Structural Requirements for Benzodiazepine Modulation of GABA-A Receptors

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DESCRIPTION (provided by applicant): Gamma-aminobutyric acid type A receptors (GABARs) are ligand-gated ion channels that mediate the majority of rapid inhibitory neurotransmission in the central nervous system. Alterations in GABAR-mediated neural inhibition have been linked to several disorders including epilepsy, schizophrenia, anxiety, and depression. Several clinically important drugs including benzodiazepines (BZDs), barbiturates, anethestics, and ethanol exert their therapeutic actions by modulating the GABA-mediated current of the GABAR. However, the exact mechanism by which these modulators alter GABA-activation of the receptor is still debated. Specifically, the structural elements underlying BZD positive and negative modulation remain unknown. The main objective of this proposal is to determine how BZDs with different functional (positive, negative, and zero modulators) and structural properties (classical and non-classical) modulate the GABAR. I will use several experimental approaches including site-directed mutagenesis, two-electrode voltage clamp, cysteine accessibility, disulfide trapping, and radioligand binding to test the hypothesis that a specific region in the receptor, Loop F of the gamma2 subunit, contributes to BZD efficacy and is important for coupling BZD binding to modulation of GABA-mediated current. Additional studies using receptors composed of tethered tandem subunits, patch clamping, and cysteine accessibility will provide insight into the mechanism by which BZDs relay their information to the GABA binding sites. Benzodiazepines are one of the most commonly prescribed classes of drugs and are used as anxiolytics, anticonvulsants, sleep aids, muscle relaxants, and antipsychotics. Research proposed in this study will enhance our understanding of the structural elements underlying the selective affinity and efficacy of benzodiazepines, and will be instrumental in the rational design of new, more effective drugs for the treatment of disorders ranging from anxiety to epilepsy.