Homology modeling of C. nuchalis SWS1. Models are based on the bovine rhodopsin template, comparing the wild type structure with mutations (A) C86F, (B) C86S, and (C) S90C. Wild type residues are indicated in black, mutant residues in red. The 11-cis retinal chromphore is indicated in purple; with K296 in light blue, the site of chromophore attachment via a protonated Schiff base linkage. Estimated distances to the protonated Schiff base are indicated along the dotted lines.