Health & Environmental Research Online (HERO)


Print Feedback Export to File
7807371 
Journal Article 
Location of chloride and its possible functions in oxygen-evolving photosystem II revealed by X-ray crystallography 
Kawakami, K; Umena, Y; Kamiya, N; Shen, JR 
2009 
1 
Proceedings of the National Academy of Sciences of the United States of America
ISSN: 0027-8424
EISSN: 1091-6490 
106 
21 
8567-8572 
English 
19433803 
WOS:000266432700030 
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.