Distinct antagonist-bound inactive states underlie the divergence in the structures of the dopamine D2 and D3 receptors

ABSTRACT Understanding how crystal structures reflect the range of possible G protein-coupled receptor (GPCR) states is critical for rational drug discovery (RDD). Combining computational simulations with mutagenesis and binding studies, we find that the structure of the dopamine D2 receptor (D 2 R)/risperidone complex captures an inactive receptor conformation that accommodates some but not all antagonist scaffolds. Indeed, we find that eticlopride binds D 2 R in a configuration very similar to that seen in the D 3 R structure, in a pose that is incompatible with the D 2 R/risperidone structure. Moreover, our simulations reveal that extracellular loops 1 and 2 (EL1 and EL2) are highly dynamic, with spontaneous transitions of EL2 from the helical conformation in the D 2 R/risperidone structure to an extended conformation similar to that in the D 3 R/eticlopride structure. Our results highlight previously unappreciated conformational diversity and dynamics in the inactive state of a GPCR with potential functional implications. These findings are also of paramount importance for RDD as limiting a virtual screen to one state will miss relevant ligands.