In vitro investigation of the photoprotection mechanism of Light Harvesting Complex II

Solar energy is used by photosynthetic organisms to drive energy required cellular processes. Is absorbed by two groups of pigments, located in the LHCs. These proteins are essential for the performance of photosynthesis, because they are involved in harvesting the light and because they protect the photosynthetic system from excess of light that cause photodamage. I performed in vitro studies mimicking the two functions of LHCII by inserting the protein in nanodiscs and in liposomes. I demonstrate that Chl excitation quenching is dependent on protein-protein interactions. I investigated the specific interactions of LHCII with PsbS. The fluorescence study of our minimal membrane models strongly suggests that the pH-dependent role of PsbS lies in creating membrane rearrangements and supercomplex remodeling that could facilitate LHCII aggregation quenching. I successfully produced 13C lutein-rLhcb1 protein in detergent, mimicking the unquenched state, and protein aggregates, mimicking the quenched state, were biochemically and spectroscopically characterized and further analysed with solid state NMR.Ring current shifts of the lutein head signals indicate that the heads are in close proximity to specific Chls (Chl a610 and Chl a602), providing for the first-time structural information about lutein-Chl interactions in LHCII in its unquenched state.