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  • 1.
    Ingelsson, Björn
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Reversible modifications of chloroplast proteins and assessment of their functions2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. PeptidylProlyl Isomerase Activity in Chloroplast Thylakoid Lumen is a Dispensable Function of Immunophilins in Arabidopsis thaliana
    Öppna denna publikation i ny flik eller fönster >>PeptidylProlyl Isomerase Activity in Chloroplast Thylakoid Lumen is a Dispensable Function of Immunophilins in Arabidopsis thaliana
    2009 (Engelska)Ingår i: Plant and Cell Physiology, ISSN 0032-0781, E-ISSN 1471-9053, Vol. 50, nr 10, s. 1801-1814Artikel i tidskrift (Refereegranskat) 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.

    Nyckelord
    Arabidopsis thaliana, Chloroplast thylakoid lumen, Cyclophilin, FKBP, Immunophilin, Peptidyl-prolyl isomerase activity
    Nationell ämneskategori
    Medicin och hälsovetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-51383 (URN)10.1093/pcp/pcp122 (DOI)
    Tillgänglig från: 2009-10-30 Skapad: 2009-10-30 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
    2. The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis
    Öppna denna publikation i ny flik eller fönster >>The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis
    Visa övriga...
    2010 (Engelska)Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, nr 10, s. 4782-4787Artikel i tidskrift (Refereegranskat) 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.

    Nyckelord
    Photosynthesis, PP2C phosphatases, thylakoid, plastid
    Nationell ämneskategori
    Medicin och hälsovetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-54602 (URN)10.1073/pnas.0913810107 (DOI)000275368400053 ()
    Tillgänglig från: 2010-03-26 Skapad: 2010-03-26 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
    3. Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis
    Öppna denna publikation i ny flik eller fönster >>Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis
    Visa övriga...
    2012 (Engelska)Ingår i: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 24, nr 6, s. 2596-2609Artikel i tidskrift (Refereegranskat) 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.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-76725 (URN)10.3410/f.717847818.793153384 (DOI)000306919300027 ()
    Anmärkning

    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|

    Tillgänglig från: 2012-04-18 Skapad: 2012-04-18 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
    4. Phosphoproteomics of Arabidopsis chloroplasts reveals involvement of the STN7 kinase in phosphorylation of nucleoid protein pTAC16
    Öppna denna publikation i ny flik eller fönster >>Phosphoproteomics of Arabidopsis chloroplasts reveals involvement of the STN7 kinase in phosphorylation of nucleoid protein pTAC16
    2012 (Engelska)Ingår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 586, nr 9, s. 1265-1271Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Elsevier, 2012
    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:liu:diva-76726 (URN)10.1016/j.febslet.2012.03.061 (DOI)000303434200003 ()
    Tillgänglig från: 2012-04-18 Skapad: 2012-04-18 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
  • 2.
    Ingelsson, Björn
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Fristedt, Rikard
    Biophysics of Photosynthesis Physics and Astronomy Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands.
    Turkina, Maria
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Phosphorylation stoichiometry determination in plant photosynthetic membranes.2015Ingår i: Plant Phosphoproteomics: Methods and Protocols / [ed] Waltraud X. Schulze, New York: Springer-Verlag New York, 2015, s. 121-134Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This chapter describes different strategies for the study of phosphorylation dynamics and stoichiometry in photosynthetic membranes. Detailed procedures for the detection, large-scale identification, and quantification of phosphorylated proteins optimized for plant thylakoid proteins are given.

  • 3.
    Ingelsson, Björn
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Shapiguzov, Alexey
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Kieselbach, Thomas
    Umeå University.
    Vener, Alexander
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    PeptidylProlyl Isomerase Activity in Chloroplast Thylakoid Lumen is a Dispensable Function of Immunophilins in Arabidopsis thaliana2009Ingår i: Plant and Cell Physiology, ISSN 0032-0781, E-ISSN 1471-9053, Vol. 50, nr 10, s. 1801-1814Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    Ingelsson, Björn
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Söderberg, Daniel
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för läkemedelsforskning. Linköpings universitet, Medicinska fakulteten.
    Strid, Tobias
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för mikrobiologi och molekylär medicin. Linköpings universitet, Medicinska fakulteten.
    Söderberg, Anita
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Bergh, Ann-Charlotte
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Loitto, Vesa-Matti
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för mikrobiologi och molekylär medicin. Linköpings universitet, Medicinska fakulteten.
    Lotfi, Kourosh
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för läkemedelsforskning. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Hematologiska kliniken US.
    Segelmark, Mårten
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för läkemedelsforskning. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Hjärt- och Medicincentrum, Njurmedicinska kliniken US.
    Spyrou, Giannis
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för mikrobiologi och molekylär medicin. Linköpings universitet, Medicinska fakulteten.
    Rosén, Anders
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för cellbiologi. Linköpings universitet, Medicinska fakulteten.
    Lymphocytes eject interferogenic mitochondrial DNA webs in response to CpG and non-CpG oligodeoxynucleotides of class C2018Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 115, nr 3, s. E478-E487Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Circulating mitochondrial DNA (mtDNA) is receiving increasing attention as a danger-associated molecular pattern in conditions such as autoimmunity, cancer, and trauma. We report here that human lymphocytes [B cells, T cells, natural killer (NK) cells], monocytes, and neutrophils derived from healthy blood donors, as well as B cells from chronic lymphocytic leukemia patients, rapidly eject mtDNA as web filament structures upon recognition of CpG and non-CpG oligodeoxynucleotides of class C. The release was quenched by ZnCl2, independent of cell death (apoptosis, necrosis, necroptosis, autophagy), and continued in the presence of TLR9 signaling inhibitors. B-cell mtDNA webs were distinct from neutrophil extracellular traps concerning structure, reactive oxygen species (ROS) dependence, and were devoid of antibacterial proteins. mtDNA webs acted as rapid (within minutes) messengers, priming antiviral type I IFN production. In summary, our findings point at a previously unrecognized role for lymphocytes in antimicrobial defense, utilizing mtDNA webs as signals in synergy with cytokines and natural antibodies, and cast light on the interplay between mitochondria and the immune system.

  • 5.
    Ingelsson, Björn
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Vener, Alexander
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Phosphoproteomics of Arabidopsis chloroplasts reveals involvement of the STN7 kinase in phosphorylation of nucleoid protein pTAC162012Ingår i: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 586, nr 9, s. 1265-1271Artikel i tidskrift (Refereegranskat)
    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.

  • 6.
    Samol, Iga
    et al.
    Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
    Shapiguzov, Alexey
    Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
    Ingelsson, Björn
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Fucile, Geoffrey
    Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
    Crèvecoeur, Michèle
    Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
    Vener, Alexander V.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Rochaix, Jean-David
    Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
    Goldschmidt-Clermont, Michel
    Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
    Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis2012Ingår i: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 24, nr 6, s. 2596-2609Artikel i tidskrift (Refereegranskat)
    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.

  • 7.
    Shapiguzov, Alexey
    et al.
    University of Geneva, Switzerland.
    Ingelsson, Björn
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Samol, Iga
    University of Geneva, Switzerland.
    Andres, Charles
    University of Neuchatel, Switzerland.
    Kessler, Felix
    University of Neuchatel, Switzerland.
    Rochaix, Jean-David
    University of Geneva, Switzerland.
    Vener, Alexander
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Goldschmidt-Clermont, Michel
    University of Geneva, Switzerland.
    The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis2010Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, nr 10, s. 4782-4787Artikel i tidskrift (Refereegranskat)
    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.

  • 8.
    Strid, Tobias
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Svartz, Jesper
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Franck, Niclas
    Linköpings universitet, Institutionen för medicin och hälsa, Internmedicin. Linköpings universitet, Hälsouniversitetet.
    Hallin, Elisabeth
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Ingelsson, Björn
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Söderström, Mats
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Hammarström, Sven
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Distinct parts of leukotriene C-4 synthase interact with 5-lipoxygenase and 5-lipoxygenase activating protein2009Ingår i: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 381, nr 4, s. 518-522Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Leukotriene C-4 is a potent inflammatory mediator formed from arachidonic acid and glutathione. 5-Lipoxygenase (5-LO), 5-lipoxygenase activating protein (FLAP) and leukotriene C-4 synthase (LTC4S) participate in its biosynthesis. We report evidence that LTC4S interacts in vitro with both FLAP and 5-LO and that these interactions involve distinct parts of LTC4S. FLAP bound to the N-terminal part/first hydrophobic region of LTC4S. This part did not bind 5-LO which bound to the second hydrophilic loop of LTC4S. Fluorescent FLAP- and LTC4S-fusion proteins co-localized at the nuclear envelope. Furthermore, GFP-FLAP and GFP-LTC4S co-localized with a fluorescent ER marker. In testing HEK293/T or COS-7 cells GFP-5-LO was found mainly in the nuclear matrix. Upon stimulation with calcium ionophore, GFP-5-LO translocated to the nuclear envelope allowing it to interact with FLAP and LTC4S. Direct interaction of 5-LO and LTC4S in ionophore-stimulated (but not un-stimulated) cells was demonstrated by BRET using GFP-5-LO and Rluc-LTC4S.

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