High-Resolution Crystal Structures of Trimeric and Rod Phycocyanin
High-Resolution Crystal Structures of Trimeric and Rod Phycocyanin
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DOI：
10.1016/j.jmb.2010.10.036
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发表时间：
2011-01-07
影响因子：
5.6
通讯作者：
Adir, Noam
中科院分区：
文献类型：
--
作者：
David, Liron;Marx, Ailie;Adir, Noam
蓝藻和红藻中的藻胆体捕光天线由两个亚结构组装而成：由总是含有藻蓝蛋白（PC）的杆包围的由别藻蓝蛋白组成的中央核心。在杆状和核心中也发现了称为连接体的无色素蛋白质。我们在这里提出了两个新的结构的PC从嗜热蓝细菌Thermosynechococcus vulcanus。我们已经确定了三聚体PC的结构为1.35埃，这是迄今为止报道的这种蛋白质的最高分辨率。我们还提出了一个结构的PC孤立在其完整的和功能杆的形式在1.5埃。杆状晶体的分析表明，除了α和β PC亚基，还有三种连接蛋白：加帽杆状连接蛋白（L-R（8.7））、杆状连接蛋白（L-R）和三种杆状-核心连接蛋白中仅有的一种（L-RC，CpcG 4），化学计量比为12：12：1：1：1。该比率表明晶体含有由两个六聚体组成的棒。棒状晶体的晶体学参数与三聚体形式的晶体学参数几乎相同，这表明连接体不影响晶体堆积并且完全嵌入棒状空腔内。吸收和荧光发射光谱红移，如预期的组装棒，这可以显示在溶液中的棒，以及在晶体中使用共聚焦荧光显微镜。晶体堆积使三个棒状连接体叠加，抵消了它们的电子密度。然而，B-因子和面向杆通道的残基的构象的分析表明连接体的存在。基于这里提出的实验证据和LR蛋白的基于同源性的模型，我们建议，连接器实际上不连接杆六聚体之间，但稳定的六聚体组装和修改杆能量吸收和转移能力。(c)2010爱思唯尔有限公司版权所有。
The phycobilisome light-harvesting antenna in cyanobacteria and red algae is assembled from two substructures: a central core composed of allophycocyartin surrounded by rods that always contain phycocyanin (PC). Unpigmented proteins called linkers are also found within the rods and core. We present here two new structures of PC from the thermophilic cyanobacterium Thermosynechococcus vulcanus. We have determined the structure of trimeric PC to 1.35 angstrom, the highest resolution reported to date for this protein. We also present a structure of PC isolated in its intact and functional rod form at 1.5 angstrom. Analysis of rod crystals showed that in addition to the alpha and beta PC subunit, there were three linker proteins: the capping rod linker (L-R(8.7)), the rod linker (L-R), and only one of three rod-core linkers (L-RC, CpcG4) with a stoichiometry of 12:12:1:1:1. This ratio indicates that the crystals contained rods composed of two hexamers. The crystallographic parameters of the rod crystals are nearly identical with that of the trimeric form, indicating that the linkers do not affect crystal packing and are completely embedded within the rod cavities. Absorption and fluorescence emission spectra were red-shifted, as expected for assembled rods, and this could be shown for the rod in solution as well as in crystal using confocal fluorescence microscopy. The crystal packing imparts superimposition of the three rod linkers, canceling out their electron density. However, analysis of B-factors and the conformations of residues facing the rod channel indicate the presence of linkers. Based on the experimental evidence presented here and a homology-based model of the LR protein, we suggest that the linkers do not in fact link between rod hexamers but stabilize the hexameric assembly and modify rod energy absorption and transfer capabilities. (c) 2010 Elsevier Ltd. All rights reserved.