David Liron, Prado Mindy, Arteni Ana A, Elmlund Dominika A, Blankenship Robert E, Adir Noam
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA.
Biochim Biophys Acta. 2014 Mar;1837(3):385-95. doi: 10.1016/j.bbabio.2013.12.014. Epub 2014 Jan 6.
The major light harvesting complex in cyanobacteria and red algae is the phycobilisome (PBS), comprised of hundreds of seemingly similar chromophores, which are protein bound and assembled in a fashion that enables highly efficient uni-directional energy transfer to reaction centers. The PBS is comprised of a core containing 2-5 cylinders surrounded by 6-8 rods, and a number of models have been proposed describing the PBS structure. One of the most critical steps in the functionality of the PBS is energy transfer from the rod substructures to the core substructure. In this study we compare the structural and functional characteristics of high-phosphate stabilized PBS (the standard fashion of stabilization of isolated complexes) with cross-linked PBS in low ionic strength buffer from two cyanobacterial species, Thermosynechococcus vulcanus and Acaryochloris marina. We show that chemical cross-linking preserves efficient energy transfer from the phycocyanin containing rods to the allophycocyanin containing cores with fluorescent emission from the terminal emitters. However, this energy transfer is shown to exist in PBS complexes of different structures as characterized by determination of a 2.4Å structure by X-ray crystallography, single crystal confocal microscopy, mass spectrometry and transmission electron microscopy of negatively stained and cryogenically preserved complexes. We conclude that the PBS has intrinsic structural properties that enable efficient energy transfer from rod substructures to the core substructures without requiring a single unique structure. We discuss the significance of our observations on the functionality of the PBS in vivo.
蓝藻和红藻中的主要光捕获复合体是藻胆体（PBS），它由数百个看似相似的发色团组成，这些发色团与蛋白质结合并以一种能够将高效单向能量转移到反应中心的方式组装。藻胆体由一个核心组成，该核心包含2至5个圆柱体，周围环绕着6至8个棒状体，并且已经提出了许多描述藻胆体结构的模型。藻胆体功能中最关键的步骤之一是从棒状亚结构到核心亚结构的能量转移。在本研究中，我们比较了来自两种蓝藻，即嗜热栖热菌和滨海红藻的高磷酸盐稳定化藻胆体（分离复合体稳定化的标准方式）与在低离子强度缓冲液中的交联藻胆体的结构和功能特性。我们表明，化学交联通过末端发射体的荧光发射保留了从含藻蓝蛋白的棒状体到含别藻蓝蛋白的核心的高效能量转移。然而，通过对负染色和低温保存复合体的X射线晶体学、单晶共聚焦显微镜、质谱分析和透射电子显微镜测定2.4埃结构所表征，这种能量转移存在于不同结构的藻胆体复合体中。我们得出结论，藻胆体具有内在的结构特性，能够在不需要单一独特结构的情况下实现从棒状亚结构到核心亚结构的高效能量转移。我们讨论了我们对藻胆体在体内功能观察结果的意义。
