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| - Early Steps of the Intramolecular Signal Transduction in Rhodopsin Explored byMolecular Dynamics Simulations
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| - We present molecular dynamics simulations of bovine rhodopsin in a membrane mimeticenvironment based on the recently refined X-ray structure of the pigment. The interactions between theprotonated Schiff base and the protein moiety are explored both with the chromophore in the dark-adapted11-cis and in the photoisomerized all-trans form. Comparison of simulations with Glu181 in differentprotonation states strongly suggests that this loop residue located close to the 11-cis bond bears a negativecharge. Restrained molecular dynamics simulations also provide evidence that the protein tightly confinesthe absolute conformation of the retinal around the C12−C13 bond to a positive helicity. 11-cis to all-trans isomerization leads to an internally strained chromophore, which relaxes after a few nanosecondsby a switching of the ionone ring to an essentially planar all-trans conformation. This structural transitionof the retinal induces in turn significant conformational changes of the protein backbone, especially inhelix VI. Our results suggest a possible molecular mechanism for the early steps of intramolecular signaltransduction in a prototypical G-protein-coupled receptor.
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