Identifying the roles of the amino terminal and first transmembrane regions of human D1-like dopaminergic receptors using mutagenesis

Abstract

Although D1-like dopaminergic receptors (D1R and D5R) share similar primary sequences, they possess distinct ligand binding and G protein-coupling properties. Since no ligands discriminate the closely related D1R and D5R, the discovery of their subtype-specific functional and physiological functions is stalled. To provide additional conformational data about the binding pocket of D1-like receptors, we assessed the functional roles of their highly divergent amino terminal cassette. Using a chimerical approach, we swapped the extracellular amino terminal (NT) and first transmembrane (TM1) regions of human D1-like receptors and found that both regions distinctly control dopamine efficacy. Furthermore, chimeras with a swapped TM1 domain have altered affinity and selectivity properties. We further identified two residues in TM1 controlling ligand binding while one of them is also crucial for dopamine efficacy. Our present results highlight structural and functional roles of TM1 and NT of human D1-like dopaminergic receptors.