Structure of the Human Dopamine D3 Receptor in Complex with a D2/D3 Selective Antagonist

Tweaking Dopamine Reception Dopamine modulates many cognitive and emotional functions of the human brain by activating G protein–coupled receptors. Antipsychotic drugs that block two of the receptor subtypes are used to treat schizophrenia but have multiple side effects. Chien et al. (p. 1091; see the Research Article by Wu et al.) resolved the crystal structure of one receptor in complex with a small-molecule inhibitor at 3.15 angstrom resolution. Homology modeling with other receptor subtypes might be a promising route to reveal potential structural differences that can be exploited in the design of selective therapeutic inhibitors having fewer side effects. Discovery of a binding site in the extracellular domain of a dopamine receptor offers hope for more selective therapeutics. Dopamine modulates movement, cognition, and emotion through activation of dopamine G protein–coupled receptors in the brain. The crystal structure of the human dopamine D3 receptor (D3R) in complex with the small molecule D2R/D3R-specific antagonist eticlopride reveals important features of the ligand binding pocket and extracellular loops. On the intracellular side of the receptor, a locked conformation of the ionic lock and two distinctly different conformations of intracellular loop 2 are observed. Docking of R-22, a D3R-selective antagonist, reveals an extracellular extension of the eticlopride binding site that comprises a second binding pocket for the aryl amide of R-22, which differs between the highly homologous D2R and D3R. This difference provides direction to the design of D3R-selective agents for treating drug abuse and other neuropsychiatric indications.