Figure 5.

Agonist-induced conformational changes detected by fluorescence spectroscopy in β₂AR labeled at Cys265 with tetramethylrhodamine maleimide (TMR-β₂AR). A. Change in the intensity of TMR-β₂AR in response to norepinephrine and dopamine. The response to norepinephrine is best fit by a two-site exponential function. The rapid and slow components of the response are illustrated by the dotted lines. B. Change in the intensity of TMR-β₂AR in response to dopamine and catechol. C. Catechol and dopamine stimulated [³⁵S]GTPγS binding to purified β₂AR reconstituted with purified Gs. D. The change in the intensity of TMR-β₂AR in response to the non-catechol partial agonist salbutamol followed by the addition of catechol. Catechol can induce a conformational change in TMR-β₂AR bound to a saturating concentration of salbutamol, indicating that salbutamol and catechol occupy non-overlapping binding sites. E. The change in the intensity of TMR-β₂AR in response to norepinephrine followed by the addition of catechol. No catechol response is observed in TMR-β₂AR bound to a saturating concentration of norepinephrine indicating that these ligands share a common binding site. F. There is no significant change in the intensity of TMR-β₂AR in response to the inverse agonist ICI118,551. Catechol can induce a conformational change in β₂AR bound to a saturating concentration of ICI118,551, indicating that these ligands do not occupy the same binding space. G. [³⁵S]GTPγS binding to purified β₂AR reconstituted with purified Gs. Catechol weakly stimulates [³⁵S]GTPγS binding and ICI118,551 inhibits basal [³⁵S]GTPγS binding. Of interest, catechol can stimulate [³⁵S]GTPγS binding in β₂AR occupied by a saturating concentration of ICI118,551. The data presented here are adapted from Swaminath et al. [88, 89].