Figure 2.

A potential energy surface representing the energy change (ΔE) as a function of the dihedral angles D₂ and D₃ of D1-Glu189. These calculations were based on the PDB coordinates (6JLL, monomer A),¹⁰ with an additional O6* remaining attached to the Ca ion of the Mn cluster. The relative energy ΔE is referenced to the metastable structure depicted in Figure S1B. White circles indicate the D₂ and D₃ values corresponding to the motion of the D1-Glu189 side chain when coupled with O6* binding to Mn_D (see Figure 3). A magenta circle represents the D₂ and D₃ values observed in the S₃ state, in which O5 and O6 either form an oxyl-oxo bond or exist as bridging oxo and terminal hydroxo ligands.