Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, 37673, South Korea; Department of Bioenergy Science and Technology, Chonnam National University, Gwangju, 61186, South Korea.
Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, 37673, South Korea.
Biochem Biophys Res Commun. 2019 Oct 8;518(1):66-71. doi: 10.1016/j.bbrc.2019.08.009. Epub 2019 Aug 8.
Preprotein import into chloroplasts is mediated by the coordinated actions of translocons at the outer and inner envelopes of chloroplasts (Toc and Tic, respectively). The cleavable N-terminal transit peptide (TP) of preproteins plays an essential role in the import of preproteins into chloroplasts. The Tic40 protein, a component of the Tic complex, is believed to mediate the import of preproteins through the inner envelope. In this study, we aimed to obtain in vivo evidence supporting the role of Tic40 in preprotein import into chloroplasts. Contrary to previous findings, the import of various preproteins with wild-type TPs showed no difference between tic40 and wild-type protoplasts of Arabidopsis thaliana. However, the import of N-terminal mutants of the RbcS protein (RbcS-nt), in which basic amino acid residues (arginine and lysine) in the central region of the TP were substituted with neutral (alanine) or acidic (glutamic acid) amino acid residues, was dependent on Tic40. In addition, in tic40 protoplasts, the inner envelope protein Tic40 tagged with HA (hemagglutinin) showed more intermediate form present in the stroma. Based on these results, we propose that protein can be imported into chloroplast by either Tic40-independent or Tic40-dependent pathways depending on the types of TP.
前体蛋白向叶绿体的导入是由叶绿体外膜和内膜上的转运体（Toc 和 Tic，分别）的协调作用介导的。前体蛋白的可切割 N 端转运肽（TP）在前体蛋白向叶绿体的导入中起着至关重要的作用。Tic40 蛋白是 Tic 复合物的一个组成部分，被认为介导前体蛋白通过内膜的导入。在这项研究中，我们旨在获得支持 Tic40 在前体蛋白向叶绿体导入中的作用的体内证据。与先前的发现相反，在拟南芥 tic40 和野生型原生质体中，具有野生型 TP 的各种前体蛋白的导入没有差异。然而，RbcS 蛋白（RbcS-nt）的 N 端突变体的导入依赖于 Tic40，在该突变体中，TP 中心区域的碱性氨基酸（精氨酸和赖氨酸）被中性（丙氨酸）或酸性（谷氨酸）氨基酸取代。此外，在 tic40 原生质体中，用 HA（血凝素）标记的内膜蛋白 Tic40 在基质中表现出更多的中间形式。基于这些结果，我们提出，根据 TP 的类型，蛋白质可以通过 Tic40 独立或 Tic40 依赖的途径导入叶绿体。
