Allosteric activation of proto-oncogene kinase Src by GPCR-beta-arrestin complexes

G protein-coupled receptors (GPCRs) initiate signaling cascades via G-proteins and beta-arrestins (beta arr). beta arr-dependent actions begin with recruitment of beta arr to the phosphorylated receptor tail and are followed by engagement with the receptor core. beta arrs are known to act as adaptor proteins binding receptors and various effectors, but it is unclear whether in addition to the scaffolding role beta arrs can allosterically activate their downstream targets. Here we demonstrate the direct allosteric activation of proto-oncogene kinase Src by GPCR-beta arr complexes in vitro and establish the conformational basis of the activation. Whereas free beta arr1 had no effect on Src activity, beta arr1 in complex with M2 muscarinic or beta 2-adrenergic receptors reconstituted in lipid nanodiscs activate Src by reducing the lag phase in Src autophosphorylation. Interestingly, receptor-beta arr1 complexes formed with a beta arr1 mutant, in which the finger-loop, required to interact with the receptor core, has been deleted, fully retain the ability to activate Src. Similarly, beta arr1 in complex with only a phosphorylated C-terminal tail of the vasopressin 2 receptor activates Src as efficiently as GPCR-beta arr complexes. In contrast, beta arr1 and chimeric M2 receptor with nonphosphorylated C-terminal tail failed to activate Src. Taken together, these data demonstrate that the phosphorylated GPCR tail interaction with beta arr1 is necessary and sufficient to empower it to allosterically activate Src. Our findings may have implications for understanding more broadly the mechanisms of allosteric activation of downstream targets by beta arrs.