Elucidation of Molecular Mechanisms of Protein Translocation across the Chloroplast Envelope

• Project/Area Number: 19H03183
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 43030:Functional biochemistry-related
• Research Institution: Osaka University
• Principal Investigator: Nakai Masato 大阪大学, 蛋白質研究所, 准教授 (90222158)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥17,290,000 (Direct Cost: ¥13,300,000、Indirect Cost: ¥3,990,000); Fiscal Year 2022: ¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000); Fiscal Year 2021: ¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000); Fiscal Year 2020: ¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000); Fiscal Year 2019: ¥5,590,000 (Direct Cost: ¥4,300,000、Indirect Cost: ¥1,290,000)
• Keywords: 葉緑体 / タンパク質輸送 / タンパク質膜透過 / 細胞内蛋白質輸送 / 蛋白質膜透過 / オルガネラ / 植物 / 生合成 / 超分子複合体 / 膜タンパク質複合体

Outline of Research at the Start

葉緑体は、数千の葉緑体蛋白質が正しく葉緑体内へ運ばれることにより維持される。この輸送は外包膜と内包膜の蛋白質膜透過装置、TOCおよびTICと、Ycf2輸送モーターによって行われている。われわれはTICとYcf2輸送モーターがそれぞれ１メガダルトン、２メガダルトンという膜蛋白質複合体であることを明らかにし、すべての構成因子を決定した（Plant Cell 2018, Science 2013）。またTOC複合体も１メガダルトンの複合体であることを報告している。これらメガコンプレックスがどのように連動して葉緑体蛋白質をサイトゾル側からストロマ側まで輸送しているのか作動原理の解明を目指す。

Outline of Final Research Achievements

Majority of nuclear-encoded chloroplast proteins are synthesized in the cytosol as a larger preprotein and are then translocated across the outer and inner envelope membranes through TOC and TIC, respectively. Complete translocation of preproteins across the inner envelope membrane to the stroma occurs with the help of a TIC translocon-associated import motor at the stromal side of the inner envelope. Structural details of these mega complexes have still to be investigated. For this sake, we have tried to establish the method to obtain adequate purified complexes for cryoEM structural studies in both quality and quantity.

Academic Significance and Societal Importance of the Research Achievements

葉緑体への蛋白質輸送機構の構造レベルでの理解は、生命が光合成に特化した細胞内小器官としての葉緑体をいかに獲得してき得たのか、その根源の理解に必須の研究課題である。本研究成果を足掛かりとして、この精密な分子装置の構造機能連関の全容の解明に一歩近づいたと言える。

Research Products

• [Int'l Joint Research] University of California, San Francisco/University of California, Los Angeles/Princeton University(米国)
• [Int'l Joint Research] University of Geneva(スイス)
• [Int'l Joint Research] University of Munster(ドイツ)
• [Journal Article] Tic12, a 12-kDa essential component of the translocon at the inner envelope membrane of chloroplasts in Arabidopsis (2022)
  • Author(s): Zhao Xueyang、Higa Takeshi、Nakai Masato
  • Journal Title: The Plant Cell Volume: 34 Issue: 11 Pages: 4569-4582
  • DOI: 10.1093/plcell/koac240
  • Peer Reviewed
• [Journal Article] A distinct class of GTP-binding proteins mediates chloroplast protein import in Rhodophyta (2022)
  • Author(s): Baek Sanghun、Imamura Sousuke、Higa Takeshi、Nakai Yumi、Tanaka Kan、Nakai Masato
  • Journal Title: Proceedings of the National Academy of Sciences Volume: 119 Issue: 34 Pages: 2208277119-2208277119
  • DOI: 10.1073/pnas.2208277119
  • Peer Reviewed / Open Access
• [Journal Article] Coexpressed subunits of dual genetic origin define a conserved supercomplex mediating essential protein import into chloroplasts (2020)
  • Author(s): Ramundo Silvia、Asakura Yukari、Salom? Patrice A.、Strenkert Daniela、Boone Morgane、Mackinder Luke C. M.、Takafuji Kazuaki、Dinc Emine、Rahire Mich?le、Cr?vecoeur Mich?le、Magneschi Leonardo、Schaad Olivier、Hippler Michael、Jonikas Martin C.、Merchant Sabeeha、Nakai Masato、Rochaix Jean-David、Walter Peter
  • Journal Title: Proceedings of the National Academy of Sciences Volume: 117 Issue: 51 Pages: 32739-32749
  • DOI: 10.1073/pnas.2014294117
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Reply: The Revised Model for Chloroplast Protein Import (2020)
  • Author(s): Nakai Masato
  • Journal Title: The Plant Cell Volume: 32 Issue: 3 Pages: 543-546
  • DOI: 10.1105/tpc.19.00821
  • Peer Reviewed / Open Access
• [Presentation] More surprises in chloroplast protein import (2022)
  • Author(s): Masato Nakai
  • Organizer: EMBO Workshop "New challenges in protein translocation across membranes"
  • Int'l Joint Research / Invited
• [Remarks] 緑色植物界に共通する葉緑体形成メカニズムを解明：緑藻から植物へと受け継がれた仕組み
  • URL: https://resou.osaka-u.ac.jp/ja/research/2020/20201207_1