Download MendeleyLocation of chloride and its possible functions in oxygen-evolving photosystem II revealed by X-ray crystallography
Kawakami, K., Umena, Y., Kamiya, N., Shen, J.-R.(2009) Proc Natl Acad Sci U S A 106: 8567-8572
- PubMed: 19433803
- DOI: https://doi.org/10.1073/pnas.0812797106
- Primary Citation of Related Structures:
3A0B, 3A0H - PubMed Abstract:
The chloride ion, Cl(-), is an essential cofactor for oxygen evolution of photosystem II (PSII) and is closely associated with the Mn(4)Ca cluster. Its detailed location and function have not been identified, however. We substituted Cl(-) with a bromide ion (Br(-)) or an iodide ion (I(-)) in PSII and analyzed the crystal structures of PSII with Br(-) and I(-) substitutions. Substitution of Cl(-) with Br(-) did not inhibit oxygen evolution, whereas substitution of Cl(-) with I(-) completely inhibited oxygen evolution, indicating the efficient replacement of Cl(-) by I(-). PSII with Br(-) and I(-) substitutions were crystallized, and their structures were analyzed. The results showed that there are 2 anion-binding sites in each PSII monomer; they are located on 2 sides of the Mn(4)Ca cluster at equal distances from the metal cluster. Anion-binding site 1 is close to the main chain of D1-Glu-333, and site 2 is close to the main chain of CP43-Glu-354; these 2 residues are coordinated directly with the Mn(4)Ca cluster. In addition, site 1 is located in the entrance of a proton exit channel. These results indicate that these 2 Cl(-) anions are required to maintain the coordination structure of the Mn(4)Ca cluster as well as the proposed proton channel, thereby keeping the oxygen-evolving complex fully active.
Organizational Affiliation:
Division of Bioscience, Graduate School of Natural Science and Technology/Faculty of Science; Okayama University, Okayama 700-8530, Japan.
