PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

Systematic characterization of in vivo protein phosphorylation in photosynthetic thylakoid membranes by mass spectrometry. Alexander Vener^*,1, Maria Hansson¹, Maria Turkina¹, Arsenio Villarejo², Inger Carlberg³, ¹ Division of Cell Biology, Linköping University, Linköping, Sweden² Department of Plant Physiology, University of Umeå, Umeå, Sweden³ Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden

ABSTRACT- Complete genome sequencing for Arabidopsis thaliana, rice and C. reinhardtii allowed for a full-power application of modern mass spectrometry to study functional proteomics of photosynthesis. It became feasible to analyze post-translational modifications for numerous proteins from plants and algae in distinct physiological conditions. We adopted and developed dedicated mass spectrometric techniques for characterization of en masse protein phosphorylation in photosynthetic membranes. We identified 18 in vivo phosphorylation sites in proteins from photosynthetic membranes of plants and green alga and discovered 4 previously unknown phosphoproteins. Earlier unknown phosphorylation sites were found in N-termini of membrane proteins TMP14, PsbH and CP29 from Arabidopsis thaliana and green alga C. reinhardtii. In addition to the light-induced phosphorylation of integral membrane proteins in plant thylakoids we found phosphorylation of two peripheral proteins: PsaD, the first phosphoprotein identified in photosystem I; and TSP9, Thylakoid Soluble Phosphoprotein of 9 kDa. TSP9 is a plant-specific protein that becomes multiply phosphorylated in thylakoids exposed to light and then releases from the membranes. It is implied in possible signaling regulating expression of photosynthetic proteins following light perception by thylakoid membrane. Phosphorylation of two previously uncharacterized peripheral thylakoid proteins was found induced during acclimation of green alga C. reinhardtii to low CO₂. Multiple phosphorylation sites have been mapped in one of these proteins. This protein is also encoded by low CO₂-inducible gene. The studies of in vivo protein phosphorylation in plants and algae in different environmental conditions reveal the regulatory and signaling network for adjustment and acclimation of photosynthetic machinery to stress and changes in the surroundings.

KEY WORDS: redox control, thylakoid membrane, protein phosphorylation, light regulation