Abstract

The GABA_A 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 GABA_A receptor protein.