Revealing the light-harvesting properties of Photosytem I. From single antenna to supercomplex

PhD ceremony: Ms. I.E. Wientjes, 16.15 uur, Senaatskamer Academiegebouw, Broerstraat 5, Groningen

Dissertation: Revealing the light-harvesting properties of Photosytem I. From single antenna to supercomplex

Promotor(s): prof. R. Groce

Faculty: Mathematics and Natural Sciences

Photosynthesis is the process in which light energy is used to convert carbon dioxide into carbohydrates. Oxygenic photosynthesis is driven by two photosystems, Photosystem I and Photosystem II. This thesis describes a detailed analysis of the light-harvesting properties of higher plant Photosystem I. Photosystem I is a pigment-protein supercomplex, composed of a core complex and four light-harvesting proteins, Lhca1-4. We study the system at various levels of complexity, from individual antennas to supercomplexes. In the most detailed level, the level of the monomers, we investigated how the spectroscopic properties of the red forms of Lhca4 are modulated by the protein environment. At the next level we studied the light-harvesting properties of the Lhca1/4 and the Lhca2/3 dimer. Using assemble experiments we revealed the absorption and emission properties as well as the inter-monomer transfer rates. We also studied the emission properties of the Lhca complexes at the single-molecule level. The results showed that the Lhca complexes can reversible switch off their entire red-emission band by a conformational change, meaning that it is essential to consider the flexibility of the Lhc proteins in order to understand their spectroscopic properties. At the following level we have studied PSI complexes with reduced antenna size or altered antenna composition. Finally, we have presented a comprehensive picture of the excitation energy transfer routes and rates in the entire photosystem I supercomplex.