Contributions of the GABA(A) receptor alpha(1) subunit to the structure and dynamics of the neurotransmitter binding pocket.

摘要

The γ-aminobutyric acid type A (GABA_A) receptor is the major inhibitory neurotransmitter receptor in the brain. It plays a role in epilepsy, anxiety, and sleeplessness, and interacts with several clinically prescribed drugs, including benzodiazepines and barbiturates. It is a member of the ligand-gated ion channel superfamily of receptors, which also includes the nicotinic acetylcholine, glycine, and serotonin type three receptors. These receptors are allosteric proteins; neurotransmitter binding occurs distant from the channel, and the mechanisms behind how ligand binding transduces to channel gating are not understood. The first step towards understanding this process is to elucidate the secondary structure of the binding pocket, and to identify conformational movements that occur within or near the binding site during allosteric processes such as ligand binding, channel gating, and drug modulation. The goals of my thesis were to map binding site regions on the α₁ subunit of the GABA_A receptor, and to elucidate conformational movements that occur within these regions during orthosteric ligand binding, channel gating, and barbiturate and benzodiazepine allosteric modulation.; Using the substituted cysteine accessibility method, I examined the secondary structure of three binding site regions of the α₁ subunit. I identified six amino acid residues that line the binding pocket. I determined that a negative subsite exists within the binding pocket, which provides information about the orientation of GABA during binding. I also identified residues that are specifically involved in mediating agonist versus antagonist actions.; I monitored conformational movements within or near the binding pocket during allosteric processes and identified residues that change accessibility during competitive antagonist binding, channel gating, and allosteric modulation induced by barbiturates and benzodiazepines. Finally, I identified a region of the α₁ subunit located between a GABA binding site region and a benzodiazepine binding site region that is involved in allosteric coupling of these two binding pockets. Overall, my thesis work has contributed to our understanding of the structure and dynamics of the neurotransmitter binding pocket of the GABA_A receptor.