Genetically encoded intrabody sensors illuminate structural and functional diversity in GPCR-β-arrestin complexes

Interaction of {beta}-arrestins ({beta}arrs) upon agonist-stimulation is a hallmark of G protein-coupled receptors (GPCRs) resulting in receptor desensitization, endocytosis and signaling. Although overall functional roles of {beta}arrs are typically believed to be conserved across different receptors, emerging data now clearly unveils receptor-specific functional contribution of {beta}arrs. The underlying mechanism however remains mostly speculative and represents a key missing link in our current understanding of GPCR signaling and regulatory paradigms. Here, we develop synthetic intrabody-based conformational sensors that help us visualize the assembly and trafficking of GPCR-{beta}arr1 complexes in cellular context for a broad set of receptors with spatio-temporal resolution. Surprisingly, these conformational sensors reveal a previously unappreciated level of diversity in GPCR-{beta}arr complexes that extends beyond the current framework of affinity-based classification and phosphorylation-code-based interaction patterns. More importantly, this conformational diversity arising from spatial signature of phosphorylation sites manifests directly in the form of distinct functional outcomes, including even opposite contribution of {beta}arrs in signal-transduction for different receptors. Taken together, these findings uncover that despite an overall similar interaction and trafficking patterns; critical structural and functional differences exist in {beta}arr complexes for different GPCRs that define and fine-tune receptor-specific downstream responses.