β2E153 Residue at Loop B of GABAAR Is Involved in Agonist Stabilization and Gating Properties

γ-Aminobutyric acid type A receptors (GABA_ARs) are pentameric ligand-gated ion channels mediating fast inhibitory neurotransmission in the mammalian brain. Although recent structural and kinetic studies have advanced understandings regarding their activation mechanisms, the molecular determinants coupling agonist binding to channel gating remain unclear. We investigated the contribution of the β₂E153 residue, located on loop B of the extracellular domain, to the activation of α₁β₂γ₂ GABA_ARs. Macroscopic and single-channel patch clamp recordings were used to characterize two β₂E153-mutants: charge reversal (β₂E153K) and hydrophobic substitution (β₂E153A). Both substitutions disrupted normal receptor kinetics, with β₂E153K selectively accelerating deactivation and β₂E153A affecting both deactivation and desensitization. Single-channel analysis showed that β₂E153A reduced open probability and mean open times, consistent with altered gating transitions inferred from kinetic modeling. Structural inspection suggested that β₂E153 forms electrostatic interactions with β₂K196 and β₂R207 to stabilize loop C and maintain the agonist-bound conformation. The disruption of this interaction likely destabilizes loop C, leading to weakened agonist binding and modified gating. Overall, our results identify β₂E153 as a key element in the long-range allosteric network linking the binding site to the channel gate in GABA_ARs.