Mapping of Dopamine D₃ Receptor Binding Site by Pharmacological Characterization of Mutants Expressed in Cho Cells with the Semliki Forest Virus System

Abstract

Nine mutants and the wild-type human dopamine D₃ receptor were expressed at high levels in BHK and CHO cells using the Semliki Forest virus system and were analysed for receptor binding with several structurally different dopamine D₃ ligands. The mutation His349Leu showed a significant decrease in pK_i values for raclopride, dopamine and GR218231, but an increase in affinity for GR99841. Thr369Val had an increase in pK_i for both GR99841 and 7-OH-DPAT. The receptor modelling based on sequence alignment with bacteriorhodopsin indicated that Thr369 and His349 are located on the inside of the ligand binding pocket and the effect of the mutagenesis was therefore expected. The change in binding affinity for Thr369Val could be due to the location in the transmembrane domain VII close to the aspartate residue in domain III, the postulated counter ion for dopamine.