Structural basis of α 1A -adrenergic receptor activation and recognition by an extracellular nanobody.

The α 1A- adrenergic receptor (α 1A AR) belongs to the family of G protein-coupled receptors that respond to adrenaline and noradrenaline. α 1A AR is involved in smooth muscle contraction and cognitive function. Here, we present three cryo-electron microscopy structures of human α 1A AR bound to the endogenous agonist noradrenaline, its selective agonist oxymetazoline, and the antagonist tamsulosin, with resolutions range from 2.9 Å to 3.5 Å. Our active and inactive α 1A AR structures reveal the activation mechanism and distinct ligand binding modes for noradrenaline compared with other adrenergic receptor subtypes. In addition, we identified a nanobody that preferentially binds to the extracellular vestibule of α 1A AR when bound to the selective agonist oxymetazoline. These results should facilitate the design of more selective therapeutic drugs targeting both orthosteric and allosteric sites in this receptor family.