UC San Diego

GABAA receptors belong to the Cys-loop superfamily of ligand gated ionchannels and are the major inhibitory ionotropic neurotransmitter receptors in the central nervous system. Binding of the neurotransmitter GABA to GABAA receptors results in opening of an intrinsic chloride channel, which in most cases reduces the neuronal excitability. Dysfunction of the GABAA receptors leads to neurological and mental illnesses including insomnia, anxiety and epilepsy. GABAARs are targeted by diverse and important therapeutics and recreational drugs such as barbiturates, benzodiazepines, anticonvulsants, neurosteroids, anesthetics, ethanol and others. Chapter 1 of my dissertation is devoted to introducing the pharmacology and mechanism of gating of the family of Cys-loop receptors, with an emphasis on the GABAA receptor. In the Chapter 2, I focus on the infamous drug methaqualone, widely known as Quaalude, which targets and positively modulates GABAA receptors, yet its structural mechanism of action was unknown. Methaqualone is a central nervous system (CNS) depressant that was used clinically as an anxiolytic and sedative, and due to its euphoric properties quickly became a recreational drug in the 1960s-80s. It is now popular as a recreational drug, and many of its synthetic derivatives can be found around the world. Chapter 2 is devoted to investigation of the mechanism of action of quinazolinone drugs on the GABAA receptor using structural, mutagenesis and electrophysiological methods. The overall goal of my research was to understand how the quinazolinone family of drugs allosterically modulates receptor activity. GABAARs mediate ion conductance through changes in structural conformation as they transition through their so-called gating cycle. The gating cycle comprises three major functional states: resting, activated, and desensitized. To date, the activated-state structure has been resolved for other members of the Cys-loop superfamily, however the GABAAR activated state structure remains absent. Chapter 3 is devoted to my efforts in obtaining the activated state structure of the GABAA receptor with an overall goal to understand the gating mechanism of GABAARs. Finally, in Chapter 4, I discuss currently available studies on Cys-loop receptor superfamily gating. I address challenges encountered during this study and limitations coming from membrane mimetics, and propose further directions.