The role of intrinsically disordered domains in regulating G protein coupled receptor signaling

The α2A adrenergic receptor (α2AAR) is a clinically important target for various diseases including hypertension, diabetes and chronic pain. Here, using single-molecule fluorescence resonance energy transfer imaging, we show how agonist-specific activation dynamics in both structured transmembrane domain (TMD) and intrinsically disorders regions (IDRs) of α2AAR lead to diverse signaling profiles. Through seven pairs of strategically designed fluorophore labels, we systematically investigate the real-time conformational changes of α2AAR. Our study reveals unique TM6 dynamics in α2AAR, featured by a high energy barrier for agonist-induced outward movements essential for activation. In contrast, we identify agonist-specific conformational dynamics of a partially disordered extracellular loop (ECL2), highlighting its role as a dynamic regulatory module that controls receptor function. Moreover, we characterize the conformational landscapes of the long third intracellular loop (ICL3), revealing its compact structural features and membrane-proximal localization in the basal state, where it acts as a negative allosteric regulator in transducer coupling. Furthermore, we identify multiful functional sub-states of ICL3 that are dynamically modulated by both kinase phosphorylation and drug efficacy. These findings offer previously underappreciated structural and dynamic insights into α2AAR function governed by both TMD and IDRs, and may open up new avenues for the development of better therapeutics.