Figure 1.

Location of the mutated residues. A: Alignment of the TM3 and TM6 segments of rhodopsin, β₂-adrenergic, PTH and BLT1 receptors. The sequences of human BLT1, bovine rhodopsin, human β₂-adrenergic receptor, and opossum PTHR were aligned using Clustal W.²⁴. The residues mutated in each receptor are underlined. The residues in the TM6 segment of the β₂-adrenergic and PTH receptors directly involved in cation coordination are given in bold.¹⁹ B: Model of the 7TM helices showing the position of the mutated residues in TM3 and TM6. The model is presented from the cytoplasmic face. The residues in TM3 (V¹¹⁹) and TM6 (R²¹⁸ and T²¹⁹) that have been replaced by histidines are indicated. The figure in (B) was prepared in VMD.²⁵