Post-translational modifications orchestrate the intrinsic signaling bias of GPR52

Despite recent advances in G-protein-coupled receptor (GPCR) biology, the regulation of GPCR activation, signaling and function by post-translational modifications (PTMs) remains largely unexplored. In this study of GPR52, an orphan GPCR with exceedingly high constitutive G-protein activity that is emerging as a neurotherapeutic target, we discovered its disproportionately low arrestin recruitment activity. After profiling the N-glycosylation and phosphorylation patterns, we found that these two types of PTMs differentially shape the intrinsic signaling bias of GPR52. While N-terminal N-glycosylation promotes constitutive G_s signaling possibly through favoring the self-activating conformation, phosphorylation in helix 8, to our great surprise, suppresses arrestin recruitment and attenuates receptor internalization. In addition, we uncovered the counteracting roles of N-glycosylation and phosphorylation in modulating GPR52-dependent accumulation of the huntingtin protein in brain striatal cells. Our study provides new insights into the regulation of intrinsic signaling bias and cellular function of an orphan GPCR through distinct PTMs in different motifs.