Iwasiow, Rafal M2013-11-082013-11-0820042004Source: Dissertation Abstracts International, Volume: 66-05, Section: B, page: 2441.http://hdl.handle.net/10393/29118http://dx.doi.org/10.20381/ruor-19602Dopamine mediates its effects through the interaction with five distinct receptors that make up the D1-like (D1 and D5) and D2-like (D2, D3, and D4) families. Dopamine receptors are members of the heptahelical G protein-coupled receptor (GPCR) family. D1-like and D2-like receptors couple to the activation and inhibition of adenylyl cyclase, respectively. Dysfunction in dopaminergic signaling has been shown to contribute, among others to the etiology of Parkinson's disease, schizophrenia, and hypertension. The high degree of structural identity between D1 and D5 receptors has hampered the development of subtype-selective drugs. Despite the structural similarities, D1 and D5 receptor subtypes exhibit distinct ligand binding and G protein coupling properties. The objective of this thesis is to delineate the structural determinants involved in the distinct ligand binding and G protein coupling properties of D1 and D5 receptors Using chimeric and mutagenesis studies I demonstrate that differences in the primary sequence within the terminal receptor locus (a region encompassing TM6, third extracellular loop (EL3), TM7, and the cytoplasmic tail) are responsible for the functional differences of D1 and D5 receptors. I describe the EL3 domain as a key determinant in the binding of antipsychotic drugs (inverse agonists) and the agonist-mediated maximal activation of adenylyl cyclase. This study highlights a novel domain (EL3) regulating binding of inverse agonists at GPCRs. Furthermore, I describe a molecular interplay between TM6 and EL3 which mediates the subtype-specific phenotypes and activation of D1 and D5 receptors. In addition, I demonstrate that in spite of structural and functional similarities, D1-like receptors undergo a different regulatory pathway upon agonist stimulation. Specifically I demonstrate that the D5 receptor can undergo phosphorylation-independent desensitization and endocytosis. Overall, the work described in this thesis provides insight into the molecular basis of D1-like receptor signaling.255 p.enBiology, Neuroscience.Thesis