Cryo-EM Structure of the β3 Adrenergic Receptor Reveals the Molecular Basis of Subtype Selectivity

β3 AR is the last piece of β adrenergic receptor and predominantly expressed in adipose tissue and urinary bladder, and thus has emerged as attractive drug targets for treatments of type2 diabetes, obesity, and overactive bladder (OAB). Here we report a 3.2 A cryo-electron microscopy structure of the β3 AR-Gs complex bound to the selective agonist mirabegron, a first-in-class drug for OAB. Comparison of this structure with the previously reported β1 AR and β2 AR structures revealed a unique activation mechanism upon mirabegron binding to the orthosteric site. Moreover, the narrower exosite in β3 AR forms a perpendicular pocket for mirabegron. Mutational analyses demonstrated that the structural differences in the exosite, rather than amino-acid divergence, define the drug selectivity among the β adrenergic receptor subtypes. Our findings provide a molecular basis for β-AR subtype selectivity, allowing design of more selective agents with fewer adverse effects.