A. structural model of the wild type Dopamine D4 receptor with bound ligand L750,667 (stick model and colored atom type with C-green, O-red, N-blue, H-white, I-purple) 19. The residues F2.61 and V3.28 in the second and third transmembrane domain (seen as orange sticks) aid in favorable interactions with the ligand. B. structural model of the wild type Dopamine D2 receptor with bound ligand L750,667. The residues V2.61 and F3.28 residues in TM2 and TM3 poses steric hindrance to the ligand.