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Elife. 2018 Jun 22;7. pii: e32499. doi: 10.7554/eLife.32499.

Measuring ligand efficacy at the mu-opioid receptor using a conformational biosensor.

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Department of Pharmacology, University of Michigan Medical School, Ann Arbor, United States.
Edward F Domino Research Center, University of Michigan, Ann Arbor, United States.
Department of Pharmaceutical Chemistry, School of Pharmacy, University of California San Francisco, San Francisco, United States.
Department of Pharmacology, University of California San Diego School of Medicine, La Jolla, United States.


The intrinsic efficacy of orthosteric ligands acting at G-protein-coupled receptors (GPCRs) reflects their ability to stabilize active receptor states (R*) and is a major determinant of their physiological effects. Here, we present a direct way to quantify the efficacy of ligands by measuring the binding of a R*-specific biosensor to purified receptor employing interferometry. As an example, we use the mu-opioid receptor (µ-OR), a prototypic class A GPCR, and its active state sensor, nanobody-39 (Nb39). We demonstrate that ligands vary in their ability to recruit Nb39 to µ-OR and describe methadone, loperamide, and PZM21 as ligands that support unique R* conformation(s) of µ-OR. We further show that positive allosteric modulators of µ-OR promote formation of R* in addition to enhancing promotion by orthosteric agonists. Finally, we demonstrate that the technique can be utilized with heterotrimeric G protein. The method is cell-free, signal transduction-independent and is generally applicable to GPCRs.


GPCR; biochemistry; chemical biology; drug discovery; efficacy; ligand; molecular biophysics; mouse; opioid; structural biology

[Indexed for MEDLINE]
Free PMC Article

Conflict of interest statement

KL, JM, AM, RS, JT No competing interests declared

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