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Regulation of photosynthesis -Cytochrome b6f in redox regulation -Two novel proteases acting on an N-terminal peptide of LHCII

Ström, Jörgen LU (2005)
Abstract (Swedish)
Popular Abstract in Swedish

I växter sker fotosyntesen i kloroplasten. Vid fotosyntes omvandlas vatten och koldioxid, med hjälp av solljus, till energirika molekyler. Dessa molekyler används dels för att bygga upp andra viktiga molekyler i växten men också för att växten skall kunna utföra kontrollerade kemiska reaktioner. En viktig del i fotosyntesen är själva ljusinsamlandet. Ljusinsamlandet sker vid de två reaktionscentra, fotosystem I och fotosystem II. De olika fotosystemen absorberar ljus med olika egenskaper. Absorberat ljus skapar en linjär elektrontransport som börjar vid fotosystem II och slutar vid fotosystem I. För att få optimal fotosyntes behöver man kunna balansera det inkommande ljuset till de olika... (More)
Popular Abstract in Swedish

I växter sker fotosyntesen i kloroplasten. Vid fotosyntes omvandlas vatten och koldioxid, med hjälp av solljus, till energirika molekyler. Dessa molekyler används dels för att bygga upp andra viktiga molekyler i växten men också för att växten skall kunna utföra kontrollerade kemiska reaktioner. En viktig del i fotosyntesen är själva ljusinsamlandet. Ljusinsamlandet sker vid de två reaktionscentra, fotosystem I och fotosystem II. De olika fotosystemen absorberar ljus med olika egenskaper. Absorberat ljus skapar en linjär elektrontransport som börjar vid fotosystem II och slutar vid fotosystem I. För att få optimal fotosyntes behöver man kunna balansera det inkommande ljuset till de olika fotosystemen. Detta sker delvis genom att en del av antennen flyttas till det fotosystem som mottar minst ljusmängd. En signal för att antennen skall förflyttas kommer från mängden av elektroner som befinner sig emellan fotosystem I och fotosystem II. Finns det många elektroner mellan de olika fotosystemen flyttas antennen till fotosystem I. Finns det däremot få elektroner mellan systemen flyttas antennen till fotosystem II.



I mitt arbete har jag undersökt hur situationen med många elektroner mellan fotosystemen kan ge en signal till antennen att röra sig mot fotosystem I. Det har gjorts på två olika sätt, dels har vi studerat fosfatinbindning till cytokrom b6f-komplexet. Vi tror att detta kan vara en signal som föregår antennförflyttningen. Här har vi kunnat visa att vissa aminosyror är nu mindre troliga för fosforylering medan andra är mer intressanta. Dessutom har vi i en annan del av studien renat upp b6f-komplexet för att studera dess olika elektronbärares inbördes förmåga att plocka upp elektroner. Detta är viktigt för att förstå vad som leder till fosforyleringen av b6f-komplexet. I dessa mätningar kunde vi skilja de olika elektronbärarna åt. Med hjälp av denna kunskap kan vi i vidare experiment bestämma hur elektronbärarna inbördes reagerar på olika elektronmängder i kloroplasten och vad som ger signalen till antennförflyttning.



In en annan del av mitt arbete har jag studerat möjliga vägar för nedbrytningen av antennen. Alla proteiner som tillverkas, bryts också till sist ner igen. Denna nedbrytningsprocess utförs av proteaser, vilka finns i alla levande organismer. Vid höga ljusmängder kan den fotosyntetiska antennen göra mer skada än nytta i kloroplasten. Det är känt att mängden av antenner minskar vid höga ljusnivåer. Vi har funnit och karakteriserat två tidigare icke kända proteaser som har potential att bryta ner den flyttbara antennen. Ett av proteasen återfinns i den vattenlösliga delen av kloroplasten, stroman. Detta proteas har identifierats som ett kloroplast glutamyl endopeptidase cGEP. Det andra proteaset är membranassocierat och aktiveras när det finns rikligt med elektroner i kloroplasten. Vi har indirekt sett att dessa proteaser kan vara viktiga för nedbrytningen av den flyttbara antennen i kloroplasten. (Less)
Abstract
In higher plants photosynthesis takes place in the chloroplast. This work focuses on two different processes that effects photosynthesis. Firstly, we studied the events occurring prior to the phosphorylation of LHCII. Secondly, we also studied two novel proteases, with the potential to degrade LHCII.



In oxygenic photosynthesis two different photosystems partake in the gathering of light, PSI and PSII. They use slightly different wavelength for photochemistry. Since the photosystems are coupled in series, a light favouring one photosystem over the other leads to unbalanced electron transport. This unbalanced electron transport causes the interconnecting electron transport chain to be either reduced or oxidized. In this... (More)
In higher plants photosynthesis takes place in the chloroplast. This work focuses on two different processes that effects photosynthesis. Firstly, we studied the events occurring prior to the phosphorylation of LHCII. Secondly, we also studied two novel proteases, with the potential to degrade LHCII.



In oxygenic photosynthesis two different photosystems partake in the gathering of light, PSI and PSII. They use slightly different wavelength for photochemistry. Since the photosystems are coupled in series, a light favouring one photosystem over the other leads to unbalanced electron transport. This unbalanced electron transport causes the interconnecting electron transport chain to be either reduced or oxidized. In this work we have seen, using Blue-native gels and P32-labelled protein assays, that the b6f-complex becomes phosphorylated during reducing conditions. We also suggest different amino acids as candidates for this phosphorylation.



Cytochrome b6f complex is vital for regulatory events taking place in the chloroplast. In the b6f-complex there are four different hemes, three of them (cyt f, heme bH and bL) are known to be involved in conveying electrons from the plastoquinone pool to PSI, whereas the fourth heme (heme ci), function remains unknown. An important first step to understand electron flow through this complex is to be able to study the redox centra individually. Using purified b6f-complex together with magnetic circular dicroism (MCD), we monitored the reduction of the individual hemes. We also assigned spectral features to the newly discovered heme ci. With these results and further measurements will gives the tool to correlated phosphorylation of b6f-complex with redox state of the hemes in the complex.



Two novel chloroplast proteases are described. One protease was found in the stroma and the other protease is associated with the thylakoid membrane. Both proteases are capable of cleaving a peptide resembling the N-terminal part of LHCII. The stromal protease identified as a glutamyl endo peptidase was given the name cGEP. The thylakoid-associated protease seems to be under redox-control, activated by different reducing compounds, with a pH-optima around 7, and decreased activity around pH 8. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Doctor Pfannschmidt, Thomas, Jena University
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Plant biochemistry, Växtbiokemi, cGEP, proteolysis, protease, protein phosphorylation, redox regulation, light-harvesting antenna, cytochrome b6f, chloroplast, Photosynthesis
pages
91 pages
publisher
Department of Plant Biochemistry, Lund University
defense location
Lecture hall A Center for Chemistry and Chemical engineering Getingevägen 60 222 41 Lund Sweden
defense date
2005-06-07 13:15
ISBN
91-973969-8-2
language
English
LU publication?
yes
id
156a98da-990f-4fc9-811a-44a15d7ed3a9 (old id 545061)
date added to LUP
2007-10-13 13:13:55
date last changed
2016-09-19 08:45:06
@phdthesis{156a98da-990f-4fc9-811a-44a15d7ed3a9,
  abstract     = {In higher plants photosynthesis takes place in the chloroplast. This work focuses on two different processes that effects photosynthesis. Firstly, we studied the events occurring prior to the phosphorylation of LHCII. Secondly, we also studied two novel proteases, with the potential to degrade LHCII.<br/><br>
<br/><br>
In oxygenic photosynthesis two different photosystems partake in the gathering of light, PSI and PSII. They use slightly different wavelength for photochemistry. Since the photosystems are coupled in series, a light favouring one photosystem over the other leads to unbalanced electron transport. This unbalanced electron transport causes the interconnecting electron transport chain to be either reduced or oxidized. In this work we have seen, using Blue-native gels and P32-labelled protein assays, that the b6f-complex becomes phosphorylated during reducing conditions. We also suggest different amino acids as candidates for this phosphorylation.<br/><br>
<br/><br>
Cytochrome b6f complex is vital for regulatory events taking place in the chloroplast. In the b6f-complex there are four different hemes, three of them (cyt f, heme bH and bL) are known to be involved in conveying electrons from the plastoquinone pool to PSI, whereas the fourth heme (heme ci), function remains unknown. An important first step to understand electron flow through this complex is to be able to study the redox centra individually. Using purified b6f-complex together with magnetic circular dicroism (MCD), we monitored the reduction of the individual hemes. We also assigned spectral features to the newly discovered heme ci. With these results and further measurements will gives the tool to correlated phosphorylation of b6f-complex with redox state of the hemes in the complex.<br/><br>
<br/><br>
Two novel chloroplast proteases are described. One protease was found in the stroma and the other protease is associated with the thylakoid membrane. Both proteases are capable of cleaving a peptide resembling the N-terminal part of LHCII. The stromal protease identified as a glutamyl endo peptidase was given the name cGEP. The thylakoid-associated protease seems to be under redox-control, activated by different reducing compounds, with a pH-optima around 7, and decreased activity around pH 8.},
  author       = {Ström, Jörgen},
  isbn         = {91-973969-8-2},
  keyword      = {Plant biochemistry,Växtbiokemi,cGEP,proteolysis,protease,protein phosphorylation,redox regulation,light-harvesting antenna,cytochrome b6f,chloroplast,Photosynthesis},
  language     = {eng},
  pages        = {91},
  publisher    = {Department of Plant Biochemistry, Lund University},
  school       = {Lund University},
  title        = {Regulation of photosynthesis -Cytochrome b6f in redox regulation -Two novel proteases acting on an N-terminal peptide of LHCII},
  year         = {2005},
}