The structure of Loop 2 is important for agonist and ethanol sensitivity in glycine and GABAA receptors

Glycine receptors (GlyRs) and γ-aminobutyric type A receptors (GABAARs) are recognized as the primary mediators of neuronal inhibition in the central nervous system (CNS). There is a large body of evidence that implicates GABAARs in the behavioral effects of ethanol and building evidence supports the notion that ethanol acting on GlyRs causes at least a subset of its behavioral effects. For several decades, GlyRs and GABAARs have been studied at the molecular level for targets for ethanol action. Despite the advances in understanding the effects of ethanol in vivo and in vitro, the precise molecular sites and mechanisms of action for ethanol in ligand-gated ion channels (LGICs) in general, and in GlyRs and GABAARs specifically, are just now starting to become understood. The present dissertation focuses on studies we conducted that address this issue using molecular biology, pressure antagonism, electrophysiology and molecular modeling strategies to probe, identify and model the initial molecular sites and mechanisms of ethanol action in GlyRs and GABAARs. Specifically, this work focuses on the Loop 2 region in the extracellular domain of GlyRs and GABAARs and (1) Provides evidence that position 52 in Loop 2 is a target for ethanol action and antagonism in GlyRs; (2) Demonstrates that the structural bases for the actions of ethanol and pressure on this common target are different and (3) Provides strong evidence that the structure of Loop 2 in GlyRs, GABA ARs and possibly across LGICs may be a key factor in controlling the sensitivity of these receptors to ethanol. Collectively, the studies provide new models and mechanisms for ethanol action in GlyRs and GABAARs.