Laser Flash Studies of Bacterial Photosynthesis

University Of Washington, Seattle WA

Investigators

Abstract

The objective of this study is to improve understanding of the roles of vibrational motions and relaxations in the initial steps of energy transfer and charge separation in photosynthetic bacterial antenna complexes and reaction centers. The work will involve a combination of experimental and computational approaches. Fluctuations of the fluorescence amplitude, emission spectrum and anisotropy will be measured over a broad range of temperatures to study the dynamics of structural transitions of the proteins. Coherent nuclear oscillations of the stimulated emission spectrum will be measured following excitation of reaction centers and antenna complexes with femtosecond flashes in order to explore the flow of energy from one vibrational mode to another. Reaction centers with mutations of ionizable residues will be studied to probe how changes in protein vibrations and electrostatic interactions affect the spectroscopic properties of the bacteriochlorophyll molecules that serve as electron carriers. In the computational work, molecular dynamics simulations will be used to study vibrational relaxations in the reaction center and to identify protein vibrational modes that are coupled to electron transfer. The vibrational coupling and relaxation dynamics visualized in these simulations will be used to develop a realistic, density-matrix model of photosynthetic electron transfer. These studies will increase our understanding of the early steps of photosynthesis, which are fundamental to virtually all life on earth. In addition, the results may help to clarify the importance of vibrational motions and relaxations in other electron-transfer systems such as the mitochondrial respiratory chain. Broader Impact: The project will contribute to the education of graduate students in Biochemistry and the Interdisciplinary Program in Biomolecular Structure and Design (BMSD). A broader group of graduate students will be exposed to results from the research in a course on "Optical Spectroscopy in Molecular Biophysics". Undergraduate Biochemistry, Biology and Chemistry students as well as promising high school students from underrepresented minorities will participate directly in the research. Instrumentation constructed as part of the project will be available to the interested researchers.