Supramolecular structures of thylakoid membrane protein complexes:supercomplex organization under different environmental conditions

In this dissertation electron microscopy has been used as a main technique for structural characterization of the photosynthetic protein complexes isolated from different organisms. The photosynthetic processes are conducted by membrane-embedded protein complexes in the thylakoid membrane, known as photosystem I and II (PSI and PSII). The structural organization and architecture of the photosystems varies depending on species and the photic environment. In the first study, knock-out mutants of the moss Physcomitrella patens reveal the role of subunit Lhcb9 in regulation of the antenna size under low light conditions. Similarly, in a following study of the isolated supercomplexes from Norway spruce we show the presence of large PSII supercomplexes and PSII megacomplexes, while PSI binds multiple LHCII trimers under varying light adaptation conditions. Another study represents the organization and size of light-harvesting antenna of PSI from the colonial green alga Botryococcus braunii. Based on electron microscopy analysis, we concluded that the larger light-harvesting antenna in Botryococcus braunii is important for the cells in the interior of a colony. Our study on the diatom Thalassiosira pseudonana revealed the presence of a larger PSI and a unique PSII structure which might be necessary for capturing and regulation of the excitation energy. The structural characterization of Chlorella ohadii PSI shows an additional core subunit PsaM and also pigments bound to the antenna proteins which enable a high photosynthetic performance under extreme light intensities in the desert