preprint":false},{"year":2018,"finding":"Methional acts as an allosteric modulator of T1R1/T1R3 by binding the transmembrane domain of T1R1; it serves as a positive allosteric modulator (PAM) for human T1R1/T1R3 and a negative allosteric modulator (NAM) for mouse T1R1/T1R3; the PAM/NAM switch depends on specific amino acid residues at the bottom of the allosteric pocket in the T1R1 transmembrane domain.","method":"Interspecies chimeric receptor expression, site-directed mutagenesis, functional receptor assays, molecular modeling","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis plus chimeric receptors plus functional assays identify binding site and switching mechanism","pmids":["30087430"],"is_preprint":false},{"year":2014,"finding":"L-Theanine activates T1R1+T1R3 and elicits umami taste; site-directed mutagenesis shows L-theanine binds the L-amino acid orthosteric binding site in the Venus flytrap domain of T1R1 and shows synergy with IMP.","method":"Functional receptor expression assay, site-directed mutagenesis, IMP synergy assay","journal":"Amino acids","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis identifies binding site with functional validation","pmids":["24633359"],"is_preprint":false},{"year":2011,"finding":"Nonsynonymous SNPs in TAS1R1 (A110V and R507Q in the N-terminal ligand-binding domain) severely impair in vitro T1R1/T1R3 response to MSG; molecular modeling provides structural explanation for the functional loss.","method":"Functional expression of SNP variants in heterologous cells, Ca²⁺ assay, molecular modeling","journal":"Chemical senses","confidence":"Medium","confidence_rationale":"Tier 1 — functional expression with mutagenesis, single lab","pmids":["21422378"],"is_preprint":false},{"year":2009,"finding":"Nonsynonymous SNPs C329T (A110V) and G1114A in TAS1R1 are significantly associated with glutamate nontasting/tasting phenotypes in humans, implicating specific residues of the TAS1R1 ligand-binding domain in individual differences in MSG sensitivity.","method":"Human population genotyping, psychophysical taste testing, RT-PCR and immunohistochemistry of fungiform papillae","journal":"The American journal of clinical nutrition","confidence":"Medium","confidence_rationale":"Tier 3 — human genotype-phenotype association with receptor expression confirmation, no functional reconstitution","pmids":["19571223"],"is_preprint":false},{"year":2012,"finding":"Genetic labeling experiments in Tas1r1-mCherry reporter mice show Tas1r1-expressing taste cells are predominantly located in fungiform papillae, are completely segregated from bitter (Tas2r131) cells, and are also present in the testis; approximately 50% of mCherry cells co-express T1R2 and T1R3, indicating T1R1 cells can participate in both umami and sweet receptor complexes.","method":"Knock-in reporter mouse, fluorescence microscopy, single-cell RT-PCR","journal":"Chemical senses","confidence":"Medium","confidence_rationale":"Tier 2 — direct genetic labeling with cellular characterization, single lab","pmids":["23010799"],"is_preprint":false},{"year":2014,"finding":"Mouse neutrophils express functional T1R1/T1R3; stimulation with L-alanine or L-serine (T1R1/T1R3 ligands) elicits ERK and p38 MAPK phosphorylation, chemotactic migration, and attenuation of LPS-induced TNF-α production via inhibition of NF-κB activity and STAT3 phosphorylation.","method":"RNA sequencing, qRT-PCR, signaling assays (Western blot), chemotaxis assay, cytokine ELISA","journal":"BMB reports","confidence":"Medium","confidence_rationale":"Tier 2 — functional receptor expression confirmed with multiple downstream readouts, single lab","pmids":["25301019"],"is_preprint":false},{"year":2019,"finding":"Branched chain amino acids (L-leucine, L-isoleucine) stimulate CCK secretion from porcine jejunum via T1R1/T1R3; pre-treatment with lactisole (a T1R1/T1R3 inhibitor) significantly reduces BCAA-induced CCK secretion and attenuates upregulation of T1R1/T1R3 expression.","method":"Porcine jejunum tissue explants, pharmacological inhibition with lactisole, CCK ELISA, RT-PCR and Western blot","journal":"Food & function","confidence":"Medium","confidence_rationale":"Tier 2 — ex vivo pharmacological inhibition with multiple readouts, single lab","pmids":["31098606"],"is_preprint":false},{"year":2017,"finding":"The Venus flytrap (VFT) domain of the cat T1R1 (cT1R1-NTD) expressed in E. coli and refolded can bind L-amino acids with Kd in the micromolar range; IMP potentiates L-amino acid binding and IMP itself binds the extracellular domain in the absence of L-amino acids.","method":"Recombinant protein expression and refolding, intrinsic tryptophan fluorescence binding assay, circular dichroism, size-exclusion chromatography/light scattering","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution of ligand binding with biophysical validation, single lab","pmids":["29084235"],"is_preprint":false},{"year":2018,"finding":"The T1R1 VFT (Venus flytrap) domain immobilized on a graphene FET biosensor binds monosodium glutamate with ~1 nM sensitivity; IMP enhances the signal analogously to the human taste system, confirming that the isolated VFT domain retains functional umami ligand binding.","method":"Recombinant VFT domain production, graphene FET biosensor, real-time binding measurement","journal":"Biosensors & bioelectronics","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution of isolated domain binding, single lab","pmids":["30005383"],"is_preprint":false},{"year":2022,"finding":"Purified T1R1-VFT binds umami ligands (MSG, disodium succinate, beefy meaty peptide, IMP) at a 1:1 stoichiometry via hydrogen bond, van der Waals, and electrostatic interactions; binding is spontaneous, exothermic, and induces conformational changes (α-helix unfolding) that stabilize the active pocket conformation.","method":"Recombinant protein production, multispectroscopic techniques (fluorescence quenching), isothermal titration calorimetry, molecular dynamics simulation","journal":"Journal of agricultural and food chemistry","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstitution with thermodynamic and structural characterization, single lab","pmids":["36098631"],"is_preprint":false},{"year":2010,"finding":"The giant panda Tas1r1 gene is a pseudogene; the functional constraint on Tas1r1 was relaxed ~4.2 Ma, coinciding with the dietary switch to bamboo, establishing a causal link between loss of T1R1 umami receptor function and herbivory.","method":"Sequencing of all six Tas1r1 exons across carnivore species, dN/dS ratio analysis, molecular clock estimation","journal":"Molecular biology and evolution","confidence":"Medium","confidence_rationale":"Tier 3 — evolutionary/genomic analysis without direct functional reconstitution; strong comparative evidence","pmids":["20573776"],"is_preprint":false}],"current_model":"TAS1R1 forms a heterodimeric class C GPCR with T1R3; the T1R1 Venus flytrap domain binds L-amino acids (particularly L-glutamate in humans) and IMP at distinct orthosteric and allosteric sites, activating intracellular Ca²⁺/PLCβ/ERK signaling that stimulates mTORC1 and inhibits autophagy, while in gut enteroendocrine cells the receptor drives CCK secretion in response to luminal amino acids, and in spermatozoa it maintains basal quiescence by suppressing Ca²⁺ and cAMP levels."},"narrative":{"teleology":[{"year":2009,"claim":"Establishing that human genetic variation in TAS1R1 explains individual differences in umami perception linked specific SNPs in the ligand-binding domain to MSG sensitivity, grounding human taste phenotypes in receptor sequence.","evidence":"Human genotype–phenotype association with psychophysical taste testing","pmids":["19571223"],"confidence":"Medium","gaps":["No functional reconstitution of variant receptors in this study","Population sample limited in ethnic diversity","Effect sizes on taste thresholds not fully delineated"]},{"year":2010,"claim":"Demonstrating that Tas1r1 pseudogenization in the giant panda correlates with dietary shift to herbivory established an evolutionary framework linking T1R1 function to amino acid dietary dependence.","evidence":"Comparative genomic sequencing of Tas1r1 across carnivores, dN/dS and molecular clock analysis","pmids":["20573776"],"confidence":"Medium","gaps":["Correlational evolutionary evidence without direct functional rescue","Does not address whether other amino acid sensors compensate"]},{"year":2011,"claim":"Functional reconstitution of TAS1R1 SNP variants (A110V, R507Q) confirmed that specific residues in the N-terminal domain are required for MSG responsiveness, moving from association to mechanism.","evidence":"Heterologous expression of variant receptors with Ca²⁺ functional assay and molecular modeling","pmids":["21422378"],"confidence":"Medium","gaps":["Single-lab study","No crystal structure to validate modeled binding changes"]},{"year":2012,"claim":"Identification of T1R1/T1R3 as a cell-surface amino acid sensor that activates mTORC1 and suppresses autophagy revealed a metabolic signaling role far beyond taste, confirmed in vivo by increased autophagy in TAS1R3-knockout mice.","evidence":"siRNA knockdown with mTORC1 localization/phosphorylation assays in cell lines; TAS1R3-KO mouse autophagy phenotyping in heart, muscle, and liver","pmids":["22959271","23222068"],"confidence":"High","gaps":["Downstream signaling intermediates between receptor and mTORC1 not fully mapped","Relative contribution of T1R1/T1R3 versus other amino acid sensors (SLC38A9, Sestrin2) not resolved"]},{"year":2012,"claim":"Demonstrating that T1R1 knockdown in enteroendocrine cells selectively reduces amino acid-stimulated CCK secretion established the receptor as a gut nutrient sensor coupling luminal amino acids to hormone release.","evidence":"siRNA knockdown in STC-1 cells, CCK ELISA, pharmacological inhibition, intestinal tissue explants","pmids":["23203156"],"confidence":"High","gaps":["In vivo KO confirmation in gut CCK release not yet shown in this study","Downstream signaling pathway to CCK vesicle exocytosis not defined"]},{"year":2012,"claim":"Characterization of Tas1r1-null spermatozoa revealed a non-gustatory role in maintaining sperm quiescence via tonic suppression of Ca²⁺ and cAMP, expanding receptor function to reproductive physiology.","evidence":"Tas1r1-deficient reporter mouse, acrosomal reaction assay, intracellular Ca²⁺ and cAMP measurements, immunofluorescence","pmids":["22427794"],"confidence":"High","gaps":["Ligand that activates T1R1/T1R3 in reproductive tract not identified","Whether constitutive receptor activity versus tonic agonism underlies quiescence is unresolved"]},{"year":2012,"claim":"Genetic reporter mapping showed T1R1-expressing taste cells are predominantly in fungiform papillae, segregated from bitter cells, and can co-express T1R2/T1R3 sweet receptor subunits, clarifying the cellular organization of taste receptor expression.","evidence":"Tas1r1-mCherry knock-in reporter mouse, fluorescence microscopy, single-cell RT-PCR","pmids":["23010799"],"confidence":"Medium","gaps":["Functional consequence of T1R1/T1R2/T1R3 co-expression not tested","Reporter fidelity versus endogenous protein not independently validated"]},{"year":2013,"claim":"Chimeric and mutant receptor analyses resolved that T1R1 ligand specificity depends on two separable determinants in its VFT domain—an orthosteric amino acid site and non-orthosteric modulatory sites—establishing the structural basis for species-specific tuning.","evidence":"Human–mouse chimeric receptors, site-directed mutagenesis (12 residues), functional heterologous expression assays, molecular modeling","pmids":["24214976"],"confidence":"High","gaps":["No high-resolution crystal or cryo-EM structure available","Precise IMP-binding residues not fully resolved"]},{"year":2013,"claim":"T1R1-KO mice showed abolished IMP synergy in nerve recordings but retained residual glutamate responses via mGluR1/mGluR4, defining T1R1 as essential for umami synergy but not the sole glutamate detector in taste.","evidence":"T1R1 knockout mouse, chorda tympani and glossopharyngeal nerve recordings, mGluR antagonist pharmacology","pmids":["23339178"],"confidence":"High","gaps":["Quantitative contribution of each mGluR to residual response not fully delineated","Central processing of parallel glutamate signals not addressed"]},{"year":2014,"claim":"Discovery that T1R1/T1R3 activation by luminal amino acids initiates the colonic peristaltic reflex and CGRP release, confirmed by loss-of-function in T1R1-KO mice, extended the gut chemosensory role to motility control.","evidence":"T1R1-KO mice, flat-sheet colonic preparation, electrophysiology, CGRP ELISA","pmids":["25324508"],"confidence":"High","gaps":["Cell type (enterochromaffin, enteroendocrine, or neuronal) initiating the reflex not resolved","Downstream neural circuit not mapped"]},{"year":2014,"claim":"Identification of functional T1R1/T1R3 in neutrophils that drives amino acid-induced chemotaxis and attenuates NF-κB/TNF-α signaling expanded the receptor's role to innate immune modulation.","evidence":"RNA-seq, signaling assays, chemotaxis assay, cytokine ELISA in mouse neutrophils","pmids":["25301019"],"confidence":"Medium","gaps":["Single-lab finding not yet replicated independently","In vivo immune phenotype of T1R1-KO not assessed","Receptor coupling (Gα subunit) in neutrophils not identified"]},{"year":2016,"claim":"Delineation of the T1R1/T1R3 → PLCβ → Ca²⁺ → ERK1/2 → mTORC1 signaling cascade for methionine in myotubes provided the first ordered intracellular signaling pathway downstream of the receptor.","evidence":"siRNA knockdown in C2C12 myotubes, Ca²⁺ measurement, ERK1/2 and mTORC1 phosphorylation assays","pmids":["27727170"],"confidence":"Medium","gaps":["Single-lab study","Whether PLCβ is directly activated by Gα or βγ subunits not determined"]},{"year":2017,"claim":"Biophysical reconstitution of the isolated T1R1 VFT domain demonstrated direct, IMP-potentiated L-amino acid binding with micromolar affinity, confirming that the extracellular domain is sufficient for ligand recognition.","evidence":"Recombinant cat T1R1-NTD expressed in E. coli, intrinsic fluorescence binding assay, CD spectroscopy, SEC-MALS","pmids":["29084235"],"confidence":"Medium","gaps":["Refolded protein may not fully recapitulate native conformation","Binding affinities not validated for human T1R1"]},{"year":2018,"claim":"Identification of methional as a transmembrane-domain allosteric modulator whose PAM/NAM activity switches between human and mouse T1R1 revealed a second modulatory site in the TMD, distinct from the VFT allosteric pocket.","evidence":"Interspecies chimeric receptors, site-directed mutagenesis, functional assays, molecular modeling","pmids":["30087430"],"confidence":"High","gaps":["No direct structural visualization of the TMD allosteric pocket","Endogenous TMD modulators not identified"]},{"year":2022,"claim":"Thermodynamic and conformational characterization of purified T1R1-VFT binding to multiple umami ligands established 1:1 stoichiometry and α-helix unfolding upon ligand engagement, providing a mechanistic model for VFT activation.","evidence":"Recombinant T1R1-VFT, fluorescence quenching, ITC, molecular dynamics simulation","pmids":["36098631"],"confidence":"Medium","gaps":["Full-length receptor structure in active/inactive states still lacking","Single-lab biophysical study"]},{"year":null,"claim":"A high-resolution structure of the full-length T1R1/T1R3 heterodimer, the identity of endogenous ligands in non-taste tissues, the precise Gα subunit coupling in each cell type, and the relative contribution of T1R1/T1R3 versus other amino acid sensors to mTORC1 regulation remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No cryo-EM or crystal structure of full-length heterodimer","Endogenous ligands in reproductive tract and immune cells unknown","Gα coupling specificity in non-taste tissues not determined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,2,4,6,7,14]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,5,13]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3,16,17,18]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,7,8,14]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-8963743","term_label":"Digestion and absorption","supporting_discovery_ids":[2,6,15]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[4,12]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[14]}],"complexes":["T1R1/T1R3 heterodimer"],"partners":["TAS1R3","TAS1R2"],"other_free_text":[]},"mechanistic_narrative":"TAS1R1 encodes the ligand-binding subunit of the T1R1/T1R3 heterodimeric class C GPCR that functions as the primary sensor of L-amino acids across taste, gut, immune, reproductive, and metabolic contexts. The T1R1 Venus flytrap domain contains an orthosteric site for L-amino acids (especially L-glutamate in humans) and distinct allosteric sites for nucleotide enhancers such as IMP, with species-specific tuning determined by key residues in both the VFT and transmembrane domains [PMID:24214976, PMID:30087430, PMID:24633359]. Receptor activation couples through PLCβ → Ca²⁺ → ERK1/2 to stimulate mTORC1 and suppress autophagy in multiple tissues, while in enteroendocrine cells it drives CCK secretion and in colonic mucosa it initiates the peristaltic reflex [PMID:22959271, PMID:23203156, PMID:25324508]. In spermatozoa, constitutive T1R1 activity maintains quiescence by suppressing basal Ca²⁺ and cAMP, and in neutrophils, amino acid sensing through T1R1/T1R3 triggers chemotaxis and modulates inflammatory cytokine production [PMID:22427794, PMID:25301019]."},"prefetch_data":{"uniprot":{"accession":"Q7RTX1","full_name":"Taste receptor type 1 member 1","aliases":["G-protein coupled receptor 70"],"length_aa":841,"mass_kda":93.1,"function":"Putative taste receptor. TAS1R1/TAS1R3 responds to the umami taste stimulus (the taste of monosodium glutamate). 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(Orlando, Fla.)","url":"https://pubmed.ncbi.nlm.nih.gov/26341315","citation_count":25,"is_preprint":false},{"pmid":"9680334","id":"PMC_9680334","title":"Cloning and sequencing of the gene encoding the cell surface glycoprotein of Haloarcula japonica strain TR-1.","date":"1997","source":"Extremophiles : life under extreme conditions","url":"https://pubmed.ncbi.nlm.nih.gov/9680334","citation_count":25,"is_preprint":false},{"pmid":"3023604","id":"PMC_3023604","title":"Initiation of swimming activity by trigger neurons in the leech subesophageal ganglion. III. Sensory inputs to Tr1 and Tr2.","date":"1986","source":"Journal of comparative physiology. A, Sensory, neural, and behavioral physiology","url":"https://pubmed.ncbi.nlm.nih.gov/3023604","citation_count":25,"is_preprint":false},{"pmid":"25301019","id":"PMC_25301019","title":"Mouse neutrophils express functional umami taste receptor T1R1/T1R3.","date":"2014","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/25301019","citation_count":24,"is_preprint":false},{"pmid":"35792387","id":"PMC_35792387","title":"Umami polypeptide detection system targeting the human T1R1 receptor and its taste-presenting mechanism.","date":"2022","source":"Biomaterials","url":"https://pubmed.ncbi.nlm.nih.gov/35792387","citation_count":24,"is_preprint":false},{"pmid":"28265263","id":"PMC_28265263","title":"Genome Sequence of Desulfurella amilsii Strain TR1 and Comparative Genomics of Desulfurellaceae Family.","date":"2017","source":"Frontiers in microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/28265263","citation_count":24,"is_preprint":false},{"pmid":"27172902","id":"PMC_27172902","title":"Cisplatin induces tolerogenic dendritic cells in response to TLR agonists via the abundant production of IL-10, thereby promoting Th2- and Tr1-biased T-cell immunity.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27172902","citation_count":23,"is_preprint":false},{"pmid":"39265305","id":"PMC_39265305","title":"Screening and identification of novel umami peptides from yeast proteins: Insights into their mechanism of action on receptors T1R1/T1R3.","date":"2024","source":"Food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/39265305","citation_count":23,"is_preprint":false},{"pmid":"21702720","id":"PMC_21702720","title":"Targeting human inducible regulatory T cells (Tr1) in patients with cancer: blocking of adenosine-prostaglandin E₂ cooperation.","date":"2011","source":"Expert opinion on biological 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mutation","url":"https://pubmed.ncbi.nlm.nih.gov/30216591","citation_count":21,"is_preprint":false},{"pmid":"35991310","id":"PMC_35991310","title":"Roles of type 1 regulatory T (Tr1) cells in allergen-specific immunotherapy.","date":"2022","source":"Frontiers in allergy","url":"https://pubmed.ncbi.nlm.nih.gov/35991310","citation_count":20,"is_preprint":false},{"pmid":"29084235","id":"PMC_29084235","title":"Biophysical and functional characterization of the N-terminal domain of the cat T1R1 umami taste receptor expressed in Escherichia coli.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/29084235","citation_count":20,"is_preprint":false},{"pmid":"21958749","id":"PMC_21958749","title":"Isolation, expansion and functional assessment of CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients awaiting kidney transplantation.","date":"2011","source":"Transplant immunology","url":"https://pubmed.ncbi.nlm.nih.gov/21958749","citation_count":20,"is_preprint":false},{"pmid":"28604806","id":"PMC_28604806","title":"Prostaglandin E2 inhibits Tr1 cell differentiation through suppression of c-Maf.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/28604806","citation_count":19,"is_preprint":false},{"pmid":"38775286","id":"PMC_38775286","title":"Exploring the Relationship between Small Peptides and the T1R1/T1R3 Umami Taste Receptor for Umami Peptide Prediction: A Combined Approach.","date":"2024","source":"Journal of agricultural and food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/38775286","citation_count":18,"is_preprint":false},{"pmid":"24000232","id":"PMC_24000232","title":"Do polymorphisms in the TAS1R1 gene contribute to broader differences in human taste intensity?","date":"2013","source":"Chemical senses","url":"https://pubmed.ncbi.nlm.nih.gov/24000232","citation_count":18,"is_preprint":false},{"pmid":"35274217","id":"PMC_35274217","title":"Mesenchymal Stem Cells Alleviate Inflammatory Bowel Disease Via Tr1 Cells.","date":"2022","source":"Stem cell reviews and reports","url":"https://pubmed.ncbi.nlm.nih.gov/35274217","citation_count":18,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":48067,"output_tokens":4631,"usd":0.106833},"stage2":{"model":"claude-opus-4-6","input_tokens":8203,"output_tokens":3560,"usd":0.195022},"total_usd":0.301855,"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\": 2012,\n      \"finding\": \"The heterodimeric GPCR T1R1/T1R3 functions as a direct sensor of extracellular amino acid availability and regulates mTORC1 signaling; knockdown of T1R1/T1R3 reduces amino acid-stimulated mTORC1 activation, alters mTORC1 localization, downregulates pathway inhibitors, upregulates amino acid transporters, blocks translation initiation, and induces autophagy.\",\n      \"method\": \"siRNA knockdown in cell lines, mTORC1 localization imaging, phosphorylation assays, autophagy assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (knockdown, localization, pathway readouts) in a single study; replicated conceptually in a companion commentary\",\n      \"pmids\": [\"22959271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"TAS1R1-TAS1R3 senses extracellular amino acids at the cell surface, activates mTORC1, and inhibits autophagy; fasted TAS1R3−/− mice show increased autophagy in heart, skeletal muscle and liver, confirming the in vivo role.\",\n      \"method\": \"Knockout mouse model, autophagy assays in multiple tissues\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined in vivo phenotypic readout, corroborating the companion Molecular Cell paper\",\n      \"pmids\": [\"23222068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"T1R1-T1R3 expressed in gut enteroendocrine (STC-1) cells senses L-amino acids (Phe, Leu, Glu but not Trp) and drives CCK secretion; siRNA knockdown of T1R1 in STC-1 cells significantly reduces Phe-, Leu-, and Glu-stimulated (but not Trp-stimulated) CCK release; IMP potentiates this response, consistent with canonical T1R1/T1R3 pharmacology.\",\n      \"method\": \"siRNA knockdown, CCK ELISA, pharmacological inhibition (gurmarin), intestinal tissue explants\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with specific phenotypic readout, pharmacological corroboration, and ex vivo tissue validation\",\n      \"pmids\": [\"23203156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"T1R1/T1R3 ligand specificity is determined by two distinct determinants in the Venus flytrap (VFT) domain of T1R1: an orthosteric ligand-binding site controlling acidic amino acid selectivity, and non-orthosteric sites that modulate receptor activity independently of IMP allosteric modulation; 12 key residues were identified by chimeric receptor and point-mutant analysis.\",\n      \"method\": \"Chimeric human-mouse receptor analysis, site-directed mutagenesis, heterologous receptor expression assays, molecular modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis and molecular modeling; multiple orthogonal mutant series\",\n      \"pmids\": [\"24214976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"T1R1-knockout mice show a severe deficit in IMP-elicited umami synergy in gustatory nerve recordings but retain substantial residual glutamate responses mediated by metabotropic glutamate receptors (mGluR1/mGluR4); T1R1-expressing taste cells also contribute partly to sweet sensitivity.\",\n      \"method\": \"T1R1 knockout mouse, chorda tympani and glossopharyngeal nerve recordings, mGluR antagonist pharmacology, single-cell RT-PCR, conditioned taste aversion\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — full KO with electrophysiological recordings and pharmacological dissection of receptor contributions\",\n      \"pmids\": [\"23339178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Tas1r1 and Tas1r3 are expressed in murine and human spermatozoa, localized to the flagellum and acrosomal cap; Tas1r1-null spermatozoa display spermatogenic abnormalities, increased spontaneous acrosomal reaction, and significantly elevated basal cytosolic Ca²⁺ and cAMP concentrations, indicating that Tas1r1 maintains sperm quiescence through constitutive or tonic receptor activity.\",\n      \"method\": \"Tas1r1-deficient mCherry reporter mouse, acrosomal reaction assays, intracellular Ca²⁺ and cAMP measurements, immunofluorescence localization\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple quantitative cellular phenotype readouts and subcellular localization data\",\n      \"pmids\": [\"22427794\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Activation of luminal T1R1/T1R3 by monosodium glutamate or L-cysteine in the distal colon initiates the peristaltic reflex (ascending contraction, descending relaxation) and CGRP release; T1R1-knockout mice fail to show MSG-evoked peristaltic reflex, confirming receptor necessity.\",\n      \"method\": \"T1R1 knockout mice, flat-sheet colonic preparation, electrophysiology, CGRP ELISA, video pellet propulsion recording\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with specific physiological readouts and pharmacological corroboration\",\n      \"pmids\": [\"25324508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Methionine activates mTORC1 via the T1R1/T1R3 → PLCβ → Ca²⁺ → ERK1/2 signal transduction cascade in C2C12 myotubes; siRNA knockdown of T1R1 abolishes Met-induced mTORC1 activation.\",\n      \"method\": \"siRNA knockdown, Ca²⁺ measurement, ERK1/2 phosphorylation assay, mTORC1 activity assay\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with defined signaling readouts, single lab\",\n      \"pmids\": [\"27727170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Methionine and valine activate mTOR signaling in bovine mammary epithelial cells through TAS1R1/TAS1R3 by elevating intracellular Ca²⁺; TAS1R1 siRNA knockdown decreases intracellular Ca²⁺ and reduces mTOR, S6K1, and 4EBP1 phosphorylation, as well as β-casein (CSN2) mRNA abundance.\",\n      \"method\": \"siRNA knockdown, intracellular Ca²⁺ measurement, Western blot for mTOR pathway components, RT-qPCR\",\n      \"journal\": \"Journal of dairy science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA KD with multiple downstream readouts, single lab\",\n      \"pmids\": [\"30268610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Methional acts as an allosteric modulator of T1R1/T1R3 by binding the transmembrane domain of T1R1; it serves as a positive allosteric modulator (PAM) for human T1R1/T1R3 and a negative allosteric modulator (NAM) for mouse T1R1/T1R3; the PAM/NAM switch depends on specific amino acid residues at the bottom of the allosteric pocket in the T1R1 transmembrane domain.\",\n      \"method\": \"Interspecies chimeric receptor expression, site-directed mutagenesis, functional receptor assays, molecular modeling\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis plus chimeric receptors plus functional assays identify binding site and switching mechanism\",\n      \"pmids\": [\"30087430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"L-Theanine activates T1R1+T1R3 and elicits umami taste; site-directed mutagenesis shows L-theanine binds the L-amino acid orthosteric binding site in the Venus flytrap domain of T1R1 and shows synergy with IMP.\",\n      \"method\": \"Functional receptor expression assay, site-directed mutagenesis, IMP synergy assay\",\n      \"journal\": \"Amino acids\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis identifies binding site with functional validation\",\n      \"pmids\": [\"24633359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Nonsynonymous SNPs in TAS1R1 (A110V and R507Q in the N-terminal ligand-binding domain) severely impair in vitro T1R1/T1R3 response to MSG; molecular modeling provides structural explanation for the functional loss.\",\n      \"method\": \"Functional expression of SNP variants in heterologous cells, Ca²⁺ assay, molecular modeling\",\n      \"journal\": \"Chemical senses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — functional expression with mutagenesis, single lab\",\n      \"pmids\": [\"21422378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Nonsynonymous SNPs C329T (A110V) and G1114A in TAS1R1 are significantly associated with glutamate nontasting/tasting phenotypes in humans, implicating specific residues of the TAS1R1 ligand-binding domain in individual differences in MSG sensitivity.\",\n      \"method\": \"Human population genotyping, psychophysical taste testing, RT-PCR and immunohistochemistry of fungiform papillae\",\n      \"journal\": \"The American journal of clinical nutrition\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — human genotype-phenotype association with receptor expression confirmation, no functional reconstitution\",\n      \"pmids\": [\"19571223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Genetic labeling experiments in Tas1r1-mCherry reporter mice show Tas1r1-expressing taste cells are predominantly located in fungiform papillae, are completely segregated from bitter (Tas2r131) cells, and are also present in the testis; approximately 50% of mCherry cells co-express T1R2 and T1R3, indicating T1R1 cells can participate in both umami and sweet receptor complexes.\",\n      \"method\": \"Knock-in reporter mouse, fluorescence microscopy, single-cell RT-PCR\",\n      \"journal\": \"Chemical senses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct genetic labeling with cellular characterization, single lab\",\n      \"pmids\": [\"23010799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Mouse neutrophils express functional T1R1/T1R3; stimulation with L-alanine or L-serine (T1R1/T1R3 ligands) elicits ERK and p38 MAPK phosphorylation, chemotactic migration, and attenuation of LPS-induced TNF-α production via inhibition of NF-κB activity and STAT3 phosphorylation.\",\n      \"method\": \"RNA sequencing, qRT-PCR, signaling assays (Western blot), chemotaxis assay, cytokine ELISA\",\n      \"journal\": \"BMB reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional receptor expression confirmed with multiple downstream readouts, single lab\",\n      \"pmids\": [\"25301019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Branched chain amino acids (L-leucine, L-isoleucine) stimulate CCK secretion from porcine jejunum via T1R1/T1R3; pre-treatment with lactisole (a T1R1/T1R3 inhibitor) significantly reduces BCAA-induced CCK secretion and attenuates upregulation of T1R1/T1R3 expression.\",\n      \"method\": \"Porcine jejunum tissue explants, pharmacological inhibition with lactisole, CCK ELISA, RT-PCR and Western blot\",\n      \"journal\": \"Food & function\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ex vivo pharmacological inhibition with multiple readouts, single lab\",\n      \"pmids\": [\"31098606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The Venus flytrap (VFT) domain of the cat T1R1 (cT1R1-NTD) expressed in E. coli and refolded can bind L-amino acids with Kd in the micromolar range; IMP potentiates L-amino acid binding and IMP itself binds the extracellular domain in the absence of L-amino acids.\",\n      \"method\": \"Recombinant protein expression and refolding, intrinsic tryptophan fluorescence binding assay, circular dichroism, size-exclusion chromatography/light scattering\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of ligand binding with biophysical validation, single lab\",\n      \"pmids\": [\"29084235\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The T1R1 VFT (Venus flytrap) domain immobilized on a graphene FET biosensor binds monosodium glutamate with ~1 nM sensitivity; IMP enhances the signal analogously to the human taste system, confirming that the isolated VFT domain retains functional umami ligand binding.\",\n      \"method\": \"Recombinant VFT domain production, graphene FET biosensor, real-time binding measurement\",\n      \"journal\": \"Biosensors & bioelectronics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of isolated domain binding, single lab\",\n      \"pmids\": [\"30005383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Purified T1R1-VFT binds umami ligands (MSG, disodium succinate, beefy meaty peptide, IMP) at a 1:1 stoichiometry via hydrogen bond, van der Waals, and electrostatic interactions; binding is spontaneous, exothermic, and induces conformational changes (α-helix unfolding) that stabilize the active pocket conformation.\",\n      \"method\": \"Recombinant protein production, multispectroscopic techniques (fluorescence quenching), isothermal titration calorimetry, molecular dynamics simulation\",\n      \"journal\": \"Journal of agricultural and food chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with thermodynamic and structural characterization, single lab\",\n      \"pmids\": [\"36098631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The giant panda Tas1r1 gene is a pseudogene; the functional constraint on Tas1r1 was relaxed ~4.2 Ma, coinciding with the dietary switch to bamboo, establishing a causal link between loss of T1R1 umami receptor function and herbivory.\",\n      \"method\": \"Sequencing of all six Tas1r1 exons across carnivore species, dN/dS ratio analysis, molecular clock estimation\",\n      \"journal\": \"Molecular biology and evolution\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — evolutionary/genomic analysis without direct functional reconstitution; strong comparative evidence\",\n      \"pmids\": [\"20573776\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TAS1R1 forms a heterodimeric class C GPCR with T1R3; the T1R1 Venus flytrap domain binds L-amino acids (particularly L-glutamate in humans) and IMP at distinct orthosteric and allosteric sites, activating intracellular Ca²⁺/PLCβ/ERK signaling that stimulates mTORC1 and inhibits autophagy, while in gut enteroendocrine cells the receptor drives CCK secretion in response to luminal amino acids, and in spermatozoa it maintains basal quiescence by suppressing Ca²⁺ and cAMP levels.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"TAS1R1 encodes the ligand-binding subunit of the T1R1/T1R3 heterodimeric class C GPCR that functions as the primary sensor of L-amino acids across taste, gut, immune, reproductive, and metabolic contexts. The T1R1 Venus flytrap domain contains an orthosteric site for L-amino acids (especially L-glutamate in humans) and distinct allosteric sites for nucleotide enhancers such as IMP, with species-specific tuning determined by key residues in both the VFT and transmembrane domains [PMID:24214976, PMID:30087430, PMID:24633359]. Receptor activation couples through PLCβ → Ca²⁺ → ERK1/2 to stimulate mTORC1 and suppress autophagy in multiple tissues, while in enteroendocrine cells it drives CCK secretion and in colonic mucosa it initiates the peristaltic reflex [PMID:22959271, PMID:23203156, PMID:25324508]. In spermatozoa, constitutive T1R1 activity maintains quiescence by suppressing basal Ca²⁺ and cAMP, and in neutrophils, amino acid sensing through T1R1/T1R3 triggers chemotaxis and modulates inflammatory cytokine production [PMID:22427794, PMID:25301019].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Establishing that human genetic variation in TAS1R1 explains individual differences in umami perception linked specific SNPs in the ligand-binding domain to MSG sensitivity, grounding human taste phenotypes in receptor sequence.\",\n      \"evidence\": \"Human genotype–phenotype association with psychophysical taste testing\",\n      \"pmids\": [\"19571223\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional reconstitution of variant receptors in this study\", \"Population sample limited in ethnic diversity\", \"Effect sizes on taste thresholds not fully delineated\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that Tas1r1 pseudogenization in the giant panda correlates with dietary shift to herbivory established an evolutionary framework linking T1R1 function to amino acid dietary dependence.\",\n      \"evidence\": \"Comparative genomic sequencing of Tas1r1 across carnivores, dN/dS and molecular clock analysis\",\n      \"pmids\": [\"20573776\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Correlational evolutionary evidence without direct functional rescue\", \"Does not address whether other amino acid sensors compensate\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Functional reconstitution of TAS1R1 SNP variants (A110V, R507Q) confirmed that specific residues in the N-terminal domain are required for MSG responsiveness, moving from association to mechanism.\",\n      \"evidence\": \"Heterologous expression of variant receptors with Ca²⁺ functional assay and molecular modeling\",\n      \"pmids\": [\"21422378\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"No crystal structure to validate modeled binding changes\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identification of T1R1/T1R3 as a cell-surface amino acid sensor that activates mTORC1 and suppresses autophagy revealed a metabolic signaling role far beyond taste, confirmed in vivo by increased autophagy in TAS1R3-knockout mice.\",\n      \"evidence\": \"siRNA knockdown with mTORC1 localization/phosphorylation assays in cell lines; TAS1R3-KO mouse autophagy phenotyping in heart, muscle, and liver\",\n      \"pmids\": [\"22959271\", \"23222068\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling intermediates between receptor and mTORC1 not fully mapped\", \"Relative contribution of T1R1/T1R3 versus other amino acid sensors (SLC38A9, Sestrin2) not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrating that T1R1 knockdown in enteroendocrine cells selectively reduces amino acid-stimulated CCK secretion established the receptor as a gut nutrient sensor coupling luminal amino acids to hormone release.\",\n      \"evidence\": \"siRNA knockdown in STC-1 cells, CCK ELISA, pharmacological inhibition, intestinal tissue explants\",\n      \"pmids\": [\"23203156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo KO confirmation in gut CCK release not yet shown in this study\", \"Downstream signaling pathway to CCK vesicle exocytosis not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Characterization of Tas1r1-null spermatozoa revealed a non-gustatory role in maintaining sperm quiescence via tonic suppression of Ca²⁺ and cAMP, expanding receptor function to reproductive physiology.\",\n      \"evidence\": \"Tas1r1-deficient reporter mouse, acrosomal reaction assay, intracellular Ca²⁺ and cAMP measurements, immunofluorescence\",\n      \"pmids\": [\"22427794\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ligand that activates T1R1/T1R3 in reproductive tract not identified\", \"Whether constitutive receptor activity versus tonic agonism underlies quiescence is unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Genetic reporter mapping showed T1R1-expressing taste cells are predominantly in fungiform papillae, segregated from bitter cells, and can co-express T1R2/T1R3 sweet receptor subunits, clarifying the cellular organization of taste receptor expression.\",\n      \"evidence\": \"Tas1r1-mCherry knock-in reporter mouse, fluorescence microscopy, single-cell RT-PCR\",\n      \"pmids\": [\"23010799\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of T1R1/T1R2/T1R3 co-expression not tested\", \"Reporter fidelity versus endogenous protein not independently validated\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Chimeric and mutant receptor analyses resolved that T1R1 ligand specificity depends on two separable determinants in its VFT domain—an orthosteric amino acid site and non-orthosteric modulatory sites—establishing the structural basis for species-specific tuning.\",\n      \"evidence\": \"Human–mouse chimeric receptors, site-directed mutagenesis (12 residues), functional heterologous expression assays, molecular modeling\",\n      \"pmids\": [\"24214976\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution crystal or cryo-EM structure available\", \"Precise IMP-binding residues not fully resolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"T1R1-KO mice showed abolished IMP synergy in nerve recordings but retained residual glutamate responses via mGluR1/mGluR4, defining T1R1 as essential for umami synergy but not the sole glutamate detector in taste.\",\n      \"evidence\": \"T1R1 knockout mouse, chorda tympani and glossopharyngeal nerve recordings, mGluR antagonist pharmacology\",\n      \"pmids\": [\"23339178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of each mGluR to residual response not fully delineated\", \"Central processing of parallel glutamate signals not addressed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery that T1R1/T1R3 activation by luminal amino acids initiates the colonic peristaltic reflex and CGRP release, confirmed by loss-of-function in T1R1-KO mice, extended the gut chemosensory role to motility control.\",\n      \"evidence\": \"T1R1-KO mice, flat-sheet colonic preparation, electrophysiology, CGRP ELISA\",\n      \"pmids\": [\"25324508\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell type (enterochromaffin, enteroendocrine, or neuronal) initiating the reflex not resolved\", \"Downstream neural circuit not mapped\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of functional T1R1/T1R3 in neutrophils that drives amino acid-induced chemotaxis and attenuates NF-κB/TNF-α signaling expanded the receptor's role to innate immune modulation.\",\n      \"evidence\": \"RNA-seq, signaling assays, chemotaxis assay, cytokine ELISA in mouse neutrophils\",\n      \"pmids\": [\"25301019\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding not yet replicated independently\", \"In vivo immune phenotype of T1R1-KO not assessed\", \"Receptor coupling (Gα subunit) in neutrophils not identified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Delineation of the T1R1/T1R3 → PLCβ → Ca²⁺ → ERK1/2 → mTORC1 signaling cascade for methionine in myotubes provided the first ordered intracellular signaling pathway downstream of the receptor.\",\n      \"evidence\": \"siRNA knockdown in C2C12 myotubes, Ca²⁺ measurement, ERK1/2 and mTORC1 phosphorylation assays\",\n      \"pmids\": [\"27727170\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Whether PLCβ is directly activated by Gα or βγ subunits not determined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Biophysical reconstitution of the isolated T1R1 VFT domain demonstrated direct, IMP-potentiated L-amino acid binding with micromolar affinity, confirming that the extracellular domain is sufficient for ligand recognition.\",\n      \"evidence\": \"Recombinant cat T1R1-NTD expressed in E. coli, intrinsic fluorescence binding assay, CD spectroscopy, SEC-MALS\",\n      \"pmids\": [\"29084235\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Refolded protein may not fully recapitulate native conformation\", \"Binding affinities not validated for human T1R1\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identification of methional as a transmembrane-domain allosteric modulator whose PAM/NAM activity switches between human and mouse T1R1 revealed a second modulatory site in the TMD, distinct from the VFT allosteric pocket.\",\n      \"evidence\": \"Interspecies chimeric receptors, site-directed mutagenesis, functional assays, molecular modeling\",\n      \"pmids\": [\"30087430\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No direct structural visualization of the TMD allosteric pocket\", \"Endogenous TMD modulators not identified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Thermodynamic and conformational characterization of purified T1R1-VFT binding to multiple umami ligands established 1:1 stoichiometry and α-helix unfolding upon ligand engagement, providing a mechanistic model for VFT activation.\",\n      \"evidence\": \"Recombinant T1R1-VFT, fluorescence quenching, ITC, molecular dynamics simulation\",\n      \"pmids\": [\"36098631\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full-length receptor structure in active/inactive states still lacking\", \"Single-lab biophysical study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of the full-length T1R1/T1R3 heterodimer, the identity of endogenous ligands in non-taste tissues, the precise Gα subunit coupling in each cell type, and the relative contribution of T1R1/T1R3 versus other amino acid sensors to mTORC1 regulation remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No cryo-EM or crystal structure of full-length heterodimer\", \"Endogenous ligands in reproductive tract and immune cells unknown\", \"Gα coupling specificity in non-taste tissues not determined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 4, 6, 7, 14]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 5, 13]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3, 16, 17, 18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 7, 8, 14]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-8963743\", \"supporting_discovery_ids\": [2, 6, 15]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [4, 12]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"complexes\": [\n      \"T1R1/T1R3 heterodimer\"\n    ],\n    \"partners\": [\n      \"TAS1R3\",\n      \"TAS1R2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}