The function and pharmacology of γ-aminobutyric acid type A receptors (GABAARs) are of great physiological and clinical importance and have long been thought to be determined by the channel pore–forming subunits. We discovered that Shisa7, a single-passing transmembrane protein, localizes at GABAergic inhibitory synapses and interacts with GABAARs. Shisa7 controls receptor abundance at synapses and speeds up the channel deactivation kinetics. Shisa7 also potently enhances the action of diazepam, a classic benzodiazepine, on GABAARs. Genetic deletion of Shisa7 selectively impairs GABAergic transmission and diminishes the effects of diazepam in mice. Our data indicate that Shisa7 regulates GABAAR trafficking, function, and pharmacology and reveal a previously unknown molecular interaction that modulates benzodiazepine action in the brain.

Highlights d Despite sharing 97% amino acid identity, NLGN4X and NLGN4Y are differentially regulated d NLGN4Y cannot traffic to the surface due to one amino difference from NLGN4X d A cluster of autism-associated variants in NLGN4X surrounds the critical amino acid d NLGN4X autism-associated variants display a deficit in trafficking similar to NLGN4Y

PSD-95 is a scaffolding protein that regulates the synaptic localization of many receptors, channels, and signaling proteins. The NLGN gene family encodes single-pass transmembrane postsynaptic cell adhesion molecules that are important for synapse assembly and function. At excitatory synapses, NLGN1 mediates transsynaptic binding with neurexin, a presynaptic cell adhesion molecule, and also binds to PSD-95, although the relevance of the PSD-95 interaction is not clear. We now show that disruption of the NLGN1 and PSD-95 interaction decreases surface expression of NLGN1 in cultured neurons. Furthermore, PKA phosphorylates NLGN1 on S839, near the PDZ ligand, and dynamically regulates PSD-95 binding. A phosphomimetic mutation of NLGN1 S839 significantly reduced PSD-95 binding. Impaired NLGN1/PSD-95 binding diminished synaptic NLGN1 expression and NLGN1-mediated synaptic enhancement. Our results establish a phosphorylation-dependent molecular mechanism that regulates NLGN1 and PSD-95 binding and provides insights into excitatory synaptic development and function.PKA | NLGN1 | phosphorylation | PSD-95 P SD-95, a member of membrane-associated guanylate kinases (MAGUK) protein family, is a major constituent of glutamatergic excitatory synapses and is specifically enriched at the postsynaptic density (PSD) (1). A large number of channels, receptors, and adhesion molecules bind to the PSD-95/Discs large/ZO-1 (PDZ), Src-homology-3, and guanylate kinase (GK) domains of PSD-95 (1, 2). As a scaffolding protein at excitatory synapses, PSD-95 has been intensively studied vis a vis the organization of glutamatergic postsynaptic signaling. In fact, synaptic expression and transmission of N-methyl-D-aspartate receptors (NMDARs) and α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs) are regulated by PSD-95 via direct physical interaction or coordination with auxiliary proteins (3-6). Numerous studies have demonstrated critical roles of PSD-95 in the formation and maintenance of dendritic spines, and recent reports have focused on PSD-95 and the molecular mechanisms underlying synapse maturation and plasticity.Neuroligins (NLGNs) are type I membrane proteins and postsynaptic cell adhesion molecules. NLGNs were initially reported as endogenous neurexin (NRXN) ligands (7,8). NLGNs and NRXNs form a transsynaptic interaction, which is important for spinogenesis and functional synapse formation (9, 10). Five NLGN isoforms (NLGN1, NLGN2, NLGN3, NLGN4X, and NLGN4Y) are identified in humans (7,11). In fact, all identified NLGN isoforms show high similarity in amino acid sequence. In addition, the defined protein binding domains in the cytoplasmic region, including the PDZ ligand, are well conserved in all NLGN isoforms (11,12). However, isoform-specific mechanisms regulating synaptic localization are not fully understood.Because NLGN1 and PSD-95 are both localized to excitatory synapses, and their direct interaction via third PDZ domain of PSD-95 was identified in an early study (13), PSD-95 and NLGN1 have been investiga...