PARENT SESSION

Symposium S8B Supermolecular organization of the photosynthetic apparatus
Friday September 3rd, 2004 8:30 AM-10:30 AM Room 210A
Chair: Jan Dekker
Co-Chair: André Verméglio

Supramolecular protein organization in grana thylakoids: Evidence for a structured arrangement. Helmut Kirchhoff^*,1, Silvia Haferkamp¹, Ira Tremmel¹, Winfried Haase², Ulrich Kubitscheck³, ¹ Institut für Botanik, Münster, Germany^{2 3}

ABSTRACT- The distribution of photosystem (PS) II complexes in grana thylakoids derived from electron microscopic images of freeze-fractured chloroplasts are examined using mathematical methods (nearest neighbor distribution function and pair correlation function). The data were compared with purely random distributions of recently published protein supercomplexes calculated by a Monte Carlo Simulation. The analysis reveals a non-random protein distribution in grana thylakoids. Ordering forces lead to a structured arrangement on a supramolecular level. Neighboring PSII are significantly more separated than would be the case in a purely random distribution. These results are explained by structural models, in which boundary lipids and light harvesting complex (LHC)II trimers are arranged in-between neighboring PSII. Furthermore the significance of the protein density for the supramoleculare organsiation is examined by fusion of isolated grana thylakoids with liposomes. The fusion products are analyzed by Ficoll gradient ultracentrifugation, room temperature and 77 K fluorescence spectroscopy and freeze-fracture electron microscopy. The data indicate that dilution of the protein density in grana thylakoids leads to a disconnection of LHCII from PSII supercomplexes. This emphasizes the importance of the protein density for the supramolecular protein organization and the energy transduction in grana membranes.

KEY WORDS: grana thylakoids, Photosystem II, protein organization