Extended Data Fig. 6. The two most stable hydrogen-bonds of protonated O6 (in both S₃ and S₃′ state).

Upon oxidation of Tyr_Z (Tyr161), the relative stability of the two reported conformers is reversed, conformer-a becoming more stable than conformer-b, thus favouring the oxyl radical formation as described elsewhere²⁶. In both cases, the deprotonated Asp61 is stably interacting with the W1 water molecule. Relevant distances are highlighted by thin lines and reported in both panels for comparison. Manganese atoms are shown in pink, calcium as cyan sphere, oxygen in red, carbon in cyan, and hydrogen in white.