Chapter 29

Fig. 29.4 Comparison of the crystal structures of inactive (green) and active rhodopsin. The photoactivation is triggered by retinal, when its cyclohexene ring shifts because of an isomerization of the 11-double bond from a cis to a trans configuration. This movement is translated to Trp265 and from there through a cascade of water-mediated H-bonds all the way to the “ionic lock,” which is made up of Glu134, Arg135, and Glu247. The salt bridges are dissolved, and the binding site for the binding epitope of the α-domain of the G protein is established.