Fig. 1. An overview of Photosystem II and the main water channels and networks from the OEC to the lumenal side.

a (Left) The structure of PS II showing the membrane-embedded helices and the extrinsic subunits in beige. The OEC and the water channels, in addition to the Yz network, are shown in color. The Kok cycle of the water oxidation reaction that is triggered by the absorption of photons is shown on the right and highlighted with a blue circle. b A detailed view of the water channels showing the waters within each channel (O1 Channel red dotted, O4 Channel blue dotted, and Cl1 Channel green dotted). The region highlighted with solid yellow represents the Yz network. Residues involved in forming bottlenecks in the channels are shown in black.