Infrared Spectroscopic Studies of Plant Photosynthesis

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Oxygenic photosynthesis occurs in plants, cyanobacteria, and algae and is essential in the maintenance of life on earth. This type of photosynthesis requires the concerted action of two light-absorbing reaction centers, which convert light energy into a transmembrane charge separation. One of these reaction centers, photosystem II catalyzes the oxidation of water and produces molecular oxygen and reduced plastoquinone. Photosystem II accumulates the four oxidizing equivalents necessary for oxygen production at a manganese-containing catalytic site. The sequentially oxidized forms of the catalytic site are called the S states. Photosystem II consists both of integral, membrane-spanning subunits and of extrinsic subunits, that do not span the membrane. A subset of these extrinsic subunits is known to influence light-driven electron and proton transfer events. The extrinsic subunit known as the manganese stabilizing protein, MSP, prevents loss of manganese from the PSII active site and is required for optimal rates of oxygen evolution. In this multidisciplinary project, vibrational spectroscopy will be used to obtain detailed information about structural changes occurring during the S state cycle. The ultimate goal is to determine how oxygen-oxygen bond formation occurs in photosynthetic oxygen evolution. In addition, vibrational spectroscopy will be employed to test a possible mechanism by which MSP may influence water oxidation. Finally, the idea that MSP changes conformation or folds when it binds to the PSII reaction center will be tested using X-ray scattering. These experiments will provide new information about the function and assembly of complex membrane proteins.