β-arrestin1 directly engages Gαs to sustain endosomal GPCR signaling

Beta-arrestin1 directly interacts with Gs to maintain endosomal GPCR signaling. Unlike conventional beta-arrestins that terminate G protein-coupled receptor (GPCR) signaling, internalized receptors paradoxically sustain beta-arrestin1-dependent Gs/cAMP signaling from endosomes. The mechanism behind this counterintuitive behavior has been unclear, as previous studies showed receptor-beta-arrestin1-G protein assemblies positioned on opposite sides of the receptor without any contact between them.

By investigating the parathyroid hormone type 1 receptor (PTH1R), researchers discovered that beta-arrestin1 binds Gs directly and engages its nucleotide-free state more strongly than it interacts with Gβγ. A cryo-electron microscopy structure of the agonist-bound PTH1R-beta-arrestin1-Gs complex at 3.1 Å resolution elucidates the interaction: beta-arrestin1 anchors to the phosphorylated receptor C-tail, leaving the transmembrane core free for Gs, and reorients to form a direct three-node interface.

This interface clamps the Switch I, Switch II, and 3/β5 regions of Gs, with either side of the interface disruption leading to complex assembly abolishment and selective collapse of the internalization-dependent phase of cAMP production. Notably, the same interface governs beta-arrestin1-Gs coupling at the glucagon-like peptide-1 receptor.

Consequently, beta-arrestin1 functions as a positive regulator, keeping Gs in a signaling-competent state, thereby providing a unifying structural basis for sustained endosomal GPCR signaling.