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 (ßarr). ßarr-dependent actions begin with recruitment of ßarr to the phosphorylated receptor tail and are followed by engagement with the receptor core. ßarrs are known to act as adaptor proteins binding receptors and various effectors, but it is unclear whether in addition to the scaffolding role ßarrs can allosterically activate their downstream targets. Here we demonstrate the direct allosteric activation of proto-oncogene kinase Src by GPCR-ßarr complexes in vitro and establish the conformational basis of the activation. Whereas free ßarr1 had no effect on Src activity, ßarr1 in complex with M2 muscarinic or ß2-adrenergic receptors reconstituted in lipid nanodiscs activate Src by reducing the lag phase in Src autophosphorylation. Interestingly, receptor-ßarr1 complexes formed with a ßarr1 mutant, in which the finger-loop, required to interact with the receptor core, has been deleted, fully retain the ability to activate Src. Similarly, ßarr1 in complex with only a phosphorylated C-terminal tail of the vasopressin 2 receptor activates Src as efficiently as GPCR-ßarr complexes. In contrast, ßarr1 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 ßarr1 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 ßarrs.