PDF(Pubmed)
Abstract：
The ring-like peripheral light-harvesting complex 2 (LH2) expressed by many phototrophic purple bacteria is a popular model system in biological light-harvesting research due to its robustness, small size, and known crystal structure. Furthermore, the availability of structural variants with distinct electronic structures and optical properties has made this group of light harvesters an attractive testing ground for studies of structure-function relationships in biological systems. LH2 is one of several pigment-protein complexes for which a link between functionality and effects such as excitonic coherence and vibronic coupling has been proposed. While a direct connection has not yet been demonstrated, many such interactions are highly sensitive to resonance conditions, and a dependence of intra-complex dynamics on detailed electronic structure might be expected. To gauge the sensitivity of energy-level structure and relaxation dynamics to naturally occurring structural changes, we compare the photo-induced dynamics in two structurally distinct LH2 variants. Using polarization-controlled 2D electronic spectroscopy at cryogenic temperatures, we directly access information on dynamic and static disorder in the complexes. The simultaneous optimal spectral and temporal resolution of these experiments further allows us to characterize the ultrafast energy relaxation, including exciton transport within the complexes. Despite the variations in PPC molecular structure manifesting as clear differences in electronic structure and disorder, the energy-transport and-relaxation dynamics remain remarkably similar. This indicates that the light-harvesting functionality of purple bacteria within a single LH2 complex is highly robust to structural perturbations and likely does not rely on finely tuned electronic- or electron-vibrational resonance conditions.
摘要：
许多光养紫色细菌表达的环状外围捕光复合物2（LH2）由于其鲁棒性而成为生物捕光研究中的流行模型系统，小尺寸,和已知的晶体结构。此外，具有独特电子结构和光学特性的结构变体的可用性使这组光收集器成为研究生物系统中结构-功能关系的有吸引力的试验场。LH2是几种色素-蛋白质复合物之一，已提出了功能性与诸如激子相干性和振动耦合之类的效应之间的联系。虽然尚未证明直接联系，许多这样的相互作用对共振条件高度敏感，并且可以预期复杂内部动力学对详细电子结构的依赖性。为了衡量能级结构和松弛动力学对自然发生的结构变化的敏感性，我们比较了两种结构不同的LH2变体中的光诱导动力学。在低温下使用偏振控制的2D电子光谱，我们直接访问有关复合体中动态和静态无序的信息。这些实验的同时最佳光谱和时间分辨率进一步使我们能够表征超快能量弛豫，包括配合物内的激子传输。尽管PPC分子结构的变化表现为电子结构和无序的明显差异，能量传输和松弛动力学仍然非常相似。这表明单个LH2复合物中紫色细菌的光捕获功能对结构扰动是高度稳健的,并且可能不依赖于精细调谐的电子或电子振动共振条件。
