Dynamics in Photosynthetic Oxygen Evolution

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

Solar power has the capacity to meet the world's increasing needs for energy. In plants and algae, natural photosynthesis uses light energy to remove electrons from water to form oxygen, and then directs the electrons to biochemical reactions that power the cell. This NSF funded research project will give new insight into the chemical steps necessary to carry out photosynthetic oxygen production. In particular, information will be gained about how the photosystem II protein complex binds and activates water, along with the roles played by other participants in the process such as calcium, chloride. Many different spectroscopic approaches will be employed to study this light-induced water oxidation cycle. To help interpret the spectra, the proteins will be modified to contain non-natural amino acids that will serve as unique probes of structure and function. The intellectual merit of this project is a more complete understanding of the photosynthetic water oxidation process, which will lay the groundwork for new design strategies to address the pressing global need for inexpensive and renewable sources of energy. The research activities will advance the teaching, training, and learning of underrepresented groups who are at different stages of training and from different types of academic settings. The water splitting process is initiated by light-driven excitation of chlorophyll. This event causes a charge separation across a membrane. This electron transfer is mediated stepwise by a chain of electron acceptors and leads to the conservation of solar energy. The water splitting reaction is catalyzed in the photosynthetic reaction center, photosystem II, by a manganese-calcium metal cluster and a redox-active tyrosine residue. Photosystem II consists of multiple protein subunits. One, termed PsbO, is an intrinsically disordered protein, which, along with chloride, plays an important role in facilitating catalysis. The oxygen-evolving cycle involves a coordinated light-driven process, in which negatively charged electrons and positively charged protons are removed from water bound to the metal center. A critical feature of natural photosynthesis is the use of sunlight to oxidize water. Artificial systems, which use water as an electron source, would provide affordable and sustainable fuel production. To understand photosynthetic water oxidation chemistry, it is necessary to decipher the precise coordination of light-driven proton and electron transfer reactions. Also, the functional role of the intrinsically disordered subunit, PsbO, calcium, and chloride must be elucidated. The work includes participation by underrepresented groups in science and collaborations with non-PhD granting colleges, including an historically black college for women.