Localization and integration of thylakoid protein translocase subunit cpTatC.
Localization and integration of thylakoid protein translocase subunit cpTatC.
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DOI：
10.1111/j.1365-313x.2009.03816.x
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发表时间：
2009-06
期刊：
影响因子：
--
通讯作者：
Cline K
中科院分区：
文献类型：
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作者：
Martin JR;Harwood JH;McCaffery M;Fernandez DE;Cline K
类囊体膜具有独特的蛋白质补充，其中大部分在细胞质中合成，输入到基质中，并通过特异性类囊体移位酶移位到类囊体膜中。已知的类囊体移位酶含有核心多跨膜整合亚基，其也是核编码的并且在整合到类囊体膜中之前输入到叶绿体中。类囊体转位酶在决定类囊体的组成中起着重要作用，但核心转位酶亚基整合到膜中的方式尚不清楚。我们利用生物化学和遗传学方法研究叶绿体达特转位酶核心亚基cpTatC整合到类囊体膜中的情况。在体外进口分析表明，cpTatC正确定位到类囊体，如果进口到完整的叶绿体，但它不整合到孤立的类囊体。体外转运肽加工和嵌合前体输入实验表明，cpTatC具有基质靶向转运肽。导入时间过程和追踪测定证实cpTatC通过基质中间体靶向类囊体，表明它可能通过已知的类囊体易位途径之一整合。然而，cpSecA-cpSecY和cpTat途径的化学抑制剂并不妨碍cpTatC定位到类囊体时，用于进口测定。从缺乏cpSecY或Alb 3的拟南芥突变体中分离的膜的分析表明，cpTatC膜整合或组装到cpTat受体复合物中都不是必需的。这些数据表明存在另一个易位酶，可能是一个致力于叶绿体易位酶的整合。
Thylakoid membranes have a unique complement of proteins, most of which are synthesized in the cytosol, imported into the stroma, and translocated into thylakoid membranes by specific thylakoid translocases. Known thylakoid translocases contain a core multi-spanning, membrane-integrated subunit which is also nuclear-encoded and imported into chloroplasts before being integrated into thylakoid membranes. Thylakoid translocases play a central role in determining the composition of thylakoids, yet the manner by which the core translocase subunits are integrated into the membrane is not known. We used biochemical and genetic approaches to investigate integration of the core subunit of the chloroplast Tat translocase, cpTatC, into thylakoid membranes. In vitro import assays show that cpTatC correctly localizes to thylakoids if imported into intact chloroplasts, but it does not integrate into isolated thylakoids. In vitro transit peptide processing and chimeric precursor import experiments suggest that cpTatC possesses a stroma-targeting transit peptide. Import time course and chase assays confirmed that cpTatC targets to thylakoids via a stromal intermediate, suggesting that it might integrate through one of the known thylakoid translocation pathways. However, chemical inhibitors to the cpSecA-cpSecY and cpTat pathways did not impede cpTatC localization to thylakoids when used in import assays. Analysis of membranes isolated from Arabidopsis thaliana mutants lacking cpSecY or Alb3 showed that neither is necessary for cpTatC membrane integration or assembly into the cpTat receptor complex. These data suggest the existence of another translocase, possibly one dedicated to the integration of chloroplast translocases.