Mechanism and Macromolecular Organization in Photosynthetic Reaction Centers

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9807559BoxerThe goal of this project is to study the mechanism of the charge separation and recombination steps in reaction centers (RCs) from photosynthetic bacteria. Specific approaches to these problems include: (i) quantitative analysis of the absorption and Stark spectra of mutants that affect the special pair (P) using an analytical treatment of the coupling between locally-excited and charge transfer states to obtain information on the electronic properties of 1P; (ii) application of the higher-order Stark method developed in this laboratory to study the mechanism of electron transfer and the origins of unidirectional electron transfer, (iii) creation of an RC that does not bind carotenoid and measurements in these carotenoid-free RCs of phosphorescence spectra of the special pair and the activation energy of 3P decay to determine the energetics of the primary charge separation in RC mutants; (iv) estimation of differences in electronic coupling on the L-vs M-side using ultrafast singlet energy transfer in RC mutants; and (v) use of RCs in supported lipid bilayers as a nucleation site for assembling and imaging the organization of photosynthetic membrane components using lateral electric field-induced concentration profiles and atomic force microscopy.Photosynthesis is the process by which solar energy is converted into useful fuel. As such, the processes involved are among the most important in nature. Furthermore, the elementary steps involved, energy transfer, electron transfer and proton transfer, are among the most universal processes in chemistry and biology. The photosynthetic reaction center is beautifully crafted to optimize each of these processes and this research aims to understand how this works. By working with a system whose function is initiated by light, it is possible to study the mechanism under very well defined conditions, something that is rarely possible with complex biological systems. The answers to the particular technical questions posed by this research also impact wider issues of long distance electron transfer and electrostatics in proteins, with further implications and applications in materials science and the analysis of self-assembly in complex systems.