FIGURE 2.

H-bond network around Y_Z/D. Energetically optimized atomic coordinates for (a) deprotonated Y_Z, (b) protonated Y_Z, (c) deprotonated Y_D, and (d) protonated Y_D. Only for D1-His¹⁹⁰/D2His¹⁸⁹ and H₂O, polar hydrogen atoms involved in H-bonds are displayed explicitly by small-sized dark-shaded spheres. Nitrogen atoms are displayed by medium-sized light-shaded spheres, oxygen atoms by medium-sized dark-shaded spheres, and Mn and Ca ions are shown by large spheres (manganese, dark-shaded; calcium, light-shaded). Original positions of Y_Z/D and D1-His¹⁹⁰/D2-His¹⁸⁹ from the PSII crystal structure are shown by dark-shaded sticks; energetically optimized positions are shown in light shading. Orientations of H-atoms and some H-bonds are indicated by thin lines.