title: Eukaryotic Hsp70 chaperones in the intermembrane space of chloroplasts.
abstract: Multiple eukaryotic Hsp70 typically localized in the cytoplasm are also distributed to the intermembrane space of chloroplasts and might thereby represent the missing link in energizing protein translocation. Protein translocation into organelles is a central cellular process that is tightly regulated. It depends on signals within the preprotein and on molecular machines catalyzing the process. Molecular chaperones participate in transport and translocation of preproteins into organelles to control folding and to provide energy for the individual steps. While most of the processes are explored and the components are identified, the transfer of preproteins into and across the intermembrane space of chloroplasts is not yet understood. The existence of an energy source in this compartment is discussed, because the required transit peptide length for successful translocation into chloroplasts is shorter than that found for mitochondria where energy is provided exclusively by matrix chaperones. Furthermore, a cytosolic-type Hsp70 homologue was proposed as component of the chloroplast translocon in the intermembrane space energizing the initial translocation. The molecular identity of such intermembrane space localized Hsp70 remained unknown, which led to a controversy concerning its existence. We identified multiple cytosolic Hsp70s by mass spectrometry on isolated, thermolysin-treated Medicago sativa chloroplasts. The localization of these Hsp70s of M. sativa or Arabidopsis thaliana in the intermembrane space was confirmed by a self-assembly GFP-based in vivo system. The localization of cytosolic Hsp70s in the stroma of chloroplasts or different mitochondrial compartments could not be observed. Similarly, we could not identify any cytosolic Hsp90 in the intermembrane space of chloroplast. With respect to our results we discuss the possible targeting and function of the Hsp70 found in the intermembrane space.
authors.affiliation: Molecular Cell Biology of Plants, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany.|Institute of Biochemistry II, Goethe University, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
authors.forename: Tihana
authors.initials: T
authors.lastname: Bionda
authors.affiliation: Molecular Cell Biology of Plants, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany.
authors.forename: Lucia E
authors.initials: LE
authors.lastname: Gross
authors.affiliation: Molecular Cell Biology of Plants, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany.|Biochemistry and Molecular Biology, ZBMZ, and BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, Stefan-Meier-Str. 17, 79104, Freiburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Becker
authors.affiliation: Pharmaceutical Chemistry, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany.|Syngenta Ltd., Jealott's Hill International Research Centre, Bracknell, Berkshire, RG42 6EY, UK.
authors.forename: Dimitrios G
authors.initials: DG
authors.lastname: Papasotiriou
authors.affiliation: Molecular Cell Biology of Plants, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany.|Institute for Cardiovascular Physiology, Goethe University, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
authors.forename: Matthias S
authors.initials: MS
authors.lastname: Leisegang
authors.affiliation: Pharmaceutical Chemistry, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Karas
authors.affiliation: Molecular Cell Biology of Plants, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany. schleiff@bio.uni-frankfurt.de.|Molecular Cell Biology of Plants, Cluster of Excellence Frankfurt, Goethe University, Max von Laue Str. 9, 60438, Frankfurt, Germany. schleiff@bio.uni-frankfurt.de.|Buchmann Institut for Molecular Life Sciences, Max von Laue Str. 9, 60438, Frankfurt, Germany. schleiff@bio.uni-frankfurt.de.
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D013058:Mass Spectrometry; D000455:Medicago sativa / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D018532:Pisum sativum / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport
chemical_list: D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D010940:Plant Proteins
keywords: Chloroplasts intermembrane space; Hsp70; Protein targeting; TOC complex