Figure 5: X-ray crystallography of the C1C2GA mutant.

(a) Photographs of C1C2WT (left) and C1C2GA mutant (right). (b) Side view of the superimposed structures of C1C2WT (grey) and C1C2GA (green). The regions around the putative Zn²⁺-binding site and the β-ionone ring of the retinal molecule are highlighted in the blue and yellow rectangles, respectively. The N-terminal region only seen in C1C2GA is coloured blue. The putative Zn²⁺, depicted by a cpk model, is coloured pink, and retinal molecules, depicted by stick models, are coloured grey (C1C2WT) and yellow (C1C2GA), respectively. (c) Magnified view of the blue highlighted region in b. Pink spheres and black dashed lines represent Zn²⁺ and hydrogen bonds, respectively. (d,e) Magnified views of the yellow highlighted region in b, in which the retinal molecules and surrounding residues are shown as stick models (d) and cpk models (e).