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. 2018 Apr 5;293(21):8161–8172. doi: 10.1074/jbc.RA118.001794

Figure 5.

Figure 5.

The two CBD–PHY-Y263F crystal forms and the absorption spectra of CBD–PHY variant crystals. A, overall dimer structure of pre-illuminated (red) and dark (blue) crystal forms of CBD–PHY-Y263F. Biliverdin (BV) is shown in sticks. B, absorption spectra of CBD–PHY WT CBD–PHY and Y263F variant crystallized in the dark. The WT crystal shown here is crystallized in a published Pfr condition (9), and the Y263F variant was crystallized in the “dark” condition reported in this paper. The crystals had characteristic Pr spectra with a maximum at 700 nm (dark). The CBD–PHY crystals could be partially photoswitched with 660-nm light, whereas CBD–PHY-Y263F crystals responded only little to red light (illuminated). C, electron densities of the tongue region of both crystal structures. D, structure of the D-ring surroundings in CBD–PHY variants. Dark (left) and pre-illuminated (right) Y263F structures differ in the side-chain orientations of residues Tyr176, His201, and Phe203. These orientations are supported by the 2Fo − Fc electron density maps. However, weak positive electron density (*) at the sites where these residues would reside in the Pr state imply traces of Pr-state orientations in the pre-illuminated structure. See Fig. S2B for a comparison with published Pr and Pfr structures. The 2Fo − Fc maps (blue) are plotted at 1.0 RMSD, and Fo − Fc maps are plotted at 3.0 RMSD.