Molecular switches involving the AP-2 β2 appendage regulate endocytic cargo selection and clathrin coat assembly

Clathrin-associated sorting proteins (CLASPs) expand the repertoire of endocytic cargo sorted into clathrin-coated vesicles beyond the transmembrane proteins that bind physically to the AP-2 adaptor. LDL and GPCRs are internalized by ARH and β-arrestin, respectively. We show that these two CLASPs bind selectively to the AP-2 β2 appendage platform via an α-helical [DE] nX 1-2 FXX[FL]XXXR motif, and that this motif also occurs and is functional in the epsins. In β-arrestin, this motif maintains the endocytosis-incompetent state by binding back on the folded core of the protein in a β strand conformation. Triggered via a β-arrestin/ GPCR interaction, the motif must be displaced and must undergo a strand to helix transition to enable the β2 appendage binding that drives GPCR-β-arrestin complexes into clathrin coats. Another interaction surface on the β2 appendage sandwich is identified for proteins such as eps15 and clathrin, suggesting a mechanism by which clathrin displaces eps15 to lat