Resolution and Reconstitution of Photosystem I in Cyanobacteria and Higher Plants: Molecular Biological and Physicochemical Studies

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This research program aims at understanding the structure,function and organization of the Photosystem I reaction center in cyanobacteria and green plants.The advances made so far include a biological method to introduce alternative quinones into the A1site,an experimental approach to determine whether electron transfer is uni-or bi-directional among the symmetrically-located electron transfer cofactors,and a determination of the 3-dimensional NMR solution structure of unbound PsaC.This,combined with newly-available structural information about the 3-dimensional spatial arrangement of atoms from X-ray crystallography and the electron spin density distribution in cofactors from magnetic resonance spectroscopy,has opened new avenues for research in PS I. One is the effect of biological incorporation of alternative quinones into the A1 site for studies of the effect of Gibbs free energy changes on rates of forward and backward electron transfer, and for studies of the electron density distribution within the A1 - acceptor. Another is the protein-protein interactions at the molecular level between the PsaA,PsaB, PsaC,and PsaD subunits,and focuses especially on the changes in secondary structure that take place when PsaC docks with its protein partners in PS I.The goal is to determine the dynamic interactions that occur among these to produce a functional PS I complex.These studies promise to have an impact on the understanding of protein factors responsible for conferring redox properties to organic cofactors and on the understanding of protein-protein interactions in the assembly of multi-component,membrane-bound complexes.Hence,this work should have relevance well beyond the realm of oxygenic photosynthesis