title: Hsp90 is involved in the regulation of cytosolic precursor protein abundance in tomato.
abstract: Cytosolic chaperones are involved in the regulation of cellular protein homeostasis in general. Members of the heat stress protein 70 and 90 (Hsp70 or Hsp90) families assist the transport of preproteins to organelles such as chloroplasts or mitochondria. In addition, Hsp70 was described to be involved in the degradation of chloroplast preproteins that accumulate in the cytosol. Because a similar function has not been established for Hsp90, we analyzed the influences of Hsp90 and Hsp70 on the protein abundance in the cellular context using an in vivo system based on mesophyll protoplasts. We observed a differential behavior of preproteins in respect to the cytosolic chaperone dependent regulation. Some preproteins like pOE33 show a high dependence on Hsp90, whereas the abundance of preproteins like pSSU is more strongly dependent on Hsp70. The E3 ligase Chip appears to have a more general role in the control of cytosolic protein abundance. We discuss why the different reaction modes are comparable to the cytosolic unfolded protein response.
authors.affiliation: Molecular Cell Biology of Plants, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany.
authors.forename: Bodo
authors.initials: B
authors.lastname: Tillmann
authors.affiliation: Molecular Cell Biology of Plants, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Röth
authors.affiliation: Molecular Cell Biology of Plants, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Bublak
authors.affiliation: Molecular Cell Biology of Plants, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany Buchman Institute for Molecular Life Sciences, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany Institute of Cell Biology, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Sommer
authors.affiliation: Cluster of Excellence 'Macromolecular Complexes', Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany Institute of Cell Biology, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany.
authors.forename: Ernst H K
authors.initials: EH
authors.lastname: Stelzer
authors.affiliation: Molecular Cell Biology of Plants, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany.
authors.forename: Klaus-Dieter
authors.initials: KD
authors.lastname: Scharf
authors.affiliation: Molecular Cell Biology of Plants, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany Buchman Institute for Molecular Life Sciences, Goethe-Universität, Max-von-Laue Str. 9, Frankfurt am Main, Germany schleiff@bio.uni-frankfurt.de.
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
keywords: CPR; Chip; Hsp70; Hsp90; cytosolic unfolded protein response; preprotein degradation