Submitted to the Department of Structural Biology.
Ph.D. Stanford University 2014
G protein-coupled receptors (GPCRs) constitute the largest single family of transmembrane receptors in humans, and play important roles in the regulation of normal human physiology and the pathogenesis of disease. The muscarinic acetylcholine receptors are a subfamily of GPCRs, and mediate the parasympathetic effects of acetylcholine, in addition to playing critical roles in cognition, memory, and maintenance of metabolic homeostasis. The muscarinic receptors have long served as an important model system for understanding GPCR function in general. Moreover, muscarinic receptors are important targets in the treatment of disease, and are also responsible for many of the side effects of commonly used therapeutic drugs targeting other receptors. To better understand these important receptors, I employed X-ray crystallography to determine the structures of the M2 and M3 muscarinic receptors in inactive, antagonist-bound conformations. Next, I used these structures for computational ligand screening, leading to the identification of over a dozen new muscarinic ligands. Finally, I determined the structure of the M2 muscarinic receptor in an active conformation stabilized by an antibody fragment. Similarly, a second structure of the M2 receptor bound to a positive allosteric modulator was resolved, offering structural insights into the allosteric modulation of GPCRs by drug-like molecules. Taken together, this work provides a framework for the interpretation of the extensive and growing body of biological and pharmacological data regarding muscarinic receptor function, and lays a foundation for future studies of muscarinic receptor biology.