Localization and Functions of Novel Proteins in Cyanobacterial Photosystem II

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Photosystem II, a membrane protein complex in cyanobacteria and chloroplasts, mediates a unique reaction in the biosphere, oxidation of water to molecular oxygen. Although the exact molecular mechanism of photosynthetic oxygen evolution remains elusive, it is known that a cluster of manganese, calcium and chloride ions is essential for this activity. The long-term goal of this project is to define the roles of various protein components of photosystem II in the mechanism of water oxidation. Proteomic analysis of a highly active PSII preparation from the cyanobacterium Synechocystis 6803 has identified four novel proteins, Sll1390, Sll1252, Sll1414, Sll1130, as well as the PsbP and PsbQ proteins, which were previously thought to be present only in higher plant and green algal chloroplasts. This project includes detailed biochemical and genetic studies to determine the cellular localization, and functions of the above proteins in cyanobacterial and plant photosystem II.By harvesting solar radiation, the photosystem II complex contributes to half of the biomass production on our planet. During the past year, X-ray crystal structure of a cyanobacterial photosystem II complex has been described at a 3.8A resolution. However, a more detailed understanding of the organization and functions of the protein components of photosystem II are necessary to fully comprehend the mechanism of photosynthetic O2-evolution. The proposed experiments are expected to complement anticipated higher resolution X-ray crystallographic analysis of photosystem II to gain such a level of understanding. These experiments will also shed new light on the evolution of the form and function of photosystem II from cyanobacteria to higher plants. In addition, this project will provide state-of-the-art research opportunities to a number of undergraduate, graduate and postdoctoral trainees.