Biased agonism and allosteric modulation of GPR183- a 7TM receptor also known as EBV-induced EBI2
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BACKGROUND AND PURPOSE: The G protein-coupled receptor Epstein Barr virus-induced gene 2 (EBI2, also known as GPR183) is activated by oxysterols and plays a pivotal role for proper B cell migration during immune responses. While the molecular basis of agonist binding has been addressed in several studies, the concept of biased agonism of EBI2 has not been explored.
EXPERIMENTAL APPROACH: We investigated the effects of the EBI2 endogenous agonist 7α,25-OHC on G protein-dependent and -independent pathways as well as sodium ion allosterism using site-directed mutagenesis and functional studies. Moreover, we generated a homology model of EBI2 to investigate the structural basis of the allosteric modulation by sodium.
KEY RESULTS: We show that residue N114, located in the middle of TM-III at position III:11/3.35, functions as an efficacy switch. Thus, substituting N114 with an alanine (N114A) completely abolishes Gαi activation by 7α,25-OHC even though the specific binding of the [(3) H]-7α,25-OHC radioligand increases. In contrast, the N114A mutant is still able to recruit β-arrestin and even with enhanced the potency (18.7-fold) compared to EBI2 WT. Underscoring the key role of N114, we also show that sodium has an negative allosteric effect on oxysterol binding and that this is mediated via N114. This is further supported by molecular modelling of the ion binding site based on a EBI2 homology model. Conclusions and Implications Collectively, our data points to N114 as a key residue for EBI2 signaling controlling the balance between G protein-dependent and -independent pathways and facilitating sodium binding.
|Tidsskrift||British Journal of Pharmacology|
|Status||Udgivet - 2017|