Artificial membranes as model systems for the investigation of lipid protein interactions in the thylakoid membranes of vascular plants and the green alga Mantoniella squamata

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The experiments outlined in the application are thought to complement the results of the first two years of the DFG project. To further study the importance of the thylakoid lipid MGDG for the de-epoxidation of LHCII-associated violaxanthin (Vx), we want to incorporate different LHCIIs into liposomes constructed of bilayer (DGDG, PC) and inverted hexagonal phase forming lipids (MGDG, PE). These liposomes will be tested in de-epoxidation assays with different isolated violaxanthin de-epoxidases. The experiments are of importance for the understanding of Vx de-epoxidation in-vivo, as the defined liposomes resemble the situation in the natural thylakoid membrane. Liposomes will also be constructed from neutral (MGDG, DGDG) and negatively charged lipids (SQDG, PG) to further study the lipid effect on the structure of the LHCII. These experiments should support our observation that negatively charged lipids lead to a strong disaggregation of the LHCII, whereas neutral lipids stabilize the higher order structure, thus implying that in the native membrane special lipid domains exist. We will also focus on the primitive green alga M. squamata, where we want to perform comparable experiments as outlined above for the vascular plant LHCII. The third year of the project will also include a quantitative lipid analysis of M. squamata, with a special focus on the fatty acid composition of thylakoid lipids and the newly found DGTA. Finally, native MGDG from M. squamata will be prepared to analyse the effect of fatty acids with a different degree of saturation on the Vx de-epoxidation.