Project title: The Role of LHCII Environment in Regulating the Light Harvesting in Green Plants.
Summary: Photosynthetic organisms are frequently exposed to fluctuations in light intensity of their environment. High light increases the fraction of "unused" excitation in the photosynthetic membrane which is potentially harmful, resulting in a long-term reduction in plant/algal productivity called photoinhibition. The component of the photosynthetic membrane most vulnerable to high light is Photosystem II (PSII). This photosystem has evolved a mechanism that works to protect against excess light via a prompt opening of a channel which dissipates excess energy harmlessly as heat, a process called NPQ. The molecular mechanism of NPQ includes light-triggered generation of a proton gradient across the membrane that affects the structural state of the PSII light harvesting antenna (LHCII). How exactly proton gradient triggers LHCII transition in protective state is unknown. There are indications that the changes in the membrane environment of this major photosynthetic complex are involved.
The key objective of this PhD project will be to analyse the changes in the photosynthetic membrane geometry, interactions of LHCII with other proteins and surrounding lipid composition. The structural alterations in the thylakoid membrane will be studied using electron microscopy (negative staining, freeze-fracture). LHCII interactions in the NPQ state will be assessed using various biochemical techniques (immune-labelling, pull-downs and preparations of oligomeric complexes with amphipols). Lipid analysis will be performed using state of the art mass-spectrometry. LHCII will be incorporated into liposomes along with PsbS protein and proton gradient-generating pumps such as bacteriorhodopsin to reproduce NPQ.