Stromal Hsp70 Is Important for Protein Translocation into Pea and Arabidopsis Chloroplasts
Stromal Hsp70 Is Important for Protein Translocation into Pea and Arabidopsis Chloroplasts
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DOI：
10.1105/tpc.109.071415
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发表时间：
2010-05-01
期刊：
影响因子：
11.6
通讯作者：
Li, Hsou-min
中科院分区：
文献类型：
--
作者：
Su, Pai-Hsiang;Li, Hsou-min
Hsp70 家族蛋白充当驱动蛋白质易位至线粒体和内质网的马达。 Hsp70 是否参与蛋白质输入叶绿体尚未解决。我们在此展示了两种基质 cpHsc70（cpHsc70-1 和 cpHsc70-2）中的拟南芥敲除突变体，在早期发育阶段蛋白质输入叶绿体中存在缺陷。发现蛋白质输入在前体易位穿过包膜的步骤中受到影响。从溶解的包膜中，基质 cpHsc70 与输入前体和化学计量量的 Tic110 和 Hsp93 特异性共免疫沉淀。此外，与外膜上的受体相比，cpHsp70 对于光合和非光合蛋白质的输入都很重要。这些数据表明 cpHsc70 是一般输入的叶绿体易位子的一部分，并且对于驱动易位进入基质很重要。我们进一步分析了 cpHsc70 与其他建议的运动系统 Hsp93/Tic40 的关系。来自 cphsc70-1 hsp93-V 双突变体的叶绿体比单突变体具有更严重的输入缺陷，表明这两种蛋白质平行发挥作用。 cphsc70-1 tic40 双敲除是致命的，进一步表明 cpHsc70-1 和 Tic40 具有重叠的基本功能。总之，我们的数据表明叶绿体有两个促进蛋白质易位到基质中的伴侣系统：cpHsc70 系统和 Hsp93/Tic40 系统。
Hsp70 family proteins function as motors driving protein translocation into mitochondria and the endoplasmic reticulum. Whether Hsp70 is involved in protein import into chloroplasts has not been resolved. We show here Arabidopsis thaliana knockout mutants of either of the two stromal cpHsc70s, cpHsc70-1 and cpHsc70-2, are defective in protein import into chloroplasts during early developmental stages. Protein import was found to be affected at the step of precursor translocation across the envelope membranes. From solubilized envelope membranes, stromal cpHsc70 was specifically coimmunoprecipitated with importing precursors and stoichiometric amounts of Tic110 and Hsp93. Moreover, in contrast with receptors at the outer envelope membrane, cpHsp70 is important for the import of both photosynthetic and nonphotosynthetic proteins. These data indicate that cpHsc70 is part of the chloroplast translocon for general import and is important for driving translocation into the stroma. We further analyzed the relationship of cpHsc70 with the other suggested motor system, Hsp93/Tic40. Chloroplasts from the cphsc70-1 hsp93-V double mutant had a more severe import defect than did the single mutants, suggesting that the two proteins function in parallel. The cphsc70-1 tic40 double knockout was lethal, further indicating that cpHsc70-1 and Tic40 have an overlapping essential function. In conclusion, our data indicate that chloroplasts have two chaperone systems facilitating protein translocation into the stroma: the cpHsc70 system and the Hsp93/Tic40 system.