Protein Control of Electron Transfer Pathways in Photosynthesis

点击翻译按钮获取中文摘要

The initial solar energy conserving event in photosynthesis is the transfer of an electron between an excited donor and a neighboring acceptor molecule in the reaction center, an intrinsic membrane protein-pigment complex. In this project the PI will continue his studies of the purple nonsulfur bacterium Rhodobacter sphaeroides, investigating the driving force and temperature dependence of the initial electron transfer reactions. The PI has used a form of reaction diffusion theory, applied previously to electron transfer in viscous solvents, to describe the complex kinetics of electron transfer as a function of driving force and temperature. This approach has been remarkably successful, implying that protein conformational changes initiated by light absorption control the observed kinetics instead of a static barrier crossing between two potential surfaces. Several important questions have been raised by this work that need to be answered. First, the nature of the protein motion and the spectroscopic signal at 280 nm that appears to be a probe of this motion are unclear. It is currently hypothesized that this is due to tryptophan residues responding to changes in the protein environment, but this remains to be proven. Second, a more detailed mechanistic exploration of the relationship between protein relaxation and electron transfer is necessary. This new model provides an opportunity to determine the reorganization energy, driving force and coupling for a whole series of mutants as a function of temperature, resulting in a much more complete mechanistic picture of initial photosynthetic electron transfer than has ever been available previously. Finally, this work will be merged with current directed evolution approaches to produce mutants that undergo high yield electron transfer along the normally unused cofactor pathway (the B-side). A very similar set of studies as a function of driving force and temperature will then be performed on these mutants to explore the mechanistic similarities and differences between the two electron transfer pathways. The PI is involved in expanding interdisciplinary research at both the graduate and undergraduate levels. The PI has seven undergraduates working with him, two directly on this project. In addition, the concepts involved in photosynthetic research are used to enrich his teaching in both physical chemistry and biochemistry. For example, the PI teaches a course on bio-nanotechnology as part of a learning community project at ASU in which sophomores explore the science, policy and sociology of nanotechnology. The PI is also the director of an NSF IGERT program in biomolecular nanotechnology. The photosynthetic reaction center is a premier example of an optoelectronic device at the nanoscale and the concepts from this work are one of the key examples of biomolecular nanotechnology studied by the IGERT students. The PI is also the current director of the ASU BioEnergy Research Initiative, a new initiative growing out of ASU's Photosynthesis Center that seeks to take our growing understanding of photosynthetic processes and utilize them in the development of new energy sources and means of energy transduction. Finally, the PI directs the Center for BioOptical Nanotechnology in the Biodesign Institute. In this role, he directly interfaces with a large number of private, commercial and citizens groups, and these discussions form the basis for a new approach to community-embedded research, in which the needs of society and the process of discovery are integrated in a new hybrid model for interdisciplinary research. This project is jointly supported by Molecular Biophysics in the Division of Molecular and Cellular Biosciences in the Directorate for Biological Sciences and the Experimental Physical Chemistry Program in the Division of Chemistry in the Mathematical and Physical Sciences Directorate.