A metastable GαS/β-arrestin complex sustains endosomal PTH1R signaling

A metastable PTH1R–beta-arrestin1–GαS complex sustains endosomal cAMP signaling, with endosome-specific Gas–arrestin interaction revealed by compartment-restricted inhibition.

• Why it matters: GPCRs are typically silenced when beta-arrestin binds phosphorylated receptors, yet some receptors keep producing cAMP after internalization. The missing piece was how the GαS–beta-arrestin complex functions in endosomes in live cells.
• What they did: In intact cells, confocal imaging with a nucleotide-free GαS nanobody and single-molecule localization microscopy mapped activated GαS, beta-arrestin1, and agonist-occupied PTH1R on the same endosomes versus the plasma membrane. FRET and an endosome-restricted GαS inhibitor tested whether the sustained cAMP phase depends on endosomal complex formation.
• The result: FRET showed a specific GαS–beta-arrestin interaction only on endosomes, and the endosome-restricted Gas inhibitor abolished the sustained cAMP phase without changing receptor internalization. Simulations indicated the complex is metastable, with GαS release via a rigid-body rotation while beta-arrestin1 tightens receptor contacts.

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