J. Benešová1, S.T. Liffers2, C. König2, E. J. Boekema3, M. Rögner2
1Institut of Physical Biology, University of South Bohemia, CZ - 373 33 Nové Hrady, Czech Republic
2Faculty for Biolgy, Department of Plant Biochemistry, Ruhr-University Bochum, D - 44801 Bochum, Germany
3Biophysical Chemistry, University of Groningen, NL - 9747 AG Groningen, The Netherlands
Most recent structural data on photosystem 2 (PS2), the first membrane protein complex in the photosynthetic electron transport chain, confirm that this complex exists as a functional dimer in the thylakoid membrane of cyanobacteria [1, 2]. Besides the membrane embedded part of this dimer with dimensions of 190 Å x 100 Å x 40 Å, this complex also extends about 10 Å out of the membrane in the stromal region and 55 Å in the lumen; the latter is referred to as the oxygen evolving complex, harbouring the water-splitting site. Developing an approriate method to reconstitute dimeric PS2 into liposomes should finally help to answer the fundamental question concerning its structure-based function: Is a dimeric structure a prerequisite for optimal watersplitting activity (monomeric complexes, solubilized by detergent, are active, too, although at a lower level) and which is the impact of the lipid-phase-composition on the water-splitting activity? Here we present data on the orientation of reconstituted dimeric PS2 from the cyanobacterium Thermosynechococcus elongatus and also give indications for its activity within the liposomes and monomer-dimer distribution (by EM analysis).