Structure of an Endosomal Signaling GPCR–G Protein–β-arrestin Mega-Complex

Classically, G protein-coupled receptors (GPCRs) are thought to activate G protein from the plasma membrane and are subsequently desensitized by β-arrestin (βarr). However, some GPCRs continue to signal through G protein from internalized compartments, mediated by a GPCR–G protein–βarr ’megaplex’. Nevertheless, the megaplex’s molecular architecture remains unknown. Here, we present its cryo-electron microscopy structure, which shows simultaneous engagement of human G protein and bovine βarr to the core and phosphorylated tail, respectively, of a single active human chimeric β(2)-adrenergic receptor with the C-terminal tail of the arginine vasopressin type 2 receptor (β(2)V(2)R). All three components adopt their canonical active conformations, suggesting that a single megaplex GPCR is capable of simultaneously activating G protein and βarr. Our findings provide a structural basis for GPCR-mediated sustained, internalized G protein signaling.