The structural basis of agonist-induced activation in constitutively active rhodopsin

Structural studies of active states of the visual pigment rhodopsin, a G protein-coupled receptor, have previously been limited to apoprotein or opsin forms that do not contain the agonist all-trans-retinal. Two groups now report structures that reveal more details of the transformations involved in rhodopsin activation. Choe et al. solve the X-ray crystal structure of the metarhodopsin II intermediate of the photoreceptor rhodopsin, and Standfuss et al. determine the structure of a constitutively active mutant of rhodopsin bound to a peptide derived from the C-terminus of the G protein transducin.