Structure of the M2 muscarinic receptor-β-arrestin complex in a lipid nanodisc

Following agonist activation, G protein-coupled receptors (GPCRs) recruit β-arrestin, which desensitizes heterotrimeric G protein signaling and promotes receptor endocytosis(1). Additionally, β-arrestin directly regulates many cell signaling pathways that can induce cellular responses distinct from that of G proteins(2). Here we present a cryo-electron microscopy (cryoEM) structure of β-arrestin1 (βarr1) in complex with muscarinic acetylcholine-2-receptor (M2R) reconstituted in lipid nanodiscs. The M2R-βarr1 structure shows a multimodal network of flexible interactions, including binding of the βarr1 N-domain to phosphorylated receptor residues and βarr1 finger loop insertion into the M2R seven-transmembrane bundle, which adopts a conformation similar to that in the M2R-heterotrimeric G(o) protein structure(3). Moreover, the cryoEM map reveals that the βarr1 C-domain edge engages the lipid bilayer. Through atomistic simulations, biophysical, biochemical, and cellular assays, we show that the C-edge is critical for stable complex formation, βarr1 recruitment, receptor internalization, and desensitization of G protein activation. Taken together, these data suggest the cooperative interactions of β-arrestin with both the receptor and phospholipid bilayer contribute to its functional versatility.