Identification of allosteric sites and ligand-induced modulation in the dopamine receptor through large-scale alchemical mutation scan

G protein coupled receptors, particularly class A GPCRs are arguably the most important class of membrane receptors and preferred targets for drug development. Despite extensive research on how ligands modulate the receptor response, discovering new, highly specific ligands remains challenging. However, finding residues outside the conserved microswitches that affect the active–inactive state equilibrium and are specific for a certain receptor, can be beneficial for the design of ligands with higher receptor selectivity. Focusing on the human dopamine receptor 2 (DRD2), we uncover crucial residues for the activation modulation using alchemical non-equilibrium free energy calculations. Our findings match with literature on activation microswitches and experimental studies, while also uncovering novel important residues. Further, we analyzed mutation-induced changes in residue contact networks and found that modulating these networks can lead to a stabilization of the respective opposite state, an effect that could as well be achieved by well-engineered (small) ligands. This way we provide insights into the mechanism of action of the well-known drugs risperidone and bromocriptine and showcase on these two examples how our data can be used for the design of new ligands.