An Epilepsy-Related Region in the GABAA Receptor Mediates Long-Distance Effects on GABA and Benzodiazepine Binding Sites
Format of Original
American Society for Pharmacology and Experimental Therapeutics
The GABAA receptor mutation γ2R43Q causes absence epilepsy in humans. Homology modeling suggests that γ2Arg43, γ2Glu178, and β2Arg117 participate in a salt-bridge network linking the γ2 and β2 subunits. Here we show that several mutations at these locations exert similar long-distance effects on other intersubunit interfaces involved in GABA and benzodiazepine binding. These mutations alter GABA-evoked receptor kinetics by slowing deactivation, enhancing desensitization, or both. Kinetic modeling and nonstationary noise analysis for γ2R43Q reveal that these effects are due to slowed GABA unbinding and slowed recovery from desensitization. Both γ2R43Q and β2R117K also speed diazepam dissociation from the receptor’s benzodiazepine binding interface, as assayed by the rate of decay of diazepam-induced potentiation of GABA-evoked currents. These data demonstrate that γ2Arg43 and β2Arg117 similarly regulate the stability of both the GABA and benzodiazepine binding sites at the distant β/α and α/γ intersubunit interfaces, respectively. A simple explanation for these results is that γ2Arg43 and β2Arg117 participate in interactions between the γ2 and β2 subunits, disruptions of which alter the neighboring intersubunit binding sites in a similar fashion. In addition, γ2Arg43 and γ2Glu178 regulate desensitization, probably mediated within the transmembrane domains near the pore. Therefore, mutations at the γ/β intersubunit interface have specific long-distance effects that are propagated widely throughout the GABAA receptor protein.