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Wiesemann K, Simm S, Mirus O, Ladig R, Schleiff E. Regulation of two GTPases Toc159 and Toc34 in the translocon of the outer envelope of chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA. PROTEINS AND PROTEOMICS 2019; 1867:627-636. [PMID: 30611779 DOI: 10.1016/j.bbapap.2019.01.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 12/20/2018] [Accepted: 01/02/2019] [Indexed: 01/03/2023]
Abstract
The GTPases Toc159 and Toc34 of the translocon of the outer envelope of chloroplasts (TOC) are involved in recognition and transfer of precursor proteins at the cytosolic face of the organelle. Both proteins engage multiple interactions within the translocon during the translocation process, including dimeric states of their G-domains. The units of the Toc34 homodimer are involved in the recognition of the transit peptide representing the translocation signal of precursor proteins. This substrate recognition is part of the regulation of the GTPase cycle of Toc34. The Toc159 monomer and the Toc34 homodimer recognize the transit peptide of the small subunit of Rubisco at the N- and at the C-terminal region, respectively. Analysis of the transit peptide interaction by crosslinking shows that the heterodimer between both G-domains binds pSSU most efficiently. While substrate recognition by Toc34 homodimer was shown to regulate nucleotide exchange, we provide evidence that the high activation energy of the GTPase Toc159 is lowered by substrate recognition. The nucleotide affinity of Toc34G homodimer and Toc159G monomer are distinct, Toc34G homodimer recognizes GDP and Toc159G GTP with highest affinity. Moreover, the analysis of the nucleotide association rates of the monomeric and dimeric receptor units suggests that the heterodimer has an arrangement distinct from the homodimer of Toc34. Based on the biochemical parameters determined we propose a model for the order of events at the cytosolic side of TOC. The molecular processes described by this hypothesis range from transit peptide recognition to perception of the substrate by the translocation channel.
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Affiliation(s)
- Katharina Wiesemann
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9, D-60438 Frankfurt, Germany
| | - Stefan Simm
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9, D-60438 Frankfurt, Germany; Frankfurt Institute for Advanced Studies, Ruth-Moufang-Straße 1, D-60438 Frankfurt, Germany
| | - Oliver Mirus
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9, D-60438 Frankfurt, Germany
| | - Roman Ladig
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9, D-60438 Frankfurt, Germany; Cluster of Excellence Frankfurt, Goethe University, D-60438 Frankfurt, Germany
| | - Enrico Schleiff
- Department of Molecular Cell Biology of Plants, Goethe University, Max-von-Laue Str. 9, D-60438 Frankfurt, Germany; Frankfurt Institute for Advanced Studies, Ruth-Moufang-Straße 1, D-60438 Frankfurt, Germany; Cluster of Excellence Frankfurt, Goethe University, D-60438 Frankfurt, Germany; Buchmann Institute for Molecular Life Sciences, Goethe University, Max-von-Laue Str. 15, D-60438 Frankfurt, Germany.
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Lumme C, Altan-Martin H, Dastvan R, Sommer MS, Oreb M, Schuetz D, Hellenkamp B, Mirus O, Kretschmer J, Lyubenova S, Kügel W, Medelnik JP, Dehmer M, Michaelis J, Prisner TF, Hugel T, Schleiff E. Nucleotides and substrates trigger the dynamics of the Toc34 GTPase homodimer involved in chloroplast preprotein translocation. Structure 2014; 22:526-38. [PMID: 24631462 DOI: 10.1016/j.str.2014.02.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Revised: 01/29/2014] [Accepted: 02/01/2014] [Indexed: 12/13/2022]
Abstract
GTPases are molecular switches that control numerous crucial cellular processes. Unlike bona fide GTPases, which are regulated by intramolecular structural transitions, the less well studied GAD-GTPases are activated by nucleotide-dependent dimerization. A member of this family is the translocase of the outer envelope membrane of chloroplast Toc34 involved in regulation of preprotein import. The GTPase cycle of Toc34 is considered a major circuit of translocation regulation. Contrary to expectations, previous studies yielded only marginal structural changes of dimeric Toc34 in response to different nucleotide loads. Referencing PELDOR and FRET single-molecule and bulk experiments, we describe a nucleotide-dependent transition of the dimer flexibility from a tight GDP- to a flexible GTP-loaded state. Substrate binding induces an opening of the GDP-loaded dimer. Thus, the structural dynamics of bona fide GTPases induced by GTP hydrolysis is replaced by substrate-dependent dimer flexibility, which likely represents a general regulatory mode for dimerizing GTPases.
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Affiliation(s)
- Christina Lumme
- Physics Department E22 and IMETUM, Technical University Munich, 85748 Garching, Germany
| | - Hasret Altan-Martin
- Institute of Molecular Cell Biology of Plants, Goethe University, 60438 Frankfurt, Germany
| | - Reza Dastvan
- Institute of Physical and Theoretical Chemistry, Goethe University, 60438 Frankfurt, Germany; Cluster of Excellence "Macromolecular Complexes", Goethe University, 60438 Frankfurt, Germany; Center for Biomolecular Magnetic Resonance, Goethe University, 60438 Frankfurt, Germany; Department of Molecular Physiology & Biophysics, Vanderbilt University, 741 Light Hall, 2215 Garland Avenue, Nashville, TN 37232, USA
| | - Maik S Sommer
- Institute of Molecular Cell Biology of Plants, Goethe University, 60438 Frankfurt, Germany
| | - Mislav Oreb
- Physics Department E22 and IMETUM, Technical University Munich, 85748 Garching, Germany
| | - Denise Schuetz
- Institute of Physical and Theoretical Chemistry, Goethe University, 60438 Frankfurt, Germany; Cluster of Excellence "Macromolecular Complexes", Goethe University, 60438 Frankfurt, Germany; Center for Biomolecular Magnetic Resonance, Goethe University, 60438 Frankfurt, Germany
| | - Björn Hellenkamp
- Physics Department E22 and IMETUM, Technical University Munich, 85748 Garching, Germany
| | - Oliver Mirus
- Institute of Molecular Cell Biology of Plants, Goethe University, 60438 Frankfurt, Germany
| | - Jens Kretschmer
- Institute of Molecular Cell Biology of Plants, Goethe University, 60438 Frankfurt, Germany
| | - Sevdalina Lyubenova
- Institute of Physical and Theoretical Chemistry, Goethe University, 60438 Frankfurt, Germany; Cluster of Excellence "Macromolecular Complexes", Goethe University, 60438 Frankfurt, Germany; Center for Biomolecular Magnetic Resonance, Goethe University, 60438 Frankfurt, Germany
| | | | - Jan P Medelnik
- Institute of Molecular Cell Biology of Plants, Goethe University, 60438 Frankfurt, Germany
| | - Manuela Dehmer
- Institute of Molecular Cell Biology of Plants, Goethe University, 60438 Frankfurt, Germany
| | | | - Thomas F Prisner
- Institute of Physical and Theoretical Chemistry, Goethe University, 60438 Frankfurt, Germany; Cluster of Excellence "Macromolecular Complexes", Goethe University, 60438 Frankfurt, Germany; Center for Biomolecular Magnetic Resonance, Goethe University, 60438 Frankfurt, Germany
| | - Thorsten Hugel
- Physics Department E22 and IMETUM, Technical University Munich, 85748 Garching, Germany
| | - Enrico Schleiff
- Institute of Molecular Cell Biology of Plants, Goethe University, 60438 Frankfurt, Germany; Cluster of Excellence "Macromolecular Complexes", Goethe University, 60438 Frankfurt, Germany; Center for Membrane Proteomics, Goethe University, 60438 Frankfurt, Germany.
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Shi LX, Theg SM. The chloroplast protein import system: from algae to trees. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1833:314-31. [PMID: 23063942 DOI: 10.1016/j.bbamcr.2012.10.002] [Citation(s) in RCA: 138] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 09/07/2012] [Accepted: 10/01/2012] [Indexed: 01/15/2023]
Abstract
Chloroplasts are essential organelles in the cells of plants and algae. The functions of these specialized plastids are largely dependent on the ~3000 proteins residing in the organelle. Although chloroplasts are capable of a limited amount of semiautonomous protein synthesis - their genomes encode ~100 proteins - they must import more than 95% of their proteins after synthesis in the cytosol. Imported proteins generally possess an N-terminal extension termed a transit peptide. The importing translocons are made up of two complexes in the outer and inner envelope membranes, the so-called Toc and Tic machineries, respectively. The Toc complex contains two precursor receptors, Toc159 and Toc34, a protein channel, Toc75, and a peripheral component, Toc64/OEP64. The Tic complex consists of as many as eight components, namely Tic22, Tic110, Tic40, Tic20, Tic21 Tic62, Tic55 and Tic32. This general Toc/Tic import pathway, worked out largely in pea chloroplasts, appears to operate in chloroplasts in all green plants, albeit with significant modifications. Sub-complexes of the Toc and Tic machineries are proposed to exist to satisfy different substrate-, tissue-, cell- and developmental requirements. In this review, we summarize our understanding of the functions of Toc and Tic components, comparing these components of the import machinery in green algae through trees. We emphasize recent findings that point to growing complexities of chloroplast protein import process, and use the evolutionary relationships between proteins of different species in an attempt to define the essential core translocon components and those more likely to be responsible for regulation. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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Affiliation(s)
- Lan-Xin Shi
- Department of Plant Biology, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
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Abstract
Abstract
Protein transport, especially into different cellular compartments, is a highly coordinated and regulated process. The molecular machineries which carry out these transport processes are highly complex in structure, function, and regulation. In the case of chloroplasts, thousands of protein molecules have been estimated to be transported across the double-membrane bound envelope per minute. In this brief review, we summarize current knowledge about the molecular interplay during precursor protein import into chloroplasts, focusing on the initial events at the outer envelope.
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