In the present case, since amino-aromatic bonding between the Reversine agonist “switch” Tyr4 of Ang II and the agonist switch-binding residue Asn111 of the AT1 receptor is responsible for initiating receptor activation, we speculated that aromaticity of the ligand as an agonist may be important for the activation of AT1 receptor. The neutral antagonist R239470 with an aromatic ring may act as an agonist. Using the substituted cysteine accessibility mapping method, Martin et al. identified the residues within TM3 of the AT1 receptor that contribute to the formation of the binding site pocket and found that constitutive activation of AT1 receptor causes slight counterclockwise rotation of TM3. We speculated that an inverse agonist, neutral antagonist and agonist would induce different changes in the conformation of TM3 of AT1 receptor. To address this question, we systematically mutated the AT1 receptor and examined whether olmesartan-related compounds would induce agonism, and subsequently analyzed the specific action of an inverse agonist, neutral antagonist and agonist on the receptor conformation with respect to stabilization around TM3 as assessed by SCAM and molecular modeling of the AT1 receptor. Based on the results of these experiments, we developed a new agonist from the inverse agonist against the AT1 receptor and demonstrated the ligand-induced specific action on changes in the conformation of TM3 in the receptor. In the present study, small molecules with similar structures, olmesartan, R239470 and R794847, acted as an inverse agonist, neutral antagonist and agonist, respectively. These molecules induced specific actions in TM3 of AT1 receptor. Notably, activation of most GPCRs induces a certain change in the conformation of TM3. Our site-directed mutagenesis and SCAM studies support the novel concept that ligand-induced changes in the conformation of TM3 play a role in GPCR activation in a native membrane environment. Although it is now generally accepted that individual ligands can induce different receptor conformations, little is known about the actual differences at the molecular level. To gain information about the transition from an inactive receptor conformation to an active conformation, several different techniques have been developed and used over the past decade. While the crystal structures of GPCRs obtained from the rhodopsin, opsin, and ß1 and ß2-AR systems have recently been described, the crystal structures of AT1 receptor have not been elucidated. In addition, despite the importance of these structures for GPCR research, crystallography has major limitations with regard to characterizing and understanding the physiological importance of receptors. Using a native membrane environment, we systematically mutated the AT1 receptor and examined the specific effects of olmesartan, R239470 and R794847 on the conformation of the AT1 receptor with respect to stabilization of TM3 as assessed by SCAM and molecular modeling of the AT1 receptor. While activating ligands stabilize receptor conformations that increase signaling through G proteins.