Fig. 1.

The primary sequence of MUV (A, cytoplasmic side up) and a similarity-based model of the MUV binding site, with selected atoms of the retinal chromophore numbered (B, extracellular side up). The secondary structure elements (e.g., transmembrane segments) shown are based on the crystal structure of bovine rhodopsin. The five amino acids shown in larger yellow circles correspond to S85 in TM2; E108 in TM3, at the same position as the rhodopsin counterion (E113); E176 and S181 in β-strands 3 and 4 (EII, extracellular loop 2), respectively; and K291 in TM7, the retinal binding site (K296 in rhodopsin).