 Arrestin binding to phosphorylated, active receptor also enables receptor signaling through arrestin partner proteins.Thus the GRK/arrestin system serves as a complex signaling switch for G protein-coupled receptors.GRK2 and the closely related GRK3 phosphorylate receptors at sites that encourage arrestin-mediated receptor desensitization, internalization and trafficking rather than arrestin-mediated signaling (in contrast to GRK5 and GRK6, which have the opposite effect).