Proton egress pathway during the S1–S2 transition of the Oxygen Evolving Complex of Photosystem II (original) (raw)

Photosystem II uses water as the ultimate electron source of the photosynthetic electron transfer chain. Water is oxidized to dioxygen at the Oxygen Evolving Complex (OEC), a Mn4CaO5 inorganic core embedded in the lumenal side of PSII. Water-filled channels are thought to bring in substrate water molecules to the OEC, remove the substrate protons to the lumen, and may transport the product oxygen. Three water-filled channels, denoted large, narrow, and broad, that extend from the OEC towards the aqueous surface more than 15 Å away are seen. However, the actual mechanisms of water supply to the OEC, the removal of protons to the lumen and diffusion of oxygen away from the OEC have yet to be established. Here, we combine Molecular Dynamics (MD), Multi Conformation Continuum Electrostatics (MCCE) and Network Analysis to compare and contrast the three potential proton transfer paths during the S1 to S2 transition of the OEC. Hydrogen bond network analysis shows that the three channels a...