Inagaki J, Fujita Y, Hase T, Yamamoto Y
Department of Cell Chemistry, Institute of Cellular and Molecular Biology, Okayama, 700-8558, Japan.
Biochem Biophys Res Commun. 2000 Oct 22;277(2):436-42. doi: 10.1006/bbrc.2000.3702.
It is currently thought that chloroplasts of higher plants were derived from endosymbiont oxygenic photosynthetic bacteria (primary endosymbiosis), while Euglena, a photosynthetic protista, gained chloroplasts by secondary endosymbiosis (i.e., incorporation of a photosynthetic eukaryote into heterotrophic eukaryotic host). To examine if the protein transport inside chloroplasts is similar between these organisms, we carried out heterologous protein import experiments with Euglena precursor proteins and spinach chloroplasts. The precursor of a 30-kDa subunit of the oxygen-evolving complex (OEC30) from the thylakoid lumen of Euglena chloroplasts contained the N-terminal signal, stroma targeting, and thylakoid transfer domains. Truncated preOEC30s lacking the N-terminal domain were post-translationally imported into spinach chloroplasts, transported into the thylakoid lumen, and processed to a mature protein. These results showed that protein translocations within chloroplasts in Euglena and higher plants are similar and supported the hypothesis that Euglena chloroplasts are derived from the ancestral Chlorophyta.
目前认为，高等植物的叶绿体源自内共生的产氧光合细菌（初级内共生），而光合原生生物眼虫则通过次级内共生获得叶绿体（即将光合真核生物并入异养真核宿主）。为了研究这些生物体中叶绿体内部的蛋白质转运是否相似，我们用眼虫前体蛋白和菠菜叶绿体进行了异源蛋白导入实验。来自眼虫叶绿体类囊体腔的放氧复合体30 kDa亚基（OEC30）的前体包含N端信号、基质靶向和类囊体转运结构域。缺失N端结构域的截短前OEC30在翻译后被导入菠菜叶绿体，转运到类囊体腔，并加工成成熟蛋白。这些结果表明，眼虫和高等植物叶绿体中的蛋白质转运相似，并支持眼虫叶绿体源自祖先绿藻的假说。
