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Review
. 2022 Sep;153(3):135-156.
doi: 10.1007/s11120-022-00921-y. Epub 2022 Jun 13.

Binding and functions of the two chloride ions in the oxygen-evolving center of photosystem II

Ko Imaizumi  1 , Kentaro Ifuku  2
Affiliations
Review

Binding and functions of the two chloride ions in the oxygen-evolving center of photosystem II

Ko Imaizumi et al. Photosynth Res. 2022 Sep.

Abstract

Light-driven water oxidation in photosynthesis occurs at the oxygen-evolving center (OEC) of photosystem II (PSII). Chloride ions (Cl-) are essential for oxygen evolution by PSII, and two Cl- ions have been found to specifically bind near the Mn4CaO5 cluster in the OEC. The retention of these Cl- ions within the OEC is critically supported by some of the membrane-extrinsic subunits of PSII. The functions of these two Cl- ions and the mechanisms of their retention both remain to be fully elucidated. However, intensive studies performed recently have advanced our understanding of the functions of these Cl- ions, and PSII structures from various species have been reported, aiding the interpretation of previous findings regarding Cl- retention by extrinsic subunits. In this review, we summarize the findings to date on the roles of the two Cl- ions bound within the OEC. Additionally, together with a short summary of the functions of PSII membrane-extrinsic subunits, we discuss the mechanisms of Cl- retention by these extrinsic subunits.

Keywords: Chloride ions; Extrinsic proteins; Oxygen-evolving center; Photosystem II; PsbP; PsbQ.

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