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PeptidylProlyl Isomerase Activity in Chloroplast Thylakoid Lumen is a Dispensable Function of Immunophilins in Arabidopsis thaliana
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.
Umeå University.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
2009 (English)In: Plant and Cell Physiology, ISSN 0032-0781, E-ISSN 1471-9053, Vol. 50, no 10, 1801-1814 p.Article in journal (Refereed) Published
Abstract [en]

Chloroplast thylakoid lumen of Arabidopsis thaliana contains 16 immunophilins, five cyclophilins and 11 FK506-binding proteins (FKBPs), which are considered protein folding catalysts, although only two of them, AtFKBP13 and AtCYP20-2, possess peptidylprolyl cis/trans isomerase (PPIase) activity. To address the question of the physiological significance of this activity, we obtained and characterized Arabidopsis mutants deficient in the most active PPIase, AtFKBP13, and a double mutant deficient in both AtFKBP13 and AtCYP20-2. Two-dimensional gel electrophoresis of isolated thylakoid lumen, as well as immunoblotting analyses of major photosynthetic membrane protein complexes did not reveal differences in protein composition between the mutants and the wild type. No changes in the relative content of photosynthetic proteins were found by differential stable isotope labeling and liquid chromatographymass spectrometry (LC-MS) analyses. PPIase activity was measured in vitro in isolated thylakoid lumen samples using two different synthetic peptide substrates. Depending on the peptide substrate used for the assay, the PPIase activity in the thylakoid lumen of the mutants lacking either AtFKBP13 or both AtFKBP13 and AtCYP20-2 was as low as 10 or 2 of that in the wild type. Residual PPIase activity detected in the double mutant originated from AtCYP20-3, a cyclophilin from chloroplast stroma contaminating thylakoid lumen preparations. None of the mutants differed from the wild-type plants when grown under normal, cold stress or high light conditions. It is concluded that cellular functions of immunophilins in the thylakoid lumen of chloroplasts are not related to their PPIase capacity and should be investigated beyond this enzymatic activity.

Place, publisher, year, edition, pages
2009. Vol. 50, no 10, 1801-1814 p.
Keyword [en]
Arabidopsis thaliana, Chloroplast thylakoid lumen, Cyclophilin, FKBP, Immunophilin, Peptidyl-prolyl isomerase activity
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-51383DOI: 10.1093/pcp/pcp122OAI: oai:DiVA.org:liu-51383DiVA: diva2:274588
Available from: 2009-10-30 Created: 2009-10-30 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Reversible modifications of chloroplast proteins and assessment of their functions
Open this publication in new window or tab >>Reversible modifications of chloroplast proteins and assessment of their functions
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oxygenic photosynthesis is the process of solar energy conversion into chemical energy in the form of carbohydrates. This event is carried out by plants, algae and cyanobacteria and represents the starting point of the food chain in which most organisms are fed. Due to never-ending changes in the surrounding environment, these photoautotrophic organisms have evolved different acclimatizing strategies to optimize photosynthesis. Many of these fine-tuning mechanisms are dependent on reversible modifications of proteins on a post-translational level. In my research I have been focused on such reversible modifications of proteins in the organelle where photosynthesis takes place – the chloroplast – using the model plant Arabidopsis thaliana.

Within chloroplasts, light-driven reactions of photosynthesis are catalyzed by several multi-subunit protein complexes in the thylakoid membrane. Proteins need to be folded properly in order to function correctly. A rate-limiting step of protein folding is the isomerization of the peptide bond around proline, a step that is catalyzed by enzymes possessing peptidyl-prolyl cis-trans isomerase (PPIase) activity. Within the thylakoid lumen, only two proteins have been found to possess PPIase activity, FKBP13 and CYP20-2. Both these enzymes belong to a protein superfamily called immunophilins - ubiquitous proteins attributed with several different functions. By characterization of Arabidopsis mutants lacking FKBP13 and CYP20-2 I found that PPIase activity is a dispensable function of immunophilins in the thylakoid lumen.

A common post-translational modification of chloroplast proteins is phosphorylation. Protein phosphorylation alters protein functions and is a reversible mechanism utilized by plants for rapid acclimation to changes in the incident light. These events require the action of kinases and phosphatases that either add or remove phosphate groups on proteins, respectively. I have characterized mutants deficient in protein phosphatases responsible for dephosphorylation of thylakoid proteins. These phosphatases, PPH1 and PBCP, represent key players in acclimation of the photosynthetic machinery to changes in light quality/quantity. In addition, I discovered that phosphorylation of pTAC16, a protein associated with the chloroplast gene-expression machinery, depends on the presence of STN7; a light-regulated protein kinase located in the thylakoid membrane. This finding could provide a link between the redox state of the photosynthetic apparatus and chloroplast gene expression.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 67 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1296
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-76727 (URN)978-­‐91-­‐7519-­‐952-­‐8 (ISBN)
Public defence
2012-05-16, Eken, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2012-08-21Bibliographically approved

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Ingelsson, BjörnShapiguzov, AlexeyVener, Alexander

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