Role of Tyr356(7.43) and Ser190(4.57) in Antagonist Binding in the Rat β1-Adrenergic Receptor

Site-directed mutagenesis and photoaffinity labeling experiments suggest the existence of at least two distinct binding orientations for aryloxypropanolamine competitive antagonists in the β-adrenergic receptor (β-AR), one where the aryloxy moiety is located near transmembrane α-helix 7 (tm 7) and another where it is near tm 5. To explore a hydrophobic pocket involving tms 1, 2, 3, and 7 for potential aryloxy interaction sites, we selected Tyr356(7.43) and Trp134(3.28) in the rat β1-AR for site-directed mutagenesis studies. Ser190(4.57) was also investigated, as the equivalent residues are known antagonist interaction sites in the muscarinic M1 and the dopamine D2 receptors. Binding affinities (pKi) of a series of structurally diverse aryloxypropanolamine competitive antagonists were determined for wild type and Y356A, Y356F, W134A, and S190A mutant rat β1-ARs stably expressed in Chinese hamster ovary cells. To visualize possible antagonist/receptor interactions, the compounds were docked into a three-dim...