Researchers create 'movie' to capture important step in photosynthesis

An international team of scientists, including researchers from Lawrence Berkeley National Laboratory, used crystallography and spectroscopy technology to capture an important step during photosynthesis. Published in the journal Proceedings of the National Academy of Sciences on May 20, the study looked specifically at a chemical reaction that occurs during photosynthesis, in which two water molecules split to form one oxygen molecule. The findings could help researchers develop technology such as artificial photosynthetic devices that mimic nature. Researchers have known the structure of photosystem II, the protein that facilitates the reaction, for 20 years, according to Berkeley Lab senior scientist Nicholas Sauter. Scientists, however, are still trying to understand the more specific details of the reaction. “Nature has figured out how to do this conversion very efficiently,” said Ruchira Chatterjee, a co-author of the study and Berkeley Lab staff research associate. “We want to understand what nature does and what principles it uses so that people can work on it and develop on it.” During the process by which sunlight splits water and releases oxygen, water goes through four different states. The team’s overall goal is to better understand the specific details of the transformations that the molecules undergo between each state of the process, according to co-author and Berkeley Lab senior scientist Junko Yano. This paper looked at one intermediary portion of that process. Yano added that new technologies have recently allowed the field to become more advanced. The team has been working with X-ray free-electron lasers located in partnering laboratories for the past 10 years. This device enables researchers to analyze the protein in which the reaction takes place and see specific points during the reaction. “It was a new facility, new method. We needed to develop several techniques, which enables our experiment,” Yano said. “That's why it's taking a long time, but we are slowly advancing.” Essentially, this technology helped the team create a “movie” for one segment of the reaction. By doing this, the researchers were able to see that, between these two states of the chemical reaction, one of the two water molecules enters to start the water-splitting reaction. The study shows only a part of the full reaction, but the group hopes to eventually continue the “movie” of the entire reaction using this technology, once all the facilities involved return to their normal operations. “It's taken us a very long time to get where we are, and that's because it's been so hard to zoom in at atomic detail,” Sauter said. “The next step is to continue in time to see how the next water molecule comes into the reaction, and then how they're bonded together.”