Homo-oligomerization of the human adenosine A_2A receptor is driven by the intrinsically disordered C-terminus

G protein-coupled receptors (GPCRs) have long been shown to exist as oligomers with functional properties distinct from those of the monomeric counterparts, but the driving factors of oligomerization remain relatively unexplored. Herein, we focus on the human adenosine A_2A receptor (A_2AR), a model GPCR that forms oligomers both in vitro and in vivo. Combining experimental and computational approaches, we discover that the intrinsically disordered C-terminus of A_2AR drives receptor homo-oligomerization. The formation of A_2AR oligomers declines progressively with the shortening of the C-terminus. Multiple interaction types are responsible for A_2AR oligomerization, including disulfide linkages, hydrogen bonds, electrostatic interactions, and hydrophobic interactions. These interactions are enhanced by depletion interactions, giving rise to a tunable network of bonds that allow A_2AR oligomers to adopt multiple interfaces. This study uncovers the disordered C-terminus as a prominent driving factor for the oligomerization of a GPCR, offering important insight into the effect of C-terminus modification on receptor oligomerization of A_2AR and other GPCRs reconstituted in vitro for biophysical studies.