Novel High-Field EPR Studies of Photosynthetic Reaction Centers

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9600940 Budil This project is directed towards characterizing the structural features governing the primary light reaction in photosynthetic organisms using novel high-field electron magnetic resonance methods. The excellent spectral resolution at high field provides a new means of probing the structure of the primary reactant radicals. Orientation selectivity at high frequency will be exploited to carry out "g-magnetophotoselection" experiments that will relate magnetic properties to the optical properties of the primary reactants. Where possible, single crystal studies will be undertaken in order to correlate the magnetic tensors of the reactants directly with the ground state structure of the RC. Structural influences will also be investigated by a novel "electrostatic mapping" approach in which nitroxide spin labels are introduced at specific amino acid residues of the protein using site-directed mutagenesis. The electric field sensitivity of high-frequency nitroxide spectra will enable direct exploration of local electrostatics at selected sites in the reaction center, providing significant new information about the protein microenvironment that guides the primary photochemistry. %%% The broader research goal of this project is to develop new magnetic resonance techniques for probing dynamic macromolecular structures, with an immediate focus on the structure and function of the photochemical reaction centers in photosynthetic organisms. High-frequency electron magnetic resonance will be used to probe the microscopic structure of the primary reactants and the surrounding protein, as well as the photochemical reaction dynamics. The educational goals of this program will integrate advanced physical concepts, with an emphasis on magnetic resonance methods, into training in molecular biology. New opportunities will be created for students to augment their cooperative education experience at Northeastern University by engaging directly in the development of new biophysical methodologies in collaboration with local entrepreneurial companies. ***