Biochemistry Department, George S Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
J Biol Chem. 2010 Jan 29;285(5):3478-86. doi: 10.1074/jbc.M109.072645. Epub 2009 Nov 18.
Photosystem I functions as a sunlight energy converter, catalyzing one of the initial steps in driving oxygenic photosynthesis in cyanobacteria, algae, and higher plants. Functionally, Photosystem I captures sunlight and transfers the excitation energy through an intricate and precisely organized antenna system, consisting of a pigment network, to the center of the molecule, where it is used in the transmembrane electron transfer reaction. Our current understanding of the sophisticated mechanisms underlying these processes has profited greatly from elucidation of the crystal structures of the Photosystem I complex. In this report, we describe the developments that ultimately led to enhanced structural information of plant Photosystem I. In addition, we report an improved crystallographic model at 3.3-A resolution, which allows analysis of the structure in more detail. An improved electron density map yielded identification and tracing of subunit PsaK. The location of an additional ten beta-carotenes as well as five chlorophylls and several loop regions, which were previously uninterpretable, are now modeled. This represents the most complete plant Photosystem I structure obtained thus far, revealing the locations of and interactions among 17 protein subunits and 193 non-covalently bound photochemical cofactors. Using the new crystal structure, we examine the network of contacts among the protein subunits from the structural perspective, which provide the basis for elucidating the functional organization of the complex.
光系统 I 作为阳光能量转换器，催化蓝藻、藻类和高等植物产氧光合作用的初始步骤之一。从功能上讲，光系统 I 捕获阳光，并通过一个复杂而精确组织的天线系统将激发能量传递，该系统由一个色素网络组成，传递到分子的中心，在那里它用于跨膜电子转移反应。我们目前对这些过程背后复杂机制的理解，很大程度上得益于对光系统 I 复合物晶体结构的阐明。在本报告中，我们描述了最终导致植物光系统 I 结构信息增强的发展情况。此外，我们还报告了分辨率为 3.3-A 的改进晶体结构模型，该模型允许更详细地分析结构。改进的电子密度图可识别和追踪亚基 PsaK。现在可以对以前无法解释的另外十个β-胡萝卜素以及五个叶绿素和几个环区进行建模。这代表了迄今为止获得的最完整的植物光系统 I 结构，揭示了 17 个蛋白亚基和 193 个非共价结合的光化学辅助因子的位置和相互作用。我们使用新的晶体结构从结构角度检查蛋白亚基之间的接触网络，这为阐明复合物的功能组织提供了基础。
