Mutation at GABA binding site (alpha1F64) affects both binding and gating properties of GABAA receptors

In spite of broad knowledge of GABAAR pharmacokinetics, molecular mechanisms of conformation transitions remain elusive. Intriguingly, GABA binding site is distant from the channel gate (ca. 5 nm). In this study we searched for residues at GABA binding site involved in conveying binding energy to the channel gate of α1β2γ2 GABAARs. Mutation at α1F64 decreased the receptor affinity (shifted dose-response and reduced binding rate in racing protocol) and, in addition, strongly influenced onset, deactivation and desensitization of currents elicited by saturating agonist, indicating gating modification. Non-stationary variance analysis of GABA- or pentobarbital-evoked currents showed that the cysteine mutation strongly decreased the open channel probability confirming its impact on receptor gating. We conclude that α1F64 residue, although located at the binding site, strongly affects gating properties of GABAA receptors. Supported by NCN Grant 350/B/P01/2011/40 to JWM.