Comparison of water networks in plant and cyanobacterial photosystem II based on a 2.44 Å resolution structure from Arabidopsis thaliana

Photosystem II (PS II) is a large membrane-bound protein complex that catalyzes light-driven water oxidation in plants and cyanobacteria. Here, we present the first high-resolution structure of an intact and active PS II from Arabidopsis thaliana at 2.44 Å resolution, which to date represents the highest resolution structure of PS II from higher plants. At this improved resolution we are able to identify many water molecules within the PS II structure, including waters around the water-splitting manganese cluster, the non-heme iron, and within the water/proton channels connecting these active sites to the protein exterior. By comparing this new Arabidopsis thaliana structure to the highest resolution PS II structure from cyanobacteria, we identified conserved features which are likely to be essential in the water networks of plants and cyanobacteria. Our findings further the understanding of the importance and design principles of protein-water-cofactor interactions in photosynthetic water splitting and quinone reduction in photosystem II.