RT Journal Article SR Electronic T1 A State-Dependent Salt-Bridge Interaction Exists across the β/α Intersubunit Interface of the GABAA Receptor JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 662 OP 671 DO 10.1124/mol.110.068619 VO 79 IS 4 A1 Kurt T. Laha A1 David A. Wagner YR 2011 UL http://molpharm.aspetjournals.org/content/79/4/662.abstract AB The GABAA receptor is a multisubunit protein that transduces the binding of a neurotransmitter at an intersubunit interface into the opening of a central ion channel. The structural components that mediate the steps involved in this action are poorly defined. A large amount of work has focused on clarifying the specific functions and interactions of residues believed to surround the GABA binding pocket. Here, we explored two charged residues (β2Asp163 and α1Arg120), which have been suggested by homology models to participate in a salt-bridge interaction. When mutated to alanine, both single mutants, as well as the double mutant, increase EC50-GABA, decrease the GABA binding rate, and accelerate deactivation and GABA unbinding rates. Double-mutant cycle analysis demonstrates that the effects of each alanine mutation on the GABA binding rate were additive and independent. In contrast, a significant coupling energy was found during an analysis of deactivation time constants. Using kinetic modeling, we further demonstrated that the GABA unbinding rates, in particular, are strongly coupled. These data suggest that β2Asp163 and α1Arg120 form a state-dependent salt bridge, interacting when GABA is bound to the receptor but not when the receptor is in the unbound state.