Disease relevance of Gphn

• Gephyrin-(2-188) forms trimers in solution, and a sequence motif thought to be involved in molybdopterin binding is highly conserved between gephyrin and the E. coli protein [1].
• Gephyrin is present on the postsynaptic membrane of amacrine cells and ganglion cells [2].

High impact information on Gphn

• In hippocampal neurons, GSK3β signaling affects gephyrin phosphorylation at Ser270 to regulate formation and plasticity at GABAergic synapses [3].
• In spinal neurons, synaptic targeting of the inhibitory glycine receptor (GlyR) depends on the expression of the anchoring protein gephyrin [4].
• Moreover, gephyrin binds with high affinity to polymerized tubulin and has been postulated to link the GlyR to the subsynaptic cytoskeleton [5].
• Thus, gephyrin is essential for localizing the GlyR to presumptive postsynaptic plasma membrane specializations [5].
• Ultrastructural studies have shown that the peripheral membrane protein gephyrin, which co-purifies with the postsynaptic inhibitory glycine receptor (GlyR) upon affinity chromatography, is situated on the cytoplasmic face of glycinergic postsynaptic membranes [5].
• This protein, named gephyrin (from the Greek gamma epsilon phi upsilon rho alpha, bridge), is thought to anchor the GlyR to subsynaptic microtubules [6].

Chemical compound and disease context of Gphn

• The Drosophila molybdenum cofactor gene cinnamon is homologous to three Escherichia coli cofactor proteins and to the rat protein gephyrin [7].
• Lithium Chloride is therapeutically used to treat patients with biopolar disorder; however, its mode of action has been unclear so far. Lithium affects gephyrin clustering via the GSK3β pathway and its influence on Gephyrin Ser270 phosphorylation. Lithium mediated increase in gephyrin clustering at GABAergic synapses in hippocampus (CA1 and molecular layer), is mirrored by an increased size of PSD-95 clusters in the same region [3].

Biological context of Gphn

• In brain, at least five different gephyrin mRNAs are generated by alternative splicing [6].
• Here, we show that full-length gephyrin is a trimer and that its proteolysis in vitro causes the spontaneous dimerization of its C-terminal region (gephyrin-E), which binds a GlyR beta-subunit-derived peptide with high and low affinity [8].
• Binding of gephyrin to the GlyR is exclusively mediated by the E domain, and the binding site was mapped to one of its sub-domains (residues 496-654) [9].
• Previously, we reported that gene expression for the GABA(A) receptor clustering protein gephyrin was significantly downregulated in the BLA after fear acquisition (Ressler et al., 2002) [10].
• In the present study we intended to determine the capacity of these two splice variants to accumulate at inhibitory synaptic terminals and to colocalize with gephyrin, and to find out whether phosphorylation of Ser343 has any effect on GABAAR distribution [11].

Anatomical context of Gphn

• In this work, seven isoforms of gephyrin were cloned from adult rat spinal cord, some of then containing new cassettes [12].
• Regulation of gephyrin and GABAA receptor binding within the amygdala after fear acquisition and extinction [10].
• Biochemical studies of the patient's fibroblasts demonstrate that gephyrin catalyzes the insertion of molybdenum into molybdopterin and suggest that this novel form of MoCo deficiency might be curable by molybdate supplementation [13].
• Because gephyrin expression can rescue a MoCo-deficient mutation in bacteria, plants, and a murine cell line, it became clear that gephyrin also plays a role in MoCo biosynthesis [13].
• Gephyrin is ubiquitously expressed, and was initially found in the central nervous system, where it is essential for clustering of inhibitory neuroreceptors in the postsynaptic membrane [14].

Associations of Gphn with chemical compounds

• Gephyrin antisense oligonucleotides prevent glycine receptor clustering in spinal neurons [5].
• Besides its structural role, gephyrin is involved in the biosynthesis of the molybdenum cofactor that is essential for all molybdenum-dependent enzymes in mammals [9].
• These results identify the C5 splice variant of gephyrin as a factor regulating the transmitter-appropriate degree of GlyR accumulation at inhibitory synapses [15].
• Consequently, gephyrin is not a ligand for the proline-binding motif of profilins, as suspected previously [16].
• Many synapses showed both GABAA beta 3 and gephyrin immunoreactivity, and at most of these synapses GABA and glycine were enriched in the presynaptic axon [17].

Co-localisations of Gphn

• Parvalbumin-positive dendrites did not display any increase in co-localizing gephyrin-positive structures [18].

Regulatory relationships of Gphn

• A corresponding production of stable, carboxy-terminal gephyrin fragments of 48-50 kDa occurred within 1 min of proteolytic activation and was blocked by the selective calpain inhibitor CX295 [19].
• Calpain-1 clips gephyrin clusters in a Ca2+ dependent mechanism to regulate plasticity at GABAergic synapses [3].
• Simultaneous immunolabeling for gephyrin and cell-specific markers showed that granule cells and parvalbumin-positive interneurons express gephyrin [18].
• In the rat, all neurons classified as Renshaw cells (n = 487) also contained calbindin D28k-immunoreactivity, and all calbindin D28k-immunoreactive cells located in the ventral-most region of lamina VII expressed the characteristic gephyrin labeling and morphology of Renshaw cells [20].

Other interactions of Gphn

• Calpain-1 interaction with gephyrin is not GSK3β dependent [3].
• PIN possesses two binding grooves, that have been shown to interact with several targets, including neuronal NO synthase, dynein intermediate chain, myosin V, the proapoptotic protein Bim, the scaffolding proteins DAP1alpha and gephyrin, and the transcription factor NRF-1 [21].
• Variants of the receptor/channel clustering molecule gephyrin in brain: distinct distribution patterns, developmental profiles, and proteolytic cleavage by calpain [19].
• These studies reveal an unsuspected heterogeneity in the modes of attachment of postsynaptic proteins to the cytoskeleton and support the idea that PSD-95 and gephyrin may be core scaffolding components independent of the actin or tubulin cytoskeleton [22].
• Large, intensely stained, gephyrin-positive clusters were distributed along distinct dendrites, and most of them were positive for parvalbumin [18].
• Furthermore, agrin immunoreactive axons were found adjacent to gephyrin, the postsynaptic glycine receptor-associated protein [23].

Analytical, diagnostic and therapeutic context of Gphn

• By using isothermal titration calorimetry, a high affinity (K(d) = 0.2-0.4 microm) and low affinity (K(d) = 11-30 microm) binding site for the GlyRbeta-loop was found on holo-gephyrin and the E domain, respectively, with a binding stoichiometry of two GlyRbeta-loops per E domain in both cases [9].
• After treatment with alkaloids affecting the cytoskeleton, the morphology of post-synaptic gephyrin clusters was analyzed by confocal immunofluorescence microscopy [24].
• With light nonradioactive in situ hybridization (ISH), we observe that GlyR alpha subunit mRNAs are present in both somata and dendrites of most neurons of the ventral horn of rat spinal cord, whereas the beta subunit and gephyrin mRNAs are predominantly in somata [25].
• Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed that the glycine receptor alpha1, alpha2, beta subunits and gephyrin mRNAs were expressed at comparable levels in strychnine-treated and untreated cultures [26].
• In this study we have used immunocytochemistry to characterize a population of Waldeyer cells which were identified by the presence of high levels of the glycine receptor-associated protein gephyrin on their cell bodies and proximal dendrites [27].

References