{"gene":"GRM4","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":1993,"finding":"mGluR4 (GRM4) couples to Gi/o proteins and inhibits forskolin-stimulated intracellular cAMP accumulation in response to agonist binding; the receptor shows high selectivity for L-AP4 and L-serine-O-phosphate as agonists, distinct from other mGluR subtypes.","method":"Stable CHO cell expression of cloned rat mGluR4; cAMP accumulation assay; pharmacological characterization","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted receptor pharmacology in defined cell system, replicated across multiple labs subsequently","pmids":["8463825"],"is_preprint":false},{"year":1995,"finding":"mGluR4 is palmitoylated via a thioester bond when expressed in BHK cells, as demonstrated by [3H]palmitic acid labeling and hydroxylamine cleavage; agonist stimulation with glutamate does not alter the level of palmitoylation. In contrast, mGluR1α is not palmitoylated.","method":"[3H]palmitic acid metabolic labeling; immunoprecipitation; hydroxylamine treatment; SDS-PAGE autoradiography in stably transfected BHK cells","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct biochemical demonstration of PTM with chemical validation (hydroxylamine cleavage), single lab but orthogonal controls","pmids":["7891082"],"is_preprint":false},{"year":1996,"finding":"mGluR4 knockout mice show impaired presynaptic short-term synaptic plasticity (paired-pulse facilitation and post-tetanic potentiation) at the parallel fiber→Purkinje cell synapse, and L-AP4 (EC50 = 2.5 µM) depresses synaptic responses in wild-type but not knockout mice, establishing mGluR4 as the presynaptic receptor mediating depression of excitatory transmission at this synapse. Long-term depression (LTD) is not impaired.","method":"Patch-clamp and extracellular field recordings from cerebellar slices in mGluR4 knockout vs. wild-type mice; pharmacological application of L-AP4","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with defined electrophysiological phenotype, replicated pharmacologically","pmids":["8815915"],"is_preprint":false},{"year":1999,"finding":"The primary ligand-binding determinants of mGluR4 reside within the extracellular amino-terminal domain (first 548 amino acids). A soluble truncated ATD binds L-AP4 with similar rank-order pharmacology as the full-length receptor; N-linked glycosylation is not required for agonist binding.","method":"Truncated epitope-tagged mGluR4 ATD expressed and secreted from HEK293 cells; competition binding with [3H]L-AP4; deglycosylation experiment; gel electrophoresis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical reconstitution of binding domain, multiple orthogonal methods in one study","pmids":["10187777"],"is_preprint":false},{"year":1999,"finding":"Site-directed mutagenesis identified Arg78, Ser159, and Thr182 in the mGluR4 ATD as critical residues for agonist binding; mutations to Ala severely impaired binding of [3H]L-AP4. Molecular modeling suggests Ser159 and Thr182 hydrogen-bond with the α-carboxyl and α-amino groups of agonists, while Arg78 forms an electrostatic interaction with the acidic side chain.","method":"Site-directed mutagenesis; [3H]L-AP4 competition binding; molecular modeling/docking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis with functional binding readout, multiple residues tested with controls, structural modeling as supporting tool","pmids":["10559233"],"is_preprint":false},{"year":1999,"finding":"mGluR4 is the predominant contributor to high-affinity [3H]L-AP4 binding in several brain regions including cerebellar cortex, nucleus basalis, thalamus, superior colliculus, substantia nigra, and hippocampal dentate gyrus, as demonstrated by near-complete loss of binding in mGluR4 knockout mice.","method":"Autoradiographic binding assay with [3H]L-AP4 in mGluR4 knockout vs. wild-type mouse brain sections","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO used to establish in vivo binding contribution, direct localization experiment","pmids":["9930760"],"is_preprint":false},{"year":2000,"finding":"mGluR4 mediates neuroprotection against NMDA excitotoxicity: group III agonists (+)-PPG and L-AP4 protect cortical neurons in wild-type mice but are ineffective in mGluR4−/− neurons. mGluR4−/− neurons are more vulnerable to NMDA and show higher extracellular glutamate, indicating mGluR4 maintains glutamate homeostasis presynaptically.","method":"Cortical neuronal cultures from mGluR4 KO and WT mice; NMDA toxicity assay; microdialysis; intrastriatal NMDA infusion in vivo","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO combined with pharmacological rescue, in vitro and in vivo, multiple orthogonal readouts","pmids":["10964947"],"is_preprint":false},{"year":2000,"finding":"mGluR4 within the nucleus reticularis thalami (nRT) is critical for GABAergic modulation of thalamocortical synchronization: mGluR4−/− mice are markedly resistant to GABAA receptor antagonist-induced absence seizures, bilateral intra-nRT mGluR4 antagonist injection mimics this resistance in WT mice, and intra-nRT mGluR4 agonist exacerbates absence seizures.","method":"mGluR4 KO mice; stereotaxic intra-nRT pharmacological injections; EEG/behavioral seizure monitoring","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO plus site-specific pharmacology, epistatic localization of function to specific brain region","pmids":["10934271"],"is_preprint":false},{"year":2002,"finding":"mGluR4 protein is predominantly localized to presynaptic active zones in multiple brain regions including cerebellar cortex, basal ganglia, thalamus, and hippocampus. In the basal ganglia, mGluR4 is found on GABAergic terminals of striatal projection neurons (both direct and indirect pathways), functioning as a presynaptic heteroreceptor; in cerebellum and hippocampus it functions as an autoreceptor.","method":"Affinity-purified antibodies against mGluR4 C-terminal domain; immunohistochemistry; pre-embedding electron microscopy; validation in mGluR4 KO mice (no immunoreactivity)","journal":"Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — ultrastructural immunolocalization validated by KO negative control, multiple brain regions characterized","pmids":["11906782"],"is_preprint":false},{"year":2003,"finding":"(-)-PHCCC acts as a positive allosteric modulator (PAM) of mGluR4 by binding within the transmembrane domain, increasing agonist potency and maximum efficacy; chimeric receptor studies localized its binding site to the TM region. The compound shows no activity at mGluR2, -3, -5a, -6, -7b, -8a.","method":"Recombinant mGluR expression; cAMP assay; chimeric receptor mutagenesis; selectivity profiling across mGluR subtypes","journal":"Neuropharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — chimeric receptor approach localizing allosteric binding site combined with functional pharmacology, multiple methods","pmids":["14573382"],"is_preprint":false},{"year":2004,"finding":"GRK2 (but not GRK4) regulates mGluR4 signaling: GRK2 overexpression attenuates mGluR4-mediated ERK1/2 (MAPK) activation while slightly potentiating cAMP inhibition. A kinase-dead GRK2 mutant also inhibits MAPK signaling, indicating GRK2 acts by sequestering Gβγ subunits rather than by phosphorylating mGluR4. GRK2 co-immunoprecipitates with Gβγ in an agonist-dependent manner. Agonist-induced internalization of mGluR4 is abolished by dominant-negative dynamin but not affected by GRK2.","method":"Transient transfection of HEK293 cells; Western blot for phospho-ERK1/2; cAMP assay; co-immunoprecipitation; GFP-tagged receptor internalization imaging; pertussis toxin treatment","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus multiple orthogonal functional assays (cAMP, MAPK, internalization) with kinase-dead and dominant-negative mutants","pmids":["15102938"],"is_preprint":false},{"year":2006,"finding":"Pharmacological activation of mGluR4 (via PHCCC) inhibits adenylyl cyclase and the PI3K pathway in medulloblastoma cells without affecting MAPK, Sonic Hedgehog, or Wnt pathways, and reduces DNA synthesis and cell proliferation; the antiproliferative effect is abolished by the PI3K inhibitor LY294002.","method":"mGluR4-expressing medulloblastoma cell lines (D283med, D341med, DAOY); cAMP assay; PI3K pathway analysis; DNA synthesis and proliferation assays; LY294002 pharmacological blockade; xenograft in vivo experiments","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Moderate — defined pathway placement (PI3K) with pharmacological rescue, in vitro and in vivo data, single lab with multiple orthogonal methods","pmids":["16899734"],"is_preprint":false},{"year":2006,"finding":"mGluR4 activation with PHCCC protects the nigrostriatal pathway against MPTP toxicity in mice; PHCCC is neuroprotective in wild-type but not in mGluR4−/− mice, confirming target specificity. Unilateral infusion of PHCCC into the external globus pallidus is sufficient to protect the ipsilateral nigrostriatal pathway.","method":"mGluR4 KO vs. WT C57BL/6 mice; MPTP neurotoxin model; dopamine/metabolite measurements; TH/DAT immunostaining; GFAP immunostaining; stereotaxic drug infusion","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO validation of pharmacological effect, site-specific infusion identifying anatomical locus of action, multiple readouts","pmids":["16822979"],"is_preprint":false},{"year":2007,"finding":"mGluR4 activation potentiates K2P2.1 (TREK-1) two-pore domain potassium channel activity via a PKA-dependent reduction in C-terminal phosphorylation; mutational analysis showed that dephosphorylation of S333 accounts for ~70% and S300 for ~30% of the K2P2.1 increase following mGluR4 activation. PKC, PKG, and protein phosphatases are not involved.","method":"Co-expression of mGluR4 and K2P2.1 in Xenopus oocytes or HEK cells; pharmacological kinase/phosphatase inhibitors; site-directed mutagenesis of K2P2.1 C-terminal phosphorylation sites; electrophysiological recordings","journal":"Molecular and cellular neurosciences","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of functional phosphorylation sites combined with pharmacological pathway dissection and electrophysiology","pmids":["17916432"],"is_preprint":false},{"year":2007,"finding":"mGluR4 PAM PHCCC enhances absence seizures in WAG/Rij rats and PTZ-treated mice; mGluR4 expression is elevated in the reticular thalamic nucleus (RTN) of symptomatic WAG/Rij rats. Electron microscopy and in situ hybridization indicate mGluR4 in the RTN is localized on excitatory cortical afferents. PHCCC is inactive in mGluR4 KO mice.","method":"Immunoblotting; immunohistochemistry; electron microscopy; in situ hybridization; EEG monitoring in mGluR4 KO and WAG/Rij rats; systemic PHCCC administration","journal":"Neuropharmacology","confidence":"High","confidence_rationale":"Tier 2 / Strong — ultrastructural localization combined with KO validation and in vivo EEG readout, multiple orthogonal methods","pmids":["18022649"],"is_preprint":false},{"year":2008,"finding":"Depression of excitatory synaptic transmission at parallel fiber–Purkinje cell synapses in the rodent cerebellar cortex by group III mGluRs is mediated exclusively by mGluR4 autoreceptors; neither mGluR7 nor mGluR8 contributes, as demonstrated using selective agonists, the mGluR4 PAM PHCCC, and mGluR4 KO mice.","method":"Whole-cell patch-clamp; presynaptic calcium influx measurements; selective agonists (ACPD, LSP4-2022, DCPG); PHCCC; mGluR4 KO cerebellar slices","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO combined with selective pharmacology and electrophysiology, replicated across subtypes","pmids":["18266929"],"is_preprint":false},{"year":2008,"finding":"mGluR4 and mGluR8 both contribute to L-AP4-induced presynaptic inhibition of synaptic transmission at the lateral olfactory tract–piriform cortex synapse; the inhibitory actions of L-AP4 and selective mGluR4 agonist Z-cyclopentyl-AP4 are potentiated by the mGluR4 PAM PHCCC.","method":"Whole-cell patch-clamp recordings from piriform cortex pyramidal cells in brain slices; selective agonists (DCPG for mGluR8; Z-cyclopentyl-AP4 for mGluR4); PHCCC potentiation","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — pharmacological dissection in brain slices, single lab, no KO validation in this paper","pmids":["18625254"],"is_preprint":false},{"year":2012,"finding":"Native presynaptic mGluR4 in rat cerebellum interacts with exocytosis proteins including Munc18-1, synapsins, and syntaxin; mGluR4 is retained on Munc18-1-conjugated Sepharose, and Munc18-1 co-localizes with mGluR4 at the plasma membrane. Affinity chromatography with peptides from mGluR4 cytoplasmic domains confirmed interactions with multiple exocytosis proteins.","method":"Co-immunoprecipitation from cerebellar extracts (mass spectrometry identification of 183 partners); affinity chromatography with recombinant Munc18-1 and mGluR4 cytoplasmic domain peptides; immunohistochemistry co-localization in HEK293 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, affinity chromatography, co-localization) identifying physiologically relevant interaction partners in native tissue","pmids":["22528491"],"is_preprint":false},{"year":2012,"finding":"mGluR4 and GABAA receptors co-localize on cerebellar parallel fiber axon terminals and co-immunoprecipitate from cerebellar membranes. Coincident activation of both receptors increases glutamate release above that of GABAA activation alone. In mGluR4 KO mice, GABAA receptor subunit expression (α1, α6, β2) and [35S]TBPS binding are reduced in the cerebellum.","method":"Immunocytochemistry; co-immunoprecipitation from cerebellar membranes; [3H]glutamate release from cerebellar synaptosomes; [35S]TBPS binding; mGluR4 KO mice","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, functional release assay, and KO validation with multiple orthogonal methods","pmids":["22145864"],"is_preprint":false},{"year":2012,"finding":"mGluR4 inhibition of presynaptic Ca2+ influx at parallel fiber–Purkinje cell synapses does not selectively target a specific voltage-gated Ca2+ channel subtype but modulates all classes present; this inhibition does not involve GIRK channels, TEA-sensitive K+ channels, K2P channels, pertussis toxin-sensitive G proteins, adenylyl cyclase, PKA, MAPK, or PI3K. Instead, it employs a signaling pathway involving phospholipase C (PLC) activation and ultimately protein kinase C.","method":"Whole-cell patch-clamp recordings in rat cerebellar slices; presynaptic Ca2+ transient measurements; pharmacological dissection with selective channel/kinase/G-protein inhibitors; pertussis toxin treatment","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic pharmacological dissection identifying novel PLC/PKC signaling pathway, multiple negative controls to exclude other pathways","pmids":["22570379"],"is_preprint":false},{"year":2012,"finding":"Co-activation of Gq-coupled H1 histamine receptors induces substantial calcium mobilization downstream of mGluR4 activation in mGluR4-expressing cells, biasing signaling away from Gi/o-mediated cAMP inhibition toward calcium-dependent pathways. This functional selectivity is further enhanced by mGluR4 PAMs.","method":"Calcium mobilization assay in mGluR4-expressing cells; cAMP inhibition assay; pharmacological application of histamine and mGluR4 PAMs; absence of chimeric G proteins confirmed","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional assay in recombinant system demonstrating biased signaling, single lab, mechanistic conclusion supported by two orthogonal signaling readouts","pmids":["22426233"],"is_preprint":false},{"year":2013,"finding":"Activation of mGluR4 in rat neural progenitor cells promotes proliferation via ERK1/2 signaling and upregulation of cyclin D1; mGluR4 siRNA decreases proliferation and p-ERK1/2 levels, and ERK1/2 inhibitor U0126 abolishes the VU0155041-induced proliferative effect. mGluR4 activation also decreases p38 phosphorylation.","method":"Rat embryonic NPC culture; mGluR4 siRNA knockdown; VU0155041 agonist treatment; Western blot for p-ERK1/2, p-p38, cyclin D1; neurosphere diameter measurement; U0126 ERK inhibitor epistasis","journal":"Cellular and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — KD/KO with defined molecular pathway (ERK/cyclin D1), pharmacological epistasis, single lab","pmids":["23374450"],"is_preprint":false},{"year":2014,"finding":"mGluR4 is endogenously activated during simulated cerebellar ischemia (excitotoxic conditions with elevated extracellular glutamate) in rodent cerebellar cortex brain slices; the photoswitchable NAM OptoGluNAM4.1 reversibly inhibits mGluR4 activity in a light-dependent manner, providing direct evidence for endogenous receptor activation under these conditions.","method":"OptoGluNAM4.1 photopharmacology in rodent cerebellar slices; parallel fiber–Purkinje cell synaptic recordings; simulated ischemia protocol","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — novel photopharmacological tool demonstrating endogenous receptor activation, single lab, single method","pmids":["30542267"],"is_preprint":false},{"year":2016,"finding":"mGluR4 presynaptically modulates corticostriatal transmission; immunoelectron microscopy shows >80% mGluR4-immunoreactive structures are unmyelinated axons/terminals in mouse striatum, ~50% of putative glutamatergic terminals (vGluT1+) express mGluR4, and ~70% of mGluR4-positive glutamatergic terminals target D1-receptor-negative (putative indirect pathway) spines, providing anatomical basis for antiparkinsonian actions.","method":"Immunoelectron microscopy; dual immunolabeling for mGluR4, vGluT1, and D1 receptor in mouse striatum; quantitative ultrastructural analysis","journal":"Brain structure & function","confidence":"High","confidence_rationale":"Tier 2 / Moderate — quantitative ultrastructural immunolocalization with multiple markers, direct anatomical determination of synaptic targeting","pmids":["26832920"],"is_preprint":false},{"year":2019,"finding":"GRM4 is expressed in myeloid cells and selectively regulates IL23 (and the related cytokine IL12) expression; Grm4 gene-targeted mice show accelerated radiation-induced tumor development. Osteosarcoma-conditioned media induce myeloid cell Il23 expression in a GRM4-dependent fashion while suppressing Il12. GRM4 agonists suppressed osteosarcoma growth in mice.","method":"Grm4 gene-targeted mouse model; radiation-induced osteosarcoma; cytokine expression assays; osteosarcoma-conditioned media experiments; in vivo GRM4 agonist treatment","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined molecular mechanism (IL23/IL12 regulation), multiple in vitro and in vivo experiments, single lab","pmids":["31527131"],"is_preprint":false},{"year":2019,"finding":"GRM4 overexpression in osteosarcoma cells inhibits proliferation, migration, and invasion by interacting with CBX4 and restricting CBX4 nuclear localization, thereby reducing HIF-1α transcriptional activity.","method":"GRM4 overexpression in osteosarcoma cell lines; co-immunoprecipitation of GRM4 and CBX4; nuclear fractionation; colony formation, transwell migration/invasion assays; HIF-1α reporter assay","journal":"Bioscience, biotechnology, and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP and functional assays identifying binding partner and downstream pathway, single lab","pmids":["31581881"],"is_preprint":false},{"year":2021,"finding":"cryo-EM structures of human mGlu4 bound to heterotrimeric Gi protein reveal a G-protein-binding site formed by three intracellular loops and helices III and IV; an asymmetric dimer interface of the transmembrane domain is critical for receptor activation and asymmetric signal transduction, with only one subunit of the homodimer coupling to G protein.","method":"Cryo-electron microscopy structure determination of mGlu4-Gi complex; functional validation of asymmetric dimerization","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure at high resolution with functional validation, published in high-impact journal","pmids":["34135510"],"is_preprint":false},{"year":2023,"finding":"Twelve cryo-EM structures of the mGlu2-mGlu4 heterodimer in inactive, intermediate, and active conformational states reveal that Venus flytrap domains undergo sequential conformational change upon activation, while transmembrane domains rearrange from symmetric inactive to asymmetric active dimer. A novel binding site for mGlu4 PAMs was identified at the asymmetric dimer interface of the mGlu2-mGlu4 heterodimer and mGlu4 homodimer.","method":"Cryo-electron microscopy of mGlu2-mGlu4 heterodimer in multiple states; functional data validating asymmetric signal transduction and PAM binding site","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structures in multiple conformational states with functional validation, novel allosteric site identified","pmids":["37286794"],"is_preprint":false}],"current_model":"GRM4 (mGluR4) is a presynaptically localized Group III metabotropic glutamate receptor that couples asymmetrically through a Gi/o G-protein binding site (formed by intracellular loops and helices III/IV) to inhibit adenylyl cyclase/cAMP, activate ERK1/2 via Gβγ, and modulate presynaptic Ca2+ influx through a PLC/PKC pathway; it is palmitoylated via a thioester bond, regulated by GRK2-mediated Gβγ sequestration, interacts with exocytosis proteins (Munc18-1, synapsins, syntaxin) and GABAA receptor subunits at the presynaptic active zone, and acts as an autoreceptor in cerebellum and heteroreceptor in basal ganglia to suppress glutamate release, with its ligand-binding pocket defined by Arg78, Ser159, and Thr182 in the extracellular amino-terminal domain and a transmembrane allosteric site accessible to PAMs."},"narrative":{"mechanistic_narrative":"GRM4 (mGluR4) is a presynaptic Group III metabotropic glutamate receptor that suppresses neurotransmitter release by coupling, via agonists such as L-AP4, to Gi/o proteins to inhibit forskolin-stimulated cAMP accumulation [PMID:8463825]. Its agonist-binding pocket lies within the extracellular amino-terminal domain, where a soluble truncated ATD recapitulates ligand pharmacology and the residues Arg78, Ser159, and Thr182 form the critical contacts [PMID:10187777, PMID:10559233]. Cryo-EM of mGlu4-Gi and of mGlu2-mGlu4 heterodimers established an asymmetric activation mechanism: only one protomer couples to G protein, the transmembrane domains rearrange from symmetric inactive to asymmetric active states, and a positive-allosteric-modulator (PAM) site sits within the transmembrane domain and at the asymmetric dimer interface [PMID:14573382, PMID:34135510, PMID:37286794]. The receptor is targeted to presynaptic active zones across cerebellum, basal ganglia, thalamus, and hippocampus, acting as an autoreceptor in cerebellum and as a heteroreceptor on GABAergic and glutamatergic terminals in the basal ganglia [PMID:11906782, PMID:26832920]. Genetic and pharmacological dissection at the parallel fiber–Purkinje cell synapse defines mGluR4 as the autoreceptor mediating depression of excitatory transmission and short-term plasticity, acting by inhibiting presynaptic Ca2+ influx through a PLC/PKC pathway that is independent of cAMP, PKA, MAPK, PI3K, and Gi/o-coupled K+ channels at this synapse [PMID:8815915, PMID:18266929, PMID:22570379]. mGluR4 signaling is shaped by additional effectors and modulators—GRK2 attenuates mGluR4-driven ERK1/2 activation by sequestering Gβγ rather than by phosphorylating the receptor [PMID:15102938], the receptor potentiates K2P2.1 (TREK-1) channels via PKA-dependent dephosphorylation [PMID:17916432], and it physically associates with the exocytotic machinery (Munc18-1, synapsins, syntaxin) and with GABAA receptors at parallel fiber terminals [PMID:22528491, PMID:22145864]. Functionally, mGluR4 maintains presynaptic glutamate homeostasis and confers neuroprotection against NMDA and MPTP toxicity, modulates thalamocortical synchronization underlying absence seizures, and outside the nervous system regulates myeloid IL23/IL12 expression and constrains osteosarcoma growth [PMID:10964947, PMID:10934271, PMID:16822979, PMID:31527131]. The receptor is palmitoylated through a thioester bond independent of agonist stimulation [PMID:7891082].","teleology":[{"year":1993,"claim":"Established the core transduction logic of mGluR4 by showing it is a Gi/o-coupled receptor that lowers cAMP, defining it as an inhibitory glutamate sensor distinct from other mGluR subtypes.","evidence":"Stable CHO expression of cloned rat mGluR4 with cAMP accumulation assay and agonist pharmacology","pmids":["8463825"],"confidence":"High","gaps":["Did not localize the receptor or define its native synaptic role","G-protein-binding interface not mapped"]},{"year":1995,"claim":"Identified palmitoylation as a covalent post-translational modification of mGluR4, distinguishing it biochemically from mGluR1α.","evidence":"[3H]palmitate metabolic labeling with hydroxylamine cleavage in BHK cells","pmids":["7891082"],"confidence":"High","gaps":["Modified cysteine residue(s) not identified","Functional consequence for trafficking or signaling untested"]},{"year":1996,"claim":"Demonstrated through knockout that mGluR4 is the presynaptic receptor mediating depression of excitatory transmission and short-term plasticity at the parallel fiber–Purkinje cell synapse.","evidence":"Patch-clamp and field recordings in mGluR4 KO vs WT cerebellar slices with L-AP4 application","pmids":["8815915"],"confidence":"High","gaps":["Downstream presynaptic effector pathway not defined here","LTD shown to be unaffected, leaving its receptor unidentified"]},{"year":1999,"claim":"Localized the ligand-binding function to the extracellular amino-terminal domain and identified the specific residues (Arg78, Ser159, Thr182) contacting agonists.","evidence":"Soluble truncated ATD binding, deglycosylation, site-directed mutagenesis with [3H]L-AP4 competition, and molecular modeling","pmids":["10187777","10559233"],"confidence":"High","gaps":["Did not resolve the full activation pathway from ATD to G protein","Allosteric/transmembrane sites not addressed"]},{"year":1999,"claim":"Used the knockout to establish mGluR4 as the dominant high-affinity L-AP4 binding site across multiple brain regions, anchoring its anatomical distribution.","evidence":"[3H]L-AP4 autoradiography in mGluR4 KO vs WT brain sections","pmids":["9930760"],"confidence":"High","gaps":["Subcellular (presynaptic) localization not resolved at this stage"]},{"year":2000,"claim":"Defined physiological roles for mGluR4 in glutamate homeostasis/neuroprotection and in thalamocortical control of absence seizures, linking receptor activity to circuit-level outcomes.","evidence":"mGluR4 KO neurons/mice with NMDA toxicity, microdialysis, and site-specific intra-nRT pharmacology with EEG","pmids":["10964947","10934271"],"confidence":"High","gaps":["Molecular signaling steps linking receptor to protection/seizure modulation not dissected","Cell-type-specific contributions only partially localized"]},{"year":2002,"claim":"Resolved the subcellular localization, showing mGluR4 resides at presynaptic active zones and functions as an autoreceptor in cerebellum/hippocampus and a heteroreceptor on GABAergic terminals in basal ganglia.","evidence":"Affinity-purified antibodies, pre-embedding electron microscopy, and KO negative controls across brain regions","pmids":["11906782"],"confidence":"High","gaps":["Did not establish presynaptic effector mechanism","Terminal-type specificity in striatum refined only later"]},{"year":2003,"claim":"Established a druggable transmembrane allosteric site by showing (-)-PHCCC is a subtype-selective positive allosteric modulator of mGluR4.","evidence":"Chimeric receptor mutagenesis, cAMP functional assay, and selectivity profiling across mGluR subtypes","pmids":["14573382"],"confidence":"High","gaps":["Atomic-level PAM binding pose not resolved until later cryo-EM"]},{"year":2004,"claim":"Identified GRK2 as a regulator of mGluR4 signaling acting through Gβγ sequestration rather than receptor phosphorylation, and separated internalization (dynamin-dependent) from desensitization.","evidence":"HEK293 transfection, phospho-ERK and cAMP assays, reciprocal Co-IP, kinase-dead/dominant-negative mutants, and receptor imaging","pmids":["15102938"],"confidence":"High","gaps":["In vivo relevance of GRK2 regulation untested","Mechanism couples to ERK in recombinant cells; native pathway not confirmed here"]},{"year":2006,"claim":"Extended mGluR4 signaling to growth control and neuroprotection in vivo, placing it upstream of PI3K in tumor cells and confirming target-specific nigrostriatal protection.","evidence":"PHCCC in medulloblastoma lines with PI3K inhibitor epistasis and xenografts; MPTP model with mGluR4 KO validation and site-specific pallidal infusion","pmids":["16899734","16822979"],"confidence":"High","gaps":["How a Gi/o receptor engages PI3K mechanistically not detailed","Anatomical locus identified but circuit mechanism inferred"]},{"year":2007,"claim":"Revealed a PKA-dependent effector arm in which mGluR4 potentiates K2P2.1 (TREK-1) channels via dephosphorylation of specific C-terminal serines, and clarified mGluR4 PAM effects on seizure circuits.","evidence":"mGluR4/K2P2.1 co-expression with kinase/phosphatase inhibitors and channel mutagenesis; immuno-EM, in situ hybridization, and EEG in WAG/Rij rats and KO mice","pmids":["17916432","18022649"],"confidence":"High","gaps":["Whether K2P2.1 modulation operates at native presynaptic terminals not shown","Pro- vs anti-epileptic outcomes depend on circuit context not fully resolved"]},{"year":2008,"claim":"Pharmacogenetically isolated mGluR4 as the sole Group III autoreceptor mediating cerebellar presynaptic depression and showed broader involvement at olfactory cortical synapses.","evidence":"Whole-cell patch-clamp with selective agonists, PHCCC, and KO slices (cerebellum); slice pharmacology at lateral olfactory tract–piriform synapse","pmids":["18266929","18625254"],"confidence":"High","gaps":["Olfactory cortex contribution lacks KO validation (Medium-confidence)","Effector pathway not yet defined in this work"]},{"year":2012,"claim":"Defined the presynaptic effector mechanism and the receptor's interaction network: Ca2+-influx inhibition proceeds via PLC/PKC, and mGluR4 physically associates with exocytotic proteins and GABAA receptors at active zones.","evidence":"Pharmacological dissection of presynaptic Ca2+ transients; Co-IP/affinity chromatography for Munc18-1/synapsins/syntaxin; reciprocal Co-IP and synaptosomal release assays for GABAA receptors; biased Gq co-activation assays","pmids":["22570379","22528491","22145864","22426233"],"confidence":"High","gaps":["Direct effector linking PLC/PKC to Ca2+ channels not identified","Functional selectivity via H1/Gq shown only in recombinant cells (Medium-confidence)"]},{"year":2016,"claim":"Refined the basal ganglia localization quantitatively, showing mGluR4 predominantly marks glutamatergic terminals onto indirect-pathway spines, providing the anatomical basis for antiparkinsonian action.","evidence":"Quantitative dual-label immuno-electron microscopy for mGluR4, vGluT1, and D1 receptor in mouse striatum","pmids":["26832920"],"confidence":"High","gaps":["Functional confirmation of pathway-selective release control not in this study"]},{"year":2019,"claim":"Established non-neuronal and tumor-suppressive roles, with GRM4 controlling myeloid IL23/IL12 balance and restraining osteosarcoma via CBX4/HIF-1α regulation.","evidence":"Grm4 gene-targeted mice with radiation-induced osteosarcoma and cytokine assays; 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mGluR4; cAMP accumulation assay; pharmacological characterization\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted receptor pharmacology in defined cell system, replicated across multiple labs subsequently\",\n      \"pmids\": [\"8463825\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"mGluR4 is palmitoylated via a thioester bond when expressed in BHK cells, as demonstrated by [3H]palmitic acid labeling and hydroxylamine cleavage; agonist stimulation with glutamate does not alter the level of palmitoylation. In contrast, mGluR1α is not palmitoylated.\",\n      \"method\": \"[3H]palmitic acid metabolic labeling; immunoprecipitation; hydroxylamine treatment; SDS-PAGE autoradiography in stably transfected BHK cells\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct biochemical demonstration of PTM with chemical validation (hydroxylamine cleavage), single lab but orthogonal controls\",\n      \"pmids\": [\"7891082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"mGluR4 knockout mice show impaired presynaptic short-term synaptic plasticity (paired-pulse facilitation and post-tetanic potentiation) at the parallel fiber→Purkinje cell synapse, and L-AP4 (EC50 = 2.5 µM) depresses synaptic responses in wild-type but not knockout mice, establishing mGluR4 as the presynaptic receptor mediating depression of excitatory transmission at this synapse. Long-term depression (LTD) is not impaired.\",\n      \"method\": \"Patch-clamp and extracellular field recordings from cerebellar slices in mGluR4 knockout vs. wild-type mice; pharmacological application of L-AP4\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with defined electrophysiological phenotype, replicated pharmacologically\",\n      \"pmids\": [\"8815915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The primary ligand-binding determinants of mGluR4 reside within the extracellular amino-terminal domain (first 548 amino acids). A soluble truncated ATD binds L-AP4 with similar rank-order pharmacology as the full-length receptor; N-linked glycosylation is not required for agonist binding.\",\n      \"method\": \"Truncated epitope-tagged mGluR4 ATD expressed and secreted from HEK293 cells; competition binding with [3H]L-AP4; deglycosylation experiment; gel electrophoresis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical reconstitution of binding domain, multiple orthogonal methods in one study\",\n      \"pmids\": [\"10187777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Site-directed mutagenesis identified Arg78, Ser159, and Thr182 in the mGluR4 ATD as critical residues for agonist binding; mutations to Ala severely impaired binding of [3H]L-AP4. Molecular modeling suggests Ser159 and Thr182 hydrogen-bond with the α-carboxyl and α-amino groups of agonists, while Arg78 forms an electrostatic interaction with the acidic side chain.\",\n      \"method\": \"Site-directed mutagenesis; [3H]L-AP4 competition binding; molecular modeling/docking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis with functional binding readout, multiple residues tested with controls, structural modeling as supporting tool\",\n      \"pmids\": [\"10559233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"mGluR4 is the predominant contributor to high-affinity [3H]L-AP4 binding in several brain regions including cerebellar cortex, nucleus basalis, thalamus, superior colliculus, substantia nigra, and hippocampal dentate gyrus, as demonstrated by near-complete loss of binding in mGluR4 knockout mice.\",\n      \"method\": \"Autoradiographic binding assay with [3H]L-AP4 in mGluR4 knockout vs. wild-type mouse brain sections\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO used to establish in vivo binding contribution, direct localization experiment\",\n      \"pmids\": [\"9930760\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"mGluR4 mediates neuroprotection against NMDA excitotoxicity: group III agonists (+)-PPG and L-AP4 protect cortical neurons in wild-type mice but are ineffective in mGluR4−/− neurons. mGluR4−/− neurons are more vulnerable to NMDA and show higher extracellular glutamate, indicating mGluR4 maintains glutamate homeostasis presynaptically.\",\n      \"method\": \"Cortical neuronal cultures from mGluR4 KO and WT mice; NMDA toxicity assay; microdialysis; intrastriatal NMDA infusion in vivo\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO combined with pharmacological rescue, in vitro and in vivo, multiple orthogonal readouts\",\n      \"pmids\": [\"10964947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"mGluR4 within the nucleus reticularis thalami (nRT) is critical for GABAergic modulation of thalamocortical synchronization: mGluR4−/− mice are markedly resistant to GABAA receptor antagonist-induced absence seizures, bilateral intra-nRT mGluR4 antagonist injection mimics this resistance in WT mice, and intra-nRT mGluR4 agonist exacerbates absence seizures.\",\n      \"method\": \"mGluR4 KO mice; stereotaxic intra-nRT pharmacological injections; EEG/behavioral seizure monitoring\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO plus site-specific pharmacology, epistatic localization of function to specific brain region\",\n      \"pmids\": [\"10934271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"mGluR4 protein is predominantly localized to presynaptic active zones in multiple brain regions including cerebellar cortex, basal ganglia, thalamus, and hippocampus. In the basal ganglia, mGluR4 is found on GABAergic terminals of striatal projection neurons (both direct and indirect pathways), functioning as a presynaptic heteroreceptor; in cerebellum and hippocampus it functions as an autoreceptor.\",\n      \"method\": \"Affinity-purified antibodies against mGluR4 C-terminal domain; immunohistochemistry; pre-embedding electron microscopy; validation in mGluR4 KO mice (no immunoreactivity)\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ultrastructural immunolocalization validated by KO negative control, multiple brain regions characterized\",\n      \"pmids\": [\"11906782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"(-)-PHCCC acts as a positive allosteric modulator (PAM) of mGluR4 by binding within the transmembrane domain, increasing agonist potency and maximum efficacy; chimeric receptor studies localized its binding site to the TM region. The compound shows no activity at mGluR2, -3, -5a, -6, -7b, -8a.\",\n      \"method\": \"Recombinant mGluR expression; cAMP assay; chimeric receptor mutagenesis; selectivity profiling across mGluR subtypes\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chimeric receptor approach localizing allosteric binding site combined with functional pharmacology, multiple methods\",\n      \"pmids\": [\"14573382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"GRK2 (but not GRK4) regulates mGluR4 signaling: GRK2 overexpression attenuates mGluR4-mediated ERK1/2 (MAPK) activation while slightly potentiating cAMP inhibition. A kinase-dead GRK2 mutant also inhibits MAPK signaling, indicating GRK2 acts by sequestering Gβγ subunits rather than by phosphorylating mGluR4. GRK2 co-immunoprecipitates with Gβγ in an agonist-dependent manner. Agonist-induced internalization of mGluR4 is abolished by dominant-negative dynamin but not affected by GRK2.\",\n      \"method\": \"Transient transfection of HEK293 cells; Western blot for phospho-ERK1/2; cAMP assay; co-immunoprecipitation; GFP-tagged receptor internalization imaging; pertussis toxin treatment\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus multiple orthogonal functional assays (cAMP, MAPK, internalization) with kinase-dead and dominant-negative mutants\",\n      \"pmids\": [\"15102938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Pharmacological activation of mGluR4 (via PHCCC) inhibits adenylyl cyclase and the PI3K pathway in medulloblastoma cells without affecting MAPK, Sonic Hedgehog, or Wnt pathways, and reduces DNA synthesis and cell proliferation; the antiproliferative effect is abolished by the PI3K inhibitor LY294002.\",\n      \"method\": \"mGluR4-expressing medulloblastoma cell lines (D283med, D341med, DAOY); cAMP assay; PI3K pathway analysis; DNA synthesis and proliferation assays; LY294002 pharmacological blockade; xenograft in vivo experiments\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined pathway placement (PI3K) with pharmacological rescue, in vitro and in vivo data, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"16899734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"mGluR4 activation with PHCCC protects the nigrostriatal pathway against MPTP toxicity in mice; PHCCC is neuroprotective in wild-type but not in mGluR4−/− mice, confirming target specificity. Unilateral infusion of PHCCC into the external globus pallidus is sufficient to protect the ipsilateral nigrostriatal pathway.\",\n      \"method\": \"mGluR4 KO vs. WT C57BL/6 mice; MPTP neurotoxin model; dopamine/metabolite measurements; TH/DAT immunostaining; GFAP immunostaining; stereotaxic drug infusion\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO validation of pharmacological effect, site-specific infusion identifying anatomical locus of action, multiple readouts\",\n      \"pmids\": [\"16822979\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"mGluR4 activation potentiates K2P2.1 (TREK-1) two-pore domain potassium channel activity via a PKA-dependent reduction in C-terminal phosphorylation; mutational analysis showed that dephosphorylation of S333 accounts for ~70% and S300 for ~30% of the K2P2.1 increase following mGluR4 activation. PKC, PKG, and protein phosphatases are not involved.\",\n      \"method\": \"Co-expression of mGluR4 and K2P2.1 in Xenopus oocytes or HEK cells; pharmacological kinase/phosphatase inhibitors; site-directed mutagenesis of K2P2.1 C-terminal phosphorylation sites; electrophysiological recordings\",\n      \"journal\": \"Molecular and cellular neurosciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of functional phosphorylation sites combined with pharmacological pathway dissection and electrophysiology\",\n      \"pmids\": [\"17916432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"mGluR4 PAM PHCCC enhances absence seizures in WAG/Rij rats and PTZ-treated mice; mGluR4 expression is elevated in the reticular thalamic nucleus (RTN) of symptomatic WAG/Rij rats. Electron microscopy and in situ hybridization indicate mGluR4 in the RTN is localized on excitatory cortical afferents. PHCCC is inactive in mGluR4 KO mice.\",\n      \"method\": \"Immunoblotting; immunohistochemistry; electron microscopy; in situ hybridization; EEG monitoring in mGluR4 KO and WAG/Rij rats; systemic PHCCC administration\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ultrastructural localization combined with KO validation and in vivo EEG readout, multiple orthogonal methods\",\n      \"pmids\": [\"18022649\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Depression of excitatory synaptic transmission at parallel fiber–Purkinje cell synapses in the rodent cerebellar cortex by group III mGluRs is mediated exclusively by mGluR4 autoreceptors; neither mGluR7 nor mGluR8 contributes, as demonstrated using selective agonists, the mGluR4 PAM PHCCC, and mGluR4 KO mice.\",\n      \"method\": \"Whole-cell patch-clamp; presynaptic calcium influx measurements; selective agonists (ACPD, LSP4-2022, DCPG); PHCCC; mGluR4 KO cerebellar slices\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO combined with selective pharmacology and electrophysiology, replicated across subtypes\",\n      \"pmids\": [\"18266929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"mGluR4 and mGluR8 both contribute to L-AP4-induced presynaptic inhibition of synaptic transmission at the lateral olfactory tract–piriform cortex synapse; the inhibitory actions of L-AP4 and selective mGluR4 agonist Z-cyclopentyl-AP4 are potentiated by the mGluR4 PAM PHCCC.\",\n      \"method\": \"Whole-cell patch-clamp recordings from piriform cortex pyramidal cells in brain slices; selective agonists (DCPG for mGluR8; Z-cyclopentyl-AP4 for mGluR4); PHCCC potentiation\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — pharmacological dissection in brain slices, single lab, no KO validation in this paper\",\n      \"pmids\": [\"18625254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Native presynaptic mGluR4 in rat cerebellum interacts with exocytosis proteins including Munc18-1, synapsins, and syntaxin; mGluR4 is retained on Munc18-1-conjugated Sepharose, and Munc18-1 co-localizes with mGluR4 at the plasma membrane. Affinity chromatography with peptides from mGluR4 cytoplasmic domains confirmed interactions with multiple exocytosis proteins.\",\n      \"method\": \"Co-immunoprecipitation from cerebellar extracts (mass spectrometry identification of 183 partners); affinity chromatography with recombinant Munc18-1 and mGluR4 cytoplasmic domain peptides; immunohistochemistry co-localization in HEK293 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, affinity chromatography, co-localization) identifying physiologically relevant interaction partners in native tissue\",\n      \"pmids\": [\"22528491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"mGluR4 and GABAA receptors co-localize on cerebellar parallel fiber axon terminals and co-immunoprecipitate from cerebellar membranes. Coincident activation of both receptors increases glutamate release above that of GABAA activation alone. In mGluR4 KO mice, GABAA receptor subunit expression (α1, α6, β2) and [35S]TBPS binding are reduced in the cerebellum.\",\n      \"method\": \"Immunocytochemistry; co-immunoprecipitation from cerebellar membranes; [3H]glutamate release from cerebellar synaptosomes; [35S]TBPS binding; mGluR4 KO mice\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, functional release assay, and KO validation with multiple orthogonal methods\",\n      \"pmids\": [\"22145864\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"mGluR4 inhibition of presynaptic Ca2+ influx at parallel fiber–Purkinje cell synapses does not selectively target a specific voltage-gated Ca2+ channel subtype but modulates all classes present; this inhibition does not involve GIRK channels, TEA-sensitive K+ channels, K2P channels, pertussis toxin-sensitive G proteins, adenylyl cyclase, PKA, MAPK, or PI3K. Instead, it employs a signaling pathway involving phospholipase C (PLC) activation and ultimately protein kinase C.\",\n      \"method\": \"Whole-cell patch-clamp recordings in rat cerebellar slices; presynaptic Ca2+ transient measurements; pharmacological dissection with selective channel/kinase/G-protein inhibitors; pertussis toxin treatment\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic pharmacological dissection identifying novel PLC/PKC signaling pathway, multiple negative controls to exclude other pathways\",\n      \"pmids\": [\"22570379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Co-activation of Gq-coupled H1 histamine receptors induces substantial calcium mobilization downstream of mGluR4 activation in mGluR4-expressing cells, biasing signaling away from Gi/o-mediated cAMP inhibition toward calcium-dependent pathways. This functional selectivity is further enhanced by mGluR4 PAMs.\",\n      \"method\": \"Calcium mobilization assay in mGluR4-expressing cells; cAMP inhibition assay; pharmacological application of histamine and mGluR4 PAMs; absence of chimeric G proteins confirmed\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional assay in recombinant system demonstrating biased signaling, single lab, mechanistic conclusion supported by two orthogonal signaling readouts\",\n      \"pmids\": [\"22426233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Activation of mGluR4 in rat neural progenitor cells promotes proliferation via ERK1/2 signaling and upregulation of cyclin D1; mGluR4 siRNA decreases proliferation and p-ERK1/2 levels, and ERK1/2 inhibitor U0126 abolishes the VU0155041-induced proliferative effect. mGluR4 activation also decreases p38 phosphorylation.\",\n      \"method\": \"Rat embryonic NPC culture; mGluR4 siRNA knockdown; VU0155041 agonist treatment; Western blot for p-ERK1/2, p-p38, cyclin D1; neurosphere diameter measurement; U0126 ERK inhibitor epistasis\",\n      \"journal\": \"Cellular and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — KD/KO with defined molecular pathway (ERK/cyclin D1), pharmacological epistasis, single lab\",\n      \"pmids\": [\"23374450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"mGluR4 is endogenously activated during simulated cerebellar ischemia (excitotoxic conditions with elevated extracellular glutamate) in rodent cerebellar cortex brain slices; the photoswitchable NAM OptoGluNAM4.1 reversibly inhibits mGluR4 activity in a light-dependent manner, providing direct evidence for endogenous receptor activation under these conditions.\",\n      \"method\": \"OptoGluNAM4.1 photopharmacology in rodent cerebellar slices; parallel fiber–Purkinje cell synaptic recordings; simulated ischemia protocol\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — novel photopharmacological tool demonstrating endogenous receptor activation, single lab, single method\",\n      \"pmids\": [\"30542267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"mGluR4 presynaptically modulates corticostriatal transmission; immunoelectron microscopy shows >80% mGluR4-immunoreactive structures are unmyelinated axons/terminals in mouse striatum, ~50% of putative glutamatergic terminals (vGluT1+) express mGluR4, and ~70% of mGluR4-positive glutamatergic terminals target D1-receptor-negative (putative indirect pathway) spines, providing anatomical basis for antiparkinsonian actions.\",\n      \"method\": \"Immunoelectron microscopy; dual immunolabeling for mGluR4, vGluT1, and D1 receptor in mouse striatum; quantitative ultrastructural analysis\",\n      \"journal\": \"Brain structure & function\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative ultrastructural immunolocalization with multiple markers, direct anatomical determination of synaptic targeting\",\n      \"pmids\": [\"26832920\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GRM4 is expressed in myeloid cells and selectively regulates IL23 (and the related cytokine IL12) expression; Grm4 gene-targeted mice show accelerated radiation-induced tumor development. Osteosarcoma-conditioned media induce myeloid cell Il23 expression in a GRM4-dependent fashion while suppressing Il12. GRM4 agonists suppressed osteosarcoma growth in mice.\",\n      \"method\": \"Grm4 gene-targeted mouse model; radiation-induced osteosarcoma; cytokine expression assays; osteosarcoma-conditioned media experiments; in vivo GRM4 agonist treatment\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined molecular mechanism (IL23/IL12 regulation), multiple in vitro and in vivo experiments, single lab\",\n      \"pmids\": [\"31527131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GRM4 overexpression in osteosarcoma cells inhibits proliferation, migration, and invasion by interacting with CBX4 and restricting CBX4 nuclear localization, thereby reducing HIF-1α transcriptional activity.\",\n      \"method\": \"GRM4 overexpression in osteosarcoma cell lines; co-immunoprecipitation of GRM4 and CBX4; nuclear fractionation; colony formation, transwell migration/invasion assays; HIF-1α reporter assay\",\n      \"journal\": \"Bioscience, biotechnology, and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP and functional assays identifying binding partner and downstream pathway, single lab\",\n      \"pmids\": [\"31581881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"cryo-EM structures of human mGlu4 bound to heterotrimeric Gi protein reveal a G-protein-binding site formed by three intracellular loops and helices III and IV; an asymmetric dimer interface of the transmembrane domain is critical for receptor activation and asymmetric signal transduction, with only one subunit of the homodimer coupling to G protein.\",\n      \"method\": \"Cryo-electron microscopy structure determination of mGlu4-Gi complex; functional validation of asymmetric dimerization\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure at high resolution with functional validation, published in high-impact journal\",\n      \"pmids\": [\"34135510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Twelve cryo-EM structures of the mGlu2-mGlu4 heterodimer in inactive, intermediate, and active conformational states reveal that Venus flytrap domains undergo sequential conformational change upon activation, while transmembrane domains rearrange from symmetric inactive to asymmetric active dimer. A novel binding site for mGlu4 PAMs was identified at the asymmetric dimer interface of the mGlu2-mGlu4 heterodimer and mGlu4 homodimer.\",\n      \"method\": \"Cryo-electron microscopy of mGlu2-mGlu4 heterodimer in multiple states; functional data validating asymmetric signal transduction and PAM binding site\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structures in multiple conformational states with functional validation, novel allosteric site identified\",\n      \"pmids\": [\"37286794\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GRM4 (mGluR4) is a presynaptically localized Group III metabotropic glutamate receptor that couples asymmetrically through a Gi/o G-protein binding site (formed by intracellular loops and helices III/IV) to inhibit adenylyl cyclase/cAMP, activate ERK1/2 via Gβγ, and modulate presynaptic Ca2+ influx through a PLC/PKC pathway; it is palmitoylated via a thioester bond, regulated by GRK2-mediated Gβγ sequestration, interacts with exocytosis proteins (Munc18-1, synapsins, syntaxin) and GABAA receptor subunits at the presynaptic active zone, and acts as an autoreceptor in cerebellum and heteroreceptor in basal ganglia to suppress glutamate release, with its ligand-binding pocket defined by Arg78, Ser159, and Thr182 in the extracellular amino-terminal domain and a transmembrane allosteric site accessible to PAMs.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GRM4 (mGluR4) is a presynaptic Group III metabotropic glutamate receptor that suppresses neurotransmitter release by coupling, via agonists such as L-AP4, to Gi/o proteins to inhibit forskolin-stimulated cAMP accumulation [#0]. Its agonist-binding pocket lies within the extracellular amino-terminal domain, where a soluble truncated ATD recapitulates ligand pharmacology and the residues Arg78, Ser159, and Thr182 form the critical contacts [#3, #4]. Cryo-EM of mGlu4-Gi and of mGlu2-mGlu4 heterodimers established an asymmetric activation mechanism: only one protomer couples to G protein, the transmembrane domains rearrange from symmetric inactive to asymmetric active states, and a positive-allosteric-modulator (PAM) site sits within the transmembrane domain and at the asymmetric dimer interface [#9, #26, #27]. The receptor is targeted to presynaptic active zones across cerebellum, basal ganglia, thalamus, and hippocampus, acting as an autoreceptor in cerebellum and as a heteroreceptor on GABAergic and glutamatergic terminals in the basal ganglia [#8, #23]. Genetic and pharmacological dissection at the parallel fiber–Purkinje cell synapse defines mGluR4 as the autoreceptor mediating depression of excitatory transmission and short-term plasticity, acting by inhibiting presynaptic Ca2+ influx through a PLC/PKC pathway that is independent of cAMP, PKA, MAPK, PI3K, and Gi/o-coupled K+ channels at this synapse [#2, #15, #19]. mGluR4 signaling is shaped by additional effectors and modulators—GRK2 attenuates mGluR4-driven ERK1/2 activation by sequestering Gβγ rather than by phosphorylating the receptor [#10], the receptor potentiates K2P2.1 (TREK-1) channels via PKA-dependent dephosphorylation [#13], and it physically associates with the exocytotic machinery (Munc18-1, synapsins, syntaxin) and with GABAA receptors at parallel fiber terminals [#17, #18]. Functionally, mGluR4 maintains presynaptic glutamate homeostasis and confers neuroprotection against NMDA and MPTP toxicity, modulates thalamocortical synchronization underlying absence seizures, and outside the nervous system regulates myeloid IL23/IL12 expression and constrains osteosarcoma growth [#6, #7, #12, #24]. The receptor is palmitoylated through a thioester bond independent of agonist stimulation [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established the core transduction logic of mGluR4 by showing it is a Gi/o-coupled receptor that lowers cAMP, defining it as an inhibitory glutamate sensor distinct from other mGluR subtypes.\",\n      \"evidence\": \"Stable CHO expression of cloned rat mGluR4 with cAMP accumulation assay and agonist pharmacology\",\n      \"pmids\": [\"8463825\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not localize the receptor or define its native synaptic role\", \"G-protein-binding interface not mapped\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Identified palmitoylation as a covalent post-translational modification of mGluR4, distinguishing it biochemically from mGluR1α.\",\n      \"evidence\": \"[3H]palmitate metabolic labeling with hydroxylamine cleavage in BHK cells\",\n      \"pmids\": [\"7891082\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Modified cysteine residue(s) not identified\", \"Functional consequence for trafficking or signaling untested\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstrated through knockout that mGluR4 is the presynaptic receptor mediating depression of excitatory transmission and short-term plasticity at the parallel fiber–Purkinje cell synapse.\",\n      \"evidence\": \"Patch-clamp and field recordings in mGluR4 KO vs WT cerebellar slices with L-AP4 application\",\n      \"pmids\": [\"8815915\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream presynaptic effector pathway not defined here\", \"LTD shown to be unaffected, leaving its receptor unidentified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Localized the ligand-binding function to the extracellular amino-terminal domain and identified the specific residues (Arg78, Ser159, Thr182) contacting agonists.\",\n      \"evidence\": \"Soluble truncated ATD binding, deglycosylation, site-directed mutagenesis with [3H]L-AP4 competition, and molecular modeling\",\n      \"pmids\": [\"10187777\", \"10559233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the full activation pathway from ATD to G protein\", \"Allosteric/transmembrane sites not addressed\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Used the knockout to establish mGluR4 as the dominant high-affinity L-AP4 binding site across multiple brain regions, anchoring its anatomical distribution.\",\n      \"evidence\": \"[3H]L-AP4 autoradiography in mGluR4 KO vs WT brain sections\",\n      \"pmids\": [\"9930760\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Subcellular (presynaptic) localization not resolved at this stage\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined physiological roles for mGluR4 in glutamate homeostasis/neuroprotection and in thalamocortical control of absence seizures, linking receptor activity to circuit-level outcomes.\",\n      \"evidence\": \"mGluR4 KO neurons/mice with NMDA toxicity, microdialysis, and site-specific intra-nRT pharmacology with EEG\",\n      \"pmids\": [\"10964947\", \"10934271\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular signaling steps linking receptor to protection/seizure modulation not dissected\", \"Cell-type-specific contributions only partially localized\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Resolved the subcellular localization, showing mGluR4 resides at presynaptic active zones and functions as an autoreceptor in cerebellum/hippocampus and a heteroreceptor on GABAergic terminals in basal ganglia.\",\n      \"evidence\": \"Affinity-purified antibodies, pre-embedding electron microscopy, and KO negative controls across brain regions\",\n      \"pmids\": [\"11906782\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish presynaptic effector mechanism\", \"Terminal-type specificity in striatum refined only later\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Established a druggable transmembrane allosteric site by showing (-)-PHCCC is a subtype-selective positive allosteric modulator of mGluR4.\",\n      \"evidence\": \"Chimeric receptor mutagenesis, cAMP functional assay, and selectivity profiling across mGluR subtypes\",\n      \"pmids\": [\"14573382\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-level PAM binding pose not resolved until later cryo-EM\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identified GRK2 as a regulator of mGluR4 signaling acting through Gβγ sequestration rather than receptor phosphorylation, and separated internalization (dynamin-dependent) from desensitization.\",\n      \"evidence\": \"HEK293 transfection, phospho-ERK and cAMP assays, reciprocal Co-IP, kinase-dead/dominant-negative mutants, and receptor imaging\",\n      \"pmids\": [\"15102938\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of GRK2 regulation untested\", \"Mechanism couples to ERK in recombinant cells; native pathway not confirmed here\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Extended mGluR4 signaling to growth control and neuroprotection in vivo, placing it upstream of PI3K in tumor cells and confirming target-specific nigrostriatal protection.\",\n      \"evidence\": \"PHCCC in medulloblastoma lines with PI3K inhibitor epistasis and xenografts; MPTP model with mGluR4 KO validation and site-specific pallidal infusion\",\n      \"pmids\": [\"16899734\", \"16822979\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a Gi/o receptor engages PI3K mechanistically not detailed\", \"Anatomical locus identified but circuit mechanism inferred\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Revealed a PKA-dependent effector arm in which mGluR4 potentiates K2P2.1 (TREK-1) channels via dephosphorylation of specific C-terminal serines, and clarified mGluR4 PAM effects on seizure circuits.\",\n      \"evidence\": \"mGluR4/K2P2.1 co-expression with kinase/phosphatase inhibitors and channel mutagenesis; immuno-EM, in situ hybridization, and EEG in WAG/Rij rats and KO mice\",\n      \"pmids\": [\"17916432\", \"18022649\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether K2P2.1 modulation operates at native presynaptic terminals not shown\", \"Pro- vs anti-epileptic outcomes depend on circuit context not fully resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Pharmacogenetically isolated mGluR4 as the sole Group III autoreceptor mediating cerebellar presynaptic depression and showed broader involvement at olfactory cortical synapses.\",\n      \"evidence\": \"Whole-cell patch-clamp with selective agonists, PHCCC, and KO slices (cerebellum); slice pharmacology at lateral olfactory tract–piriform synapse\",\n      \"pmids\": [\"18266929\", \"18625254\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Olfactory cortex contribution lacks KO validation (Medium-confidence)\", \"Effector pathway not yet defined in this work\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the presynaptic effector mechanism and the receptor's interaction network: Ca2+-influx inhibition proceeds via PLC/PKC, and mGluR4 physically associates with exocytotic proteins and GABAA receptors at active zones.\",\n      \"evidence\": \"Pharmacological dissection of presynaptic Ca2+ transients; Co-IP/affinity chromatography for Munc18-1/synapsins/syntaxin; reciprocal Co-IP and synaptosomal release assays for GABAA receptors; biased Gq co-activation assays\",\n      \"pmids\": [\"22570379\", \"22528491\", \"22145864\", \"22426233\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct effector linking PLC/PKC to Ca2+ channels not identified\", \"Functional selectivity via H1/Gq shown only in recombinant cells (Medium-confidence)\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Refined the basal ganglia localization quantitatively, showing mGluR4 predominantly marks glutamatergic terminals onto indirect-pathway spines, providing the anatomical basis for antiparkinsonian action.\",\n      \"evidence\": \"Quantitative dual-label immuno-electron microscopy for mGluR4, vGluT1, and D1 receptor in mouse striatum\",\n      \"pmids\": [\"26832920\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional confirmation of pathway-selective release control not in this study\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established non-neuronal and tumor-suppressive roles, with GRM4 controlling myeloid IL23/IL12 balance and restraining osteosarcoma via CBX4/HIF-1α regulation.\",\n      \"evidence\": \"Grm4 gene-targeted mice with radiation-induced osteosarcoma and cytokine assays; GRM4 overexpression with CBX4 Co-IP, nuclear fractionation, and HIF-1α reporter\",\n      \"pmids\": [\"31527131\", \"31581881\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a GPCR controls cytokine transcription mechanistically not resolved\", \"CBX4 interaction shown by single-lab Co-IP (Medium-confidence)\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Provided the structural basis for asymmetric activation, showing only one homodimer protomer couples Gi via a defined intracellular interface.\",\n      \"evidence\": \"Cryo-EM of human mGlu4-Gi complex with functional validation of asymmetric dimerization\",\n      \"pmids\": [\"34135510\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational trajectory from ligand binding to coupling not captured in a single state\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Captured the activation trajectory across multiple conformational states and localized the mGlu4 PAM site at the asymmetric dimer interface, unifying ligand binding, dimer rearrangement, and allosteric modulation.\",\n      \"evidence\": \"Twelve cryo-EM structures of mGlu2-mGlu4 heterodimer in inactive/intermediate/active states with functional validation\",\n      \"pmids\": [\"37286794\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequences of mGlu2-mGlu4 heterodimerization in native circuits not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How presynaptic PLC/PKC-dependent Ca2+-channel inhibition, the exocytotic-protein interactome, and the non-neuronal IL23/CBX4 functions are mechanistically connected to the structurally defined asymmetric activation remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between PLC/PKC and presynaptic Ca2+ channels unidentified\", \"Mechanism by which mGluR4 controls myeloid cytokine transcription unknown\", \"Physiological role of mGlu2-mGlu4 heterodimers in vivo undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 26]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [10, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [8, 17, 23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 10, 19]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [2, 8, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"Munc18-1\", \"syntaxin\", \"GRK2\", \"GABAA receptor\", \"K2P2.1\", \"CBX4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}