Cytoplasmic tail composition modulates the G protein and arrestin-3 signaling bias of the adhesion GPCR LPHN2.

The class B2 Adhesion GPCRs (aGPCRs) combine cell adhesion with GPCR signaling to control diverse developmental and physiological processes. How aGPCRs interact with and integrate distinct groups of effectors including G proteins, arrestins, and G protein receptor kinases (GRKs) remains unclear. Here, we find that diversity in the aGPCR C-terminal intracellular tail modulates G protein activation, arrestin-3 recruitment, and utilization of selective GRKs in LPHN2, a postsynaptic aGPCR essential for synapse formation. The C-terminal tail of LPHN2 is required for G protein activation and arrestin-3 recruitment. LPHN2 with an intact tail recruits arrestin-3 in the absence of G protein activation, suggesting constitutive arrestin-3-biased signaling. Alternative splicing of the LPHN2 tail modulates G protein activation and arrestin-3 binding independently, supporting that it controls G protein vs arrestin-3 bias. GRKs are important but not essential for arrestin-3 recruitment to LPHN2. Moreover, GRK2 increases arrestin-3 recruitment only in a subset of LPHN2 variants. Collectively, these results show that the mechanisms of the interactions of class B2 aGPCRs and arrestin are distinct from those of class A GPCRs and that splicing of the LPHN2 C-terminal tail determines G protein vs arrestin bias.