Subunit Organization of a Synechocystis Hetero-Oligomeric Thylakoid FtsH Complex Involved in Photosystem II Repair
Subunit Organization of a Synechocystis Hetero-Oligomeric Thylakoid FtsH Complex Involved in Photosystem II Repair
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DOI：
10.1105/tpc.112.100891
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发表时间：
2012-09-01
期刊：
影响因子：
11.6
通讯作者：
Nield, Jon
中科院分区：
文献类型：
--
作者：
Boehm, Marko;Yu, Jianfeng;Nield, Jon
FtsH金属蛋白酶是光系统II（PSII）修复循环的关键组分，其在光中起维持光合活性的作用。尽管它们的生理重要性，类囊体FtsH复合物的结构和亚基组成仍然不确定。诱变先前已经揭示，由蓝细菌集胞藻属PCC 6803编码的四种FtsH同源物在功能上是不同的：FtsH 1和FtsH 3是细胞活力所需的，而FtsH 2和FtsH 4是必需的。为了深入了解FtsH 2，这是参与选择性D1蛋白降解过程中PSII修复，我们使用了一株集胞藻6803表达谷胱甘肽S-转移酶（GST）标记的衍生物（FtsH 2-GST）分离FtsH 2含复合物。生化分析表明，FtsH 2-GST与FtsH 3形成异源寡聚复合物。在野生型菌株中，FtsH 2也与FtsH 3相互作用，而FtsH 3缺失的突变体，如ftsH 2（-）突变体，显示D1降解受损。FtsH 3还与FtsH 1形成单独的异源复合物，从而解释了为什么FtsH 3比FtsH 2对细胞活力更重要。我们研究了分离的FtsH 2-GST/FtsH 3复合物的结构，使用透射电子显微镜和单粒子分析。在26埃的分辨率下获得的三维结构模型显示，该复合物是六聚体，由交替的FtsH 2/FtsH 3亚基组成。
FtsH metalloproteases are key components of the photosystem II (PSII) repair cycle, which operates to maintain photosynthetic activity in the light. Despite their physiological importance, the structure and subunit composition of thylakoid FtsH complexes remain uncertain. Mutagenesis has previously revealed that the four FtsH homologs encoded by the cyanobacterium Synechocystis sp PCC 6803 are functionally different: FtsH1 and FtsH3 are required for cell viability, whereas FtsH2 and FtsH4 are dispensable. To gain insights into FtsH2, which is involved in selective D1 protein degradation during PSII repair, we used a strain of Synechocystis 6803 expressing a glutathione S-transferase (GST)-tagged derivative (FtsH2-GST) to isolate FtsH2-containing complexes. Biochemical analysis revealed that FtsH2-GST forms a hetero-oligomeric complex with FtsH3. FtsH2 also interacts with FtsH3 in the wild-type strain, and a mutant depleted in FtsH3, like ftsH2(-) mutants, displays impaired D1 degradation. FtsH3 also forms a separate heterocomplex with FtsH1, thus explaining why FtsH3 is more important than FtsH2 for cell viability. We investigated the structure of the isolated FtsH2-GST/FtsH3 complex using transmission electron microscopy and single-particle analysis. The three-dimensional structural model obtained at a resolution of 26 angstrom revealed that the complex is hexameric and consists of alternating FtsH2/FtsH3 subunits.