Photosystem I (PSI) is located in the thylakoid membrane and part of the light reaction of oxygenic photosynthesis. It mediates the ultrafast and highly efficient electron transfer chain which makes it the most efficient energy converter in nature. Due to that, PSI is very interesting for future biotechnological approaches capturing light and directly converting it into chemical energy. To mimic PSI artificially, a better understanding of the molecular changes of PSI during the light reaction is necessary. Approaches to improve structural data quality, can encompass improving already existing preparation protocols or isolate, purify and crystallize tPSI with new detergents. We will be presenting a brief overview of results from recent XFEL experiments. We were able to measure tPSI purified and crystallized with the detergent n -dodecyl β-D-maltoside (β-DM) at four different delay times after light activation at a resolution of around 2.4 to 2.7 Å. Light induced changes of orientation and location of the protein environment, certain pigments and water network were detected. Additionally, our data revealed that the flexibility differs between the electron transfer branches within PSI and for different oligomeric states of PSI. Previous spectroscopic work has observed various ratios between the transfers along the two branches for different PSI preparations. To explain the origin of differences in electron transfer branching ratios especially between the different oligomeric states of PSI we have compared the structures of PSI around the transfer branches showing a correlation between preferred electron transfer branch and protein structure flexibility.
Moritz Kretzschmar (2026) studied this question.