Investigation of G-protein specificity and biased agonism at the beta-2 adrenergic receptor (β2AR)

The beta-2-adrenergic receptor (β2AR) is a prototypical G-protein coupled receptor (GPCR). In cardiomyocytes, β2AR couples to the G-protein subtypes Gs and Gi to regulate cardiac function. We used this system to investigate the molecular determinants of biased agonism and G-protein specificity. We developed a Gi-biased agonist, LM189, that we used to obtain the Cryo-EM structure of the β2AR-Gi complex. Spectroscopic investigations by electron paramagnetic resonance spectroscopy (EPR) and single-molecule FRET (smFRET) show that distinct intermediate states, differentially stabilized by balanced and biased ligands, contribute to G-protein specificity. Understanding the basis of specificity and bias is important to design safer drugs that target GPCRs with reduced side effects.