Structure and Function of Supercomplexes of Photosystem I with its Peripheral Antenna Systems in Green Algae and Cyanobacteria

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Photosynthesis is the main process on Earth that converts light energy from the sun into chemical energy accessible for living organisms. The products of photosynthesis ultimately provide all higher life on earth with energy and produce all oxygen in the atmosphere. The aim of this project is to unravel the structure and function of the large molecular solar energy converter Photosystem I (PSI) and to determine the interaction of its peripheral antenna systems in eukaryotes (plants and green algae) and prokaryotes (cyanobacteria). The photosystem I complex consists of 12-14 proteins to which more than 120 cofactors (chlorophylls and carotenoids) are bound. Furthermore, photosystem I is dynamically coupled to additional peripheral antenna systems to further increase the efficiency of light capturing. The project aims to unravel the structure and function of both the plant-type photosystem I in a supercomplex with the light harvesting complex I and the cyanobacterial photosystem I in its supercomplex with 18 IsiA proteins. The overall goal of the project is the determination of the structure of both photosystem I-antenna supercomplexes in plant-type and cyanobacterial photosystem I. The experimental setup includes crystallization and structure-determination by X-ray structure analysis, the design of structurally and functionally improved complexes by mutagenesis and functional investigations by time-resolved spectroscopy. The project will lead to detailed insights into the structural organization of the photosynthetic system in prokaryotes and eukaryotes and will unravel the functional coupling of the external antenna complexes to the core units of photosynthesis. Furthermore the project will provide new insights into protein assembly during the formation of large supercomplexes of membrane proteins. Broader ImpactsKnowledge of the atomic details of the structure of giant Photosystem I supercomplexes will boost our understanding of the mechanisms of basic processes of bio-solar energy conversion. Moreover, this will help to elucidate structure-functional relationships between the photosynthetic reaction centers and their peripheral antennas in the supercomplexes that determine a higher efficiency and flexibility of the energy conversion in the bio-solar systems than in man-made systems. The project will thereby provide broad impacts for the development of new concepts for solar energy converters that mimic nature. Furthermore, fundamental understanding of the photosynthetic processes could lead to the development of plants with enhanced photosynthetic ability and increased tolerance to many kinds of environmental stress. One of the aims of the project is to use gained knowledge for boosting students' interest in revealing the secrets of natural energy conversion and enhancing their motivation in studying science. The project will also give an opportunity to inform the public on recent discoveries in this exciting area.