A critical residue in the α(1)M2–M3 linker regulating mammalian GABA(A) receptor pore gating by diazepam

Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs that modulate activity of GABA(A) receptors (GABA(A)Rs), 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 α(1)M2–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 (α(1)L9'Tβ(2)γ(2L)) directly activated by BZDs. We identify a specific residue whose mutation (α(1)V279A) 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.