TAILIEUCHUNG - Báo cáo khoa học: Protein transport in chloroplasts ) targeting to the intermembrane space

The import of proteins destined for the intermembrane space of chloro-plasts has not been investigated in detail up to now. By investigating energy requirements and time courses, as well as performing competition experiments, we show that the two intermembrane space components Tic22 and MGD1 (. ) both engage the Toc machinery for crossing the outer envelope, whereas their pathways diverge thereafter. | ỊFEBS Journal Protein transport in chloroplasts - targeting to the intermembrane space Lea Vojta Jurgen Soil and Bettina Bolter University of Munich Department of Botany Munich Germany Keywords intermembrane space MGD1 Tic Tic22 Toc Correspondence J. Soll University of Munich Botany Menzinger Strasse 67 80638 Munich Germany Fax 49 89 17861185 Tel 49 89 17861245 E-mail soll@ The import of proteins destined for the intermembrane space of chloroplasts has not been investigated in detail up to now. By investigating energy requirements and time courses as well as performing competition experiments we show that the two intermembrane space components Tic22 and MGD1 . both engage the Toc machinery for crossing the outer envelope whereas their pathways diverge thereafter. Although MGD1 appears to at least partly cross the inner envelope Tic22 very likely reaches its mature form in the intermembrane space without involving stromal components. Thus different pathways for intermembrane space targeting probably exist in chloroplasts. Received 29 May 2007 revised 31 July 2007 accepted 1 August 2007 doi Protein import into organelles not only requires translocation into the organelle but also sorting to the various subcompartments. Chloroplasts are highly structured organelles that contain three distinct membrane systems . the outer and inner envelope membrane and the photosynthetic thylakoid membranes as well as three soluble subcompartments the thylakoid lumen the stroma and the intermembrane space. The large majority of chloroplast proteins are encoded by nuclear genes synthesized in the cytosol and post-translationally imported into the organelle 1 2 . In the cytosol preproteins associate with different molecular chaperones . Hsp70 or Hsp90 . This interaction determines the primary receptor at the chloroplast surface that is chosen by the preprotein chaperone complex 3 . Toc64 recognizes Hsp90-associated preproteins .

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