Constitutive G protein coupling profiles of understudied orphan GPCRs

A large number of GPCRs are potentially valuable drug targets but remain understudied. Many of these lack well-validated activating ligands and are considered orphan receptors, and G protein coupling profiles have not been defined for many orphan GPCRs. Here we asked if constitutive receptor activity can be used to determine G protein coupling profiles of orphan GPCRs. We monitored nucleotide-sensitive interactions between 48 understudied orphan GPCRs and five G proteins (240 combinations) using bioluminescence resonance energy transfer (BRET). No receptor ligands were used, but GDP was used as a common G protein ligand to disrupt receptor-G protein complexes. Constitutive BRET between the same receptors and beta-arrestins was also measured. We found sufficient GDP-sensitive BRET to generate G protein coupling profiles for 22 of the 48 receptors we studied. Altogether we identified 48 coupled receptor-G protein pairs, many of which have not been described previously. We conclude that receptor-G protein complexes that form spontaneously in the absence of guanine nucleotides can be used to profile G protein coupling of constitutively-active GPCRs. This approach may prove useful for studying G protein coupling of other GPCRs for which activating ligands are not available.

Automated summary

A study aimed to determine the G protein coupling profiles of orphan GPCRs using constitutive receptor activity. Out of 48 understudied orphan GPCRs, 22 were found to have sufficient GDP-sensitive bioluminescence resonance energy transfer (BRET) to generate G protein coupling profiles. A total of 48 coupled receptor-G protein pairs were identified, many of which were previously undescribed. This approach may be useful for studying G protein coupling of other GPCRs lacking activating ligands.