Activation of the β2-Adrenergic Receptor Involves Disruption of an Ionic Lock between the Cytoplasmic Ends of Transmembrane Segments 3 and 6*

By J. Ballesteros, A. Jensen, G. Liapakis, S. Rasmussen, Lei Shi, U. Gether, J. Javitch. Journal of Biological Chemistry, 2001

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The movements of transmembrane segments (TMs) 3 and 6 at the cytoplasmic side of the membrane play an important role in the activation of G-protein-coupled receptors. Here we provide evidence for the existence of an ionic lock that constrains the relative mobility of the cytoplasmic ends of TM3 and TM6 in the inactive state of the β2-adrenergic receptor. We propose that the highly conserved Arg-1313.50 at the cytoplasmic end of TM3 interacts both with the adjacent Asp-1303.49 and with Glu-2686.30 at the cytoplasmic end of TM6. Such a network of ionic interactions has now been directly supported by the high-resolution structure of the inactive state of rhodopsin. We hypothesized that the network of interactions would serve to constrain the receptor in the inactive state, and the release of this ionic lock could be a key step in receptor activation. To test this hypothesis, we made charge-neutralizing mutations of Glu-2686.30 and of Asp-1303.49 in the β2-adrenergic receptor. Alone and in combination, we observed a significant increase in basal and pindolol-stimulated cAMP accumulation in COS-7 cells transiently transfected with the mutant receptors. Moreover, based on the increased accessibility of Cys-2856.47 in TM6, we provide evidence for a conformational rearrangement of TM6 that is highly correlated with the extent of constitutive activity of the different mutants. The present experimental data together with the recent high-resolution structure of rhodopsin suggest that ionic interactions between Asp/Glu3.49, Arg3.50, and Glu6.30may constitute a common switch governing the activation of many rhodopsin-like G-protein-coupled receptors.

Subfields: Cellular and Molecular Neuroscience, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/f1b3cfcae74412797fbda4d475fed48de3c4a8be

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Citations in the corpus

The structure and function of G-protein-coupled receptors (2009, background): “For β 2 AR, mutation of these residues increases constitutive activit”
News from the protein mutability landscape. (2013, background): “Among these, we find (1) D79, for which a mutation to N was shown to affect binding of catecholamines and to produce an uncoupling between the receptor and stimulatory G-proteins [92,93], and (2) D130, for which mutations to A or N were shown to increase pindolol-stimulated cAMP accumulation [94,95]”
The Molecular Basis of G Protein–Coupled Receptor Activation (2018, background): “30A in β2AR increase basal activity but do not change agonist-induced activity (42, 43).”