Chuang Meng-Rong, Chen Lih-Jen, Li Hsou-Min
Institute of Molecular Biology Academia Sinica Taipei Taiwan.
Present address: Department of Food Science and Biotechnology National Chung Hsing University Taichung Taiwan.
Plant Direct. 2021 Nov 7;5(11):e356. doi: 10.1002/pld3.356. eCollection 2021 Nov.
Chloroplasts are divided into six subcompartments: the outer membrane, intermembrane space, and inner membrane of the envelope, the stroma, the thylakoid membrane, and the thylakoid lumen. Compared with our knowledge of protein import into other subcompartments, extremely little is known about how proteins are imported into the intermembrane space of the envelope. Tic22 was one of the first proteins identified as localizing to the intermembrane space and the only one for which import has been analyzed in some detail. However, conflicting results have been obtained concerning whether the general translocon is used to import Tic22 into the intermembrane space. Taking advantage of available translocon component mutants, we reanalyzed import of Tic22. We reveal reduced in vitro import of Tic22 preprotein (prTic22) into chloroplasts isolated from the Arabidopsis and mutants, which are functional knockdown mutants of the outer-membrane channel Toc75 and the intermembrane space linker Tic236, respectively. Import competition experiments also showed that prTic22 import was reduced by excess amounts of a stroma-targeted preprotein. Our results indicate that prTic22 uses at least part of the general translocon for import into the intermembrane space.
被膜的外膜、膜间隙、内膜，基质，类囊体膜和类囊体腔。与我们对蛋白质导入其他亚区室的了解相比，我们对蛋白质如何导入被膜膜间隙的了解极少。Tic22是最早被鉴定定位于膜间隙的蛋白质之一，也是唯一对其导入过程进行了一些详细分析的蛋白质。然而，关于是否使用通用转运体将Tic22导入膜间隙，已得出相互矛盾的结果。利用现有的转运体组分突变体，我们重新分析了Tic22的导入过程。我们发现，从拟南芥 和 突变体中分离出的叶绿体中，Tic22前体蛋白（prTic22）的体外导入减少，这两种突变体分别是外膜通道Toc75和膜间隙连接蛋白Tic236的功能敲除突变体。导入竞争实验还表明，过量的基质靶向前体蛋白会降低prTic22的导入。我们的结果表明，prTic22至少部分使用通用转运体导入膜间隙。
