Inger Carlberg

Research Project: 
Signalling and regulation of photosynthetic membranes

Research groups & Co-workers
Department of Biochemistry, Stockholm University
Inger Carlberg (phone (+46)-8-16 2489, email: ingerc@dbb.su.se), Yang Dan-Hui, Martin Vink.

Division of Cell Biology, Linköping University
Torill Hundal (phone (+46)-13-22 5346; email: torhu@ibk.liu.se), Said Eshaghi, Cornelia Spetea.

Project description
Three and half billion years ago, living organisms developed the machinery to capture and efficiently use the most plentiful of all energy sources - sunlight. Today, photosynthesis occurs on a vast scale, so much so that just in a few hours the amount of organic material produced globally is equal to the total weight of the human population of the world.

In energy terms, global photosynthesis captures more than 10 times the total energy requirements of mankind (food and fuels) and was of course the origin of the fossil fuels. In this project, we study photosynthetic energy conversion on the molecular level using a combination of biochemical, biophysical and molecular genetical techniques. The ultimate goal is to obtain basic structural and functional information about the photosynthetic machinery to pave the way for creation of devices for artifical photosynthesis and for the development of more efficient and stress-tolerant plants.

Light can be both good and bad for photosynthesis. Even though light is the ultimate substrate for photosynthesis, light of too high intensity can be harmful to the plant. This photoinactivation is targetted to photosystem II - the pigment protein system that catalyzes the important water-splitting reaction. Photoinactivation does not only lead to impairment of electron transport but also to photodamage and degradation of the important D1-protein of the photosystem II reaction centre. Photosynthesis is repaired by synthesis of new copies of the D1-protein and assembly of new functional photosystem II complexes. We are trying to identify the proteases involved in this process. A recent discovery that GTP regulates this process is of particular importance, providing new insights into the D1 turnover process, as well as suggesting a hitherto over-looked possible role of GTP and G-proteins in thylakoid signalling and regulation.

Several of the proteins of photosystem II and its light-harvesting chlorophyll binding proteins are phosphorylated. We are investigating how this protein phosphorylation adjusts the "intake" of light-energy into photosystem II and thereby regulates the energy balance between the two photosystems. The role of thioredoxin in this regulation is investigated. We also try to understand the role of protein phosphorylation in regulating degradation of the D1-protein during light-stress conditions and during photoinhibition. Of particular importance is to elucidate the significance of the occurrence of immunophilin- like proteins in thylakoids and how they can regulate protein dephosphorylation.

Collaborations
The group has several international collaborations and many visiting scientists are involved in the research. In particular the group has established links with Imperial College, London, U.K., University of Turku, Finland, the Hebrew University, Jerusalem, Israel, Washington University, St. Louis, USA and University of Münich, FRG.

References

Acknowledgments
These projects are supported by the Swedish Natural Science Research Council, and the Swedish Council for Forestry and Agricultural Research.