KCTD16 is an auxiliary subunit of GABA-B receptors that modulates the pharmacology and kinetics of receptor signaling. It contains an N-terminal BTB/POZ domain that forms an open pentamer and binds to the GABAB2 C-terminal tail in a 1:5 stoichiometry. Unlike KCTD12 which promotes rapid desensitization, KCTD16 generally confers sustained, non-desensitizing GABA-B receptor responses. KCTD16 is enriched in brain regions including thalamus, hippocampus, and amygdala, where it shapes postsynaptic inhibitory currents through GIRK channels. Notably, KCTD16 does not function as a Cullin3 E3 ligase adaptor, distinguishing it from other KCTD family members.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0042734 presynaptic membrane | IBA GO_REF:0000033 | ACCEPT | Summary: KCTD16 localizes to presynaptic membranes as part of GABA-B receptor complexes. Mouse brain studies show KCTD16 expression in regions with both presynaptic and postsynaptic localization (Metz et al. 2011). UniProt confirms presynaptic cell membrane localization. Reason: IBA annotation is well-supported. KCTD16 functions as an auxiliary subunit of GABA-B receptors which are present at presynaptic terminals where they modulate neurotransmitter release via Gbetagamma signaling to voltage-gated calcium channels. This is consistent with the established role of GABA-B receptors in presynaptic inhibition. Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md In mouse brain KCTD16 shows high expression across thalamic nuclei and is enriched in hippocampal CA1, amygdala (lateral/basolateral nuclei) and dentate regions |
| GO:0045211 postsynaptic membrane | IBA GO_REF:0000033 | ACCEPT | Summary: KCTD16 is a component of postsynaptic GABA-B receptor complexes where it modulates GIRK channel-mediated inhibitory currents. Immunolocalization studies show KCTD16 at neuronal somata and neuropil (Metz et al. 2011). Reason: IBA annotation is well-supported. KCTD16 tethers to GABAB2 C-terminus and shapes Gbetagamma-GIRK signaling kinetics at postsynaptic sites. Structural studies confirm the KCTD16-GABAB2 interaction (Zuo et al. 2019, PNAS). UniProt also confirms postsynaptic cell membrane localization. Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md By tethering to GABAB2 and shaping Gbetagamma availability and GIRK channel interactions, KCTD16 contributes to the amplitude and temporal profile of postsynaptic inhibitory currents file:human/KCTD16/KCTD16-deep-research-falcon.md Immunolocalization shows KCTD16 at granule cell somata and neuropil in dentate gyrus and colocalization with GABAB2 in specific layers, supporting a postsynaptic role |
| GO:0043235 receptor complex | IBA GO_REF:0000033 | MODIFY | Summary: KCTD16 is an integral auxiliary subunit of the GABA-B receptor complex. Multiple structural studies have demonstrated that KCTD16 pentamers bind the GABAB2 C-terminal tail. Reason: While GO:0043235 (receptor complex) is correct, a more specific term exists. KCTD16 specifically forms part of the G protein-coupled GABA receptor complex (GABA-B receptor). The term GO:1902712 (G protein-coupled GABA receptor complex) is the appropriate specific term for GABA-B receptors. Proposed replacements: G protein-coupled GABA receptor complex Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md Native GBR complexes comprise principal subunits GABAB1 and GABAB2 plus auxiliary KCTDs (notably KCTD8, KCTD12/12b, KCTD16) file:human/KCTD16/KCTD16-deep-research-falcon.md Human KCTD16 is a BTB/POZ-domain auxiliary protein that constitutively associates with the GABAB2 C-terminus in a 1:5 pentameric arrangement |
| GO:0008277 regulation of G protein-coupled receptor signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: KCTD16 modulates GABA-B receptor signaling kinetics, particularly the amplitude and temporal profile of GIRK-mediated responses. Unlike KCTD12, KCTD16 generally produces sustained, non-desensitizing responses. Reason: This annotation accurately captures the core biological process function of KCTD16. The protein regulates GABA-B receptor (a GPCR) signaling by modulating the kinetics and amplitude of downstream effector responses. Structural and electrophysiological studies demonstrate this regulatory function. Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md KCTD16 modulates GBR signaling kinetics and amplitude, particularly in coupling to G protein-gated inwardly rectifying K+ channels (GIRK) file:human/KCTD16/KCTD16-deep-research-falcon.md KCTD8 and KCTD16 generally confer primarily non-desensitizing/sustained responses |
| GO:0042734 presynaptic membrane | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation consistent with IBA and UniProt localization data for presynaptic membrane. Reason: This IEA annotation is consistent with the experimentally-supported IBA annotation and UniProt subcellular localization data. GABA-B receptors with KCTD16 auxiliary subunits are present at presynaptic terminals. Supporting Evidence: UniProtKB:Q68DU8 Presynaptic cell membrane |
| GO:0042802 identical protein binding | IEA GO_REF:0000117 | ACCEPT | Summary: KCTD16 forms homopentamers via its BTB/POZ domain. Crystal structures confirm the pentameric assembly. Reason: This annotation is well-supported by structural evidence. KCTD16 forms an open pentamer through its BTB/T1 domain, as demonstrated by X-ray crystallography (PDB 6OCP, 5A15). UniProt confirms homopentamer formation. Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md The KCTD16 BTB/T1 domain forms an open pentamer that wraps around one copy of the GABAB2 C-terminal peptide file:human/KCTD16/KCTD16-deep-research-falcon.md The KCTD16 T1/BTB domain forms an open pentamer that binds one GABAB2 C-terminal peptide (1:5 stoichiometry; structure deposited PDB 6OCP) |
| GO:0045211 postsynaptic membrane | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation consistent with IBA and UniProt localization data for postsynaptic membrane. Reason: This IEA annotation is consistent with the experimentally-supported IBA annotation and UniProt subcellular localization data showing postsynaptic cell membrane localization. Supporting Evidence: UniProtKB:Q68DU8 Postsynaptic cell membrane |
| GO:0051260 protein homooligomerization | IEA GO_REF:0000002 | ACCEPT | Summary: KCTD16 forms homopentamers through its BTB/POZ domain. This pentamerization is essential for its function as a GABA-B receptor auxiliary subunit. Reason: This annotation is strongly supported by structural evidence. Crystal structures show KCTD16 forms an open pentamer via its BTB/T1 domain (Zuo et al. 2019, Pinkas et al. 2017). The pentamerization is functionally important for receptor complex assembly. Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md The KCTD16 T1/BTB domain forms an open pentamer that binds one GABAB2 C-terminal peptide (1:5 stoichiometry; structure deposited PDB 6OCP) file:human/KCTD16/KCTD16-deep-research-falcon.md the T1/BTB mediates pentamer formation |
| GO:0005515 protein binding | IPI PMID:26960425 Yeast Two-Hybrid Screening for Proteins that Interact with t... | REMOVE | Summary: This annotation derives from a yeast two-hybrid study that identified KCTD16 as an interactor of APP (amyloid precursor protein) extracellular domain. The interaction was confirmed in mammalian cells. Reason: GO:0005515 (protein binding) is an uninformative annotation that should be avoided. The referenced study (Yu et al. 2016) is a high-throughput yeast two-hybrid screen for APP interactors. While the interaction was confirmed, there is no clear physiological relevance established for a KCTD16-APP interaction, and this does not represent the core function of KCTD16. More informative molecular function terms should be used instead, such as the GABA-B receptor binding function. Supporting Evidence: PMID:26960425 After confirming the interactions in the mammalian system, mutated PLP1, members of the FLRT protein family, and KCTD16 were shown to interact with APP |
| GO:0043235 receptor complex | IEA GO_REF:0000107 | MODIFY | Summary: IEA annotation for receptor complex membership, consistent with KCTD16 role as GABA-B receptor auxiliary subunit. Reason: While correct that KCTD16 is part of a receptor complex, the more specific term GO:1902712 (G protein-coupled GABA receptor complex) should be used since KCTD16 specifically associates with GABA-B receptors. Proposed replacements: G protein-coupled GABA receptor complex Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md Functions as an auxiliary subunit of neuronal GABAB receptors |
| GO:0031795 G protein-coupled GABA receptor binding | IDA file:human/KCTD16/KCTD16-deep-research-falcon.md | NEW | Summary: KCTD16 directly binds to the GABAB2 subunit of the G protein-coupled GABA-B receptor via its BTB/T1 domain. Structural studies have mapped the binding interface. Reason: This molecular function annotation captures the core activity of KCTD16 as a GABA-B receptor auxiliary subunit. The BTB/T1 domain of KCTD16 directly binds the C-terminal tail of GABAB2 with characterized interfacial residues (Q34, F80, P101, E102 on KCTD16; I898, Y903, L904 on GABAB2). Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md The KCTD16 BTB/T1 domain forms an open pentamer that wraps around one copy of the GABAB2 C-terminal peptide, establishing a 1:5 GB2 peptide:KCTD16 stoichiometry. Key interfacial residues include KCTD16 Q34, F80, P101, E102 and GABAB2 I898, Y903, L904 file:human/KCTD16/KCTD16-deep-research-falcon.md KCTD family H1 domains can oligomerize to bind multiple Gbetagamma heterodimers cooperatively in a 5:5 complex |
| GO:0031683 G-protein beta/gamma-subunit complex binding | ISS file:human/KCTD16/KCTD16-deep-research-falcon.md | NEW | Summary: KCTD16 H1 domain binds Gbetagamma subunits, analogous to KCTD12. This interaction shapes GABA-B receptor signaling kinetics. Reason: KCTD16, like other GABA-B associated KCTDs, possesses an H1 domain that engages Gbetagamma subunits. While the detailed kinetic effects differ from KCTD12 (which causes desensitization), the structural architecture for Gbetagamma binding is conserved. This is a key molecular function enabling KCTD16 to modulate GPCR signaling. Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md KCTD family H1 domains can oligomerize to bind multiple Gbetagamma heterodimers cooperatively in a 5:5 complex, enabling rapid desensitization of GBR-GIRK signaling by stripping Gbetagamma from GIRK after initial activation file:human/KCTD16/KCTD16-deep-research-falcon.md KCTD8/16 possess additional C-terminal features (including H2) that oppose desensitization |
| GO:0099602 neurotransmitter receptor regulator activity | ISS file:human/KCTD16/KCTD16-deep-research-falcon.md | NEW | Summary: KCTD16 functions as a neurotransmitter receptor regulator by modulating GABA-B receptor activity, kinetics, and desensitization properties. Reason: This molecular function term accurately describes KCTD16 function. It directly modulates GABA-B receptor activity by binding to GABAB2 and influencing the kinetics of downstream GIRK channel responses. UniProt states it increases agonist potency and alters G-protein signaling kinetics. Supporting Evidence: file:human/KCTD16/KCTD16-deep-research-falcon.md Functions as an auxiliary subunit of neuronal GABAB receptors, modulating receptor expression and the amplitude/kinetics of GIRK-mediated K+ currents file:human/KCTD16/KCTD16-deep-research-falcon.md KCTD16 modulates GBR signaling kinetics and amplitude, particularly in coupling to G protein-gated inwardly rectifying K+ channels (GIRK) |
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