Figure 5. Two correlated photochemical events guide the primary photorespone of phytochrome proteins.

(a). The structures (DrBphP_dark, blue and DrBphP_1ps, beige) indicate that rotation of the D-ring initiates breakage of non-covalent bonds of the propionates to the protein scaffold. Even the C- and A-rings are displaced significantly and the pyrrole water is dislocated from its original location at 1 ps (shade). (b). The same structures are overlayed with the complete photosensory core in Pr state (PDB ID 4O0P, pink) (Takala et al., 2014). The scissor-like separation of Asp207 and Tyr263 could result in breakage of the hydrogen bonds to Arg466 of the conserved PRXSF motif located in the PHY-tongue region.