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Phosphorylation in the thylakoid membrane - role of substrate activation
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phosphorylation of specific side chains in target proteins by protein kinases is a major means of regulation of cellular processes. In the thylakoid membrane of higher plants, the redox-controlled phosphorylation of photosystem II (PSII) and light-harvesting complex II (LHCII) proteins regulates energy distribution between the two photosystems and PSII protein dynamics. The thylakoid proteins are phosphorylated by several distinct kinases that are subject to different control mechanisms. Regulation of LHCII kinase(s) activation is signalled by the redox-state of the plastoquinone pool and the cytochrome b6/f complex and modulated by the thiol redox-state of the chloroplast. Phosphorylation of PSII core-complex proteins may be achieved by PSII core associated kinase(s) that are regulated by the redox-state of the plastoquinone pool alone without involvement of the cytochrome b6/f complex. The identities of the protein kinases in the thylakoid membrane are still unknown. In this work a kinase enriched fraction obtained from a spinach thylakoid extract by perfusion chromatography is described. This fraction phosphorylates isolated LHCII and the CP43 protein of isolated PSII cores and exhibits a major protein kinase band of 64 kDa.

This work further demonstrates that, in addition to the well-studied redox-regulation of the protein kinases in the thylakoid membrane, phosphorylation can also be modulated at the substrate level. The exposure of the phosphorylation sites of both the LHCII and the CP43 protein to the respective protein kinases is regulated by light-induced conformational changes. This so-called substrate activation increases the phosphorylation level of both proteins. However, illumination for long times and/or in high light in situ, in the intact thylakoid, induces a dramatic decrease in the phosphorylation level of the LHCII under conditions preventing phosphorylation. The implications of these light-induced conformational changes at the substrate level are discussed in relation to energy distribution between the two photosystems and the dynamics of the thylakoid membrane as a whole. Furthermore, the effect of xantophyll pigments on the light-induced conformational changes and thylakoid protein phosphorylation is presented.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University , 2002. , 58 p.
Keyword [sv]
Fotosyntesen, Biokemi
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-142866Libris ID: 8393084ISBN: 91-7265-387-6 (print)OAI: oai:DiVA.org:su-142866DiVA: diva2:1094882
Public defence
2002-02-22, 14:00 (English)
Opponent
Note

Härtill 5 uppsatser

Available from: 2017-05-11 Created: 2017-05-11 Last updated: 2017-10-20Bibliographically approved

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