Fig. 1: Co-expression of GR wild-type and mutants with canthaxanthin.

a GR wild-type with only retinal (blue line), GR-expressed with both retinal and carotenoid (black line), single mutation G178W expressed with both retinal and carotenoid (green line). Complete chromophore extraction from purified samples showed blue, black, and green (dot line), respectively. b Absorption spectra of the mutant on helix E near glycine 178, carotenoid locked motif. c Absorption spectra of mutant on helix F, carotenoid aligned motif. d Local view of targeting mutation site, a structure alignment of GR (pdb:6nwd) and XR (pdb:3ddl), and the purified GR variants co-expressed with retinal/carotenoid.