Retinal dynamics underlie its switch from inverse agonist to agonist during rhodopsin activation

Abstract

In seeking to understand G protein-coupled receptor (GPCR)-mediated signaling, X-ray and magnetic resonance approaches have played important roles—yet neither the protein dynamics nor the plasticity of GPCRs are amenable to study. Here we show that solid-state 2H NMR relaxation elucidates picosecond-nanosecond timescale motions of the retinal ligand that impact upon larger-scale functional dynamics of rhodopsin in membranes. A multiscale activation mechanism is put forward, whereby retinal initiates collective helix fluctuations in the Meta I–Meta II equilibrium on the microsecond-millisecond timescale.

Solid-state 2 H NMR relaxation illuminates functional dynamics of retinal cofactor in membrane activation of rhodopsin

“…Solid-state NMR spectroscopy (28) is particularly important, as it gives knowledge of both protein structure and dynamics in a membrane lipid environment (29). We show here that 2 H NMR relaxation (30,31) delivers crucial missing information that cannot be obtained by any other method.…”

“…If only 2 H NMR spectra were recorded ( Fig. 1 C-E) we might conclude that few differences exist among the retinylidene methyl groups-yet site-specific variations in retinal mobility are clearly evident (29). Notably, the 2 H NMR relaxation rates differ by up to an order of magnitude, due to the internal dynamics of the retinylidene ligand.…”

“…By contrast, the C9-and C13-Me groups have T 1Z and T 1Q minima at lower temperatures, outside the measured range. Note that the T 1Z and T 1Q minima occur at higher temperature (to the left) for slower motions, and conversely at lower temperature (to the right) for faster motions (29). At a given minimum, the effective correlation time τ c is related to the Larmor (resonance) frequency ω 0 by τ c ≈ 1∕ω 0 ¼ 2 ns.…”

The Significance of G Protein-Coupled Receptor Crystallography for Drug Discovery

“…Were large scale movements of entire helices before G protein binding involved, it is thermodynamically unlikely that the equilibrium between the states could be potentiated by a simple protonation/deprotonation event(s). This line of reasoning can be extended, taking into the changes observed in retinal dynamics that occur upon photoactivation and the multiple activated states that this implies (only a subset of which are capable of activating G protein) (Struts et al, 2011).…”

Molecular Aspects of Opioid Receptors and Opioid Receptor Painkillers

“…Numerous experimental approaches have been utilized to investigate GPCR structure and activation including: solution and solid-state NMR, fluorescence, IR and UV spectroscopy, spin-labeling, site-directed mutagenesis, substituted cysteine accessibility, disulphide crosslinking, engineering metal-binding sites, and identification of constitutively active mutants. (Gether 2000;Meng and Bourne 2001;Parnot, Miserey-Lenkei et al 2002;Decaillot, Befort et al 2003;Hubbell, Altenbach et al 2003;Struts, Salgado et al 2011) Experimentally and computationally, the importance of the lipid membrane should be recognized. It is well documented that membrane composition affects receptor function.…”