Functional Roles of D2-Lys317 and the Interacting Chloride Ion in the Water Oxidation Reaction of Photosystem II As Revealed by Fourier Transform Infrared Analysis

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• 作者：Hiroyuki Suzuki ; Jianfeng Yu ; Takashi Kobayashi ; Hanayo Nakanishi ; Peter J. Nixon ; Takumi Noguchi
• 刊名：Biochemistry
• 出版年：2013
• 出版时间：July 16, 2013
• 年：2013
• 卷：52
• 期：28
• 页码：4748-4757
• 全文大小：479K
• 年卷期：v.52,no.28(July 16, 2013)
• ISSN：1520-4995

文摘

Photosynthetic water oxidation in plants and cyanobacteria is catalyzed by a Mn₄CaO₅ cluster within the photosystem II (PSII) protein complex. Two Cl^{鈥?/sup> ions bound near the Mn₄CaO₅ cluster act as indispensable cofactors, but their functional roles remain to be clarified. We have investigated the role of the Cl鈥?/sup> ion interacting with D2-K317 (designated Cl-1) by Fourier transform infrared spectroscopy (FTIR) analysis of the D2-K317R mutant of Synechocystis sp. PCC 6803 in combination with Cl鈥?/sup>/NO₃鈥?/sup> replacement. The D2-K317R mutation perturbed the bands in the regions of the COO鈥?/sup> stretching and backbone amide vibrations in the FTIR difference spectrum upon the S₁ 鈫?S₂ transition. In addition, this mutation altered the 15N isotope-edited NO₃鈥?/sup> bands in the spectrum of NO₃鈥?/sup>-treated PSII. These results provide the first experimental evidence that the Cl-1 site is coupled with the Mn₄CaO₅ cluster and its interaction is affected by the S₁ 鈫?S₂ transition. It was also shown that a negative band at 1748 cm鈥? arising from COOH group(s) was altered to a positive intensity by the D2-K317R mutation as well as by NO₃鈥?/sup> treatment, suggesting that the Cl-1 site affects the pK_a of COOH/COO鈥?/sup> group(s) near the Mn₄CaO₅ cluster in a common hydrogen bond network. Together with the observation that the efficiency of the S₃ 鈫?S₀ transition significantly decreased in the core complexes of D2-K317R upon moderate dehydration, it is suggested that D2-K317 and Cl-1 are involved in a proton transfer pathway from the Mn₄CaO₅ cluster to the lumen, which functions in the S₃ 鈫?S₀ transition.}