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Coupling ligand structure to specific conformational switches in the β2-adrenoceptor


G protein–coupled receptors (GPCRs) regulate a wide variety of physiological functions in response to structurally diverse ligands ranging from cations and small organic molecules to peptides and glycoproteins. For many GPCRs, structurally related ligands can have diverse efficacy profiles. To investigate the process of ligand binding and activation, we used fluorescence spectroscopy to study the ability of ligands having different efficacies to induce a specific conformational change in the human β2-adrenoceptor (β2-AR). The 'ionic lock' is a molecular switch found in rhodopsin-family GPCRs that has been proposed to link the cytoplasmic ends of transmembrane domains 3 and 6 in the inactive state1,2,3. We found that most partial agonists were as effective as full agonists in disrupting the ionic lock. Our results show that disruption of this important molecular switch is necessary, but not sufficient, for full activation of the β2-AR.

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Figure 1: Molecular model of the β2-AR.
Figure 2: Fluorescence intensity of the bimane-attached Cys271.
Figure 3: Bimane response to catechol and noncatechol agonists.
Figure 4: Functional interactions of β2-AR–Δ5-Cys271+Trp135 with dopamine and catechol.

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This work was supported by grants from the US National Institutes of Health (Grant 5 RO1 NS28471 to B.K. and Grant R01 DA14896 to D.F.) and the Mather's Charitable Foundation (to B.K.).

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Correspondence to Brian Kobilka.

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Supplementary information

Supplementary Fig. 1

Site-specific labeling of Cys271 in the β2-AR. (PDF 658 kb)

Supplementary Fig. 2

Isoproterenol binding to bimane-labeled β2-AR-Δ5-Cys271+Trp135. (PDF 531 kb)

Supplementary Table 1

Equilibrium dissociation constants for ligand binding to the β2-AR-Δ5-Cys271 and β2-AR-Δ5-Cys271+Trp135 receptors. (PDF 99 kb)

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Yao, X., Parnot, C., Deupi, X. et al. Coupling ligand structure to specific conformational switches in the β2-adrenoceptor. Nat Chem Biol 2, 417–422 (2006).

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