The membrane-associated CpcG2-phycobilisome in Synechocystis:: A new photosystem I antenna
The membrane-associated CpcG2-phycobilisome in Synechocystis:: A new photosystem I antenna
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DOI：
10.1104/pp.107.099267
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发表时间：
2007-06-01
期刊：
影响因子：
7.4
通讯作者：
Ikeuchi, Masahiko
中科院分区：
文献类型：
--
作者：
Kondo, Kumiko;Ochiai, Yuriko;Ikeuchi, Masahiko
藻胆体（phycobilisome，PBS）是蓝藻和含胆素的红藻进行光合作用所必需的超分子天线复合物。虽然PBS的基本结构是广泛保守的，但藻胆蛋白、核心结构和接头多肽在不同物种中显示出显著的多样性。相比之下，我们最近报道，单细胞蓝细菌集胞藻属PCC 6803拥有两种类型的PBS，不同的是它们的互连“杆-核心连接器”蛋白（CpcG 1和CpcG 2）。发现CpcG 1-PBS等同于常规PBS，而CpcG 2-PBS保留藻蓝蛋白杆，但缺乏中央核心。本研究描述了CpcG 1-PBS和CpcG 2-PBS的功能分析。基于低温荧光对细胞和类囊体膜估计的从PBS到光系统的特定能量转移表明，与CpcG 1-PBS相比，CpcG 2-PBS优先将光能转移到光系统I（PSI），尽管它们能够转移到两个光系统。cpcG 2干扰物中增加的光系统化学计量比（PSI/ PSII）也支持优先的能量转移。cpcG 2干扰物在弱PSII光下持续表现出生长迟缓，其中PSI的激发是有限的。高盐条件下类囊体膜的分离表明CpcG 2-PBS与膜紧密结合，而CpcG 1-PBS则部分释放。CpcG 2的特征在于其C-末端疏水片段，其可以将CpcG 2-PBS锚到类囊体膜或PSI复合物。进一步的序列分析表明，CpcG 2-like蛋白含有一个C-末端疏水片段，广泛分布于许多蓝藻。
The phycobilisome (PBS) is a supramolecular antenna complex required for photosynthesis in cyanobacteria and bilin-containing red algae. While the basic architecture of PBS is widely conserved, the phycobiliproteins, core structure and linker polypeptides, show significant diversity across different species. By contrast, we recently reported that the unicellular cyanobacterium Synechocystis sp. PCC 6803 possesses two types of PBSs that differ in their interconnecting "rod-core linker'' proteins (CpcG1 and CpcG2). CpcG1-PBS was found to be equivalent to conventional PBS, whereas CpcG2-PBS retains phycocyanin rods but is devoid of the central core. This study describes the functional analysis of CpcG1-PBS and CpcG2-PBS. Specific energy transfer from PBS to photosystems that was estimated for cells and thylakoid membranes based on low-temperature fluorescence showed that CpcG2-PBS transfers light energy preferentially to photosystem I (PSI) compared to CpcG1-PBS, although they are able to transfer to both photosystems. The preferential energy transfer was also supported by the increased photosystem stoichiometry (PSI/ PSII) in the cpcG2 disruptant. The cpcG2 disruptant consistently showed retarded growth under weak PSII light, in which excitation of PSI is limited. Isolation of thylakoid membranes with high salt showed that CpcG2-PBS is tightly associated with the membrane, while CpcG1-PBS is partly released. CpcG2 is characterized by its C-terminal hydrophobic segment, which may anchor CpcG2-PBS to the thylakoid membrane or PSI complex. Further sequence analysis revealed that CpcG2-like proteins containing a C-terminal hydrophobic segment are widely distributed in many cyanobacteria.