Structural basis of α1A-adrenergic receptor activation and recognition by an extracellular nanobody

Abstract

The α1A-adrenergic receptor (α1AAR) belongs to the family of G protein-coupled receptors that respond to adrenaline and noradrenaline. α1AAR is involved in smooth muscle contraction and cognitive function. Here, we present three cryo-electron microscopy structures of human α1AAR 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 α1AAR 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 α1AAR 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.

Highly biased agonism for GPCR ligands via nanobody tethering

“…Efforts to apply Nb-ligand tethering to other receptors will require Nbs (or antibodies) that bind to the extracellular receptor face. At current, there are limited number of examples of Nbs that bind surface-exposed regions of GPCRs [45][46][47][48][49][50] , and only some of these Nbs have been structurally characterized [51][52][53] . New Nb screening technologies 54,55 are emerging and will likely facilitate further progress.…”

Identification of a Novel Subtype-Selective α1B-Adrenoceptor Antagonist

“…In the past decade, advances in GPCR structural biology have provided many structures of the β-ARs in both active and inactive states , and, more recently, structures of α 1A -AR, α 2A -AR, , α 2B‑ AR, and α 2C -AR . These studies provide valuable information for understanding subtle structural differences between β- and α 2 -AR subtypes and have enabled structure-based drug discovery (SBDD) of novel selective ligands. , Recently, we determined the crystal structure of the α 1B -AR bound to the modestly α 1B -AR-selective inverse agonist (+)-cyclazosin, representing an important resource to enable the development of α 1B -AR-selective compounds.…”

“…In the past decade, advances in GPCR structural biology have provided many structures of the β-ARs in both active and inactive states 1,22 and, more recently, structures of α 1A -AR, 23 α 2A -AR, 24,25 α 2B-AR, 26 and α 2C -AR. 27 These studies provide valuable information for understanding subtle structural differences between βand α 2 -AR subtypes and have enabled structure-based drug discovery (SBDD) of novel selective ligands.…”

Structure elucidation of a human melanocortin-4 receptor specific orthosteric nanobody agonist

“…The de novo discovery of antibodies that activate signaling with a similar e cacy as the endogenous agonist ligand is notoriously di cult. Indeed, despite multiple reports describing positive allosteric modulating nanobodies that increase agonist a nity or signaling potency or e cacy at low ligand tonus 19,20,21,22,23 , only a few are reported to agonize the GPCR in the absence of any ligand. Some of the reported agonistic antibodies have been designed by ligand tethering (genetically fusing or grafting agonist ligand motifs into the antibody hypervariable complementarity determining region (CDR)) 24,25,26 or by structure-informed engineering 27 .…”