PsbU Provides a Stable Architecture for the Oxygen-Evolving System in Cyanobacterial Photosystem II

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• 作者：Natsuko Inoue-Kashino ; Yasuhiro Kashino ; Kazuhiko Satoh ; Ichiro Terashima ; and Himadri B. Pakrasi
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：September 13, 2005
• 年：2005
• 卷：44
• 期：36
• 页码：12214 - 12228
• 全文大小：355K
• 年卷期：v.44,no.36(September 13, 2005)
• ISSN：1520-4995

文摘

PsbU is a lumenal peripheral protein in the photosystem II (PS II) complex of cyanobacteriaand red algae. It is thought that PsbU is replaced functionally by PsbP or PsbQ in plant chloroplasts.After the discovery of PsbP and PsbQ homologues in cyanobacterial PS II [Thornton et al. (2004) PlantCell 16, 2164-2175], we investigated the function of PsbU using a psbU deletion mutant (PsbU) ofSynechocystis 6803. In contrast to the wild type, PsbU did not grow when both Ca²⁺ and Cl^- wereeliminated from the growth medium. When only Ca²⁺ was eliminated, PsbU grew well, whereas whenCl^- was eliminated, the growth rate was highly suppressed. Although PsbU grew normally in the presenceof both ions under moderate light, PS II-related disorders were observed as follows. (1) The mutant cellswere highly susceptible to photoinhibition. (2) Both the efficiency of light utilization under low irradianceand the chlorophyll-specific maximum rate of oxygen evolution in PsbU cells were 60% lower thanthose of the wild type. (3) The decay of the S2 state in PsbU cells was decelerated. (4) In isolated PSII complexes from PsbU cells, the amounts of the other three lumenal extrinsic proteins and the electrondonation rate were drastically decreased, indicating that the water oxidation system became significantlylabile without PsbU. Furthermore, oxygen-evolving activity in PsbU thylakoid membranes was highlysuppressed in the absence of Cl^-, and 60% of the activity was restored by NO₃^- but not by SO₄^2-, indicatingthat PsbU had functions other than stabilizing Cl^-. On the basis of these results, we conclude that PsbUis crucial for the stable architecture of the water-splitting system to optimize the efficiency of the oxygenevolution process.