Viewing rare conformations of the β <sub>2</sub> adrenergic receptor with pressure-resolved DEER spectroscopy
Michael T. Lerch, Rachel A. Matt, Matthieu Masureel, Matthias Elgeti, Kaavya Krishna Kumar, Daniel Hilger, Bryon Foys, Brian K. Kobilka, Wayne L. Hubbell
Abstract
Significance The molecular origin of basal activity in G protein coupled receptors and its suppression by inverse agonists are poorly understood. Here we employ pressure-resolved DEER spectroscopy to explore the structural origin of basal activity and the mechanism of inverse agonism in the β 2 adrenergic receptor. Collectively, the results support a conformational selection model wherein basal activity is due to a preexisting equilibrium between inactive and active conformations in the unliganded receptor, and inverse agonists stabilize the inactive conformation. Furthermore, the results illustrate the importance of rare states in molecular mechanisms of protein function and the capability of pressure-resolved DEER for revealing structural features of sparsely populated conformations of membrane proteins and for determining their thermodynamic properties.