β-arrestin recruitment facilitates a direct association with G proteins

Abstract

G protein-coupled receptors (GPCRs) are targets for almost a third of all FDA-approved drugs. GPCRs are known to signal through both heterotrimeric G proteins and {beta}-arrestins. Traditionally these pathways were viewed as largely separable, with G proteins primarily initiating downstream signaling while {beta}-arrestins modulate receptor trafficking and desensitization in addition to regulating their own signaling events. Recent studies suggest an integrated role of G proteins and {beta}-arrestins in GPCR signaling, however the cellular and biochemical requirements for G protein: {beta}-arrestin interactions remain unclear. Here we show that G proteins and {beta}-arrestins can directly interact. Through utilization of {beta}-arrestin-biased receptors and artificially enforced {beta}-arrestin relocalization, we demonstrate that recruitment of {beta}-arrestin to the plasma membrane is sufficient to interact with the G protein Gi. Using purified proteins, we show that Gi directly interacts with {beta}-arrestin. In addition, we find that Gi family members differ in their degree of association with {beta}-arrestin, and that a large degree of this selectivity resides within the alpha helical domain of Gi. These findings delineate the cellular and biochemical conditions that drive direct interactions between G proteins and {beta}-arrestins and illuminate the molecular basis for how they work together to effect GPCR signaling.