Structure of Sr-substituted photosystem II at 2.1 Å resolution and its implications in the mechanism of water oxidation

• DOI: 10.1073/pnas.1219922110
• Publication Date: 2013-02-21T07:23:24Z
• Authors: Faisal Hammad Mek...; Yasufumi Umena; Keisuke Kawakami; Jian-Ren Shen
• Keywords: Oxygen-evolving complex; Oxygen evolution; Cubane; Elongation

Oxygen-evolving complex of photosystem II (PSII) is a tetra-manganese calcium penta-oxygenic cluster (Mn4CaO5) catalyzing light-induced water oxidation through several intermediate states (S-states) by mechanism that not fully understood. To elucidate the roles Ca(2+) in this and possible location substrates process, we crystallized Sr(2+)-substituted PSII from Thermosynechococcus vulcanus, analyzed its crystal structure at resolution 2.1 Å, compared it with 1.9 Å native PSII. Our analysis showed position Sr was moved toward outside cubane Mn4CaO5-cluster relative to Ca(2+), resulting general elongation bond distances between surrounding atoms corresponding Ca-containing cluster. In particular, identified an apparent distance one two terminal ligands W3, whereas Sr-W4 much changed. This result may contribute decrease oxygen evolution upon Sr(2+)-substitution, suggests weak binding rather mobile nature particular molecule (W3), which turn implies involvement as substrate O-O formation. addition, PsbY subunit, absent PSII, found Sr-PSII structure.