A critical residue in the αM2-M3 linker regulating mammalian GABA receptor pore gating by diazepam.

Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs that modulate activity of GABA receptors (GABARs), neurotransmitter-gated ion channels critical for synaptic transmission. However, the physical basis of this modulation is poorly understood. We explore the role of an important gating domain, the αM2-M3 linker, in linkage between the BZD site and pore gate. To probe energetics of this coupling without complication from bound agonist, we use a gain of function mutant (αL9'Tβγ) directly activated by BZDs. We identify a specific residue whose mutation (αV279A) more than doubles the energetic contribution of the BZD positive modulator diazepam (DZ) to pore opening and also enhances DZ potentiation of GABA-evoked currents in a wild-type background. In contrast, other linker mutations have little effect on DZ efficiency, but generally impair unliganded pore opening. Our observations reveal an important residue regulating BZD-pore linkage, thereby shedding new light on the molecular mechanism of these drugs.