X-RAY ABSOPTION STUDY ON BACTERIOCHLOROPHYLL ORGANIZATION IN CHLOROSOMES

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。绿色体是丝状和硫绿色光合成细菌的捕光复合体。叶绿体是自然界中发现的唯一一种光合作用天线复合体，其中的叶绿素分子不是由蛋白质基质组织的，而是通过各种细菌-叶绿素(BCHL)分子之间的相互作用来组织的。它也是唯一一个结构信息仍然稀缺的天线复合体。指导叶绿体自组装的活性部位之一是BCHL卟啉环上的中心镁原子。我们的目标是通过X射线吸收光谱探测镁原子中心的周围环境来阐明绿小体中分子间结合的细节。所需的光子能量范围从1300 eV到2000 eV及以上。我们的计划是将天然叶绿体中的BCHL键与一系列具有已知结构的多晶叶绿素样品进行比较。此外，我们的模拟表明，可以从XANES和EXAFS信号中获得邻近BCHL分子的镁配位数和与氧原子的键长。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Chlorosomes are light harvesting complexes from filamentous and sulphur green photo-synthetic bacteria. The chlorosome is the only photosynthetic antenna complex found in nature in which the chlorophyll molecules are not organized by a protein matrix, but by interactions between the various bacteriochlorophyll (BChl) molecules themselves. It is also the only antenna complex for which structural information is still scarce. One of the active sites guiding the self-assembly of chlorosomes is the central magnesium atom in the BChl porphyrin ring. We aim to elucidate the details of the inter-molecular bonding in chlorosomes by probing the surroundings of the magnesium site with X-ray absorption spectroscopy. The required photon energies range from 1300 eV to 2000 eV and above. Our plan is to compare the BChl bonding in native chlorosomes to a series of polycrystalline chlorophyll samples with known structures. In addition, our simulations show that Mg-coordination numbers and bond lengths to oxygen atoms from neighboring BChl molecules can be obtained from the XANES and EXAFS signals.