Noncanonical scaffolding of G αi and β-arrestin by G protein-coupled receptors.

Heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) are common drug targets and canonically couple to specific G _α protein subtypes and β-arrestin adaptor proteins. G protein-mediated signaling and β-arrestin-mediated signaling have been considered separable. We show here that GPCRs promote a direct interaction between G _αi protein subtype family members and β-arrestins regardless of their canonical G _α protein subtype coupling. G _αi :β-arrestin complexes bound extracellular signal-regulated kinase (ERK), and their disruption impaired both ERK activation and cell migration, which is consistent with β-arrestins requiring a functional interaction with G _αi for certain signaling events. These results introduce a GPCR signaling mechanism distinct from canonical G protein activation in which GPCRs cause the formation of G _αi :β-arrestin signaling complexes.
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