Hsin Jen, Strümpfer Johan, Sener Melih, Qian Pu, Hunter C Neil, Schulten Klaus
Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, USA.
New J Phys. 2010 Aug 1;12. doi: 10.1088/1367-2630/12/8/085005.
Light absorption and the subsequent transfer of excitation energy are the first two steps of the photosynthetic process, carried out by protein-bound pigments, mainly bacteriochlorophylls (BChls), in photosynthetic bacteria. BChls are anchored in light-harvesting (LH) complexes, such as light-harvesting complex I (LH1), which directly associates with the reaction center (RC), forming the RC-LH1 core complex. In Rhodobacter sphaeroides, RC-LH1 core complexes contain an additional protein, PufX, and assemble into dimeric RC-LH1-PufX core complexes. In the absence of light-harvesting complexes II, the former complexes can aggregate into a helically ordered tubular photosynthetic membrane. We examined the excitation transfer dynamics in a single RC-LH1-PufX core complex dimer using the hierarchical equations of motion for dissipative quantum dynamics that accurately, yet computationally costly, treat the coupling between BChls and their protein environment. A widely employed description, generalized Förster theory, was also used to calculate the transfer rates of the same excitonic system in order to verify the accuracy of this computationally cheap method. Additionally, in light of the structural uncertainties in the Rhodobacter sphaeroides RC-LH1-PufX core complex, geometrical alterations were introduced in the BChl organization. It is shown that the energy transfer dynamics is not affected by the considered changes in the BChl organization, and that generalized Förster theory provides accurate transfer rates. An all-atom model for a tubular photosynthetic membrane is then constructed on the basis of electron microscopy data, and the overall energy transfer properties of this membrane are computed.
光吸收以及随后的激发能转移是光合过程的前两个步骤，由光合细菌中与蛋白质结合的色素（主要是细菌叶绿素，BChls）来执行。BChls锚定在光捕获（LH）复合物中，如光捕获复合物I（LH1），它直接与反应中心（RC）结合，形成RC-LH1核心复合物。在球形红细菌中，RC-LH1核心复合物含有一种额外的蛋白质PufX，并组装成二聚体RC-LH1-PufX核心复合物。在没有光捕获复合物II的情况下，前者复合物可以聚集成螺旋有序的管状光合膜。我们使用耗散量子动力学的层次运动方程研究了单个RC-LH1-PufX核心复合物二聚体中的激发转移动力学，该方程能准确但计算成本高昂地处理BChls与其蛋白质环境之间的耦合。还使用了一种广泛应用的描述方法——广义Förster理论来计算同一激子系统的转移速率，以验证这种计算成本低的方法的准确性。此外，鉴于球形红细菌RC-LH1-PufX核心复合物在结构上的不确定性，对BChl的组织进行了几何改变。结果表明，能量转移动力学不受BChl组织中所考虑变化的影响，并且广义Förster理论提供了准确的转移速率。然后根据电子显微镜数据构建了管状光合膜的全原子模型，并计算了该膜的整体能量转移特性。
