Color Change of Proteorhodopsin by a Single Amino Acid Replacement at a Distant Cytoplasmic Loop

Switching from red to pink: It has been believed that only the amino acids near the retinal chromophore are responsible for the color tuning of rhodopsins. Herein is reported a color change of proteorhodopsin, an archaeal-type rhodopsin in marine bacteria, by mutation of Ala178 to Arg at the E–F loop. The red shift at a neutral pH value amounts to 20 nm (see graph).