A secondary structure model of rhodopsin showing the cytoplasmic, TM,
and the ID domains. The 10 cysteines are shown in yellow with black
circles; the three ID cysteines are highlighted by bolder circles.
Amino acid sequences adjoining the three cysteines of interest (for
identification of the disulfide bonds) are color coded for each
cysteine: red for Cys-110, green for Cys-185, and blue for Cys-187.
Native rhodopsin contains a disulfide bond between Cys-110 and Cys-187
(indicated by dashed line). The RP mutants studied here are located in
the TM domain (shown in blue boxes): G89D (helix II), L125R (helix
III), A164V (helix IV), and H211P (helix V).