Structure-Function studies of Photosystem II
Abstract
Over the last fifty years, the multi-component protein complex Photosystem II (PSII) and the biological water oxidation have been extensively studied to understand unique properties of the oxygen evolving complex (OEC) and other co-factors of PSII. X-ray diffraction and spectroscopy studies provided high resolution crystal structures of this protein complex and chemical properties of OEC. Recent radiation-damage free serial XFEL diffraction experiments begin to resolve molecular dynamics during the turnover of the OEC and within the channels leading to the active center that are proposed to facilitate substrate water delivery and product egress.
In this research project we are combining biophysical techniques specialized to photosynthesis research such as time-resolved membrane inlet mass spectrometry (TR-MIMS), EPR Spectroscopy, Joliot Electrode and Fluorescence spectroscopy with the structural data obtained with Cryo-EM and X-ray diffraction. Specifically, the goal is to study site directed mutatants of PSII in Synechocystis sp. PCC 6803 that either block or open specific pathways in order to identify the function of each pathway, providing crucial insights into the design principles of photosystem II that allow efficient light-induced water oxidation. For these samples we have already collected extensive biophysical data that attest their high relevance for this study. Importantly, the structures of the mutants obtained by Cryo-EM will be essential for the interpretation of the biophysical experiments and thus for answering our research question.
We already obtained the wild type CryoEM structure and had a considerable progress in the image processing of the three channel mutant PSII's. In this allocation we are aiming process new EM-microscopy data we collected to enhance the quality of the CryoEM maps. This will require concatenation of the new data to the datasets we already have in our previous storage allocation.
