Absorption Linear Dichroism Measured Directly on a Single Light-Harvesting System: The Role of Disorder in Chlorosomes of Green Photosynthetic Bacteria
Absorption Linear Dichroism Measured Directly on a Single Light-Harvesting System: The Role of Disorder in Chlorosomes of Green Photosynthetic Bacteria
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DOI：
10.1021/ja111475z
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发表时间：
2011-05-04
影响因子：
15
通讯作者：
Vacha, Martin
中科院分区：
文献类型：
--
作者：
Furumaki, Shu;Vacha, Frantisek;Vacha, Martin
叶绿体是光合细菌的捕光触角，含有大量自聚集的细菌叶绿素（BChl）分子。它们具有独特的光物理性质，使它们能够吸收光并以非常高的效率转移激发能。然而，产生BChl分子在聚集体中的物理性质的分子水平的组织仍然没有完全理解。其中一个原因是在叶绿体结构中的异质性，这引起了结构和能量紊乱的等级。在这份报告中，我们第一次直接测量吸收线性二色性（LD）的个人，孤立的叶绿体。连同荧光检测的三维LD，这些实验揭示了大量的单叶绿体水平上的无序的形式分布的LD可观察到的绿色体从野生型细菌Chlorobaculum tepidum。荧光光谱参数，例如峰值波长和带宽，是聚合物激子性质的量度。这些参数上获得的个人叶绿体与所观察到的LD分布是不相关的，并表明所观察到的障碍是由于内部结构紊乱沿着的叶绿体长轴。激子的障碍，也是目前没有表现在LD分布。的LD参数分布，这是相对自由的结构紊乱的影响的限制值，定义的激子偶极矩是相对于BChl分子的二维聚集体的表面取向的角度范围。对一个三突变体的实验结果表明，突变体的叶绿体内部结构紊乱明显减少，对称性增强，符合有序同心圆柱体模型。不同的值的跃迁偶极矩取向是一致的BChl的突变体和野生型叶绿体中的不同分子水平的组织。
Chlorosomes are light-harvesting antennae of photosynthetic bacteria containing large numbers of self-aggregated bacteriochlorophyll (BChl) molecules. They have developed unique photophysical properties that enable them to absorb light and transfer the excitation energy with very high efficiency. However, the molecular-level organization, that produces the photophysical properties of BChl molecules in the aggregates, is still not fully understood. One of the reasons is heterogeneity in the chlorosome structure which gives rise to a hierarchy of structural and energy disorder. In this report, we for the first time directly measure absorption linear dichroism (LD) on individual, isolated chlorosomes. Together with fluorescence-detected three-dimensional LD, these experiments reveal a large amount of disorder on the single-chlorosome level in the form of distributions of LD observables in chlorosomes from wild-type bacterium Chlorobaculum tepidum. Fluorescence spectral parameters, such as peak wavelength and bandwidth, are measures of the aggregate excitonic properties. These parameters obtained on individual chlorosomes are uncorrelated with the observed LD distributions and indicate that the observed disorder is due to inner structural disorder along the chlorosome long axis. The excitonic disorder that is also present is not manifested in the LD distributions. Limiting values of the LD parameter distributions, which are relatively free of the effect of structural disorder, define a range of angles at which the excitonic dipole moment is oriented with respect to the surface of the two-dimensional aggregate of BChl molecules. Experiments on chlorosomes of a triple mutant of Chlorobaculum tepidum show that the mutant chlorosomes have significantly less inner structural disorder and higher symmetry, compatible with a model of well-ordered concentric cylinders. Different values of the transition dipole moment orientations are consistent with a different molecular level organization of BChl's in the mutant and wild-type chlorosomes.