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Figure 4
Time-resolved motions in the coordinating ligands of the OEC. The protein environment near the OEC appears to undergo conformational changes in response to the oxidation of the cluster after each light flash. Shown are the omit map densities of each of the carboxyl­ate oxygens in D1-Asp170 and D1-Glu189 in the (a) S2 → S3 and (b) S3 → S0 transitions, and (c) a more detailed omit map density of each of the carboxyl­ate oxygens and the Cγ atom of Asp170. For the omit maps of the carboxyl­ate oxygens, the same color legend to depict the σ levels used in (a) and (b) have been used. The color legend for the Cγ atom omit map is provided in the figure. (d) Possible model for the movement of Asp170, suggesting it could be detached from the Ca for certain time points in both transitions in synchronization with the water insertion event. Mn atoms are shown as purple, Ca atoms as green and O atoms as red spheres.

IUCrJ
Volume 10| Part 6| November 2023| Pages 642-655
ISSN: 2052-2525
https://doi.org/10.1107/S2052252523008928