Principal Investigator
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P17 Enrico Schleiff
Professor
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Institute of Molecular Biosciences
Biocenter
Goethe-University Frankfurt a.M.
Max-von-Laue-Str. 9
60438 Frankfurt am Main, Germany
Phone +49 (0)69 79 82 92 85
Fax +49 (0)69 79 82 92 86
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P17 Dynamics, function and structural composition of the Toc-core complex
The subdivision of cells into different compartments paralleled the development of the eukaryotic kingdom, enforcing the communication between different intracellular compartments and the exchange of information regarding their functionality. The most complex form of this synchronization is the dualism of complexes of endosymbiotically derived organelles with respect to the place of synthesis of their components. Thereby, protein translocation of cytosolically synthesized proteins across organellar membranes has to be considered the highest form of communication between different cellular subspaces. The mechanistic and structural description of the molecular processes during transport of proteins across membranes is the ultimate goal of our project. The object of study is the translocon localized in the outer envelope of chloroplasts, annotated as Toc complex. This consists of five proteins: Toc159, Toc75, Toc64, Toc34 and Toc12 (Fig. 1). With the exception of Toc12, all components are known in P. sativum (model plant for biochemical analysis) and A. thaliana (model plant for genetics). By the combined analysis of individual components, reconstituted systems and complexes in endogenous membranes by cell biological, biochemical, biophysical and structural approaches we aim to circumstantiate this process. The communication between individual components of the core translocon during translocation and the energetics of this event will be the focus of the project.
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- Fig. 1: The translocon at the outer chloroplast envelope. Translocation of precursor proteins across the outer membrane depends on chaperones (yellow), proteins in the outer envelope membrane (orange), the inner envelope membrane (blue) and stroma (not shown). Nucleotide requirements are indicated. The outer membrane localized complex can be divided into a “core complex” composed of Toc159, Tocc34 - which are regulated by phosphorylation - and Toc75. Toc64 and Toc12 form a complex involved in perception of Hsp90 delivered precursor proteins and, together with Tic22 and the intermembrane space localized Hsp70, in the assembly of an intermembrane space (IMS) complex for the transfer across the intermembrane space. The model represents a scheme of participating components not considering stoichiometric relations or organ specific distributions (see Oreb et al., 2008).
- Fig. 2: The regulation of the Toc-complex. At first, Toc34 recognizes the incoming plastid preprotein at the chloroplast surface. In a GTP-dependent manner (left) the protein is handed over to the main import receptor Toc159 (bottom), which subsequently facilitates the insertion of the protein into Toc75-channel (right). By GTP to GDP exchange, the complex is regenerated for a new import cycle (top). Phosphorylation of either Toc34 or Toc159 impedes the complex by dissociation of Toc34 (top-right). Center: crystal structure of the Toc34 GTPase domain (Koenig et al., 2008).
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Publications
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Ruprecht, M., Bionda, T., Sato, T., Sommer, M.S., Endo, T. and Schleiff, E. (2010) On the impact of precursor unfolding during protein import into chloroplasts. Mol Plant 3, 499-508.
Bionda, T., Koenig, P., Oreb, M., Tews, I. and Schleiff, E. (2008) pH sensitivity of the GTPase Toc33 as a regulatory circuit for protein translocation into chloroplasts. Plant Cell Phys 49, 1917-1921.
Oreb, M., Höfle, A., Mirus, O. and Schleiff, E. (2008) Phosphorylation regulates the assembly of chloroplast import machinery. J Exp Bot 59, 2309-2316.
Koenig, P., Oreb, M., Rippe, K., Muhle-Goll, C., Sinning, I., Schleiff, E. and Tews, I. (2008) On the significance of Toc-GTPase homodimers. J Biol Chem 283, 23104-23112.
Koenig, P., Oreb, M., Höfle, A., Kaltofen, S., Rippe, K., Sinning, I., Schleiff, E. and Tews, I. (2008) The GTPase cycle of the chloroplast import receptors Toc33/Toc34 – Implications from monomeric and dimeric structures. Structure 16, 585-596.
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Collaborations
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Kühlbrandt (P1), Ziegler (P4), Schwalbe (P13), Wachtveitl (P14), Mäntele (P5), Dötsch/Bernhard (P2), Glaubitz (P6), Abele (P9), Müller (P14), Tampé (P16), Fendler/Bamberg (P10)