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Figure 4
SaBphP2. (a) SaBphP2 in the Pr (blue, this work) and Pfr (orange) states. The structure of the Pfr state was determined by single-particle cryo-EM (PDB entry 8upm). Subunits A and B of the homodimer as well as the PAS, GAF and PHY domains are marked. The position of the chromophore pocket is marked by the blue oval in subunit B. The sensory tongue (red dotted square) transitions from a β-sheet in Pr to an α-helical conformation in Pfr. Note: the sensory-tongue transition is not observed in our experiments even 700 ms after photoabsorption. (b) DED features (green, positive; red, negative) around BV 700 ms after photoactivation. The four rings of BV (A–D) are labeled. The structure of the chromophore with ring D in the E configuration as found at a 33 ms pump–probe time delay (PDB entry 7jri) is overlayed (orange) as a guide to the eye. The conserved pyrrole water (PW) is ejected from its initial position (blue arrow) and returns at 700 ms at a new site (orange arrow). (c) Overlay of BV in the Pr (this work) and Pfr [salmon; PDB entry 8upm as in (a)] states. The sensory-tongue structure in the Pfr state is shown in blue and selected residues in the PRXSF motif are highlighted in orange. A hydrophilic core area near the returning PW location is marked by the purple cloud

IUCrJ
Volume 12| Part 1| January 2025|
ISSN: 2052-2525
https://doi.org/10.1107/S2052252524010868