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Kinetic, energetic, and mechanical differences between dark-state rhodopsin and opsin.

Structure (London, England : 1993) (2013-02-26)
Shiho Kawamura, Moritz Gerstung, Alejandro T Colozo, Jonne Helenius, Akiko Maeda, Niko Beerenwinkel, Paul S-H Park, Daniel J Müller
ABSTRACT

Rhodopsin, the photoreceptor pigment of the retina, initiates vision upon photon capture by its covalently linked chromophore 11-cis-retinal. In the absence of light, the chromophore serves as an inverse agonist locking the receptor in the inactive dark state. In the absence of chromophore, the apoprotein opsin shows low-level constitutive activity. Toward revealing insight into receptor properties controlled by the chromophore, we applied dynamic single-molecule force spectroscopy to quantify the kinetic, energetic, and mechanical differences between dark-state rhodopsin and opsin in native membranes from the retina of mice. Both rhodopsin and opsin are stabilized by ten structural segments. Compared to dark-state rhodopsin, the structural segments stabilizing opsin showed higher interaction strengths and mechanical rigidities and lower conformational variabilities, lifetimes, and free energies. These changes outline a common mechanism toward activating G-protein-coupled receptors. Additionally, we detected that opsin was more pliable and frequently stabilized alternate structural intermediates.

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Sigma-Aldrich
all trans-Retinal, powder, ≥98%