Structure and Function of the Alpha3Beta4 Nicotinic Acetylcholine Receptor

Nicotinic acetylcholine receptors are pentameric ligand-gated ion channels that are essential for the proper function of the central and peripheral nervous systems. The α3β4 subtype is highly expressed in the autonomic ganglia, where it contributes to signal transduction from the central nervous system to the periphery. Moreover, α3β4 receptors are found in key brain regions that modulate reward circuits and have therefore been identified as potential targets for anti-addiction therapeutics. Given the physiological importance of this protein, I sought to understand the molecular mechanisms underlying ligand recognition, channel gating, and ion permeation in the α3β4 nicotinic acetylcholine receptor. Paramount to this goal was the pursuit of a high-resolution structure of the α3β4 subtype. I initially attempted to determine a crystal structure of this receptor before taking advantage of recent technological advances in cryo-electron microscopy. Using this method, I solved the first structure of the α3β4 nicotinic receptor, which was also the first high-resolution structure of any nicotinic acetylcholine receptor in a lipidic environment. By obtaining structural information of the protein bound to a non-selective nicotinic agonist as well as an α3β4-selective ligand, I was able to draw conclusions regarding ligand-selectivity in the nicotinic receptor family. Furthermore, these structures provided a detailed view of the ordered regions of the intracellular domain for the first time, giving insight into the full ion permeation pathway of these channels. This work also provided a blueprint to examine other outstanding questions in the field. Specifically, I used structural and functional approaches to begin to understand the consequences of accessory subunit incorporation, the role of multivalent cations in the desensitization of nicotinic receptors, and the role of the intracellular domain in ion selectivity and rectification.