Author:
Van Eps Ned,Caro Lydia N.,Morizumi Takefumi,Kusnetzow Ana Karin,Szczepek Michal,Hofmann Klaus Peter,Bayburt Timothy H.,Sligar Stephen G.,Ernst Oliver P.,Hubbell Wayne L.
Abstract
Conformational equilibria of G-protein–coupled receptors (GPCRs) are intimately involved in intracellular signaling. Here conformational substates of the GPCR rhodopsin are investigated in micelles of dodecyl maltoside (DDM) and in phospholipid nanodiscs by monitoring the spatial positions of transmembrane helices 6 and 7 at the cytoplasmic surface using site-directed spin labeling and double electron–electron resonance spectroscopy. The photoactivated receptor in DDM is dominated by one conformation with weak pH dependence. In nanodiscs, however, an ensemble of pH-dependent conformational substates is observed, even at pH 6.0 where the MIIbH+ form defined by proton uptake and optical spectroscopic methods is reported to be the sole species present in native disk membranes. In nanodiscs, the ensemble of substates in the photoactivated receptor spontaneously decays to that characteristic of the inactive state with a lifetime of ∼16 min at 20 °C. Importantly, transducin binding to the activated receptor selects a subset of the ensemble in which multiple substates are apparently retained. The results indicate that in a native-like lipid environment rhodopsin activation is not analogous to a simple binary switch between two defined conformations, but the activated receptor is in equilibrium between multiple conformers that in principle could recognize different binding partners.
Funder
NIH
Jules Stein Professor Endowment
National Eye Institute Core Grant
Canada Excellence Research Chairs, Government of Canada
Anne and Max Tanenbaum Chair in Neuroscience
NIH GM
ERC Advanced Grant
Publisher
Proceedings of the National Academy of Sciences
Cited by
82 articles.
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