Structural basis of agonist specificity of α(1A)-adrenergic receptor

α(1)-adrenergic receptors (α(1)-ARs) play critical roles in the cardiovascular and nervous systems where they regulate blood pressure, cognition, and metabolism. However, the lack of specific agonists for all α(1) subtypes has limited our understanding of the physiological roles of different α(1)-AR subtypes, and led to the stagnancy in agonist-based drug development for these receptors. Here we report cryo-EM structures of α(1A)-AR in complex with heterotrimeric G-proteins and either the endogenous common agonist epinephrine or the α(1A)-AR-specific synthetic agonist A61603. These structures provide molecular insights into the mechanisms underlying the discrimination between α(1A)-AR and α(1B)-AR by A61603. Guided by the structures and corresponding molecular dynamics simulations, we engineer α(1A)-AR mutants that are not responsive to A61603, and α(1B)-AR mutants that can be potently activated by A61603. Together, these findings advance our understanding of the agonist specificity for α(1)-ARs at the molecular level, opening the possibility of rational design of subtype-specific agonists.