Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Reversible modifications of chloroplast proteins and assessment of their functions
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
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: urn:nbn:se:liu:diva-76727ISBN: 9789175199528 (print)OAI: oai:DiVA.org:liu-76727DiVA: diva2:516435
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: 2017-12-18Bibliographically approved
List of papers
1. PeptidylProlyl Isomerase Activity in Chloroplast Thylakoid Lumen is a Dispensable Function of Immunophilins in Arabidopsis thaliana
Open this publication in new window or tab >>PeptidylProlyl Isomerase Activity in Chloroplast Thylakoid Lumen is a Dispensable Function of Immunophilins in Arabidopsis thaliana
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.

Keyword
Arabidopsis thaliana, Chloroplast thylakoid lumen, Cyclophilin, FKBP, Immunophilin, Peptidyl-prolyl isomerase activity
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-51383 (URN)10.1093/pcp/pcp122 (DOI)
Available from: 2009-10-30 Created: 2009-10-30 Last updated: 2017-12-12Bibliographically approved
2. The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis
Open this publication in new window or tab >>The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis
Show others...
2010 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 10, 4782-4787 p.Article in journal (Refereed) Published
Abstract [en]

The ability of plants to adapt to changing light conditions depends on a protein kinase network in the chloroplast that leads to the reversible phosphorylation of key proteins in the photosynthetic membrane. Phosphorylation regulates, in a process called state transition, a profound reorganization of the electron transfer chain and remodeling of the thylakoid membranes. Phosphorylation governs the association of the mobile part of the light-harvesting antenna LHCII with either photosystem I or photosystem II. Recent work has identified the redox-regulated protein kinase STN7 as a major actor in state transitions, but the nature of the corresponding phosphatases remained unknown. Here we identify a phosphatase of Arabidopsis thaliana, called PPH1, which is specifically required for the dephosphorylation of light-harvesting complex II (LHCII). We show that this single phosphatase is largely responsible for the dephosphorylation of Lhcb1 and Lhcb2 but not of the photosystem II core proteins. PPH1, which belongs to the family of monomeric PP2C type phosphatases, is a chloroplast protein and is mainly associated with the stroma lamellae of the thylakoid membranes. We demonstrate that loss of PPH1 leads to an increase in the antenna size of photosystem I and to a strong impairment of state transitions. Thus phosphorylation and dephosphorylation of LHCII appear tobe specifically mediated by the kinase/phosphatase pair STN7 and PPH1. These two proteins emerge as key players in the adaptation of the photosynthetic apparatus to changes in light quality and quantity.

Keyword
Photosynthesis, PP2C phosphatases, thylakoid, plastid
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-54602 (URN)10.1073/pnas.0913810107 (DOI)000275368400053 ()
Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2017-12-12Bibliographically approved
3. Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis
Open this publication in new window or tab >>Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis
Show others...
2012 (English)In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 24, no 6, 2596-2609 p.Article in journal (Refereed) Published
Abstract [en]

Reversible protein phosphorylation plays a major role in the rapid acclimation of the photosynthetic apparatus to changes in light. Two paralogous kinases phosphorylate subsets of thylakoid membrane proteins. STN7 phosphorylates LHCII, the light harvesting antenna of photosystem II (PSII), to balance the activity of the two photosystems through state transitions. STN8 which is mainly involved in phosphorylation of PSII influences folding of the thylakoid membranes and repair of PSII after photo-damage. The rapid reversibility of these acclimatory responses requires the action of protein phosphatases.

In a reverse genetic screen we have identified the chloroplast PP2C phosphatase, PBCP (PHOTOSYSTEM II CORE PHOSPHATASE), which is required for efficient dephosphorylation of PSII. Its targets identified by immunoblotting and mass spectrometry largely coincide with those of the kinase STN8. The recombinant phosphatase is active in vitro on a synthetic substrate or on isolated thylakoids. Thylakoid folding and degradation of D1 after photo-damage are affected in the absence of PBCP, while its over-expression alters the kinetics of state transitions. PBCP and STN8 form an antagonistic kinase and phosphatase pair whose substrate specificity and physiological function are distinct from those of STN7 and the counteracting phosphatase PPH1 (TAP38), but their activities may overlap to some degree.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76725 (URN)10.3410/f.717847818.793153384 (DOI)000306919300027 ()
Note

On the day of the defence date the title of the article was The role of PHOTOSYSTEM II CORE PHOSPHATASE in light acclimation of photosynthesis in Arabidopsis.

Funding agencies|SystemsX.ch (RTD Plant Growth in a Changing Environment)||Swiss National Foundation|3100AO-11771231003A_133089/1|FP7 Marie-Curie Initial Training Network (ITN) COSI|ITN 2008 GA 215-174|EMBO postdoctoral fellowship||Swedish Research Council|2008-5490|

Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2017-12-07Bibliographically approved
4. Phosphoproteomics of Arabidopsis chloroplasts reveals involvement of the STN7 kinase in phosphorylation of nucleoid protein pTAC16
Open this publication in new window or tab >>Phosphoproteomics of Arabidopsis chloroplasts reveals involvement of the STN7 kinase in phosphorylation of nucleoid protein pTAC16
2012 (English)In: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 586, no 9, 1265-1271 p.Article in journal (Refereed) Published
Abstract [en]

Light-regulated protein kinases STN7 and STN8 phosphorylate thylakoid membrane proteins and also affect expression of several chloroplast proteins via yet unknown mechanisms. Comparative phosphoproteomics of acetic acid protein extracts of chloroplasts from Arabidopsis thaliana wild type, stn7, stn8 and stn7stn8 mutants yielded two previously unknown findings: (i) neither STN7 nor STN8 kinase was required for phosphorylation of Ser-48 in Lhcb1.1–1.3 proteins; and (ii) phosphorylation of Thr-451 in pTAC16 protein was STN7-dependent. pTAC16 was found distributed between thylakoids and nucleoid. Its knockout did not affect the nucleoid protein composition and the Thr-451 phosphorylated protein was excluded from the nucleoid. Thr-451 of pTAC16 is conserved in all studied plants and its phosphorylation may regulate membrane-anchoring functions of the nucleoid.

Place, publisher, year, edition, pages
Elsevier, 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76726 (URN)10.1016/j.febslet.2012.03.061 (DOI)000303434200003 ()
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2017-12-07Bibliographically approved

Open Access in DiVA

Reversible modifications of chloroplast proteins and assessment of their functions(671 kB)604 downloads
File information
File name FULLTEXT01.pdfFile size 671 kBChecksum SHA-512
8a345da725c5ab012cd95b227593e17fe9b1f71e224e7963403929aa66ce88e8ba2c7df51b56a3681b90dfcacdafde9ea40bfe7eadee0cb57efe0d2b2f3978ea
Type fulltextMimetype application/pdf
omslag(334 kB)31 downloads
File information
File name COVER01.pdfFile size 334 kBChecksum SHA-512
f2ab84f1dcd7a0cbed6014e89ef3ca4d968624fcee60b20488abaeb146794124a947337458870f45c497e5902f6e47d322d3aca55deed296081844b5ef5f7723
Type coverMimetype application/pdf

Search in DiVA

By author/editor
Ingelsson, Björn
By organisation
Cell BiologyFaculty of Health Sciences
Medical and Health Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 604 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 723 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf