Dynamics of Electron Transfer-PSI/Ferredoxin

Arizona State University, Scottsdale AZ

Investigators

Abstract

Intellectual Merit This project aims to make a movie of molecules at work. The molecule of interest is called Photosystem I (PSI), and is present in all green plants. Together with another molecule (Photosystem II), these are responsible for photosynthesis, which maintains our biosphere by degrading carbon dioxide (an important contributor to Global Warming) and by splitting water to provide the oxygen in our atmosphere. Making this movie will entail use of the world's first X-ray laser, at Stanford (the DOE's Linac Coherent Light Source(LCLS)), which produces extremely brief "snap-shot" X-ray diffraction images of groups of molecules. This project is a study of "nanocrystals" of the molecules, which are periodically arranged clusters containing perhaps 20 molecules on a side. The molecules, which must be wet, are sprayed in a vacuum across the X-ray beam in a special liquid jet of micron dimensions. This gas-focussing jet (somewhat similar to an ink-jet printer) was developed under NSF support in a previous grant. In this first attempt to record atomic motion by snap-shot diffraction from membrane protein nanocrsystals, a red laser beam will be used to initiate the separation (or "undocking") of a second molecule (ferredoxin) from PSI, then, after a brief delay, an X-ray snapshot will be recorded. Frames of a movie will be accumulated by varying the delay time. Several snapshots, read out from the LCLS detector 60 times per second, will be added together for each frame. Broader Impacts The broader impact of the project includes the training of postdoctoral researchers and a graduate student, and the dissemination of the results in journals and on the web. In addition the project and results will be actively promoted in a number of outreach programs, including the Lawrence Berkeley Laboratory Outreach program, the Open Days at ASU Physics, the Arizona Science Fair, the Outreach program of the Eyring Center at ASU and in the Arizona High School Teacher Training Program. There will be continued participation in these programs, where the methods and results of the research are explained to students in a pedagogically sound manner. This work is directly relevant to efforts to reduce global warming since it provides an atomic mechanism for a crucial step in the process of photosynthesis.