Structural and Functional Analysis of Photosystem I

Project: Research project

Project Details

Description

The cyanobacterial Photosystem I reaction center is a light-driven oxidoreductase catalyzing electron transport from cytochrome c533 to ferredoxin. The long-term goal of this research program is to understand the structure and function of the Photosystem I reaction center. In this project biochemical resolution and reconstitution are combined with site-directed mutagenesis and protein overproduction in E.coli to produce reaction centers with altered spectroscopic and electron transport properties. Building upon our most recent results and the tools developed and mutants constructed in the current funding period, the following long-term goals will be addressed: 1. The roles of FA AND/OR FB in the room-temperature photoreduction of ferredoxin (or flavodoxin) and NADP+ via FNR. 2. Biochemical characterization of the two forms of FNR identified in Synechococcus sp. PCC 7002. 3. Characterization of the remaining genes encoding PS I polypeptides in Synechococcus sp. PCC 7002. 4. The roles of PsaD and PsaE in PS I structure and function. 5. The mechanism of the specific interactions between the PS I complex and ferredoxins and flavodoxin. 6. The 3-dimensional structures of the PsaC, PsaD, PsaE, and FNR proteins. 7. The nature of the PsaE- and NdhF-dependent paths of electron transport in P700+ re-reduction. %%% All life on Earth ultimately depends on solar light energy capture during photosynthesis, a process which leads to the reduction and fixation of carbon dioxide and the evolution of oxygen gas as a by- product. Light energy capture and transduction takes place in multiprotein complexes known as reaction centers, which utilize the light energy to initiate oxidation-reduction reactions and electron transfer events which result in the production of chemical energy (in the form of ATP) and chemical reductant (in the form of NADPH). In oxygenic photosynthesis--the type which occurs in green plants, algae, and bacteria known as cyanobacteria--the cooperation of two reaction centers, denoted Photosystems I and II, are required. The long-term goal of the research here proposed is to understand the structural organization of the Photosystem I reaction center and to unravel specific details of the electron transfer events that lead to charge separation, charge stabilization, and electron transfer to soluable carriers in this reaction center. The proposed project is a marriage of two different research disciplines and is the result of a close collaboration and coordination of our research activities with those of the laboratory of Dr. John H. Goldbeck (Dept. of Biochemistry, University of Nebraska). A combination of modern molecular genetics, recombinant DNA technology, site directed mutagenesis, protein overproduction and protein biochemistry (my lab) is combined with biochemical reconstitution, modern ultra-fast laser spectroscopy, electron spin resonance (ESR) spectroscopy, and other biophysical measurements (the Golbeck laboratory). We will also jointly characterize alternative electron transport pathways involving the Photosystem I reaction center (e.g, cyclic electron transport) and function of the alternative electron acceptors ferredoxin and flavodoxin. Through our work we hope to provide a better understanding of photosynthetic solar energy capture and photochemical conversion.

StatusFinished
Effective start/end date9/1/922/28/98

Funding

  • National Science Foundation: $423,000.00

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