tailieunhanh - Báo cáo khoa học: Protein transport in organelles: The composition, function and regulation of the Tic complex in chloroplast protein import

It is widely accepted that chloroplasts derived from an endosymbiotic event in which an early eukaryotic cell engulfed an ancient cyanobacterial pro-karyote. During subsequent evolution, this new organelle lost its autonomy by transferring most of its genetic information to the host cell nucleus and therefore became dependent on protein import from the cytoplasm. | MINIREVIEW Protein transport in organelles The composition function and regulation of the Tic complex in chloroplast protein import J. Philipp Benz1 2 Jurgen Soil1 2 and Bettina Bolter1 2 1 Plant Biochemistry Ludwig-Maximilians-Universitat Munchen Munich Germany 2 Munich Center for Integrated Protein Science CiPSM Ludwig-Maximilians-Universitat Munchen Munich Germany Keywords chloroplast import motor preprotein channel redox regulation Tic complex translocon Correspondence J. Soll Plant Biochemistry Ludwig-Maximilians-Universitat Munchen GroBhaderner Strasse 2-4 D-82152 Munich Germany Fax 49 89 2180 74752 Tel 49 89 2180 74750 E-mail soll@ Website http Received 31 July 2008 accepted 11 December 2008 doi It is widely accepted that chloroplasts derived from an endosymbiotic event in which an early eukaryotic cell engulfed an ancient cyanobacterial prokaryote. During subsequent evolution this new organelle lost its autonomy by transferring most of its genetic information to the host cell nucleus and therefore became dependent on protein import from the cytoplasm. The so-called general import pathway makes use of two multisubunit protein translocases located in the two envelope membranes the Toc and Tic complexes translocon at the outer inner envelope membrane of chloroplasts . The main function of both complexes which are thought to work in parallel is to provide a protein-selective channel through the envelope membrane and to exert the necessary driving force for the translocation. To achieve high efficiency of protein import additional regulatory subunits have been developed that sense and quickly react to signals giving information about the status and demand of the organelle. These include calcium-mediated signals most likely through a potential plastidic calmodulin as well as redox sensing . via the stromal NADP NADPH pool . In this minireview we briefly summarize the present knowledge of how the Tic .