Structure-based calculations of the optical spectra of the LH2 bacteriochlorophyll-protein complex from Rhodopseudomonas acidophila
Structure-based calculations of the optical spectra of the LH2 bacteriochlorophyll-protein complex from Rhodopseudomonas acidophila
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DOI：
10.1111/j.1751-1097.1996.tb03106.x
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发表时间：
1996-09-01
影响因子：
3.3
通讯作者：
Scheer, H
中科院分区：
文献类型：
--
作者：
Sauer, K;Cogdell, RJ;Scheer, H
对紫色非硫光合细菌嗜酸红球藻10050菌株的捕光复合物2（LH 2）细菌叶绿素-蛋白质天线复合物的分子结构进行了研究，给出了该复合物中27个细菌叶绿素（BChl）分子的位置和取向。计算结果支持了BChl的18个紧密耦合环与B850的归属（BChl在850 mm处吸收）和较大直径的平行环9个弱耦合BChl到B800，计算出近红外中所有显著允许的跃迁垂直于C9对称轴，与该膜相关复合物的偏振研究一致，使用相对介电常数匹配B800和B850组分的最大吸收（介电常数）为2.1，我们分配不同的网站能量（分别为12 500和12 260 cm（-1）），激子耦合在B850发色团之间特别强，最近邻之间的成对相互作用能接近300 cm（-1），与室温下的实验吸收带宽相当。对于全套18个B850发色团，导致1200 cm（-1）宽的激子歧管。一些上激子态应该导致弱吸收和可能更强的CD特征，这些预测从计算等待实验验证。
The molecular structure of the light-harvesting complex 2 (LH2) bacteriochlorophyll-protein antenna complex from the purple non-sulfur photosynthetic bacterium Rhodopseudomonas acidophila, strain 10050 provides the positions and orientations of the 27 bacteriochlorophyll (BChl) molecules in the complex, Our structure-based model calculations of the distinctive optical properties (absorption, CD, polarization) of LH2 in the near-infrared region use a point-monopole approximation to represent the BChl Q(y) transition moment, The results of the calculations support the assignment of the ring of 18 closely coupled BChl to B850 (BChl absorbing at 850 mm) and the larger diameter, parallel ring of 9 weakly coupled BChl to B800, All of the significantly allowed transitions in the near infrared are calculated to be perpendicular to the C9 symmetry axis, in agreement with polarization studies of this membrane-associated complex, To match the absorption maxima of the B800 and B850 components using a relative permittivity (dielectric constant) of 2.1, we assign different site energies (12 500 and 12 260 cm(-1), respectively) for the Q(y) transitions of the respective BChl in their protein binding sites, Excitonic coupling is particularly strong among the set of B850 chromophores, with pairwise interaction energies nearly 300 cm(-1) between nearest neighbors, comparable with the experimental absorption bandwidths at room temperature, These strong interactions, for the full set of 18 B850 chromophores, result in an excitonic manifold that is 1200 cm(-1) wide. Some of the upper excitonic states should result in weak absorption and perhaps stronger CD features, These predictions from the calculations await experimental verification.