Location of chloride and its possible functions in oxygen-evolving photosystem II revealed by X-ray crystallography.
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.
Kawakami
Keisuke
K
Division of Bioscience, Graduate School of Natural Science and Technology/Faculty of Science; Okayama University, Okayama 700-8530, Japan.
Umena
Yasufumi
Y
Kamiya
Nobuo
N
Shen
Jian-Ren
JR
D001665:Binding Sites; D001966:Bromine / Q000737:chemistry / Q000378:metabolism; D002712:Chlorides / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics; D007455:Iodine / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
D002712:Chlorides; D045332:Photosystem II Protein Complex; D007455:Iodine; D010100:Oxygen; D001966:Bromine