Orientations of Carboxylate Groups Coupled to the Mn Cluster in the Photosynthetic Oxygen-Evolving Center As Studied by Polarized ATR-FTIR Spectroscopy
Orientations of Carboxylate Groups Coupled to the Mn Cluster in the Photosynthetic Oxygen-Evolving Center As Studied by Polarized ATR-FTIR Spectroscopy
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DOI：
10.1021/bi1002647
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发表时间：
2010-04-13
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：
Lizasa, Mitsuhiro;Suzuki, Hiroyuki;Noguchi, Takumi
有必要阐明光系统 II (PSI I) 中 Mn 簇周围氨基酸的结构和相互作用，以了解光合放氧的分子机制。在这项研究中，首次将偏振衰减全反射傅里叶变换红外光谱（ATR-FTIR）应用于PSII，以研究与析氧Mn簇耦合的羧酸根的取向。将来自菠菜的 PSII 膜定向在硅 ATR 晶体的表面上，获得 S-1 -> S-2 跃迁的闪光诱导偏振 ATR-FTIR 差值光谱（S-2/S-1 光谱）。根据使用相同取向的样品通过缓冲液交换记录的偏振 Q(A)(-)/Q(A) 差异光谱中的半醌 CO 峰估计马赛克分布的膜取向分布。根据偏振 S-2/S-1 ATR-FTIR 光谱中对称 COO 谱带的二向色比估计与 Mn 簇耦合的羧酸基团的方向。我们发现，由于直接连接到 Mn 簇或通过氢键网络，大多数在 S-1 -> S-2 转变过程中受到干扰的羧酸基团具有相对于膜法线 34-48 度相对较窄的角度范围内的取向。根据先前 FTIR 研究和 X 射线结构的信息，讨论了所获得的方向和 S-2 形成时的变化的含义。本研究的结果表明，偏振 ATR-FTIR 差异光谱是研究光合蛋白中氧化还原辅因子和偶联氨基酸侧链的方向及其反应引起的变化的有效方法。
It is essential to clarify the structures and interactions of amino acids surrounding the Mn cluster in photosystem II (PSI I) to understand the molecular mechanism of photosynthetic oxygen evolution. In this study, polarized attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was applied for the first time to PSII to investigate the orientation of carboxylate groups coupled to the oxygen-evolving Mn cluster. PSII membranes from spinach were oriented on the surface of a silicon ATR crystal, and flash-induced polarized ATR-FTIR difference spectra for the S-1 -> S-2 transition (S-2/S-1 spectra) were obtained. The distribution of membrane orientations by mosaic spread was estimated from the semiquinone CO peak in polarized Q(A)(-)/Q(A) difference spectra recorded using the same oriented sample by buffer exchange. The orientations of carboxylate groups coupled to the Mn cluster were estimated from the dichroic ratios of the symmetric COO- bands in the polarized S-2/S-1 ATR-FTIR spectra. We found that most of the carboxylate groups perturbed during the S-1 -> S-2 transition, due to direct ligation to the Mn cluster or though a hydrogen bond network, have orientations in a relatively narrow angle range of 34-48 degrees with respect to the membrane normal. Implications of the obtained orientations and the changes upon formation of S-2 are discussed on the basis of the information from previous FTIR studies and the X-ray structures. The results in this study show that polarized ATR-FTIR difference spectroscopy is a fruitful method for investigating the orientations and their reaction-induced changes in redox cofactors and coupled amino acid side chains in photosynthetic proteins.