Assembly and Function of the Cyanobacterial Photosystem II Complex

Oklahoma State University, Stillwater OK

Investigators

Abstract

The photosystem II (PSII) complex found in plants, algae, and cyanobacteria is a chlorophyll-protein complex located in specialized internal cell membranes called thylakoids. PSII catalyzes the crucial water-splitting reaction that uses solar energy to produce the activated hydrogen required for food and energy production throughout the Earth's biosphere. At the same time, the PSII is responsible for the production of essentially all the gaseous oxygen on Earth. Despite its global importance, PSII can also be considered the "Achilles Heel" of photosynthetic organisms. This is because it is prone to damage from the very light that it uses as an energy source. Consequently, PSII is under a constant state of repair owing to this incessant light damage. The project will elucidate the poorly understood repair mechanism with a focus on the assembly of the catalytic metals necessary for oxygen evolution. In addition to the fundamental research, the project will provide extensive training opportunities for undergraduate and graduate students in in the areas of biochemistry, biophysics, and molecular genetics. Moreover, the is a large outreach component of the project that is designed to provide research opportunities for pre-service and in-service high school teachers. The project will investigate the multistep assembly of the metal cluster (Mn4CaO5) catalytic center of the PSII water-splitting complex. Recent work has revealed the migration of damaged PSII to specialized "repair zones" located in the peripheral regions of the cell. The project tests the hypotheses that (1) loss of the the Mn4CaO5 triggers the migration to repair zones and (2) the assembly of the Mn4CaO5 cluster occurs efficiently only after migration of the damaged PSII complex to these repair zones. Because light also drives Mn4CaO5 assembly, the process can be precisely controlled using flashes of light, which will allow new insights into the broad problem of metal cluster assembly in proteins. The work will use a genetically transformable cyanobacterium and an array of techniques that probe the assembly process with molecular resolution. State-of-the-art biophysical and molecular genetic techniques are being developed and utilized by the PI and collaborators. These include synthetic DNA, high-speed polarography, EPR, and FTIR techniques.