Beta-arrestin 1 mediated Src activation via Src SH3 domain revealed by cryo-electron microscopy

Beta-arrestins ({beta}arrs) are key regulators and transducers of G-protein coupled receptor signaling; however, little is known of how {beta}arrs communicate with their downstream effectors. Here, we report the first structural insights into the fundamental mechanisms driving {beta}arr-mediated signal transduction. Using cryo-electron microscopy, we elucidate how {beta}arr1 recruits and activates the non-receptor tyrosine kinase Src, the first identified signaling partner of {beta}arrs. {beta}arr1 engages Src SH3 through two distinct sites, each employing a different recognition mechanism: a polyproline motif in the N-domain and a non-proline-based interaction in the central crest region. At both sites {beta}arr1 interacts with the aromatic surface of SH3, disrupting the autoinhibited conformation of Src and directly triggering its allosteric activation. This structural evidence establishes {beta}arr1 as an active regulatory protein rather than a passive scaffold and suggests a potentially general mechanism for {beta}arr-mediated signaling across diverse effectors.