Protonation State of a Key Histidine Ligand in the Iron-Quinone Complex of Photosystem II as Revealed by Light-Induced ATR-FTIR Spectroscopy
Protonation State of a Key Histidine Ligand in the Iron-Quinone Complex of Photosystem II as Revealed by Light-Induced ATR-FTIR Spectroscopy
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DOI：
10.1021/acs.biochem.0c00810
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发表时间：
2020-11-17
期刊：
影响因子：
2.9
通讯作者：
Noguchi, Takumi
中科院分区：
文献类型：
--
作者：
Kimura, Masakazu;Kato, Yuki;Noguchi, Takumi
光系统II（PSII）中的铁-醌复合物由两个质体醌电子受体Q（A）和Q（B）以及连接它们的非血红素铁组成。已经表明，附近的组氨酸残基在PSII中的铁-醌复合物的电子和质子转移反应中起重要作用。本研究利用衰减全反射傅里叶变换红外光谱（ATR-FTIR）研究了非血红素铁与Q（B）桥连的D1-H215的质子化/去质子化反应。闪光诱导的Fe 2 +/Fe 3 + ATR-FTIR差光谱测量与PSII膜在pH值为5.0-7.5的范围内。在组氨酸的CN伸缩区，在1094 cm（-1）处的负峰强度随pH升高而增加，该峰归属于D1-H215的去质子化阴离子形式。奇异值分解分析提供了一个由于D1-H215去质子化的组分，其在Fe 3+状态下的pK（a）类似于5.5，而在Fe 2+状态下没有组氨酸去质子化的组分。这一观察结果支持了先前的提议，即D1-H215负责Fe 2+氧化后的质子释放[Berthomieu，C.，和Hienerwadel，R.（2001）Biochemistry 40，4044-4052]。碳酸氢根配体的C-13同位素编辑条带对非血红素铁的pH依赖性进一步表明，碳酸氢根到碳酸根的去质子化在pH
The iron-quinone complex in photosystem II (PSII) consists of the two plastoquinone electron acceptors, Q(A) and Q(B), and a non-heme iron connecting them. It has been suggested that nearby histidine residues play important roles in the electron and proton transfer reactions of the iron-quinone complex in PSII. In this study, we investigated the protonation/deprotonation reaction of D1-H215, which bridges the non-heme iron and Q(B), using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Flash-induced Fe2+/Fe3+ ATR-FTIR difference spectra were measured with PSII membranes in the pH range of 5.0-7.5. In the CN stretching region of histidine, the intensity of a negative peak at 1094 cm(-1), which was assigned to the deprotonated anion form of D1-H215, increased as the pH increased. Singular-value decomposition analysis provided a component due to deprotonation of D1-H215 with a pK(a) of similar to 5.5 in the Fe3+ state, whereas no component of histidine deprotonation was resolved in the Fe2+ state. This observation supports the previous proposal that D1-H215 is responsible for the proton release upon Fe2+ oxidation [Berthomieu, C., and Hienerwadel, R. (2001) Biochemistry 40, 4044-4052]. The pH dependence of the C-13 isotope-edited bands of the bicarbonate ligand to the non-heme iron further showed that deprotonation of bicarbonate to carbonate does not take place at pH