In order to identify the amino acids responsible for coupling selectivity between GPCRs and G-proteins, we examined the protein-protein interface of two different ternary complexes, the agonist-bound β2AR-Gαs crystal structure and, based on the β2AR-Gαs-structure, two homology models of the dopaminergic D2 receptor (D2R), a drug target of particular interest for the treatment of neuropsychiatric disorders including Parkinson’s disease and schizophrenia [19], in complex with dopamine and Gαi1. This evidence concerns the gene ADRB2 and Parkinson disease.