, 2008). Gephyrin was first identified as a 93 KDa polypeptide that copurified with affinity-purified glycine receptors (Pfeiffer et al., 1982), the principal inhibitory neurotransmitter receptors in BAY 73-4506 the spinal cord. Molecular cloning and targeted deletion in mice revealed

that gephyrin is a multifunctional protein that is broadly expressed and essential for postsynaptic clustering of glycine receptors and also for molybdenum cofactor (Moco) biosynthesis in nonneural tissues (Prior et al., 1992, Kirsch et al., 1993, Feng et al., 1998, Sola et al., 2004 and Dumoulin et al., 2009). Gephyrin interacts with microtubules (Kirsch et al., 1995) as well as several regulators of microfilament dynamics including profilin I and II (Mammoto et al., 1998) and members of the mammalian enabled (Mena)/vasodilator-stimulated phosphoprotein (VASP) family (Figures 3B and 5A) (Giesemann et al., 2003). The N-terminal gephyrin domain known as G-gephyrin assumes a trimeric structure (Schwarz et al., 2001 and Sola et al.,

2001), whereas the C-terminal E domain forms a dimer (Schwarz et al., 2001, Xiang et al., 2001 and Sola et al., 2004). These domain interactions are essential for oligomerization and clustering of gephyrin at postsynaptic sites (Saiyed et al., 2007). The clustering function of gephyrin is regulated by select residues within PI3K inhibitor the E-domain that are dispensable for E-domain dimerization (Lardi-Studler et al., 2007). Moreover, the linker region between E and G domains of gephyrin is thought to interact with microtubules however (Ramming et al., 2000). Thus, gephyrin has the structural prerequisites to form a microtubule and microfilament-associated hexagonal protein lattice that may organize the spatial distribution of receptors and other proteins in the postsynaptic membrane. Gephyrin has long been established as a phosphoprotein (Langosch et al., 1992), although to date few studies have addressed the relevance of this modification. Zita et al. (2007) showed preliminary evidence that

gephyrin is phosphorylated by proline-directed kinase(s) and that this is essential for interaction of gephyrin with the peptidyl-prolyl cis/trans isomerase Pin1 ( Figure 5A). Pin1-induced conformational changes of gephyrin were found to be essential for maximal clustering of glycine receptors, suggesting a similar function for Pin1 in regulating gephyrin destined for GABAergic synapses. Recently, an unbiased proteomic screen using mass spectrometry mapped the first specific phosphorylation sites to S188, S194, and S200 of gephyrin ( Huttlin et al., 2010). Treatment of cultured neurons with inhibitors of the phosphatases PP1α and PP2A caused a significant loss of gephyrin from inhibitory synapses ( Bausen et al., 2010).