Role of PsbV-Tyr137 in photosystem II studied by site-directed mutagenesis in the thermophilic cyanobacterium Thermosyne
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ORIGINAL ARTICLE
Role of PsbV‑Tyr137 in photosystem II studied by site‑directed mutagenesis in the thermophilic cyanobacterium Thermosynechococcus vulcanus Yanan Xiao1,2 · Qingjun Zhu1,2 · Yanyan Yang1 · Wenda Wang1 · Tingyun Kuang1 · Jian‑Ren Shen1,3,4 · Guangye Han1 Received: 1 December 2019 / Accepted: 19 April 2020 © Springer Nature B.V. 2020
Abstract PsbV (cytochrome c550) is one of the three extrinsic proteins of photosystem II (PSII) and functions to maintain the stability and activity of the Mn4CaO5 cluster, the catalytic center for water oxidation. PsbV-Y137 is the C-terminal residue of PsbV and is located at the exit of a hydrogen-bond network mediated by the D1-Y161-H190 residue pair. In order to examine the function of PsbV-Y137, four mutants, PsbV-Y137A, PsbV-Y137F, PsbV-Y137G, and PsbV-Y137W, were generated with Thermosynechococcus vulcanus (T. vulcanus). These mutants showed growth rates similar to that of the wild-type strain (WT); however, their oxygen-evolving activities were different. At pH 6.5, the oxygen evolution rates of Y137F and Y137W were almost identical to that of WT, whereas the oxygen evolution rates of the Y137A, Y137G mutants were 64% and 61% of WT, respectively. However, the oxygen evolution in the latter two mutants decreased less at higher pHs, suggesting that higher pHs facilitated oxygen evolution probably by facilitating proton egress in these two mutants. Furthermore, thylakoid membranes isolated from the PsbV-Y137A, PsbV-Y137G mutants exhibited much lower levels of oxygen-evolving activity than that of WT, which was found to be caused by the release of PsbV. In addition, PSII complexes purified from the PsbV-Y137A and PsbV-Y137G mutants lost all of the three extrinsic proteins but instead bind Psb27, an assembly cofactor of PSII. These results demonstrate that the PsbV-Tyr137 residue is required for the stable binding of PsbV to PSII, and the hydrogen-bond network mediated by D1-Y161-H190 is likely to function in proton egress during water oxidation. Keywords Photosystem II · Extrinsic proteins · PsbV · Hydrogen-bond network · Site-directed mutagenesis · Watersplitting Abbreviations Chl Chlorophyll DCMU 3-(3,4-Dichlorophenyl)-1,1-dimethylurea * Jian‑Ren Shen [email protected]‑u.ac.jp * Guangye Han [email protected] 1
Photosynthesis Research Center, Key Laboratory of Photobiology, Institute of Botany, Chinese Academy of Sciences, No. 20, Nanxincun, Xiangshan, Beijing 100093, China
2
University of Chinese Academy of Sciences, Yuquan Rd, Shijingshan District, Beijing 100049, China
3
The Innovative Academy of Seed Design, Chinese Academy of Sciences, No. 1 Beichen West Rd., Beijing 100101, China
4
Research Institute of Interdisciplinary Science, Graduate School of Natural Science and Technology, Okayama University, Tsushima Naka 3‑1‑1, Okayama 700‑8530, Japan
HEPES 4-(2-Hydroxyethyl)-1-piperazine ethanesulfonic acid MES 2-(N-Morpholino) ethanesulfonic acid OEC Oxygen-evolving complex PPBQ 2-Phenyl-p-benzoquinone PSI Photosystem I PSII Photosystem
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