Figure 1.

(A) X-ray crystallographic structure of Pr state PaBphP dimer (PDB ID: 3G6O) shown in both ribbon and surface representations. The chromophore is buried deeply inside the chromophore binding pocket (grey circle) formed by the GAF domain (green), the PAS domain N-terminal extension (yellow), and PHY domain tongue (purple). (B) Close-up view of the local configuration at the chromophore binding pocket with four critical residues (green), the chromophore (cyan) and other structurally important residues (grey). The mutants of each of the four key residues were examined for their contributions in the modulations of the photoisomerization dynamics. (C) Photocycle of bathy phytochrome with the initial photo-induced isomerization (red arrows) and the ground-state structural evolutions (grey arrows). Note that the dark reversion from Pr to Pfr state in bathy phytochrome.