Affinage

GPHN

Gephyrin · UniProt Q9NQX3

Length
736 aa
Mass
79.7 kDa
Annotated
2026-06-10
12 papers in source corpus 13 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 4/4 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

Gephyrin (GPHN) is a bifunctional protein that operates both as the principal scaffold organizing inhibitory postsynaptic densities and as an essential enzyme in molybdenum cofactor biosynthesis (PMID:11418245). In its enzymatic role, gephyrin is required during molybdenum cofactor assembly for insertion of molybdenum into the cofactor, and loss-of-function mutations abrogate all molybdoenzyme activities (PMID:12754701, PMID:21031595). In its scaffolding role, full-length gephyrin assembles hierarchically: a stable dimer forms the basic oligomeric unit that further builds into tetramers and hexamers, and a critical segment of its flexible central linker adopts alternative conformations, one of which occludes the receptor-binding site and which harbors key phosphorylation sites, coupling phosphorylation state to receptor binding [PMID:bio_10.1101_2025.09.01.673457]. Gephyrin clusters glycine and GABA-A receptors at the membrane through its C-terminal MoeA-homology E-domain, which is required for glycine receptor binding [PMID:12684523, PMID:bio_10.1101_2024.10.17.618879]. Synaptic targeting depends on collybistin, which drives gephyrin self-oligomerization into a high-molecular-weight complex stabilized by plasma-membrane phosphoinositides, while phosphorylation at Ser325 abolishes complex formation and impairs clustering [PMID:bio_10.1101_2025.01.20.633899]; a C-domain palmitoylation site (Cys212) is additionally required for correct synaptic targeting [PMID:bio_10.1101_2025.08.26.672322]. Receptor stability and diffusion are tuned by WNK1/SPAK-dependent phosphorylation of the central linker, which stabilizes GABA-A receptors at inhibitory synapses [PMID:bio_10.1101_2025.09.05.674425]. The scaffold is organized into activity-dependent sub-synaptic nanodomains whose remodeling controls synaptic strength [PMID:bio_10.1101_2024.11.29.625981], and gephyrin is required for maintenance of inhibitory synaptic structure [PMID:bio_10.1101_2024.09.23.614589]. Chromosomal translocation can fuse the gephyrin C-terminal half to MLL, generating an MLL-GPHN fusion in leukemia (PMID:11579461).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2001 Medium

    Establishing gephyrin as a dual-function protein resolved whether one gene served both synaptic and metabolic roles, defining it as both a glycine-receptor anchor to subsynaptic microtubules and a molybdenum cofactor biosynthesis factor.

    Evidence Knockout mouse analysis with gene structure determination and localization studies

    PMID:11418245

    Open questions at the time
    • Did not resolve the structural basis for either function
    • No molecular mechanism for how the same protein partitions between cytosolic enzymatic and synaptic scaffolding roles
  2. 2003 Medium

    Mapping the receptor-interaction determinant showed that glycine receptor binding requires an intact C-terminal MoeA-homology E-domain, localizing the scaffolding interface and showing that an N10Y mutation and splice variation do not disrupt clustering.

    Evidence Yeast two-hybrid, functional clustering assay, RT-PCR isoform analysis, and mutagenesis

    PMID:12684523

    Open questions at the time
    • No structural detail of the E-domain/receptor interface
    • Affinity and stoichiometry of binding not defined
  3. 2003 Medium

    Patient mutation analysis confirmed gephyrin is indispensable specifically for the molybdenum insertion step of cofactor assembly, establishing the metabolic consequence of loss-of-function.

    Evidence Human mutation analysis combined with biochemical phenotyping of molybdoenzyme activities in patients

    PMID:12754701 PMID:21031595

    Open questions at the time
    • No in vitro reconstitution of the molybdenum insertion reaction
    • Catalytic mechanism of metal insertion not defined
  4. 2001 Medium

    Characterization of a t(11;14) leukemia-associated MLL-GPHN fusion documented gephyrin involvement in oncogenic gene rearrangement and proposed a topoisomerase-II/NHEJ generation mechanism.

    Evidence cDNA library screening, fusion transcript identification, and genomic breakpoint analysis in a single patient

    PMID:11579461

    Open questions at the time
    • No functional reconstitution of the fusion protein
    • Contribution of the gephyrin portion to leukemogenesis unknown
  5. 2024 Medium

    Reconstituting gephyrin-GlyR clusters in a heterologous system revealed that clustering itself modulates glycine affinity via the receptor beta-subunit N-terminus and that neuroligin-2 enlarges clusters, linking scaffold assembly to receptor function.

    Evidence Heterologous expression clustering assay, electrophysiology, and mutagenesis of the GlyR beta subunit (preprint)

    PMID:bio_10.1101_2024.10.17.618879

    Open questions at the time
    • Performed in heterologous cells rather than native synapses
    • Stoichiometry of gephyrin within micron-sized clusters not defined
  6. 2024 Medium

    A zebrafish loss-of-function study extended gephyrin function beyond the postsynapse, implicating it in selective axon-class-dependent myelination by oligodendrocytes.

    Evidence Zebrafish gphnb loss-of-function genetics with imaging of myelin sheath length and distribution per axon class (preprint)

    PMID:bio_10.1101_2024.10.02.616365

    Open questions at the time
    • No biochemical mechanism for the oligodendrocyte interaction identified
    • Relevance to mammalian myelination unknown
  7. 2024 Medium

    In vivo super-resolution imaging established that the inhibitory scaffold is organized into sub-synaptic domains that undergo activity-dependent nanoscale remodeling, functionally weakening axo-axonic contacts.

    Evidence dSTORM super-resolution microscopy in vivo, chemogenetic manipulation, and electrophysiological measurement of synaptic strength (preprint)

    PMID:bio_10.1101_2024.11.29.625981

    Open questions at the time
    • Molecular trigger linking activity to SSD volume change unknown
    • Specificity for axo-axonic versus axo-dendritic synapses mechanistically unexplained
  8. 2024 Low

    A light-controlled targeted degradation tool confirmed that gephyrin is causally required for maintenance of inhibitory synaptic structure.

    Evidence Photoactivatable optogenetic degradation (paGFE3) with immunofluorescence of gephyrin and synapse markers (preprint)

    PMID:bio_10.1101_2024.09.23.614589

    Open questions at the time
    • Tool demonstration without deeper mechanistic dissection
    • Does not distinguish acute structural roles from secondary effects of protein loss
  9. 2025 High

    Cryo-EM and reconstitution defined the hierarchical oligomerization of full-length gephyrin (dimer to tetramer to hexamer) and revealed a linker conformation that occludes the receptor-binding site, mechanistically coupling phosphorylation to receptor binding.

    Evidence Cryo-electron microscopy, biochemical reconstitution, and mutational analysis (preprint)

    PMID:bio_10.1101_2025.09.01.673457

    Open questions at the time
    • Conformational switching not visualized in native synapses
    • Which kinases act on the linker sites in this structural context not established
  10. 2025 High

    Reconstitution of the gephyrin-collybistin complex showed collybistin drives gephyrin self-oligomerization into a >5 MDa assembly, with phosphoinositides promoting membrane targeting and Ser325 phosphorylation acting as a negative switch on complex formation.

    Evidence Biochemical reconstitution, Ser325 mutagenesis, phosphoinositide binding assays, and synaptic clustering assays (preprint)

    PMID:bio_10.1101_2025.01.20.633899

    Open questions at the time
    • Kinase responsible for Ser325 phosphorylation in vivo not identified
    • Structure of the high-molecular-weight complex not resolved
  11. 2025 Medium

    Identification of WNK1/SPAK-dependent phosphorylation of two central-linker residues established a signaling pathway that tunes GABA-A receptor diffusion, clustering, and stability, with behavioral consequences in vivo.

    Evidence Phosphorylation site identification and mutagenesis, live imaging of receptor diffusion, electrophysiology, and in vivo anxiety behavior assay (preprint)

    PMID:bio_10.1101_2025.09.05.674425

    Open questions at the time
    • Relationship between WNK sites and the Ser325/cryo-EM linker sites not integrated
    • Direct phosphorylation in vivo versus via SPAK not fully separated
  12. 2025 Medium

    A knock-in mouse of the C-domain microdeletion Delta199-233 showed that loss of the palmitoylation site (Cys212) is required for correct synaptic targeting and that targeting can be uncoupled from in vitro receptor affinity.

    Evidence Knock-in mouse, immunofluorescence of synaptic clustering, electrophysiology of inhibitory transmission, and PSD-95 cluster analysis (preprint)

    PMID:bio_10.1101_2025.08.26.672322

    Open questions at the time
    • Direct demonstration that Cys212 palmitoylation alone drives targeting not isolated from the broader deletion
    • Mechanism of excitatory synapse compensation unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the cytosolic molybdenum-cofactor function and the synaptic scaffolding function are coordinated within a single protein, and how the multiple linker phosphorylation switches (WNK sites, Ser325) are integrated to control oligomerization and receptor binding in vivo, remain unresolved.
  • No integrated model of phosphorylation-state combinations
  • Spatial/temporal partitioning between metabolic and synaptic pools undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 4 GO:0016740 transferase activity 2 GO:0008092 cytoskeletal protein binding 1
Localization
GO:0005886 plasma membrane 2 GO:0005829 cytosol 1 GO:0005856 cytoskeleton 1
Complex memberships
gephyrin-collybistin complexinhibitory postsynaptic density

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 GlyR-gephyrin binding is dependent on the presence of an intact C-terminal MoeA homology (E-domain) of gephyrin. The N10Y missense mutation and alternative splicing of GPHN transcripts do not disrupt GlyR-gephyrin interactions or collybistin-induced cell-surface clustering. Yeast two-hybrid, functional clustering assay, RT-PCR isoform analysis, mutagenesis The Journal of biological chemistry Medium 12684523
2003 Gephyrin (encoded by GEPH/GPHN) is required during molybdenum cofactor assembly for insertion of molybdenum into the cofactor; loss-of-function mutations abrogate all molybdoenzyme activities. Human mutation analysis combined with biochemical phenotyping of molybdoenzyme activities in patients Human mutation Medium 12754701 21031595
2001 Gephyrin functions as a peripheral membrane scaffolding protein anchoring glycine receptors to subsynaptic microtubules; it also plays a role in GABA-A receptor localization at the synapse and in molybdenum cofactor biosynthesis, as established by knockout mouse phenotypes. Knockout mouse analysis, gene structure determination, localization studies Gene Medium 11418245
2001 In a translocation t(11;14)(q23;q24)-associated leukemia, the GPHN C-terminal half (including a tubulin-binding site and MoeA homology domain) is fused to MLL AT-hook and DNA methyltransferase homology domains, generating an MLL-GPHN fusion protein. Genomic breakpoint analysis identified topoisomerase-II DNA-binding sites spanning both breakpoints, suggesting VP16/topoisomerase-II-induced double-strand breaks and non-homologous end joining as the generation mechanism. cDNA library screening, fusion transcript identification, genomic breakpoint analysis Genes, chromosomes & cancer Medium 11579461
2024 Gephyrin assembles with heteromeric α2β glycine receptors (GlyRs) into micron-sized clusters at the plasma membrane. Neuroligin-2 further increases cluster sizes and GlyR concentration. A positively charged N-terminus sequence of the GlyR β subunit is essential for glycine affinity modulation through clustering. Ligand re-binding to adjacent clustered GlyRs alters kinetics but not chemical equilibrium. Heterologous expression clustering assay, electrophysiology, mutagenesis of GlyR β subunit N-terminus bioRxivpreprint Medium bio_10.1101_2024.10.17.618879
2024 In zebrafish, Gephyrin (Gphnb) is enriched in myelin on GABAergic and glycinergic axons. Loss of gphnb causes longer myelin sheaths specifically on GABAergic axons and shifts myelin placement toward glutamatergic axons at the expense of GABAergic axons, indicating gephyrin mediates selective axon-class-dependent myelination by oligodendrocytes. Zebrafish gphnb loss-of-function genetics, imaging of myelin sheath length and distribution per axon class bioRxivpreprint Medium bio_10.1101_2024.10.02.616365
2025 Cryo-EM combined with biochemical reconstitution and mutational analyses shows that full-length gephyrin forms a stable dimer as the basic oligomeric unit, which further assembles into linear and oblique tetramers and linear hexamers. A critical segment of the flexible central linker adopts two distinct conformations, one of which occludes the receptor-binding site, and this segment harbors key phosphorylation sites, providing a mechanistic link between phosphorylation state, linker conformation, and receptor binding. Cryo-electron microscopy, biochemical reconstitution, mutational analysis bioRxivpreprint High bio_10.1101_2025.09.01.673457
2025 Collybistin induces gephyrin self-oligomerization into a high-molecular-weight (>5 MDa) gephyrin-collybistin complex at GABAergic synapses. Plasma-membrane phosphoinositides promote complex formation and are critical for membrane targeting and stabilization. Gephyrin phosphorylation at Ser325 abolishes complex formation with collybistin, impairing collybistin-dependent gephyrin clustering at GABAergic synapses. Biochemical reconstitution of gephyrin-collybistin complex, phosphorylation site mutagenesis (Ser325), phosphoinositide binding assays, synaptic clustering assays bioRxivpreprint High bio_10.1101_2025.01.20.633899
2025 WNK1 kinase (and its effector SPAK) directly phosphorylates two previously uncharacterized residues in the central linker region of gephyrin. This phosphorylation controls GABA-A receptor synaptic diffusion, clustering, membrane stability, and endocytosis at inhibitory synapses. Activation of WNK signaling stabilizes GABA-A Rs at inhibitory synapses; inhibition enhances receptor internalization. Expression of a phospho-mimetic form of gephyrin at WNK-targeted sites produces anxiolytic effects in vivo. Phosphorylation site identification and mutagenesis, live imaging of receptor diffusion, electrophysiology of GABAergic currents, in vivo behavioral assay (anxiety) bioRxivpreprint Medium bio_10.1101_2025.09.05.674425
2025 A knock-in mouse model of the gephyrin microdeletion Δ199-233 (within the C-domain, removing a region that includes the S-palmitoylation site at Cys212) disrupts synaptic targeting of gephyrin in dissociated hippocampal neurons. Despite unexpectedly facilitating receptor interaction in vitro, inhibitory signal transmission is reduced. Compensatory changes occur at excitatory synapses (smaller but more numerous PSD-95 clusters). Loss of the C-domain palmitoylation site is required for correct synaptic targeting. Knock-in mouse model, immunofluorescence of synaptic clustering in hippocampal neurons, electrophysiology of inhibitory transmission, PSD-95 cluster analysis bioRxivpreprint Medium bio_10.1101_2025.08.26.672322
2024 Gephyrin, the main inhibitory receptor scaffold, is organized into sub-synaptic domains (SSDs) in vivo with distinct nanoscale arrangements depending on subcellular location and presynaptic partner. Chronic chemogenetic increases in cortical activity cause a reduction in gephyrin SSD volume specifically at axo-axonic (but not axo-dendritic) synapses, functionally weakening those contacts, demonstrating activity-dependent nanoscale remodeling of the inhibitory scaffold. dSTORM super-resolution microscopy in vivo, chemogenetic manipulation, electrophysiological measurement of synaptic strength bioRxivpreprint Medium bio_10.1101_2024.11.29.625981
2024 An E3 ligase-dependent tool (paGFE3) that targets the RING domain of Mdm2 to gephyrin degrades gephyrin protein and ablates inhibitory synapses in response to 400 nm light, confirming that gephyrin is required for maintenance of inhibitory synaptic structure. Photoactivatable optogenetic degradation system (paGFE3), immunofluorescence of gephyrin levels and inhibitory synapse markers bioRxivpreprint Low bio_10.1101_2024.09.23.614589

Source papers

Stage 0 corpus · 12 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 Rare exonic deletions implicate the synaptic organizer Gephyrin (GPHN) in risk for autism, schizophrenia and seizures. Human molecular genetics 121 23393157
2011 Molybdenum cofactor deficiency: Mutations in GPHN, MOCS1, and MOCS2. Human mutation 106 21031595
2003 Mutations in the molybdenum cofactor biosynthetic genes MOCS1, MOCS2, and GEPH. Human mutation 99 12754701
2003 Isoform heterogeneity of the human gephyrin gene (GPHN), binding domains to the glycine receptor, and mutation analysis in hyperekplexia. The Journal of biological chemistry 97 12684523
2012 Orthostatic hypotension and novel blood pressure-associated gene variants: Genetics of Postural Hemodynamics (GPH) Consortium. European heart journal 32 22504314
1983 Proteolytic processing of phage lambda tail protein gpH: timing of the cleavage. Virology 25 6220513
2001 The human gephyrin (GPHN) gene: structure, chromosome localization and expression in non-neuronal cells. Gene 16 11418245
2001 GPHN, a novel partner gene fused to MLL in a leukemia with t(11;14)(q23;q24). Genes, chromosomes & cancer 15 11579461
1999 The gene for 2-phosphoglycolate phosphatase (gph) in Escherichia coli is located in the same operon as dam and at least five other diverse genes. Biochimica et biophysica acta 12 10572959
2018 The FRA14B common fragile site maps to a region prone to somatic and germline rearrangements within the large GPHN gene. Genes, chromosomes & cancer 5 30411419
2025 Association and functional study of ATP6V1D and GPHN gene polymorphisms with depression in Chinese population. World journal of psychiatry 1 40309610
2025 LncRNA-GPHN Regulates Epilepsy by Inhibiting Apoptosis via the miR-320/YWHAH Axis in an Immature Rat Model of Status Epilepticus. Journal of cellular and molecular medicine 1 40346986

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