{"gene":"KCTD16","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2019,"finding":"Crystal structure of the KCTD16 oligomerization (BTB) domain reveals it forms an open pentamer; a single GABAB2 C-terminal peptide binds to the interior of this open pentamer. Mutation of specific interface residues disrupted both biochemical association and functional modulation of GABAB receptors and GIRK channels, establishing the structural basis for KCTD16's interaction with and modulation of the GABAB receptor.","method":"X-ray crystallography, site-directed mutagenesis, co-immunoprecipitation, electrophysiology (GIRK current recordings)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure combined with mutagenesis validating the interface and functional electrophysiology in a single rigorous study","pmids":["30971491"],"is_preprint":false},{"year":2016,"finding":"KCTD16 hetero-oligomerizes with KCTD12 through self-interacting T1 and H1 homology domains. In the hippocampus, approximately two-thirds of KCTD16 associates with KCTD12. KCTD12/KCTD16 hetero-oligomers associate with both the GABAB receptor and the G-protein, imparting unique kinetic properties on Kir3 (GIRK) currents distinct from either homo-oligomer alone, and prolong slow IPSCs in hippocampal pyramidal neurons.","method":"Co-immunoprecipitation from mouse hippocampus, BRET in live cells, electrophysiology in heterologous cells and KCTD knockout mouse neurons","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP from native tissue, live-cell BRET, and electrophysiology in knockout mice provide multiple orthogonal methods with rigorous controls","pmids":["28003345"],"is_preprint":false},{"year":2017,"finding":"The BTB domain of KCTD16 forms an open pentamer (confirmed by SAXS and crystal structure), and unlike other KCTD family members tested (KCTD10, KCTD13, KCTD17), KCTD16 did not bind Cullin3 (Cul3) in solution, indicating it does not function as a canonical Cul3-dependent E3 ubiquitin ligase subunit.","method":"X-ray crystallography, small-angle X-ray scattering (SAXS), size-exclusion chromatography, Cul3 binding assay","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure confirmed by SAXS, direct Cul3 binding assay; single lab but two orthogonal structural/biochemical methods","pmids":["28963344"],"is_preprint":false},{"year":2014,"finding":"KCTD16 slightly but significantly increases GABA affinity at recombinant GABAB receptors, as measured by G-protein activation assays. KCTD16, as an auxiliary subunit, differentially regulates G-protein signaling of the GABAB receptor.","method":"[35S]GTPγS binding assay, BRET between G-protein subunits, Kir3 current recordings in transfected CHO cells and hippocampal neurons","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays in a single lab, consistent results across methods","pmids":["25196734"],"is_preprint":false},{"year":2019,"finding":"A peptide-based inhibitor of the KCTD/GABAB receptor protein-protein interaction was developed using the GABAB receptor-binding epitope of KCTD; X-ray crystallography and SEC-MALS revealed that this inhibitor induces oligomerization of KCTD16 into a distinct hexameric structure, distinct from its normal open pentamer.","method":"μSPOT peptide array, X-ray crystallography, SEC-MALS, co-immunoprecipitation from mouse brain lysates","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — crystal structure and SEC-MALS in single lab; novel finding about inhibitor-induced hexamerization","pmids":["31509708"],"is_preprint":false},{"year":2017,"finding":"In knockout mouse experiments, the auxiliary subunit KCTD16 influences both thalamic spindle oscillation strength and frequency, consistent with KCTD16 regulating network activity through both GABAB(1a,2) and GABAB(1b,2) receptors.","method":"Electrical and optogenetic activation of thalamic spindles in acute slices from KCTD knockout mice, pharmacological experiments","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined electrophysiological phenotype; single lab, one primary method","pmids":["29106983"],"is_preprint":false},{"year":2016,"finding":"Kctd16 knockout mice exhibit impaired extinction of auditory fear memory and increased contextual fear memory compared to wild-type littermates, establishing KCTD16 as a regulator of fear memory processing through its role as an auxiliary GABAB receptor subunit.","method":"Auditory and contextual fear conditioning/extinction in Kctd16-/- and Kctd16+/- mice","journal":"Behavioural brain research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with specific behavioral phenotype; single lab, single behavioral paradigm","pmids":["27717812"],"is_preprint":false},{"year":2024,"finding":"KCTD16, as an auxiliary GABAB receptor subunit, anchors HCN channels (containing HCN2/HCN3 subunits) to GABAB receptors in dopamine neurons of the VTA. This interaction facilitates HCN channel activation during IPSPs, counteracting the late phase of GABAB receptor-mediated inhibition. KCTD16 knockout mice show prolonged inhibition of VTA dopamine neuron firing and increased anxiety-like behavior under stress.","method":"Co-immunoprecipitation (KCTD16-HCN interaction), optogenetic inhibition of VTA neurons, patch-clamp electrophysiology, CRISPR/Cas9 conditional knockout in VTA neurons, behavioral anxiety assays, pharmacological HCN channel blockade","journal":"Neurobiology of disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction demonstrated, multiple independent approaches (KO mouse, CRISPR, pharmacology, electrophysiology) converging on the same mechanism","pmids":["39914775"],"is_preprint":false},{"year":2024,"finding":"The vesicular protein synaptotagmin-11 (Syt11) binds directly to KCTD16 (the auxiliary GABAB receptor subunit) and to Cav2.2 channels, recruiting GABAB receptors and Cav2.2 channels to post-Golgi vesicles to facilitate assembly of GBR/Cav2.2 signaling complexes, and stabilizes them at the neuronal plasma membrane.","method":"Co-immunoprecipitation, Syt11 knockout mouse analysis (presynaptic GBR and Cav2.2 levels, neurotransmitter release, presynaptic inhibition)","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP identifying binding and KO mouse with defined presynaptic phenotype; single lab","pmids":["38698221"],"is_preprint":false},{"year":2016,"finding":"KCTD16 was identified as an interactor of the extracellular domain of amyloid precursor protein (APP) by yeast two-hybrid screening, and the interaction was confirmed in a mammalian cell system.","method":"Yeast two-hybrid screening, mammalian co-immunoprecipitation confirmation","journal":"Neuroscience bulletin","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP confirmation of yeast two-hybrid hit, single lab, no functional follow-up on KCTD16 specifically","pmids":["26960425"],"is_preprint":false},{"year":2020,"finding":"A dual enhancer-silencer element (DES-K16) was identified within an intron of the Kctd16 gene in mouse spermatocytes; deletion of DES-K16 in GC-2spd(ts) cells increased Kctd16 expression, suggesting the element functions as a cis-regulatory silencer of Kctd16 in spermatocytes.","method":"Chromatin epigenetic profiling (H3K4me1, H3K27ac, H3K27me3), in vitro reporter gene assay, CRISPR/Cas9 deletion in GC-2spd(ts) cells, RT-PCR","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assay and deletion experiment with gene expression readout; single lab, two orthogonal methods","pmids":["33121685"],"is_preprint":false},{"year":2026,"finding":"KCTD16 is expressed in dorsal horn and DRG neurons and modulates GABAB receptor-mediated presynaptic inhibition of nociceptive transmission. KCTD16 knockout mice show increased mechanical thresholds and significantly reduced baclofen-mediated anti-allodynic efficacy. Patch-clamp recordings showed that in KCTD16-/- dorsal horn neurons, baclofen-induced suppression of excitatory transmission was markedly attenuated following inflammation.","method":"Immunohistochemistry, KCTD16 knockout mice, behavioral assays (von Frey, thermal sensitivity, carrageenan inflammation model), whole-cell patch-clamp recordings (mEPSCs, mIPSCs), calcium imaging in DRG neurons","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined electrophysiological and behavioral phenotypes; single lab, multiple orthogonal methods","pmids":["41592618"],"is_preprint":false}],"current_model":"KCTD16 is an auxiliary subunit of metabotropic GABAB receptors that forms an open pentamer via its BTB domain; this pentamer binds the GABAB2 C-terminal tail at a defined interface to modulate G-protein (Kir3/GIRK channel) signaling kinetics, slow IPSC duration, fear memory extinction, thalamic oscillations, and nociceptive transmission; it also hetero-oligomerizes with KCTD12 to generate unique receptor subtypes, anchors HCN channels to GABAB receptors at VTA synapses to limit IPSP duration and anxiety, and is scaffolded to Cav2.2-containing presynaptic complexes via synaptotagmin-11, while uniquely lacking the ability to bind Cullin3 and thus not functioning as a canonical E3 ubiquitin ligase subunit."},"narrative":{"mechanistic_narrative":"KCTD16 is an auxiliary subunit of metabotropic GABAB receptors that shapes the kinetics, network consequences, and behavioral outputs of GABAB signaling in the nervous system [PMID:30971491, PMID:25196734]. Its BTB/oligomerization domain assembles into an open pentamer whose interior accommodates a single GABAB2 C-terminal peptide; disruption of this interface abolishes both biochemical association and functional modulation of GABAB receptors and GIRK (Kir3) currents, defining the structural basis for its action [PMID:30971491]. As an auxiliary subunit it increases GABA affinity at the receptor and differentially tunes G-protein activation [PMID:25196734], and it can hetero-oligomerize with KCTD12 through self-interacting T1 and H1 domains to generate receptor populations with kinetic properties distinct from either homo-oligomer, prolonging slow IPSCs in hippocampal neurons [PMID:28003345]. Beyond gating G-protein output, KCTD16 serves as a molecular scaffold: it anchors HCN2/HCN3-containing channels to GABAB receptors in VTA dopamine neurons to limit the late phase of GABAB-mediated inhibition [PMID:39914775], and it is recruited together with Cav2.2 channels into presynaptic GABAB signaling complexes via direct binding to the vesicular protein synaptotagmin-11 [PMID:38698221]. Distinct from other KCTD proteins, KCTD16 does not bind Cullin3 and therefore does not function as a canonical Cul3-dependent E3 ubiquitin ligase substrate adaptor [PMID:28963344]. Through these activities KCTD16 regulates thalamic spindle oscillations [PMID:29106983], fear memory extinction and contextual fear [PMID:27717812], stress-related anxiety [PMID:39914775], and GABAB-dependent presynaptic inhibition of nociceptive transmission in the spinal dorsal horn [PMID:41592618].","teleology":[{"year":2014,"claim":"Established that KCTD16 is not merely a binding partner but an auxiliary subunit that functionally tunes GABAB receptor signaling, by showing it raises GABA affinity and shapes G-protein activation.","evidence":"[35S]GTPγS binding, inter-G-protein BRET, and Kir3 current recordings in CHO cells and hippocampal neurons","pmids":["25196734"],"confidence":"Medium","gaps":["Quantitative magnitude of affinity change is small","Structural basis of the interaction was not resolved here","Did not address oligomeric state or hetero-oligomerization"]},{"year":2016,"claim":"Resolved whether KCTD16 acts alone or combinatorially by demonstrating it hetero-oligomerizes with KCTD12 to confer unique Kir3 kinetics, explaining receptor subtype diversity in native tissue.","evidence":"Reciprocal Co-IP from mouse hippocampus, live-cell BRET, and electrophysiology in KCTD knockout neurons","pmids":["28003345"],"confidence":"High","gaps":["Stoichiometry of mixed oligomers in vivo not defined","Functional consequences in non-hippocampal circuits not tested"]},{"year":2016,"claim":"Connected KCTD16 to a behavioral phenotype, establishing it as a regulator of fear memory processing through its GABAB auxiliary role.","evidence":"Auditory and contextual fear conditioning/extinction in Kctd16 knockout and heterozygous mice","pmids":["27717812"],"confidence":"Medium","gaps":["Circuit and synaptic locus mediating the behavior not pinpointed","Single behavioral paradigm","Molecular mechanism linking KO to extinction deficit not dissected"]},{"year":2017,"claim":"Distinguished KCTD16 from canonical KCTD E3-ligase adaptors by showing its BTB domain forms an open pentamer yet, unlike KCTD10/13/17, fails to bind Cullin3.","evidence":"X-ray crystallography, SAXS, size-exclusion chromatography, and direct Cul3 binding assay","pmids":["28963344"],"confidence":"High","gaps":["Why KCTD16 cannot engage Cul3 at the residue level not fully mapped","Did not test all family members"]},{"year":2017,"claim":"Extended KCTD16 function to network-level activity by showing it shapes thalamic spindle oscillation strength and frequency through GABAB receptors.","evidence":"Electrical and optogenetic activation of thalamic spindles in slices from KCTD knockout mice with pharmacology","pmids":["29106983"],"confidence":"Medium","gaps":["Cell-type-specific contribution within thalamic circuitry not resolved","Single primary method"]},{"year":2019,"claim":"Provided the atomic-level mechanism for KCTD16's action by solving the open-pentamer structure bound to a single GABAB2 C-terminal peptide and validating the interface functionally.","evidence":"X-ray crystallography, interface mutagenesis, Co-IP, and GIRK current recordings","pmids":["30971491"],"confidence":"High","gaps":["Structure of full-length KCTD16 with intact GABAB receptor not determined","Dynamics of pentamer–G-protein coupling not captured"]},{"year":2019,"claim":"Demonstrated the KCTD16/GABAB interface is druggable and that ligand binding can remodel KCTD16 oligomerization, by developing a peptide inhibitor that drives hexamer formation.","evidence":"μSPOT peptide array, X-ray crystallography, SEC-MALS, and Co-IP from mouse brain lysates","pmids":["31509708"],"confidence":"Medium","gaps":["In vivo efficacy of the inhibitor not shown","Functional consequence of hexamerization on signaling not established"]},{"year":2024,"claim":"Revealed a scaffolding function beyond G-protein gating, showing KCTD16 anchors HCN2/HCN3 channels to GABAB receptors in VTA dopamine neurons to limit inhibitory duration and constrain stress-induced anxiety.","evidence":"Reciprocal Co-IP, optogenetics, patch-clamp, CRISPR conditional KO in VTA, pharmacology, and anxiety assays","pmids":["39914775"],"confidence":"High","gaps":["Direct vs. indirect nature of KCTD16–HCN contact not structurally resolved","Generality across other HCN-expressing circuits untested"]},{"year":2024,"claim":"Identified a trafficking/assembly route for presynaptic GABAB signaling, showing synaptotagmin-11 binds KCTD16 and Cav2.2 to recruit and stabilize GBR/Cav2.2 complexes at the membrane.","evidence":"Co-IP and Syt11 knockout mouse analysis of presynaptic GBR/Cav2.2 levels, neurotransmitter release, and presynaptic inhibition","pmids":["38698221"],"confidence":"Medium","gaps":["KCTD16-specific requirement (vs. other auxiliary subunits) not isolated","Single lab"]},{"year":2026,"claim":"Placed KCTD16 in sensory circuits by demonstrating it is required for GABAB-mediated presynaptic inhibition of nociceptive transmission and for full baclofen anti-allodynic efficacy.","evidence":"Immunohistochemistry, KCTD16 KO mice, von Frey/thermal/carrageenan behavioral assays, patch-clamp, and DRG calcium imaging","pmids":["41592618"],"confidence":"Medium","gaps":["Whether the dorsal horn role uses the same hetero-oligomer/scaffold mechanisms as central circuits not established","Single lab"]},{"year":2020,"claim":"Characterized cis-regulatory control of Kctd16 expression by identifying a dual enhancer-silencer intronic element that represses the gene in spermatocytes.","evidence":"Epigenetic profiling, reporter assays, and CRISPR deletion in GC-2spd(ts) cells with RT-PCR","pmids":["33121685"],"confidence":"Medium","gaps":["Physiological function of KCTD16 in spermatocytes not defined","Trans-acting factors binding the element not identified"]},{"year":null,"claim":"How KCTD16's distinct functional modes — G-protein kinetic tuning, KCTD12 hetero-oligomerization, HCN anchoring, and Syt11-dependent presynaptic assembly — are combinatorially deployed across different neuron types and whether they share a common structural logic remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated model linking scaffolding and signaling roles in a single circuit","Full-length receptor-complex structures lacking","Non-neuronal/spermatocyte roles uncharacterized functionally"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[7,8]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[7,8]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,3,7]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[5,6,11]}],"complexes":["GABAB receptor auxiliary KCTD complex","KCTD12/KCTD16 hetero-oligomer","GABAB receptor/Cav2.2 presynaptic complex"],"partners":["GABBR2","KCTD12","HCN2","HCN3","SYT11","CACNA1B","APP"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q68DU8","full_name":"BTB/POZ domain-containing protein KCTD16","aliases":["Potassium channel tetramerization domain-containing protein 16"],"length_aa":428,"mass_kda":49.1,"function":"Auxiliary subunit of GABA-B receptors that determine the pharmacology and kinetics of the receptor response. Increases agonist potency and markedly alter the G-protein signaling of the receptors by accelerating onset and promoting desensitization (By similarity)","subcellular_location":"Presynaptic cell membrane; Postsynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/Q68DU8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCTD16","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCTD16","total_profiled":1310},"omim":[{"mim_id":"619713","title":"CADHERIN-RELATED FAMILY, MEMBER 2; CDHR2","url":"https://www.omim.org/entry/619713"},{"mim_id":"613423","title":"POTASSIUM CHANNEL TETRAMERIZATION DOMAIN-CONTAINING PROTEIN 16; KCTD16","url":"https://www.omim.org/entry/613423"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Centrosome","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"},{"location":"Mid piece","reliability":"Additional"},{"location":"Principal piece","reliability":"Additional"},{"location":"End piece","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":7.1},{"tissue":"retina","ntpm":1.8}],"url":"https://www.proteinatlas.org/search/KCTD16"},"hgnc":{"alias_symbol":["KIAA1317"],"prev_symbol":[]},"alphafold":{"accession":"Q68DU8","domains":[{"cath_id":"3.30.710.10","chopping":"25-121","consensus_level":"high","plddt":89.0829,"start":25,"end":121},{"cath_id":"3.30.1410","chopping":"163-177_187-277","consensus_level":"high","plddt":91.0095,"start":163,"end":277}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q68DU8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q68DU8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q68DU8-F1-predicted_aligned_error_v6.png","plddt_mean":69.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCTD16","jax_strain_url":"https://www.jax.org/strain/search?query=KCTD16"},"sequence":{"accession":"Q68DU8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q68DU8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q68DU8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q68DU8"}},"corpus_meta":[{"pmid":"31197948","id":"PMC_31197948","title":"KCTD: 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immunology","url":"https://pubmed.ncbi.nlm.nih.gov/42220482","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.02.13.25322223","title":"Integrative Genome-Wide Association Studies of COVID-19 Susceptibility and Hospitalization Reveal Risk Loci for Long COVID","date":"2025-02-14","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.13.25322223","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":20047,"output_tokens":3176,"usd":0.053891,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10626,"output_tokens":3994,"usd":0.07649,"stage2_stop_reason":"end_turn"},"total_usd":0.130381,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structure of the KCTD16 oligomerization (BTB) domain reveals it forms an open pentamer; a single GABAB2 C-terminal peptide binds to the interior of this open pentamer. Mutation of specific interface residues disrupted both biochemical association and functional modulation of GABAB receptors and GIRK channels, establishing the structural basis for KCTD16's interaction with and modulation of the GABAB receptor.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, co-immunoprecipitation, electrophysiology (GIRK current recordings)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure combined with mutagenesis validating the interface and functional electrophysiology in a single rigorous study\",\n      \"pmids\": [\"30971491\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"KCTD16 hetero-oligomerizes with KCTD12 through self-interacting T1 and H1 homology domains. In the hippocampus, approximately two-thirds of KCTD16 associates with KCTD12. KCTD12/KCTD16 hetero-oligomers associate with both the GABAB receptor and the G-protein, imparting unique kinetic properties on Kir3 (GIRK) currents distinct from either homo-oligomer alone, and prolong slow IPSCs in hippocampal pyramidal neurons.\",\n      \"method\": \"Co-immunoprecipitation from mouse hippocampus, BRET in live cells, electrophysiology in heterologous cells and KCTD knockout mouse neurons\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP from native tissue, live-cell BRET, and electrophysiology in knockout mice provide multiple orthogonal methods with rigorous controls\",\n      \"pmids\": [\"28003345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The BTB domain of KCTD16 forms an open pentamer (confirmed by SAXS and crystal structure), and unlike other KCTD family members tested (KCTD10, KCTD13, KCTD17), KCTD16 did not bind Cullin3 (Cul3) in solution, indicating it does not function as a canonical Cul3-dependent E3 ubiquitin ligase subunit.\",\n      \"method\": \"X-ray crystallography, small-angle X-ray scattering (SAXS), size-exclusion chromatography, Cul3 binding assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure confirmed by SAXS, direct Cul3 binding assay; single lab but two orthogonal structural/biochemical methods\",\n      \"pmids\": [\"28963344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"KCTD16 slightly but significantly increases GABA affinity at recombinant GABAB receptors, as measured by G-protein activation assays. KCTD16, as an auxiliary subunit, differentially regulates G-protein signaling of the GABAB receptor.\",\n      \"method\": \"[35S]GTPγS binding assay, BRET between G-protein subunits, Kir3 current recordings in transfected CHO cells and hippocampal neurons\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays in a single lab, consistent results across methods\",\n      \"pmids\": [\"25196734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A peptide-based inhibitor of the KCTD/GABAB receptor protein-protein interaction was developed using the GABAB receptor-binding epitope of KCTD; X-ray crystallography and SEC-MALS revealed that this inhibitor induces oligomerization of KCTD16 into a distinct hexameric structure, distinct from its normal open pentamer.\",\n      \"method\": \"μSPOT peptide array, X-ray crystallography, SEC-MALS, co-immunoprecipitation from mouse brain lysates\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure and SEC-MALS in single lab; novel finding about inhibitor-induced hexamerization\",\n      \"pmids\": [\"31509708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In knockout mouse experiments, the auxiliary subunit KCTD16 influences both thalamic spindle oscillation strength and frequency, consistent with KCTD16 regulating network activity through both GABAB(1a,2) and GABAB(1b,2) receptors.\",\n      \"method\": \"Electrical and optogenetic activation of thalamic spindles in acute slices from KCTD knockout mice, pharmacological experiments\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined electrophysiological phenotype; single lab, one primary method\",\n      \"pmids\": [\"29106983\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Kctd16 knockout mice exhibit impaired extinction of auditory fear memory and increased contextual fear memory compared to wild-type littermates, establishing KCTD16 as a regulator of fear memory processing through its role as an auxiliary GABAB receptor subunit.\",\n      \"method\": \"Auditory and contextual fear conditioning/extinction in Kctd16-/- and Kctd16+/- mice\",\n      \"journal\": \"Behavioural brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with specific behavioral phenotype; single lab, single behavioral paradigm\",\n      \"pmids\": [\"27717812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"KCTD16, as an auxiliary GABAB receptor subunit, anchors HCN channels (containing HCN2/HCN3 subunits) to GABAB receptors in dopamine neurons of the VTA. This interaction facilitates HCN channel activation during IPSPs, counteracting the late phase of GABAB receptor-mediated inhibition. KCTD16 knockout mice show prolonged inhibition of VTA dopamine neuron firing and increased anxiety-like behavior under stress.\",\n      \"method\": \"Co-immunoprecipitation (KCTD16-HCN interaction), optogenetic inhibition of VTA neurons, patch-clamp electrophysiology, CRISPR/Cas9 conditional knockout in VTA neurons, behavioral anxiety assays, pharmacological HCN channel blockade\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction demonstrated, multiple independent approaches (KO mouse, CRISPR, pharmacology, electrophysiology) converging on the same mechanism\",\n      \"pmids\": [\"39914775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The vesicular protein synaptotagmin-11 (Syt11) binds directly to KCTD16 (the auxiliary GABAB receptor subunit) and to Cav2.2 channels, recruiting GABAB receptors and Cav2.2 channels to post-Golgi vesicles to facilitate assembly of GBR/Cav2.2 signaling complexes, and stabilizes them at the neuronal plasma membrane.\",\n      \"method\": \"Co-immunoprecipitation, Syt11 knockout mouse analysis (presynaptic GBR and Cav2.2 levels, neurotransmitter release, presynaptic inhibition)\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP identifying binding and KO mouse with defined presynaptic phenotype; single lab\",\n      \"pmids\": [\"38698221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"KCTD16 was identified as an interactor of the extracellular domain of amyloid precursor protein (APP) by yeast two-hybrid screening, and the interaction was confirmed in a mammalian cell system.\",\n      \"method\": \"Yeast two-hybrid screening, mammalian co-immunoprecipitation confirmation\",\n      \"journal\": \"Neuroscience bulletin\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP confirmation of yeast two-hybrid hit, single lab, no functional follow-up on KCTD16 specifically\",\n      \"pmids\": [\"26960425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A dual enhancer-silencer element (DES-K16) was identified within an intron of the Kctd16 gene in mouse spermatocytes; deletion of DES-K16 in GC-2spd(ts) cells increased Kctd16 expression, suggesting the element functions as a cis-regulatory silencer of Kctd16 in spermatocytes.\",\n      \"method\": \"Chromatin epigenetic profiling (H3K4me1, H3K27ac, H3K27me3), in vitro reporter gene assay, CRISPR/Cas9 deletion in GC-2spd(ts) cells, RT-PCR\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assay and deletion experiment with gene expression readout; single lab, two orthogonal methods\",\n      \"pmids\": [\"33121685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"KCTD16 is expressed in dorsal horn and DRG neurons and modulates GABAB receptor-mediated presynaptic inhibition of nociceptive transmission. KCTD16 knockout mice show increased mechanical thresholds and significantly reduced baclofen-mediated anti-allodynic efficacy. Patch-clamp recordings showed that in KCTD16-/- dorsal horn neurons, baclofen-induced suppression of excitatory transmission was markedly attenuated following inflammation.\",\n      \"method\": \"Immunohistochemistry, KCTD16 knockout mice, behavioral assays (von Frey, thermal sensitivity, carrageenan inflammation model), whole-cell patch-clamp recordings (mEPSCs, mIPSCs), calcium imaging in DRG neurons\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined electrophysiological and behavioral phenotypes; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"41592618\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KCTD16 is an auxiliary subunit of metabotropic GABAB receptors that forms an open pentamer via its BTB domain; this pentamer binds the GABAB2 C-terminal tail at a defined interface to modulate G-protein (Kir3/GIRK channel) signaling kinetics, slow IPSC duration, fear memory extinction, thalamic oscillations, and nociceptive transmission; it also hetero-oligomerizes with KCTD12 to generate unique receptor subtypes, anchors HCN channels to GABAB receptors at VTA synapses to limit IPSP duration and anxiety, and is scaffolded to Cav2.2-containing presynaptic complexes via synaptotagmin-11, while uniquely lacking the ability to bind Cullin3 and thus not functioning as a canonical E3 ubiquitin ligase subunit.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KCTD16 is an auxiliary subunit of metabotropic GABAB receptors that shapes the kinetics, network consequences, and behavioral outputs of GABAB signaling in the nervous system [#0, #3]. Its BTB/oligomerization domain assembles into an open pentamer whose interior accommodates a single GABAB2 C-terminal peptide; disruption of this interface abolishes both biochemical association and functional modulation of GABAB receptors and GIRK (Kir3) currents, defining the structural basis for its action [#0]. As an auxiliary subunit it increases GABA affinity at the receptor and differentially tunes G-protein activation [#3], and it can hetero-oligomerize with KCTD12 through self-interacting T1 and H1 domains to generate receptor populations with kinetic properties distinct from either homo-oligomer, prolonging slow IPSCs in hippocampal neurons [#1]. Beyond gating G-protein output, KCTD16 serves as a molecular scaffold: it anchors HCN2/HCN3-containing channels to GABAB receptors in VTA dopamine neurons to limit the late phase of GABAB-mediated inhibition [#7], and it is recruited together with Cav2.2 channels into presynaptic GABAB signaling complexes via direct binding to the vesicular protein synaptotagmin-11 [#8]. Distinct from other KCTD proteins, KCTD16 does not bind Cullin3 and therefore does not function as a canonical Cul3-dependent E3 ubiquitin ligase substrate adaptor [#2]. Through these activities KCTD16 regulates thalamic spindle oscillations [#5], fear memory extinction and contextual fear [#6], stress-related anxiety [#7], and GABAB-dependent presynaptic inhibition of nociceptive transmission in the spinal dorsal horn [#11].\",\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Established that KCTD16 is not merely a binding partner but an auxiliary subunit that functionally tunes GABAB receptor signaling, by showing it raises GABA affinity and shapes G-protein activation.\",\n      \"evidence\": \"[35S]GTPγS binding, inter-G-protein BRET, and Kir3 current recordings in CHO cells and hippocampal neurons\",\n      \"pmids\": [\"25196734\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Quantitative magnitude of affinity change is small\", \"Structural basis of the interaction was not resolved here\", \"Did not address oligomeric state or hetero-oligomerization\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Resolved whether KCTD16 acts alone or combinatorially by demonstrating it hetero-oligomerizes with KCTD12 to confer unique Kir3 kinetics, explaining receptor subtype diversity in native tissue.\",\n      \"evidence\": \"Reciprocal Co-IP from mouse hippocampus, live-cell BRET, and electrophysiology in KCTD knockout neurons\",\n      \"pmids\": [\"28003345\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Stoichiometry of mixed oligomers in vivo not defined\", \"Functional consequences in non-hippocampal circuits not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Connected KCTD16 to a behavioral phenotype, establishing it as a regulator of fear memory processing through its GABAB auxiliary role.\",\n      \"evidence\": \"Auditory and contextual fear conditioning/extinction in Kctd16 knockout and heterozygous mice\",\n      \"pmids\": [\"27717812\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Circuit and synaptic locus mediating the behavior not pinpointed\", \"Single behavioral paradigm\", \"Molecular mechanism linking KO to extinction deficit not dissected\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Distinguished KCTD16 from canonical KCTD E3-ligase adaptors by showing its BTB domain forms an open pentamer yet, unlike KCTD10/13/17, fails to bind Cullin3.\",\n      \"evidence\": \"X-ray crystallography, SAXS, size-exclusion chromatography, and direct Cul3 binding assay\",\n      \"pmids\": [\"28963344\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Why KCTD16 cannot engage Cul3 at the residue level not fully mapped\", \"Did not test all family members\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended KCTD16 function to network-level activity by showing it shapes thalamic spindle oscillation strength and frequency through GABAB receptors.\",\n      \"evidence\": \"Electrical and optogenetic activation of thalamic spindles in slices from KCTD knockout mice with pharmacology\",\n      \"pmids\": [\"29106983\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Cell-type-specific contribution within thalamic circuitry not resolved\", \"Single primary method\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided the atomic-level mechanism for KCTD16's action by solving the open-pentamer structure bound to a single GABAB2 C-terminal peptide and validating the interface functionally.\",\n      \"evidence\": \"X-ray crystallography, interface mutagenesis, Co-IP, and GIRK current recordings\",\n      \"pmids\": [\"30971491\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Structure of full-length KCTD16 with intact GABAB receptor not determined\", \"Dynamics of pentamer–G-protein coupling not captured\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated the KCTD16/GABAB interface is druggable and that ligand binding can remodel KCTD16 oligomerization, by developing a peptide inhibitor that drives hexamer formation.\",\n      \"evidence\": \"μSPOT peptide array, X-ray crystallography, SEC-MALS, and Co-IP from mouse brain lysates\",\n      \"pmids\": [\"31509708\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"In vivo efficacy of the inhibitor not shown\", \"Functional consequence of hexamerization on signaling not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a scaffolding function beyond G-protein gating, showing KCTD16 anchors HCN2/HCN3 channels to GABAB receptors in VTA dopamine neurons to limit inhibitory duration and constrain stress-induced anxiety.\",\n      \"evidence\": \"Reciprocal Co-IP, optogenetics, patch-clamp, CRISPR conditional KO in VTA, pharmacology, and anxiety assays\",\n      \"pmids\": [\"39914775\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Direct vs. indirect nature of KCTD16–HCN contact not structurally resolved\", \"Generality across other HCN-expressing circuits untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified a trafficking/assembly route for presynaptic GABAB signaling, showing synaptotagmin-11 binds KCTD16 and Cav2.2 to recruit and stabilize GBR/Cav2.2 complexes at the membrane.\",\n      \"evidence\": \"Co-IP and Syt11 knockout mouse analysis of presynaptic GBR/Cav2.2 levels, neurotransmitter release, and presynaptic inhibition\",\n      \"pmids\": [\"38698221\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"KCTD16-specific requirement (vs. other auxiliary subunits) not isolated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Placed KCTD16 in sensory circuits by demonstrating it is required for GABAB-mediated presynaptic inhibition of nociceptive transmission and for full baclofen anti-allodynic efficacy.\",\n      \"evidence\": \"Immunohistochemistry, KCTD16 KO mice, von Frey/thermal/carrageenan behavioral assays, patch-clamp, and DRG calcium imaging\",\n      \"pmids\": [\"41592618\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Whether the dorsal horn role uses the same hetero-oligomer/scaffold mechanisms as central circuits not established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Characterized cis-regulatory control of Kctd16 expression by identifying a dual enhancer-silencer intronic element that represses the gene in spermatocytes.\",\n      \"evidence\": \"Epigenetic profiling, reporter assays, and CRISPR deletion in GC-2spd(ts) cells with RT-PCR\",\n      \"pmids\": [\"33121685\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Physiological function of KCTD16 in spermatocytes not defined\", \"Trans-acting factors binding the element not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How KCTD16's distinct functional modes — G-protein kinetic tuning, KCTD12 hetero-oligomerization, HCN anchoring, and Syt11-dependent presynaptic assembly — are combinatorially deployed across different neuron types and whether they share a common structural logic remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated model linking scaffolding and signaling roles in a single circuit\", \"Full-length receptor-complex structures lacking\", \"Non-neuronal/spermatocyte roles uncharacterized functionally\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 3, 7]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [5, 6, 11]}\n    ],\n    \"complexes\": [\n      \"GABAB receptor auxiliary KCTD complex\",\n      \"KCTD12/KCTD16 hetero-oligomer\",\n      \"GABAB receptor/Cav2.2 presynaptic complex\"\n    ],\n    \"partners\": [\n      \"GABBR2\",\n      \"KCTD12\",\n      \"HCN2\",\n      \"HCN3\",\n      \"SYT11\",\n      \"CACNA1B\",\n      \"APP\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}