Figure 6.

Proposed structural model of the OEC of PSII in the S₁ state (top), as described by the DFT QM/MM hybrid model obtained at the ONIOM-EE (UHF B3LYP/lacvp,6−31G(2df),6−31G:AMBER) level where the putative substrate waters labeled *fast and *slow are coordinated to Mn(4) and Ca²⁺, respectively [13], and superposition with the 1S5L X-ray diffraction model [20] (blue, bottom panel), shown in Figure 4. All amino acid residues correspond to the D1 protein subunit unless otherwise indicated.