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Update in nucleotide-dependent processes in plant chloroplasts
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
2008 (English)In: Current Knowledge in Plant Cell Compartments / [ed] Spetea, C.Thuswaldner, S., Kerala: Research Signpost Publisher , 2008, 105-149 p.Chapter in book (Other academic)
Abstract [en]

Chloroplasts are photosynthetically active plastids found in all green plant cells. They have two types of membranes, the double envelope membrane surrounding the organelle and the thylakoid membrane containing the photosynthetic machinery. The envelope membrane represents the interface between the cytosol and chloroplast stroma, whereas the thylakoid membrane is the interface between the stroma and the lumenal space. This chapter attempts to give an update in nucleotide-dependent processes in plant chloroplasts. The current knowledge is that ATP is produced in the light-dependent photosynthetic reactions in the thylakoid membrane, and is used during CO2-fixation in the stroma as well as in the energy-dependent processes occurring on the thylakoid and envelope membranes. There is also increasing evidence that the thylakoid lumen is a chloroplast compartment with an unexpectedly active nucleotide metabolism, expanding its function beyond a bioenergetic perspective. Here we will discuss three distinct classes of chloroplast nucleotide-binding proteins: (i) transporters involved in ATP synthesis, translocation and utilization; (ii) nucleoside diphosphate kinases, involved in conversion of ATP to other nucleotides; and (iii) GTP-binding proteins, using the energy of GTP hydrolysis to drive various processes during chloroplast biogenesis, function and turnover. The main aspects reviewed for each chloroplast protein will be prediction, proteomic and/or individual identification, in vitro biochemical characterization and in planta functional analysis.

Place, publisher, year, edition, pages
Kerala: Research Signpost Publisher , 2008. 105-149 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-14184ISBN: 978-81-308-0104-9OAI: diva2:22836
Available from: 2007-01-15 Created: 2007-01-15 Last updated: 2013-08-26Bibliographically approved
In thesis
1. Nucleotide-binding Proteins in the Plant Thylakoid Membrane
Open this publication in new window or tab >>Nucleotide-binding Proteins in the Plant Thylakoid Membrane
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Life on Earth is dependent on the oxygen produced through photosynthesis. The thylakoid membrane is the site for the light-driven reactions of photosynthesis, which oxidize water and supply energy in the form of ATP, mainly for carbon fixation. The utilization of ATP in the lumenal space of the thylakoid has not been considered in the past. In the latest years, increasing evidence for nucleotide metabolism in the thylakoid lumen of plant chloroplasts has been presented; ATP transport across the thylakoid membrane, and GTP binding to the PsbO extrinsic subunit of the water-oxidizing photosystem II (PSII) complex.

In this thesis, various methods for prediction, identification, and characterization of novel plant proteins, are described. Nucleotide-binding motifs and nucleotide-dependent processes are reviewed, and the experimental data is discussed. 1) A thylakoid ATP/ADP carrier (TAAC) in Arabidopsis thaliana was identified and functionally characterized, and 2) the spinach PsbO protein was characterized as a GTPase. The Arabidopsis At5g01500 gene product is predicted as a chloroplast protein and to be homologous to the well-studied mitochondrial ADP/ATP carrier. The putative chloroplast localization was confirmed by transient expression of a TAAC-green fluorescent protein fusion construct. Immuno detection with peptide-targeted antibodies and immunogold electron microscopy showed the thylakoid as the main localization of TAAC, with a minor fraction in the chloroplast envelope. TAAC is readily expressed in etiolated seedlings, and its level remains stable throughout the greening process. Its expression is highest in developing green tissues and in leaves undergoing senescence or abiotic stress. It is proposed that the TAAC protein supplies ATP for energy-dependent reactions during thylakoid biogenesis and turnover. Recombinant TAAC protein was functionally integrated in the cytoplasmic membrane of Escherichia coli, and was shown to specifically transport ATP/ADP in a protonophore-sensitive manner, as also reported for mitochondrial AACs.

The PsbO protein stabilizes the oxygen-evolving complex of PSII and is ubiquitous in all oxygenic photosynthetic organisms, including cyanobacteria, green algae, and plants. So far only the 3D-structure of the cyanobacterial PsbO is available. Four GTP-binding motifs in the primary structure of spinach PsbO were predicted from comparison with classic GTP-binding proteins. These motifs were only found in the plant PsbOs, in the -barrel domain of the homologous 3D-structure. Using circular dichroism and intrinsic fluorescence spectroscopy, it was shown that MgGTP induces specific structural changes in the PsbO protein. Spinach PsbO has a low intrinsic GTPase activity, which is considerably stimulated when associated with a dimeric PSII complex. GTP stimulates the dissociation of PsbO from PSII under both inhibitory and non-inhibitory light conditions. A role for PsbO as a GTPase in the function of the oxygen-evolving complex and PSII repair is proposed.

35 p.
Linköping Studies in Health Sciences. Thesis, ISSN 1100-6013 ; 79
plant, Arabidopsis, photosynthesis, thylakoid membrane, nucleotide-binding
National Category
Biochemistry and Molecular Biology
urn:nbn:se:liu:diva-7934 (URN)91-85643-03-3 (ISBN)
2007-01-26, Linden, Health University, entry 65, Linköpings University, Linköping, 13:00 (English)
Available from: 2007-01-15 Created: 2007-01-15 Last updated: 2009-03-10

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