Structures of thromboxane A2 receptor intracellular domain and Gαq C -terminal domain: Their roles in receptor-G protein coupling
Human thromboxane A2 receptor (TP) belongs to the G protein coupling receptor family and signals through Gq protein coupling. We have used multiple experimental approaches to characterize the structure/function relationship of important segments and residues of the TP and the α-subunit of the Gq protein. High-resolution 2D NMR technique was used to determine the 3D structures of constrained peptides mimicking the first, second and third intracellular loops of TP. The NMR-determined structures were then used to refine a homology model of the TP. Binding pocket of the Gαq protein was defined by this NMR refined model of TP and the residues in contact with Gαq protein were predicted. Furthermore, a 15 residue peptide corresponding to the C-terminal domain of the Gq protein α subunit (Gαq-Ct peptide) was synthesized and its interactions with TP purified from a baculovirus expression system in the presence and absence of an agonist were characterized using fluorescence and NMR spectroscopic studies. The results indicate that TP binds to Gαq-Ct peptide with a Kd of 17µM in the absence of agonist activation while agonist activated TP receptor binds Gαq-Ct peptide with a Kd of 240µM. When compare with the other well-characterized Gαt protein, the C-terminus of Gαq shows a different solution structure and undergoes a different conformation change when binding to TP receptor.
Wu, Jiaxin, "Structures of thromboxane A2 receptor intracellular domain and Gαq C -terminal domain: Their roles in receptor-G protein coupling" (2008). Texas Medical Center Dissertations (via ProQuest). AAI3343819.