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Abstract
<p class="first" id="d1746096e151">Rhodopsin, a prototypical G protein-coupled receptor,
is a membrane protein that can
sense dim light. This highly effective photoreceptor is known to be sensitive to the
composition of its lipidic environment, but the molecular mechanisms underlying this
fine-tuned modulation of the receptor’s function and structural stability are not
fully understood. There are two competing hypotheses to explain how this occurs: 1)
lipid modulation occurs via solvent-like interactions, where lipid composition controls
membrane properties like hydrophobic thickness, which in turn modulate the protein’s
conformational equilibrium; or 2) protein-lipid interactions are ligand-like, with
specific hot spots and long-lived binding events. By analyzing an ensemble of all-atom
molecular dynamics simulations of five different states of rhodopsin, we show that
a local ordering effect takes place in the membrane upon receptor activation. Likewise,
docosahexaenoic acid acyl tails and phosphatidylethanolamine headgroups behave like
weak ligands, preferentially binding to the receptor in inactive-like conformations
and inducing subtle but significant structural changes.
</p>