Bacterial Reaction Centers With New Photochemical Properties

Arizona State University, Scottsdale AZ

Investigators

Abstract

In all photosynthetic systems, the primary energy transduction event is the light-induced generation of a charge-separated state in a pigment-protein complex. Although the specific pathways vary among organisms, the general pattern is remarkably conserved, and an understanding of these processes serves as the basis for current designs of artificial systems that mimic the photosynthetic process. The usefulness of the reaction center from Rhodobacter sphaeroides as a model for photosystem II is illustrated by previous work in which a redox-active Mn cofactor was bound to the reaction center at a location analogous to that of the Mn cluster of photosystem II. The first specific aim of the project is to characterize the properties of the bound Mn and other new metal cofactors in the reaction center. A wide variety of spectroscopic techniques will be utilized to determine the structural properties, the electronic structure of the metal cofactor, and the electron transfer properties, providing the basis for understanding the specificity for metal binding, the factors that control the activity of the metal, and how reactions involving metal cofactors are controlled by protein interactions. The second specific aim is to design proteins with multinuclear Mn clusters. The assembly of clusters will be approached by three independent avenues: a semi-synthetic method in which a variety of Mn compounds will be bound to the protein, the application of the self-assembly principles of the Mn cluster of photosystem II, and the introduction of new ligands for the binding of binuclear and tetranuclear Mn clusters. The incorporation of new Mn cofactors should shed light into the molecular requirements for the binding of metal clusters to proteins. The insight gained regarding electron transfer proteins with new metal cofactors should provide the foundation for the design of proteins capable of light-driven metal-based catalysis. Achievement of the research goals should have an impact on understanding photosynthesis and the development of solar-energy devices. Broader impacts The project provides multidisciplinary training for undergraduate and graduate students and international exposure through collaborations. Many project concepts, notably the role of photosynthesis in energy utilization and the fundamentals of spectroscopic techniques used to study reaction centers, will be included in the development of courses for students of different backgrounds, as well as a textbook for undergraduate education authored by the principal investigator.