Spectroscopic properties of reaction center pigments in photosystem II core complexes: Revision of the multimer model
Spectroscopic properties of reaction center pigments in photosystem II core complexes: Revision of the multimer model
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DOI：
10.1529/biophysj.107.123935
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发表时间：
2008-07-01
影响因子：
3.4
通讯作者：
Renger, Thomas
中科院分区：
文献类型：
--
作者：
Raszewski, Grzegorz;Diner, Bruce A.;Renger, Thomas
与来自细长热聚球藻和集胞藻属物种PCC 6803的光系统II核心复合物中功能状态的光诱导形成相关的吸光度差光谱（例如，P（+）Pheo（-），P（+）Q（A）（-），P-3）的量子化学性质。此外，还分析了特殊对叶绿素P-D1的轴向配体D1-His（198）和与辅助叶绿素Chl（D1）最近的氨基酸残基D1-Thr（179）的定点突变对反应中心色素光谱特性的影响。使用颜料跃迁能（网站能量）确定以前从独立的实验D1-D2-cytb 559复合物，计算和实验光谱之间的良好协议。D1-D2-cytb 559和光系统II核心复合物中反应中心色素的位置能量的唯一差异涉及Chl（D1）。与孤立的反应中心相比，Chl（D1）的位点能量红移了4 nm，并且在核心复合物中分布不均匀。网站的能量导致初级电子转移在低温下启动的激发态，强烈本地化的Chl（D1），而不是从离域状态假设在前面描述的多聚体模型。这一结果与早期关于特殊对突变体的实验数据以及我们先前关于D1-D2-cytb 559复合物的计算结果一致。计算表明，在5 K时，反应中心的最低激发态比形成激子二聚体的两个特殊对叶绿素P-D1和P-D2的低能激子态低约10 nm。只有在假设Chl（D1）和P-D1的位能随温度变化时，才能在此模型中理解野生型差谱的实验温度依赖性，当温度从5 K升高到300 K时，上述能隙从10 nm减小到6 nm。在生理温度下，所有色素对平衡激发态P星都有相当大的贡献。在环境温度下，Chl（D1）的贡献是P-D1的两倍，使得在这些条件下，初级电荷分离可能由Chl（D1）引发。吸光度差谱的计算提供了独立的证据，在初级电子转移后的空穴稳定在P-D1，和生理危险的电荷重组三联体，这可能会在光应力下形成，平衡Chl（D1）和P-D1之间。
Absorbance difference spectra associated with the light-induced formation of functional states in photosystem II core complexes from Thermosynechococcus elongatus and Synechocystis sp. PCC 6803 (e.g., P(+)Pheo(-), P(+)Q(A)(-), P-3) are described quantitatively in the framework of exciton theory. In addition, effects are analyzed of site-directed mutations of D1-His(198), the axial ligand of the special-pair chlorophyll P-D1, and D1-Thr(179), an amino-acid residue nearest to the accessory chlorophyll Chl(D1), on the spectral properties of the reaction center pigments. Using pigment transition energies (site energies) determined previously from independent experiments on D1-D2-cytb559 complexes, good agreement between calculated and experimental spectra is obtained. The only difference in site energies of the reaction center pigments in D1-D2-cytb559 and photosystem II core complexes concerns Chl(D1). Compared to isolated reaction centers, the site energy of Chl(D1) is red-shifted by 4 nm and less inhomogeneously distributed in core complexes. The site energies cause primary electron transfer at cryogenic temperatures to be initiated by an excited state that is strongly localized on Chl(D1) rather than from a delocalized state as assumed in the previously described multimer model. This result is consistent with earlier experimental data on special-pair mutants and with our previous calculations on D1-D2-cytb559 complexes. The calculations show that at 5 K the lowest excited state of the reaction center is lower by similar to 10 nm than the low-energy exciton state of the two special-pair chlorophylls P-D1 and P-D2 which form an excitonic dimer. The experimental temperature dependence of the wild-type difference spectra can only be understood in this model if temperature-dependent site energies are assumed for Chl(D1) and P-D1, reducing the above energy gap from 10 to 6 nm upon increasing the temperature from 5 to 300 K. At physiological temperature, there are considerable contributions from all pigments to the equilibrated excited state P-star. The contribution of Chl(D1) is twice that of P-D1 at ambient temperature, making it likely that the primary charge separation will be initiated by Chl(D1) under these conditions. The calculations of absorbance difference spectra provide independent evidence that after primary electron transfer the hole stabilizes at P-D1, and that the physiologically dangerous charge recombination triplets, which may form under light stress, equilibrate between Chl(D1) and P-D1.